High performance polymers and their nanocomposites 9781119363651, 1119363659, 9781119363811, 1119363810, 9781119363880, 1119363888

Table of contents :
Content: Preface xv1 High-Performance Polymer Nanocomposites and Their Applications: State of Art and New Challenges 1PM Visakh1.1 Liquid Crystal Polymers 11.2 Polyamide 4, 6, (PA4,6) 31.3 Polyacrylamide 41.4 Effect of Nanostructured Polyhedral Oligomeric Silsesquioxone on High Performance Poly(urethane-Imide) 51.5 Thermoplastic Polyimide 51.6 Performance Properties and Applications of Polytetrafluoroethylene (PTFE) 71.7 Advances in High-Performance Polymers Bearing Phthalazinone Moieties 91.8 Poly(ethylene Terephthalate)-PET and Poly(ethylene Naphthalate)-PEN 111.9 High-Performance Oil Resistant Blends of Ethylene Propylene Diene Monomer (EPDM) and Epoxydized Natural Rubber (ENR) 141.10 High Performance Unsaturated Polyester/f-MWCNTs Nanocomposites Induced by F- Graphene Nanoplatelets 152 Liquid Crystal Polymers 27Andreea Irina Barzic, Raluca Marinica Albu and Luminita Ioana Buruiana 2.1 Introduction and History 272.2 Polymerization 292.2.1 Synthesis of Lyotropic LC Polymers 302.2.2 Synthesis of Thermotropic LC Polymers 312.3 Properties 322.3.1 Rheology 322.3.2 Dielectric Behavior 352.3.3 Magnetic Properties 362.3.4 Mechanical Properties 362.3.5 Phases and Morphology 392.4 Processing 412.4.1 Injection Molding 412.4.2 Extrusion 422.4.3 Free Surface Flow 432.4.4 LC Polymer Fiber Spinning 442.5 Blends Based on Liquid Crystal Ppolymers 442.6 Composites of Liquid Crystal Polymers 462.7 Applications 492.7.1 LC Polymers as Optoelectronic Materials 492.7.2 Liquid Crystalline Polymers in Displays 502.7.3 Sensors and Actuators 512.8 Environmental Impact and Recycling 522.9 Concluding Remarks and Future Trends 54Acknowledgment 543 Polyamide 4,6, (PA4,6) 59Emel Kuram and Zeynep Munteha Sahin3.1 Introduction and History 593.2 Polymerization and Fabrication 603.3 Properties 693.4 Chemical Stability 723.5 Compounding and Special Additives 723.6 Processing 733.7 Applications 833.8 Blends of Polyamide 4,6, (PA4,6) 843.9 Composites of Polyamide 4,6, (PA4,6) 893.10 Nanocomposites of Polyamide 4,6, (PA4,6) 903.11 Environmental Impact and Recycling 943.12 Conclusions 984 Polyacrylamide (PAM) 105Ma?gorzata Wi?niewska4.1 Introduction and History 1054.2 Polymerization and Fabrication 1074.3 Properties 1104.4 Chemical Stability 1114.5 Compounding and Special Additives 1124.6 Processing 1134.7 Applications 1144.8 Blends of Polyacrylamide 1164.9 Composites of Polyacrylamide 1184.10 Nanocomposites of Polyacrylamide 1194.11 Environmental Impact and Recycling 1214.12 Conclusions 1225 Effect of Nanostructured Polyhedral Oligomeric Silsesquioxone on High Performance Poly(urethane-imide) 133Dhorali Gnanasekaran5.1 Introduction 1345.2 Experimental 1365.3 Results and Discussion 1385.4 Conclusions 1456 Thermoplastic Polyimide (TPI) 149Xiantao Feng and Jialei Liu6.1 Introduction and History 1496.2 Polymerization and Fabrication 1506.2.1 Thermoplastic Polyimides Based on BEPA 1506.2.2 Thermoplastic Polyimides based on PMDA 1536.2.3 Thermoplastic Polyimides Based on BTDA 1546.2.4 Thermoplastic Polyimides Based on ODPA 1576.2.5 Thermoplastic Polyimides Based on BPDA 1576.2.6 Thermoplastic Copolyimides 1586.3 Properties 1606.3.1 TPI Based on BEPA 1606.3.2 Thermoplastic Polyimides based on PMDA 1636.3.3 TPI Based on ODPA 1636.3.4 Thermoplastic Polyimides Based on BPDA 1686.3.5 Thermoplastic Copolyimides 1706.4 Chemical Stability 1706.4.1 Hydrolytic Stability 1706.4.2 Oxidative Stability 1746.5 Compounding 1756.5.1 Chloromethylation 1756.5.2 Sulfonation 1786.5.3 Phosphorylation 1786.5.4 Bromination 1786.5.5 Arylation 1816.6 Processing 1816.6.1 Injection Molding 1816.6.2 Compression Molding 1826.6.3 Extrusion Molding 1846.6.4 Coating 1846.6.5 Spinning [40] 1866.7 Applications 1866.7.1 Membranes 1866.7.2 Adhesives 1886.7.3 Composites 1896.7.3.1 Skybond 1906.7.4 Engineering Plastics 1906.7.4.1 VESPEL Plastics 1906.7.4.2 ULTEM Plastics [48, 49] 1916.7.4.3 AURUM Plastics [50] 1926.7.4.3 Ratem Plastics [51] 1926.8 Blends of Thermoplastic Polyimide (TPI) 1936.8.1 TPI Blends with TPI 1936.8.2 Polyamic Acid Blending 1956.9 Composites of Thermoplastic Polyimide (TPI) 1966.9.1 LaRC Composites 1976.9.2 Skybond 2026.9.3 PAI Polyamide-Imide Composites 2056.10 Nanocomposites of Thermoplastic Polyimide (TPI) 2086.10.1 TPI/silver Nanocomposite 2086.10.2 TPI/Fe-FeO Nanocomposite 2106.10.3 TPI/Carbon Nanocomposites 2116.10.4 TPI/CF/TiO2 Nanocomposite 2146.11 Environmental Impact and Recycling 2146.12 Conclusions 2157 Performance Properties and Applications of Polytetrafluoroethylene (PTFE) - A Review 221E. Dhanumalayan and Girish M Joshi7.1 Introduction 2217.2 Properties of PTFE 2237.2.1 Physical Properties of PTFE 223Surface Properties 2237.2.2 Tribological Property of PTFE Surface 2247.2.3 Mechanical Properties of PTFE 2267.2.4 Chemical Properties of PTFE 228Solubility of PTFE 2287.2.5 Thermal Properties of PTFE 228Thermal transport property of PTFE composites 2297.2.6 Electrical Properties of PTFE 229Dielectric property of PTFE 2297.2.7 Optical and Spectral Properties of PTFE 2307.3 Processing and Casting Techniques of PTFE 2317.3.1 Casting of PTFE by Melt-Processing Method 2327.3.2 Sintering of PTFE 2337.3.3 Molding Techniques of PTFE 2337.3.4 Casting of PTFE by Extrusion 2367.3.5 Solution Blending of PTFE 2377.3.6 PTFE Coating Methods 2387.4 Applications of PTFE in Various Fields 2387.4.1 PTFE in Automotive Industries 2387.4.2 PTFE in Petrochemical and Power Industries 2397.4.3 PTFE in Aerospace Industries 2407.4.4 PTFE in Food Processing Industries 2417.4.5 PTFE Applications in Chemical Industries 2427.4.6 PTFE in Biomedical and Pharmaceutical Applications 2427.4.7 PTFE in Electrical Applications 2437.4.8 PTFE for Defense Applications 2437.4.9 Application of PTFE Ice-Phobic Surfaces 2437.4.10 Application of PTFE in Water and Air Purification Process 2447.5 Different Forms of PTFE 2447.5.1 Fine Powder of PTFE for Foaming Applications 2447.5.2 Granular Form of PTFE 2457.5.3 Resin Form of PTFE 2457.5.4 Paste Form of PTFE 2457.5.5 Emulsion Form of PTFE 2467.6 Various Grades of PTFE 2467.6.1 Carbon-Reinforced PTFE 2467.6.2 Glass Fiber-Reinforced PTFE 2477.6.3 Bronze-Filled PTFE Composites 2477.6.4 Graphite Filled PTFE 2487.6.5 Molybdenum Disulfide (MoS2)-Filled PTFE 2487.7 Nanocomposites of PTFE 2487.8 Future Prospects of PTFE 2547.9 Conclusion 2568 Advances in High-Performance Polymers Bearing Phthalazinone Moieties 267Jinyan Wang, Cheng Liu, Shouhai Zhang and Xigao Jian8.1 Introduction 2688.2 A New Mmonomer: 1, 2-Dihydro-4-(4-Hydroxyphenyl)-1-(2H)-Phthalazinone 2698.3 Synthesis and Properties of Phthalazinone-Containing Polyarylethers 2718.3.1 Poly(phthalazinone Ether Sulfone Ketone)s (PPESKs) 2718.3.2 Poly(phthalazinone Ether Ketone Ketone) (PPEKK) and Its Copolymers 2748.3.3 Poly(phthalazinone Ether Nitrile Sulfone Ketone)s (PPENSKs) 2758.3.4 Poly(aryl Ether) Containing Aryl-S-Triazine and Phthalazinone Moieties 2798.4 Polyamides and Polyimides Containing Phthalazinone Moieties 2858.5 Phthalazinone-Containing Polyarylates 2918.6 Phthalazinone-Containing Ppolybenzimidazole 2928.7 Conclusions and Prospects 293Acknowledgments 2949 Poly(ethylene terephthalate)-PET and Poly(ethylene naphthalate)-PEN 301Luigi Sorrentino, Marco D' Auria and Eugenio Amendola9.1 Introduction 3029.2 Synthesis of PET and PEN 3049.2.1 PET Production 3129.3 Processing of Neat Polymers 3139.3.1 Materials Feeding 3159.3.2 Melting and Compounding 3169.3.3 Venting 3169.3.4 Metering 3169.3.5 Temperature Managing 3179.3.6 Die Forming and Post-Die Treatments 3179.3.7 Tandem Extruders Cconfiguration 3179.4 Nanocomposites 3189.4.1 Isodimensional Nanoparticles 3199.4.2 Clay Nanoparticles 3219.4.3 Carbon-Based Nanoparticles 3249.5 Nanocomposites Production Processes 3259.5.1 In Situ Polymerization 3269.5.2 Solution Intercalation (Or Solution Blending) 3289.5.3 Direct Mixing 3299.5.4 Melt Compounding (High Shear Mixing) 3309.5.5 Three Roll Milling 3329.5.6 Dispersion Aids (Ultrasounds) 3339.5.7 Solid-State Shear Processing 3359.5.8 Combined Approaches 3369.6 Structural and Functional Properties 3369.6.1 Mechanical Behavior 3379.6.2 Thermal Resistance 3409.6.3 Transport Properties 3419.6.4 Electrical Conductivity 3439.6.5 Rheological Properties 34610 High-Performance Oil-Resistant Blends of Ethylene Propylene Diene Monomer (EPDM) and Epoxidized Natural Rubber (ENR) 361D.K. Setua and G.B. Nando10.1 Introduction 36210.2 Experimental 36510.3 Result and Discussion 36710.3.1 Optimization of Curing System for the ENR/EPDM Blends 36710.3.2 Optimization of Blend Ratio for the ENR/EPDM Blends 36910.3.3 Optimization of MAH Concentration for Maleation of EPDM 36910.3.4 Characterization of ENR-MA-G-EPDM Blends 37310.3.5 Optimization of Processing Temperature for ENR-MA-G-EPDM Blends 37510.3.6 Compatibility Characteristics of ENR-MA-G-EPDM Blends 37510.3.6.1 Ultrasonic Velocity Measurements in Solution 37510.3.6.2 Thermomechanical Analysis (TMA) 37710.3.6.3 Scanning Electron Microscopy (SEM) Studies 37810.3.7 Evaluation of the Mechanical Properties of Individual Rubbers and Blends 37910.3.7.1 Stress-Strain Properties 37910.3.7.2 Determination of Hardness 38210.3.7.3 Oil Swelling Studies 38310.3.7.4 Aging Studies 38510.3.7.5 Thermogravimetric Analysis (TGA) 38610.3.8 Effect of Addition of Carbon Black in ENR/MA-G-EPDM Blend 38810.4 Summary and Conclusions 38811 High-Performance Unsaturated Polyester/f-MWCNTs Nanocomposites Induced by f-Graphene Nanoplatelets 393Shivkumari Panda, Dibakar Behera, Tapan Kumar Bastia and Prasant Rath11.1 Introduction and History 39411.1.1 Polymerization 39411.1.2 Fabrication 39511.1.2.1 Hand Lay-Up 39511.1.2.2 Spray Lay-Up 39711.1.2.3 Compression Molding 39711.1.2.4 Filament Winding 39811.1.3 Chemical Stability of UPE 39811.1.4 Compounding and Special Additives 39811.1.5 Applications 40111.2 Nanocomposites of UPE11.2.1 Experimental Details 40311.2.1.1 Materials 40311.2.1.2 Methods 40311.2.2 Instruments and Measurements 40511.2.2.1 Fourier Transform Infrared (FTIR) Spectroscopy 40511.2.2.2 Scanning Electron Microscopy (SEM) 40511.2.2.3 Transmission Electron Microscope (TEM) 40611.2.2.4 Contact Angle Determination 40611.2.2.5 Dynamic Mechanical Analysis 40611.2.2.6 Impact Testing 40611.2.2.7 Water Absorption Capacity Determination 40611.2.3 Results and Discussion 40711.2.3.1 FTIR Analysis 40711.2.3.2 SEM Analysis 40811.2.3.3 TEM Analysis 41011.2.3.4 Contact Angle 41111.2.3.5 Thermomechanical Properties of UPE/Single Filler and UPE/Hybrid Filler Nanocomposites 41211.2.3.6 Water Absorption Capacity 414

Citation preview

High Performance Polymers and Their Nanocomposites

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

High Performance Polymers and Their Nanocomposites

Edited by

Visakh P.M. and Semkin A.O.

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 © 2019 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 Names: P. M., Visakh, editor. | O., Semkin A., editor. Title: High performance polymers and their nanocomposites / edited by Visakh P.M. and Semkin A.O. Description: Hoboken, NJ : Wiley-Scrivener, 2018. | Includes bibliographical references. | Identifiers: LCCN 2018041153 (print) | LCCN 2018042492 (ebook) | ISBN 9781119363811 (ePub) | ISBN 9781119363880 (ePDF) | ISBN 9781119363651 (hardcover) Subjects: LCSH: Polymers. | Polymeric composites. Classification: LCC TA455.P58 (ebook) | LCC TA455.P58 H5475 2018 (print) | DDC 620.1/92--dc23 LC record available at https://lccn.loc.gov/2018041153 Cover image: Pixabay.Com Cover design: 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 1 High-Performance Polymer Nanocomposites and Their Applications: State of Art and New Challenges Visakh P.M. 1.1 Liquid Crystal Polymers 1.2 Polyamide 4, 6, (PA4,6) 1.3 Polyacrylamide 1.4 Effect of Nanostructured Polyhedral Oligomeric Silsesquioxone on High Performance Poly(urethane-Imide) 1.5 Thermoplastic Polyimide 1.6 Performance Properties and Applications of Polytetrafluoroethylene (PTFE) 1.7 Advances in High-Performance Polymers Bearing Phthalazinone Moieties 1.8 Poly(ethylene Terephthalate)—PET and Poly(ethylene Naphthalate)—PEN 1.9 High-Performance Oil Resistant Blends of Ethylene Propylene Diene Monomer (EPDM) and Epoxydized Natural Rubber (ENR) 1.10 High Performance Unsaturated Polyester/f-MWCNTs Nanocomposites Induced by F-Graphene Nanoplatelets References

2 Liquid Crystal Polymers Andreea Irina Barzic, Raluca Marinica Albu and Luminita Ioana Buruiana 2.1 Introduction and History 2.2 Polymerization

xiii 1 1 3 4

5 5 7 9 11

14

15 16

27 27 29 v

vi

Contents 2.2.1 Synthesis of Lyotropic LC Polymers 2.2.2 Synthesis of Thermotropic LC Polymers 2.3 Properties 2.3.1 Rheology 2.3.2 Dielectric Behavior 2.3.3 Magnetic Properties 2.3.4 Mechanical Properties 2.3.5 Phases and Morphology 2.4 Processing 2.4.1 Injection Molding 2.4.2 Extrusion 2.4.3 Free Surface Flow 2.4.4 LC Polymer Fiber Spinning 2.5 Blends Based on Liquid Crystal Polymers 2.6 Composites of Liquid Crystal Polymers 2.7 Applications 2.7.1 LC Polymers as Optoelectronic Materials 2.7.2 Liquid Crystalline Polymers in Displays 2.7.3 Sensors and Actuators 2.8 Environmental Impact and Recycling 2.9 Concluding Remarks and Future Trends Acknowledgment References

3 Polyamide 4,6, (PA4,6) Emel Kuram and Zeynep Munteha Sahin 3.1 Introduction and History 3.2 Polymerization and Fabrication 3.3 Properties 3.4 Chemical Stability 3.5 Compounding and Special Additives 3.6 Processing 3.7 Applications 3.8 Blends of Polyamide 4,6, (PA4,6) 3.9 Composites of Polyamide 4,6, (PA4,6) 3.10 Nanocomposites of Polyamide 4,6, (PA4,6) 3.11 Environmental Impact and Recycling 3.12 Conclusions References

30 31 32 32 35 36 36 39 41 41 42 43 44 44 46 48 49 50 51 52 53 54 54

59 60 60 69 73 74 74 81 86 88 91 94 99 100

Contents vii

4 Polyacrylamide (PAM) Małgorzata Wiśniewska 4.1 Introduction and History 4.2 Polymerization and Fabrication 4.3 Properties 4.4 Chemical Stability 4.5 Compounding and Special Additives 4.6 Processing 4.7 Applications 4.8 Blends of Polyacrylamide 4.9 Composites of Polyacrylamide 4.10 Nanocomposites of Polyacrylamide 4.11 Environmental Impact and Recycling 4.12 Conclusions References

5 Effect of Nanostructured Polyhedral Oligomeric Silsesquioxone on High Performance Poly(urethane-imide) Dhorali Gnanasekaran 5.1 Introduction 5.2 Experimental 5.3 Results and Discussion 5.4 Conclusions References

6 Thermoplastic Polyimide (TPI) Xiantao Feng and Jialei Liu 6.1 Introduction and History 6.2 Polymerization and Fabrication 6.2.1 Thermoplastic Polyimides Based on BEPA 6.2.2 Thermoplastic Polyimides Based on PMDA 6.2.3 Thermoplastic Polyimides Based on BTDA 6.2.4 Thermoplastic Polyimides Based on ODPA 6.2.5 Thermoplastic Polyimides Based on BPDA 6.2.6 Thermoplastic Copolyimides 6.3 Properties 6.3.1 TPI Based on BEPA 6.3.2 Thermoplastic Polyimides Based on PMDA 6.3.3 TPI Based on ODPA 6.3.4 Thermoplastic Polyimides Based on BPDA

105 105 107 110 111 112 113 114 116 118 119 120 122 123

133 134 136 138 146 146

149 149 150 150 153 154 157 157 158 160 160 163 163 168

viii

Contents 6.3.5 Thermoplastic Copolyimides Chemical Stability 6.4.1 Hydrolytic Stability 6.4.2 Oxidative Stability 6.5 Compounding 6.5.1 Chloromethylation 6.5.2 Sulfonation 6.5.3 Phosphorylation 6.5.4 Bromination 6.5.5 Arylation 6.6 Processing 6.6.1 Injection Molding 6.6.2 Compression Molding 6.6.3 Extrusion Molding 6.6.4 Coating 6.6.5 Spinning 6.7 Applications 6.7.1 Membranes 6.7.2 Adhesives 6.7.3 Composites 6.7.3.1 Skybond 6.7.4 Engineering Plastics 6.7.4.1 VESPEL Plastics 6.7.4.2 ULTEM Plastics 6.7.4.3 AURUM Plastics 6.7.4.4 Ratem Plastics 6.8 Blends of Thermoplastic Polyimide (TPI) 6.8.1 TPI Blends with TPI 6.8.2 Polyamic Acid Blending 6.9 Composites of Thermoplastic Polyimide (TPI) 6.9.1 LaRC Composites 6.9.2 Skybond 6.9.3 PAI Polyamide–Imide Composites 6.10 Nanocomposites of Thermoplastic Polyimide (TPI) 6.10.1 TPI/silver Nanocomposite 6.10.2 TPI/Fe-FeO Nanocomposite 6.10.3 TPI/Carbon Nanocomposites 6.10.4 TPI/CF/TiO2 Nanocomposite 6.11 Environmental Impact and Recycling 6.12 Conclusions References 6.4

170 170 170 174 175 175 178 178 178 181 181 181 182 184 184 186 186 186 188 189 190 190 190 191 192 192 193 193 195 196 197 202 205 208 208 210 211 214 214 215 215

Contents ix

7 Advances in High-Performance Polymers Bearing Phthalazinone Moieties Jinyan Wang, Cheng Liu, Shouhai Zhang and Xigao Jian 7.1 Introduction 7.2 A New Mmonomer: 1, 2-Dihydro-4-(4-Hydroxyphenyl)-1-(2H)-Phthalazinone 7.3 Synthesis and Properties of Phthalazinone-Containing Poly(aryl ether)s 7.3.1 Poly(phthalazinone ether sulfone ketone)s (PPESKs) 7.3.2 Poly(phthalazinone ether ketone ketone) (PPEKK) and Its Copolymers 7.3.3 Poly(phthalazinone ether nitrile sulfone ketone)s (PPENSKs) 7.3.4 Polyarylether) Containing Aryl-S-triazine and Phthalazinone Moieties 7.4 Polyamides and Polyimides Containing Phthalazinone Moieties 7.5 Phthalazinone-Containing Polyarylates 7.6 Phthalazinone-Containing Polybenzimidazole 7.7 Conclusions and Prospects Acknowledgments References

8

Poly(ethylene terephthalate)—PET and Poly(ethylene naphthalate)—PEN Luigi Sorrentino, Marco D’ Auria and Eugenio Amendola 8.1 Introduction 8.2 Synthesis of PET and PEN 8.2.1 PET Production 8.3 Processing of Neat Polymers 8.3.1 Materials Feeding 8.3.2 Melting and Compounding 8.3.3 Venting 8.3.4 Metering 8.3.5 Temperature Managing 8.3.6 Die Forming and Post-Die Treatments 8.3.7 Tandem Extruders Configuration 8.4 Nanocomposites

221 222 222 225 225 228 229 233 239 245 246 248 248 249

255 256 258 266 267 269 270 270 270 271 271 271 272

x

Contents 8.4.1 Isodimensional Nanoparticles 8.4.2 Clay Nanoparticles 8.4.3 Carbon-Based Nanoparticles 8.5 Nanocomposites Production Processes 8.5.1 In Situ Polymerization 8.5.2 Solution Intercalation (Or Solution Blending) 8.5.3 Direct Mixing 8.5.4 Melt Compounding (High Shear Mixing) 8.5.5 Three Roll Milling 8.5.6 Dispersion Aids (Ultrasounds) 8.5.7 Solid-State Shear Processing 8.5.8 Combined Approaches 8.6 Structural and Functional Properties 8.6.1 Mechanical Behavior 8.6.2 Thermal Resistance 8.6.3 Transport Properties 8.6.4 Electrical Conductivity 8.6.5 Rheological Properties References

9 High-Performance Oil/Fuel-Resistant Blends of Ethylene Propylene Diene Monomer (EPDM) and Epoxidized Natural Rubber (ENR) D.K. Setua and G.B. Nando 9.1 Introduction 9.2 Experimental 9.3 Result and Discussion 9.3.1 Optimization of Curing System for the ENR/EPDM Blends 9.3.2 Optimization of Blend Ratio for the ENR/EPDM Blends 9.3.3 Optimization of MAH Concentration for Maleation of EPDM 9.3.4 Characterization of ENR-MA-G-EPDM Blends 9.3.5 Optimization of Processing Temperature for ENR-MA-G-EPDM Blends 9.3.6 Compatibility Characteristics of ENR-MA-G-EPDM Blends 9.3.6.1 Ultrasonic Velocity Measurements in Solution

273 275 278 279 280 282 283 284 287 287 289 289 289 290 295 296 298 301 304

315 316 319 322 322 323 326 328 329 330 330

Contents xi 9.3.6.2 Thermomechanical Analysis (TMA) 9.3.6.3 Scanning Electron Microscopy (SEM) Studies 9.3.7 Evaluation of the Mechanical Properties of Individual Rubbers and Blends 9.3.7.1 Stress–Strain Properties 9.3.7.2 Determination of Hardness 9.3.7.3 Oil/Fuel Swelling Studies 9.3.7.4 Aging Studies 9.3.7.5 Thermogravimetric Analysis (TGA) 9.3.8 Effect of Addition of Carbon Black in ENR/MA-G-EPDM Blend 9.4 Summary and Conclusions Acknowledgement References

10

High-Performance Unsaturated Polyester/f-MWCNTs Nanocomposites Induced by f-Graphene Nanoplatelets Shivkumari Panda, Dibakar Behera, Tapan Kumar Bastia and Prasant Rath 10.1 Introduction and History 10.1.1 Polymerization 10.1.2 Fabrication 10.1.2.1 Hand Lay-Up 10.1.2.2 Spray Lay-Up 10.1.2.3 Compression Molding 10.1.2.4 Filament Winding 10.1.3 Chemical Stability of UPE 10.1.4 Compounding and Special Additives 10.1.5 Applications 10.2 Nanocomposites of UPE 10.2.1 Experimental Details 10.2.1.1 Materials 10.2.1.2 Methods 10.2.2 Instruments and Measurements 10.2.2.1 Fourier Transform Infrared (FTIR) Spectroscopy 10.2.2.2 Scanning Electron Microscopy (SEM)

332 332 335 335 336 337 342 342 343 344 344 344

347 348 348 349 349 351 351 352 352 352 355 356 357 357 357 359 359 359

xii

Contents 10.2.2.3

Transmission Electron Microscope (TEM) 10.2.2.4 Contact Angle Determination 10.2.2.5 Dynamic Mechanical Analysis 10.2.2.6 Impact Testing 10.2.2.7 Water Absorption Capacity Determination 10.2.3 Results and Discussion 10.2.3.1 FTIR Analysis 10.2.3.2 SEM Analysis 10.2.3.3 TEM Analysis 10.2.3.4 Contact Angle 10.2.3.5 Thermomechanical Properties of UPE/Single Filler and UPE/Hybrid Filler Nanocomposites 10.2.3.6 Water Absorption Capacity Conclusion and Future Challenges References Index

360 360 360 360 360 360 360 362 364 365

366 368 369 370 373

Preface Many of the recent research accomplishments in the area of high performance polymers, their preparation, structure-properties and their nanocomposites are summarized in High Performance Polymers and Their Nanocomposites. Among the many topics discussed are liquid crystal polymers, polyamide 4,6 and polyacrylamide, and the influence of nanostructured multifunctional polyhedral oligomeric silsesquioxane on surface morphology. Also discussed are thermoplastic polyimide, and polytetrafluoroethylene’s performance properties and applications. A review of polymer containing phthalazinone moieties is presented along with a discussion of poly(ethylene terephthalate) and poly(ethylene naphthalate) polyesters; high-performance oil-resistant blends of ethylene propylene diene monomer and epoxidized natural rubber; and unsaturated polyester nanocomposites reinforced with functionalized nanofillers. This book will be a very valuable reference source for university and college faculties, professionals, post-doctoral research fellows, senior graduate students, and researchers from R&D laboratories working in the area of high performance polymers and their nanocomposites. The various chapters in this book are contributed by prominent researchers from industry, academia and government/private research laboratories across the globe, making it an up-to-date record on the major findings and observations in the field. The first chapter discusses the state-of-the-art of high performance polymer nanocomposites and new challenges relating to them. The second chapter introduces the concepts of liquid crystal polymers (LCPs) and also gives their historical background. Because the method used to obtain these compounds is an important issue, the main synthesis routes are described. In order to understand the solution properties of LCPs some rheological aspects are highlighted, together with some basic characteristics in solid phase, like dielectric behavior, magnetic properties, mechanical resistance and phase morphology. Since the features of LCPs are also affected by the applied processing methodology, basic aspects concerning injection molding, extrusion, free surface flow and LCP fiber spinning are xiii

xiv

Contents

briefly addressed. The practical importance of blends and composites with LCP phase is emphasized in various industrial areas such as optoelectronics, displays, sensors and actuators. Several essential aspects are disclosed regarding the environmental impact of LCPs and concerns about their recycling. Considering the high demand for products based on LCPs, the corresponding market is expected to expand, but efforts still must be made to improve their performance and reduce preparation costs. Various topics on polyamide 4,6 and its properties are discussed in the third chapter. Polyamide (PA) or nylon is one of the engineering plastics employed in many engineering components. At high temperatures, PA4,6 provides excellent properties such as high stiffness, creep resistance, thermal stability, and fatigue resistance, along with good toughness. Also, PA4,6 shows better chemical resistance to acidic salts, methanol, mineral salts, oils and grease. Its excellent mechanical properties at high temperatures, low friction, excellent resistance to wear and excellent chemical resistance make PA4,6 polymer a good candidate for a broad range of technical applications in electrical, electronic and automotive industries among others. Therefore, studies about the polymerization, properties, chemical stability, processing and applications of PA4,6 are presented in this chapter. The blends, composites and nanocomposites of PA4,6 with other polymers are also mentioned, along with its environmental impact and recycling possibility. The fourth chapter of this book discusses polyacrylamide and its nanocomposites. Polyacrylamide (PAM) polymers are a synthetic group with a great variety of macromolecular compounds. Polyacrylamide is very soluble in water, with the solution’s viscosity being linearly dependent on polymer molecular weight; and PAM amide with weak basic character undergoes hydrolysis, halogenation, methylation and sulfonation reactions. This chapter is mainly divided into two parts. The first part discusses the history of PAM and its polymerization, fabrication, properties, chemical stability, compounding, special additives, processing and applications. Whereas the second part deals with various topics such as blends and composites of PAM, its nanocomposites, environmental impact and recycling. The effect of nanostructured polyhedral oligomeric silsesquioxone (POSS) on high performance poly(urethane-imide) (PUI) is the topic of the fifth chapter, in which the author discusses different research studies related to POSS. Successfully embedding POSS in the PUI membrane through chemical bonding and the vital role of POSS on the surface morphology of prepared membranes were studied. A range of PUI-POSS membranes were prepared by a facile in-situ polymerization reaction based on different loadings of POSS and their surface morphology was characterized by

Contents

xv

atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The thermal stability of PUI-POSS nanocomposite membranes were analyzed by thermogravimetric analysis (TGA). The TEM images revealed the dispersion behavior of POSS in the membranes, which was found to be in the range of 10 to 20 nm size. SEM images showed no agglomeration even at the higher content of POSS. Three-dimensional AFM images of the membranes indicated a slight increase in roughness when POSS content was increased. The gel content, fractional free volume (FFV) and density of the PUI-POSS membranes were calculated, and effectively correlated with surface morphology studies. The obtained results showed that the prepared membrane is excellent for gas transport studies. The next chapter mainly focuses on the polymerization, processing, properties and applications of thermoplastic polyimide (TPI). The polymerization and properties are introduced by their basic polymer units such as BEPA, PMDA, BTDA, ODPA, BTDA, etc. The blends, composites and nanocomposites of TPI are also described in this chapter, including compounding with other molecules of TPI. Its environmental impact and recyclability are briefly discussed at the end of the chapter. Advances in high performance polymers containing phthalazinone moieties are discussed in the seventh chapter. The authors of the chapter explain that high performance polymer materials have excellent performance in high temperatures and are indispensable in aerospace, electronics, electrical engineering, high-speed rail, and other important high-tech fields. Progress in the synthesis and performance of phthalazinone-containing polyarylethers (including poly(phthalazinone ether sulfone ketone) s, poly(phthalazinone ether nitrile sulfone ketone)s, poly(phthalazinone ether sulfone ketone ketone)s, and poly(triaryl triazine ring)s), polyamides, polyimides, polyarylates, and polybenzimidazoles is also reviewed. Because the phenyl-phthalazinone structure is a twisted, non-coplanar, and fused ring, the above polymers are not only heat resistant, but also soluble. The processing methods are diverse and include both thermoforming (molding, extrusion, injection, etc.) and solution processing. Hence, these polymers have a wide range of applications. In the eitgth chapter, poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) polyesters are discussed in a wide range of review studies. The first part of this chapter discusses the synthesis of PET and PEN, PET production, processing of neat polymers, materials feeding, melting, compounding, venting, metering, temperature managing, die forming and post-die treatments, and tandem extruders configuration. The second part of the chapter relates to PET and PEN nanocomposites,

xvi

Contents

in which the authors explain the preparation of polyester-based nanocomposites using different preparation methods, and also characterize them with different types of techniques. In the ninth chapter, different topics relating to high-performance oilresistant blends of ethylene propylene diene monomer (EPDM) and epoxidized natural rubber (ENR) are discussed. Among the many subtopics discussed in the first part of the chapter are optimization of the curing system and blend ratio for the ENR/EPDM blends, the optimization of maleic anhydride (MAH) concentration for maleation of EPDM, and the characterization and compatibility characteristics of ENR-MA-g-EPDM blends and optimization of their processing temperature. The second part of the chapter mainly focuses on characterization methods such as ultrasonic velocity measurements in solution, thermomechanical analysis, scanning electron microscopy studies, evaluation of the mechanical properties of individual rubbers and blends, stress-strain properties, determination of hardness, oil swelling and aging studies, and thermogravimetric analysis. Finally, the effect of addition of carbon black in ENR/MA-g-EPDM blend is also explained. The subject of the final chapter is high performance unsaturated polyester/f-MWCNTs nanocomposites induced by f-graphene nanoplatelets. The focus of the chapter is mainly on the unique properties of unsaturated polyester resin (UPE) as well as preparation of a hybrid UPE nanocomposite incorporated with chemically functionalized multiwalled carbon nanotubes (f-MWCNTs) and functionalized graphene nanoplatelets (f-GNPs) through a solution mixing procedure. The chapter’s authors tried to compile the detailed preparation and characterization techniques of both functionalized nanofillers and the hybrid UPE nanocomposites with a focus on the effect of nanofiller loading. Owing to the incorporation of f-MWCNTs and f-GNPs hybrid into UPE, a large surface area was created which resulted in strong interfacial adhesion between the efficient hybrid nanofiller networks and the matrices. Thorough analysis of the results showed the formation of efficient hybrid nanocomposite with improved properties. The produced nanomaterial successfully proved its candidacy for high performance UPE-based nanocomposites with a variety of applicabilities in the realm of functionalized nanocomposites. In conclusion, the editors would like to express their sincere gratitude to all the contributors to this book, whose excellent support and enthusiasm ensured the successful completion of this venture. We are grateful to them for the commitment and sincerity they showed towards their contributions. We would like to thank all the reviewers who have taken their valuable time to make critical comments on each chapter. We also thank the

Contents xvii publisher, John Wiley and Sons Ltd. and Scrivener Publishing, for recognizing the demand for such a book, and for realizing the increasing importance of the area of high performance polymers and their nanocomposites and for starting such a new project, the subject of which only a few other publishers have touched. Dr. Visakh P. M. Dr. Artem Semkin Tomsk, Russia September 2018

1 High-Performance Polymer Nanocomposites and Their Applications: State of Art and New Challenges Visakh P.M. Faculty of Electronic Engineering, Department of Physical Electronics, TUSUR University, Tomsk, Russia

Abstract This chapter deals with a brief account on various topics in high performance polymers nanocomposites and their applications. It discusses the various topics such as liquid crystal polymers (LCP), polyamide 4, 6, (PA4,6), polyacrylamide (PAM), the influence of nanostructured multifunctional polyhedral oligomeric silsesquioxone on surface morphology, thermoplastic polyimide (TPI), performance properties and applications of polytetrafluoroethylene (PTFE), polymer containing phthalazinone moieties, polyesters: poly(ethylene terephthalate) – PET, poly(ethylene naphthalate) – PEN, high performance oil resistant blends of ethylene propylene diene monomer (EPDM), epoxydised natural rubber(ENR), unsaturated polyester and also nanocomposites from this by reinforcing functionalized nanofillers. Keywords: High performance polymers, liquid crystal polymers, polyamide, polyacrylamide, thermoplastic polyimide, poly(ethylene terephthalate), ethylene propylene diene monomer, epoxydised natural rubber

1.1

Liquid Crystal Polymers

Liquid crystals (LC) combine the long-range positional and orientational order found in solid crystals and the statistical long-range disorder typical for isotropic liquids [1]. This point represents a milestone that opened Corresponding author: [email protected] Visakh P.M. and Semkin A.O. (eds.) High Performance Polymers and Their Nanocomposites, (1–26) © 2019 Scrivener Publishing LLC

1

2

High Performance Polymers and Their Nanocomposites

a novel area of research that gained the attention of physicists, chemists, and engineers for several decades. LCs may have some similarities with those of living state since mobility and structural organization of biological and synthetic LCs represent an ideal medium for catalytic action involved in growth and reproduction processes of cells. Liquid crystals phase with external fields, such as electric, magnetic, or mechanical ones, offers many possibilities to shape these materials [2]. For this reason, they are found in several applicative domains, such as electronics (displays, photonic devices and polarization-independent instruments) or medicine (biosensors for optically probing biological systems, biomimicking color-producing structures, lenses, and muscle-like actuators) [3]. A good example in this category of materials is given by poly(γbenzyl-L-glutamate) or cellulose derivatives [4]. Side chain LC polymers that result from free-radical process are prepared using various types of initiating factors such as temperature or electromagnetic radiations. Rheological properties of LC polymers, registered in the simplest coneplate geometry, are very complex in regard to homogeneous isotropic polymer solutions [5]. Cholesteric LC polymers can be obtained from optically active macromolecular compounds or optically active mixtures [6]. The molecular centers of gravity do not present long-range order but the molecules have the tendency to be parallel to LC director. Smectic phase has attracted much attention in scientific community, which revealed more than 10 smectic modifications. This led to a variety of polymeric materials with different architectural features. Most LC polymers are attractive for sintering flows owing to their reduced viscosity but the orientation degree is not as high as expected. Another limitation of such materials arises from the high viscosity at low shear stress that impedes the fusion of the particles. Melt rheology tests showed decreased viscosity of thermoplastics after introduction of LC polymer. Higher interfacial adhesion between the isotropic and anisotropic components was noticed at low shear rates as a slight increase in the melt viscosity. LC polymer composites can be obtained from cellulose derivatives, such as hydroxypropyl cellulose (HPC). Nishio et al., [7] revealed that utilization of the 2-hydroxyethyl methacrylate (HEMA) solvent enables through its polymerization preparation of multiphasic materials with cholesteric nature of the mesophase over limited concentration and temperature ranges. LC polymers find application in a wide range of domain, the most important being in electroluminescent display devices or nonlinear optical materials in the case of main chain LC polymers. For side chain LC polymers, the most known applications are replacements for small molecules in LC displays or passive optical films with tailored optical properties.

Polymer Nanocomposites and Their Applications

1.2

3

Polyamide 4, 6, (PA4,6)

Polyamide (PA) or nylon is one of the engineering plastics employed in many engineering components. Various types of PA such as PA6, PA6,6, and PA4,6 are available in the market. Polyamides (PAs) can both be made from one type of monomer or two types of monomers. Among the various types of PAs, PA4,6 is a new engineering plastic. PA4,6 was mentioned as early as the 1930s in the literature [8], and this researcher reported that the melting point was 278 °C, which was confirmed by Coffman et al., [9] in 1947. Ke and Sisko [10] synthesized PA4,6 with a melting point of 293 °C by interfacial polymerization. Aubineau et al., [11] prepared PA4,6 from adipoyl chloride in chloroform solution. However, the significant and commercial quantities of PA4,6 were not available until the 1980s. Nowadays, PA4,6 is commercially available in the market (DSM) under the trade name Stanyl. PA4,6 gives excellent properties at high temperatures such as high stiffness, high creep resistance, high thermal stability, good toughness, and high fatigue resistance [12]. However, fire resistance of PA4,6 is weak [13]. PA4,6 fibers with diameters in the range of 30–200 nm were manufactured by the electrospinning technique [14]. The diameters of the PA4,6 nanofibers were adjusted by changing the concentration of the polymer solution during electrospinning, and the nanofibers with diameters ranging from 1 μm to 1 nm were prepared. Properties such as excellent mechanical properties at high temperatures, low friction, excellent resistance to wear, and excellent chemical resistance of PA4,6 make this polymer a good material candidate for the broad range of technical applications such as electrical, electronic, and automotive industries [15]. PA4,6 is used in automotive components, motor sensors, microswitches, auto connectors, motor components, and bobbins [16]. The properties of high dimensional and thermal stability and resistance against peak temperatures of PA4,6 result in good material for applications in the close vicinity of an engine where very high temperatures can be obtained for a short period. Toughened PA4,6 has a large potential for the extruded tubing applications owing to the retention of the elongation at elevated temperature. Toughened PA4,6 is better suitable in the applications where high temperature retention of stiffness and creep modulus are required. Impact modified PA4,6 is an ideal for the automotive usage due to the retention of ductility, stiffness, and creep modulus at elevated temperatures. In the literature, tensile strength, flexural strength, compressive strength, compressive modulus, frictional coefficient, and specific wear rate of glass- and carbon-fiber-reinforced PA4,6 composites were predicted by an artificial neural network [17].

4

High Performance Polymers and Their Nanocomposites

Water absorption diminishes the properties of polymeric materials and limits its applications in the industry. The knowledge about the water uptake in PA4,6 matrix is very important for the manufacturers in the countries with a climate of high humidity. PA4,6 is soluble in water and ethanol; however, water is a better solvent than ethanol. Vapor pressure of water rises with heating [69].

