Polymer waste management 9781119536086, 1119536081

Table of contents :
Preface xi1 General Aspects 11.1 History of the Literature 21.2 Amount of Wastes 21.3 Metal Content in Wastes 41.3.1 Waste Poly(ethylene) and Pure High Density Poly(ethylene) 41.4 Analysis Procedures 41.4.1 Fluorescence Labeling 41.4.2 Time-Gated Fluorescence Spectroscopy 61.4.3 Content of Flame Retardants 61.4.4 Identification of Black Plastics 71.4.5 Raman Spectroscopy 91.4.6 Life Cycle Assessment 101.4.7 Analysis of Contaminated Mixed Waste Plastics 121.4.8 Construction and Household Plastic Waste 141.4.9 Models for Forecasting the Composition of Waste Materials 141.5 Standards 161.5.1 Circular Economy Package 161.5.2 SPI Codes 171.5.3 Test Samples for Biodegradation 191.5.4 Mixed Municipal Waste 211.5.5 Aerobic Composting 211.5.6 Contaminants in Recycled Plastics 221.6 Special Problems with Plastics 221.6.1 Stability of Plastics 221.6.2 Additives 231.6.3 Plastics in Food 241.6.4 Seawater 251.6.5 Landfill 371.6.6 Electronic Waste 38References 402 Environmental Aspects 512.1 Pollution of the Marine Environment 512.1.1 Pathways of Plastics into the Marine Environment 542.1.2 Deleterious Effects on the Marine Environment 552.1.3 Reports Concerning Special Locations 552.1.4 Analysis Methods 562.1.5 Plastic Preproduction Pellets 592.1.6 Leaching of Plastics 602.1.7 Micro-plastics 602.1.8 Marine Animals 652.2 Pollution of the Terrestrial Environment 712.2.1 Waste Generation 712.2.2 Disposal in Landfills 712.2.3 Plastic Materials for Packaging 72References 733 Recycling Methods 793.1 Alternative Plastic Materials 803.2 Mechanical Recycling 813.2.1 Poly(lactic acid) 813.2.2 Nanocellulose Coated Poly(ethylene) Films 843.2.3 Electric Uses 843.3 Primary Recycling 863.4 Renewable Polymer Synthesis 873.4.1 Natural Solvents for Expanded Poly(styrene) 943.4.2 Landfill Methane Recycling 973.4.3 Anaerobic Landfill 973.4.4 Simulated Semi-aerobic Landfill 993.5 Preparation and Regeneration of Catalysts 1003.5.1 Reuse of ZSM-5 Zeolite 1003.5.2 Modification of Zeolites 1003.6 Pyrolysis Methods 1013.6.1 Fluidized-Bed Reactor 1043.7 Metallized Plastics Waste 1053.7.1 Rotary Kiln Pyrolysis 1063.8 Mixed Plastics 1083.8.1 Grinding and Cleaning 1083.8.2 Reductant in Ironmaking 1093.9 Separation Processes 1113.9.1 Automated Sorting of Waste 1113.9.2 Sorting According to Density 1123.9.3 Hydrocyclonic Separation of Waste Plastics 114 3.9.4 Froth Flotation 1143.10 Triboelectrostatic Separation 1263.11 Wet Gravity Separation 1273.11.1 Selective Dissolution/Precipitation Technique for Polymer Recycling 1283.12 Supercritical Water 1293.13 Solvent Treatment 132References 1364 Recovery of Monomers 1454.1 Process for Obtaining a Polymerizable Monomer 1454.2 Pyrolysis in Carrier Gas 1464.3 Fluidized Bed Method 1474.4 Recovery of Monomers from Waste Gas Streams 1474.5 Polyolefins 1484.6 Poly(styrene) 1494.6.1 Methods with Supercritical Materials 1494.6.2 Volcanic Tuff and Florisil Catalysts 1504.6.3 Base-Promoted Iron Catalysis 1514.6.4 Composite Catalysts 1514.6.5 Fluidized-Bed Reactor 1524.6.6 Catalytic Acid and Basic Active Centers 1534.7 Phenolic Resins 1544.8 Poly(carbonate) 1554.8.1 Poly(bisphenol A carbonate) 1564.9 Poly(ethylene terephthalate) 1574.9.1 Acrylic Monomers 1574.9.2 Acrylic Aromatic Amide Oligomers 1594.9.3 Terephthalic Acid 1594.9.4 Terephthalic dihydrazide 1604.9.5 Aminolytic Depolymerization 1614.9.6 Hydrogenation Reaction 1634.10 Nylon 1634.10.1 Recovery of Caprolactam 1634.10.2 Hexamethylene diamine 1644.11 Poly(urethane) 1654.12 Sequential Processes for Mixed Plastics 1664.13 Waste Fiber Reinforced Plastics 1674.13.1 Supercritical Methyl Alcohol 1674.13.2 Ionic Liquid Treatment 1684.13.3 N,N-Dimethylaminopyridine for Depolymerization 1684.13.4 Subcritical Water 1694.13.5 Fiber-Matrix Separation for Carbon Fiber Recycling 170References 1705 Recovery into Fuels 1755.1 Poly(ethylene) 1755.1.1 Aromatic Fuel Oils from Poly(ethylene) 1755.2 Thermal and Catalytic Processes 1765.2.1 Optimization of Temperature and Catalyst 1775.3 Mixed Waste Plastics 1805.3.1 Fuel-like Feedstocks 1815.3.2 Production of Transportation Fuels5.3.3 Co-pyrolysis of Waste Vegetable Oil 183 and Waste Poly(ethylene) Plastics 1865.3.4 Refining Method for Recycling Waste Plastics 1865.4 Hydrocarbon Fuels 1895.4.1 Pyrolysis into Premium Oil Products 1895.4.2 Gasoline, Kerosene, and Diesel 1895.4.3 Two-Stage Pyrolysis Catalysis 1935.4.4 Continuous Preparation 1945.4.5 Continuous Cracking Technology 1955.5 High-Value Hydrocarbon Products 1965.6 Purified Crude Oil 1985.7 Lubricating Oil 2045.8 Waxes and Grease Base Stocks 2065.9 Co-pyrolysis of Landfill Recovered Plastic Wastes and Used Lubrication Oils 2085.10 PVC Wastes 2095.11 Iron Oxide Catalyst 2105.12 Landfill 2105.12.1 Landfill Mining Project 2105.12.2 Slow Pyrolysis 2115.12.3 Pyrolysis Oils from Landfill Waste 212References 2146 Specific Materials 2196.1 Catalysts for Recycling 2196.2 Polyolefins 2196.2.1 Thermal and Catalytic Conversion 2206.2.2 Catalytic Cracking of Polyolefins 2206.2.3 Fast Pyroylysis of PolyolefinWastes 2256.2.4 Low Density Poly(ethylene) 2256.2.5 High Density Poly(ethylene) 2326.2.6 Poly(propylene) 2596.3 Poly(styrene) 2616.3.1 Influence of Temperature in Pyrolysis 2626.3.2 Degradation of Poly(styrene) in the Presence of Hydrogen 2626.3.3 Production of Enhanced Amounts of Aromatic Compounds 2646.3.4 Poly(styrene) with Flame Retardants 2676.4 Poly(carbonate) 2686.4.1 Effect of Metal Chlorides 2686.5 Poly(ethylene terephthalate) 2716.5.1 Poly(ethylene terephthalate) Flakes 2716.5.2 Chemical Recycling 2726.5.3 Flake and Pellet Process 2756.5.4 Bio-based Plastics 2756.6 Poly(vinyl chloride) 2766.6.1 Separation Techniques for PVC Waste Plastics 2766.6.2 Surface Treatment 2766.7 Pyrolysis of Mixed Plastics 2786.7.1 Pyrolysis of PE and PVC Mixtures 2796.7.2 Waste Catalyst for Hazardous Chlorine-Containing Plastic 2806.7.3 Catalytic Hydrocracking of Post-Consumer Plastic Waste 2806.7.4 Debromination of Pyrolysis Oil 2826.7.5 Commingled Post-Consumer Polymer 2836.7.6 Waste Packaging Separation 2856.7.7 Hospital Wastes 2866.7.8 Agricultural Plastic Film Wastes 2876.8 Technical Biopolymers 2886.8.1 Mechanical Recyclability 2886.8.2 Hydrolytic Degradation 2886.8.3 Measurement of Renewable Bio-source Content 2896.9 Co-processing of Waste Plastics and Petroleum Residue 2916.9.1 Co-processing with Light Arabian Crude Oil 2916.10 Automotive Waste Plastics 2926.10.1 Lightweight Aggregates 2946.10.2 Titanium Nitride Film on Steel Substrate 2976.11 Phthalates 2976.12 Enzymatic Degradation 2986.13 ElectronicWaste 2996.13.1 Main Plastics in Electronic Waste 3026.13.2 Recycling of Compact Discs 3026.13.3 Liquid Crystal Displays 3046.13.4 Pyrolysis of Printed Circuit Boards 3056.13.5 Metal Recovery 3056.13.6 Influence of Virgin Poly(carbonate) and Impact Modifier 3096.14 Fiberglass Reinforced Plastics 3096.15 Usage in Concrete 3146.15.1 Plastic Waste as Fuel in Cement Production 3146.15.2 Constructional Works 3156.15.3 Lightweight Concrete 3166.15.4 Bakelite Plastic Waste 3166.15.5 Plastics from Waste of Electric and Electronic Equipment 3176.15.6 Plastic Aggregates 3186.15.7 Waste Plastics as Fiber 3186.15.8 Fiber Reinforced Plastic Waste Powder 3196.15.9 Domestic Waste Plastics 3206.15.10 Usage in Pavement 3216.15.11 Usage in Gypsum Blocks 3246.16 Recycling of Floor Coverings 324References 326Index 337Acronyms 337Chemicals 340General Index 345

Citation preview

Polymer Waste Management

Scrivener Publishing 100 Cummings Center, Suite 541J Beverly, MA 01915-6106 Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected])

Polymer Waste Management

Johannes Karl Fink

This edition first published 2018 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA © 2018 Scrivener Publishing LLC For more information about Scrivener publications please visit www.scrivenerpublishing.com. All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, except as permitted by law Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.

Wiley Global Headquarters 111 River Street, Hoboken, NJ 07030, USA For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose No warranty may be created or extended by sales representatives, written sales materials, or promotional statements for this work The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make This work is sold with the understanding that the publisher is not engaged in rendering professional services The advice and strategies contained herein may not be suitable for your situation You should consult with a specialist where appropriate Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Library of Congress Cataloging-in-Publication Data ISBN 978-1-119-53608-6

Cover images: Pixabay.Com Cover design by: Russell Richardson Set in size of 11pt and Minion Pro by Exeter Premedia Services Private Ltd., Chennai, India

Printed in the USA 10 9 8 7 6 5 4 3 2 1

Contents Preface

xi

1 General Aspects 1.1 History of the Literature 1.2 Amount of Wastes 1.3 Metal Content in Wastes 1.3.1 Waste Poly(ethylene) and Pure High Density Poly(ethylene) 1.4 Analysis Procedures 1.4.1 Fluorescence Labeling 1.4.2 Time-Gated Fluorescence Spectroscopy 1.4.3 Content of Flame Retardants 1.4.4 Identification of Black Plastics 1.4.5 Raman Spectroscopy 1.4.6 Life Cycle Assessment 1.4.7 Analysis of Contaminated Mixed Waste Plastics 1.4.8 Construction and Household Plastic Waste 1.4.9 Models for Forecasting the Composition of Waste Materials 1.5 Standards 1.5.1 Circular Economy Package 1.5.2 SPI Codes 1.5.3 Test Samples for Biodegradation 1.5.4 Mixed Municipal Waste 1.5.5 Aerobic Composting 1.5.6 Contaminants in Recycled Plastics 1.6 Special Problems with Plastics 1.6.1 Stability of Plastics 1.6.2 Additives 1.6.3 Plastics in Food 1.6.4 Seawater

1 2 2 4

v

4 4 4 6 6 7 9 10 12 14 14 16 16 17 19 21 21 22 22 22 23 24 25

vi

Contents 1.6.5 Landfill 1.6.6 Electronic Waste References

2

Environmental Aspects 2.1 Pollution of the Marine Environment 2.1.1 Pathways of Plastics into the Marine Environment 2.1.2 Deleterious Effects on the Marine Environment 2.1.3 Reports Concerning Special Locations 2.1.4 Analysis Methods 2.1.5 Plastic Preproduction Pellets 2.1.6 Leaching of Plastics 2.1.7 Micro-plastics 2.1.8 Marine Animals 2.2 Pollution of the Terrestrial Environment 2.2.1 Waste Generation 2.2.2 Disposal in Landfills 2.2.3 Plastic Materials for Packaging References

3

Recycling Methods 3.1 Alternative Plastic Materials 3.2 Mechanical Recycling 3.2.1 Poly(lactic acid) 3.2.2 Nanocellulose Coated Poly(ethylene) Films 3.2.3 Electric Uses 3.3 Primary Recycling 3.4 Renewable Polymer Synthesis 3.4.1 Natural Solvents for Expanded Poly(styrene) 3.4.2 Landfill Methane Recycling 3.4.3 Anaerobic Landfill 3.4.4 Simulated Semi-aerobic Landfill 3.5 Preparation and Regeneration of Catalysts 3.5.1 Reuse of ZSM-5 Zeolite 3.5.2 Modification of Zeolites 3.6 Pyrolysis Methods 3.6.1 Fluidized-Bed Reactor 3.7 Metallized Plastics Waste 3.7.1 Rotary Kiln Pyrolysis 3.8 Mixed Plastics 3.8.1 Grinding and Cleaning 3.8.2 Reductant in Ironmaking

37 38 40 51 51 54 55 55 56 59 60 60 65 71 71 71 72 73 79 80 81 81 84 84 86 87 94 97 97 99 100 100 100 101 104 105 106 108 108 109

Contents vii 3.9

Separation Processes 3.9.1 Automated Sorting of Waste 3.9.2 Sorting According to Density 3.9.3 Hydrocyclonic Separation of Waste Plastics 3.9.4 Froth Flotation 3.10 Triboelectrostatic Separation 3.11 Wet Gravity Separation 3.11.1 Selective Dissolution/Precipitation Technique for Polymer Recycling 3.12 Supercritical Water 3.13 Solvent Treatment References 4 Recovery of Monomers 4.1 Process for Obtaining a Polymerizable Monomer 4.2 Pyrolysis in Carrier Gas 4.3 Fluidized Bed Method 4.4 Recovery of Monomers from Waste Gas Streams 4.5 Polyolefins 4.6 Poly(styrene) 4.6.1 Methods with Supercritical Materials 4.6.2 Volcanic Tuff and Florisil Catalysts 4.6.3 Base-Promoted Iron Catalysis 4.6.4 Composite Catalysts 4.6.5 Fluidized-Bed Reactor 4.6.6 Catalytic Acid and Basic Active Centers 4.7 Phenolic Resins 4.8 Poly(carbonate) 4.8.1 Poly(bisphenol A carbonate) 4.9 Poly(ethylene terephthalate) 4.9.1 Acrylic Monomers 4.9.2 Acrylic Aromatic Amide Oligomers 4.9.3 Terephthalic Acid 4.9.4 Terephthalic dihydrazide 4.9.5 Aminolytic Depolymerization 4.9.6 Hydrogenation Reaction 4.10 Nylon 4.10.1 Recovery of Caprolactam 4.10.2 Hexamethylene diamine 4.11 Poly(urethane) 4.12 Sequential Processes for Mixed Plastics

111 111 112 114 114 126 127 128 129 132 136 145 145 146 147 147 148 149 149 150 151 151 152 153 154 155 156 157 157 159 159 160 161 163 163 163 164 165 166

viii

Contents 4.13 Waste Fiber Reinforced Plastics 4.13.1 Supercritical Methyl Alcohol 4.13.2 Ionic Liquid Treatment 4.13.3 N,N-Dimethylaminopyridine for Depolymerization 4.13.4 Subcritical Water 4.13.5 Fiber-Matrix Separation for Carbon Fiber Recycling References

5 Recovery into Fuels 5.1 Poly(ethylene) 5.1.1 Aromatic Fuel Oils from Poly(ethylene) 5.2 Thermal and Catalytic Processes 5.2.1 Optimization of Temperature and Catalyst 5.3 Mixed Waste Plastics 5.3.1 Fuel-like Feedstocks 5.3.2 Production of Transportation Fuels 5.3.3 Co-pyrolysis of Waste Vegetable Oil and Waste Poly(ethylene) Plastics 5.3.4 Refining Method for Recycling Waste Plastics 5.4 Hydrocarbon Fuels 5.4.1 Pyrolysis into Premium Oil Products 5.4.2 Gasoline, Kerosene, and Diesel 5.4.3 Two-Stage Pyrolysis Catalysis 5.4.4 Continuous Preparation 5.4.5 Continuous Cracking Technology 5.5 High-Value Hydrocarbon Products 5.6 Purified Crude Oil 5.7 Lubricating Oil 5.8 Waxes and Grease Base Stocks 5.9 Co-pyrolysis of Landfill Recovered Plastic Wastes and Used Lubrication Oils 5.10 PVC Wastes 5.11 Iron Oxide Catalyst 5.12 Landfill 5.12.1 Landfill Mining Project 5.12.2 Slow Pyrolysis 5.12.3 Pyrolysis Oils from Landfill Waste References

167 167 168 168 169 170 170 175 175 175 176 177 180 181 183 186 186 189 189 189 193 194 195 196 198 204 206 208 209 210 210 210 211 212 214

Contents ix 6

Specific Materials 6.1 Catalysts for Recycling 6.2 Polyolefins 6.2.1 Thermal and Catalytic Conversion 6.2.2 Catalytic Cracking of Polyolefins 6.2.3 Fast Pyroylysis of PolyolefinWastes 6.2.4 Low Density Poly(ethylene) 6.2.5 High Density Poly(ethylene) 6.2.6 Poly(propylene) 6.3 Poly(styrene) 6.3.1 Influence of Temperature in Pyrolysis 6.3.2 Degradation of Poly(styrene) in the Presence of Hydrogen 6.3.3 Production of Enhanced Amounts of Aromatic Compounds 6.3.4 Poly(styrene) with Flame Retardants 6.4 Poly(carbonate) 6.4.1 Effect of Metal Chlorides 6.5 Poly(ethylene terephthalate) 6.5.1 Poly(ethylene terephthalate) Flakes 6.5.2 Chemical Recycling 6.5.3 Flake and Pellet Process 6.5.4 Bio-based Plastics 6.6 Poly(vinyl chloride) 6.6.1 Separation Techniques for PVC Waste Plastics 6.6.2 Surface Treatment 6.7 Pyrolysis of Mixed Plastics 6.7.1 Pyrolysis of PE and PVC Mixtures 6.7.2 Waste Catalyst for Hazardous Chlorine-Containing Plastic 6.7.3 Catalytic Hydrocracking of Post-Consumer Plastic Waste 6.7.4 Debromination of Pyrolysis Oil 6.7.5 Commingled Post-Consumer Polymer 6.7.6 Waste Packaging Separation 6.7.7 Hospital Wastes 6.7.8 Agricultural Plastic Film Wastes 6.8 Technical Biopolymers 6.8.1 Mechanical Recyclability 6.8.2 Hydrolytic Degradation 6.8.3 Measurement of Renewable Bio-source Content

219 219 219 220 220 225 225 232 259 261 262 262 264 267 268 268 271 271 272 275 275 276 276 276 278 279 280 280 282 283 285 286 287 288 288 288 289

x

Contents 6.9 Co-processing of Waste Plastics and Petroleum Residue 6.9.1 Co-processing with Light Arabian Crude Oil 6.10 Automotive Waste Plastics 6.10.1 Lightweight Aggregates 6.10.2 Titanium Nitride Film on Steel Substrate 6.11 Phthalates 6.12 Enzymatic Degradation 6.13 ElectronicWaste 6.13.1 Main Plastics in Electronic Waste 6.13.2 Recycling of Compact Discs 6.13.3 Liquid Crystal Displays 6.13.4 Pyrolysis of Printed Circuit Boards 6.13.5 Metal Recovery 6.13.6 Influence of Virgin Poly(carbonate) and Impact Modifier 6.14 Fiberglass Reinforced Plastics 6.15 Usage in Concrete 6.15.1 Plastic Waste as Fuel in Cement Production 6.15.2 Constructional Works 6.15.3 Lightweight Concrete 6.15.4 Bakelite Plastic Waste 6.15.5 Plastics from Waste of Electric and Electronic Equipment 6.15.6 Plastic Aggregates 6.15.7 Waste Plastics as Fiber 6.15.8 Fiber Reinforced Plastic Waste Powder 6.15.9 Domestic Waste Plastics 6.15.10 Usage in Pavement 6.15.11 Usage in Gypsum Blocks 6.16 Recycling of Floor Coverings References

Index Acronyms Chemicals General Index

291 291 292 294 297 297 298 299 302 302 304 305 305 309 309 314 314 315 316 316 317 318 318 319 320 321 324 324 326 337 337 340 345

Preface The scientific literature with respect to plastic recycling increased dramatically after the mid-1970s and remains a growing field, since the production of polymers, and thus the problems concerning the disposal of these materials after their life cycle, are continuously growing. Recently, in several countries, official announcements and warnings concerning the pollution caused by plastic wastes have been published. For these reasons, the problems of plastic waste management have been collected from several recent scientific publications in this monograph. Plastic recycling refers to a method that can regain the original plastic material. However, there are still more sophisticated methods available for the treatment and management of waste plastics. These methods include the following: Basic primary recycling, where the materials are sorted as such and collected individually. In chemical recycling, the monomers and related compounds are sampled by special chemical treatments. Other methods, such as pyrolysis can produce fuels from waste plastics, etc. These methods and others are treated in one of the chapters. The book starts with general aspects, such as amount of plastics production, types of waste plastics, analysis procedures for identification of waste plastic types, standards for waste treatment and contaminants in recycled plastics. Then, in another chapter, environmental aspects, such as pollution in the marine environment, such as ingestion of plastics by marine animals, and pollution in landfills are dealt with. Furthermore, the recycling methods for plastics and then the methods for the recovery of monomers are reported in detail. Also, the advantages of the use of bio-based plastics are discussed. Another chapter deals with the recovery into fuels, since this has also become an important aspect. Finally, specific materials are detailed, including recycling methods for individual plastic types, and special catalysts. Here, special uses are also reported, such as the use of plastic fibers in concrete and others. xi

xii

Preface

This textmay be of importance for scientists engaged in the problems of plastics waste management and also for the education of students that are interested in the current problems of plastics recycling. The text focuses on the basic issues and also the literature of the past decade. The book provides a broad overview of plastic recycling procedures and waste management.

How to Use This Book Utmost care has been taken to present reliable data. Because of the vast variety of material presented here, however, the text cannot be complete in all aspects, and it is recommended that the reader study the original literature for more complete information.

Index There are three indices: an index of acronyms, an index of chemicals, and a general index. In the index of chemicals, compounds that occur extensively are not included at every occurrence, but rather when they appear in an important context. When a compound is found in a figure, the entry is marked in boldface letters in the chemical index.

Acknowledgements I am indebted to our university librarians, Dr. Christian Hasenhüttl, Dr.  Johann Delanoy, Franz Jurek, Margit Keshmiri, Dolores Knabl Steinhäufl, Friedrich Scheer, Christian Slamenik, Renate Tschabuschnig, and Elisabeth Groß for their support in literature acquisition. In addition, many thanks to the head of my department, ProfessorWolfgang Kern, for his interest and permission to prepare this text. I also want to express my gratitude to all the scientists who have carefully published their results concerning the topics dealt with herein. This book could not have been otherwise compiled. Last, but not least, I want to thank the publisher, Martin Scrivener, for his abiding interest and help in the preparation of the text. In addition, my thanks go to Jean Markovic, who made the final copyedit with utmost care. Johannes Fink Leoben, 11th July 2018

Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

1 General Aspects Economic, ecological, and technical aspects of plastic waste handling have been summarized in monographs (1–4). Plastics have become an indispensable ingredient of human life. They are non-biodegradable polymers mostly containing carbon, hydrogen, and a few other elements such as chlorine, nitrogen, etc. Rapid growth of the world population has led to increased demand for commodity plastics (5). The total plastics production in the world is shown in Table 1.1. Table 1.1 Plastics production in the world (6). Year

Mt

1950 1977 1989 2002 2009 2011 2015

1.5 50 100 200 250 280 322

A list of acronyms and initials used in the waste management industry has been published (7). 1

1

2

Polymer Waste Management

1.1 History of the Literature The issue of recycling of plastics was not important for scientists before the 1970s. The amount of literature concerning plastics recycling is collected in Table 1.2. Table 1.2 The literature with plastics recycling in the title of the papers found in Google Scholar in March 2018. Time range

Number of references

1970–1975 1976–1980 1981–1985 1986–1990 1991–1995 1996–2000 2001–2005 2006–2010 2011–2015 2016–2018

21 25 34 132 412 384 262 248 195 65

As can be seen from Table 1.2, the boom started in the mid-1980s.

1.2 Amount of Wastes The plastic wastes produced in the European Union in 2007 was about 52.5 M t (8, 9). In 2008, 60 M t were produced in Europe and the global production in 2008 was 245 M t (10). In 2007 the amount of post-consumer plastic wastes obtained in the EU that year was 24.6 M t, which is similar to that in 2008 (8, 10). The total waste generated per year in 2010 in Pakistan was about 31 M t per. In big Pakistani cities such as Karachi, about 7 to 8 M t of solid waste is generated. It is estimated that about 6% to 8% of solid waste is post-consumer plastic waste, while only 10% of this amount is recycled (11). The quantities of recycled poly(vinyl chloride) (PVC) in Europe are shown in Table 1.3.

General Aspects

3

Table 1.3 Quantities of recycled PVC in Europe (12). Year

Amount [t]

2003 2004 2005 2006 2007 2008 2013 2014

14255 18077 38793 82812 149463 194150 360000 440468

Also, the problems of plastics wastes in other countries have been highlighted, such as, in India (13) and Bangladesh (14, 15). Consequently, there is a growing social concern related to the management of the plastic wastes, which should proceed according to a hierarchical approach in agreement with the following order: waste minimization, reuse, recycling, energy recovery and landfilling (16). In 2014, nine countries in Europe reached a recovery ratio of more than 95% of the post-consumer plastic waste (6). The amounts are shown in Table 1.4. Table 1.4 Plastics recycling in European countries (6). Country Switzerland Austria Netherlands Germany Sweden Luxembourg Denmark Belgium Norway

Recycling Energy recovery Total Amount in % per weight 24.5 28.0 30.3 37.9 37.8 28.5 33.7 31.2 39.7

75.3 71.6 68.9 61.2 60.6 69.3 63.9 65.8 56.6

99.8 99.6 99.2 99.1 98.4 97.8 97.6 97.0 96.3

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Polymer Waste Management

1.3 Metal Content in Wastes 1.3.1

Waste Poly(ethylene) and Pure High Density Poly(ethylene)

The metal content of both waste poly(ethylene) (PE) and pure high density poly(ethylene) (HDPE) used in a specific study (9) is shown in Table 1.5. Table 1.5 Metal content of poly(ethylene) samples (9). Metal

Pure HDPE Waste PE [%] per weight

Al Ca Cr Cu Fe Mg Na Pb Ti Zn

0.002 0.001 0.004 0.000 0.000 0.000 0.001 0.000 0.000 0.021

0.015 0.070 0.003 0.162 0.003 0.003 0.013 0.009 0.151 0.006

In pure HDPE, the total metal content is very low and accounts for less than 0.03%. In contrast, the metal content in waste PE is much higher and accounts for roughly 0.4%. The main metals present are Cu and Ti with a share of 0.162% and 0.151%, respectively (9).

1.4 Analysis Procedures 1.4.1

Fluorescence Labeling

The demand for polymers in combination with their high durability following rather short life phases ensures the flow of plastic waste into landfills (17). Therefore, plastic recycling has become indispensable. In order to produce economically attractive products based on recycled plastics, mono-fractional compositions of waste polymers are required. However, existing measurement technologies, such as near infrared spectroscopy used in sorting facilities, show limitations with

General Aspects

5

regard to the separation of complex mixtures of plastic flakes, especially when dark and black plastics are part of them. An innovative approach to overcome these obstacles and provide high sorting purities is to label di erent types of plastics with unique combinations of fluorescence markers, also known as tracers, which can be considered as optical fingerprints. They are incorporated into the virgin plastic resins at ppm levels during the production process and do not a ect either the visual appearance nor the structural and mechanical integrity of the materials. The goal is to realize the practical use of this concept in industrial processes. An industrial applicable spectroscopic measurement system has been designed and implemented that can identify polymer flakes with a size of a few millimeters transported on a conveyor belt in real time based on the emitted fluorescence of incorporated organic markers. In addition to the implementation of the opto-electrical measurement system, a multi-threading software application has been developed and realized which controls the hardware and collects the measured data and finally classifies the data (17). In recent years, great e ort has been expended in the development of the automated identification and sorting methods for postconsumer plastics in the waste streams that are reaching recycling processes (18). The final properties of the recycled materials largely depend on the purity of the plastic residue. The use of fluorescence spectroscopy has been explored as a technique to identify certain waste polymers. In particular, the use of fluorescent markers for removing, for technical or safety related issues, selected HDPE containers from the waste stream has been studied. The results of this study indicate that identification by extrinsic fluorescence can be easily achieved even with a small proportion of markers of 10 3 % without a significant change to the polymer structure. The e ect of thermal, hygrothermal and photochemical degradation on the fluorescence emission has been analyzed. Although the signal intensity decreases during the accelerated degradation, distinguishable fluorescent emission can be recorded even after sample exposure to aggressive conditions, thus enabling the correct identification of the marked plastics (18).

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Polymer Waste Management

1.4.2

Time-Gated Fluorescence Spectroscopy

For the production of high-quality parts from recycled plastics, a very high purity of the plastic waste to be recycled is mandatory (19). The incorporation of fluorescent tracers, i.e., markers, into plastics during the manufacturing process helps overcome the typical problems of non-tracer based optical classification methods. Despite the unique emission spectra of fluorescent markers, the classification may become di cult when the host plastics show a strong autofluorescence that may spectrally overlap the fluorescence of the marker. Increasing the marker concentration is not a good option from an economic perspective and might also adversely a ect the properties of the plastics. A method that can suppress the autofluorescence in the needed signals is time-gated fluorescence spectroscopy. However, timegated fluorescence spectroscopy is associated with a lower signalto-noise ratio, which may result in larger classification errors. In order to optimize the signal-to-noise ratio, the best time-gated fluorescence spectroscopy parameters were investigated and validated. A model for the fluorescence signal for plastics labeled with four specifically designed fluorescent markers was used. The implementation of time-gated fluorescence spectroscopy on a measurement and classification prototype system has also been demonstrated. Mean values for a sensitivity of 99.93% and a precision of 99.80% could be achieved in this study. This shows that a highly reliable classification of plastics can be achieved in practice (19). 1.4.3

Content of Flame Retardants

The process of disassembling large plastic components from waste electrical and electronic equipment can increase the recovered value (20). A higher quality and significantly higher mechanical properties can be achieved by the proposed process compared to post-shredder recycling. Today, the application of infrared spectroscopy and X-ray fluorescence in the sorting step enables the recycling of unrecovered plastics by the determination of their chemical structure and flame retardant content (20).

General Aspects 1.4.4

7

Identification of Black Plastics

Black polymers represent a much wider variety of materials than household plastic waste since they are mostly used for technical applications with special requirements (21). Various additives and filler materials, which are added in order to achieve specific properties of the plastics, complicate the identification, since spectra of the same kind of plastic can vary dramatically if di erent types or amounts of additives, e.g., flame retardants, fibers, or soot, are contained in the plastic parts. Even lacquer films on the plastic part surface prevent any spectral identification and have to be removed before measurement. The importance of characterizing black polymers has led to a wide range of IR techniques, e.g., attenuated total reflection (22, 23), infrared transmission (24), emission spectroscopy (25), and photoacoustic spectroscopy (26). Photoacoustic spectroscopy is the measurement of the e ect of absorbed electromagnetic energy, particularly of light, on matter by means of acoustic detection (27). Also, the use of reflectance measurements was demonstrated for characterizing soot filled polymers (28, 29). 1.4.4.1

Terahertz Spectroscopy

For a modern recycling cycle, a 100% mono-fraction sorting of plastic waste is needed. The final stage in most sorting machines is based on optical sensors like hyperspectral optical camera systems. These systems cannot detect black plastics because the reflectance is too low for stable detection. T Hz systems o er the possibility of a spectroscopy analysis of shredded plastics (30, 31). From an economic viewpoint, full spectroscopy systems which cover a large area of the T Hz region are too expensive. Test measurements have shown the possibility to separate plastics with electronic T Hz systems. The limitations in bandwidth can be compensated by external height sensors and sophisticated mathematic methods. The system operates between 84 G Hz and 96 G Hz (31). Since the relevant plastics exhibit no specific absorption lines in this frequency

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Polymer Waste Management

range, a broadband approach is necessary to accumulate slight differences in dielectric properties. Using this technique, enough entropy can be gathered so that a machine learning algorithm can be trained to di erentiate between di erent materials. 1.4.4.2

Middle Infrared Spectroscopy

The identification of black polymers which contain about 0.5% to 3% mass percent soot or black master batch is still a problem in recycling sorting processes (21). Near infrared spectroscopy of non-black polymers o ers reliable and fast identification, and is therefore suitable for industrial application. However, this method cannot be used for black polymers, because small amounts of carbon black or soot absorb all light in the near infrared spectral region. However, a spectroscopy in the mid-infrared spectral region offers a possibility to identify black polymers. Mid-infrared spectral measurements can be carried out with Fourier transform infrared (FTIR) spectrometry, but the measurements are not fast enough to meet the economic requirements in sorting plants. In contrast, spectrometer systems based on the photon up-conversion technique are fast and sensitive enough and can be applied to sort black polymer parts. Such systems are able to measure several thousand spectra per second. Hence, they are suitable for industrial applications (21). In the middle infrared spectral region from 2.5 μ m to about 16 μ m wavelength, which corresponds to a wave number range from 4000 to about 600 cm 1 , the di erent kinds of plastic material show additional vibrational modes, like deformation, rocking, and twisting modes, due to their molecular structure (21). In addition to the C H group, other molecule groups, like O H, N H and O C also contribute with their fundamental vibrations to the spectral features. The various molecular groups with their di erent vibrational modes generate a unique spectrum of each polymer in the spectral range between 2500 cm 1 and 600 cm 1 . This allows a definite identification of the polymer type. Therefore, this spectral range is called the fingerprint region, and middle infrared spectroscopy is the predominant analytical method for polymer characterization (21). Another important advantage of this spectral range is that reflectance

General Aspects

9

spectra can be measured which allow the identification of black polymers. The reflectance spectra of a black poly(propylene) (PP) polymer part and a non-black part are compared in Figure 1.1.

Figure 1.1 Reflectance spectra of a black Poly(propylene) and a non-black Poly(propylene), reproduced from an open access article (21).

In the study, the results of the measurements were collected and analyzed by a principal component analysis method (21). Principal component analysis is a statistical procedure that uses an orthogonal transformation to convert a set of observations of possibly correlated variables into a set of values of linearly uncorrelated variables called principal components (32, 33). 1.4.5

Raman Spectroscopy

Raman spectroscopy has potential for application in waste plastic recycling when large-scale, accurate sorting processes are required (34). A high-accuracy rapid system for sorting a plurality of waste products by polymer type has been developed (35).

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Polymer Waste Management

Raman spectroscopy and other complex identification techniques are used to identify and sort post-consumer plastics for recycling. The procedure reads information unique to the molecular structure of the materials to be sorted to identify their chemical compositions and uses rapid high-volume sorting techniques to sort them into product streams at commercially viable throughput rates. The system uses a laser diode for irradiating the material sample, a spectrograph is used to determine the Raman spectrum of the material sample and a microprocessor-based controller is employed to identify the polymer type of the material sample (35). In addition, a high-speed Raman identifier has been developed with a 3 ms measuring time (34). This identifier could be successfully integrated into an online sorting system in a shredded plastic recycling plant. A practical-scale (200–600 kg h 1 ) demonstration facility was constructed with 50 Raman apparatuses on a 30 cm wide conveyor with a speed of 100 m min 1 . This device also included preprocessing using specific gravity classification and putty removal. The Raman identification system was used to control air jets to sort PP, poly(styrene) (PS), and an acrylonitrile-butadiene-styrene (ABS) copolymer with high accuracy from shredded plastics from post-consumer electrical appliances. The method of Raman plastic identification can also provide solutions to problems at recycling sites such as the detection of brominated flame retardants and the identification of black plastics (34). 1.4.6

Life Cycle Assessment

Life cycle assessment (LCA) is a technique to assess environmental impacts associated with all the stages of a product’s life from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling (36, 37). The basic idea of LCA is that all environmental burdens connected with a product or service should be assessed, back to the raw materials and down to the removal of waste (38). LCA is the only environmental assessment tool which avoids positive ratings for measurements which only consists of the shifting of burdens.

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In the years from 1990 to 1993, the development of LCA was presented in a series of workshops at SETAC and SETAC-Europe, which culminated in the Code of Practice of 1993 (39). The basic structure which is now underlying the standardizing activities of ISO (38, 40) is 1. 2. 3. 4.

Goal definition and scoping, Life cycle inventory analysis, Impact assessment, and Improvement assessment.

Also, the limitations of the LCA, the relationship between the LCA phases, and conditions for use of value choices and optional elements are described (40). There is software available for support of LCA studies (41–43). The basic issues of LCA have been described in several monographs (44–47). For example, the Italian system of plastic packaging waste recycling, that collected and mechanically recycled the post-consumer PE and poly(ethylene terephthalate) (PET) liquid containers, has been investigated using this technique (48). The phases of collection, compaction, sorting, reprocessing and refuse disposal were individually analyzed and quantified in terms of energy and material consumptions as well as the emissions into the environment. The main goal of this study was the quantification of the real advantage of plastic container recycling and the definition of criteria, to be environmentally compatible and economically sustainable. Also, the environmental impacts of lifetime extension versus energy e ciency for video projectors were investigated using LCA (49). The results of the LCA study showed that the use stage dominates the life cycle impacts of the global warming potential and the primary energy demand. For the metal depletion potential, the production stage accounts for most of the total life cycle load. The highest shares in production emissions were identified for electronic components, i.e., printed wired boards and integrated circuits. Reconditioning and reuse of a secondary projector resulted in minor environmental impacts in comparison to the replacement and use of a primary projector with an energy e ciency increase of 5%. The saving potential of the primary energy demand is higher only in the

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Polymer Waste Management

case of a 10% more e cient device as compared to the secondary projector (49). 1.4.7

Analysis of Contaminated Mixed Waste Plastics

Mixed waste plastics, especially those obtained from municipalities, typically contain many di erent types of contaminants that must be removed or otherwise dealt with in any e ective plastic reclamation process (50). Such contaminants can include, for example, non-melting fillers, pigments, wood, paper or metal, as well as a variety of plastics that may not be suitable for use as a feed material. Various polymeric materials that may be present in mixed waste plastics may include PE, PP, PS, PET, ethylene-vinyl acetate, poly(vinylidene chloride) (saran), ABS, and the like. The ability to use a higher percentage of mixed waste plastics in the manufacture of new products, including composite wood and plastic building materials, is highly desirable. Although many products have been manufactured successfully using scrap or recycled plastics of various types, the variability that exists in the composition and cleanliness of batches of mixed waste plastics obtained over time from either the same or di erent sources has previously caused serious problems with raw materials processing and manufacturing. For example, the reclamation and reuse of a PE film is particularly problematic. In 2005, the U.S. Environmental Protection Agency reported that less than 3% of all PE film was recycled (51). Consequently, millions of tons per year of PE film is buried in landfills and never reused. Such films can include, for example, trash bags, shopping bags, bubble wrap, shrink wrap, meat packing wrap, blood bags, nursery films, and greenhouse films. Various analytical methods have been used in the past to determine the types and properties of plastic present in mixed waste plastics, but with limited success (50). For example, batches of mixed, reclaimed plastics have been analyzed by pressing a sample of the material between two hot plates at a suitable temperature to form a test plaque, which is then cut up and repressed several more times to make it more homogeneous. Sometimes the polymers present in such test plaques can be

General Aspects

13

determined by visual inspection, although this method is highly inaccurate and only allows for gross distinctions to be made. At other times the samples may contain contaminant inclusions that are not representative of the entire batch and thus can skew the analysis. Other methods believed to have been tried to characterize mixed reclaimed plastics include, for example, melt filtration and solvent extraction. More recently, the use of di erential scanning calorimetry for various purposes has been described and explained. It has been found that the color contribution to the composite of the component plastic can be characterized by measuring a thoroughly homogenized sample of the plastic, and measuring its color parameters with a reflectance spectrophotometer. Furthermore, more useful information can be obtained by mixing small amounts of known pigments (black and white) with the material prior to homogenization, with subsequent homogenization, and color analysis. Measuring and correlating the results of such testing allow us to predict the e ects of their raw material on the subsequent composite board color, which may be pigmented. It is believed that the use of prior known methods that did not thoroughly homogenize the samples would yield unforeseeable results due to small particles of highly pigmented plastic (50). Such methods of analysis can be used to calculate the properties of materials recycled from a plurality of various batches that can be mixed together, i.e., reformulated, in the final stage (50). Such methods allow the manufacturers to produce green products with a high percentage of reclaimed plastics without the need for separating the various components of the mixed waste plastics in the manner that has previously been required. Using these methods, manufacturers can now reformulate various batches of mixed waste plastics into feed materials for new products by blending together calculated amounts of various batches that, when combined, either alone or with some portion of virgin resin, yield a feed material having a set of physical properties falling within a desired, predetermined target window (50).

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Polymer Waste Management

1.4.8

Construction and Household Plastic Waste

The recyclability of construction and household plastic waste collected from local landfills has been studied (52). Samples were processed from mixed plastic waste by injection molding. In addition, blends of pure plastics, PP and PE were processed as a reference set. Reference samples with known plastic ratio were used as the calibration set for quantitative analysis of plastic fractions in recycled blends. The samples were tested for the tensile properties. Scanning electron microscope-energy-dispersive X-ray spectroscopy was used for elemental analysis of the blend surfaces and FTIR analysis was used for the quantification of the plastics contents (52). 1.4.9

Models for Forecasting the Composition of Waste Materials

Several methods to forecast the amount of waste that will emerge have been developed (53–57). These methods have also been applied to forecast the generation of electronic waste in several regional and national studies. The material flow analysis (MFA) model can be used to describe, investigate, and evaluate the metabolism of anthropogenic systems (58). This model is based on the principle of mass conservation and can be used to quantify the flow of materials in a system defined by spatial and temporal boundaries. In an MFA model, the flows and the stocks interact with each other. The stocks increase when the inflows exceed the outflows of a system, and the stocks decrease when the outflows exceed the inflows. A flow diagram of a stock-based model is shown in Figure 1.2. The principle of the stock-based model can be described by the following equations: F in t

St

1

F out t

(1.1)

F in t k

dk

(1.2)

St M

F

out t k 1

in Here, F in t and F t k are the product inflows entering society in year t and year t k, respectively. F out is the outflow of obsolete t

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15

Production , Fabrication and Manufacturing

Product Input

Society Use

Stock

Dis carde d Product Output

Waste Management and Recycling

Figure 1.2 Flow diagram of a stock-based model (54).

products in year t. St and St 1 are the in-use stocks of product in year t and year t 1, respectively. M is the maximum lifetime of the product and dk is the lifetime distribution density value (54). Using this model, forecasts can be made based on information concerning the stock by (54): 1. Modeling the product lifetime distribution, 2. Extrapolating the stocks based on past information, and 3. Determining the initial year. Substance Flow Analysis (STAN) is a free software that supports the performance of a material flow analysis (MFA) (59). The basic idea behind STAN is the combination of all necessary features of a MFA in one software product: Graphical modeling, data management, calculations and graphical presentation of the results. Application examples of this software have been detailed (59). Also, an innovative model to forecast the composition of electronic waste materials has been presented (60, 61). The methodology is based on the distribution delay forecasting method presented by Chancerel (62). A distribution delay forecasting method, also referred to as a market supply model, uses sales

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Polymer Waste Management

and average lifetime distribution data to forecast the amount of waste that will be discarded (60). The challenge to forecast emerging waste streams with a distribution delay method is to obtain detailed and reliable data on the historic numbers of products that were sold. In addition, the number of products that will be placed on the market in the near future should also be taken into account to make a correct forecast. In order to demonstrate the applicability and of this proposed methodology, it was applied to forecast the evolution of plastic housing waste from flat panel displays and monitors, TVs, cathode ray tube TVs and cathode ray tube monitors. The results of the forecasts indicated that a wide variety of plastic types and additives, such as flame retardants, are found in the housings of similar products. This case study demonstrates that the proposed methodology allows the identification of the trends in the evolution of the material composition of waste streams (60).

1.5 Standards The standard ISO 15270:2008 provides guidance for the development of standards and specifications covering plastics waste recovery, including recycling (63). The standard establishes the di erent options for the recovery of plastics waste arising from pre-consumer and post-consumer sources. It also establishes the quality requirements that should be considered in all steps of the recovery process, and provides general recommendations for inclusion in material standards, test standards and product specifications. Consequently, the process stages, requirements, recommendations and terminology presented in the standard are intended to be of general applicability (63). 1.5.1

Circular Economy Package

The European Commission recently introduced a circular economy package, setting ambitious recycling targets and identifying waste plastics as a key area where major improvements and focus is necessary (64). The importance of plastics as a landmark case for the circular economy is denoted by the significant report on the new plastics

General Aspects

17

economy released by the Ellen MacArthur Foundation. The multiple array of challenges facing used plastics has been vividly exemplified in a recent International Solid Waste Association (ISWA) report looking at the PP case. The collection modalities were detailed. A crucial aspect a ecting the quantity and quality of recycling was investigated, using recent empirical serial data from household dry recyclables collection in the United Kingdom, and specifically within the devolved administration of England (64). In addition, the big challenges and big opportunities in the United Kingdom and other international locations were documented (65). 1.5.2

SPI Codes

The ASTM International Resin Identification Coding System, often abbreviated as the RIC, is a set of symbols appearing on plastic products that identify the plastic resin out of which the product is made (66). It was developed originally by the Society of the Plastics Industry, now the Plastics Industry Association, in 1988, but has been administered by ASTM International since 2008 (67). The Plastics Industry (SPI) has given seven recycling codes for plastics. However, only two plastic types are commonly recycled with current methods: PET (SPI Code 1) and HPDE (SPI Code 2). The codes are given in Table 1.6. Table 1.6 Plastics Industry (SPI) recycling codes (68). SPI Code 1 4 7

Usage PET LDPE Other

SPI Code 2 5

Usage HDPE PP

SPI Code 3 6

Usage PVC PS

Subsequently, the codes are highlighted. 1.5.2.1

SPI Code 1: PET

A principal benefit of chemolysis for the breakdown of PET is that the complete reversion to the starting materials is possible. The depolymerization can be achieved with catalysts or with base and heating. Isolated monomers are well suited for repolymerization

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Polymer Waste Management

and include bishydroxyethylene terephthalate, dimethyl terephthalate, and terephthalic acid via the transesterification with ethylene glycol, methanol, water, or a hydroxide. Discolored monomers produced with these processes cannot be used for a bottle-to-bottle process. However, transition-metal, Lewis-acid, and organic catalysts have been shown to facilitate transesterification to yield color-free monomers and are predicted to facilitate a closed-loop process for PET bottle recycling. 1.5.2.2

SPI Code 2 and 4: HDPE and LDPE

The thermal depolymerization of HDPE takes place above 400°C. Early studies on the volatiles found date back as early as 1954, when it was noted that decomposition proceeded through radicalbased mechanisms, and little low molecular weight ethylene was recovered. Instead, a wax-like substance (so-called Arge wax) was formed. A co-catalytic system based on a tandem dehydrogenationmetathesis sequence was applied to PE (69). The depolymerization relies on the selectively of one catalyst to dehydrogenate PE, forming internal double bonds, and an olefin metathesis catalyst to cleave the polymer into smaller segments at the double bonds (68). 1.5.2.3

SPI Code 3: PVC

One of the most problematic polymers for the environment, but also one of the most inexpensive and widely used, is PVC. Although PVC is useful for a large range of applications, it has a significant negative environmental impact when it breaks down. PVC releases phthalate plasticizers and chlorine-containing hydrocarbons, i.e., dioxins, during its environmental degradation in landfills or during thermal treatment. Thermal degradation products also include hydrochloric acid, tar, and a benzene-containing liquid fraction. In the presence of HCl, degradation of PVC is autocatalyzed and is thought to occur by radical-based reactions (68). 1.5.2.4

SPI Code 5: PP

The presence of an sp3-hybridized carbon in the PP backbone poises it for breakdown, especially in the presence of oxygen, from nor-

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mal environmental exposure and in mechanical recycling processes. Therefore, stabilizers must be added before reprocessing. If they are absent, the molecular weight is severely diminished (and crystallinity is increased) even after the first melting and remolding steps. The molecular weight can drop by 20% in the first cycle and by over 60% by the third cycle if no stabilizer is present. The state-of-the-art depolymerization techniques for PP involve pyrolysis over catalysts to produce products containing three to seven carbons with varying levels of saturation to be used for fuel. Catalysts to target selective and clean propylene regeneration have yet to be developed (68). 1.5.2.5

SPI Code 6: PS

As a result of sorting limitations in recycling plants, PS is not typically recycled in the U.S. Catalytic breakdown of PS has been reported in the presence of solid supported base or acid. Depending on the reaction conditions, low molecular weight dimers and oligomers and varying amounts of monomers can be isolated. In 2015, a study used mealworms to digest polystyrene. The products of isotopic labeling studies revealed that after mealworm digestion, 13 CO was observed in addition to fecula and other 13 C-labeled 2 biomass (68). 1.5.3

Test Samples for Biodegradation

With the increasing use of plastics, their recovery and disposal have become a major issue (70). As a first priority, recovery should be promoted. Complete recovery of plastics, however, is di cult. For example, plastic litter, which comes mainly from consumers, is difficult to recover completely. Additional examples of plastics which are di cult to recover are fishing tackle, agricultural mulches and water-soluble polymers. These plastic materials tend to leak from closed waste management cycles into the environment. Biodegradable plastics are now emerging as one of the options available to solve such environmental problems. Plastic materials, such as products or packaging, which are sent to composting facilities should be potentially biodegradable. Therefore, it is very important to determine the potential biodegradability

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Polymer Waste Management

of such materials and to obtain an indication of their biodegradability in natural environments (70). The standard ISO 10210:2012 describes methods for the preparation of test samples used in the determination of the ultimate aerobic and anaerobic biodegradability of plastic materials in an aqueous medium, soil, controlled compost or anaerobic digesting sludge (71). The methods described there are designed to provide dimensional consistency of test samples, resulting in improved reproducibility of test results during the determination of the ultimate biodegradability of the product. These methods apply to the following materials (71): 1. Natural and or synthetic polymers, copolymers or mixtures of these, 2. Plastic materials that contain additives, such as plasticizers or colorants, 3. Plastic composite materials that contain organic or inorganic fillers, and 4. Products made from the above materials. The standard ISO 13975:2012 specifies a method of evaluating the ultimate anaerobic biodegradability of plastic materials in a controlled anaerobic slurry digestion system with a solids concentration not exceeding 15%, which is often found for the treatment of sewage sludge, livestock feces or garbage. The test method is designed to yield a percentage and rate of conversion of the organic carbon in the test materials to carbon dioxide and methane produced as biogas. The method applies to the following materials, provided they have a known carbon content (72): 1. Natural and or synthetic polymers, copolymers or mixtures, 2. Plastic materials that contain additives such as plasticizers, colorants, or other compounds, and 3. Water-soluble polymers. The standard does not apply to materials which exhibit inhibitory e ects on the test microorganisms at the concentration chosen for the test (72). The ultimate aerobic biodegradability of plastic materials in an aqueous medium can be measured by the oxygen demand in a closed respirometer (70).

General Aspects

21

The standard ISO 18830:2016 specifies a test method to determine the degree and rate of aerobic biodegradation of plastic materials when settled on marine sandy sediment at the interface between seawater and the seafloor, by measuring the oxygen demand in a closed respirometer (73). The method is a simulation under laboratory conditions of the habitat found in di erent seawater sediment-areas in the sea, e.g., in a benthic zone where sunlight reaches the ocean floor, i.e., photic zone that, in marine science, is addressed as a sublittoral zone. Similarly, the standard ISO 19679:2016 is a test method to determine the degree and rate of aerobic biodegradation of plastic materials when settled on marine sandy sediment at the interface between seawater and the seafloor, by measuring the evolved carbon dioxide (74). Furthermore, the aerobic biodegradability of plastic materials in an aqueous medium can be determined by the analysis of the evolved carbon dioxide in the course of degradation (75–77). 1.5.4

Mixed Municipal Waste

The standard ISO 15985:2014 concerns a method for the evaluation of the ultimate anaerobic biodegradability of plastics based on organic compounds under high-solids anaerobic digestion conditions by the measurement of evolved biogas at the end of the test (78). This method is particularly designed to simulate the typical anaerobic digestion conditions for the organic fraction of a mixed municipal solid waste. The test material is exposed in a laboratory test to a methanogenic inoculum derived from anaerobic digesters operating only on pretreated household waste. The anaerobic decomposition takes place under high-solids, i.e., more than 20% total solids and static non-mixed conditions. The test method is designed to yield the percentage of carbon in the test material and its rate of conversion to evolved carbon dioxide and methane, i.e., biogas (78). 1.5.5

Aerobic Composting

The standard ISO 16929:2013 can be used to determine the degree of disintegration of plastic materials in a pilot-scale aerobic composting test under defined conditions (79). It forms part of an overall scheme

22

Polymer Waste Management

for the evaluation of the compostability of plastics as outlined in ISO 17088 (80). The test method explained in ISO 16929:2013 (79) can also be used to determine the influence of the test material on the composting process and the quality of the compost obtained. It cannot be used to determine the aerobic biodegradability of a test material (79). The standard ISO 20200:2015 contains a method for determining the degree of disintegration of plastic materials when exposed to a laboratory-scale composting environment (81). The method is not applicable to the determination of the biodegradability of plastic materials under composting conditions. Further testing is necessary to be able to determine the compostability. 1.5.6

Contaminants in Recycled Plastics

Dirt, paper and mixtures of polymeric materials complicate the interpretation of data from procedures used to identify the contaminants in recycled plastics. Existing ASTM and ISO methods have been collected along with currently practiced industrial techniques for the identification and classification of contaminants in recycled plastics flakes or pellets (82). A procedure has been presented for separating recycled plastics based on their color and a procedure for washing dirty, ground plastic, which results in separation of light materials with a density of smaller than 1.00 g cm 3 (83). The method is not intended to represent generic washing procedures used in the plastics recycling industry. The procedures described herein are solely for the preparation of plastic samples for use in other analytical tests. The procedure includes a room temperature wash step to facilitate separation of paper, for example, labels, followed by washing at an elevated temperature.

1.6 Special Problems with Plastics 1.6.1

Stability of Plastics

The opportunities and risks with regard to polymers have been elucidated in a monograph (84).

General Aspects

23

One of the reasons for the great versatility of many synthetic polymers is their high resistance against environmental influences (85). However, this fact leads to extremely low degradation and long residence times for synthetic polymers once they enter the environment. The degradation of synthetic polymers can generally be classified as biotic or abiotic, following di erent mechanisms, depending on a variety of physical, chemical, or biological factors. During the degradation process, polymers are converted into smaller molecular units, e.g., oligomers, monomers, or chemically modified versions. Also, some plastic types are possibly completely mineralized. The most important processes for the degradation of synthetic polymers are (85): 1. Physical degradation due to abrasive forces, heating cooling, freezing thawing, wetting drying, 2. Photodegradation, usually by UV light, 3. Chemical degradation, i.e., oxidation or hydrolysis, and 4. Biodegradation by organisms such as bacteria, fungi, or algae. 1.6.2

Additives

Plastics waste management is faced with challenges regarding the pollution caused by various chemical additives in plastic products used for enhancing polymer properties and prolonging their life (86). Despite the usefulness of such additives in the functionality of polymer products, their potential to contaminate soil, air, water and food is problematic. These additives may migrate and undesirably lead to human exposure, e.g., via food contact with these materials. Also, the additives can be released from plastics during the various recycling and recovery processes and from the products produced from recyclates (86). The additives used can be subdivided into the following categories (87): 1. Functional additives such as stabilizers, antistatic agents, flame retardants, plasticizers, lubricants, slip agents, curing agents, foaming agents, biocides, etc.,

24

Polymer Waste Management 2. Colorants such as pigments, soluble azocolorants, 3. Fillers such as mica, talc, kaolin, clay, calcium carbonate, barium sulfate, and 4. Reinforcing materials such as glass fibers and carbon fibers.

Subsequently, the properties and fields of application of the individual materials are explained (86). Compatibilizers are substances that can be used to enable the creation of special resin blends. The individual components of the resins would be otherwise incompatible. Plasticizers are used for improving the flexibility, durability and stretchability of polymeric films. At the same time, they reduce melt flow in extrusion processes. Antioxidants are also used in polymers to delay the overall oxidative degradation of plastics when they are exposed to UV radiation. Heat stabilizers can prevent thermal degradation of polymers when exposed to elevated temperatures, both in the course of use and during thermal processing. Slip agents can significantly reduce the surface coe cient of friction of a polymer. In addition to providing lubrication of the film surface, they can be used to enhance the antistatic properties of a polymer. For example, this results in better mold release properties. A lot of problems have been described and cited in other studies which deal with additives for polymers (86). The propensity, or ability, of plastics to sorb persistent organic pollutants, such as dioxins, is also known to potentially cause problems. 1.6.3

Plastics in Food

Methods for identification and quantification of micro-plastics in food, including seafood, have been reported in the literature (88). However, in some of the studies, quality assurance to avoid contamination from the air and equipment is not described, and it is not always clear how a particle is identified as being a plastic. The methods described for micro-plastics include one or more of the following steps (88): 1. Extraction and degradation of biogenic matter, 2. Detection and quantification (enumeration), and 3. Characterization of the plastic.

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Some of the described methods for degradation of the biogenic matter have the drawback that some plastics are degraded to a certain degree. Enumeration is performed by examining the samples with the naked eye or with the aid of a microscope. In the literature, micro-plastics have been classified or named in several ways, including microfibers, film spherules, bead fragment, and films. Advanced techniques for the characterization and identification of the type of plastic are by FTIR and Raman spectrometry. Another technique to obtain structural information on the plastic is pyrolysis gas chromatography (GC) mass spectroscopy (MS). Here, the identification is performed by the comparison with standard spectra or pyrograms of plastic (88). The occurrence of micro-plastics in seafood and food has been reviewed (88). A short description of the experiments is summarized in Table 1.7. Table 1.7 Studies of micro-plastics in seafood and food (88). Food type Epipelagic fish Pelagic and demersal fish Commercial fish Brown shrimp Mussels Molluscs Oysters Honey Beer

1.6.4

Reference (89) (90) (91–93) (94) (95–97) (98) (92) (99) (100)

Seawater

The environmental consequences of plastic waste are visible in the increasing levels of global plastic pollution both on land and in the oceans (101). Plastic debris has been detected worldwide in all major marine habitats, in sizes from microns to meters (102). In response, concerns about risks to marine wildlife upon exposure to the varied forms of plastic debris have increased, stimulating new research into the

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Polymer Waste Management

extent and consequences of plastics contamination in the marine environment. Among the 132 studies on marine litter, 103 of them have been reviewed in the scientific literature (103). Also, 770 personal care products were assessed to determine the occurrence, concentration and size distribution of PE microbeads (104). It was believed that the Southern Ocean was relatively free of micro-plastic contamination. However, recent studies and citizen science projects in the Southern Ocean have reported micro-plastics in deep-sea sediments and surface waters (105). Estimates showed that the levels of micro-plastic pollution released into this region from ships and scientific research stations were likely to be negligible at the scale of the Southern Ocean, however, may be significant on a local scale. Sea surface transfer from lower latitudes may contribute to the plastic concentrations in the Southern Ocean. Plastics contamination in the marine environment was first reported nearly 50 years ago, less than two decades after the rise of commercial plastics production, when less than 50 Mt were produced per year (102). The contamination of marine and freshwater ecosystems with plastic, and especially with micro-plastics, is a global ecological problem of increasing scientific concern (106). This has stimulated a great deal of research on the occurrence of micro-plastics, interaction of micro-plastics with chemical pollutants, the uptake of micro-plastics by aquatic organisms, and the resulting (negative) impact of micro-plastics. The major issues of micro-plastics in aquatic environments have been reviewed, with the principal aims to (106): 1. Characterize the methods applied for micro-plastics analysis (including sampling, processing, identification, and quantification), indicate the most reliable techniques, and discuss the further improvements required, 2. Estimate the abundance of micro-plastics in marine freshwater ecosystems and clarify the problems that hamper the comparability of such results, and 3. Summarize the existing literature on the uptake of microplastics by living organisms.

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In 2014, global plastics production surpassed 300 Mt y 1 (102). By 2015, the global production of plastics increased to 322 Mt y 1 , which approaches the total weight of the human population produced in plastic every year (107). Approximately half is used for packaging and other disposables, 40% of plastic waste is not accounted for in managed landfills or recycling facilities, and 4.8 Mt y 1 to 12.7 Mt y 1 enter the ocean as macroscopic litter and micro-plastic particles. It has been argued that such mismanaged plastic waste is similar to other persistent pollutants, such as dichlorodiphenyltrichloroethane, cf. Figure 1.3, or polychlorinated biphenyls, which once threatened a silent spring on land. Such a scenario now seems possible in the ocean, where plastic cannot be easily removed, accumulates in organisms and sediments, and persists much longer than on land. Cl Cl

Cl

Cl

Cl

Figure 1.3 Dichlorodiphenyltrichloroethane.

New evidence indicates a complex toxicology of plastic microand nanoparticles on marine life, and transfer up the food chain, including to people. Solutions to the current crisis of accumulating plastic pollution have been detailed, suggesting a Global Convention on Plastic Pollution that incentivizes collaboration between governments, producers, scientists, and citizens (107). The concentrations and the distribution of micro-plastics in oceans around the world has been reported (108). The global distribution of micro-plastics in the environment, and the fate and impact on marine biota, especially the food chain, has been discussed. Plastic pollution is ubiquitous throughout the marine environment (109). Estimates of the global abundance and the weight of floating plastics showed insu cient data, particularly from the Southern Hemisphere and remote regions. An estimate of the total number of plastic particles and their weight floating in the world’s oceans has been reported from 24

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expeditions in the years 2007 to 2013 across all five subtropical gyres, costal Australia, the Bay of Bengal and the Mediterranean Sea. Using an oceanographic model of floating debris dispersal calibrated by these data, and correcting for wind-driven vertical mixing, a minimum of 5.25 trillion particles weighing 268,940 t have been estimated. When comparing between four size classes, two microplastics smaller than 4.75 mm and meso- and macroplastic greater than 4.75 mm, a tremendous loss of micro-plastics is observed from the sea surface compared to expected rates of fragmentation, suggesting there are mechanisms at play that remove the smaller type plastic particles from the ocean surface (109). Plastic debris in the marine environment has been widely documented, but the quantity of plastic entering the ocean from waste generated on land is unknown (110). By linking worldwide data on solid waste, population density, and economic status, the mass of land-based plastic waste entering the ocean was estimated. It was calculated that 275 Mt of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 Mt entering the ocean. The population size and the quality of waste management systems largely determine which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025 (110). Micro-plastics have been documented in marine environments worldwide, where they pose a potential risk to biota (111). Until now, environmental interactions between micro-plastics and lower trophic organisms are only poorly understood. Coastal shelf seas are rich in productivity but also experience high levels of micro-plastic pollution. In these habitats, fishes have an important ecological and economic role. In their early life stages, planktonic fish larvae are vulnerable to pollution, environmental stress and predation. the occurrence of micro-plastic ingestion in wild fish larvae has been assessed. Fish larvae and water samples were taken across three sites (10, 19 and 35 km from shore) in the western English Channel from April to June 2016. Micro-plastics were ingested by 2.9% of fish larvae (n 347), of which 66% were blue fibers. The ingested microfibers closely resembled those identified within water samples.

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With distance from the coast, the larval fish density increased significantly (P < 0.05), while waterborne micro-plastic concentrations (P < 0.01) and incidence of ingestion decreased (111). A global model of plastic inputs from rivers into oceans based on waste management, population density and hydrological information has been presented (112). The model is calibrated against measurements available in the literature. It has been estimated that between 1.15 and 2.41 Mt of plastic waste currently enters the ocean every year from rivers, with over 74% of emissions occurring between May and October. The top 20 polluting rivers, mostly located in Asia, account for 67% of the global total. The findings of this study provide the baseline data for ocean plastic mass balance exercises, and assist in prioritizing future plastic debris monitoring and mitigation strategies. The subtropical ocean gyres are recognized as great marine accumulation zones of floating plastic debris. However, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources (113). In a study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition (113). Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the thermohaline circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector has been hypothesized as an important sink of plastic debris (113). Micro-plastics could be a vehicle for metal transport in marine and freshwater environments because they have the potential to adsorb considerable concentrations of metals and may remain suspended for long periods of time, allowing distribution with water

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movements (88). No studies were identified that have assessed the contribution of metals adsorbed by micro-plastics in food. 1.6.4.1

Sampling and Analysis

The concentrations of micro-plastics in aqueous samples are relatively low compared to those in the sediments (85). Therefore, a large volume of the water samples (up to hundreds of liters) is usually filtered during the sampling process to obtain a representative sample. The sampling of the water surface is carried out in most cases with neuston or plankton nets supported by a flow meter to determine the accurate sample volume. These nets are used in different mesh sizes ranging from 50 μ m to 3,000 μ m, while 300 μ m is the most commonly used mesh size among all studies. This sampling method leads to nonquantitative sampling of micro-plastics with particle sizes smaller than 300 μm. The nets with smaller mesh sizes are prone to clogging. To overcome this problem, new methods have been developed using filter cascades that result in a size fractionation during the sampling and the reduction of the matrix burden of the small mesh sizes (114). At the moment, there is no commonly accepted sampling strategy for sediment samples (85). First, the sediment samples must be divided into samples from the shoreline and the riverbed or lakebed. The collection of bed sediments by sediment grabs provides relatively comparable results due to the standardized sampling instrument. The use of corers allows the determination of micro-plastic depth profiles, however, this technique results in small sample volumes. During the sampling process and the sample preparation, it is important to avoid any contact with other plastic equipment to keep the contamination by the method low (85). Pyrolysis Methods. The reliable recognition of micro-plastics particles is limited and underlies substantial uncertainties (115). Therefore, spectroscopic methods are necessary to ensure the plastic nature of isolated particles, determine the polymer type and obtain particle count related quantitative data. Curie-point pyrolysis GC MS combined with thermochemolysis has been demonstrated

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as an excellent analytical tool to simultaneously identify and optionally quantify micro-plastics in environmental samples on a polymer specific mass related trace level. This method is independent of any mechanical preselection or particle appearance. For this purpose, polymer characteristic pyrolysis products and their indicative fragment ions were used to analyze eight common types of plastics. The method has been tested with selected fish samples after an enzymatic-chemical pretreatment. This approach with mass related results is complementary to common FTIR and Raman methods, providing particle counts of individual polymer particles (115). Extraction of Micro-plastics in Fish Samples. The quantification of micro-plastic in the stomachs of various biota is central to assessing the impact and extent of plastic pollution and to determining its pathways through food webs and sinks (116). The development of techniques to isolate and characterize micro-plastic is, however, still in progress and methodologies across di erent studies are barely standardized (117). The monitoring of plastics in fish has been integrated into the European Union’s Marine Strategy Framework Directive (118) and Oslo-Paris Commission (OSPAR) (119) guidelines. OSPAR has requested a common monitoring protocol for plastic particles in fish stomachs, which was provided through a special advice report (120). Several classes of digesting solutions have been employed to extract micro-plastics from biological matrices. However, the performance of digesting solutions across di erent temperatures has never been systematically investigated (121). The e ciency of di erent oxidative agents (NaClO or H2 O2 ), bases (NaOH or KOH), and acids (HCl or HNO3 ) both concentrated and diluted 5% in digesting fish tissues at room temperature of 40°C, 50°C, and 60°C was measured. Afterwards, the treatments that were e cient in digesting the biological materials were evaluated for their compatibility with eight major plastic polymers, assessed through recovery rate, Raman spectroscopy analysis, and morphological changes. Among the tested solutions, NaClO, NaOH, and diluted acids did not result in a satisfactory digestion e ciency at any of the temperatures. The treatment with H2 O2 at 50°C e ciently digested

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the biological materials, although it decreased the recovery rate of nylon 6 and nylon 66 and altered the color of PET fragments. Similarly, concentrated HCl and HNO3 treatments at room temperature fully digested the fish tissues, but also fully dissolved nylon 6 and nylon 66. Furthermore, the recovery rate of most or all of the tested polymers was reduced. A potassium hydroxide solution fully eliminated the biological matrices at all temperatures. However, at 50°C and 60°C, it degraded PET, reduced the recovery rate of PET and PVC, and changed the color of nylon 66. The treatment of biological materials with a 10% KOH solution and incubating at 40°C was found to be both time e cient and cost-e ective in digesting biological materials, and had no impact on the integrity of the plastic polymers. Furthermore, coupling this treatment with a NaI-based extraction method created a promising protocol to isolate micro-plastics from whole fish samples (121). 1.6.4.2

Plastic Additives in Marine Environments

Only a few studies have focused on plastic additives in marine environments (122). These chemicals are incorporated into plastics from which they can leach out as most of them are not chemically bound. As a consequence of plastic accumulation and fragmentation in oceans, plastic additives could represent an increasing ecotoxicological risk for marine organisms. The main classes of plastic additives identified in the literature, their occurrence in the marine environment, as well as their e ects on and transfers to marine organisms have been reviewed (122). Polybrominated diphenyl ethers, phthalates, nonylphenols, bisphenol A and antioxidants were found to be the most common plastic additives occurring in marine environments. Moreover, the transfer of these plastic additives to marine organisms has been demonstrated both in laboratory and field studies. It has been proposed that the upcoming research should be focused on the toxicity of micro-plastics including the plastic additives as potential hazards for marine organisms. Furthermore, a greater focus on the transport and fate of plastic additives is required considering that these chemicals may easily leach out from plastics (122).

