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Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities (2023)

Chapter: 2 Plastics Properties, Production, and Markets

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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
×
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
×
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
×
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
×
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
×
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
×
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
×
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Suggested Citation:"2 Plastics Properties, Production, and Markets." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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19 Plastics and plastic-based products began to be mass produced during the 1960s and 1970s, when consumers desired plastics as replacements for traditional materials because they were inexpensive, versatile, lightweight, sanitary, and easy to manufacture into a variety of forms. The ensuing rapid growth in plastics production and plastic-based products has been ex- traordinary, surpassing most other man-made materials (IBISWorld 2022; Statista 2022a, 2022b).1 Plastic products have also come into use in the construction sector, such as in cement additives, for building enclosure sheeting, and other applications. While plastic has many valuable uses, the continuing expansion of sin- gle-use plastic products and packaging has led to significant environmental, social, economic, and health consequences due to the plastics waste gener- ated. As an example, Americans purchase about 50 billion plastic water bottles per year, averaging about 13 bottles per month for every person in the United States (Earthday.org 2022; UN Environment Programme n.d.), while the world uses more than 100 million plastic bottles every single day (Grand View Research 2022). More than 40 percent of plastic (Chen et al. 2021; Cowan et al. 2021; Plastic Oceans 2022) is used only once, either as single-use plastic or as packaging, before it becomes plastics waste and, if mismanaged, stays in the environment for a very long time. 1 Cement production reached an estimated 92 million metric tons in the United States in 2021, the highest production volume recorded in the period of consideration (Statista 2022a). In 2021, around 87 million metric tons of steel were produced in the United States (Statista 2022b). 2 Plastics Properties, Production, and Markets

20 RECYCLED PLASTICS IN INFRASTRUCTURE The U.S. plastics and plastic-based industry accounted for an estimated US$432 billion2 in shipments and more than 1 million jobs in 2019, accord- ing to the 2020 Size & Impact Report from the Plastics Industry Associa- tion (Goldsberry 2020). The plastics industrial ecosystem includes tools, such as plastics extrusion and injection molding (Rapid Direct 2022), that make millions of plastic parts and products. The global injection-molding plastics market size was valued at US$284.7 billion in 2021 and expected to be US$303.7 billion in 2022. Any impact on plastics production will also have an effect on this market (Grand View Research 2022). This chapter covers plastics production and market segments of the seven major types of plastic used to make plastic-based products. Manu- facturing requires ongoing innovation in various forms of injection and extrusion molding of the virgin plastic polymers to make products. Market drivers that make plastics ubiquitous in our products, processes, and lives are described. POLYMERS AND PLASTICS Plastics are polymers, where polymers are macromolecules made up of repeating units called monomers. A polymer made from a single repeating unit is known as a homopolymer; a copolymer is a polymer formed from two (or more) different types of monomers. There are two basic types of polymers: natural and synthetic. Natural polymers, also called biopolymers, are naturally occurring materials, formed during the life cycles of green plants, animals, bacteria, and fungi. Synthetic polymers are primarily de- rived from petroleum oil or natural gas or, to a smaller degree, from biologi- cal resources, such as straw or woodchips (Di Bartolo et al. 2021; NASEM 2022). In both cases, synthetic polymers are created by various polymeriza- tion reactions (NASEM 2022). An example of a plastic made from a single monomer is ethylene (CH2=CH2), using a process called polymerization to make polyethylene (PE). When two different monomers are reacted, a copolymer is made. Copolymerization reactions are designed to make plas- tics with varying properties by combining two or more monomers. Other chemical processes used in their synthesis include condensation, polyad- dition, and cross-linking reactions. Most of these polymers are formed from chains of carbon atoms, with or without the attachment of oxygen, nitrogen, or sulfur atoms. Each polymer chain consists of several thousand repeating monomer units. Examples of other monomers are propylene, styrene, ethylene glycol, and vinyl chloride, which upon polymerization 2 This reported value is higher than the US$112.3 billion discussed further below. This value could possibly include distributors, retailers, and intermediaries that serve as agents between the producers and the manufacturers of plastic-based products.