1.3

Polyacrylamide

The first synthesis of polyacrylamide (PAM) was performed in 1893 by Charles Moreau—the French pharmacist and chemist. He obtained PAM using acryloyl chloride and ammonia at low temperature. The commercial production of PAM began in the United States in 1954. The acrylamide (AM) monomer obtained from acrylonitrile was used in homopolymerization to obtain non-ionic polyacrylamide. The most important areas of polyacrylamide applications are the flocculation process in the wastewaters treatment, enhanced oil recovery, sludge dewatering, paper production, and improvement of cultivated soil stability [18–23]. Polyacrylamide with the molecular formula (C3H5NO)n is called, according to the IUPAC nomenclature, poly(2-propenamide) or poly(1carbamoylethylene). Polyacrylamide and its derivatives are also used in paper-making technologies. For example, N-chloropolyacrylamide (N-ClPAM), obtained from the N-chlorination of polyacrylamide, was applied for the improvement of paper strength. It was proved that N-Cl-PAM reacts with the hydroxyl and carboxyl groups of the cellulose forming strong covalent bonds between the polymeric agents and fibers. The polyacrylamide blending with ammonia borane (AB) was prepared through a sol-mixing method by Li and co-workers [24]. This blend was used as a new polymeric storage of hydrogen. The dehydrogenation kinetics and the possible way of H2 release were examined. It was demonstrated that the dehydrogenation properties of AB-PAM blend are significantly better than pure ammonia borane. The polyacrylamide blends with other synthetic polymers were prepared and fully characterized. For example, PAM hybrid with poly(vinyl alcohol)—PVA was prepared through the blending of PAM and PVA using crosslinking with glutaraldehyde (Glu) [25]. The blends of PVA and polyvinyl pyrrolidone—PVP were prepared and tested for their usage as corrosion inhibitors for aluminum in the acidic medium in the temperature range of 30–60 °C [26]. Ni and coworkers [27] prepared in situ gold/polyacrylamide hybrid nanoparticles

Polymer Nanocomposites and Their Applications

5

(Au/PAM) in an ethanol solution at room temperature and normal pressure using γ irradiation. Pan and Chen [28] obtained the polyacrylamide silver/polyacrylamide (Ag/PAM) nanocomposites subjecting the mixture of silver nitrate (AgNO3) and PAM solutions to ultraviolet irradiation.

1.4

Effect of Nanostructured Polyhedral Oligomeric Silsesquioxone on High Performance Poly(urethane-Imide)

Organic–inorganic hybrid materials such as polyhedral oligomeric silsesquioxones (POSS) are accepted as a new class of advanced materials, because they can be synthesized or processed using versatile approaches and have own tunable properties. POSS cubic molecules show a rigid framework structure closely related to that of silica, and POSS is one of the most important fillers as well as functionally tailored nanomaterial in nanotechnology. The large variety of substitution pattern allows silsesquioxane specifically POSS to be incorporated into almost any conventional polymer either by blending or by covalent attachments [29–31]. Chattopadhyay et al., [32] synthesized two different sets of poly(urethaneimide/clay) hybrids from two types of polyester polyols. Avadhani et al., [33] have prepared novel poly(urethane-imide) by utilizing diisocyanates containing built-in imide group. In addition, Yeganeh et al., [34] have synthesized poly(urethane-imide) by the reaction of isocyanate-terminated PU prepolymer with glycols containing imide function as a chain extender.

1.5

Thermoplastic Polyimide

Polyimide (PI) is a polymer of imide monomers. In those of polymers, Phthalimide polymer is the most important one. The last ones are the most used polyimides because of their good thermostability such as the Phthalimide polymers mentioned earlier. Thermosetting polyimides are known for thermal stability, good chemical resistance, excellent mechanical properties, and characteristic orange/yellow color. The polyimide cannot be melted or injection-molded and therefore has some limitations for complicated design and productivity. E.I. du Pont de Nemours and Company published a patent that described the synthesis of Thermoplastic copolyimides in 2001. The polymers were the reaction products of components

6

High Performance Polymers and Their Nanocomposites

comprising an aromatic dianhydride component, an aromatic diamine component, and an end capping component. Overall, thermoplastic polyimides (TPIs) are stable for dilute acid, but most of the TPIs are hydrolyzed materials, especially in the alkaline solution. Moreover, this makes TPI special to the other polymers. We could recycle the dianhydrides and diamines by alkaline hydrolysis reaction. For example, the recycling rate is up to 80–90% through the hydrolysis for Membrane Kapton. Similar to other aromatic polymers, TPIs are not stable for concentrated sulfuric acid, concentrated nitric acid, and halogens. DeIasi et al., [35] reported the effect of an aqueous environment on the properties of Kapton polyimide film. Immersion of specimens in distilled water at 25–100 °C for time periods ranging from one hour to several hundred hours resulted in a decrease in the ultimate tensile strength of the polymer from 157.32 MPa to approximately 95.76 MPa. After the polymerization and the fabrication of the TPI, some processing procedures are needed to make the raw TPI polymers into products. The processing procedures include the following: Injection molding, Compression molding, Extrusion molding, Coating, and Spinning. TPI could strongly cohere with several substrates, such as metals, nonmetals, and polymers. TPI-based adhesives were widely used in aerospace and electronics industries. Titanium alloys are widely used in aerospace, and they have very high tensile strength and toughness. They are light in weight, and have extraordinary corrosion resistance and the ability to withstand extreme temperatures. Hergenrother et al., [36] used LaRC-CPI for the adhesion of the titanium alloys. The results suggest that the adhesive performance is no good when the molecular weight is too higher or lower. Commonly, low temperature and high pressure will lead to good adhesive performance. ULTEM is a family of PEI products manufactured by SABIC as a result of acquiring the General Electric Plastics Division in 2007, developed by Joseph G. Wirth in the early 1980s. ULTEM resins are used in medical and chemical instrumentation due to their heat resistance, solvent resistance, and flame resistance. There are two ways to fabricate the TPI blends: the one is polyimide blends with polymide; the other is polyamic acid blending method (TPI must be soluble). As the second way, due to the amido acid exchange reaction, the formation of copolymers is inevitable, and there are many impact factors on the properties of the TPI blends, such as blending conditions, time, and temperature. Tong et al., [37] reported the preparation of rodlike/flexible polyimide blends is feasible by utilizing poly(amic acid) amine salt precursors, which are free from the intermolecular transamidation reaction. Compared to poly(amic ester)s, the preparation of poly(amic acid) amine salts is much

Polymer Nanocomposites and Their Applications

7

more straightforward and easier. In addition, poly(amic acid) amine salts as PI precursors are used more and more in practice. Khalil Faghihi and Meisam Shabanian [38] reported a TPI/silver nanocomposite. The soluble polyimide–silver nanocomposite containing chalcone moieties as a photo sensitive group was synthesized by a convenient ultraviolet irradiation technique. A precursor such as AgNO3 was used as the source of the silver particles. Thanh Hoai Lucie Nguyen et al., [39] reported another TPI/silver nanocomposite, which is based on silver nanowires and thermoplastic polyamide. The typical fabrication procedure of the composite is as follows: a volume of Ag NW suspension was added to the PI/NEP solution under sonification. This suspension was film coated on a glass plate and placed in an oven at 80 °C for 30 min to evaporate the solvent. Jiahua Zhu et al., [40] used the commercialized TPI Martrimid 5218 to fabricate the TPI–Fe–FeO nanocomposite. Pure PI and Fe–FeO/PI nanocomposite fibers with various Fe@FeO nanoparticle loadings (5, 10, 20, and 30 wt%) are fabricated by the electrospinning process. It has been found that polyimide films prepared with the SWCNT/1 complexes showed higher tensile strengths and storage moduli than that of the neat polyimide film and polyimide nanocomposite films prepared with pristine SWCNTs at the same loading levels. The films fabricated with the TPI nanocomposites also had higher Tg and better high-temperature stability than both the neat polyimide films and corresponding nanocomposite films prepared with pristine SWCNTs. Smirnova et al., [41] reported TPI/Carbon nanocomposite. They have studied the effects of additives of single-walled carbon nanotubes prepared via electric-arc synthesis and carbon nanofibers produced via gas-phase synthesis on the crystallization capacities and mechanical and electric properties of composite films. Li [42] reported a TPI/CF/TiO2 nanocomposite, which was prepared through compression molding as milled CF/ TPI mixtures without further melt mixing. The incorporation of TiO2 leads to a significant improvement in friction and wear properties of the CF/TPI composite.

1.6

Performance Properties and Applications of Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) is a fluoroplastic polymer, which is classified among thermoplastics that are providing diverse applications in various domains. PTFE is derived from the monomer tetrafluoroethylene

8

High Performance Polymers and Their Nanocomposites

(TFE). PTFE is a high molecular weight compound because of the strongly bonded fluorine atoms and exhibits high crystalline nature. It has been preferred as nonstick coating material to withstand high temperature cycles. PTFE is an engineering polymer in terms of mechanical uses such as lubrication, bearing balls, and polymeric gears. Owing to improved properties, PTFE has been playing a crucial role in majority of chemical and medical applications. In clinical applications, the PTFE coatings preferred for implants, stents, and biomedical instrumentations due to the inert characteristics [43]. PTFE has been treated with plasma to obtain pore on the surfaces. Surface morphology study reveals the appearance of parallel pore layers during plasma treatment. Plasma treatment deploys contact angle as a function of treatment time [44]. The bipolar Argon plasma treatment of PTFE also supports the same as with plasma treatment there is an increase in surface free energy [45]. A virgin PTFE reveals the ultimate friction resistance property therefore optimized for different types of lubrication. As a function of glass fiber, carbon, and graphite loading, there has been a strong influence over friction properties [46]. A wear mechanism was reported for metal precursor-based PTFE composites. Glass fiber (GF) and carbon fiber (CF)-filled PTFE were tested for the abrasion resistance capacity. The abrasiveness and surface morphology of the worn surfaces of GF/PTFE and CF/PTFE was studied using scanning electron microscope (SEM). The wear volume was certainly lost in GF/PTFE than CF/PTFE. Under various weight loads, CF/PTFE poses better abrasion resistance because of the adhesion of carbon fibers with the PTFE matrix [47]. PTFE is ductile in nature and obviously remains low in mechanical phase when compared to other polymers but PTFE has a good advantage in constructing mechanical device parts by loading filler components. Compression test on two grades of PTFE exhibited good mechanistic performance. The increase in thermal conductivity depends upon the filler material’s shape, size and thermal properties. The fillers generally provide the heat transfer path, which was the reason for increase in thermal conductivity [48]. The purpose of this work was to compare all the three grades for their respective optical properties. The samples were analyzed using spectroscopic ellipsometer. Further results revealed that the optical characteristics varied for three different grades of Teflon® AF with respect to the TFE content [49]. In general, PTFE has been manufactured by free-radical polymerization of TFE monomer. Polymerization of TFE in a hybrid carbon dioxide/aqueous medium was tried. Based on this method, the TFE monomers have been successfully polymerized and the results exhibit similar characteristics to that of common known methods [50]. PTFE reinforced

Polymer Nanocomposites and Their Applications

9

with short glass fibers [SGF) were optimized for injection molding. On injection of PTFE/SGF, the above-mentioned parameters can significantly improve the strength and impact resistance [51]. Finally the PTFE mixed fumaric acid are drawn out as porous rods by extrusion. The pore densities might depend on the volume fraction of fumaric acid during the extrusion process [52]. The coating process begins by passing the fabric material through the emulsion and the PTFE particles are held to adhere over the surfaces. For the improving adherence, additionally some fluorine compounds such as FEP [Fluorinated ethylene propylene) or PFA (Perfluoroalkoxy alkanes) were included while coating [53]. Polytetrafluoroethylene (PTFE) has been conferred as the most consumed fluoropolymer across the world. Since the discovery of PTFE, the material is flourishing in all ways, and the applications are found to be countless. Over the years, the growth of PTFE in domestic, industrial and defense applications is consistently increasing with no barriers. PTFE coatings on gear tooth exhibited the notable performance and work life on operating temperature of 30°C when compared to other polymer coats [54]. The high thermal stability of PTFE is an advantage to utilize it as a good heat exchanger and in coal power plants. According to the work, waste heat management can be done with the help of PTFE. Concerning the dayto-day energy needs, the current metal heat exchangers can be replaced by PTFE [55]. PTFE is chemically inert and its surface resists chemical contact. In the work, it was noted that PTFE is resistant to alkali–acid during cleaning cycles, and the aging was higher when compared to the rubber gaskets [56]. Different from other polymers, fluoropolymers have the ability to withstand harsh temperature and chemical circumstances hence providing applications such as coating for acid containers, tubes, hoses, and valves for transferring chemicals, and filtration of chemical compounds.

1.7

Advances in High-Performance Polymers Bearing Phthalazinone Moieties

Researchers have devoted a great deal of attention to develop the processing or solubility of the above aromatic heterocyclic polymers. One approach introduces an aryl ether linkage into the polymer backbone [57] to increase the flexibility of the molecular chain and produce amorphous polymers. A novel wholly aromatic heterocyclic poly(aryl ether)s containing phthalazinone moieties was first reported by Hay research group, and

10

High Performance Polymers and Their Nanocomposites

then by Jian in 1993 [58–60]. These polymers show the desired heat resistance with Tg values of more than 250 °C and reasonable solubility in some organic solvents. Jian et al., reported that [61] fast speed of removal of water has a negative effect on the molecular weight distribution of the resulting polymers to be rather wide when chlorobenzene is chosen as azeotropic agent; whereas, xylene is a favorable factor for high molecular weight of the polymer with relatively narrow polydispersity. Poly(aryl ether nitrile)s (PAENs), whose characteristic is pendant cyano groups, have been identified as high performance thermoplastics [62]. Their pendent cyano groups give them several favorable properties such as higher thermooxidative and thermal stability than non-cyano-containing poly(aryl ether)s [63], good flame retardancy, good adhesion to many substrates due to interaction with other functional groups through polar interaction [64], and also provide a potential site for polymer cross-linking [65, 66]. The side groups connected to phenyl-phthalazinone segment endow the resultant polymers with good solubility while maintaining other attractive properties. The solubility of the polymers obtained are further improved than non-substituted analogue [67] except chloro-polymers due to the pendent methyl or phenyl groups in the polymer side chains that help to enlarge the average intermolecular distance of those polymers. There were some reports to demonstrate the moderate trimerization of the cyano-containing polymers in the presence of Lewis acids such as zinc chloride at normal pressure [68]. A small quantity of terephthalonitrile (TPH, 2.9 wt% relative to the CN-PPEAs) was used to increase the concentration of cyano groups in the curing system, and zinc chloride (ZnCl2, 1.9 wt% relative to the CN-PPEAs) was selected as catalyst. Other cyano-endcapped samples, such as aromatic bis(ether nitrile)s [44] and oligomeric phthalazinone-base poly(arylene ether nitrile)s with different terminal cyano contents (PPEN-DC), were also prepared and their curing reactions were investigated elaboratively. The pendant cyano groups of PPEN-DC are observed to be less reactive to cyclize while the terminal cyano groups demonstrate much higher reactivity in s-triazine forming reaction. The phthalonitrile resin has been proven to be a unit of high efficiency for raising cyano concentration and improving reactivity [70,71]. The incorporation of the phthalazinone structure increases the solubility of polyamides, maintains their excellent heat resistance, and improves their mechanical properties. Polyamide-imides, generated by introducing amide groups into the main chain of the polyimide, have heat resistance similar to polyimides with improving the solubility and processing performance relative to polyimide. The polyamide-imides are widely used in insulating paints, enamel insulated wires, and other fields. We have

Polymer Nanocomposites and Their Applications

11

synthesized a series of phthalazinone-containing polyamide-imides [72]. U-polymer synthesized via a copolycondensation of bisphenol A and terephthalic acid/isophthalic acid mixture has good weather resistance and transparency with utility in lampshades and mirrors in electrical engineering. Polybenzimidazole (PBI) has been recently attracted more attention to develop its application in fuel cells components because of its high mechanical properties, excellent thermal stability and chemical resistance.

1.8

Poly(ethylene Terephthalate)—PET and Poly(ethylene Naphthalate)—PEN

PET is the most common thermoplastic polymer of the polyester family and is used for food and beverage packaging, textile fibers, thermoforming and fiber reinforced plastic production for engineering applications. The characteristic transition temperatures of PET are very good, since it melts at 250 °C and has a glass transition temperature of 75 °C. Another component of the commercially available polyesters family, PEN is the only one that has adequate performances for the inclusion in the high performance thermoplastics (HPTPs) class, because it has a glass transition temperature of 125 °C and a melting temperature higher than 265 °C. PET makes up about 7% of world polymer production and is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC). PET and PEN have a huge potential as matrix for nanocomposites because they have very good mechanical and functional properties but their cost is pretty low, thus resulting in a very high performance/cost ratio among all polymers. Several nanoparticles of different shape factors have been investigated as thermoplastic polyester reinforcement. Planar nanoparticles, such as MMT or graphene, have demonstrated to allow a strong enhancement of heat deflection and glass transition temperatures, and of the elastic and dynamic mechanical performances. PET nanocomposites have been produced through different routes, but melt blending techniques at temperatures well above 250 °C are preferred due to the ease of the process and its productivity [73–75]. As the organic modifier in conventional clay nanoparticles is not able to bear high processing temperature, more thermally stable modifiers have been investigated to allow a good intercalation and to limit polymer degradation during extrusion [76]. Polyethylene terephthalate, also referred to as poly(ethylene terephthalate) or poly(oxyethyleneoxyterephthaloyl) and abbreviated as PET, is the most common thermoplastic polymer of the

12

High Performance Polymers and Their Nanocomposites

polyester family and is used for food and beverage packaging, textile fibers, thermoforming, and fiber-reinforced plastic production for engineering applications. Various combinations of reactants and process conditions can be used to synthesize polyesters. PET is synthesized from the terephthalic acid and the monoethylene glycol. The addition of nanoparticles to PET and PEN matrix allows to overcome some of the practical drawbacks related to the preparation of conventional composites. The exhaustive treatment of PET nanocomposites is far beyond the scope of the present publication. Therefore, few selected cases will be described as representative examples. Silicon dioxide or silica nanoparticles are added to PET or PEN for improvement of physical and mechanical properties, such as heat deflection temperature (HDT), modulus, thermal stability, and barrier properties to gases and vapors. If nanoparticles are added into the matrix, there must be a strong interaction between the particle and polyester macromolecules to allow a homogeneous dispersion of filler and to prevent the nanoparticles aggregation. Many researchers made great efforts to solve the problem of how to make the nanoparticles well dispersed in the polymer matrix [77, 78 ]. In addition, nanoparticles offer various property enhancements at lower loadings owing to higher surface-to-volume ratio compared to the conventional particles. Therefore, nanocomposites offer exciting properties, which permit their use in automotive, aerospace, electronics, and engineering applications [79]. Nanopowder-based nanocomposites did not show significant mechanical performance improvement, but were able to increase the crystallization properties of PET nanocomposite, such in the case of silica nanoparticles [80, 81]. In [82], polyester-based nanocomposite materials were prepared by melt intercalation. To analyze the effects of different organoclays on nanocomposite performance, montmorillonites modified with two different organic modifiers were employed as fillers. The obtained samples were submitted to morphological and mechanical analysis, with the aim of evaluating their possible application as structural materials in the automotive and aerospace fields. Carbon-based nanofillers do not show thermal degradation issues and the thermal and thermo-oxidative degradation issues during PET and PEN based-nanocomposites processing can be substantially reduced with their use. Graphene [83] and expanded graphite [84] have been successfully melt blended into PET and increased mechanical (both static and dynamic mechanical) and functional (thermal stability, electrical conductivity) properties were achieved. Carbon nanotubes were used as reinforcing nano-phase in PET and showed a similar behavior with respect to graphite nanoparticles [85–88].

Polymer Nanocomposites and Their Applications

13

PET nanocomposites have been widely investigated for the sorption [89, 90] and crystallization kinetics [91, 92] points of view and different routes have been explored to increase its molecular weight in order to improve related performances. To increase rheological properties, reactive extrusion is the main technique used to bond polymer end groups through the use of multifunctional epoxy-based additives or pyromellitic dianhydride [93–96]. In order to limit degradation phenomena related to the organic modifier present as intercalant of platelets, exfoliated graphite has been considered by Kim and Macosko [97] for the preparation of nanoreinforced PEN nanocomposites. They obtained a very good dispersion of graphene sheets, using a twin screw extruder, and significant improvements in viscosity, electrical conductivity, gas barrier, and mechanical properties were achieved. In addition, the use of exfoliated graphite nanocomposites resulted in strong improvements with respect to micro-sized graphite composites. In situ polymerization is a method based on the use of one or more monomers (or oligomers) that are in situ linearly polymerized or crosslinked within nanoparticles and was the first method used to synthesize nanocomposites [98], such as polymer–layered silicate nanocomposites based on polyamide 6 [99–100]. Gao et al., investigated PET/CaCO3 nanoparticles [101, 102]. They modified the hydrophobic calcium carbonate nanoparticles with stearic acid (SA) as the modifying agent. The surface modification of CaCO3, allowed a good dispersion of nanoparticles and a better thermal stability and superior crystallization property. Xu et al., studied graphite nanoplatelet/PET nanocomposites to produce fibers [103]. They obtained a good dispersion through the use of a preliminary dispersant treatment. Paszkiewicz et al., produced PET nanocomposites with different shaped nanofillers (1D, 2D) to investigate their effects on barrier and mechanical properties [104, 105]. Organomodified ZnAl layered double hydroxide LDH/PET nanocomposites were produced by Tsai et al., [106]. Also in this case, the use of a compatibilizer helped in increasing the properties of the composites. PET/Clay nanocomposites were prepared via in situ polymerization by Jahangiri, and coworkers [107] via in situ interlayer polycondensation of dimethyl terephthalate and ethylene glycol. PET/Al2O3 nanocomposites were also prepared by Lim et al., [108]. Owing to the challenging conditions needed to prepare a solution of PET or PEN macromolecules, very few attempts were made with this technology and for the most part the authors worked on organoclays. Ou et al., investigated the synthesis and nucleating effect of montmorillonite on crystallization of PET/montmorillonite nanocomposites [109, 110]. The thermal stability of LDH-filled PET nanocomposites was studied by Xu

14

High Performance Polymers and Their Nanocomposites

et al., [111]; whereas, Goodarzi et al., [112] studied the effects of two aspect ratio-type nanoparticles (cylindrical and sheet) on the thermal properties and chain folding free energy of PET-based nanocomposites. No works are available for PEN. Hernández et al., [113] prepared PET/carbon nanotubes nanocomposites with direct mixing, and compared their performances with nanocomposites from in situ polymerization methods. They found that direct mixing was more effective in increasing the nanocomposite performances, such as electrical conductivity or transparency to light. Melt compounding consists in the mixing of polymer and nanoparticles in the melt state under high shear conditions applied using internal mixers, single or twin screw extruders, or three roll mills [114]. The use of high temperatures, needed for PET and PEN processing, and the high shear rates applied can induce a modification of the nanoparticles characteristics, both geometric or superficial [115] and undesired aggregation of particles can occur. Furthermore, it is very difficult to reach an efficient dispersion of nanoparticles, whose aspect ratio can be heavily reduced in particular for planar (graphene, graphite nanosheets, nanoclays) or linear (carbon nanotubes, nanofibres) nanoparticles. A wide literature is available on the preparation of carbon nanotubes-based PET nanocomposites by melt compounding. Some examples come from Logakis at al. [116, 117]. All they were able to greatly improve the mechanical or functional properties of PET only after a proper dispersion of the nanofiller, in particular after a proper surface treatment. In [118], Li and Jeong investigated the electrical properties of PET/expanded graphite (EG) nanocomposites by measuring the electrical volume resistivity of nanocomposite films as a function of EG content.

1.9

High-Performance Oil Resistant Blends of Ethylene Propylene Diene Monomer (EPDM) and Epoxydized Natural Rubber (ENR)

Blend of NBR with polyvinyl chloride (PVC) is a unique example of miscible rubber—plastic blend [119]. However, most important commercial rubber blends comprising of rubber with thermoplastics {known as thermoplastic elastomer (TPE), e.g., NBR/polypropylene (PP), EPDM/PP ,etc.} and rubber–rubber blends of NR/polybutadiene (BR), NR/ ethylene propylene diene monomer (EPDM) rubber and NBR /EPDM are immiscible [120–123]. The physical compatabilization is achieved either by (a) modification of the polymeric structure to enhance miscibility through

Polymer Nanocomposites and Their Applications

15

specific physical interactions, (b) controlled crystallization of phase components as means to develop a lock-in type of morphology, or (c) the addition of a block or graft copolymer as a compatibilizer (e.g., addition of polyethylene—co-maleic anhydride in PP/EPDM blends) [124–128]. Setua and White have reported on their flow visualization studies on mixing of elastomer blends based on NBR and ethylene propylene (EPM) rubber and observed that chlorinated polyethylene (CPE) elastomer can act as a suitable compatabilizer and could generate finer phase morphology of these blends associated with a faster rate of mixing [129–131]. Setua et al., [132–135] have further reported on the use of sophisticated analytical techniques to characterize the compatibility in variety of elastomer blends and TPEs. The aim of the present work is to develop a high performance oil resistant rubber compound based on EPDM and epoxidized natural rubber (ENR) for development of seal, ‘O’ ring, gaskets etc. for use in strategic sectors like Defence, Aerospace as well as in automotive sectors. There are many rubber–rubber blends and TPEs, e.g., ENR/NBR, ENR/ PVC, ENR/PVDF, having very good oil and weather resistances. Blends of EPDM/ENR satisfy properties of most rubber automotive parts and possibly those of tires, e.g., very good flexing, anti-fatigue, and dynamic mechanical properties, relatively low compression set, wet skid/grip, frictional and wear resistances [136]. In case of solid ENR-EPDM blends, propagation of longitudinal and transverse ultrasonic waves in the blends with varied EPDM content have been studied using pulse echo method at frequency of 2MHz. The parameters e.g., density of the blends, longitudinal/shear/Young’s modulus, Poisson’s ratio, crosslink density, microhardness, etc. were either measured or calculated and the variation correlated with the microstructure of the blends [137]. One of the major advantages of ENR is its oil resistance properties, beside scope of continuous high temperature operations. This is basically due to the presence of polar epoxy groups in the main chain. However, EPDM has poor oil resistant properties. The blends of ENR/EPDM are likely to generate better oil resistance in EPDM. As the ENR ratio in the blends is increased, the oil resistance property also improved.

1.10

High Performance Unsaturated Polyester/ f-MWCNTs Nanocomposites Induced by F- Graphene Nanoplatelets

The term unsaturated polyester (UPE), a combination of reactive polymers and reactive monomers, encompasses a very broad field of reinforced

16

High Performance Polymers and Their Nanocomposites

plastics in general and glass fiber-reinforced thermosetting resin in particular. They are used in a wide range of commercial products such as plastics, fibers, composites, and coating applications [138–139]. There have been growing interests in incorporating carbon-based nanofillers such as carbon black, expanded graphite, and carbon nanotube (CNTs) in the preparation of polymeric nano composites [140, 141]. Currently, Graphene Nano Platelets (GNPs), one of the stiffest known 2D honeycomb type carbon materials, have achieved the extensive attention of the modern scenario owing to its inherently high mechanical strength with good electrical and thermal conductivity. Good dispersion of the CNTs and GNPs are compulsory that may lead to the formation of efficient three dimensional networks [142, 143]. Here attempts have been made to achieve stable and fine dispersed GNPs and MWCNTs in UPE matrix by amine functionalization. Again preparation of the MWCNTs-GNPs/UPE hybrid nanocomposite is an alternative method to obtain cost effective nanocomposites with balanced properties. The nanofillers are functionalized with triethylene tetra mine (TETA) to get amine functionalized carbon nanofillers to facilitate the dispersion process. Then, both NH2-f-MWCNTs and NH2-f-GNPs were added with the UPE matrix. Here, both the functionalized carbon nanofillers protect each other from reaggregation and three-dimensional networks of f-MWCNTs and f-GNPs/UPE have been developed with enhanced properties. The contact angles of nanocomposites ratio of 1:1wt% f-GNPs and f-MWCNTs are higher than that for neat UPE [144]. It may be due to improved work of adhesion between the nanofillers and matrix. Again higher contact angle value demonstrates homogeneous and compact nanofillers coverage on the matrix by resulting poor water affinity.

References 1. Percec, V., Gomes, A.D.S., Lee, M., Molecular engineering of liquid crystal polymers by living polymerization. XI. Synthesis and characterization of poly{ 11-[(4-cyano-4 -trans-α-cyanostilbene) oxy] undecanyl vinyl ether}. J. Polym. Sci. A Polym. Chem., 29(11), 1615–1622, 1991. 2. Figueiredo Neto, A.M., Salinas, S.R.A. The physics of lyotropic liquid crystals phase transitions and structural properties. New York, Oxford University Press, 2005. 3. Woltman, S.J., Jay, G.D., Crawford, G.P., Liquid-crystal materials find a new order in biomedical applications. Nat. Mater., 6(12), 929–938, 2007. 4. Collyer, A.A. Liquid crystal polymers: from structures to applications. London, Elsevier, 1992.

Polymer Nanocomposites and Their Applications

17

5. Acierno, D., Collyer, A.A. Rheology and Processing of Liquid Crystal Polymers. Glasgow, Springer, 1996. 6. Wunderlich, B., Grebowicz, J., Thermotropic Mesophases and Mesophase Transitions of Linear, Flexible Macromolecules. Liquid Crystal Polymers II/ III Volume 60/61 of the series Advances in Polymer Science, 1–59, 2005. 7. Nishio, Y., Yamane, T., Takahashi, T., Morphological studies of liquid‐crystalline cellulose derivatives. I. Liquid‐crystalline characteristics of hydroxypropyl cellulose in 2‐hydroxyethyl methacrylate solutions and in polymer composites prepared by bulk polymerization. J. Polym. Sci: Polymer Physics Edition, 23, 1043–1052, 1985. 8. Carothers, W.H., Polymerization. Chem. Rev., 8(3), 353–426, 1931. 9. Coffman, D.D., Berchet, G.J., Peterson, W.R., Spanagel, E.W., Polymeric amides from diamines and dibasic acids. J. Polym. Sci., 2(3), 306–313, 1947. 10. Ke, B., Sisko, A.W., Differential thermal analysis of high polymers. III. Polyamides. J. Polym. Sci., 50(153), 87–98, 1961. 11. Aubineau, C., Audebert, R., Champetier, G., Bulletin de la Societe Chimique France, 2, 533–539, 1970. 12. Demco, D.E., Litvinov, V.M., Rata, G., Popescu, C., Phan, K.-H., Schmidt, A, et al, Investigation of thermal aging of polyamide 4,6 by 1H solid-state NMR. Macromol. Chem. Phys., 208(19–20), 2085–2095, 2007. 13. Biron, M. Thermoplastics and Thermoplastic Composites. 2nd edition, 2012. 14. Bergshoef, M.M., Vansco, G.J., Transparent nanocomposites with ultrathin, electrospun nylon-4,6 fiber reinforcement. Adv. Mater., 11(16), 1362–1365, 1999. 15. Demco, D.E., Litvinov, V.M., Rata, G., Popescu, C., Phan, K.-H., Schmidt, A., et al., Investigation of thermal aging of polyamide 4,6 by 1H solid-state NMR. Macromol. Chem. Phys., 208(19–20), 2085–2095, 2007. 16. Mckeen, L.W. Effect of Creep and other Time Related Factors on Plastics and Elastomers. 3rd Edition, 2015. 17. Jiang, Z., Zhang, Z., Friedrich, K., Prediction on wear properties of polymer composites with artificial neural networks. Compos. Sci. Technol., 67(2), 168–176, 2007. 18. Taylor, K.C., Nasr-El-Din, H.A., Water-soluble hydrophobically associating polymers for improved oil recovery: A literature review. J. Petrol. Sci. Petroleum Science and Engineering, 19(3–4), 265–280, 1998. 19. Sojka, R.E., Bjorneberg, D.L., Entry, J.A., Lentz, R.D., Orts, W.J., Polyacrylamide in agriculture and environmental land management. Adv. Agronomy, 92, 75–162, 2007. 20. Nasser, M.S., James, A.E., The effect of polyacrylamide charge density and molecular weight on the flocculation and sedimentation behaviour of kaolinite suspensions. Sep. Purif. Technol., 52(2), 241–252, 2006. 21. Pefferkorn, E., Polyacrylamide at Solid/Liquid Interfaces. J. Colloid Interface Sci., 216(2), 197–220, 1999.

18

High Performance Polymers and Their Nanocomposites

22. Zhang, X.C., Miller, W.P., Polyacrylamide Effect on Infiltration and Erosion in Furrows. Soil Science Society of America Journal, 60(3), 866–872, 1996. 23. Lee, H.K., Jong, W.L., Synthesis and applications of polyacrylamide derivatives in the wet end of papermaking (Part II. Reactive N-chloropolyacrylamide), J. Polym. Res, 4, 119–128, 1997. 24. Li, S.F., Tang, Z.W., Tan, Y.B., Yu, X.B., Polyacrylamide blending with ammonia borane: a polymer supported hydrogen storage composite. Journal of Physical Chemistry C, 116, 1544–1549, 2012. 25. Helen, M., Viswanathan, B., Murthy, S.S., Poly(vinyl alcohol)-polyacrylamide blends with cesium salts of heteropolyacid as a polymer electrolyte for direct methanol fuel cell applications. J. Appl. Polym. Sci., 47, NA–47, 2010. 26. Umoren, S.A., Ebenso, E.E., Blends of polyvinyl pyrrolidone and polyacrylamide as corrosion inhibitors for aluminium in acidic medium. Indian Journal of Chemical Technology, 15, 355–363, 2008. 27. Ni, Y., Ge, X., Zhang, Z., Ye, Q., In situ single-step synthesis of gold/polyacrylamide nanocomposites in an ethanol system. Mater. Lett., 55(3), 171– 174, 2002. 28. Pan, W., Chen, Y., Preparation of Ag–polyacrylamide nanocomposites by ultraviolet irradiation technique. Applied Mechanics and Materials, 47, 442199–442202, 2011. 29. Haddad, T.S., Lichtenhan, J.D., The incorporation of transition metals into polyhedral oligosilsesquioxane polymers. J. Inorg. Organomet. Polym., 5(3), 237–246, 1995. 30. Mantz, R.A., Jones, P.F., Chaffee, K.P., Lichtenhan, J.D., Gilman, J.W., Ismail, I.M.K, et  al, Thermolysis of Polyhedral Oligomeric Silsesquioxane (POSS) Macromers and POSS−Siloxane Copolymers. Chem. Mater., 8(6), 1250– 1259, 1996. 31. Haddad, T.S., Lichtenhan, J.D., Hybrid Organic−Inorganic Thermoplastics: Styryl-Based Polyhedral Oligomeric Silsesquioxane Polymers. Macromolecules, 29(22), 7302–7304, 1996. 32. Chattopadhyay, D.K., Mishra, A.K., Sreedhar, B., Raju, K.V.S.N., Thermal and viscoelastic properties of polyurethane-imide/clay hybrid coatings. Polym. Degrad. Stab., 91(8), 1837–1849, 2006. 33. Avadhanl, C.V., Wadgaonkar, P.P., Khisti, R.S., Gunjikar, V.G., Vernekar, S.P., Synthesis and characterization of imide containing diisocyanates and poly(imide-urethane)s therefrom. Polymer Bulletin, 23(2), 163–169, 1990. 34. Yeganeh, H., Barikani, M., Noei Khodabadi, F., Synthesis and properties of novel thermoplastic poly(urethane-imide)s. Eur. Polym. J., 36(10), 2207– 2211, 2000. 35. DeIasi, R., Russell, J., Aqueous degradation of polyimides. J. Appl. Polym. Sci., 15(12), 2965–2974, 1971. 36. Hergenrother P.M., Havens S.J. Sampe J., 4, 13, 1988.

Polymer Nanocomposites and Their Applications

19

37. Tong, Y.J., Huang, X.D., Chung, T.S., A New Strategy To Prepare Rodlike/ Flexible Polyimide Blends through Poly(amic acid) Amine Salt Precursors. Macromolecules, 34(17), 5748–5751, 2001. 38. Faghihi, K., Shabanian, M., Synthesis and Characterization of Polyimide– Silver Nanocomposite Containing Chalcone Moieties in the Main Chain by UV radiation. Journal of Thermoplastic Composite Materials, 25(1), 89, 89–99, 2012. 39. Nguyen, T.H.L., Quiroga Cortes, L., Lonjon, A., Dantras, E., Lacabanne, C., High conductive Ag nanowire–polyimide composites: Charge transport mechanism in thermoplastic thermostable materials. J. Non. Cryst. Solids, 385, 34–39, 2014. 40. Zhu, J.H., Wei, S.Y., Chen, X.L., Karki, A.B., 41. Smirnova, V.E., Gofman, I.V., Ivan’Kova, E.M., Didenko, A.L., Krestinin, A.V., Polym. Sci., 55, 268, 2013. 42. Li, Z., Yang, T., Du, Y., Dynamic finite element simulation and transient temperature field analysis in thermoplastic composite tape lay-up process. J. Thermoplastic Compos. Mater., 28(4), 558–573, 2015. 43. Bureau, C., Garcia-Pagan, J.C., Otal, P., Pomier-Layrargues, G., Chabbert, V., Cortez, C, et  al, Improved clinical outcome using polytetrafluoroethylene-coated stents for TIPS: results of a randomized study. Gastroenterology, 126(2), 469–475, 2004. 44. Lai, C.-L., Liou, R.-M., Chen, S.-H., Huang, G.-W., Lee, K.-R., Preparation and characterization of plasma-modified PTFE membrane and its application in direct contact membrane distillation. Desalination, 267(2-3), 184– 192, 2011. 45. Pelagade, S.M., Singh, N.L., Rane, R.S., Mukherjee, S., Deshpande, U.P., Ganesan, V, et al, Investigation of Surface Free Energy for PTFE Polymer by Bipolar Argon Plasma Treatment. JSEMAT, 02(02), 132–136, 2012. 46. Khedkar, J., Negulescu, I., Meletis, E.I., Sliding wear behavior of PTFE composites. Wear, 252(5-6), 361–369, 2002. 47. Li J., Ran Y. Evaluation of the friction and wear properties of PTFE composites filled with glass and carbon fiber. KGaA, WeinheimMat.-wiss. u.Werkstofftech, 41, 2010. 48. Joseph, T., Uma, S., Philip, J., Sebastian, M.T., Electrical and thermal properties of PTFE-Sr2ZnSi2O7 composites. J Mater Sci: Mater Electron, 22, 1000– 1009, 2011. 49. Yang, M.K., French, R.H., Tokarsky, E.W., Optical properties of Teflon® AF amorphous fluoropolymers, J. Micro/Nanolith.MEMS MOEMS, 7, 033010– 033011, 2008. 50. Romack, T.J., Kipp, B.E., DeSimone, J.M., Polymerization of Tetrafluoroethylene in a Hybrid Carbon Dioxide/Aqueous Medium. Macromolecules, 28(24), 8432–8434, 1995. 51. Tzeng, C.J., Yang, Y.K., Lin, Y.H., Tsai, C.H., A study of optimization of injection process parameters for SGF and PTFE reinforced PC composites

20

52.

53. 54.

55.

56.

57.

58. 59.

60.

61.

62. 63.

64.

65.

High Performance Polymers and Their Nanocomposites using neural network and response surface methodology. Int. J. Adv. Manuf. Technol., 63(5-8), 691–704, 2012. Kanazawa, T., Matsuda, Y., Tasaka, S., Fabrication of a porous structure of poly(tetrafluoroethylene) from a mixture with fumaric acid. Polym. J., 42(6), 509–513, 2010. Llorens, J., Woodhead Publishing Series in Textiles. Fabric Structures in Architecture. Dearn, K.D., Hoskins, T.J., Petrov, D.G., Reynolds, S.C., Banks, R., Applications of dry film lubricants for polymer gears, Published by Elsevier. Wear, 299, 29899–108, 2013. Wenpeng, H., Hui, Z., Application of PTFE heat exchanger in Low Temperature Waste Heat of Big Coal-fired Power Plants, Applied Mechanics and Materials. Applied Mechanics and Materials, Trans Tech Publications, Switzerland, Vols. 789-790, 503–507, 2015. StorgaRds, E., Simola, H., Sjoè Berg, A.-M., Wirtanen, A.G., Hygiene Of Gasket Materials Used In Food Processing Equipment Part 2: Aged Materials, 77(Part C), 1999. Hergenrother, P.M., Connell, J.W., Labadie, J.W., Poly, H.J.L., Poly(arylene ether)s containing heterocyclic units. High Perform. Polym., 117, 67–110, 1994. Berard, N., Hay, A.S., Polymers from hydroxyphenylphthalazinones. Polym. Prep., 34, 148–149, 1993. Jian, X.G., Hay, A.S., Zheng, H.B., Poly(aryl ether sulfone) containing phthalazinone moiety and its preparation methods. Chinese patent ZL93109180, 2, 1993. Jian, X.G., Hay, A.S., Zheng, H.B., Poly(aryl ether ketone) containing phthalazinone moiety and its preparation methods. Chinese patent ZL93109179, 29, 1993. Lihong Xiao ., Cheng Liu ., Gongxiong Liao ., Yuan Zhang ., Xigao Jian ., Synthesis and Characterization of Novel Copoly(aryl ether sulfone) Containing Phthalazinone and Biphenyl Moieties. High Performance Polymers, 22(3), 274–285, 2010. Rao, V.L., Saxena, A., Poly, N.K.N., arylene ether nitriles. J Macromol Sci Part C Polym Rev, 42, 513–540, 2002. Matsuo, S., Murakami, T., Takasawa, R., Synthesis and properties of new crystalline poly(arylene ether nitriles. J. Polym. Sci. A Polym. Chem., 31(13), 3439–3446, 1993. Sivaramakrishnan, K.P., Marvel, C.S., Aromatic polyethers, polysulfones, and polyketones as laminating resins. II. J. Polym. Sci. Polym. Chem. Ed., 12(3), 651–662, 1974. Saxena, A., Rao, V.L., Prabhakaran, P.V., Ninan, K.N., Synthesis and characterization of polyamides and poly(amide–imide)s derived from 2,2-bis(4-aminophenoxy) benzonitrile. Eur. Polym. J., 39(2), 401–405, 2003.