General Aspects 1.6.4.3

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Erosion of Floating Plastic Pieces

Erosion has been tested as a possible mechanism for the decrease of the size of plastic pieces floating in oceans (123). A seawater wave tank fitted in an artificial UV light weathering chamber was built to study the behavior of PP injected pieces under close ocean-like conditions. In air, the pieces undergo a degradation in the bulk with a decrease of mechanical properties. Here only a small change of the crystal properties and nearly no change of the surface chemistry is observed. Weathering in the seawater wave tank shows only surface changes, with no e ect on crystals or mechanical properties with loss of small pieces of matter in the submicron range and a change of surface chemistry. This suggests the presence of an erosion dispersion mechanism. Such a mechanism could explain why no particles smaller than about 1 mm are found when plastic debris at sea is collected. They are much smaller pieces, eroded from plastic surfaces by a mechano-chemical process, similar to the erosion mechanism found in the dispersion of agglomerate under flow (123). 1.6.4.4

Modeling of the Transport to Seas

Plastic pollution is considered one of today’s main environmental problems and plastic waste in oceans, rivers and streams (124) also are potential risks to human health (125). Recent estimates indicate that rivers transport between 1.15 Mt y 1 and 2.41 Mt y 1 of plastic waste to the oceans (112). The quantification of the transport of plastic debris from river to sea is crucial for assessing the risks of plastic debris to human health and the environment (126). A global modeling approach has been presented in order to analyze the composition and quantity of point-source micro-plastic fluxes from European rivers to the sea. This model accounts for different types and sources of micro-plastics entering the river systems via point sources. The information of these sources were combined with the information concerning sewage management and plastic retention during river transport for the largest European rivers.

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The sources of micro-plastics include personal care products, laundry, household dust, and tire and road wear particles. The modeled micro-plastics exported by rivers to seas are collected in Table 1.8. Table 1.8 Micro-plastics exported by rivers to seas (126). Type Tire and road wear particles Plastic-based textiles abraded during laundry Plastic fibers in household dust Microbeads in personal care products

Amount [%] 42 29 19 10

The export of micro-plastic di ers largely among the European rivers, as a result of di erences in socioeconomic development and technological status of sewage treatment facilities (126). About two thirds of the micro-plastics modeled in the study flow into the Mediterranean Sea and into the Black Sea. This can be explained by the relatively low micro-plastic removal e ciency of sewage treatment plants in the river basins draining into these two seas. Sewage treatment is generally more e cient in river basins draining into the North Sea, the Baltic Sea and the Atlantic Ocean. The model was also used to explore the future trends up to the year 2050. The scenarios indicate that in the future river export of micro-plastics may increase in some river basins, but decrease in others. Remarkably, for many basins a reduction in river export of micro-plastics from point sources was calculated, mainly due to an anticipated improvement in sewage treatment (126). 1.6.4.5

Extraction of Micro-plastics in Mussels

Procedures for the digestion of mussel soft tissues and extraction of the of micro-plastics have been compared (127). A complete tissue digestion could be achieved with 1 M NaOH, 35% HNO3 , and protease at 9.6 UHb ml 1 (unit hemoglobin per milliliter). However, the use of HNO3 caused an unacceptable destruction of some micro-plastics. The recovery of micro-plastics spiked into mussels was similar (93% 10%) for NaOH and the enzyme digestions. Thus, the use of industrial enzymes based on digestion

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e ciency, micro-plastic recovery, and avoidance of caustic chemicals is recommended (127). 1.6.4.6

Microbial Contamination

It has been found that plastic debris can act as a substrate for diverse microbial communities (128–131). Microorganisms, including plastic decomposing organisms and pathogens, have been shown to colonize micro-plastics. Furthermore, in the ocean such communities have been shown to be distinct from microbial communities in the surrounding surface water. However, the relevance to food and the consequences to human health are unknown. 1.6.4.7

Micro-plastics in Commercial Fish

Micro-plastic ingestion has been reported for several marine species, however, the level of contamination in transitional systems and associated biota is less known (132). The occurrence of micro-plastic ingestion in three commercial fish species has been assessed (132): Sea bass (Dicentrarchus labrax), seabream (Diplodus vulgaris) and flounder (Platichthys flesus) from the Mondego estuary (Portugal). Micro-plastics were extracted from the gastrointestinal tract of 120 individuals by visual inspection and digestion solution. A total amount of 157 particles has been extracted from 38% of the total fish samples, i.e., 96% fibers, with 1.67 0.27 (SD) micro-plastics per fish. A significantly higher amount of ingested micro-plastics was recorded for D. vulgaris (73%). The dominant polymers identified by μ -FTIR were polyester, PP and rayon, a semi-synthetic fiber (132). The ingestion of micro-plastics and natural fibers, smaller than 5 mm, was investigated for two commercial fish species in the western Mediterranean Sea: Sardina pilchardus and Engraulis encrasicolus (133). The gastrointestinal tracts from 210 individuals from 14 stations were examined. Of the small pelagic fish S. pilchardus and E. encrasicolus, 14.28% – 15.24% were found to have ingested micro-plastics and natural fibers. Fibers were the most frequent particle types with an amount of 83%.

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FTIR analysis showed that PET was the most common microplastics material in an amount of 30%. The results showed that both micro-plastics and natural fibers of anthropogenic origin are common throughout the pelagic environment along the Spanish Mediterranean coast (133). Juvenile polar cods (Boreogadus saida) were investigated for the presence of plastics in their stomachs (134). Polar cod is considered a key species in the Arctic ecosystem. The fishes were collected both directly from underneath the sea ice in the Eurasian Basin and in open waters around Svalbard. The stomachs of 72 individuals were analyzed under a stereo microscope. Two stomachs contained nonfibrous micro-plastic particles. μ -FTIR analysis confirmed that the particles consisted of epoxy resin and a mix of kaolin with poly(methyl methacrylate) (134). Fibrous objects were excluded from the analysis to avoid bias due to contamination with airborne microfibers. A systematic investigation of the risk for a secondary microfiber contamination during analytical procedures showed that precautionary measures in all procedural steps were critical. Based on the two nonfibrous objects found in polar cod stomachs, the results showed that the ingestion of micro-plastic particles by this ecologically important fish species is possible. With increasing human activity, plastic ingestion may act as an increasing stressor on polar cod in combination with ocean warming and sea ice decline in peripheral regions of the Arctic Ocean (134).

1.6.4.8

Seabirds and Marine Plastic Debris

The literature concerning the issue of seabirds and marine plastics has been collected (135). It was found that of 69 seabird species that commonly occur in the northeastern Atlantic, 25 had evidence of ingesting plastic. However, the data on plastic ingestion was available for only 49% of all species, with 74% of investigated species recorded as having ingested plastic. For many species, the sample sizes were small or not reported, and only 39% of studies were from the 21st century, whilst information from multiple countries and years was only available for 11 species.

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This indicates that there is very little knowledge about the current prevalence of plastic ingestion and nest incorporation for many species, several of them globally threatened. Furthermore, in the majority of studies, the metrics reported were inadequate to carry out robust comparisons among locations and species or perform meta-analysis experiments (135). 1.6.4.9

Micro-plastics in Spanish Table Salt

Micro-plastics have been found in several sea salt samples from di erent countries, indicating that sea products are irremediably contaminated by micro-plastics (136). Analysis has been done on 21 di erent samples of commercial table salt from Spain for micro-plastics content and nature. The samples comprise sea salts and well salts, before and after packing. The micro-plastic content was found to be 50–280 MPs kg 1 of salt, PET being the most frequently found polymer, followed by PP and PE, with no significant di erences among all the samples. The results indicated that even though the microparticles might originate from multiple sources, there is a background presence of micro-plastics in the environment (136). 1.6.5 1.6.5.1

Landfill Ingestion by Gulls

Plastic waste and plastic debris have been recognized as widespread, common and problematic environmental pollutants (137). An important consequence of this pollution is the ingestion of plastic debris by wildlife. Assessing the degree to which di erent species ingest plastics, and the potential e ects of these plastics on their health are important research needed for understanding the impacts of plastic pollution. Plastic and other types of debris ingestion have been examined in three sympatric overwintering gull species (Herring gulls [Larus smithsonianus], Great Black-backed Gulls [Larus marinus], and Iceland Gulls [Larus glaucoides]) to understand how debris ingestion di ers among species, age classes and sexes in gulls. Also, an assessment was made on how plastic burdens can be associated with body condition to investigate how gulls may be

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a ected by debris ingestion. There were no di erences among the species, age classes or sexes in the incidence of debris ingestion, i.e., plastic or otherwise, of the mass or number of debris pieces ingested. No correlation was found between ingested plastics burdens and the individual conditions. Gulls ingested plastic debris, but also showed high levels of other debris types as well, including metal, glass and building materials, including a metal piece of debris found within an abscess in the stomach. Thus, when the health e ects of debris ingestion on gulls, and other species that ingest debris, is of interest, either from a physical or chemical perspective, it may be necessary to consider all debris types and not just plastic burdens as is often currently done for seabirds (137). 1.6.6

Electronic Waste

Recycling of waste from electric and electronic equipment is important not only to reduce the amount of waste requiring treatment, but also to promote the recovery of valuable materials (138). Many countries and organizations have drafted national legislation to improve the reuse, recycling and other forms of material recovery of waste from electric and electronic equipment to reduce the amount and types of materials disposed in landfills. The management of electrical and electronic waste in China and India has been comparatively evaluated (139). It has been concluded that the recycling capacity should be increased and thus the amount of waste from electric and electronic equipment contaminating the environment and endangering human health should be decreased. The useful life of consumer electronic devices is comparatively short, and it decreases as a result of rapid changes in equipment features and capabilities. This creates a large waste stream of obsolete electronic equipment, electronic waste (140). Even when there are conventional disposal methods for electronic waste, these methods have disadvantages from both the economic and environmental viewpoints. Therefore, new electronic waste management methods need to be developed. The recycling programs and collection methods that are available have been described (140). Also, the methods that are available to recover materials from electronic waste have been reviewed. These

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are in particular recycling technologies for the glass, plastics, and metals found in electronic waste. For plastics, chemical feedstock recycling, mechanical recycling, and thermal recycling methods are used. Also, recovery processes for copper, lead, and precious metals such as silver, gold, platinum, and palladium have been reviewed (140). Waste of electric and electronic equipment is diverse and complex in terms of the materials used (141). The characterization of this waste stream is of paramount importance for developing a cost-e ective and environmentally friendly recycling system. For a maximum separation of the materials, waste of electric and electronic equipment should be shredded into small, even fine particles, generally below 5 mm or 10 mm. 1.6.6.1

Poly(vinyl chloride)

Hazardous chlorinated plastic, i.e., PVC, comprises around 6%–8% of the total mixed plastics in electronic waste. When it is subjected to incineration or uncontrolled burning processes for disposal, recycling, or metals recovery, its high chlorine content can contribute to the formation of highly toxic and persistent chlorinated dioxins (142, 143). Subjecting PVC to mechanical recycling is also problematic. Even when present in only small quantities, it worsens the recycling ratio by forming compounds with the main plastics and otherwise deteriorating them (144, 145). When PVC is landfilled, some of its chemical additives may leach, adding to the overall contaminant burden of landfill leachate (146– 148). Therefore, any end-of-life product or waste stream from products containing hazardous chlorinated plastics must be managed in a way that minimizes the potential impact on human health and the environment (149). 1.6.6.2

Uncontrolled Electronic Waste Recycling

Environmental pollution due to uncontrolled electronic waste recycling activities has been reported in a number of locations in China (150).

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Guiyu is a traditional rice-growing village located in southeastern Guangdong Province (PR China), which has turned into an intensive electronic waste recycling site (151). Incomplete combustion of electronic waste in open air and dumping of processed materials are the major sources of various toxic chemicals. The concentrations of persistent organic pollutants, such as flame retardants, dioxins and furans, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and heavy metal or metalloid concentrations of di erent environmental media at this place have been detailed (151). It has been concluded that detailed investigations should be done, especially on tracking the exposure pathways of di erent toxic chemicals which may a ect the workers and local residents, especially mothers, infants and children. The microbial community structure and function in sediments from electronic waste contaminated rivers in the Guiyu area of China have been investigated (152). The river sediments from Guiyu were severely polluted by toxic organic pollutants and heavy metals. Statistical analysis experiments revealed that toxic organic compounds contributed more to the observed variations in the sediment microbial community structure and predicted functions (24.68% and 8.89%, respectively) than heavy metals (12.18% and 4.68%) (152). For example, high levels of heavy metals in rice in an electronic waste recycling area have been documented (153). Also, high concentrations of heavy metals in surface dust have been reported in the region of Guiyu (154).

References 1. M. Chanda and S.K. Roy, Vol. 75 of Plastics Engineering Series, chapter 2. CRC Press, Boca Raton, London, New York, 2016. 2. R. Francis, ed., Recycling of Polymers: Methods, Characterization and Applications, Wiley-VCH, Weinheim, Germany, 2016. 3. N. Rudolph, R. Kiesel, and C. Aumnate, Understanding Plastics Recycling: Economic, Ecological, and Technical Aspects of Plastic Waste Handling, Carl Hanser Verlag GmbH Co KG, 2017.

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19. P. Fomin, D. Zhelondz, and C. Kargel, Applied Spectroscopy, Vol. 71, p. 919, 2017. 20. F. Wagner, J. Peeters, J. De Keyzer, J. Duflou, and W. Dewulf, Disassembly based plastics recycling from waste electrical and electronic equipment (weee) for high value applications, in Plastics Recycling Technology, Cologne, 2017. Centre for Industrial Management. 21. W. Becker, K. Sachsenheimer, and M. Klemenz, Polymers, Vol. 9, p. 435, Sep 2017. 22. W.W. Hart, P.C. Painter, J.L. Koenig, and M.M. Coleman, Applied Spectroscopy, Vol. 31, p. 220, 1977. 23. R.T. Graf, J.L. Koenig, and H. Ishida, Comparison of FT-IR transmission, specular reflectance, and attenuated total reflectance spectra of polymers in H. Ishida, ed., Fourier Transform Infrared Characterization of Polymers, pp. 385–395. Springer US, Boston, MA, 1987. 24. E.F. Devlin, Journal of Polymer Science: Polymer Letters Edition, Vol. 19, p. 189, 1981. 25. J.M. Chalmers, M.W. Mackenzie, J.L. Sharp, and R.N. Ibbett, Analytical Chemistry, Vol. 59, p. 415, 1987. 26. J.M. Chalmers, M.W. Mackenzie, and N. Poole, Microchimica Acta, Vol. 95, p. 249, Jan 1988. 27. Wikipedia contributors, Photoacoustic spectroscopy — wikipedia, the free encyclopedia, 2018. [Online; accessed 29-March-2018]. 28. W. Becker and N. Eisenreich, Using spectroscopic methods for identification of technical plastics from E& E and Elv sector, in Proceedings of the Going Green-Care Innovation Conference, Vienna, Austria, pp. 13– 16, 2006. 29. W. Becker, Prozessanalytik in der kunststo ffindustrie in R.W. Kessler, ed., Prozessanalytik, chapter 18, pp. 551–570. Wiley-Blackwell, 2006. 30. D. Nüssler, N. Pohl, J. Küls, K. Hein, and D. Stein, THz imaging for recycling of black plastics, in Microwave Conference, pp. 1–4, Berlin, 2014. GEMiC, VDE. 31. A. Küter, S. Reible, T. Geibig, D. Nüßler, and N. Pohl, Technisches Messen, Vol. 85, p. 191, 2017. 32. Wikipedia contributors, Principal component analysis — wikipedia, the free encyclopedia, 2018. [Online; accessed 29-March-2018]. 33. T. Næs, T. Isaksson, T. Fearn, and T. Davies, A User Friendly Guide to Multivariate Calibration and Classification, NIR publications, Chichester, UK, 2002. 34. H. Kawazumi, A. Tsuchida, T. Yoshida, and Y. Tsuchida, High-performance recycling system for waste plastics using raman identification in I. Dincer, A. Midilli, and H. Kucuk, eds., Progress in Sustainable Energy Technologies Vol II: Creating Sustainable Development, pp. 519–529. Springer International Publishing, Cham, 2014.

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35. E.J. Sommer and J.T. Rich, Application of Raman spectroscopy to identification and sorting of post-consumer plastics for recycling, US Patent 6 313 423, assigned to National Recovery Technologies, Inc. (Nashville, TN), November 6, 2001. 36. J. Guinée, The International Journal of Life Cycle Assessment, Vol. 6, p. 255, Sep 2001. 37. Wikipedia contributors, Life-cycle assessment — wikipedia, the free encyclopedia, 2018. [Online; accessed 13-March-2018]. 38. W. Klöp er, Environmental Science and Pollution Research, Vol. 4, p. 223, Dec 1997. 39. F. Consoli, Guidelines for life-cycle assessment. A code of practice, Technical report, Society of Environmental Toxicology and Chemistry (SETAC), Brussels, Belgium, 1993. 40. Technical Committee:ISO TC 207 SC 5, Environmental management – life cycle assessment – principles and framework, ISO Standard 14040, International Organization for Standardization, Geneva, Switzerland, 2006. 41. M. Goedkoop, M. Oele, J. Leijting, T. Ponsioen, and E. Meijer, Introduction to LCA, electronic: https: www.pre-sustainability.com download SimaPro8IntroductionToLCA.pdf, 2016. 42. N. N., What is the best life cycle assessment (LCA) software?, electronic: https: www.researchgate.net post What_is_the_best_Life_ Cycle_Assessment_LCA_software, 2018. 43. H. Levin, Life cycle assessment software, tools and databases, electronic: http: www.buildingecology.com sustainability life-cycle-assessment life-cycle-assessment-software, 2018. 44. M. Curran, ed., Environmental Life-cycle Assessment, McGraw-Hill, New York, 1996. 45. D.F. Ciambrone, Environmental Life Cycle Analysis, CRC Press, Boca Raton, FL, 1997. 46. O. Jolliet, M. Saade-Sbeih, and S. Shaked, Environmental Life Cycle Assessment, CRC Press, Boca Raton, 2016. 47. Springer, The International Journal of Life Cycle Assessment, Journal Series. 48. U. Arena, M.L. Mastellone, and F. Perugini, The International Journal of Life Cycle Assessment, Vol. 8, p. 92, Mar 2003. 49. C.W. Cheung, M. Berger, and M. Finkbeiner, The International Journal of Life Cycle Assessment, Vol. 23, p. 82, Jan 2018. 50. J.G. Brooks and C.L. Becker, Method for processing and analyzing contaminated mixed waste plastics to produce reformulated, blended feed materials having a desired plastic content, US Patent 8 106 104, assigned to Advanced Environmental Recycling Technologies, Inc. (Springdale, AR), January 31, 2012.

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51. N.N., Advancing sustainable materials management: Facts and figures, EPA Web Archive EPA 530-R-06-011, United States Environmental Protection Agency, Washington, DC, 2005. 52. I. Turku, T. Kärki, K. Rinne, and A. Puurtinen, Waste Management & Research, Vol. 35, p. 200, 2017. 53. P.H. Brunner and H. Rechberger, The International Journal of Life Cycle Assessment, Vol. 9, p. 337, Sep 2004. 54. L. Zhang, Z. Yuan, and J. Bi, Resources, Conservation and Recycling, Vol. 55, p. 1087, 2011. 55. J. Huisman, M. Van der Maesen, R.J.J. Eijsbouts, F. Wang, C.P. Baldé, and C.A. Wielenga, United Nations University, ISP–SCYCLE, Bonn, Germany, Vol. 15, 2012. 56. M. Polák and L. Drápalová, Waste Management, Vol. 32, p. 1583, 2012. 57. L. Schebek, W.-R. Poganietz, S. Feifel, and S. Ziemann, Technological innovation and anthropogenic material flows in S. Hartard and W. Liebert, eds., Competition and Conflicts on Resource Use, pp. 135– 153. Springer International Publishing, Cham, 2015. 58. P. Baccini and H.-P. Bader, Regionaler Stoff haushalt: Erfassung, Bewertung und Steuerung, Spektrum, Akad. Verlag, 1996. 59. O. Cencic and H. Rechberger, Journal of Environmental Engineering and Management, Vol. 18, p. 3, 2008. 60. J.R. Peeters, P. Vanegas, K. Kellens, F. Wang, J. Huisman, W. Dewulf, and J.R. Duflou, Waste Management, Vol. 46, p. 28, 2015. 61. P. Vanegas, J.R. Peeters, W. Dewulf, D. Cattrysse, and J.R. Duflou, Procedia CIRP, Vol. 26, p. 601, 2015. 12th Global Conference on Sustainable Manufacturing – Emerging Potentials. 62. P. Chancerel, Substance flow analysis of the recycling of small WEEE. An assessment of the recovery of gold and palladium. Ph.D thesis, Uni Berlin, Institut für Technischen Umweltschutz, Berlin, Germany, 2010. 63. Technical Committee: ISO TC 61 SC 14, Plastics – guidelines for the recovery and recycling of plastics waste, ISO Standard 15270, International Organization for Standardization, Geneva, Switzerland, 2008. 64. J.N. Hahladakis, M. Atseyinku, E. Iacovidou, P. Purnell, P.T. Williams, and C.A. Velis, Impact of dry recyclables collection schemes on plastics recycling in the UK: Circular economy highly depends on collection logistics, in E. Gidarakos, R. Cossu, and R. Stegmann, eds., CRETE 2016. Proceedings CRETE 2016, Fifth International Conference on Industrial & Hazardous Waste Management, September 2016. 65. M.P. Bates, Plastics recycling: The big challenges, the big opportunities UK and international, in Recoup Annual Conference, September 2016.

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66. Wikipedia contributors, Resin identification code — wikipedia, the free encyclopedia, 2018. [Online; accessed 24-March-2018]. 67. ASTM International, Standard practice for coding plastic manufactured articles for resin identification, ASTM Standard D7611 D7611M-13e1, ASTM International, West Conshohocken, PA, 2013. 68. J.M. García, Chem., Vol. 1, p. 813, 2016. 69. X. Jia, C. Qin, T. Friedberger, Z. Guan, and Z. Huang, Science Advances, Vol. 2, 2016. 70. Technical Committee: ISO TC 61 SC 14, Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium – method by measuring the oxygen demand in a closed respirometer, ISO Standard 14851, International Organization for Standardization, Geneva, Switzerland, 1999. 71. Technical Committee: ISO TC 61 SC 14, Plastics – methods for the preparation of samples for biodegradation testing of plastic materials, ISO Standard 10210, International Organization for Standardization, Geneva, Switzerland, 2012. 72. Technical Committee: ISO TC 61 SC 14, Plastics – determination of the ultimate anaerobic biodegradation of plastic materials in controlled slurry digestion systems – method by measurement of biogas production, ISO Standard 13975, International Organization for Standardization, Geneva, Switzerland, 2012. 73. Technical Committee: ISO TC 61 SC 14, Plastics – determination of aerobic biodegradation of non-floating plastic materials in a seawater sandy sediment interface – method by measuring the oxygen demand in closed respirometer, ISO Standard 18830, International Organization for Standardization, Geneva, Switzerland, 2016. 74. Technical Committee: ISO TC 61 SC 14, Plastics – determination of aerobic biodegradation of non-floating plastic materials in a seawater sediment interface – method by analysis of evolved carbon dioxide, ISO Standard 19679, International Organization for Standardization, Geneva, Switzerland, 2016. 75. Technical Committee: ISO TC 61 SC 14, Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium – method by analysis of evolved carbon dioxide, ISO Standard 14852, International Organization for Standardization, Geneva, Switzerland, 1999. 76. Technical Committee: ISO TC 61 SC 14, Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions – method by analysis of evolved carbon dioxide – part 1: General method, ISO Standard 14855-1, International Organization for Standardization, Geneva, Switzerland, 2012.

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77. Technical Committee: ISO TC 61 SC 14, Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions – method by analysis of evolved carbon dioxide – Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test, ISO Standard 14855-2, International Organization for Standardization, Geneva, Switzerland, 2007. 78. Technical Committee: ISO TC 61 SC 14, Plastics – determination of the ultimate anaerobic biodegradation under high-solids anaerobic-digestion conditions – method by analysis of released biogas, ISO Standard 15985, International Organization for Standardization, Geneva, Switzerland, 2014. 79. Technical Committee: ISO TC 61 SC 14, Plastics – determination of the degree of disintegration of plastic materials under defined composting conditions in a pilot-scale test, ISO Standard 16929, International Organization for Standardization, Geneva, Switzerland, 2013. 80. Technical Committee: ISO TC 61 SC 14, Specifications for compostable plastics, ISO Standard 17088, International Organization for Standardization, Geneva, Switzerland, 2012. 81. Technical Committee: ISO TC 61 SC 14, Plastics – determination of the degree of disintegration of plastic materials under simulated composting conditions in a laboratory-scale test, ISO Standard 20200, International Organization for Standardization, Geneva, Switzerland, 2015. 82. ASTM International, Standard guide for techniques to separate and identify contaminants in recycled plastics, ASTM Standard ASTM D5577, ASTM International, West Conshohocken, PA, 2010. 83. ASTM International, Standard practice for separation and washing of recycled plastics prior to testing, ASTM Standard ASTM D6288-17, ASTM International, West Conshohocken, PA, 2017. 84. P. Eyerer and A. Franck, Plastics and structural components: The environment and recycling in P. Eyerer, ed., Polymers–Opportunities and Risks I, in Vol. 11 of The Handbook of Environmental Chemistry, chapter 6, pp. 391–427. Springer, Berlin, Heidelberg, 2010. 85. S. Klein, I.K. Dimzon, J. Eubeler, and T.P. Knepper, Analysis, occurrence, and degradation of microplastics in the aqueous environment in M. Wagner and S. Lambert, eds., Freshwater Microplastics, in Vol. 58 of The Handbook of Environmental Chemistry, chapter 3, pp. 51–67. Springer, Cham, 2018. 86. J.N. Hahladakis, C.A. Velis, R. Weber, E. Iacovidou, and P. Purnell, Journal of Hazardous Materials, Vol. 344, p. 179, 2018. 87. E. Hansen, N.H. Nilsson, D. Lithner, and C. Lassen, COWI in cooperation with Danish Technological Institute, Vol. 148, 2013. 88. EFSA Panel on Contaminants in the Food Chain (CONTAM), EFSA Journal, Vol. 14, p. e04501, 2016.

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89. C.M. Boerger, G.L. Lattin, S.L. Moore, and C.J. Moore, Marine Pollution Bulletin, Vol. 60, p. 2275, 2010. 90. A.L. Lusher, M. McHugh, and R.C. Thompson, Marine Pollution Bulletin, Vol. 67, p. 94, 2013. 91. D. Neves, P. Sobral, J.L. Ferreira, and T. Pereira, Marine Pollution Bulletin, Vol. 101, p. 119, 2015. 92. C.M. Rochman, A. Tahir, S.L. Williams, D.V. Baxa, R. Lam, J.T. Miller, F.-C. Teh, S. Werorilangi, and S.J. Teh, Scientific Reports, Vol. 5, p. 14340, 2015. 93. C.D. Rummel, M.G. Löder, N.F. Fricke, T. Lang, E.-M. Griebeler, M. Janke, and G. Gerdts, Marine Pollution Bulletin, Vol. 102, p. 134, 2016. 94. L.I. Devriese, M.D. van der Meulen, T. Maes, K. Bekaert, I. Paul-Pont, L. Frère, J. Robbens, and A.D. Vethaak, Marine Pollution Bulletin, Vol. 98, p. 179, 2015. 95. B.D. Witte, L. Devriese, K. Bekaert, S. Ho man, G. Vandermeersch, K. Cooreman, and J. Robbens, Marine Pollution Bulletin, Vol. 85, p. 146, 2014. 96. L. Van Cauwenberghe and C.R. Janssen, Environmental Pollution, Vol. 193, p. 65, 2014. 97. J. Li, D. Yang, L. Li, K. Jabeen, and H. Shi, Environmental Pollution, Vol. 207, p. 190, 2015. 98. A. Naji, M. Nuri, and A.D. Vethaak, Environmental Pollution, Vol. 235, p. 113, 2018. 99. G. Liebezeit and E. Liebezeit, Food Additives & Contaminants: Part A, Vol. 30, p. 2136, 2013. 100. G. Liebezeit and E. Liebezeit, Food Additives & Contaminants: Part A, Vol. 31, p. 1574, 2014. 101. J.M. Garcia and M.L. Robertson, Science, Vol. 358, p. 870, 2017. 102. K.L. Law, Annual Review of Marine Science, Vol. 9, p. 205, 2017. 103. F. Schneider, S. Parsons, S. Clift, A. Stolte, and M.C. McManus, Marine Pollution Bulletin, Vol. 128, p. 162, 2018. 104. J.L. Conkle, C.D.B. Del Valle, and J.W. Turner, Environmental management, Vol. 61, p. 1, 2018. 105. C.L. Waller, H.J. Gri ths, C.M. Waluda, S.E. Thorpe, I. Loaiza, B. Moreno, C.O. Pacherres, and K.A. Hughes, Science of The Total Environment, Vol. 598, p. 220, 2017. 106. N.P. Ivleva, A.C. Wiesheu, and R. Niessner, Angewandte Chemie International Edition, Vol. 56, p. 1720, 2017. 107. B. Worm, H.K. Lotze, I. Jubinville, C. Wilcox, and J. Jambeck, Annual Review of Environment and Resources, Vol. 42, p. 1, 2017. 108. H. Auta, C. Emenike, and S. Fauziah, Environment International, Vol. 102, p. 165, 2017.

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109. M. Eriksen, L.C.M. Lebreton, H.S. Carson, M. Thiel, C.J. Moore, J.C. Borerro, F. Galgani, P.G. Ryan, and J. Reisser, PloS One, Vol. 9, p. e111913, 2014. 110. J.R. Jambeck, R. Geyer, C. Wilcox, T.R. Siegler, M. Perryman, A. Andrady, R. Narayan, and K.L. Law, Science, Vol. 347, p. 768, 2015. 111. M. Steer, M. Cole, R.C. Thompson, and P.K. Lindeque, Environmental Pollution, Vol. 226, p. 250, 2017. 112. L.C.M. Lebreton, J. Van der Zwet, J.-W. Damsteeg, B. Slat, A. Andrady, and J. Reisser, Nature Communications, Vol. 8, p. 15611, 2017. 113. A. Cózar, E. Martí, C.M. Duarte, J. García-de Lomas, E. van Sebille, T.J. Ballatore, V.M. Eguíluz, J.I. González-Gordillo, M.L. Pedrotti, F. Echevarría, R. Troublè, and X. Irigoien, Science Advances, Vol. 3, 2017. 114. M.G.J. Löder and G. Gerdts, Methodology used for the detection and identification of microplastics — a critical appraisal in M. Bergmann, L. Gutow, and M. Klages, eds., Marine Anthropogenic Litter, chapter 8, pp. 201–227. Springer, Cham, 2015. 115. M. Fischer and B.M. Scholz-Böttcher, Environmental Science & Technology, Vol. 51, p. 5052, 2017. 116. O. Setälä, V. Fleming-Lehtinen, and M. Lehtiniemi, Environmental Pollution, Vol. 185, p. 77, 2014. 117. K. Enders, R. Lenz, S. Beer, and C.A. Stedmon, ICES Journal of Marine Science, Vol. 74, p. 326, 2017. 118. G. Hanke, Guidance on monitoring of marine litter in European seas, Technical report, MSFD Technical Subgroup on Marine Litter, Joint Research Centre IES, Ispra (VA), Italy, 2013. 119. Wikipedia contributors, Ospar convention — wikipedia, the free encyclopedia, 2018. [Online; accessed 24-February-2018]. 120. A. Cooper and OSPAR, Ospar request on development of a common monitoring protocol for plastic particles in fish stomachs and selected shellfish on the basis of existing fish disease surveys, Ospar request, ICES, 2015. 121. A. Karami, A. Golieskardi, C.K. Choo, N. Romano, Y.B. Ho, and B. Salamatinia, Science of The Total Environment, Vol. 578, p. 485, 2017. 122. L. Hermabessiere, A. Dehaut, I. Paul-Pont, C. Lacroix, R. Jezequel, P. Soudant, and G. Duflos, Chemosphere, Vol. 182, p. 781, 2017. 123. A.-M. Resmeri¸ta˘ , A. Coroaba, R. Darie, F. Doroftei, I. Spiridon, B.C. Simionescu, and P. Navard, Marine Pollution Bulletin, Vol. 127, p. 387, 2018. 124. D.K.A. Barnes, F. Galgani, R.C. Thompson, and M. Barlaz, Philosophical Transactions of the Royal Society of London B: Biological Sciences, Vol. 364, p. 1985, 2009. 125. S.L. Wright and F.J. Kelly, Environmental Science & Technology, Vol. 51, p. 6634, 2017.

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126. M. Siegfried, A.A. Koelmans, E. Besseling, and C. Kroeze, Water Research, Vol. 127, p. 249, 2017. 127. A.I. Catarino, R. Thompson, W. Sanderson, and T.B. Henry, Environmental Toxicology and Chemistry, Vol. 36, p. 947, 2017. 128. J.P. Harrison, M. Sapp, M. Schratzberger, and A.M. Osborn, Marine Technology Society Journal, Vol. 45, p. 12, 2011. 129. E.R. Zettler, T.J. Mincer, and L.A. Amaral-Zettler, Environmental Science & Technology, Vol. 47, p. 7137, 2013. 130. J.P. Harrison, M. Schratzberger, M. Sapp, and A.M. Osborn, BMC Microbiology, Vol. 14, p. 232, 2014. 131. A. McCormick, T.J. Hoellein, S.A. Mason, J. Schluep, and J.J. Kelly, Environmental Science & Technology, Vol. 48, p. 11863, 2014. 132. F. Bessa, P. Barría, J.M. Neto, J.P. Frias, V. Otero, P. Sobral, and J. Marques, Marine Pollution Bulletin, Vol. 128, p. 575, 2018. 133. M. Compa, A. Ventero, M. Iglesias, and S. Deudero, Marine Pollution Bulletin, Vol. 128, p. 89, 2018. 134. S. Kühn, F.L. Schaafsma, B. van Werven, H. Flores, M. Bergmann, M.B. Egelkraut-Holtus, Marionand Tekman, and J.A. van Franeker, Polar Biology, pp. 1–10, Feb 2018. 135. N.J. O’Hanlon, N.A. James, E.A. Masden, and A.L. Bond, Environmental Pollution, Vol. 231, p. 1291, 2017. 136. M.E. Iñiguez, J.A. Conesa, and A. Fullana, Scientific Reports, Vol. 7, p. 8620, 2017. 137. S. Seif, J.F. Provencher, S. Avery-Gomm, P.-Y. Daoust, M.L. Mallory, and P.A. Smith, Archives of Environmental Contamination and Toxicology, pp. 1–12, 2017. 138. B.R. Babu, A.K. Parande, and C.A. Basha, Waste Management & Research, Vol. 25, p. 307, 2007. 139. A.K. Awasthi and J. Li, Renewable and Sustainable Energy Reviews, Vol. 76, p. 434, 2017. 140. H.-Y. Kang and J.M. Schoenung, Resources, Conservation and Recycling, Vol. 45, p. 368, 2005. 141. J. Cui and E. Forssberg, Journal of Hazardous Materials, Vol. 99, p. 243, 2003. 142. R.D. Pascoe and B. O’Connell, Waste Management, Vol. 23, p. 845, 2003. 143. M.S. Reddy, K. Kurose, T. Okuda, W. Nishijima, and M. Okada, Journal of Hazardous Materials, Vol. 147, p. 1051, 2007. 144. A. Asadinezhad, M. Lehocky, ` P. Sáha, and M. Mozetiˇc, Materials, Vol. 5, p. 2937, 2012. 145. S.R. Mallampati, J.H. Heo, and M.H. Park, Journal of Hazardous Materials, Vol. 306, p. 13, 2016.

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146. H. Wagenaar, K. Langeland, R. Hardman, Y. Sergeant, K. Brenner, P. Sandra, C. Rappe, A. Fernandes, and T. Tiernan, Chemosphere, Vol. 36, p. 1, 1998. 147. Waste Concern, Persistent toxins in the PVC life cycle: Potential exposures from cradle to grave, Electronic, US Green Building Council, New York, 2003. Inform, Strageties fo a better Environment. 148. H. Li, L. Yu, G. Sheng, J. Fu, and P. Peng, Environmental Science & Technology, Vol. 41, p. 5641, 2007. 149. Greenpeace International, Why BFRs and PVC should be phased out of electronic devices, Report, Greenpeace International, Amsterdam, 2010. 150. C. Luo, C. Liu, Y. Wang, X. Liu, F. Li, G. Zhang, and X. Li, Journal of Hazardous Materials, Vol. 186, p. 481, 2011. 151. M.H. Wong, S.C. Wu, W.J. Deng, X.Z. Yu, Q. Luo, A.O.W. Leung, C.S.C. Wong, W.J. Luksemburg, and A.S. Wong, Environmental Pollution, Vol. 149, p. 131, 2007. 152. J. Liu, X. Chen, H.-Y. Shu, X.-R. Lin, Q.-X. Zhou, T. Bramryd, W.-S. Shu, and L.-N. Huang, Environmental Pollution, Vol. 235, p. 171, 2018. 153. J. Fu, Q. Zhou, J. Liu, W. Liu, T. Wang, Q. Zhang, and G. Jiang, Chemosphere, Vol. 71, p. 1269, 2008. 154. A.O.W. Leung, N.S. Duzgoren-Aydin, K.C. Cheung, and M.H. Wong, Environmental Science & Technology, Vol. 42, p. 2674, 2008.

Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

2 Environmental Aspects The risk perception of plastic pollution has been documented in a monograph (1). Here, the historical development is presented along with the process in which plastic pollution has been recognized as an important environmental problem by scientists, the public, and policymakers. Smart recycling techniques have been documented, which should, as much as possible, be environmentally friendly (2). Some methods for the recycling of several materials have been presented, including plastics and wood, and reasons are given as to why composting of polymers is important.

2.1 Pollution of the Marine Environment Marine debris is an important threat to ocean diversity and health (3, 4). The results of the eighth annual horizon scan of emerging issues likely to a ect global biological diversity, the environment, and conservation e orts in the future have been presented. The reported issues include new developments in energy storage and fuel production, sand extraction, potential solutions to combat coral bleaching and invasive marine species, and blockchain technology. This is a global problem that can have intense local impacts on wildlife, human health, aesthetic values, and the economy. The management of marine plastic debris has been described in a monograph (5). LITTERBASE is a newly launched online database of information from 1,300 peer-reviewed publications that provides analysis and

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visualization of human-generated marine litter worldwide (6). This comprehensive resource can be helpful to coordinate international actions against a lethal form of aquatic pollution (7). Marine plastic pollution has become a global environmental concern. It is a growing issue as a result of the increase in the production of plastics. In 2015, the global production of petroleum-based plastics exceeded 300 Mt. A consequence of this large amount of plastics being produced is an increased abundance of plastic litter in the ocean and along the shoreline (8). It has been estimated that 4.8 Mt to 12.7 Mt of plastic litter enters the ocean environment each year, making this issue one of utmost importance (9, 10). In addition, this pollution has the potential to accumulate organic contaminants, such as carcinogenic polychlorinated biphenyls (11–13), polycyclic aromatic hydrocarbons (14), and polybrominated diphenyl ethers (15), as well as toxic metals (16). An e ort has been made to guide future research and assist mitigation approaches to marine conservation, and a list of 16 priority research questions was generated based on the expert opinions of 26 researchers from around the world, whose research expertise spans several disciplines, and covers each of the world’s oceans and the taxa most at risk from plastic pollution. The study highlights the growing concern related to threats posed to marine wildlife from micro-plastics and fragmented debris, the need for data at scales relevant to management, and the urgent need to develop interdisciplinary research and management partnerships to limit the release of plastics into the environment and curb the future impacts of plastic pollution (17). Rankings of marine debris with respect to marine animals are collected in Table 2.1. The Regional Action Plan (RAP) is designed as a flexible tool providing a set of actions to address marine litter. It contains actions requiring collective activity within the framework of the OSPAR Commission through, where applicable, OSPAR measures (i.e., decisions or recommendations) and or other agreements such as guidelines. The Regional Action Plan sets out the policy context for OSPAR’s work on marine litter, describes the various types of actions that OSPAR will work on over the coming years and provides a timetable to guide the achievement of these actions (19). The main objectives of the RAP are to (19):

Environmental Aspects

Table 2.1 Rankings of marine debris (18). Waste

Average

Buoys traps pots Monofilament Fishing nets Plastic bags Plastic utensils Balloons Butts Caps Food packaging Other EPS packaging Hard plastic cont. Plastic food lids Straws stirrers Takeout containers Cans Beverage bottles Unidentified plastic fragment Cups and plates Glass bottles Paper bags

1 2.3 2.7 5.7 5.7 6.7 7.3 7.7 8.7 9.7 11.3 11.3 12.3 15.3 15.7 16 16.3 16.7 17.7 20

Bird

Turtle

1 3 2 4 7 8 5 9 10 11 6 13 14 15 17 12 16 18 19 20

1 2 3 9 4 5 12 6 7 8 13 10 11 18 14 17 19 15 16 20

Mammal 1 2 3 4 6 7 5 8 9 10 15 11 12 13 16 19 14 17 18 20

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Polymer Waste Management Prevent and reduce marine litter pollution in the North-East Atlantic and its impact on marine organisms, habitats, public health and safety and reduce the socioeconomic costs it causes, Remove litter from the marine environment where practical and feasible, Enhance knowledge and awareness on marine litter, Support Contracting Parties in the development, implementation and coordination of their programmes for litter reduction, including those for the implementation of the Marine Strategy Framework Directive, and Develop management approaches to marine litter that are consistent with accepted international approaches.

2.1.1

Pathways of Plastics into the Marine Environment

The pathways of plastics into the marine environment have been depicted (20), from resin production through loss or discard. Such pathways are shown in Figure 2.1.

Resin

Plastic products

In use

Catastrophic events Lost pellets

Discarded

Fishing and agriculture

Shipping

Wastewater discharge

Ocean science

Properly managed waste

Other ships and platforms

Improperly managed waste

Figure 2.1 Pathways of plastics into the marine environment (20).

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Properly managed waste is collected and contained in a robust waste management infrastructure designed to minimize loss to the environment. In contrast, improper management includes open dumping, disposal in open, i.e., uncontained, landfills, and littering. Here, wastewater discharge is considered as a proper management. However, plastic microbeads used as abrasives in many personal care products as well as fibers released from synthetic clothing upon washing can enter household wastewater (21). The first point of loss is the spillage or mishandling of industrial resin pellets, millimeter-sized quasi-spherical beads that constitute the plastic feedstock. Spilled pellets can directly enter waterways or be washed into wastewater or stormwater drains (US EPA 1993) (22). Resin pellets were among the first plastic debris items reported in the ocean (23), and they have been detected at sea and on beaches worldwide. 2.1.2

Deleterious E ff ects on the Marine Environment

The deleterious e ects of plastic debris on the marine environment have been reviewed (24). A large number of marine species are known to be harmed and or killed by plastic debris, which could jeopardize their survival, in particular since many of these species are already endangered by other forms of anthropogenic activities. The predominance of plastics in the marine litter has been clearly documented. Its proportion varies consistently between 60% and 80% of the total marine debris (25). Marine animals are mostly a ected through entanglement in and ingestion of plastic litter. Other lesser known threats include the use of plastic debris by invader species and the absorption of polychlorinated biphenyls from ingested plastics. Also hazardous are less conspicuous forms, such as plastic pellets and scrubbers (24). 2.1.3 2.1.3.1

Reports Concerning Special Locations Japan Tsunami 2011

Marine debris has become one of the leading threats to the Pacific ocean. On March 11, 2011, the Great East Japan Earthquake and Tsunami washed away an estimated 5 Mt of debris in a single, tragic event (26).

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Shoreline surveys, disaster debris reports and ocean drift models were used to investigate the temporal and spatial trends in the arrival of tsunami marine debris. The increase in debris influx to surveyed North American and Hawaiian shorelines was substantial and significant, representing a 10 time increase over the baseline in northern Washington State, where a long-term data set was also available. The tsunami brought di erent types of debris along the coast, with high-windage items dominant in Alaska and British Columbia and large, medium-windage items in Washington State and Oregon. The recorded cumulative debris landing in North America was close to 100,000 items in the period of the four years that were studied. Mitigation and monitoring activities, such as shoreline surveys, provided crucial data and monitoring for potential impacts. Such studies should be continued in the future (26). 2.1.4 2.1.4.1

Analysis Methods Standardized Methods

Regulations were developed for the reduction of plastic wastes at sea, such as MARPOL Annex V (27) and others, that were detailed in the literature (28). The methods of quantifying ingested debris in marine megafauna have been reviewed (29). Here recommendations for standardization have also been detailed. The anti-microbead norm that plastic microbeads should be removed from personal care products has been gaining global influence since 2012 (30). By 2018, the world was on track to eliminate microbeads from rinse-o products within a decade, reducing micro-plastics flowing into oceans by 1–2%. This confirms the power of environmental norms, but how and why this phaseout is occurring – unequally across jurisdictions, with firms creating loopholes, missing deadlines and limiting the scope of reforms – also reveals innate weaknesses of bottom-up, ad hoc norm di usion as a way of improving marine governance. These weaknesses are heightened when economic stakes are high, solutions are complex and costly, authority is fragmented across jurisdictions and corporate resistance is strong (30). In a case study,

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the use of standardized methods was examined to report ingested debris in Northern Fulmars (Fulmarus glacialis). Standardized methods aim to harmonize the data that are available to facilitate large-scale comparisons and meta-analysis of plastic accumulation in a variety of taxa. If standardized methods are adopted, future plastic ingestion research will be better able to inform questions related to the impacts of plastics across taxonomic, ecosystem and spatial scales. Several recommendations were made that are specific to seabirds, but useful for all taxonomic groups where ingested pollution is studied. For seabirds, the methods used by the North Sea Fulmar Study (31–33) have been adopted widely, but not universally. It is recommended that all publications reporting ingested plastics in seabirds use this protocol as it o ers a comprehensive and flexible framework for the quantification and classification of marine debris. In addition to this method and classification framework, it is recommended to report data on variables that have been shown to influence plastic accumulation in marine megafauna, and particularly information on collection method, date and location of collection, age, and sex. For other groups of marine megafauna it has been recommended to adopt the North Sea Fulmar Study plastic classification system, which separates debris into user and industrial categories, and then further subtypes, as well as the same standard minimum metrics outlined above (29). In a European context, such standardization has started with recommended procedures for marine turtles and fish and results for plastic ingestion by seals (34, 35). The recommended reporting guidelines for all marine megafauna plastic ingestion studies should report (29): 1. 2. 3. 4.

Location and timing of sampling, Method of sampling, Sample size, Frequency of occurrence of ingested plastics (with a 95% confidence interval: Je reys interval (36)), 5. Mean (with standard deviation and error), median and range of mass of ingested plastics individual (including all individuals sampled),

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2.1.4.2

Styrene Oligomers

The degree of qualitative contribution of the internal and external factors of an area contaminated by poly(styrene) (PS) to the coastal marine environment was studied (37). Whether or not the debris originates from the area itself was also assessed. In the study, the concentrations of styrene oligomers were monitored as an indicator of PS plastic pollution along the coastlines of the Pacific Ocean. A styrene trimer (2,4,6-triphenyl-1-hexene), styrene dimers (2,4-diphenyl-1-butene, 1,3-diphenylpropane), and styrene monomer that are all derived from PS were analyzed. These compounds are shown in Figure 2.2.

H 2C H

2,4,6-Triphenyl-1-hexene CH2

1,3-Diphenyl propane

2,4-Diphenyl-1-butene

Figure 2.2 Styrene oligomers.

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59

Sand samples were taken from the surface of the coast and from a 30 cm depth along the seashore. At two sampling points, about 100 g of sand was collected using a stainless steel shovel, and was stored in a glass container. Surface seawater samples were taken at a water depth of 40 cm and subjected to cotton plug filtration using a stainless steel beaker. The volume of the water sampled was 5 l – 10 l, which was then extracted in the field with dichloromethane. Biphenyl was added as the surrogate standard for the recovery test. The oligomers were measured using a gas chromatography mass spectroscopy technique (37). The data concerning population density and concentrations of the styrene oligomers in the seawater and sea sand of coastal beaches are shown in Table 2.2. Table 2.2 Population density, concentrations of the styrene oligomers in seawater and in sea sand (37). Region

Alaska, USA Hawaii Island, USA Rishiri Island, JP Rebun Island, JP Tsushima Island, JP Maui, USA Sado Island, JP Fukue Island, JP Guam, USA Jeju Island, Korea O’ahu Island, USA Okinawa Island, JP Los Angeles, USA Busan, Korea San Francisco, USA

2.1.5

Population persons per km2

Oligomers in seawater [ng l 1]

Oligomers in sand [ng g 1]

0.49 18 30.81 39.3 58.18 62.5 73.93 170.01 320 327.1 617 1083.6 3176 4600 6800

0.93 57.82 2.88 10.58 374.36 467.41 1.07 382.88 4.32 3165.1 0.1 1.17 1.26 45.45 22.03

0.74 1.42 718 413 3516.93 170.4 90.12 173.85 1402.7 204.48 16.07 69.25 2906.8 2.57 816.1

Plastic Preproduction Pellets

Plastic preproduction pellets are found in environmental samples all over the world (38). Their presence is often linked to spills during

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production and transportation. For a better understanding of how these pellets end up in the environment, the release of plastic pellets from a poly(ethylene) (PE) production site in a case study of an area on Sweden’s west coast was assessed. The case study encompassed field measurements to evaluate the level of pollution and pathways, models and drifters to investigate the potential spread and a revision of the legal framework and the company permits. The case study showed that millions of pellets are released from the production site annually. But it was also shown that there are national and international legal frameworks that if implemented could help to prevent these spills. Bearing in mind the negative e ects observed by plastic pollution, there is an urgent need to increase the responsibility and accountability for these spills (38).

2.1.6

Leaching of Plastics

Micro-plastics are often ingested by marine organisms. However, the marine life is not only threatened by the physical damage plastic items can cause but also by the possible chemical pollution resulting from the leaching of plastic additives or other adsorbed chemicals on the plastics’ surface during long-range transport (39). Plastic additives include plasticizers, flame retardants and color pigments. Examples of chemicals are shown in Table 2.3 and in Figure 2.3. The demonstrated toxicity of some of these molecules has led to national and international legislations that are limiting or banning their use. However, a wide variety of substances are still found in plastic products and little is known about their impact on the marine and terrestrial environment (39).

2.1.7

Micro-plastics

An elevated number of marine species is known to be a ected by plastic contamination, and a still more integrated ecological risk assessment of these materials has become important for research studies (40).

Environmental Aspects

Table 2.3 Example of chemicals (39). Chemical

Shortcut

Dimethyl phthalate Diethyl phthalate Diisobutyl phthalate Di-n-butyl phthalate Benzyl butyl phthalate Bis(2-ethylhexyl) phthalate Tripropyl phosphate Triisobutyl phosphate Tri-n-butyl phosphate Tris(2-chloroethyl) phosphate Tris(1-chloro-2-propyl) phosphate Tris-(dichlorisopropyl) phosphate Triphenyl phosphate 2-Ethylhexyl diphenyl phosphate Tri(2-ethylhexyl) phosphate

O

DMP DEP DiBP DnBP BBzP DEHP TPP TiBP TnBP TCEP TCPP TDCP TPhP EHDPP TEHP

O O CH3

O CH2

CH3

O CH3

O CH2

CH3

O

O

Dimethyl phthalate

Diethyl phthalate

Cl

Cl

O

O O P

Cl

O

O O P

O

O

Tris(2-chloroethyl) phosphate

Triisobutyl phosphate

Figure 2.3 Plastic additives.

61

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Beside the entanglement and ingestion of macro-debris by large vertebrates, micro-plastics are accumulated by planktonic and invertebrate organisms, thus being transferred along food chains. Negative consequences include the loss of nutritional value of diet, physical damages, exposure to pathogens and transport of alien species. In addition, plastics may contain chemical additives and e ciently adsorb several environmental contaminants, thus representing a potential source of exposure to such compounds after ingestion. Complex ecotoxicological e ects have been reported, but the fate and impact of micro-plastics in the marine environment are still far from being fully clarified (40). The development of reproducible methods for micro-plastic recovery and characterization is an important issue. The methods of recovering micro-plastics from marine samples have been reviewed (41). The methods of separation of micro-plastics and identification methodologies for seawater, sediment and marine organisms have been detailed. Also, the e ciency of methods was examined, including processing time, recovery rates, and the potential destruction of micro-plastics. Visual examination and acid digestion were found to be the most common separation methods for seawater samples and organisms, while density flotation was the primary method used for sediments. Only a few studies reported recovery rates, or investigated the physical or chemical impact on plastics. This knowledge gap may lead to misidentification of plastic or unreliable pollution estimates. In the future, factors, such as, biomass loading, recovery rates, and chemical compatibility, should be considered to allow for an appropriate methodology (41). Methods describing the separation and identification of microplastics from environmental samples are highly variable (41). Existing separation methods include visual separation (42, 43), flotation separation (12, 44), acid (45, 46), alkaline (47, 48), and oxidative or enzyme digestion (49, 50). With regards to the acid, alkaline, oxidative and enzymatic digestions, in some instances it is not known whether the chemicals used impact on the structural and or chemical integrity of micro-plastics, possibly reducing the accuracy of identification (41).

Environmental Aspects 2.1.7.1

63

Temporal Trends in Pollution

Micro-plastics with a size smaller than 5 mm were extracted from sediment cores collected in Japan, Thailand, Malaysia, and South Africa by density separation after hydrogen peroxide treatment to remove biofilms and identified using Fourier transform infrared (FTIR) (51). Carbonyl and vinyl indices were used to avoid the identification of biopolymers as plastics. Micro-plastics composed of a variety of polymers, including PE, poly(propylene) (PP), PS, poly(ethylene terephthalate), PE, PP copolymers, and poly(acrylate)s could be identified in the sediments. Micro-plastics between 315 μ m and 5 mm were found. Most of them were in the range of 315 μm to 1 mm. The abundance of micro-plastics in surface sediment varied from 100 pieces per kg-dry sediment in a core collected in the Gulf of Thailand to 1900 pieces per kg-dry sediment in a core collected in a canal in Tokyo Bay. The far higher stock of PE and PP composed micro-plastics in sediment compared with surface water samples collected in a canal in Tokyo Bay suggests that sediment is an important sink for micro-plastics (51). According to dated sediment cores from Japan, micro-plastic pollution started in the 1950s, and their abundance increased markedly toward the surface layer (i.e., 2000s). In all the sediment cores from Japan, Thailand, Malaysia, and South Africa, the abundance of micro-plastics increased toward the surface, suggesting the global occurrence of an increase in micro-plastic pollution over time (51). Also, the distribution of micro-plastics was investigated in the sediments of five sampling sites from the northern Tunisian coast during June 2017 (52). The micro-plastics were categorized according to type, color and size. Representative micro-plastics from the five sites were isolated for polymer identification using FTIR spectroscopy in attenuated total reflectance mode. The results of the study showed that micro-plastics were recovered from all sediment samples, indicating for the first time their extensive distribution on the Tunisian coast. Fibers, fragments, Styrofoam , pellets and films were the types found. A total of three polymer types were identified, PE, PP, and PS. Except for industrial pellets, the presence of micro-plastics is likely

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due to the degradation of marine plastic debris accumulating at each site (52). 2.1.7.2

Methodologies Used for Identification

The methodologies used for the identification and quantification of micro-plastics from the marine environment have been compared and reviewed (53). Here, three main sampling strategies could be identified: Selective, volume-reduced, and bulk sampling. Most sediment samples came from sandy beaches at the high tide line, and most seawater samples were taken at the sea surface using neuston nets. Four steps were distinguished during sample processing: Density separation, filtration, sieving, and visual sorting of micro-plastics. Visual sorting was one of the most commonly used methods for the identification of micro-plastics, using type, shape, degradation stage, and color as criteria. The chemical and physical characteristics, e.g., specific density, were also used. The most reliable method to identify the chemical composition of micro-plastics is infrared spectroscopy. Most studies reported that plastic fragments were PE and PP polymers. Most of the studies reported two main size ranges of micro-plastics: 500 μ m to 5 mm, which are retained by a 500 μ m sieve net, and 1 μ m to 500 μ m, or fractions thereof, that are retained on filters (53). 2.1.7.3

Neuston Net Tow

The most common method for sea surface sampling is a neuston net tow. This method captures micro-plastic from large water volumes, and although widely employed, it is specifically designed for studying the ecology of plankton (10). Its e ectiveness for micro-plastic research is limited by the net’s mesh size as well as the likelihood of contamination. In a study, a 1 l surface grab sampling method was compared to a 335 μ m neuston net tow. Grab sampling collected over three orders of magnitude more micro-plastic per volume of water as well as a smaller size range and greater proportion of nonfibrous plastic than sampling with a neuston net. Consequently, solely relying on neuston net samples

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65

appears to result in an underestimation of the extent of micro-plastic pollution. For studies aiming to capture and sort larger micro-plastics without a microscope, the neuston tow method is preferred, since it samples a greater volume of water, increasing the potential of capturing micro-plastic pieces. Grab sampling can capture plastic at the microscale and nanoscale and in environments where neuston nets are impractical, but the small volume of water sampled may result in high variability among samples. The comparison of these techniques comes at a critical time in which sampling methods need standardization for the accurate measurement of the distribution and composition of micro-plastic in aquatic environments worldwide (10). 2.1.8 2.1.8.1

Marine Animals Seabirds

The first observation of seabirds ingesting plastic debris was published in the late 1960s (54). The intrinsic properties and widespread presence of plastic particles in the marine environment have profound e ects on birds that are inhabiting the oceans (55). Industrial and user plastics composed of PS, PE,PP, PS, foamed PS, and poly(vinyl chloride) are the most prevalent forms of plastic marine pollution. Their dispersal and accumulation, in average densities of 1000 to 4000 pieces per km2 , are controlled by surface currents, wind patterns, and di erent geographic inputs. Seabirds of the order Procellariiformes are most vulnerable to the e ects of plastic ingestion due to their smaller gizzard their inability to regurgitate ingested plastics. Planktivores have a higher incidence of ingested plastics than do Piscivores. The former are more likely to confuse plastic pellets with copepods, euphausiids, and cephalopods. The physiological e ects related to the ingestion of plastics include obstruction of the gastrointestines and of subsequent passage of food into the intestines, blockage of gastric enzyme secretion, diminished feeding stimulus, lowered steroid hormone levels, delayed ovulation and reproductive failure.

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As the manufacture of plastic and its use increases, the subsequent disposal at sea becomes more extensive. Therefore, the impact of discarded plastic on birds inhabiting the marine environment may also be expected to increase (55). Threat of Plastic Pollution to Seabirds. A spatial risk analysis was performed using predicted debris distributions and ranges for 186 seabird species to model their debris exposure (56). The model was adjusted using published data on plastic ingestion by seabirds. In studies reported in the literature between 1962 and 2012, 80 of 135, i.e., 59%, of the species had ingested plastic, and, within those studies, an average 29% of the individuals had plastic in their gut. Standardizing the data for time and species, the estimated ingestion rate would reach up to 90% of the individuals if these studies had been conducted in 2015. The rate of ingestion is calculated using the number of individuals with and without plastic in their gut. Some of the results are shown in Table 2.4. The highest area of expected impact was estimated at the Southern Ocean boundary in the Tasman Sea between Australia and New Zealand, which is in contrast to previous studies that identified this area as having low anthropogenic pressures and concentrations of marine debris. In the current study, it was predicted that plastics ingestion is increasing in seabirds, and that it will reach 99% of all species by 2050. However, e ective waste management can reduce this threat (56). Ingestion of Plastics by Seabirds. The ingestion of marine debris by wildlife, and in particular the ingestion of plastics by seabirds, has been widely documented (57, 58). Seabirds, e.g., fulmars, are e ective biological monitors of floating plastic marine debris (59). Fulmars belong to the tubenosed bird families of albatrosses and petrels order Procellariiformes. They only come ashore to breed and never forage on land or in fresh water but exclusively far out at sea. Fulmars have a wide distribution over the northern North Atlantic and Pacific Oceans, with a population estimated at 15–30 million individuals (60).

Environmental Aspects Table 2.4 Rate of ingestion (56). Common name

Ingestion rate

Crested Auklet Least Auklet Whiskered Auklet Kittlitz’s Murrelet Marbled Murrelet Pigeon Guillemot Rhinoceros Auklet Parakeet Auklet Atlantic Pu n Horned Pu n Tufted Pu n Cassin’s Auklet Ancient Murrelet Xantus’s Murrelet Common Murre Thick-billed Murre Black-footed Albatross Laysan Albatross Tristan Albatross Wandering Albatross Sooty Albatross Atlantic Yellow-nosed Albatross Great Frigatebird White-bellied Storm-Petrel European Storm-Petrel Polynesian Storm-Petrel Grey-backed Storm-Petrel Wilson’s Storm-Petrel Band-rumped Storm-Petrel Fork-tailed Storm-Petrel Leach’s Storm-Petrel Markham’s Storm-Petrel Tristram’s Storm-Petrel White-faced Storm-Petrel Bonaparte’s Gull Common Black-headed Gull Glaucous-winged Gull Heermann’s Gull Laughing Gull Mew Gull

0.2 0 0.01 0 0 0.02 0.02 0.61 0 0.37 0.21 0.18 0 0 0.01 0.01 0.56 0.91 0 0 0 0.06 0 0.24 0 0 0.27 0.36 0 0.92 0.26 0.08 0.1 0.78 0.17 1 0.11 0.13 0.14 0.25

67

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Fulmars are now considered as a formal marine litter indicator in the OSPAR (Oslo Paris Convention for the Protection of the Marine Environment of the North-East Atlantic) and the European MSFD (Marine Strategy Framework Directive). Some results have been published (31, 61, 62). Long-term data reveal a high abundance of plastic in the southern North Sea, gradually decreasing to the north at increasing distance from population centers, with lowest levels in high Arctic waters. Since the 1980s, preproduction plastic pellets in North Sea fulmars have decreased by ca. 75%, while user plastics varied without a strong overall change. Similar trends were found in net-collected floating plastic debris in the North Atlantic subtropical gyre, with a ca. 75% decrease in plastic pellets and no obvious trend in user plastic. The decreases in pellets suggest that changes in litter input are rapidly visible in the environment not only close to presumed sources, but also far from land. Floating plastic debris is rapidly lost from the ocean surface to other as-yet undetermined sinks in the marine environment (59).

Northern Fulmars. Northern fulmars are ideal monitors of the trends in marine plastic pollution (63). These animals are shown in Figure 2.4. Northern fulmars are suitable for testing because they have a tendency only to regurgitate indigestible items such as plastic when they are feeding chicks, and so the retention time for ingested plastics in the non-breeding season is in the order of weeks to months (65, 66). The stomach contents of beached northern fulmar (Fulmarus glacialis) have been found to be a cost-e ective biomonitor in Europe. Here, the stomach contents of 67 fulmars from the beaches in the eastern North Pacific in 2009–2010 were evaluated (63). It was found that 92.5% of the fulmars had ingested an average of 36.8 pieces, or 0.385 g of plastic. The ingestion of plastics in these fulmars is among the highest recorded globally. In comparison to earlier studies in the North Pacific, these findings indicate an increase in plastic ingestion over the past 40 years (63).

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69

Figure 2.4 Northern fulmars. Reprinted from Wikipedia, licence: GFDL CC-by-2.5 (64).

The plastic pollution in the Labrador Sea was investigated using the seabird northern fulmar (Fulmarus glacialis) as a biological monitoring species (67). For more than two years, 70 fulmars were sampled and it was found that 79% had ingested plastic, with an average of 11.6 pieces or 0.151 g per bird. Overall, 34% of all fulmars exceeded the Ecological Quality Objective (EcoQO) for marine litter, having ingested 0.1 g of plastic material. The EcoQO for marine litter defines the acceptable ecological quality as the situation where no more than 10% of the fulmars exceed a level of 0.1 g of plastic in the stomach (68). The percentages of fulmars in various regions with ingested plastics are shown in Table 2.5. 2.1.8.2

Whale Sharks

The whale shark is a slow moving, filter feeding carpet shark and the largest known extant fish species (70). The largest confirmed individual had a length of 12.65 m and a weight of about 21.5 t. The whale shark is found in open waters of the tropical oceans and is rarely found in water below 21°C.

