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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Practical guidance to sustainable packaging and its challenges with analysis of various packaging materials and their interactions with different environments
Degradation, Stabilization, and Recycling of Packaging Materials analyzes packaging materials and their interactions with different environments, discussing the degradation processes of different materials like plastics, wood, paper, glass, and metal, providing specific strategies to address these degradation processes, and exploring solid waste management, recent developments in recycling, and the principles of eco-friendly packaging design.
Organized into two parts, the first section of this book provides a comprehensive examination of how environmental factors such as heat, shear, light, air, packaged products, and stress affect packaging materials, focusing on the chemistry of their deterioration and stabilization methods. The second section explores solid waste management, recent developments in recycling, and key principles of eco-friendly packaging design, culminating in an extensive discussion of legal and regulatory aspects.
The book includes case studies and problem sets in each chapter, with solutions to the problems in an appendix in the back of the book.
Written by a team of highly qualified authors, Degradation, Stabilization, and Recycling of Packaging Materials includes discussion on:
- Structure of tinplate and tin-free steel, corrosion in lacquered cans, and effects of producing, processing, and storing metals
- Recyclable versus repulpable paper, uses of recycled papers, wet-strength papers, non-wood fibers as paper sources, and contamination issues with paper recycling
- Plastic recycling rates, plastic scrap exports in the US and abroad, chemical versus mechanical plastic recycling, hydrocracking of plastics, and PE and PET recycling
- Lightweight glass bottles, strategies to modify or strengthen glass, and the real recyclability of glass
Presenting advanced technical knowledge that demystifies the sustainable packaging landscape Degradation, Stabilization, and Recycling of Packaging Materials is a critical resource for researchers, students, and industry professionals in the field of materials science and packaging to evaluate challenges related to solid waste and devise effective disposal strategies.
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Table of Contents
Cover
Table of Contents
Title Page
Copyright Page
Preface
1 Introduction
1.1 General Introduction
1.2 What Are Some Ideal Properties of Packaging?
1.3 Liquid Resistance and Barrier Properties
1.4 End‐of‐Life (EoL) Outcomes
1.5 Life‐Cycle Assessment (LCA) and Techno‐Economic Analysis (TEA)
1.6 Open‐Looped Versus Closed‐Loop Processes
1.7 Recycling
1.8 Biodegradable and Compostable Packaging
1.9 Concluding Remarks
References
2 Plastics
2.1 Introduction
2.2 How Are Polymers Named?
2.3 Molecular Architecture
2.4 Polymer Characterization Techniques
2.5 Microscopy Techniques
2.6 Physical State of a Polymer
2.7 Thermal Transitions
2.8 Mechanical Properties
2.9 Degradation of Polymers/Plastics
2.10 Wanted Versus Unwanted Degradation in Polymers
2.11 Do all Polymers Degrade at the Same Rate?
2.12 Types of Polymer Degradation
2.13 Methods for Studying Polymer Degradation
2.14 Stabilization of Polymers
2.15 Summary
Problem Set
References
3 Wood
3.1 Introduction
3.2 Wood Degradation
3.3 Chemical Degradation
3.4 Biological Decomposition (Decay)
Problem Set
References
4 Paper Degradation and Stabilization
4.1 Introduction
4.2 Durability and Permanence
4.3 Biological Degradation of Paper
4.4 Wet‐Strength Papers
4.5 Sustainable Materials for Paper Coating for Packaging Applications
4.6 Concluding Remarks
Problem Set for Chapter 4
References
5 Glass
5.1 Advantages of Glass
5.2 Disadvantages of Glass
5.3 Glass Chemistry
5.4 Chemical Corrosion
5.5 Physical Stability and Strength of Glass
5.6 Chemical Modification and/or Strengthening
5.7 Conclusions
Problem Set
References
6 Degradation and Stabilization of Metals
6.1 Benefits of Metals as Packaging
6.2 Disadvantages of Metals as Packaging
6.3 Basic Aspects of Metal Corrosion
6.4 Elements Required for Corrosion
6.5 Role of Liquid Water in Corrosion
6.6 Methods for Protecting Metals Used in Packaging from Corrosion
6.7 Structure of Tinplate and Tin‐Free Steel
6.8 Corrosion in Plain (Uncoated) Tin Cans
6.9 Corrosion in Lacquered Cans
6.10 Effects of Products, Processing, and Storage
6.11 VCI Packaging Materials
6.12 Corrosion of Aluminum
6.13 Lacquer Coatings for Cans
6.14 Concluding Remarks
Problem Set for Chapter 6
References
Further Reading
7 Solid Waste Issues
7.1 Overview of Packaging Waste in U.S. Municipal Solid Waste
7.2 Disposal of Packaging Materials
7.3 Recovery
7.4 Reuse and Waste Reduction
7.5 Recycling
7.6 Motivation
7.7 MRFs
7.8 Comparative Advantages and Disadvantages
7.9 Concluding Remarks
Problem Set for Chapter 7
References
8 Recycling of Metal and Glass
8.1 Overview
8.2 Metal Recycling
8.3 Open‐Loop and Closed‐Loop Recycling
8.4 Steel Recycling Process
8.5 Aluminum Recycling (Figure 8.4)
8.6 Glass Recycling
8.7 Summary
Problem Set for Chapter 8
References
9 Paper and Paperboard Recycling
9.1 Sorting Phase
9.2 Processing Phase
9.3 Processing Phase: Pulp Screening and Cleaning
9.4 Processing Phase: Deinking
9.5 Processing Phase: Refining, Color Stripping, and Bleaching
9.6 Processing Phase: Papermaking
9.7 Recyclable Versus Repulpable Paper
9.8 Uses of Recycled Paper
9.9 Contamination Issues
9.10 Concluding Remarks
Problem Set for Paper Recycling
References
10 Plastics Recycling
10.1 Introduction
10.2 Plastic Recycling Rates
10.3 Recycling of Plastics Packaging
10.4 What Is the Impact of Impurities in Plastics Mechanical Recycling?
10.5 United States Plastic Scrap Exports
10.6 Plastic Recycling Elsewhere
10.7 Global Plastic Recycling Rates
10.8 CO
2
Footprint of Different Ways of Plastic Disposal
10.9 Terminology in Plastic Recycling
10.10 Emerging Trends in Recycling
10.11 Trends in Chemical Recycling
10.12 Concluding Remarks
Problem Set for Chapter 10
References
11 Legal, Regulatory, EPR, and Green Design
11.1 Introduction
11.2 EU Packaging Directives
11.3 Extended Producer Responsibility (EPR)
11.4 Green Design
11.5 The Path Forward for Packaging Sustainability
11.6 Concluding Remarks
Problem Set for Chapter 11
References
Further Reading
Appendix 1: Solutions to Problem Sets
A.1 Problem Set for Chapter 2
A.2 Problem Set for Chapter 3
A.3 Problem Set for Chapter 4
A.4 Problem Set for Chapter 5
A.5 Problem Set for Chapter 6
A.6 Problem Set for Chapter 7
A.7 Problem Set for Chapter 8
A.8 Problem Set for Chapter 9
A.9 Problem Set for Chapter 10
A.10 Problem Set for Chapter 11
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Examples of various homopolymers and copolymers and their nomencl...