PLASTICS PROPERTIES, PRODUCTION, AND MARKETS 21 or copolymerization result in a variety of virgin plastics. These in turn are the basic raw materials used to make a plethora of familiar consumer and manufactured plastic products. To customize the properties of a plastic, producers use different polymerization and copolymerization processes (Odian 2004; Young 1987) and various chemical reaction strategies to form the targeted copolymer products. The length, combination of monomers, and structure of these side chains influence the properties of the plastic. There are three principal classes of polymers: thermoplastics, thermo- sets, and elastomers. Differentiation among these classes is best defined by their behavior under applied heat. A thermoplastic may be repeatedly deformed by heating, melted, and re-formed upon cooling, as long as tem- peratures are maintained below decomposition temperature. In contrast, thermoset plastics have a fixed chemical structure that resists deformation upon heating; these materials can be decomposed at high temperature (com- busted) but do not melt. An elastic substance can stretch and bounce back. Thermoplastic elastomers (TPEs), sometimes referred to as thermoplastic rubbers, have elastic properties in varying degrees. These materials tend to deform when stretched, a process also known as necking. An example of a TPE3 is styrene-butadiene-styrene block copolymer, while high-density poly- ethylene (HDPE) is a thermoplastic with very little elastomeric property. PROCESSABILITY AND PROPERTIES The processability of a plastic is related to the class of polymers in which it is found. Thermoplastics generally have a linear or branched macromol- ecule structure depending on the type of copolymerization. A thermoplastic may be repeatedly heated and cooled without loss of structure. But thermo- sets are formed via a chemical reaction that results in a final cross-linking network within the thermoset plastic. The cross-linking means thermosets harden upon heating and cannot easily be molded or recycled after their initial formation. Thermoplastics can be molded repeatedly because they do not undergo chemical change in their composition when heated. Examples include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) (Jenkins et al. 1996). Thermoplastics, depending on the target end product, are typically processed via injection, extrusion, compression, blow molding,4 or ther- moforming. Thermoplastics need to be melted and at some point cooled to 3 According to Ceresana, a market research company, about 40 percent of the TPE mar- ket is in the automotive sector. https://ceresana.com/en/produkt/market-study-thermoplastic- elastomers. 4 Industry in the United States prefers the term “molding”; however, outside the United States the term “moulding” is more frequently used.

22 RECYCLED PLASTICS IN INFRASTRUCTURE the end product. The potential for repeated melting and re-forming makes thermoplastics amenable to recycling via re-manufacturing. Typical ther- moplastics (HDPE, low-density polyethylene [LDPE], linear low-density polyethylene [LLDPE], PP, PVC, PET, and PS) melt at temperatures be- tween 100°C and 250°C.5 Approximately 75 percent of thermoplastics are hydrocarbon plastics made from carbon- and hydrogen-based monomers (NASEM 2022). As discussed above, thermosets are cross-linked and once formed do not melt. Examples include epoxies and some polyurethanes (other poly- urethanes that can melt are thermoplastic). Thermoset plastics are thus not amenable to recycling by melting and reforming. Plastics achieve properties of strength, toughness, and stiffness based on how many monomer units or combinations of monomers (copolymers, terpolymers) are joined to form the polymer chain, which can be a branched chain6—LDPE, for example. The arrangement of polymer chains can be random or more orderly. Polymer plastics that are loosely organized tend to be amorphous, whereas more ordered polymer chains are semicrystalline solids (Sperling 2005). There can be hundreds to thousands of monomer units per polymer chain depending on the end properties of the polymers and the plastic-based product for which it has been designed. Some plas- tics, HDPE, for example, can form crystals. Others, like PET, a versatile engineering plastic, will convert from an amorphous state to a crystallized state, ready for drying, when agitated while heated to 180°F (82°C). These crystals impart specific property advantages, particularly water vapor bar- rier properties for HDPE and water and gas barrier properties for PET. Other thermoplastics, such as PS and PVC, are always amorphous and have no sharply defined melting points. Some plastics, such as LDPE and LLDPE, are mostly semicrystalline. PP can be partially crystalline or entirely amorphous (Maddah 2016). Plastics generally deform without strain recovery.7 Interestingly, one of the first uses of synthetic plastics (celluloid) was in replacing ivory for billiard balls. While celluloid is elastic and recovers deformation like ivory when struck, it is also combustible and explosive (called guncotton). Modern plastics are not explosive, although most will support a flame, like cellulose, only some burn hotter. 5 See Appendix J for melting points of specific thermoplastics. 6 Branched-chain polymers (i.e., polymers that look like minuscule tree branches) are poly- mers with a nonlinear backbone. This branching changes their material properties. 7 Unlike other thermoplastic elastomers, styrene-butadiene-styrene block copolymer (SBS) recovers when deformed. For this reason, SBS is widely used as a modifier for asphalt in pave- ments and for roofing.