70

Polymer Waste Management Table 2.5 Percentages of fulmars with ingested plastics (69). Location

Time period 2002–2006

2005–2009

2ßß7–2011

Percentages Scottish Islands East England Channel SE North Sea Skagerrak area Faroe Islands

48 59 61 57 49 43

59 77 86 57 53 46

57 76 86 60 55 40

The whale shark (Rhincodon typus) is an endangered species (71). This animal can be exposed to the ingestion of plastic material as a result of their filter feeding activity, in particular on the surface of the sea. An ecotoxicological investigation was performed on whale sharks sampled in the Gulf of California. Here, the potential interaction of this species with plastic debris and related sorbed contaminants was explored. Because of the di culty in collecting stranded specimens, an indirect approach using skin biopsies was done for the evaluation of the ecotoxicological status of whale sharks (71). The levels of organic chlorine-containing compounds, polybrominated diphenyl ethers, plastic additives, and related biomarkers were investigated. Twelve whale biopsy samples of the shark skin were collected in January 2014 in La Paz Bay (BCS, Mexico). An investigation concerning the concentration of micro-plastics and the polymer composition in seawater samples from the same area was also carried out. The mean concentration values found are shown in Table 2.6. Table 2.6 Mean concentration values (71). Materials

Concentration [ng g 1 ]

Polychlorinated biphenyl compounds Dichloro diphenyl trichloro alkanes Polybrominated diphenyl ethers Hexachlorobenzene

8.42 1.31 0.29 0.19

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71

2.2 Pollution of the Terrestrial Environment The basic environmental problem is that plastics are highly inert and, unlike cotton or paper, cannot be readily degraded under natural conditions. Plastics are hydrocarbon polymers made from fossil resources such as crude oil, natural gas, and coal (72). Although naturally occurring hydrocarbons have been used as energy sources via combustion since ancient times, it is not possible to simply adopt the combustion of hydrocarbon-rich plastic waste for energy production. Burning waste plastics releases toxic chemicals into the air, causing serious long-term health problems (73, 74) 2.2.1

Waste Generation

Waste is typically categorized based on its point of generation. The categories include municipal, commercial, industrial, agricultural, construction and demolition (C&D) (75). The annual global consumption of the major plastic resins is considerable. Films, e.g., carrier bags and plastic sheets, are easiest to escape containment as wind-blown debris and are likely the major component of terrestrial plastic litter. However, plastic litter also includes discarded fishing equipment, food and beverage packaging and many other items that are present in the marine environment. Films are dominated by low density poly(ethylene) and linear low density poly(ethylene). In the U.S.A., plastic recycling is largely limited to drink containers, although local authorities continue to expand the types of plastics collected for recycling. In general, citizen participation rather than industrial capacity limits the quantities of plastics recycled. E orts to provide incentives for recycling can increase the fraction recycled (75). 2.2.2

Disposal in Landfills

Now, most of the unrecycled plastic waste is disposed of in landfills. According to the United States Environmental Protection Agency, 9.5% of the plastic material in the United States municipal solid

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Polymer Waste Management

waste stream was recycled in 2014. Another 15% was combusted for energy, while 75.5% was sent to landfills (76). This approach to plastic waste management raises two critical problems: The exhaustion of limited landfill space and the removal of energy-rich fuel resources from the carbon cycle. The current attempts to address these issues are hindered by a lack of available, well-understood alternatives to landfilling. Chemical recycling (77,78), such as pyrolysis (79,80), catalytic degradation (81, 82), and gasification (83), is now believed to be the most appropriate technique for the recovery of heat energy from plastic waste streams. Burning waste plastics can release toxic chemicals into the air, thus causing serious long-term health problems (73, 75) The concerns about usage and disposal are diverse and include accumulation of waste in landfills and in natural habitats, physical problems for wildlife resulting from ingestion or entanglement in plastic, the leaching of chemicals from plastic products and the potential for plastics to transfer chemicals to wildlife and humans (73). The most important overriding concern, is that the current usage is not sustainable (73). Around 4% of the world oil production is used as a feedstock to make plastics and a similar amount is used as energy in the process. 2.2.3

Plastic Materials for Packaging

More than a a third of the current plastic production is used to make items of packaging, which are then rapidly discarded (72). Given our declining reserves of fossil fuels, and finite capacity for disposal of waste to landfill, this linear use of hydrocarbons, via packaging and other short-lived applications of plastic, is simply not sustainable. There are solutions, including material reduction, design for end-of-life recyclability, increased recycling capacity, development of bio-based feedstocks, strategies to reduce littering, the application of green chemistry life cycle analysis and revised risk assessment approaches. Such measures will be most e ective through the combined actions of the public, industry, scientists and policymakers. There is some urgency, as the quantity of plastics produced in the first

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73

10 years of the current century is likely to approach the quantity produced in the entire preceding century (73). Substantial quantities of plastic have accumulated in the natural environment and in landfills. Around 10% of the municipal waste stream consists of plastic materials (84).

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10. A.P.W. Barrows, C.A. Neumann, M.L. Berger, and S.D. Shaw, Anal. Methods, Vol. 9, p. 1446, 2017. 11. E.L. Teuten, J.M. Saquing, D.R.U. Knappe, M.A. Barlaz, S. Jonsson, A. Björn, S.J. Rowland, R.C. Thompson, T.S. Galloway, R. Yamashita, D. Ochi, Y. Watanuki, C. Moore, P.H. Viet, T.S. Tana, M. Prudente, R. Boonyatumanond, M.P. Zakaria, K. Akkhavong, Y. Ogata, H. Hirai, S. Iwasa, K. Mizukawa, Y. Hagino, A. Imamura, M. Saha, and H. Takada, Philosophical Transactions of the Royal Society of London B: Biological Sciences, Vol. 364, p. 2027, 2009. 12. J.P.G.L. Frias, P. Sobral, and A.M. Ferreira, Marine Pollution Bulletin, Vol. 60, p. 1988, 2010. 13. J. Bellas, J. Martinez-Armental, A. Martinez-Cámara, V. Besada, and C. Martinez-Gómez, Marine Pollution Bulletin, Vol. 109, p. 55, 2016. 14. C.M. Rochman, E. Hoh, T. Kurobe, and S.J. Teh, Scientific Reports, Vol. 3, p. 3263, 2013. 15. K. Tanaka, H. Takada, R. Yamashita, K. Mizukawa, M.-A. Fukuwaka, and Y. Watanuki, Marine Pollution Bulletin, Vol. 69, p. 219, 2013. 16. E. Nakashima, A. Isobe, S. Kako, S. Magome, N. Deki, T. Itai, and S. Takahashi, Interdiscip. Stud. Environ. Chem. Environ. Model. Anal., pp. 271–277, 2011. 17. A.C. Vegter, M. Barletta, C. Beck, J. Borrero, H. Burton, M.L. Campbell, M.F. Costa, M. Eriksen, C. Eriksson, A. Estrades, B.D.H. Gilardi, J.A. Ivar do Sul, J.L. Lavers, B. Lazar, L. Lebreton, W.J. Nichols, C.A. Ribic, P.G. Ryan, Q.A. Schuyler, S.D.A. Smith, H. Takada, K.A. Townsend, C.C.C. Wabnitz, C. Wilcox, L.C. Young, and M. Hamann, Endangered Species Research, Vol. 25, p. 225, 2014. 18. C. Wilcox, N.J. Mallos, G.H. Leonard, A. Rodriguez, and B.D. Hardesty, Marine Policy, Vol. 65, p. 107, 2016. 19. N.N., Regional action plan for prevention and management of marine litter in the north-east Atlantic, Status report, OSPAR Commission, London, UK, 2016. 20. K.L. Law, Annual Review of Marine Science, Vol. 9, p. 205, 2017. 21. M.A. Browne, P. Crump, S.J. Niven, E. Teuten, A. Tonkin, T. Galloway, and R. Thompson, Environmental Science & Technology, Vol. 45, p. 9175, 2011. 22. E. Rykken, Risk assessment evaluation manual interim, Risk assessment guidance for superfund, U.S. Environmental Protection Agency, Washington, DC, 2012. electronic: http: www.epa.gov oswer riskassessment ragse 5 24 2013. 23. E.J. Carpenter and K.L. Smith, Science, Vol. 175, p. 1240, 1972. 24. J.G.B. Derraik, Marine Pollution Bulletin, Vol. 44, p. 842, 2002. 25. M.R. Gregory and P. Ryan, Pelagic plastics and other seaborne persistent synthetic debris: A review of southern hemisphere perspectives in J.M. Coe

Environmental Aspects

26. 27.

28.

29.

30. 31.

32.

33. 34.

35. 36.

37. 38. 39.

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and D.B. Rogers, eds., Marine Debris–Sources, Impacts and Solutions, chapter 5, pp. 49–66. Springer-Verlag, New York, 1997. C.C. Murray, N. Maximenko, and S. Lippiatt, Marine Pollution Bulletin, 2018. N. N., Prevention of pollution by garbage from ships, MARPOL Annex V, International Maritime Organisation, United Nations, London, UJ, 2016. electronic: Availableat:http: www.imo.org en OurWork environment pollutionprevention garbage Pages Default.aspx. N. Brennholt, M. Heß, and G. Rei erscheid, Freshwater microplastics: Challenges for regulation and management in M. Wagner and S. Lambert, eds., Freshwater Microplastics: Emerging Environmental Contaminants?, pp. 239–272. Springer International Publishing, Cham, 2018. J.F. Provencher, A.L. Bond, S. Avery-Gomm, S.B. Borrelle, E.L.B. Rebolledo, S. Hammer, S. Kühn, J.L. Lavers, M.L. Mallory, A. Trevail, and J.A. van Franeker, Analytical Methods, Vol. 9, p. 1454, 2017. P. Dauvergne, Environmental Politics, Vol. 0, p. 1, 2018. J.A. van Franeker, C. Blaize, J. Danielsen, K. Fairclough, J. Gollan, N. Guse, P.-L. Hansen, M. Heubeck, J.-K. Jensen, G.L. Guillou, B. Olsen, K.-O. Olsen, J. Pedersen, E.W. Stienen, and D.M. Turner, Environmental Pollution, Vol. 159, p. 2609, 2011. Nitrogen Deposition, Critical Loads and Biodiversity. N. N., Guidelines for monitoring of plastic particles in stomachs of fulmars in the North Sea area, EIHA 15 5 12 Add.1, OSPAR Commission, London, 2015. electronic: http: www.ospar.org convention agreements?q fulmar. N. N., Plastic particles in fulmar stomachs in the North Sea, Technical report, OSPAR Commission, London, 2017. N. N., Guidance on monitoring of marine litter in European seas, Publications o ce of the European Union, Marine Strategy Framework Directive, Luxembourg, 2013. E.L.B. Rebolledo, J.A.V. Franeker, O.E. Jansen, and S.M. Brasseur, Marine Pollution Bulletin, Vol. 67, p. 200, 2013. Wikipedia contributors, Binomial proportion confidence interval — Wikipedia, the free encyclopedia, https: en.wikipedia.org w index.php?title Binomial_proportion_confidence_interval&oldid 832472232, 2018. [Online; accessed 13-April-2018]. B.G. Kwon, S.-Y. Chung, S.-S. Park, and K. Saido, Environmental Pollution, Vol. 234, p. 167, 2018. T.M. Karlsson, L. Arneborg, G. Broström, B.C. Almroth, L. Gipperth, and M. Hassellöv, Marine Pollution Bulletin, Vol. 129, p. 52, 2018. N. Schmidt, J. Castro-Jiménez, V. Fauvelle, and R. Sempéré, Zooplankton and plastic additives—insights into the chemical pollution of the low-trophic level of the Mediterranean marine food web, in M. Cocca, E. Di Pace, M.E. Errico, G. Gentile, A. Montarsolo, and R. Mossotti,

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58. S. Kühn, B.R.E. L., and J.A. Van Franeker, Deleterious eff ects of litter on marine life in M. Bergmann, L. Gutow, and M. Klages, eds., Marine Anthropogenic Litter, chapter 4, pp. 75–116. Springer Verlag, Berlin, 2015. 59. J.A. van Franeker and K.L. Law, Environmental Pollution, Vol. 203, p. 89, 2015. 60. Species factsheet: Fulmarus glacialis, Report, BirdLife International, Cambridge, United Kingdom, 2018. electronic: http: datazone. birdlife.org species factsheet northern-fulmar-fulmarus-glacialis. 61. J.A. Van Franeker, Alterra Rapport, Vol. 672, p. 247, 2004. 62. P.G. Ryan, C.J. Moore, J.A. van Franeker, and C.L. Moloney, Philosophical Transactions of the Royal Society of London B: Biological Sciences, Vol. 364, p. 1999, 2009. 63. S. Avery-Gomm, P.D. O’Hara, L. Kleine, V. Bowes, L.K. Wilson, and K.L. Barry, Marine Pollution Bulletin, Vol. 64, p. 1776, 2012. 64. T. Müller and Wikipedia contributors, Fulmar — wikipedia, the free encyclopedia, 2018. [Online; accessed 15-March-2018], licence: https: creativecommons.org licenses by 2.5 . 65. P.G. Ryan and S. Jackson, Marine Pollution Bulletin, Vol. 18, p. 217, 1987. 66. P.G. Ryan, Marine Pollution Bulletin, Vol. 19, p. 125, 1988. 67. S. Avery-Gomm, J.F. Provencher, M. Liboiron, F.E. Poon, and P.A. Smith, Marine Pollution Bulletin, Vol. 127, p. 817, 2018. 68. N.N., Background document for the ecoqo on plastic particles in stomachs of seabirds, Biodiversity Series 355, OSPAR Commission, London, UK, 2008. 69. N.N., Litter in the marine environment – plastic particles in fulmar stomachs, Status Report EIHA14 AS02, OSPAR Commission, London, UK, 2014. 70. Wikipedia contributors, Whale shark — wikipedia, the free encyclopedia, 2018. [Online; accessed 17-March-2018]. 71. M.C. Fossi, M. Baini, C. Panti, M. Galli, B. Jiménez, J. Muñoz-Arnanz, L. Marsili, M.G. Finoia, and D. Ramírez-Macías, Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology, Vol. 199, p. 48, 2017. 72. C.-F. Chow, W.-L. Wong, C.-W. Chan, and C.-S. Chan, Waste Management, 2018. in press. 73. R.C. Thompson, C.J. Moore, F.S. vom Saal, and S.H. Swan, Philosophical Transactions of the Royal Society of London B: Biological Sciences, Vol. 364, p. 2153, 2009. 74. C.-F. Chow, W.-L. Wong, K.Y.-F. Ho, C.-S. Chan, and C.-B. Gong, Chemistry –A European Journal, Vol. 22, p. 9513, 2016. 75. C.-F. Chow, W.-M.W. So, T.-Y. Cheung, and S.-K.D. Yeung, Plastic waste problem and education for plastic waste management in S.C. Kong, T.L. Wong, M. Yang, C.F. Chow, and K.H. Tse, eds., Emerging Practices

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Polymer Waste Management in Scholarship of Learning and Teaching in a Digital Era, pp. 125–140. Springer Singapore, 2017. N.N., Advancing sustainable materials management 2014 fact sheet, EPA Web Archive EPA 530-R-17-01, United States Environmental Protection Agency, Washington, DC, 2016. K. Ragaert, L. Delva, and K.V. Geem, Waste Management, Vol. 69, p. 24, 2017. G. Lopez, M. Artetxe, M. Amutio, J. Bilbao, and M. Olazar, Renewable and Sustainable Energy Reviews, Vol. 73, p. 346, 2017. S.M. Al-Salem, P. Lettieri, and J. Baeyens, Waste Management, Vol. 29, p. 2625, 2009. A. Aboulkas, T. Makayssi, L. Bilali, K. El Harfi, M. Nadifiyine, and M. Benchanaa, Fuel Processing Technology, Vol. 96, p. 209, 2012. S. Wong, N. Ngadi, T.A. Tuan Abdullah, and I.M. Inuwa, Industrial & Engineering Chemistry Research, Vol. 55, p. 2543, 2016. X. Zhang and H. Lei, RSC Adv., Vol. 6, p. 6154, 2016. M. Puig-Arnavat, J.C. Bruno, and A. Coronas, Renewable and Sustainable Energy Reviews, Vol. 14, p. 2841, 2010. D.K.A. Barnes, F. Galgani, R.C. Thompson, and M. Barlaz, Philosophical Transactions of the Royal Society of London B: Biological Sciences, Vol. 364, p. 1985, 2009.

Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

3 Recycling Methods Recycling is becoming more important as the waste generation rates increase globally. As long as non-environmentally degradable plastics are produced, the development of improved recycling techniques must continue in order to decrease additional material consumption and to reduce nondegradable plastic waste content in landfills (1). The di erent possibilities for recycling plastic wastes have been reviewed (2). Closed-loop recycling of pure, well-defined wastes is a problem only in critical applications. On the other hand, The recycling of mixed wastes gives rise to a number of technical and economic di culties. Direct processing is di cult because of the di erent melting behavior and thermal stability of the various components, and, moreover, leads to polymer alloys with poor mechanical properties and marketing potential (2). Sorting processes may yield fractions with insu cient purity. Compatibilizing additives are expensive and not very e cient. The future of recycling depends on the development of new markets for plastics with inferior properties and on processing methods to improve the properties of mixed plastics. Pyrolysis and hydrolysis open a range of interesting developments, but their economic and technical feasibility remain to be proven. Incineration, biodegradation and tipping cannot be considered to be fully satisfactory disposal methods, and recycling should be encouraged wherever it is economically and technically feasible (2).

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3.1 Alternative Plastic Materials It is expected that the progress in polymer science will eventually give rise to alternative plastic materials that may eliminate the need for the production of petroleum-based and other nondegradable plastics altogether. Recent studies have investigated the development of naturally based polymers (3–5) One drawback that often surrounds sustainable materials development is the seemingly pervasive notion that improving the environmental suitability of materials comes with a sacrifice in material functionality (6). Studies reporting material selection strategies often weigh material capabilities against environmental sustainability (7), and many recycling processes in general are assumed to bring about some degree of material deterioration (8). However, it could be concluded that use of recycled plastics for some composite applications can have clear environmental advantages over conventional virgin plastics in certain cases (8). The presented results are best for the civil and infrastructural application, due to their significant potential to lower the environmental impact. The impact of recycled composites on automotive applications is at best, equivalent to that of virgin composites; however, slight reduction or variation in properties of plastic waste feedstock could drastically raise the environmental impact to that of virgin alternatives. So, in automotive sector applications, substituting or replacing virgin plastic component with a recycled plastic component is not advisable unless significant weight reductions are obtained at equivalent functional performance (8). Recycling data have been collected from municipalities in Ontario during 2005–2010 (1). The e ects of di erent recycling policy tools were tested. The recycling programs were compared based on demographic characteristics. Also, accepting more materials and commingling increased recycling in municipalities. There was no di erence in the recovery rates of municipalities that had weekly bag limits of seven or more when compared to those with limits of six or less. Nevertheless, when comparing municipalities with weekly bag limits of three or less to those with higher limits, a significantly higher mean recovery rate was revealed in the

Recycling Methods 81 group with stricter limits. Municipalities with user-pay programs showed consistently higher recovery rates than those without such programs (1).

3.2 Mechanical Recycling The issues of mechanical and chemical recycling of solid plastic waste have been reviewed (9, 10). An overview of current sorting technologies, specific challenges for mechanical recycling, such as thermomechanical or lifetime degradation and the immiscibility of polymer blends, has been given. Also, some industrial examples, such as poly(ethylene terephthalate) (PET) recycling, and solid plastic waste from post-consumer packaging, end-of-life vehicles or electric and electronic devices, have been detailed. Mechanical recycling of plastic waste involves a number of treatments and preparation steps (11). This is a costly and energy-intensive process. However, mechanical recycling engines try to reduce these steps and working hours as much as possible. In general, the first step in a mechanical recycling process involves the size reduction of the plastic to a more suitable form such as pellets, powder or flakes. This is usually achieved by milling, grinding or shredding. The stages of mechanical recycling are shown in Figure 3.1. The mechanical recycling of waste of electric and electronic equipment has been reviewed (13). 3.2.1

Poly(lactic acid)

The e ect of simulated mechanical recycling processes on the structure and properties of poly(lactic acid) (PLA) has been investigated (14). A commercial grade of PLA was melt compounded and compression molded, then subjected to two di erent recycling processes. The first recycling process consisted of an accelerated aging and a second melt processing step. The other recycling process included an accelerated aging, a washing process and a second melt processing step.

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Plastics waste

Water

Pigments

Additives

Milling

Washing

Agglutination

Storage

Extrusion

Quenching

Final product

Granulation

Figure 3.1 Stages of mechanical recycling (12).

Recycling Methods 83 Measurements of the intrinsic viscosity indicated that both recycling processes e ect a degradation of PLA, which is more pronounced in the sample subjected to the washing process. Di erential scanning calorimetry (DSC) results suggested an increase in the mobility of the polymer chains in the recycled materials. However, the degree of crystallinity of PLA seemed to be unchanged. The optical, mechanical and gas barrier properties of PLA do not seem to be largely a ected by the degradation su ered during the di erent recycling processes. These results suggest that despite the degradation of PLA, the impact of just the di erent simulated mechanical recycling processes on the final properties is limited. Thus, the potential use of recycled PLA in packaging applications is not endangered (14). Also, a PLA-montmorillonite nanocomposite was tested in a similar way as described above (15). The e ect of two di erent mechanical recycling processes was studied. The two recycling processes included accelerated thermal and photochemical aging steps to simulate the degradation experienced by post-consumer plastics during their service life. The recycled materials showed increased thermal, optical and gas barrier properties due to the improved clay dispersion, which was observed by X-ray di raction and transmission electron microscopy. The PLA was compounded with 30% chalk and 5% of a biobased plasticizer using a twin screw extruder (16). The plasticizer, Grindsted Soft-N-Safe (17), is based on castor oil. The plasticizer is prepared from castor oil, which is first hydrogenated, then esterified with glycerol to create a monoglycerol. The obtained compound is finally esterified with acetic acid to react with the hydroxyl groups. The inclusion of the plasticizer moves the glass transition temperature towards lower temperatures, which occurs at 44°C. Mechanical recycling of the obtained compound was studied by multiple extrusions up to six cycles. The degradation was monitored by mechanical and thermal tests. Tensile and flexural tests did not reveal a major degradation after six cycles of processing. The DSC analysis did not show any significant change of the thermal properties. Also, Fourier transform infrared (FTIR) experiments did not show significant changes. Finally, the material was characterized by melt flow index (MFi) and by proton nuclear magnetic resonance. Both tests revealed that some degradation had occurred.

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The proton nuclear magnetic resonance tests showed that the chain length was reduced. Also, the MFi test showed that a degradation occurred. However, it could be shown that PLA filled with chalk can be recycled by repeated extrusion for up to 6 cycles, without a severe degradation (16). 3.2.2

Nanocellulose Coated Poly(ethylene) Films

The mechanical recycling of low density poly(ethylene) (LDPE) films coated with a thin layer of cellulose nanofibrils was investigated (18). Cellulose nanofibrils act as e ective barrier materials against oxygen and mineral oil residues. Two di erent cellulose nanofibril grades were tested. Both materials were applied onto a plasma activated LDPE film using a pilot coating line. The coated films were shredded with the help of liquid nitrogen, compacted and compounded with virgin LDPE and compatibilizer, and processed into cast films and injection molded test specimens. The cellulose nanofibril coatings were completely blended as microscale agglomerates in the LDPE matrix. The e ect of these agglomerates on the barrier and heat sealing properties was statistically insignificant in comparison to a recycled uncoated LDPE. The mechanical properties were found to be only moderately changed. Therefore, cellulose nanofibril-coated LDPE films can be recycled back into films without sacrificing the characteristic properties of the base polymer (18). 3.2.3

Electric Uses

Currently only a limited number of these plastics are mechanically recycled on an industrial scale while the majority are thermally treated for energy recovery (19). However, there is significant potential for value recovery and for lowering the environmental impact of plastics. Therefore, research is being done to develop new mechanical recycling processes based on the disassembly of plastic components and the sorting of these plastics based on identification by spectroscopic methods. A case study has been evaluated concerning the recycling of a acrylonitrile-butadiene-styrene (ABS) terpolymer from liquid crys-

Recycling Methods 85 tal display TVs. The quality of the recyclates was evaluated by mechanical testing and injection molding of thin-walled products. The results showed that with direct reapplication of the obtained ABS without compounding, high mechanical properties could be achieved when compared to post-shredder recycled ABS. However, the remaining impurities in the polymer matrix limit the applicability of the recycled plastics to components without either structurally critical or aesthetical requirements (19). 3.2.3.1

Batteries

The increasing usage of electrical drive systems and stationary energy storage worldwide has resulted in a high demand for raw materials for the production of lithium-ion batteries (20). To prevent further shortages of these crucial materials, ecological and e cient recycling processes of lithium-ion batteries are needed. Common industrial processes are mostly pyro-metallurgical and, as such, are energy and cost intensive. Certain projects are aimed at a realization of a new energy-e cient recycling process, without high temperatures and tracing mechanical process steps. Mechanical processes were thoroughly investigated by experiments in a laboratory and within technical scale, describing gas release of aged and non-aged lithium-ion batteries during dry crushing, intermediates, and products of the mechanical separation. It was also found that applying a second crushing step increases the yield of the coating materials, but also enables more selective separation. The results indicated a safe and ecological recycling process with a material recycling rate of at least 75% (20). An integrated process to handle bulk spent lithium manganese (LiMn2 O4 ) batteries to recycle high-value-added products in situ without any additives has been proposed (21). By mechanical separation, the mixed electrode materials, mainly including binder, graphite and LiMn2 O4 , are initially obtained from spent batteries. Then, the reaction characteristics for the oxygen-free roasting of mixed electrode materials were analyzed. These results showed that mixed electrode materials can be converted in situ into manganese oxide (MnO) and lithium carbonate (Li2 CO3 ) at 800°C for 45 min.

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In this process, the binder is evaporated and decomposed into gaseous products, which can be collected to avoid disposal costs. Finally, 91.30% of the lithium resource as Li2 CO3 is leached from roasted powders by water and then high-value-added Li2 CO3 crystals are further gained by evaporating the filter liquid. The filter residues are burned in air to remove the graphite and the final residues are obtained as manganous-manganic oxide (Mn3 O4 ) (21). 3.2.3.2

Photovoltaic Modules

A mechanical recycling process for photovoltaic modules has been described (22). The research was focused on a minimal impact on the environment with the lowest possible financial costs. It has been found that it is very di cult to obtain metals from the mixture of recycled photovoltaic modules with glass. In the case of the mixture without glass, the entire process was found to be faster, easier and cheaper. From the entire mechanical recycling process it can be seen that the crushed material that may contain up to 0.07% silver is not economically advantageous to process chemically. From an economic point of view, the final operation should be the mechanical separation of aluminum and glass. The amount of saved material due to photovoltaic module recycling until the year 2025 was estimated. Recycling could save up to 351,500 t of glass, 51,500 t of aluminum, 13,567 t of silicon and 425 t of silver (22).

3.3 Primary Recycling Primary recycling, also known as re-extrusion, is the reintroduction of scrap, industrial or single polymer plastic edges and parts into the extrusion cycle in order to produce products of a similar material (11). Primary recycling uses scrap plastic materials that have similar features as the original products (23). Primary recycling is only feasible with semi-clean scrap. Therefore it is not very popular. A useful example of primary recycling is the injection molding of LDPE crates according to specifications. Crates that do not meet

Recycling Methods 87 the specifications are palletized and reintroduced into the recycling loop or the final stages of the manufacturing. Most of the plastic solid waste that is recycled is from process scrap from industry. It is recycled via primary recycling techniques (11). Primary recycling can also involve the re-extrusion of post-consumer plastics. Here, households are the main source of such a waste stream. However, in the recycling of household waste a number of challenges are found, namely the need for a selective and a segregated collection.

3.4 Renewable Polymer Synthesis Because both transporting low density expanded poly(styrene) (EPS) waste and cleaning it to remove contaminant residue greatly increase cost and time required for EPS recycling, an overwhelming majority of food-contaminated EPS waste (e.g., an EPS cup with residual soda inside it) is not recycled (11, 24). EPS recycling is often subcategorized into three groups (25–27): 1. Material recycling, the reduction of the EPS volume using compression or dissolution in solvent, 2. Chemical recycling, the breaking of covalent bonds to regenerate monomers or other small molecules, and 3. Thermal recycling, the combustion of EPS waste to generate energy. The change in density of waste EPS at di erent oven temperatures in a 15 min period is shown in Figure 3.2. Traditionally, the most cost-e ective method of recycling EPS has been to heat non-contaminated EPS waste above its glass transition and or compact it to produce densified, recycled polystyrene. Since mechanical densifiers require that EPS be contaminant free before compaction, mechanical densification is not ideal for recycling food or drink contaminated waste items and not practical for recycling the roughly 70% of EPS waste that is used for single-use food and beverage packaging (27). An alternative material recycling method for EPS is a solventbased approach, in which clean EPS waste is dissolved in a suitable

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Density/[kg m-3]

250 200 150 100 50 0 0

20

40

60

80

100

120

140

160

Temperature/[ ], 15 min Figure 3.2 Change in density of waste EPS at di erent oven temperatures (26).

organic solvent such as acetone. The dissolution process results in the densification of the EPS waste, and the removal of the solvent a ords recycled polymeric products. Solvent-based recycling has been shown to be suitable for some contaminated EPS substrates because many contaminants are insoluble in solvents that dissolve EPS and can be removed using coarse filtration after EPS dissolution (28). The solubility and behavior of EPS in multiple solvents has been previously reported (29, 30). The solubility of poly(styrene) (PS) foams in solvents has been determined gravimetrically as the minimum solvent weight necessary to completely dissolve a weighted sample of EPS foam (29). The solubility was expressed as the mass of PS and the solvent volume ratio expressed in ml. The solubility of EPS in certain solvents is shown in Table 3.1 and Table 3.2. Some solvents are shown in Figure 3.3. EPS has been shown to be especially soluble in aromatic solvents such as toluene. However, these solvents are not in good agreement with green chemistry and, therefore, they should not be used for the recycling process.

Recycling Methods 89

Table 3.1 Solubility of EPS at 25°C in certain solvents (29). Solvent

Solubility [g ml 1 ]

Benzene Toluene Xylene Tetrahydrofuran Chloroform 1,3-Butanediol 2-Butanol Linalool Geraniol d-Limonene p-Cymene Terpineol Phellandrene Eucalyptol Water Nitrobenzene N,N-Dimethylformamide

0.68 0.60 0.40 0.96 1.28 0.00 0.00 0.00 0.0 0.26 0.30 0.00 0.28 0.10 0.00 0.13 0.31

Table 3.2 Solubility of PS at 50°C in cyclic monoterpenes (30). Solvent 1,8-Cineole (R)-Limonene α-Phellandrene α-Terpinene γ -Terpinene Terpinen-4-ol Terpinolene Terpinyl acetate Bornyl acetate α-Pinene β-Pinene Abies oil Eucalyptus oil

Solubility [g g 1 ] 0.947 1.817 0.981 1.971 2.171 1.450 1.914 1.511 1.264 0.702 0.809 0.847 0.964

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CH3

HO CH3

OH

H 3C

CH3

Linalool

H 3C

CH3 Geraniol

CH3

H 3C

CH3

CH3

H 3C

CH3 OH

α-Phellandrene

Terpineol CH3

CH3

H 3C

OH CH3

Terpinen-4-ol

H 3C

CH2

Limonene

Figure 3.3 Solvents.

Recycling Methods 91 Studies have also reported the solubility of EPS in the naturally occurring citrus fruit extract D-limonene (31), which has a similar dielectric constant to that of toluene (32). Also, the time required for the dissolution in certain solvents is an important aspect for recycling. These times are given at certain temperatures in Table 3.3. Table 3.3 Time required for the dissolution (30). Temperature Solvent

30°C

40°C 50°C Time [s]

1,8-Cineole (R)-Limonene α-Phellandrene α-Terpinene γ -Terpinene Terpinen-4-ol Terpinolene Terpinyl acetate Bornyl acetate α-Pinene β-Pinene Abies oil Eucalyptus oil

2,954 255 390 263 265 86,400 228 3,025 15,822 86,400 3,213 2,507 1,625

985 184 321 191 193 1,864 173 1,289 3,504 1,225 690 964 657

497 145 235 147 147 747 134 715 1,333 564 366 665 406

60°C

70°C

384 102 166 114 119 417 103 418 753 295 242 329 286

214 85 125 90 96 290 74 344 411 171 142 184 186

In the late 1990s and early 2000s Sony Corporation instituted a solvent-based recycling e ort in Japan, in which D-limonene was used to recycle EPS waste, which was reclaimed from solution by evaporation of D-limonene. Sony’s report of this recycling process is extremely in-depth, but this recycling e ort appears to have been abandoned sometime between 2004 and 2006 (33). Considering the low inherent value of recycled polystyrene, Sony’s apparent decision to cease this recycling e ort may have been financially motivated. Other studies have reported limonenebased recycling processes in which PS is reclaimed from solution in limonene using electrospinning or by precipitation by mixing with supercritical carbon dioxide (34, 35). Electrospinning is a process for the production of polymer fibers from polymer solutions, with diameters in the range of 10 nm – 500 nm and high surface areas per unit mass. Such nanofibers have

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received a lot of attention for a wide variety of applications, such as biomedical applications, sensors, and filtration methods (34). An electrospinning process is schematically shown in Figure 3.4. Collecting Surface

Capillary Fiber

High Voltage Power Supply

Figure 3.4 Electrospinning process.

The concentration of EPS in the solution can a ect the electrospinning results. If the concentration of polymer is too diluted the polymer jet may spray small drops instead of a continuous fiber jet, or it may spin out fibers that have beads of polymer. If the solution is too concentrated the electrical forces may not be strong enough to form the jet (34). Supercritical carbon dioxide can be used to reclaim the limonene that was used before as solvent for PS (35). Limonene has a high solubility for PS at elevated temperatures and almost a complete insolubility at moderated pressures of 77 bar and low temperatures of 30°C. The limonene concentration as mol fraction in the CO2 exit stream on the amount of limonene in a mixture of limonene and PS at 40°C and 7.7 MPa is shown in Figure 3.5. A process for sustainable materials development has been described that combines polymer recycling with a new method in renewable polymer synthesis to achieve nanocomposite polymeric products with high-performance material capabilities (27).

Recycling Methods 93 0.0021

Mol Fraction of Limonene

0.002 0.0019 0.0018 0.0017 0.0016 0.0015 0.0014 0.0013 0.0012 0

1

2

3

4

5

6

7

Limonene in Mixture/[g] Figure 3.5 Limonene concentration in the carbon dioxide exit stream (35).

This process enables the simultaneous densification, purification, and recycling of polymeric substrates in a one-pot procedure. The process, although applicable to numerous recyclable polymers and corresponding solvent monomer co-monomer formulations, has been demonstrated through a process for recycling EPS waste. The di culties associated with EPS recycling have been shown. It is estimated that over 3 Mt of EPS are produced each year globally, with roughly 70% of EPS products being used for single-use food and beverage packaging. The waste polymer recovery process consists of (27): Placing polymer waste and water-solvable contaminants in a biphasic solvent mixture, having a solvent(s) that dissolves the polymer and solvents that dissolve the water-solvable or water-dispersible contaminants into an aqueous solution. Discarding the aqueous or other immiscible solution and recovering the polymer solvent, and reclaiming dissolved polymer waste by polymerization of solvent, which is also made to function as a monomer, to a ord multicomponent composite reclaimed polymeric products.

94

Polymer Waste Management The same process as before but reducing the polymer waste to small particles, adding water or water-like solvent, separating the polymer waste from the water-solvable or water-dispersible contaminant in water by filtering or allowing polymer foam waste particulates to float to the top of the water or water-like solvent and decanting before placing it in biphasic solvents, discarding the contaminated aqueous solution.

3.4.1

Natural Solvents for Expanded Poly(styrene)

The recycling of natural resources and waste products is the most important process in the concept of green chemistry. The utilization of biomass has been a significant topic, whereas the recycling of petroleum resources has not received similar attention (36). EPS is widely used in packing and building materials and for electrical and thermal insulation owing to its light weight and low thermal and electrical conductivities. The porosity of EPS is very high, with 98% of the apparent volume being porous. In the mid2010s, more than 2 Mt of EPS have been produced in the world per year. The rate of material recycling is relatively high among commodity plastics (37). For the recycling of EPS, melting or solvent treatment is required to reduce the volume and to be reshaped (38, 39). The melting process is simple, but brings about some chemical degradation and cannot avoid debasing the quality of the original PS, so a solvent treatment is, in many respects, more desirable for an e ective recycling system. Although there are various solvents for PS, e.g., hydrocarbons, alkyl halides, aromatics, esters, and ketones, petroleum-based solvents are not favorable to the global environment. Limonene, which is a component of citrous oils, was derived from the above concept, and it is a pioneer of natural solvents for EPS (33, 40, 41). Lately, the recycling of EPS using limonene has been realized in practical use at a semi-industrial scale. However, peel corresponding to approximately 1,000 oranges is necessary to extract 100 ml of limonene (42).

Recycling Methods 95 Except for limonene, there are only a few reports on the natural solvents for EPS. However, the dissolution of PS in naturally abundant monoterpenes is possible (36). Terpene is a biomolecular hydrocarbon. Its structural backbone contains an isoprene unit. According to the number of an isoprene unit, they are called monoterpene (C10 ), sesquiterpene (C15 ), diterpene (C20 ), sesterterpene (C25 ), etc. Many monoterpenes are liquid at room temperature and are the main components of essential oils. In particular, the leaf oils of Abies sachalinensis and Eucalyptus species, in that the growth is comparatively fast, may be suitable biomasses because they are not utilized e ectively and are containing many monoterpenes (36). Terpene and terpenoid contents in these plants are shown in Table 3.4. Some compounds are shown in Figure 3.6. Table 3.4 Terpene and terpenoid content (36). Terpene Compound Bornyl acetate d-Limonene β-Phellandrene α-Pinene β-Pinene Myrcene p-Cymene 1,8-Cineole

Abies sachalinensis Eucalyptus Content [%] 27.0 22.6 15.6 13.3 9.7 1.9 0.4 0

0 3.1 0 37.9 0.5 0.4 2.9 29.9

Other compounds, such as geranyl acetone, geranyl formate, and citronellyl acetate, have a similar dissolving power as high as geranyl acetate. These compounds can be found in the essential oils of the Picea genus and citrus oils. These values are higher than those of typical cyclic monoterpenes. Currently, it entails a high cost to gather natural solvents for the recycling of waste EPS. Therefore, the recovery and reuse of the solvents are required. Terpenes and PS can be simply recovered by steam distillation of a solution of PS in terpenes (36).

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Polymer Waste Management

O O Bornyl acetate

α-Phellandrene

Pinene

Limonene

β-Phellandrene

Myrcene

Figure 3.6 Terpenes.

Recycling Methods 97 3.4.2

Landfill Methane Recycling

Environmental implications of non-biodegradable plastics in landfills have raised major concerns (43). The use of biodegradable plastics is the best alternative, as they are environmental friendly, with great recycling potential, and can be produced using renewable resources such as waste materials, methane and simple carbon sources. Biodegradable plastics are eco-friendly, however, they pose a risk of emitting methane under anaerobic conditions in landfills. Landfill methane can be e ectively used for the production of biodegradable plastic by methanotrophs. The current approaches to plastic disposal have been reviewed, along with alternatives to plastic waste management. Also, the potential for the cost-e ective production of poly(3-hydroxybutyrate) (PHB) using methanotrophs for manufacturing biodegradable plastics has been examined. The data input for this analysis has been derived from Australian landfill methane emissions, the average PHB content of methanotrophs and applied to a case scenario in Sydney, Australia. The results from this study suggest that this approach to biodegradable plastic production can be economically viable and pricecompetitive with synthetic plastics (43). In small landfills, 162 t y 1 of methane can be recovered to produce 71 t y 1 of PHB. On the other hand, in large landfills, 7,480 t y 1 of methane can be recovered to produce 3,252 t y 1 of PHB. The costs of the PHB production can be reduced to prices, meeting the market value of synthetic plastic by increasing production volumes through building a centralized extraction and refinement facility suitable for large metropolitan cities (43). 3.4.3

Anaerobic Landfill

Most plastic waste bags are intended to be deposited in landfills where not enough oxygen likely exists for the oxo-degradable material of the bags to completely degrade in the expected time. A plastic film can be produced by blending a polymer with particles encapsulating an oxidizing agent such as hydrogen peroxide (44). The production may run as follows:

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Polymer Waste Management

Preparation 3–1: First, a suitable amount of the oxidizing agent is dissolved in an aqueous phase, e.g., deionized water. Then, a water-in-oil emulsion is created by adding the aqueous phase containing the oxidizing agent to an organic phase containing poly(lactic-co-glycolic acid) (PLGA) in dichloromethane, chloroform, or some other organic solvent with vigorous stirring. Next, a water-in-oil emulsion is created by adding the water-in-oil emulsion to an aqueous PVA solution with further stirring for a suitable period of time, e.g., approximately 1 min. The organic solvent is subsequently allowed to evaporate, or is extracted. In the case of evaporation, the water-in-oil emulsion is maintained at reduced or atmospheric pressure with stirring at a controlled rate as the organic solvent evaporates. In the case of extraction, the water-in-oil emulsion is transferred to a large quantity of water, optionally, with surfactant, or some other quenching medium to extract the organic solvent. The resultant PLGA microspheres are then washed and dried. In double emulsion processes, the stirring rate and the solvent choice may be utilized to control encapsulation e ciency and final particle size. An example of such a synthetic procedure for the fabrication of PLGA microspheres has been disclosed (45).

Hollow hydrogel capsules are another example of a microcapsule nanocapsule type that may be used to encapsulate the oxidizing agent. Such capsules contain a hydrogel shell having a hydrolyzed and crosslinked polymerized composition. Hollow hydrogel capsules may be prepared, for example, using in-situ hydrolysis and crosslinking. An example of such a synthetic procedure for the fabrication of hollow hydrogel capsules has been disclosed (46). Polymer microcapsules can also be made via photopolymerization. The microcapsules can be prepared using hydrodynamic phenomena, e.g., multiphase laminar flow in a microscale channel, in combination with on-the-fly photopolymerization of a polymerizable shell fluid, such as a solution containing 4-hydroxybenzoic acid and a suitable photoinitiator. An example of such a synthetic procedure for the fabrication of such polymers and other polymer microcapsules has been presented (47). Protein microcapsules made via sonochemical technology are another example of a microsphere nanocapsule type that may be used to encapsulate the oxidizing agent (48). Lysozyme microcapsules may be used to encapsulate the oxidizing agent. Such microcapsules may be prepared by layering an oil-water emulsion on the surface of a lysozyme solution, and then sonicating the layered system at the oil water interface.

Recycling Methods 99 The oxidizing agent can also be encapsulated in a matrix of a composite microparticle or a composite nanoparticle. The matrix of the composite microparticle or nanoparticle into which the oxidizing agent is encapsulated may comprise any suitable material, e.g., silica xerogel. For example, hydrogen peroxide may be incorporated into a silica xerogel matrix using the sol-gel technique (49). The presence of the oxidizing agent within the plastic film ensures the degradation of the article of manufacture, e.g., a plastic bag, when it is disposed of in an anaerobic environment, such as a landfill. The particles can be microcapsules or nanocapsules, each having a polymer shell encapsulating a core that includes the oxidizing agent (44). 3.4.4

Simulated Semi-aerobic Landfill

The biodegradation of waste plastics, such as high density poly(ethylene) (HDPE), LDPE, poly(propylene) (PP), and PS in a simulated semi-aerobic landfill was investigated under a di erent range of aeration rates of 1 ml min 1 to 2 ml min 1 concurrently with a constant rate of a synthetic landfill gas. The oxidation of methane was found throughout the waste bed of a 1 ml min 1 aerated lysimeter, while methane was absolutely oxidized at the bottom of 2 ml min 1 aerated lysimeter. After 3 months of the experiment, aeration of 1 ml min 1 showed higher significant percentage losses of weight (15%–20% HDPE and 5%–9% PP) than those of 2 ml min 1 (11%–12%, HDPE and 1%–2%, PP) where high methane oxidation rate appeared. The variety of species of methanotrophs, heterotrophs, and autotrophs was revealed using PCR-DGGE technique. Only heterotrophs (Burkholderia sp.), nitrifying bacteria (Nitrosomonas sp. AL212, Nitrobacter winogradkyi), Type I methanotrophs (Methylobactor sp. and Methylococcus capsulatus), Type II methanotrophs (Methylocystic sp., Methylocella sp.) were found to correlate with plastics degradation in the lysimeters under di erent conditions. Many low molecular weight hydrocarbon compounds, such as alkane, alkene, alcohol, acid and epoxide, were detected as biodegraded products. In conclusion, biodegradation of plastic wastes in semi-aerobic landfill could be accelerated by supplying an optimum aeration in proportion to methane available in the waste bed (50).

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3.5 Preparation and Regeneration of Catalysts 3.5.1

Reuse of ZSM-5 Zeolite

A study of the regeneration and reuse of ZSM-5 zeolite in the pyrolysis of a plastic mixture has been carried out in a semi-batch reactor at 440°C (51). When a spent ZSM-5 catalyst was used, the aromatic content of the liquids drastically decreased from 95.2% to 78.4%, due to the fact that most of the strong acid sites responsible for the aromatization reactions have probably been blocked by coke and char particles. However, the total aromatic content of the liquid obtained in this experiment (78.4%) was still higher than that obtained in the thermal experiment (67.7%). This indicates that the zeolite still retains some catalytic activity. This fact can also be observed in the carbon number of liquid fractions, where the decrease in the C5 to C9 fraction of the liquids obtained with the spent zeolite is not as high as the mentioned decrease in aromatics. It has also been found that after one pyrolysis experiment the zeolite loses quite a lot of its activity, which is reflected in both the yields and the products’ quality. However, this deactivation was found to be reversible, since after regeneration heating at 550°C in oxygen atmosphere, the catalyst recovered its initial activity, generating similar products and in equivalent proportions to those obtained with a fresh catalyst (51). The main components of the pyrolysis liquids have been determined by GC-MS. The amounts in area percentage are collected in Table 3.5. 3.5.2

Modification of Zeolites

Synthetic zeolite catalysts were modified by metal loading and used for real end-of-life vehicle plastic waste pyrolysis (52). ZSM-5 and y-zeolite catalysts were loaded by Ce2 , Cu2 , Fe2 , Fe2 , H , Mg2 , Ni2 , Sn2 , and Zn2 . The catalysts were loaded by 8% to 10% of metal ions. The catalytic e ects of both parent and metal loaded catalysts were tested by thermogravimetric analysis. The results for end-of-life vehicle thermal and thermocatalytic pyrolysis using di erent catalysts are shown in Table 3.6. Here,

Recycling Methods 101 Table 3.5 Main components of the pyrolysis liquids (% area in GC) (51). Product Toluene Dimethyl heptene Ethylbenzene Xylenes Styrene α-Methyl styrene Methyl-napththalene

No Cat. Thermal 8.1 7.8 5.7 – 46.3 3.2 –

Fresh 12.3 1.8 10.6 10.1 31.4 4.5 3.3

ZSM-5 type Spent Regenerated 9.9 5.4 9.0 2.0 42.9 4.4 4.9

13.2 1.2 11.2 13.1 23.7 3.8 4.9

the temperatures with a yield of 5%, 95% and maximum yield are collected. The morphology of the catalysts and other properties were investigated by N2 adsorption-desorption isotherms, FTIR spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray fluorescent spectroscopy. Significant di erences in micropore, mesopore and macropore surface area, and the average pore diameter were found. In general, the surface areas could be decreased by metal loading onto the catalyst surface. Parent y-zeolite had larger surface areas than the parent ZSM-5 catalyst. In general, y-zeolite-based catalysts had smaller grains and the distribution was also narrower than that of the ZSM-5-based catalysts (52). Based on first order kinetic approach, the reaction kinetic parameters were also calculated and evaluated. Waste end-of-life vehicle started to decompose at 426°C (T5%) and finished at 525°C (T95%). The catalysts can also decrease the activation energies of the decomposition reaction (52).

3.6 Pyrolysis Methods Examples of plastic pyrolysis methods are summarized in Table 3.7. Pyrolysis is a suitable process for recycling polymer composites because the thermal decomposition products of the polymer matrix evaporate, and thus the reinforcement materials can be recovered

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Table 3.6 Results for end-of-life vehicle thermal and thermocatalytic pyrolysis (52). Catalyst No catalyst ZSM-5 H ZSM-5 Ce ZSM-5 Cu ZSM-5 Fe(II) ZSM-5 Fe(III) ZSM-5 Mg ZSM-5 Ni ZSM-5 Sn ZSM-5 Zn ZSM-5 y-zeolite H y-zeolite Ce y-zeolite Cu y-zeolite Fe(II) y-zeolite Fe(III) y-zeolite Mg y-zeolite Ni y-zeolite Sn y-zeolite Zn y-zeolite

Temperature [°C] for yield of 1% max % 95% 426 349 360 408 405 398 391 362 349 374 408 336 322 388 402 322 406 310 408 349 381

488 450 452 454 458 449 458 471 452 464 467 430 428 459 457 473 474 458 464 470 473

525 510 509 514 519 505 510 510 520 511 518 519 520 510 508 514 507 519 517 510 505

Recycling Methods 103

Table 3.7 Plastic pyrolysis methods (53). Process from

Heating method

Union Carbide

Extruder, followed by annular pyrol. tube, electrically heated Extruder Tubular reactor, externally heated Tubular reactor, superheated steam as a heat carrier Catalytic fixed-bed reactor Fluidized bed catalytic reactor Stirred tank reactor, polymer bath Tank reactor with circulation pump and reflux cooling Polymer bath, formed by PE and PS Stirred tank reactor, salt bath Fluidized bed Fluidized bed molten salt bath

Japan Steel Works Japan Gasoline Co. Prof. Tsutsumi

Nichimen Toyo Engineering Corp. Mitsui Shipbuilding Engineering Co. Mitsubishi Heavy Ind. Kawasaki Heavy Ind. (Kakogawa Works) Ruhrchemie AG, Oberhausen Japan Gasoline Co. Prof. Sinn, Prof. Kaminsky, Univ. of Hamburg

Reaction temp. [°C]

Capacity [t d 1 ]

420–600

0.035–0.07

500–650

0.5 420–455

24–30

400-500

0.7–2.4

400–450

5

380–450

1.2

450 640–840

0.2 Lab. scale

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and reused. The products of pyrolysis carried out at an appropriate temperature are monomers and other valuable chemicals. The pyrolysis reactions and products of frequently used thermoplastics and thermosets in polymer composites have been described in a chapter of a monograph (54). The published results on pyrolysis of various polymer composites have been discussed in order to understand the requirements of successful plastic composite recycling by pyrolysis. Also, the environmental concerns related to the pyrolysis of polymer composites containing flame retardants have been discussed and some methods have been referenced for decreasing or eliminating toxic and harmful compounds from the pyrolysis products of halogenated flame retardants. 3.6.1

Fluidized-Bed Reactor

Established methods of waste plastics pyrolysis are done in a Fluidized-Bed (55,56). Grainy inert materials, for example, quartz, sand or ceramic crumb, are used for making a fluidized-bed (57). This material can be used as a circulating heat carrier, which is heated in a separate apparatus. A fluidizing agent is inert gas or circulating pyrolysis gas. Preliminary shredding of a feedstock is necessary for this technology. A reactor is provided with equipment for supplying feedstock and withdrawing any possible solid residue. A gas stream (pyrolysis products and fluidizing gas) and particles of inert material, escaping from the location of a fluidized bed, are separated within a cyclone. In comparison with other methods of waste plastics processing, for example, those carried out in the rotary kiln reactor and the shaft reactor, pyrolysis in a fluidized bed has the following advantages (57): Design simplicity, compactness, no moving parts (for the kiln reactor), low operating cost and lower capital cost, increased product yields, and enhanced product quality. These advantages are associated with well-known properties of a fluidized bed: Uniformity of temperature field without temperature gradients (those gradients are typical for the above-mentioned packed bed reactors), e ective mass exchange and the possibility of using a circulating solid heat carrier. However, the fluidization technique also has disadvantages when it is used for chemical processes, such as pyrolysis, requiring very

Recycling Methods 105 short residence time. Among these disadvantages are: Mixing feedstock into the whole volume of a fluidized bed, impossible to ensure short contact time, and back mixing of the pyrolysis products. The problems can be solved by the way that waste plastics preliminary shredded are delivered to the top of a downflow tubular reactor (downer). A hot circulating grainy inert heat carrier is also supplied to this downer from a feeder-fluidized bed apparatus, which is located above the downer. The carrier is heated in a separate fluidized bed apparatus-combustor and is supplied in the said feeder-apparatus by a transport line. The shredded waste plastics and some quantity of inert gas entrained from the fluidized bed of the feeder are mixed with the heat carrier, causing melting and pyrolysis of waste plastics in a downflow stream. Pyrolysis proceeds at a temperature between 300°C and 600°C and the formed hydrocarbons residence time of 0.5 to 3 s, producing hydrocarbon oils (57).

3.7 Metallized Plastics Waste The use of metallized plastics has increased significantly over recent decades, especially in food packaging, due to the superior performance of these lightweight laminated materials (58). Currently there is no recycling or treatment solution for these materials. However, these multi-layered plastic and aluminium films can be problematic in plastics or aluminium recycling plants as they cannot be readily separated, and so are highly unlikely to be recovered. Hence, these materials are usually disposed of in landfills or incinerated, imposing a considerable burden on the environment. A new concept has been developed for using metallized plastics as a secondary resource for industry, thereby overcoming the current limitations of conventional recycling technologies. The electronic structure and chemical bonding of metallized plastics using microstructure investigation, FTIR, mass spectroscopy and X-ray photoelectron spectroscopy (XPS) characterizations have been investigated. It was shown that there is a strong binding between the metal and polymer at their interface. This makes the recycling of metallized plastic components a formidable task (58).

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To successfully recycle these materials, metallized plastics must considered as a single component or input, and potentially good source of Al, C, Si and Ti. Extracting these elements as raw materials using conventional mining consumes significant energy. Utilizing metallized plastics as an alternative source of Al, C, Si, and Ti promises to reduce energy usage and greenhouse gas emissions, and alleviate the negative environmental impacts of landfilling and resource depletion (58). 3.7.1

Rotary Kiln Pyrolysis

A rotary kiln is a pyroprocessing device used to raise materials to a high temperature in a continuous process (59). The kiln is a cylindrical vessel, inclined slightly to the horizontal, which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down towards the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by a flame inside the kiln. The art of rotary kiln technology and rotary kiln principles have been described (60). Also, the pyrolysis of polymers containing heteroatoms using this technique has been detailed. A method and an apparatus for fast pyrolysis of biomass in rotary kilns has been described (61). Systems and methods for achieving fast pyrolysis of wood and other carbonaceous solids in rotary reactors have been detailed. The heating, feeding and condensing methods result in high oil yields near those currently achieved with more complicated fast pyrolysis systems. High intensity burners can be arranged and controlled to produce high heating rates and uniform temperature on the rotating cylindrical walls of the reactors. The feeding system delays the onset of pyrolysis until the solids fall onto the heated kiln walls. The pyrolysis gases and vapors can be rapidly withdrawn and quenched with recycled liquids. The first condenser incorporates

Recycling Methods 107 a clean out nozzle. Char products are readily separated and discharged into a heat exchanger where heat is recovered and used together with heat from reactor flue gas to dry the solids prior to being fed to the reactor. A view of a transverse section of the rotary reactor is shown in Figure 3.7. This view shows the location of the rolling bed of

Figure 3.7 Transverse section of rotary reactors (61).

solid particles inside the reactor body. The top of the rolling bed of particles is generally flat and disposed at the angle of repose of the material. As particles are carried upward and reach the top surface of the material, they begin to fall downward. When the falling particles reach the lower portion of the kiln wall they remain near stationary with respect to the heated wall until they again reach the top of the rotating bed. The particles that are in contact with the kiln wall draw heat very rapidly. A high intensity burner is directed toward the outside of the reactor wall at the location where the inside of the wall is in contact with the particles. The burner is disposed such that an extension of the centerline of burner intersects the center of mass 108 of the circulating bed. The burner is disposed such that the burner is directed towards the reactor body and the burner flames and combustion gasses directly contact the reactor body (61). Recycled pyrolysis gas and natural gas is combusted in the burners to heat the reactor. It has been determined that, in many cases, the non-condensable gas products will supply the necessary energy

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to heat the reactor. The condensable gasses (oil) and the char are collected as useful products. Thus, this reactor is largely self-su cient while converting waste and by-products into usable products. Hot combustion products flowing at high velocity directly impact the reactor body wall. A device that senses the temperature of the kiln wall is preferably an infrared sensor. The sensor is connected to a burner control system that adjusts the fuel flow to maintain a specified temperature set point. Experimentally measured product yields are used to determine the optimum set point temperatures for di erent feed materials (61).

3.8 Mixed Plastics 3.8.1

Grinding and Cleaning

A method for recycling of all types of waste plastic has been reported (62). In a method for the grinding and cleaning of waste plastic, in particular mixed plastic, a compactate or an agglomerate is produced from film shavings or other film remainders and chopped plastic parts (63). The agglomerate drastically reduces the volume of the waste plastic and can thus can be easily transported. In this state, it is largely used for power generation (62). A large portion of dirt, impurities and adherences thereby remain in the agglomerate or compactate. In this process, knowledge assumes that such a compactate or agglomerate can be easily ground and is suitable for further processing and refining. The grinding preferably occurs in a disk or drum refiner in the presence of water. A fine-particle fraction is removed from the ground material emerging from the refiner. The remaining ground material is washed or mechanically dehydrated and dried. Through further processing, such ground material can be used as a replacement for wood in composite wood boards, as a filler material in various applications and, if the degree of purification is appropriate, even with pure plastic or high-quality sorted recycling plastics for the production of plastic parts. Another area of application is the production of so-called wood plastic composites. During the production of such parts, a mixture

Recycling Methods 109 of wood and plastic particles is produced either through dry mixture and direct processing or through compounding with the help of an extruder, an agglomerator, a heating mixer or a heating-cooling mixer and processed into shaped parts. Agglomerates or compactates, from flakes or other plastic parts, are ground in at least one refiner stage in the presence of water, to form ground material emerging from the at least one refiner stage. From a portion of the ground material emerging from at least one refiner stage, fine particles are removed with the water. The remaining ground material is washed and mechanically dehydrated and dried and, optionally, the dehydrated ground material is again ground in another refiner stage in the presence of water and then dehydrated and dried. The grinding of the agglomerate or compactate is performed in at least one refiner stage using a disk refiner having two disks, the disks of which have engaging teeth, which are arranged separated on concentric circles, wherein there are gaps between neighboring teeth of the concentric circles in which the gaps of the concentric circles are each big enough that the agglomerate or compactate to be ground can pass freely through the gaps (62). 3.8.2

Reductant in Ironmaking

A method of making iron involves using waste polymer material as a solid fuel charged to an iron melting vessel and or using gaseous decomposition products from pyrolysis of waste polymer material as a gaseous fuel supplied to the vessel (64). Relatively large quantities of waste polymer materials can thereby be disposed of without landfill usage, while a substantial portion of their energy value is recovered for heating and melting the ironbearing material in the vessel. The waste polymer material may comprise reaction injection molding compounds and precursors thereof, sheet mold compounds and precursors thereof, car flu , i.e., nonmetallic residue from the recycling of automobiles, scrap rubber tires and others. Waste sheet molding compounds including calcium carbonate filler can be charged to the ironmaking vessel such that the calcium carbonate therein is released and functions as a flux at the ironmaking temperature involved to remove impurities from the iron. As

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a result, limestone additions to the vessel can be reduced or eliminated (64). One of the major obstacles to the implementation of an appropriate plastics recycling scheme is the inhomogeneity of many plastics waste (65). Most of the existing recycling schemes require a feedstock that is reasonably pure and contains only items made from a single polymer type. However, in reality, waste plastics contain a mixture of plastic types, and are often contaminated with non-plastic items. This demands sorting out, which is expensive and very labor intensive. The reduction of reagent grade iron oxide by mixed plastic waste has been investigated with experiments conducted in a laboratoryscale horizontal tube furnace. Composite pellets of reagent grade iron oxide (97% Fe2 O3 ) with a mixed plastic waste consisting of 50% HDPE, 30% PP, 10% LDPE, and 10% PET were rapidly heated at 1520°C under high purity argon gas and the o -gas was continuously analyzed for CO, CO2 , and CH4 using an online infrared gas analyzer. The extent of reduction after ten minutes was determined for each carbonaceous reductant and the results were compared with the extent of reduction by conventional metallurgical coke under the same experimental conditions. The results show that iron oxide can be e ectively reduced to produce metallic iron using mixed plastic waste as reductant. An improvement in extent of reduction was observed over metallurgical coke and the individual polymers when mixed plastic waste was used as reductant. This eliminates the need to sort out individual plastics from municipal solid waste for their e ective utilization as reductants in ironmaking (65). Also, waste poly(urethane) (PU) has been tested as reductant for ironmaking (66). PU contains high levels of carbon and hydrogen that can be recovered for use as reductant in metal extraction processes. Composite pellets were formed from mixtures of iron oxide and post-consumer PU. The iron oxide-PU composites were heated from room temperature to 1200°C and then between 1200°C–1600°C in a continuous stream of pure argon and the o -gas was analyzed continuously using an infrared gas analyzer. The extent of reduction was determined at temperatures of 1200°C and 1550°C. Gas emission studies revealed the emission of large volumes of the reductant gas CO and CO2 . It could be demonstrated

Recycling Methods 111 that post-consumer PU is e ective at reducing iron oxide to produce metallic iron with a complete reduction achieved in less than 4 min at 1550°C (66).

3.9 Separation Processes 3.9.1

Automated Sorting of Waste

A crucial prerequisite for plastics recycling forming an integral part of municipal solid waste management is sorting of useful materials from source-separated municipal solid waste. The recent advances in physical processes, sensors, and actuators used as well as control- and autonomy-related issues in the area of automated sorting and recycling of source-separated municipal solid waste have been reviewed (67). The percentage of materials of municipal solid waste are summarized in Table 3.8. Table 3.8 Materials of municipal solid waste (67). Material Fabric Wood Glass Plastic Paper Non-ferrous Ferrous

Amount [%] by weight 12 11 10 27 40 5 6

Several review articles have frequently been reported in areas related to automated or semiautomated waste sorting for recycling (67). Also, various sorting techniques for separating plastic materials have been detailed (68). This review is primarily focused on nonsensor-based design, development, and testing of wet- and dry-based separating sorting techniques. Chemical recycling and energy recovery from plastic solid waste have been reviewed (11, 69).

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The energy recovery, mechanical and chemical recycling and separation methods of poly(vinyl chloride) (PVC) waste have been presented (70). The removal of impurities from aluminum debris has been surveyed (71). The triboelectrostatic separation techniques for sorting plastic from waste has been presented (72). Also, the physical processing of waste to segregate recyclables from municipal solid waste has been detailed (73). This review mainly focused on case studies of operational experience without emphasizing many aspects of automation, including material handling, sensors and control. 3.9.2

Sorting According to Density

A materials-separation process has been described. The process is shown schematically in Figure 3.8. This process includes a (74): 1. Materials collection stage, 2. Materials preparation stage, and 3. Materials separation stage. The three stages include a materials collection stage in which paper, metal, and plastic materials are first collected and combined and thereafter the metal and paper materials are separated from the plastic materials and the plastic materials are then baled to establish a mixed-plastics bale. In a materials preparation stage the mixedplastics bale is first broken apart, then ground to produce a mixture of flakes made of several plastic materials, and then cleaned to remove contaminants. The third step is a materials separation stage in which a first plastic material is removed from the mixture of flakes using a higher-density separation operation and then a second plastic material is separated from a third plastic material using a lower-density separation operation. During the materials separation stage, a higher-density fluid is used in a higher-density separation operation and a lower-density fluid is used in a subsequent lower-density separation operation (74). As higher-density fluid, water can be used. A lower-density fluid is a vegetable oil having a density in a range of about 0.91 g cm 3 to about 0.94 g cm 3 . The vegetable oil can be soybean oil, but also may be rape seed oil, sunflower seed oil, coconut oil, cotton seed

Recycling Methods 113

Materials Collection Stage

Collect paper metals and plastics

Sort plastics from metals and paper

Bale the plastics to establish a bale

Materials Preparation Stage

Clean flakes

Grind stream to establish flakes

Breake the bale to establish a stream

Materials Separation Stage

Separate plastics according to density

Figure 3.8 Materials separation process (74).

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oil, or linseed oil. Soybean oil has a density in the range of about 0.92 g cm 3 to about 0.93 g cm 3 , which causes PP with a density of less than about 0.92 g cm 3 to float on the lower-density fluid and HDPE with a density of greater than 0.94 g cm 3 to sink in the lower-density fluid. The lower-density fluid may also include additives or modifiers to increase its oxidative stability, decrease surface tension, and modify the density. Also, the cleaning operation may include magnetically separating metal particles from the plastic flakes using a magnet, hot-water washing and and cold-water washing to remove contaminants (74). 3.9.3

Hydrocyclonic Separation of Waste Plastics

The hydrocyclonic separation can be used for the separation of waste plastics because of its characteristics of high G force and good dispersing action generated from the shearing e ect of the internal flow (75). The removal of low density plastic with the hydrocyclone was found to be problematic due to a carryover of liquid leaving with the underflow stream. The separation of high impact poly(styrene) (HIPS) and ABS with the hydrocyclone was only partially successful, even with a closely sized product (76). Based on their di erence in densities, PETand PVC particles could be separated with help of the centrifugal sedimentation and shearing dispersion in a hydrocyclone (75). A solid-liquid hydrocyclone was used for the separation. The nominal diameter of the hydrocyclone was 70 mm, and the diameter of the underflow orifice was 20 mm. The diameter of the overflow orifice ranged from 20 mm to 30 mm. The test results showed that the Newton e ciency can reach above 80%, i.e., the purity of PVC could reach 93.2% while the purity of PET could reach 94.5% (75). 3.9.4

Froth Flotation

Froth flotation is a process for the selective separation of hydrophobic materials from hydrophilic materials (77). This method has been used in mineral processing, paper recycling and wastewater treatment industries. Historically, this process was first used in the 20th

Recycling Methods 115 century in the mining industry. Froth flotation depends on the selective adhesion of air bubbles to mineral surfaces in a slurry (77). Recently, froth flotation has also been used for recycling of polymers. Froth flotation is a promising method to solve a key problem of the recycling process, namely separation of plastic mixtures. The recent literature on plastics flotation, focusing on specific features compared to ores flotation, strategies, methods and principles, flotation equipment, and current challenges has been reviewed (78, 79). The strategy options for the separation of plastics by froth flotation are shown in Figure 3.9. Mixture of hydrophobic plastics

Surface treatment

Selective wetting

Mixture of (partly) wettable plastics

Surface treatment

Selective hydrophobization

Figure 3.9 Strategies for the separation of plastics by froth flotation (78).

Sink-float separation in water requires that the particles be well wetted to avoid misplacement due to attaching air bubbles and nonselective clustering (flocculation) (78). A frequently used method to obtain the wetting of plastic particles in recycling is friction washing, in which the plastic particles are exposed to high shear forces in a stirred vessel or tube. A similar e ect is obtained by wet grinding of plastics in a cutting mill. As a result of the above treatments, the plastic particles lose a great deal of their natural hydrophobicity, thus making the mixture unsuitable for separation by froth flotation using the selective-wetting approach. In addition, the hydrophobicity of plastics from durable consumer goods, such as automotive parts, may be a ected

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due to aging. It appears, therefore, that the application of the selective-wetting method is restricted to the separation of virgin plastic scrap and post-consumer scrap in which the natural hydrophobicity of the components is still su cient (78). A representative list of specific plastic materials capable of being treated by froth flotation, including the specific gravity and contact angle, measured at 20°C, is presented in Table 3.9. Table 3.9 Specific gravity and contact angles (80). Polymer

Specific Gravity [g cm 1 ]

Low density poly(ethylene) High density poly(ethylene) Poly(ethylene) (medium density) Poly(propylene) Poly(propylene) (flame retardant) Poly(propylene) (talc reinforced) Poly(propylene) (calcium carbonate reinforced) Poly(propylene) (mica reinforced) Poly(vinyl chloride) (flexible) Poly(vinyl chloride) (rigid) Poly(styrene) (gen. purpose) Poly(styrene) (medium impact) Poly(styrene) (high impact) Acrylic Modified Acrylic Acrylonitrile-butadiene-styrene Acrylonitrile-butadiene-styrene (medium impact) Acrylonitrile-butadiene-styrene (high impact) Acrylonitrile-butadiene-styrene (flame retardant) Acrylonitrile-butadiene-styrene (nylon alloy)

Contact Angle[°]

0.914 0.945 0.930 0.900 1.25 1.00 1.00

92 87 90 88 86 92 88

1.00

96

1.30 1.30 1.05 1.04 1.04 1.19 1.19 1.05 1.05

87 83 89 85 83 78 68 77 71

1.05

79

1.21

84

1.06

73

The wettability of plastic surfaces by water can be increased by grafting hydrophilic functionalities, such as O, OH, and COOH, onto the polymer chains that are located on the surface. This can be achieved by wet oxidative chemical reactions, plasma treatment,

Recycling Methods 117

Table 3.9 (cont.) Specific gravity and contact angles (80) Polymer

Specific Gravity [g cm 1 ]

Styrene Acrylonitrile Styrene butadiene Ethylene Vinyl Acetate copolymer Poly(butylene) Styrenic Terpolymer Poly(methyl pentene) Poly(carbonate) Thermoplastic Polyester Nylon (transparent) Nylon (type 66) Nylon (type 6) Cellulose acetate Cellulose acetate butyrate Cellulose acetate propionate Urethane elastomer (polyester) Urethane elastomer (polyether) Polysulfone Acetal Resin (homopolymer) Acetal Resin (copolymer) Polyphenylene sulfide Polyallomer

Contact Angle[°]

1.04 1.01 0.945

83 91 82

0.901 1.02 0.830 1.20 1.27 1.14 1.14 1.14 1.29 1.20 1.21 1.20 1.14 1.24 1.41 1.41 1.65 0.899

94 72 96 80 73 77 65 78 62 73 65 81 98 87 82 77 77 89

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corona discharge, and photografting methods. Also, several other methods have been explained (78). Actually, a combination of the selective-wetting method with the selective hydrophobization technique might yield the best results in many practical applications (78). In terms of separation methods, plastics flotation can be divided into (79): 1. 2. 3. 4.

