Plastic Waste Treatment and Management: Gasification Processes 3031311590, 9783031311598

Table of contents :
Preface
Contents
Contributors
Plastic Types and Applications
1 Definition and Essential Concepts
2 Classifications
2.1 Origin
2.2 Structure of Repeating Unit
2.3 Chain Structure
2.4 Thermal Response
2.5 Polymerization Process
2.6 Polymerization Mechanism and Kinetics
2.7 Tacticity
2.8 Form and Uses
3 Applications
3.1 Packaging
3.2 Textile
3.3 Hydrogels
3.4 Shape Memory Polymers
3.5 Self-Cleaning Polymers
3.6 Biomedical Applications
3.7 Energy Generation and Storage
3.8 Water and Wastewater Treatment
4 Conclusions
References
Collected Plastic Waste Forecasting by 2050
1 Introduction
2 Preliminary Data Analysis
2.1 Global Plastic Production
2.2 Global Plastic Waste Generation
3 Models for Time Series Forecasting
3.1 Regression
3.2 Simple Linear Regression
3.3 Polynomial Regression
3.4 Autoregressive Integrated Moving Average (ARIMA)
4 Projections Until 2050 Using Mentioned Algorithms
4.1 Global Plastic Production Forecasting
4.2 Global Plastic Waste Generation
5 Plastic Waste Management Scenarios
6 Conclusions
References
Plastic Waste Gasification
1 Introduction
2 Thermochemical Processes of Plastic Waste Management
3 Gasification
3.1 Drying Region
3.2 Pyrolysis Region
3.3 Oxidation Region
3.4 Reduction Region
4 Types of Gasifier
4.1 Up-Draft Gasifier
4.2 Down-Draft Gasifier
4.3 Cross-Draft Gasifier
4.4 Fluidized Bed Gasifier
4.5 Entrained Bed Gasifier
References
Air Plastic Waste Gasification
1 Air Gasification Process
2 Air Gasification Modeling of Plastic Waste by Equilibrium Constant Method
3 Air Gasification Modeling of Plastic Waste by Gibbs/Lagrange Coupled Method
4 Energy Analysis on Air Gasification of Plastic Waste
5 Exergy Analysis on Air Gasification of Plastic Waste
6 Performance Evaluation of Air Gasification of Plastic Waste
7 Modeling Validation of Air Gasification of Plastic Waste
7.1 Modeling Validation of Air Gasification of Plastic Waste Based on Equilibrium Constant Method
7.2 Modeling Validation of Air Gasification of Plastic Waste Based on Gibbs/Lagrange Coupled Method
References
Steam Plastic Waste Gasification
1 Steam Gasification Process
2 Steam Gasification Modeling of Plastic Waste by Equilibrium Constant Method
3 Steam Gasification Modeling of Plastic Waste by Gibbs/Lagrange Coupled Method
4 Energy Analysis on Steam Gasification of Plastic Waste
5 Exergy Analysis on Steam Gasification of Plastic Waste
6 Performance Evaluation of Steam Gasification of Plastic Waste
7 Modeling Validation of Steam Gasification of Plastic Waste
7.1 Modeling Validation of Steam Gasification of Plastic Waste Based on Equilibrium Constant Method
7.2 Modeling Validation of Steam Gasification of Plastic Waste Based on Gibbs/Lagrange Coupled Method
References
Evaluation of Air Polyurethane Foam Waste Gasification
1 Introduction
2 Air Gasification Evaluation of Flexible Polyurethane Foam Waste
3 Effect of Moisture Content on Air Gasification of Flexible Polyurethane Foam Waste
4 Effect of Equivalence Ratio on Air Gasification of Flexible Polyurethane Foam Waste
5 Effect of Temperature on Air Gasification of Flexible Polyurethane Foam Waste
6 Conclusions
References
Evaluation of Steam Polyurethane Foam Waste Gasification
1 Steam Gasification Evaluation of Flexible Polyurethane Foam Waste
2 Effect of Moisture Content on Steam Gasification of Flexible Polyurethane Foam Waste
3 Effect of Steam to Flexible Polyurethane Foam Waste Ratio on Steam Gasification of Flexible Polyurethane Foam Waste
4 Effect of Temperature on Steam Gasification of Flexible Polyurethane Foam Waste
5 Conclusions
References
Multi-criteria Decision-Making Analysis of Plastic Waste Gasification
1 Plastic Waste Types Considered for Multi-criteria Decision Analysis
2 Performance of Plastic Waste Types in Air Gasification
3 Performance of Plastic Waste Types in Steam Gasification
4 Technique for Order Preference by Similarity to Ideal Solution (Topsis)
5 Topsis Analysis for Plastic Waste Gasification
5.1 TOPSIS Analysis for Plastic Waste Air Gasification
5.2 TOPSIS Analysis for Plastic Waste Steam Gasification
6 Closing Remarks
References