Polymer Nanocomposites and Their Applications

21

66. GP, Y., Liu, C., Wang, J.Y., GH, L., Han, Y.J., Synthesis, J.X.G., characterization, and crosslinking of soluble cyano-containing poly(arylene ether)s bearing phthalazinone moiety. Polymer, 51, 100–109, 2010. 67. GP, Y., Liu, C., Zhou, H.X., Wang, J.Y., Jian, X.G., Synthesis and characterization of soluble copoly(arylene ether sulfone phenyl-s-triazine)s containing phthalazinone moieties in the main chain. Polymer, 50, 4520–4528, 2009. 68. Verborgt, J., Marvel, C.S., Aromatic polyethers, polysulfones, and polyketones as laminating resins. J. Polym. Sci. Polym. Chem. Ed., 11(1), 261–273, 1973. 69. GP, Y., Liu, C., Wang, J.Y., XP, L., Jian, X.G., Heat-resistant aromatic S-triazine-containing ring-chain polymers based on bis(ether nitrile)s: synthesis and properties. Polym. Degrad. Stab., 95, 2445–2452, 2010. 70. Keller, T.M., Synthesis and Polymerization of Multiple Aromatic Ether Phthalonitriles. Chem. Mater., 6(3), 302–305, 1994. 71. Keller, T.M., Dominguez, D.D., High temperature resorcinol-based phthalonitrile polymer. Polymer, 46(13), 4614–4618, 2005. 72. Zhu, X., Jian, X., Soluble aromatic poly(ether amide)s containing aryl-, alkyl-, and chloro-substituted phthalazinone segments. J. Polym. Sci. A Polym. Chem., 42(8), 2026–2030, 2004. 73. Tsai, T.-Y., Li, C.-H., Chang, C.-H., Cheng, W.-H., Hwang, C.-L., Wu, R.J., Preparation of Exfoliated Polyester/Clay Nanocomposites. Adv. Mater., 17(14), 1769–1773, 2005. 74. Ghasemi, H., Carreau, P.J., Kamal, M.R., Uribe-Calderon, J., Preparation and characterization of PET/clay nanocomposites by melt compounding. Polym. Eng. Sci., 51(6), 1178–1187, 2011. 75. Özen, İlhan., İnceo lu, F., Acatay, K., Mencelo lu, Y.Z., Comparison of melt extrusion and thermokinetic mixing methods in poly(ethylene terephthalate)/montmorillonite nanocomposites. Polymer Engineering & Science, 52, 1537–1547, 2012. 76. Scamardella, A.M., Vietri, U., Sorrentino, L., Lavorgna, M., Amendola, E., Foams based on poly(ethylene terephthalate) nanocomposites with enhanced thermal stability. Journal of Cellular Plastics, 48(6), 557–576, 2012. 77. Hsu, Y.G., Lin, F.J., Organic-inorganic composite materials from acrylonitrile-butadiene-styrene copolymers (ABS) and silica through an in-situ solgel process. J. Appl. Polym. Sci., 75(2), 275–283, 2000. 78. Jang, L.W., Kang, C.M., Lee, D.C., A new hybrid nanocomposite prepared by emulsion copolymerization of ABS in the presence of clay. J. Polym. Sci. B Polym. Phys., 39(6), 719–727, 2001. 79. Rahman, I.A., Padavettan, V., Synthesis of Silica Nanoparticles by Sol-Gel: Size-Dependent Properties, Surface Modification, and Applications in SilicaPolymer Nanocomposites—A Review. J. Nanomater., 75, 1–15, 2012. 80. Liu, W., Tian, X., Cui, P., Li, Y., Zheng, K., Yang, Y., Preparation and characterization of PET/silica nanocomposites. J. Appl. Polym. Sci., 91(2), 1229– 1232, 2004.

22

High Performance Polymers and Their Nanocomposites

81. Bikiaris, D., Karavelidis, V., Karayannidis, G., A New Approach to Prepare Poly(ethylene terephthalate)/Silica Nanocomposites with Increased Molecular Weight and Fully Adjustable Branching or Crosslinking by SSP. Macromol. Rapid Commun., 27(15), 1199–1205, 2006. 82. Garcés, J.M., Kuperman, A., Millar, D.M., Olken, M.M., Pyzik, A.J., Rafaniello, W., Synthetic Inorganic Materials. Adv. Mater., 12(23), 1725– 1735, 2000. 83. Bin, Z.H., Zheng, W.G., Yan, Q., Electrically conductive polyethylene terephthalate/graphene nanocomposites prepared by melt compounding. Polymer, 51, 1191–1196, 2010. 84. Li, M., Jeong, Y.G., Poly, J.Y.G., Poly(ethylene terephthalate)/exfoliated graphite nanocomposites with improved thermal stability, mechanical and electrical properties. Composites Part A Applied Science and Manufacturing, 42(5), 560–566, 2011. 85. Kim, J.Y., Choi, H.J., Kang, C.S., Kim, S.H., Influence of modified carbon nanotube on physical properties and crystallization behavior of poly(ethylene terephthalate) nanocomposite. Polym. Compos., 14, NA–0, 2009. 86. Yesil, S., Bayram, G., Poly, B.G., Poly(ethylene terephthalate)/carbon nanotube composites prepared with chemically treated carbon nanotubes. Polym. Eng. Sci., 51(7), 1286–1300, 2011. 87. May-Pat, A., Avilés, F., Toro, P., Yazdani-Pedram, M., Cauich-Rodriguez, J.V., Mechanical properties of PET composites using multi-walled carbon nanotubes functionalized by inorganic and itaconic acids. Express Polym. Lett., 6(2), 96–106, 2012. 88. Aurilia, M., Sorrentino, L., Iannace, S., Modelling physical properties of highly crystallized polyester reinforced with multiwalled carbon nanotubes. Eur. Polym. J., 48(1), 26–40, 2012. 89. Baldwin, D.F., Shimbo, M., Suh, N.P., The Role of Gas Dissolution and Induced Crystallization During Microcellular Polymer Processing: A Study of Poly (Ethylene Terephthalate) and Carbon Dioxide Systems. J. Eng. Mater. Technol., 117(1), 62–74, 1995. 90. Pavel, D., Shanks, R., Molecular dynamics simulation of diffusion of O2 and CO2 in blends of amorphous poly(ethylene terephthalate) and related polyesters. Polymer, 46(16), 6135–6147, 2005. 91. Ghasemi, H., Carreau, P.J., Kamal, M.R., Isothermal and non-isothermal crystallization behavior of PET nanocomposites. Polym. Eng. Sci., 52(2), 372–384, 2012. 92. Ke, Y., Long, C., Qi, Z., Crystallization, Q.Z., Crystallization, properties, and crystal and nanoscale morphology of PET-clay nanocomposites. J. Appl. Polym. Sci., 71(7), 1139–1146, 1999. 93. Japon, S., Boogh, L., Leterrier, Y., Månson, J.-A.E., Reactive processing of poly(ethylene terephthalate) modified with multifunctional epoxy-based additives. Polymer, 41(15), 5809–5818, 2000.

Polymer Nanocomposites and Their Applications

23

94. Xanthos, M., Young, M.-W., Karayanndis, G.P., Bikiaris, D.N., Reactive modification of polyethylene terephthalate with polyepoxides. Polym. Eng. Sci., 41(4), 643–655, 2001. 95. Xanthos, M., Wan, C., Dhavalikar, R., Karayannidis, G.P., Bikiaris, D.N., Identification of rheological and structural characteristics of foamable poly(ethylene terephthalate) by reactive extrusion. Polym. Int., 53(8), 1161– 1168, 2004. 96. Nguyen, Q.T., Japon, S., Luciani, A., Leterrier, Y., Månson, J.-A.E., Molecular characterization and rheological properties of modified poly(ethylene terephthalate) obtained by reactive extrusion. Polym. Eng. Sci., 41(8), 1299–1309, 2001. 97. Kim, H., Macosko, C.W., Morphology and Properties of Polyester/Exfoliated Graphite Nanocomposites. Macromolecules, 41(9), 3317–3327, 2008. 98. Shen, Z., Simon, G.P., Cheng, Y.-B., Comparison of solution intercalation and melt intercalation of polymer–clay nanocomposites. Polymer, 43(15), 4251–4260, 2002. 99. Fukushima, Y., Okada, A., Kawasumi, M., Swelling Poly-6-Amide By Poly-6Amide. Clay Miner., 23, 27–34, 1988. 100. Yano, K., Usuki, A., Okada, A., Kurauchi, T., Kamigaito, O., Synthesis and properties of polyimide–clay hybrid. J. Polym. Sci. A Polym. Chem., 31(10), 2493–2498, 1993. 101. Gao, W., Ma, X., Liu, Y., Wang, Z., Zhu, Y., Effect of calcium carbonate on PET physical properties and thermal stability. Powder Technology, 244, 45– 51, 2013. 102. Gao, W., Ding, L., Zhu, Y., Effect of Surface Modification on the Dispersion, Thermal Stability and Crystallization Properties of PET/CaCO3 Nanocomposites. TSD, 54(3), 230–237, 2017. 103. Xu, Q., Wang, C., Wang, B., Chen, Y., Wang, H., In situ polymerization and characterization of graphite nanoplatelet/poly(ethylene terephthalate) nanocomposites for construction of melt-spun fibers. RSC Adv., 7(53), 33477– 33485, 2017. 104. Paszkiewicz, S., Kwiatkowska, M., Rosłaniec, Z., Szymczyk, A., Jotko, M., Lisiecki, S., The influence of different shaped nanofillers (1D, 2D) on barrier and mechanical properties of polymer hybrid nanocomposites based on PET prepared by in situ polymerization. Polym. Compos., 37(7), 1949–1959, 2016. 105. Paszkiewicz, S., Szymczyk, A., Špitalský, Z., Soccio, M., Mosnáček, J., Ezquerra, T.A, et al, Electrical conductivity of poly(ethylene terephthalate)/ expanded graphite nanocomposites prepared by in situ polymerization. J. Polym. Sci. B Polym. Phys., 50(23), 1645–1652, 2012. 106. Tsai, T.-Y., Bunekar, N., The effect of organomodified ZnAl LDH for in situ synthesis and the properties of poly(ethylene terephthalate) nanocomposites. RSC Adv., 6(70), 65291–65298, 2016. 107. Jahangiri, M., Jafari, S.H., Khonakdar, H.A., Tarameshlou, M., Ahmadi, I.F., Preparation of PET/clay nanocomposites via in situ polymerization in the

24

108.

109.

110.

111.

112.

113.

114.

115. 116.

117.

118.

119.

High Performance Polymers and Their Nanocomposites presence of monomer-activated organoclay. J. Vinyl Addit. Technol., 21(1), 70–78, 2015. Lim, S.K., Choi, W.M., Choi, H.J., Synthesis and Characterization of Poly(Ethylene Terephthalate) /Al2O3 Nanocomposites. Adv. Mater. Res., 717, 54–57, 2013. CF, O., MT, H., Lin, J.R., The Nucleating Effect of Montmorillonite on Crystallization of PET/Montmorillonite Nanocomposite. J. Polym. Res., 10, 127–132, 2003. CF O., MT H., Lin J.R. Synthesis and characterization of poly(ethylene terephthalate) nanocomposites with organoclay. J. Appl. Polym. Sci., 91, 140–145, 2004. Xu, K., Chen, G., Shen, J., Exfoliation and dispersion of micrometer-sized LDH particles in poly(ethylene terephthalate) and their nanocomposite thermal stability. Appl. Clay Sci., 76, 75114–75119, 2013. Goodarzi, V., Shadakhtar, A., Sirousazar, M., Mortazavi, M., GhaniyariBenis, S., Effects of cylindrical and sheet types of nanoparticles on thermal properties and chain folding free energy of poly(ethylene terephthalate. Journal of Reinforced Plastics and Composites, 32(11), 846–859, 2013. Hernández, J.J., García-Gutiérrez, M.C., Nogales, A., Rueda, D.R., Kwiatkowska, M., Szymczyk, A, et  al, Influence of preparation procedure on the conductivity and transparency of SWCNT-polymer nanocomposites. Compos. Sci. Technol., 69(11-12), 1867–1872, 2009. Kalaitzidou, K., Fukushima, H., Drzal, L.T., A new compounding method for exfoliated graphite–polypropylene nanocomposites with enhanced flexural properties and lower percolation threshold. Compos. Sci. Technol., 67(10), 2045–2051, 2007. Jeong, H.-K., Lee, Y.P., Jin, M.H., Kim, E.S., Bae, J.J., Lee, Y.H., Thermal stability of graphite oxide. Chem. Phys. Lett., 470(4-6), 255–258, 2009. Logakis, E., Pissis, P., Pospiech, D., Korwitz, A., Krause, B., Reuter, U, et al, Low electrical percolation threshold in poly(ethylene terephthalate)/multiwalled carbon nanotube nanocomposites. Eur. Polym. J., 46(5), 928–936, 2010. Kim, J.Y., Park, H.S., Kim, S.H., Multiwall-carbon-nanotube-reinforced poly(ethylene terephthalate) nanocomposites by melt compounding. J. Appl. Polym. Sci., 103(3), 1450–1457, 2007. Li, M., Jeong, Y.G., Poly(ethylene terephthalate)/exfoliated graphite nanocomposites with improved thermal stability, mechanical and electrical properties. Composites Part A Applied Science and Manufacturing, 42(5), 560–566, 2011. Passador, F.R., Rodolfo, A Jr., Pessan, L.A., In Situ Dynamic Vulcanization of Poly(Vinyl Chloride)/Acrylonitrile-butadiene Rubber Blends. J. Macromol. Sci. Pt. B, 48(2), 282–298, 2009.

Polymer Nanocomposites and Their Applications

25

120. Zhang, H., Datta, R.N., Talma, A.G., Noordermeer, J.W.M., Maleic-anhydride grafted EPM as compatibilising agent in NR/BR/EPDM blends. Eur. Polym. J., 46(4), 754–766, 2010. 121. Sirqueira, A.S., Soares, B.G., Compatibilization of Natural Rubber/EPDM Blends by Anhydride‐ and Mercapto‐functionalized Copolymers. Macromol. J. Sci. Pt.B., 46(4), 639–650, 2007. 122. Nicolini, A., De Campos Rocha, Tatiana Louise Ávila., Maldaner Jacobi, M.A., Louise, T., De, A., Rocha, C., Dynamically Vulcanized PP/EPDM Blends: Effect of Composition and Curing Agents. J. Elast. Plast., 41(5), 433– 446, 2009. 123. Botros, S.H., Tawfic, M.L., Synthesis and Characteristics of MAH-g-EPDM Compatibilized EPDM/NBR Rubber Blends. J. Elast. Plast., 38(4), 349–365, 2006. 124. Suma, N., Joseph, R., Francis, D.J., Kautsch. Gummi Kunstst, 43, 1095, 1990. 125. Hong, K.M., Noolandi, J., Macromolecules, 14,727, 1991. 126. Pan, J., Hu, H., Huang, Z., Duan, Y., Study of nitrile-butadiene rubber and polypropylene (NBR/PP) grafting cross-linked system. Polym. Plast. Technol. Eng., 40(5), 605–613, 2001. 127. Grigoryeva, O.P., Karger-Kocsis, J., Kocsis, J.K., Melt grafting of maleic anhydride onto an ethylene–propylene–diene terpolymer (EPDM). Eur. Polym. J., 36(7), 1419–1429, 2000. 128. Ezzati, P., Ghasemi, I., Karrabi, M., Azizi, H., Iranian Polym. J., 17, 669, 2008. 129. Setua, D.K., White, J.L., Kaut. Gummi Kunststoffe, 44, 137, 1991. 130. Setua, D.K., White, J.L., Polym. Eng. and Sci., 31, 1742, 1991. 131. Setua, D.K., White, J.L., Kaut. Gummi Kunststoffe, 44, 821, 1991. 132. Setua, D.K., Pandey, K.N., Saxena, A.K., Mathur, G.N., Characterization of elastomer blend and compatibility. J. Appl. Polym. Sci., 74(3), 480–489, 1999. 133. Pandey, K.N., Setua, D.K., Mathur, G.N., Determination of the compatibility of NBR-EPDM blends by an ultrasonic technique, modulated DSC, dynamic mechanical analysis, and atomic force microscopy. Polym. Eng. Sci., 45(9), 1265–1276, 2005. 134. Setua, D.K., Gupta, Y.N., On the use of micro thermal analysis to characterize compatibility of nitrile rubber blends. Thermochim. Acta, 462(1-2), 32–37, 2007. 135. Setua, D., Development of Thermoplastic Elastomers by Blending of Nitrile Rubbers with Nylon 6 in an Internal Mixer and by Reactive Mixing in a Twin Screw Extruder. J. Bionanosci., 10(5), 403, 1–413, 2016. 136. Chan, B.L., Potential Application of ENR/EPDM Blends. AJSTD, 33(1), 48, 2016. 137. Afifi, H.A., El Sayed, A.M., Ultrasonic properties of ENR-EPDM rubber blends. Polym. Bull., 50(1-2), 115–122, 2003. 138. Goodman, I., Rhys, J. A. eds Saturated Polymers. London, Iliffe, 1965 . 139. Morgan, P.W., Condensation Polymers:By Interfacial and Solution Methods. New York, Inerscience Publishers, 1965.

26

High Performance Polymers and Their Nanocomposites

140. Potts, J.R., Dreyer, D.R., Bielawski, C.W., Ruoff, R.S., Graphene-based polymer nanocomposites. Polymer, 52(1), 5–25, 2011. 141. Stankovich, S., Dikin, D.A., Dommett, G.H., Kohlhaas, K.M., Zimney, E.J., Stach, E.A, et  al, Graphene-based composite materials. Nature, 442(7100), 282–286, 2006. 142. Kumar, S., Sun, L.L., Caceres, S., Li, B., Wood, W., Perugini, A, et al, Dynamic synergy of graphitic nanoplatelets and multi-walled carbon nanotubes in polyetherimide nanocomposites. Nanotechnology, 21(10), 105702, 2010. 143. Li, J., Wong, P.S., Kim, J.K., Hybrid nanocomposites containing carbon nanotubes and graphite nanoplatelets. Mater. Sci. Eng., A, 484, 483660–483663, 2008. 144. Luo, Y., Zhao, Y., Duan, Y., Du, S., Surface and wettability property analysis of CCF300 carbon fibers with different sizing or without sizing. Mater. Des., 32(2), 941–946, 2011.

2 Liquid Crystal Polymers Andreea Irina Barzic, Raluca Marinica Albu and Luminita Ioana Buruiana* “Petru Poni” Institute of Macromolecular Chemistry, Iasi, Romania

Abstract Liquid crystal materials based on polymers represent an important topic in current research. This chapter presents some introductive notions, including the history of liquid crystal polymers (LCPs). An important issue is the obtaining method of these compounds, so the main synthesis routes are described. In order to understand the solution properties of LCPs, some rheological aspects are highlighted, together with some basic characteristics in solid phase, such as dielectric behavior, magnetic properties, mechanical resistance, and phase morphology. The features of LCPs are also affected by the applied processing methodology. In this context, the chapter briefly presents basic aspects concerning injection molding, extrusion, free surface flow, and LCP fiber spinning. The practical importance of blends and composites with LCP phase is emphasized in various industrial areas, such as optoelectronics, displays, sensors, and actuators. Several essential aspects that regard environmental impact and recycling concerns are disclosed. Analyzing the high demands for products based on LCPs, the corresponding market is expected to expand, but still efforts must be made to improve their performance and reduce the costs. Keywords: Liquid crystals, rheology, dielectric behavior, fiber spinning, displays

2.1

Introduction and History

More than 120 years ago, F. Reinitzer noticed a peculiar behavior in the melting process of cholesterol benzoate [1]. The discovery led to a new class of materials, known as liquid crystals (LC) that combine the long-range positional and orientational order found in solid crystals and the statistical *Corresponding author: [email protected] Visakh P.M. and Semkin A.O. (eds.) High Performance Polymers and Their Nanocomposites, (27–58) © 2019 Scrivener Publishing LLC

27

28

High Performance Polymers and Their Nanocomposites

long-range disorder typical for isotropic liquids [2]. This point represents a milestone that opened a novel area of research that gained the attention of physicists, chemists, and engineers for several decades. As a consequence, the 58th meeting of Faraday Society in 1933 was devoted to this subject. After a couple of decades, Gray [3] published one of the most comprehensive books at that time. Additional monographs that provide basic information on classification (thermotropic and lyotropic phases), molecular structures, and properties of several types of LC were written by Kelker [4], Demus [5], and Luckhurst [6]. In 1922, Lehmann [7] revealed that certain characteristics of LCs may have some similarities with those of living state since mobility and structural organization of biological and synthetic LCs represent an ideal medium for catalytic action involved in growth and reproduction processes of cells. Furthermore, the introduction of a simple nematic LC in devices had revolutionized the display technology. From this point, an explosive progress has been noted in design and construction of a variety of devices, such as laptops, smart phones, computers, and digital projectors [8–10]. The intense collaboration between academic and industry researcher expanded the implications of liquid crystal science toward more exciting topics that make reference to new uses in optics, novel composites, and biotechnology [11]. In the past years, other unique aspects of LC materials are highlighted and the curious LC states of matter were studied in new contexts. The knowledge in this area was extrapolated to polymer science, determining a rebirth into a metamorphosed state based on macromolecular compounds with considerable potential for new types of applications. The unique subtle balance between order and fluidity of such polymeric materials gives rise to a wide range of spectacular phenomena that are not entirely explored. Based on the theories developed by Onsager [12] and Flory [13], a first report on a main chain thermotropic LC appeared in 1975 and continued by deGennes, which introduced the concept of flexible spacer [14]. A variety of mesogens were proved to give rise to mesophases in polymers. Depending on their structure, they can be divided into amphiphilic and non-amphiphilic (with or without lipophilic and hydrophilic groups). In some cases, mesogens can induce amphotropic mesophases, in which LC phase can be determined by changing temperature, solvent, or both [15]. The mesogens can exhibit various shapes (rod, disc, star), and they be found in main chain, side chain, or both, leading to complex polymer architectures [16]. A typical feature of side chain LC polymers relies on the fact that the backbone adopts a random-coil conformation when placed in a good solvent or is melted. In the nematic phase, the conformation of the polymer is easily distorted; whereas, in the smectic phase, the flexibility of chains determines the degree of distortion [17].

Liquid Crystal Polymers

29

Macromolecular compounds with a well-defined molecular positioning in all three dimensions attract considerable attention owing to their peculiar properties, which can be precisely tuned. The optical, electrical, and mechanical characteristics of such high molecular weight materials are very complex as a result of the variety of self-organizing molecular configurations. Moreover, the interaction of polymers in LC phase with external fields, such as electric, magnetic, or mechanical ones, offers many possibilities to shape these materials [18]. For this reason, they are found in several applicative domains, such as electronics (displays, photonic devices, and polarization-independent instruments) or medicine (biosensors for optically probing biological systems, biomimicking color-producing structures, lenses, and muscle-like actuators) [11]. In some cases, the LC polymers are not meeting all demands imposed by pursued application, so it is necessary to make small changes in material structure to solve the shortcomings [19]. A good alternative for such situations is to introduce a special additive that can render the missing property. In this context, many studies showed that preparation of blends or composites represents a successful route to obtain high performance products through a simple and low cost procedure. The aim of this chapter is to provide a snapshot of the exciting discoveries in the field of materials based on polymers with LC features with an emphasis on the aspects of physics, chemistry, and material science. The most significant approaches to create multicomponent materials containing LC phase are described by highlighting the issues involved in designing optimal balance between structure and properties as demanded in applications. The practical importance of such materials is presented, emphasizing critical points involved in display/electro-optic devices or bioengineering instruments. The approached topic is highly interdisciplinary and thus of interest also to researchers working in this area since providing a critical analysis of the essential outstanding challenges in each applicative domain.

2.2

Polymerization

There are several synthesis procedures that are used for preparation of polymers with LC phase. Among them, the most utilized are radical polymerization and polycondensation [20–23]. In the first case, the initialization of the reactions can be achieved through several factors, such as photostimuli or free radicals. The monomers used in such reaction must have properties that are similar to traditional LC, especially anisotropic shape.

30

High Performance Polymers and Their Nanocomposites

The polymerizable groups can be placed either at the ends of the backbone [24] or in side chains [25]. In order to create networks based on LC polymers, a suitable alternative is to attach one, two, or more functional groups that enable the desired reaction. Although several polymerizable groups have been investigated, the most utilized are the acrylates and the methacrylates owing to their high reactivity when exposed to UV radiations in the presence of a small concentration of a free-radical-generating photoinitiator.

2.2.1 Synthesis of Lyotropic LC Polymers Most main chain LC polymers can form anisotropic solutions because of their backbone conformations and less owing to the mesogenic units from the main chain. A good example in this category of materials is given by poly(γ-benzyl-L-glutamate) or cellulose derivatives [19]. The latter present a helical architecture of chains and in combination with the adequate solvent form lyotropic phase. In cases where the mesogenic groups of lyotropic polymers are found in side chains preparation procedure involves utilization of specific terminal groups placed at the end of hydrophobic chains. Side chain LC polymers that result from free-radical process are prepared using various types of initiating factors such as temperature or electromagnetic radiations. In this category, it is integrated Kevlar and other type of polyamides with surfactant molecules as the monomeric side chains. The amphiphilic character of surfactants determines packing of the micellar aggregates into partially ordered systems at high concentrations, enhancing the anisotropy of the material [19]. This fact connected with the numerous possibilities on microstructure formation gives valuable clues concerning the immense variation of polymer types and points of binding. The utilized surfactants can be divided as a function of the nature of hydrophilic “head,” which can be cationic, anionic non-ionic, or zwitter-ionic. Two cases can be distinguished: (1) materials that are obtained from amphiphiles with polymerizable hydrophilic units and (2) compounds with the pendant side chains extend from the hydrophobic backbone. The LC properties of polymers are affected by structure of the side chain mesogen, length of flexible spacer, and also by rigidity of polymer skeleton; the latter is influenced both by molecular weight and polydispersity index. The phase transitions of lyotropic LC side chain polymers in aqueous media can be exploited to produce comb-shaped LC polymers [26].

Liquid Crystal Polymers

31

2.2.2 Synthesis of Thermotropic LC Polymers Among the procedures used to obtain thermotropic main chain LC polymers, one can mention interfacial polymerization or by high-temperature solution polymerization from diphenols and dicarboxylic acid chlorides. This methodology leads to polymers where the rigid-rod units alternate regularly with the disrupting sequences [19]. The major issue of thermotropic main chain LC polymers is that in order to obtain the desired macromolecular design one must disrupt the regularity of the intractable para-linked aromatic polymers to the point at which mesomorphic behavior is showed below the decomposition temperature. These compounds are mainly polymers based on the linear ester or ester/amide bonds. Thermotropic side chain polymers can be made by the polymerization of substituted monomers using addition or condensation procedure. The mesogenic entities are annexed onto a preformed polymer that demands mutual functionality. Addition polymerization can be used in many ways for LC compound synthesis, which is commonly activated by reactive free radicals. Polymerizations are performed sometimes via thermal homolysis of azobisisobutyronitrile in a solvent such as toluene, chlorobenzene, or tetrahydrofuran [19]. In the final stage, the product is isolated through several re-precipitation from a non-solvent and annealed at a temperature a little smaller than the clearing point. Commercial products are synthetized by an ester exchange reaction between acetoxyaryl groups and the carboxylic acid group and removal of acetic acid [19]. The operation is performed at temperatures above the crystalline melting point of the macromolecular compound. The bulk of the reaction is done at normal atmospheric pressure after which the oligomers are polymerized to high molecular weights by setting vacuum conditions. The latter facilitate formation of LC phase and the melt presents shear opalescence. Condensation polymerization starting with the phenyl esters of the diacids with the aryl dials is a route for achieving partially ordered systems [19]. The melting point is very important to take into consideration for thermotropic materials prepared by a condensation reaction. Polymers that have high melting points require a heat-transfer medium, where the temperature of the stirred reaction mixture was enhanced progressively for several hours. The methodology can be improved by utilization of macromolecular stabilizers and/or hydrophobic inorganic ones, which tend to lay at the surface of the polymer droplet and help avoiding flocculation when temperature is augmented to enable the polymerization final step [19]. In case of polymers with low melting points, it is expected to agglomerate in the heat-transfer

32

High Performance Polymers and Their Nanocomposites

medium when stabilizer lacks. However, such materials can be obtained by this procedure and the molecular weight of the compound is not viscosity limited. This was the case of melt polycondensation where the sample has to be extruded from the autoclave. Different from the latter procedure, the polymerization can be accomplished at temperatures found under the melting one and vacuum is no longer a demanding condition for high molecular weight since the acetic acid is easily removed from droplets. The procedure provides materials with peculiar unsheared form [19]. To overcome the limitations concerning the molecular weight, the reactions can be done in solid state by increasing the temperature while maintaining it under melting point [19]. Such type of procedure can also be implemented for accomplishment of high-melting polymers by producing an oligomer by the melt route. This is continued by solid-phase polymerization to finalize the polymerization. Novel and functional side chain LC polymers are constructed by polymerization of certain monomers (e.g., acrylic ones) in the presence of free radical initiators. Another preparation procedure relies on effective enzymatic procedure for transesterification, resulting acrylic monomers with methoxybiphenyl mesogenic pendants [19]. If the same system is subjected to radical polymerization, the final product exhibited lower molecular weight and the nematic phase was noticed in a smaller range of temperature [20]. Percec and Shaffer [27] have also reported thermotropic polyketones obtained by the Friedel–Crafts arylation of biphenyl and fluorene with α,ω-dicarboxylic acid alkanes in combination with a phosphorous condensing agent.

2.3

Properties

2.3.1

Rheology

Flow behavior in different regimes of strain amplitude provides specific information on the analyzed material. When the sample is subjected to small amplitude oscillatory shear, one can investigate the microstructure of the LC polymer. If experiments are extended to large-strain steadystate shear flow, one can achieve data concerning the behavior of specimen when extrusion or molding processes are applied. The viscoelastic response recorded during dynamic measurements reflects degree of sample deformability in shear field. For elucidating the reaction to deformation of LC polymer, such experiments require utilization of Cox–Merz rule [28]. The latter describes the correlation between complex viscosity

Liquid Crystal Polymers

33

as a function of frequency and steady shear viscosity as a function of shear rate. This empirical equation is respected by many thermoplastic materials, excepting the case of aromatic polyesters. The dynamic response is affected by amplitude of deformation [29] with the complex viscosity decreasing as the strain amplitude is lower. For isotropic melts, there is evidence that the first normal stress difference (N1) is almost double the elastic modulus (G’). When dealing with thermotropic samples, the correlation between small amplitude dynamic measurements and large strain is no longer respected. Even so, oscillatory tests represent a useful tool for detection of transitions during temperature sweeps and to examine changes after applying a mechanical or thermal history. Rheological properties of LC polymers, registered in the simplest coneplate geometry, are very complex in regard with homogeneous isotropic polymer solutions [28]. For this reason, in the first stage, it is essential to investigate transient behavior prior considering the steady-state data. The torque (or shear stress) presents a maximum at a low strain, which is about two or three units of shear [28, 30]. After that the torque decreases and then begins to take higher values as the time passes, resulting a second maximum at a large strain. The latter seems to be independent of the shear rate imposed. After removing deformation force and reversing the flow, no small-strain maximum is noticed. The first maximum appears analogous to that remarked for isotropic polymers when the shear rate is larger than that for the onset of shear thinning region. The main distinction between isotropic and thermotropic samples arises from the fact that the onset of nonlinear viscoelastic behavior, such as shear thinning, occurs at a significantly smaller shear rate for thermotropic polymers than for isotropic polymers of similar viscosity [28]. Moreover, the second maximum in torque is not observed in the rheology of isotropic samples. These maxima are usually seen in what is often referred to as the constant viscosity region of the flow curve. The relationship between rheology and morphology is very complex. Although the response might be different from one polymer to another, there is general agreement concerning the nature of the transient shear stress. In this context, there is a transient negative normal stress, which in most cases becomes positive. Negative steady normal stresses are usually noticed for lyotropic systems. A schematic correlation between rheological and morphological features of an LC polymer is presented in Figure 2.1. Polymers with well-defined molecular positioning when dissolved in an appropriate solvent display isotropic rheological properties below a limiting concentration [31, 32]. The latter depends on the molecular weight of the macromolecular compound. Above this concentration, an additional

34

High Performance Polymers and Their Nanocomposites

Viscosity

Texture

Stress or time

Figure 2.1 Schematic representation of relationship between morphology and rheology for LC polymer materials.

birefringent phase appears along with the isotropic one, both co-existing in equilibrium. The birefringent phase spread in the isotropic one starts to form spherulites as a result of interfacial tension between the two media. Further increase in concentration determines existence of only one phase, namely the birefringent one with a typical liquid crystalline texture. The isotropic–anisotropic transition for lyotropic polymer systems is sensitive to viscosity dependence on concentration and shear rate. The dependence of apparent viscosity on shear rate may be divided mainly into two important regions [33]: the yielding zone at lower rates exhibiting a thinning behavior; the Newtonian (constant viscosity) plateau zone above a certain critical shear rate. At very high shear rates, one can distinguish a shear-thinning domain reflecting the viscoelastic behavior of sample. Below the critical shear rate, the polymer solution is assumed to flow with retention of superstructure

Liquid Crystal Polymers

35

in which the elements are packed in a regular fashion. In these conditions, Bragg elements are not easy re-oriented even when deforming force is removed. Conversely, above the critical shear rate, the superstructure disrupted into smaller elements that may reach the dimensions of Bragg elements. Therefore, when stopping shear perturbation, these elements are able to reorient very fast. So, uniformity of the orientation of Bragg elements can be improved [33].

2.3.2 Dielectric Behavior In the presence of electric fields, the permanent dipole moments from the LC polymer are re-arranged and also the induced ones contribute to total polarizability of the materials. If the LC compound lacks of polar molecules, the induced polarization is determined by two parts: (1) the electronic polarization, which is the result electron clouds deformation in each atom of the LC molecule, and (2) the ionic polarization, which is determined by the relative dislocation of the atoms constituting the molecule [34]. For LC polymers based on polar molecules, a supplementary contribution is observed, namely the dipolar polarization. All these phenomena contribute to the total molecular polarizability (P) and are affected by the magnitude of the electric field frequency. In relation to this aspect, the order is as follows: Pelectronic < Pionic < Pdipolar. Given the positional ordering of the LC materials, one can distinguish a great anisotropy of polarizability parallel and perpendicular to the long molecular axis. The dipole–dipole interactions between the molecules are stronger than those occurring in the presence of magnetic field. In other words, the local electric field on a LC molecule can be obtained by addition of the external electric field and that produced by the dipole moments of corresponding to other LC molecules constituting the sample. The internal field tensor is a molecular tensor, which is independent of the macroscopic dielectric anisotropy [34]. For a given molecule, the permanent dipole moment has a fixed value. So, in order to contribute to the dielectric constant, the LC molecule has to reorient. This is facilitated when the frequency of the external field is low enough so that the molecule is able to follow the oscillations of electric field. In case of rod-like LCs, it is easier to rotate around the long molecular axis in regard with the sort molecular axis. It results that the characteristic frequency on the perpendicular direction to LC director is higher than that obtained for parallel direction. When the angle between permanent dipole and long molecular axis has low values, the material will exhibit positive values for dielectric anisotropy.

36

High Performance Polymers and Their Nanocomposites

For molecules with big permanent dipole moment and large angle between this parameter and LC director, the opposite is noticed [34]. Thus, dielectric anisotropy is negative at low frequencies, but when the angle has intermediate values the dielectric anisotropy becomes positive in low frequencies domain and subsequently changes sign when increasing frequency after exceeding the crossover frequency. At very high frequencies (infrared region), the dipolar polarization no longer affects the dielectric properties and the anisotropy takes positive values.

2.3.3 Magnetic Properties Macromolecular compounds with LC phase are diamagnetic media. The anisotropic nature of these materials leads to magnetic susceptibilities, which are distinct along the direction of LC director and perpendicular to it [19, 34]. The magnetic interaction between the LC molecules is not strong enough, so the local magnetic field of the molecules is almost the same as the applied magnetic field. In the presence of such external perturbation, one might notice different responses to the applied field, which are influenced by the angle between the long molecular axis and the field intensity. In order to facilitate the physical and mathematical description of the effects generated by magnetic field in LC polymers, one can consider a parallel component and a perpendicular component of external field, expressing the magnetization as a tensor. From its complex expression, one can extract magnetic susceptibility along the considered directions and thus magnetic anisotropy, which is usually positive and independent of the order parameter.

2.3.4 Mechanical Properties Polymers with lyotropic phase can often form fibers. For this reason, most reports make reference to the tensile and thermal properties of fibrillar structures [35]. Lyotropic polymers processed as fibers and films present anisotropic mechanical properties. However, aspects concerning transverse properties of these materials are less investigated comparatively with longitudinal properties. The analysis of mechanical performance includes the contributions of elastic, viscoelastic, and plastic deformation processes. In the tensile curve of polymer fibers, there are two stress levels that can be distinguished: the yield stress and the tensile stress [35]. The first consists in a big decrease of the slope of the stress–strain curve, while the second is stress at fracture. There are some properties, such as fatigue, and abrasion resistance that

Liquid Crystal Polymers

37

can be viewed as a synergism between anisotropic mechanical and thermal characteristics. Their implications on fiber morphology are not entirely elucidated. When performing experiments regarding tensile properties of lyotropic polymer fibers, one may notice a straight part up to a type of yield point at certain strain value and then the dependence takes form of a concave curve up to fracture. This makes the major part of the tensile curve. It can be assumed that up to the yield strain the fibrillar architecture is extended without damaging the hydrogen bonds among the fibers. Upon reaching the yield point, these bonds undergo a rupture process and a distinct deformation process takes place. This is highlighted by the changes in the slopes of the tensile curves, observed before and after the yield point. In the next stage of the deformation, one can distinguish a steady increase of the dynamic modulus as a result of gradual contraction of the orientation distribution of the macromolecules. This is known as stretching of the lyotropic polymer fibers [36]. Another issue that must be closely investigated during examination of tensile deformation relies on the recovery after unloading. Beyond the yield point, the extended fibers became oriented but they are not able to fully recover after cessation of external force. The recoverable extension exhibits an instantaneous recovery ascribed to elastic and viscoelastic or delayed elastic contributions. Additional extension applied to the fibers up to similar maximum extension less influences the permanent deformation, but in the same time a small hysteresis occurs. Also, a typical feature of fibers prepared from lyotropic polymers consists in that the hysteresis recorded during repeated loading is very small in regard with that of fibers obtained from semi-crystalline polymers. The LC polymer fibers present a complex creep behavior, which can be divided into two components: primary creep (recoverable with time) and secondary creep (non-recoverable with time) [19, 35]. The latter can be usually neglected in condition of pre-conditioning from mechanical point of view the fibers. This means that at first the fiber was stretched to a strain much higher than the strain that will be reached in the end, during the next creep experiment. In this context, the obtained creep data can be correlated with the viscoelastic characteristics of the sample. In many cases, the results have revealed that the viscoelastic behavior of polymer fibers can be discussed in terms of a serial arrangement of an elastic spring associated with the chain modulus and a viscoelastic element that accounts for macromolecules rotations caused by shear deformation of the crystallites from the sample.

38

High Performance Polymers and Their Nanocomposites

Delayed elasticity is characteristic to disorderly molecular arrangement in amorphous polymers or of disordered domains in crystalline materials. This property is assumed to be determined by thermally activated processes and could implicate entropy-elastic forces. Strength of fibers and films is an important problem when LC polymers must be implemented into devices. If the length of chains is similar to the gauge length of fiber test sample and arranged parallel to the fiber axis, then the stress recorded at fracture is identical to failure stress. The latter is determined by the covalent forces in the chain, and theoretical results reveal that it represents about 15% of theoretical chain modulus [19]. For fibers made from polymers of low molecular weight, it was noticed that intermolecular slippage implicate the disruption of secondary bonds take place in preference to chain fracture. At high molecular weights, both primary and secondary bonds rupture, leading to tensile curves with brittle fracture. This gradual change in the failure process from slippage to chain fracture determines the absence of a simple relation between fiber tenacity and chain length. Thermotropic LC polymers present tensile strengths and stiffness related on the degree of orientation achieved during heating/cooling the sample to reach birefringent phase [37]. Also, these properties are limited to some extent by the processing method and type of finite product. For this reason, mechanical properties of compression-molded unoriented LC polymers are not so different from that of a conventional isotropic polymer. Main chain LC polymers subjected to injection molding have superior mechanical moduli comparatively to that of glass-fiberreinforced isotropic thermoplastics with the high orientation, bringing major contribution to the stiffness of the molding [28]. As the magnitude of elongational flow is higher, the values of mechanical moduli are enhanced, leading to big tensile strengths for such type of LC polymers. Moreover, they present a significant fall-off in mechanical modulus during temperature variation and, although this can be determined by control of the component parts of the LC system, this is not ideal for an engineering resin. However, this is partly compensated by the outstanding high stiffness and strength of main chain LC polymers at room temperature and also by the fact that mechanical properties are not much changed at high temperatures (>200 °C). Finite products made from such compounds have high anisotropy ratio, namely the difference in properties along and across the flow direction, increasing with the degree of orientation. The latter is affected by the presence of a distinct phase in the system. So, it is interesting to remark that when adding fillers in conventional isotropic thermoplastics, the anisotropy ratio is higher than that of the reinforced LC

Liquid Crystal Polymers

39

polymers. This might be explained on the basis that LC molecular alignment is perturbed by the presence of reinforcement agent. Thus, the insertion of flexible units in the backbone of thermotropic polymers seems to affect the molecular linearity, having also a significant impact on warpage and shrinkage by altering the crystallization behavior of macromolecules. All these aspects must be closely analyzed when designing LC polymers for high precision molding applications.