Gamma flotation, Adsorption of reagents, Surface modification, and Physical regulation.

Gamma flotation is also addressed as liquid-vapor surface tension control. In gamma flotation, an appropriate organic liquid, such as aqueous solutions of methanol, is commonly used to control the surface tension of the flotation liquid (81, 82) 3.9.4.1

Poly(vinyl chloride)

Several studies were conducted to separate PVC from binary plastics (83–85). However, many di erent types of plastics exist in a waste stream. Treatment with calcium hypochlorite was proposed for the separation of hazardous PVC plastic from mixed plastic wastes by froth flotation (86). Plastic particles were treated with calcium hypochlorite solution in a thermostat-controlled water bath. After calcium hypochlorite treatment, filtration was conducted to separate plastic particles and the calcium hypochlorite solution. The particles were rinsed with tap water before the flotation experiments. Plastics with particle sizes of 2.0 mm – 2.5 mm were used, and the fraction of the plastic particles in calcium hypochlorite solution was 10%. For the separation of binary plastics, the fraction of plastic particles was 20%. For the separation of multi-plastics, poly(methyl methacrylate) (PMMA), PVC, PET, ABS, poly(carbonate) (PC), and PS waste plastics with sizes of 2.0 mm – 2.5 mm were mixed in the mass ratio of 1:1:1:1:1:1 and subjected to the calcium hypochlorite treatment with a fraction of 24% (86).

Recycling Methods 119 The flotation behavior of a single plastic indicates that PVC can be separated from PET, ABS, PS, PC, and PMMA by froth flotation combined with a calcium hypochlorite treatment. The mechanism of the calcium hypochlorite treatment was examined by a contact angle measurement, SEM, FTIR spectroscopy, and X-ray photoelectron spectroscopy. Under optimum conditions, the separation of PVC from binary plastics with di erent particle sizes can be e ciently achieved. The minimum purity of the plastics obtained is shown in Table 3.10. Table 3.10 Purity (86). Polymer Poly(carbonate) Acrylonitrile-butadiene-styrene Poly(methyl methacrylate) Poly(styrene) Poly(ethylene terephthalate)

Purity [%] 96.8 98.5 98.8 97.4 96.3

The separation of PVC from multi-plastics was further conducted by a two-stage flotation. PVC can be separated e ciently from mixed plastic wastes with residue content of 0.37%. In addition, reusing the calcium hypochlorite solution is possible (86). 3.9.4.2

Poly(ethylene terephthalate)

The separation of PET from municipal waste plastics by froth flotation combined with alkaline pretreatment was investigated (87). The optimum conditions of alkaline pretreatment are 10% sodium hydroxide, 20 min at 70°C. After alkaline pretreatment under optimum conditions, the flotation separation of PET from ABS, PS, PC, or PVC was achieved with high purity and e ciency. The purity of PET was found to be 98.46% and the recovery was above 92.47% (87). Metals and nonmetallic materials obtained from printed circuit boards can be separated by a conventional Denver D12 flotation cell (88). The bubble superficial surface rate and the percentage of solids in the feed was changed to evaluate the recovery of nonmetallic material in overflow product (concentrate) and the metal material

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in underflow (tailings). The solids content in feed is the most influential parameter in nonmetallic material recovery. A flotation circuit has been proposed, as well as a flotation mechanism, for this unconventional mix (88). 3.9.4.3

Fenton Pretreatment

The Fenton reagent is a combination of hydrogen peroxide and ferrous ion, and has a super oxidative capacity due to the hydroxyl radical generated by the reaction between hydrogen peroxide and ferrous ion (89). Therefore, a Fenton reagent has been widely applied to wastewater treatment and the degradation of toxic organic pollutants (90). The mechanisms of reaction between Fenton reagent and organics can be explained by the following chemical equations (91): Fe2

H2 O2

Fe3

OH

OH

(3.1)

Organic compounds with hydrogen units can be attacked by the hydroxyl radicals through abstracting protons and producing organic radicals (R ), which are highly reactive and can react with H2 O2 . Therefore, organic compounds can be oxidized and introduced some oxygen-containing groups in the molecular structure of organics (89). In a recent study, the surface treatment with Fenton reagent was applied to the flotation separation of ABS and PVC. After the treatment, the floatability of ABS showed a dramatic decrease, while the floatability of PVC was not a ected. The optimum conditions are a molar ratio of H2 O2 to Fe2 of 10000, a H2 O2 concentration of 0.4 M l 1 , a pH of 5.8, a treatment time of 2 min, a temperature of 25°C, a frother concentration of 15 mg l 1 , and a flotation time of 3 min. Particle sizes and mixing ratios were also investigated. Plastic mixtures of ABS and PVC with di erent particle sizes and mixing ratios can be e ectively separated. The purity of ABS and PVC are up to 100% and 99.78%, respectively; the recovery of ABS and PVC are up to 99.89% and 100%, respectively. A practical, environmentally friendly and e ective reagent, namely Fenton, was originally applied to surface treatment of ABS and PVC waste plastics for flotation separation of their mixtures (89).

Recycling Methods 121 In another study, it was shown that simulated sunlight conditions could initiate the Fenton reaction, thus rapidly decomposing most inert polymer waste, including poly(ethylene) (PE), PP, and PVC, to yield heat and carbon dioxide (92). The activation reaction is shown in Figure 3.10. Poly(ethylene) CH2

CH2

SO3FeCl2 CH2

CH2

CH

CH

CH

CH2

CH

CH2

Poly(vinyl) chloride Cl

SO3FeCl2

CH

CH2

CH2

CH2

CH

CH

Poly(propylene) CH3 CH

CH3 CH2

CH

SO3FeCl2 CH2

C

CH

CH3

C

CH2

CH3

Figure 3.10 Activation for the Fenton reaction (92).

The polymer treatment is done according to the following procedure (92): Preparation 3–2: PE, PP, and PVC are crushed to obtain particle sizes of 125 μm to 250 μ m before use. Each plastic material in an amount of 2.0 g is suspended or dissolved in 50 ml of refluxing 1,1,2,2-tetrachloroethane (in the case of PE activation, chloroform was used instead of 1,1,2,2-tetrachloroethane) with a stirring rate of 200 rpm. Then, a mixture of dichloromethane and chlorosulfuric acid (15 ml, in a ratio of 2:1 by volume) is added dropwise to the suspension solution over 30 min. The resulting brown suspension was further heated at 65°C with stirring at 200 rpm for 2 h. After the removal of the the organic solvent from the reaction mixture, a FeCl3 solution (0.75 M, 100 ml) is added and the mixture was allowed to stir under ambient conditions overnight. The black solid obtained by centrifugation was washed with deionized water until the supernatant became colorless. The solids were oven-dried at 80°C.

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Then, the light-accelerated decomposition of energetic plastic materials into CO2 via the Fenton reaction is performed as: Preparation 3–3: The before obtained plastic materials were crushed to obtain particle sizes of 125 μ m – 250 μ m before use. Each activated powder (0.15 g) was suspended in 85 ml of deionized water by ultrasonication for 10 min. The initial pH of the mixture was adjusted to 2.5. Then, 30% H2 O2 (10 mL, 650 mmol g 1 of activated plastic) was added to the suspension, and the final volume was adjusted to 100 ml with deionized water. The reaction was initiated by placing the reaction mixture 30 cm from a UV-Vis lamp (model 66142 mercury-xenon arc lamp; Newport) and was stirred under ambient conditions for 2 h. The light-triggered reaction was studied with respect to the input light power, which ranged from 0 W to 500 W. The reaction mixtures were filtered through a 1.0 μ m pore-size membrane filter. The carbon contents of the reaction mixtures were determined using a Shimadzu TOC-L CSH high-sensitivity total organic analyzer. The amount of remaining solid plastic material was recorded.

This energy conversion process is completely controlled via the on–o switching of the light source. In addition, various working conditions (pH, amount of H2 O2 , and reaction time) were studied to further investigate the controlling factors of the light-accelerated decomposition of the energetic plastics. The activated polymers were completely mineralized into CO2 at pH values between 2.5 and 7.0. Values below 2 hindered the light-accelerated Fenton reaction and reduced the amount of CO2 released, resulting in an incomplete mineralization (92). 3.9.4.4

Ammonia Pretreatment

The flotation separation of PC and ABS waste plastics combined with ammonia pretreatment has been investigated (93). The PC and ABS polymers show a similar hydrophobicity. An ammonia treatment selectively changes the floatability of PC, while ABS is insensitive to an ammonia treatment. Contact angle measurements indicated the dropping of flotation recovery of PC that can be correlated to a decline of the contact angle. X-ray photoelectron spectroscopy demonstrated reactions on the PC surface. These reactions make the PC surface more hydrophilic (93).

Recycling Methods 123 The separation of PC and ABS waste plastics was conducted based on the flotation behavior of the single plastic. At di erent temperatures, PC and ABS mixtures were separated e ciently through froth flotation with an ammonia pretreatment for di erent times (13 min at 23°C, 18 min at 18°C, and 30 min at 23°C). For both polymers, the purity and recovery was more than ca. 95.3%. The purity of PC and ABS was found to be up to 99.72% and 99.23%, respectively. In summary, it was concluded that the ammonia treatment possesses a superior applicability (93). Also, the flotation separation of PC and PS waste plastics was found to be successful using the ammonia modification (94). Ammonia modification only had a little e ect on the flotation behavior of PS, while it significantly changed that of PC. The PC recovery in the floated product drops from 100% to 3.17% when modification time is 13 min and then rises to 100% after longer modification (94). Contact angle of PC and PS samples before and after ammonia treatment was determined at 23°C, and the results are shown in Table 3.11. Table 3.11 Contact angle (94). Time [min]

0

Polymer PC PS

5

13

20

30

Contact angle [degree] 73.12° 72.90°

65.91° 71.14°

62.33° 69.32°

66.22° 70.11°

75.62° 69.56°

The separation e ciency of PC ABS mixtures at di erent temperatures is shown in Table 3.12. As shown in Table 3.12, the mixtures of ABS and PC plastics could be separated e ciently through flotation separation at di erent temperatures after ammonia treatment. The purity of overflowed product ABS and the submerged product PC is larger than 95.31%, and the recovery of ABS and PC is larger than 95.35%. The purity of PC and ABS is up to 99.72% and 98.09%, respectively (93).

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Table 3.12 Separation of PC ABS mixtures at di erent temperatures (93). T [°C] Product

Yield [%]

14 14 14 18 18 18 23 23 23

50.97 49.03 100.00 51.32 48.68 100.00 49.74 50.25 100.00

3.9.4.5

Overflowed ABS Submerged PC Feed Overflowed ABS Submerged PC Feed Overflowed ABS Submerged PC Feed

Purity [%] PC ABS 4.69 100.00 50.93 3.52 99.72 50.40 1.91 96.81 49.60

95.31 0.00 49.07 96.48 0.28 49.60 98.09 3.19 50.40

Recovery [%] PC ABS 4.65 95.35 100.00 3.59 96.41 100.00 1.91 98.09 100.00

100.00 0.00 100.00 99.73 0.27 100.00 96.82 3.18 100.00

Potassium Permanganate Pretreatment

A process has been developed for the separation of ternary waste plastics by froth flotation. The plastics used were PC, PVC, and PMMA (95). A pretreatment of the plastics with potassium permanganate (KMnO4 ) solution was conducted to aid the flotation separation of the polymers. A two-stage process was used for the separation these waste plastics. Washing is necessary before separation, but it is not presented in the process since it is not key procedure of the process. Size reduction, which promotes liberation of di erent components and provides suitable particle sizes for separation, is imperative before separation. PC is first separated through the KMnO4 treatment and froth flotation (first stage). Then, PVC and PMMA plastics are further treated with KMnO4 solution, and separation of the mixtures is again achieved by flotation (second stage). The amount of KMnO4 employed in the process is very small, and reusing KMnO4 solution makes the developed process greener. The e ect of the parameters of the pretreatment, including the concentration of KMnO4 , treatment time, temperature and stirring rate on flotation recovery were investigated by single factor experiments. The surface treatment with KMnO4 selectively changes the flotation behavior of PC, PVC, and PMMA, thus enabling the sepa-

Recycling Methods 125 ration of the plastics by a froth flotation process. The mechanism of the surface treatment was studied by FTIR, SEM, and XPS. The e ect of froth concentration and the flotation time on the flotation behavior of plastic mixtures was further studied for flotation separation (95). The optimized conditions for separation of PC were found to be KMnO4 concentration of 2 m mol l 1 , a treatment time of 10 min, a temperature of 60°C, a stirring rate of 300 rpm, a flotation time of 1 min, and a frothing concentration of 17.5 mg l 1 . Under optimum conditions, PVC and PMMA mixtures are also separated e ciently by froth flotation associated with KMnO4 treatment. The purity of PC, PVC and PMMA was found to be up to 100%, 98.41% and 98.68%, respectively, while the recovery reaches 96.82%, 98.71% and 98.38%, respectively. An economic analysis manifested remarkable profits from this process. Reusing the KMnO4 solution is feasible, thus making this process more green (95). 3.9.4.6

Selective Surface Hydrophilization

The treatment of PVC by a nanometallic Ca CaO composite has been found to selectively hydrophilize its surface, thus enhancing its wettability and thereby promoting its separation from electronic waste plastics by means of froth flotation (96). The treatment considerably decreased the water contact angle of PVC by about 18 degrees. The SEM images of the PVC plastic after treatment showed significant changes in the surface morphology in comparison to other plastics. These reveal a marked decrease of concentration of chlorine simultaneously with dramatic increase of oxygen on the surface of the PVC samples. Also, an increase of other hydrophilic functional groups on the PVC surface could be shown by XPS experiments (96). Froth flotation at a mixing speed of 100 rpm was found to be optimal. Here, 100% of the PVC was separated into a settled fraction of 96.4% purity, even when the materials fed into the reactor were of nonuniform size and shape. The total recovery of PVC-free plastics in electronic waste reached nearly 100% in the floated fraction. This is a significant improvement from the 20.5% of light plastics that can be recovered by means of a conventional wet gravity separation. Thus, the hybrid method of

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nanometallic Ca CaO treatment and froth flotation is e ective in the separation of hazardous chlorinated plastics from electronic waste plastics (96).

3.10 Triboelectrostatic Separation Triboelectrostatic separation has become one of the most important and promising materials processing techniques. In the last century, triboelectrostatic separation methods have undergone continuous development and are well established in the mineral processing industry for separation of minerals and beneficiation of coal or raw ore (72). Since the 1970s, this technique has also been assessed for the separation of mixed plastics. Since the triboelectrostatic separation method is a dry process, it is free from the problem of wastewater disposal and can be easily operated. The recoveries and the purities in studies indicate that it is an e ective method for separating plastic waste of reasonable size. Because it has many advantages over other separation methods, more and more relevant research into triboelectrostatic separation for plastic recycling has been carried out in recent years. Triboelectrostatic separation exhibits a high e ciency, low cost and no concerns regarding water disposal or secondary pollution, with a wider processing range of particle size especially suitable for crushed or granular plastic waste. For the mixed plastic waste scraps of particle size in the millimeter range, triboelectrostatic separation undoubtedly has great advantages, which indicates a promising future for this technique in plastic recycling. It is well known that when two materials with di erent surface properties come into contact with each other, they may get charged. This tribocharging phenomenon is also known as contact electrification or frictional electrification when materials rub against each other. As for short contact during collision, it can also be addressed as impact charging. It is generally believed that the mechanism of charge transfer in tribocharging can be explained by three mechanisms: electron transfer, ion transfer, and material transfer (72). Among the above-explained mechanisms, electron transfer mechanism is the most important and widely accepted since it has suc-

Recycling Methods 127 cessfully explained the metal-metal contact electrification. When two di erent materials come into contact with each other, electron transfer happens until their Fermi levels become equal. Tribocharging can be done with a rotating tube, rotary blades, vibrating devices, cyclone, propeller-type tribocharger, or a fluidized bed (72). The tribocharged mixed plastic particles are commonly fed into an electric field separator and deflect to high voltage static electrodes according to the Coulomb forces acting on them. The configuration of electric field plays an important role in the separation process. Designs utilized in the triboelectrostatic separation of plastic waste can be roughly divided into three types: free-fall electric field, roll-type electric field and vertical electric field for upflow fluidized particles (72).

3.11 Wet Gravity Separation Wet gravity separation can be used to separate heavy plastics of specific gravity of greater than 1.0 g cm 3 , including PVC, ABS, PET, PS, HIPS, styrene acrylonitrile copolymer, poly(amide), PMMA, and poly(oxymethylene), from light plastics of specific gravity less than 1.0 g cm 3 , including PP and PE (96–99). However, a further separation of PVC from other heavy plastics is di cult due to their similar specific gravities. Various techniques have been developed for PVC separation such as electrostatic separation (13, 100–102), gravity separation, and selective dissolution (103, 104). In addition, automated sorters have been developed to obtain the desired purity at a reasonable throughput. These typically have expensive polymer identification systems based on laser scanning and infrared or X-ray spectroscopy (105, 106). Flotation, an alternative method, has recently received attention due to its e ective separation of plastics with similar properties, including density, dielectric constant, and surface hydrophobicity (78, 93, 107). The separation by flotation is based upon selective attachment of bubbles to the particles to be separated. This requires that the particle surfaces have su cient di erences in wettability (108, 109).

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Because most plastics are hydrophobic in their natural state, selective-wetting of one or more components is necessary for the separation. Several strategies for the PVC surface treatment are available. In some cases, it is necessary to utilize two or more techniques consecutively to gain the desired modification level. The major research conducted in this field has dealt with the influence of plasma and flame treatments upon PVC surface chemistry under di erent working environments (110, 111) As an alternative to plasma exposure, high-energy irradiation (electron, gamma, and UV radiation) has been utilized to alter the PVC surface chemistry for various purposes. Such methods require rather expensive equipment but are also not safe in terms of hazardous materials being exposed to the living environment (112–114) Also, ozone treatment has been applied successfully to PVC surface modification (115, 116). However, the use of ozonation systems requires additional measures for air pollution control. The contact angles of certain polymers can be modified by an ozonization reaction (99). The changes in the contact angles by ozonization of some polymers are shown in Table 3.13. Table 3.13 Changes of the contact angles of certain polymers due to ozonization (99). Polymer PVC PC PMMA PET

Contact angle [degree] Before ozonization After ozonization 90.3 87.4 88.1 88.8

68.4 84.9 87.3 86.9

The results of the study indicated that a selective recovery of PVC and rubber from automobile shredder residue polymers can be accomplished in a three-step process involving a gravity separation, ozonation and froth flotation (99). 3.11.1

Selective Dissolution Precipitation Technique for Polymer Recycling

The selective dissolution precipitation technique for polymer recycling consists of the following steps (103):

Recycling Methods 129 1. Cutting the waste into smaller pieces and, if necessary, washing with water. 2. Preliminary separation of the initial mixture into two or more mixtures by floatation in water or another liquid. 3. Addition of a solvent (S) that selectively dissolves only one of the polymers under certain conditions. 4. Filtration to remove the nondissolved polymers. 5. Addition of an antisolvent to precipitate the dissolved polymer. 6. Filtration and drying of the precipitated polymer. 7. Separation of the solvent nonsolvent mixture by distillation for reuse. 8. Application of the same procedure for each polymer of the mixture. Two solvent nonsolvent systems, three dissolution temperatures and four initial polymer concentrations were investigated (104). The e ect of these parameters on the percents of recovery of the three model polyolefins (LDPE, HDPE, PP) and several commercial products based on these polymers is shown in Table 3.14. Table 3.14 Polymer recovery by the dissolution reprecipitation technique (104). Solvent Nonsolvent

T [°C]

Concentration [% w v]

Toluene n-hexane Xylene n-hexane Xylene n-hexane Xylene n-hexane Xylene n-hexane Xylene n-hexane Xylene n-hexane

110 50 100 140 140 140 140

5 5 5 5 10 15 20

Recovery [%] LDPE HDPE PP 97.7 63.2 98.9 99.7 99.8 99.8 95.9

96.7 6.4 98.3 99.6 99.7 99.7 99.4

98.2 4.9 75.5 98.7 99.7 99.9 97.4

3.12 Supercritical Water One of the most intriguing and environmentally sound approaches to breaking down plastics is simply to use water alone, heated into

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its supercritical state. This chemical-free technology has been comprehensively discussed (117). When water is heated to 374.4°C or above, the pressure concomitantly generated is 217.7 atm and the water then becomes a powerful new reactive solvent. Temperatures above 400°C seem to make the water even more e ective in its new role (118). For example, it now dissolves PS and breaks it down in 100% yield into a mixture of styrene, α-methyl styrene, styrene dimers and trimers, toluene, ethylbenzene, isopropylbenzene, 1,3-diphenylpropane and 1,3-diphenylbutane. Apparently the water and the plastic undergoes a water gas reaction and hydrogen is released to combine with the chain fragments from the plastics. This could be demonstrated by the use of deuterium oxide in place of water and the consequent finding of deuterium in the fragments. However, since nearly all water-plastic reactions have been run in a batch mode on a very small scale, the chemistry so elegantly elucidated does not provide answers to the questions necessary for the future development of a commercially-sized, practical, continuous, supercritical water-based process (119, 120). A method for transforming a selected polymeric material into a plurality of reaction products using supercritical water has been described. This method consists of (120): 1. Conveying the selected polymeric material, e.g., biomass, a waste plastic, or a combination of these materials, through an extruder, wherein the extruder is configured to continuously convey the selected polymeric material to a supercritical fluid reaction zone, 2. Injecting hot compressed water into the supercritical fluid reaction zone, while the extruder is conveying the selected polymeric material into the supercritical fluid reaction zone so as to yield a mixture, 3. Retaining the mixture within the reaction zone for a period of time su cient to yield the plurality of reaction products. The device is shown in Figure 3.11. The reaction zone may be characterized by a tubular reactor having an adjustably positionable inner tubular spear, wherein the tubular reactor and the inner tubular spear further define an annular space within the reaction zone, and wherein the mixture

Recycling Methods 131

Figure 3.11 Device for using supercritical water (119).

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Polymer Waste Management

flows through the annular space and into a reaction products chamber (120).

3.13 Solvent Treatment The dissolution of plastics has long been known and practiced. For instance, a plastic is dissolved in a solvent to prepare a solution, which is applied to the surface of the solid object to be coated with this plastic or is used in adhering two or more solid objects. Selective dissolution methods have been proposed for separating physically mixed or commingled solid plastics comprising various polymers by purely mechanical means. These methods take advantage of the fact that the solubilities of plastics are dissimilar in di erent organic solvents, and they vary based on temperature. Some selective dissolution methods for separating physically mixed or commingled plastics into individual plastics, each comprising a single polymer, have been developed on the basis of the solubility characteristics of plastics. Methods have also been developed to dissolve an individual plastic or polymer with one or more solvents. Such methods deploy a wide variety of organic solvents. For example, a process of recovering substantially pure PET from contaminated scrap PET via solvent dissolution under high pressure has been described (121). This process acts at temperatures ranging from ambient temperature to about 250°C. The solvents used here are aliphatic alcohols, including methyl alcohol, ethyl alcohol, normal propanol, isopropanol, and mixtures of these compounds (121). Also, processes of recovering a polyester polymer from discarded dyed polyester fibers has been described (122–124). This process uses solvent dissolution and dye stripping. The solvents deployed here are collected in Table 3.15. Some of these compounds are shown in Figure 3.12. In addition, an exhaustive survey is available that has revealed a wide range of organic solvents (125). Unconsolidated pieces of a material dissolve far faster in a liquid state than in a solid state at any given temperature, e.g., a material after and before melting, respectively, as long as they do not be-

Recycling Methods 133

Table 3.15 Solvents for recovering a polyester polymer (122– 124). Solvent

Solvent

p-Chloroanisole Nitrobenzene Acetophenone Propylene carbonate 1,1,2,2-Tetrachloroethane Quinoline Ethylene carbonate Propylene carbonate Chloroform Carbon tetrachloride o-Phenylphenol Trifluoroacetic acid Trichlorophenol Diphenyl ether Benzophenone Dimethyl formamide p-Dichlorobenzene Phenanthrene 1,2,2-Trifluoroethane o-Xylene m-Xylene

Dichloromethane 1,1,1-Trichloroethane Trichloroacetic acid Dimethyl sulfoxide 2,6-Dimethyl phenol 1,1,1,3,3,3-Hexafluoro-isopropanol Naphthalene m-Cresol Phenol Tetrahydronaphthalene p-Phenylphenol o-Chlorophenol Diphenyl Methyl naphthalene Diphenyl methane Benzyl alcohol Acenaphthene Ethylene glycol p-Dichlorobenzene p-Xylene Tetrahydrofuran

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NO2

H3 C OH OH m-Cre s ol

Phe nol

O

CH3

Be nzophe none

F

O

Nitrobe nze ne

1-Me thyl naphthalene

CH3

F C F

OH

Trifluoroace tic acid

CH3

o-Xyle ne

Te trahydronaphthale ne

Figure 3.12 Solvents for recovering a polyester polymer.

Recycling Methods 135 come consolidated as molten mass or masses upon melting, thereby reducing the surface area available for mass transfer or dissolution. Compositions have been described that contain a turpentine liquid for the decomposition of plastics containing a chlorine-containing polymer or a thermosetting polymer (125). The turpentine liquid may contain the specific compounds shown in Table 3.16. Some compounds are shown in Figure 3.13. Table 3.16 Specific compounds in a turpentine liquid (125). Compound

Compound

Natural turpentine Synthetic turpentine Mineral turpentine Pine oil α-Pinene β-Pinene α-Terpineol β-Terpineol γ -Terpineol 3-Carene Anethole Dipentene (p-Mentha-1,8-diene) α-Terpene β-Terpene γ -Terpene Nopol Pinane Camphene p-Cymene Anisaldehyde 2-Pinane hydroperoxide 3,7-Dimethyl-1,6-octadiene Isobornyl acetate Terpin hydrate Ocimene 2-Pinanol Dihydromyrcenol Isoborneol Alloocimene Alloocimene alcohols Geraniol 7-Hydroxydihydrocitronellal Camphor p-menthan-8-ol α-Terpinyl acetate Citral Citronellol 7-Methoxydihydrocitronellal 10-Camphorsulfonic acid p-Menthene p-Menthan-8-yl acetate Citronellal Menthone Menthol 2-Methoxy-2,6-dimethyl-7,8-epoxyoctane

Preferably, the weight of the plastic sample is reduced by 70% as compared to weight of the plastic sample before contacting with turpentine liquid. Even more preferably, the entire plastic sample is dissolved or decomposed in the turpentine liquid. An example for such a process is described as follows (125): About 2 g of nearly spherical, rigid LDPE pellets with a diameter of about 0.42 cm and a specific gravity of about 0.92 were dissolved in about

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H 3C

CH3

CH2

CH3 OH

H 3C

CH3

Nopol

H 3C

Ocimene

CH3 CH3 OH

CH3 CH3 HO

Isoborneol

CH3 2-Pinanol

Figure 3.13 Turpentine liquid compounds.

40 g of α-terpineol serving as the solvent at about 100°C, which is slightly below the average melting point of LDPE, and under ambient pressure in a graduated glass bottle. The bed of LDPE pellets floating at the top portion of the solvent was agitated manually by shaking the bottle every several minutes. At about 19 min, swelling and softening of the LDPE pellets were detected by pressing them to the wall of the bottle with a hand-held metal rod. Moreover, blurring of the boundary between the solvent and the bed of LDPE pellets was observed. At about 29 min, the LDPE pellets were clearly observed to start disappearing. The LDPE pellets were hardly distinguishable from the solvent after about 41 min, thereby indicating their total dissolution into the solvent to form a homogeneous, transparent solution (125).

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Recycling Methods 139 41. T. Noguchi, H. Tomita, K. Satake, and H. Watanabe, Packaging Technology and Science, Vol. 11, p. 39, 1998. 42. R.L. Coleman, E.D. Lund, M.G. Moshonas, D.B. Slope, E.C. Humphries, J. Ehteridge, G.H. Sidaway, W. Bond, G.E. Hart, and S.E. Chao, Journal of Food Science, Vol. 34, p. 610, 1969. 43. K. Chidambarampadmavathy, O.P. Karthikeyan, and K. Heimann, Renewable and Sustainable Energy Reviews, Vol. 71, p. 555, 2017. 44. J. Kuczynski, D. Neuman-Horn, J.F. Prisco, and K.J. Przybylski, Method and composition to ensure degradation of plastic films in an anaerobic environment, such as a landfill, US Patent Application 20 170 029 582, assigned to International Business Machines Corp., February 2, 2017. 45. H.K. Makadia and S.J. Siegel, Polymers, Vol. 3, p. 1377, 2011. 46. P.W. Livanec and S.A. Klasner, Hollow hydrogel capsules and methods of using the same, US Patent Application 20 140 174 724, assigned to Halliburton Energy Services, Inc., Houston (TX), June 26, 2014. 47. H.-J. Oh, S.-H. Kim, J.-Y. Baek, G.-H. Seong, and S.-H. Lee, Journal of Micromechanics and Microengineering, Vol. 16, p. 285, 2006. 48. E.K. Skinner and G.J. Price, Chem. Commun., Vol. 48, p. 9260, 2012. 49. S. Bednarz, B. Rys, and D. Bogdal, Molecules, Vol. 17, p. 8068, July 2012. 50. S. Muenmee, W. Chiemchaisri, and C. Chiemchaisri, International Biodeterioration & Biodegradation, Vol. 113, p. 244, 2016. 51. A. López, I. de Marco, B.M. Caballero, A. Adrados, and M.F. Laresgoiti, Waste Management, Vol. 31, p. 1852, 2011. 52. N. Miskolczi, T. Juzsakova, and J. Sója, Journal of the Energy Institute, p. in press, 2017. 53. R.J. Evans and H.L. Chum, Pyrolysis and hydrolysis of mixed polymer waste comprising polyethyleneterephthalate and polyethylene to sequentially recover, US Patent 5 821 553, assigned to Midwest Research Institute (Kansas City, MO), October 13, 1998. 54. M. Blazsó, Pyrolysis for recycling waste composites in V. Goodship, ed., Management, Recycling and Reuse of Waste Composites, Woodhead Publishing Series in Composites Science and Engineering, chapter 5, pp. 102–121. Woodhead Publishing, 2010. 55. K.C. Kirkwood, S.A. Leng, and D.W. Sims, Polymer cracking, US Patent 5 364 995, assigned to BP Chemicals Limited (London, GB2), November 15, 1994. 56. S. Hardman, S.A. Leng, and D.C. Wilson, Polymer cracking, US Patent 5 481 052, assigned to BP Chemicals Limited (London, GB2), January 2, 1996. 57. V. Stankevitch, Process for the conversion of waste plastics to produce hydrocarbon oils, US Patent 6 534 689, assigned to Pyrocat Ltd. (Migdal HaEmek, IL), March 18, 2003.

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58. N. Gorjizadeh, F. Pahlevani, and V. Sahajwalla, Journal of Materials and Environmental Sciences, Vol. 8, p. 1599, 2017. 59. Wikipedia contributors, Rotary kiln — wikipedia, the free encyclopedia, 2017. [Online; accessed 7-April-2018]. 60. A. Hornung and H. Seifert, Rotary kiln pyrolysis of polymers containing heteroatoms in Feedstock Recycling and Pyrolysis of Waste Plastics: Converting Waste Plastics into Diesel and Other Fuels, chapter 20, pp. 549– 567. Wiley-Blackwell, 2006. 61. R.L. Coates, B.R. Coates, and J.L. Coates, Method and apparatus for fast pyrolysis of biomass in rotary kilns, US Patent 8 999 017, assigned to Coates Engineering, LLC (Salt Lake City, UT), April 7, 2015. 62. M. Hofmann and A. Gercke, Method for recycling all waste plastics in particular mixed plastics, US Patent 8 388 873, assigned to CVP Clean Value Plastics GmbH (Buxtehude, DE), March 5, 2013. 63. M. Hofmann, A. Feddern, and J.-M. Lo er, Method and apparatus for comminuting and cleaning of waste plastic, US Patent 7 757 974, assigned to CVP Clean Value Plastics GmbH (Buxtehude, DE), July 20, 2010. 64. K.B. Agarwal, Iron making method using waste polymer material, US Patent 5 244 490, assigned to General Motors Corporation (Detroit, MI), September 14, 1993. 65. J.R. Dankwah, T. Amoah, J. Dankwah, and A.Y. Fosu, Ghana Mining Journal, Vol. 15, p. 73, 2015. 66. J.R. Dankwah and W.K. Buah, Ghana Mining Journal, Vol. 17, p. 73, 2017. 67. S.P. Gundupalli, S. Hait, and A. Thakur, Waste Management, Vol. 60, p. 56, 2017. Special Thematic Issue: Urban Mining and Circular Economy. 68. G. Dodbiba and T. Fujita, Physical Separation in Science and Engineering, Vol. 13, p. 165, October 2004. 69. A. Rahimi and J.M. García, Nature Reviews Chemistry, Vol. 1, p. 0046, 2017. 70. M. Sadat-Shojai and G.-R. Bakhshandeh, Polymer Degradation and Stability, Vol. 96, p. 404, 2011. 71. G. Gaustad, E. Olivetti, and R. Kirchain, Resources, Conservation and Recycling, Vol. 58, p. 79, 2012. 72. G. Wu, J. Li, and Z. Xu, Waste Management, Vol. 33, p. 585, 2013. Special Thematic Issue: Urban Mining. 73. C. Cimpan, A. Maul, M. Jansen, T. Pretz, and H. Wenzel, Journal of Environmental Management, Vol. 156, p. 181, 2015. 74. R. Flores, Separation process for plastics materials, US Patent 9 067 214, assigned to Berry Plastics Corporation (Evansville, IN), June 30, 2015.

Recycling Methods 141 75. H. Yuan, S. Fu, W. Tan, J. He, and K. Wu, Waste Management, Vol. 45, p. 108, 2015. Urban Mining. 76. R.D. Pascoe, Waste Management, Vol. 26, p. 1126, 2006. 77. Wikipedia contributors, Froth flotation — wikipedia, the free encyclopedia, 2018. [Online; accessed 25-January-2018]. 78. N. Fraunholcz, Minerals Engineering, Vol. 17, p. 261, 2004. Processing and Disposal of Minerals Industry Waste ’03. 79. C.-Q. Wang, H. Wang, J.-G. Fu, and Y.-N. Liu, Waste Management, Vol. 41, p. 28, 2015. 80. J.-Y. Hwang, Separation of normally hydrophobic plastic materials by froth flotation, US Patent 5 377 844, assigned to Nimco Shredding Co. (Newark, NJ), January 3, 1995. 81. S. Kelebek, G.W. Smith, J.A. Finch, and S. Yörük, Separation Science and Technology, Vol. 22, p. 1527, 1987. 82. R. Buchan and B. Yarar, JOM, Vol. 47, p. 52, Feb 1995. 83. C. Wang, H. Wang, J. Fu, L. Zhang, C. Luo, and Y. Liu, Waste Management, Vol. 45, p. 112, 2015. 84. N.T. Thanh Truc and B.-K. Lee, Environmental Science & Technology, Vol. 50, p. 10580, 2016. 85. C. Wang, H. Wang, Y. Liu, and L. Huang, Journal of Cleaner Production, Vol. 139, p. 866, 2016. 86. J. Wang, H. Wang, C. Wang, L. Zhang, T. Wang, and L. Zheng, Waste Management, Vol. 69, p. 59, 2017. 87. C.-Q. Wang, H. Wang, and Y.-N. Liu, Waste Management, Vol. 35, p. 42, 2015. 88. P.M. Gallegos-Acevedo, J. Espinoza-Cuadra, and J.M. Olivera-Ponce, Journal of Mining Science, Vol. 50, p. 974, Sep 2014. 89. J.-C. Wang, H. Wang, L.-L. Huang, and C.-Q. Wang, Waste Management, Vol. 67, p. 20, 2017. 90. S. Figueroa, L. Vázquez, and A. Alvarez-Gallegos, Water Research, Vol. 43, p. 283, 2009. 91. E. Neyens and J. Baeyens, Journal of Hazardous Materials, Vol. 98, p. 33, 2003. 92. C.-F. Chow, W.-L. Wong, C.-W. Chan, and C.-S. Chan, Waste Management, 2018. in press. 93. C.-Q. Wang, H. Wang, Q. Liu, J.-G. Fu, and Y.-N. Liu, Waste Management, Vol. 34, p. 2656, 2014. 94. C.-Q. Wang, H. Wang, G.-H. Gu, Q.-Q. Lin, L.-L. Zhang, L.-L. Huang, and J.-Y. Zhao, Waste Management, Vol. 51, p. 13, 2016. 95. C.-Q. Wang, H. Wang, and L.-L. Huang, Waste Management, Vol. 65, p. 3, 2017. 96. S.R. Mallampati, J.H. Heo, and M.H. Park, Journal of Hazardous Materials, Vol. 306, p. 13, 2016.

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97. R.D. Pascoe and B. O’Connell, Waste Management, Vol. 23, p. 845, 2003. 98. T. Takoungsakdakun and S. Pongstabodee, Separation and Purification Technology, Vol. 54, p. 248, 2007. 99. M.S. Reddy, K. Kurose, T. Okuda, W. Nishijima, and M. Okada, Journal of Hazardous Materials, Vol. 147, p. 1051, 2007. 100. I.I. Inculet, G.S.P. Castle, and J.D. Brown, Particulate Science and Technology, Vol. 16, p. 91, 1998. 101. S. Pongstabodee, N. Kunachitpimol, and S. Damronglerd, Waste Management, Vol. 28, p. 475, 2008. 102. C.-H. Park, H.-S. Jeon, H.-S. Yu, O.-H. Han, and J.-K. Park, Environmental Science & Technology, Vol. 42, p. 249, 2008. 103. G. Pappa, C. Boukouvalas, C. Giannaris, N. Ntaras, V. Zografos, K. Magoulas, A. Lygeros, and D. Tassios, Resources, Conservation and Recycling, Vol. 34, p. 33, 2001. 104. D.S. Achilias, C. Roupakias, P. Megalokonomos, A.A. Lappas, and E.V. Antonakou, Journal of Hazardous Materials, Vol. 149, p. 536, 2007. Pollution Prevention and Restoration of the Environment. 105. E.J. Sommer and J.T. Rich, Application of Raman spectroscopy to identification and sorting of post-consumer plastics for recycling, US Patent 6 313 423, assigned to National Recovery Technologies, Inc. (Nashville, TN), November 6, 2001. 106. S.R. Ahmad, Environmental Technology, Vol. 25, p. 1143, 2004. 107. H. Alter, Resources, Conservation and Recycling, Vol. 43, p. 119, 2005. 108. F. Burat, A. Güney, and M.O. Kangal, Waste Management, Vol. 29, p. 1807, 2009. 109. H. Wang, C.-Q. Wang, and J.-G. Fu, Waste Management, Vol. 33, p. 2623, 2013. 110. J. Drelich, T. Payne, J.H. Kim, J.D. Miller, R. Kobler, and S. Christiansen, Polymer Engineering & Science, Vol. 38, p. 1378, 1998. 111. B.R. Schmitt, H. Kim, and M.W. Urban, Journal of Applied Polymer Science, Vol. 71, p. 1, 1999. 112. L. Cota, M. Avalos-Borja, E. Adem, and G. Burillo, Radiation Physics and Chemistry, Vol. 44, p. 579, 1994. 113. D. Sinha, T. Swu, S.P. Tripathy, R. Mishra, K.K. Dwived, and D. Fink, Radiation E ffects and Defects in Solids, Vol. 158, p. 593, 2003. 114. C.-H. Jung, I.-T. Hwang, H.-J. Kwon, Y.-C. Nho, and J.-H. Choi, Polymers for Advanced Technologies, Vol. 21, p. 135, 2010. 115. T. Okuda, K. Kurose, W. Nishijima, and M. Okada, Ozone: Science & Engineering, Vol. 29, p. 373, 2007. 116. K. Kurose, T. Okuda, S. Nakai, T.-Y. Tsai, W. Nishijima, and M. Okada, Surface Review and Letters, Vol. 15, p. 711, 2008. 117. P.E. Savage, Chemical Reviews, Vol. 99, p. 603, 1999.

Recycling Methods 143 118. H. Kwak, H.-Y. Shin, S.-Y. Bae, and H. Kumazawa, Journal of Applied Polymer Science, Vol. 101, p. 695, 2006. 119. G. Allan, T.E. Loop, and J.D. Flynn, Biomass and waste plastics to neodiesel and valuable chemicals via supercritical water, US Patent 8 057 666, assigned to Xtrudx Technologies, Inc. (Seattle, WA), November 15, 2011. 120. T.E. Loop, J.D. Flynn, G. Allan, S.C. Van Swearingen, and K.O. Gaw, Biomass and waste plastics depolymerization machine and methods via supercritical water, US Patent 8 980 143, March 17, 2015. 121. M.F. Meyer, Jr., R.L. Combs, and W.C. Wooten, Jr., Purification of impure scrap poly(ethylene terephthalate), US Patent 3 701 741, assigned to Eastman Kodak Co., October 31, 1972. 122. N.C. Sidebotham, P.D. Shoemaker, and C.W. Young, III, Polyester polymer recovery from dyed polyester fabrics, US Patent 4 003 881, assigned to Monsanto Company (St. Louis, MO), January 18, 1977. 123. N.C. Sidebotham, P.D. Shoemaker, and C.W. Young, III, Polyester polymer recovery from dyed polyester fibers, US Patent 4 137 393, assigned to Monsanto Company (Decatur, AL), January 30, 1979. 124. Y. Mizumoto and S. Hasegawa, Method for treating waste high-polymer mixture, US Patent 4 031 039, assigned to Mitsubishi Jukogyo Kabushiki Kaisha (Tokyo, JA), June 21, 1977. 125. L.-T. Fan and S.R. Shafie, Compositions and methods for recycling plastics comprising polymers via solvent treatment, US Patent 8 883 867, assigned to Green Source Holdings LLC (Austin, TX), November 11, 2014.

Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

4 Recovery of Monomers 4.1 Process for Obtaining a Polymerizable Monomer A process for obtaining a polymerizable monomer can be performed by (1): 1. Contacting a waste of thermoplastic acrylic and styrenic resin with a fluid heat transfer medium, 2. Cooling the resulting decomposed product, and 3. Subjecting it to distillation. This method uses not only a molten mixed metal as an inorganic heat transfer medium, but also an additional organic heat transfer medium, so that the plastic waste does not just float on the molten metal. Inorganic heat transfer media are mixtures or alloys of zinc, bismuth, tin, antimony, and lead, which are molten at very low temperatures alone, or in the presence of added inorganic salts, such as sodium chloride, etc., which are molten at less than 500°C. The molten organic medium is a thermoplastic resin. Examples are other waste resins such as atatic poly(propylene) (PP), other polyolefins, or tar pitch. The added thermoplastic is also partially thermally decomposed into products that end up together with the desired monomers, and, therefore, distillation and other procedures must be used to obtain the purified monomer (1). However, since this method is experienced with acrylic polymers which are known to decompose thermally into their corresponding 14 145

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monomers, no means for identifying catalyst and temperature conditions are mentioned that permit the decomposition of that polymer in the presence of others, without substantial decomposition of the other polymers, in order to make it easier to purify the monomer from the easier to decompose plastic or other high-value chemicals from this polymer (2). Another method of treating waste plastics in order to recover useful components derived from at least one monomer selected from aliphatic and aromatic unsaturated hydrocarbons consists of (3): 1. Melting the waste plastic, bringing the melt into contact with a particulate solid heat medium in a fluidized state maintained at a temperature of between 350°C to 650°C to cause pyrolysis of the melt, and 2. Collecting and condensing the resultant gaseous product to recover a mixture of liquid hydrocarbons. Published examples produce mixtures of components, all of which must be collected together and subsequently subjected to extensive purification (3). No procedure is evidenced or taught for a ecting fractionation in the pyrolysis itself by virtue of the catalysts and correct temperature choice (2).

4.2 Pyrolysis in Carrier Gas A process of fast pyrolysis in a carrier gas to convert a plastic waste feedstream with a mixed polymeric composition occurs in a manner in which the decomposition from the polymer into its monomeric constituents occurs prior to the pyrolysis of other plastic components therein (2, 4). In detail, such a process can be done by (2): 1. Selecting a first temperature program range to cause the pyrolysis of the polymer, 2. Selecting a catalyst and support for treating the feedstreams with the catalyst to e ect acid or base catalyzed reaction pathways to maximize yield or enhance separation of the monomeric constituent in the temperature range, 3. Di erentially heating the feedstream at a heat rate within the first temperature program range to provide di erential pyrolysis for selective recovery of optimum quantities of the

Recovery of Monomers 147 high-value monomeric constituent prior to pyrolysis of other plastic components, 4. Separating the monomeric constituents, 5. Selecting a second higher temperature range to cause pyrolysis of an another monomeric constituent of the plastic waste and di erentially heating the feedstream at the higher temperature program range to cause pyrolysis of the di erent high-value monomeric constituent, and 6. Separating the other monomeric constituent.

4.3 Fluidized Bed Method A process for thermal decomposition of polymers such as poly(methyl methacrylate) is using the fluidized bed approach. This method consists of (5): Taking finely divided polymers of grain size less than 5 mm and wind-sifting and pyrolyzing said polymer grains at a temperature which is at least 100°C over the depolymerization temperature to produce monomeric products. However, this is a conventional process that exemplifies the utility of thermal processing in general for recovery of monomers from acrylic polymers which, along with poly(tetrafluoroethylene), are the only classes of polymers which have monomers recovered in high yield by thermal decomposition (2, 6).

4.4 Recovery of Monomers from Waste Gas Streams Gas phase polymerization is the predominant reactor technology used to produce olefin plastic resins. The catalysts are contained in solid substrate particles from which the polymer chains grow. The particles are fluidized in a fluidized bed by a gas stream containing the monomers. A process for rejecting a reactor by-product from the polymerization reactor in an olefin polymerization process has been described (7). The waste gas stream of unreacted monomers, reactor by-products and light components are treated in an absorption process to

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additionally recover the monomers. The absorption process consists of contacting the reactor waste gas streams with an absorption solvent in an absorption zone to produce a gas stream comprising the light components, and a liquid stream containing the absorption solvent, absorbed reactor by-product and the absorbed monomers. Then, the liquid stream is fractionated in a distillation column to produce a distillation column bottoms stream that is the absorption solvent which is conveyed to the absorption zone, and an overhead stream comprising the monomers and reactor by-product which is further fractionated in a splitter column to reject the reactor by-product as a bottoms stream. The recovered monomers from the splitter overhead can be conveyed to the reactor. In a preferred embodiment, the absorption solvent consists essentially of components derived from the reactor waste gas stream so that no external solvent is required (7).

4.5 Polyolefins A study was done to increase the yield of gaseous olefins, i.e., monomers as a feedstock for the polymerization process, and to test the applicability of a commercial Ziegler-Natta catalyst TiCl4 MgCl2 for cracking a mixture of polyolefins consisting of 46% low density poly(ethylene), 30% high density poly(ethylene), and 24% PP (8). Two sets of experiments have been carried out at 500°C and 650°C via catalytic pyrolysis (1% of Z-N catalyst) and at 650°C and 730°C using only thermal pyrolysis. These experiments have been conducted using a laboratory-scale, fluidized quartz-bed reactor with a capacity of 1 kg h 1 to 3 kg h 1 . The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas liquid solid mass fractions via thermal pyrolysis were 36.9 48.4 15.7% and 42.4 44.7 13.9% at 650°C and 730°C, respectively; while via catalytic pyrolysis were 6.5 89.0 4.5% and 54.3 41.9 3.8% at 500°C and 650°C, respectively. At 650°C, the generation of monomer increased by 55% up to 23.6% of total pyrolysis products distribution while the catalyst was added. The obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive

Recovery of Monomers 149 processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in plastic waste management (8, 9).

4.6 Poly(styrene) Waste poly(styrene) (PS) has become a major environmental concern, due to its large production quantities and non-biodegradable nature. Provided that the high molecular weight material can be broken down into useful low molecular weight hydrocarbons, waste PS can be regarded as a highly valuable feedstock (10). One of the most attractive processes is the catalytic degradation of PS (11). This process enables the obtainment of the styrene monomer at relatively low temperature with a high selectivity.

4.6.1 4.6.1.1

Methods with Supercritical Materials Supercritical Water

The recovery of styrene monomer can be accomplished by using a supercritical water partial oxidation technology (10). This technology uses the unique properties of supercritical water in an oxygendeficient environment to partially oxidize the polymer. By using this technique, PS has been successfully depolymerized into monomer, oligomer, and other useful hydrocarbons in a relatively short residence time with high e ciency. The kinetics and feasibility of the supercritical water partial oxidation process were experimentally investigated using di erent oxygen-feed conditions. The styrene selectivity of the process, based on the product mass versus the feed mass, was determined to be as high as 71%, and was found to depend very strongly on the polymer oxygen ratio. While the styrene selectivity was very high, the selectivity for benzene, toluene, and other hydrocarbons was substantially lower. This process was also compared with the pyrolysis in the presence of supercritical water at the same temperature and pressure (10).

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4.6.1.2

Supercritical Solvents

The degradation of PS in supercritical benzene, toluene, ethylbenzene and p-xylene was studied at temperatures of 310°C to 370°C and pressures of 4.0 MPa to 6.0 MPa using a fast degradation process (12). The supercritical degradation method has unique properties, such as excellent heat and mass transfer. By using this technique, PS could be successfully depolymerized into monomer, dimer and other products in a very short reaction time with a high conversion. Toluene used as supercritical solvent was more e ective than other solvents such as benzene, ethylbenzene and p-xylene for the recovery of styrene from PS, though the conversions of PS were similar in all the above solvents. The highest yield of styrene obtained from PS in supercritical toluene at 360°C for 20 min reached 77%. The reaction mechanism consists of the depolymerization of PS and secondary reactions in the closed system. In summary, it was found that di erent supercritical solvents a ected these processes di erently (12). 4.6.2

Volcanic Tu and Florisil Catalysts

The thermal and catalytic degradation of PS waste over two di erent samples of natural volcanic tu catalyst compared with florisil catalyst has been carried out in order to establish the conversion degree into styrene monomer (13). The PS waste was subjected to a thermal degradation process in the range of 380°C to 500°C in the presence of the catalysts in a ratio of 1:10 in mass of catalyst:PS. The catalysts were characterized by N2 adsorption-desorption isotherms (BET), scanning electron microscopy and Fourier transform infrared (FTIR) spectroscopy. The influences of temperature and the type of catalysts on the yields and on the distribution of the end products obtained by thermal and catalytic degradation of PS waste were studied. The maximum yield of liquid products were obtained at a degradation temperature of 460°C and were between 83.45% and 90.11%. The liquid products were characterized by gas chromatography (GC) mass spectroscopy (MS) and FTIR. The results from GC MS showed that the liquid products contained the styrene monomer

Recovery of Monomers 151 in amounts of up to 55.62%. The FTIR spectra of liquid products indicated the specific vibration bands of the functional groups of compounds of liquid products. The amounts of styrene monomer obtained were influenced by the structural and textural properties of the catalyst (13). 4.6.3

Base-Promoted Iron Catalysis

Modified Fe-based catalysts were used for the catalytic degradation of expanded poly(styrene) (EPS)waste (11). Here a carboanion compound may lead to a high selectivity of styrene monomer in the catalytic degradation of PS. The properties of the catalysts used in the study are shown in Table 4.1. Table 4.1 Properties of the used catalysts (11). Catalyst Fe Al2 O3 Fe-K Al2 O3 Fe-Ba Al2 O3 Fe-Zn Al2 O3 Fe-Mg Al2 O3

Composition [%]

SBET [m2 g 1 ]

20:100 20:10:100 20:10:100 20:10:100 20:10:100

128.5 154.6 152.8 100.8 138.4

Pore size [Å] 95.2 96.2 95.4 115.9 98.1

Pore volume [cm3 g 1 ] 0.31 0.35 0.36 0.29 0.34

The yield of oil and the yield of styrene monomer were increased in the presence of Fe-based catalysts and with increasing reaction temperature. The yield of oil and styrene monomer were obtained over Fe K Al2 O3 at a relative low reaction temperature of 400°C in an amount of 92.2% and 65.8%, respectively. The value of the energy of activation is obtained as 194 kJ mol 1 for the thermal degradation of the EPS waste. However, the energy of activation was decreased considerably from 194 to 138 kJ mol 1 in the presence of the catalysts Fe K Al2 O3 (11). 4.6.4

Composite Catalysts

The process of pyrolysis of waste PS was investigated in detail. Ten kinds of catalysts such as cerous sulfate, rare earth chlorides and composite catalyst were used (14). The pyrolytic products of waste

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PS were benzene, toluene, styrene and α-methyl styrene, and were identified by GC MS. The activities of the catalyst were as follows: composite catalyst(I) composite catalyst(II) Ba(NO3 )2 Fe2 O3 CeSO4 CuO rare earth chloride ZnO CaO A12 O3 . The optimum conditions of degradation over composite catalyst (I) were selected by orthogonal experiments. The average yields of pyrolytic products, styrene content and total yields of styrene were 95.0%, 96.8% and 91.9% respectively under degradation conditions of 28 min to 53 min at 390°C under atmospheric pressure, and a catalyst mass fraction of 0.80%. The yield of styrene monomer was 82.3%. Its purity was 99.9%, obtained by a simple distillation method (14). In another study, the process of the thermal pyrolysis of waste PS was studied by using catalysts such as cerous nitrate, composite catalyst and rare earth chloride and others (15). The pyrolytic products of waste PS were benzene, methylbenzene, styrene and ethylbenzene, which were identified using GC. The results show the order of catalytic e ects as follows: Composite catalyst rare earth chloride cerous nitrate. The optimum condition of the degradation over composite catalyst was also studied. The yields of pyrolytic products and styrene content were 89.5% and 97.4% respectively under the degradation condition for 30 min at 390°C, under atmospheric pressure, and a catalyst content of 0.75%. The output of styrene monomer was 84.5% and its purity was above 99.9% using a simple distillation method (15). 4.6.5

Fluidized-Bed Reactor

A specially designed laboratory fluidized-bed reactor apparatus was developed for the pyrolysis of PS waste in the range of 450°C to 700°C with nitrogen as the carrier gas and 20–40 mesh quartz sand as the fluidization medium, operating isothermally at atmospheric pressure (16). The mass balance of the pyrolysis of PS in the temperature range of 450°C to 700°C is listed in Table 4.2. The yield of styrene monomer reached a maximum of 78.7% at a pyrolysis temperature of 600°C. Some monoaromatics with boiling

Recovery of Monomers 153 Table 4.2 Mass balance of the pyrolysis of PS in the temperature range of 450°C to 700°C (16). Products 450

Amount [%] Pyrolysis temperature [°C] 500 550 600 650

700

Liquid products Cracking gas Coke

97.6 – 0.2

96.4 0.04 0.2

95.3 0.26 0.2

98.7 0.65 0.2

90.7 1.51 0.2

90.2 3.54 0.2

Total products

97.8

96.6

95.8

99.5

92.5

93.9

point lower than 200°C could also be obtained as high octane gasoline fraction. Styrene monomer with 99.6% purity was obtained after vacuum distillation of the liquid products, which could be used as the raw material to produce high-quality PS (16). 4.6.6

Catalytic Acid and Basic Active Centers

The influence of the acid and basic properties of a catalyst on the selectivity of degradation of PS was studied (17). The properties of silica-alumina SiO2 –Al2 O3 (45%) dotted with NaOH from 1 to 20% and γ Al2 O3 containing 1% to 8% NaOH or H2 SO4 were examined using the test reactions of cumene (acid) and diacetone alcohol (base) transformation. These catalysts were used in PS degradation reactions. It was found that the PS decomposition involves thermal and catalytic transformation. In the first case, two main reaction pathways are involved (17): 1. Gradual depolymerization to the monomer (styrene), and 2. Pyrolysis leading to the formation of di erent volatile oligomers, i.e., dimers, trimers, and tetramers. The latter species react solely over the catalyst active centers. Linear dimers of styrene activated by Brønsted acid sites undergo decomposition to styrene and ethylbenzene as well as to toluene and α-methyl styrene. The consecutive transformation of the products leads to a simultaneous hydrogen (H and H ) production and coke formation.

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The latter ions are active in hydrogen transfer reactions which cause hydrogenation of styrene to ethylbenzene. In the presence of base catalysts, a selective styrene formation takes place and transformation leading to coke is slower, hence ethylbenzene formation is suppressed. On the other hand, in the presence of acid catalysts, linear dimers can also isomerize to cyclic derivatives which after dealkylation give benzene and methylindane. The later product in isomerization and hydrogen transfer reactions forms methylindene and naphthalene. The higher styrene oligomers reactions are catalyzed by both acid and basic sites, leading mainly to the monomer, i.e., styrene (17).

4.7 Phenolic Resins The pyrolysis of a complex waste stream of phenolic resins was controlled to convert the stream into useful high-value monomers (18). Examples of these plastics include thermoset phenolic resins. An example of these plastics is novolac, which are a large source of materials. Wastes of these materials are also produced in the manufacturing plants. Other examples are phenolic resins, which produce phenol and cresols upon pyrolysis, in addition to chars. When phenol formaldehyde resins are pyrolyzed, they produce a series of methyl substituted phenolic monomers and dimers in a yield of about 50%. The product selectivity can be controlled by control of the heating rate. A novolac was made from phenol, P N oil, and formaldehyde (1:1:0.3), catalyzed with H2 SO4 and cured with 10% Hexa at 330°C for 10 min. The P N oil is a phenolic material that was derived from the pyrolysis of pine and separated from the crude oil by solvent extraction (19). It was shown that the P N oil can be substituted in novolac up to 50% without degradation of performance. This novolac was pyrolyzed at a heating rate of 40°C min 1 to a final temperature of 700°C. Two groups of compounds can be distinguished by time-resolved mass spectral data analysis. A first group of compounds appears at 400°C and is composed of two homologous series: one based on dihydroxybenzene and one on the dimer bisphenol A. The second group has a maximum at 450°C and is composed of a homologous series based on phenol and its methyl derivatives. The ability to control the relative amounts of these two

Recovery of Monomers 155 groups allows the recovery of valuable starting materials that can be substituted for phenol in novolac formulations in much the same way as the P N oil is substituted (18). The subsequently described method for optimization uses identifying the catalyst and temperature conditions that permit decomposition of a given polymer in the presence of others, without substantial decomposition of the other polymers, in order to make it easier to purify the monomer from the easier to decompose plastic. Molecular beam mass spectrometry was used to characterize the components of the feed steam. This helps to find out the conditions of catalytically treating the feedstream to a ect acid thermal reaction pathways, and di erentially heating the feedstream according to a heat rate program using the predetermined molecular beam mass spectrometry data to provide optimum quantities of the monomer products (18). The results of molecular beam mass spectrometry applied to pyrolysis indicate that there are basically three methods of controlling the pyrolysis of phenolic resin containing synthetic polymers (18): 1. The utilization of the di erential e ect of temperature on the pyrolysis of di erent components, 2. The feasibility of performing acid-catalyzed and base-catalyzed reactions in the pyrolysis environment to guide product or monomer distribution, and 3. The use of coreactants to alter products such as steam or oxygen.

4.8 Poly(carbonate) Poly(carbonate) (PC) was decomposed into phenol, bisphenol A and p-isopropenylphenol by the reaction at 130°C to 300°C in water (20). The decomposition reaction was accelerated by the addition of Na2 CO3 , and the yield of identified products reached 68% in the reaction at 250°C for 1 h. By using the decomposed products, a prepolymer of a phenol resin could be synthesized (20).

156 4.8.1

Polymer Waste Management Poly(bisphenol A carbonate)

The various and widespread uses of PC polymers require a meaningful and environmentally friendly disposal method (21). Wastes containing PC can produce high yields of bisphenol A, the monomer precursor of PC, phenol (precursor to bisphenol A), as well as 4-propenylphenol (22). PC shows a high limiting oxygen index (LOI 27). Thus, it can produce a large amount of char in the course of combustion (23). PC is widely used in mixture with other polymers with the aim of enhancing resistance to external factors. Typical mixtures include PC with poly(butylene-terephthalate) or with acrylonitrile-butadiene-styrene (ABS). The latter exhibit e ective flame retardant properties upon the addition of conventional halogen and or non-halogen flame retardant agents, and this supports their large use in electrical appliances. The properties of PC make it appropriate for durable goods applications. PC is used in the construction of many everyday products, including CDs and DVDs, dinnerware, computer casings, medical equipment, bicycle helmets, automotive parts, packaging, sports and optical materials. Other applications are for paintings and covertures of buildings. High pressure hydrolysis can be a convenient way of recycling PC (23). The depolymerization of PC with water in a microwave reactor has been suggested as a recycling method (21). The hydrolysis was investigated in an alkaline (NaOH) solution using a phase-transfer catalyst. As phase-transfer catalyst, 1-hexadecyl trimethylammonium bromide was used. The experiments were carried out in a sealed microwave reactor, in which the reaction pressure, temperature and microwave power were continuously controlled and recorded. In the hydrolysis products, a bisphenol A monomer was obtained and identified by FTIR spectroscopy. A degradation of PC higher than 80% can be obtained at 160°C after a microwave irradiation time of either 40 min or 10 minn using either a 5% or 10% (w v) NaOH solution, respectively. Gel permeation chromatography, thermogravimetric analysis (TGA) and di erential scanning calorimetry (DSC) measurements of the residues from PC revealed that the degradation mechanism occurs through surface erosion. Greater than 85% degradation was achieved when waste CDs were treated with the same method.

Recovery of Monomers 157 These results confirm the importance of the microwave power technique as a promising recycling method for PC-based waste plastics, resulting in a monomer recovery in addition to a substantial energy saving (21). 4.8.1.1

Catalysts in a Fixed-Bed Reactor

For the thermal recycling of PC-based plastics, nine di erent catalysts with variations in properties, such as porosity and acidity basicity, were introduced in a bench-scale pyrolysis system together with the PC polymeric material, and the pyrolysis fractions were collected and analyzed (24). The liquid product consisted mainly of phenols and substituted phenols as well as the original monomer. Due to the commercial value of these products in the chemical industry, it is expected to enhance the economic viability of the process. The results showed a reduction in the degradation temperature in the presence of all catalytic materials, depending on the pore characteristics and the acidic nature of the solid. It seems that in the presence of the basic catalysts, PC degradation leads to lower molecular weight compounds and high phenolic fractions in the liquid produced. In terms of reduction in the production of the monomer, pore size rather than acidity appears to be the determining factor (24). The product yields from the pyrolysis of PC using di erent catalysts are shown in Table 4.3.

4.9 Poly(ethylene terephthalate) Poly(ethylene terephthalate) (PET) can be recycled in many ways. However, there is a need for development of other environment friendly recycling techniques (25). 4.9.1

Acrylic Monomers

Acrylic and allylic monomers could be synthesized from bis(2-hydroxyethyl) terephthalate (26). This was obtained by the glycolysis of post-consumer PET with boiling ethylene glycol. The bifunctional monomer bis(2-(acryloyloxy)ethyl) terephthalate was obtained from acryloyl chloride. The allylic monomers 2-(((allyloxy)carbonyl)oxy)

158

Polymer Waste Management Table 4.3 Product yields from the pyrolysis of PC (24). Catalyst

Yield in % of polymer Liquid Gas Solid

Non-catalytic ZSM-5 ZSM-5 eq dil. Silicalite USY Al-MCM-41 γ -Al2 O3 MgO-HP MgO-MP CaO

57.03 57.47 47.25 58.32 40.80 48.75 38.49 51.01 52.32 49.70

18.46 19.06 20.80 20.32 22.82 20.29 22.07 18.37 17.75 12.49

24.50 23.47 31.95 21.36 36.39 30.96 39.45 30.61 29.93 37.80

ethyl (2-hydroxyethyl) terephthalate and bis(2-(((allyloxy)carbonyl)oxy)ethyl) terephthalate were obtained from allyl chloroformate. The crosslinking reaction was studied in bulk polymerization using two di erent thermal initiators. The monomers were analyzed by 1 H nuclear magnetic resonance spectroscopy and the crosslinked polymers were analyzed by infrared spectroscopy. A gel content of higher than 90% was obtained for the acrylic monomer. In the case of the mixture of the allylic monomers, the crosslinked polymer was 80% using dibenzoyl peroxide as initiator, with a waste 24 times less reactive than the acrylic monomer (26). The monomers were also evaluated as crossslinking agents for acrylic acid and methacrylic acids using a thermally initiated polymerization (27). The obtained copolymers showed a higher thermal stability than the corresponding acrylic homopolymers. The compounds were also tested for dental formulations as Bis-glycidyl methacrylate (GMA) substitutes in heat curing resin composites. In spite of its lower reactivity, only bis(2-(((allyloxy)carbonyl)oxy)ethyl) terephthalate was able to substitute Bis-GMA, due to its high solubility in the triethylene glycol dimethacrylate comonomer. Resin formulations containing nanosized silica and a mixture of Bis-GMA triethylene glycol dimethacrylate or bis(2-(((allyloxy)carbonyl)oxy)ethyl) terephthalate triethylene glycol dimethacrylate were prepared in order to compare physical and chemical proper-

Recovery of Monomers 159 ties. Water sorption, solubility, and flexural strength were found to be statistically similar for both formulations. However, flexural modulus was lower and the conversion of the double bonds was higher for the bis(2-(((allyloxy)carbonyl)oxy)ethyl) terephthalate resin, which could make it appropriate for its potential use in dental resin composites (27). 4.9.2

Acrylic Aromatic Amide Oligomers

Hydrazine monohydrate was used to depolymerize PET waste (28). From these products, an acrylic aromatic amide oligomer could be synthesized. This product was synthesized under ambient conditions and was used in the preparation of the acrylic oligomer with the reaction of acryloyl chloride prepared from acrylic acid. The acrylic oligomer was characterized by spectroscopic techniques such as FTIR, 1 H-NMR, UV, MS, TGA, and DSC. Also, other analytical techniques were used, such as, the iodine value. The proposed structure of the oligomer could be confirmed by spectral analysis and from other techniques. The acrylic oligomer, when mixed with other acrylate monomers, such as, methylmethacrylate, ethylhexylacrylate, acrylic acid, and a photoinitiator, can be cured by UV radiation and can thus be used as an adhesion promoter on a metal glass surface (28). 4.9.3

Terephthalic Acid

Terephthalic acid was prepared from waste PET samples. PET mineral water bottles were procured and crushed into a fine powder of various particle size, ranging from 100 μ m to 800 μ m. Other materials used were sodium hydroxide, tetrachloroethane, phenol, and pyridine. The reaction runs as follows (29): Preparation 4–1: The conversion of the PET waste powder was carried out in a 250 cm3 round bottom flask equipped with a reflux water condenser heating assembly at atmospheric pressure and temperature 80°C to 160°C. 10 g of PET waste powder of di erent sizes, 2 g to 9 g of sodium hydroxide, 1.0-5.0 cm3 of pyridine and 100 cm3 of double distilled water was charged in the round bottom flask. Then, the mixture was refluxed for various time intervals such as 30 min to 150 min. The reaction mixture was filtered for the separation of unreacted PET waste powder. The filtrate was treated with concentrated hydrochloric

Polymer Waste Management

160

acid until the solution became acidic in nature. A white precipitate of terepthalic acid was obtained.