Citation preview

Engineering Materials

Rezgar Hasanzadeh Parisa Mojaver   Editors

Plastic Waste Treatment and Management Gasification Processes

Engineering Materials

This series provides topical information on innovative, structural and functional materials and composites with applications in optical, electrical, mechanical, civil, aeronautical, medical, bio- and nano-engineering. The individual volumes are complete, comprehensive monographs covering the structure, properties, manufacturing process and applications of these materials. This multidisciplinary series is devoted to professionals, students and all those interested in the latest developments in the Materials Science field, that look for a carefully selected collection of high quality review articles on their respective field of expertise. Indexed at Compendex (2021) and Scopus (2022)

Rezgar Hasanzadeh · Parisa Mojaver Editors

Plastic Waste Treatment and Management Gasification Processes

Editors Rezgar Hasanzadeh Department of Mechanical Engineering, Faculty of Engineering Urmia University Urmia, Iran

Parisa Mojaver Department of Mechanical Engineering, Faculty of Engineering Urmia University Urmia, Iran

ISSN 1612-1317 ISSN 1868-1212 (electronic) Engineering Materials ISBN 978-3-031-31159-8 ISBN 978-3-031-31160-4 (eBook) https://doi.org/10.1007/978-3-031-31160-4 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Dedicated to our parents, who know neither the plastic waste treatment and management nor the gasification process but teach us all of them.

Preface

Plastic has become one of the most ubiquitous materials in the world, with applications in a vast array of industries. They are materials that can be molded or shaped into various forms and are made from synthetic or semi-synthetic organic compounds. Plastics are widely used in many different industries and applications. Some of the most common applications for plastics include packaging, construction, automotive, and electronic components. Plastics are also used in medical devices and implants, sports equipment and food storage containers. The widespread use of plastics is due to their low cost, durability, and versatility. Due to the extensive usages of plastics, plastic waste is a major environmental issue, as it can take centuries to break down and pollutes both land and water. There are some efforts being made to reduce plastic waste, such as recycling programs and bans on single-use plastics. However, more needs to be done to address this problem. In recent years, there has been a growing concern over the accumulation of plastic waste in the environment since its treatment is challenging due to its complex composition. Various thermochemical processes have been proposed for the treatment of plastic waste, including combustion, pyrolysis, and gasification. Plastic waste gasification is a process in which plastic waste is converted into a valuable gaseous fuel called syngas. This process has many advantages over other methods of plastic waste treatment and management, such as incineration or landfilling. First, gasification is much more efficient than other methods such as incineration, meaning that more energy can be recovered from the same amount of plastic waste. Second, gasification produces a gaseous fuel that can be used to generate electricity or heat, making it a valuable resource. Third, gasification does not produce harmful emissions like dioxins and furans, which are released when plastics are burned. Fourth, gasification can be used to treat mixed plastic waste streams that contain both organic and inorganic materials. This is important because it allows us to recycle plastic materials that would otherwise end up in landfill. Fifth, the process of gasification is relatively clean and quiet, making it suitable for use in urban areas. Overall, gasification is an attractive option for treating and managing plastic waste. It is efficient, produces valuable resources, and does not produce harmful emissions.

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With proper planning and implementation, gasification can play a key role in reducing our reliance on landfill and incineration of plastic waste. In this edited book, we aimed to present a comprehensive overview on the gasification process as an efficient and valuable technique for plastic waste treatment and management. Chapter Plastic Types and Applications deals with introducing the most important plastic types and their applications in different fields. The plastic waste generation and its forecasting by 2050 using time-series algorithms are the objectives of Chap. Collected Plastic Waste Forecasting by 2050. Different thermochemical processes for treating plastic waste especially gasification process are introduced in Chap. Plastic Waste Gasification. Modeling of air and steam plastic waste gasification using two thermodynamic techniques are conducted in Chaps. Air Plastic Waste Gasification and Steam Plastic Waste Gasification, respectively. As a case study, polyurethane foam waste is considered as the feedstock of a gasification process and its air gasification is evaluated in Chap. Evaluation of Air Polyurethane Foam Waste Gasification while Chap. Evaluation of Steam Polyurethane Foam Waste Gasification deals with evaluation of steam gasification of polyurethane foam waste. Chapter Multi-criteria Decision-Making Analysis of Plastic Waste Gasification provides a comprehensive multi-criteria decision-making analysis on the air and steam gasification of most prevalent plastic waste types. The editors and authors hope that the contents of this book will be a step forward in the development of gasification process for treatment and management of plastic waste. Urmia, Iran March 2023