Table 2.2 Various polymerization methods and typical dispersity ranges obta...
Table 2.3 Bond dissociation energies of various single bonds (kJ/mol) (the ...
Table 2.4 Volatile products obtained from the pyrolysis of polypropylene at...
Table 2.5 Monomer yield in the pyrolysis of selected polymers.
Table 2.6 Typical single‐bond dissociation energies.
Table 2.7 Characteristic maximum absorption wavelengths and associated ener...
Table 2.8 The effect of various photostabilizers at 1 wt% concentration on ...
Table 2.9 Examples of some stabilizers that are used for various polymers [3...
Chapter 6
Table 6.1 Types of steel typically used in cans.
Table 6.2 Relationship between the purity of aluminum and the corrosion rat...
Chapter 7
Table 7.1 Products generated in U.S. MSW with details regarding packaging, ...
Table 7.2 Products generated in U.S. MSW with details on packaging, in perc...
Table 7.3 Generation, recycling, composting, combustion with energy recover...
Table 7.4 Emission pollution control during WTE between 1990 and 2005 (Befo...
Chapter 8
Table 8.1 Formula used to calculate EU recycling rates for glass containers...
List of Illustrations
Chapter 2
Figure 2.1 A condensation reaction leads to nylon‐6,10.
Figure 2.2 An additional polymerization leads to polystyrene, where styrene ...
Figure 2.3 Plots of molecular weight versus percent monomer conversion for c...
Figure 2.4 Common examples of thermoplastics and thermosets.
Figure 2.5 Plot of the weight fraction versus the molecular weight (
M
n
) [3]....
Figure 2.6 Influence of the molecular weight on the viscosity of a polymer....
Figure 2.7 Photographs of a transparent cup (a) and an opaque plastic photo ...
Figure 2.8 Various characteristic transition temperatures in a typical DSC t...
Figure 2.9 Bond cleavage generates two polymeric free radicals.
Figure 2.10 Illustration of activation energies for the cleavage of primary,...
Figure 2.11 Polymerization and depolymerization reactions. The forward react...
Figure 2.12 Thermogravimetric analysis of various forms of plastic waste, in...
Figure 2.13 PET degradation through depolymerization.
Figure 2.14 Thermal degradation of polyvinyl chloride.
Figure 2.15 First step in the thermal degradation of polyvinyl acetate (rate...
Figure 2.16 Thermal degradation of poly(methyl methacrylate).
Figure 2.17 Thermal degradation of PP via: (a) chain scission, (b) hydrogen ...
Figure 2.18 Chain scission in PP following hydroperoxide decomposition. (Not...
Figure 2.19 Oxidative chain scission in polyethylene.
Figure 2.20 Example of a reaction involving the recombination of free radica...
Figure 2.21 Polyethylene oxidation reactions [30].
Figure 2.22 Polypropylene oxidation [30].
Figure 2.23 Relative rates of oxidation of various polymers. A higher value ...
Figure 2.24 Scale of wavelengths and energies in the electromagnetic spectru...
Figure 2.25 A Norrish I reaction [30].
Figure 2.26 A Norrish II reaction.
Figure 2.27 A Norrish III reaction.
Figure 2.28 Mechanical degradation. Notice that in the first picture at the ...
Figure 2.29 Development of a microcrack due to propagation of free‐radical r...
Figure 2.30 Mechanical degradation of PVC.
Figure 2.31 Schematic depiction of the oxidation cycle. The figure is modifi...
Figure 2.32 Illustration of how chain‐breaking electron acceptors (CB‐A anti...
Figure 2.33 Addition of a stabilizer to a free radical. S stands for stabili...
Figure 2.34 Reaction route through which benzoquinone acts as an antioxidant...
Figure 2.35 Structure of a galvinoxyl free radical.
Figure 2.36 Structure of a nitroxyl free radical.
Figure 2.37 Removal of an alkylperoxide by a CB‐D antioxidant to yield a hyd...
Figure 2.38 Structure of an arylamine.
Figure 2.39 Reactions involving arylamine antioxidants.
Figure 2.40 Antioxidant reactions of BHT.
Figure 2.41 Resonance structures of a hindered phenol free radical.
Figure 2.42 Derivatives of BHT are used as commercial antioxidants.
Figure 2.43 Structure of vitamin E.
Figure 2.44 Reaction of tris(nonylphenyl) phosphite, with the phosphorous un...
Figure 2.45 Structure of octoxybenzophenone.
Figure 2.46 General structure of the benzotriazole family.
Figure 2.47 Schematic illustration of the ways through which benzophenones a...
Figure 2.48 Structure of NDC.
Figure 2.49 Structures of the HALS stabilizers listed in Table 2.8.
Figure 2.50 Chemical structure of dialkyl tin dimaleate. (top) and dialkyl t...
Figure 2.51 Chemical structure of a dialkyl tin thioglycolate compound.
Figure 2.52 Ways through which metal carboxylates can react (M denotes a met...
Figure 2.53 Metal salt can eliminate conjugation (alternating double bonds) ...
Chapter 3
Figure 3.1 Photographs of a stack of wood pallets (left) and a wood crate fo...
Figure 3.2 Illustration of checks that have formed on wood due to weathering...
Figure 3.3 Composition of Aspen.
Figure 3.4 Structure of cellulose.
Figure 3.5 Examples of structures found in lignin molecules. This shows only...
Figure 3.6 Diagram showing the structures of wood cells.