The yield of terepthalic acid with the variation of the amount of sodium hydroxide is shown in Table 4.4. Also, the variation of yield with particle size is shown in Table 4.5, and the e ect of temperature is shown in Table 4.6. Table 4.4 Yield of terepthalic acid with the variation of the amount of sodium hydroxide (29). Amount of NaOH [g]

Yield of terepthalic acid [%]

2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

26.0 39.0 52.0 65.0 77.5 87.0 85.0 75.0

Table 4.5 Yield of terepthalic acid with the variation of the particle size of PET (29). Particle size of PET waste [μ m] 100 200 300 400 500 600 700 800

4.9.4

Yield of terepthalic acid [%] 90.0 88.5 86.0 80.6 69.0 60.0 55.0 52.0

Terephthalic dihydrazide

The degradation of PET waste by making use of hydrazine monohydrate was investigated at ambient temperature and pressure (30). The aminolyzed end products obtained were characterized with chemical tests and spectroscopic techniques, i.e., infrared spec-

Recovery of Monomers 161 Table 4.6 Yield of terepthalic acid with the variation of the reaction temperature (29). Reaction temperature [°C]

Yield of terepthalic acid [%]

60 80 100 120 140 160 170

8.0 48.5 71.0 83.5 88.5 87.5 85.0

troscopy, UV-visible spectroscopy and nuclear magnetic resonance spectroscopy (NMR), and DSC. The end product was characterized as terephthalic dihydrazide. This material was further used in poly(vinyl chloride) (PVC) compounding as secondary plasticizer. The hardness, tensile strength, elongation at break, thermal stability, and compatibility of the PVC sheet were studied. It was suggested that this aminolyzed product could find potential application as secondary plasticizer in PVC formulations (30). 4.9.5 4.9.5.1

Aminolytic Depolymerization Ambient Temperature and Normal Pressure

The degradation of PET waste using its aminolysis with various amines has been studied (25). The degradation experiments were carried out at ambient temperature and at normal pressure. The amines used to study the degradation of the PET waste were methylamine, ethylamine, and n-butyl amine. Here, the degradation of the PET waste is completed within 45 d. The aminolyzed products obtained in this way were characterized by using various conventional techniques such as infrared spectroscopy, NMR and DSC. The products were found to be N-alkyl terephthalamides. It was concluded that a useful method of PET recycling can be performed by using various amines (25).

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4.9.5.2

Aminolysis in Sunlight

Post-consumer PET bottle wastes were cut into very small slides and then subjected to an aminolysis process with ethanolamine as a degradative agent in the presence of one catalyst from the three used in the experiments (31). The catalysts used were dibutyl tin oxide, sodium acetate, and cetyltrimethyl ammonium bromide. The reaction was performed in sunlight. Sunlight is a beneficial, clean, cheap, and renewable source of energy. The end product, which was a white precipitate of bis(2-hydroxyethylene) terephthalamide, was subjected to spectrophotometric and thermal analysis. The product was characterized to asses its suitability for use in pigments in anticorrosive paint formulations. In general, this process was a green, environmentally friendly degradation based on the utilization of solar energy for the aminolysis reaction using simple, cheap, available chemicals as catalysts (31). 4.9.5.3

Microwave Irradiation Heating

The aminolytic depolymerization of PET bottle waste with hydrazine monohydrate by conventional and nonconventional (with microwave irradiation) heating was carried out using simple chemicals as catalysts, such as sodium acetate and sodium sulfate (32). The yield of the product was optimized through the variation of the time of aminolysis, the catalyst concentration, and the ratio of PET to hydrazine monohydrate. The pure product could be obtained in a good yield of 86%. It was characterized by FTIR, NMR, and DSC. It was identified as terephthalic dihydrazide (32). 4.9.5.4

Quaternary Ammonium Salt Catalyst

Waste flakes of PET, i.e., blow-molded-grade industrial waste, were degraded using aqueous methylamine and ammonia at room temperature in the presence and absence of quaternary ammonium salt as a catalyst (33). The catalyst reduced the time required for the degradation of the PET waste. The degraded products were analyzed with IR, NMR MS, and DSC. These products could be identified as N,N’-dimethylterephthalamide and terephthalamide in the case of methylamine and ammonia, respectively, as reactants (33).

Recovery of Monomers 163 4.9.6

Hydrogenation Reaction

The preparation of 1,4-cyclohexanedimethanol has been investigated by the hydrogenation of bis(2-hydroxyethylene terephthalate) (34). This compound was obtained from waste PET. The influences of various reaction parameters, including temperature, pressure and time, on the hydrogenation reaction were studied, and the 100% conversion of bis(2-hydroxyethylene terephthalate) and 78% yield of 1,4-cyclohexanedimethanol were achieved with Pd C and Cu-based catalysts. X-ray di raction, low temperature N2 adsorption-desorption and H2 temperature programmed reduction were used to characterize the Cu-based catalysts. It could be shown that the Cu Cu0 species are the active sites. Thus, not only could a new route for the production of 1,4-cyclohexanedimethanol be demonstrated, but also an approach for the e cient utilization of waste PET (34).

4.10 Nylon 4.10.1

Recovery of Caprolactam

A process has been described using fast pyrolysis in a carrier gas to convert a plastic waste feedstream into a value of the monomeric constituents (35). The recovery of caprolactam from nylon 6 can be obtained by pyrolysis at mild temperatures of near 300° C in the presence of selected catalysts, such as alumina, silica, and others in their basic forms, achieved by the addition of alkali alkaline earth metal hydroxides to these catalysts. In this way, nylon 6 can be pyrolyzed to give high yields of the monomer caprolactam (35). The decomposition of a waste polyamide material into a economically valuable monomer under relatively mild hydrothermal conditions is a key technology for the development of waste recycling (36). This reaction is traditionally catalyzed by homogeneous acids, which would result in a di cult separation and corrosion of the equipment.

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4.10.1.1

Solid Catalysts

Solid catalysts for the hydrolysis of waste monomer casting nylon in subcritical water were investigated (36). There are a series of γ -Al2 O3 supported solid acid catalysts and some commercial zeolites. Zeolite H-β-25 exhibited the highest activity among the H-form zeolites, and a better recyclability than the γ -Al2 O3 supported solid acids. According to the kinetic analysis and reaction pathway exploration, the generation and consumption of linear oligomers, which are the intermediate products, were accelerated when using the zeolite H-β-25 because of the microporous structure (36). The solid products obtained before the complete hydrolysis became less thermodynamically stable than raw polyamide material as the degree of hydrolysis increased (37). According to the characterization of liquid phase products, the monomer casting polyamide was depolymerized to cyclic and linear oligomers, which were further converted to the target monomer ε -caprolactam by gradual chain scission. The zeolite H-β was proved to be a promising solid catalyst which increased the degree of hydrolysis from 31% to more than 60% at 300°C and 50 min, and facilitated the production of the intermediates with specific structure due to the microporous topology (37).

4.10.2

Hexamethylene diamine

The recovery of the monomer hexamethylene diamine in the form of the dibenzoyl derivative of hexamethylene diamine from nylon waste rope powder was carried out by degradation of nylon waste powder of nylon rope waste (38). The minimum amount of nylon waste powder and hydrochloric acid required for a maximum recovery of hexamethylene diamine and dibenzoyl hexamethylene diamine, cf. Figure 4.1, was found to be 5 g and 5 N, 50 ml hydrochloric acid respectively (38). It was further observed that the maximum time and temperature required for getting a maximum yield of dibenzoyl hexamethylene diamine was 120 min and 800°C, respectively.

Recovery of Monomers 165

H

H

N

N

O

O

Figure 4.1 Dibenzoyl hexamethylene diamine.

4.11 Poly(urethane) Processes concerning the recycling and recovery of poly(urethane) (PU) composites have been reviewed. The various types of PU waste products, consisting of either old recycled parts or production waste, are generally reduced to a more usable form, such as flakes, powder or pellets, depending on the particular type of PU being recycled. The various recycling technologies for material and chemical recycling of PU materials have greatly contributed to improve the overall image regarding the recyclability of PUs. The most important techniques are regrinding, hydrolysis, and glycolysis. A regrinding technology has been successfully used to recycle PU foam in automotive seating. The hydrolysis of PU results in the formation of diamines like diphenyl methane diamine (39). The hydrolysis of PU foams is particularly interesting since they have a very low density (30 kg m 3 ) and thus take up considerable storage space (40). The product yields are outstanding. Almost 100% of the polyether and 90% of the amine can be recovered. The regenerated materials can be reused directly, together with a fresh starting material, for the same foam material. Another chemical treatment scheme is glycolysis, which is the reaction of the polymer with diols at temperatures above 200°C. The glycolysis of PUs can be economically acceptable. However, problems may arise because more contamination in the post-consumer material is tolerated (39). The current technologies can recover the inherent energy value of polyurethanes and reduce fossil fuel consumption. Energy recovery is considered the only suitable disposal method for recovered material for which no markets exist or can be created.

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Waste-to-energy and other thermal processing activities involving gasification, pyrolysis and two-stage combustion have contributed to the disposal of significant amounts of scrap PU without many di culties (39).

4.12 Sequential Processes for Mixed Plastics The use of a controlled heating rate makes the resolution of the individual polymer pyrolysis products possible, even from a complex mixed plastic waste stream (22). Sequential processes consisting of the initial operation at low temperature with catalysts, e.g., base or other catalysts, may recover key monomers such as caprolactam, styrene, and low boiling solvents such as benzene. The initial pyrolysis can be followed by high temperature in the presence of steam, to convert PU components into aniline or diamino compounds or diisocyanate. The types of compounds and their proportions can be tailored by the operating conditions. Examples of suitable reactive media include amines, such as ammonia, and other gases such as hydrogen. Support for the feasibility of such processes comes from the analytical area of pyrolysis as a method of determination of composition of composites, for instance, based on styrene copolymers, ABS–PC blends (22, 41). The molecular beam mass spectrometry technique can be used to rapidly study the pyrolysis of the major components of a variety of industrial and municipal wastes stream to determine optimum methods for a temperature programmed, di erential pyrolysis for selective product recovery (22). A process of using fast pyrolysis in a carrier gas to convert a plastic waste feedstream with a mixed polymeric composition in a manner such that pyrolysis of a given polymer to its high-value monomeric constituent occurs prior to pyrolysis of other plastic components therein is as follows (22): 1. Selecting a catalyst and support for treating said feedstreams with said catalyst to e ect acid or base-catalyzed reaction pathways to maximize yield or enhance separation of said high-value monomeric constituent in said temperature program range,

Recovery of Monomers 167 2. Di erentially heating said feedstream at a heat rate within the first temperature program range to provide di erential pyrolysis for selective recovery of optimum quantities of the high-value monomeric constituent prior to pyrolysis of other plastic components, 3. Separating the high-value monomeric constituents, 4. Selecting a second higher temperature range to cause pyrolysis of a di erent high-value monomeric constituent of said plastic waste and di erentially heating the feedstream at the higher temperature program range to cause pyrolysis of the di erent high-value monomeric constituent, and 5. Separating the di erent high-value monomeric constituent. This method has also been proposed for the recycling of mixtures of PC and ABS (42).

4.13 Waste Fiber Reinforced Plastics 4.13.1

Supercritical Methyl Alcohol

A method for the chemical recycling of plastics has been developed (43). The formation of recycled polymers from the recovered monomeric materials of solubilized waste fiber reinforced plastics under supercritical alcoholic conditions has been elucidated. The treatment of waste fiber reinforced plastics with supercritical methyl alcohol resulted in the formation of monomeric organic compounds that mainly contained dimethyl phthalate and propylene glycol. The presence of these materials was confirmed by GC and NMR analysis. The obtained products were mixed with new dimethyl phthalate and glycols in various ratios to form unsaturated polyesters. The polymerization proceeded successfully for all mixing ratios of the recovered dimethyl phthalate and the new dimethyl phthalate. Hardness tests on these recycled polymers indicated that the polymer made from a 1:1 mixture of recovered and new dimethyl phthalate had almost the same level of hardness as the polymers made from new materials. Also, the formation of recycled fiber reinforced plastics were examined, using glass fibers and monomeric materials recovered through the investigated depolymerization method (43).

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4.13.2

Ionic Liquid Treatment

Waste fiber reinforced plastics and unsaturated polyesters could be readily depolymerized by subjecting them to a treatment with ionic liquids under heating (44). The use of microwaves for heating e ectively progressed the depolymerization reaction, whereas the conventional heating method was ine ective for this purpose. The monomeric material, i.e., phthalic anhydride, was isolated by direct distillation from the reaction pot under reduced pressure with yields of more than 90%. The glass fibers could be recovered in a pure form. Also, the e ective removal of PS could be achieved. Ionic liquids were useful for several iterations of the depolymerization reaction, and the purification of the used ionic liquids was also found to be possible (44). 4.13.3

N,N-Dimethylaminopyridine for Depolymerization

The e ects of reduction in the amounts of N,N-dimethylaminopyridine, cf. Figure 4.2, used for the depolymerization waste fiber reinforced plastics (containing polyesters) were examined (45). CH 3 N

N CH 3

Figure 4.2 N,N-Dimethylaminopyridine.

The treatment of waste fiber reinforced plastic in the presence of 1% or 2% N,N-dimethylaminopyridine resulted in the successful recovery of monomeric materials that could be employed in the polymerization process to produce recycled plastic. However, the separation of the linker units from glass fiber was not found to be successful. The depolymerization reaction of waste fiber reinforced plastics with 1% of N,N-dimethylaminopyridine runs as follows (45): A mixture of waste fiber reinforced plastics (7 kg), methanol (15 l), and N,N-dimethylaminopyridine (70 g) was placed in an autoclave (30 l) and heated for 6 h at 270°C under nitrogen atmosphere. The pressure in the reaction vessel increased to 12.8 MPa. After cooling, the methanol solution was separated from the reaction mixture and

Recovery of Monomers 169 concentrated in vacuo, yielding 22.5% (1.576 kg) of black oil. After NMR and GC MS analysis, the dimethyl phthalate content was estimated to be 60%. The residue was extracted with ethyl acetate in a Soxhlet extraction apparatus. The ethyl acetate extract was then concentrated in vacuo, yielding 4.3% (0.304 kg) of a white solid material. The remaining insoluble residue of 80.2% (5.611 kg) consisted of a mixture of glass fiber and insoluble resin residue. The recovered monomer (35 g, obtained from the reaction catalyzed by 2% of N,N-dimethylaminopyridine, which contained 25% of dimethyl phthalate) was dissolved in an appropriate solvent (350 ml) and activated charcoal (35 g) was added. The mixture was heated at a refluxing temperature for 20 h. After cooling, the charcoal was filtered and the filtrate was concentrated in vacuo to obtain the purified recovered monomeric material. The purity of the recovered monomeric material, when treated with activated charcoal, could be improved to about 70%. This resulted in an e ective decoloration of the recovered monomer. The purified material, after undergoing a repolymerization process, provided a high-quality recycled plastic, which is comparable to plastic materials that are produced from new monomers (45). 4.13.4

Subcritical Water

A thermosetting polyester resin that is used in fiber reinforced plastic is di cult to be recycled since it cannot be remolded like a thermoplastic resin (46). Subcritical water and soluble alkali were applied to hydrolyze thermosetting polyester resins of fiber reinforced plastic to recover a styrene-fumaric acid copolymer in a high yield (46, 47). Styrenefumaric acid copolymer is a functional polymer and has the same molecular structure as that of styrene-maleic acid copolymer, which is applied as high-value-added additive. Potassium hydroxide contributed to accelerate the hydrolysis reaction and to provide water solubility to the styrene-fumaric acid copolymer. The optimized reaction conditions based on the yield of the styrene-fumaric acid copolymer were at either a temperature of 230°C, reaction time of 2 h, and with a KOH concentration of 0.38 mol l 1 , or 230°C at 1 h, and 0.72 mol l 1 for sodium hydroxide.

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It could be verified that this method has the potential to recycle thermosetting polyester resins of fiber reinforced plastics in order to produce a styrene-fumaric acid copolymer (46, 47). 4.13.5

Fiber-Matrix Separation for Carbon Fiber Recycling

A fiber-matrix separation method has been presented that was applied to carbon fiber reinforced thermosetting resins with two different media (water and a water ethanol mixture) under subcritical and supercritical conditions (48). The influence of the di erent experimental conditions, the nature of the solvents and temperature on the properties of the recycled carbon fibers have been studied. This has been performed with regard to the e ciency of the removal of the thermoset resin from the fibers, as well, as the surface and mechanical properties of the recycled carbon fibers. It could be demonstrated that the recycling with both media provides recycled carbon fibers with promising qualities for reuse in carbon fiber reinforced polymers of the second generation. Besides, the water ethanol mixture tends to achieve better results than pure water and creates recycled carbon fibers with mechanical and surface properties comparable to that of virgin carbon fibers. Also, the mechanism of polymer degradation has been discussed with regard to the nature of the dissolved chemicals in the reactive media (48).

References 1. T. Tatsumi, K. Ogawa, Y. Tanaka, K. Ueno, and S. Daikoku, Process for the thermal decomposition of thermoplastic resins with a heat transfer medium, US Patent 3 974 206, assigned to Mitsubishi Gas Chemical Company, Inc. (JA), August 10, 1976. 2. R.J. Evans and H.L. Chum, Pyrolysis and hydrolysis of mixed polymer waste comprising polyethyleneterephthalate and polyethylene to sequentially recover, US Patent 5 821 553, assigned to Midwest Research Institute (Kansas City, MO), October 13, 1998. 3. H. Nishizaki, Method for treating waste plastics, US Patent 3 901 951, assigned to Director-General of the Agency of Industrial Science and Technology (Tokyo, JA), August 26, 1975.

Recovery of Monomers 171 4. R.J. Evans and H.L. Chum, Controlled catalytic and thermal sequential pyrolysis and hydrolysis of mixed polymer waste streams to sequentially recover monomers or other high value products, US Patent 5 359 099, assigned to Midwest Research Institute (Kansas City, MO), October 25, 1994. 5. S.P. Mannsfeld, K.J. Paulsen, and E. Buchholz, Method for treating waste plastics, US Patent 3 494 958, assigned to Evonik Degussa GmbH, February 10, 1970. 6. A. Buekens, Conservation & Recycling, Vol. 1, p. 247, 1977. 7. Y.R. Mehra and R.H. Stodghill, Absorption process for rejection of reactor byproducts and recovery of monomers from waste gas streams in olefin polymerization processes, US Patent 5 681 908, assigned to Advanced Extraction Technologies, Inc. (Houston, TX), October 28, 1997. 8. P.J. Donaj, W. Kaminsky, F. Buzeto, and W. Yang, Journal of Waste Management, 2011. 9. J. Scheirs and W. Kaminsky, eds., Feedstock Recycling and Pyrolysis of Waste Plastics: Converting Waste Plastics into Diesel and Other Fuels, Wiley-Blackwell, 2006. 10. W.D. Lilac and S. Lee, Advances in Environmental Research, Vol. 6, p. 9, 2001. 11. J.-S. Kim, W.-Y. Lee, S.-B. Lee, S.-B. Kim, and M.-J. Choi, Catalysis Today, Vol. 87, p. 59, 2003. 9th Korea-Japan Symposium on Catalysis. 12. H. Ke, T. Li-hua, Z. Zi-bin, and Z. Cheng-fang, Polymer Degradation and Stability, Vol. 89, p. 312, 2005. 13. M.R. Filip, A. Pop, I. Perhai¸ta, M. Moldovan, and R. Tru¸sc˘a, Central European Journal of Chemistry, Vol. 11, p. 725, May 2013. 14. Z.-m. Liu, X. Jiang, and Y.-p. Liu, Petrochemical Technology, Vol. 32, p. 885, 2003. 15. L. Deshuang, Z. Sufen, L. Jianhua, W. Muli, Y. Zhuyang, and Z. Hanjiang, Journal of Dongguan Institute of Technology, Vol. 1, p. 9, 2004. 16. Y. Liu, J. Qian, and J. Wang, Fuel Processing Technology, Vol. 63, p. 45, 2000. 17. M. Marczewski, E. Kaminska, ´ H. Marczewska, M. Godek, G. Rokicki, and J. Sokołowski, Applied Catalysis B: Environmental, Vol. 129, p. 236, 2013. 18. H.L. Chum and R.J. Evans, Controlled catalytic and thermal sequential pyrolysis and hydrolysis of phenolic resin containing waste streams to sequentially recover monomers and chemicals, US Patent 5 136 111, assigned to MRI Ventures, Inc. (Kansas City, MO), August 4, 1992. 19. H.L. Chum and S.K. Black, Process for fractionating fast-pyrolysis oils, and products derived therefrom, US Patent 4 942 269, assigned to Midwest Research Institute (Kansas City, MO), July 17, 1990.

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20. A. Ikeda, K. Katoh, and H. Tagaya, Journal of Materials Science, Vol. 43, p. 2437, Apr 2008. 21. G.P. Tsintzou, E.V. Antonakou, and D.S. Achilias, Journal of Hazardous Materials, Vol. 241-242, p. 137, 2012. 22. R.J. Evans and H.L. Chum, Controlled catalytic and thermal sequential pyrolysis and hydrolysis of mixed polymer waste streams to sequentially recover monomers or other high value products, US Patent 5 216 149, assigned to Midwest Research Institute (Kansas City, MO), June 1, 1993. 23. G. Bozzano, M. Dente, and R. Del Rosso, Poly(bisphenol a carbonate) recycling: High pressure hydrolysis can be a convenient way in D.S. Achilias, ed., Material Recycling-Trends and Perspectives, chapter 4, pp. 115–132. InTechOpen, 2012. 24. E. Antonakou, K. Kalogiannis, S. Stefanidis, S. Karakoulia, K. Triantafyllidis, A. Lappas, and D. Achilias, Polymer Degradation and Stability, Vol. 110, p. 482, 2014. 25. R.K. Soni, S. Singh, and K. Dutt, Journal of Applied Polymer Science, Vol. 115, p. 3074, 2010. 26. A. Cruz-Aguilar, A.M. Herrera-González, R.A. Vázquez-García, D. Navarro-Rodríguez, and J. Coreño, IOP Conference Series: Materials Science and Engineering, Vol. 45, p. 012007, 2013. 27. J. Coreño Alonso, A. Cruz Aguilar, C.E. Cuevas-Suárez, R.A. Vázquez García, and A.M. Herrera-González, Journal of Applied Polymer Science, Vol. 132, p. n a, 2015. 28. R.K. Soni, M. Teotia, and K. Dutt, Journal of Applied Polymer Science, Vol. 118, p. 638, 2010. 29. D.B. Patil and V. Batra, J. Chem. & Cheml. Sci., Vol. 2, p. 102, July 2012. 30. R.K. Soni, K. Dutt, A. Jain, S. Soam, and S. Singh, Journal of Applied Polymer Science, Vol. 113, p. 1090, 2009. 31. M.E. Tawfik, N.M. Ahmed, and S.B. Eskander, Journal of Applied Polymer Science, Vol. 120, p. 2842, 2011. 32. Y.S. Parab, N.D. Pingale, and S.R. Shukla, Journal of Applied Polymer Science, Vol. 125, p. 1103, 2012. 33. R.K. Soni and S. Singh, Journal of Applied Polymer Science, Vol. 96, p. 1515, 2005. 34. X. Guo, J. Xin, X. Lu, B. Ren, and S. Zhang, RSC Adv., Vol. 5, p. 485, 2015. 35. R.J. Evans and H.L. Chum, Controlled catalytic and thermal sequential pyrolysis and hydrolysis of polymer waste comprising nylon 6 and a polyolefin or mixtures of polyolefins to sequentially recover monomers or other high value products, US Patent 5 359 061, assigned to Midwest Research Institute (Kansas City, MO), October 25, 1994. 36. W. Wang, L. Meng, K. Leng, and Y. Huang, Polymer Degradation and Stability, Vol. 136, p. 112, 2017.

Recovery of Monomers 173 37. W. Wang, L. Meng, J. Yu, F. Xie, and Y. Huang, Journal of Analytical and Applied Pyrolysis, Vol. 125, p. 218, 2017. 38. D.B. Patil and S.V. Madhamshettiwar, Oriental Journal of Chemistry, Vol. 30, p. 105, 2014. 39. K.M. Zia, H.N. Bhatti, and I.A. Bhatti, Reactive and Functional Polymers, Vol. 67, p. 675, 2007. 40. S. Kumar, A.K. Panda, and R.K. Singh, Resources, Conservation and Recycling, Vol. 55, p. 893, 2011. 41. V.M. Ryabikova, A.N. Zigel, and G.S. Popova, Vysokomol. Soedin. A, Vol. 32, p. 882, 1990. 42. R.J. Evans and H.L. Chum, Controlled catalystic and thermal sequential pyrolysis and hydrolysis of polycarbonate and plastic waste to recover monomers, US Patent 5 321 174, assigned to Midwest Research Institute (Kansas City, MO), June 14, 1994. 43. A. Kamimura, E. Konno, S. Yamamoto, T. Watanabe, K. Yamada, and F. Tomonaga, Journal of Material Cycles and Waste Management, Vol. 11, p. 38, Feb 2009. 44. A. Kamimura, S. Yamamoto, and K. Yamada, ChemSusChem, Vol. 4, p. 644, 2011. 45. A. Kamimura, Y. Akinari, T. Watanabe, K. Yamada, and F. Tomonaga, Journal of Material Cycles and Waste Management, Vol. 12, p. 93, Jun 2010. 46. T. Nakagawa and M. Goto, Engineering Journal, Vol. 19, p. 1, October 2015. 47. T. Nakagawa and M. Goto, Polymer Degradation and Stability, Vol. 115, p. 16, 2015. 48. L. Henry, A. Schneller, J. Doerfler, W.M. Mueller, C. Aymonier, and S. Horn, Polymer Degradation and Stability, Vol. 133, p. 264, 2016.

Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

5 Recovery into Fuels Here, mainly the recovery of plastic wastes into fuels is discussed. However, some issues are also dealt with in Chapter 6, since special polymers and methods are discussed there. The conversion techniques of liquid fuel from waste plastic materials have been reviewed (1). The recent conversion techniques of fuel oil from waste plastics and their utilization in a compression ignition engine have been discussed. Also, the e ect of various parameters like catalysts, reaction temperature, and reaction time of the aforementioned conversion techniques were discussed in this review.

5.1 Poly(ethylene) 5.1.1

Aromatic Fuel Oils from Poly(ethylene)

Di erential scanning calorimetry (DSC)-thermogravimetric analysis (TGA) was used as a screening tool of a commercially available and a synthesized catalyst for the degradation of poly(propylene) (PP) (2). In the experiments, all the runs were performed with a load of 50% of the catalyst. The surface area, porosity, and acidity of the catalysts are shown in Table 5.1. The results were compared with those of PP plus 50% pure silica having no catalytic activity. The degradation behavior of PP using Zeolyst-713 as catalyst exhibited a much higher degradation activity than the other catalysts used in the experiments. Moreover, it

175

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Polymer Waste Management Table 5.1 Properties of the catalysts (3).

Catalysts NiMo loaded on [TiO2 alpha alumina AP-1 USY] Extrudates KC-2710 (AKZO Nobel) Z-713 (Zeolyst Int.) HC-100 (UOP) RCD-8 (UOP)

Surface area [m2 g 1 ]

Pore volume [cm3 g 1 ]

Acidity [%]

359.0

0.42

1.48

182.0 221 231 210

0.23 0.34 0.25 0.21

2.96 1.41 3.67 2.19

contributed to a lowering of the initial stage temperature, showing a shape-selective e ect. DSC-TGA tools such as onset temperature (Ton ), temperature of maximum rate of degradation (Tmax ), T99% , activation energy, enthalpy change in the process and coke content were used for screening (2). It was concluded that the pore construction and the unique acid properties of the Zeolyst-713 catalyst as well as proper reaction temperatures were significant influential factors to fully exert this e ect. Also, the kinetics of the catalytic thermogravimetric degradation of PP used for domestic purposes was investigated with an alumino-silicate catalyst. Zeolyst-713 was observed to lower the energy of activation and enhances the activity of degradation in comparison with thermal degradation without a catalyst (2). Furthermore, the catalytic degradation of poly(ethylene) (PE) in the presence of synthetic alumino-silicates has been studied (4).

5.2 Thermal and Catalytic Processes Feedstock recycling of plastic waste by thermal and catalytic processes is a promising route to eliminate this refuse, which is harmful to the environment. At the same time, products that are useful as fuels or chemicals are obtained (5). During the past decade, this option has undergone an important evolution from a promising scientific idea to an alternative that

Recovery into Fuels 177 is very close to reality with commercial opportunities. Thus, several commercial processes have been developed worldwide, most of them especially addressing the preparation of diesel fuel. The most remarkable achievements of the field have been reviewed, thus providing a fundamental insight into this area (5). Pyrolysis is the known process of thermal destruction of hydrocarbons in oxygen-free environment under temperature of 400°C–900°C and small excess pressure (6). This process is widely used in petroleum refinery for obtaining low molecular monomers from naphtha, and can be used for waste plastics processing with fuels production as an alternative to incineration or landfilling. A number of operating condition variables a ect the thermal destruction. These are the so-called 3 T’s: temperature, time (residence time), and turbulence (or mixing). It is possible to understand turbulence as the method of gas solid (feedstock) contacting and conditions of mixing pyrolysis products together with gas. A degree of reduction in size has an essential e ect. High temperature of 700°C–900°C and short residence times (1 s and less) are used for obtaining a great quantity of low molecular monomers from petroleum feedstock. It is an endothermic process demanding heat supply from outside (6). 5.2.1

Optimization of Temperature and Catalyst

The optimization of the reactor temperature and catalyst weight for plastic cracking into fuels has been described using a response surface methodology (7). The response surface technique is aimed at (8): 1. Designing experiments to provide adequate and reliable measurements of the response, 2. Developing a mathematical model having the best fit to the data obtained from the experimental design, and 3. Determining the optimal value of the independent variables that produces maximum or minimum value of the response. The operating parameters which most a ect the performance of the catalytic cracking process are the reactor temperature, followed by the catalyst weight. Increasing the reactor temperature signif-

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icantly improves the cracking performance due to the increasing catalyst activity. The optimal operating conditions of the reactor temperature were about 550°C and a catalyst weight of about 1.25 g were produced with respect to maximum liquid fuel product yield of 29.67%. The liquid fuel product consists of gasoline range hydrocarbons C4 to C13 with a favorable heating value of 44,768 kJ kg 1 (7). 5.2.1.1

Catalytic Cracking of Heavy Fractions of PE

Automotive waste plastics are considered a potential source of fuels and chemicals (9). The feedstock in experimental tests was represented by the heaviest fractions from the distillation of a pyrolysis oil obtained from the pyrolysis of a high density poly(ethylene) (HDPE) wax and a PP wax. Due to their very high viscosity, both polymer waxes were, prior to processing, diluted in atmospheric gas oil. Mixtures with hydrotreated vacuum gas oil were also prepared and processed under simulated fluid catalytic cracking conditions via a MAT-test (microactivity test). The microactivity test provides data to assess the relative performance of a fluid catalytic cracking (FCC) catalyst (10). Because results are a ected by catalyst pretreatment, feedstock characteristics, test equipment, and operating parameters, adherence to this test method is a prerequisite for correct interpretation of results. The product distribution was similar to the one shown by the commercial FCC process: light gases, liquefied petroleum gas, gasoline fraction, light and heavy cycle oil (9). To maintain optimal performance a commercial FCC equilibrium catalyst was used. When processing the HDPE and PP waxes, high yields of profiling products, such as propylene and gasoline, were obtained. In the case of the PP wax feed without vacuum gas oil, the yield of gasoline was even higher than in the case of pure hydrotreated vacuum gas oil. When cracking HDPE wax feed mixtures, the product distribution was oriented more towards the production of propylene. The composition of the liquid products considering all types of feedstock consisted mainly of i-alkanes and aromatics. The calculated values of microactivity for the HDPE wax and the PP wax

Recovery into Fuels 179 feedstock, with or without hydrotreated vacuum gas oil, were significantly higher than in the case of pure hydrotreated vacuum gas oil (9). 5.2.1.2

Spent FCC Catalyst

The catalytic cracking of HDPE at 500°C using a spent FCC catalyst agglomerated with bentonite in an amount of 50% was studied in a conical spouted bed reactor (11). The reaction could be carried out in a continuous regime when 1 g min 1 of HDPE was fed with no bed defluidization problems. The results that were obtained in these experiments, i.e., total conversion, and high yields of a gasoline with a C5 –C11 fraction of 50% and C2 –C4 olefins of 28%, were explained by favorable reactor conditions and good catalyst properties. These results were compared with those for a catalyst prepared in the laboratory by agglomerating a commercial HY zeolite with a ratio of SiO2 to Al2 O3 of 5.2. The conical spouted bed is a suitable reactor for enhancing the physical steps of melting the polymer and coating the catalyst with the melted polymer (11). In addition, high heat and mass transfer rates promote the devolatilization. Short residence times minimize secondary reactions from olefins by enhancing primary cracking products. The mesoporous and macroporous structure of the spent FCC catalyst matrix enhances the di usion of long polymer chains, whereas the zeolite crystals have micropores that give a proper shape selectivity to form the lumps of gasoline and light olefins. Because of long use in reaction-regeneration cycles, the moderate acidity of the spent FCC catalyst minimizes the secondary reactions of hydrogen transfer, and so restricts the formation of aromatics and para ns, as well as the reactions of overcracking and condensation and, therefore, the coke formation. The spent FCC catalyst exhibits a low deactivation rate and is regenerable by coke combustion with air at 550°C. Consequently, the use of a catalyst with the sole cost of a simple agglomeration and the production of value-added product streams make the process of polyolefin catalytic cracking a promising option for refinery integration (11).

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5.3 Mixed Waste Plastics Raw waste materials are usually urban and industrial waste plastics, that normally contain many non-recyclable plastics, such as PP, PE, poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and poly(styrene) (PS) (12). For the recycling of those waste plastics, some kinds of pretreatment may be required. Usually, such waste plastics are sorted roughly at individual homes or waste collection sites before they are brought to a recycling plant. At the recycling plant, the waste plastics are subjected to separation by one or more separator. There are normally magnetic selection separators and air-blowing selection separators. The magnetic selection is primarily for separating the relatively big metal wires, or other metal parts, while the air-blowing (or wind) selection is primarily for separating dust or dirt contained in the wastes, and reducing water contents. After the pretreatment, the waste plastics are sent to the system detailed below. A system and method of converting waste plastics into hydrocarbon oil has been described (12). The system consists of a thermal cracking reactor in which the waste plastics are cracked at a temperature in the range of 270–800°C to obtain partly gaseous hydrocarbons, partly liquid hydrocarbons, and remaining residues. A continuous thermal cracking and residual discharging portion is connected to have the liquid hydrocarbons gradually and fully cracked into gaseous hydrocarbons, while the residues are discharged at a residual discharge outlet. In addition, a chlorine removal portion is connected to receive the gaseous hydrocarbons to remove chlorine from it. A catalytic cracking reactor is connected to the chlorine removal portion to have the gaseous hydrocarbons catalytic cracking with an acid catalyst. A three-stage cooling portion is adopted to have the catalytically cracked gaseous hydrocarbons fully converted into liquid hydrocarbons, i.e., hydrocarbon oil. A pressurized activation reaction portion is provided to remove small amounts of sulfur, nitrogen, and phosphorus from the liquid hydrocarbons to obtain purified hydrocarbon oils (12). Also, an oil reconversion device for waste plastics has been described (13). The device thermally cracks a waste plastic by heating it and converts a generated cracker gas into oil by cooling it.

Recovery into Fuels 181 The oil reconversion device is equipped with a melting bath, which has a first crucible placed inside a first coil, induction-heats the first coil by feeding a high frequency current through the first coil, and melts solid waste plastics such as PE, PS, and PVC contained in the first crucible at around 250°C (70°C for PVC), which is a relatively low temperature to obtain a molten plastic. The thermal cracking bath has a second crucible placed inside a second coil, induction-heats the second crucible by feeding high frequency current through the second coil, and thermally cracks the molten plastic contained in the second crucible by heating it to a high temperature of around 450°C (170°C for PVC), to generate a cracker gas, which when cooled obtains a heavy oil (13). 5.3.1

Fuel-like Feedstocks

The thermal degradation of waste polymers was carried out as a suitable technique for converting plastics into liquid hydrocarbons, which could be used as feedstock materials (14, 15). The catalytic degradation of waste plastics (PE and PS) was investigated in a batch reactor using di erent catalysts, i.e., FCC, ZSM-5 and clinoptilolite. The e ects of catalysts and their average grain size on the properties of main degradation products (gases, gasoline, diesel oil) were investigated. A temperature range of 410–450°C was used in the process. Both equilibrium FCC catalyst and natural clinoptilolite zeolite catalyst showed a good catalytic activity to produce light hydrocarbon liquids. The ZSM-5 catalyst produced the highest amount of gaseous products. The gases and liquids formed in cracking reactions were analyzed by gas chromatography. The liquid products consisted of a wide spectrum of hydrocarbons distributed within the C5 –C28 carbon number range depending on the cracking parameters. The composition of hydrocarbons had linear non-branched structure in the case of PE, while from PS more aromatics (ethylbenzene, styrene, toluene, and benzene) were produced. The yields of volatile products increased with increasing degradation temperature. The olefin content of liquids was measured with an infrared technique and an olefin concentration of 50% to 60% was observed.

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The concentration of the unsaturated compounds increased with decreasing temperature and in the presence of catalysts. The activation energies were calculated on the basis of the composition of volatile products. The apparent activation energies were decreased by catalysts and catalyst caused both carbon chain and double bond isomerization (14). 5.3.1.1

Conversion into Fuels

Investigation of the thermal and catalytic pyrolysis of waste plastics, such as prescription bottles (e.g., PP, HDPE), landfill liners (PE), packing materials (PS), and foams (poly(urethane)) into crude plastic oils was done by TGA (16). In the first phase of the study, a statistical design experiments approach identified the reaction temperature and time as the most important factors influencing product oil yield. Kinetic parameters including activation energy were determined for both catalytic and noncatalytic processes. These showed a reduction in the activation energy for the catalytic reactions. In the second phase, the interactions of reaction temperature and time with a number of catalysts were investigated to determine the e ect on the yield of crude plastic oil. It was found that Y-zeolites increased the conversion at reduced temperature for PP and PE, while spent fluid catalytic cracking and sulfated zirconia catalysts supported pyrolytic decomposition of PS and PU foams. Response surface methodology was utilized to optimize the conditions for the pyrolytic decomposition of PP. The results were then validated through batch-scale experiments, and the resulting crude oils were characterized and distilled into motor gasoline, diesel #1, diesel #2, and vacuum gas oil fractions. Catalysts enhanced cracking at lower temperatures and narrowed the molecular weight (hydrocarbon) distribution in the crude oils. Chemical characterization of the crude oils indicated an increased gasoline range fraction in oils obtained in the presence of catalyst while the distillate fractions were more evenly distributed among gasoline range and diesel range hydrocarbons in the absence of catalyst. The distillates obtained were characterized for fuel properties, elemental composition, boiling point, and molecular weight

Recovery into Fuels 183 distribution. The fuel properties of the diesel-range distillate (diesel fraction) were comparable to those of ultra-low sulfur diesel (16). 5.3.2

Production of Transportation Fuels

Coprocessing reactions with waste plastics, petroleum residues, and coal were performed to determine the individual and blended behavior of these materials using lower pressure and cheaper catalysts (17). The plastic used was PP. The thermodegradative behavior of PP and blends of PP, petroleum residues, and coal were investigated in the presence of solid hydrocracking catalysts. A comparison among various catalysts has been performed on the basis of observed temperatures. Higher temperatures of initial weight loss of PP shifted to lower values by the addition of petroleum residues and coal. In order to establish the optimum reaction conditions, the coprocessing reactions of single and binary systems using low density poly(ethylene) (LDPE) and HDPE resid were performed at di erent temperatures and for di erent duration times. The percentage of gaseous products was generally low when the NiMo catalyst was used in comparison to other catalysts (18). The e ect of the catalyst on the product distribution for selected single component systems is shown in Table 5.2. The reaction conditions were 430°C, 60 min, and 8.3 MPa H2 . The catalysts were also tested in a fixed-bed microreactor for the pyrolysis of PP, petroleum residues and coal, alone and blended together in nitrogen and hydrogen atmosphere (17). High yields of liquid fuels in the boiling range of 100°C to 480°C and gases were obtained along with a small amount of heavy oils and insoluble material, such as gums and coke. The results obtained on the coprocessing of PP with coal and petroleum residues have been found to be very encouraging, as this method appears to be quite feasible to convert plastic materials into liquefied coal products and to upgrade the petroleum residues and waste plastics (17). The combination of petroleum residues and coal facilitated the coal conversion to some liquid products. However, the overall product yield for petroleum residues was decreased upon combining coal with petroleum residues.

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Table 5.2 E ect of the catalyst on the product distribution (18). Catalyst HDPE H Z F N LDPE H Z F N PS H Z F N PP H Z F N PET H Z F N Resid H Z F N HXs THFs H F

Product distribution [%] TOLs THFs IOM Conversion

Gas

HXs

8.5 7.2 7.5 9.6

24.7 36.7 26.5 30.7

6.0 8.2 4.0 5.5

4.5 5.5 7.0 4.0

56.2 42.1 54.5 49.6

43.6 57.3 45.0 50.0

14.4 11.5 12.2 11.6

18.9 29.5 21.5 24.1

3.8 5.5 4.0 3.6

6.5 8.5 9.2 9.5

56.6 44.5 53.0 51.2

43.2 55.0 46.4 48.8

7.0 8.5 5.6 5.0

83.2 85.4 80.5 81.5

9.5 5.9 12.9 13.8

0 0 0 0

0 0 0 0

100.0 100.0 100.0 100.0

7.0 8.5 6.5 2.1

37.5 40.2 42.2 35.6

8.0 11.0 10.2 14.7

11.7 10.0 14.0 19.2

35.0 30.2 26.9 28.4

64.2 69.7 73.1 71.6

8.7 9.2 5.9 3.5

38.2 45.5 40.2 37.8

16.2 11.0 25.0 29.8

9.0 8.2 7.5 7.1

27.5 25.6 20.8 21.8

72.1 73.9 78.6 78.2

15.5 16.0 12.0 10.3

70.2 71.2 69.5 71.5

2.2 3.8 11.5 10.2

4.5 3.5 2.0 2.5

7.0 5.2 4.5 5.0

92.4 94.5 95.0 94.5

Hexane solubles Tetrahydrofuran solubles Hydrocracking catalyst DHC-32 FCC catalyst

TOLs IOM Z

Toluene solubles Insoluble organic matter ZSM-5

N

NiMo catalyst

Recovery into Fuels 185 Also, the e ect of varying the hydrogen pressure in the coprocessing reactions was studied on a PP, petroleum residues, coal system, in the ratio of 2:3:2. The reactions were performed at 430°C for 60 min using 3% by weight of catalysts. The hydrogen pressures used in the reactions were 3.45 M Pa, 6.9 M Pa, and 8.3 M Pa. With a decrease in the hydrogen gas pressure both liquid products and conversion percent showed a decrease with an increase in the gas formation. At 8.3 M Pa the liquid products and conversion were as high as 82.4% and the THF solubles were also low at 8.3 M Pa. So, the lowering of the hydrogen pressure was found to a ect the boiling range of the liquid product material at low H2 pressure and high yields of insoluble material. Hydrogen pressure, 8.3 M Pa, proved to be more e ective for maximum conversion of reactants into liquid hydrocarbons (17). A comprehensive study of industrial and automotive plastics waste was done with regard to several amounts of an equilibrium FCC catalyst (19). The polymers used were PP, PE, PS, an ethylene propylene copolymer, and a thermoplastic elastomer based on the ethylene propylene diene terpolymer and polypropylene. As catalyst, amounts of 0%, 10%, and 25% of FCC catalyst were used. Here, the catalyst suitability for the thermolysis process was evaluated. The experiments were carried out in the fixed-bed reactor. The reaction time and product yields depend on the ratio of the catalyst and the feedstock. The catalyst results in the formation of branched C7 to C7 hydrocarbons as the main products, as well as the formation of an increased content of aromatic compounds. According to the composition of the liquid products, it was concluded that acidity of the catalyst is excellent only for the thermolysis of PE and that the products obtained from this raw material are liquid only in the case of catalytic thermolysis (19). Aromatization indexes, competitive parameter, the relative amounts of aromatization and isomerization reactions, and the ratio of unsaturated and saturated hydrocarbons were estimated for non-aromatic raw materials to evaluate mechanistic pathways of the processes. It was determined that catalytic reactions mainly occur in the lower temperature range. They run via a free-radical mechanism as the reaction temperature increases. Also, the kinetic and thermodynamic parameters were estimated for all raw materials using data from TGA, which appeared depen-

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dent on the ratio of catalyst to polymer and the plastic type used. The appropriate amount of catalyst for each raw material was evaluated for the production of diesel and gasoline cuts (19). 5.3.3

Co-pyrolysis of Waste Vegetable Oil and Waste Poly(ethylene) Plastics

The production of high-quality renewable hydrocarbon fuels through catalytic pyrolysis of waste vegetable oil and PE with ZrO2 Al2 O3 TiO2 polycrystalline ceramic foam as catalyst in the high pressure reaction kettle was investigated (20). The e ects of reaction temperature, time, catalyst amount and material feeding ratio were checked. The optimal condition was achieved when the reaction temperature was 430°C, the reaction time was 40 min, the dosage of the catalyst was 15%, the quality ratio of waste vegetable oil and waste PE plastic was 1:1, and liquid product yield was 65.9%. The gas chromatography (GC)-mass spectroscopy analysis indicated that the saturated hydrocarbon percentage in the liquid product pyrolysis was close to 100%. The pyrolysis gas and liquid products were analyzed to deduce co-pyrolysis catalyst mechanism. In comparison to biodiesel, the pyrolysis oil heat value was higher. Freezing point and cold filter plugging point were better than those of biodiesel. The low temperature fluidity was good. This study proved the feasibility of deriving renewable hydrocarbon fuel from the co-pyrolysis of waste vegetable oil and waste PE plastics with a ZrO2 Al2 O3 TiO2 polycrystalline ceramic foam catalyst (20). 5.3.4

Refining Method for Recycling Waste Plastics

A refining apparatus and a refining method for recycling waste plastics has been described (21). The refining apparatus contains a feeding device, a pyrolysis furnace, a chloride-decomposing device, a first condensation device, temporary storage, a still, a sieve plate tower, a second condensation device, and a receiving tank. A schematic diagram of the raw oil-obtaining device of a refining apparatus for recycling waste plastics is shown in Figure 5.1.

Recovery into Fuels 187

Figure 5.1 Schematic diagram of a device to obtain raw oil (21).

The waste plastics are cracked in the pyrolysis furnace to produce a gas by heating. Then the chlorides of the plastic gas are removed by a chloride-decomposing device using ammonia to produce a first oil gas. The first oil gas is condensed by the first condensation device to produce raw oil. The raw oil is then heated by the still to produce a second oil gas. The second oil gas is sieved by the sieve plate tower to produce a third oil gas. The third oil gas is condensed by the second condensation device to produce finished oil received by the receiving tank (21). The pyrolysis furnace can be a metal material cylinder which can electromagnetically heat the waste plastics in the pyrolysis furnace and irradiate with microwave to the heated waste plastics so as to crack the waste plastics to produce the plastic gas through a shorter duration and limited energy resource. For example, the pyrolysis furnace can have a frequency conversion electromagnetic heater, which transforms electrical energy into heat energy via electromagnetic induction. For instance, the alternating current of 220 V or 380 V and 60 Hz is transformed into a high frequency voltage of 20–40 kHz, and the current of the high frequency voltage flows through a coil to produce an alternating magnetic field of high-speed transformation, so that the conductive metal material produces a number of vortexes in the metal for enabling the metal material cylinder to promptly heat

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itself, thereby warming up the waste plastics. Then, microwave is irradiated to the waste plastics, which are warmed up by the electromagnetic heater. The microwave energy can be absorbed by the waste plastics according to the interaction of the waste plastics and the microwave to reduce the activating energy among the particles of the waste plastics. So, the micro-densification speed of the waste plastics can be accelerated to quicken the sinter of the waste plastics for producing the plastic gas. The chloride-decomposing device that uses ammonia is assembled above the rotary kiln of the pyrolysis furnace. For example, the chloride-decomposing device can be an ammonia cylinder assembled above the rotary kiln. When the pyrolysis furnace produces the plastic gas, the plastic gas will be reacted with the ammonia in the chloride-decomposing device to remove the chlorides, which is contained in the plastic gas, and produce the first oil gas and the mixed gas without chlorides. The mixed gas can be hydrogen, nitrogen and a non-condensing gas, e.g., methane, ethane, propane or butane. Furthermore, a gas channel is assembled between the chloride-decomposing device and the pyrolysis furnace, such that the plastic gas floats into the chloride-decomposing device along the gas channel. The first condensation device is connected with the chloride-decomposing device via a pipe for enabling the first oil gas, which is produced by the chloride-decomposing device, to float into the first condensation device along the pipe. The first oil gas is condensed by the first condensation device to produce a raw oil. The first condensation device can be a shell and tube condenser having water tubes. When the first oil gas and the mixed gas float into the first condensation device and contact the water tubes, the first oil gas is condensed as fluid to produce the raw oil because the first oil gas has the higher boiling point. Besides, because the boiling point of the mixed gas is lower, the mixed gas will not be condensed as a fluid. Moreover, the temporary storage is assembled under the first condensation device, so that the raw oil produced by the first condensation device flows into the temporary storage along a channel (21).

Recovery into Fuels 189

5.4 Hydrocarbon Fuels 5.4.1

Pyrolysis into Premium Oil Products

The pyrolysis of PP and HDPE into fuel-like products was investigated over a temperature range of 250°C to 400°C (22). The product yields as a function of temperature were studied. The total conversion as high as 98.66% (liquid: 69.82%, gas: 28.84%, and residue: 1.34%) was achieved at 300°C in the case of PP and 98.12% (liquid: 80.88%, gas: 17.24%, and residue: 1.88%) in the case of HDPE at 350°C. The liquid fractions were analyzed using Fourier transform infrared (FTIR) spectroscopy and GC-MS. The results showed that the liquid fractions consisted of a wide range of hydrocarbons mainly distributed within the range of C6 to C16 . The liquid product obtained in the case of PP is enriched in the naphtha range hydrocarbons. Similarly, the liquid product obtained in the case of HDPE is also enriched in the naphtha range hydrocarbons with a preponderance of gasoline and diesel-range hydrocarbons. The % distribution of para nic, olefinic, and naphthenic hydrocarbons in liquid product derived from PP is 66.55%, 25.7%, and 7.58%, respectively, whereas in the case of HDPE, the percentual distribution is 59.70%, 31.90%, and 8.40%, respectively. Upon comparing the hydrocarbon group type yields, PP gave high yield of para nic hydrocarbons while HDPE gave high yields of olefins and naphthenes. The whole liquid fractions and their corresponding distillates fractions were also analyzed for fuel properties. The results indicated that the derived liquid fractions were fuel-like and met the fuel grade criteria (22). 5.4.2

Gasoline, Kerosene, and Diesel

The conversion of waste plastics material to hydrocarbon fuel products, particularly transportation fuels, has been reported (23). The transportation fuel is selected from the group of gasoline, diesel, and jet fuel. The waste plastics material can be obtained from any suitable source, such as a municipal solid waste facility and from agricultural and horticultural activity. Basically, any plastic material can be used,

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but for economic reasons waste plastics material are preferred that are substantially free of PET and PVC. These materials show relatively poor conversion e ciency and lead to the formation of terephthalic acid and hydrochloric acid, respectively, which, if not separated from the plastics feed, will result in an undesirable acidized oil product. Thus, it is preferred that the plastics material feed contain preferably less than about 3%, or substantially no PET or PVC. The plastics material feed, which can contain from about 10% to about 50% dirt, is reduced to an e ective size, then dried, if needed, to a moisture level of 2% and less, then screened to remove dirt, then densified into nuggets of at least about 160 kg m 3 , then pyrolyzed. There is a substantial absence of oxygen in the pyrolysis zone where the material is heated. The pyrolysis temperature is 150°C–600°C. In a preferred embodiment, the plastics waste material is coprocessed with up to about 50% of a petroleum-based waste hydrocarbon material (23). It was further discovered that the fuel gas produced during the pyrolysis process, which is preferably flared, can be subjected to a heat recovery system to improve operating e ciency of the facility. The recovered heat is su cient to significantly reduce utility requirements for both the drying operation and the reformer operation (23). 5.4.2.1

Thermocatalytic Conversion

The thermocatalytic conversion processes for waste plastics have been investigated (24). The reaction conditions and the quantification of types of catalysts used for the conversion processes influenced the quality of the resultant hydrocarbons. The yields of various products obtained using di erent processes are shown in Table 5.3. The thermocatalytic process can solve the problem of halogen contents in the PVC type plastics by converting them into residues with the use of NaHCO3 and AgNO3 , which capture the chlorinetype products from the gaseous hydrocarbons. The addition of catalysts in the reactor reduces the requirement of higher temperature operations like thermal cracking processes and produces more liquefied products. It has been observed that the

Recovery into Fuels 191 Table 5.3 Yields from di erent processes (24). Polymer

Oil [%]

Gas [%]

Residue [%]

Aromatics [%]

Pyrolysis Process PE PP PS PVC PET

93 95 71

7 5 2

0 0 27

64.1

4.3

23.3

16.4 18.8 100 27.6

Liquidation Process PE PP PS PVC PET

95 95 2 77 27

5 5 2 38 27

0 0 22 52 41

15.5 17.1 100 52.7 22

aromatic plastic contents should be observed during the conversion process to obtain fuels based on allowable aromatic contents according to the fuel standards and emission regulations implemented in respective regions. The temperature of the process needs to be controlled as per the boiling points of the mixture contents to avoid the formation of a vapor in the reactor, which could cause a sticky adherence to the reactor walls. A continuous liquid fractionating distillation process can reduce the formation of light gases in the yield (24). It was also found that a mixture of LDPE, HDPE, PP and PS yield 87.19% fuel using 20% of a ZnO catalyst at 200°C to 400°C in a steel reactor. The so-obtained fuels can be used directly in automotive engines or can be retreated in the refineries to divide into gasoline and diesel fuels as per carbon chains. Since the plastic feedstocks do not contain any sulfur components the produced fuel can be treated as clean enough. Thus, the fuels produced from this process can be considered as one of the potential alternative resources of fuel production, resulting in an e ective reduction of plastic wastes (24).

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5.4.2.2

Conversion of Polymer-Containing Materials to Petroleum Products

Conventional technologies for the conversion of polymer-containing materials to petroleum products are directed to convert polymer-containing materials, such as plastic, into petroleum products, including crude oil. However, the conventional technologies are limited to relatively low crude oil and diesel yields, slower throughput, higher operating costs, and higher capital expenses (25). Newly developed technologies do not su er from these disadvantages. The reactor, the system and the developed method lead to a higher yield of crude oil and diesel, with a quicker throughput rate, at a lower operating expense and a lower capital expense. Here, the focus is on producing as much diesel-quality oil as possible and minimizing the wax that other technologies create by ensuring an ideal reaction time, and allowing lower carbon chains more time to develop into diesel. Furthermore, specific constructions of the reactor allow for a shorter reaction time that results in more polymer-containing materials converting into vapors that lead to petroleum products each minute and hence each hour and day. In addition, embodiments of the reactor are designed such that the process can be run continuously 24 h per day, 7 d per week, thus increasing or maximizing output. Also, the overall system is intended to be as automated as possible so that minimal intervention is required. Basically, the apparatus includes a feeder part, a reactor part, and a condenser system part. The polymer-containing material is fed through an inlet in the feeder, and heat is applied to the reactor, while there is an outlet from the condenser for the product to exit. The condensing system may contain four stages. It condenses vapors at four di erent temperatures. The main purpose of the condensing system is to cool the hot vapors enough for condensation to occur and for them to be in a liquid phase. The condensing system can also be configured to do this cooling in stages in order to separate di erent boiling ranges of the product. The result of a four stage condensing system is the separation of four distinct liquid products. Hot vapor that is produced in the reactor is drawn through the condensing system starting with the first condenser. The first stage

Recovery into Fuels 193 condenser can be used as a reflux column. The vapor leaves the first condenser as either a liquid at a temperature between 93°C and a maximum of what the temperature of the reactor is, or as a vapor. The vapor that exits the first condenser moves into the second condenser where it is set at a lower temperature than the first condenser but at least higher than 10°C. Again, the vapor leaves the second condenser either in liquid form or as vapor that proceeds into the third condenser. In the third condenser the vapor is again cooler further at a temperature lower than that of the second condenser but at least higher than 10°C. From this third condenser the vapor leaves as either liquid or as vapor into the fourth condenser. In this fourth condenser the vapor is cooled down significantly between about room temperature to at least above 4°C to capture the last of the available liquids with the remainder exiting as vapor, which will typically be light hydrocarbon gases. The reactor is rotated. The ideal rotational speed of the rotation of the reactor is guided by the internal augers of the reactor, which mix the polymer-containing materials inside the reactor. The rotating action of the reactor facilitates stirring and mixing of the feed materials on the inside and also allows for even heating of the exterior wall of the reactor chamber. The reactor heats and stirs the polymer-containing material or wax to a liquid material state. The liquid in the reactor temperature can be 400°C–550°C. In other embodiments, the liquid may be a higher or lower temperature. The reactor contains a longitudinally situated cylindrical tube, which is indirectly heated on the exterior. This could be heated with hot gases from a combustion source or hot gases from an electric source (25). 5.4.3

Two-Stage Pyrolysis Catalysis

A two-stage pyrolysis-catalysis technology of HDPE has been investigated (26). A pyrolysis of the plastic was done in the first stage followed by the catalysis of the evolved hydrocarbon pyrolysis gases in the second stage using solid acid catalysts to produce gasoline range hydrocarbon oil in the range of C8 to C11 . The catalytic process involved staged catalysis, where a mesoporous catalyst was layered on top of a microporous catalyst with the

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aim of maximizing the conversion of the waste plastic to gasoline range hydrocarbons. The catalysts used were mesoporous MCM-41 followed by microporous ZSM-5. Di erent MCM-41:zeolite ZSM-5 catalyst ratios were also tested. The MCM-41 and zeolite ZSM-5 were also used alone for comparison (26). The results showed that by using the staged catalysis a high yield of oil product of 83.15% was obtained from HDPE at a MCM-41:ZSM-5 ratio of 1:1 in the staged pyrolysis-catalysis process. The main gases produced were C2 (mainly ethene), C3 (mainly propene), and C4 (mainly butene and butadiene) gases. In addition, the oil product was highly aromatic with 95.85% of the oil consisting of 97.72% of gasoline range hydrocarbons. In addition, pyrolysis-staged catalysis using a 1:1 ratio of MCM-41 to zeolite ZSM-5 was investigated for the pyrolysis-catalysis of several real-world waste plastic samples from various industrial sectors. These samples were agricultural waste plastics, building reconstruction plastics, mineral water container plastics and household food packaging waste plastics. The results showed that an e ective conversion of these waste materials could be achieved and significant concentrations of gasoline range hydrocarbons could be obtained (26). 5.4.4

Continuous Preparation

A method for the continuous preparation of gasoline, kerosene, and diesel oil from waste plastics has been developed (27). The method contains the following steps: 1. Crushing and sorting, 2. Subjecting a melt of the waste plastics to a first catalytic reaction in which the waste plastic melt is in contact with a nickel or nickel alloy catalyst to be dehydrogenated while being decomposed, 3. Subjecting the dehydrogenated and decomposed waste plastic melt to a fluid catalytic cracking, as a second catalytic reaction to produce a gasoline-based fraction at a high fraction, 4. Fractionating the cracked material into a gasoline-based fraction, a kerosene fraction, and a diesel oil fraction, and

Recovery into Fuels 195 5. Reforming the gasoline-based fraction to produce a high octane number gasoline. This method allows gasoline to be prepared from the waste plastics in a high fraction and an e cient manner, thereby contributing to resource reclamation and the protection of the environment (27).

5.4.5

Continuous Cracking Technology

Waste rubber or plastics can be converted into gasoline, diesel oil and others after being cracked, which not only provides a good means of disposing of the industrial rubbish, like rubber, plastics, etc., from waste tires, but also provides a new plan for the improvement of decreasing resources and energy (28). However, almost none of the present technologies can realize a continuous production. Besides, the existing technology costs are high. A continuously cracking technology of waste rubber or plastics and its equipment has been presented (28). This technology has high security but low cost. It can realize the continuous and industrial production of oil by use of waste rubber or plastics. The cracking course is to extrude and transport the catalyst and rubber or plastics with the aim of separating air or preventing oxidization and transporting raw materials into the sealed cracking chamber, i.e., to expel air among and in raw materials out of the cracking chamber while transporting materials into it, which ensures material delivery and separation in both the cracking chamber and air outside. In the cracking chamber, the raw materials are transported from the inlet orifice to the discharge hole by the corresponding unit, cracking is finished in this process, and finally the products are automatically deviated through the discharge hole, which is also separated from the air outside. Via this process, the security in the cracking chamber can be ensured, and the continuous and industrial manufacture achieved. In addition, a lot of detailed examples have been presented on how to guide this process (28).

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5.5 High-Value Hydrocarbon Products A method has been presented that enables obtaining high-value hydrocarbon products from waste plastics in inert gas atmosphere in which wastes are continuously fed into the extruder and melted (29, 30). Then the polymers are depolymerized in a thermolysis reactor and depolymerization product vapors are conducted into a preliminary separation unit. Here an introductory separation of the materials takes place. The thus-obtained fractions are hydrorefined and then conducted into a secondary separation unit and an additional finishing operations unit. It was found that using the two processes of separation of the product in fractions, firstly before hydrorefining and secondly after hydrorefining, ensures the precise separation of fractions and enables avoidance of secondary degradation reactions of temperature-sensitive products. This ensures a high purity grade of the products and also a great flexibility of all processes and the opportunity of getting a wide range of di erent products depending on the requirements of the market (30). An important novelty of the process is the sequence in which the hydrora nation processes is performed (30). Hydrogenation is the first process and hydrodesulfurization is the next process. Such an order ensures removal of sulfur, nitrogen and oxide compounds and aromatic compound impurities up to the level of a few or several ppm, and also the reduction of energy costs for heating the feedstock stream, because secondary heating in the hydrogenation reactor causes exothermal character of this reaction. The additional use of a catalytic dewaxing process of oil fractions improves their properties as commercial products by reducing the pour point of the obtained oils (30). Also, an apparatus for conducting the thermolysis of plastic waste with continuous waste plastics feeding and continuous removal of the carbonization products and reaction leftovers has been described (31–33). The apparatus includes a feeding system, an extruder, a reactor for thermolysis, a dual agitator housed within the reactor, a trigger system in operative connection with the reactor, a flux heater, and a collecting system in operative connection with the reactor. The

Recovery into Fuels 197 reactor for thermolysis has a height at least 1.5 times bigger than its diameter. The trigger system contains a circulation pump and the collecting system has a three-way valve in an external circulation loop. The apparatus is arranged such that the extruder follows the feeding system, the reactor follows the extruder, the trigger system is at the bottom of the reactor, and the flux heater and collecting system follow the reactor (33). The device is shown in Figure 5.2 and explained below.

Figure 5.2 Apparatus for conducting the thermolysis of plastic waste with continuous waste plastics feeding (33).

The apparatus for conducting thermolysis of plastic waste is characterized by a granulated or leaf-shaped feedstock feeding system 1 to the extruder 2. The plastic waste is plasticized in the extruder 2, heated up to 300°C–330°C and fed through inlet piece 17 to reactor 3, in which the thermolysis process takes place. The height of reactor 3 is two times bigger than its diameter. The reactor 3 is equipped with a dual high-speed propeller 7 with di erent propeller blade angles. Dual high-speed propeller 7 is calked by inert gas cooled by liquid. Reactor 3 is equipped with

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two internal vertical ba es on the walls 9 and 9’. The shaft of the agitator is equipped with additional stabilizing bars 11. Moreover, the reactor 3 is equipped with an independent accessory agitator 10 which eliminates the formation of foam. In the bottom of the reactor 3 the inspection flange 12 and anti-whirl device 13 are set up. The thermolysis process of molten plastic is carried out in a temperature from 390°C to 460°C and with 200 to 700 rpm speed of the agitator. In the bottom of the thermolysis reactor 3 is a reaction mixture outlet piece 14 and a mechanical filter 16. A plasticized polymer is fed through the outlet piece 14 and circulation pump 6 to external circulation loop 4 with a velocity of flow 6 to 9 m3 h 1 . A filter 22 is set up before the circulation pump 6. In the circulation loop 4 the reaction mixture flows through a three-way valve 8 and through electrical flux heater 5, which controls process temperature. The heating power of the flux heater is 70 kW to 90 kW. The mixture of the vapors and the liquid is continuously conducted through inlet piece 15 back to thermolysis reactor 3. The vapors from the process are collected in another part of the system 23 and condensed into liquid product. Thermolysis residues are also collected continuously by external circulation loop 4 in the discharge system through a three-way valve 8 dividing pumped stream of reaction mixture on stream conducted to residue cooling system 18 and leftovers tank 19 and main product stream conducted through flux heater 5 and inlet piece 15 situated tangentially to the reactor wall. Under the bottom of reactor 3 there is a bottom emergency trigger valve 20, which is equipped with drain mechanism 21. The drain mechanism 21 is a manual or pneumatic punch. The thermolysis process is carried out in an inert gas atmosphere. The thermolysis product is a very wide hydrocarbon fraction for further rework (33).

5.6 Purified Crude Oil Methods for recycling waste plastic can convert the waste plastic into a form of purified crude oil that includes one or more organic molecular species and that is substantially free of impurities such as acids and metals (34, 35). A schematic view of such a system is given in Figure 5.3.

Recovery into Fuels 199

Figure 5.3 System for recycling waste plastic (34).