Dr. Rezgar Hasanzadeh Dr. Parisa Mojaver

Contents

Plastic Types and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mahboube Mohamadi

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Collected Plastic Waste Forecasting by 2050 . . . . . . . . . . . . . . . . . . . . . . . . . . Amir Reza Gharibi, Reza Babazade, and Rezgar Hasanzadeh

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Plastic Waste Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parisa Mojaver, Ata Chitsaz, Seyyed Joneid Hasannejad, and Morteza Khalilian

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Air Plastic Waste Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parisa Mojaver and Shahram Khalilarya

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Steam Plastic Waste Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parisa Mojaver, Shahram Khalilarya, and Ata Chitsaz

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Evaluation of Air Polyurethane Foam Waste Gasification . . . . . . . . . . . . . Rezgar Hasanzadeh, Taher Azdast, and Chul B. Park

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Evaluation of Steam Polyurethane Foam Waste Gasification . . . . . . . . . . . 105 Rezgar Hasanzadeh and Taher Azdast Multi-criteria Decision-Making Analysis of Plastic Waste Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Rezgar Hasanzadeh, Ali Doniavi, and Marc A. Rosen

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Contributors

Taher Azdast Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Reza Babazade Department of Industrial Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Ata Chitsaz Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Ali Doniavi Department of Industrial Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Amir Reza Gharibi Department of Industrial Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Seyyed Joneid Hasannejad Institute for Energy Systems and Thermodynamics, TU Wien, Vienna, Austria Rezgar Hasanzadeh Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Shahram Khalilarya Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Morteza Khalilian Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Mahboube Mohamadi Department of Polymer Engineering, Faculty of Engineering, Urmia University, Urmia, Iran Parisa Mojaver Department of Mechanical Engineering, Faculty of Engineering, Urmia University, Urmia, Iran

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Chul B. Park Microcellular Plastics Manufacturing Laboratory (MPML), Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, ON, Canada Marc A. Rosen Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Oshawa, ON, Canada

Plastic Types and Applications Mahboube Mohamadi

Abstract Plastics, as a generic name for polymers in the literature, represent an advanced class of materials with unique structures and tailored properties. The tremendous increase in industrial demand for polymers is due to their wide application range, which is connected to enhancing the quality of our daily lives. Therefore, comprehensive knowledge of these particular materials and an introduction to their characteristics are essential before any further discussion. Though this topic in polymer science is widely investigated, there is a demand to summarize the basic definitions and different classifications of polymeric materials as a reference for future discussions which are addressed in this chapter. Additionally, this chapter reviews recent advances in the development of new polymeric materials with potential applications in various fields, besides their common uses, to emphasize the reasons for the need of vast production and usage of polymers in recent decades. Keywords Plastics · Polymers · Classifications · Applications

1 Definition and Essential Concepts The common term “plastics” often refers to the general concept of polymers, and they are used interchangeably in the literature in many cases [1, 2]. The wide-ranging applications of polymers in everyday use around us make them a group of materials with an enormously important role in modern society. This is why polymers have completely integrated themselves into daily life, as evident from the increased production and usage volume over the past decades [3]. It is also the reason that they have been a subject of continuing interest in both academia and industry. Thus, an in-depth understanding of the definition, structures, classifications, properties, and applications of polymeric materials seems vital before any further discussion about them.

M. Mohamadi (B) Department of Polymer Engineering, Faculty of Engineering, Urmia University, Urmia, Iran e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Hasanzadeh and P. Mojaver (eds.), Plastic Waste Treatment and Management, Engineering Materials, https://doi.org/10.1007/978-3-031-31160-4_1

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Fig. 1 a Ethylene monomers, polymerization process, and extended structure of polyethylene (PE). b Structural repeating unit of PE in parenthesis. n denotes the degree of polymerization and refers to the number of “mers” in a polymer structure

In the simplest definition, a polymer is a long-chain molecule or a macromolecule consisting of smaller molecules known as monomers before they are converted into polymers. The monomers are chemically bonded together via a polymerization process. The component that repeatedly appears in the structure of the polymer is the structural repeating unit which is also referred to as a “mer”. The name polymer has a Greek origin consisting of two parts: “poly” meaning many, and “meros” meaning parts or units. In other words, a long chain known as a polymer is formed by the connection of many of the same parts by the polymerization reaction. Most commercial polymers are organic in nature and are based on covalent compounds of carbon. Nowadays, polymers offer tremendous technological potential in several areas, such as medical devices, protection against corrosion, building and construction, packaging, automobiles, defense products, and etc. [4]. Polyethylene (PE) is counted as one of the popular and significant thermoplastics, which is widely used for packaging, containers, tubing, and household goods. In Fig. 1, monomer, extended structure, polymerization reaction, and repeating unit of PE are illustrated as an example for clarification of the concepts described above.