Figure 3.7 Relative proportions of lignin, hemicellulose, and cellulose acro...
Figure 3.8 Structure of a tree.
Figure 3.9 Darkening of heartwood. The heartwood toward the interior of this...
Chapter 4
Figure 4.1 Reaction between urea and formaldehyde leading to DMU.
Figure 4.2 Condensation polymerization of DMU leading to a three‐dimensional...
Figure 4.3 Synthetic route leading to melamine.
Figure 4.4 Synthetic route leading from melamine to monomethylol melamine an...
Figure 4.5 Synthetic route leading to a PPE resin. (a) Synthesis of PPC prec...
Figure 4.6 Relationship between the amount of wet strength resin applied and...
Chapter 6
Figure 6.1 Photograph of a typical can used in food packaging applications....
Figure 6.2 Photographs of various metal containers that have undergone corro...
Figure 6.3 Figure illustrating the components of a galvanic cell. In the abo...
Figure 6.4 Schematic depiction of the galvanic series.
Figure 6.5 Schematic depiction of a typical corrosion cell, showing corrosio...
Figure 6.6 Structure of tinplate – not to scale! Note that all layers combin...
Figure 6.7 Structure of tin‐free steel (TFS).
Figure 6.8 In tinplate steel can, the corrosion chemistry involves several s...
Figure 6.9 Corrosion in a lacquered can, showing tin‐dissolving (left) and i...
Figure 6.10 General relationship between the thickness of a lacquer coating ...
Figure 6.11 Metal plaques (copper, steel, and galvanized steel) stored at 95...
Figure 6.12 Examples of Alumishape™ bottles manufactured by Kingston Aluminu...
Chapter 7
Figure 7.1 Products generated in MSW in the United States in 2018 U.S. Envir...
Figure 7.2 Materials generated in MSW in 2018 [10] / U.S. Environmental Prot...
Figure 7.3 Solid waste management hierarchy, with better options shown at th...
Figure 7.4 Total and per capita MSW generation rates. *The rise in MSW gener...
Figure 7.5 Recycling, composting, combustion, and landfilling of MSW from 19...
Figure 7.6 MSW disposition in 2018. [12] / U.S. Environmental Protection Age...
Figure 7.7 Number of landfills in the United States from 1988 to 2009. [13] ...
Figure 7.8 Recycling and composting of U.S. MSW between 1960 and 2018. U.S. ...
Figure 7.9 A comparative analysis of MSW EoL outcomes (by percentage) in the...
Figure 7.10 Landfill disposal rates in the United States. Based on 2008 data...
Figure 7.11 Average landfill tipping fees in the United States from 1980 to ...
Figure 7.12 Average cost to landfill municipal solid waste in the United Sta...
Figure 7.13 Illustration showing the structure of a modern landfill [20]. Re...
Figure 7.14 Waste to energy incinerations in the United States. Based on 200...
Figure 7.15 Sources of lead in U.S. MSW, 2000
Figure 7.16 Sources of cadmium in U.S. MSW, 2000
Figure 7.17 Sources of mercury in U.S. MSW, 2000
Figure 7.18 Yard waste composting programs in various regions of the United ...
Figure 7.19 States with bans on the landfilling or incineration of yard wast...
Figure 7.20 Recycling and composting amounts (Data from the EPA report) [6]....
Figure 7.21 Recycling and composting percentages.
Figure 7.22 A photograph of finished compost. Bernard Dejean / Wikimedia Com...
Figure 7.23 Recovery rates for U.S. MSW by material.
Figure 7.24 Recovery amounts for U.S. MSW by material.
Figure 7.25 Recovery rates for U.S. MSW by product.
Figure 7.26 Recovery amounts for U.S. MSW by product.
Figure 7.27 Map showing U.S. bottle deposit states. Image used with permissi...
Chapter 8
Figure 8.1 Recycling rates of various packaging materials in Europe [3].
Figure 8.2 An example of a steel recycling logo [5].
Figure 8.3 Recycling rates of various materials in 2018 [9].
Figure 8.4 An example of an aluminum recycling label.
Figure 8.5 Recycling rates for aluminum beverage cans.
Figure 8.6 Recycling amounts for various types of aluminum for various years...
Figure 8.7 Recycling rates for various types of aluminum packaging for vario...
Figure 8.8 European aluminum beverage can recycling rates in 2021 [18].
Figure 8.9 Amounts of glass packaging recycled in various years.
Figure 8.10 Glass packaging recycling rates in various years.
Figure 8.11 Collection rates of glass containers to be used for recycling in...
Chapter 9
Figure 9.1 Waste management scenarios for paper and paperboard materials [1]...
Figure 9.2 Recycling of paper and paperboard from nondurables.
Figure 9.3 Recycling rates for paper and paperboard from nondurables.
Figure 9.4 Amounts of paper and paperboard packaging recycled in the United ...
Figure 9.5 Recycling rates for paper and paperboard packaging in the United ...
Figure 9.6 Uses of recycled paper in 2016 and 2018.
Figure 9.7 Uses of OCC in 2007 (as percentages).
Figure 9.8 Uses of old newspapers in 2007 (as percentages).
Figure 9.9 Uses of recycled printing and writing paper in 2007.
Figure 9.10 Uses and origin of recycled paper in Europe, by sector, for the ...
Figure 9.11 European paper recycling, 1991–2023.
Figure 9.12 2022 paper recycling rates by region.
Chapter 10
Figure 10.1 Plastic waste in durable, nondurable goods, and packaging contai...
Figure 10.2 Use of plastics by resin in durables (D), nondurables (ND), and ...
Figure 10.3 Recycling of plastic packaging in the United States.
Figure 10.4 Recycling rates for plastic packaging in the United States.
Figure 10.5 U.S. recycling rates for plastics and for packaging plastics in ...
Figure 10.6 Nonbottle rigid plastics recycling, shown as totals for the year...
Figure 10.7 U.S. Post‐consumer Non‐Bottle Rigid Plastic Recovered in 2018 By...
Figure 10.8 Total plastic bag recycling [11].
Figure 10.9 Plastic film and bag recovered by category [12].
Figure 10.10 Postconsumer plastics recycled in 2022 (in millions of pounds) ...
Figure 10.11 EPS recycling, both post‐consumer and post‐industrial (EPS‐IA)....
