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Suggested Citation:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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:"8 Plastics Redesign for Recycling." 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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175 8 Plastics Redesign for Recycling As demonstrated in preceding chapters, the recycling and reuse of plastics waste is impeded by a range of factors. Supply of and demand for quality recycled plastics are often at levels too low to justify the expense of collect- ing and processing the material. Composite materials, with their mixture of polymers, are difficult to separate. Additives incorporated in polymers become contaminants when considering reuse. Design decisions created the challenges of incorporated additives and the production of composite plastic materials. The mixtures of plastic ma- terials used in manufacturing many consumer and industrial products pose difficult challenges for recycling. For example, a plastic bottle might include layers of different types of plastics, with each plastic layer designed to meet a specific function. This product complexity significantly complicates the ability to recycle plastics waste if the different types of plastic in a single product cannot be easily isolated into the basic polymer materials (Heller et al. 2020; Marquis 2022). This chapter examines two distinct strategies (see Figure 8-1) that are being pursued toward the formulation of new plastics. Oriented toward next-generation plastics and plastic products, these strategies enable bet- ter recycling in two ways: (1) new chemical compositions, structures, and properties realized through materials chemistry (next-generation plastics), and (2) simplified product formulation through reengineered product re- design (next-generation plastic products). After a short introduction of the rationales driving the development of next-generation plastic products, this chapter provides a general overview of plastic formulations that are under development and a summary of several ongoing research and development

176 RECYCLED PLASTICS IN INFRASTRUCTURE (R&D) initiatives that have been launched to advance this field. In general, reducing the amount of plastics waste in either landfills or the environment is often cited as a motivation for creating next-generation plastics, but there are unique requirements for next-generation plastic products that could be recycled into materials that meet the performance needs of infrastructure applications. It is important to emphasize that plastics recycling for in- frastructure applications must not be considered as simply a “graveyard” to capture and store plastics waste, but rather the plastics must meet or exceed performance specifications for particular applications and provide meaningful benefits (e.g., lighter weight, reduced fouling, thermal insula- tion). R&D in this area has, therefore, focused on two different aspects: creating products from current plastics that are more apt to be suitable for recycling (e.g., excluding additives and/or avoiding multilayer or composite construction) and making new plastic compositions and structures. Often, these two approaches are divergent, but in other cases they are complemen- tary. For instance, improved properties that arise from changes in the mo- lecular composition and structure of the materials chemistry may provide opportunities for both simplified product design and enhanced recyclability (by mechanical or chemical recycling). As discussed in this chapter, these objectives could facilitate their use in infrastructure but could also intro- duce additional challenges (e.g., biodegradable plastics, the economic and supply chain challenges of new plastics) that would need to be investigated by economic and environmental life-cycle assessments. FIGURE 8-1 Two distinct strategies for next-generation plastics and plastic prod- ucts, designed for enhanced recyclability, which may operate divergently or syner- gistically and may result in unintended consequences or adverse effects.

PLASTICS REDESIGN FOR RECYCLING 177 DRIVERS AND RATIONALE FOR NEXT-GENERATION PLASTICS AND PLASTIC PRODUCTS Only a small fraction of plastics waste is recycled globally. Approximately 12 percent of spent plastic is reused or recycled, approximately 25 percent is incinerated, and approximately 60 percent ends up in the environment, such as landfills, dumps, public land, or bodies of water (Hundertmark et al. 2018; Lange 2021). Government agencies and industries across the world recognize that recycling systems need to be improved and plastics waste needs to be reduced. For example, 380 signatories in the United States signed a 2018 pledge to improve the nation’s recycling system (USEPA 2022a), 72 percent of the top 300 companies on the Fortune Global 500 list have committed to reduce plastics waste (Duke University 2022), and the European Union has developed action plans to reduce plastic pollution, especially marine litter, and create a circular plastics economy (European Commission 2018, 2022). Thus, the need to reformulate plastics and en- hance their reuse, recovery, and recyclability to reduce environmental im- pact during feedstock extraction, production, and waste management has been well established. As discussed in Chapter 5, policy has a significant effect on the supply of and demand for recycled plastics. Increased demand driven by poli- cies such as minimum content requirements or elimination of single-use products can impact future polymer and plastic product designs. Extended Producer Responsibility policies have increased producer interest in inno- vations because the burden shifts to them for product end-of-life manage- ment. These innovations may include reduction of color additives, longer life spans of products, and designs that improve recyclability of products. The need to reduce adverse environmental impacts of plastics has also been a significant driver of recent innovation toward reduction of virgin plastic production (i.e., light weighting; increasing life span; eliminating packaging; designing for recycling, repairing, and reusing), recycling (i.e., sorting, mechanical and chemical recycling, digital technology), and rede- sign (i.e., sustainable sourcing of feedstocks and built-in degradability). Likewise, the construction industry has looked at ways to minimize mate- rial waste through purchasing decisions, improved designs, aggressive re- cycling of demolition and construction debris, and use of recycled plastics in infrastructure (Nodehi and Taghvaee 2022). As discussed in preceding chapters, some important goals driving inter- est in plastics recycling in infrastructure are • Reducing plastics pollution; • Utilizing plastics as feedstocks to enhance supply chains, lifetime, and closed-loop resource utilization;