PLASTICS PROPERTIES, PRODUCTION, AND MARKETS 23 Like the billiard ball example, other organic8 synthetic plastics were developed to replace natural materials because of their better properties and lower cost. Plastics were sometimes created to provide a whole new range of functions, such as those of films. Today, synthetic plastics are designed with specific products and performance in mind and, therefore, they are designed to exhibit specific properties. No single plastic meets the needs that the range of commercial plastics satisfies, nor are all plastics produced in the same way. The target properties need to be specified in order to select the appropriate virgin plastic. Depending on the melting point,9 the melt viscosity, and the melt strength,10 different processes are used to make the same product type from different plastics. Large HDPE bottles are made using extrusion blow molding (EBM)11 (see Figure 2-1). PET bottles larger than approximately 100 ml are made by injection stretch blow molding (see Figure 2-2). Blending Plastics While some thermoplastics materials will blend with others—polyethylenes of a similar melt flow rate (MFR) will blend with each other, for example— most thermoplastics do not blend advantageously with other thermoplas- tics. Researchers are then challenged to look for a “compatibilizer” to see how they can blend one thermoplastic with another. For example, polyeth- ylene and polypropylene can be blended only in small amounts before their properties degrade. PET does not blend with the other plastics in ways that provide any benefit in properties (Padhan and Gupta 2015). Molecular weight, which is controlled by the number of monomer units in the polymer, is a key property that, among other things, matters for the processability and the recyclability of plastics (Ragaert et al. 2017). The higher the molecular weight, the stronger the plastic and the more viscous the molten plastic becomes. For HDPE, the melt viscosity is measured by the MFR.12 The MFR for EBM bottles is less than 1 gram per 10 minutes of controlled test extrusion. For injection-molded tubs and bowls, the MFR 8 Materials with compositions of carbon, hydrogen, oxygen, and sometimes additional elements. 9 The processing temperature to achieve the needed molten plastic viscosity. 10 The property of the molten plastic to stick together. 11 Process where plastic is melted in an extruder and expelled into a hollow tube or parison. The parison is then closed into a water-cooled mold. As a next step, compressed air is blown into the parison to inflate its hollow interior and form it into the desired shape. https://www. mjspackaging.com/catalogsearch/result/?q=injection+stretch+blow+molding. 12 Melt flow rate (MFR) or melt flow index is a measure of the resistance to flow (viscosity) of the polymer melt at a given temperature under a given force for a predetermined period of time (Industrial Physics 2022).

24 RECYCLED PLASTICS IN INFRASTRUCTURE can be 25 to 50 grams per 10 minutes. Mixing high (25 to 50 grams per 10 minutes) MFR polyethylene with a low (0.3 grams per 10 minutes) MFR plastic is problematic (Bremner et al. 1990), highlighting one of the chal- lenges in plastics processing and recycling: sorting by melt flow rate. PLASTIC TYPES Standards organization ASTM International lists more than 700 different plastics in the standard ASTM D1600, and there are more that are not FIGURE 2-1 Schematic of extrusion blow molding process. FIGURE 2-2 Schematic of injection stretch blow molding process. SOURCE: Adapted from Weyh 2010.