2.3.5

Phases and Morphology

The long-range orientational order is widely found in lyotropic LC phases, and, in certain cases, the medium-range positional order in one or two dimensions is also present [38]. A distinction in regard with thermotropic polymers is that lyotropic nematics and cholesterics could exhibit shortrange positional order among micelles, allowing creation of pseudolamellar structure. At relatively high temperatures, the micellar isotropic phase corresponding to direct and inverted structures is observed in some zones of the lyotropic phase diagrams. The explanation can be given by considering the fact that the shape anisotropy of micelles is related to temperature and concentration of the counterparts [39]. At low molecular concentrations of amphiphilic compound, the micelles tend to keep their spherical shape; whereas, at higher concentrations, the shape is altered and space orientation is poor. In particular conditions, there lyotropic mixtures constituted from isolated micelles with orthorhombic symmetry. They form locally a pseudo-lamellar structure. The lyotropic nematic phases can be divided in three types: calamitic nematic, discotic nematic, and biaxial character nematic [19, 28, 38]. The cholesteric phase can be achieved when introducing in nematic phase a chiral molecule or if a mixture is derived from a chiral amphiphilic molecule [40]. Similar to nematic phase, one may distinguish three types of lyotropic cholesterics: discotic cholesteric, calamitic cholesteric, and biaxial cholesteric phase. The micelles are able to spontaneously arrange themselves into a helical structure with a certain pitch. The latter can be tuned by changing several parameters, such as concentration of chiral compound, temperature, pressure, and the shape anisotropy of the micelles [41]. In the lamellar phase, amphiphilic structures are disposed as supermolecular aggregates, leading to layers with big shape anisotropy. When the amphiphilic part is organized as long cylinder-like aggregates with pronounced anisotropy in terms of shape one may notice formation of hexagonal phase. Parallel cylinders, with diameter double the length of amphiphilic molecule, are arranged on a two-dimensional hexagonal

40

High Performance Polymers and Their Nanocomposites

lattice, in a plane orthogonal to the axes. Polymorphism in lyotropic materials has many facets [28]. They can be viewed as aggregates with the form of long unfolded ribbons forming a two-dimensional lattice in the normal plane to the ribbons axes. Such morphology is noticed for lyotropic mixtures with at least two amphiphiles. In case of cubic micellar phase, the micelles constitute a cubic (face-centered or body-centered) lattice [28]. Thermotropic meshophases can be categorized into three types: nematic, cholesteric, and smectic [42]. The first one results in case of materials that are optically inactive or by racemic mixtures. When long-range translational order lacks in regard with long-range orientational order, the nematic has uniaxial character. Cybotactic nematic phases exhibit a shortrange, smectic-like organization of the molecular centers in planes. There are two forms of this phase: skewed cybotactic phase in which groups of molecules have their centers of gravity placed in a plane situated at an angle in regard with LC director and normal cybotactic phase, where the angle has a value of about 90°. Cholesteric LC polymers can be obtained from optically active macromolecular compounds or optically active mixtures [42]. The molecular centers of gravity do not present long-range order but the molecules have the tendency to be parallel to LC director. Smectic phase has attracted much attention in scientific community, which revealed more than 10 smectic modifications. This led to a variety of polymeric materials with different architectural features [42]. Generally, the mesophases present numerous singularities in the distribution of the molecules, which are characteristics of the structural particularities of the ordered phases. These aspects can reveal, in simple experimental situations, LC textures with different regularity. Nematic textures are noticed under the form of round objects, named droplets. When cooling the polymer droplets begin to couple, resulting larger structures from which stable texture finally occurs. Also, threaded, Schlieren, and marbled textures are observed for nematic polymers [39, 42]. If the substrate surface on which LC polymer is subjected to a suitable treatment one may notice planar layers in which the director is disposed parallel to the surface. Among the methods employed to generate reproducible planar alignment, rubbing with velvet or diamond paste is the most applied [43]. This results in uniformly aligned LCs—aspect that lies at the basis of manufacturing displays. The cholesteric polymers may form planar textures with the twist axis orthogonal to the plane of the film. There are often occurring alignment discontinuities under the form of pattern-like cracks [34]. In the area of planar texture, these materials can show reflection colors; the asymmetrical

Liquid Crystal Polymers

41

color variations that are seen upon rotating the analyzer are good indication of optical activity. Cholesteric homopolymers may have a twisted structure leading to non-planar fan-shaped, focal-conic, or polygonal textures. Moreover, when chirality is present, it is hard to make the difference between cholesterics or smectics [34]. The solution is to add a nematic solute that determines the increase of pitch and emphasizes the planar structures. Smectics present many textures, and most times their observation is difficult. Smectic A phases present textures that are probably relying on the focal-conic arrangement, where the ellipses and hyperbolae cannot always be distinguished in the microscopic image. Smectic C variations display two microscopic textures: the Schlieren texture and the focal-conic fan texture. In conditions of modifying a nematic to a smectic A or smectic C phase, transient stripes in the form of a myelinic texture (known as striated texture) are often remarked [44].

2.4

Processing

Polymers in LC phase can be processed through several techniques depending on the desired shape and properties pursued for the final product. The processing step is most related to rheological behavior of the LC material. The most used methods for processing these materials are presented in Figure 2.2.

2.4.1

Injection Molding

Injection molding is a processing method that combines the benefits resulted from low viscosity and high stiffness of LC materials [45]. However, there are other characteristics that have minor influence on the processability of such polymers. Among them, the implications of low thermal expansion coefficient can be mentioned, which gives low warpage and shrinkage in the molding. Low shrinkage, in combination with the low viscosity of the melt, enables precision molding of highly complex shapes that cannot be obtained with other materials. The degree of orientation in a molding is affected by the flow path. Radial orientation in the surface layer is generated during radial flow in an injection molding. This is owing to the strong shear flows in the vicinity of the mold wall. However, the same flow is able to create hoop orientation in the center because of the stretching flows along the central plane.

42

High Performance Polymers and Their Nanocomposites Methods for processing of LC ploymers

EXTRUSION Pellets Thermocouple Polymer INJECTION MOULDING

Screw motions

Barrel Nozzle

Pellets

Split mold

FREE SURFACE FLOW SPINNING Pellets

Ejector Pins

Extruder Screw motions

Barrel Nozzle Sprue

LC polymer Pump Spinning system

Resulting products

Quench air

Spinning filaments Winding unit

Tubing and pipes

Films and sheets

Structural parts

Figure 2.2 Methods for processing LC polymers and the resulting products.

Utilization of orientation patterns render to the molding a laminated structure that can be controlled by the use of technologies like multi livefeed injection molding [45]. Low viscosity samples subjected to injection molding are not advantageous. Even if it is easy to fill a mold, there is an inconvenience that arises from the fact that the LC material will splash over into the gaps at the mold parting surfaces. This is a big issue when applying high pressure during mold filling, but if this parameter has optimal values such samples are more indicated than conventional isotropic melt of the same viscosity [28]. Because the entrance pressure drop for LC polymer melts is a lot greater comparatively with isotropic ones, the flow behavior into the flash region is constrained. One of the most problematic aspects concerning the injection molding of LC polymers comes from the control of weld lines in the sample.

2.4.2

Extrusion

The majority of processing steps of polymeric materials are based on single screw extruder. In order to be able to work in the best conditions, it is desirable that the sample adhere to the barrel wall and in the same time to slide on the screw. In practice, things stay different since the adherence prevails at the polymer/screw interface [46]. In case of thermotropic polymers, they have a low viscosity after melting and because the barrel wall

Liquid Crystal Polymers

43

is heated (in the feed zone) at a bigger temperature comparatively with the screw an issue appears since the sample would lubricate the flow and prevents adequate pumping. To avoid the shortcoming a good solutions is to keep the barrel temperatures in the feed zone below the melting point of the polymer. This could help to ensure uniform pumping, thus optimizing the performance of the processing procedure. The screw extruder reflects the mechanical history of specimen, which in turn is affected by shear between relatively moving surfaces. In these conditions, the morphology of LC polymer is in continuous changing. In classical screw extruders, the shear rates present medium values (50 s-1). However, in the vicinity of the flight tip of the screw, it increases up to one order of magnitude providing the conditions to modify the microstructure of thermotropic polymers. The shearing intensity should have utmost value when using injection molding. In addition, the homogeneity of specimens is improved when high screw-back speeds are present in processing device. To achieve a product with a well-defined shape would be better to eliminate post-extrusion swelling. The aspect is less desirable in injection molding where, instead of smoothly expanding from the gate as it enters the mold, the melt moves forwards and subsequently partially freezes before the mold is completely filled. A solution for this problem is to use a gate having higher sizes than the standard ones.

2.4.3

Free Surface Flow

This method is mostly applicable to LC polymer films. Thermotropic materials are less appropriate for such type of processing. Rod-like macromolecules are very easily oriented along a certain direction, but they are not so fitted for biaxial orientation. There are two types of film process: melt and solid phase drawing. The latter is performed at temperatures below melting point of specimen, which should also possess a moderately high viscosity and an elastic character to support the bubble and render stability [28]. Stenter processes, where a uniaxially oriented sheet is comprised at the edges and drawn sideways, must be accomplished in region of sufficiently solid sample to stand the hold of the stenter clips. The lack of the “rubbery” region in LCP polymers and the reduced performance when drawing the material in transverse direction lead to splitting predisposition of the product. To achieve biaxial orientation, other methodologies were proposed, such as counter-rotating annular die and core [28], even if they were not implemented at commercial level. Most LC polymers are attractive for sintering flows owing to their reduced viscosity but the orientation degree is not as high as expected. Another limitation of such materials

44

High Performance Polymers and Their Nanocomposites

arises from the high viscosity at low shear stress that impedes the fusion of the particles. A potential alternative on such technology is represented by an extension of “splat” forming. The procedure implies shooting molten droplets toward a surface and after impact they begin to flow out and orient. A succession of such “splatted” droplets could help to construct an in-plane oriented structure. Free surface flows are also noticed during injection molding. This takes place particularly at the advancing front of the flow.

2.4.4 LC Polymer Fiber Spinning Spinning is a procedure that allows preparation of fibers by the extrusion of polymer (in solution or melt stage) through a metal die marked with symmetrically arranged small holes to provide continuous “fluid” strands [47]. In the next step, the strands undergo a post-die treatment that involves both stretching and cooling (for melts) and cold drawing. In this way, very fine fibers with extremely anisotropic features are obtained. The chain orientation and extension influence the modulus and strength of polymer fibers. The morphological features of the product are also affected by the drawing technique particularly by the drawing conditions, like drawing ratio. Prior to start a spinning process, one must closely examine the sample potential for fiber forming. For this reason, rheological behavior of the extrudate in the post-extrusion region should be adapted in such manner that a coherent filament can be drawn into the quenching or coagulating zone. For all polymers, there is an upper limit to the extrusion rate or a lower limit to the length of the drawing region. Outside this optimal range, the liquid stream or filament is disrupted. So, another important step is to determine the best processing conditions. However, as a result of kinks, folds, and chain entanglements, the theoretical modulus limits for flexible macromolecular fibers are not reached.

2.5

Blends Based on Liquid Crystal Polymers

The miscibility of LC polymers with compounds having low molar mass is essential for elucidation of LC phases and obtaining multicomponent materials with well-defined phase transitions. Several miscibility rules were proposed for low molecular weight LC. The basic idea is that one can consider a good miscibility between two LC phases if they are isomorphic and thus belong to the same mesophase [48]. However, the opposite idea is

Liquid Crystal Polymers

45

not valid. When blending polymers in LC phase with other LCs of different molecular weight, the phenomenology is more complicated since there are deviations from the mixture or log additive rule concerning viscosity. So, there are several possibilities: the additive rule is respected the increase of viscosity over values of additive rule is noticed (regardless the miscibility of components) because of the strong interactions across the interface the reduction of viscosity under additive rule limits for immiscible systems, where adhesion at the interface is low and the interactions are weak both second and third situation might occur for samples with a concentration-dependent change in morphology. The above-described situations also implicate variations in the elasticity of the blends such that when the viscosity is a maximum, the elasticity is a minimum inversely [48]. Few reports are dealing with elasticity evolution in systems where an isotropic polymer is blended with other with LC character. Most of the measurements are performed from the swelling ratios, which for LC polymers are low. Thus, polymers with mesophases can be useful in processing other (intractable) polymers since they reduce viscosity of the blend. Literature [49,50] reports a variety of blends based on partially ordered macromolecular systems. So, LC polymers can be mixed with other LCs or with engineering polymers. In the following paragraphs, we describe few important case studies. Ambrosino and Sixou [51] have prepared a blend of two LC polymers (cellulose derivatives) by keeping constant the solid concentration and varying the ration between the two counterparts. Depending on the system composition, they obtain anisotropic, isotropic, or biphasic materials. The recorded flow curves are composed of three regions typical for LCs. Deviations from additivity were also noted for viscosity as a function of polymer ratio in solution. The same is observed when the two compounds are in melt state. The negative ones are ascribed to phase separation and the positive ones to homogenous mixing. All prepared blends of cellulosic derivatives reveal domains of shear rates where the first normal-stress difference is negative. This is mainly found in anisotropic LC polymers. From the investigation, it was concluded that the isotropic solutions become anisotropic by shearing the system, whose concentration is close to the critical concentration.

46

High Performance Polymers and Their Nanocomposites

Other studies describe preparation and characterization of blends that contain liquid crystal polymers and isotropic ones. Kozlowski and Koslowska [52] have blended Vectra A950 in LC phase with polysulfone or polypropylene in various ratios. Morphology inspections revealed an augmented interfacial adhesion and different orientation level of a dispersed phase. Melt rheology tests showed decreased viscosity of thermoplastics after introduction of LC polymer. Higher interfacial adhesion between the isotropic and anisotropic components was noticed at low shear rates as a slight increase in the melt viscosity. In a series of studies, Barzic et al., [53, 54] prepared mixtures of a cholestric polymer with isotropic and thermostable polymers. This is a good method to produce materials that can adopt the molecular arrangement and keep it under certain temperature or irradiation conditions. The basic idea is to use a LC polymer that under shearing develops a specific band texture, which can be further imprinted to the other counterpart. The first key point to accomplish this relies on the interaction between the counterparts, such as hydrogen bonds that are favoring the preservation of induced texture. Another aspect that has to be considered is the conformation of the isotropic component, which depending on its flexibility, planarity, and symmetry can easily follow the supramolecular arrangement of the used cholesteric polymer. For the cases when the latter is blended with thermostable polymers that are not able to interact with it, one may observe that the resulting morphology and rheological behavior are affected by small changes in main chain structure of isotropic component. Immiscibility of LC and isotropic polymers is not always an undesirable aspect. When analyzing the morphologies in such blends, it is important to give attention to the step of incorporation of a longitudinal LC polymer as the minor phase can lead to the desired features. In conditions of the appropriate concentration, melt interaction, rheology, and deformation during processing, the system can fibrillate and have the role of both viscosity reducer and stiffening agent.

2.6

Composites of Liquid Crystal Polymers

Composites of liquid crystal polymers represent a relatively new category of materials with practical implications in various industries. Such systems are phase-separated, the factors triggering this being numerous, like temperature, polymerization procedure and solvent quality [28]. Another important aspect that has to be analyzed is the free energy that determines whether a composite represents a homogeneous single phase or

Liquid Crystal Polymers

47

phase separates to form a heterogeneous mixture. In the case which the free energy has lower values than that observed for heterogeneous mixture, the composite is found in the homogeneous phase. Moreover, the process of phase separation is determined by the details of the curve of the mixing free energy as a function of the system composition [34]. Calculation of the second-order derivative of the free energy versus concentration dependence one may find a criterion for phase separation. For positive values of the derivative, from graphical point of view is it is unfeasible to draw a straight line that is tangential to the free energy curve at two points. Therefore, the system does not undergo a phase separation. On the contrary, for negative values of the derivative, the free energy dependence presents a maximum at a fraction within a certain zone. So, it is easy to draw a straight line tangential to the free energy graph. The single homogeneous phase does not exhibit great stability in that region, and phase separation cannot be avoided. LC polymer composites can be obtained from cellulose derivatives, like hydroxypropyl cellulose (HPC). Nishio et al., [55] revealed that utilization of the 2-hydroxyethyl methacrylate (HEMA) solvent enables through its polymerization preparation of multiphasic materials with cholesteric nature of the mesophase over limited concentration and temperature ranges. The LC character remains relatively stable even on increasing temperature, in comparison with the HPC/water system. Optical analysis indicated that HPC-HEMA composite present isotropic solution (below 43 wt %), biphasic solution (43–55 wt %), and pure anisotropic solution (above 55 wt %) at room temperature. The resulted composite exhibited interesting morphological features in round particles made from parallelstacked, disk-like lamellae and aggregate bodies generated by coalescence of neighboring particles. The morphology was explained on the basis of shrinking stress generated concomitantly by polymerization. Another work of Cheng et al., [56] discusses the utility of the thermotropic LC polymers in preparation of composites. Nanoparticles are inserted in these compounds, resulting materials with improved characteristics in terms of mechanical, electrical, and thermal properties.” This opened multiple perspectives in nanotechnologies sustaining their continuous development. Among the embedded fillers in LC polymers, carbonbased nanofillers (CNTs, graphene, fullerene) are by far preferred owing to their outstanding properties. There are some challenges in the fabrication of CNT/thermotropic polymer nanocomposites, such as inherent in the dispersion of CNTs into the matrix, the alignment of CNTs in the polymer, and the load-transfer between the two phases. A widely applied solution is to functionalize the filler, but the choice of the type of attached

48

High Performance Polymers and Their Nanocomposites

groups on CNTs surface is the state of art for scientists working in this area. Another issue arises from the immiscibility between the LC polymers and other ones. This can be remediated by adding carbon-based fillers having their surface modified with an appropriate functional group. Other original and yet unpublished results show that lyotropic form of HPC subjected to shearing is useful for alignment of carbon nanotubes (CNTs). The rheological experiments indicated that elastic modulus is sensitive to the composite microstructure changes. So, the dependence of storage modulus on shear frequency is useful to observe the formation of percolation structure. Atomic force microscopy revealed that shearing at low reinforcement amounts is useful for orientation of the filler along the shearing direction. This is also aided by the ordering of the HPC matrix, which after shear force cessation develops the band texture. Another study of Kim [57] discusses fabrication of LC polymer composites through simple melt blending of thermotropic procedure. The system is formed from LC polyester in which there are various amounts of modified CNTs. Rheological test indicated that the composites present higher complex viscosity and more distinct shear thinning behavior than the matrix as a result of interactions among the phases. This was particularly observed at low frequency region comparatively with high frequency domain. The interactions influenced the relaxation tendency of chains in the material. The decrease in the slopes of shear moduli was ascribed to formation of the network-like structures through the interactions among the filler particles, inducing the pseudo solid-like behavior of these composites. Addition of CNT in the LC matrix contributed to increase in thermal stability by playing the role of effective physical barrier against the thermal decomposition. Modification of the reinforcement agent had a great impact on the mechanical properties by intensification of adhesion between the two phases of the composite, while maintaining uniform dispersion of CNT in the LC matrix. The employed procedure of fabrication can optimize the morphology and preferential orientation of CNT during the melting process, providing in the same time good interfacial adhesion between CNT and thermotropic polymer. The advances in the science of carbon-filled LC polymer composites indicate high potential for their use in everyday applications.

2.7

Applications

LC polymers find application in a wide range of domain, the most important being in electroluminescent display devices or non-linear optical materials

Liquid Crystal Polymers

49

in the case of main chain LC polymers. For side chain LC polymers, the most known applications are replacements for small molecules in LC displays or passive optical films with tailored optical properties. Other types of LC, that is, ferroelectric, are used as pressure and temperature sensors, being also seen as really interesting materials in optical computing and signal processing owing to their special characteristics. All these applications require specific micro-architecture obtained by photopolymerization as a result of cross-linking. Conversely, the new trends in LC applications deal with LC elastomers, used as tunable lasers and artificial muscles.

2.7.1 LC Polymers as Optoelectronic Materials The main aspect that must be considered for LC application in devices is the orientation of the macromolecule field. Although the intrinsic mobility of liquid phase is a key parameter in this case, there are also some drawbacks that have to be overcome. Thus, the electrical charged molecules tend to move in the direction of the electrodes and in the vicinity of other type of molecules, and they are constrained by the solubility in the LC phase. In this context, the combination between mesogenic groups with flexible groups from the polymers can resolve this issue and, at the same time, is maintaining the intrinsic orientation of the active macromolecules. Such type of polymers are formed of mesogenic groups attached on the flexible main chains of polymer or of mesogenic side groups positioned on a non-liquid crystalline polymer backbone by flexible spacer. From these two possibilities, the side chain positioning is the most suitable solution. The viscosity is increased in this case, mainly due to the presence of the main chain. Cell leakage can be enhanced until there is no necessary any cell containment, and also can determine the future utilization in flexible and large-area displays [58]. Anchoring new groups on the main chain of LC polymer is a very exciting perspective owing to the fact that the active molecules attached have no restriction concerning solubility degree or the risk of segregation. One can remark some benefits, such as obtaining multifunctional materials, with the objective to render elements of piezoelectric, dichroic, or fluorescent characteristics. Copolymerization reaction can manage to control mesophase stability, by decreasing the number of mesogenic side groups on the backbone unit or, also, by mixing side groups with different lengths or flexible spacer. Once the LC material is formed, there is a dramatic change in its microarchitecture. Thus, the new structures—spherulitis—appear as a result of a nucleation and growth process. In the side chain LC polymers, the crystallization process is inhibited and cooling the mesophase maintains the

50

High Performance Polymers and Their Nanocomposites

glass microstructure. Also, glass transition temperature (Tg) is increased by the polymer main chain. Moreover, if a stiff backbone is chosen, one may increase Tg in order to obtain a stable glass for indefinite period of time, at environmental temperature. The capacity to fix a LC structure into a solid state provides several applications in which those types of materials can generate specific structure with high performance in solid state. In the main chain LC polymers, the crystallization process is not easy to inhibit. Still, one can reduce or even prevent crystallization by obtaining a random copolymer by decreasing the melting point; by this, the polymer can be designed without degradation. The essential features of these systems, such as lower crystallinity and small and discrete size and shape of the crystallites, makes the glass to preserve the main microarchitecture aspects of the mesophase. At the same time, the light scattering present in thin films is very small, almost minimal.

2.7.2 Liquid Crystalline Polymers in Displays In order to obtain a performed electro-active LC polymer, one should accomplish as much as can be from the functionality of the small molecule. Side chain polymeric materials maintain the characteristics of a solid due to the properties of the polymer backbone, and, at the same time, have some of the liquid phase mobility in the mesogenic groups. It is well known that a liquid crystal device that depends on the field determines that molecular orientation of its activity can be performed with polymeric analogues. Degree of molecular motion (namely chiral smectic device) is compatible with the side chain architecture of the polymer. These systems exhibit great promise for the future displays because they do not have the need to incorporate a thin film transistor within the display itself. LC polymers have found application as passive materials with optic properties that can be adapted for increasing the performance of small molecule display [34]. There are still several limits in the actual generation of displays, the most important being their low brightness and small viewing angle. However, these could be overcome by introducing pre-aligned films of liquid crystal phase into device [59]. Furthermore, displays with aligned and mechanically fixed small molecules are managed to be manufactured for attractive application. The optic application that have in foreground displays based on small ferroelectric molecules, have presented some shortcomings that counts in the desire to compete at commercial level. Among them, ease of ferroelectric LC alignment of being destroyed by some small mechanic shocks is worth to mention. This fact makes the above-mentioned system improper

Liquid Crystal Polymers

51

for portable applications. In order to exceed this, some efforts have been made for settling the LC microstructure through blending with a suitable mononer, and further to proceed in situ polymerization for obtaining a polymer network [59]. Frequently, the used polymer is a non-mesogenic epoxy that has the phase region that separates smectic layer before curing (formed as a result of photopolymerization), forming in this way a special architecture that consolidates the LC structure and could bound the two surfaces of the cell. A different approach of this matter refers to the addition of an alternative cross-linkable mesogen into LC or to crosslink mesogens themselves [34]. The obtained systems are ferroelectric gels and contain in their composition about 90% of unreacted mesogens. The aligned polymeric architecture presents an essential impact on the behavior of the mesogens with low molar mass. Thus, the network imparts the structure into different zones with various sizes and switching voltages, having the aim of obtaining the ferroelectric material appropriate for grayscale applications. Other possibility to stabilize nematic LC displays is to employ polymers that found application as light shutters for windows. Display devices that use small molecule LC are based on polymer alignment layers, the most common known being rubbed polyimides [43]. Owing to difficulty to control the rubbing process and desire to avoid any other damage that might affect the device, the efforts were headed to find alternative methods for alignment technique. In this context, the modification of the alignment direction under polarized light was developed [59].

2.7.3

Sensors and Actuators

Ferroelectric LC and polymers exhibit exciting properties as sensors, as a result of the polar ordering of the mesogens. These systems present an intrinsic polarization, namely spontaneous polarization (Ps) that depends on the orientation degree from LC medium. An external stimulus that modifies this order determines a change in Ps, registered as a modification of the voltage across the device. In this context, could be remembered temperature that cause pyroelectric effect, and pressure that induce piezoelectric effect. For manufacturing an efficient temperature sensor, the thermal stability of LC must be improved, by cross-linking reaction. Conversely, the piezoelectric effect is dependent on the LC phase behavior. Although the sample analyzed in the literature [59] may suggest the possible application as artificial muscle, the piezoelectric effect obtained is very small. So, additional large voltages will be required for the proper functioning of this device. Other approach to mimic artificial muscle is thermally

52

High Performance Polymers and Their Nanocomposites

induced shape modification in nematic-isotropic phase transition in LC elastomers or using a lateral anchor of single crystal nematic elastomer [34]. All that research evidenced that LC elastomers show properties similar with skeletal muscle, namely stresses of 210 kPa, undergo stress of 35–45% and sub-second relaxation time. Still, there are a number of unresolved issues before these systems to be integrated into robots or prostetic limbs. Among them, an efficient heating/cooling system must be integrated within the device. LC network employed as actuators operates using a light beam [59]. The bonds formed after photo-isomerization process irradiated with ultraviolet light, and the modification that arises in molecular shape is seen as a change in macroscopic network of the product. These spin up on an axis perpendicular to the polarization plane of the light. Irradiation without visible ray beam returns the material in the initial smooth state, ready to be turned on still around different axes. The miniaturization process would manage to enhance the speed, although the switching time indicated by the actuator is quite small. This type of LC polymers may be recommended in nanotechnology applications, like in some future nanomachine, as light activated driving device [15].

2.8

Environmental Impact and Recycling

The evolution of electronic equipment has also a less desired effect for environment since many devices such as smartphones, computers, tablets, and TVs are accumulating at worldwide level. The content of waste products relies on toxic metals and other dangerous chemicals, such as brominated flame retardants, polycyclic or halogenated aromatic hydrocarbons. Some of them are encountered in LC displays and might leach out of landfills into groundwater and streams. Composition of such devices is as follows: 48% metals, 25% plastic, 8% printed circuit boards, 6% panel, 7% glass, 3% waste, 2% cables, and 1% lamps. Among them, there are 26 compounds that are able to determine acute toxicity in humans [60]. The possibility to make end-of-life LCDs a source of secondary raw materials would favor a proper management with a consequent reduction of toxic metals and hazardous materials dispersions. From an environmental point of view, indium recovery is considered a very significant aspect to create effective strategies so that the import of this from a different country to be diminished [61,62]. Moreover, another big problem is when the mercury amount from the fluorescent lamp from fluorescent-backlight LCD monitor comes in contact with

Liquid Crystal Polymers

53

aqueous media. In this context, it becomes methylated mercury in sediments, and the toxicity of these compounds has awful effect on all living organisms by interfering with brain development of a fetus and normal functioning of the nervous system of adults. The manufacturing processes of LC display involves distinct chemical substances that have considerable impact on the abiotic ecosystem generating serious global climate changes, such as: global warming owing to sulfur hexafluoride, reduction of ozone layer caused by hydro-fluorocarbons, acid rain because of hydrochloric/hydrofluoric acids, and nutrient enrichment with nitrogen and phosphorous. The latter has undesired effects on biological activity at water surface where fast-growing organisms, such as algae, surpass established organisms like fish. Furthermore, the organic compounds that are leaching into water cause depletion of dissolved oxygen, which in turn limits the survival rate of living organisms. One measure of this impact is biological oxygen demand (BOD). Another negative effect is seen in water quality. Given its cloudy character, induced by pollution, only a fraction of the usual amount of sunlight travels through this medium damaging the existence of plants and other light dependent organisms, thus reducing biological activity. As a general remark, it can be observed that even LC displays consume less energy than CRT monitors, and the managements of their wastes require tremendous amount of energy. Therefore, LCD monitors can augment the solid waste generation (e.g., sludge and coal by-products) in those places where the electricity comes from non-renewable sources. The identification of all disastrous effect on the environment has alarmed the scientists, manufacturing engineers, and those preoccupied to prevent pollution, to remediate these problems. The first step relies on careful establishing of the recycling procedures. The main steps involve the following: collection, pre-processing, and end-processing, each phase typically carried out by specialized operators. This serious issue also impacts the fabrication steps and methodology by replacing some of the used contaminants with less polluting compounds.

2.9

Concluding Remarks and Future Trends

Regardless the bad effects on the nature, LC materials are still of interest for many applications. Amplification of mesophase polymers utilization is expected to determine partly the replacement of metals, ceramics, thermosets, and other high-performance thermoplastics by suitable design into the following several generations of devices. Their unique properties

54

High Performance Polymers and Their Nanocomposites

can be easily tuned by inserting specific additives with variable miscibility (blends or composites) expanding their applicative horizon. One deficiency of these multiphase materials is the poor interphase adhesion, which limits the strength of the system. Also, it is hard to prepare specimens that contain other than a unidirectional microfibril/filler orientation. This confines the applications to those demanding high mechanical anisotropy. Future research is expected to be devoted for improving these issues. Analyzing the increased consumption in various end-use industries (electrical & electronics, automotive, aerospace, industrial, medical, cookware, etc.), the LC polymers market is expected to enlarge at a high CAGR over the forecast period (2017–2027) [63]. The key challenges that most market players are confronting involve their low welding strength and so on. Nonetheless, efforts are being made to enhance their physical and chemical performance to overcome such shortcomings. In the future it is expected that such compounds will have lower costs, and more aspects concerning their anisotropy will be clarified in order to expand their applications. In fact, the most important applications for these materials probably have not yet been discovered.

Acknowledgment This work was supported by a grant of the Roumanian National Authority for Scientific Research and Innovation, CNCS – UEFISCDI, project PN-IIRU-TE-2014-4-2976, no. 256/1.10.2015, stage 2017.

References 1. Reinitzer, F., Beiträge zur Kenntniss des Cholesterins. Monatsh. Chem., 9(1), 421–441, 1888. 2. Percec, V., De Souza Gomez, A., Lee, M., Molecular engineering of liquid crystal polymers by living polymerization. XI. Synthesis and characterization of poly{ 11-[(4-cyano-4 -trans-α-cyanostilbene) oxy] undecanyl vinyl ether}, J. Polym. Sci. Part A, 29, 1615–1622, 1991. 3. Gray, G.W. Molecular Structure and the Properties of Liquid Crystals. London and New York, Academic Press, 1962. 4. Kelker, H., Survey of the early history of liquid crystals, Mol. Cryst. Liq. Cryst., 165, 1–43, 1988. 5. Demus, D., Plenary Lecture. One hundred years of liquid-crystal chemistry: Thermotropic liquid crystals with conventional and unconventional molecular structure. Liq. Cryst., 5(1), 75–110, 1989.

Liquid Crystal Polymers

55

6. Luckhurst, G.R., Gray, G.W. The Molecular Physics of Liquid Crystals. London and New York, Academic Press, 1979. 7. Lehman. in Handbuch der Biologischen Arbeitsmethoden, ed E. Arberhalden, Physik-Chem. Methoden, Untersuchung des Verhaltens gelster Stoffe, Ab. III, Teil A2. Urban and Schwarzenberg, Munich. pp. 123–352, 1922. 8. Lagerwall, J.P.F., Scalia, G., A new era for liquid crystal research: Applications of liquid crystals in soft matter nano-, bio- and microtechnology. Current Applied Physics, 12(6), 1387–1412, 2012. 9. White, T.J., Broer, D.J., Programmable and adaptive mechanics with liquid crystal polymer networks and elastomers. Nat. Mater., 14(11), 1087–1098, 2015. 10. Lim, G., Okumura, Y., Higuchi, H., Kikuchi, H., Low-temperature properties of polymer-stabilised liquid-crystal blue phases. Chem. phys. chem., 15(7), 1447–1451, 2014. 11. Woltman, S.J., Jay, G.D., Crawford, G.P., Liquid-crystal materials find a new order in biomedical applications. Nat. Mater., 6(12), 929–938, 2007. 12. Onsager, L., The effects of shape on the interaction of colloidal particles. Ann. N. Y. Acad. Sci., 51(4), 627–659, 1949. 13. Flory, P.J., Phase Equilibria in Solutions of Rod-Like Particles. Proc. Roy. Soc., 234(1196), 73–89, 1956. 14. deGennes, P.G., One type of nematic polymers. Comptes Rendus Hebdomadaires des Seances de L’ Academie des Sciences Serie B, 281, 101–103, 1975. 15. Donald, A.M., Windle, A.H., Hanna, S. Liquid Crystalline Polymers. Cambridge University Press, 2005. 16. Noël, C., Navard, P., Liquid crystal polymers. Prog. Polym. Sci., 16(1), 55–110, 1991. 17. Noel, C., Macroscopic structural characterisaton of side chain liquid crystal polymers. In: McArdle C. B, ed. Side Chain Liquid Crystal Polymers. New York, Chapman and Hall. p. 159, 1989. 18. Figueiredo Neto, A.M., Salinas, S.R.A., phase transitions and structural properties. The physics of lyotropic liquid crystals. New York, Oxford University Press, 2005. 19. Collyer, A.A., Structures to Applications. Liquid Crystal Polymers. London, Elsevier, 1992. 20. Ciferri, A., Krigbaum, W.R., Meyer, R.B. Polymer liquid crystals. New York, Academic Press, 1982. 21. Chen, B.-K., Tsay, S.-Y., Chen, J.-Y., Synthesis and properties of liquid crystalline polymers with low Tm and broad mesophase temperature ranges. Polymer, 46(20), 8624–8633, 2005. 22. Yu, Z., Tu, H., Wan, X., Chen, X., Zhou, Q.-F., Synthesis and characterization of mesogen-jacketed liquid-crystal polymers based on 2,5-bis(4 -alkoxyphenyl) styrene. J. Polym. Sci. A Polym. Chem., 41(10), 1454–1464, 2003. 23. Chen, X.F., Shen, Z., Wan, X.H., Fan, X.H., Chen, E.Q., Ma, Y, et al, Mesogenjacketed liquid crystalline polymers. Chem. Soc. Rev., 39(8), 3072–3101, 2010.

56

High Performance Polymers and Their Nanocomposites

24. Liu, D., Broer, D.J., Liquid crystal polymer networks: preparation, properties, and applications of films with patterned molecular alignment. Langmuir, 30(45), 13499–13509, 2014. 25. Keller, P., Thomsen, D.L., Li, M.-H., Facile and inexpensive synthesis of α,β,β’deuterated liquid crystalline and classical acrylate monomers. Macromolecules, 35(2), 581–584, 2002. 26. Ahn, S., Im, K., Chang, T., Chambon, P., Fernyhough, C.M., 2D-LC characterization of comb-shaped polymers using isotope effect. Anal. Chem., 83(11), 4237–4242, 2011. 27. Shaffer, T.D., Percec, V., Thermotropic polyketones - a new class of main chain liquid-crystalline polymers. Polymer Bull, 14, 367–374, 1985. 28. Acierno, D., Collyer, A.A. Rheology and Processing of Liquid Crystal Polymers. Glasgow, Springer, 1996. 29. Wissbrun, K.F., Observations on the Melt Rheology of Thermotropic Aromatic Polyesters. Brit. Poly. J., 12(4), 163–169, 1980. 30. Sircar, S., Wang, Q., Dynamics and rheology of biaxial liquid crystal polymers in shear flows. J. Rheol. (N. Y. N. Y)., 53(4), 819–858, 2009. 31. Ernst, B., Navard, P., Band textures in mesomorphic (hydroxypropyl) cellulose solutions. Macromolecules, 22(3), 1419–1422, 1989. 32. Cosutchi, A.I., Hulubei, C., Stoica, I., Ioan, S., Morphological and structuralrheological relationship in epiclon-based polyimide/hydroxypropylcellulose blend systems. J. Polym. Res., 17(4), 541–550, 2010. 33. Onogi, S., Asada, T., Rheology and rheo-optics of polymer liquid crystals. In: Marrucci Giuseppe A. G, Luigi N, eds. Rheology. 1. New York, Plenum. pp. 127–147, 1980. 34. Yang, D.K., Wu, S.T. Fundamental of liquid crystal devices. USA, Wiley, 2006. 35. Brostow, W. Mechanical and thermophysical properties of polymer liquid crystals. London, Chapman & Hall, 1998. 36. Northolt, M.G., Tensile deformation of poly(p-phenylene terephthalamide) fibres, an experimental and theoretical analysis. Polymer, 21(10), 1199–1204, 1980. 37. Ozturk, H.B. Mechanical and thermal properties of thermotropic liquid crystalline copolyester (tlcp) and its mixtures with poly(ethyleneterephthalate) and denture base poly(methyl methacrylate). Thesis, The Graduate School of Natural and Applied Sciences of Middle East Technical University, 2004. 38. Kihara, H., Miura, T., Morphology of a hydrogen-bonded LC polymer prepared by photopolymerization-induced phase separation under an isotropic phase. Polymer, 46(23), 10378–10382, 2005. 39. Figueiredo Neto, A.M., Structure of lyotropic nematic complex fluids. In: P. Toledano , Figueiredo Neto A. M, eds. Phase transitions in complex fluids. Singapore, World Scientific. pp. 151–172, 1998. 40. Dierking, I., Chiral Liquid Crystals: Structures, Phases, Effects. Symmetry, 6(2), 444–472, 2014.

Liquid Crystal Polymers

57

41. Radley, K., Reeves, L.W., Tracey, A.S., Effect of counterion substitution on the type and nature of nematic lyotropic phases from nuclear magnetic resonance studies. J. Phys. Chem., 80(2), 174–182, 1976. 42. Wunderlich, B., Grebowicz, J., Thermotropic mesophases and mesophase transitions of linear, flexible macromolecules. Adv. Polym. Sci., 60(6), 1–59, 1984. 43. Stoica, I., Barzic, A.I., Hulubei, C., The impact of rubbing fabric type on surface roughness and tribological properties of some semi-alicyclic polyimides evaluated from atomic force measurements. Appl. Surf. Sci., 268, 442–449, 2013. 44. Walba, D.M., Yang, H., Shoemaker, R.K., Keller, P., Shao, R., Coleman, D.A, et  al, Main-Chain Chiral Smectic Polymers Showing a Large Electroclinic Effect in the SmA* Phase. Chem. Mater., 18(19), 4576–4584, 2006. 45. Thomas, S., Visakh, P.M. Handbook of engineering and specialty thermoplastics. Volume 3: Polyethers and polyesters. John Wiley & Sons, 2011. 46. Fink, J.K., A concise guide to industrial polymers. Reactive polymers fundamentals and applications. William Andrew, 2013. 47. Acierno, D., Incarnato, L., Nobile, M.R., Frigione, M. Proceedings of the X convegno italiano di scienza e tecnologia delle macromolecole, Ferrara. Italy. pp. 869–872, 1991. 48. Dutta, D., Fruitwala, H., Kohli, A., Weiss, R.A., Polymer blends containing liquid crystals: A Review. Polym. Eng. Sci., 30(17), 1005–1018, 1990. 49. Li, Y., Shi, W., Sun, Z., Pan, Y., Sheng, X., Li, J., The structure and properties of polyamide/liquid crystal polymer blends, J. Macromol. Sci. Part B, 1064–1072, 2012. 50. Paolo La Mantia, F. Thermotropic liquid crystal polymer blends. CRC Press, 1993. 51. Ambrosino, S., Sixou, P., Rheology of a mixture of liquid-crystal polymers in solution. J. Polym. Sci. B Polym. Phys., 32(1), 77–84, 1994. 52. Kozlowski, M., Kozlowska, A., Liquid Crystal Polymer Blends. Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 353(1), 581–588, 2000. 53. Barzic, A.I., Hulubei, C., Avadanei, M.I., Stoica, I., Popovici, D., Polyimide precursor pattern induced by banded liquid crystal matrix: Effect of dianhydride moieties flexibility. J. Mater. Sci., 50(3), 1358–1369, 2015. 54. Stoica, I., Barzic, A.I., Hulubei, C., Polyimide embedding in lyotropic polymer matrix for surface-related applications: rheological and microscopy investigations, Rev. Roum. Chim, 61, 575–581, 2016. 55. Nishio, Y., Yamane, T., Takahashi, T., Morphological studies of liquid-crystalline cellulose derivatives I. Liquid-crystalline characteristics of hydroxypropyl cellulose in 2-hydroxyethyl methacrylate solutions and in polymer composites prepared by bulk polymerization. J. Polym. Sci.: Polymer Physics Edition, 23, 1043–1052, 1985.