2 Classifications According to different criteria such as origin, polymerization process, chemical structure, physical properties, mechanical behavior, and thermal characteristics, polymers can be classified into many possible categories. Some of the most well-known and vital classifications are summarized in the following sub-sections.

2.1 Origin This is the simplest and most general way to classify polymeric substances, that is, natural, synthetic, or semi-synthetic. Natural polymers are available in nature and originate from plants or animals with a designed primary task to sustain life [5]. Polysaccharides, nucleic acids, and proteins are the three main sources of natural

Plastic Types and Applications

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polymers. Natural rubber, starch, cellulose, collagen, chitin, deoxyribonucleic acid (DNA), and ribonucleic acid (RNA) are well-known examples [5, 6]. With the discovery of synthetic polymers in the nineteenth century, the polymer industry experienced rapid expansion. They are synthesized in a chemical laboratory and are mainly derived from petroleum using controlled polymerization conditions to produce polymers with the properties to meet specific requirements. The majority of the in-use polymers around us are made of synthetic polymers like polyolefins, polyamides, and polyesters. Organic or inorganic polymers could be considered as a subset of synthetic polymers. In this sense, the presence or absence of carbon atoms in the chain backbone distinguishes between organic and inorganic polymers. Despite the availability of organic synthetic polymers owing to the petrochemical industry, inorganic ones containing oxygen, silicon, nitrogen, or phosphorus in their backbones can be utilized for high-tech applications [7]. Chemical modifications of natural polymers with the purpose of optimizing some of their properties and characteristics result in the third group, called semi-synthetic polymers. Vulcanized natural rubber or esters and ethers of cellulose are examples of semi-synthetic polymers [5, 8].

2.2 Structure of Repeating Unit Depending on the type of monomer participating in the chain backbone of the macromolecule, polymers can be classified as homopolymers or copolymers. Polymers with only one type of monomer or repeating unit are so-called homopolymers, while the ones with more than one type of repeating unit or one monomer specie in their structures are copolymers. Also, there are terpolymers, which refer to the macromolecules synthesized in the presence of three different monomers by specific reactions. Regarding the randomness or the existence of specific order between the structural units in the copolymers, they may form different copolymers, including statistical, alternating, random, block, graft and so on [9].

2.3 Chain Structure Based on the molecular structure, polymers are classified as: linear, branched, and crosslinked/network. When the polymer is a collection of long linear chains linked together by covalent bonds, with no branches or chemical links with neighboring chains, the resultant polymer is linear [10]. Regarding the ability of the backbone chains to be closely packed together, they generally indicate higher densities and melting points along with advanced tensile strength. Branched polymers, on the other hand, consist of branches of short or long length located at random points along the chain backbone. The monomer must be capable of

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Fig. 2 Schematic representation of possible molecular structures in polymers

growing in more than two directions, and hence, the monomer must have a functionality greater than two [10]. Low or imperfect packing of the main chains in branched polymers leads to materials with lower densities and melting points. Commonly, branching occurs as a result of shortfalls during the polymerization process, but it can also happen intentionally in order to modify the internal structure and properties of the polymer. Thermoplastics consist of linear or branched polymers. Crosslinked polymers are formed when chemical bonds grow in three-dimensional directions from the side chains emerging from individual polymer chains [5]. This network structure develops due to the curing process through heating or adding curing agents [6]. The existence of irreversible chemical bonds in the structure of crosslinked polymers and restricted chain-segment mobility make them hard and brittle materials that cannot be recycled or reshaped upon heating. The interest of industries in them is because of their insolubility in different solvents, high strength, excellent dimensional stability, and heat resistivity [6, 9]. In recent years, more complicated structures have been developed, like dendrimers or dendrons with advanced medical applications. They can be defined as perfectly hyper-branched polymers with tree-like structures. They are three-dimensional, monodisperse, and mostly globular macromolecules consisting of a typically symmetric well-defined inner core covered by many branches attached to it [11]. Different classification of polymers based on their molecular structure is depicted in Fig. 2.