Figure 10.12 Example of a label for PET from the SPI Coding System. Tomia / ...
Figure 10.13 Resin Identification Codes (RICs), as specified by ASTM D7611 [...
Figure 10.14 Plastic scrap exports during 2018–2023, with the record‐high ye...
Figure 10.15 Top five U.S. plastic scrap export destinations in 2023 [24].
Figure 10.16 Global plastic waste outcomes in 2019 [26].
Figure 10.17 CO
2
‐equivalent emission indices for various EoL scenarios for d...
Figure 10.18 Mechanical versus chemical recycling.
Figure 10.19 Flow scheme depicting the dissolution‐precipitation approach.
Figure 10.20 Example of a water bottle with digital watermarking. To the hum...
Figure 10.21 Overview of the recycling landscape for various types of plasti...
Figure 10.22 PET recycling via bottle‐to‐bottle conversion (Path #1), bottle...
Figure 10.23 Uses of recycled PET.
Figure 10.24 Chemical recycling by solvolysis. Inset image of the recovered ...
Figure 10.25 Chemical and mechanical recycling routes for polyurethanes.
Figure 10.26 Flow scheme for the melt reprocessing of polyurethane [71].
Figure 10.27 Conversion of PS into formic acid, benzoic acid, and acetopheno...
Figure 10.28 Uses of Recycled HDPE bottles, 2018.
Figure 10.29 Yields of different products obtained over time using a HZSM‐5 ...
Figure 10.30 Effect of platinum loading (0.50, 0.75, and 1.00 wt%) at 330 °C...
Figure 10.31 Flow scheme for the solvent‐based recycling process for PP. Not...
Figure 10.32 Schematic depiction showing the use of STRAP technology to reco...
Chapter 11
Figure 11.1 Photograph of a container with a BOPP label with CleanFlake tech...
Guide
Cover Page
Table of Contents
Title Page
Copyright Page
Preface
Begin Reading
Appendix 1: Solutions to Problem Sets
Index
Wiley End User License Agreement
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Degradation, Stabilization, and Recycling of Packaging Materials
Muhammad Rabnawaz
Michigan State UniversityEast Lansing, Michigan, United States
Susan E.M. Selke
Michigan State UniversityEast Lansing, Michigan, United States
Ian Wyman
Michigan State UniversityEast Lansing, Michigan, United States
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Preface
This book is a critical resource for researchers, students, and industry professionals in the field of materials science and packaging. While this book is aimed at packaging students/professionals, it will equally benefit students and professionals working in fields such as automotive, construction, furniture, and other related sectors. It offers a detailed analysis of various packaging materials and evaluates efforts to enhance their sustainability.
Organized into two parts, the first section (Chapters 2–6) of this book provides a comprehensive examination of how environmental factors such as heat, shear, light, air, packaged products, and stress affect packaging materials, focusing on the chemistry of their deterioration and stabilization methods. The second section (Chapters 7–11) explores solid waste management, recent developments in recycling, and key principles of eco‐friendly packaging design, culminating in an extensive discussion of legal and regulatory aspects. This book presents advanced technical knowledge that demystifies the sustainable packaging landscape, equipping readers with technological and policy advancements, and is written with the aim of providing a valuable asset that will promote a more sustainable future.
Readers will gain the ability to:
Grasp the complex interactions that exist between packaging materials and various environments, appreciating their practical relevance.
Comprehend and articulate plastic degradation processes and have a firm understanding of methods to address these degradation processes.
Acquire insights into the degradation behaviors of wood, paper, glass, and metal, and suggest specific stabilization strategies for each of these materials.
Evaluate challenges related to solid waste, devise effective disposal strategies, and advocate for recycling and waste minimization in current waste management practices.
Evaluate the latest developments in plastic recycling, demonstrating an understanding of contemporary issues and their solutions.
Apply new legislation as a framework for implementing and promoting the use of sustainable packaging.
Book Outline
Chapter 1. Introduction
Chapter 2. Plastics: Stabilization and Degradation
Chapter 3. Wood: Degradation and Stabilization
Chapter 4. Paper/Paperboard: Degradation and Stabilization
Chapter 5. Glass: Degradation and Stabilization
Chapter 6. Metal: Degradation and Stabilization
Chapter 7. Solid Waste Issues
Chapter 8. Recycling of Metal and Glass
Chapter 9. Paper and Paperboard Recycling
Chapter 10. Plastics Recycling
Chapter 11. Legal, Regulatory, EPR, and Green Design
1Introduction
This book is the only book that offers comprehensive insights into all packaging materials, how packaging materials interact with their surroundings, and how they are affected by their environments, such as packaged products, heat, light, air, stress, and so on. The book also covers strategies used to stabilize these materials against their environment. In addition, the impact of stabilizing strategies on recycling is also discussed. Other topics include solid waste management, recycling, and strategies for reducing waste. The book concludes with a focus on advancements in plastic recycling, packaging‐related laws, and principles of eco‐friendly packaging design.
In this chapter, we will provide a brief introduction to packaging sustainability issues. Subsequently, Chapters 2–6 will take a deeper look at individual packaging materials, their advantages and disadvantages, as well as the sustainability issues that should be considered for each. In particular, packaging materials that will be discussed in these chapters will include plastics (Chapter 2), wood (Chapter 3), paper (Chapter 4), glass (Chapter 5), and metals (Chapter 6). The degradation pathways and stabilization strategies of some of these materials will also be discussed. Issues relating to packaging’s impact on municipal solid waste systems and how this waste is handled, and how issues are addressed will be discussed in Chapter 7. Subsequently, the recycling of packaging materials will be discussed in Chapters 8–10, with the recycling of metals and glass being covered in Chapter 8, paper and paperboard recycling being the focus of Chapter 9, and plastics recycling being discussed in Chapter 10. Last, Chapter 11 will discuss packaging policies, extended producer responsibility (EPR), legal frameworks, and other policies, as well as green design principles and how they are being used to strengthen, incentivize, mandate, and promote packaging sustainability. It is hoped that this book will provide valuable insight into the landscape, challenges, and opportunities in sustainable packaging.