The plastic recycling system includes a heating system that is configured to deliver heat to a plastic feedstock. The heating system can comprise any suitable heating mechanism, such as, for example, a combustion burner, a fluidized-bed burner, a retort, or any other such heating system. In some applications, the heating system operates at a high and steady temperature. The plastic feedstock can consist of waste plastics of one or more varieties (e.g., mixed plastics), and may include trace amounts of non-plastic contamination or impurities. For example, the impurities may be of an external nature (e.g., water, foodstu s, labeling, soil, paper, or cellulose waste) or may result from internal amendments (e.g., glass, metal, iron, bromine, and or chlorine). The plastic feedstock may be provided in a ground, chipped, or other form that can promote the transfer of heat thereto. The heat provided by the heating system can be su cient to crack or depolymerize the plastic feedstock and convert at least a portion thereof into a vapor. The vapor can include one or more gaseous organic species, one or more gaseous inorganic species, and or one or more varieties of entrained particles. In particular, the vapor can include depolymerized nonpolar organic gases, which may be

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desirable for collection and refinement, and which can be mixed with impurities. The organic gases can include, for example, one or more para ns, olefins, naphthenes, aromatics, and or other classes of hydrocarbon materials. The mixed-in impurities can include, for example, inorganic acids (e.g., hydrochloric acid, hydrobromic acid), entrained metals or metalloids (e.g., cadmium, iron, antimony); and or organic acids (e.g., terephthalic acid). In some embodiments, the vapor may include additional molecular species, such as polar organic molecules, which may or may not be collected with the nonpolar organic molecules. For example, the vapor can include one or more alcohols, ketones, ethers, phenols, carboxylic acids, or other polar organic molecules. The plastic feedstock may be heated under vacuum conditions, or under negative pressure. In other embodiments, the plastic feedstock may be heated under positive pressure. In still other or further embodiments, the plastic feedstock may be heated under atmospheric pressure conditions, or under any suitable combination of the foregoing, e.g., the pressure may be varied during a heating event. The vapor can be delivered to a vapor treatment system that effects a phase change of at least a portion of the vapor such that certain molecules transition from a gaseous state to a liquid state. The vapor treatment system may also be referred to as a vapor treatment unit or a vapor treatment vessel. The vapor treatment system illustrated in Figure 5.3 includes a pH adjusted solution that is used to e ect the condensation. Moreover, the pH adjusted solution can be configured to absorb at least a portion of the impurities from the vapor. Embodiments of the solution can readily absorb organic acids, inorganic acids, metals, metalloids, and or certain polar organic molecules. The term pH adjusted solution is used in a broad sense and includes solutions that are not pH neutral and that exhibit any or all of the various properties described herein. For example, a pH adjusted solution can be formulated to remove impurities from the vapor, and can be immiscible with condensed oils so as to be readily separated therefrom. For example, in some embodiments, the pH adjusted solution can comprise an acidic solution, which may, in some cases, be strongly acidic. In further embodiments, the pH adjusted solution

Recovery into Fuels 201 can comprise a bu ered aqueous solution adjusted to a desired pH value. In various embodiments, the pH adjusted solution can have a pH value that is less than 7, less than about 6.5, less than about 6, less than about 5.5, less than about 5, less than about 4, or less than about 3. The pH adjusted solution can include one or more chemical amendments of any suitable variety to achieve the desired properties of the solution. Such properties can include, for example, the ability to remove one or more impurities from the vapor and or a high immiscibility with oil. Adjustment or optimization of one or more of the foregoing properties may be achieved by altering the concentration of one or more chemical amendments within the pH adjusted solution. For example, the presence, combination, and or concentration of one or more materials within the pH adjusted solution can optimize removal of contaminants from the vapor as it interacts with the pH adjusted solution. The pH adjusted solution can include strong and or weak inorganic acids (e.g., hydrochloric acid, acetic acid), one or more pH bu er solutions (e.g., acetic acid sodium acetate), one or more chelating agents (e.g., ethylenediamine tetraacetic acid), and one or more coagulants or flocculants (e.g., calcium hydroxide, polyacrylamide). The vapor treatment system can be configured to e ect direct contact between the vapor received therein and the pH adjusted solution, as depicted at the broken arrow in Figure 5.3. For example, as further discussed below, in some embodiments, the pH adjusted solution may be sprayed into contact with the vapor, whereas in other embodiments, the vapor may be bubbled through the solution. The pH adjusted solution can absorb or dissolve portions of the vapor, e.g., organic acids, inorganic acids, metals, metalloids, and or certain polar organic molecules. The pH adjusted solution also can be provided at a lower temperature than that of the vapor such that the solution condenses at least those portions of the vapor that are immiscible therein, e.g., nonpolar organic molecules. The portions of the condensed vapor that are immiscible in the pH adjusted solution, i.e., the hydrophobic portions, can be readily separated from the solution. The separation takes place within the vapor treatment system, or takes place within a separator that is independent of the vapor treatment system. In some systems and methods, the plastic is heated under vacuum

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conditions to e ect depolymerization of the plastic, which yields a vapor, and the vapor is then directly contacted with a pH adjusted solution in a vapor treatment system. In some systems and methods, a continuous batch process is employed (35). Methods for conditioning synthetic crude oils that may be obtained from waste plastics have been described (36). Synthetic crude oils obtained from pyrolysis of synthetic polymers may exhibit highly variable contaminant profiles. This is particularly true when recycled polymer material is sourced from mixed waste plastic and or rubber. Such materials can be, and often are, contaminated with water, foodstu s, labeling materials, soil, paper, or cellulose waste. Moreover, recycled synthetic polymers often include internal amendments, such as glass, metal, iron, bromine, and or chlorine. Even further, in the course of capturing and condensing hydrocarbons obtained from a pyrolytic process, fine particulate material, including particulate carbon black, may be drawn o and entrained within the synthetic crude product as the hydrocarbons generated from pyrolysis are condensed. Systems for conditioning such synthetic crude oils have been detailed (36). The conditioning system may be implemented as a stand alone system where synthetic crude is delivered to the system, conditioned, and collected for storage, further processing, use, or sale. Also, the conditioning system may be integrated into a synthetic crude production process, with the synthetic crude being delivered directly to the conditioning system as output from a crude oil production process without intermediate storage or transportation steps. A schematic view of such a system is given in Figure 5.4. Here, the conditioning system includes a synthetic crude delivery system, a process solution delivery system, a mixer, and a separator for partitioning the conditioned synthetic crude from the process solution. The process solution delivery system delivers the process solution to the mixer, and the synthetic crude is delivered to the mixer by the synthetic crude delivery system. This is done because the synthetic crude oil and and the process solution are generally immiscible. The synthetic crude and process solution are blended by the mixer prior to delivery to the separator (36). As contemplated herein, a process solution is an alkaline aqueous solution exhibiting a pH of about 8 or above and can be prepared

Recovery into Fuels 203

Crude oil delvery

Conditioned Crude oil

Mixer

Process solution delvery

Separator

Process solution return

Figure 5.4 Systems for conditioning synthetic crude oils (36).

by dissolving a caustic amendment, such as a water-soluble base, in an aqueous carrier. In particular embodiments, the process solution may be prepared using one or more bases selected from potassium hydroxide, calcium hydroxide, cesium hydroxide, barium hydroxide, sodium hydroxide, strontium hydroxide, and lithium hydroxide.

The process solution may be bu ered to maintain a desired pH. In specific embodiments, the pH of the process solution is above a pH of about 8 but not higher than a pH of about 10. For example, a caustic process solution may have a pH of between a pH of about 9 and a pH of about 10. It has been found that increasing the pH above a pH of about 10 may result in the saponification of the crude oil or production of a stable emulsion as the synthetic crude and the process solution are mixed. The process solution may not only serve to reduce the total acid number of the synthetic crude, but the caustic wash it provides may capture polar impurities, metals, or other impurities that have an a nity to or will partition into an alkaline solution (36).

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5.7 Lubricating Oil Manufacturers of mechanical and hydraulic equipment regularly increase the viscometric requirements for lubricating compositions used in such equipment (37). These increases are driven by a desire for reduced maintenance and lubricating composition replacement, a desire for laws and regulations for reduced environmental emissions, and by the closer tolerances of moving parts, higher operating temperatures, and other changes in new equipment designs. Therefore, it would be advantageous to have a relatively inexpensive process for producing high viscosity index (VI) lubricating compositions. Such a process would ideally utilize a readily available inexpensive feedstock. The VI is an arbitrary, unitless measure of the change of viscosity with temperature, mostly used to characterize the viscosity-temperature behavior of lubricating oils (38). As lower the VI, as more the viscosity is a ected by changes of the temperature. The VI was originally measured on a scale from 0 to 100. However, advancements in lubrication science have led to the development of oils with much higher VIs (38). The viscosity index can be calculated using the following formula: VI

100

L L

U H

.

(5.1)

Here, U is the kinematic viscosity of the oil at 40°C, and L and H are values based on the oil’s kinematic viscosity at 100°C. These L and H values can be found in ASTM D2270 (39). The term high viscosity index mineral oil or lubricating oil composition means (37): 1. A viscosity index of at least 90 for a mineral oil having a viscosity of 3.0 cSt at 100°C, 2. A viscosity index of at least 105 for a lubricating oil composition having a viscosity of 4 cSt at 100°C, 3. A viscosity index of at least 115 for a lubricating oil composition having a viscosity of 5.0 cSt at 100°C, and 4. A viscosity index of at least 120 for a lubricating oil composition having a viscosity of 7.0 cSt at 100°C.

Recovery into Fuels 205 A process of making a lubricating oil composition consists of the following steps (37): 1. Contacting a waste plastics feed including mainly PE in a pyrolysis zone at pyrolysis conditions, whereby at least a portion of the waste plastics feed is cracked, thereby forming a pyrolysis zone e uent including 1-olefins and n-para ns, 2. Passing the pyrolysis zone e uent, including a heavy fraction and a middle fraction, the pyrolysis e uent middle fraction including 1-olefins, to a separations zone; where the pyrolysis e uent heavy fraction portion is separated from the pyrolysis e uent middle fraction, 3. Passing the pyrolysis e uent heavy fraction to a hydrogenation zone, and 4. Passing at least a portion of the hydrogenation zone e uent to a catalytic isomerization dewaxing zone, where at least a portion of the hydrogenation zone e uent is contacted with a isomerization dewaxing catalyst at isomerization dewaxing conditions, thereby forming a high VI lubricating oil composition. The waste plastics feed should contain mainly PE. The pyrolysis zone has a temperature of from about 500°C to about 700°C. The dewaxing catalyst may be an intermediate pore-size molecular sieve selected from ZSM-22, ZSM-23, SSZ-32, ZSM-35, SAPO-11, SM-3, and mixtures of these catalysts (37). In addition, a process for making a lubricating base oil with a viscosity index of at least 110 can be done using the following steps (40): 1. Combining a waxy light neutral base oil and a wax derived from pyrolyzing a plastics feed comprising PE to form a blend, 2. Hydroisomerization dewaxing the blend, and 3. Recovering the lubricating base oil from an e uent from the hydroisomerization dewaxing step. The viscosity index is an empirical, unitless number indicating the e ect of temperature change on the kinematic viscosity of petroleum products, such as lubricating base oils. The higher the

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viscosity index of an oil, the lower its tendency to change viscosity with temperature. The viscosity index can be determined by ASTM D2270-10 (39). Hydroisomerization dewaxing may occur in one or more steps, either before or after fractionating of the base oil into one or more fractions. The hydroisomerization dewaxing is intended to improve the oxidation stability, UV stability, and the appearance of the product by removing aromatics, olefins, color bodies, and solvents. A general description of hydroisomerization dewaxing can be found in the literature (41, 42). An example of the preparation runs as follows (40): Preparation 5–1: A hydrocracked waxy light neutral base oil was isomerized over a Pt SSZ-32 catalyst, containing 35% CATAPAL® alumina binder in a continuous feed high pressure pilot plant with once-through hydrogen gas. The run conditions were 1.0 h 1 liquid hourly space velocity, 300°C, 1935 psig total pressure, and 5.70 MSCF bbl (thousand standard cubic feet per barrel, 1015 m3 n 3 ) H2 . Downstream of the isomerization catalyst was a second reactor containing a Pd on silica-alumina hydrofinishing catalyst run at 1.0 h 1 liquid hourly space velocity and 232°C.

5.8 Waxes and Grease Base Stocks Manufacturers of mechanical equipment, food packagers, and other users of wax and grease for lubricating, sealing, and other uses have a continuing need for wax and grease compositions. The manufacturing of these waxes and greases is usually expensive (43). This may be typically due to the pricey petroleum feed required in such manufacturing process. The melting point of waxes ranges between 45°C to 130°C and the flash point, i.e., the lowest temperature at which the wax can vaporize to form an ignitable mixture in air, ranges between 180°C to 350°C. Such waxes may be mostly derived by refining crude petroleum. The waxes may also be derived from natural secretions of plants and animals. Furthermore, the waxes may be synthetically produced using processes such as the Fischer-Tropsch process. There have been several discoveries of gas reservoirs, mostly methane reservoirs, and using the Fischer-Tropsch process for the conversion into higher chain length hydrocarbons to give gasoline,

Recovery into Fuels 207 lubricating oils, grease base stocks, and waxes. However, the products produced in this way are relatively more expensive and thus there is a need to utilize the readily available PE waste and recycle them to produce the same materials at considerably lower cost. Mixed PE waste can be converted to make waxes and grease base stocks (43). PE waste may be available as shopping bags, grocery bags sacks of HDPE, milk pouches of LDPE and stationery files of linear low density poly(ethylene). Primary granules of PE may also be used for producing the waxes and grease base stocks. The method for the production of waxes and grease base stocks uses catalytic depolymerization. Here, the mixed PE waste is preheated to form a molten mixed PE waste. Then, the depolymerization reaction of the molten mixed PE waste is started. The depolymerization reaction uses a catalyst in a high pressure reactor at a desired temperature using heaters in the high pressure reactor. The catalyst is disposed on a stirring blade. Progression of the depolymerization reaction of the molten mixed PE waste is allowed to continue until a pressure in the high pressure reactor reaches a desired value. The heaters are then turned o and the depolymerization reaction of the molten mixed PE waste is stopped when the pressure in the reactor reaches the desired value. In summary, the mixed PE waste is converted to wax or grease base stock (43). The properties of the wax obtained through the depolymerization reaction described above have been compared against a commercially available ARGE wax, i.e., a type of Fischer-Tropsch wax. The results are shown in Table 5.4. Table 5.4 Properties of waxes (43). Property Melting point (°C) Average carbons Solubility in acetone (%) Solubility in cyclohexane (%) Acid value Saponification number IR spectra NMR spectra

ARGE wax

Wax obtained here

105 47 28 69 0 0

97 48 17.5 75 0 0 Identical Identical

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It can be observed from the data in Table 5.4 that the properties of both waxes are comparatively similar. On the other hand, it has been found that the wax obtained from the depolymerization of the HDPE waste has a broader molecular weight distribution and a slightly higher melting point, but is otherwise comparable to the microcrystalline wax produced using the processes described here (43).

5.9 Co-pyrolysis of Landfill Recovered Plastic Wastes and Used Lubrication Oils A preliminary study for the development of a co-pyrolysis process of plastic wastes excavated from a landfill and used lubrication oils has been presented (44). The goal of this study was to produce an alternative liquid fuel for industrial use. First, TGA experiments were carried out with pure plastic materials, such as HDPE, LDPE, PP and PS and also oils, a motor oil and a mixture of used lubrication oils, in order to investigate the interactions occurring between a plastic and an oil during their co-pyrolysis. It seems that the main decomposition event of each component takes place at higher temperatures when the components are mixed than when they are alone, possibly because the two components stabilize each other during their co-pyrolysis. These interactions depend on the nature of the plastic and the oil. In addition, co-pyrolysis experiments took place in a laboratory-scale reactor using a mixture of excavated plastic wastes and used lubrication oils. On the one hand, the influence of some key operating parameters on the outcome of the process was analyzed. It was possible to produce an alternative fuel for industrial use whose viscosity is lower than 1 Pa s at 90°C from a plastic oil mixture with an initial plastic mass fraction between 40% and 60% by proceeding at a maximum temperature included in the range of 350°C to 400°C. On the other hand, the amount of energy required to successfully co-pyrolyze under lab conditions, 1 kg of plastic oil mixture with an initial plastic mass fraction of 60%, was estimated at about 8 MJ. This amount of energy is largely used for the thermal cracking of the molecules. It is also shown that per kg of mixture introduced in the laboratory reactor, 29 MJ can be recovered from the combustion

Recovery into Fuels 209 of the liquid resulting from the co-pyrolysis. Hence, this co-pyrolysis process could be economically viable, provided heat losses are addressed carefully when designing an industrial reactor (44).

5.10 PVC Wastes The increase of waste PVC plastic production is a serious environmental problem issue for today (45). PVC plastic consumption is increasing day by day all over the world. Out of the total amount of all types of plastics used, 6% are PVC plastic. PVC plastic can serve as a potential resource with the correct treatment and its conversion into hydrocarbon raw materials or useful fuel. PVC plastic has a high chlorine content with the percentage of chlorine being 56% by total weight. A PVC plastic incineration process needs a high energy demand and during the incineration time toxic chlorine compounds are emitted, which create environmental, ecological and human health problems. The chlorine components need to be removed by washing with alkali compounds before producing a fuel. A thermal degradation process with 5% zinc oxide (ZnO) can reduce the chlorine content. It results in polymer chain generating product with a heavy molecular weight and some uncontrolled chlorine content. In detail, the process runs as (45): Waste plastic PVC for the production of liquid hydrocarbon fuels on a laboratory-scale was used for a thermal degradation process with 5% zinc oxide catalyst with 1% activated carbon and at temperature of 75ºC to 400ºC under atmospheric pressure in the presence of oxygen and under a Labconco fume hood. The experimental sample used was 75 g and a glass reactor was used. The ground waste plastic sample was put into the reactor chamber together with the catalyst. When the PVC waste plastic started to melt a liquid phase was formed, which was then converted into vapor. The vapor passed through a condenser unit and it returned to liquid form. The conversion into fuel was found to be 35.6%. The density of the fuel was 0.81 g ml 1 . During the conversion, not all vapor came out as a light gas because the boiling point of the gas

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was very low. A cleaning of the light gas was done with a AgNO3 and a NaOH NaHO3 solution. After an alkaline washing, a water wash was also done. The alkali wash and water wash resulted in the formation of sodium chloride and silver chloride. Finally, the percentage of light gas was found to be 34.47%. From PVC waste plastic the total conversion amount was 70.07%. The thermal degradation of waste PVC produces only 35.6% of liquid product, some light gas of 34.47% and the rest is residue of 29.93%. The thermal degradation temperature used was 75ºC to 400ºC. This produced fuel can be used for feedstock refinery for potential energy generation (45).

5.11 Iron Oxide Catalyst An attempt was made to convert a waste plastic mixture containing PP and PS into a light grade fuel (46). The laboratory-scale experiments were done at a temperature range of 180ºC to 430ºC. A pyrex glass reactor and a pyrex fractional column were used in the experiments. The column temperature of the light grade fractional fuel collection was 65ºC. A total amount of 250 g waste was used and a ferric oxide catalyst was used in an amount of 5% by weight. The run time of the experiment was 5.25 h. The density of the fuel product was found to be 0.72 g ml 1 and the color of the fuel was light yellow and fully transparent. The analysis of the fuel indicated hydrocarbon compounds in the range of C4 to C15 . Also, aromatic-related hydrocarbon compounds such as benzene, toluene, ethylbenzene, and styrene were discovered. The so produced light grade fuel can be used in internal combustion engines and can produce electricity or feed for the refinery industry (46).

5.12 Landfill 5.12.1

Landfill Mining Project

The potential of plastic waste in old landfills as a resource to produce refuse-derived fuel was investigated (47). Old landfill contents at di erent ages of 4-5, 5-10 and over 10 years old were excavated and

Recovery into Fuels 211 sorted. The combustible part consisted mostly of plastics. A high calorific value of the plastic waste of 33.11–43.41 MJ kg 1 was found. Also, a full-scale landfill mining project took place in 2012–2013 in Estonia at the Kudjape landfill (48). As a result of mining, mixed plastic waste was separated from excavated material. After sieving and shredding, the received plastic fraction was washed and dried for further research. The waste plastic may be incinerated for energy and heat recovery or used as solid recovered fuel in the cement industry. However, it may be more favorable to reprocess this material into liquid fuel. A series of experiments were performed to study the pyrolysis of landfill plastic after burial of up to ten years. Mixed plastic was treated thermally by a semi-coking process as used by the thermal treatment of oil shale in Estonia. These studies indicated that oil, gas and solid carbon-rich residue can be received. All of these products are valuable as an energy source. 5.12.2

Slow Pyrolysis

A study concerning fuel oil production by conventional slow pyrolysis using plastic waste from a municipal landfill has been presented (49). Here, the di erent proportions of liquid fuel produced from landfill plastic obtained by non-catalyst conventional slow pyrolysis were studied. The landfill plastic was collected from Warinchamrap municipality landfill in Thailand. In the investigation, the recycling of model and waste products based on PP, LDPE, HDPE, and mixed plastic were examined using conventional slow pyrolysis and distillation methods. The properties of liquid fuel from plastic waste compared to petroleum diesel fuel are shown in Table 5.5. PP was converted into 80% liquid fuel, LDPE to 73% liquid fuel, HDPE to 70% liquid fuel, and mixed plastic to 46% liquid fuel. The distillation liquid fuel included high-quality liquid fuels. The liquid fuels derived from the waste plastic found in the municipal landfill was very similar to petroleum diesel oil (49). The experimental results showed that the reactivity of conventional slow pyrolysis and distillation can be controlled by temperature, time, and energy. The various types of plastic found in the

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Table 5.5 Properties of liquid fuel from plastic waste and petroleum diesel fuel (49). Fuel Type 1

Cal. value [MJ kg ] Viscosity [cSt] Gravity [g cm 3 ] Cetane index Flash point [°C] Distill. temp. [°C] Distill. temp. [°C] Distill. temp. [°C]

Diesel

PP

LDPE

HDPE

Mixed

45.5 3.162 0.834 64 75 250 300 350

40 1.97 0.75 40 25 100 160 270

41.5 2.31 0.78 40 25 100 175 285

42.5 2.42 0.80 51 40 100 210 320

42 2.63 0.80 55 50 100 220 335

municipal landfill were converted into di ering amounts of liquid fuel. 5.12.3

Pyrolysis Oils from Landfill Waste

Waste material pyrolysis has proven useful for the production of pyrolysis oils (50). However, the physical properties and the chemical composition of pyrolysis oils are greatly influenced by the feedstock. It is well established that lignin- and cellulose-rich material produces pyrolysis oils high in aromatic oxygen-containing compounds, whereas pyrolysis oils produced from other sources, such as plastics and household wastes, have been far less characterized. Three fast pyrolysis oils produced from landfill waste, recycled plastics, and pine forestry residue were compared using elemental analysis, FTIR spectroscopy, comprehensive 2D GC, Fourier transform ion cyclotron resonance mass spectrometry, and liquid chromatography (50). Comprehensive 2D GC, Fourier transform ion cyclotron resonance mass spectrometry, and liquid chromatography provide an insight into the chemical composition of pyrolysis oils, whereas FTIR identifies the functional groups. Landfill and plastic pyrolysis oils were found to contain higher hydrocarbon content that resulted from little or no cellulosic material in their feedstock. In contrast, pine pyrolysis oil is more aromatic

Recovery into Fuels 213 and contains a higher abundance of polar species due to the number of oxygen functionalities. The hydrocarbons in a pyrolysis oil from plastics are more saturated than in landfill and pine pyrolysis oils. Due to their lower oxygen content, landfill and plastic pyrolysis oils are more attractive than pine pyrolysis oil as potential fuel candidates (50). 5.12.3.1

Recovery Potential from Landfill Mining

Plastics have been the most consumed materials of human societies in recent decades (51). Meanwhile, they are one of the major products obtained from landfill mining. The characteristics of the landfill mined plastic wastes and their recovery potential have become the key points to determine the feasibility of landfill mining projects. Municipal solid waste samples of di erent storage years have been collected from the landfill. A mechanical screening and manual separation were done to sort out plastic wastes. A typical old landfill of 24 storage years located in central China was used as an example. According to this research, plastic wastes accounted for 10.62 5.12% of the total stored wastes in this old landfill. The types and properties of these materials are collected in Table 5.6. Table 5.6 Plastic waste types in a landfill (51). Type

Amount [%]

Plastic bags (total) White PE plastic bags Colored PE plastic bags Other plastic bags Other plastics (i.e., PP, PVC, PS) Average moisture content Average impurities content Volatile matter Ash Fixed carbon Calorific value MJ kg

1

69.13 11.34 29.77 28.02 30.87 19.96 71.02 87.09 10.84 2.07

4.65 6.31 0.55 1.19 0.85

43.18 1.49

Surface image analysis using scanning electron microscopy showed that normal cleaning techniques had di culty in thor-

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oughly getting rid of all the impurities on the surface of plastic bags excavated from an old landfill, which will impede plastic wastes from being mechanically recycled as renewable materials or being chemically recycled by either pyrolysis, gasification, or hydrogenation. Incineration or treating as residue-derived fuels for recovering energy was found to be the most practical way to process landfill mining plastic wastes under the normal cleaning techniques (51).

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43.

Polymer Waste Management plastics, US Patent 9 080 107, assigned to Clariter IP S.A. (GrandDuchedu, LU), July 14, 2015. A. Podeszfa, B. Karbowy, and B. Samardakiewicz, Apparatus and method for conducting thermolysis of plastic waste in continuous manner, US Patent 8 674 154, assigned to Clariter IP S.A. (Grand-Duche du, LU), March 18, 2014. D. Fra¸czak, B. Karbowy, and B. Samardakiewicz, Apparatus for conducting thermolysis of plastic waste in a continuous manner, US Patent 8 680 349, assigned to Clariter IP S.A. (Grand-Duche Du, LU), March 25, 2014. D. Fra¸czak, B. Karbowy, and B. Samardakiewicz, Apparatus for conducting thermolysis of plastic waste and method of thermolysis in continuous manner, US Patent 9 376 632, assigned to Clariter IP S.A. (Luxembourg, LU), June 28, 2016. K.C. DeWhitt, Systems and methods for recycling plastic, US Patent 8 193 403, assigned to Agilyx Corporation (Tigard, OR), June 5, 2012. K.C. DeWhitt, Systems, and methods for recycling plastic, US Patent 9 145 520, assigned to Agilyx Corporation (Beaverton, OR), September 29, 2015. J.M. Bennett and K.C. DeWhitt, Systems and methods for conditioning synthetic crude oil, US Patent 9 162 944, assigned to Agilyx Corporation (Beaverton, OR), October 20, 2015. S.J. Miller, G.P. Hu man, and N. Shah, Method for conversion of waste plastics to lube oil, US Patent 6 150 577, assigned to Chevron U.S.A., Inc. (Camino Ramon, CA), November 21, 2000. Wikipedia contributors, Viscosity index — Wikipedia, the free encyclopedia, https: en.wikipedia.org w index.php?title Viscosity_index& oldid 832150216, 2018. [Online; accessed 14-April-2018]. ASTM International, Standard practice for calculating viscosity index from kinematic viscosity at 40°C and 100°C, ASTM Standard ASTM D2270-10, ASTM International, West Conshohocken, PA, 2016. S.J. Miller, Process for making high viscosity index lubricating base oils, US Patent 8 480 880, assigned to Chevron U.S.A. Inc. (San Ramon, CA), July 9, 2013. B.E. Stangeland and C.J. Egan, Production of stable lubricating oils by sequential hydrocracking and hydrogenation, US Patent 3 852 207, assigned to Chevron Research Company (San Francisco, CA), December 3, 1974. S.J. Miller, Hydrogenation of a hydrocrackate using a hydrofinishing catalyst comprising palladium, US Patent 4 673 487, assigned to Chevron Research Company (San Francisco, CA), June 16, 1987. A. Kumar and P. Kumar, Method for producing waxes and grease base stocks through catalytic depolymerisation of waste plastics, US

Recovery into Fuels 217

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45. 46. 47.

48.

49. 50. 51.

Patent 8 664 458, assigned to Greenmantra Recycling Technologies Ltd. (Toronto, CA), March 4, 2014. S. Breyer, L. Mekhitarian, B. Rimez, and B. Haut, Waste Management, Vol. 60, p. 363, 2017. Special Thematic Issue: Urban Mining and Circular Economy. M. Sarker and M.M. Rashid, Res. Inven. Int. J. Eng. Sci, Vol. 1, p. 29, 2012. M. Sarker and M.M. Rashid, Int. J. Renew. Energy Technol. Res., Vol. 2, p. 17, 2013. B. Charnnok, P. Kirirat, and S. Chaiprapat, Potential conversion of plastic waste in old landfill to fuel, in KKU International Engineering, Vol. 931 of Advanced Materials Research, pp. 844–848. Trans Tech Publications, 7 2014. D. Suštšik, H. Riisalu, R. Muoni, and M. Kriipsalu, Landfill plastic to liquid oil, in Proceedings from Linnaeus ECO-TECH ’14. Linnaeus University, 2014. C. Santaweesuk and A. Janyalertadun, International Journal of Environmental Science and Development, Vol. 8, p. 168, March 2017. R.L. Ware, S.M. Rowland, R.P. Rodgers, and A.G. Marshall, Energy & Fuels, Vol. 31, p. 8210, 2017. C. Zhou, W. Fang, W. Xu, A. Cao, and R. Wang, Journal of Cleaner Production, Vol. 80, p. 80, 2014.

Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

6 Specific Materials 6.1 Catalysts for Recycling Ine cient primary recycling methods have caused almost all materials to be landfilled as an end-of-life treatment (1). Therefore, the development of cost-e cient chemical recycling methods signifies considerable economic and scientific opportunities. Our future relationship with plastics will rely on two approaches to polymer recycling (1): 1. The design of depolymerization catalysts, and 2. The development of recyclable polymers for targeted applications. Catalysts for depolymerization should be (1): 1. Inexpensive processes competitive with virgin material prices, 2. Stable to air, moisture, and organic or metal salt contaminants, 3. E ective in heterogeneous mixtures, and 4. Highly active for polymer-to-monomer conversion.

6.2 Polyolefins Methods for the characterization of waste polyolefin blends using thermal and imaging techniques aimed at development of products have been described in a monograph (2).

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220 6.2.1

Polymer Waste Management Thermal and Catalytic Conversion

The composition of the gaseous products obtained from the pyrolysis of poly(ethylene) (PE) at 400°C using di erent methods are shown in Table 6.1. Table 6.1 Gaseous products obtained from PE pyrolysis (3, 4). Product

Thermal

Methane Ethane Ethylene Propane Butane C5 C6

22.7 27.4 1.4 26.6 11.0 6.9 2.1

Catalytic 12.4 20.4 2.3 30.4 20.3 5.6 3.3

Hydrocracking 21.1 21.2 0.1 23.7 20.7 7.3 3.8

In the experiments it was found that the optimum thermal cracking temperature of waste polyolefines is 410–430°C, in the case of catalytic process a lower temperature of around 390°C can be used, with reaction time of ca. 1.5 h. More than a 90% yield of gas and liquid fractions with a boiling point lower than 360°C was attained. A dependency was found between the process parameters, feed composition and product yield as well as composition of the obtained fuel fractions (3). 6.2.2

Catalytic Cracking of Polyolefins

The field of the catalytic cracking of polyolefins over solid acids has been reviewed (5, 6). The role that is played by the catalysts toward the synthesis of fuels and chemicals has been detailed, as well as the reaction systems currently used. Initially, conventional solid acids, such as micrometer sized crystal zeolites and silica-alumina, were used to establish the relationship among their activity, selectivity, and deactivation in the polyolefin cracking and the inherent properties of the catalysts, such as acidity and pore structure. However, the occurrence of steric and di usional hindrances for entering the zeolite micropores posed by the bulky nature of the

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polyolefins has highlighted the importance of having easily accessible acid sites, either through mesopores or by a high external surface area. This fact resulted in the investigation of mesoporous materials (Al-MCM-41, Al-SBA-15) and nanozeolites, which allowed an increase in the catalytic activity, especially for poly(propylene) (PP). Further advances arose by the application of hierarchical zeolites. Their bimodal micropore-mesopore size distribution has turned them into the most active catalysts for polymer cracking. Thus, hierarchical zeolites may be regarded as a clear breakthrough in this field. Also, other materials with a high accessibility toward the active sites, such as extra-large pore zeolites, delaminated zeolites, or pillared zeolite nanosheets, can also be considered as potentially promising catalysts. From the commercial point of view, two-step processes seem to be the most feasible option, including a combination of thermal treatments with subsequent catalytic conversion and reforming, which allows the catalytic activity to be preserved against di erent types of deactivation (6). A method for catalytically cracking waste plastics has been presented, wherein the e ciency in decomposition is high (7). The device is shown in Figure 6.1. Even PE composed of linear chain molecules, which is di cult in decomposition, is decomposable at a low temperature. The process is simple since the dechlorination can be achieved at the same time as the catalytically cracking waste plastics in one reaction vessel. Also, oil fractions can be recovered at 50% or more on a net yield basis. The method for catalytically cracking waste plastics has a constitution in which waste plastics are loaded as a raw material into a granular fluid catalytic cracking catalyst heated to a temperature range from 350°C to 500°C inside a reaction vessel, thereby decomposing and gasifying the waste plastics in contact with the fluid catalytic cracking catalyst (7). The catalyst is a zeolite, namely, an acid catalyst.

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Figure 6.1 Device for catalytically cracking waste plastics (7).

6.2.2.1

Catalyst Deactivation

The deactivation of three di erent catalysts used in the cracking of high density poly(ethylene) (HDPE) has been compared (8). The catalysts used were HZSM-5, Hß and HY zeolites agglomerated with bentonite and alumina. The reactions have been carried out in a conical spouted bed reactor (CSBR) at 500°C, and as plastic material HDPE was fed in a continuous mode of 1 g min 1 for up to 15 h of reaction time. The HZSM-5 zeolite catalyst showed high yields of C2 –C4 olefins of 57%. Moreover, it is the one least influenced by deactivation throughout the run, which is explained by the lower deterioration of its physical properties and acidity. The results of temperature program combustion and transmission electron microscopy show that the growth of coke is hindered in the HZSM-5 zeolite pore structure. The high N2 flow rate used in the CSBR enhances coke precursor circulation towards the outside of the zeolite crystal channels (8). When the pore diameter of the zeolite is increased, bimolecular reactions (hydrogen transfer and oligomerizations), condensations and cyclizations are enhanced, yielding a more aromatic coke (9). In addition, the pore topology of the HZSM-5 zeolite improves the

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flow of coke precursors, also favored by the high flow rate of N2 to the outside of the catalyst. The HZSM-5 catalyst preserves its activity for a longer time of reaction. The catalytic and thermal cracking of PE waste were investigated in continued tube reactor system (10). HZSM-5 and equilibrium fluid catalytic cracking (FCC) type catalysts were tested. A SEM microgram of FCC is shown in Figure 6.2 and a SEM microgram of coked FCCI is shown in Figure 6.3.

Figure 6.2 SEM microgram of FCC, reprinted from (10) with permission from Elsevier.

Both the resistance to deactivation and the regeneration process of the catalyst were studied. A reaction temperature of 545°C and a residence time of 20 min were used for the cracking treatment. The reaction products were analyzed and the textural properties of catalysts were also determined (10). It was found that after the first reaction run the FCC catalyst lost 75% of its cracking activity. On the other hand, in the case of the HZSM-5 catalyst, the rate of deactivation was higher. The cracking activity of the catalyst could be improved by a regeneration process with only 2%–3% compared to the coked catalyst. Also, an isomerization e ect of the catalysts was observed. The

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Figure 6.3 SEM microgram of coked FCC, reprinted from (10) with permission from Elsevier.

e ect of the coked FCC catalyst could be improved by the regeneration process with 50%; in the case of HZSM-5 it was only 25% (10). 6.2.2.2

Effect of the Acidity

The e ect of the acidity of the HZSM-5 zeolite catalyst on the cracking of high density PE in a conical spouted bed reactor has also been elucidated (11). HDPE has been pyrolyzed at 500°C in a conical spouted bed reactor with two catalysts prepared with HZSM-5 zeolites with SiO2 Al2 O3 ratios of 30 and 80. The HDPE was fed continuously to the catalyst bed. The results showed a good performance of the conical spouted bed reactor in minimizing the limitations of the physical steps of the process. The deactivation of the catalysts is very low and it could be demonstrated that the moderation of the acidity is useful in modifying the product distribution. The SiO2 Al2 O3 ratio increment involves a decrease in the total acidity and in the acid strength, resulting in a higher yield of low molecular weight olefins and that of the non-aromatic fraction, and a decrease in the yields of aromatic components and C1 –C4 para ns. The coke deposited on the catalyst was heterogeneous in nature

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and was constituted by two types of coke, which are deposited on the exterior and the interior of the crystalline channels of the HZSM-5 zeolite. The evolution of the coke is attenuated as the SiO2 Al2 O3 ratio of the zeolite is increased (11). 6.2.3

Fast Pyroylysis of Polyolefin Wastes

A mixture of post-commercial polyolefin waste was pyrolyzed over various microporous and mesoporous catalysts using a fluidizedbed reactor operating isothermally at ambient pressure (12). The yield of the volatile hydrocarbons with zeolitic nano-catalysts (n-ZSM-5 > n-MOR > n-USY) were higher than with non-zeolitic catalysts (MCM-41 > ASA). MCM-41 with large mesopores and ASA with weaker acid sites resulted in a highly olefinic product mixture with a wide carbon number distribution, whereas n-USY yielded a saturate-rich product mixture with a wide carbon number distribution and substantial coke levels. A model based on kinetic and mechanistic considerations which take into account chemical reactions and catalyst deactivation for the catalytic degradation of commingled polyolefin waste has been investigated (12). This model represents the benefits of product selectivity for the chemical composition, such as alkanes, alkenes, aromatics and coke, in relation to the performance and the particle size selection of the catalyst used as well as the e ect of the fluidizing gas and reaction temperature. 6.2.4

Low Density Poly(ethylene)

A thermogravimetric analysis (TGA) curve of poly(ethylene) is shown in Figure 6.4. Used low density poly(ethylene) (LDPE) samples were catalytically pyrolyzed in a batch reactor under atmospheric pressure (13). For the maximum conversion into chemicals, which could be used for feedstock recovery, optimum conditions such as temperature, catalyst weight and reaction time were optimized. Also, a wide range of acidic and basic catalysts, like silica, calcium carbide, alumina, magnesium oxide, zinc oxide and homogeneous mixture of silica and alumina, were tested.

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100

Weight/[%]

80

60

40

20

0 100

200

300

400

500

600

Temperature/[ C]

Figure 6.4 TGA curve of poly(ethylene) (13).

In the case of thermal pyrolysis, the hydrocarbon chain is cracked into free radicals in the case of a high temperature. These free radicals are highly unstable and undergo either a process of chain rearrangement or fission of the carbon-carbon bond at the β position, as shown in Figure 6.5.

CH3

+

CH3

CH2

CH3

CH2

+

CH2

CH2

CH3

CH2

CH2

CH3

CH2

+

CH3

CH2

CH2

CH2

+

CH3

CH3

CH4

CH2

CH2

+

+

CH3

CH2

H

CH2

CH3

CH3

Figure 6.5 Chain cracking in the case of thermal pyrolysis (13).

On the other hand, in the case of catalytic pyrolysis, the hydrocarbon chain is broken down with the help of catalyst in the presence of heat into either a carbocation or a carbanion. This is shown in Figure 6.6. Though the catalyst CaC2 was better with respect to reaction time, the e ciency of conversion into liquid for SiO2 as catalyst was found

Specific Materials

CH3

CH3

CH3

CH3

CH3

+

CH3

CH2

CH3

CH2

CH3

CH3

CH3

CH4

CH2

+

+

CH2

227

CH2

+

+

CH3

CH2

H

CH2

CH2

+

CH3

CH3

Figure 6.6 Chain cracking in the case of catalytic pyrolysis (13).

to be maximum at optimum conditions. These two catalysts could be chosen as suitable catalysts for the catalytic pyrolysis of LDPE. The results of the column separation using di erent solvents indicate that the oxide-containing catalyst could be best suited for selective conversion into polar and aromatic products while the CaC2 catalyst could be adopted for the selective conversion into aliphatic products (13). The liquid products obtained from catalytic pyrolysis were also characterized by physical and chemical tests. Among the physical tests, density, specific gravity, API gravity, viscosity, kinematic viscosity, aniline point, flash point, Watson characterization constant, freezing point, diesel index, refractive index, gross calorific value, net calorific value and ASTM distillation were determined according to IP and ASTM standard methods for fuel values. Here it was observed that the results for the liquid fractions are comparable with the standard results of physical tests for gasoline, kerosene and diesel fuel oil. From the bromine water and KMnO4 tests it was observed that the obtained liquid is a mixture of olefins and aromatic hydrocarbons. This was further confirmed by Bromine number tests. The values of which lie in the range of 0.1 g ml 1 to 12.8 g ml 1 , which are in the range for an olefin mixture. Phenol and carbonyl contents were quantified using UV and visible spectroscopy and the values are in the range of 1 μ g ml 1 to 8920 μ g ml 1 and 5 μ g ml 1 to 169 μ g ml 1 for both phenols and carbonyls, respectively.

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The components of the di erent hydrocarbons in the oil mixture could be separated by column chromatography and fractional distillation followed by a characterization with Fourier transform infrared (FTIR) spectroscopy (13). The interpretation of the FTIR spectra indicated that the catalytic pyrolysis of LDPE leads to the formation of a complex mixture of alkanes, alkenes, carbonyl group containing compounds, like aldehydes, ketones, aromatic compounds, and substituted aromatic compounds like phenols. From these results it could be concluded that the catalytic pyrolysis of LDPE leads to a valuable resource recovery and reduction of waste problem (13).

6.2.4.1

Prodegradants

The e ect of degraded plastic with prodegradants on the properties of LDPE was studied (14). A mixture of LDPE with 5% of a prodegradant (oxo-degradable) additive was prepared by melt processing using a mixer chamber. Then, the degradation of the mixtures was evaluated by exposing the oxo-degradable LDPE in a Xenon arc chamber for 300 h. The degraded material was characterized by FTIR in order to assess the carbonyl index and the hydroperoxide band. Then, di erent percentages of the degraded material of 1%, 5%, 10%, 20%, and 50% were incorporated into the neat LDPE. Mechanical and rheological tests were carried out to evaluate the recycling process of these blends. It could be shown that the increment of the content of the degraded material in the neat LDPE decreased the mechanical strength and the processability of blends due to the imminent thermal degradation. All the test results showed that the incorporation of the degraded material causes a considerable reduction in the matrix properties during the reprocessing. Nevertheless, at low concentrations, the properties of the oxo-degradable blends were found to be similar to the neat LDPE (14).

Specific Materials 6.2.4.2

229

Zeolite Catalysts

Low density poly(ethylene) was converted into hydrocarbons over Zn- and H-ZSM-11 zeolite catalysts in a fixed-bed reactor during 20 min and 60 min reaction time, 0.5 and 2.0 polymer to catalyst mass ratio at 500°C (15). The zeolites were synthesized by conventional techniques and characterized by X-ray di raction (XRD), pyridine FTIR and N2 adsorption. The adsorbed pyridine spectra demonstrated that new Lewis sites were formed after Zn exchange, and that the relationship between Lewis and Brønsted sites in the ZnZSM-11 zeolite (3.53) was much higher than that in the H-ZSM-11 zeolite (0.09). Thermal analytical studies confirmed that the temperature of decomposition of the polymer can be decreased as much as about 145°C when the catalysts were added. As compared to the thermal degradation, the catalytic conversion produced less solid residues and much higher amounts of gas and liquid hydrocarbons. The catalysts showed di erent yield profiles: the H-ZSM-11 zeolite yielded more gases, while the Zn-ZSM-11 zeolite yielded more liquid products. Notably, over Zn-ZSM-11 zeolite, these liquid products were mainly aromatic, and depending on experimental conditions (higher temperature, longer reaction time, smaller polymer catalyst relationship), aromatic selectivity could be increased to almost 100% (15). The product distribution in the conversion of LDPE over Zn-ZSM-11 catalyst is shown in Table 6.2. Here, the reaction temperature was 500°C and the reaction time was 60 min. Table 6.2 Product distributions from Zn-ZSM-11 catalyzed pyrolysis waste di erent ratios of plastic waste (15). Polymer catalyst ratio Gaseous Liquid Aromatics

0.5 1 21 Yield [%] 40.06 55.12 52.98

31.09 67.82 21.95

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6.2.4.3

Decrosslinking Extrusion

Among various polymer wastes, management of crosslinked plastics is a major environmental problem requiring a solution (16). Among the various crosslinked plastics, the recycling of crosslinked PE materials is of great importance due to the presence of a threedimensional network. Ultrasonically Aided Extrusion. Environmentally friendly technologies have been developed for decrosslinking of crosslinked polymers based on ultrasonically assisted single screw extruders and twin screw extruders (16). In particular, the decrosslinking of peroxide crosslinked HDPE and LDPE using an ultrasonic single screw extruder and a twin screw extruder has been investigated. Barrel pressure, die pressure and ultrasonic power consumption during extrusion were recorded. Swelling, rheological, thermal analysis and tensile tests were used to elucidate the structure-property relationships of decrosslinked PEs (16). The frequency dependencies of the storage and loss moduli, complex viscosity and tangent loss of the polymers and their decrosslinked networks can be described by the post-critical gel model with its parameters correlated with gel fraction and crosslinking density. The dynamic, thermal and tensile properties of the decrosslinked samples are greatly a ected by the type of preferential bond breakage. It was found that the decrosslinking of LDPE is more di cult than that of HDPE. An analysis based on the Horikx function (17) showed a highly preferential breakage of the crosslinks during decrosslinking of HDPE (16). In contrast to decrosslinking of HDPE, the presence of long-chain branching in LDPE was found to lead to the breakage of its main chains during decrosslinking. An improvement and a reduction in mechanical properties of the decrosslinked polymers are observed in comparison with those of the crosslinked virgin polymers. These di erences occur due to the occurrence of a highly preferential breakage of the crosslinks during ultrasonic decrosslinking (16). Also, a process model for the ultrasonic decrosslinking of peroxide crosslinked PE has been proposed (18,19). The model was based

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on a model that describes the ultrasonic devulcanization of rubber vulcanizates under static conditions. The bubble cavitation during ultrasonic wave propagation in a viscoelastic solid containing small concentration of voids has been considered. The ultrasonic power consumption and the acoustic pressure in a bubble filled polymer is calculated based on linear acoustic analysis. The rupture of network is modeled by considering the breakage of main chains caused by the large deformation arising during the bubble oscillation. The model does not require kinetic parameters assigned to describe the rupture of the network. Supercritical Decrosslinking Extrusion. It has been shown that an extrusion process can be used as a continuous reactor for the recycling of crosslinked PE via a supercritical methanol decrosslinking reaction (20). A multistage single screw extruder with a methanol injection pump was customized for the continuous supercritical decrosslinking reaction. The reaction temperature ranged from 360°C to 390°C. The amount of methanol feed was varied from 0 to 7 ml min 1 . The extruder provided the crosslinked polymers with the supercritical conditions of methanol during continuous process. The gel content of PE decreased with the increase in the reaction temperature and methanol content. Although PE experienced supercritical methanol for less than 2 min retention time in the continuous supercritical extruder, it was completely decrosslinked above 390°C at a methanol feeding rate of 7 ml min 1 (20). A kinetic study was done on the supercritical decrosslinking reaction of silane-crosslinked PE in a continuous process (21). The decrosslinking reaction in a continuous process corresponded to the first order reaction model in which the reaction rate was linearly proportional to the gel content. The residual gel content exponentially decreased with reaction time. In addition, various sub- and supercritical fluids with di erent polarity characters were investigated to find a safe alternative medium for continuous decrosslinking of silane-crosslinked PE. Like methanol, all examined fluids, including ethanol, propanol, and water, exhibited a first order reaction kinetics with regard to the gel content in a continuous decrosslinking process. The reaction rate

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constant values for the various fluids at 380°C are summarized in Table 6.3. Table 6.3 Reaction rate constants (22). Fluid Supercritical methanol Supercritical ethanol Supercritical 2-propanol Subcritical water

Rate constant [min 1 ] 2.806 2.569 2.383 2.130

As a nontoxic fluid with a reaction kinetics very comparable to that of methanol, ethanol was found to be the best alternative medium for the continuous decrosslinking reaction of silane-crosslinked PE (22). 6.2.5

High Density Poly(ethylene)

High density poly(ethylene) is one of the largest used commodity plastics due to its vast applications in many fields. Due to its non-biodegradability and short lifetime, HDPE contributes significantly to the problem of municipal waste management. To avert environment pollution of HDPE wastes, they must be recycled and recovered. On the other hand, steady depletion of fossil fuels and increasing energy demands have motivated researchers and technologists to search for and develop di erent energy sources. Waste to energy has been a significant way to utilize the waste sustainably and simultaneously meet the energy demand (4). 6.2.5.1

Atomistic Simulation of Poly(ethylene) Degradation

A comprehensive study of the volatile thermal degradation of HDPE across a temperature range of 300 K to 1823 K was done using molecular dynamics simulation (23). Degradation methods at temperatures higher than around 1373 K generate significant quantities of reducing gases and hydrogen molecules, which are beneficial for the steelmaking industry. The results provide an understanding of phase transformation of HDPE from the solid state to gas that occurs during superheating at

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steelmaking’s electric arc furnace environment. These findings o er a new method for eliminating end-of-life HDPE from landfill (23). 6.2.5.2

Dependence on Pyrolysis Method

Thermal and catalytic degradation using spent FCC catalyst of waste HDPE at 430°C into fuel oil were carried out with a stirred semibatch operation (24). The product yields are dependent on the method of pyrolysis. In Table 6.4 the product yields from di erent pyrolysis methods are collected. These are the yields of gas, liquid and residue obtained from thermal and catalytic degradation of waste HDPE at 430°C. Table 6.4 Product yields from di erent pyrolysis methods (24). Method Thermal degradation Catalytic degradation

Gas [%]

Liquid [%]

Residue [%]

20.0 19.4

75.5 79.7

4.5 0.9

The catalytic degradation had lower degradation temperature, faster liquid product rate and more olefin products as well as shorter molecular weight distributions of gasoline range in the liquid product than thermal degradation. These results confirmed that the catalytic degradation using spent FCC catalyst could be a better alternative method to solve a major environmental problem of waste plastics (24). 6.2.5.3

Batch Pyrolysis

Waste HDPE was collected from the National Institute of Technology Rourkela, Orissa, India campus waste yard (25). The plastic waste was cut into small pieces of ca. 1 cm2 and used in the thermal pyrolysis reaction. The proximate analysis of waste HDPE was done according to ASTM D3173-75 (26) and the ultimate analysis was done by using a CHNS analyzer (Elementar Vario El Cube CHN-O). The calorific value of the raw material was found by using ASTM D5868-10a (27). The pyrolysis setup consisted of a semi-batch reactor made of stainless steel tube with a length of 145 mm, an internal diameter of

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37 mm, and an outer diameter of 41 mm. The device was sealed at one end and had an outlet tube at the other end. The reactor was heated externally by an electric furnace, with the temperature being measured by a thermocouple fixed inside the reactor, and temperature being controlled by an external proportional-integral-derivative (PID) (28) controller. Each pyrolysis reaction was loaded with 20 g of a waste plastics sample. The condensable liquid products wax were collected through the condenser and weighed. After pyrolysis, the solid residue left inside the reactor was weighed. Then the weight of gaseous volatile product was calculated from the material balance. Reactions were carried out at di erent temperatures ranging from 400ºC to 550ºC (25). The proximate and ultimate analysis of the waste HDPE sample showed the following: The volatile matter was 100% in the proximate analysis, due to the absence of ash in the waste HDPE sample. Its degradation occurs with a minimal formation of residue. The oxygen was found to be 5.19% in the ultimate analysis of the waste HDPE. The oxygen in the waste HDPE sample may not be due to the fillers but rather to other ingredients that are added to the resin in the manufacturing of HDPE. The e ect of temperature on the reaction time for the pyrolysis of waste HDPE plastic has been found to be as follows: The pyrolysis reaction rate increased and the reaction time decreased with an increase in temperature. High temperature supports the easy cleavage of bonds and thus speeds up the reaction and lowers the reaction time. HDPE, with a long linear polymer chain with low branching and a high degree of crystallinity, led to high strength properties and thus required more time for decomposition. This shows that temperature has a significant e ect on reaction time and the yield of liquid, wax and gaseous products (25). The yield of liquid was found to be highest at 450ºC. In contrast, highly volatile products are obtained at low temperature. The products obtained at 500ºC and 550ºC are viscous liquid and wax and the product obtained at 600ºC is only wax. The yield of liquid increases as the holding time increases from 1 h to 4 h at temperatures from 400ºC to 450ºC. However, as the holding time increases from 4 h to 6 h, the yield of liquid decreases. The reaction time decreases with an increase in

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temperature. In summary, it has been shown that a simple batch pyrolysis method can convert waste HDPE to liquid hydrocarbon products with a significant yield, which varies with temperature (25). 6.2.5.4

Two-Step Pyrolysis

A two-step process has been used for the selective production of light olefins by the thermal cracking of HDPE (29). The polymer was continuously fed into a CSBR that operated at 500°C. Here a yield of 93% of waxes and C12 –C21 hydrocarbons could be obtained. Then, the volatile product stream was cracked downstream in a multitubular reactor with quartz tubes in the range of 800°C–950°C, with short residence times of 0.016 s to 0.032 s. In this stage, a yield of 77% of light olefins in the range of C2 –C4 could be obtained by operating at 900°C. The maximum yields of ethylene, propylene, and butenes are 40.4%, 19.5%, and 17.5%, respectively. Due to the short residence time of the products in the reactor, the yield of aromatics is only 6.2%. The high light olefin yield occurs due to the excellent performance of both steps. The CSBR allows maximizing the yield of waxes and avoiding defluidization problems. The operating conditions in the multitubular reactor, such as low concentration of the compounds in the volatile stream and short volatile residence times, are suitable for minimizing secondary reactions (29). 6.2.5.5

Co-pyrolysis with Lignite

The pyrolysis of HDPE in an open system was studied (30). Plastic food packing bags were used as a source of HDPE. Pyrolysis was performed at temperatures of 400°C, 450°C, and 500°C, which were chosen based on TGA. The pyrolysis of HDPE yielded liquid, gaseous and solid products. A rise in temperature resulted in an increased conversion of HDPE into liquid and gaseous products. The main constituents of liquid pyrolysates are 1-n-alkenes, n-alkanes and terminal n-dienes (30). The composition of the liquid products indicates that the so-performed pyrolysis of HDPE could not serve as a stand-alone operation for producing gasoline or diesel,

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but preferably as a pretreatment to yield a product to be blended into a refinery or petrochemical feedstream.

The advantage of the liquid pyrolysate in comparison to crude oil is extremely low content of aromatic hydrocarbons and absence of polar compounds. Gaseous products have desirable composition and consist mainly of methane and ethene. Solid residues do not produce ash by combustion and have high calorific values. Co-pyrolysis of HDPE with mineral-rich lignite indicated positive synergetic e ect at 450°C and 500°C, which is reflected through increased experimental yields of liquid and gaseous products in comparison to theoretical ones (30). The co-pyrolysis was performed in a mass ratio of 1:1 of lignite to HDPE. The yields of the pyrolysis products are shown in Table 6.5.

Table 6.5 Yields of the pyrolysis products (30). T [°C]

High density poly(ethylene) Liquid Gas

400 450 500

12.96 21.32 33.94

T [°C]

Lignite Liquid

400 450 500

1.11 1.19 1.20

Solid

7.41 11.51 15.77

79.63 67.17 50.29

Gas

Solid

16.02 19.82 29.08

82.87 78.99 78.22

Lignite High density poly(ethylene) Liquid Gas Solid T [°C] 400 450 500

7.49 15.79 23.95

11.37 21.08 40.01

81.14 63.13 36.04

Some calorific value data from various materials are collected in Table 6.6.

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Table 6.6 Calorific value data (31). Material

Calorific value [MJ kg 1 ]

Recycled or virgin PP Flax fiber Glass fiber PP flax fiber at 30% v v PP glass fiber at 30% v v

6.2.5.6

48.9 20 0 35.02 10.75

Catalytic Degradation

Catalysts. Following, a series of suitable catalyst types are detailed. Also examples of their usages are given. Fluid Catalytic Cracking Catalysts. The catalytic degradation of HDPE was carried out under nitrogen using a laboratory fluidized-bed reactor that was operating at 360°C with a feed ratio of catalyst to polymer of 2:1 and at 450°C with a feed ratio of catalyst to polymer of 6:1 under atmospheric pressure (32). The catalysts used were ZSM-5, US-Y, ASA (amorphous silicaalumina), fresh FCC commercial catalyst (Cat-A) and equilibrium FCC catalysts with di erent levels of metal poisoning. ZSM-5 is a powder form catalyst support, ammonium Y-zeolite. Also, US-Y is a zeolite-based catalyst. The initial results for polymer degradation at 360°C with a catalyst to polymer ratio of 2:1 in a fluidized-bed reactor in terms of the yield of volatile hydrocarbon products were: Model catalysts were greater than commercial FCC catalyst and these were greater than E-Cats. However, when the process conditions more closely resembled the FCC conditions, the fresh commercial FCC catalyst was more favorable in terms of the yield of volatile hydrocarbon products. The degradation of HDPE using E-Cats, although found to be reduced, was similar to ASA with regard to product selectivity and yield. Also, the level of metal contamination did not a ect the generated product stream. A simple economic evaluation of the polymer recycling process has been reported showing that a catalytic system based on E-Cats appears comparable with regard to costs for a commercial thermal cracking plant (32).

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Feedstock recycling of HDPE over FCC catalysts in a ratio of 1:6 was carried out using a laboratory fluidized-bed reactor that was operating at 450°C (33). Fresh and steam deactivated commercial FCC catalysts with different levels of rare earth oxide (REO) were compared as well as the used FCC catalysts with di erent levels of metal poisoning. Fresh FCC catalysts gave the highest results of HDPE degradation in terms of yield of volatile hydrocarbon product. Meanwhile, steamed FCC catalysts and the used FCC catalysts showed similar but lower yields. In summary, the product yields from HDPE cracking showed that the level of metal contamination (nickel and vanadium) did not a ect the product stream generated from polymer cracking. This study showed promising results as an alternative technique for the cracking and recycling of polymer waste (33). A commercial FCC catalyst based on a zeolite active phase has been used in the catalytic pyrolysis of HDPE (34). The experiments have been carried out in a conical spouted bed reactor provided with a feeding system for continuous operation. Di erent treatments have been applied to the catalyst to improve its behavior. The optimization of catalyst steaming and pyrolysis temperature have been investigated in order to maximize the production of a diesel oil fraction. Initially, the performance of the fresh catalyst was studied at 500°C. Here, 52% gas yield, 35% light liquid fraction and a low yield of compounds with higher molecular weight of 13% are obtained. After mild steaming at 760°C for 5 h, the results show a significant improvement with regard to the product distribution. The yield of gas decreases to 22%, and the yield of light liquid is similar to that of the fresh one (38%), whereas the yield of the desired higher molecular weight fraction increases to 38%. The best results have been obtained when a severe steaming is applied to the catalyst at 816°C for 8 h and a reduced pyrolysis temperature of 475°C. Here a significant reduction in the gaseous fraction to 8% is observed. The light liquid fraction has also been found to be reduced to 22%, but the yield of diesel fraction increases to 69% (34). The main components in the C1 to C8 fraction obtained in the

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catalytic pyrolysis of HDPE carried out at 475°C using the severely steamed FCC catalyst are shown in Table 6.7. ZSM-5 and HZSM-5. HDPE was pyrolyzed using various catalysts in a laboratory fluidized-bed reactor operating isothermally at ambient pressure (35). An HZSM-5 catalyzed degradation resulted in much larger amounts of volatile hydrocarbons compared with degradation over non-zeolitic catalysts (MCM-41 and SAHA). When an HZSM-5 was used as a cracking additive in combination with a non-zeolitic catalyst (MCM-41 and SiO2 –Al2 O3 ), the solid mixed catalysts produced less gas with a lower loss of gasoline than HZSM-5. MCM-41 with large mesopores and SAHA with weaker acid sites resulted in a highly olefinic product and gave rise to the broadest carbon range of C3 –C7 . Both SAHA and MCM-41 materials allow bulky reactions to occur, leading to the generation of coke and subsequently deactivation of the catalyst (35). A mixture of post-consumer PE waste (HDPE LDPE) was pyrolyzed over various catalysts using a fluidized-bed reactor operating in the 290°C–430°C range under atmospheric pressure (36). The catalysts that were used in this study are shown in Table 6.8. The yield of volatile hydrocarbons for zeolitic catalysts (HZSM-5 > HUSY > HMOR) gave higher yield than non-zeolitic catalysts (SAHA, MCM-41). The di erences in the yields of products and the distributions of the products can be attributed to the nature of catalyst and the reaction temperature. The product distributions with HZSM-5 contained more olefinic materials with about 60% in the range of C3 –C5 . However, both HMOR and HUSY produced more para nic streams with large amounts of isobutane and both catalysts were deactivated in the course of the degradation. MCM-41 and SAHA showed the lowest conversion and generated an olefin-rich product which rises to the broadest carbon range of C3 –C7 . A kinetic model based on a lumping reaction scheme for the observed products and catalyst deactivation has been investigated. The proposed reaction pathway is shown in Figure 6.7. The model exhibited a good representation of the experimental results (36). When the products of PE waste degradation are compared

240

Polymer Waste Management Table 6.7 Main products (C1–C8) obtained from HDPE pyrolysis (34). Product Methane Ethene Propane Propene n-Butane i-Butane 2-Methyl-1-propene Other butenes 2-Methylbutane 3-Methyl-1-butene n-Pentane 1,4-Hexadiene Cyclohexene 2-Ethyl-3-metilbutene 2,4-Dimethyl-1-pentene 3-Ethyl-1-pentene 1,3-Dimethylcyclopentane Methylhexanes Methylhexenes Methylhexadienes Toluene Ethylmethylcyclopentanes Dimethylhexanes Dimethylhexenes 2-Ethyl-3-hexene 2,5-Dimethyl-1,5-hexadiene Methylheptanes 3-Methylenheptane Methylheptenes Octenes Ethylbenzene Xylenes 2,6-Dimethyl-2-heptene 3,3-Dimethyl-1,6-heptadiene Methyloctenes n-Nonane (1-Methylethyl)benzene Trimethylbenzenes Ethylmethylbenzenes

Yield [%] 0.23 0.86 0.02 2.40 0.87 0.64 0.13 3.08 0.74 0.54 0.22 0.13 0.08 0.19 0.10 0.16 0.07 0.60 0.41 0.19 0.42 0.13 0.12 0.39 0.20 0.08 0.29 0.15 0.47 0.59 0.19 1.28 0.13 0.09 0.10 0.20 0.33 2.46 1.03

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Table 6.8 Catalysts used in the catalytic degradation of PE PP polymer waste (36). Catalyst

Micropore size [nm]

HUSY HZSM-5 HMOR SAHA MCM-41

0.74 0.55 0.65 3.15 4.2

BET area [cm2 g 1 ] 603 397 562 274 815

Si Al ratio 6.0 25 6.3 2.6 17.5

Light gases

Polymer

Gasoline

Coke

Figure 6.7 Reaction pathway of the lumping reaction (36).

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over the various cracking catalysts, the results reflect the di ering cracking e ect of the zeolites compared with the non-zeolitic materials. Much higher involatile residues were observed when using SAHA as the catalyst in comparison to HZSM-5 and HUSY. This can be explained in terms of the nature of the acid sites. SAHA is made up predominantly of weaker Lewis sites compared to the predominantly more acidic Brønsted sites found in the zeolite-based catalysts. Thus, both acidity and di usion constraints within the individual micropores of each catalyst can play significant roles in the observed product distribution. Two series of hierarchical nanocrystalline ZSM-5 zeolites were prepared by di erent synthesis strategies (37): At low temperature and from silanized seeds. In particular, the catalysts were prepared by using three silanization agents: Isobutyltriethoxysilane, 3-aminopropyl-trimethoxysilane, and phenylaminopropyltrimethoxysilane. The low temperature synthesis of ZSM-5 aggregates has been detailed elsewhere (38). ZSM-5 can be formed by aggregates of nanocrystals with ultra-small crystal size of 10 nm to 20 nm. A hydrothermal crystallization technique is used that results in clear synthesis mixtures at low temperatures of 70°C to 90°C under atmospheric pressure. Compared with the conventional autoclave treatment, this method leads to a significant reduction in the crystal size, although with lower zeolite yields, which has been assigned to the mild conditions used, i.e., low temperature and atmospheric pressure. The nanosized ZSM-5 exhibits a very high external surface area of typically around 200 m2 g 1 , as a consequence of its small crystallites. This makes this material a potentially interesting catalyst for the conversion of bulky molecules (38). TEM micrographs of calcined hierarchical ZSM-5 samples indicate that they are formed by aggregates of small nanounits. The crystalline nanounits are small with sizes in the range of 5 nm to 20 nm, depending on the sample. The TEM micrographs are shown in Figure 6.8. The external surface areas ranged from 150 m2 g 1 to 250 m2 g 1 (37). The catalysts were tested for the cracking of pure LDPE and HDPE at 340°C and of waste PE at 360°C. The hierarchical zeolites showed quite a higher activity, with values even six times higher than a standard nanocrystalline sample

Specific Materials

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Figure 6.8 TEM micrographs of calcined hierarchical ZSM-5 samples, reprinted from (37), with permission from Elsevier.

used as reference, i.e., n-HZSM-5. The activity values decreased from LDPE to HDPE due to the occurrence of some degree of branching in the former polymer, which act as preferential cracking sites. The major products were C1 to C4 hydrocarbons (in the range of 30% to 70%, mostly C3 to C4 olefins) and C5 to C12 hydrocarbons in the range of 20% to 60%. The share of these compounds depends on both the polyolefin type and the catalyst type (37). The amount of C13 to C40 hydrocarbons was found to be practically negligible (smaller than 1%) due to the high acid strength of the zeolites, which promotes end-chain cracking reactions. In summary, hierarchical nanocrystalline HZSM-5 zeolites prepared from silanized protozeolitic units showed higher activities than the hierarchical nanocrystalline HZSM-5 samples synthesized at low temperature and atmospheric pressure. The di erences were especially remarkable in the case of waste PE cracking. These results were ascribed to the stronger acidity of the hierarchical zeolite samples that were prepared from silanized seeds (37). Aromatization of Waste over HZSM-5 with Metals. The incorporation of metals into a catalyst can enhance the production

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of upgraded fuels and chemicals in the product stream. Metals incorporated on several catalyst support materials, such as zeolite, activated carbon and silica-alumina, for pyrolysis-catalysis of plastic waste for the production of fuel and chemicals have been investigated (39–41). Pyrolysis-catalysis of HDPE was carried out in a fixed-bed, twostage reactor for the production of upgraded aromatic pyrolysis oils (42). The tested catalysts were Y-zeolite impregnated with transitionmetal promoters with a 1% and 5% metal loading of Ni, Fe, Mo, Ga, Ru, and Co to determine the influence on aromatic fuel composition. The pyrolysis of the HDPE took place at 600°C in the first stage of the reactor system and the evolved pyrolysis gases were passed to the second stage catalytic reactor, which had been preheated to 600°C. The loading of the metals on the Y-zeolite catalyst resulted in a higher production of aromatic hydrocarbons in the product oil with a greater concentration of single-ring aromatic hydrocarbons. The single-ring aromatic compounds consisted of mainly toluene, ethylbenzene and xylenes. The two-ring hydrocarbons were mainly naphthalene and their alkylated derivatives. In addition, there was a reduction in the production of multiple-ring aromatic compounds such as phenanthrene and pyrene. The surface area and the porosity of the prepared metal-Y-zeolite catalysts are shown in Table 6.9. Table 6.9 Surface area and porosity of the catalysts (42). Catalysts Metal content [%] Ni-Y-zeolite (NiYZ) Fe-Y-zeolite (FeYZ) Mo-Y-zeolite (MoYZ) Ga-Y-zeolite (GaYZ) Ru-Y-zeolite (RuYZ) Co-Y-zeolite (Co-YZ)

BET surface area [m2 g 1 ] 1

5

357 340 422 424 405 431

311 293 376 396 418 383

Pore volume [cm3 g 1 ]

Pore size [nm]

1

5

1

5

0.23 0.22 0.26 0.27 0.25 0.27

0.19 0.20 0.25 0.25 0.27 0.25

2.02 1.99 1.71 1.86 1.72 1.74

2.19 2.37 2.02 1.84 2.13 2.01

The addition of the promoter metals appeared to have only a small influence on aromatic oil content, but they increased the hydrogen yield from the HDPE. However, there was significant carbon deposition on the catalysts in the range of 14% to 22% for the 1%

Specific Materials

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metal-Y-zeolite catalysts, which increased to 18%–26% for the 5% metal-Y-zeolite catalysts (42). Scanning electron microscopy (SEM) imaging was used to characterize the reacted metal-Y-zeolite catalysts. These images identify the types of carbon deposited on the reacted catalyst. The SEM images of the modified zeolites are shown in Figure 6.9. Noticeable on these micrographs are the filamentous-type deposits of carbon on the catalyst surface, particularly in the samples with a 5% metal loading. Aromatization of Waste over HZSM-5 with Gallium Oxides. H-ZSM-5 zeolite-supported gallium oxides were studied as aromatization catalysts for a pyrolysate from a polyolefin (43). The catalysts were prepared by a conventional physical mixing method with a gallium content of 1.0% and 4.5% and were reduced in flowing hydrogen at 585°C. To test the activity of these catalysts, a polyolefin sample was pyrolyzed and passed over a heated catalyst layer. The product was analyzed by gas chromatography (GC) mass spectroscopy (MS). A continuous flow fixed-bed reactor was used for aromatization of a model gas of the polyolefin pyrolysate. For chlorine-free sources at 450°C, the catalyst with only 1.0% gallium exhibited activity comparable to a gallium silicate catalyst. For chlorine-contaminated sources, the catalyst with 4.5% gallium sustained catalytic activity for long periods. From the results of the activity tests, it was found that zeolite-supported gallium catalysts prepared by the physical mixing method are suitable for converting polyolefin into aromatic hydrocarbons (43). Nanocrystalline β-Zeolite. Three pairs of the proton form of β-zeolites with similar Si Al ratios, but notably di erent crystallite sizes of 10 nm to 1500 nm, were prepared in basic or fluoride media and tested as catalysts for the liquid phase degradation of HDPE at 380°C and atmospheric pressure (44). Among these catalysts, a nanocrystalline β-zeolite with the lowest Si Al ratio of 10.7 and the smallest crystallite size of 10 nm was found to show a high degradation activity and also a remarkable high yield

246

Polymer Waste Management

Figure 6.9 Scanning electron microscope images of (a) the Y-zeolite and (b) the 1 w% Co-Y-zeolite and (c) the 5% Co-Y-zeolite after pyrolysis-catalysis of the high density poly(ethylene); reprinted from (42) open access from Elsevier.