178 RECYCLED PLASTICS IN INFRASTRUCTURE • Improving the economics, processing, energy, properties, and per- formance of infrastructure; and • Meeting policy and regulatory demands. These goals present opportunities for new types of materials and pro- cesses that allow solutions that improve infrastructure but are not merely creating long-term storage of plastics within infrastructure. Most appli- cations of recycled plastics in transportation (Chapter 6) and nontrans- portation (Chapter 7) infrastructure are nascent and have not achieved systematic deployment. Some of the applications have proven to be suc- cessful in meeting the above goals and some have not. To date, only a few applications (e.g., drainage pipes, marine pilings, sound barrier walls) have proven commercially viable. Any use of recycled plastics in transportation or other infrastructure has to provide proven technical (engineering per- formance), environmental, social, and economic benefits, while considering the life cycle (from planning to end-of-life disposition) of the infrastructure component. Observed limitations in use in recycled plastics in infrastructure involve specific plastic properties, such as incompatibility with other materials in the mix, additive interference (plasticizers, fillers, stabilizers, colorants, etc.), melting temperatures, immiscibility of plastic mixtures, and reduced recyclability of the infrastructure materials (Awoyera and Adesina 2020; Lange 2021). Plastic material design thus has an important role in determin- ing potential for recycling and reuse of a particular material. Approaches to designing plastics for recycling into infrastructure uses and to achieve the four goals listed above may include those presented in Table 8-1. CONSIDERATIONS FOR NEXT-GENERATION PLASTICS AND PLASTIC PRODUCTS IN INFRASTRUCTURE APPLICATIONS Any current or future plastic material that is to be used in transportation or nontransportation infrastructure has special requirements. These re- quirements may or may not be aligned with the short-term needs that are expected with the single-use plastics applications for which much plastic material is produced. Key challenges include requirements for strength, stability under environmental conditions, and durability for infrastructure applications versus lability that may be preferred for short-term, single use. It is important to match the polymer chemical stability with its use and intended use conditions and to consider extreme conditions that may be encountered intentionally or inadvertently. Plastic materials are expected to maintain performance and exhibit resilience during their implementa- tion and then to offer properties that facilitate mechanical recycling with

PLASTICS REDESIGN FOR RECYCLING 179 maintenance of polymer structural integrity or to possess mechanisms for breakdown and building back up for chemical recyclability. There are op- portunities for diversity in plastics compositions, structures, and properties during the recycling process. All plastics recycling approaches present tech- nical and economic challenges, as examined in previous chapters. TABLE 8-1 Potential Approaches, Examples, and Desired Outcomes of Designing and Utilizing Recycled Plastics Waste for Infrastructure Approach Examples and Desired Outcomes Utilize engineering controls in the redesign of plastic products for recycling from the beginning, with a key driver to meet quality and specifications. • Remove green color from Sprite bottles to improve PET recycling. • Decrease the use of additives, multilayers, and mixed plastics, such as PET bottles with a label or cap made of PE or PP. • Find alternatives to polymer stabilizers, which reduce recyclability. Utilize materials chemistry to design new material compositions or structures that improve recyclability and accomplish performance standards. • Replace current plastics with new polymer materials that do not require the use of additives or multilayers for mechanical performance, thermal properties, UV stability, colors, etc. (e.g., Dow’s ENGAGE®, NORDEL®, AFFINTIY®, ELITE®, INNATE®) Develop new materials that would readily serve as feedstocks for infrastructure use, while being repeatedly recyclable. • Ideally, develop materials that are infinitely recyclable. Develop compatibilizers to facilitate blending, mixed recycling, etc. • Create grafted or other copolymer structures that facilitate blending to expand the recyclability of mixed plastics waste streams. Utilize sustainable sources of polymer building blocks to increase building block complexity and create opportunities for expansion of material properties. • Coinciding with the energy transition away from fossil fuels, biobased feedstocks are being increasingly explored as sustainable sources of building blocks, ideally with improved performance during application and enhanced recyclability. Develop plastics that can be utilized in extreme environments. • Design plastics with thermal stability, triggered regeneration, structural editing, healability, and/or infinite recyclability (e.g., for deep sea applications or distant space voyage and inhabitation). Design degradable polymers that do not require recycling. • Utilize degradable polymer materials that can be easily broken down into environmentally friendly byproducts. NOTE: PE = polyethylene; PET = polyethylene terephthalate; PP = polypropylene; UV = ultraviolet.