PLASTICS PROPERTIES, PRODUCTION, AND MARKETS 25 included on the list. Another ASTM standard, ASTM D7611, “Standard Practice for Coding Plastic Manufactured Articles for Resin Identification,” lists and defines the Resin Identification Code (RIC) (ASTM 2022). The RIC was created in 1988 to facilitate recycling of plastics used in packag- ing, the motivation for this effort. State laws, such as California Public Resource Code 18010-18017, require the use of the RIC on selected rigid plastic containers. Thirty-nine states in the United States require the use of the RIC. Table 2-1 presents the RIC as per ASTM D7611. TABLE 2-1 Resin Identification Code Resin Identification Code (RIC) Polymer Name Common Products Polyethylene terephthalate (also PET) Bottle, jars, containers, trays, carpet High-density polyethylene Bottles, milk jugs, bags,a containers, toys Polyvinyl chloride Pipes, siding, pool liners, bags, shoes, tile Low-density polyethylene (another form is linear low- density polyethylene, or LLDPE) Bags, wrap, squeezable bottles, flexible container lids, agricultural film, cable coating Polypropylene Tupperware plastics, yogurt tubs, hangers, diapers, straws Polystyrene or expanded polystyrene (PS/EPS) Disposable cups and plates, take-out container, packing peanuts Polycarbonate, nylon, acrylonitrile, butadiene styrene (ABS), acrylic, polylactide (PLA) CDs, safety glasses, medical storage, baby bottles a Plastics bags are manufactured with HDPE, LDPE, and LLDPE. While most shopping bags (e.g., grocery store bags) are manufactured with HDPE, LDPE is typically used for tear-away dry cleaner bags, and LLDPE is used for heavier and thicker bags, for example those used by clothing stores (Sciencing 2018). SOURCE: RIC and related polymers from ASTM D7611 (ASTM 2022). It is important to note that the RIC is not a recycling code; it should not be

26 RECYCLED PLASTICS IN INFRASTRUCTURE taken as implying anything about recyclability, actual recycling, or recycled content. Recyclability depends on the mix of different types of resins and additives within a single plastic product, among other factors. Copolymers Copolymers are plastics made with two or three different monomers. This is done to attain an enhancement of some property. Copolymers are generally difficult to recycle. Here are some examples: Polyethylene terephthalate glycol (PETG): This is a glycol-modified ver- sion of PET. A second glycol (ethylene glycol is the primary) is included to ensure the plastic is always amorphous. It is not compatible for blending with PET. Due to their different melting points, when processed together PETG melts and becomes tacky while PET remains solid. The combined melted PETG and solid PET form clumps that create processing challenges. (Staub 2017) High-impact polystyrene: Otherwise brittle polystyrene is made tough by incorporating rubber into the PS structure. It is compatible for blending with other PSs. PLASTICS PRODUCTION AND USE Geyer et al. (2017) estimated annual production of plastic globally through 2017, when it reached 350 million metric tons (MMT), as shown in Figure 2-3, which also breaks this production down by plastic type. The Organisa- tion for Economic Co-operation and Development (OECD 2022) estimates that annual global plastics use reached 460 MMT in 2019. Figure 2-4 pro- vides a summary of historical global use of plastics by industry, where it can be seen that building, construction, and transportation represent some of the largest plastics users. Current annual plastics use in North America has been estimated to be 84 MMT (OECD 2022). Six polymers make up ap- proximately 90 percent of the plastics produced (NASEM 2022). The plas- tic types used in greatest quantity (by weight) globally are LDPE, HDPE, and PP (Geyer 2020); these three plastic types also are the most produced in the United States (Di et al. 2021; Heller et al. 2020). The main reason for their preferred use is that LDPE, HDPE, and PP resist damage by water, air, grease, and cleaning solvents; they are easy to shape into products that are light but robust; and they can be produced using relatively inexpensive natural gas (The Conversation 2018). The production of PET, which is widely used for beverage container products, is also significant and may be underreported (NASEM 2022). The global production trends shown in Figure 2-3 are consistent with those observed for North America (NASEM

PLASTICS PROPERTIES, PRODUCTION, AND MARKETS 27 2022). The growth rate of plastic use globally is estimated at 8.5 percent per year since 1950 (Chalmin 2019), with the increase in single-use prod- ucts contributing significantly. The generally short service life of plastic products has led to an ac- cumulation of plastics waste in landfills and the environment, with im- pacts exacerbated by the recalcitrant-to-biodegradation nature of plastic FIGURE 2-3 Global production of plastics by polymer. NOTE: Mt = MMT = million metric tons. SOURCE: Geyer 2020. FIGURE 2-4 Global annual primary plastics production by consuming sector from 1950 to 2017. NOTE: Mt = MMT = million metric tons. SOURCE: Geyer 2020.