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of liquid products of ca. 80%, together with a high selectiveness for C7 to C12 hydrocarbons. This was explained on the basis of its very large external surface area and its high acidity in comparison to the other β-zeolites that were examined (44). HUSY Zeolite Catalysts. HUSY zeolites are hierarchical H-style ultra-stable Y-zeolites (45). For example, hierarchical H-style ultra-stable Y-zeolites with abundant interconnected mesopores have been prepared using a sequential post-synthesis strategy that includes steaming dealumination and mixed-alkali desilication. Zeolite Y is a synthetic material, similar to faujasite, a natural occurring material (46). The catalytic decomposition processes of LDPE and HDPE have been studied using a HUSY zeolite as catalyst in a batch reactor under dynamic conditions (47). The evolution of the gaseous and condensed products that were produced at di erent temperatures was analyzed and compared to that obtained under similar conditions in the thermal pyrolysis of LDPE and HDPE. The behavior of the gases generated from both poly(ethylene)s was similar, olefins being the more abundant species. Great changes were observed in the composition of the gases evolved at di erent temperatures. Isopara ns and olefins showed two maxima at low and high temperatures, whereas the remaining compounds generated presented only one maximum at high temperatures. The analysis of the condensed products revealed some di erences between the two poly(ethylene) types at the end of the process. Two maxima, one at low and another at high temperatures, appeared in the catalytic pyrolysis of HDPE, where isopara ns and aromatics were the most abundant condensed products obtained at each maximum. However, in the case of LDPE, n-para ns were the main products at the very end of the process. These di erent outcomes could be related to the progressive deactivation of the zeolite (47).

Barium Carbonate. Waste HDPE was degraded thermally and catalytically using BaCO3 as a catalyst under di erent conditions of temperature, ratio of catalyst to polymer and time (48). The oil collected at optimum conditions of 450°C, ratio of catalyst to

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polymer of 0.1, and 2 h reaction time was fractionated at di erent temperatures. The fuel property of the fractions and the parent oil was evaluated according to their physicochemical parameters for fuel tests. The results were compared with the standard values for gasoline, kerosene and diesel oil. Boiling point distribution curves were plotted from the gas chromatographic study of the samples and compared with that of the standard gasoline, kerosene, and diesel. The oil samples were analyzed using GC MS in order to find out their composition. The physical parameters and the composition of the parent oil and its fractions support the resemblance of the samples with standard fuel oils. The light fractions best match with gasoline, the middle fractions match with kerosene and the heavier fractions match with diesel oil in almost all of the characteristic properties (48). The composition of the catalytic oil fractionated at several temperatures have been detailed (48). The oil fraction distilled at 200°C was found to contain hydrocarbons from heptane to heptadecane. The oil fraction distilled at 200°C was found to contain hydrocarbons from 1-decene to heneicosane. The oil fraction distilled at 300°C was found to contain hydrocarbons from cyclopentane to heptacosane. Thus, increasing the distillation temperature, the composition of the oil was altered due to inclusion of some heavier hydrocarbons distilled at higher temperature. In summary, the study indicated that the use of BaCO3 as a catalyst for the conversion of HDPE into fuel oil greatly reduces the formation of wax (48). Azoisobutylnitrile. The pyrolysis of LDPE, HDPE, PP, poly(ethylene terephthalate) (PET) and poly(styrene) (PS) plastics with 2,2 -azobisisobutyronitrile (AIBN) was done individually under nitrogen atmosphere (49). A series of single (plastic AIBN) and binary (mixed plastics AIBN) compositions were carried out in a 25 cm3 micro-autoclave reactor. The optimum conditions for this study were: 5% AIBN by weight of total plastics, 60 min, 45 bar, and 420°C. It was found that HDPE, LDPE, and PP showed a maximum cracking and produced the highest amounts of liquid and gaseous products. The pyrolysis

Specific Materials

249

of PET and PS plastics with AIBN yielded a comparatively significant amount of insoluble organic materials. In other reactions, fixed ratios of mixed plastics were pyrolyzed with AIBN that showed excellent yields of liquid hydrocarbons. These results showed a very significant increase in the liquid portions of the products by the usage of AIBN in the pyrolysis of plastics. The use of AIBN in the pyrolysis of plastics seems to be feasible and an environmental friendly alternative for maximizing the liquid fuels or chemical feedstocks in higher amounts (49). Silicon Mesoporous Molecular Sieve. A K2 O Si-MCM-41 molecular sieve was prepared by impregnating Si-MCM-41 with KNO3 (50). The obtained material was characterized by XRD, FTIR, TEM, and N2Ad De. The results indicated that K2 O Si-MCM-41 has a typical mesoporous structure, and the long-range order of K2 O MCM-41 became poorer with the increase of K2 O. The catalytic properties of K2 O Si-MCM-41 were investigated in the course of pyrolysis with PS. The results were compared with those obtained using CaO, Si-MCM-41, and Al-MCM-41 as catalysts. It was shown that K2 O Si-MCM-41 has a better catalytic activity. The e ect of preparation conditions on the activity of K2 O Si-MCM-41 was discussed. KNO3 was almost completely decomposed into K2 O at an optimum calcination temperature of 600°C. Under the optimum conditions of mass percentage of K2 O 9%, temperature 400°C, a ratio of catalyst to polymer of 0.02 and a reaction time of 0.5 h, the conversion of PS was 90.53%, the yield of liquid products was 85.67%, and the yield of styrene reached 69.02% (50). Waste Catalysts. The recycling technologies of spent FCC catalysts have been reviewed (51). Spent FCC catalysts can be used as a cement or mortar additive in order to partially reduce the amount of fresh cement without a ecting its final chemical and mechanical properties. At the moment, this is the most investigated route for such spent catalysts (51). The reuse of industrial by-products or waste used for concrete production o ers many benefits such as:

250

Polymer Waste Management 1. Environmental benefits from exploitation of natural resources, less disposal issues, energy saving, reduction of greenhouse gas emissions, 2. Economic benefits since by-products are cheaper compared to original materials and can be used as secondary raw materials, and 3. Technological advantages due to the enhancement of several properties of mortars and concrete such as long-term strength development, sulfate resistance and rheological properties.

The calcination of spent FCC catalysts at 450°C to 850°C increased the pozzolanic activity of the materials. Mortars with 10% calcined catalyst at a curing time of 3 d to 28 d exhibited a strength of 8–18% greater than that of untreated samples. Catalytic cracking of HDPE in the presence of FCC catalysts with a 1:6 ratio was carried out using a laboratory fluidized-bed reactor operating at 450°C (52). Two fresh and two steam deactivated commercial FCC catalysts with di erent levels of rare earth oxide (REO) were compared, as well as the two used FCC catalysts (E-Cats) with di erent levels of metal poisoning. Also, inert microspheres (MS3) were used as a fluidizing agent to compare with thermal cracking process at a BP pilot plant in Grangemouth, Scotland, which used sand as its fluidizing agent. The results of the HDPE degradation in terms of yield of volatile hydrocarbon product are fresh FCC catalysts, steamed FCC catalysts, and used FCC catalysts. The thermal cracking process using MS3 showed a product distribution at 450°C, as collected in Table 6.10. Table 6.10 Product distribution (52). Product Wax Hydrocarbon gases Gasoline Coke Nonvolatile products

Amount [%] by weight 46 14 8 0.1 32

Specific Materials

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The overall product distributions of fresh, steamed and used FCC catalysts are shown in Table 6.11. Table 6.11 Overall product distributions of fresh, steamed and used FCC catalysts (52). Product type

Cat-F

Product distribution [%] Cat-g Cat-FS Cat-GS ECat-1

Ecat-2

Gaseous Liquid Coke Wax Nonvolatile

62.3 9.0 8.1 0 20.6

59.7 6.8 10.5 0 23.1

62.8 1.3 1.8 0 34.1

41.8 7.2 4.4 0 46.6

46.3 7.8 5.9 0 40.0

64.5 1.4 1.5 0 32.6

The compositions of the catalysts used in Table 6.11 have been reported in detail (52). E-Cat 1 and E-Cat 2 contain a lot of nickel and vanadium. E-Cats are alkene-rich compared with steam deactivated Cat-FS and Cat-GS; the E-Cats showed negligible loss in overall conversion of HDPE due to metal contamination from a previous FCC process. In general, the product yields from HDPE cracking showed that the level of metal contamination (nickel and vanadium) did not a ect the product stream generated from polymer cracking (52). In summary, promising results as an alternative technique for the cracking and recycling of polymer waste have been found. A mixture of post-consumer wastes of PE, PP, PS with poly(vinyl chloride) (PVC) waste was pyrolyzed over cracking catalysts using a fluidizing reaction system in a FCC process operating isothermally at ambient pressure (53). The main products of post-consumer waste plastics are shown in Table 6.12. The degradation was performed at a reaction temperature of 390°C over various cracking catalysts. The fluidizing nitrogen rate was 600 ml min 1 , at a catalyst to plastic ratio of 30%, a catalyst particle size of 125 μm to 180 μm, and a total time of collection of 60 min. The influences of the catalyst types and the reaction conditions, including reaction temperatures, ratios of catalyst to plastic feed, flow rates of fluidizing gas and catalyst particle sizes, was examined. A model based on kinetic and mechanistic considerations

252

Polymer Waste Management

Table 6.12 Main products of post-consumer waste plastics (53). Yields [%] Gaseous Liquid Residue Involatile residue Coke HCl

RCat-s1

Silicalite

82.4 3.8 11.7 9.3 2.4 2.1

13.5 1.4 85.1 83.2 1.9 1.4

HUSY

ZSM-5

SAHA

85.6 3.3 8.6 4.1 4.5 2.5

88.3 3.4 6.4 4.9 1.5 1.9

84.1 3.6 10.5 8.4 2.1 1.8

associated with chemical reactions and catalyst deactivation in the acid-catalyzed degradation of plastics has been developed. The results of this study were found to be useful for determining the e ects of catalyst types and reaction conditions on both the product distribution and selectivity from commingled plastic waste, and especially for the utilization of post-use commercial FCC recycled catalysts for producing valuable hydrocarbons in a fluidizing cracking process. Moreover, the use of this recycled modified FCC spent catalyst (RCat-s1) together with an optimal reaction system can be an adequate option, since it may lead to a cheaper process with valuable products and can also be further used as a dual recycling of chlorine-containing hazardous waste plastics and a post-use commercial catalyst waste from FCC refinery (53). Recovery of Precious Metals from Spent Catalysts. Processes for the recovery of the precious metals present in spent catalysts have been described in the literature. Particularly representative thereof are those which are principally based on a stage of acidic leaching of the spent catalysts containing the species to be recovered, this stage typically being carried out in the presence of an oxidizing agent. Precious metal values, e.g., platinum, palladium and rhodium, and, also, other valuable elements, e.g., rare earths and cerium, can be recovered from a wide variety of compositions of matter and articles of manufacture, for example, waste or spent catalysts, such as vehicular post-combustion catalysts, by (54): Comminuting such composition article into a finely divided state,

Specific Materials

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Intimately admixing the composition with sulfuric acid, Calcining the resulting admixture at a temperature ranging from 150°C to 450°C, and Leaching the calcined admixture in an aqueous medium with H ions and cl ions. Here, a solid residue substantially depleted of such precious metal values is obtained, and a liquid solution that contains such precious metals (54). Also, a process for forming a bulk hydroprocessing catalyst has been described (55). This method uses sulfiding of a catalyst precursor made in a co-precipitation reaction. Up to 60% of the metal precursor feeds do not react to form catalyst precursor and end up in the supernatant as metal residuals. The metals can be recovered in a chemical precipitation step, wherein the supernatant is mixed with at least one of the acids, a sulfide-containing compound, a base, and combinations thereof to precipitate at least 50% of metal ions in at least one of the metal residuals, wherein the precipitation is carried out at a preselected pH. The scheme of the process is shown in Figure 6.10

Figure 6.10 Bulk hydroprocessing process (55).

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Polymer Waste Management

Then, the precipitate is isolated and recovered, yielding an e uent stream. The precipitate and or the e uent stream can be further treated to form at least a metal precursor feed which can be used in the co-precipitation reaction. The process generates an e uent to waste treatment containing less than 50 ppm of metals (55). Rare Earth Elements. Methods of recovering rare earth elements from a rare earth-containing material have been reported (56). The rare earth elements can be extracted from catalysts, as well as sorbents and sorbent-containing materials. It has been discovered that the performance of the catalyst improves when reacting a fresh or spent catalyst or sorbent with a solution containing an extracting agent, such as an acid or a base. The catalyst should contain both alumina and a molecular sieve and or a sorbent. The reaction is performed under mild conditions of treatment such that the majority of the base material does not dissolve into the solution. Additionally, some metals in the catalyst can be removed from the catalyst (56). Some of the metals that can be removed have economic significance for reuse, such as the rare earth elements of La, Ce, Pr, and Nd. Others metals have negative environmental impact and thus their removal for recycling or separate disposal is preferred. Certain of these metals can be incorporated back into the improved catalyst. This fact also provides improved performance benefits (56). A flowchart of this procedure is shown in Figure 6.11. Conical Spouted Bed Reactor. The catalytic pyrolysis of HDPE on a HY zeolite catalyst has been carried out in a CSBR at 500°C, and individual products have been monitored with the aim of obtaining product distribution data (57). The basic reactor is shown in Figure 6.12. The CSBR does not exhibit defluidization problems in the pyrolysis of plastics. Actually, 69% of the product stream corresponded to the gasoline fraction of C5 –C10 . In particular, this fraction fulfills European Union requirements for commercial gasoline and its RON index of 96.5 is of the same order as standard automotive fuel. The other obtained products were

Specific Materials

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Figure 6.11 Schematic diagram of the method of recovering rare earth elements (56).

Figure 6.12 Schematic of a conical spouted bed reactor, reprinted from (57) with permission from Elsevier.

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Polymer Waste Management

mainly gases, especially propylene and butenes, although there was also a heavy fraction consisting of aromatics with more than one ring and unreacted waxes (57). The octane rating index is a measure of the resistance of petrol and other fuels to autoignition in spark ignition internal combustion engines (58, 59). The octane number (or research octane number, RON) of a fuel is measured in a test engine, and is defined by comparison with the mixture of 2,2,4-trimethylpentane (i-octane) and heptane, which would have the same anti-knocking capacity as the tested fuel, i.e., the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. The RON of n-heptane and i-octane are defined as exactly 0 and 100 (59). A list of RON numbers for various individual compounds is shown in Table 6.13. Table 6.13 RON numbers (59). Compound Hexadecane n-Octane n-Heptane Diesel fuel 2-Methylheptane n-Hexane 1-Pentene 2-Methylhexane 1-Heptene n-Pentane n-Butanol Methane

RON
Al-PILC-450 Fe-PILC-450 > Fe-PILC-300 > Al-PILC-Fe-450. The presence of heavy gas oil improves the oil yield from both thermal and catalytic pyrolysis of HDPE, which can be attributed to the solvency e ect of heavy gas oil. The pyrolysis oils were analyzed by GCAR-MS and their profiles were compared to the standard diesel. The oil from the HGO HDPE pyrolysis using the catalyst Fe-PILC-Fe-300 was more similar to the GC-MS homologous series of standard diesel. That catalyst produced a light linear hydrocarbon content which was 63% higher than that produced with zeolite (61). 6.2.5.8

Heavy Fuel by Thermal Cracking

A LDPE waste plastic was transformed into heavy fuel by using fractional distillation column process with a liquefaction process (62). For experimental purpose, two types of temperature profiles were used, one for LDPE waste plastic liquefaction temperature and another one for fractional distillation column temperature. In this experiment liquefaction temperature ranges of 100°C to 420°C and fractional distillation temperature ranges of 340°C to 365°C were obtained. LDPE waste plastic to heavy fuel production was performed without adding any kind of catalyst in the presence of oxygen and without using a vacuum system. GC MS indicated that the LDPE waste plastic produced heavy fuel hydrocarbon chain range of C5 to C28 and light gases were also present in the hydrocarbon range of C1 to C4 (62). 6.2.5.9

Tertiary Recycling to Fuel

Plastics being of petrochemical origin, they have an inherently high calorific value. Thus they can be converted back to useful energy. Many studies have been carried out to convert the waste plastics into liquid fuel by thermal and catalytic pyrolysis and this has led to the establishment of a number of successful firms converting waste plastics to liquid fuels (4). Tertiary recycling also includes chemical recycling. The terms chemical recycling and feedstock recycling of plastics are sometimes

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collectively referred to as advanced recycling technologies. In these processes, solid plastic materials are converted into smaller molecules as chemical intermediates through the use of heat and or chemical treatment. The chemical intermediates are usually liquids or gases, but sometimes solids or waxes are suitable for their use as feedstocks for petrochemicals and plastics. Quaternary recycling includes the recovery of the energy content of plastic wastes. Owing to a lack of other recycling possibilities, incineration (combustion) aimed at the recovery of energy is currently the most e ective way to reduce the volume of organic material. The production and consumption of HDPE has been reviewed, also di erent methods of recycling of plastic with special reference to chemical degradation of HDPE to fuel. Also, di erent factors that a ect these degradations, the kinetics and mechanism of these reaction have been elucidated (4). 6.2.6 6.2.6.1

Poly(propylene) Polymer Carbon Dots

The upcycling of plastic waste into photoluminescence carbon dots (C-Dots) has been reported (63). The recycling was conducted on a PP plastic waste using a simple heating process at around its melting point temperatures of 200°C, 250°C, and 300°C. The optical properties and size as well as structure of C-Dots polymer from the PP plastic waste could be successfully identified. The polymer C-Dots from plastic waste recycling have absorption spectra at the 340–550 nm wavelength range. A very rare phenomenon on the emission spectra was obtained as two emission peak wavelengths of 410 nm (3.03 eV) and 440 nm (2.83 eV) occured. C-Dots polymer from the PP plastic waste has an average size of 5.3 nm (obtained at 200°C), 4.9 nm (250°C), and 4.2 nm (300°C) (63). The alteration of the optical properties of absorption spectra and emission spectra, as well as particle size of C-Dots polymer are caused by structural change of the PP plastic waste due to heating treatment in the recycling process. During the heating process on the waste, the carbon chain binds oxygen from the environment and

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forms a carbonyl group on the wave number 1638 cm 1 , which is the main constituent of C-Dots polymer. Due to the above-mentioned facts, recycling of a PP plastic waste into C-Dots polymers has great potential to be used as materials for photocatalyst, bioimaging, as well as sensors in optoelectronic materials (63). 6.2.6.2

Carbon Nanotubes

The production of valuable hydrogen and carbon nanotubes (CNTs) has obtained growing interest for the management of waste plastics through thermochemical conversion technology (64). The development of catalysts is one of the key factors for this process to improve the hydrogen production and the quality of CNTs. Ni SiO2 and Fe SiO2 catalysts with di erent metal particle sizes were investigated in relation to their performance in the production of hydrogen and CNTs from catalytic gasification of waste PP, using a two-stage fixed-bed reaction system. The influences of the type of metals and the crystal size of metal particles on product yields and the production of CNTs in terms of morphology have been studied using GC, XRD, temperature program oxidation (TPO), SEM, etc. The production, yield, and gas composition from catalytic gasification of PP by the application of nickel- and iron-based catalysts are shown in Table 6.15. Table 6.15 Performance of nickel- and iron-based catalysts (64). Yields

Fe/ SiO2 S

Gas [%] Carbon [%] H2 [mmol g 1 ]

Fe/ SiO2 L

Ni/ SiO2 S

Ni/ SiO2 L

63.90 29.00 25.60

51.20 16.00 18.10

52.50 16.00 22.60

7.80 50.30 22.70 19.20

3.30 42.20 43.50 11.00

6.32 47.74 38.31 7.62

49.20 26.00 15.40

Gas concentrations [% v v] CO H2 CH4 C2 –C4

5.32 41.72 39.16 13.80

The results showed that the Fe-based catalysts, in particular with large particle size of ca. 80 nm, produced the highest yield of hydro-

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gen of 25.60 m mol per g of plastic and the highest yield of carbons of 29%, as well as the largest fraction of graphite carbons. Both Fe- and Ni-based catalysts with larger metal particles produced a higher yield of hydrogen compared with the catalysts with smaller metal particles, respectively. Furthermore, the CNTs formed using the Ni SiO2 -S catalyst (with the smallest metal particles around 8 nm) produced a large amount of amorphous carbons, which are undesirable for the process of CNTs production (64).

6.2.6.3

Metal-Oxide-Impregnated Bentonites

The pyrolysis of PP and HDPE in the absence and presence of plain and metal-oxide-impregnated bentonite clays was investigated (65). The following metal-oxide-impregnated bentonite clays were used: Acid-washed bentonite clay (AWBC), Zn AWBC, Ni AWBC, Co AWBC, Fe AWBC, and Mn AWBC. Thermal and catalytic runs were performed at 300°C in the case of PP and at 350°C in the case of HDPE for a contact time of 30 min. The e ects of di erent catalysts and their concentrations on the overall yields and the yields of liquid, gas, and residue were studied. The e cacy of each catalyst has been reported on the basis of the highest liquid yields. The derived liquid products were analyzed by FTIR GC MS. The analysis confirmed the presence of para ns, olefins, and naphthenes. The results also indicate the catalytic role of impregnated bentonite clays compared to plain bentonite clay with the optimum e ciency shown by Co AWBC in the case of PP and Zn AWBC in the case of HDPE toward the formation of liquid products in a desirable range of carbon atoms with the enrichment of olefins and naphthenes in the case of PP and para ns and olefins in the case of HDPE, in comparison to a simple thermal pyrolysis experiment (65).

6.3 Poly(styrene) The recent progress concerning the recycling of PS-based plastics has been reviewed (66).

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6.3.1

Influence of Temperature in Pyrolysis

To convert PS into a liquid much heat energy is needed. Pyrolysis has been used as the method to process PS into a liquid product. The characteristics of the heating process and the properties of the liquid product have been elucidated. This liquid can be used as a fuel (67). A fixed-bed reactor with SUS 316L as the base material was constructed to decompose the PS using an electric heater, which was controlled using a digital PID controller. A power sensor was mounted in the electrical circuit to monitor the power that entered the heater and a data acquisition system was used to record data. The reaction temperature was varied from 350°C to 550°C. No sweep gas was injected into the system. The vapor flows naturally based on its partial pressure. The temperature of the cooling water was varied according to two conditions, water at ambient temperature and cold water. To condense the pyrolysis vapor to a liquid oil, a double-pipe condenser was constructed. The thermocouples were installed at many points of the system to monitor temperature change in the system. The maximum liquid yield was obtained at reaction temperature 500°C with cooling water with a temperature of 16.59°C. An operating temperature below 500°C would produce more wax, and above 500°C much gas will be produced. The liquid can be applied as fuel with heating value 43.83 mJ kg 1 , a density of 0.89 g ml 1 , and 0.78 cSt of kinematic viscosity (67). 6.3.2 6.3.2.1

Degradation of Poly(styrene) in the Presence of Hydrogen Low Temperature Degradation

A low temperature degradation method of PS in benzene is carried out in the presence of hydrogen using iron(III) oxide catalyst at 170°C–240°C (68). The e ects of temperature, catalyst loading and polymer loading on degradation were studied in hydrogen atmosphere. The degradation has also been carried out using di erent initial hydrogen partial pressures. The time-dependent molecular weight was calculated using the viscosity average method. It is found that the degradation is enhanced considerably in the presence of hydrogen and followed a

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random degradation chain scission. A random degradation kinetic model of Kelen has been used to estimate the degradation rate constants (69). The thermal degradation rate constants were calculated using the correlations at given catalyst loading and initial hydrogen partial pressure with varying temperature. The frequency factor and activation energy are also determined using the Arrhenius equation (68). 6.3.2.2

Elevated Temperature Degradation

The degradation of waste PS polystyrene has been done in the presence of hydrogen using several metal oxide catalysts at elevated temperature and pressure for the purpose of recycling (70). Benzene was used as a solvent for degradation. The initial hydrogen pressure in the autoclave is kept at 7.0 kg cm 2 and the degradation experiments were carried out at 240°C. In the absence of hydrogen, the thermal degradation of PS below the ceiling temperature using a catalyst usually takes place through a random bond scission process. A kinetic model for the catalytic degradation of PS in the presence of a large excess of hydrogen was developed by Balakrishnan and Guria (68). After degradation, degraded PS residue was separated and analyzed by FTIR spectroscopy. The filtrate was analyzed by GC in order to elucidate the degradation mechanism of PS (70). The degradation rate is enhanced in the presence of hydrogen. The time-dependent weight average molecular weight of the degraded PS has been determined by the viscosity method. Degradation rate constants for the di erent catalysts were calculated based on the proposed degradation mechanism. An alkali metal oxide catalyst showed a higher reactivity towards PS degradation as compared to the transition-metal oxide catalyst. Thus, the degradation rate constant decreases with the increase in electronegativity of metal element of the catalyst (70). The pseudo first order degradation rate constants for PS using di erent metal oxide catalysts are collected in Table 6.16. Here, the degradation rate constants increase with the decrease in the electronegativity values of metal element in the catalyst.

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Polymer Waste Management Table 6.16 Pseudo first order degradation rate constants (70). Catalyst CaO (II) MnO2 (IV) TiO2 (IV) PbO (II) Fe2O3 (III) HgO (II) ZnO (II) CrO3 (VI)

Rate constant [10

6

min 1 ]

47.95 39.27 12.13 4.45 4.46 4.27 2.12 1.89

Manganese (IV) oxide is a transition-metal catalyst, but it shows a higher reactivity due to its reduction towards stable manganese (II) oxide in the degradation environment. Also, the degradation rate constant of PS could be correlated with the catalyst activity, i.e., electronegativity of metal element in the catalyst (70). 6.3.3

Production of Enhanced Amounts of Aromatic Compounds

A process for pyrolyzing hydrocarbonacetous materials has been described, wherein polymers are degraded with a slow heating rate which creates a specific temperature gradient, and the substantial absence of oxygen (71). The feedstock of hydrocarbonacetous materials can be utilized by conventional pyrolytic processes in the form of scrap material, for example, scrap PS, acrylonitrile-butadiene-styrene (ABS), tires, PE, PP, scrap paint, scrap adhesive, automotive waste (flu ), and scrap resin. The preferred charge material is a random well-mixed polymer scrap. That is, the charge material should be a combination of poly(butadiene), a styrene-butadiene copolymer, polyisoprene, etc. Polymers yielding halogenated material upon pyrolysis can be tolerated, but due to their corrosive e ect, are not desired. Specific characteristics include large reactor sizes, large amounts of charged hydrocarbonacetous materials, low heat input rates, a formation of a pyrolyzate char material on the reactor heating surface having a temperature gradient across said pyrolyzate char ma-

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terial, substantial absence of oxygen, etc. (71). The device is shown in Figure 6.13 and explained below. Referring to Figure 6.13, a preferred apparatus for carrying out the process would include a feed hopper 10 which feeds polymer scrap to a incline conveyor 12, which at its upper end feeds the scrap into an auger feed 14 from where it is fed into a rotary dryer 16 having a flue gas exit pipe 18. An auger air lock 20 feeds a multistage double walled vessel shown generally at 22. The vessel 22 includes an upper inner walled vessel 24 and an upper outer walled vessel 26. There is an upper vertical connecting tube 28 between the upper inner walled vessel 24 and a lower inner walled vessel 30. The lower inner walled vessel 30 is surrounded by a lower outer walled vessel 32 and a lower discharge tube 34 extends from the lower inner walled vessel through the lower outer walled vessel to a horizontal discharge tube with air lock 36 which discharges char 38. A line 40 extends from the upper inner walled vessel 24 through the upper outer walled vessel to heat exchanger 42 and then to valve 44 to a liquid line 46 for product storage and a loop gas line 48 which extends to valve 50 on the lower outer walled vessel 32. Line 52 extends from the upper inner walled vessel 24 through the upper outer walled vessel 26 to heat exchanger 54. Line 56 extends from lower inner walled vessel 30 through lower outer walled vessel 32 to heat exchanger 58 lines 52 and 56 extend respectively from heat exchangers 54 and 58 to a valve 60 which diverts the stream to liquid line 62 which extends to product storage. Loop gas line 64 extends back to valve 50 to inject gas into burner 51 which leads to the space between the lower outer walled vessel 32 and the lower inner walled vessel 30. This hot-burned flue gas continues to flow upwardly between the upper inner walled vessel 24 and the upper outer walled vessel 26 and then past the auger air lock 20 so as to heat the material flowing downwardly through the auger air lock 20. The hot flue gas then flows through 16 then out 18, preheating the incoming material. The conversion of PS waste plastic to renewable energy or naphtha grade fuel through a fractional distillation process was applied (72). The liquefaction temperature range was 250°C–430°C and the fractional column temperature was 110°C–135°C for naphtha grade fuel separation. The thermal degradation of PS waste

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Figure 6.13 Apparatus for pyrolysis of hydrocarbonacetous materials (71).

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plastic to renewable energy or naphtha grade chemical production was done without adding any kind of cracking catalyst and without vacuum system. For experimental purpose, a raw sample of 1 kg of PS waste plastic was used and the degradation experiment was performed under a Labconco fume hood in a fully closed system. The whole experiment was performed in a stainless steel reactor. The produced fuel was analyzed using GC MS, FTIR, and di erential scanning calorimetry (DSC). The sulfur content in the produced fuel was found to be less than the environmental protection agency level and the fuel could be used for chemical feedstock refinery for further modification (72). 6.3.4

Poly(styrene) with Flame Retardants

The thermal degradation of high impact poly(styrene) containing brominated flame retardants and antimony trioxide was conducted at di erent temperatures with the presence of various additives in a fixed-bed reactor (73). The additives were red mud, limestone and natural zeolite. The e ect of the pyrolysis temperature on the yield of the products and the bromine content in the oil products was investigated. It was found that a maximum oil yield of 84.38% was obtained at a pyrolysis temperature of 500°C. However, the pyrolysis temperature had no significant impact on the bromine reduction in the oil products (73). The bromine in the flame retardant was mainly transferred into the oil products, where the bromine content was in the range of 7.96% – 8.56%. With the aim of removing bromine and antimony from the oils, the additives were used to investigate the influence on the product yield and composition, especially on the bromine and antimony removal ability from the oil products. It was found that all of the additives could significantly lower the bromine and antimony content in the oils and the red mud was the most e ective. The presence of red mud could reduce the bromine and antimony content from 8.21% and 1.84% when no additive was employed to 0.84% and 0.35%, respectively. In addition, the distribution and the

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fate of bromine and antimony in the residues were studied in detail by SEM and XRD analysis (73).

6.4 Poly(carbonate) Poly(carbonate) (PC), is an important engineering polymer with a variety of optical and technical applications, whose demand is increasing year by year. Its consumption in 2008 was estimated to have reached 3.3 M t (74). The three di erent routes for PC recycling are: 1. Direct recycle (mechanical recycling or blending with other materials), 2. Treatment via chemical methods, and 3. Thermochemical methods (pyrolysis). The available methods for PC recycling and their mechanisms were recorded and their potential and weaknesses have been reviewed (74). Apart from methods, such as pyrolysis and degradation via chemical routes, other recent developed methods, such as decomposition in the presence of enzymes, have also been reported. Also, the main degradation methods of PC blends have also been presented. 6.4.1

E ect of Metal Chlorides

The treatment of waste PC to e ciently reduce its degraded residue has been investigated (75). An isothermal reactor was used under continuous nitrogen flow at atmospheric pressure to pyrolyze either PC alone and also in the presence of metal chloride. Some metal chlorides were shown to be catalytically active for the degradation of PC at 400°C, which increased the degradation conversion from 8.5% to more than 58.3%. Among those active metal chlorides, ZnCl2 and SnCl2 were shown to produce higher liquid product yields. The e ects of particle size of PC, temperature, the weight ratio of metal chloride to PC and the degradation time on the degradation conversion of PC without and with these two most active metal chlorides were studied.

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The e ect of degradation temperature on the degradation of PC using ZnCl2 and SnCl2 as catalysts is shown in Table 6.17. Table 6.17 E ect of degradation temperature (75). Temperature [°C]

PC alone

300 325 350 400 450 475 500 550

– – 0.5 8.5 64.6 71.4 73.8 75.9

PC ZnCl2 7.0 26.1 73.5 81.6 85.1 88.1 89.8 87.8

PC SnCl2 10.6 73.1 77.7 83.2 83.1 79.2 78.6 80.2

Also, the liquid products were analyzed for the PC degradation alone and with catalysts. The results are shown in Table 6.18. The e ect of the particle size of PC at various temperatures on the degradation conversion of PC alone showed that if the degradation occurs at low ( 350°C) or high ( 500°C) temperature, the PC particle size does not a ect the conversion. However, in the medium temperature range, a smaller particle size can obtain better conversion. The e ect of particle size is greatest at 400°C and the conversion for particle sizes smaller than 0.35 mm is roughly four to five times higher than for particle sizes between 0.50 mm and 0.71 mm. The degradation conversion of PC with catalysts as a function of degradation time at 325°C using a nitrogen flow rate of 100 mL min 1 with a size of PC of 0.50 mm to 0.71 mm, and a weight ratio of metal chloride to PC of 0.1 is shown in Figure 6.14. However, at 400°C under similar conditions, the degradation conversion reaches 80% after ca. 5 min. The results of the liquid product analysis by GC MS demonstrated that the product composition of PC degradation over the metal chlorides is much simpler than that of degradation alone. The main liquid product is phenol, p-isopropylphenol, diphenyl carbonate, and bisphenol A for all cases (75).

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Table 6.18 E ect of degradation temperature (75). Product

PC alone PC ZnCl2 PC SnCl2 Amount [GC Area %]

Toluene Xylene Cumene Phenol o-Cresol m-Cresol m-Ethylphenol p-Isopropylphenol p-Propylphenol m-tert-Butylphenol 1,2,4,5-Tetramethylbenzene Diphenyl ether p-tert-Butylacetophenone 4-Methyldiphenyl ether Diphenyl propane 2-Methylbenzofuran p-Tolyl ether p-Cumyl phenol Diphenyl carbonate p-Tolyl phenyl carbonate 2-tert-Butyl-6-phenylphenol Bisphenol A

0.88 1.25 0.51 8.22 1.18 10.09 11.22 11.29 3.16 0.56 1.97 0.20 – 0.70 0.40 – 0.52 6.36 13.44 0.69 7.88 18.60

– – – 18.30 0.34 1.22 – 24.80 – 0.60 – 13.10 0.98 – – 7.41 – – 14.46 – – 18.79

– – – 16.50 – – – 18.97 – 0.89 – 15.60 2.80 – – 8.24 – – 12.50 – – 24.50

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90 80

Conversion/[%]

70 60 50 40 30 20 10

SnCl2 ZnCl2

0 0

50

100

150

200

250

300

350

Time/[min] Figure 6.14 Degradation conversion (75).

6.5 Poly(ethylene terephthalate) Poly(ethylene terephthalate) is used on a large scale for containers in the food industry, especially for beverage bottles (76). Therefore, large quantities of spent waste containers are produced, which can no longer be returned to the filling process. Methods and plants for recycling these waste containers and processing them to regain a PET source material suited for use with food for the production of new containers are known. Such a recycling plant may be provided directly upstream of a production line for the production of new PET containers, where the recycled product coming from the recycling plant can directly be introduced, for example, into an injection molding machine for the production of preforms as starting product for new PET bottles. 6.5.1

Poly(ethylene terephthalate) Flakes

The quality of recycled transparent poly(ethylene terephthalate) can be examined in a wafer or plaque formed by melting a representative sample and quenching it to prevent crystallization (77).

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Specific contaminants and impurities can be detected, such as aluminum particles, dirt particles, paper, and fibers. Here, the overall color of the plaque is indicative of oxidizable contaminants such as ethylene-vinyl acetate (EVA) glue residue and the number of bubbles present in the plaque gives an indication of the moisture content of the sample (77). 6.5.2

Chemical Recycling

The various process options for the chemical recycling of PET waste may be categorized as follows (78): 1. Regeneration of base monomers: Methanolysis for dimethyl terephthalate and hydrolysis for producing pure terephthalic acid and ethylene glycol, 2. Conversion into oligomers using glycolysis or solvolysis, 3. Use of glycolyzed waste for value-added products, 4. Conversion into speciality chemicals by aminolysis or ammonolysis, and 5. Conversion into speciality intermediates for use in plastics and coatings. 6.5.2.1

Glycolysis with Lewis Acidic Ionic Liquids

Poly(ethylene terephthalate) waste from a local market was depolymerized using ethylene glycol in the presence of Lewis acidic ionic liquids 1-methyl-3-butylimidazolium zinc trichloride [Bmim] ZnCl3 (79). Qualitative analysis showed that bis(2-hydroxyethyl) terephthalate was the main product. In comparison to the ionic liquid 1-methyl-3-butylimidazolium chloride [Bmim]Cl, the Lewis acidic ionic liquids showed a high catalytic activity in the glycolysis of PET. The yield of bis(2-hydroxyethyl) terephthalate was achieved at 100% and 83.8% with a low catalyst ([Bmim] ZnCl3 ) loading of only 0.16%. This catalyst can be reused up to five times. 1 H-NMR results showed that the recovered catalyst was similar to the fresh one. A mechanism of the glycolysis of PET catalyzed by [Bmim] ZnCl3 has been proposed. The cation in the catalyst interacts with the carbonyl oxygen (>C O) in the ester, and then the oxygen in the

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hydroxyl of ethylene glycol attacks the carbon cation of the ester group, forming a tetrahedral intermediate. Afterwards, the hydrogen leaves the ethylene glycol. Then, the electrons on the oxygen in -OM transfer form >C O. The acyl-oxygen cleaves, and the OCH2 CH2 group leaves, combining with H to form HO CH2 CH2 groups. These transfer processes repeat, and the bis(2-hydroxyethyl) terephthalate monomer is formed (79). 6.5.2.2 Microwave Reactor Recycling of PET using hydrolysis, glycolysis and aminolysis under microwave irradiation has been proposed. PET recycling in a microwave reactor has been proved to be a very beneficial method, resulting not only in material recovery but also in a substantial energy savings (78). Hydrolytic Depolymerization. The recycling of PET was examined using a hydrolytic depolymerization method in an alkaline solution under microwave irradiation (80). The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. The main products found were the monomers terephthalic acid and ethylene glycol. The e ect of reaction temperature, time, amount of PET and alkaline concentration on the degree of PET depolymerization and recovery of the monomers was investigated. Microwave irradiation was found to reduce the time needed to achieve a specific degradation of PET significantly, with almost complete depolymerization occurring in 30 min at 180°C and only 46 W of microwave power. The usage of a phase-transfer catalyst, i.e., trioctylmethylammonium bromide, resulted in the same amount of unreacted PET but at significantly lower depolymerization temperatures (80). Glycolytic Depolymerization. The recycling of waste PET bottles was examined using glycolytic depolymerization with diethylene glycol under microwave irradiation (81). It was investigated if depolymerization using microwave energy could provide the same product distribution while carried out in milder experimental conditions and or shorter reaction times.

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The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled. Experiments under constant temperature or microwave power were carried out at several time intervals. The main glycolysis product was analyzed and identified using FTIR spectroscopy. In the experiments that were carried out under constant microwave power, the complete depolymerization was observed at irradiation powers greater than 150 W for 2 min, or 100 W for 5 min. In the constant temperature experiments, it was found that at temperatures below 150°C no degradation takes place, whereas complete depolymerization takes place at temperatures greater than or equal to 180°C for 5 min. When these results are compared to a conventional heating, where more than 4 h are needed for a complete PET degradation, the importance of the microwave power technique and the substantial energy savings achieved are confirmed (81). Aminolytic Depolymerization. The aminolytic depolymerization of PET taken from waste soft drink bottles, under microwave irradiation, is proposed as a recycling method with possible substantial energy savings (82). The reaction was carried out with ethanolamine and without the use of any other catalyst in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. Experiments at constant temperature or microwave power were carried out for several time periods. The main product, bis(2-hydroxyethyl) terephthalamide, was identified using FTIR spectroscopy and DSC. It was found that the depolymerization of PET can be favored by increasing temperature, time and microwave power. The average molecular weight of the PET residues, determined using viscosity measurements, was found to decrease with the percentage of PET degradation. To some extent, this indicated a random chain scission mechanism. A complete depolymerization reaction was found to occur in less than 5 min when the irradiation power applied was 100 W or at a temperature of 260°C. These results support the use of the microwave-assisted aminolytic degradation as a very beneficial method for the recycling of PET wastes (82).

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275

Flake and Pellet Process

There are recycling plants for PET which are each designed for a specific type of recycling product (76). For example, the recycling plant may be designed for the production of so-called flakes or the production of pellets. In principle, flakes are the products from a grinder, which have been cleaned, sorted and decontaminated for use in foodstu s. Pellets are products from an extruder, where they were homogenized by thermal influence. Both production methods have advantages and disadvantages. The advantages of the flake process lie in a small energy input, in the fact that no acetaldehyde is formed, that the intrinsic viscosity is not reduced, that possibly contained foreign plastics cannot coalesce, and that drying is possible at low temperatures. The disadvantages of the flake process are that flakes are less suitable for being admixed to newly produced PET and that foreign plastics can oxidize. The advantages of the pellet process lie in a simple and unproblematic admixture to virgin material, and in the use of a melt filter filtration technique for removing finest particles. The disadvantages of the pellet process lie in a considerably greater energy input, in the risk that acetaldehyde is formed, and that foreign plastics may coalesce, so that no homogeneous PET is obtained (76). A device has been designed that allows both the operation of the flake process and the pellet process (76). The unit consists of two plants, one doing the flake process and the other doing the pellet process. The controllers of the plants are configured such that the user merely has to preselect a specific process line, so as to start the desired process. Where necessary, a manual switching may be required for opening and closing special access openings and for inserting and removing blind covers (76). 6.5.4

Bio-based Plastics

A method for reclaiming a bio-based plastic material consists of (83): Receiving a plastic container comprised of PET, the container including an identifier; determining container content information from or via the identifier,

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Polymer Waste Management Using or referring to the identifier to sort the PET container from other PET containers based on whether the PET container being sorted includes bio-based plastic material, and Segregating PET containers including bio-based plastic material from PET containers that do not include bio-based plastic material.

The identifier used with bio-based resins and articles produced from these, may include chemical tracers that are added to or included with a bio-based resin. During the production of a plastic resin, such as PET or PE, the manufacturer may include certain tracers that serve to distinguish the resin produced by the manufacturer from similar resins produced by other manufacturers. These tracers may be organic chemicals added in very small amounts. The tracer is preferably a compound not normally present in the standard polymerization process, but, at such small levels, the tracer will not negatively or adversely a ect the resulting polymer’s suitability with respect to recyclability or functionality. The tracers may be optionally added during the melt polymerization phase or the solid-state polymerization stage. Using a tracer, molecular or chemical testing of resin batches could be used to determine the origin, identity or provenance (83).

6.6 Poly(vinyl chloride) 6.6.1

Separation Techniques for PVC Waste Plastics

Separation techniques for PVC waste plastics are collected in Table 6.19. 6.6.2

Surface Treatment

Several strategies for PVC surface treatment are known. In some cases, it is necessary to utilize two or more techniques consecutively to gain the desired modification level (85). The methods modify the surface by introducing superficial functionalities, by which many surface characteristics, such as hydrophilicity, roughness, etc., can be regulated to a great extent. This often makes the controlled

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Table 6.19 Separation techniques for PVC waste plastics (84). Method

Remarks

Manual separation Selective dissolution process

Sorting by hand Selective dissolving of PVC in organic solvents and then reclaiming of the dissolved material Sorting according to di erences in density through a centrifugal force field

Hydrocyclone separation Melt filtration Selective flotation process Liquid-fluidized bed classification

X-ray fluorescence method Laser-induced plasma spectroscopy method Triboelectrostatic separation

Separation by melt filtration at temperature of 204°C through continuous screen changing equipment Surface treatment of plastics having similar densities (PVC and PET), with subsequent froth flotation using nonionic surfactants Gravimetric separation in water as a fluidizing medium through a selective thermal particle density modification induced by step changes in the fluidizing water temperature Spectroscopic separation through a characteristic backscattering from chlorine atoms in PVC Spectroscopic separation through analysis of the atomic emission lines generated by focusing high-energy laser radiations on plastics Electrostatic separation by charging of plastics, with subsequent segregation of materials through an electric field

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modification of the surface intended for a certain application a demanding project. Plasma treatment is an extensively used technique of enormous potential for surface modification. Plasma is defined as a partially ionized gas containing free electrons, ions, and radicals, as well as neutral particles. High-energy irradiation includes γ -radiation, β-irradiation (electron beam), and ion radiation. Ion radiation is widely used to achieve either ion implantation at the top surface layer or to deposit coatings. For this purpose, several ions like hydrogen, noble gases, gold, etc., are employed. Ultraviolet treatment is widely applied as a surface modification technique usually in the presence of a photoinitiator photosensitizer and induces a combination of functionalization and ablation reactions. Exposure to ozone e ects a surface oxidization as a consequence of ozone formation and decomposition reactions. This can also be carried out along with UV irradiation to favorably guide the reaction kinetics. However, degradation is an unwanted phenomenon which may arise after ozone treatment and can be controlled somewhat by adjusting the exposure time. The technique is usually employed as pretreatment after which grafting of certain chemical entities can be accomplished (85).

6.7 Pyrolysis of Mixed Plastics Thermal and catalytic pyrolysis of PS with LDPE, HDPE, PP, and PET plastics was carried out in a 25 cm3 stainless steel microreactor at around 430°C–440°C under 5.5–6.0 MPa of N2 gas pressure for 1 h (86). Three reactions of each plastic with PS were conducted in the ratio of 1:1, 1:2, and 1:3. The amount of PS was varied to elucidate its role and reactivity. In all of the coprocessing reactions, a ratio of 1:1 a orded the best yields of pyrolytic oils formation. Simulated distillation of the hexane-soluble portion showed that the low boiling fractions were not found and fractions were obtained

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only after 96°C boiling point. This could be due to the vaporization of high volatile components. In most of the binary pyrolysis experiments, the light cycle oil fractions have lower recovery than heavy cycle oil. Studies using GC identified some very important chemical compounds present in the liquid products obtained from the pyrolysis of mixed plastics. The results obtained here have confirmed the usefulness and feasibility of the pyrolysis process of the mixed plastics as an alternative approach to feedstock recycling (86). 6.7.1

Pyrolysis of PE and PVC Mixtures

The e ective factors, such as temperature, catalyst percentage, and PVC composition, on the pyrolysis of a mixture of mainly polyolefins in the presence of polyvinyl chloride by a new catalyst based on alumina were investigated (87). The catalyst used, was a ferrous material with Al2 O3 . The pyrolysis experiments were carried out in a semi-batch reactor under ambient atmospheric conditions. Three main types of polyolefins, HDPE, LDPE, and PP, were used in the presence of PVC. The mixtures are shown in Table 6.20. Table 6.20 Polyolefins (87). Sample

HDPE

LDPE

PP

PVC

Content in % per weight 1 2

39 35

24 23

34 32

3 10

A factorial design was employed as the design of experiments (87). The analysis of variance for the results showed that the main e ects are significant. However, interactions were not significant. A change in temperature can cause catalyst performance to liquid production. On the other hand, the analysis of variance for the gas showed that there is a significant interaction between temperature and catalyst to the gaseous production. That is, the gaseous production is related to catalyst performance due to the reaction temperature level. On the other hand, there is not significant interaction between catalyst and PVC to the yield of liquid production (87).

280 6.7.2

Polymer Waste Management Waste Catalyst for Hazardous Chlorine-Containing Plastic

A plastic waste (PE PP PS PVC) was pyrolyzed over a series of postuse FCC catalysts using a fluidizing reaction system similar to the FCC process operating isothermally at ambient pressure (88). The experiments with these catalysts showed good yields of valuable hydrocarbons with di ering selectivity in the final products depending on reaction conditions. A model based on kinetic considerations associated with chemical reactions and catalyst deactivation in the catalytic degradation of plastics has been developed (88). A greater product selectivity was observed with a hybrid catalyst of MCM-41 Cat-R1 with more than 70.5% olefins products. It could be shown that the catalytic degradation of post-consumer chloro-commingled plastics over these recycled catalysts coped with the utility of fluidizing cracking system was shown to be a useful method for the production of potentially valuable hydrocarbons (88). 6.7.3

Catalytic Hydrocracking of Post-Consumer Plastic Waste

Catalytic hydrocracking using a mildly exothermic process has been proposed for feedstock recycling of post-consumer plastic waste (89). Metal loaded zeolite catalysts were used at much reduced temperatures of 200°C to 350°C to convert mixed plastic waste at significantly shorter reaction times of typically 5 min. This allows the use of a continuous processing method. High purity HDPE, PP, PS, PET, and PVC were used in powder form of less than 400 μm or pellet form. These materials were used as model polymers for hydrocracking tests. The zeolite catalysts used were 0.5% and 1% Pt on USY and the acidic H form of zeolites were ion-exchanged with Pt(NH3 )4 Cl2 to get the relevant Pt loadings and were confirmed by acid digestion and inductively coupled plasma emission spectroscopy analysis. The ion-exchanged catalysts were then pelletized and sieved to a particle size of 0.3 mm to 0.5 mm. Catalysts were calcined in a tubular reactor with a flow of air (50 ml min 1 ) at 450°C for 240 min and reduced with H2 (50 ml min 1 ) at 450°C for 240 min; slow heating and cooling ramps (2°C min 1 ) were used.

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Hydrocracking tests were carried out in a 300 cm3 stainless steel stirred autoclave (Parr, USA), heated by an electric band heater at SOG Ltd in Runcorn. The reactor was loaded with 18 g of the polymer and 1.8 g of catalyst, avoiding the contact with air, flushed and pressurized with H2 at room temperature to the desired pressure (between 1.5 to 5. 5 MPa). Sampling of the products was achieved using an evacuated 1000 cm3 sampling bomb placed in an ice bath. Experiments were duplicated to ensure reproducibility and provide run-to-run comparison of mass balances. Gas and liquid products separated in the sampling bomb, along with those remaining in the reactor were collected, the liquid was weighed and volume of gases at atmospheric pressure measured. Gases were analyzed by GC. The e ective conversion with a turbine agitator was found to be 55% but an anchor-type agitator produced almost 100% conversion at 270°C and 5.5 MPa H2 pressure. In both cases the overall product distribution was similar, varying from C3 to C14 . An increase of the temperature increased lighter product yield with increasing amounts of gas. Only negligible amounts of products heavier than C14 were found at any temperature. The total conversion was obtained at the three temperatures studied from 270°C to 350°C using 5.5 MPa initial H2 pressure and 1% Pt USY. The product distribution, cf. Table 6.21, showed no significant di erences in the profile for any of the three di erent temperatures and all catalysts gave C4 as the major product with little or no C1 and C2 . Table 6.21 Product distribution as a function of temperature and hydrogen pressure using HDPE with 1% Pt USY (89). T [°C] H2 initial P [MPa] Gas [%] Gasoline [%] Diesel [%] Coke [%]

350 5.5

310 5.5

270 5.5

270 3.5

270 1.5

58.9 40.8 0.0 3.9

43.5 56.0 0.0 4.9

33.4 65.9 0.3 5.0

35.2 63.7 0.2 8.8

12.0 23.4 0.2 17.4

When the reaction temperature was lowered to 210°C at a pressure

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of 5.5 MPa of H2 , all of the HDPE was consumed, so resulting in a total conversion (89). 6.7.4

Debromination of Pyrolysis Oil

Polymer mixtures containing 8 g of HDPE or PS and 2 g of ABS copolymer containing a polybrominated epoxy-type flame retardant (ABS-Br) were thermally degraded at 450°C (90, 91). FeOOH and two carbon composites based on iron (Fe C) and calcium (Ca C) were used for the catalytic decomposition and their e ect on the bromine and nitrogen amount and distribution in pyrolysis oil was determined by GC atomic emission detector analysis. It was found that iron-based catalysts could remove the bromine from the pyrolysis oil and decreased the nitrogen amount by converting nitrile compounds into ammonia. The calcium carbon composite had a lower e ect especially on the pyrolysis of the PS ABS-Br mixture. These liquid products can be used as fuel oil or feedstock in petroleum refinery (91). In addition, the pyrolysis of a brominated flame retardant containing high impact polystyrene mixed with PET was performed at 430°C under atmospheric pressure by a batch operation (92). The addition of PET to the brominated high impact polystyrene significantly a ected the formation of decomposition products and the degradation behavior. The following facts were observed upon the addition of PET (92): 1. The rate of formation and the yield of liquid products decreased, 2. The residue and gaseous products formation increased, 3. The average carbon number of liquid products was reduced from 12.5 to 9.1, 4. The yield of high molecular weight hydrocarbons (C16 to C20 ) decreased, and the amount of hydrocarbons from C6 to C10 doubled, 5. Heavy waxy compounds were formed on the top of the glass reactor wall in addition to the solid residue on the bottom of the reactor, and 6. Antimony compounds were observed in the solid residue, as opposed to the formation of antimony tribromide (SbBr3 )

Specific Materials

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detected in the liquid products of brominated flame retardant in the absence of PET. The debromination of the brominated liquid hydrocarbons was examined using iron- and calcium-based carbon composites for the production of halogen-free liquid hydrocarbons, which can be used as a feedstock in a refinery or as a fuel (92). 6.7.5

Commingled Post-Consumer Polymer

A commingled post-consumer polymer was pyrolyzed over spent FCC commercial catalyst (ECat-1) using a laboratory fluidized-bed reactor that was operating isothermally at ambient pressure (93). The influence of the reaction conditions, including catalyst, temperature, ratios of commingled polymer to catalyst feed and flow rates of fluidizing gas, was elucidated. The conversion for the spent FCC commercial catalyst of 82.7% exhibited a much higher yield than silicate with only 14%. The highest yield of nearly 87% was obtained by using ZSM-5 as catalyst. In the case of PP, the FCC catalysts and amorphous silica-alumina (SAHA) significantly reduced the activation energy in comparison to a pure thermal process, and zeolites (ZSM-5 and HUSY) further reduced the activation energy. However, silicate catalysts had very minimal e ect on the degradation of PP at a temperature similar to that of thermal cracking (94). A greater product selectivity was observed with ECat-1 as a recycled catalyst with about 56% olefins products in the range of C3 –C7 (93). The product distributions from an ECat-1 catalyzed degradation of a commingled post-consumer polymer at di erent ratios of polymer to catalyst with a reaction temperature of 400°C, a catalyst particle size of 75 μ m to 180 μm, a fluidizing nitrogen rate of 600 ml min 1 and a total time of collection of 30 min are shown in Table 6.22. The selectivity could be further influenced by changes in the conditions of the reaction. Valuable hydrocarbons of olefins and i-olefins were produced by using low temperatures and short contact times.

284

Polymer Waste Management Table 6.22 Product distributions from an ECat-1 (93). Yield [%]

Ratio of polymer to catalyst [%] 10 20 30 40 60

Gaseous Liquid Residue Involatile residue Coke HCl

85.4 4.2 9.7 7.3 2.4 0.5

83.9 4.8 10.8 8.7 2.1 0.5

82.7 5.3 11.5 9.2 2.3 0.5

81.5 6.3 11.8 9.8 1.7 0.4

80.3 6.9 12.3 10.7 1.6 0.5

Mass balance [%]

89.4

91.4

92.6

92.5

90.4

A kinetic model based on a lumping reaction scheme for the observed products and catalyst coking deactivations has been investigated (95). The model gave a good representation of experiment results. Moreover, this model provides the benefits of lumping product selectivity in each reaction step, in relation to the performance of the FCC equilibrium catalyst used, the e ect of reaction temperature, and the particle size selected. The average value of the activation energy and the value of coke content determined from TGA for the catalytic degradation of PP are shown in Table 6.23. Table 6.23 Activation energy and coke content (94). Catalyst type FCC-s1 HUSY ZSM-5 SAHA Silicalite

Activation energy [kJ mol 1 ] 87.1 76.4 72.5 91.7 143.4

Coke content [%] 5.7 8.2 0.1 0.6 0.2

As can be seen in Table 6.23, the FCC-s1 catalysts reduce the activation energy in comparison to the amorphous silica-alumina (SAHA) catalysts. The spent FCC catalysts have a much milder acidity than zeolites and a bimodal pore structure including mesopores as well as micropores which are initially available for the degradation of large molecules. Zeolite-based catalysts (ZSM-5) with a very

Specific Materials

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strong acidity with almost entirely Brønsted acid sites result in a significant decrease of the activation energy (94). The results also demonstrated that the use of a spent FCC commercial catalyst with appropriate reaction conditions can have the ability to control both the product yield and product distribution from polymer degradation, thus, potentially leading to a cheaper process with more valuable products (93).

6.7.6

Waste Packaging Separation

Plastic wastes coming from a waste packaging separation and classification plant have been pyrolyzed in a semi-batch nonstirred autoclave, swept by a continuous flow of N2 (96). The plastic waste contained 39.5% PE, 34.2% PP, 16.2% PS and expanded poly(styrene), and some other minor materials. Temperatures in the range of 400°C to 600°C have been explored, and it has been found that over 460°C a total thermal decomposition of the waste plastics takes place. Three catalysts have been tested: HZSM-5, red mud, and AlCl3 . Solid yields of about 5–7%, liquid yields in the range of 40–70% and gas yields in the range of 12–24% were obtained. The liquid products were a mixture of C5 –C20 compounds with a very high proportion of aromatics (greater than 70%). Such liquids contain significant amounts of valuable chemicals such as styrene (20–40%), toluene (9–15%), and ethylbenzene (7–16%). Thermal pyrolysis oils were a wax-like product which solidified at room temperature, whereas the oils obtained with any of the catalysts were less viscous and maintained their liquid state at room temperature. The catalyst HZSM-5 favored the gas production, increased the amount of aromatic compounds and decreased the number of carbons of the oils. AlCl3 did not modify the pyrolysis yields but gave rise to lighter liquids. Red mud produced higher liquid yields and the liquids were less viscous, but a clear e ect on the carbon number of the oils was not observed (96).

286 6.7.7

Polymer Waste Management Hospital Wastes

A mixture of hospital post-commercial polymer waste containing LDPE, HDPE PP, and PS was pyrolyzed using a variety of catalysts in a fluidized-bed reactor that was operating isothermally at ambient pressure (97). The yield of volatile hydrocarbons with zeolitic catalysts (ZSM-5 > MOR > USY) were higher than with non-zeolitic catalysts (MCM-41 > ASA). MCM-41 with large mesopores and ASA with weaker acid sites resulted in a highly olefinic product mixture with a wide carbon number distribution, whereas USY yielded a saturate-rich product mixture with a wide carbon number distribution and substantial coke levels. The systematic experiments indicated that the use of various catalysts improves the yield of hydrocarbon products and can provide a better selectivity in the product distributions. A model based on kinetic and mechanistic considerations was developed, which takes into account the chemical reactions and the catalyst deactivation for the catalytic degradation of a commingled polymer waste. This model represents the benefits of product selectivity for the chemical composition, such as alkanes, alkenes, aromatics, and coke, in relation to the performance and the particle size selection of the catalyst used as well as the e ect of the fluidizing gas and reaction temperature (97). In other studies, a mixture of post-consumer PE, PP, and PS with PVC waste was pyrolyzed in the presence of cracking catalysts using a fluidizing reaction system that was operating isothermally at ambient pressure (98, 99). The influence of catalyst types and reaction conditions, including reaction temperatures, ratios of catalyst to plastic feed, flow rates of fluidizing gas and catalyst particle sizes, was examined. Good yields of valuable hydrocarbons with di ering selectivity in the final products depending on reaction conditions were demonstrated (99). The product distributions shown from FCC-R1 catalyzed pyrolysis of waste plastics (WPs#4) at di erent fluidizing N2 rates are shown in Table 6.24. The reaction temperature was 390°C, the catalyst to plastic ratio was 30% and the catalyst particle size was 125–180 μ m.

Specific Materials

287

Table 6.24 Product distributions from FCC-R1 catalyzed pyrolysis waste at fluidizing nitrogen rates (99). Yield [%]

Fluidizing N2 rate [ml min 1 ] 900 760 600 450 300

Gaseous Liquid Residue Involatile residue Coke HCl

84.6 4.5 8.8 6.6 2.2 2.1

83.1 4.8 9.4 7.0 2.4 2.1

82.4 3.8 11.7 9.3 2.4 2.1

82.1 3.9 11.8 9.5 2.3 2.2

81.3 3.8 12.5 10.4 2.4 2.0

The product distributions from FCC-R1 catalyzed pyrolysis of waste plastics (WPs#4) at di erent ratios of plastic waste are shown in Table 6.25. Here, the reaction temperature was 390°C, the fluidizing N2 rate was 600 ml min 1 and the catalyst particle size was 125–180 μ m. Table 6.25 Product distributions from FCC-R1 catalyzed pyrolysis waste at di erent ratios of plastic waste (99).

6.7.8

Yield [%]

Ratio of plastic waste to catalyst [%] 100 200 600 300 600

Gaseous Liquid Residue Involatile residue Coke HCl

85.5 3.1 9.2 6.5 2.7 2.3

84.2 3.3 10.4 7.9 2.5 2.1

82.4 3.8 11.7 9.3 2.4 2.1

81.5 5.0 12.2 10.1 2.1 1.8

79.5 5.7 13.1 11.1 2.0 1.7

Agricultural Plastic Film Wastes

Feedstock recycling by catalytic cracking of a real plastic film waste from Almeria greenhouses (Spain) towards valuable hydrocarbon mixtures has been studied using several acid catalysts (100). The plastic film waste was mostly made up of ambient degraded LDPE and EVA copolymer. The vinyl acetate content was around

288

Polymer Waste Management

4%. Nanocrystalline HZSM-5 zeolite with a crystal size of around 60 nm was the only catalyst capable of completely degrading the refuse at 420°C despite using a very small amount of catalyst. The mass ratio of plastic to catalyst was 50. However, mesoporous catalysts (Al-SBA-15 and Al-MCM-41), unlike those occurring with virgin LDPE, showed fairly close conversions to that of thermal cracking. Nanocrystalline HZSM-5 zeolite led to 60% selectivity towards C1 –C5 hydrocarbons, mostly valuable C3 –C5 , which would improve the profitability of an industrial recycling process. The remarkable performance of nanocrystalline HZSM-5 zeolite was ascribed to its high content of strong external acid sites due to its nanometer dimension, which are very active for the cracking of bulky macromolecules. Hence, nanocrystalline HZSM-5 is a promising catalyst for a feasible feedstock recycling process by catalytic cracking (100).

6.8 Technical Biopolymers The recycling of bioplastics, their blends and thermoplastic biocomposites, with a special focus on mechanical recycling of bio-based materials, has been reviewed (101). 6.8.1

Mechanical Recyclability

The mechanical recyclability of the technical biopolymers poly(trimethylene terephthalate) (PTT), cellulose acetate butyrate, poly(butylene succinate), and a polyhydroxy alkanoate blend (PHBV PBAT) was evaluated by assessing the e ect of a repeated polymer processing method (102). This method is extrusion without further compounding with virgin material or additives. 6.8.2

Hydrolytic Degradation

Reprocessing-induced hydrolytic degradation was found to be the prevalent aging mechanism of the investigated biopolymer grades. However, susceptibility to hydrolysis, and thus maintenance of the performance characteristics, di ered strongly between the biopolymer types.

Specific Materials

289

A high potential for mechanical recycling was especially exhibited by PTT and cellulose acetate butyrate. By taking advantage of appropriate additivation, the mechanical recyclability of poly(butylene succinate) and PHBV PBAT has also been assumed to be high (102). 6.8.3

Measurement of Renewable Bio-source Content

Renewable bio-based plastics represent a class of plastics made from renewable biomass source materials. These materials may include food or non-food crops including, for example, corn, rice, soy, or other sugar and starch-producing plants (103). Special plastics may be formed partially or fully from renewable bio-derived materials. All living matter is composed of three types of carbon: 12 C, 13 C, and 14 C. 12 C, which has 6 neutrons and 6 protons, is the most abundant form of carbon on the planet, comprising approximately 98.9% of all carbon isotopes. 13 C, which has 7 neutrons and 6 protons, is the second most abundant form of carbon on the plant, comprising approximately 1.1% of all carbon isotopes. 14 C, which has 8 neutrons and 6 protons, is the least abundant carbon isotope, and is present in only trace amounts, approximately 14 parts per trillion compared to the total carbon content. Unlike 14 C, which is continuously generated from the interaction of the sun and the upper atmosphere, the amount of 13 C is essentially fixed and finite over the period of several human lifetimes. Most of the 13 C that is present today has been around since the formation of the solar system. However, due to cycles that introduce more carbon into the atmosphere, bio-renewable bio-derived materials and nonrenewable petroleum-derived materials have remarkably di erent 13 C levels. It is possible to determine the amount of carbon in a product that is derived from renewable bio-based materials relative to the total amount of carbon in the entire product. This is because renewable biomass contains a well-characterized amount of 14 C that can be easily di erentiated from other materials, such as fossil fuels, that do not contain any 14 C. The percentage of a given product that is derived from renewable bio-based materials is generally measured by accelerator mass spectrometry (AMS) or liquid scintillation counters (LSCs).

290

Polymer Waste Management

Generally, LSC is considered relatively low precision and requires extensive sample preparation as well as long counting times that can take from days to weeks. AMS provides a higher precision, but the capital and operating costs are high. In addition, processing time for third party vendor analysis of AMS can be long. Therefore, there is a need for a method to measure the renewable bio-source carbon content of a renewable bioplastic resin manufactured in a production facility e ciently and cost-e ectively. In particular, in order to optimize the manufacturing process such that the maximum amount of renewable biomaterial can be produced, there is a need to quickly and reliably measure the renewable biosource carbon content of a renewable bioplastic resin manufactured in a production facility over time, particularly during transition periods in the process where nonrenewable petroleum-derived plastic starting materials are swapped out for renewable bio-derived plastic starting materials (103). Improved methods for measuring the renewable bio-source carbon content and the renewable bio-content in renewable bioplastic resins have been presented. Such methods include (103): 1. Measuring delta carbon-13 (δ 13 C) values of the renewable bioplastic resin samples throughout a production run, 2. Determining the actual renewable bio-source carbon content of two renewable bioplastic samples in the first step with the lowest and the highest δ 13 C value, 3. Correlating the δ 13 C values from the first step with the actual renewable bio-source carbon content of the second step for the two resin samples, 4. Indirectly determining the renewable bio-source carbon content of the remaining resin samples in the production run based on said correlation, and 5. Calculating the renewable bio-content from the renewable bio-source carbon content. Preferably, the δ 13 C values are measured by combustion-cavity ring-down spectrometry (ORDS). Also, the δ 13 C values can be measured by total organic carbon-cavity ring-down spectrometry (iTOC-CRDS) and the actual renewable bio-source carbon content is determined by AMS.

Specific Materials

291

A correlation plot of iTOC-CRDS-measured δ 13 C values versus AMS-measured renewable bio-source carbon content for five PET films is illustrated in Figure 6.15. -23 -23.5

δ C13 content

-24 -24.5 -25 -25.5 -26 -26.5 -27 -27.5 0

5

10

15

20

Biosource carbon/[%] Figure 6.15 Correlation plot of iTOC-CRDS-measured C13 values versus AMS-measured renewable bio-source carbon content for PET films (103).

In addition, there are also standard methods available for the determination of the bio-based content of solid, liquid, and gaseous samples (104, 105). The described procedures are similar to those described above.