58

High Performance Polymers and Their Nanocomposites

56. Cheng, H.K.F., Basu, T., Sahoo, N.G., Li, L., Chan, S.H., Current Advances in the Carbon Nanotube/Thermotropic Main-Chain Liquid Crystalline Polymer Nanocomposites and Their Blends. Polymers, 4(2), 889–912, 2012. 57. Kim, J.Y., Carbon nanotube-reinforced thermotropic liquid crystal polymer nanocomposites. Materials, 2(4), 1955–1974, 2009. 58. Jackson jr, W.J., Liquid Crystal Polymers. XI. Liquid Crystal Aromatic Polyesters: Early History and Future Trends. Molecular Crystals and Liquid Crystals Incorporating Nonlinear Optics, 169(1), 23–49, 1989. 59. O’Mara, W.C., Liquid crystal flat panel displays. New York, Springer, 1993. 60. Savvilotidou, V., Hahladakis, J.N., Gidarakos, E., Determination of toxic metals in discarded Liquid Crystal Displays (LCDs. Resources, Conservation and Recycling, 92, 108–115, 2014. 61. Rocchetti, L., Amato, A., Beolchini, F., Recovery of indium from liquid crystal displays. J. Clean. Prod., 116, 299–305, 2016. 62. Amato, A., Rocchetti, L., Beolchini, F., Environmental impact assessment of different end-of-life LCD management strategies. Waste Manag., 59, 432–441, 2017. 63. http://www.futuremarketinsights.com/reports/liquid-crystal-polymers-market

3 Polyamide 4,6, (PA4,6) Emel Kuram1,* and Zeynep Munteha Sahin2 1

Department of Mechanical Engineering, Gebze Technical University, Gebze/Kocaeli, Turkey 2 Department of Chemistry, Gebze Technical University, Gebze/Kocaeli, Turkey

Abstract Polyamide (PA) or nylon is one of the engineering plastics employed in many engineering components. Various kinds of PA such as PA6, PA6,6, and PA4,6 are available in the market. Among the various kinds of PAs, PA4,6 is a new engineering plastic. PA4,6 is a type of PA prepared from tetramethylenediamine and adipic acid. PA4,6 has a high content of amide groups, a high flexibility of polymer chains, and a symmetric chain structure. Owing to these characteristic features, melting temperature, rate of crystallization, and crystallinity of PA4,6 are higher than that of PA6 and PA6,6 polymers. Therefore, PA4,6 gives excellent properties at high temperatures such as high stiffness, high creep resistance, high thermal stability, good toughness, and high fatigue resistance. In addition, PA4,6 shows better chemical resistance to acidic salts, methanol, mineral salts, oils, and greases. Excellent mechanical properties at high temperatures, low friction, excellent resistance to wear, and excellent chemical resistance of PA4,6 make this polymer a good candidate for the broad range of technical applications such as electrical, electronic, and automotive industries. Therefore, in this chapter, the studies about polymerization, properties, chemical stability, processing, and applications of PA4,6 were presented. The blends, composites, and nanocomposites of PA4,6 with other polymers were also mentioned in the current chapter. Environmental impact and recycling possibility of PA4,6 polymer were also presented. Keywords: Polyamide 4, 6, chemical properties, processing, mechanical properties, nanocomposites, environmental impact and recycling

*Corresponding author: [email protected] Visakh P.M. and Semkin A.O. (eds.) High Performance Polymers and Their Nanocomposites, (59–104) © 2019 Scrivener Publishing LLC

59

60

3.1

High Performance Polymers and Their Nanocomposites

Introduction and History

Polyamide (PA) or nylon is one of the engineering plastics employed in many engineering components. Various kinds of PA such as PA6, PA6,6, and PA4,6 are available in the market. Polyamides (PAs) can both be made from one kind of monomer or two kinds of monomers. When PA was formed using two monomers, the numeric suffixes indicate the number of carbon atoms present in the molecular structures of the diamine and diacid, respectively. PAs have relatively high melting point when compared to other polymers owing to the hydrogen bonds that form between recurring amide groups. Hydrogen bonding plays the dominant role in melting behavior and other properties of these polymers [1]. Among the various kinds of PAs, PA4,6 is a new engineering plastic. PA4,6 was mentioned as early as the 1930s in the literature [2], and this researcher reported that the melting point was 278 °C, which was confirmed by Coffman et al., [3] in 1947. Ke and Sisko [4] synthesized PA4,6 with a melting point of 293 °C by interfacial polymerization. Aubineau et al., [5] prepared PA4,6 from adipoyl chloride in chloroform solution. However the significant and commercial quantities of PA4,6 was not available until the 1980s [6]. Nowadays, PA4,6 is commercially available in the market (DSM) under the trade name Stanyl. PA4,6 fills the gap between traditional engineering polymers (PA6, PA6,6, polyesters, etc.) and exotic plastics (liquid-crystal polymer, polyether ether ketone, polysulfones, etc.) [7]. PA4,6 is superior as compared to other PAs owing to its higher strength and modulus [8].

3.2

Polymerization and Fabrication

PA4,6 (tetramethylene adipamide) is a type of PA prepared from tetramethylenediamine and adipic acid that was synthesized first by Carothers as early as 1938 and now is commercially available (by DSM under the trade name Stanyl). The monomers employed to fabricate PA4,6 are 1,4-diaminobutane and adipic acid [9]. Ke and Sisko [4] fabricated PA4,6 with an interfacial polymerization by employing 1,6-adipoyl chloride in chloroform and 1,4-diaminobutane in water. However, this technique had some drawbacks such as the cost and toxicity of 1,6-adipoyl chloride and low molecular weight PA4,6 product was obtained. The melt polymerization of PA4,6 is rather difficult owing to the high melting point. Moreover, oxidation, thermal degradation, and cyclization of 1,4-diaminobutane to pyrrolidine may take place during the reaction,

7.6

7.2

7.4

7.6

7.8

8.0

8.3

7.2

7.4

7.6

7.7

7.8

7.8

II

III

IV

V

VI

VII

VIII

IX

X

XI

XII

XIII

pH Salt

I

Sample

–

–

–

–

–

–

–

–

–

–

–

–

–

Additives*

220

220

220

220

220

220

220

220

220

220

220

220

220

Temperature (°C)

1

1

1

1

1

1

1

1

1

1

1

1

1

Time (h)

Step 1 (Closed system)

Table 3.1 Reaction conditions and properties of samples [10].

305

305

305

305

305

305

290

290

290

290

290

290

–

Temperature (°C)

Step 2 (Vacuum)

1

1

1

1

1

1

1

1

1

1

1

1

–

Time (h)

m

m

m

m

m

m

s

s

s

s

s

s

Physical state during reaction

1.55

1.54

1.56

1.65

1.45

1.29

2.09

1.99

2.01

1.69

1.32

1.34

0.18

Inherent viscosity, ηinh

(Continued)

Yellow

Yellow

Yellow

Yellow

Yellow

Yellow

Light yellow

Light yellow

Light yellow

Light yellow

Light yellow

Light yellow

Colorless

Color

Polyamide ,, (PA,) 61

7.6

XV

220

220

AA, 1.25% TDMA, 0.62%

Temperature (°C)

–

Additives*

2

2

Time (h)

Step 1 (Closed system)

*AA=Adipicacid; TDMA = Tetramethyl diammonium acetate s=solid state; m=melt

7.6

pH Salt

Sample

XIV

Cont.

Table 3.1

290

280

290

280

Temperature (°C)

Step 2 (Vacuum)

2

2

2

2

Time (h)

s

s

Physical state during reaction

1.03

1.72

Inherent viscosity, ηinh

Colorless

Light yellow

Color

62 High Performance Polymers and Their Nanocomposites

Polyamide ,, (PA,)

63

thus leading to low molecular weight PA4,6 [10]. Beamen and Cramer [11] synthesized PA4,6 by a two-step melt polymerization and achieved a product with an inherent viscosity of 0.84. The interfacial polymerization of PA4,6 is difficult as compared to longer-chain PA6,6 and PA6,10 [10]. One of the polymerization methods to obtain PA4,6 with high molecular weight is solid-state polymerization (SSP). SSP is performed in the absence of a solvent; therefore, this process is known as environmentally friendly polymerization technique [12]. Low operating temperature is the main advantage of SSP, which hinders the thermal degradation of polymer with high melting point and unwanted side reactions. Its drawback is the lower reaction rate when compared to melt polymerization [13]. Gaymans et al., [10] synthesized PA4,6 from the salt of 1,4-diaminobutane and adipic acid. The polymerization was conducted in two steps (Table 3.1). They achieved high molecular weight PA4,6 by reaction for 1h at 215 °C in a closed system and for 1h in vacuo in the temperature range of 290–305 °C. It was confirmed that the reactions at 290 °C were occurred in the solid state; whereas, the reactions at 305 °C in the melt. These researchers also found that the melting temperature (Tm) was between 283 and 319 °C. Three kinds of poly(butylene adipamide) (PA4,6) were synthesized with 4,6 salt (adipic acid) and poly(butylene–2,5–furandicarboxylamide) (PA-4,F) salt with a molar ratio of 4,6 salt to 4,F salt of 9:1 (PA-F-10), 8:2 (PA-F-20), and 7:3 (PA-F-30). The polymerization process was carried out in two steps: prepolymerization at 170–220 °C for 7h in the presence of water and SSP at 200–240 °C under a nitrogen (N2) and water gas flow. The addition of a 10mol % PA-4,F into PA4,6 induced in the slight increment in the intrinsic viscosity (ηinh) and glass-transition temperature (Tg) after 12 h of SSP at 220 °C. The intrinsic viscosity increased with the increase in the SSP temperature and reaction time [12]. PA4,6 with a high molecular weight was prepared in supercritical carbon dioxide (sc-CO2) by utilizing one-step three-stage polymerization method employing the salt formed from 1,4-diaminobutane and 1,6-adipic acid as a monomer. To increase the molecular weight (Mv), the polymerization process was divided into three stages: precondensation, postcondensation, and vacuum. Reaction conditions and molecular weights of the samples are summarized in Table 3.2. The precondensation process was conducted at a temperature of 190 °C under 30 MPa for 2–3 hr. The postcondensation stage was performed in sc-CO2 for 3–5 hr at a temperature of 280 °C under 15 MPa. In vacuum stage, the system was evacuated for 0.5–1 hr in order to increase the molecular weight by eliminating water. As can be seen from Table 3.2, 48200 is the

180

190

200

210

190

190

190

190

190

190

190

190

190

II

III

IV

V

VI

VII

VIII

IX

X

XI

XII

XIII

2

2

2

2

2

2

2

2

2

2

2

2

2

30

30

30

30

30

30

30

30

30

30

30

30

30

Pressure (MPa)

280

280

280

280

280

280

280

290

270

280

280

280

280

3

3

3

5

4

2

1

3

3

3

3

3

3

Time (h)

Temperature (°C)

Time (h)

Temperature (°C)

I

Sample

Postcondensation

Precondensation

Table 3.2 Reaction conditions and molecular weights of samples [13].

15

15

15

15

15

15

15

15

15

15

15

15

15

Pressure (MPa)

45

40

0

30

30

30

30

30

30

30

30

30

30

Time in vacuum (min)

4.82

4.30

2.59

2.32

3.15

3.57

2.96

2.50

2.96

2.68

3.46

3.96

1.27

Mv ×104

(Continued)

White

White

White

White

White

White

White

White

White

White

White

White

White

Color

64 High Performance Polymers and Their Nanocomposites

XIV

Sample

Table 3.2

190

2

30

280

3

Time (h)

Temperature (°C)

Pressure (MPa)

Temperature (°C)

Time (h)

Postcondensation

Precondensation

Cont.

15

Pressure (MPa)

60

Time in vacuum (min)

4.17

Mv ×104

White

Color

Polyamide ,, (PA,) 65

66

High Performance Polymers and Their Nanocomposites

Table 3.3 Effect of postcondensation time. Prepolymer with PTMO (Mv 1130), 48%PA and postcondensed at 255 °C [14]. Time (h)

[‒NH2] (meq/g)

[COOH] (meq/g)

ηinh (dl/g)

0

0.330

0.325

0.32

2.5

0.058

0.020

0.75

5

0.039

–

0.94

16

0.033

0.023

1.21

29

0.033

0.002

1.31

highest molecular weight of the sample obtained from the experiments [13]. It was concluded that the polymerization temperatures for the precondensation and postcondensation are the most important parameters as far as molecular weight is concerned. Amine-terminated polytetramethylene oxide (PTMO) and PA4,6 salt were used to synthesize PA4,6-PTMO segmented block copolymers. Adipic acid was employed to balance the amine and acid groups in the reaction system. The copolymers were prepared by a two-step method, a prepolymerization with a solvent and a postcondensation in the solid state. First, prepolymers were synthesized at 200–210 °C in the presence of a pyrrolidone solvent. The prepolymers were postcondensed at atmospheric pressure in a nitrogen environment and at temperature of 255 °C. The influence of postcondensation time is presented in Table 3.3. 0 h of postcondensation time has excess quantities of amine groups. After condensing the end group concentrations decreased and ηinh increased. In this way, high molecular weight copolymers could be achieved. It was found that the melting temperatures of PA4,6 block copolymers were high in the range of 200–270 °C and the torsion modulus were constant up to these high melting temperatures. When PA content decreased, the melting temperatures of the block copolymers decreased (Tables 3.4 and 3.5). The reduction of the melting temperature of block copolymers was due to the decrease in lamellar thickness as a result of a decrease in PA block length. It was also stated that 48% PA content sample injection molded well [14]. SSP of PA-4,T/4,6 copolyamides composed of PA-4,T and PA4,6 in various molar ratios were studied employing a mixture of N2 and steam as the sweep fluid in the range of 220–260 °C reaction temperatures.

Polyamide ,, (PA,)

67

Table 3.4 Properties of PTMO (Mv 1130) block copolymers [14]. PA (%)

Extractable (%)

Tm (°C)

100

1

289

77

8

66*

Tc (°C)

ΔHa (J/gPA)

Tg(PTMO) (°C)

Tg(PA) (°C)

257

84

–

80

270

233

78

−75

65

0

269

234

77

−70

52

48

28

268

231

60

−70

50

35

38

258

217

60

−70

40

9

100

–

–

–

−65

–

*Extracted sample.

Table 3.5 Properties of PTMO (Mv 800) block copolymers [14]. PA (%)

Extractable (%)

Tm (°C)

Tc (°C)

ΔHa (J/gPA)

Tg(PTMO) (°C)

Tg(PA) (°C)

100

1

289

257

84

–

80

49

5

265

227

69

−70

50

35

26

248

212

31

−70

50

25

34

196

148

21

−70

50

12

100

–

–

–

−70

–

Prepolymers were synthesized by melt polyamidation with stoichiometric ratios of diamine and diacid. Prepolymers had different PA-4,T contents (28.2, 37.9, and 47.8 mol%). SSP conducted at 260 °C for 48h gave a high molecular weight copolyamide with an intrinsic viscosity of 2.469 dl/g. When PA-4,T content increased, the rate of SSP decreased. The polymers synthesized from the higher PA-4,T content prepolymer gave higher glass transition, melting, and decomposition temperatures than those of the polymers synthesized from the lower PA-4,T content prepolymer [15]. Molecular weight or intrinsic viscosity of PA4,6 under different reaction conditions by different polymerization methods are summarized in Table 3.6.

215 °C, 2 h, N2 (4 MPa); 290 °C, 1 h, in vacuum 155–200 °C, 160 min; 260 °C, 6 h, N2/H2O Heated to 300 °C in 15 min, N2; 260 °C, 3.5 h, N2/H2O

PA4,6 salt

PA4,6 salt

PA4,6 salt in water (90%)

PA4,6 salt in N-methylpyrrolidone (40%)

Two-step melt polymerization

Two-step solid-state polymerization

220 °C, 1–2 hr, N2;>283 °C, 1–2 hr, in vacuum

1% solution in 96% sulfuric at 20 °C

1% solution in 96% sulfuric at 20 °C

0.5% solution in 98% formic acid at 30 °C

0.5% solution in m-cresol at 30 °C

190 °C, 2 h, sc-CO2 (30 MPa); 280 0.6% solution in 90% °C, 3h, sc-CO2 (15 MPa); 2800 °C, formic acid at 25 °C 45 min, in vacuum

PA4,6 salt

One-step three-stage polymerization

Measurement conditions

Heated to 280 °C, 5–8 hr, sc-CO2 (30 0.6% solution in 90% MPa) formic acid at 25 °C

Reaction conditions

PA4,6 salt

Starting material

One-step polymerization

Polymerization methods

4.13 [17]

4.90–34700 [16]

2.09 [10]

0.84 [11]

2.37–48200 [13]

6000 [13]

ηinh or Mv

Table 3.6 Molecular weight or intrinsic viscosity (ηinh) of PA4,6 under different reaction conditions by different polymerization Methods.

68 High Performance Polymers and Their Nanocomposites

Polyamide ,, (PA,)

3.3

69

Properties

PA4,6 backbone has a high content of amide groups and a high flexibility of polymer chains [18]. In addition, the chain structure of PA4,6 is symmetric [19]. Owing to these characteristic properties, PA4,6 possesses a higher melting temperature, rate of crystallization, and crystallinity than that of PA6 and PA6,6 polymers. Therefore, PA4,6 gives excellent properties at high temperatures such as high stiffness, high creep resistance, high thermal stability, good toughness, and high fatigue resistance [18]. However, fire resistance of PA4,6 is weak [20]. Some physical properties of PA4,6 polymer are summarized in Table 3.7. PA4,6 crystallized with a single peak at 2θ=21.23°, which indicates that PA4,6 crystallized in the γ-phase (hexagonal structure) during isothermal crystallization and the crystallization temperature (Tc) was found to be 280 °C for PA4,6. PA4,6 demonstrated two crystalline transition on cooling from the crystallization temperature. The first transition was a typical Brill transition and it was about 40 °C below the Tc.The second one was approximately 140–150 °C below the Tc and was from the high-temperature (HT) α-phase to the room temperature (RT) α-phase [21]. Polymer properties are affected by the crystallization process through the crystal structure and morphology. Zhang et al., [22] used differential scanning calorimetry (DSC) to study isothermal and nonisothermal crystallization kinetics of PA4,6. The crystallization activation energies were found to be 568.25 and 337.80 kJ/mol for isothermal and nonisothermal crystallization, respectively. The isothermal crystallization kinetics results of PA4,6 are summarized in Table 3.8. The crystallization behavior of PA4,6 was studied by solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) measurements. The lamellar thickness was found to be constant during the crystallization [23, 24]. With the crystallization, the thickness of the crystalline and amorphous phases increased and decreased, respectively. Tm0 was achieved as 350 °C. ΔHm0 was found as 270 J/g [23]. The crystallization mechanism of PA4,6 was proposed by Yamanobe et al., [23] as follows. As the temperature of the melt sample decreased to the crystallization temperature, the formation of the hydrogen bond occurred. Crystalline phase size was found to be small, and the crystal structure was not energetically stable at this stage. The amorphous phase was mobile, and the conformation of this phase involved in the gauche-conformation around the βB–βB bond. As the crystallization progressed, the crystal structure became stable, altered to the monoclinic structure, and formed the hydrogen bond

H

N

H

N

O

O

n

OH

60–70

Crystallinity* (%)

*Determined by wide-angle X-rays scattering (WAXS). **Mass percentage of the water uptake by injection molded plates at 35 °C.

H

Structure

Table 3.7 Physical Characteristics of PA4,6 [18].

12.4

Water uptake** (wt.-%)

80

Tg (°C)

260

Tc (°C)

290

Tm (°C)

70 High Performance Polymers and Their Nanocomposites

Polyamide ,, (PA,)

71

Table 3.8 Results of the isothermal crystallization kinetics of PA4,6 [22]. Properties

Units

Values

Equilibrium melting point (Tm0)

°C

307.10

Equilibrium melting enthalpy (ΔHm0)

J/g

155.58

Chain width (α0)

nm

0.484

Thickness of a monomolecular layer (b0)

nm

0.369

Lateral surface free energy (σ)

erg/cm2

8.28

End surface energy (σe)

erg/cm2

138.54

Work of chain folding (q)

kcal/mol

7.12

kJ/mol

568.25

Crystallization activation energy (ΔE)

Table 3.9 Mechanical properties of PA4,6 [27].

Yield stress (MPa) 56.5

Elongation at break (%) 106.0

Modulus of elasticity (MPa) 11288.8

Shore D hardness 78.5

sheet structure. The crystalline phase grew at the same time. The thickness of the crystalline phase increased with the decrement in the thickness of the amorphous phase. The mobility of the amorphous phase was restricted during the final step of the crystallization. Molecular dynamics simulations considering the occurrence of chain folding were carried out to study the structure of PA4,6 lamellar crystals. Results revealed that the packing preferences of PA in the lamellar crystals were not changed by alternations in the chain folding mechanism [25]. Annealing of the crystals at temperatures nearly below the Brill transition resulted in enrichment in β structure and the increment chain-folding order [26]. Kalacska [27] employed pin-on-plate and pin-on-disc tests to determine the dry friction coefficient (μ) of PA4,6 (Table 3.9) against a ground structural steel surface. Test conditions are given in Table 3.10. It was found that the friction of PA4,6 increased with the increased load (Table 3.11). The initial friction coefficient of PA4,6 was found to be as 0.28. It increased to 0.86 after 10 min sliding, and then decreased to 0.73 when sliding 20 min

Ra 0.05–0.1

100

Ra 0.05–0.1 23

Friction path radius (mm)

Disk surface roughness (μm)

Ambient temperature (°C)

pv = data of friction system design of thermoplastics

100

2

Surface load (MPa)

23

5

0.75

0.75

Period of test (h)

0.4

0.4

Pin-on-disc II (pv = 2 MPa. ms–1)

Sliding speed (m/s)

Pin-on-disc I (pv = 0.8 MPa.ms–1)

Table 3.10 Test conditions [27].

23

Ra 0.05–0.1

Dynamic program path

0–20

1–5 cycles

0–0.4

Pin-on-plate dynamic tests (pv regime 0–8 MPa.ms–1)

72 High Performance Polymers and Their Nanocomposites

Polyamide ,, (PA,)

73

Table 3.11 Friction values for PA4,6 [27]. Dynamic pin-on-plate μav cycle 1 0.10

Pin-on-disc I

Pin-on-disc II

μav complete

μav

μmax

μav

μmax

0.11

0.27

0.32

0.30

0.31

Table 3.12 Some mechanical/physical properties of toughened PA4,6 (dry as molded) [33]. Properties

Units

Values

Tensile strength

MPa

59

Izod impact

J/m

1120

Flexural modulus

MPa

1860

Heat deflection (1.82MPa)

°C

90

Melting point

°C

295

and remained the steady-state friction until stopping the friction test [28]. At the steady-state case, the friction coefficient of PA4,6 was higher than that of PA6 (approximately 0.55 [29]) and PA6,6 (approximately 0.67 [30]). The higher friction coefficient of PA4,6 may be owing to the strong hydrogen bonding in PA4,6. Adhesive wear and melting flow were found to be the main wear mechanisms of PA4,6 against steel. PA4,6 formed belt-like and spiral rod-like wear debris during the sliding process [28].

3.4

Chemical Stability

PA4,6 shows better chemical resistance especially to acidic salts [31]. Chemical resistance of PA4,6 is good to methanol, mineral salts, oils, and greases [20]. It was found that the degradation of PA4,6 was a surface phenomenon therefore oxygen diffusion limited. PA4,6 is more stable than PA6,6 owing to its lower oxygen permeability, probably caused by its higher crystallinity and density of the amorphous phase [32].

74

3.5

High Performance Polymers and Their Nanocomposites

Compounding and Special Additives

Additives employed in PA are as follows: Heat stabilizers Lubricants Plasticizers Pigments Fungicides Flame retarders Nucleating agents Impact modifiers Reinforcing fillers Proper reinforcement and/or fillers are added to PA4,6 to further enhance its properties. An organo-montmorillonite was added to PA4,6 as the reinforcing filler [19]. It was reported that the incorporation of the organo-montmorillonite increased Young’s and flexural modulus of PA4,6. However, the elongation at break was inversely influenced. A maleated polyolefin elastomer was incorporated to PA4,6 as the toughener [19]. The stiffness of PA4,6 reduces with the addition of the toughening agent, and this influence is more pronounced at higher temperatures [33]. Some mechanical/physical properties of toughened PA4,6 are given in Table 3.12. It was stated that the glass-fiber reinforced flame retardant PA4,6 showed higher performance than the unreinforced one [34].

3.6

Processing

Following points are considered in the processing of PAs [35]. The tendency of water absorption. The high melting point of the homopolymers. The low melt viscosity of the homopolymers. The tendency of the material to oxidise at high temperatures. The extensive shrinkage during cooling due to the crystallinity. PA4,6 polymer has a higher crystallinity, melting temperature, and crystallization rate than PA6 and PA6,6 due to the presence of the high

Polyamide ,, (PA,)

75

Table 3.13 Properties of extruders.

Screw diameter (D, mm)

Extruder

Length to diameter (L/D)

Die diameter (D0, mm)

Short single screw (S50)

50

10

3

Single screw (S30)

30

30

3

Single screw (S40)

40

40

3

Co-rotating twin screw (T30)

30

40

3

Table 3.14 The carboxyl content (CC), intrinsic viscosity ([ηinh]), viscosityaverage molecular weight (Mv ), and length of glass-fiber (L) of recycled PA4,6 (RPA46) and its extruded products [34]. CC (×10–5 mol g–1)

[ηinh] (mg dl–1)

Mv×104

L (μm)

RPA46

8.06

1.35

3.62

266.2

RPA46-S50

9.12

1.29

3.38

246.1

RPA46-S30

9.85

1.24

3.20

229.6

RPA46-S40

10.02

1.19

3.04

212.3

RPA46-T30

10.56

1.07

2.64

177.7

Samples

concentration of amide groups, the flexibility of the polymer chain, and the uniform length of the hydrocarbon segments between the amide groups. Therefore, PA4,6 polymer is easily processed and cycle times reduce during injection molding process [7]. Zhang et al., [34] recycled the 30% of glass-fiber reinforced flame retardant PA4,6 (RPA46) with a co-rotating twin screw and three different single screws. The properties of used extruders are summarized in Table 3.13. Zhang et al., [34] declared that the extrusion process degraded PA4,6 macromolecules and the degradation degree was dependent on the screw shear force. Carboxyl content (CC) values increased and viscosity-average molecular weight (Mv) values decreased when L/D of single screw increased from 10 to 40 (Table 3.14). These researchers claimed that the degradation of PA4,6 during extrusion can be diminished by decreasing the screw

76

High Performance Polymers and Their Nanocomposites 170 160 150 140

Tensile strength (MPa)

130 120 110 100 90 80 70 60 50 40 30 20 10 0 RPA46

RPA46-S50

RPA46-S30

RPA46-S40

RPA46-T30

Samples

Figure 3.1 Tensile strength results.

length or increasing the depths of the gaps. The degree of glass-fiber breakage in twin screw extruder was higher than that of other extruded products by single screw extruders. During extrusion processes, the degree of glassfiber breakage can be diminished by reducing screw length and residence time or increasing the depths of the gaps. Polymer suffers thermo-mechanical degradation during extrusion process, which results in the change at the mechanical properties. Impact, tensile, and flexural strength values decreased when L/D of single screw increased from 10 to 40 (Figures 3.1– 3.3). The mechanical properties in twin screw extruder were lower than that of other extruded products by single screw extruders. Shear thinning behavior was observed for all RPA4,6 samples, and all samples elucidated the characterization of non-Newtonian fluid. A significant reduction in the viscosity of RPA4,6 and its extruded products at higher shear rates was found. Results showed that the thermal (Table 3.15), flame retardant (Table 3.16), and mechanical (Figures 3.1–3.3) properties of RPA46-S50 were in acceptable values. High-speed spinning and spin drawing technologies were employed to spin PA4,6/6 textile fibers. In the high-speed spinning technique, the fibers (partially oriented yarns, POYs) were spun at a constant throughput

Polyamide ,, (PA,)

77

100 90

Impact strength (J/m)

80 70 60 50 40 30 20 10 0 RPA46

RPA46-S50

RPA46-S30

RPA46-S40

RPA46-T30

Samples

Figure 3.2 Impact strength results.

of 44 g/min. Moreover, velocities were in the range of 2000–5000 m/ min. In the spin-drawing technique, the fibers (fully drawn yarns, FDYs) were spun at approximately 600 m/min. Spherulites and orientationally ordered crystallites were found at the same time up to spinning speeds of 3500 m/min. When fibers were spun at higher speeds, the spherulite structure disappeared. Increasing spinning speeds resulted in the increment in the orientation in the fibers. At low velocities (200°C). It was stated that molecular weight of PA4,6 was not changed by the dissolution process [1]. Vinken et al. [65] showed that the water in the superheated state is a good solvent for dissolution and recrystallization of PA4,6. It is also stated that the melting temperature of PA4,6 can be suppressed by almost 100 °C in the presence of superheated water. The dissolution of PA4,6 in superheated water is a physical process and no chemical change occurs unless polymer retains in water solution above its dissolution temperature for more than 10 min.

3.12

Conclusions

PA4,6 is a type of PA prepared from tetramethylenediamine and adipic acid that was synthesized first by Carothers as early as 1938 and now is

100 High Performance Polymers and Their Nanocomposites commercially available in the market under the trade name Stanyl. PA4,6 has a high content of amide groups, a high flexibility of polymer chains, and a symmetric chain structure. Owing to these characteristic features, melting temperature, rate of crystallization, and crystallinity of PA4,6 are higher than that of PA6 and PA6,6 polymers. Therefore, PA4,6 gives excellent properties at high temperatures such as high stiffness, high creep resistance, high thermal stability, good toughness, and high fatigue resistance. In addition, PA4,6 shows better chemical resistance to acidic salts, methanol, mineral salts, oils, and greases. Excellent mechanical properties at high temperatures, low friction, excellent resistance to wear, and excellent chemical resistance of PA4,6 make this polymer a good candidate for the broad range of technical applications such as electrical, electronic, and automotive industries. PA4,6 polymer is easily processed and cycle times reduce during injection molding process. It is reported that the extrusion process degraded PA4,6 macromolecules. PA4,6 has good mechanical properties; however, this type of polymer easily absorbs moisture because of the presence of amide group that can easily interact with water molecules present in the air, which reduces its dimensional stability and mechanical properties. These shortcomings are compensated with the incorporation of HDPE into PA4,6 to enhance the mechanical properties of PA4,6. Proper reinforcement and/or fillers are added to PA4,6 to further improve its properties. MoS2 filler, glass-fiber, aramid fiber, Al and Al2O3 powders are employed to develop PA4,6 composites and organo-montmorillonite, m-MWNT and GnO are utilized to manufacture PA4,6 nanocomposites to improve the properties of PA4,6. Water absorption diminishes the properties of polymeric materials and limits its applications in the industry. Polymer waste was broken down into reusable materials (fuel or chemicals) in the chemical recycling. PAs have advantageous properties; however, the recycling of PAs is technically a challenging task and requires high pressure and/or high temperature. It is declared that water and ethanol are solvents for PA4,6; however, acetic acid is not a solvent for PA4,6. The dissolution of PA4,6 in superheated water is mainly a physical process.

References 1. Rastogi, S., Terry, A.E., Vinken, E., Dissolution of Hydrogen-Bonded Polymers in Water: A Study of Nylon-4,6. Macromolecules, 37(24), 8825–8828, 2004. 2. Carothers, W.H., Polymerization. Chem. Rev., 8(3), 353–426, 1931.

Polyamide ,, (PA,) 101 3. Coffman, D.D., Berchet, G.J., Peterson, W.R., Spanagel, E.W., Polymeric amides from diamines and dibasic acids. J. Polym. Sci., 2(3), 306–313, 1947. 4. Ke B, Sisko A.W. Differential thermal analysis of high polymers. III. Polyamides, Journal of Polymer Science, 50, 87–98, 1961. 5. Aubineau, C., Audebert, R., Champetier, G.. Bulletin de la Societe Chimique France, 2, 533–539, 1970. 6. Roerdink, E., Warnier, J.M.M., Preparation and properties of high molar mass nylon-4,6: a new development in nylon polymers. Polymer, 26(10), 1582– 1588, 1985. 7. Adriaensens, P., Pollaris, A., Carleer, R., Vanderzande, D., Gelan, J., Litvinov, V.M., Quantitative magnetic resonance imaging study of water uptake by polyamide 4,6. Polymer, 42(42), 7943–7952, 2001. 8. Yamada Y., Kurobe T., Toyooka Y. XPS study of transfer films of MoS2 filled nylon-46 composites sliding against steel counterfaces. J. Mater. Sci. Lett., 20(6), 577–579, 2001. 9. McKeen, L.W. Permeability Properties of Plastics and Elastomers. 3rd edition, 2012. 10. Gaymans, R.J., Van Utteren, T.E.C., Van Den Berg, J.W.A., Schuyer, J., Preparation and some properties of nylon 46. Journal of Polymer Science. Polymer Chemistry Edition, 15(3), 537–545, 1977. 11. Beaman, R.G., Cramer, F.B., Polymer characterization: A typical copolyamide system. J. Polym. Sci., 21(98), 223–235, 1956. 12. Endah, Y.K., Han, S.H., Kim, J.H., Kim, N.-K., Kim, W.N., Lee, H.-S, et  al, Solid-state polymerization and characterization of a copolyamide based on adipic acid, 1,4-butanediamine, and 2,5-furandicarboxylic acid. J. Appl. Polym. Sci., 133(18), 43391, 2016. 13. Zhang, Z., Huang, K., Liu, Z., Synthesis of high molecular weight nylon 46 in supercritical carbon dioxide. Macromolecules, 44(4), 820–825, 2011. 14. Gaymans, R.J., Schwering, P., de Haan, J.L., Nylon 46-polytetramethylene oxide segmented block copolymers. Polymer, 30(6), 974–977, 1989. 15. Kim, Y.J., Yohana, K.E., Lee, H.-shik., Kim, J., Solid-state polymerization of semiaromatic copolyamides of nylon-4,T and nylon-4,6: composition ratio effect and thermal properties. Ind. Eng. Chem. Res., 51(49), 15801–15810, 2012. 16. Gaymans, R.J., Edmond, H.J.P.U.S., Patent 4,480, 036, 1983. 17. Warnier, J.M.M., Knape, P.M.U.S., Patent 5,371, 174, 1994. 18. Demco, D.E., Litvinov, V.M., Rata, G., Popescu, C., Phan, K.-H., Schmidt, A, et al, Investigation of thermal aging of polyamide 4,6 by 1H solid-state NMR. Macromol. Chem. Phys., 208(19–20), 2085–2095, 2007. 19. Chiu, F.-C., Deng, T.-L., Polyamide 4,6 nanocomposites with and without the use of a maleated polyolefin elastomer as a toughener. Mater. Chem. Phys., 125(3), 769–776, 2011. 20. Biron, M. Thermoplastics and Thermoplastic Composites. 2nd edition, 2012.

102 High Performance Polymers and Their Nanocomposites 21. Ramesh, C., New crystalline transitions in nylons 4,6, 6,10, and 6,12 using high temperature X-ray diffraction studies. Macromolecules, 32(11), 3721– 3726, 1999. 22. Zhang, Q., Zhang, Z., Zhang, H., Mo, Z., Isothermal and nonisothermal crystallization kinetics of nylon-46. J. Polym. Sci. B Polym. Phys., 40(16), 1784– 1793, 2002. 23. Yamanobe, T., Kurihara, Y., Uehara, H., Komoto, T., Structure and characterization of nylon 46. J. Mol. Struct., 829(829), 80–87, 2007. 24. Atkins, E.D.T., Hill, M., Hong, S.K., Keller, A., Organ, S., Lamellar structure and morphology of nylon 46 crystals: a new chain folding mechanism for nylons. Macromolecules, 25(2), 917–924, 1992. 25. León, S., Alemán, C., Bermúdez, M., Muñoz-Guerra, S., Structure of Nylon 46 Lamellar Crystals: An Investigation Including Adjacent Chain Folding. Macromolecules, 33(23), 8756–8763, 2000. 26. Bermudez, M. Structure and morphology of nylon 46 lamellar crystals: Electron microscopy and energy calculations. J Polym Sci B Polym Phys, 38(1), 41–52, 2000. 27. Kalacska, G., An engineering approach to dry friction behaviour of numerous engineering plastics with respect to the mechanical properties. Express Polym. Lett., 7(2), 199–210, 2013. 28. Cong, P., Xiang, F., Liu, X., Li, T., Morphology and microstructure of polyamide 46 wear debris and transfer film: In relation to wear mechanisms. Wear, 265(7–8), 1100–1105, 2008. 29. Gao, J., Tribochemical effects in formation of polymer transfer film. Wear, 245, 100–106, 2000. 30. Chen, Z.-B., Li, T.-S., Yang, Y.-L., Zhang, Y., Lai, S.-Q., The effect of phase structure on the tribological properties of PA66/HDPE blends. Macromol. Mater. Eng., 289(7), 662–671, 2004. 31. Mckeen, L.W. Effect of Creep and other Time Related Factors on Plastics and Elastomers. 3rd edition, 2015. 32. Gijsman, P., Tummers, D., Janssen, K., Differences and similarities in the thermooxidative degradation of polyamide 46 and 66. Polym. Degrad. Stab., 49(49), 121–125, 1995. 33. Harding, J.A., An introduction to toughened polyamide-4,6. J. Vinyl Addit. Technol., 2(1), 76–79, 1996. 34. Zhang, S., Wang, P., Tan, L., Huang, H., Jiang, G., Relationship between screw structure and properties of recycled glass fiber reinforced flame retardant nylon 46. RSC Adv., 5(5), 13296–13306, 2015. 35. Brydson, J. Plastic Materials. 7th edition. Elsevier, 1999. 36. Schmack, G., Schreiber, R., Veeman, W.S., Hofmann, H., Beyreuther, R., Relation between molecular orientation and mechanical properties in differently processed polyamide 4.6/6 textile yarns. J. Appl. Polym. Sci., 66(2), 377–385, 1997.

Polyamide ,, (PA,) 103 37. Bergshoef, M.M., Vancso, G.J., Transparent nanocomposites with ultrathin, electrospun nylon-4,6 fiber reinforcement. Adv. Mater., 11(16), 1362–1365, 1999. 38. Wang, C., Jheng, J.-H., Chiu, F.-C., Electrospun nylon-4,6 nanofibers: solution rheology and Brill transition. Colloid Polym. Sci., 291(10), 2337–2344, 2013. 39. Huang, C., Chen, S., Lai, C., Reneker, D.H., Qiu, H., Ye, Y, et al, Electrospun polymer nanofibres with small diameters. Nanotechnology, 17(6), 1558–1563, 2006. 40. Uecker, J.C., Tepper, G.C., Rosell-Llompart, J., Ion-assisted collection of Nylon-4,6 electrospun nanofibers. Polymer, 51(22), 5221–5228, 2010. 41. Mikheev, A.Y., Shlyapnikov, Y.M., Kanev, I.L., Avseenko, A.V., Morozov, V.N., Filtering and optical properties of free standing electrospun nanomats from nylon-4,6. Eur. Polym. J., 75(75), 317–328, 2016. 42. De Schoenmaker, B., Van der Schueren, L., Ceylan, Özgür., De Clerck, K., Electrospun polyamide 4.6 nanofibrous nonwovens: parameter study and characterization. Journal of Nanomaterials, 2012(12), 1–9, 2012. 43. De Schoenmaker, B., Van der Schueren, L., Zugle, R., Goethals, A., Westbroek, P., Kiekens, P, et al, Effect of the relative humidity on the fibre morphology of polyamide 4.6 and polyamide 6.9 nanofibres. J. Mater. Sci., 48(4), 1746–1754, 2013. 44. Pollaris, A., Combined quantitative NMR imaging and relaxometry on polymer materials: a fundamental study of rubbers and water uptake in polyamide 46. Thesis, 2003. 45. Zhao, N.N., Zheng, J.W., Ying, Y., Jiang, L.Q., Che, S.L., Qiao, L., Double melting behaviour of PA46 matrix composites. Materials Research Innovations, 18, 483–486, 2014. 46. Suzuki, A., Endo, A., Preparation of high modulus nylon 46 fibres by hightemperature zone-drawing. Polymer, 38(12), 3085–3089, 1997. 47. Van Ruiten, J., Riedel, R., Deblieck, R., Brouwer, R., Penning, J.P., Drawability and attainable mechanical properties of polyamide yarn using true stress-true strain curves. Journal of Materials Science, 36(13), 3119–3128, 2001. 48. Gordon, D.H., Kukureka, S.N., The wear and friction of polyamide 46 and polyamide 46/aramid-fibre composites in sliding–rolling contact. Wear, 267(1-4), 669–678, 2009. 49. Ha, C.-S., Ko, M.-G., Cho, W.-J., Miscibility of nylon 46 and ethylene-vinyl alcohol copolymer blends. Polymer, 38(5), 1243–1246, 1997. 50. Bulte, A., Mulder, M.H.V., Smolders, C.A., Strathmann, H., Diffusion induced phase separation with crystallizable nylons. I. Mass transfer processes for nylon 4,6. J. Memb. Sci., 121(121), 37–49, 1996. 51. Bulte, A.M.W., Mulder, M.H.V., Smolders, C.A., Strathmann, H., Diffusion induced phase separation with crystallizable nylons. II. Relation to final membrane morphology. J. Memb. Sci., 121(1), 51–58, 1996. 52. Lhommeau, C., Toillon, S., Pith, T., Kessler, L., Jesser, C., Pinget, M., Polyamide 4,6 membranes for the encapsulation of Langerhans islets: preparation,

104 High Performance Polymers and Their Nanocomposites physico-chemical properties and biocompatibility studies. J. Mater. Sci. Mater. Med., 8(3), 163–174, 1997. 53. Xiang, F., Li, T.-sheng., Liu, X.-jun., Cong, P.-hong., Lv, R.-guo., Effect of compatibilizer on the transfer and tribological behaviors of PA46/HDPE polyblends. Tribol. Lett., 22(3), 279–288, 2006. 54. Cong, P., Xiang, F., Liu, X., Li, T., Effect of crystalline form on the tribological properties of PA46/HDPE polyblends. Wear, 265(7–8), 1106–1113, 2008. 55. La Carrubba V, Bulters M, Zoetelief W. Dependence of coefficient of volumetric thermal expansion (CVTE) of glass fiber reinforced (GFR) polymers on the glass fiber content. Polym Bull, 59(6), 813–824, 2008. 56. Zhang, Z., Friedrich, K., Velten, K., Prediction on tribological properties of short fibre composites using artificial neural networks. Wear, 252(7–8), 668– 675, 2002. 57. Jiang, Z., Zhang, Z., Friedrich, K., Prediction on wear properties of polymer composites with artificial neural networks. Compos. Sci. Technol., 67(2), 168– 176, 2007. 58. Reinicke, R., Haupert, F., Friedrich, K., On the tribological behaviour of selected, injection moulded thermoplastic composites. Composites Part A, 29(7), 763–771, 1998. 59. Chiu, F.-C., Kao, G.-F., Polyamide 46/multi-walled carbon nanotube nanocomposites with enhanced thermal, electrical, and mechanical properties. Composites Part A, 43(1), 208–218, 2012. 60. Chiu, F.-C., Huang, I.-N., Phase morphology and enhanced thermal/mechanical properties of polyamide 46/graphene oxide nanocomposites. Polym. Test., 31(7), 953–962, 2012. 61. Yanagihara, N., Ohgane, K., Studies on the oxidative degradation of nylons by nitrogen dioxide in supercritical carbon dioxide. Polym. Degrad. Stab., 101, 115–121, 2014. 62. Polk, M.B., Leboeuf, L.L., Shah, M., Won, C.-Y., Hu, X., Ding, W., Nylon 66, nylon 46, and Pet phase-transfer-catalyzed alkaline depolymerization at atmospheric pressure. Polym. Plast. Technol. Eng., 38(3), 459–470, 1999. 63. Vulic, I., Jacobs, R.E.W.E., Thermal catalytic depolymerization of polyamides. Polymer Bulletin, 31(1), 55–60, 1993. 64. Wevers, M.G.M., Mathot, V.B.F., Pijpers, T.F.J., Goderis, B., Groeninckx, G., Progress in Understanding of Polymer Crystallization. In: Reiter G, Strobl G. R, eds. Full dissolution and crystallization of polyamide 6 and polyamide 4.6 in water and ethanol. 714. Springer. pp. 151–168, 2007. 65. Vinken, E., Terry, A.E., van Asselen, O., Spoelstra, A.B., Graf, R., Rastogi, S., Role of superheated water in the dissolution and perturbation of hydrogen bonding in the crystalline lattice of polyamide 4,6. Langmuir, 24(12), 6313– 6326, 2008.