1.1 General Introduction
The packaging sector has a market value of 1.1 trillion USD globally as of 2023, which is projected to increase [1]. Therefore, it is evident that the packaging sector has a key influence on the economy and the environment. The vast majority of retail items sold today come in some form of packaging, whether these goods be food, medicines, cosmetics, consumer electronics, or other merchandise. Given the consumable nature of many of these products (especially food), it becomes readily apparent why packaging has such an impact on our everyday life, the economy, and the environment. In this chapter, we will briefly introduce some general concepts relating to packaging, which will be followed by a more detailed discussion in the subsequent chapters.
As we begin to look into packaging, it will be helpful to discuss some general concepts as well as some terms that are relevant to this topic.
1.2 What Are Some Ideal Properties of Packaging?
There are a number of roles that packaging fulfils, such as protecting goods against damage (including impacts in some cases), helping to maintain freshness, preventing contamination and spoilage of the product, conveying information about the product to consumers (this is usually done through labels, which can either be added onto the package or are printed directly on the package), as well as attracting the attention of consumers to help promote sales.
Depending on the application and the goods being packaged, a number of properties can be desirable and should be considered before a new package is selected. One of these properties includes its ability to prevent the passage of water vapor, oxygen, or other gases into the product (these are often referred to as barrier properties). Another consideration to take into account is the water or grease resistance of a packaging material, mainly if the product is susceptible to damage or contamination by water or oils. The weight of the packaging material is another important consideration, especially if the goods are likely to be shipped over long distances. The mechanical properties of a particular format can also be an important consideration, as in some cases, flexibility may be desirable, while rigidity may be preferable in other circumstances. The raw materials required to produce the packaging will also be an important factor in many cases. Ideally, these raw materials should be inexpensive and readily available. Due to environmental concerns, there is a trend toward seeking renewable biobased materials rather than those that are derived from nonrenewable petroleum. Alternatively, it is also highly desirable from a sustainability perspective to utilize recycled materials as feedstocks or raw materials to produce new packaging. Another consideration is the recyclability of the packaging at the end of its service lifetime, as some materials are easier to recycle than others.
A given material will have certain inherent advantages and drawbacks, depending on the intended packaging application. For example, plastics are relatively lightweight and tend to have good barrier properties. On the other hand, plastics are often derived from petroleum‐based resources (although biobased plastics are also available), and they tend to break down into microplastics, which can proliferate in the environment. Meanwhile, paper and paperboard packaging is highly desirable from a sustainability perspective but has poor water and grease resistance and offers only very limited barrier protection in the absence of coatings. These are a few examples of packaging materials, but we will discuss all this in greater depth in Chapters 2–5.
1.3 Liquid Resistance and Barrier Properties
As noted above, the barrier properties, as well as the oil and grease resistance of a packaging material, are often an important consideration when one is designing or selecting a new packaging material or format. Although these properties may not seem to directly impact the sustainability of packaging material, they are key criteria that are often required in order for the packaging to effectively fulfill its purpose of protecting the packaged goods. In addition, these properties do have some implications toward sustainability as the packaging with good liquid resistance and barrier properties can help to prevent food spoilage or damage to the packaged goods, thereby helping to minimize waste. Meanwhile, materials that do not meet these criteria will not be suitable candidates for new packaging, even if they are highly sustainable.
Some tests that are performed to evaluate liquid resistance include Cobb tests [2], kit rating tests, as well as contact angle measurements. Cobb tests are employed to measure the amount of water that has been absorbed by paper and paperboard over a certain timespan (typically 60, 180, or 1800 seconds) in units of g/m2. Meanwhile, kit rating tests are typically employed to evaluate the oil resistance of a given surface and have ratings in the range of 0–12, with a kit rating of 12 corresponding to the highest kit rating on this scale [3]. These tests are performed with a series of liquids with different viscosities and surface tensions (or “aggressiveness”), which have kit ratings in the range of 1–12, with the liquid with the kit number of 1 being the least aggressive (least likely to stain the paper) and the liquid with the kit number of 12 being the most aggressive. The kit rating of a paper substrate is assigned to the kit number of the liquid with the highest kit number that did not leave a stain. There may seem to be a slight discrepancy between the kit ratings of a sample (0–12) and the kit numbers of the test liquids [1–11]. This situation exists because a sample with a kit rating of 0 would have become stained by the least aggressive test liquid with a kit number of 1 and thus would be considered to have “failed” the kit rating test with that liquid, thus resulting in the sample being assigned a kit rating of 0. Meanwhile, a high contact angle can suggest that the liquid has resistance against that particular liquid. The contact angle can be influenced by various properties of an underlying solid, such as its surface energy and roughness. Some ways through which gas barrier properties are measured include the water vapor transmission rate, oxygen transmission rate, as well as carbon dioxide transmission rate (CO2TR) [4], which are the respective rates at which water vapor, oxygen, and carbon dioxide permeate through a material. Lower transmission rates would correspond to higher gas barrier properties. While high‐barrier properties are often desirable, in some cases a certain degree of breathability may be desired, such as with the packaging of produce.
1.4 End‐of‐Life (EoL) Outcomes
The scenario or outcome refers to the eventual fate of a product. In the context of this book, the EoL outcomes being focused on are packaging materials, or used packaging. Before environmental issues became a focus of concern, there were fewer EoL scenarios for packaging than there are today. In the past, some of the main outcomes for used packaging were disposal at landfills, littering, or in some cases they were simply burned. In situations where a material was reused or recycled in the past, this was often done primarily for economic considerations rather than environmental. The range of EoL scenarios has expanded greatly in recent years, largely due to the push for sustainable packaging. From an environmental perspective, some EoL outcomes are much more desirable than others. For example, landfilling is a rather wasteful EoL outcome, as the packaging materials that are sent to landfills are no longer used as feedstock or source material for subsequent use. In addition, waste in landfills can, in some cases, leach into the nearby ecosystem. While landfilling is still in use, efforts have been underway to minimize reliance on landfilling as an EoL outcome. Recycling efforts have grown significantly in recent years. Efforts have been underway to adopt biodegradable or compostable packaging, which can break down either in the environment or under composting conditions, respectively.