180 RECYCLED PLASTICS IN INFRASTRUCTURE Some guiding principles for the design of next-generation plastics and plastic products in infrastructure include the following: • Maximize correlation between plastic durability and conditions and lifetime for use, with mechanisms built in to provide selective routes for mechanical recycling, chemical recycling, mechanical upcycling, chemical upcycling, and/or (bio)degrading the materials. • Prioritize next-generation plastics that are capable of full circular- ity, economically, and ultimately designed to allow for infinite recyclability. • Design next-generation plastics to avoid the production or persis- tence of microplastics (Appendix F). • Design next-generation plastics that possess pathways for scalable production. • Create manufacturing processes for existing or next-generation plastics with attention to strategies and practicalities for recycling processes (e.g., avoiding mixed plastics classes and reducing other complexities as can be justified). • In the design of next-generation plastics, give careful consideration to characteristics and interplays between sustainability, durability, degradability, recyclability, and/or upcyclability. • When designing next-generation plastics, apply a holistic consider- ation of their production, use, lifetime, and potential degradation under intended or extreme conditions including upstream/down- stream risks, adverse effects, and competition for other societal needs. DIVERSE DIRECTIONS FOR NEXT-GENERATION PLASTICS AND PLASTIC PRODUCTS Next-generation plastics and plastic products have the potential to create value, enhance performance specifications, meet policy drivers, and expand applications scope, all while improving circularity (see Chapters 4 and 5) and increasing the availability and diversity of recycled plastics feedstocks (Ellen MacArthur Foundation 2023; The SustainAbility Institute 2023; U.S. Depart- ment of Energy [USDOE] 2020). As previously mentioned, there are two distinct approaches to improve recyclability of next-generation materials. The simplest involves engineering redesigns to existing plastic materials in the for- mation and formulation of new types of plastic products. More complicated, yet with broader scope and possibility, is the design of next-generation plas- tics from the molecular scale with new materials chemistry. There are also intersections and synergies between these two approaches. For example, next- generation materials chemistry can facilitate simpler engineering redesigns.

PLASTICS REDESIGN FOR RECYCLING 181 The Green Chemistry and Green Engineering programs of the U.S. Environmental Protection Agency (USEPA) work in these two spaces (see Box 8-1). The Green Chemistry program’s mission is to speed the adoption of chemical products and processes that reduce or eliminate hazardous sub- stances (USEPA 2022b). The mission of the Green Engineering program is the design, commercialization, and use of processes and products in ways that reduce pollution, promote sustainability, and minimize negative human health effects and environmental risks while ensuring economic viability and efficiency (USEPA 2022c). USEPA and other federal agencies have been conducting research and other activities to support advancement of green chemistry and green engi- neering. These efforts are in response to U.S. legislation and also to science BOX 8-1 USEPA Green Chemistry and Engineering Programs The U.S. Environmental Protection Agency (USEPA) Office of Pollution Prevention and Toxics, following its charges under the Toxic Substances Control Act and the Pollution Prevention Act, initiated and manages several programs that encourage and support companies to reduce and prevent pollution through material and product design. These programs include the following: • Green Chemistry (USEPA 2022b) • Green Engineering (USEPA 2022c) • Greener Products and Services (USEPA 2022d) • Green Chemistry Challenge (USEPA 2022e) These green design/manufacturing programs, initiated in the 1990s, provide detailed guidance and information about resources available from USEPA and from other government and private-sector sources. For example, leveraging research and experience from USEPA and elsewhere, the Green Chemistry and Green Engineering program websites (USEPA 2022b, 2022c) provide information about fundamental principles, funding sources, related USEPA reports and data- bases, and other useful information. The Greener Products and Services website (USEPA 2022d) provides guidance and information for consumers, institutional purchasers, federal purchasers, and manufacturers. The USEPA Green Chemistry Challenge (USEPA 2022e) is an annual awards program that promotes and supports the development of novel tech- nologies that incorporate the principles of green chemistry into chemical design, manufacture, and use. The Green Chemistry Challenge program was initiated by USEPA in 1996 and is conducted in partnership with the American Chemical Society Green Chemistry Institute and other chemical community organizations. Over the 26 years of the awards program, USEPA has recognized more than 130 chemical technologies, a number of which have related to new types of plastics and plastic production processes (USEPA 2022f).