4 Polyacrylamide (PAM) Małgorzata Wiśniewska Department of Radiochemistry and Colloids Chemistry Faculty of Chemistry, Maria Curie-Sklodowska University

Abstract Polyacrylamide (PAM) polymers are synthetic group of a great variety of macromolecular compounds. Owing to the wide possibilities of their macromolecules modification, many substances differfing in structure and properties can be obtained. Among them non-ionic, anionic, and cationic polyacrylamides, as well as polyacrylamide gels can be distinguished. Polyacrylamide is well soluble in water, viscosity of its solution is linearly dependent on polymer molecular weight, and PAM amide with weak basic character undergoes reactions of hydrolysis, halogenation, methylation, and sulfonation. This polymer is used as a modifier of solid surface properties in various composite materials (including nanocomposites) and formation of polymeric blends with different additives. The most important PAM practical applications cover areas of wastewater purification, oil extraction from natural reservoirs (enhanced oil recovery method), control of soil rain erosion, mineral processing, metallurgy, papermaking industry, food processing, cosmetics production, drug delivery systems, etc. The range of potential applications of PAM is constantly increasing owing to the intensively developing procedures of its modification and preparation of new hybrid materials. Keywords: Polyacrylamide, ionic PAM, cationic PAM, adsorption, copolymerization, PAM gels, PAM blends, PAM composites

4.1

Introduction and History

The group of synthetic polymers known as polyacrylamides (PAM) includes a large number of macromolecular compounds possessing neutral (non-ionic) and ionic character—anionic, cationic, and amphoteric [1]. A Corresponding author: [email protected] Visakh P.M. and Semkin A.O. (eds.) High Performance Polymers and Their Nanocomposites, (105–132) © 2019 Scrivener Publishing LLC

105

106 High Performance Polymers and Their Nanocomposites CH

C NH2

CH2

CH

O

C

n

NH 2

CH2

O

n

Figure 4.1 Delocalization of electrons in the amide group—boundary resonant structures.

great variety of polyacrylamide polymers with different charge densities, molecular weights (reaching up to several million Daltons), and structures (linear, branched, and crosslinked—gels) can be obtained. Non-ionic PAM, containing only amide groups, exhibits high hydrophilic character— greater than that of the other water-soluble polymers [2]. This results from the fact that in the amide group there is a coupling of the free electron pair of the nitrogen atom with the double bond of the carbonyl group. In this way, the resonant structures are formed (Figure  4.1). The occurrence of such bipolar boundary moieties causes that the polyacrylamide is a compound of high polarity (high values of dipole moment) [3]. The evidence of strong hydrophilic character of polyacrylamide is the absence of phase separation in the PAM aqueous solutions within the wide temperature range covering the broadly understood standard conditions. The ideal (theta) temperature of this system is equal to −38 °C (θ—phase separation occurs as a result of cooling) [4]. Moreover, PAM was soluble in nonaqueous liquids, such as formamide, ethylene glycol, and glycerol characterized by hydrophilic properties. Polyacrylamide is insoluble in the other organic solvents, that is, acetone, aliphatic alcohols, aliphatic, and aromatic hydrocarbons. The first synthesis of polyacrylamide was performed in 1893 by Charles Moreau—the French pharmacist and chemist. He obtained PAM using acryloyl chloride and ammonia at low temperature. The commercial production of PAM began in the United States in 1954. The acrylamide (AM) monomer obtained from acrylonitrile was used in homopolymerization to obtain non-ionic polyacrylamide. Next, the alkali hydrolysis of amide groups in neutral polymer to carboxyl ones led to the anionic polyacrylamide preparation. In the 1970s, the American Merck and Halliburton companies carried out the first successful synthesis of cationic polyacrylamide—Poly(DiMethylDiAllylAmmonium Chloride)—PDMDAAC. In the 1990s, the synthesis methods concerning the amphoteric and zwitterionic forms of polyacrylamide were developed. The polyacrylamide gel (crosslinked form of acrylamide and bisacrylamide copolymer) was used

Polyacrylamide (PAM) 107 CH n C NH2

CH2 O

CH initiator

C

CH2 O

NH2

n

Figure 4.2 Basic reaction of non-ionic polyacrylamide synthesis.

for the protein separation by electrophoresis for the first time in 1959 (so called polyacrylamide gel electrophoresis technique [5]). The most important areas of polyacrylamide applications are the flocculation process in the wastewaters treatment, enhanced oil recovery, sludge dewatering, paper production, and improvement of cultivated soil stability [6–11].

4.2

Polymerization and Fabrication

Non-ionic PAM is obtained in the reaction of radical polymerization of acrylamide in the aqueous solution (Figure 4.2) [12]. The redox systems consisting of potassium persulfate (K2S2O8) and sodium hydrogen sulfate (NaHSO4) are used as an initiator [13]. The conditions of polymerization reaction are as follows: temperature 20–35 °C, pH 4–5.5, and time 5–7 hr [14]. In this reaction, heat in an amount of 81.7 kJ/mol is produced. The molecular weight of the polymer is controlled by the addition of isopropyl alcohol or sulfur compounds. Temperature is the most important parameter in the non-ionic PAM synthesis, because above 60 °C hydrolysis of amide groups to carboxyl ones takes place. In this way, the anionic form of polyacrylamide (AN PAM) can be obtained. The inverse emulsion polymerization proceeds in the water–oil (w/o) emulsion, in which monomer aqueous solution represents the dispersed phase and the organic solvent is the dispersive medium. This technique is used for preparation of hydrophilic polymers, for example, polyacrylamides [15]. The process is very fast. The rate of inverse emulsion polymerization increases with the initiator concentration increase and significantly decreases with the emulsifier concentration rise. Among the methods of anionic PAM synthesis, the greatest importance was gained by homopolymerization with the alkaline hydrolysis process and copolymerization reaction [16].

108 High Performance Polymers and Their Nanocomposites CH2 CH

n

CH2 CH

m

CH2 CH

C O

C O

C O

NH2

O Na

NH2

CH2 CH

m C O

HN

SO3 Na

O

R

O

n

N H

O Na

SO3 Na

O NH2

Figure 4.3 Copolymerization reaction of acrylamide (AM) with the anionic monomers— SA and AMPS. http://read.nxtbook.com/wiley/plasticsengineering/september2014/ watersolublefreeradicaladd.html

The first way involves the non-ionic polyacrylamide polymerization and hydrolysis of its neutral amide groups to carboxyl ones under alkaline conditions (pH >7). The hydrolysis process can be performed after the PAM polymerization (homopolymerization posthydrolysis process) or during the polymerization reaction (homopolymerization cohydrolysis process). The copolymerization reaction of acrylamide (AM) with another anionic monomer leads to the ionic polymer formation. As the anionic monomer, acrylic acid (AA) and its sodium (sodium acrylate—SA) as well as ammonium salts (2-acylamido-2-methylpropane sulfonic acid— AMPS) can be applied (Figure 4.3). The main reaction of cationic polyacrylamide (CT PAM) synthesis is free radical copolymerization of acrylamide with the cationic monomer. The most commonly used monomers containing positively charged functional groups are as follows: acryloxyethyltrimethyl ammonium chloride (DAC), methaacryloxyethyltrimethyl ammonium chloride (DMC), dimethyldiallyl ammonium chloride (DMDAAC), diallyldimethyl ammonium chloride (DADMAC), and acryloyloxyethyltrimethyl ammonium chloride (AETAC) [17]. The exemplary copolymerization reactions leading to the CT PAM obtaining are presented in Figure 4.4. The free radical copolymerization of anionic and cationic PAM synthesis can be realized using different synthesis technologies, i.e. aqueous solution polymerization, dispersion polymerization [18], inverse emulsion polymerization, as well as photo [19] and ionizing radiation [20] initiated polymerization. The amphoteric polyacrylamide (AM PAM) can be obtained through seeded dispersion copolymerization using acrylamide,

Polyacrylamide (PAM) 109 O NH2 O N Cl

N CH3)3Cl

O

R

CH2 CH C O

n

CH2 CH C O

R

m

CH3 O CH2 CH2 N CH3 CH3

NH2

n C O N NH2

m

Figure 4.4 Copolymerization reaction of acrylamide (AM) with the cationic monomers—AETAC and DADMAC. http://read.nxtbook.com/wiley/plasticsengineering/ september2014/watersolublefreeradicaladd.html CH2 CH

CH2 CH

CH2 CH

CH2 CH

CH2 CH

C O

C O

C O

C O

C O

NH2

NH

NH2

NH2

NH2

NH2

NH2

NH2

C O

C O

C O

CH2 NH C O CH2 CH

CH2 CH

CH2 CH

CH2 CH

Figure 4.5 Copolymerization reaction of acrylamide (AM) with bis-acrylamide. http:// www.bio-rad.com/LifeScience/pdf/Bulletin_1156.pdf

methacrylatoethyltrimethyl ammonium chloride, and acrylic acid as monomers in the ammonium sulfate solution [21]. Polyacrylamide gels (PAG) are formed in the copolymerization reaction of acrylamide and bis-acrylamide (N,N’-methylene-bis-acrylamide) (Figure  4.5). This reaction is usually initiated by ammonium persulfate ((NH4)2S2O8) and tetramethylethylenediamine. The latter one enhanced free radicals formation from (NH4)2S2O8. Next, the formed radicals react with acrylamide monomers converting them into free radicals. Activated monomers participate in the copolymerization reaction. The formed polymeric chains are randomly crosslinked by bis-acrylamide, and gel structures are created. The size of gel pores can be controlled by the monomer concentration and the copolymerization conditions (initiator type, temperature, oxygen presence, solution pH, time) [22].

110 High Performance Polymers and Their Nanocomposites

4.3

Properties

Polyacrylamide with the molecular formula (C3H5NO)n is called, according to the IUPAC nomenclature, poly(2-propenamide) or poly(1-carbamoylethylene). Polyacrylamide can be present in three different forms: solid—as a white powder or microbeads, aqueous solution or inverse emulsion—PAM is located in the water droplets coated with a surfactant and suspended in mineral oil. The PAM density is 1.302 g/cm3 (23 °C), the refractive index is n20/D 1.452, the glass transition temperature is 153 °C, and the softening temperature is 210 °C. It has good thermal stability [23, 24]. Polyacrylamide is well soluble in water, even in cold liquid (under mechanical stirring conditions) forming a transparent solution. Temperature practically does not influence its solubility in the case of PAM with a lower molecular weight and a low polymer concentration. For high viscosities of aqueous polymer solution (provided by high PAM concentration and high molecular weight), the amount of dissolved polymer depends on temperature. Polyacrylamide has a limited solubility (over 1%) in other solvents, such as glycerol, ethylene glycol, formaldehyde, acetic acid, and lactic acid. For this reason, these compounds can be used as a plasticizer in the laminating process of polyacrylamide. PAM undergoes swelling (without dissolving) in propionic acid and propylene glycol; whereas, it is not soluble in acetone and hexane [25]. PAM exhibits medium hygroscopic properties. Polyacrylamide in the form of powder can be stored for the long period of time. As for the liquid form of polyacrylamide (when PAM concentration is greater than 17%) in the pH range 3–9, no significant changes in the solution viscosity are observed. The time of such solutions storage can be even longer than one year. The viscosity of polyacrylamide solution increases linearly with the rise of its molecular weight [26, 27]. Even small concentrations of highmolecular polyacrylamide can affect strongly the intrinsic viscosity of its solution. This property finds practical usage in the process supporting the oil extraction from the natural reservoir [28]. The ionic form of highmolecular polyacrylamide (with the molecular weights of the order of several and dozen million Daltons) possesses strong flocculation properties. The PAM macromolecules show great affinity for solid particles leading to their binding through the polymer bridges. In such a way, the effective flocculation of dispersed particles occurs and the undesirable solid phase can be successfully separated from the liquid. The polyacrylamide

Polyacrylamide (PAM) 111 flocculants are widely and commonly applied in water treatment technologies [29, 30].

4.4

Chemical Stability

The amide groups in the PAM structure are of significantly weaker basic character (and simultaneously stronger acidic nature) compared to the amine groups. The main reason for this is the presence of the acyl fragment –CO– bound directly with nitrogen atom in the PAM -CONH2 functional group. Polyacrylamide is chemically active and can react with many compounds [31, 32]. The PAM amide groups undergo reactions that are similar to those of amides with small molecular weight. From the practical point of view, the most important reaction of polyacrylamide is the hydrolysis process leading to obtaining the PAM anionic form (see section 4.2) [33]. This reaction results in the anionic carboxyl groups formation in the following way: − − − → − − − (4.1) Polyacrylamide hydrolysis is irreversible. It can proceed in both acidic and alkaline solutions according to the following reactions: −

−

−

−

−

−

→ − − −−→ −

− −

−

(4.2) (4.3)

− −

As a result of Hofmann’s degradation (under the action of HBrO), the polymer amide groups were converted to the primary amine ones (conversion degree about 94%)—the polyvinyl amine is formed [34]: −

−

− −−−→ −

−

−

(4.4)

Applying the PAM reaction with 80% hydrazine, polyacrylic hydrazide is formed (the conversion degree of amide groups is about 85%) [12]: −

−

− −−−−−−−→ −

−

−

−

−

(4.5)

The N–H bond in the PAM amide groups undergoes halogenation and bromination according to the following reaction [3]: −

−

− −−−−−−→ −

−

−

(4.6)

The polyacrylamide reaction with formaldehyde in the alkaline solution leads to the methylolation of its functional groups [2]: −

−

− −−−→ −

−

−

(4.7)

112 High Performance Polymers and Their Nanocomposites The compound obtained in the above reaction (7) can be subjected to sulfonation using sulfate(IV) or bisulfate(IV) [2]: −

−

− −−−→ −

−

− −

(4.8) As a result of such modification, the sulfomethylol groups of strong acidic character are introduced into the polymeric macromolecules. Additionally, the methylated groups of PAM can be treated by amine in the Mannich reaction [2]: −

−

− −−−→ −

−

−

(4.9) This process leads to the secondary amine groups formation in the polyacrylamide chains. These groups have stronger basic character than the primary amine groups produced in the Hofmann degradation.

4.5

Compounding and Special Additives

In order to change polyacrylamide properties and its aqueous solution (especially rheological), special additives can be applied. Viscosity of polyacrylamide dilute aqueous solutions can be modified by the sodium chloride, glucose and SDS (sodium dodecyl sulfate) addition [35]. It was shown that the PAM solution conditions determine conformation of macromolecules and their swelling properties. The polymer chain conformations became more and more expanded when NaCl concentration increased and the surfactant reached the SDS critical micelle concentration. Moreover, the viscosity of the dilute PAM solutions in water with acetone, ethanol, DMF (dimethylformamide), and ethylene glycol as a co-solvent was examined. For the water–acetone, water–ethanol, and water–DMF co-solvent systems, the polyacrylamide chains showed the coil-globule transition when the volume fraction of the second solvent increased. The viscosity of hydrolyzed polyacrylamide (polyelectrolyte) in the presence of different additives: NaCl salt, N-dodecylpyridinium chloride surfactant (DPC) and poly(4-vinylpyridine) was examined by Mansri and co-workers [36]. They proved that the DPC caused a larger reduction of the polymer viscosity than sodium chloride. Niranjan and Upadhyay [37] studied the effects of two cationic surfactants (dodecyl trimethyl ammonium bromide—DTAB and benzalkonium chloride—BZK) on polyacrylamide surfactant interactions. The surfactant

Polyacrylamide (PAM) 113 structure influenced both ability of the surfactant–PAM complexes formation and their CMC values. It was shown that the surfactant–polymer interactions were favored by the increase in the polymer concentration, number of –CH2 groups in the surfactant tail, and the volume of the surfactant hydrophobic head group. Ye et al. [38] synthesized the hydrophobically associated polyacrylamide (HAPAM) which contained 79.7% of amide groups, 20.2% of anionic carboxylic groups, and 0.1% of cationic groups. They examined HAPAM interactions with the zwitterionic surfactant—dodecyl dimethyl betaine (BS-12). The surface and interfacial tension measurements, apparent viscosity data, aggregation behavior, and microscopic morphology indicated that the interface activity of BS-12 surfactant was affected strongly by the polymer presence and its concentration. The interactions between the HAPAM polymer and the anionic gemini surfactant were studied by Hong and co-workers [39]. The surface/interfacial tension, apparent viscosity, and atomic force microscopy studies indicated the presence of mixed micelles. They are formed in the aqueous solution through the interactions of the gemini surfactant normal micelles and the hydrophobic parts of polymeric chains. Similar studies concerning the polyacrylamide interactions with different types of surfactants are represented widely in the scientific literature [40–44]. The effect of introduction of lithium perchlorate into the polyacrylamide hydrogels using vibrational Raman spectrometry was also studied [45]. It was evidenced that the polymeric matrix consisted of lithium and perchlorate ions separated from each other by the polyacrylamide coils. The LiClO4 additive disturbed the hydrogen bond network between the polymer and interstitial water. As a result, the hydrogel flexibility increased—the amide groups became more accessible to chemical reactions with lithium ions.

4.6

Processing

The polyacrylamide coated silicon carbide (SiC) powder was used for the preparation of homogeneous and stable suspensions containing 55 vol.% of solid at pH 5. These suspensions were characterized by proper rheological properties and low viscosities [46]. The displacement reaction for the kaolinite–formamide intercalation precursor with acrylamide was used to the kaolinite–polyacrylamide intercalation compound preparation. Polymerization was carried out at 140 °C

114 High Performance Polymers and Their Nanocomposites for 15 h with dibenzoyl peroxide as a catalyst. Then, carbothermal reduction and nitridation (CRN) at 1400 °C of the obtained kaolinite–polyacrylamide intercalation compound led to sialon (SiAlON ceramics) formation [47]. This high-temperature refractory ceramics was characterized by high strength, good thermal shock resistance, and exceptional resistance to wetting or corrosion caused by molten non-ferrous metals. Zou et al. [48] used anionic polyacrylamide for adsorption on the surfaces of ultra-low ash coal and kaolinite particles causing their selective flotation. The obtained results indicated that the physical interactions were responsible for the adsorption process, and the adsorbed PAM amount onto coal was over twice as large as that on kaolinite. It resulted in different wettability of these solids (coal became less hydrophobic), but selective enlargement of the coal particle size strengthened the fine coal flotation. Ding and Laskowski [49] proved that the dosage of quaternary amine collector in the process of coal reverse flotation could be significantly reduced by the usage of polyacrylamide (as a blinder in the potash flotation). It was shown that the reverse flotation with the simultaneous addition of PAM was selective only under specific conditions (associated with the degree of polymer anionicity). The gangue flotation was promoted only after the addition of PAM characterized by a low degree of anionicity. The quality of the clean coal was improved by formation of selective flocculated solid particles which next floated with the quaternary amine compound. Polyacrylamide and its derivatives are also used in paper making technologies. For example, N-chloropolyacrylamide (N-Cl-PAM) obtained from the N-chlorination of polyacrylamide was applied for the improvement of paper strength [50]. It was proved that N–Cl–PAM reacts with the hydroxyl and carboxyl groups of the cellulose forming strong covalent bonds between the polymeric agents and fibers. The amphoteric and cationic PAM was used as a dry strength agent in coir-based paper production [51]. These polymers were added to the coir pulp slurry in different dosages (0.5–2.0%) during stock preparation. The obtained results showed that the application of cationic PAM had better drainage compared to the anionic one.

4.7

Applications

The most important field of polyacrylamide application (especially its ionic forms) is the flocculation process of undesirable suspended solids [52–55] as well as removal of polyvalent metal ions, organic compounds, and microorganisms [56–59]. These phenomena are used in the procedures

Polyacrylamide (PAM) 115 of industrial waste water purification and drinking water treatment. PAM ability to form polymeric bridges between the colloidal particles and their effective aggregation makes polyacrylamide a very common flocculant. Contrary to coagulation (caused by simple electrolyte ions, flocculation (caused by polymeric substances) can occur even at high values of zeta potential and surface charge of solid particles. Coagulation proceeds in the colloidal suspension characterized by the zeta potential close to or equal to zero, and this is a result of disappearance of electrostatic repulsion forces between the solid particles (leading to their aggregation). Owing to a diverse structure and ionic character of polymers from the group of polyacrylamides, PAMs play a role of effective flocculants for many different classes of chemical substances (occurring in both solid and liquid phases). In addition, high viscosity of aqueous solutions with even low concentrations of polyacrylamide is decisive for its use in the oil extraction supporting processes. The enhanced oil recovery (EOR) method involves the injection of displacing fluid (for example the aqueous solution of PAM) in natural reservoirs for extraction of the oil trapped in the porous rocks [60, 61]. The polyacrylamide addition results not only in the solution viscosity increase but also in the decrease of interfacial tension between the oil and water. These two parameters are essential for efficiency of raw material extraction from natural deposits. Another important area of application of polyacrylamides (especially cross-linked) is agriculture [62, 63]. PAM is extremely efficient as the rain erosion control agent. This is due to the fact that the polymer presence improves considerably the consistency of the soil by binding loose solid particles (simultaneously maintaining surface roughness and continuity of pores). As a consequence, a significant increase in the infiltration of water occurs. In addition, PAM slightly increases the viscosity of the soil, reducing the distance between the particles. The sediment transport is also limited owing to PAM strong flocculation properties. As a result, leaching of soil during heavy rainfall is practically eliminated. Ionic polyacrylamides are also used in gardening as a nutritionalsupplement for arable land [64, 65]. They increase the aeration and porosity of the soil and reduce the packing, dust and water outflow of the soil. In this way, the substantial improvement in vigor, color, rooting depth and efficiency of seeds formation of crop plants is achieved. The other advantages of the polyacrylamide fertilizers use are as follows: reduction of water consumption, elimination of diseases and limitation of cultivation costs. Polyacrylamide hydrogels (systems in which the dispersed phase is water) are used in the production of compresses for the treatment of burns and as a soft-tissue filler in the reconstruction processes in human body

116 High Performance Polymers and Their Nanocomposites [66, 67]. They are also applied in molecular biology as a medium within which electrophoresis of proteins and nucleic acids takes place (Polyacrylamide Gel Electrophoresis—PAGE technique) [68–70]. Electrophoresis allows the separation of biomolecules regarding their charge and molecular weight (size). Two variations of this method in relation to proteins are used: electrophoresis under the native (non-denaturing) conditions and electrophoresis under the denaturing conditions (SDS-PAGE). In the latter case, the use of anionic surfactant SDS—sodium dodecyl sulfate is required. As a result, all components of the probe have the same charge and their electrophoretic mobility is therefore only a function of biopolymer molecular weight. The other applications of polyacrylamide include the following: mining operations, mineral processing, metallurgy, papermaking industry, food processing, cosmetics production, and drug delivery systems.

4.8

Blends of Polyacrylamide

The polyacrylamide blending with ammonia borane (AB) was prepared through a sol-mixing method by Li and co-workers [71]. This blend was used as a new polymeric storage of hydrogen. The dehydrogenation kinetics and the possible way of H2 release were examined. It was demonstrated that the dehydrogenation properties of AB-PAM blend are significantly better than pure ammonia borane. The obtained blend was characterized by the relatively low temperature of H2 release (equalled to 75 °C), lack of induction period, and considerable reduction of boracic impurities emission. Lewandowska [72, 73] examined the surface, viscometric and mechanical properties of chitosan/polyacrylamide (Ch/PAM) and chitosan/ partially hydrolyzed polyacrylamide (Ch/HPAM) blends of different compositions (prepared by the casting technique). The contact angle and surface free energy results proved that HPAM films are more polar than the chitosan ones. It was indicated that the used blends were miscible for all applied compositions in the mixed solution of CH3COOH and NaCl at 25 °C. The mechanical properties (ultimate tensile strength and Young modulus) were dependent on the content of chitosan and were changed irregularly. The polyacrylamide blends with other synthetic polymers were prepared and fully characterized. For example, PAM hybrid with poly(vinyl alcohol)—PVA was prepared through the blending of PAM and PVA using crosslinking with glutaraldehyde (Glu) [74]. Cesium salts of different

Polyacrylamide (PAM) 117 heteropolyacids (phosphomolybdic acid (PMA), phosphotungstic acid (PWA) and silicotungstic acid (SWA)) were introduced into the polymer network. The obtained membranes were characterized by low methanol permeability. They can be applied as the direct methanol fuel cell (DMFC) [74]. Nazim El-Din et al. [75] prepared films of polymer blends having various contents of PAM and PVA by the solution casting technique using water as a solvent. These blends were exposed to various doses of gamma radiation, up to 100 kGy. Thermal, mechanical, and morphological properties of the obtained materials were examined before and after exposure to the ionizing radiation. Compatibility and mechanical properties of the PAM/PVA blends were also studied theoretically using five molecular dynamic simulation models [76]. The blends of PVA and polyvinyl pyrrolidone—PVP were prepared and tested for their usage as corrosion inhibitors for aluminum in the acidic medium in the temperature range of 30–60 °C [77]. It was shown that as a result of PAM and PVP blending, the inhibition efficiency was improved and it increased with the increase of PVP content in the blend (which confirmed that PVP is a better inhibitor than PAM). Polyacrylamide blends with poly(ethylene oxide)—PEO were obtained in the form of stable, semi-transparent, flexible and free standing films and their properties were characterized by the FTIR analysis, Raman spectroscopy, Differential Scanning Calorimetery (DSC), Thermo Gravimetric Analysis (TGA), Derivative Thermo Gravimetric Analysis (DrTG), and UV–Vis spectrophotometry [78]. It was shown that the blend of PAM/PEO with 70/30 wt% had the best thermal, optical, and mechanical properties. The natural polymers were also used in the process of polyacrylamide blending. The biomedical important blends composed of Xanthan gum and polyacrylamide were prepared by Bhat and co-workers [79]. Sorour et al. [80] determined the best conditions for grafting of acrylamide monomers with selected polysaccharides (starch, chitosan, and alginate) using microwave and ultraviolet irradiation techniques. Potassium persulfate as an initiator and methylenebisacrylamide as a crosslinker were used in blends formation. The polyacrylamide blends containing plant fiber (cellulose) were prepared by the Abdelhak group [81]. They examined the effects of concentration of polyacrylamide, Stipa tenacissima L. fiber (from esparto grass) and their mixtures on the water retention in arid and semi-arid soil. The obtained results showed that polymer blend introducing to soil improved considerably its physical proprieties decreasing evaporation and

118 High Performance Polymers and Their Nanocomposites increasing water retention (in comparison to the other blends at the same concentration).

4.9

Composites of Polyacrylamide

Wiśniewska et al. prepared and examined the PAM composites with various metal oxides (chromium (III) oxide, aluminium(III) oxide, iron(III) oxide, silicon(IV) oxide, and magnesium(IV) oxide) [82–91]. Both nonionic and ionic (cationic and anionic) types of PAM were applied. The influence of many parameters related to the polymer and adsorbent as well as the environment conditions were examined. There were: PAM molecular weight and concentration, type and content of ionic functional groups in the polymer macromolecules, kind and concentration of the solid surface groups, pH of the solution, supporting electrolyte presence, temperature, and anionic surfactant (SDS) addition. The obtained spectrophotometric (polymer adsorbed amounts), electrokinetic (solid surface charge density and zeta potential determination), viscosimetric, thermogravimetric, and turbidimetric results enabled determination of more probable mechanism of PAM adsorption on the metal oxide surface and proved the dominant role of hydrogen bonds in this process (especially under unfavorable adsorbent–adsorbate electrostatic repulsion). It was shown that the specific conformation of adsorbed polyacrylamide macromolecules under given conditions influenced directly the stability properties of solid suspension whose particles were covered with polymeric layers. As a result of detailed analysis of the obtained data, the mechanism of colloidal suspension of metal oxide stabilization (steric, electrosteric) or destabilization (bridging flocculation, solid surface charge neutralization) in the polymer presence was proposed. Such knowledge enabled effective control of the stability of aqueous suspension of the solid containing a selected polymer which is very important from a practical point of view in relation to the application of polyacrylamide-metal oxide systems in medicine, pharmacy, cosmetology, agriculture, environment protection, and many other fields of human activity. The β-zeolite composites with polyacrylamide were prepared and used for removal of lead from the aqueous solution by Faghihian and Farsani [92]. Ulusoy and Simsek used polyacrylamide–bentonite and zeolite composites for Pb2+ ions separation [93]. The hybrid materials of natural (clinoptilolite) and synthetic (Z and YZ) zeolites with polyacrylamide were synthesized and examined concerning their adsorptive properties of

Polyacrylamide (PAM) 119 terbium ions (Tb3+) using the isotopic tracer method (160Tb was the radiotracer) [94]. The composites of polyacrylamide with carbon materials were also synthetized and characterized. For example, graphene oxide (GO) was added to the PAM hydrogels to modify their mechanical and thermal properties [95, 96]. The graphene–polyacrylamide composite was successfully used as a sensitive and selective H2O2 electrochemical sensor [97]. The electrical properties (conductivity) of multi-walled carbon nanotubes of the (MWNTs)-polyacrylamide composites prepared using the solution cast technique were characterized through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) [98]. Similar composites were examined by the fluorescence technique to explain the phenomena occurring during drying of the obtained gel [99]. The agarose–acrylamide composite native gel (CNG) system was prepared and used for separation of protein complexes characterized by the ultra-large molecular sizes (over 500 kDa). The protein–protein interactions in their native states were also analyzed [100].

4.10

Nanocomposites of Polyacrylamide

The polyacrylamide-silica nanocomposites can be prepared by the sol– gel reaction of tetraethoxysilane (TEOS) with polyacrylamide in aqueous solution [101, 102]. The obtained material was characterized by the particle–matrix morphology and the hydrogen bonding interactions playing an important role in its structure stabilization. Moreover, with the increase of TEOS content the effect of aggregate formation was more probable than the single particle growth. Such silica–PAM nanocomposite material can be used to improve the corrosion inhibition of steel subjected to unfavorable processing or environmental conditions [103]. Moreover, such hybrid material had the dielectric constant and the dielectric loss smaller than those obtained for the polymer without silica [104]. Wiśniewska et al. [105–107] examined the composites of ionic polyacrylamide (both anionic and cationic) with nanozirconia. The effects of the type of functional groups in polyacrylamide and solution pH on the adsorption, electrokinetic and stability properties of aqueous nanozirconia suspension were examined. It was demonstrated that with the pH rise adsorption of anionic PAM (containing carboxyl groups) decreases, whereas in the case of cationic PAM (containing quaternary amine groups) - it increases. The greatest impact of ZrO2 suspension stability is found for cationic PAM at pH 6 (significant improvement of dispersed system

120 High Performance Polymers and Their Nanocomposites stability). The electrosteric repulsion between the solid particles covered with the polymer possessing significantly extended conformation (total dissociation of polymer ionic groups) was responsible for it. The obtained results can be helpful for the development of modern implant coatings for tissue regeneration (excellent biocompatibility of ZrO2 with human tissue) and innovative drug delivery nanosystems (diagnostics and treatment of various diseases in medicine). The polyacrylamide nanocomposites with various metals were also prepared, and their properties were examined [108]. These composites have the advantageous properties of metals and polymers as well as exhibit many new features (which may be applied in catalysis, electronics, optics, medicine, and cosmetology). The homogeneous distribution of metal nanoparticles in the PAM matrix was a result of the polymerization of the acrylamide monomer and simultaneous formation of metal nanoparticles. Ni and co-workers [109] prepared in situ gold/polyacrylamide hybrid nanoparticles (Au/PAM) in an ethanol solution at room temperature and normal pressure using γ irradiation. Pan and Chen [110] obtained the polyacrylamide silver/polyacrylamide (Ag/PAM) nanocomposites subjecting the mixture of silver nitrate (AgNO3) and PAM solutions to ultraviolet irradiation. Such mixture can be also heated in an oven at 100 °C for 7 h, leading to the same hybrid product formation [111]. Another way of silver–polyacrylamide nanocomposite preparation is the reduction of the silver salt in the polyacrylamide matrix [112]. Different ways of synthesis of PAM nanocomposites with other metals (e.g., Pt, Pd, Cu) were described in many papers [113–115]. The other natural materials such clay [116], chitosan [117], starch [118], carbon nanotubes [119], and hydroxyapatite [120] were applied for preparation of advanced nanomaterials with polyacrylamide. Polyacrylamide was also used for stabilization on the enzyme nanoparticles, that is, β-dxylosidase, endoxylanase, and endocellulase enzymes isolated from the Thermobifida fusca moderate thermophile organism [121]. The polymeric layer had a porous structure which enabled effective diffusion of substrate molecules to the active center of the enzyme particle (the catalytic activity was maintained). It was shown that all enzymes are significantly more stable in their hybrids with polyacrylamide in comparison to their native forms.

4.11

Environmental Impact and Recycling

As already mentioned acrylamide monomers are used for the preparation of polyacrylamide. Owing to the high toxicity of acrylamide, polymerization

Polyacrylamide (PAM) 121 product must be separated from the remaining monomeric form. The high reactivity of acrylamide is a result of the presence of the conjugated double bonds of an electrophilic character and an amide group, which easily forms hydrogen bonds. Acrylamide is formed during thermal processing (above 120 °C) of food products rich in carbohydrates, mainly starch [122, 123]. It should be noted that only acrylamide in the monomeric form has toxic properties, whereas after the polymerization reaction it is neutral for human health. Acrylamide irritates the nervous system (neurotoxin) and damages the nerve cells. This compound is metabolized in the liver and is converted to more reactive and dangerous derivatives. Furthermore, it is accumulated in the body since only 10% of its contents is subjected to the process of excretion with urine [124]. Several studies have shown that it causes cancers of digestive tract, breast, and urinary bladder. Polyacrylamide shows a good biodegradability. Partially hydrolyzed polyacrylamide (HPAM) was degraded in an aerobic environment by bacterial stain (Bacillus cereus) isolated from the produced water of polymer flooding [125]. It was shown that their amide groups were the nitrogen source for microorganisms and were converted to carboxyl groups. On the other hand, the carbon backbone of these polymers could be partly utilized by the bacteria during the course of its growth. What is important, no acrylamide monomer was found. The other studies [126] confirmed that the bacterial strain (Pseudomonas putida) isolated from the dewatered sludge could metabolize PAM. The efficiency of PAM degradation was 45% under the optimum culture condition (pH 7.2, 39 °C and 100 rpm) and after the yeast extraction or glucose addition. The main products of polyacrylamide degradation were small molecular-weight oligomer derivatives in which the part of the amide groups was converted to carboxyl ones. The biodegradation did not lead to acrylamide monomers formation. Many other papers reported the efficient degradation of polyacrylamide and its ionic forms using chemical methods. Electrochemical degradation of polyacrylamide solution was examined using the three-dimensional electrode reactor, with granular activated carbon (GAC) as particle electrodes [127]. To generate hydrogen peroxide and Fenton’s electro-reactions [128], air and ferrous salt were introduced into the system. The conditions of satisfactory chemical oxygen demand removal efficiency (84%) were determined. It was shown that applied method can be an alternative way to PAM wastewater pre-treatment before being subjected to the biological process.

122 High Performance Polymers and Their Nanocomposites It was also demonstrated that chemical degradation of polyacrylamide by the alkaline hydrolysis undergoes rapidly and efficiently [129]. Significant hydrolysis takes place in the presence of sodium carbonate within 1–2 months (even at room temperature).

4.12

Conclusions

Owing to very good solubility in water, non-toxicity, biodegrability, and possibility of different modifications, polyacrylamide is a very important synthetic polymer, which finds application in many fields of human activity. There are a large number of known and described methods of synthesis of both ionic (anionic, cationic, zwitterionic) PAM linear macromolecules and cross-linked polymer network (polyacrylamide gels). The PAM molecular weight includes a broad range from a few thousand to a few million Daltons. The low-molecular weight polyacrylamides are usually used for stabilization of particles with the colloidal size (1–1000 nm). The mechanism of this process is steric or electrosteric—the polymeric layers formed on the particle surfaces ensure effective repulsion and prevent their aggregation. In the case of steric mechanism, the polymeric hindrance is formed; whereas, for the electrosteric mechanism, the charge coming from the functional groups of ionic polymer is additionally responsible for effective particle repulsion. On the other hand, high-molecular weight polyacrylamides are very efficient destabilizers of colloidal suspensions. The PAM flocculants cause the polymeric bridges formation between the solid particles, connecting them with each other. As a result, large aggregates (flocks) are formed, which sedimentate readily. These excellent properties of polyacrylamide make that this is one of the most commonly used macromolecular compounds. The lack of toxicity and degradability in the natural environment causes that it can be safely used not only in everyday products, but also in advanced technological processes. The evidence of great need for polyacrylamide is its global production in 2013 being about 1 770 000 ton per year (53.9% in Asia, 18.4% in the United States of America and 17.8% in Western Europe). The largest producer (910 000 ton/year) and consumer (597 000 ton/year) of PAM in the world is China. The other regions of big consumption are the following: USA—196 000 ton/year; Western Europe—183 000 ton/year; Middle and East Asia, Latin America, and Japan—over 40 000 ton/year for each. The constantly growing demand for new polymeric compounds with specific features for advanced applications makes that research on the

Polyacrylamide (PAM) 123 synthesis and properties of derivatives and composites of polyacrylamide will continue to be carried out intensively.

References 1. Whipple, W.L., Zheng, H., Water-Soluble Free Radical Addition Polymerizations: Polyacrylamides. Plastics Engineering, 70(8), 44–48, 2014. 2. Molyneux, P. Water-soluble synthetic polymers: properties andbehaviour. Boca Raton, Florida, CRC Press, 2000. 3. Mastalerz, P. Handbook of organic chemistry. Wroclaw, Chemical Publishing House, 1998. 4. Silberberg, A., Eliassaf, J., Katchalsky, A., Temperature-dependence of light scattering and intrinsic viscosity of hydrogen bonding polymers. J. Polym. Sci., 23(103), 259–284, 1957. 5. Li, Z., Guan, W., Lu, C., Zhou, X.R., Luo, S.Z., You, Y, et al, Hydrophobicityinduced prestaining for protein detection in polyacrylamide gel electrophoresis. Chem. Commun. (Camb.)., 52(13), 2807–2810, 2016. 6. Taylor, K.C., Nasr-El-Din, H.A., Water-soluble hydrophobically associating polymers for improved oil recovery: A literature review. J. Petrol. Sci. Eng., 19(3–4), 265–280, 1998. 7. Sojka, R.E., Bjorneberg, D.L., Entry, J.A., Lentz, R.D., Orts, W.J., Polyacrylamide in agriculture and environmental land management. Adv. Agronomy, 92, 75–162, 2007. 8. Nasser, M.S., James, A.E., The effect of polyacrylamide charge density and molecular weight on the flocculation and sedimentation behaviour of kaolinite suspensions. Sep. Purif. Technol., 52(2), 241–252, 2006. 9. Pefferkorn, E., Polyacrylamide at Solid/Liquid Interfaces. J. Colloid Interface Sci., 216(2), 197–220, 1999. 10. Zhang, X.C., Miller, W.P., Polyacrylamide effect on infiltration and erosion in furrows. Soil Science Society of America Journal, 60(3), 866–872, 1996. 11. Lee, H.-K., Jong, W.-L., Synthesis and applications of polyacrylamide derivatives in the wet end of papermaking (Part II. Reactive N-chloropolyacrylamide. J. Polym. Res., 4(2), 119–128, 1997. 12. Pielichowski, J., Puszyński, A. Plastics technology. Warsaw, ScientificTechnical Publishing House, 1998. 13. Giz, A., Çatalgil-Giz, H., Alb, A., Brousseau, J.-L., Reed, W.F., Kinetics and mechanisms of acrylamide polymerization from absolute, online monitoring of polymerization reaction. Macromolecules, 34(5), 1180–1191, 2001. 14. Lin, H.-R., Solution polymerization of acrylamide using potassium persulfate as an initiator: kinetic studies, temperature and pH dependence. Eur. Polym. J., 37(7), 1507–1510, 2001.