28 RECYCLED PLASTICS IN INFRASTRUCTURE (NASEM 2022). If plastics use and waste management continue with busi- ness as usual, the mass of plastic in the marine environment will exceed the mass of fish by 2050 (WEF 2016). Plastic materials with short service lives are of particular concern in this regard; materials with longer service lives and better management at end-of-life service, such as in infrastructure applications, are of less concern. Plastics production also presents a tremendous energy and carbon footprint. More than 99 percent of plastics are made from chemicals de- rived from fossil fuels (Center for International Environmental Law [CIEL] 2017). According to the CIEL, if trends in oil consumption and plastic pro- duction continue as expected, “the consumption of oil by the entire plastics sector will account for 20 percent of the total consumption by 2050,” up from 6 percent today. A modeling exercise by Nicholson et al. (2021) sug- gested that approximately 3.2 quads13 of energy per year are consumed to produce plastics, resulting in greenhouse gas emissions of 104 MMT carbon dioxide equivalent (CO2e).14 MARKET DRIVERS The projected global plastics market for 2022 is estimated to be US$600 billion with that in the United States close to US$60 billion (Grand View Research 2022). This ongoing market growth of plastics would not be possible without the invention of modern injection molding (Texas A&M n.d.), which is responsible for creating millions of manufactured plastic items. Just as synthetic rubber replaced natural rubber during World War II (WWII), U.S. manufacturers in the WWII and post-war periods began to use plastics to replace the more expensive paper, glass, and metal materials. Plastics market growth is driven by lower manufacturing costs, better mate- rial performance, and lower weight for components used in the automotive (fuel efficiency standards) and construction industries. Demand for various forms of polyethylene polymers (LLDPE, LDPE) in the medical and pub- lic health fields has increased further to combat the spread of COVID-19 (NASEM 2022). The use of plastics is based on functional properties, such as barriers to water, oxygen, and carbon dioxide for soft drinks. For bottles and tubs, tensile strength and high modulus matter. Package weight, overall safety from breakage, and hygiene are critical to packaging. Plastics protect the 13 A quad of energy is equivalent to 1015 British thermal units, or 1.055 × 1018 Joules in the International System. 14 Carbon dioxide equivalent (CO2e) is the number of metric tons of CO2 emissions with the same global warming potential as one metric ton of another greenhouse gas. https://www3. epa.gov/carbon-footprint-calculator/tool/definitions/co2e.html.

PLASTICS PROPERTIES, PRODUCTION, AND MARKETS 29 packaged goods and do so inexpensively and conveniently for the consumer. For durable goods, plastics are strong, are tough, do not rot or rust, and are lightweight and inexpensive compared to alternatives (Grand View Research 2022). According to the U.S. Environmental Protection Agency (USEPA 2022), in 2018, 36 million tons of plastics were generated in the United States; of that total, 15 million tons became plastic containers and packaging.15 In other words, packaging and containers constituted 40.6 percent of the plastics created for commerce. Plastics meet functional needs at low cost to the consumer. FINDINGS • The production of plastics has increased continuously since their introduction into commerce in the 1950s. At present, the plastics produced in largest quantity are HDPE, LDPE, LLDPE, and PP. Major drivers for continuous growth in plastics production and use include low cost, low weight, strength, longevity, and convenience. • Thermoplastics, including PE, PP, PET, PS, and PVC, flow when heated to temperatures above their glass transition and/or melt- ing transition temperatures and thus can be melted and molded repeatedly, as long as the temperatures are maintained below their decomposition temperatures. • The growing use of plastics globally and the general short usage life of many plastic products has led to an accumulation of plastics waste in landfills and the environment. REFERENCES ASTM. 2022. Standard Practice for Coding Plastic Manufactured Articles for Resin Identi- fication. Standard D7611/D7611M-21. https://www.astm.org/d7611_d7611m-21.html Bremner, T., Rudin, A., and Cook, D. G. 1990. Melt flow index values and molecular weight distributions of commercial thermoplastics. Journal of Applied Polymer Science 41(7- 8):1617-1627. https://doi.org/10.1002/app.1990.070410721 Center for International Environmental Law (CIEL). 2017. Fossils, Plastics, & Petrochemical Feedstocks Is the First in an Ongoing Series, Fueling Plastics. https://www.ciel.org/wp- content/uploads/2017/09/Fueling-Plastics-Fossils-Plastics-Petrochemical-Feedstocks.pdf Di, J., Reck, B. K., Miatto, A., and Graedel, T. E. 2021. United States plastics: Large flows, short lifetimes, and negligible recycling. Resources, Conservation and Recycling 167:105440. Di Bartolo, A., Infurna, G., and Dintcheva, N. T. 2021. A review of bioplastics and their adop- tion in the circular economy. Polymers 13:1229. https://doi.org/10.3390/polym13081229 15 Here we use 2018 data as the latest published values and also values not distorted by the COVID-19 pandemic.