1.5 Life‐Cycle Assessment (LCA) and Techno‐Economic Analysis (TEA)
LCA is an evaluation or analysis that takes the full life‐cycle of an item (such as packaging) into account [5, 6], with a particular emphasis on its environmental impacts throughout its full life‐cycle. While EoL scenarios refer to the final outcomes for packaging materials or waste at the end of their service lifetime, the LCA is much broader in scope, and takes into account the full lifetime of a material. This can span from obtaining the raw materials or feedstocks used to manufacture the package, to production (and even including the source of the feedstocks used to produce a given packaging product), use of that product, as well as its EoL outcomes. It also takes factors such as the impacts arising from the transportation of that material into account, as well as energy requirements needed for production as well as processes, such as recycling. Before a new packaging product is developed and manufactured, it is important for manufacturers to conduct a detailed LCA to evaluate the environmental costs that will arise over the full lifespan of that product.
TEA is another evaluation that is primarily directed toward the manufacturing phases of production, but also downstream or upstream phases can be included [7]. While LCA focuses more on the environmental aspects, TEA is often used to evaluate the economic and technical performance of a process of product, such as a form of packaging [7]. Both LCA and TEA can have critical roles in ensuring that a new packaging format is environmentally sustainable as well as viable from economics and technology perspectives.
1.6 Open‐Looped Versus Closed‐Loop Processes
An open‐loop system or process is not fully self‐contained, with either new inputs or materials (often through the extraction of virgin materials) [8] being needed for the production process, or some of the materials degrading with repeated use so that they are eventually disposed of and leave the production loop. It is noteworthy that although recycling is a key tool for achieving environmental sustainability, in many cases even recycling is not a fully closed‐loop process. For recycling to be a truly closed‐loop system, the material should be recycled for an infinite number of cycles. In the case of open‐loop recycling, the material is not recycled indefinitely and eventually leaves the cycle. In addition to avoiding the extraction of virgin materials, factors such as waste generation, water usage [9], and energy inputs must be considered in order to achieve a truly closed‐loop system.
In addition, the terms open‐loop and closed‐loop are used to refer to systems in which an item is recycled into either a different item, or alternatively into the same item. In this context, the term open‐loop refers to a system in which an item is recycled into a different product, which often is of a lower grade than the original product. In the case of closed‐loop recycling the item is recycled into the same type of product (bottle‐to‐bottle recycling would be one such example).
1.7 Recycling
As mentioned above, achieving a closed‐loop system is a key requirement for developing sustainable packaging. One of the most important ways to achieve sustainability is through recycling efforts. While recycling will be discussed in further depth in Chapters 7–9, we will briefly introduce a couple of concepts regarding recycling here. There are various types of recycling, and some materials are inherently more recyclable than others (we note that the recycling of materials such as paper, glass, and metals are discussed in Chapter 8, while plastics recycling is discussed in Chapter 9). Two of the main forms of plastic recycling are mechanical and chemical recycling. In the case of mechanical recycling [10], the used packaging material does not undergo significant chemical changes. In contrast, the material is broken down chemically into other materials, such as feedstock materials, when it is subjected to chemical recycling (in the case of plastic recycling, the polymer may be broken down into its monomers, for example). Some examples of chemical recycling processes [11] can include pyrolysis, chemolysis, fluid catalytic cracking, gasification, as well as hydrogen techniques. While this provides for the recovery of feedstocks, in some cases, the breakdown of material into fuel for use as an energy source is sometimes considered to be a form of chemical recycling.
Plastic recycling can also be divided into four categories known as primary, secondary, tertiary, and quaternary recycling [10]. Both primary and secondary recycling are forms of mechanical recycling. In the case of primary recycling, here postindustrial scrap is reused for the same purpose by grinding and reprocessing (e.g., bottle to bottle). More processing is involved for secondary recycling than for primary recycling, here postconsumer materials are first sorted, the size of the polymer materials is reduced (such as via grinding processes), and then extrusion is performed. Meanwhile, tertiary recycling is a form of chemical recycling, and is used for materials that are no longer suitable for mechanical recycling. In the case of plastics, the polymer can be reverted into its feedstock monomers. Last, quaternary recycling is used for energy recovery purposes, and is considered to be a lower‐value recovery process compared to tertiary recycling. In addition, greenhouse gas generation may become a more significant issue in quaternary recycling cases.
Depending on the recycling process involved or its effectiveness, a recycled material may be converted into something of greater, equal, or lesser value. The conversion of a waste material into a value‐added material that has greater value is referred to as upcycling, while the conversion of a recycled material into a material with less value is referred to as downcycling.
1.8 Biodegradable and Compostable Packaging
As mentioned earlier, the EoL outcomes for packaging materials are an important consideration. Ideally, the packaging materials should be reused or recycled as much as possible. However, a certain amount of packaging waste will inevitably enter the environment, whether it occurs through spills, littering, or ending up in landfills. In these situations, it is important that the material should degrade in an acceptable manner without proliferating in the environment. One way through which this can be accomplished is by ensuring that the packaging is biodegradable or compostable. There is a deeper discussion regarding the definitions of biodegradable and compostable in Sections 2.10.2 and 7.3.2. The two terms sound quite similar, but there is a subtle difference between them. It should be noted that the term biodegradable is often misused. In a broad sense, the term biodegradable simply means that the bonds that hold material together (such as in plastic‐, paper‐, and wood‐based products) can be broken via microbial activity. In a practical case, this biological degradation should occur completely at a somewhat rapid pace, but the conditions determining whether a material is considered to be biodegradable for practical use are often ill‐defined. Meanwhile, a compostable material is meant to biodegrade under specific conditions, where thermophilic conditions are achieved in a certain period. For a product to be labeled as compostable in the United States, it must satisfy the American Society for Testing and Materials (ASTM) standards D6400 and D6868, which stipulate that the material must disintegrate within 90 days without leaving harmful residue [12]. Composting criteria demand proper disintegration during composting and no adverse impacts of the compost on plant growth. Home composting is materials that decompose at natural temperatures with common microorganisms. Currently, there are no home composting ASTM or BPI standards. Only the Australian AS 5810 standard, used for TUV Austria's OK compost HOME certification, demands disintegration in six months and complete composting in a year. Thus, AS 5810 is a key indicator for home compostable products [13]. ASTM’s D20 committee on plastics is working on a test method for home composting. The D20 committee is also working with D34 (waste management committee) to develop tests for the degradation scenarios when biodegradable materials are in landfills [14].