124 High Performance Polymers and Their Nanocomposites 15. Zheng, H., Ma, J., Ji, F., Tang, X., Chen, W., Zhu, J., Synthesis and application of anionic polyacrylamide in water treatment. Asian Journal of Chemistry, 25, 7071–7074, 2013. 16. Capek, I., Inverse emulsion polymerization of acrylamide initiated by oiland water-soluble initiators: effect of emulsifier concentration. Polym. J., 36(10), 793–803, 2004. 17. Jiang, Z., Zhu, J., Cationic polyacrylamide: synthesis and application in sludge dewatering treatment. Asian Journal of Chemistry, 26, 629–633, 2014. 18. Liu, J., C. W. Y., Wu., Aqueous dispersion polymerization of acrylamide in ammonium chloride solution with water-soluble chitosan as a stabilizer. Iranian Polymer Journal, 20, 887–896, 2011. 19. Zheng, H., Liao, Y., Zheng, M., Zhu, C., Ji, F., Ma, J, et al, Photoinitiated polymerization of cationic acrylamide in aqueous solution: synthesis, characterization, and sludge dewatering performance. The Scientific World Journal, 2014, 11–11, 2014. 20. Ge, X., Ye, W., Xu, M., Zhang, Z., Ye, Q., Xu, X., Radiation copolymerization of acrylamide and cationic monomer in an inverse emulsion. Polymer, 39(10), 1917–1920, 1998. 21. Wang, C., Wang, X., Miao, C., Wu, Y., Preparation and properties of amphoteric polyacrylamide by seeded dispersion polymerization in ammonium sulfate solution. Polym. Eng. Sci., 51(9), 1742–1748, 2011. 22. Menter, P., Acrylamide polymerization – a practical approach, Electrophoresis. tech. note, 1156. 23. W . M. Leung., Axelson, D.E., Van Dyke, J.D., Thermal degradation of polyacrylamide and poly(acrylamide-co-acrylate), 25, 1825–1846, 1987. 24. Kitahara, Y., Okuyama, K., Ozawa, K., Suga, T., Takahashi, S., Fujii, T., Thermal decomposition of acrylamide from polyacrylamide. J. Therm. Anal. Calorim., 110(1), 423–429, 2012. 25. Wu, S., Shanks, R.A., Solubility study of polyacrylamide in polar solvents. J. Appl. Polym. Sci., 93(3), 1493–1499, 2004. 26. Hashmet, M.R., Onur, M., Tan, I.M., Empirical Correlations for Viscosity of Polyacrylamide Solutions with the Effects of Concentration, Molecular Weight and Degree of Hydrolysis of Polymer. J. of Applied Sciences, 14(10), 1000–1007, 2014. 27. Gao, C., Viscosity of partially hydrolyzed polyacrylamide under shearing and heat. J. Petrol. Explor. Prod. Technol., 3(3), 203–206, 2013. 28. Sabhapondit, A., Borthakur, A., Haque, I., Characterization of acrylamide polymers for enhanced oil recovery. J. Appl. Polym. Sci., 87(12), 1869–1878, 2003. 29. Mikulec, J., Palakovicova, G., Cvengros, J., Flocculation using polyacrylamide polymers for fresh microalgae. Chem. Eng. Technol., 38(4), 595–601, 2015.

Polyacrylamide (PAM) 125 30. Sun, W., Zhang, G., Pan, L., Li, H., Shi, A., Synthesis, Characterization, and Flocculation Properties of Branched Cationic Polyacrylamide. Int. J. Polym. Sci., 2013(5), 10 pages.–10, 2013. 31. Shupe, R.D., Chemical Stability of Polyacrylamide Polymers. Journal of Petroleum Technology, 33(08), 1513–1529, 1981. 32. Pei, Y., Zhao, L., Du, G., Li, N., Xu, K., Yang, H., Investigation of the degradation and stability of acrylamide-based polymers in acid solution: Functional monomer modified polyacrylamide. Petroleum, 2(4), 399–407, 2016. 33. Conix, A., Smets, G., Moens, J., Alkaline hydrolysis of amide group containing polymers. Chemical Abstracts, 54, 11545d, 1960. 34. Schiller, A.M., Suen, T.J., Ionic Derivatives of Polyacrylamide. Ind. Eng. Chem., 48(12), 2132–2137, 1956. 35. Wu, S., Shanks, R.A., Conformation of polyacrylamide in aqueous solution with interactive additives and cosolvents. J. Appl. Polym. Sci., 89(11), 3122– 3129, 2003. 36. Mansri, A., Tennouga, L., Bouras, B., Additive effect on the behavior of water-soluble hydrolyzed polyacrylamide copolymer. Journal of Material and Environmental Science, 5, 37–42, 2014. 37. Niranjan, P.S., Upadhyay, S.K., Structural effects of cationic surfactants in polyacrylamide-surfactant interaction: micellisation/adsorption of polyacrylamide. Indian J. Chem., 53A, 1402–1406, 2014. 38. Ye, Z., Guo, G., Chen, H., Shu, Z., Interaction between Aqueous Solutions of Hydrophobically Associating Polyacrylamide and Dodecyl Dimethyl Betaine. J. Chem., 2014(8), 1–8, 2014. 39. Hong, C., Er-Xiao, L., Zhong-Bin, Y., Li-Juan, H., Ping-Ya, L., Interaction of hydrophobically associating polyacrylamide with gemini surfactant. Acta Physico-Chimica Sinica, 27, 671–676, 2011. 40. Niranjan, P.S., Upadhyay, S.K., Interaction of polyacrylamide with conventional anionic and gemini anionic surfactants. J. Dispers. Sci. Technol., 32(1), 109–113, 2010. 41. Niranjan, P.S., Shukla, R., Upadhyay, S.K., Interactions of polyacrylamide with cationic Surfactants: thermodynamic and surface parameters. J. Surfactants Deterg., 15(1), 53–57, 2012. 42. Xulong, C., Yue, H., Xinwang, S., Yangwen, Z., Yugui, H., Kunpeng, W., Interaction of anionic polyacrylamide with cationic surfactants. Polym. Chem., 36, 395–398, 2015. 43. Wu, S., Shanks, R.A., Bryant, G., Properties of hydrophobically modified polyacrylamide with low molecular weight and interaction with surfactant in aqueous solution. J. Appl. Polym. Sci., 100(6), 4348–4360, 2006. 44. Lai, L., Mei, P., Wu, X.-M., Hou, C., Zheng, Y.-C., Liu, Y., Micellization of anionic gemini surfactants and their interaction with polyacrylamide. Colloid Polym. Sci., 292(11), 2821–2830, 2014. 45. da Costa, A.M.A., Amado, A.M., Molecular interactions in polyacrylamide/ lithium perchlorate hydrogel composites. Polymer, 41(14), 5361–5365, 2000.

126 High Performance Polymers and Their Nanocomposites 46. Wei, M., Zhang, G., Wu, Q., Processing of highly concentrated polyacrylamide-coated silicon carbide suspensions. Ceramics International, 30(2), 125– 131, 2004. 47. Pan, W., Gong, J., Processing and characterization of carbothermal reduction and nitridation from kaolinite-polyacrylamide intercalation compound. Key Eng. Mater., 338, 3361093–3361095, 2007. 48. Zou, W., Yu, C., Sun, C., Cao, Y., Selective adsorption of anionic polyacrylamide onto ultra - low ash coal and kaolinite. Physicochemical Problems of Mineral Processing, 52, 738–753, 2016. 49. Ding, K.J., Laskowski, J.S., Effect of conditioning on selective flocculation with polyacrylamide in the coal reverse flotation. Mineral Processing and Extractive Metallurgy, 116(2), 108–114, 2007. 50. Lee, H.K., Jong, W.L., Synthesis and applications of polyacrylamide derivatives in the wet end of papermaking (Part II. Reactive N-chloropolyacrylamide), Journal of Polymer Research, 4, 119–128, 1997. 51. Main, N.M., Talib, R.A., Rahman, R.A., Mohamed, A.Z., Ibrahim, R., Adnan, S., Effect of Amphoteric and Cationic Polyacrylamide on the Structural and Strength Properties of Coir Paper. Procedia Manufacturing, 2, 28–34, 2015. 52. Tripathy, T., De, B.R., Flocculation: a new way to treat the waste water. Journal of Physical Science, 19, 93–127, 2006. 53. Wiśniewska, M., Chibowski, S., Urban, T., Effect of the presence of cationic polyacrylamide on the surface properties of aqueous alumina suspensionstability mechanism. Appl. Surf. Sci., 320, 843–851, 2014. 54. Wiśniewska, M., Chibowski, S., Urban, T., Impact of polyacrylamide with different contents of carboxyl groups on the chromium (III) oxide adsorption properties in aqueous solution. J. Hazard. Mater., 283, 815–823, 2015. 55. Wiśniewska, M., Chibowski, S., Urban, T., Modification of the alumina surface properties by adsorbed anionic polyacrylamide—Impact of polymer hydrolysis. Journal of Industrial and Engineering Chemistry, 21, 925–931, 2015. 56. Entry, J.A., Sojka, R.E., The efficacy of polyacrylamide and related compounds to remove microorganisms and nutrients from animal wastewater. Journal of Environment Quality, 29(6), 1905–1914, 2000. 57. Barakat, M.A., New trends in removing heavy metals from industrial wastewater. Arabian Journal of Chemistry, 4(4), 361–377, 2011. 58. Amuda, O.S., Amoo, I.A., Ipinmoroti, K.O., Ajayi, O.O., Coagulation / flocculation process in the removal of trace metals present in industrial wastewater. Journal of Applied Sciences and Environmental Management, 10(3), 159–162, 2006. 59. Zendehdel, M., Barati, A., Alikhani, H., Hekmat, A., Removal of methylene blue dye from wastewater by adsorption onto semi-inpenetrating polymer network hydrogels composed of acrylamide and acrylic acid copolymer and polyvinyl alcohol. Iranian Journal of Environmental Health Science and Engineering, 7, 423–428, 2010.

Polyacrylamide (PAM) 127 60. Raffa, P., Broekhuis, A.A., Picchioni, F., Polymeric surfactants for enhanced oil recovery: A review. Journal of Petroleum Science and Engineering, 145, 723–733, 2016. 61. Abidin, A.Z., Puspasari, T., Nugroho, W.A., Polymers for Enhanced Oil Recovery Technology. Procedia Chemistry, 4, 11–16, 2012. 62. Sojka, R.E., Lentz, R.D., Westermann, D.T., Water and erosion management with multiple applications of polyacrylamide in furrow irrigation. Soil Science Society of America Journal, 62(6), 1672–1680, 1998. 63. Sojka, R.E., Bjorneberg, D.L., Entry, J.A., Lentz, R.D., Orts, W.J., Polyacrylamide in agriculture and environmental land management. Advances in Agronomy, 92, 75–162, 2007. 64. Frantz, J.M., Locke, J.C., Pitchay, D.S., Krause, C.R., Actual Performance versus theoretical advantages of polyacrylamide hydrogel throughout bedding plant production. HortScience, 40, 2040–2046, 2005. 65. Maziad, N.A., Abou El Fadl, F.I., El-Kelesh, N.A., El-Hamouly, S.H., Zeid, I.F., Gayed, H.M., Radiation synthesis and characterization of super absorbent hydrogels for controlled release of some agrochemicals. J. Radioanal. Nucl. Chem., 307(1), 513–521, 2016. 66. von Buelow, S., von Heimburg, D., Pallua, N., Efficacy and safety of polyacrylamide hydrogel for facial soft-tissue augmentation. Plast. Reconstr. Surg., 116(4), 1137–1146, 2005. 67. Madaghiele, M., Demitri, C., Sannino, A., Ambrosio, L., Polymeric hydrogels for burn wound care: Advanced skin wound dressings and regenerative templates. Burns Trauma, 2(4), 153–161, 2014. 68. Caló, E., Khutoryanskiy, V.V., Biomedical applications of hydrogels: A review of patents and commercial products. Eur. Polym. J., 65, 252–267, 2015. 69. Reisinger, V., Eichacker, L.A., Isolation of membrane protein complexes by blue native electrophoresis. Methods Mol. Biol., 424, 423–431, 2008. 70. Chi, Q., Huang, K., Polyacrylamide Gel Electrophoresis of Insulin. Anal. Lett., 40(1), 95–102, 2007. 71. Li, S.F., Tang, Z.W., Tan, Y.B., Yu, X.B., Polyacrylamide blending with ammonia borane: a polymer supported hydrogen storage composite. The Journal of Physical Chemistry C, 116(1), 1544–1549, 2012. 72. Lewandowska, K., Characterization of thin chitosan/polyacrylamide blend films. Molecular Crystals and Liquid Crystals, 590(1), 186–192, 2014. 73. Lewandowska, K., Miscibility and physical properties of chitosan and polyacrylamide blends. J. Mol. Liq., 209, 301–305, 2015. 74. Helen, M., Viswanathan, B., Murthy, S.S., Murthy, Srinivasa, Poly S., Murthy, Srinivasa., Poly(vinyl alcohol)-polyacrylamide blends with cesium salts of heteropolyacid as a polymer electrolyte for direct methanol fuel cell applications. J. Appl. Polym. Sci., 116, 437–3447, 2010. 75. El-din, H.M.N., El-Naggar, A.W.M., Ali, F.I., Nazil El-Din, H.M., Mohamed El-Naggar, A.W., Miscibility of poly(vinyl alcohol)/polyacrylamide blends before and after gamma irradiation. Polym. Int., 52(2), 225–234, 2003.

128 High Performance Polymers and Their Nanocomposites 76. Wei, Q., Wang, Y., Che, Y., Yang, M., Li, X., Zhang, Y., Molecular mechanisms in compatibility and mechanical properties of Polyacrylamide/Polyvinyl alcohol blends. J. Mech. Behav. Biomed. Mater., 65, 565–573, 2017. 77. Umoren, S.A., Ebenso, E.E., Blends of polyvinyl pyrrolidone and polyacrylamide as corrosion inhibitors for aluminium in acidic medium. Indian Journal of Chemical Technology, 15, 355–363, 2008. 78. Patel, G., Sureshkumar, M.B., Patel, P., P., Patel, M.B., Spectroscopic investigation and characterizations of PAM/PEO blends films. Soft, 04(02), 9–24, 2015. 79. Bhat, V., Shivakumar, H.R., Sheshappa, R.K., Sanjeev, G., Preparation and study on miscibility, thermal behavior of biocompatible polymer blends of xanthan Gum-polyacrylamide. Int. J. Plast. Technol., 18(2), 183–191, 2014. 80. Sorour, M., El-Sayed, M., El Moneem, N.A., Talaat, H.A., Shalaan, S, H., Marsafy, E., Characterization of hydrogel synthesized from natural polysaccharides blend grafted acrylamide using microwave (MW) and ultraviolet (UV) techniques. Starch/Stärke, 65(1-2), 172–178, 2013. 81. Abdelhak, M., Abdelkarim, H., Barbara, I., Effect of plant fiber-polyacrylamide blend on retention and evaporation water at arid and semi-arid soils of Algeria. J. Chem. Chem. Eng., 6, 7–17, 2012. 82. Chibowski, S., Wiśniewska, M., Study of electrokinetic properties and structure of adsorbed layers of polyacrylic acid and polyacrylamide at Fe2O3– polymer solution interface. Colloids and Surfaces A Physicochemical and Engineering Aspects, 208(1–3), 131–145, 2002. 83. Chibowski, M, S., Paszkiewicz, W.M., Adsorption of polyelectrolytes at manganese oxide (IV)-polymer solution interface. structure of adsorbed layers, Adsorption Science and Technology, 20, 511–522, 2002. 84. Wiśniewska, M., The temperature effect on the adsorption mechanism of polyacrylamide on the silica surface and its stability. Appl. Surf. Sci., 258(7), 3094–3101, 2012. 85. Wiśniewska, M., Chibowski, S., Urban, T., Effect of the presence of cationic polyacrylamide on the surface properties of aqueous alumina suspensionstability mechanism. Appl. Surf. Sci., 320, 843–851, 2014. 86. Wiśniewska, M., Chibowski, S., Urban, T., Impact of anionic and cationic polyacrylamide on the stability of aqueous alumina suspension—comparison of adsorption mechanism. Colloid Polym. Sci., 293(4), 1171–1179, 2015. 87. Wiśniewska, M., Chibowski, S., Urban, T., Impact of polyacrylamide with different contents of carboxyl groups on the chromium (III) oxide adsorption properties in aqueous solution. J. Hazard. Mater., 283, 815–823, 2015. 88. Wiśniewska, M., Chibowski, S., Urban, T., Modification of the alumina surface properties by adsorbed anionic polyacrylamide—Impact of polymer hydrolysis. Journal of Industrial and Engineering Chemistry, 21, 925–931, 2015. 89. Wiśniewska M., Chibowski S., Urban T. Influence of temperature on adsorption mechanism of anionic polyacrylamide in the Al2O3 –aqueous solution system. Fluid Phase Equilib, 408, 205–211, 2016.

Polyacrylamide (PAM) 129 90. Wiśniewska, M., Chibowski, S., Urban, T., Investigation of removal possibilities of colloidal alumina from aqueous solution by the use of anionic polyacrylamide. International Journal of Environmental Research, 10, 97–108, 2016. 91. Wiśniewska, M., Chibowski, S., Urban, T., Synthetic polyacrylamide as a potential flocculent to remove commercial chromium(III) oxide from aqueous suspension. Int. J. Environ. Sci. Technol., 13(2), 679–690, 2016. 92. Faghihian, H., Farsani, S.N., Modification of Polyacrylamide–β–Zeolite Composite by Phytic Acid for the Removal of Lead from Aqueous Solutions. Polish Journal of Chemical Technology, 15(1), 1–6, 2013. 93. Ulusoy, U., Simşek, S., Simswek, S., Lead removal by polyacrylamide-bentonite and zeolite composites: effect of phytic acid immobilization. J. Hazard. Mater., 127(1-3), 163–171, 2005. 94. Baybaş, D., Ulusoy, U., Polyacrylamide-clinoptilolite/Y-zeolite composites: characterization and adsorptive features for terbium. J. Hazard. Mater., 187(1-3), 241–249, 2011. 95. Shen, J., Yan, B., Li, T., Long, Y., Li, N., Ye, M., Study on graphene-oxidebased polyacrylamide composite hydrogels. Composites Part A: Applied Science and Manufacturing, 43(9), 1476–1481, 2012. 96. Shen, J., Yan, B., Li, T., Long, Y., Li, N., Ye, M., Study on graphene-oxide-based polyacrylamide composite hydrogels. Composites Part A Applied Science and Manufacturing, 43(9), 1476–1481, 2012. 97. Xie, A.-J., Liu, Q.-X., Ge, H.-L., Kong, Y., Novel H 2 O 2 electrochemical sensor based on graphene–polyacrylamide composites. Materials Technology, 30(1), 50–53, 2015. 98. Awasthi, S., Awasthi, K., Kumar, R., Srivastava, O.N., Functionalization effects on the electrical properties of multi-walled carbon nanotube-polyacrylamide composites. J. Nanosci. Nanotechnol., 9(9), 5455–5460, 2009. 99. Evingür, G.A., Pekcan, Ö., Drying of polyacrylamide-multiwalled carbon nanotube (MWNT) composites with various MWNTs contents: a fluorescence study. Journal of Polymer Engineering,, 33, 33–39, 2012. 100. Suh, M.H., Ye, P., Datta, A.B., Zhang, M., Fu, J., An agarose-acrylamide composite native gel system suitable for separating ultra-large protein complexes. Anal. Biochem., 343(1), 166–175, 2005. 101. Jang, J., Park, H., Formation and structure of polyacrylamide-silica nanocomposites by sol-gel process. J. Appl. Polym. Sci., 83(8), 1817–1823, 2002. 102. Rahman, I.A., Padavettan, V., Synthesis of Silica Nanoparticles by Sol-Gel: Size-Dependent Properties, Surface Modification, and Applications in SilicaPolymer Nanocomposites—A Review. Journal of Nanomaterials, 2012(30), 15 pages–15, 2012. 103. El-Mahdy, G.A., Atta, A.M., Al-Lohedan, H.A., Tawfik, A.M., Abdel-Khalek, A.A., Application of silica/polyacrylamide nanocomposite as anticorrosive layer for steel. International Journal of Electrochemical Science, 10, 151–161, 2015.

130 High Performance Polymers and Their Nanocomposites 104. Zikry, A.A.F., Dielectric Behavior of Silica/Polyacrylamide Nanocomposites. International Journal of Polymeric Materials and Polymeric Biomaterials, 57(4), 383–395, 2008. 105. Wiśniewska, M., Chibowski, S., Urban, T., Adsorption properties of the nanozirconia/anionic polyacrylamide system—Effects of surfactant presence, solution pH and polymer carboxyl groups content. Appl. Surf. Sci., 370356, 2016–356, 2016. 106. Wiśniewska, M., Chibowski, S., Urban, T., Nanozirconia surface modification by anionic polyacrylamide in relation to the solid suspension stability — Effect of anionic surfactant addition. Powder Technology, 302, 357–362, 2016. 107. Wiśniewska, M., Chibowski, S., Urban, T., Adsorption of cationic polyacrylamide on the surface of mesoporous nanozirconia and its influence on the solid aqueous suspension stability. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 509, 214–223, 2016. 108. Li, C., Cai, Y., Zhu, Y., Ma, M., Zheng, W., Zhu, J., Polyacrylamide–metal nanocomposites: one-pot synthesis, antibacterial properties, and thermal stability. J. Nanopart. Res., 15(9), 1922–1945, 2013. 109. Ni, Y., Ge, X., Zhang, Z., Ye, Q., In situ single-step synthesis of gold/polyacrylamide nanocomposites in an ethanol system. Mater. Lett., 55(3), 171– 174, 2002. 110. Pan, W., Chen, Y., Preparation of Ag–polyacrylamide nanocomposites by ultraviolet irradiation technique. AMM, 44-47, 2199–2202, 2011. 111. Zhang H., Zhang L. Structure and properties of Ag–polyacrylamide nanocomposites by heat treatment. Applied Mechanics and Materials, 47, 442373– 2376, 2011. 112. Mukherjee S., Mukherjee M. Nitrogen-mediated interaction in polyacrylamide–silver nanocomposites. Journal of Physics: Condensed Matter, 18, 11233–11242, 2006. 113. Zhu, J.F., Zhu, Y.J., Microwave-assisted one-step synthesis of polyacrylamidemetal (M = Ag, Pt, Cu) nanocomposites in ethylene glycol. J. Phys. Chem. B, 110(17), 8593–8597, 2006. 114. Folarin, O.M., Sadiku, E.R., Maity, A., Polymer-noble metal nanocomposites: review. International Journal of Physical Sciences, 6, 4869–4882, 2011. 115. Palza, H., Antimicrobial polymers with metal nanoparticles. Int. J. Mol. Sci., 16(1), 2099–2116, 2015. 116. Okay, O., Oppermann, W., Polyacrylamide−Clay Nanocomposite Hydrogels: Rheological and Light Scattering Characterization. Macromolecules, 40(9), 3378–3387, 2007. 117. Zhou, C., Wu, Q., A novel polyacrylamide nanocomposite hydrogel reinforced with natural chitosan nanofibers. Colloids Surf. B Biointerfaces, 84(1), 155–162, 2011. 118. Abdel-Halim, E.S., Al-Deyab, S.S., Antimicrobial activity of silver/starch/polyacrylamide nanocomposite. Int. J. Biol. Macromol., 68, 33–38, 2014.

Polyacrylamide (PAM) 131 119. Zhang, L., Shi, T., Wu, S., Zhou, H., Synthesis of carbon nanotubes/polyacrylamide nanocomposites with improved load-carrying capacity and antiwear ability. High Performance Polymers, 26(8), 970–977, 2014. 120. Bajpai, A.K., Bundela, H., γ-Radiation assisted fabrication of hydroxyapatitepolyacrylamide nanocomposites with possible application in bone implantology. J. Compos. Mater., 44(6), 757–778, 2010. 121. Hegedus, I., Nagy, E., Egyetem, P., Stabilization of activity of cellulase and hemicellulase enzymes by covering with polyacrylamide layer. Chem. Eng. Process, 95, 143–150, 2015. 122. Gertz, C., Klostermann, S., Analysis of acrylamide and mechanisms of its formation in deep-fried products. Eur. J. Lipid Sci. Technol., 104(11), 762– 771, 2002. 123. Claeys, W.L., De Vleeschouwer, K., Hendrickx, M.E., Quantifying the formation of carcinogens during food processing: acrylamide. Trends in Food Science & Technology, 16(5), 181–193, 2005. 124. Sörgel, F., Weissenbacher, R., Kinzig-Schippers, M., Hofmann, A., Illauer, M., Skott, A, et al, Acrylamide: increased concentrations in homemade food and first evidence of its variable absorption from food, variable metabolism and placental and breast milk transfer in humans. Chemotherapy, 48(6), 267–274, 2002. 125. Bao, M., Chen, Q., Li, Y., Jiang, G., Biodegradation of partially hydrolyzed polyacrylamide by bacteria isolated from production water after polymer flooding in an oil field. J. Hazard. Mater., 184(1-3), 105–110, 2010. 126. Yu, F., Fu, R., Xie, Y., Chen, W., Isolation and characterization of polyacrylamide-degrading bacteria from dewatered sludge. Int. J. Environ. Res. Public Health, 12(4), 4214–4230, 2015. 127. Kang, Z.-H., Li, H.-K., Xu, Y.-H., Chen, L., Electrolytic degradation of polyacrylamide in aqueous solution using a three-dimensional electrode reactor. Desalination and Water Treatment, 51(13-15), 2687–2694, 2013. 128. Lu, M., Wu, X., Wei, X., Chemical degradation of polyacrylamide by advanced oxidation processes. Environ. Technol., 33(7-9), 1021–1028, 2012. 129. Levitt, D.B., Pope, G.A., Jouenne, S., Chemical Degradation of Polyacrylamide Polymers Under Alkaline Conditions. SPE Reservoir Evaluation & Engineering, 14(03), 281–286, 2011.

5 Effect of Nanostructured Polyhedral Oligomeric Silsesquioxone on High Performance Poly(urethane-imide) Dhorali Gnanasekaran Dielectric Materials Division, Central Power Research Institute, Sir. C.V. Raman Road, Bangalore, India

Abstract Polyhedral oligomeric silsesquioxones (POSS) were successfully embedded into poly(urethane-imide) membrane through chemical bonding, and the vital role of POSS on the surface morphology of prepared membranes was studied. A range of poly(urethane-imide)-POSS (PUI-POSS) membranes were prepared by a facile in situ polymerization reaction based on different loadings of POSS. The surface morphology structure of POSS incorporated membranes PUI-POSS were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The hydrophilic/hydrophobic nature and surface free energy of prepared membranes were analyzed by contact angle measurements using Sessile drop method. The thermal stability of PUI-POSS nanocomposite membranes was analyzed by thermogravimetric analysis (TGA). TEM images revealed the dispersion behavior of POSS into the membranes, and it was found to be in the range of 10–20 nm size. SEM images showed no agglomeration even at the higher content of POSS. Three-dimensional AFM images of the membranes indicated a slight increase in roughness when the POSS content was increased. The gel content, fractional free volume (FFV), and density of the PUI-POSS membranes were calculated, and effectively correlated with surface morphology studies. The obtained results displayed the prepared membrane is excellent for gas transport studies. Keywords: POSS, surface morphology, roughness, surface free energy, FFV

Corresponding author: [email protected] Visakh P.M. and Semkin A.O. (eds.) High Performance Polymers and Their Nanocomposites, (133–148) © 2019 Scrivener Publishing LLC

133

134 High Performance Polymers and Their Nanocomposites

5.1

Introduction

Nowadays, intense interest is shown in the development of nanomaterials which offer exciting new challenges and opportunities in the different branches of science and technology [1, 2]. It is now widely recognized that reduction in the size of component particles influences the interfacial interactions between them, and this can, in turn, enhance the material properties to an appreciable extent [1–3]. Organic–inorganic hybrid materials such as polyhedral oligomeric silsesquioxones (POSS) are accepted as a new class of advanced materials, because they can be synthesized or processed using versatile approaches and have their own tunable properties [4–6] (Figure 5.1). Therefore, POSS compound with diameters of 1–3 nm can be possibly considered the smallest particles of silica, but unlike silica, silicones, or other fillers, and POSS molecules contain either functionalized or unfunctionalized substituent at each of the corner silicon atoms. Then, these substituent can compatibilize the POSS molecule with polymeric materials [6, 7]. In recent years, a very huge interest is shown in the development of POSS materials on membrane technology [8, 9]. Moreover, POSS cubic molecules show a rigid framework structure closely related to that of silica, and POSS is one of the most important fillers as well as functionally tailored nanomaterial in nanotechnology. In addition, owing to their size and the organic groups attached to the core, they offer a unique opportunity for preparing truly molecularly dispersed nanocomposites. Interestingly, the large variety of substitution pattern allows silsesquioxane specifically POSS to be incorporated into almost any conventional polymer either by blending or by covalent attachments [10–12]. Generally, polymer nanocomposites are defined as polymers having small amounts of nanometer size fillers that are dispersed by only several weight percentages. In most of the cases, a polymer nanocomposite with a small size of the fillers leads to a dramatic increase in interfacial area as compared with traditional composites. Thus, this interfacial area creates a significant volume fraction of interfacial polymer with properties different from the bulk polymer even at low loadings [13]. Additionally, Moore and Koros [14] have summarized the relationship between organic/inorganic membrane and surface morphology properties. They have indicated that the tradeoff phenomenon mainly derived from the non-ideal effects such as varying degrees of rigidification in the surrounding polymers, and undesirable voids and partial voids at the interfaces. Recently, Chattopadhyay et al., [15] synthesized two different

Effect of Nanostructured Polyhedral Oligomeric 135 O

O O

O

O

Si OH OH O Si O Si Si O O O O Si Si O Si O SiO O O

R O

Si

O

Si O

HO

Si

O

R

R

O

Si O Si

O R

R O

O Si

R

O

O

O R

R

Si

R

R OH Si

O

R

Si

Si

O

R

O Si

Si

O

R

O

R

R

OH

Si

Si O O

O

Si Si

R Si

O

R

O

Si

Si R

R

O

O

O Si

O

R O O

O

O Si

Si

Si R O

Si

R Si

R

R

O

Si

O

O

O

O

O

OH

Si

O

R Si

HO

O

R Si

R

O O

O

R

O O O

R

R

O

Si OH

O O

OH

Si

R Si

R

R Si

Si

O

O O

Si

Si

O

O

O

R O

R

O

Si

O Si

Si Si

Si

O Si

O

OH

R R

O

R

R

Si

O

O Si

O

Si

R

O O

O

Si

Si

HO

Si

O

O

Si O

O Si

O

O

O

R

O

O

O R Si

O Si

O

R

R

O R

Figure 5.1 Nanostructured multifunctional structure of polyhedral oligomeric silsesquioxone [6].

sets of poly(urethane-imide/clay) hybrids from two types of polyester polyols. Avadhani et al., [16] have prepared novel poly(urethane-imide) by utilizing diisocyanates containing built-in imide group. In addition, Yeganeh et al., [17] have synthesized poly(urethane-imide) by the reaction of isocyanate-terminated polyurethane PU prepolymer with glycols containing imide function as a chain extender. For instance, Zuo and coworkers [18, 19] have reported a novel approach to prepare poly(urethaneimide). Their approaches were based on the reaction of PU prepolymer and poly(amic acid) which was a precursor of polyimide (PI) giving PUIs without adding any nanomaterial (POSS) and improved thermal stability and solvent resistance.

136 High Performance Polymers and Their Nanocomposites For this motive, we studied the surface morphology, density, FFV, and gel content of various amounts of POSS incorporated poly(urethane-imide)POSS nanocomposite membranes. Surface morphology of PUI-POSS nanocomposite membranes shows good correlation with the structure– properties relationship. Excellent physical properties of poly(urethaneimide)-POSS nanocomposite membranes are suitable applications in the preparation of gas transport materials.

5.2

Experimental

Materials Heptacyclopentyl tricycloheptasiloxane triol (Cy-POSS) was synthesized by the reported literature [20]. Hexamethylene diisocyanate (HMDI, Merck, 95%), poly(dimethylsiloxane), bis(hydroxylalkyl) terminated (Mn = 5600) (PDMS, Aldrich, 99%), and dibutyltin dilaurate (DBTDL, Aldrich, 95%) were used as received. 4,4 -(Hexafluoroisopropylidene) dipthalic anhydride (Aldrich, 99%) was purified by sublimation under vacuum and tetrahydrofuran (THF, Rankem) was distilled using calcium hydride and sodium metal. All other chemicals were of analytical grade and used as received.

Characterization Gel content of nanocomposite membranes was determined by Soxhlet extraction using THF for 24 h. The insoluble materials were dried under vacuum for 50 h and weighed. The gel content of membranes was determined from the difference in the weight before and after the extraction operation. Density measurements were performed on the membranes of 1 cm × 1 cm dimensions, and an average of three readings was taken for each samples. Density of the prepared membranes was observed using a Mettler AJ100 analytical balance, which was fixed with a Mettler ME-33360 density determination kit based on Archimedes’ Principle. The relationship between calculated density, mass, and liquid density is given in Equation (1): ρ

−

ρ

(1)

where ρfilm is the predicted density, mair and mliquid are the masses calculated in air and liquid, and ρliquid is the density of the liquid.

Effect of Nanostructured Polyhedral Oligomeric 137 The density data of the membranes were used to estimate the chain packing by calculating the fractional free volume (FFV), from Equation (2): (2) where V is the total specific volume of the polymer and is obtained from the experimentally determined density of the polymer. Vo is the occupied volume of the polymeric membrane. Usually, the occupied volumes are estimated to be 1.3 times more than that of Van der Waals volume, which was estimated by the Bondi [21] method using the group contribution correlation of Van Krevelen and Hoftyzer [22]. Contact angle measurements of PUI-POSS membranes were carried out at room temperature (35 °C) by the Sessile drop method. The surface free energy of PUI-POSS nanocomposite membranes was calculated by measuring contact angle measurements in double distilled water and n-hexadecane. The contact angle was measured at five different positions for each sample, and the average was taken to obtain the significant measurements. Surface roughness of the membranes was studied using a Nanoscope III AFM instrument, and the 3D imaging was done in contact mode at room temperature in air. The membranes were cut into small pieces and placed on a grid. The grid was roofed using the commercial tip of Si3N4 provided by digital instruments. Cantilever length was kept at 200 μm with a spring constant of 0.12 N m−1. TEM images of nanocomposite membranes were recorded on membranes and digitized with a PC-controlled digital camera DXM1200 (Nikon) and were obtained (acceleration voltage = 100 kV) using a JEM 200CX (JEOL) microscope. SEM analysis was performed using JEOL 400 microscope by cutting membranes into small pieces, and the samples were first sputtered with gold. The SEM pictures were taken on the flat surface of the PUI-POSS nanocomposite membranes. Thermogravimetric analysis (TGA) was performed on a Mettler Toledo A851 TGA/SDTA instrument using the dynamic method. About 15 mg of the sample was placed in an open 150-μL alumina pans. Temperature was scanned from 25 °C to 1000 °C at a rate of 10 °C min−1 with air flowing at a rate of 50 mL min−1.

Synthesis of Poly(urethane-Imide)-POSS Nanocomposites The poly(urethane-imide)-POSS nanocomposite membranes were formed by incorporating POSS and polyimide (PI) segments into the PU matrix through direct condensation reaction. The detailed synthesis of

138 High Performance Polymers and Their Nanocomposites Table 5.1 Surface Roughness, Gel Content, Density, and FFV of the PUI-POSS Nanocomposite Membranes.

Samples

Gel content (%)

RMS (root mean square) (nm)

Density (g/cm3)

FFV

PUI-POSS-0

91

22

1.02

0.245

PUI-POSS-5

85

43

1.04

0.236

PUI-POSS-10

79

55

1.05

0.219

PUI-POSS-15

73

71

1.07

0.205

poly(urethane-imide)-POSS nanocomposite was reported in the literature [23, 24].

5.3

Results and Discussion

Gel content values of prepared nanocomposite membranes were obtained using Soxhlet apparatus, and the results are given in Table 5.1. The gel content values were emerging low at higher POSS concentration. These imply that, at higher concentration, there may be presence of few unreacted POSS molecules and more number of POSS aggregates on the surface of membranes. However, these aggregates are less bound between imide and POSS-urethane matrix. The FFV is the ratio of free volume to the observed volume, and it is used to characterize the efficiency of chain packing in the nanocomposite membranes. The FFV largely depends on the amount of free volume existing in the polymeric matrix. The formation of free volume depends on the POSS dispersed on the membrane matrix [24]. The successful chemical bonding between the bulky POSS and the polymer chains consequence conformational reorientations of polymer chains lead to the close packing of them. As a result, the free volume decreases, whereas the density of membrane matrix increases. This is clearly given in Table 5.1, where a steady decrease in free volume size and an increase in densities are seen upon the incorporation of various wt.% of POSS in the polymer matrix. For example, FFV and density calculated for the membrane with higher POSS content are 0.205 and 1.07, respectively; whereas, the same for the

Effect of Nanostructured Polyhedral Oligomeric 139

Figure 5.2 Atomic force microscopy of PUI-POSS nanocomposite membranes.

neat membrane are found to be 0.245 and 1.02, respectively. These observations indicated that gel content, FFV, and density of membranes depend on the POSS molecules and simultaneously display that membranes that are having those properties are suitable for gas permeation studies.

Surface Morphology Studies by AFM Analysis The three-dimensional topographical AFM images exhibited the micro phase separated morphology as well as surface roughness and the details, as given in Figure 5.2 and Table 5.1. The uniform surfaces with micro phase separated morphologies were observed for the PUI-POSS-0 nanocomposite membranes. Particularly, a granular type aggregation was observed on the surface of the POSS incorporated membranes (PUI-POSS-5, PUIPOSS-10, and PUI-POSS-15), and this reveals that the hydrophobic nature of POSS molecule with low surface energy compared to PUI-POSS-0 matrix POSS incorporated membranes leads to the formation of POSS aggregations on the surface of membranes. Root mean square (RMS) surface roughness of PUI-POSS-0, PUI-POSS-5, PUI-POSS-10, and PUI-POSS-15 were observed to be 22, 43, 55, and 71 nm, respectively (Table 5.1). The incorporation of POSS increased the degree of surface roughness threefold compared to that of the neat membrane (PUI-POSS-0).

140 High Performance Polymers and Their Nanocomposites

Figure 5.3 Transmission electron microscopy of PUI-POSS-5 and PUI-POSS-15 membranes.

In the case of nanocomposite membrane with high POSS concentrated membranes were showed more granular type POSS aggregates with rough surface area, indicating that the surface morphology of nanocomposites were highly affected by the addition of POSS molecule. This is most likely due to the incompatible nature of POSS molecule with polymer matrices and indicates that even the cross-linking of POSS with polymer matrices through functional group will not restrict the formation of POSS aggregation [25]. AFM image revealed that the highly heterogeneous morphology reflects the less dispersive nature of POSS molecule only at higher concentrations. From this result, elevated regions were ascribed to the rubbery PU-POSS; whereas, the flatter or lower regions were glassy polyimide. Many reports in the literature indicated that incorporation of POSS molecule in the organic polymer leads to an aggregation of POSS into micro level due to the hydrophobic nature of POSS and incompatibility with the polymer matrices [26, 27].

Surface Morphology Studies by TEM Analysis The surface morphology of PUI-POSS was observed using TEM, and the micrographs are clearly shown in Figure 5.3. The samples were prepared by directly dropping the polymer solution on the carbon-coated copper grid without additional staining or etching. On the other hand, the shadowy region representing POSS molecules were sub-micrometer and the polymer matrices appear light region with homogeneous dispersion. Similar

Effect of Nanostructured Polyhedral Oligomeric 141

Figure 5.4 Scanning electron microscopy of PUI-POSS nanocomposite membranes.

results were observed with POSS-tethered polyimides [28, 29]. This phase separation might arise from the difference between hydrogen-bond interactions of imide segments and Van der Waals interactions of the cyclopentyl groups of POSS molecules [28, 29]. PUI-POSS-10 nanocomposite membrane obviously showed a small amount of aggregated POSS. Nevertheless, at relatively high POSS concentration in PUI-POSS-15, significant aggregation was found and the particle diameter was about 50 nm. Similar result was observed by Feng et al., [30] in the case of PAS-POSS blends. The interconnected microphaseseparated morphology with a uniform domain size appears to be some of the familiar characteristics of self-assembly structures.

Surface Morphology Studies by SEM/EDX Analysis POSS dispersed environment on morphology of PUI-POSS-5, PUIPOSS-10, and PUI-POSS-15 was displayed in SEM images (Figure  5.4). All the PUI-POSS, except PUI-POSS-0, showed a microphase separation of urethane and imide segments, and a micro/nano level spheroidal dispersion of POSS-rich domains. Especially, the degree of phase separation depends on many factors such as chemical structure, molecular weight,

142 High Performance Polymers and Their Nanocomposites

PUI-POSS-10

60000

50000

c

40000

30000

20000

10000 O

Si Br

0 0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

KeV Element line

Weight %

Weight % error

Atom %

Atom % error

CK

83.57

±0.22

87.85

±0.24

OK

14.20

±0.17

11.20

±0.14

Si K

2.03

±0.01

0.91

±0.01

Si L

—

—

—

—

Br K

—

—

—

—

Br L

0.20

±0.02

0.03

±0.00

Total

100.00

100.00

Figure 5.5 SEM-EDX of PUI-POSS-10 nanocomposite membrane.

composition, and arrangement of both hard and soft segments within the nanocomposite membranes. The excellent dispersion of POSS at low concentration in nanocomposite membranes could be explained by the combination of two factors: (i) the reactivity of trisilanol group with isocyanate, so that it can incorporate POSS evenly in the network, during the early stage of polymerization and (ii) the compatibility of POSS is high in polymer matrices rather than high concentrations of POSS. From these discussions on dispersion behavior of POSS nanocomposite membrane, it was evidently showed that the aggregation of POSS molecules increases with an increase in the POSS content. Figure  5.5 showed a typical SEM/EDX image for the POSS 10 wt.% nanocomposite membrane, and this image directly explained the concentration of elements present in the prepared PUI-POSS-10 membrane. This membrane appeared to be relatively uniform, thus indicating that

Effect of Nanostructured Polyhedral Oligomeric 143 Table 5.2 Surface Free Energy of the PUI-POSS Nanocomposite Membranes.