30 RECYCLED PLASTICS IN INFRASTRUCTURE Chalmin, P. 2019. The history of plastics: From the Capitol to the Tarpeian Rock. Field Ac- tions Science Reports: The Journal of Field Actions 19:6-11. https://journals.openedition. org/factsreports/5071 Chen, Y., Awasthi, A. K., Wei, F., Tan, Q., and Li, J. 2021. Single-use plastics: Production, usage, disposal, and adverse impacts. Science of the Total Environment 752. https://doi. org/10.1016/j.scitotenv.2020.141772 The Conversation. 2018. The World of Plastics in Numbers. https://theconversation.com/ the-world-of-plastics-in-numbers-100291 Cowan, E., Booth, A. M., Misund, A., Klun, K., Rotter, A., and Tiller, R. 2021. Single-use plastic bans: Exploring stakeholder perspectives on best practices for reducing plastic pollution. Environments 8(8). https://doi.org/10.3390/environments8080081 Earthday.org. 2022. End Plastic Pollution. Fact Sheet: Single-Use Plastics. https://www.earth day.org/fact-sheet-single-use-plastics Geyer, R. 2020. Chapter 2: Production, use, and fate of synthetic polymers. In Plastic Waste and Recycling, edited by T. M. Letcher. New York: Academic Press, pp. 13-32. Geyer, R., Jambeck, J. R., and Law, K. L. 2017. Production, use, and fate of all plastics ever made. Science Advances 3(7):e1700782. Goldsberry, C. 2020. The plastic industry is essential to the U.S. economy. Plastics Today. https://www.plasticstoday.com/industry-trends/plastics-industry-essential-us-economy Grand View Research. 2022. Plastic Market Size, Share & Trend Analysis by Product (PE, PP, PU, PVC, PET, Polystyrene, ABS, PPO, Epoxy Polymers, LCP, PC, Polyamide), by Application, by End Use, and Segment Forecasts, 2022-2030. https://www.grandview research.com/industry-analysis/global-plastics-market Heller, M. C., Mazor, M. H., and Keoleian, G. A. 2020. Plastics in the US: Toward a material flow characterization of production, markets and end of life. Environmental Research Letters 15:094034. IBISWorld. 2022. Plastics & Resin Manufacturing in the US—Market Size 2003-2028. https://www. ibisworld.com/industry-statistics/market-size/plastic-resin-manufacturing-united-states Industrial Physics. 2022. What Is Melt Flow Index (MFI) and Why Is It Important? https:// industrialphysics.com/knowledgebase/articles/what-is-mfi-or-mfr-and-why-is-it-important Jenkins, A. D., Kratochvíl, P., Stepto, R. F. T., and Suter, U. W. 1996. Glossary of basic terms in polymer science (IUPAC Recommendations 1996). Pure and Applied Chemistry 68(12):2287-2311. https://doi.org/10.1351/pac199668122287 Maddah, H. A. 2016. Polypropylene as a promising plastic: A review. American Journal of Polymer Science 6(1):1-11. http://doi.org/10.5923/j.ajps.20160601.01 National Academies of Sciences, Engineering, and Medicine (NASEM). 2022. Reckoning with the U.S. Role in Global Ocean Plastic Waste. Washington, DC: The National Academies Press. https://doi.org/10.17226/26132 Nicholson, S. R., Rorrer, N. A., Carpenter, A. C., and Beckham, G. T. 2021. Manufactur- ing energy and greenhouse gas emissions associated with plastics consumption. Joule 5(3):673-686. Odian, G. G. 2004. Principles of Polymerization, 4th edition. Hoboken, NJ: John Wiley & Sons. Organisation for Economic Co-operation and Development (OECD). 2022. Global Plastics Outlook: Economic Drivers, Environmental Impacts and Policy Options. https://www. oecd-ilibrary.org/sites/de747aef-en/index.html?itemId=/content/publication/de747aef-en Padhan, R. K. and Gupta, A. A. 2015. Polyethylene terephthalate-based blends: Thermoplastic and thermoset. In Poly(Ethylene Terephthalate) Based Blends, Composites and Nano- composites, edited by P. M. Visakh and Mong Liang. William Andrew Publishing, pp. 65-73. https://doi.org/10.1016/B978-0-323-31306-3.00004-X Plastic Oceans. 2022. Plastic Pollution Facts. https://plasticoceans.org/the-facts