182 RECYCLED PLASTICS IN INFRASTRUCTURE and policy developments in Europe and elsewhere. The European Union has been a global leader in development and implementation of science and pol- icy to promote sustainable material design, use, and recycling. A recent de- velopment is the 2020 Chemicals Strategy for Sustainability adopted by the European Commission, implemented by the European Chemicals Agency (ECHA 2020). The 2020 Chemicals Strategy aims to increase protection of citizens and the environment from harmful chemicals and boost innovation by promoting the use of safer and more sustainable chemicals. The Strategy includes provisions pertaining to “sustainable chemistry.” In response, the U.S. Congress passed the 2021 Sustainable Chemistry Research and Devel- opment Act (OSTP 2022; Rizzuto 2022). The law directs that the White House Office of Science and Technology Policy (OSTP) develop a definition of “sustainable chemistry” and identify opportunities for federal agencies to encourage the development and use of sustainable chemical manufactur- ing processes and products metrics. In April 2022, OSTP issued a request for interested parties to offer definitions and explanations of “sustainable chemistry” (OSTP 2022). In addition, OSTP established an interagency Joint Subcommittee on Environment, Innovation and Public Health that includes representatives from USEPA, USDOE, the National Institute of Sci- ence and Technology, the U.S. Department of Defense, the Food and Drug Administration, and the Small Business Administration. Redesign of Plastic Products for Recyclability Complex formulations of plastics were developed, evolved, and optimized over the past century to provide the useful, durable products we encounter in everyday life. Many of the composite mixtures, multilayer systems, and additives are critical to plastics performance and may not be easily elimi- nated. However, there are several engineering or processing controls that can be applied to simplify current plastics products or reconfigurations that can be employed to improve the potential for recycling and even infinite recyclability. For instance, the size and shape of different plastics or plastic parts can be selected to facilitate disassembly, sorting, and processing. Re- moval of colorants and avoidance of products that include multiple types of plastics (e.g., for a bottle, its label and cap) have been recognized as other straightforward product redesign approaches (Mehta 2023). Design Entirely New Polymer Materials Chemistry to Serve as Next- Generation Plastics The design of new materials chemistry offers opportunities to expand the breadth of applications for plastics and recycled plastics. There is also the potential for enhanced performance, especially bringing in the rich chemical

PLASTICS REDESIGN FOR RECYCLING 183 diversity of natural products compared to the petrochemical building blocks used in the primary plastic types currently involved in recycling for use in infrastructure. However, introduction of new chemistries may come at the cost of increasing the complexity of plastics sorting and processing by vari- ous mechanical or chemical recycling techniques. This would create addi- tional barriers to increasing the limited recycling of plastics that is currently accomplished. To address plastics pollution in general, a solution may be the replacement of petrochemical-based nondegradable plastics with sustain- able, recyclable, and degradable new plastic materials. Such replacement materials may provide opportunities to not only avoid environmental per- sistence of plastics pollution, but also to improve the overall health, welfare, and safety profile of plastics and microplastics, for example, by reducing impacts to wildlife upon consumption. However, such an approach may cre- ate unintended consequences for plastics reuse in infrastructure applications, specifically in the reduction in available supply of needed feedstock material such as recycled high-density polyethylene (HDPE) plastics. Desirable near-term infrastructure targets for new plastic materials de- signs are those applications that currently employ plastics at scale, including drainage pipes, sound barrier walls, and marine pilings. These applications, all of which use HDPE and rely on its long-term durability features and require large-scale plastics waste supply chains. Meeting these targets would be challenging for a new, sustainably sourced degradable plastic intended to replace the large-scale, inexpensive access to petrochemicals that can be read- ily transformed into robust polymer materials. The constraints of scale and cost competitiveness, therefore, may limit the use of next-generation recycled plastics in innovative ways for infrastructure applications. Nonetheless, sev- eral broad strategies toward next-generation plastics are outlined here, which utilize current petrochemically sourced plastics that dominate the global plas- tics production, involve sustainably sourced alternative plastic materials, or involve a hybrid of each. Although many such strategies are currently at early stages of research, significant investments are being made by companies, gov- ernment agencies, private foundations, and other organizations throughout the world. Offices within the National Science Foundation (NSF), USDOE (see Box 8-2), and the National Institute of Standards and Technology have partnered in an NSF Emerging Frontiers in Research and Innovation program titled Engineering the Elimination of End-of-Life Plastic Waste (NSF 2021). This effort involves funding a variety of research projects (NSF 2021; USDOE 2022), centers (University of Delaware 2023; University of Minnesota 2023), institutes (Ames National Laboratory 2023), and consortia (BOTTLE 2022) whose goals (NSF 2021; USDOE 2023) in advancing the circular economy of plastics align with those described above, for improved methods of waste deconstruction and upcycling, reduced energy use and emissions during pro- duction, and redesign for a new polymers and materials economy.