6.9 Co-processing of Waste Plastics and Petroleum Residue 6.9.1

Co-processing with Light Arabian Crude Oil

Waste plastics of di erent types were catalytically co-processed with petroleum residue of light Arabian crude oil in the presence of a number of catalysts (106). The e ects of various conditions such as catalyst type, amount of catalyst, reaction time, pressure, and

292

Polymer Waste Management

temperature on the product distribution have been investigated. The waste plastic studied included LDPE, HDPE, PS, and PP. A series of single (waste plastic with catalyst) and binary (waste plastic and residue with catalyst) reactions were done in an autoclave reactor under variable reaction conditions (106). The reaction conditions used were 1%, 3%, and 5% catalysts, 30–120 min reaction time, 400°C–430°C reaction temperature and 3.45 bar to 82 bar hydrogen pressure. The product distribution achieved for the residue plastic catalyst system showed higher yields of liquid fuels in comparison to the residue plastic system. Hydrocarbon gases were formed as well, along with heavy oils, insoluble gums, and coke. At process conditions using 3% NiMo catalyst, 90 min reaction time, 82 bar hydrogen gas pressure, a temperature of 430°C, and a ratio of residue to plastic feed of 3:2 a maximum conversion of the plastics into liquid fuel oils was found (106). Catalytic coprocessing of model and waste plastics with light Arabian crude oil residue was investigated using NiMo Al2 O3 , ZSM-5, FCC, and hydrocracking catalysts. The reaction systems that were studied included LDPE, HDPE, PS, and PP. A series of single (plastic catalyst) and binary (plastic resid catalyst) reactions were carried out in a 25 cm3 autoclave microreactor under di erent conditions of weight and type of catalyst, duration, pressure, and temperature. The optimum conditions found were: 1% catalyst by weight of total feedstock weight, 60 min reaction time, 8.3 M Pa of H2 , and 430°C. The product distribution for the binary system using plastic and petroleum residue provided some encouraging results. High yields of liquid fuels in the boiling range of 100°C to 480°C and gases were obtained along with a small amount of heavy oils and insoluble material such as gums and coke. It was demonstrated that the technical feasibility of upgrading both waste plastics and petroleum residues are an alternative approach to feedstock recycling.

6.10 Automotive Waste Plastics Recycling automotive waste is very tedious and di cult due to its heterogeneous composition and nature (107). The development of a solution to recycle and reuse these potential resources is critically

Specific Materials

293

required. A monograph deals with the issues of automotive recycling (108). The challenges and several alternatives to recycling plastics in the automotive sector have been reviewed (109, 110). There are several obstacles to recycling the types of materials that are commonly used in automotive applications. Plastics that are commonly used in automotive applications include poly(urethane) (PU) foam, PP, PET, PE, PVC, and ABS. The most plausible methods to achieve a considerable reduction of automotive shredder residues are as follows (110): either recycling of separated materials and dismantled bulky parts, such as bumpers, dashboards, cushions, and front and rear windows, or else systematic sorting of the commingled and size-reduced materials resulting from shredding. For example, PU foam has been gaining widespread use in the automotive industry due to its lightweight, moldable, and durable properties (109). It is also a useful noise dampener. These desirable properties are responsible for the increase in usage of this material within vehicles despite it being a thermoset material. PU is commonly found in automotive seating applications, as well as within the interior and under the hood. Unlike some other thermoset materials, PU can be relatively easy to convert back into its original monomer. Therefore, PU, in theory, is recyclable and several technologies exist for this purpose. In reality, the location of the foam within the vehicle is not easily accessible and is often contaminated. Furthermore, it is currently not economically viable for dismantlers to segregate this inexpensive material from the end-of-life vehicles. Some other vehicle components that are commonly made of plastics include drink trays (PP), armrest finishers (PP ABS), and seatbelts (PET). Similar to PU foam components, these often do not make it to recycling due to inaccessibility and lack of economic incentive at the dismantling stage (109). Assemblies used in automotive parts are shown in Table 6.26. Several alternatives were discussed in relation to the options for plastics and composites from end-of-life vehicles. One of the first critical questions is whether or not conventional plastics are the best choice for the application being considered. In some cases,

294

Polymer Waste Management Table 6.26 Assemblies used in automotive parts (111). Part assembly

Metallic [%]

Nonmetallic [%]

70 69 60 80 44 66

30 31 40 20 56 34

Front door assembly Rear door assembly Steering wheel Steering column Dash assembly Seat assembly

bioplastics or metals may provide a superior functionality and environmental performance over the life cycle of the vehicle given the challenges of recovering plastics. So, the mindset that plastics are a preferred material choice needs to be challenged. In cases where conventional plastics are used, the best recovery alternative is likely a combination of the possible options, for example, combining recycling and energy recovery. Segregating the larger, cleaner material pieces for recycling and sending the remainder for energy recovery is a common choice. However, future e orts should look to increase the proportion destined for recycling. For thermoset materials, emerging techniques are showing promising results towards the development of new materials that can have the desirable properties of thermoset plastics while being recyclable at the end-of-life vehicle stage. Several of the alternatives could exist in combination to comprehensively address the challenges of recycling with the overall goal of improving the economics and e ciency of identifying, separating, and recovering plastics (109). 6.10.1

Lightweight Aggregates

A novel recycling approach has been established to produce lightweight aggregate by incorporating automotive shredded residual plastics into clay at 1200°C (107). The physical properties of lightweight aggregate, such as bulk density, porosity, and water absorption, have been investigated. Automotive shredded residual plastics as pore-forming or gas-releasing agent increased the porosity of a clay mixture. The incorporation of 2% of automotive shredded residual plastics into a clay

Specific Materials

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composite leads to a benefit of approximately 30% bulk density decrease and 40% porosity increase compared to a reference clay material. The obtained superior lightweight and porous aggregate products by using automotive shredded residual plastics can be used in thermal insulation materials and also as substrates in soilless cultivation. This approach could also help reduce the volume of automotive plastics in landfills and could be a potential replacement for conventional additives in manufacturing composite materials for building applications (107). X-ray fluorescence (XRF) spectroscopy and ICP ultimate analysis were performed on received clay and automotive plastic waste to determine the elemental content. The major oxides in clay and automotive waste plastics ash have been analyzed by XRF. The results are shown in Table 6.27. Table 6.27 Major oxides in clay and automotive waste plastics ash (XRF analysis) (107). Compound

Amount [%] Clay Auto

SiO2 Al2 O3 Fe2 O3 K2 O MgO Na2O TiO2 CaO Mn3 O4 P2 O5 Cr2 O3 SO3 ZnO

58.02 19.81 7.13 2.53 1.27 0.80 0.82 0.45 0.11 0.20 – – –

27.88 3.86 2.58 0.44 14.66 0.65 34.39 8.95 0.08 0.83 0.16 0.92 0.42

The results of inductively coupled plasma (ICP) analysis are shown in Table 6.28.

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Polymer Waste Management

Table 6.28 Elements in clay and automotive waste plastics ash (ICP analysis) (107). Element Al Ba Br Ca Cr Cu Fe K Mg Mn Na P Pb Sb Si Sr Ti V Zn Zr

Amount [%] Clay Auto 8.99 0.04 0.01 1.15 0.01 0.01 1.16 15.34 0.41 0.04 0.32 0.04 0.01 0.01 22.05 0.01 0.33 0.01 0.06 0.01

0.07 1.02 0.19 0.99 0.05 0.01 0.05 0.06 0.32 – 0.07 0.03 0.05 0.21 2.37 – 3.68 – 0.06 –

Specific Materials 6.10.2

297

Titanium Nitride Film on Steel Substrate

A sustainable technology to fabricate protective nanoscale TiN thin film on a steel substrate surface by using automotive waste plastics as titanium and carbon resources has been suggested (112). When automotive plastics waste is heated with steel in nitrogen atmosphere, titanium dioxide occurring in automotive waste plastics undergoes a carbothermal reduction and nitridation reactions occur on the surface of the steel substrate, thus forming a nanoscale thin film of titanium nitride on the steel surface. The synthesis of TiN film on steel substrate using this technology was confirmed by X-ray photoelectron spectrometry, high resolution X-ray di raction, field emission scanning electron microscopy, a high resolution transmission electron microscope fitted with energy dispersive X-ray spectroscopy, and inductively coupled plasma mass spectrometry techniques. This sustainably fabricated TiN film was verified to be dense, well crystallized and could provide a good oxidation resistance to the steel substrate. This sustainable fabrication technology is maneuverable, reproducible, and of great economic and environmental benefit. It not only reduces the fabrication cost of TiN coating on steel surface, but also provides a sustainable environmental solution to recycling automotive plastics waste. Moreover, high-value copper droplets and char residues were also extracted from this unique fabrication process (112).

6.11 Phthalates Phthalates are a group of chemicals produced in large volumes and are commonly used as plasticizers in plastics manufacturing (113). The potential impacts on human health require a restricted use in several applications and a need for closer monitoring of potential sources of human exposure. Although the presence of phthalates in a variety of plastics has been recognized, the influence of plastic recycling on phthalate content has been not well documented. In a study, some phthalates were analyzed in samples of waste plastics, and also in recycled plastics and in virgin plastics. The investigated phthalates are shown in Table 6.29,

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Polymer Waste Management Table 6.29 Phthalates (113). Shortcut BBzP DBP DCHP DEHP DEP DiBP DMP DnOP DPP

Chemical name

CAS number

Butyl benzyl phthalate Dibutyl phthalate Dicyclohexyl phthalate Diethylhexyl phthalate Diethyl phthalate Di-i-butyl phthalate Dimethyl phthalate Di-n-octylphthalate Dipropyl phthalate

85-68-7 84-74-2 84-61-7 117-81-7 84-66-2 84-69-5 131-11-3 117-84-0 131-16-8

Dibutyl phthalate, di-i-butyl phthalate, and diethylhexyl phthalate showed the highest frequency of detection in the investigated samples, with 360 μ g g 1 , 460 μ g g 1 , and 2700 μ g g 1 as the maximum measured concentrations, respectively. A statistical analysis of the analytical results suggested that phthalates were potentially added in the later stages of plastic product manufacturing, i.e, labeling, gluing, and others. These compounds were not removed following recycling of household waste plastics. Furthermore, diethylhexyl phthalate was identified as a potential indicator for phthalate contamination of plastics. Therefore, a close monitoring of plastics intended for phthalates-sensitive applications is recommended if recycled plastics are used as a raw material in production methods (113).

6.12 Enzymatic Degradation The high recalcitrance of many synthetic plastics results in their long persistence in the environment, and the growing amount of plastic waste ending up in landfills and in the oceans has become a global concern. In recent years, a number of microbial enzymes capable of modifying or degrading recalcitrant synthetic polymers have been identified (114). These are emerging as candidates for the development of biocatalytic plastic recycling processes, by which valuable raw materials can be recovered in an environmentally sustainable way. Microbial

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biocatalysts involved in the degradation of the synthetic plastics PE, PS, PU, and PET have been detailed. Plant polymers are the natural substrates for key enzymes capable of attacking the polymer backbones of synthetic plastics. For example, cutinases can hydrolyze cutin, an aliphatic polyester found in the plant cuticle (115). These enzymes are also able to hydrolyze the ester bonds in PET and PU (116–118). Alkane hydroxylases (AH) of the AlkB family (EC 1.14.15.3) can catalyze the degradation of hydrocarbon oligomers by terminal or subterminal oxidation (119). A recombinant AH from Pseudomonas sp.E4 expressed in Escherichia coli BL21 converted 20% of the low molecular weight PE sample to CO2 after incubation for 80 days at 37°C (120). A recombinant E. coli strain simultaneously expressing the complete AH system from Pseudomonas aeruginosa E7 including an alkane monooxygenase, rubredoxin, and rubredoxin reductase degraded about 30% of this PE sample (121). A purified hydroquinone peroxidase (EC 1.11.1.7) of the lignin-decolorizing Azotobacter beijerinckii HM121 degraded PS, an aromatic thermoplastic with a C C backbone, in a two-phase system consisting of dichloromethane and water. PS in the organic phase was rapidly converted to small water-soluble products within 5 min of reaction at 30°C in the presence of hydrogen peroxide and tetramethylhydroquinone (122).

6.13 Electronic Waste The issues of recycling of electronic waste plastics have been reviewed (123, 124). Mechanical, thermal, and feedstock recycling of electronic waste plastics were analyzed and some options assessed. Plastics recycling should be weighed against the eventual risks related to their hazardous ingredients, mainly legacy brominated fire retardants and heavy metals. The global electronic waste market creates more than 50 M t y 1 with an estimated 3% in printed wiring boards, also referred to as printed circuit boards, and an estimated 30% in plastic resins (125). The United States alone contributes between about 28–33% of the global electronic waste totals. The electronic waste market is ex-

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pected to continue to increase an estimated 10–15% annually with the global consumer appetite for newest electrical and electronic equipment. This results in a critical and worsening economic environment with a need for solutions to discarded electronic waste products. Globally, the values of precious metals, copper and aluminum (predominant in electronic waste sources) have fluctuated significantly, further reducing interest in e ectively recovering or recycling components from the ever-growing electronic waste recycling recovery market. In addition, various state regulations aim to restrict or limit landfill dumping of electronic waste sources, resulting in significantly reduced incentives for processing electronic waste sources (125). Di erent approaches have been used for processing waste electrical and electronic equipment, a term broadly referring to the spectrum of products ranging from computers, printers, and faxes to washing machines (125). In particular, waste electrical and electronic equipment is classified into the 14 distinct categories shown in Table 6.30. Table 6.30 Categories of electrical and electronic waste (125). Category Large household appliances Small household appliances IT and telecommunications equipment Consumer equipment Lighting equipment Electrical and electronic tools Toys, leisure and sports equipment Medical devices Monitoring and control instruments Automatic dispensers Display equipment Refrigeration equipment Gas discharge lamps Photovoltaic panels

Electronics recycling has historically been a very labor-intense operation (125). This is a result of the diverse compositions making

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up electronic waste sources. Plastic housings from electronic devices are ine ectively recycled and the collection, sorting, re-pelletizing and shipping costs may be twice as high as the costs for virgin raw materials based on natural gas-based feedstocks. Flat-screen displays containing mercury are another example of expense to process electronic waste sources. Each flat-screen display requires approximately 20 min for disassembly to remove the delicate mercury lamps. In addition to the ultra-high costs associated with this recycling process, the frequent mercury contamination from poor disassembly processing and breakage becomes a huge issue to recyclers. These examples demonstrate that the manual recycling of electronic waste sources does not provide a cost-e ective solution to the accumulating electronic waste supply (125). There are also safety concerns with processing electronic waste sources. A significant percentage of the recycled polymers contain toxic compounds, including halogenated hydrocarbons and organics, antimony oxides, and other polymer additive flame retardants or fire retardants. The hazards of halogenated substances in electrical and electronic equipment have been described (126). These components are formulated in plastic housings and other components of electronic waste sources to provide fire retardancy. As a result, the housings cannot easily be landfilled due to the toxic flame retardants or fire retardants. Toxins can result from the combustion of halogenated hydrocarbons and organics, generating toxic by-products such as aromatics and polycyclic aromatic hydrocarbons, halogenated dibenzodioxins, halogenated dibenzofurans, biphenyls, pyrenes, etc. Combustion processes generate these toxic materials which then must be removed downstream of the process and thereby render incineration approaches unsuccessful and or not economical. As a result, large volumes of electronic waste are shipped o shore to smelters, which are becoming less economically attractive due to high transportation, processing, and environmental costs. Moreover, the smelting process is ine cient and a large percentage of metals can be lost in the smelting process (125). A guide has been presented to inform and assist di erent stakeholders in the Nordic region to enhance the recycling of plastic

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materials from electrical and electronic waste (127). Its recommendations are presented to various parties: Consumers, authorities and policymakers, recyclers and waste operators, as well as electronics producers.

6.13.1

Main Plastics in Electronic Waste

Compositions and typical densities of the main plastics in electronic waste are shown in Table 6.31. These typical compositions were also found in previous studies (128–130) Table 6.31 Compositions and typical densities of the main plastics in an electronic waste sample (131). Polymer PP PE ABS HIPS PVC PC POM PET PA PMMA SAN

6.13.2

Percent [% w W] 16.42 4.12 30.02 21.04 7.02 5.04 1.93 3.50 2.87 4.15 3.89

1.1 0.2 2.3 1.8 0.2 0.5 0.3 0.3 0.6 0.7 0.4

Density [g cm 3 ] 0.91 0.91 1.03 1.22 1.43 1.12 1.37 1.44 1.20 1.13 1.10

0.01 0.02 0.06 0.05 0.03 0.04 0.02 0.04 0.03 0.02 0.03

Recycling of Compact Discs

An environmental method was used to recycle compact discs using tannery industrial wastewater e uent (132). The materials were characterized by TGA, also the mechanical properties and wastewater characterization before and after treatment were investigated. The final recycled compact disc was completely free of ink, and its mechanical properties were slightly enhanced after ink removal. The crystallization behavior of the compact disc remains the same after the de-inking process (132).

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After the de-inking procedure, the study was continued to the treatment of tannery e uent by conventional coagulation-flocculation followed by a Fenton treatment process. The coagulationprecipitation process removed 42%, 77%, 86%, 99%, 84%, and 85% of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), sulfides, total Kjeldahl nitrogen, and phosphorus, respectively. Unfortunately, due to its solubility in water, the coagulation process did not a ect the concentration of phenols. Therefore, the Fenton oxidation process was able to remove 100% of phenols, hydrogen sulfide, and phosphorus (132). The Fenton treatment (133, 134) is used mainly in the removal of phenols and soluble recalcitrant organics (135). 6.13.2.1

Hydroglycolysis

Hydroglycolysis of PC wastes received from optical (CDs) and digital optical discs (DVDs) to the diols derivatives of bisphenol A (BPA), namely, bis(4-hydroxybutyl hydrogen carbonate) of bisphenol A, mono(4-hydroxybutyl hydrogen carbonate) of bisphenol A, and bisphenol A itself as the major and oligomeric minor products were developed under mild and convenient conditions. Experiments were performed with the mixture of green solvents, including 1,4butanediol and water in the presence of nanoparticles TiO2 and microparticles TiO2 as the solid supports, and sodium hydroxide as the catalyst using a simple heating method and the obtained results were compared. In the here developed procedure, bis(4-hydroxybutyl hydrogen carbonate) of bisphenol A achieved and selectively converted into the mono(4-hydroxybutyl hydrogen carbonate) of bisphenol A and bisphenol A, respectively, when left in the moisturized environment. In these reactions, the e ects of various parameters, such as concentration of sodium hydroxide, the role of water as cosolvent, and nano-solid support on reaction progress, are considered. The obtained results showed that by increasing the amount of water, from 0 up to 30 pbw based on total solvent weights, as well as catalyst from 0 up to 2 pbw based on total solvents and PC wastes weight, the depolymerizing reaction was performed in high yields.

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In the meantime, bis(4-hydroxybutyl hydrogen carbonate) of bisphenol A was recovered in 80% yield, using nanoparticles as the solid support in the 30 pbw aqueous 1,4-butanediol. The depolymerization reaction time was shortened with the use of nanoparticles as the solid support when the data was compared with the experiments performed by microparticles TiO2 (136). Finally, the recyclability and e ciency of the nanoparticles were studied and the data showed the usability of this solid support for four cycles. The recovered products were characterized using 1 H NMR, 13 C NMR, FTIR, TGA, and GC MS (136). 6.13.3

Liquid Crystal Displays

Little is known about the feasibility of closing material loops for flame retardant-containing plastics (137). A series of experiments were set up to analyze the feasibility of separating plastics containing flame retardants from one specific product category, namely end-of-life liquid crystal display TVs. A manual disassembly of 43 liquid crystal display TVs showed that they contain around 31% of plastic materials. An average of 15% of these plastics are used in the front cover and 45% are used in the back cover. The remaining 40% of the plastics do not contain flame retardants and are used in the liquid crystal display device to di use and polarize the backlight. The characterization of the housings of this waste stream indicated a concentration of 18% bromine-based flame retardants and 31% phosphor-based flame retardants, with the remainder not containing flame retardants. With practical tests it could be demonstrated that after disassembly and plastic identification, the copolymer PC ABS containing a phosphor-based flame retardant can be recycled in a closed-loop system. Based on the determined plastic density distributions and the separation e ciencies of optical sorters, a purity of 82% was calculated for phosphor-based flame retardant PC ABS separated from the liquid crystal display TV after shredding. Miscibility tests indicated that for this fraction at least a factor 10 dilution with virgin material is required. In addition, higher waste volumes are required for a size reduction-based treatment to become economically viable and technical challenges still need to

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be faced, whereas closed-loop recycling of the materials from the current waste stream of the liquid crystal display TVs of di erent brands in a disassembly-based treatment has been found to be technically feasible and economically viable under European boundary conditions (137). 6.13.4

Pyrolysis of Printed Circuit Boards

The recycling of flexible printed circuit board waste through carbonization of polyimide by a dual pyrolysis process has been reported (138). The organic matter was recovered as pyrolyzed oil at low temperatures, while valuable metals and polyimide-derived carbon were e ectively recovered through secondary high temperature pyrolysis. The major component of organics extracted from flexible printed circuit board waste comprised of epoxy resins were identified as pyrolysis oils containing bisphenol A. The valuable metals (Cu, Ni, Ag, Sn, Au, Pd) in a waste flexible printed circuit board were recovered as granular shape and quantitatively analyzed via inductively coupled plasma optical emission spectrometry. In an attempt to produce a carbonaceous material with increased degree of graphitization at low heat-treatment conditions, the catalytic e ect of transition metals within flexible printed circuit board waste was investigated for the e cient carbonization of polyimide films. The morphology of the carbon powder was observed by SEM and graphitic carbonization was investigated with X-ray analysis. The composition of metal elements extracted from a flexible printed circuit board (FPCB) was compared to that from a conventionally recycled printed circuit board (PCB), as shown in Table 6.32. The results from this study may allow for propitious opportunities to salvage both organic and inorganic materials from flexible printed circuit board waste products for a sustainable future (138). 6.13.5

Metal Recovery

The increased use of computers, mobile phones, electronic equipment and other short life high-tech devices creates a growing

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Polymer Waste Management Table 6.32 Composition of metal elements extracted from FPCB and from conventionally recycled PCB (138). Polymer Cu FPCB PCB

71.44 15.00

Polymer Ag FPCB PCB FPCB PCB

0.07 0.13

Content [%] Fe Al – 9.00

– 4.70

Sn

Ni

Pb

Zn

0.02 3.10

0.11 1.30

– 2.20

– 1.00

Content [%] Au Pd Total 0.05 0.06

0.01 0.01

71.70 36.50

Flexible printed circuit board Conventionally recycled printed circuit board

amount of waste typically containing ferrous metals, copper, aluminum, zinc, rare and precious metals. This situation poses the problem of recovering and processing of metals contained in the waste. Thus, such waste constitutes a veritable source of metals. A known technique for the recovery of metals is to load the shredded waste into primary ovens or copper furnaces. This technique produces high emissions of dust, sulfur dioxide and gases containing halogens such as chlorine and bromine. The gases thus require further complex processing. Another problem with this technique is that electronic waste generates a lot of heat during combustion of the plastic they contain. Thus, the high calorific value of electronic waste is an obstacle to this technique. The frequently high aluminum content in the treated waste is another problem, since the presence of aluminum in the slag or cinders increases their melting point so that treatment becomes very di cult. Because of these various drawbacks, primary oven capacity to handle electronic waste is limited (139). Other recovery techniques use methods of fine shredding followed by magnetic and electrostatic separation to enrich and sort phases rich and poor in metals. A method has been described which uses shredding the waste into particles of 2–4 mm, electrostatic charging of the materials by friction against a drum, followed by electron bombardment, and finally sorting of the materials using an electric field (140).

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However, such techniques are expensive, especially in view of the fine shredding that is necessary, and only provide imperfect sorting and thus lead to a poor performance of precious metal recovery. Attempts have also been made to recover metals by fluidized bed pyrolysis. However, this technique has the disadvantage of mixing the metal with an additive (fluidizing medium) such as sand, quartz and the like, complicating recovery (139). Indeed, screening, which is carried out downstream from the pyrolysis, cannot e ectively separate the additive from certain metallic dusts. Furthermore, such a method consumes more energy, a part of the metals gets oxidized and metals are entrained in the gas phase. A method for treating materials containing a mixture of plastic materials and metal materials, i.e., electronic waste, has been presented (139). This method consists of: 1. 2. 3. 4.

Crushing the material to be treated, Pyrolysis of the crushed material, Neutralizing the pyrolysis gas with sodium bicarbonate, A first magnetic separation performed on the pyrolyzed material providing, on the one hand, a ferrous metal fraction and, on the other hand, non-ferrous residue, and 5. A second magnetic separation performed on the non-ferrous residue providing, on the one hand, a non-ferrous metal fraction and, on the other hand, non-magnetic residue. The shredding is performed down to a screen passage size of between 20 mm and 30 mm. The pyrolysis is performed at a temperature between 300°C and 600°C with an air factor between 0.7 and 0.98. The gases from pyrolysis contain combustion products from burners, water vapor and gases from the decomposition of epoxy resins and other carbon chain materials. These gases are burned in an additional combustion chamber at a temperature su cient to allow the destruction of dioxins. A temperature between about 850°C and about 1100°C is appropriate. Here, hydrochloric acid and hydrobromic acid are produced. The first magnetic separation is e ected by a magnet or electromagnet. The second magnetic separation is performed by an eddy current separator. To perform the magnetic extraction of non-ferrous metals using eddy currents, it is important that the non-ferrous

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metal fraction including aluminum should be essentially in its nonoxidized form. The precious metals may include gold, silver, platinum, palladium, rhodium, ruthenium, iridium or osmium. The non-magnetic residues can include copper, lead, tin, glass fibers, and carbon. This method makes it possible to eliminate epoxy resins and plastic components of electronic circuit boards, as well as chlorine and a major portion of bromine, while avoiding metal loss by oxidation or distillation in view of the low temperature and non-oxidizing conditions of the operation. The material is thus concentrated in metals. During the cooling of the combustion gases from gases produced during pyrolysis the energy contained in these gases can be recovered. The material thus pyrolyzed can advantageously be treated with conventional tools of copper metallurgy, thereby overcoming certain technological limitations of these tools and more specifically volatile matter content (carbon chains) and halogens. In the case of electronic card processing, the decomposition of epoxy resins during pyrolysis has the e ect of freeing all the components rendered integral to the base material: copper, electronic components, metal components, etc. This separation from the base material allows a very e cient use of magnetic sorting, being more e ective than separation performed by shredding very finely. Also, the e ciency of metal recovery can be maximized, in other words losses of metal during the process are minimized. Aluminum can be separated from other metals during this process so as to facilitate downstream processing of the metals recovered. In the case of pyro-metallurgical processes, aluminum does indeed have a behavior detrimental to the fluidity of slag. In the case of hydrometallurgical processes, aluminum, because of its chemical reactivity, leads to an overconsumption of chemicals. Furthermore, it is preferable to work below the melting point of aluminum to avoid traces of oxygen oxidizing the molten metal. The treatment of gases from the pyrolysis, including post-combustion, makes it possible to render the method clean without requiring any heavy manipulation of halogens, sulfur compounds or heavy metal emissions (139).

Specific Materials 6.13.6

309

Influence of Virgin Poly(carbonate) and Impact Modifier

The recovery and recycling of plastics waste, primarily PC, ABS, and high impact PS, from end-of-life electrical and electronic equipment waste has been investigated (141). The recycling of these materials was carried out using material recycling through a melt blending process. An optimized blend composition was formulated to achieve the desired properties from di erent plastics present in the electrical and electronic equipment waste. The toughness of blended plastics could be improved by the addition of 10% of virgin PC and the impact modifier (ethylene-acrylic ester-glycidyl methacrylate). The mechanical, thermal, dynamic-mechanical and the morphological properties of recycled blend were also investigated. Improved properties of the blended plastics indicate a better miscibility in the presence of a compatibilizer suitable for a high-end application (141).

6.14 Fiberglass Reinforced Plastics A method for recycling of fiberglass reinforced plastics has been presented (142). The steps used here include: 1. Grinding fiber reinforced plastic material, such as scraps, with a grinder into a predetermined length to form a ground reinforced plastic material, 2. Mixing the ground material with constituents to create a blend, 3. Pouring the blend into a mold, 4. Providing a flat insert over the poured blend within the mold, 5. Placing the mold with the blend therein into a pneumatic press, 6. Compressing the blend-impregnated mold with the pneumatic press such that the resin flows throughout the mold without air voids therein,

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Polymer Waste Management 7. Forming a panel wherein heated platens of the pneumatic press compress the blend in the mold and cause a heat-activated catalyst to initiate a curing reaction when a predetermined elevated temperature is reached to cause the blend to cure in the mold, and wherein the blend comprises a polyester resin that comprises 60–65% by weight of the blend and fiber reinforced plastic material that comprises 35–40% by weight of the blend.

The grinding machine is shown in Figure 6.16. The grinding ma-

Figure 6.16 Grinding machine (142).

chine has a throat opening that receives the fiberglass reinforced plastics scraps within a mulching compartment. Within the compartment are a plurality of knifes with carbonite corners to grind and mulch the fiberglass reinforced plastics. A built-in fan within the grinder helps to control the temperature within the grinder to eliminate any risk of spontaneous combustion. Another process used for the pyrolysis of fiberglass reinforced plastic waste in order to recover organic and inorganic components

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has been described (143). The inorganic components are obtained in such a state to allow them to be advantageously reused as raw materials for making new objects. The steps of the treatment of an unsaturated polyester resin waste consist of: 1. Prearranging a reactor, preferably of stainless steel, comprising a pyrolysis chamber, 2. Feeding the unsaturated polyester resin waste in the pyrolysis chamber, 3. Removing oxygen from the pyrolysis chamber down to a predetermined residual oxygen concentration, in particular until air is substantially eliminated from the reactor, 4. Creating a CO2 -containing environment in the pyrolysis chamber that has a CO2 volume concentration of at least 30%, preferably a volume concentration set between 80% and 100%, 5. Heating the unsaturated polyester resin waste in the pyrolysis chamber and reaching a pyrolysis temperature set between 350°C and 550°C, wherein the step of removing oxygen and the step of reaching a pyrolysis temperature are carried out in such a way that the residual oxygen concentration is attained before reaching the pyrolysis temperature, 6. Maintaining the CO2 -containing environment and controlling the temperature of said reactor so as to maintain said pyrolysis temperature in the pyrolysis chamber for a predetermined residence time, in particular set between 1 h and 5 h, responsive to the pyrolysis temperature and to the pyrolysis pressure, obtaining a gas mixture containing products of pyrolysis of the unsaturated polyester resin, and 7. Extracting the gas mixture from the pyrolysis chamber and cooling it down to a predetermined temperature so as to condensate the products of pyrolysis from the gas mixture in order to obtain a condensate liquid phase comprising a main amount of the product of pyrolysis that is separated from the uncondensed gas. With reference to the recovered organic portion, the pyrolysis thermal treatment under a CO2 flow allows very high yield values, both as absolute values and with respect to the yield values of other pyrolysis treatments.

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The organic liquid obtained by such a process is particularly suitable to be recycled to the production process of fiberglass reinforced plastics, i.e., to a new polymerization as a mixture with commercial unsaturated resins (143). The pyrolysis can be carried out in the presence of di erent gases such as: nitrogen, steam, carbon dioxide. In the presence of steam, the pyrolysis takes place along with hydrolysis reactions and solvolysis e ects. The thermal treatment under CO2 yields a liquid residue that is more abundant and homogeneous than in the previous cases, and that is free from colloidal dispersions (143). Several experiments have been reported and detailed. These tests allow concluding that the pyrolysis in the presence of carbon dioxide is surprisingly more advantageous than any pyrolysis carried out in a nitrogen or steam environment, since the former provides an organic liquid (143): 1. At a yield higher than in the prior state-of-the-art pyrolysis processes, 2. That is cheaper and easier to separate, 3. With an iodine number that is higher than in the prior stateof-the-art pyrolysis processes, and that is comparable to the one of the commercial unsaturated resins, due to the presence of molecules rich in double bonds that can be involved in crosslinking reactions, which makes the recovered product perfectly recyclable as such for manufacturing new fiberglass reinforced plastics. Samples of glass fibers obtained after the pyrolysis treatment only and after the further calcination treatment, respectively, are shown in Figure 6.17. In another study, an attempt was made to convert plastic and glass fibers into gas, oil and water glass using sodium hydroxide as reactant (144). The materials were cut into pieces with a diameter of 1 cm. Sample pieces of 4 g and sodium hydroxide of 2 g to 12 g were put into the reactor, and the reactor was heated with an electric furnace under flowing nitrogen with 160 ml min 1 . After heating to the setting temperature of 300ºC–450ºC for 1 h, the reactor was naturally cooled to room temperature.

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Figure 6.17 Samples of glass fibers as obtained after the pyrolysis treatment and after the further calcination treatment (143).

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The gas and oil generated during the reaction were collected by gas pack and oil trap, respectively. After cooling, the residue inside the reactor was washed with distilled water and filtrates to obtain the residual substance, and silicon concentration in the filtrate was measured to calculate the silicon extracted content from the glass fibers. By using pyrolysis with sodium hydroxide, the glass fiber reinforced plastics can be decomposed by converting the resin into the gases, such as hydrogen and methane, and the glass fibers into soluble salt in order to be extracted from the solution (144).

6.15 Usage in Concrete Fiber reinforced concrete is a composite material consisting of a cement-based matrix with an ordered or random distribution of fiber which can be steel, nylon, PE, and others (145). The addition of steel fiber increases the properties of concrete, e.g., flexural strength, impact strength and shrinkage properties. Several papers have been published on the use of steel fibers in concrete. 6.15.1

Plastic Waste as Fuel in Cement Production

The reutilization of waste plastics as a fuel in the cement kiln precalciner process was investigated (146). For uniform feeding into the fluidized bed calciner, waste plastics were prepared to form pellets by shredding, melting, pressing, cutting, and screening. The properties of combustion for di erent pellet size have been examined using the Computational Fluid Dynamic analysis program to minimize risk and optimize conditions of an actual proof plant. Based on the results from the computational fluid dynamic analysis, the waste plastic used for the industrial-scale experiment were 20 mm, 50 mm, and 100 mm in size. The experimental result of an actual proof plant showed a comparatively good correlation with the computational fluid dynamic analysis (146). In an e ort to reduce emissions and lower fuel costs, cement plants have explored the use of waste materials to replace coal and

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petroleum coke (147). Here, an interesting candidate is non-recyclable waste plastics. A profound knowledge of potential changes in cement kiln parameters with a change in the composition of the operating fuel prior to full-scale application is necessary. Here, a bench-scale tube furnace and a heated grid reactor were used to compare the combustion and emission changes when waste plastics displace an equivalent amount of heat from the coal coke blend (147). Trends in the results from bench-scale experiments on residual volatile organic compound emissions matched full-scale observations on kiln thermal performance. The bench-scale particulate matter emissions indicated that no significant changes were likely in full-scale stack particulate matter emissions when waste-derived fuel is used (147).

6.15.2

Constructional Works

Since it shows a maximum strength, M20 concrete is used for most of the constructional works (148). The strength of this concrete was compared with concrete obtained from shredded plastic waste varying from 2% to 8%. Experimental investigations consisted of testing physical requirements of coarse aggregates, fine aggregates, cement and the modifier. The M20 concrete was prepared as per IS SP: 23-1982 (149). The percentage of 2% to 8% of modifier was blended with the cement concrete mix and the optimum modifier content was found. Cubes were cast and tested for 1 d, 3 d, 7 d, 14 d, and 28 d strength. These tests revealed that by adding the modifier, the strength of concrete increased. At 5% optimum modifier content, the strength of the modified concrete was found to be 1.2 times greater than the plain cement concrete. By using plastic waste as modifier, the quantity of cement and sand can be reduced, hence decreasing the overall cost of construction. The modified cement concrete can be used in the construction of small drainage works and rigid pavement. This leads to a decrease in the overall thickness of the pavement (148).

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6.15.3

Lightweight Concrete

A lightweight concrete made from PS and EVA waste was studied (150,151). EVA waste from the footwear industry and waste PS were used as an aggregate in the lightweight concrete. Each of the plastic wastes was used alone, i.e., as a sole aggregate, or in combination with the other in a ratio of 1:3, 1:1, and 3:1. The water-cement ratio of 0.50 and the cement dosage of 175 kg m 3 were used for all the investigated mixtures. The test results showed that the bulk density and the thermal conductivity of the lightweight concrete tended to increase with increasing EVA waste content. The maximum compressive strength of lightweight concrete was reached with the waste materials in a ratio of 1:1. Based on these results, the application of EVA waste as a lightweight filler shows a good possibility for its use in a lightweight concrete (151). The results also indicated that lightweight concretes had good thermo-technical properties (150). A lightweight concrete with dosage of 100% PS achieved the best thermo-technical properties and had the lowest values of bulk density. At the same time, the samples had the smallest values of resistance to deformation. Increasing the content of EVA waste led to an increase in strength characteristics as well as thermal conductivity values. Lightweight concrete samples containing PVC cable waste achieved the highest bulk density and therefore the lowest thermal conductivity. However, lightweight concretes with a 100% dosage of cable did not reach the expected strength properties. The lightweight concretes using aggregate in ratio 1:1 of PS and EVA and also EVA and PVC cables reached the highest values of stress. Based on these results it can be concluded that lightweight concretes based on the recycled waste could be used in combination with more wastes. Their suitable combination can lead to achieve good thermo-technical and mechanical properties. 6.15.4

Bakelite Plastic Waste

It is prohibited to dispose of bakelite directly into landfills or by open burning for unsafe disposal and emission reasons (152).

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The characterization of bakelite plastic waste and its use as aggregates in concrete products has been done (152). The physical characteristics of bakelite plastic waste, the bulk specific gravity was 1.30–1.40 g cm 3 . The chemical composition of bakelite plastic waste, total carbon, hydrogen, oxygen, and sulfur was 53.4%, 4.0%, 11.6%, and 0.017%, respectively. The composition of the ash of bakelite, CaO, SiO2 , and SO3 was 94.53, 5.14, and 0.33%, respectively. The pH value of bakelite plastic waste and fine bakelite plastic waste was 8.10 and 12.00, respectively. Water absorption capacity of bakelite plastic waste and fine bakelite plastic waste was 0% and 25%, respectively. After grinding, bakelite plastic waste becomes a fine bakelite plastic waste. The water absorption of fine bakelite plastic waste was 25%. Bakelite plastic waste was used as aggregates in concrete products by preparing and testing mortar samples with 0%, 20%, 40%, 80%, and 100% replacement percentage at each curing age 7 d, 14 d, and 28 d. The compressive strength and density of bakelite plastic waste was lower than conventional mortar. The compressive strength decreased with increasing of replacement percentage and it increased with curing time (152). 6.15.5

Plastics from Waste of Electric and Electronic Equipment

The most frequently used methods for the modification of polymer surfaces as well as the application of treated crushed plastics from waste of electric and electronic equipment as a light aggregate in cement composites have been reviewed (153). Also, the surface modification of plastic aggregates by treatment with a combination of di erent solutions and additives was investigated. The applied procedures are shown to be e ective in improving the interfacial bond strength between plastic grains and the cement matrix. Plastic granules derived from scrapped waste plastics have a potential to be used as aggregates to replace natural gravel for making non-structural lightweight aggregate concrete. These composites offer an attractive low-cost material with consistent properties. Moreover, they would contribute to resolving some of the solid waste

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problems caused by plastic production, in addition to conserving energy (153). 6.15.6

Plastic Aggregates

A method for producing a plastic aggregate for use in concrete compositions, which includes exposing high density plastics to ultraviolet irradiation in the presence of a strong alkali, has been developed (154). The plastic may be recycled plastic which has been washed and cut into strips. Plastic aggregates have an increased a nity for common concrete binders such as Portland cement. A cement composition made with such plastic aggregates may include up to 60% by volume of a plastic aggregate. The plastic aggregates are well adapted for use in concrete compositions used to make precast concrete components. An example of the preparation is as follows (154): Preparation 6–1: A batch of concrete was made by mixing the following proportions, by weight, of the following materials: Portland cement 30%, crushed perlite 30%, plastic aggregate 30%, and water 10%. The plastic aggregate consisted of treated strips approximately 1 4 in wide and 6 in to 8 in long. The concrete was formed into a tile approximately 6 in wide, 12 in long and 3 4 in thick and allowed to cure for 7 d. Some strips were oriented transversely and other strips were oriented longitudinally in the tile. The weight of the cured tile was 21 4 pounds.

No shrink cracking of the tile was observed. When force was applied to the flat surface of the tile the tile experienced gradual failure. The overall structural integrity of the tile outside of the area of the failure was maintained. It was observed that cement appeared to be adhering well to the treated plastic strips (154). 6.15.7

Waste Plastics as Fiber

Plastic cups were used as a fiber with mean aspect ratio 158.75 and 26.49 (155). The plastic fibers were prepared by Plastic cups with two di erent thickness of 80 μm and 480 μm. The plastic cups were cut by hand to a mean length of 12.7 mm and a mean breadth of 2.8 mm. As concrete, Portland Pozzolona cement was used. The properties of this cement type are shown in Table 6.33.

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Table 6.33 Properties of the Portland Pozzolona cement (155). Property

Result

Specific gravity Normal consistency Initial setting time Final setting time Fineness of cement (using a 90 micron sieve)

2.8 g cm 3 32% 30 min 600 min 5% retained

The results of compressive strength tests are shown in Table 6.34. It is observed that maximum compressive strength is obtained when 0.9% of plastic fibers are added to concrete. Table 6.34 Compressive strength test results (155).

6.15.8

Curing time [d]

Plastics content [%]

Compressive strength [N mm 2 ]

7 7 7 7 7

0 0.3 0.6 0.9 1.2

14.52 15.85 19.04 20.07 15.55

28 28 28 28 28

0 0.3 0.6 0.9 1.2

20.15 22.21 24.06 25.7 23.92

Fiber Reinforced Plastic Waste Powder

E orts have been made to recycle glass fiber reinforced plastic waste powder and fiber in concrete and cement composites and to assess its quality (156). The results of the study revealed that the mean compressive strength of concrete composites using 5% to 50% glass fiber reinforced plastic waste powder under water curing varied from 37

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N mm 2 to 19 N mm 2 . An increase in the concentration of the glass fiber reinforced plastic waste decreased the compressive strength. However, an increase in the duration of curing from 14 d to 180 d resulted in improvement of the compressive strength of the concrete with 5% glass fiber reinforced plastic application to 45.75 N mm 2 . Moreover, the density of concrete with 50% glass fiber reinforced plastic waste was reduced by about 12% in comparison to a control sample. The bending strength in terms of modules of rupture of 12 mm thickness cement composites developed using 5% glass fiber reinforced plastic waste fiber attained 16.5 N mm 2 . These findings may pave the way for further glass fiber reinforced plastic waste recycling in precast construction products for use in various applications (156). A special waste management solution for thermoset glass fiber reinforced plastic waste-based products was assessed (157). The mechanical recycling approach, with reduction of glass fiber reinforced plastic waste to powdered and fibrous materials was applied, and the potential added value of obtained recyclates was experimentally investigated as raw material for polyester-based mortars. The use of a cementless concrete as host material for glass fiber reinforced plastic waste recyclates, instead of a conventional Portland cement-based concrete, presents an important asset in avoiding the eventual incompatibility problems arising from alkalis silica reaction between glass fibers and cementitious binder matrix. Additionally, due to the hermetic nature of resin binder, polymer-based concretes present a greater ability for incorporating recycled waste products. 6.15.9

Domestic Waste Plastics

An attempt has been made to study the influence of the addition of domestic waste plastics at a dosage of 0.5% by weight into cement (145). The changes of compressive strength and flexural strength have been assessed. An amount of 0.5% of domestic waste PE bags fibers were added to concrete. The experiments showed the following facts (145): 1. The addition increases the cube compressive strength of concrete in 7 d to an extent of 0.68%,

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2. The addition increases the cube compressive strength of concrete in 28 d to an extent of 5.12%, 3. The addition increases the cylinder compressive strength of concrete in 28 d to an extent of 3.84%, 4. The addition increases the split tensile strength to an extent of 1.63%, and 5. The increase in the various mechanical properties of the concrete mixes with PE fibers is not in the same league as that of the steel fibers. 6.15.10

Usage in Pavement

Waste plastics can be used for the application in pavements. Some examples are shown in the following sections. 6.15.10.1

Bituminous Concrete

The use of waste processed plastics has been suggested for the modification of bituminous concrete mix to minimize the produced plastic waste (158). Waste processed plastics were mixed with bituminous concrete using a dry process to get a modified mix. The Marshall method of mix design was adopted to find out the optimum bitumen content. Marshall specimens were prepared for bitumen content of 4.5%, 5.0%, 5.5%, and 6.0% with 0%, 3%, 6%, 10%, and 18% of waste plastics. The Marshall stability, flow, Marshall quotient, air voids, voids in mineral aggregates, voids filled with bitumen, retained stability, indirect tensile strength, tensile strength ratio, stripping, fatigue life, and deformations were determined and compared with neat bituminous concrete mixes. The Marshall stability method is used in pavement design to determine the optimum binder content in a pavement made from bitumen. The method was developed in 1939 by Bruce Marshall (159). The Marshall stability value for the mix with 6% of waste plastic was much higher in comparison to other mixes (158). The stability increased by 12% for mix with 6% of waste plastics in comparison to a neat bituminous concrete mix. The flow value is also within the

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limit for this modified mix. Indirect tensile strength values for an unconditioned sample of optimum bitumen content were found to be increased by 29% for the bituminous concrete mix with 6% waste plastics as compared to the indirect tensile strength value of neat bituminous concrete mix. For conditioned samples the indirect tensile strength values increased by 38% for the mix with 6%, and the retained stability was well above the required 75%. Boiling tests showed that there was no stripping of bitumen for bituminous concrete mix with 10% or more waste plastic content. Rut depth after 10,000 cycles was determined for modified and neat bituminous mixes. There was significant reduction in rutting characteristics of waste plastics modified mix. It was observed that the fatigue life of plastics modified bituminous concrete mix increased at di erent stress levels (158). It has been shown that recycled plastics composed predominantly of PE can be incorporated into a conventional asphaltic concrete used for road surfacing mixtures (160). The durability behavior, in terms of water susceptibility behavior, of the mixture results indicated that the asphaltic concrete Plastiphalt mixes have excellent resistance to water damage. Age hardening of the bitumen in the bituminous mixture is another factor that is a ecting the durability behavior of the mixture. Aging of bituminous mixtures is of increasing concern in the maintenance of flexible pavements. This process is due to factors such as volatilization, oxidation and hardening of the bitumen in the mixture. The aging behavior of asphaltic concrete Plastiphalt mixes have been presented (160). A method for oven aging was adopted in the investigation. Two oven aging methods were used, i.e., a short-term oven aging and a long-term oven aging. The laboratory experimental results on short- and long-term oven aging of the mixture indicated an improvement in all strength and sti ness parameters. 6.15.10.2

Roller Compacted Concrete

Laboratory experiments were performed to evaluate the performance of a moderate-strength roller-compacted concrete (161). The

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323

roller-compacted concrete was made from reclaimed crushed concrete used as aggregate, Class C fly ash, and waste plastic fibrous reinforcement. The motivation for evaluating this primarily waste composite was to develop a high-quality foundation layer for a conventional flexible or rigid pavement, while addressing such crucial issues as the ever-increasing solid waste disposal problem, rapidly depleting landfill spaces, and conservation of natural resources. The following objectives of the characterization of the materials were to (161, 162): 1. Evaluate the e ectiveness of recycled HDPE strips in stabilizing the tensile crack propagation through the brittle cementitious matrix, 2. Determine the strength and toughness characteristics of the composite, and 3. Suggest performance-based mixture design proportions for the recycled aggregate, fly ash, cement, and recycled plastic fibers. Because a roller-compacted concrete pavement slab will be subjected to repeated tensile stresses under tra c loads, the study was focused on instrumented split tensile and flexural tests in order to evaluate the performance of the foundation material. The results indicated that a mix containing only 8% cement and 92% recycled materials can achieve 28 d compressive strengths of up to 14 MPa and a split tension strength of 1.5 MPa. Furthermore, it was found that the plastic fibers can improve the toughness characteristics significantly in split tension but only moderately in flexure. In summary, the investigated cement-bound composite made primarily from recycled products may be an alternative material for the construction and rehabilitation of highway pavements (161). A nonlinear power law has been suggested to describe the relationship between the accumulated permanent deformation and the expended fatigue life (163). Fatigue damage computed using a dissipated energy approach indicated that the damage accumulation in this material approximately follows Miner’s rule for cumulative damage, which is often used in pavement engineering.

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6.15.11

Usage in Gypsum Blocks

A recovery method of waste glass fiber reinforced plastics has been presented (164). Among the current methods of utilization of glass fiber reinforced plastics, a physical method is most promising. After preprocessing of the waste, the short glass fiber can be used in gypsum block to improve the anti-cracking and operation performance of this material. Also, waste glass fiber reinforced plastics powder can be used in plastic fiber reinforced manhole covers to increase the mechanical strength (164).

6.16 Recycling of Floor Coverings A solvent-based separation method has been described for the total material recycling of materials used in nonwoven, woven, and tufted wares into the individual material components thereof sorted by type (165). At least one of the materials contains a polyolefin wax. As a solvent or swelling agent, halogen free, aliphatic hydrocarbons or aromatic hydrocarbons or a mixture of one or several of said solvents are used. Carpets and synthetic turfs are floorcovering constructions consisting of a primary backing, a yarn, a backcoating and often a secondary backing, such as, for example, a woven fabric, a nonwoven fabric, a foam or a heavy layer. Various plastics are used for the di erent components. The yarn in carpets is predominantly PP, PE or a polyester. PP and PE are primarily used in synthetic turf. The primary backing is usually made of PP and a polyester. An additional coating is needed to retain the yarn in the backing. The coating technologies currently employed in commercial practice utilize aqueous latex and acrylates almost exclusively as coating material for carpets (tufted, woven, and nonwoven) and PU as well as aqueous latex for synthetic turf. The use of latex and polyurethane as coating material leads to a nonreversible cure for the backcoating and hence to an end product that is not capable of full mechanical or feedstock recycling. The recovery of energy from floorcoverings, including synthetic turf by burning, is better than landfilling, but because it is based on a single use it runs counter to the concept of a circular economy,

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where a material is ideally recycled repeatedly. Therefore, energy recovery is particularly an option for compositions of matter which cannot be separated any further and also for fractions of material which have aged particularly severely and can no longer be used. The incineration residues can subsequently be further used as fillers in the concrete and cement industry. It has been found that separation via selective dissolution is a promising possibility, in particular when a thermoplastic, and hence organosolvent-soluble polyolefin wax, was used for bonding the backing and not a conventional latex or polyurethane coating. The separation of mixed plastics by selective dissolution is based on the di ering solubility of various thermoplastic polymers such as plastics and waxes, for example, in organic solvents. Suitable choices for solvent type, pressure and temperature enable the incremental production of pure solutions of polymer and the recovery of varietally pure plastics by evaporating o the solvent. The advantages of this method reside in the extremely high product quality attainable and in the possibility of being able to remove additives that often dramatically curtail the possible uses for repelletizates (165). Even polyolefin mixtures consisting of HDPE, LDPE, and PP can be separated to produce polyolefin blends containing at least 95% of the principal component (166). The selective dissolution with synthetic turf runs as follows (165): Preparation 6–2: The synthetic turf specimen used for this example consisted of an linear low density poly(ethylene) (LLDPE) yarn, a backing of PP and also a backside coating based on a PP polyolefin wax manufactured using a metallocene catalyst. First, 8 kg of waste synthetic turf from the sample described above was comminuted in a shredder and admixed with 40 kg of p-xylene, then the mixture was heated incrementally. The particular dissolution temperatures were 73°C for the PP polyolefin wax, 96°C for LLDPE and 146°C for PP. Dissolution times were below 20 min in each case. The PP polyolefin wax and the LLDPE were each extracted in 2 stages, while PP was separated o in a single stage. The component materials dissolved in the solvent were precipitated out by temperature reduction, squeezed o and dried at 40°C under reduced pressure. The solvent thus recovered was fed back into the process.

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Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

Index Acronyms ABS Acrylonitrile-butadiene-styrene, 10, 84, 156, 264 AIBN 2,2 -Azobisisobutyronitrile, 248 AMS Accelerator mass spectrometry, 289 AWBC Acid-washed bentonite clay, 261 CNT Carbon nanotube, 260 CSBR Conical spouted bed reactor, 222 DSC Di erential scanning calorimetry, 83, 156, 175, 267 EPS Expanded poly(styrene), 87, 151 EVA Ethylene-vinyl acetate, 272 FCC Fluid catalytic cracking, 178, 223 FTIR Fourier transform infrared, 8, 63, 83, 150, 189, 228 GC Gas chromatography, 25, 150, 186, 245 GMA Glycidyl methacrylate, 158 HDPE High density poly(ethylene), 4, 99, 178, 222 HIPS High impact poly(styrene), 114 LCA Life cycle assessment, 10

337

338

Index

LDPE Low density poly(ethylene), 84, 183, 225 LLDPE Linear low density poly(ethylene), 325 LSC Liquid scintillation counter, 289 MFA Material flow analysis, 14 MFi Melt flow index, 83 MS Mass spectroscopy, 25, 150, 245 NMR Nuclear magnetic resonance spectroscopy, 161 PC Poly(carbonate), 118, 155, 268 PE Poly(ethylene), 4, 60, 121, 176, 220 PET Poly(ethylene terephthalate), 11, 81, 157, 180, 248 PHB Poly(3-hydroxybutyrate), 97 PLA Poly(lactic acid), 81 PLGA Poly(lactic-co-glycolic acid), 98 PMMA Poly(methyl methacrylate), 118 PP Poly(propylene), 9, 63, 99, 145, 175, 221 PS Poly(styrene), 10, 58, 88, 149, 180, 248 PTT Poly(trimethylene terephthalate), 288 PU Poly(urethane), 110, 165, 293 PVC Poly(vinyl chloride), 2, 112, 161, 180, 251 SEM Scanning electron microscopy, 101, 245 TGA Thermogravimetric analysis, 156, 175, 225 VI High viscosity index, 204

Index XPS X-Ray photoelectron spectroscopy, 105 XRD X-Ray di raction, 229

339

340

Index

Chemicals Boldface numbers refer to Figures Abies oil, 89 Acenaphthene, 133 Acetaldehyde, 275 Acetophenone, 133 Acrylic acid, 158 Acryloyl chloride, 157, 159 Alloocimene, 135 Allyl chloroformate, 158 2-(((Allyloxy)carbonyl)oxy) ethyl (2-hydroxyethyl) terephthalate, 158 3-Aminopropyl-trimethoxysilane, 242 Anethole, 135 Anisaldehyde, 135 Azoisobutylnitrile, 248 Bentonite, 179, 222, 256, 261 Benzophenone, 134 Benzyl alcohol, 133 Benzyl butyl phthalate, 61 Bis(2-(acryloyloxy)ethyl) terephthalate, 157 Bis(2-(((allyloxy)carbonyl)oxy)ethyl) terephthalate, 158 Bis(2-ethylhexyl) phthalate, 61 Bis(4-hydroxybutyl hydrogen carbonate), 303 Bis(2-hydroxyethylene) terephthalamide, 162 Bis(2-hydroxyethylene terephthalate), 163 Bis(2-hydroxyethyl) terephthalamide, 274 Bis(2-hydroxyethyl) terephthalate, 157, 272 Bisphenol A, 155, 156, 269, 270, 303 Bornyl acetate, 89, 96 n-Butane, 240 1,3-Butanediol, 89 1,4-Butanediol, 303, 304 p-tert-Butylacetophenone, 270 Butyl benzyl phthalate, 298 2-tert-Butyl-6-phenylphenol, 270 Calcium hypochlorite, 118 Camphene, 135 Camphor, 135 10-Camphorsulfonic acid, 135 ε -Caprolactam, 164 3-Carene, 135 Cesium hydroxide, 203 Cetyltrimethyl ammonium bromide, 162

Index p-Chloroanisole, 133 o-Chlorophenol, 133 Chlorosulfuric acid, 121 1,8-Cineole, 95 Citral, 135 Citronellal, 135 Citronellol, 135 Citronellyl acetate, 95 Clinoptilolite, 181 m-Cresol, 134 o-Cresol, 270 p-Cumyl phenol, 270 1,4-Cyclohexanedimethanol, 163 Cyclohexene, 240 Cyclopentane, 248 p-Cymene, 89, 95, 135 Dibenzoyl hexamethylene diamine, 165 Di-i-butyl phthalate, 298 Dibutyl phthalate, 298 Dichlorodiphenyltrichloroethane, 27 Dicyclohexyl phthalate, 298 Diethylene glycol, 273 Diethylhexyl phthalate, 298 Diethyl phthalate, 61, 298 Dihydromyrcenol, 135 Dihydroxybenzene, 154 Diisobutyl phthalate, 61 N,N-Dimethylaminopyridine, 168 1,3-Dimethylcyclopentane, 240 Dimethyl formamide, 133 N,N-Dimethylformamide, 89 3,3-Dimethyl-1,6-heptadiene, 240 2,6-Dimethyl-2-heptene, 240 Dimethyl heptene, 101 2,5-Dimethyl-1,5-hexadiene, 240 3,7-Dimethyl-1,6-octadiene, 135 2,4-Dimethyl-1-pentene, 240 2,6-Dimethyl phenol, 133 Dimethyl phthalate, 61, 167, 298 N,N’-Dimethylterephthalamide, 162 Dimethyl terephthalate, 18 Di-n-octylphthalate, 298 Dipentene, 135 Diphenyl, 133

341

342

Index

1,3-Diphenylbutane, 130 2,4-Diphenyl-1-butene, 58 Diphenyl carbonate, 270 Diphenyl ether, 133, 270 Diphenyl methane, 133 Diphenyl methane diamine, 165 1,3-Diphenylpropane, 58, 130 Diphenyl propane, 270 Dipropyl phthalate, 298 Ethyl acetate, 169 Ethylbenzene, 210, 240 Ethylene carbonate, 133 Ethylene glycol, 18, 133, 157, 272, 273 2-Ethyl-3-hexene, 240 Ethylhexylacrylate, 159 2-Ethylhexyl diphenyl phosphate, 61 3-Ethyl-1-pentene, 240 m-Ethylphenol, 270 Eucalyptol, 89 Faujasite, 247 Geraniol, 90 Geranyl acetate, 95 Heneicosane, 248 Heptacosane, 248 Heptadecane, 248 n-Heptane, 256 1-Heptene, 256 Hexachlorobenzene, 70 1-Hexadecyl trimethylammonium bromide, 156 1,4-Hexadiene, 240 1,1,1,3,3,3-Hexafluoro-isopropanol, 133 Hexamethylene diamine, 164 7-Hydroxydihydrocitronellal, 135 Isoborneol, 136 Isobornyl acetate, 135 Isobutyltriethoxysilane, 242 p-Isopropenylphenol, 155 Isopropylbenzene, 130 p-Isopropylphenol, 269, 270 Limonene, 90, 96 Linalool, 90 p-Menthene, 135 Menthol, 135 Menthone, 135

Index 7-Methoxydihydrocitronellal, 135 2-Methoxy-2,6-dimethyl-7,8-epoxyoctane, 135 2-Methylbenzofuran, 270 2-Methylbutane, 240 3-Methyl-1-butene, 240 1-Methyl-3-butylimidazolium chloride, 272 1-Methyl-3-butylimidazolium zinc trichloride, 272 4-Methyldiphenyl ether, 270 3-Methylenheptane, 240 2-Methylheptane, 256 2-Methylhexane, 256 Methylindane, 154 1-Methyl naphthalene, 134 Methyl-napththalene, 101 2-Methyl-1-propene, 240 α-Methyl styrene, 101, 130 Myrcene, 96 Naphthalene, 133, 154, 244 Nitrobenzene, 89, 134 Nopol, 136 Ocimene, 136 i-Octane, 256 α-Phellandrene, 90, 96 β-Phellandrene, 96 Phenanthrene, 133 Phenol, 134 Phenylaminopropyltrimethoxysilane, 242 p-Phenylphenol, 133 Phthalic anhydride, 168 Pinane, 135 2-Pinanol, 136 α-Pinene, 89, 91, 95, 135 Pinene, 96 Quinoline, 133 Rubredoxin reductase, 299 Styrene, 210 Sunflower seed oil, 112 Terephthalamide, 162 Terephthalic dihydrazide, 161 Terepthalic acid, 160 β-Terpene, 135 Terpinen-4-ol, 90 α-Terpineol, 135 Terpineol, 90

343

344

Index

Terpin hydrate, 135 1,1,2,2-Tetrachloroethane, 121 Tetrahydrofuran, 133 Tetrahydronaphthalene, 134 1,2,4,5-Tetramethylbenzene, 270 Tetramethylhydroquinone, 299 Toluene, 210 p-Tolyl ether, 270 Trichloroacetic acid, 133 1,1,1-Trichloroethane, 133 Trichlorophenol, 133 Triethylene glycol dimethacrylate, 158 Tri(2-ethylhexyl) phosphate, 61 Trifluoroacetic acid, 134 1,2,2-Trifluoroethane, 133 Triisobutyl phosphate, 61 2,2,4-Trimethylpentane, 256 Trioctylmethylammonium bromide, 273 2,4,6-Triphenyl-1-hexene, 58 Triphenyl phosphate, 61 Tripropyl phosphate, 61 Tris(2-chloroethyl) phosphate, 61 o-Xylene, 134

Index

345

General Index Ablation reactions, 278 Abrasives, 55 Accelerated degradation, 5 Acidized oil, 190 Activated charcoal, 169 Activation energy, 176, 182, 263, 283, 285 Actuators, 111 Additives, 7, 16, 23, 32, 60, 267 Adhesion promoter, 159 Adsorption isotherms, 101, 150 Adsorption of reagents, 118 Aerated lysimeter, 99 Aeration rates, 99 Agglomerator, 109 Ammonolysis, 272 Anaerobic biodegradability, 20, 21 Anti-knocking capacity, 256 Anti-whirl device, 198 Anticorrosive paint formulations, 162 Antioxidants, 24, 32 Antistatic agents, 23 Arrhenius equation, 263 Artificial UV light weathering, 33 Asphaltic concrete, 322 Autoclave, 168, 242, 248, 263, 281, 292 Autofluorescence, 6 Autoignition, 256 Automated sorters, 127 Automobile shredder, 128 Automotive applications, 80, 293 Azocolorants, 24 Backcoating, 324 Batch reactor, 181, 225, 247 Beverage packaging, 71, 87, 93 Biocatalysts, 299 Biocides, 23 Biocomposites thermoplastic, 288

Biodegradability, 19, 22, 232 aerobic, 20 anaerobic, 20 Biodegradable plastics, 19, 97 Biodiesel, 186 Biofilms, 63 Biogas, 20 Bituminous concrete, 321 Black polymers, 7, 8 Blockchain technology, 51 Bubble cavitation, 231 Bubble oscillation, 231 Building reconstruction plastics, 194 Bulk hydroprocessing, 253 Bumpers, 293 Carbonyl index, 63, 228 Carbothermal reduction, 297 Carpets, 324 Catalytic activity, 100, 181, 221, 249, 272 Catalytic gasification, 260 Ceiling temperature, 263 Cellulose nanofibrils, 84 Cementless concrete, 320 Centrifugal sedimentation, 114 Chemolysis, 17 Coe cient of friction, 24 Compatibilizing additives, 79 Compostability of plastics, 22 Compression ignition engine, 175 Computer casings, 156 Concrete, vi, 249, 314 Conical spouted bed reactor, 179, 224, 238, 256 Contact electrification, 126 Contaminants, 22, 52, 62, 88, 201, 219 Coulomb forces, 127 Cracker gas, 180 Crossslinking agents, 158

346

Index

Crude oil saponification, 203 synthetic, 202 Dashboards, 293 Decoloration of monomer, 169 Decrosslinking extrusion, 230 Density flotation, 62 Devolatilization, 179 Dewaxing catalytic, 196 hydroisomerization, 205 isomerization, 205 Dissolution reprecipitation technique, 129 Domestic waste, 320 Dry crushing, 85 Electromagnetic heater, 187 Electrostatic separation, 306 Enzymatic degradation, 298 Feedstock recycling, 39, 149, 176, 237, 279, 287, 324 Fenton reagent, 120 Filter cascades, 30 Fischer-Tropsch process, 206 Fixed-bed reactor, 244 Flame retardant, 6, 10, 23, 40, 60, 104, 156, 267, 282, 304 Flexural strength, 159, 314, 320 Flocculants, 201 Flotation circuit, 120 Fluidized-bed reactor, 104, 152, 225, 237, 286 Fluorescence markers, 5 Fluorescent markers, 5 Foaming agents, 23 Fossil fuel, 72, 165, 232, 289 Froth flotation, 114, 118 Functional additives, 23 Gamma flotation, 118 Geranyl acetone, 95 Geranyl formate, 95 Glycolysis, 157, 165, 272 Greenhouse gas emissions, 106, 250

Grinding, 108, 310 Hazardous chlorinated plastic, 39, 126 Horikx function, 230 Hydrocarbonacetous materials, 264 Hydrocracking, 183, 280, 292 Hydrocyclone, 114, 277 Hydrodesulfurization, 196 Hydrofinishing catalyst, 206 Hydrometallurgical processes, 308 Hydrophobization, 118 Hydrora nation process, 196 Hydrorefining, 196 Hydrotreated vacuum gas oil, 178 Hygrothermal degradation, 5 Injection molding, 14, 85, 109, 271 Interconnected mesopores, 247 Interfacial bond strength, 317 Iron-pillared clay, 257 Ironmaking, 109 reductants, 110 Kelen model, 263 Landfill leachate, 39 Lewis acidic ionic liquids, 272 Lightweight concrete, 316 thermal conductivity, 316 Lithium-ion batteries, 85 LITTERBASE, 51 Marine biota, 27 Marine megafauna, 56 Mealworm, 19 Mechanical densification, 87 Mechano-chemical process, 33 Melt filtration, 13, 277 Mesoporous catalyst, 193, 225 Metal depletion, 11 Metal extraction, 110 Metallocene catalyst, 325 Metallurgical coke, 110 Metathesis catalyst, 18 Methanogenic inoculum, 21 Methanolysis, 272 Methanotrophs, 97, 99

Index Micro-plastics, 24, 30, 37, 52, 56, 60, 62 Microactivity test, 178 Microbeads, 26, 34, 55, 56 Microbial contamination, 35 Microcrystalline wax, 208 Microorganisms, 20, 35 Microscale agglomerates, 84 Microwave irradiation, 156, 162, 273 Microwave reactor, 156, 273, 274 Milk pouches, 207 Molecular sieve, 205, 249, 254 Monoterpenes, 95 Multitubular reactor, 235 Oceanographic model, 28 Oil reconversion device, 180 Optical sorters, 304 Optoelectronic materials, 260 Organic pollutants, 24, 40, 120 Ozonation systems, 128 Packed bed reactor, 104 Photoacoustic spectroscopy, 7 Photoluminescence, 259 Photovoltaic modules, 86 Pine forestry residue, 212 Plastic accumulation, 29, 32, 57 Plastic decomposing organisms, 35 Plasticizers, 297 Plastics flotation, 118 Plastiphalt mixes, 322 Portland cement, 318 Precalciner process, 314 Preproduction pellets, 59 Pretreatment methods, 120 Printed circuit board, 119, 299, 305 Prodegradants, 228 Pyrolysis furnace, 186, 187 Random degradation, 263, 274 Raw material extraction, 10 Recalcitrance, 298

347

Renewable polymer synthesis, 92 Repolymerization, 17, 169 Respirometer, 21 Rotary kiln, 104, 106, 188 Scrap adhesive, 264 Seatbelts, 293 Selective separation, 85, 114 Selective-wetting, 115, 128 Semi-aerobic landfill, 99 Semi-batch reactor, 100, 233, 279 Semi-coking process, 211 Silanization agents, 242 Simulated sunlight, 121 Size fractionation, 30 Solvent extraction, 13, 154 Sonochemical technology, 98 Spark ignition, 256 Splitter column, 148 Steaming dealumination, 247 Steelmaking industry, 232 Sticky adherence, 191 Styrene oligomers, 58, 154 Surface hydrophilization, 125 Synthetic clothing, 55 Tandem dehydrogenationmetathesis, 18 Terrestrial plastic litter, 71 Thermochemolysis, 30 Tribocharger, 127 Tubular reactor, 105, 280 Turbine agitator, 281 Ultrasonic devulcanization, 231 Vacuum gas oil, 178 Vinyl index, 63 Waste fiber reinforced plastics, 167 Waterborne micro-plastic, 29 Wet grinding, 115 Wettability, 116, 127 Wind-sifting, 147 Zeolite nanosheets, 221

Polymer Waste Management. Johannes Karl Fink. © 2018 Scrivener Publishing LLC. Published 2018 by John Wiley & Sons, Inc.

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