PLASTICS PROPERTIES, PRODUCTION, AND MARKETS 31 Ragaert, K., Delva, L., and Van Geem, K. 2017. Mechanical and chemical recycling of solid plas- tic waste. Waste Management 69:24-58. https://doi.org/10.1016/j.wasman.2017.07.044 Rapid Direct. 2022. What Is Plastic Extrusion: A Definitive Process Guide. https://www. rapiddirect.com/blog/plastic-extrusion-process Sciencing. 2018. Materials Used for Making Plastics Bags. https://sciencing.com/thermoplastic- polymer-5552849.html Sperling, L. H. 2005. Introduction to polymer science. In Introduction to Physical Polymer Science, edited by L. H. Sperling. https://doi.org/10.1002/0471757128.ch1 Statista. 2022a. Cement Production in the United States from 2010 to 2021. https://www. statista.com/statistics/219343/cement-production-worldwide –––. 2022b. Steel Production Figures in the U.S. from 2006 to 2021. https://www.statista.com/ statistics/209343/steel-production-in-the-us Staub, C. 2017. PET Resin Code Changes in California. Resource Recycling. https://resource- recycling.com/recycling/2017/10/24/pet-resin-code-changes-california Texas A&M. n.d. History of Plastics Part 1: Injection Molding Curriculum. Innovative Curriculum for Industrial Innovation. http://people.tamu.edu/~hsieh/ICIA/Richland- Injection-Molding-Web/Richland-Part-1-History-of-Plastics.pdf United Nations (UN) Environment Programme. n.d. Our Planet Is Choking on Plastic. https:// www.unep.org/interactives/beat-plastic-pollution U.S. Environmental Protection Agency (USEPA). 2022. Container and Packaging: Product-Spe- cific Data. https://www.epa.gov/facts-and-figures-about-materials-waste-and-recycling/ containers-and-packaging-product-specific Weyh, R. 2010. Streckbasformen.png. https://commons.wikimedia.org/wiki/File:Streckblas formen.png World Economic Forum (WEF). 2016. The New Plastics Economy Rethinking the future of plastics. https://www3.weforum.org/docs/WEF_The_New_Plastics_Economy.pdf Young, R. J. 1987. Introduction to Polymers. London: Chapman & Hall.

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Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities Get This Book
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In the U.S., most plastics waste is disposed in landfills, but a significant amount also ends up as litter on land, rivers, and oceans. Today, less than 10 percent of plastics waste is recycled in the U.S. annually. The use of recycled plastics in infrastructure applications has potential to help expand the market and demand for plastics recycling.

These are among the findings in TRB Special Report 347: Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities from the Transportation Research Board of the National Academy of Sciences, Engineering, and Medicine.

The report emphasizes that pursuing the recycling of plastics in infrastructure depends on goals, policy, and economics. To that end, life cycle economic and environmental assessments should be conducted to inform policies on plastics waste reuse.

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