1.9 Concluding Remarks
Ideally, a well‐chosen packaging material should combine several sustainability criteria, such as recyclability, renewability, cost‐effectiveness, and biodegradability/compostability. While achieving environmental sustainability is a key goal, it remains vital that the packaging is still able to fulfill its function in a highly effective manner. The choice of suitable material has a critical influence on whether the packaging will effectively fulfill its function in a sustainable manner. In addition, economics is an important factor, as sustainable packaging will not be developed if its cost is too high, and thus its economic viability is another important consideration. The upcoming chapters will provide a detailed look at the packaging comprised of different materials, the recycling considerations and processes used for these packaging formats, as well as the role that policies fulfill in the development of sustainable packaging materials. Hopefully, this book will allow students, researchers, industry professionals, and decision‐makers in both industry and government to successfully navigate the challenging yet very critical field of sustainable packaging.
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2Plastics
2.1 Introduction
Plastics have become an indispensable part of our modern lives in numerous ways, ranging from packaging to automobiles. The terms plastics and polymers are often used interchangeably, but there is a difference. In particular, “polymers” refer to large molecules made of repeating units of one or more species of atoms or groups of atoms. A couple of common examples include polyethylene (PE) and rubber. The term plastics refers to those polymers that are solid at room temperature and can be melt‐processed repeatedly. Common examples of plastics include PE, polyethylene terephthalate (PET), polystyrene (PS), etc.
On the other hand, there are polymers that cannot be melt‐processed owing to their crosslinked structures. Some common examples of these crosslinked materials include rubber, phenolics, and cellulose. These crosslinked structures are held together by covalent bonds (as is the case with rubber or phenolics) or via hydrogen bonding interactions (as is the case with cellulose). Note that there are two types of crosslinking. Physical crosslinking involves the use of noncovalent interactions, such as hydrogen bonding or ionic interactions, to form crosslinks between polymer chains. These interactions are reversible under certain conditions. On the other hand, chemical crosslinking involves the use of covalent bonds to link polymer chains together. These are permanent and are not reversible under normal conditions. Vitrimers are an emerging class of materials that belong to chemical crosslinking, but they are still reversible due to the use of dynamic reversible bonds.
2.2 How Are Polymers Named?
Let us discuss how polymers are named. Many polymers are named simply by adding the prefix “poly” in front of the name of the monomer from which the polymer has been synthesized. For example, PE is a polymer that is prepared from the monomer ethylene. Likewise, polypropylene is a polymer that is prepared from the monomer propylene. As another example, PS is a polymer that is prepared from the monomer styrene.
Some polymers are named after their structures rather than the monomers that they are prepared from. For example, PET is prepared from ethylene glycol and terephthalic acid. However, it is named PET because it has ethylene and terephthalate groups within its structure.
2.2.1 Classification of Polymers
Two well‐known classification systems for polymers include:
Classification based on the polymer structure (Carothers, 1929)
[1]
Classification based on the mechanism (Flory, 1953)
[2]
2.2.1.1 Classification Based on the Polymer Structure
According to Carothers, there are two classes of polymers based on their structures, namely, condensation and addition polymers. These types of polymers will be briefly described below.
Condensation Polymers: According to Carothers, condensation polymers are formed from polyfunctional monomers via condensation reactions involving the release of small molecules such as water, HCl, and so forth (see Figure 2.1). Some polymers, such as cellulose, are also condensation polymers as they can hypothetically be prepared via the condensation of beta‐glucose.
Addition Polymers: These polymers are formed from monomers without the loss of small molecules. Some common examples of addition polymers include PS (Figure 2.2), PE, etc.
Carothers' polymer classification revolves around functional groups participating in polymerization and has overlooked the polymerization mechanism.
Figure 2.1 A condensation reaction leads to nylon‐6,10.
Figure 2.2 An additional polymerization leads to polystyrene, where styrene (left) undergoes free‐radical vinyl polymerization to yield polystyrene (right).
2.2.1.2 Classification Based on the Mechanism
Flory classified polymers according to their polymerization mechanisms, and this classification system included two categories: Step growth and chain‐growth polymers [2].
Step‐growth polymerizations are processes that occur through a sequence of reactions, where the monomers react with other monomers to form a dimer, which then combines with another monomer to form a trimer, or with another dimer to form a tetramer. This process continues, progressively building up large polymer chains and reaches maximum polymer size when the yield approaches 100% (refer to Figure 2.3 for more detail).
Chain‐growth polymerizations result in the growth of polymer chains within a matter of minutes, such that there are substantial quantities of high molecular weight polymers and a considerable number of monomers present at any given time. The molecular weights of polymers synthesized via these reactions do not change significantly during the reaction, though more and more polymers are formed as the polymerization proceeds.
2.2.1.3 Classification Based on the Source
In this classification system, polymers can be classified as synthetic, natural, or bio‐based polymers depending on their source.
Synthetic polymers are those that are produced in industry or laboratory settings through nonbiological reactions. These polymers, which include widely used plastics such as PE, polyvinyl chloride (PVC), and more, are often preferred due to their cost‐effectiveness and customizable performance features. Synthetic polymers can be derived from petrochemical as well as biobased feedstocks. For example, poly(lactic acid) (PLA) is biobased but it is produced in industry/lab and is thus a synthetic polymer.
In contrast, natural polymers such as cellulose and polyhydroxyalkanoates (PHAs), are derived from nature. These polymers are biodegradable, but they often lack the necessary properties to be used in packaging or other applications and some of them are difficult to melt‐process; thus, their use is limited as compared to synthetic polymers. There is also another category of polymers that is known as bio‐based polymers and this represents polymers that are either naturally derived or those produced from biobased feedstock. An example of this type of polymer would be PLA. Although PLA is synthesized in laboratories or industrial settings, it is produced from naturally sourced materials such as plants.
Figure 2.3 Plots of molecular weight versus percent monomer conversion for chain‐growth (a), living (b), and step‐growth polymerization reactions (c).
2.2.1.4 Classification Based on Cost and Performance
Polymers can also be classified based on their cost and performance. Under this classification, there are three distinct categories: commodity, engineering, and specialty polymers.
Commodity polymers, which are distinguished by their low cost and high‐volume use, are commonly utilized for applications below 100 °C. Such polymers can be heated briefly for 30 min or so up to 130 °C or so, but overall, their usage is primarily limited to ambient temperature applications. Examples include polyethylene, polypropylene, PS, PET, etc.