2.4 Thermal Response The response of polymers to heat is one of the oldest and most common ways to classify them. Based on this classification, three types of polymers can be defined: thermoplastics, elastomers, and thermosets. “Thermoplastics”, often called in the short form “plastics”, are a group of polymers with linear or branched chains which are solid at ambient temperature but soften or melt when heated to elevated temperatures. This characteristic allows them to transfer into the desired shape, and be molded easily by heating. This processing is reversible, and the heating and cooling cycles can be applied several times without affecting the properties much [5]. For this reason, the recollection and recycling of plastic wastes into new products of lower added value on demand have currently

Plastic Types and Applications

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drawn considerable attention. It should be noted that the common term “plastics” in the literature sometimes refers to the general concept of polymers and also may denote the specific types of polymers, which are thermoplastics. In the latter case, plastics are a subgroup of polymers that are similar but by no means identical to polymers [10]. Depending on the existence of crystalline regions in the polymer structure, two different behaviors can be introduced by a thermoplastic material upon heating. The non-crystalline/amorphous regions experience a transition from rigid/glassy state to a more flexible state, which is called a rubbery state by increasing temperature. It is called “glass transition temperature” or “T g ”. If the polymer is semi-crystalline which means it is partially crystalline, the crystalline structure of the polymer goes through a melting process by a further increase in the temperature [12]. Unlike the thermoplastics, “thermosets” are typically rigid materials that cannot be softened or melted on heating due to having dense cross-linking networks in their structure. They are generally composed of viscous fluids with low molecular weights. Upon heating or chemical treatment, heavy chemical cross-linking (curing) occurs among individual chains, which result in the hardening of the material [12]. After this stage, the material cannot be reshaped or molded by heating, and at relatively high temperatures, it cannot flow but decomposes. Superior mechanical properties, high resistance to heat, solvents, and electricity make them a good candidate for various applications, including kitchenware, electrical insulators, and automotive components [5]. The third group is “elastomers” or “rubbers” because they can be easily stretched by applying a very slight force and recovered to the original dimensions after removal of the stress. Therefore, they are flexible and elastic which are the characteristics of rubbers. Very weak intermolecular forces between flexible chains in the elastomers may cause the chains to slide past one another and display plastic flow or deformation [5]. To prevent plastic deformation and incorporate elasticity, some degree of crosslinking should be formed in the elastomers. This process is known as the vulcanization of rubber, and the final product is vulcanized rubber [12]. Elastomers are polymers that are used above their glass-transition temperature [7].

2.5 Polymerization Process One of the oldest and yet, most important classification of polymers was proposed by Carothers in 1929. The polymers can be divided into two groups based on their polymerization process: (i) addition polymerization and (ii) condensation polymerization [7]. The monomer in addition polymerization commonly has a double or triple bond which opens during the process. The repeating unit of the final polymer is the same as the alkene or functionally-substituted alkene monomers used to make them. Three main stages are defined for the addition polymerization, including initiation, propagation, and termination steps. In the initiation step, free radicals are formed from an

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Fig. 3 Main stages of addition polymerization in polyethylene

initiator present in the process that decomposes into free radicals either thermally or photolytically [12]. This active specie attacks the monomer, opens the double bond, and therefore, new reactive radical forms. In the next stage, which is propagation, the monomers can be added sequentially to the new activation sites. The growing chain can be terminated either by combining two radical chains or by pulling hydrogen from another radical chain through a disproportionation process. The three steps of addition polymerization are schematically shown for polyethylene in Fig. 3. Radical, cationic, anionic, and catalytic coordination polymerization are the four common polymerization techniques in synthesizing addition polymers [5]. In condensation polymerization as the second class, common condensation reactions of organic components occur. In this regard, bifunctional or polyfunctional monomers are combined by the reaction of functional groups in an alternating structure. The formation of nylon 6,6 as a well-known polymer belongs to polyamides is illustrated in Fig. 4 where adipic acid (a dicarboxylic acid) and 1,6hexamethylenediamine react with each other along with the loss of water molecules. If a polymerization process meets any of the following criteria, the resultant polymer can be considered a condensation polymer: (1) loss of a small molecule in the form of water, gas, or salt during the synthesis process; (2) containing functional groups as part of the main polymer chain, such as ester, urethane, amide, or ether; (3) lack of some atoms in the repeating unit of polymer that are present in the initial monomer which can be decomposed to. If the polymerization process does not satisfy any of these, it is an addition polymer [7].

2.6 Polymerization Mechanism and Kinetics With the advancement in polymerization chemistry, certain polymers were developed that cannot be classified either in condensation or addition polymers. A good