Sample

HO θ 2

C H θ 16 34

γsp γsd (mNm−1) (mNm−1) γsv (mNm−1)

PUI-POSS-0

95.66

38.66

21.88

11.78

33.67

PUI-POSS-5

99.00

37.66

22.07

9.05

31.12

PUIPOSS-10

102.66

34.33

22.09

6.04

28.13

PUIPOSS-15

104.33

33.66

23.08

4.84

27.92

the attachments of POSS to polymer help to reduce POSS aggregation at the membrane surface. Moreover, the result showed good dispersion of the nanoparticles throughout the membrane. Similar results have also been observed by Worthley et al., [31]. Lighter regions, ranging in size from a few nanometers up to a few microns in diameter (Figure 5.4), contained a peak at 1.7 keV, corresponding to silicon (Figure 5.5). Increased silicon count (lighter regions) concentrations were observed, indicating higher the POSS nanoparticles were presented within the membranes (Figure 5.4).

Surface Morphology Studies by Contact Angle Measurements The contact angle measurements provided useful information about the surface energies of prepared nanocomposite membranes and its hydrophobic/hydrophilic nature. The polar, non-polar, and dispersion factors were calculated using the following Young and Fowks equation [32]. The angle of contact between water and n-hexadecane for all the nanocomposite membranes were measured, and the results are given in Table 5.2. Figure 5.6 shows clearly the contact angles of both the solvents [C16H34 (a) H2O (b)] on the PUI-POSS membranes. It could be clearly seen that increasing the POSS content increases the water (Figure 5.6b) contact angles which indicates that higher the surface hydrophobicity of the polymers. On the other hand, contact angles for n-hexadecane (Figure 5.6a) decrease with increase in POSS concentration. This may be due to more hydrophobic POSS aggregation on the surface of nanocomposites that we have observed in the AFM and SEM images. However, surface energy of the nanocomposites was decreased by increase in the POSS content. It was found that the

144 High Performance Polymers and Their Nanocomposites

(a)

(b)

Figure 5.6 Contact angles photographic picture of PUI-POSS nanocomposite membranes.

decrease of surface energy was mainly attributed by the polar component because of a drastic decrease in γsp from 11.78 mN m−1 to 4.84 mN m−1. From all these morphology observations, it is possible to conclude that the POSS aggregation numbers are more and spread over the surface of entire membranes, and it makes the nanocomposite membrane more hydrophobic as well as rough surface. POSS molecules played a considerable role on the surface energies of membranes. The complete schematic representations of POSS surface morphology behavior on PUI-POSS membrane were shown in Figure 5.7.

Thermal Stability of PUI-POSS Nanocomposite Membranes Mass loss curves vs. temperature of PUI-POSS nanocomposites membranes are shown in Figure  5.8. Only two major thermal decompositions were observed in the TGA curves of the nanocomposites membranes: one is around 250–330 °C and other is above 330 °C. The increase in the decomposition temperature was due to the presence of the POSS content. It was well observed that POSS was found to show drastic increase in their thermal property as the percentage of POSS increases from 5 to 15 wt.%. Similar type of observations was earlier reported by Gnanasekaran and co-workers [23, 24]. Figure 5.8 also shows that the nanocomposite membrane samples (PUIPOSS5 to PUI-POSS15) were more stable than the PUI-POSS0 membrane under thermal degradation at nitrogen conditions. Above 250 °C, the PUIPOSS0 membrane showed rapid mass loss, leaving a 5 wt.% residue at 700 °C. Between 250 °C and 600 °C, the residues of the PUI-POSS nanocomposite

Effect of Nanostructured Polyhedral Oligomeric 145 POSS Urethane Imide

nm 250 200 150 100 50 25

0.5 μm 25 20

20 15

15 10

10 5

60000

5 0 0

C 50000 40000 30000 20000 10000 O

Si Br

0 0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

KeV

Figure 5.7 Conspectus of surface morphology study of PUI-POSS nanocomposite membranes.

100 90

PUI-POSS10

80

Weight loss (%)

70 60 50 40 PUI-POSS15 30 PUI-POSS0

20

PUI-POSS5

10 0 0

100

200

300

400

500

600

700

800

Temperature (°C)

Figure 5.8 Thermogram of PUI-POSS nanocomposite membranes.

900

1000

146 High Performance Polymers and Their Nanocomposites membranes were higher than that observed for the PUI-POSS nanocomposite membranes. The presence of POSS apparently enhanced thermal stability. This can be attributed to barrier effects preventing nitrogen diffusion into the matrix and the release to the atmosphere of small molecule fragments generated during the thermal decomposition process [33].

5.4

Conclusions

Facile way of studying the influence of POSS on surface morphology was investigated using SEM, AFM, and TEM analysis. Simultaneously, gel content FFV and density of nanocomposite membranes were elaborated and correlated with surface morphology analysis. AFM confirmed the significant changes were occurred in the roughness (RMS) at the surface of nanocomposite because of the presence of silica like core POSS structure and its hydrophobic nature. The SEM analysis of the PUI-POSS confirmed the occurrence of phase separation because of the aggregations of POSS at higher concentrations. The surface energy estimation clearly showed the presence of hydrophobic groups on the surface of POSS incorporated membrane, and this result is consistent with other surface morphology analysis. Gel content, FFV, and density values were dependable with surface morphology results. Finally, these morphological characterizations and its discussions allowed us to better understand the relationship between surface morphology and POSS concentrations. Prepared nanocomposite membranes are having a capability to apply the gas-transport study because rough and hydrophobic surfaces facilitate the transfer of gas molecules.

References 1. Lichtenhan, J.D., Vu, N.Q., Carter, J.A., Gilman, J.W., Feher, F.J., Feher, F.J., Silsesquioxane-siloxane copolymers from polyhedral silsesquioxanes. Macromolecules, 26(8), 2141–2142, 1993. 2. Ayandele, E., Sarkar, B., Alexandridis, P., Polyhedral Oligomeric Silsesquioxane (POSS)-Containing Polymer Nanocomposites. Nanomaterials, 2(4), 445, 445–475, 2012. 3. Lichtenhan, J.D., Carr, M.J., Carr, M.J, Otonari, Y.A., and Carr, M.J., Linear Hybrid Polymer Building Blocks: Methacrylate-Functionalized Polyhedral Oligomeric Silsesquioxane Monomers and Polymers. Macromolecules, 28(24), 8435–8437, 1995. 4. Zou, H., Wu, S., Shen, J., Polymer/silica nanocomposites: preparation, characterization, properties, and applications. Chem. Rev., 108(9), 3893–3957, 2008.

Effect of Nanostructured Polyhedral Oligomeric 147 5. Balazs, A.C., Emrick, T., Russell, T.P., Nanoparticle polymer composites: where two small worlds meet. Science, 314(5802), 1107–1110, 2006. 6. Gnanasekaran, D., Madhavan, K., Reddy, B.S.R., Developments of polyhedral oligomeric silsesquioxanes (POSS), POSS nanocomposites and their applications: A review. J. Sci. Ind. Res., 68, 437, 2009. 7. Gnanasekaran, D., Madrhavan, K., Tsibouklis, J., Reddy, B., Nanocomposites based on copolymers of fluorinated imide and polyhedral oligomeric silsesquioxane macromonomer: microstructure and morphology studies. Polym. Int., 62(2), 190–195, 2013. 8. Neyertz, S., Gopalan, P., Brachet, P., Kristiansen, A., Männle, F., Brown, D., Oxygen Transport in Amino-Functionalized Polyhedral Oligomeric Silsesquioxanes (POSS). Soft Materials, 12(1), 113–123, 2014. 9. Cong, H., Radosz, M., Towler, B., Shen, Y., Polymer–inorganic nanocomposite membranes for gas separation. Separation and Purification Technology, 55(3), 281–291, 2007. 10. Haddad, T.S., Lichtenhan, J.D., The incorporation of transition metals into polyhedral oligosilsesquioxane polymers. J. Inorg. Organomet. Polym., 5(3), 237–246, 1995. 11. Mantz, R.A., Jones, P.F., Chaffee, K.P., Lichtenhan, J.D., Gilman, J.W., Ismail, I.M.K, et  al, Thermolysis of Polyhedral Oligomeric Silsesquioxane (POSS) Macromers and POSS−Siloxane Copolymers. Chem. Mater., 8(6), 1250–1259, 1996. 12. Haddad, T.S., Lichtenhan, J.D., Haddad Lichtenhan, T.S., and T.S., T.S., Hybrid Organic−Inorganic Thermoplastics: Styryl-Based Polyhedral Oligomeric Silsesquioxane Polymers. Macromolecules, 29(22), 7302–7304, 1996. 13. Schaefer, D.W., Justice, R.S., How Nano Are Nanocomposites? Macromolecules, 40(24), 8501–8517, 2007. 14. Moore, T.T., Koros, W.J., Koros, T.T., Non-ideal effects in organic–inorganic materials for gas separation membranes. J. Mol. Struct., 739(1–3), 87–98, 2005. 15. Chattopadhyay, D.K., Mishra, A.K., Sreedhar, B., Raju, K.V.S.N., Thermal and viscoelastic properties of polyurethane-imide/clay hybrid coatings. Polym. Degrad. Stab., 91(8), 1837–1849, 2006. 16. Avadhanl, C.V., Wadgaonkar, P.P., Khisti, R.S., Gunjikar, V.G., Vernekar, S.P., Vernekar, S.P., Vernekar, S.P., Synthesis and characterization of imide containing diisocyanates and poly(imide-urethane)s therefrom. Polymer Bulletin, 23(2), 163–169, 1990. 17. Yeganeh, H., M. Barikani, and F.N. Khodabadi, Synthesis and properties of novel thermoplastic poly(urethane imide)s. Eur. Polym. J., 36, 2207, 2000. 18. Zuo, M., Xiang, Q., Takeichi, T., Preparation and properties of novel poly(urethane-imide)s. Polymer, 39(26), 6883–6889, 1998. 19. Zuo, M., Takeichi, T., Novel method for the preparation of poly(urethane–imide)s and their properties. J. Polym. Sci. A: Polym. Chem, 35(17), 3745–3753, 1997.

148 High Performance Polymers and Their Nanocomposites 20. Pescarmona, P.P., Raimondi, M.E., Tetteh, J., McKay, B., Maschmeyer, T., Mechanistic Study of Silsesquioxane Synthesis by Mass Spectrometry and in Situ ATR FT-IR Spectroscopy. J. Phys. Chem. A, 107(42), 8885–8892, 2003. 21. Bondi, A.A., Physical properties of molecular crystals. Liquids and Gases. Wiley, New York, 1968. 22. Van Krevelen, D.W., Hoftyzer, P.J., Properties of Polymers. Their Estimation and Correlation with Chemical Structure. 2nd ed. New York, Elsevier, 1976. 23. Gnanasekaran, D., Reddy, B.S.R., Cost effective poly(urethane-imide)-POSS membranes for environmental and energy-related processes. Clean Techn. Environ. Policy, 15(2), 383–389, 2013. 24. Gnanasekaran, D., Ajit Walter, P., Asha Parveen, A., Reddy, B.S.R., Polyhedral Oligomeric Silsesquioxane–Based Fluoroimide–Containing Poly(UrethaneImide) . Membranes Synthesis, Characterization and Gas-Transport Properties. 111. p. 108, 2013. 25. Liu, L., Tian, M., Zhang, W., Zhang, L., Mark, J.E., Crystallization and morphology study of polyhedral oligomeric silsesquioxane (POSS)/polysiloxane elastomer composites prepared by melt blending. Polymer, 48(11), 3201–3212, 2007. 26. Lee, Y.-J., Kuo, S.-W., Huang, W.-J., Lee, H.-Y., Chang, F.-C., Miscibility, specific interactions, and self-assembly behavior of phenolic/polyhedral oligomeric silsesquioxane hybrids. J. Polym. Sci. B Polym. Phys., 42(6), 1127–1136, 2004. 27. Ricco, L., Russo, S., Monticelli, O., Bordo, A., Bellucci, F., ε-Caprolactam polymerization in presence of polyhedral oligomeric silsesquioxanes (POSS). Polymer, 46(18), 6810–6819, 2005. 28. Leu, C.-M., Chang, Y.-T., Wei, K.-H., Synthesis and Dielectric Properties of Polyimide-Tethered Polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposites via POSS-diamine. Macromolecules, 36(24), 9122–9127, 2003. 29. Leu, C.-M., Chang, Y.-T., Wei, K.-H., Polyimide-Side-Chain Tethered Polyhedral Oligomeric Silsesquioxane Nanocomposites for Low-Dielectric Film Applications. Chem. Mater., 15(19), 3721–3727, 2003. 30. Feng, Y., Jia, Y., Guang, S., Xu, H., Study on thermal enhancement mechanism of POSS-containing hybrid nanocomposites and relationship between thermal properties and their molecular structure. J. Appl. Polym. Sci., 115(4), 2212–2220, 2010. 31. Worthley, C.H., Constantopoulos, K.T., Ginic-Markovic, M., Markovic, E., Clarke, S., A study into the effect of POSS nanoparticles on cellulose acetate membranes. J. Memb. Sci., 431, 62–71, 2013. 32. Adamso, A.W., Interscience. Physical Chemistry of Surfaces. New York, 1960. 33. Hablot, E., Matadi, R., Ahzi, S., Avérous, L., High strain rate behaviour of renewable biocomposites based on dimer fatty acid polyamides and cellulose fibres. Compos. Sci. Technol., 70, 504–509.

6 Thermoplastic Polyimide (TPI) Xiantao Feng1 and Jialei Liu2,* 1

School of Chemistry and Pharmaceutical engineering, Huanghuai University, Zhumadian, China 2 BeijingKey Laboratory of Thermal Science and Technology, Beijing, China, Technical Institute of Physics and Chemistry, CAS Key Laboratory of Cryogenics, Beijing, China

Abstract This chapter is mainly focused on the polymerization, processing, properties, and applications of thermoplastic polyimides (TPIs). The polymerization and properties are introduced by their basic polymer units, such as BEPA, PMDA, BTDA, ODPA, BTDA, etc. The blends, composites, and nanocomposites of TPI are also described in this chapter, including the compounding with other molecules of TPI. The environmental impact and recycling is discussed briefly at the end of the chapter. Keywords: Thermoplastic polyimide, polymerization, processing, properties, applications, blends, composites, compounding, environmental impact and recycling

6.1

Introduction and History

Polyimide (PI) is a polymer of imide monomers. In those of polymers, phthalimide polymer is the most important one. According to the composition of their main chain, polyimides can be classified into three kinds as follows: Aliphatic polyimides (linear polyimides), semiaromatic polyimides, and aromatic polyimides. The last ones are the most used polyimides because of their good thermostability such as the phthalimide polymers mentioned above. According to the type of interactions between the main chains, there are two different polyimides: thermosetting polyimides and thermoplastic *Corresponding author: [email protected] Visakh P.M. and Semkin A.O. (eds.) High Performance Polymers and Their Nanocomposites (149–220) © 2018 Scrivener Publishing LLC

149

150 High Performance Polymers and Their Nanocomposites O

O

N

N

O

O

Figure 6.1 Structure of imide circle.

polyimides. Thermosetting polyimides polymerized from pyromellitic dianhydride (PMDA) and bis(4-aminophenyl)ether (ODA) have a long history of roughly 40 years since commercialization under DuPont. Thermosetting polyimides are known for thermal stability, good chemical resistance, excellent mechanical properties, and characteristic orange/yellow color. The polyimide cannot be melted or injection-molded and therefore has some limitations for complicated design and productivity. From the 1970s, the National Aeronautics and Space Administration (NASA) firstly launched the research and development of high-performance, high-temperature-resistant adhesive. This work is aimed to develop high-temperature (200 °C to 300 °C) organic adhesive in continuous use, such as aircraft structural components. The TPI resin is one of the key research areas. Compared with thermosetting polyimide material, TPI resin has good toughness, great damage tolerance, and repairable. TPI also can be used as matrix resin for continuous carbon fiber–reinforced resin composites; cryopreservation is no need for the prepared prepreg, thus significantly reducing the cost of manufacturing composite materials and improve the impact toughness of the composites, etc. On this basis, TPI materials which can be directly melted were developed, such as molding, extrusion, and injection molding processable TPI materials. The melt processable property of TPI can not only greatly reduce the costs, improve production efficiency, stabilize product quality, but also produce high value-added products with special performance and functions.

6.2

Polymerization and Fabrication

6.2.1 Thermoplastic Polyimides Based on BEPA ULTEM is one of the typical bisphenol A bisether-4-diphthalic anhydride (BEPA)–based thermoplastic polyimides; it was commercialized by

Thermoplastic Polyimide (TPI) 151 O

O

CH3 +

N

N

HO

OH

C CH3

NO2

O2N O

O

O N

O

CH3 O

O

C CH3

O

N O

n

Scheme 6.1 Synthesis route of ULTEM.

General Electric Company in 1982. ULTEM can be processed by conventional techniques such as injection molding at 360–380 °C. However, the thermos-oxidative stability of ULTEM is relatively poor owing to the presence of the thermally unstable. Takekoshi et al., [1] reported that ULTEM is produced via nitrodisplacement of bisnitroimides (scheme.6.1) with bisphenol A in polar aprotic solvents. Shi et al., [2] synthesized another several BEPA-based TPI with bisphenol A and a variety of diamines Table 6.1. TPIs based on BEPA were prepared with various aromatic diamines in the conventional two-step process via poly(amic acid) (PAA) polymerization and successive thermal imidization. A typical procedure of PAA polymerization is as follows: to a solution of 8 mmol 1,3-phenylenediamine in 40 ml of DMAc, 8 mmol BEPA powder was gradually added. The solution was stirred at room temperature for 24 h. The viscous PAA solution obtained was cast with a doctor blade and dried in an oven at 70 °C for 3 h. The dried PAA films were then thermally imidized upon a stepwise heating process of 150 °C/1h + 200 °C/1h + 250 °C/1h + 280 °C/2h under vacuum in a free-standing state. The thickness of PI films ranged from 20 to 40 μm. To obtain the homopolyimide powder, the PAA solutions were refluxed at 170 °C for 4 h and then poured into a large excess of methanol for precipitation. The obtained powder was postcured under vacuum at 250 °C/h or 280 °C/h to ensure complete imidization.

152 High Performance Polymers and Their Nanocomposites Table 6.1 Abbreviations and Structures of the Diamines. Abbreviations PDA m-PDA

Structures NH 2

H 2N H 2N

NH 2

4,4 -ODA

H 2N

3,4 -ODA

H 2N

O

O

NH 2

NH 2

O

p-BAPS

S

O

H 2N

O

NH 2

O

m-BAPS

O

H 2N

NH 2

S

O

O

O

TPER

TPEQ BAPB

H 2N

O

O

H 2N

O

H 2N

O

NH 2

NH 2

O

O

PTPEQ H 2N

o-TOL

O

O

H 3C

C H3

H 2N

NH 2 H 3C

m-TOL H 2N

NH 2 C H3

NH 2

NH 2

Thermoplastic Polyimide (TPI) 153

6.2.2 Thermoplastic Polyimides based on PMDA Pyromellitic dianhydride (PMDA) is one of the massive production and cheapest aromatic dianhydrides. Developing TPI based on PMDA could effectively lower the fabrication cost. But there are few TPIs based on PMDA due to their strong rigid structures. In the late 1980s, Mitsui Chemicals, Inc. began investigating and developing a thermoplastic polyimide to meet industry needs. As a result of these efforts, Aurum was launched. This material is synthesized from pyromellitic dianhydride (PMDA) and 4,4bis (3-aminophenoxy)biphenyl and has a high heat resistance with glass transition temperature Tg = 250 °C. AURUM is an injection-moldable semicrystalline polyimide, but it has a very slow crystallization rate. The part obtained through injection molding is amorphous, not crystalline, although Aurum is a semicrystalline polymer. The postcuring after injection molding enabled crystallization, but control of the tight dimension was not sufficient [3]. AURUM has better heat resisting property than ULTEM, but the raw material 4,4-bis (3-aminophenoxy)biphenyl is much more cost which limited its yield and applications. E.I. du Pont de Nemours and Company developed another PMDA-based TPI called VESPEL. Its Tg is up to 385 °C. S. Tarmai and A. Yamaguchi used PMDA and ether diamines to synthesize a series of TPI. The typical polymerization is as follows: A mixture of 0.0582 mol of PMDA, 0.0600 mol of diamines, 0.0036 mol of phthalic anhydride, which was a termination of a polymer chain end, 0.009 mol of 7-picoline in 123 g of m-cresol was stirred at 150 °C for 4 h, and then O

O H2N

O

O

O

O

+

NH2

O

O

O N O

O N

O

O

*

O n

Scheme 6.2 Synthesis route of AURUM.

154 High Performance Polymers and Their Nanocomposites O O O

O

O O O

+ H2N

Y

NH2

r-picoline heating in m-cresol at150°C for 4h

N O

O N

Y

O n

Scheme 6.3 Synthesis route of TPI based on PMDA.

after cooling down, the reaction mixture was poured into methanol. The precipitated polyimide was collected by filtration, followed by thorough washing with methanol and dried in a forced air oven to a temperature around the Tg of the polyimide. The other polyimide powders were prepared by the same method as mentioned above. Scheme 6.3 shows the typical synthesis route of PMDA based TPI. The structures of the ether diamines can be found in Table 6.2.

6.2.3 Thermoplastic Polyimides Based on BTDA V. Ratta et al., used 3,3ʹ,4,4ʹ-biphenonetetracarboxylic dianhydride (BTDA) and an 1,3-bis(4-aminophenoxy) benzene (TPER diamine) to synthesize one kind of high-temperature semicrystalline thermoplastic polyimides. The polyimide displays a Tg at ca. 230 °C and two prominent melting endosperms at 360 °C and 460 °C, respectively, with a sharp recrystallization exotherm following the lower melting endotherm. The reaction vessel was a three-neck round bottom flask equipped with a mechanical stirrer, nitrogen inlet, and a drying tube. Sufficient N-methylpyrrolidinone (NMP) was added to achieve a 10% solid concentration, and the solution was allowed to stir for 24 h, to afford a homogenous poly(amic acid) solution as shown in Scheme 6.4. A stepwise thermal imidization procedure was utilized. The first step was the casting of the poly(amic acid) precursor on the Pyrex glass plates. These plates were placed in the vacuum oven overnight until smooth nontacky films were obtained. Thermal imidization was achieved by raising the temperature to 100, 200, and 300 °C and holding at each of these temperatures for 1 h. The time to go from one temperature to the next was ca. 1 h each at the fastest heating rate available with the oven. After the completion of the cycle, the plates were allowed to cool to room temperature before being removed from the oven. The films were stripped off the glass plates in hot water and stored in a desiccator before use. Tapas koley et al., [6]. used a diamine monomer, 1, 4-bis-[{2'-trifluromethyl 4'-(4''-aminophenyl)phenoxy}]

Thermoplastic Polyimide (TPI) 155 Table 6.2 The structures of the etherdiamines. Abbreviations

Structures

4d-m

H 2N

NH 2

S

o 4d-p 4f-m

S

o

H 2N H 2N

4g-m

C H3 C H3

o

C H3

CF3

CF3

H 2N

4b-m

NH 2

O

o

C O

o

H 2N

o

C

H 2N

NH 2

NH 2

o 4b-p

o

C

o 4e-p

NH 2

CF3

o 4e-m

o

C

H 2N

NH 2

NH 2

CF3

o

4g-p

o

C

H 2N

NH 2

o

C

H 2N

o NH 2

C H3

o

4f-p

o

o

H 2N

O

NH 2

O O

4c-m

S

O

H 2N

O

NH 2

O

4c-p

O

H 2N

O

S O

NH 2

O

156 High Performance Polymers and Their Nanocomposites O

O H2N

O

O

O

O

O

NH2

O

O

O

O

O

NMP,25°C,24h

O

O HN OH

O

O

O

O

O

O

THERMAL 12 HOURS AT RT 1 HOUR EACH AT 100°C,200°C,300°C COOLSLOWLY

O

O

O

O

O

SOLUTION 80%MNP/20% 180°C FOR 2 HOURS

O

O N

N O

HN HO O

Tmca.410°C

O

O

n

Tgca.230°C

O N

O

O HN OH

N H HO

O

O

O

N O

n

Scheme 6.4 Synthesis route of TPER-BTDA-PA. F3C

O

O

CF3

O N O

O

O N O

n

Figure 6.2 The structure of the HQA-BTDA-based TPI.

benzene (HQA), and BTDA to synthesize one kind of BTDA-based TPI (Figure 6.2). The polyimides showed reasonably high glass-transition temperature (Tg280 °C) and high thermal stability (Td, 558 °C). The bis(ether amine) monomer was reacted with BTDA according to two-step conventional procedure to obtain poly(ether imide) membranes. A representative polymerization procedure is as follows: BPADA (0.338 g, 0.65 mmol) was added in portions into the diamine (HQA) (0.377 g, 0.65 mmol) solution in dry DMF (7.0 mL) containing in a 25 mL round bottom flask equipped with a guard tube. The mixture was left for stirring at room temperature while it is transformed to a highly viscous solution of polyamic acid (PAA) within 45–60 min. In the second step, viscous PAA solution was spread onto a clean and dry flat-bottomed Petri dish and kept in oven initially at 80 °C for overnight for slow removal of the solvent.

Thermoplastic Polyimide (TPI) 157 O O

N

O

O

O

O O

N O

N O

n

Ratem-YS-20

O

O N O

n

LaRC-IA

Figure 6.3 The structures of Ratem-YS-20 and LaRC-1A.

Finally, the thermal cyclization of the PAA to PI was achieved by sequential heating at 100, 150, 200, 250, and 300 °C, each for 1 h and at 350 °C for 30 min in an oven under nitrogen atmosphere. The resulting polyimide membranes were removed from the Petri dishes by immersing in hot water after that the membranes were dried under vacuum at 140 °C for 26 h.

6.2.4 Thermoplastic Polyimides Based on ODPA Shanghai Research Institute of synthetic resins developed one TPI with 4,4 -oxy-diphthalic anhydride (ODPA) and 4,4ʹ-oxybisbenzenamine (4,4ʹ-ODA) called Ratem-YS-20 in 1970s [7]. NASA used ODPA and 3, 4ʹ-oxybisbenzenamine (3, 4ʹ-ODA) to synthesize another TPI called LaRC-IA. The structures of these two TPI based on ODPA could be found in Figure 6.3 [8, 9]. Shi et al., [2]. also synthesized and characterized a serial TPI with ODPA and a series of diamines (4,4ʹ-ODA and 3, 4ʹ-ODA included). The synthesis route of ODPA-based TPI is just the same as the BEPA-based ones as Shi et al., reported.

6.2.5 Thermoplastic Polyimides Based on BPDA In 2001, S. Tamai et al., synthesized 3,3ʹ,4,4ʹ-biphenyltetracarboxylic dianhydride (BPDA)-based TPI. The synthesis procedure is as follows: 3,4ʹ-oxydianiline (3,4ʹ-ODA) polyimide was synthesized with 28.10 g (95.5 mmol) of BPDA, 20.03 g (100 mmol) of 3,4ʹ-ODA, 1.33 g (9 mmol) of PA, which was used for terminating the polymer chain end. A four-neck round-bottom flask equipped with a mechanical stirrer, nitrogen pad, thermometer, and a condenser with a Dean–Stark trap was used as the reaction vessel. All monomers were added to a reaction vessel and then 3-methylphenol was added to achieve a 10% solids concentration. This solution was stirred and heated under nitrogen atmosphere for 12 h at 202 °C, to afford the PA end-capped polyimide. During the reaction, the by-product, water, was removed by nitrogen flow. After cooling down, methylethyl ketone was

158 High Performance Polymers and Their Nanocomposites added to the reaction mixture. The precipitated polyimide was collected by filtration, followed by thorough washing with methylethyl ketone and dried in a forced air oven at 300 °C for 4 h under nitrogen atmosphere. The other polyimide obtained from 1,3-bis(4-aminophenoxy)benzene (TPER), and BPDA was also prepared by almost the same method as mentioned above.

6.2.6 Thermoplastic Copolyimides E.I. du Pont de Nemours and Company published a patent which described the synthesis of thermoplastic copolyimides in 2001. The polymers were the reaction products of components comprising an aromatic dianhydride component, an aromatic diamine component, and an end-capping component. The aromatic dianhydride component is selected from the group consisting of BPDA and BTDA, BPDA is preferred. The aromatic diamine component consists of a first aromatic diamine and a second aromatic diamine. The first aromatic diamine is selected from the group consisting of APB-134 and 3,4ʹ-ODA. The second aromatic diamine is selected from the group consisting of APB-133, 4,4ʹODA, MPD, APB-144,BAPS, BAPB, BAPE, BAPP, and 4,4ʹ-ODA, MPD in combination, and 4,4ʹ-ODA and PPD in combination; wherein APB133,APB-144, 4,4ʹ-ODA,BAPS, and 4,4ʹ-ODA and MPD in combination are preferred. 4,4ʹ-ODA, and 4,4ʹ-ODA and MPD in combination are most preferred. Suitable end-capping components when diamines are in excess include, but are not limited to, phthalic anhydride and naphthalic anhydride. These copolyimides have a stoichiometry in the range from 93% to 98 %, exhibit a melting point in the range of 330 °C to 385 °C, and exhibit recoverable crystallinity as determined by differential scanning calorimetry analysis. A typical synthesis procedure is as follows: Preparation of Polyimide Based on BPDA//3,4ʹ-ODA/APB-134//PA 95//70/30//10—(95% of stoichiometric dianhydride) Into a 250 mL round bottom flask equipped with a mechanical stirrer and nitrogen purge were charged 5.3695 g (0.02681 mole) of diamine 3,4ʹODA, 3.3596 g (0.01149 mole) of diamine APB-134 and 60 ml of NMP. O

O

O

N

N

O

O

O n

3,4'-ODApolyimide

Figure 6.2 The structures of TPI based on BPDA.

O N

O N

O

O

TPERpolyimide

n

Thermoplastic Polyimide (TPI) 159 After dissolution of the diamines, 10.7073 g (0.03639 mole) of dianhydride BPDA and 0.5674 g (0.00383 mole) phthalic anhydride were added with stirring under nitrogen and rinsed in with 20 ml NMP. The following day, 14.46 ml (0.153 mole) of acetic anhydride (4 × moles of diamine) and 21.36 ml (1.53 mole) of triethylamine (4 × moles of diamine) were added to the poly(amic acid) solution to effect imidization. After about 10 minutes the polymer precipitated, any clumps were broken up by manual manipulation of the mechanical stirrer, and stirring was continued for about 6 hours. The resulting polymer slurry was then added to methanol in a blender to complete precipitation and remove NMP. The polymer was separated by filtration, washed with methanol, and then dried at ca. 200 °C overnight under vacuum with a nitrogen bleed. DSC analysis (10 °C/min.) of the resulting polyimide showed a melting point of 345 °C during the first heating scan, a crystallization exotherm upon the subsequent cooling scan at 296 °C, and a melting point at 346 °C during the subsequent reheat scan, indicating recoverable crystallinity from the melt. The synthesis of other compolyimides was similar to the typical manner. Table 6.3 Abbreviations of the Diamines. Abbreviations

Diamines

APB-133

1.3-Bis(3-aminophenoxy)benzene

APB-134

1.3-Bis(4-aminophenoxy)benzene (=RODA)

APB-144

1.4-Bis(4-aminophenoxy)benzene

BAPB

4.4-Bis(4-aminophenoxy)-biphenyl

BAPE

Bis(4-[4-aminophenoxy]phenylether(=4,4'-Bis(4aminophenoxy)-diphenylether)

BAPP

2.2-Bis(4-[4-aminophenoxyl]phenyl)propane

BAPS

4,4'-Bis(4-aminophenoxy)diphenyl sulfone

MPD

1.3-Diaminobenzene

PPD

1.4-Diaminobenzene

3,4-ODA

3,4-Oxydianiline

4,4-ODA

4.4-Oxydianiline

3,3-ODA

3,3'-Oxydianiline

RODA

1,3-Bis(4-aminophenoxy)benzene(=APB134)

160 High Performance Polymers and Their Nanocomposites

6.3

Properties

In overall, TPIs have the excellent properties as follows: 1. The outstanding characteristics of TPI are excellent heat resistance, the long-term use temperature is about 230–240 °C, and the Tg is up to 250 °C. 2. Superdimensional stability. The thermal expansion coefficient of polyimide is only 50PPM/ oC, and it has good creep resistance. 3. Excellent mechanical properties. Tensile strength is about 100 MPa, impact strength is about 260 KJ/m2. 4. Good flame retardancy. The oxygen index is 36–46, low smoke rate, strong self extinguishing property. 5. Excellent electrical insulation performance. 6. Excellent oil resistance and solvent resistance. 7. High viscosity.

6.3.1

TPI Based on BEPA

ULTEM (Scheme 6.1) is one of the typical bisphenol A bisether-4-diphthalic anhydride (BEPA)-based thermoplastic polyimides; it was commercialized by General Electric Company in 1982. The properties of ULTEM are the worst of the TPI family. But the advantages of lower cost, easy to process made it popular in the market. Its global yield achieved ten thousand tons these years. The properties of ULTEM are listed in Table 6.4 Shi et al., synthesized and characterized a serial TPI based on BEPA as we mentioned in Section 6.2.1. The properties of the TPI are as shown in Table 6.4. Table 6.5 shows the properties of BEPA-based homopolyimides without any additives. The reduced viscosities of those PAAs ranged from 0.86 to 2.65 dl g−1, indicating the corresponding PIs probably had sufficiently high molecular weights. Generally speaking, the processing condition for the crystalline PIs is often limited in the range from Tm +α to Td. In many cases, aromatic PIs do not become a free-flowing liquid just above the Tm’s in contrast to common semicrystalline polymers such as poly(ethylene terephthalate). This is probably due to surviving intermolecular interactions even just above the Tm’s. Therefore, the thermo-processing temperatures for semicrystalline PIs are generally several tens of degrees higher than the Tm’s. For example, semicrystalline PI AURUM

Thermoplastic Polyimide (TPI) 161 Table 6.4 Properties of ULTEM 1000 (Pure TPI, Without Additives, No Complexes or Blends). Properties

Units

Density

g/cm3

Water absorption

%

Conditions

ULTEM 1000 1.27

23 °C,24h

0.25

23 °C, saturated impregnation

1.25 200

Heat deflection temperature

°C

18.6 kg/cm2

Coefficient of liner expansion

K-1

23 °C

6.2*10-5

Tensile strength

MPa

23 °C

107

Elongation at break

%

23 °C

60

Tensile modulus

MPa

23 °C

60

Bending strength

MPa

23 °C

3060

Flexural modulus

MPa

23 °C

148

Compressive strength

MPa

23 °C

3370

Compressive modulus

MPa

23 °C

143

Cantilever impact strength

Kg.cm/cm

23 °C, no gap

2960

23 °C, with gap

370

Rockwell hardness

109

Friction factor

Wear rate

mg

Between self ’s

0.19

With steel

0.2

CS17, 1 kg, 1000 C

10

(Tm = 388 °C) can be processed at 410 °C (α = 22 °C) [12]. However, in most cases, the upper temperature limit for the processing of aromatic PIs should be established below 400 °C in order to avoid undesirable thermal degradation such as crosslinking and also to use common molding machines. Thus, for designing TPI, the limited processing temperature range is a critical factor.

162 High Performance Polymers and Their Nanocomposites Table 6.5 The Properties of TPI Based on BEPA. the Melt Flowability Was Performed as a Qualitative Test on a Temperature-Regulated Hotplate at 400 °C. Tg (The Glass Transition Temperature); Tm (Melting Point); Td (Thermal Decomposition Temperature); Td5 (5% Weight Loss Temperature). TPI

ηred of PAA Tg (dl.g-1) (oC)

Tm (oC)

Td5 (°C) In N2 in air

Melt flowability

1

BEPA/PDA

1.86

233

no

474

449

Poor

2

BEPA /m-PDA

1.30

215

no

489

475

Good

3

BEPA/4,4ʹODA

1.76

211

no

511

501

Poor

4

BEPA/3,4ʹODA

0.83

198

no

510

508

Good

5

BEPA /TPEQ

2.65

205

no

503

491

Poor

6

BEPA /TPER

0.86

189

no

504

484

Good

7

BEPA /BAPB

1.57

217

no

514

491

Poor

8

BEPA / PTPEQ

1.28

195

no

511

504

Good

9

BEPA /p-BAPS

1.00

229

no

474

486

Poor

10

BEPA /m-BAPS

1.06

194

no

472

478

Good

11

BEPA /o-TOL

2.05

253

no

484

494

Poor

12

BEPA /m-TOL

2.01

238

no

493

491

Poor

The Tg’s of BEPA-based PIs ranged from 189 to 253 °C depending on the diamine structures, and they are 17–93 °C lower than those of the ODPA systems. The melt flowability in BEPA-based PIs varied significantly depending on the diamine structures. As shown in 16.5, m-diamines usually have good melt flowability, whereas p-diamines have poor melt flowability. It is worth noticing that all of the BEPA polyimides in this case have no Tm points. They are completely amorphous even in the PI powder

Thermoplastic Polyimide (TPI) 163 prepared via reflux of the PAA solutions. This is most likely attributed to the presence of the bent and bulky isopropylidene groups in the backbone. Among the BEPA-based PIs, only BEPA/m-PDA (ULTEM type) simultaneously satisfied the demands of a high Tg (>200 °C) and good melt flowability. This PI was the earliest developed by the General Electric Company, as an injection-moldable PI.

6.3.2 Thermoplastic Polyimides Based on PMDA In the late 1980s, Mitsui Chemicals, Inc. developed a TPI called AURUM which is based on PMDA. Its synthesis and structure could be found in Scheme 6.2. S. Tarmai and A. Yamaguchi used PMDA and ether diamines to synthesize a series of TPI. They tested the inherent viscosity (η) and Tg of the PMDA-based TPI [4].

6.3.3

TPI Based on ODPA

Shanghai Research Institute of synthetic resins developed a series TPI called Ratem-YS-20 and its properties were shown in Table 6.11. NASA used ODPA and 3,4ʹ-oxybisbenzenamine (3, 4ʹ-ODA) to synthesize another TPI called LaRC-IA. This TPI possesses good agglutinating property and thermal oxidation stability. Its properties are shown in Tables 6.12 and 6.13 [7–9]. Shi et al., synthesized and characterized a serial TPI based on ODPA as we mentioned in Section 6.2.4. The properties of the TPI are as shown in Table 6.13. Table  6.13 shows the properties of ODPA-based homopolyimides without any additives. Compared to BEPA polyimides, ODPA-based homopolyimides possess higher Tm, Tg, Td, and the viscosities. For ODPA/4,4ʹ-ODA, ODPA/3,4ʹ-ODA, ODPA/TPEQ, ODPA/TPER, and ODPA/BAPB, the PI powder prepared via reflux of the PAA solutions displayed melting peaks in the DSC scan, indicating that these PIs are semicrystalline. However, one notices that the Tm’s of some ODPA-derived PIs are too high for processing, for example Tm = 415 °C for ODPA/TPEQ and 390°C for ODPA/4,4ʹ-ODA. In ODPA/PDA and ODPA/m-PDA, both without flexible ether linkages, no Tm’s in the DSC heating process were exhibited up to 450 °C. Therefore, we estimated their Tm’s from a Tm/ Tg relation. As illustrated in Table 6.13, the ratios Tm/Tg range from 1.17 to 1.35 for semicrystalline ODPA-based PIs, clearly in agreement with an empirical equation for a series of PI systems: Tm≈1.3Tg (in kelvin) [15]. The

164 High Performance Polymers and Their Nanocomposites Table 6.6 Properties of PL450c and SP-1 (PL450c Is One of the Product Models of AURUM, SP-1 Is One of the Product Models of VESPEL, Unfilled). Properties

Units

PL450c

SP-1

Density

g/cm3

1.33

1.43

Molding shrinkage

%

0.83

Water absorption

%

0.34(23 °C,24h)

Moisture absorption

%

0.24(24h)

Tensile strength

MPa

92 (23 °C)

88 (23 °C)

58(150 °C)

42.3(260 °C)

90(23 °C)

7.5(23 °C)

90(150 °C)

6.0(260 °C)

137(23 °C)

112.7(23 °C)

88(150 °C)

63.4(260 °C)

2.94(23 °C)

3.17(23 °C)

2.55(150 °C)

1.76(260 °C)

120(23 °C)

25.3(Deformation rate 1%)

76(150 °C)

135.9(Deformation rate 10%)

Elongation at break

Bending strength

Flexural modulus

Compressive strength

%

MPa

GPa

MPa

0.24(23 °C,24h) 0.72(50 °C,48h)

Impact strength

J/m

90(With gap)

Tm

°C

388

388

Tg

°C

250

250

Melting index

g/(10min)

4.5–7.5 (385 °C/2.3lbs)

4.5–7.5 (385 °C/2.3lbs)

Coefficient of thermal expansion

10-6K-1

5.5(MD)

54(MD)

Heat deflection temperature

o

238

460

C

Thermoplastic Polyimide (TPI) 165 Table 6.6 Cont. Properties

Units

PL450c

Heat conductivity

W/(m.K)

0.17

SP-1

0.24(23 °C) Specific heat capacity

Cal/(g. °C)

0.35(40 °C)

0.24(100 °C) 0.34(300 °C)

Dielectric constant

1kHz

3.2

3.2

1MHz

3.1

3.1

Table 6.7 Long-Term Thermal Stability of AURUM [13]. Retention at 250 °C/% Properties

100h

500h

1000

2000

Tensile strength

110

95

90

90

Elongation at break

100

90

90

90

Tensile modulus

90

95

100

100