Engineering polymers, on the other hand, are more expensive and often used in lower volumes but have more resilience at high temperatures. Polycarbonates, Kevlar, and polyetheretherketone (PEEK), are all examples of engineering polymers. PET was once an engineering polymer, but became a commodity plastic because technologies emerged that reduced its cost, thus demonstrating that the category can change as technology progresses.
Figure 2.4 Common examples of thermoplastics and thermosets.
Specialty polymers are created for specific applications. For example, ethylene vinyl alcohol (EVOH) is used for high gas barrier applications, while polyvinylidene chloride (PVDC) is employed for high water, oil, gas, and water vapor barrier purposes. Specialty polymers tend to be costlier than commodity plastics.
2.2.1.5 Classification Based on Thermal Behavior
Polymers can be classified into two categories based on their thermal behavior: thermosets and thermoplastics. Thermosets are a type of polymer that cannot be remelted when they are subjected to high temperatures and shear force, whereas thermoplastics can be repeatedly remelted and reshaped when they are exposed to heat and shear force. Notably, the plastics employed in packaging are typically thermoplastics. It is important to note that thermosets constitute approximately 20% of all produced polymers, while thermoplastics account for the remaining 80%. Examples of thermosets and thermoplastics are shown in Figure 2.4.
2.3 Molecular Architecture
Polymers can also be categorized based on their molecular architecture, which refers to the arrangement of monomers during polymerization. This arrangement can lead to (1) linear, (2) branched, or (3) crosslinked structures/architecture. It is important to note that both homopolymers and copolymers can exhibit these molecular architectures – that is, they can be linear, branched, or crosslinked in structure.
What’s the big deal about molecular architecture? Indeed, a polymer’s properties depend on various factors, one of which is its molecular architecture. PE serves as a textbook example of how molecular architecture influences a polymer’s properties. Linear PE, also known as high‐density PE, is crystalline and opaque with good durability, while branched PE, also known as low‐density PE, is more flexible and transparent. This illustrates that even when the same ethylene monomer is used to create both linear and branched PE, the differences in molecular architecture result in unique properties for each polymer.
Crosslinked polymers such as those used to form rubber offer unique properties such as excellent wear resistance, chemical resistance, and longevity. Crosslinked polymers are less common in packaging, where their use is mostly limited to lids and caps for chemical containers, as well as liners for food cans.
2.3.1 Homopolymers and Copolymers
Polymers can be synthesized from one or more than one type of monomer. When a polymer is created using more than one kind of monomer, it is referred to as a copolymer. Conversely, a polymer formed from a single type of monomer is termed a homopolymer.
The primary reason for copolymerization is to modify and enhance certain properties of polymers. For instance, by incorporating a small percentage of ethylene monomer during the production of polypropylene, the resulting polymer exhibits improved optical clarity and flexibility. Examples of homopolymers and copolymers are shown in Table 2.1.
As we have seen in the previous section describing molecular architecture, there are various ways in which polymers are arranged. This is also true with copolymers, and there are various structural classes of copolymers. The most common type of copolymer is a random copolymer, in which two (or more) types of monomer units are mixed together in a random manner along the polymer chain. Examples of random copolymers are polyethylene vinyl acetate, polyethylene vinyl alcohol, and so on. In contrast, the different monomers are arranged in distinct “blocks” in the case of a block copolymer. A couple of common examples of block copolymers are PS‐block‐PE oxide and PE‐block‐polypropylene. On the other hand, the different monomers are arranged in an alternating manner in an alternating copolymer such as PS‐alt‐maleic anhydride.
2.3.2 Polymer Molecular Weights
Small molecules like water and carbon dioxide possess absolute molecular weights because these are formed in one or two steps and are kinetically and thermodynamically very stable so that they do not react further under the conditions that they are formed. However, the scenario is different for polymers. The molecular weight of a synthetic polymer does not have a fixed value; instead, it spans a range of values. This situation arises because polymer synthesis involves repeating steps. Each polymer chain is formed by consuming hundreds and sometimes even thousands of monomers. Alterations in the parameters during the polymerization, such as the concentration, temperature, and chain termination, lead to differences in polymer chain lengths. Therefore, the molecular weight of a polymer is typically expressed in terms of the average molecular weight. Number average molecular weight (Mn), weight average molecular weight (Mw), and viscosity average molecular weight (Mv) are common ways to express the average molecular weight of a polymer. Each of these averages provides unique information about the distribution and size of molecules within a polymer sample (Figure 2.5). These types of molecular weights are briefly described below.
Table 2.1 Examples of various homopolymers and copolymers and their nomenclature.
Homopolymers
Monomer nomenclature
Monomer formula
Repeating unit
Polymer nomenclature
Ethylene
CH
2
═CH
2
─[CH
2
CH
2
]─
Polyethylene
Propylene
CH
2
═CH
2
CH
3
─[CH
2
CH
2
CH
3
]─
Polypropylene
Vinyl chloride
CH
2
═CHCl
─[CH
2
CHCl]─
Poly(vinyl chloride)
Styrene
CH
2
═CH
2
C
6
H
5
─[CH
2
CH
2
C
6
H
5
]─
Polystyrene
Acrylonitrile
CH
2
═CHCN
─[CH
2
CHCN]─
Polyacrylonitrile
Vinyl acetate
CH
2
═CHOCOCH
3
─[CH
2
CHOCOCH
3
]─
Poly(vinyl acetate)
Tetrafluoroethylene
CF
2
═CF
2
─[CF
2
CF
2
]─
Polytetrafluoroethylene
Copolymers
Monomer
Monomer
Monomer
Copolymer nomenclature
Acrylonitrile
Butadiene
Styrene
Acrylonitrile butadiene styrene (ABS)
Propylene
Ethylene
Ethylene propylene (E/P)
Vinyl chloride
Vinyl acetate
Vinyl chloride/vinyl acetate
Vinyl chloride
Ethylene
Vinyl chloride/ethylene
Mn (Number Average Molecular Weight): This is the total weight of all the molecules in a sample divided by the number of molecules. It is the simplest form of average molecular weight, and it is sensitive to the presence of small molecules. The value of Mn is calculated via equation 2.1.
Figure 2.5 Plot of the weight fraction versus the molecular weight (Mn) [3]. This image is Reproduced from Odian, G, 2024/ with permission of John Wiley & Sons.
where ni is the number fraction or mol fraction of polymer chains with the molecular weight Mi.
Mw