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Fig. 4 Condensation polymerization of nylon 6,6 from adipic acid and 1,6-hexamethylenediamine

example is the polymerization of polyurethane with a kinetics similar to condensation polymerization but without the elimination of a condensation product [9]. Therefore, a more accurate classification of the polymerization routes is needed based on reaction kinetics. In this manner, two classes of polymerization mechanisms are now established: chain-growth polymerization and step-growth polymerization. Chain-growth polymerization, also known as chain polymerization, is an alternative term for addition polymerization but a more consistent name for the polymerization mechanism. The characteristics of chain-growth polymerization are described as the appearance of long chains at early stages, the addition of monomers to lengthy chains and steady disappearance of monomers during the process, no evolution of small molecules, formation of relatively high molecular weight polymers, and increase of the conversion rate by the reaction progress, not the chain length [10]. In step-growth polymerization, on the other hand, the chain growth develops step by step and in stages, and almost low molecular weight components form at early stages. It can be accompanied by the release of a small molecule. The average molecular weight of polymers is usually low to the medium range when compared to chaingrowth polymerization. In addition, the extension of the polymerization process increases both conversion and molecular weights [9, 10]. The polymers produced by these two methods have totally different properties, average molecular weight, and molecular weight distribution. Aside from classical processes described for the production of commercial polymers, newer techniques are being developed to obtain polymers with novel topologies, designed structures and properties, precise control over the chain length and monomer sequences, and defined molar masses and networks. Although the significant developments in this field are still in the experimental stages, industrial use of some of these methods has been provided. The living polymerization technique is one of the newly developed methods for the controlled formation of block copolymers [12]. The mechanism is similar to classical addition polymerization. However, there is no termination step, and the reaction continues until all monomers have been exhausted/consumed. Since the end of the chains is still reactive, the polymerization can proceed in the presence of the second type monomer, leading to synthesizing

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Fig. 5 Variation of molecular weight versus conversion rate in a chain-growth polymerization, b step-growth polymerization, and c living polymerization

a block copolymer. The variation of molecular weight versus conversion rate for different polymerization techniques is presented in Fig. 5. Other classifications can be considered from the point of view of polymerization environments (bulk, solution suspension, emulsion, dispersion, and etc.) or polymerization reactors (continuous, batch or semi-continuous polymerization reactors).

2.7 Tacticity In the linear chains with the substitute or pendant groups, such as polypropylene (PP) and poly(methyl methacrylate) (PMMA), the stereochemistry or stereoregularity of the side substituents around the chain backbone determines the degree of order termed tacticity. Three different configurations are defined based on the tacticity (Fig. 6): I.

Atactic: when the arrangement of pendant groups is random and there is a complete lack of order around the carbon backbone chain II. Isotactic: where the side substitute groups appear regularly on the same side of the plane of the backbone chain III. Syndiotactic: where the side substitute groups are positioned regularly and alternately on the polymer chain. Besides the different order and regularity of the side groups, different properties of the polymers are also affected by tacticity regarding its influence on the morphology.

2.8 Form and Uses There is a general classification of polymers from a practical point of view. On this basis, they can be categorized into two major subclasses, including general-purpose polymers and engineering polymers. General purpose or commodity polymers are easy to process and cost-effective materials to replace with metals or ceramics. Due to the mass production of commodity polymers, they have endless applications,

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Fig. 6 Spatial configuration of polystyrene along with the different tacticity regarding the position of the phenyl group attached to every other carbon atom in its backbone

such as food and beverage packaging, toys, electronic product casings, households, pipes, and etc. They are known as materials with relatively weak to medium mechanical and thermal properties and are used when exceptional properties are not required [13]. Examples are polypropylene (PP), polyethylene (PE), polystyrene (PS), and polyvinylidene chloride (PVC). On the other hand, engineering or high-performance polymers are not mass-produced compared to commodity plastics with relatively higher costs. They have superior physical, mechanical, thermal properties, and in overall, high functionality [13]. Therefore, they are designed or produced to withstand mechanical and environmental conditions in specific applications. The most common

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polymers in this category are polyamides (PA), polycarbonates (PC), and acrylonitrile butadiene styrene (ABS). The commodity plastics can also be considered as engineering ones in reinforced, blended, or copolymer forms [14]. Another classification of polymers based on their performance is according to their form, uses, and response to the applied stress. They can be classified as thermoplastics, elastomers, thermosets, fibers, resins, foams, composites (either micro or nanocomposites), and blends. The definition of thermoplastics, elastomers and thermosets are fully described in Sect. 2.4. Fibers are drawn polymers into filament-like products with a length of at least 100 times their diameter. Due to strong intermolecular forces between the polymer chains in fibers, they exhibit high tensile strength, low elongation, superior heat, and chemical resistance. Resins are typically viscous polymers with a relatively low molecular weight that can be converted into rigid materials by the curing process. They can be used to produce varnishes, adhesives, sealants, potting compounds, food glazing agents, and etc. Polymer composites, in general, are defined as a multi-phase material consisting of reinforcements/fillers with various physical shapes (particulate, fibrous, laminate, and etc.) and different origins (mineral, metal, ceramic, organic, and etc.) embedded in a polymer matrix in which synergistic properties and hence, improved performance can be achieved from both components. A polymer blend is the mixture of at least two macromolecular compounds, polymers, or copolymers to create a new material with different physical properties. Polymer blends can be broadly divided into three categories including immiscible, compatible, and miscible blends. The motivation towards polymer composites and blends is that they are much more cost-effective than the synthesis of new polymers having unknown properties [9]. In summary, all the considered types and classifications of plastics mentioned in Sect. 2 are depicted in Fig. 7. Besides the different classifications mentioned above, there are many other possible plastic types regarding developing new polymeric materials through modification or functionalization. Up to this part, this chapter provides the fundamental matters and primary classifications of plastic materials in general. As a continuation, diverse applications of polymers that significantly improved the lifestyle of humanity or developed based on specific requirements will be discussed in the following section.

3 Applications The wide application range of polymers in consumer products and everyday life has made them the first-choice materials for many usages and an excellent replacement for other materials. The everyday use of polymers in the modern world is mainly due to their lightweight, easy manufacturing, and the possible tailoring procedures that suit the needs of consumers [6]. Besides, the possibility of modifying polymers through functionalization, blending, or addition of micro/nanoparticles can broaden their present applications, and more advanced and dynamic materials will be achieved for specific applications. Typical applications of polymers extend from adhesives,

Natural

Homopolymer

Semi-synthetic

Synthetic

Linear

Copolymer

Structure of repeating unit

Cross-linked

Elastomer

Addition

Chain-growth

Step-growth

Isotactic

Polymerization mechanism and kinetics

Condensation

Polymerization process

Thermoset

Thermal response

Thermoplastic

Branched

Chain structure

Syndiotactic

Tacticity

General purpose

Atactic

Engineering

Application

Fig. 7 Various classifications of polymeric materials

Origin

Polymer classifica tions

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M. Mohamadi Electrical & electronic 4.2%

Building & Construction 4.3%

Industrial machinery Textile 0.4% 14.9%

Transportation 5.6% Consumer products 12.1%

Other 12.5%

Packaging 46%

Fig. 8 Global consumption of plastics based on the generated plastic wastes by industry in 2018 [6]

coatings, foams, pipes, tanks, packaging materials, children’s toys, and sports wares, to textile and industrial fibers, agricultural films, automobile parts, floor coverings, building, and construction. Over the past two decades, polymers have been explored for advanced and high-tech applications. The global consumption of plastics based on the generated plastic wastes are presented in Fig. 8. In the following subsections, some of them will be briefly discussed somewhat just to give the readers a basic understanding, but their applications are not limited.

3.1 Packaging Outstanding packaging ability is another important property of polymers that can be derived from thermoplastics since they are cheap and malleable, and allow a wide variety of packaging formats [15]. In addition, the possibility of recycling them on demand increases their production and importance in the future due to advancements in recycling technology, and the shift in the global demand from single-use polymers to recyclable ones [6]. The enhanced barrier properties to UV rays and gasses, long-term stability, significant toughness, good dielectric properties, heat resistance, durable mechanical strength and stiffness are the main reasons for the enormous interest of food companies in polymeric insulators and packaging materials [16]. The most widely used polymers for the packaging industry are polyethylene terephthalate, nylon, polystyrene, polyolefins, polylactide, polyamides, polyimides, epoxy resins, polyurethane and ethylene–vinyl alcohol [3, 17, 18]. Recently, active and intelligent/smart packaging materials with improved antimicrobial, mechanical, and barrier properties have been designed to extend shelf life, monitor freshness, display information on quality, improve safety, and convenience. The main feature of designing

Plastic Types and Applications

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active packaging is to adsorb or release substance from, into, and around the packaged food, which is done with the aid of some nanoparticles with antimicrobial features, including metal nanoparticles (Au, Ag and Zn), metal oxide nanoparticles, and carbon nanotubes [17]. On the other hand, intelligent packaging is capable of examining and control the packaged food condition or environment the food is surrounded during food storage using pathogen sensors, freshness indicators, and oxygen indicators [16]. Environmental concerns, the increasing burden of plastic waste disposal, the utilization of industrial food waste, and consumer demands for natural, nutritional, and healthy foods are the main motives for replacing bioplastic packaging with conventional one [19]. The two main groups of bioplastics are biobased polymers and biodegradable plastics [20]. The concept of edible films and coatings is based on the biobased polymers generated from biodegradable food industry wastes or underutilized sources of proteins, lipids, or polysaccharides [19].

3.2 Textile The textile industry can be counted as one of the most important functional areas of polymer engineering, with the first application in human clothing and extended progress in the production of intended materials in recent years. Either polymer with natural sources (such as silk, hemp wool, and cotton fibers) or synthetic base (including nylon, polyester, and rayon) are utilized with the same goal of providing the most comfortable product for a wide range of consumers [16]. Despite the advantages of natural polymers, including high mechanical strength, good biocompatibility, and desired stability in non-aqueous or aqueous solutions, their restricted applications due to their monotonous functional groups are still a problem. Synthetic polymers, on the other hand, suffer from rapid burning, low biodegradability, and skin damage. To develop the present properties and create innovative characteristics in conventional polymeric materials, novel technologies like surface functionalization via different agents have emerged. This has led to the various features which make them suitable to be used in different fields like sports, healthcare, military, and fashion [21]. Furthermore, smart textiles with the ability to sense and respect environmental changes could be provided. The main examples of these stimuli-responsive polymers are antimicrobial textiles, luminescent textiles, self-cleaning textiles, temperature-regulated textiles, moisture-wicking textiles, flame-retardant textiles, and self-healing textiles [16, 22, 23].

3.3 Hydrogels Regarding the environmental and ecosystem concerns of synthetic petroleum-based polymers, a great step towards replacing this class of polymers with sustainable and green polymers has been taken. The latter category is less toxic, more biocompatible,

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M. Mohamadi

and more environmental-friendly. Hydrogels are one of the developed green polymers with the ability to retain a great amount of moisture in their structure. They have a three-dimensional (3D) hydrophilic polymeric network owing to chemical and/or physical crosslinking with an excellent ability to absorb or retain massive water without disintegration [24, 25]. Tunable properties, high sensitivity to physiological environments, hydrophilic nature, soft tissue-like water content, and facile preparation methods of the hydrogels have led to their various applications in biotechnology and engineering, such as drug-delivery systems, cell-laden matrix, anti-fogging films, antifouling coatings, self-healing film, soft robotics, 3D printing technology, catalysis, pollutant removal, and energy storage [24, 26, 27]. Physical gels are often reversible and may dissolve by changing environmental conditions, while crosslinking polymers in the dry state or solution in “permanent” or “chemical” gels result in the formation of a network having covalent bonds between different macromolecular chains [28]. The hydrogel products can be classified on different bases as source, configuration, types of crosslinking, physical appearance, and etc. [15, 27, 29].

3.4 Shape Memory Polymers Smart/intelligent polymers are stimuli-responsive materials that can change their shapes, mechanical responses, light transmissions, controlled releases, and other functional properties under external stimuli [30–32]. According to the prominent role of self-repairing and intelligent polymers in the near future, there is a growing interest in a new class of materials, so-called shape-memory polymers (SMPs) [31]. Applying different external stimuli, especially heat, electric/magnetic field, light, a change in pH value, humidity, and redox reaction, results in the change of different properties of polymers and in specifically, their shapes by undergoing significant macroscopic deformation [33]. This temporary shape can be recovered into its permanent shape after the release of the external stimulus [34]. The combination of polymer structure and morphology, along with the applied processing and programming technology, determines the shape-memory effect of a specific polymer. The netpoints and switching domains in the molecular architecture of the SMPs control the shape changes. They can either have physical nature (entanglement coupling, crystalline phase or copolymers), or chemical origin (covalent bonds). There are comprehensive possible applications of SMPs and their composites, including aerospace engineering, sensors, actuators, morphing structures, artificial muscles, high-performance textiles, smart fabrics, SMP foams, shrinkable packaging, and self-healing plastic components in every kind of transportation vehicles [30, 31, 33].

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3.5 Self-Cleaning Polymers As the simplest definition, self-cleaning materials are easily cleaned by a water rinse, and this feature can be applied in many areas, including exterior surfaces and textiles. The usage of such materials in windows, paints, satellite dishes, solar energy panels, and automotive windshields has led to reduced maintenance costs, less labor required, and no need for detergents which provides minimal impact on the environment [35]. In addition, the application of self-cleaning polymers in the textile industry makes apparel and outdoor textiles wash-free or with the reduced number of washing cycles, offering convenience for everyday use and providing additional value to the product [35]. Two different approaches can be employed to produce self-cleaning surfaces, which require specific surface topography and chemical design of the surface to control wettability. In this regard, both superhydrophilic and superhydrophobic materials can be used. In the case of superhydrophilic polymers, the complete wettability of the surface allows water to cover the surface entirely and washes all the dirt by the formation of a continuous film. On the other side, applying superhydrophobic coatings on the surfaces force the water droplets to form high contact angle on the surface, easily roll off the surface and pick up dirt particles on their way. This is called the Lotus effect, which is inspired by the extreme water repellency and selfcleaning surface effect exhibited in Lotus leaves [36]. Some essential criteria in the superhydrophobic surfaces should be evaluated, including contact angle (>150°), the low contact angle hysteresis, low angle of the slide (