184 RECYCLED PLASTICS IN INFRASTRUCTURE BOX 8-2 Example of Federal Research and Development: Bio-Optimized Technologies to Keep Thermoplastics Out of Landfills and the Environment (BOTTLE™) Consortium The BOTTLE consortium (https://www.bottle.org) is a collective research effort led by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and it includes several national laboratories and universities. BOTTLE conducts research and development toward new and innovative ways to recycle. The consortium’s efforts include catalytic and biocatalytic strate- gies for breaking down plastics into chemical building blocks for manufacturing higher-value products (upcycling) and designing next-generation plastics that are recyclable by design. The initiative’s goals include 1. Developing scalable, cost-effective, and efficient processes to decon- struct and upcycle commodity thermoplastics and thermosets that are discarded in large quantities today. 2. Designing new biobased chemistries and associated processes for direct chemical recycling of future plastics and composites that are recyclable by design. 3. Working with industry to catalyze a new upcycling paradigm for plastics. BOTTLE has three main research thrusts: deconstruction, upcycling, and redesign. Examples of deconstruction include thermal catalysis, electrocatalysis, photocatalysis, and biocatalysis, such as the use of enzymes for plastic depo- lymerization. Examples of upcycling and redesign include the development of synthetic biodegradable plastics, circular or easily recyclable polymers, and repolymerization of deconstructed plastics into new products. Next Generation: Petrochemically Sourced Polymer Materials Having In-Built Recyclability Many new, next-generation polymer types derived from petrochemical feed- stocks and designed for enhanced product performance and recyclability are under development. Some have even been commercialized. Examples of the combination of materials chemistry and product redesign, where each contributes to enhanced mechanical recyclability, include the broad range of materials chemistries and process engineering of plastic polyolefin products developed over the past couple of decades by Dow. Key to control over the composition and structure of the polymer materials was a series of catalyst developments, including INSITE® (the developers won a Chemical & Engineering News Heroes of Chemistry Award in 2015), chain shuttling (Arriola et al. 2006), and others (reviewed by Chum and Swogger 2008) for materials chemistry control, thereby leading to variations of polyethylene architectures and copolymers (linear low-density polyethylene [LLDPE],

PLASTICS REDESIGN FOR RECYCLING 185 BOTTLE is funded by USDOE’s Bioenergy Technologies Office and Ad- vanced Materials and Manufacturing Technologies Office. The research and development is conducted by national laboratory and university partners with ex- pertise in process development and integration, chemical catalysis, biocatalysis, materials science, separation, modeling, economic analysis, and sustainability analysis. SOURCES: BOTTLE 2022; NREL 2022. Figure from BOTTLE Consortium, Elizabeth Stone/ NREL. block polymers, and others with tradenames ENGAGE®, NORDEL®, AFFINITY®, ELITE®, INNATE®, etc.). The developers of ELITE® and INNATE® were recognized by a Chemical & Engineering News Heroes of Chemistry Award in 2022 for the precise macromolecular chemical struc- tures of these materials, which afford properties that facilitate use of less plastic with equivalent high performance and easy recyclability. Process en- gineering of these innovative polyethylene analogs has been used to advance the molecular-scale polymer chain alignment and crystallinity, which further control properties and allow for “downgauging” and for product redesign that has included thinner high-strength packaging film applications (e.g., Dow’s DOWLEX polyethylene resin breathable back sheets) (Dow 2016). Some potential adverse effects and consequences related to recycling of these next-generation plastics for infrastructure, however, include reduced supply chain availability of feedstock materials available for recycled product man- ufacturing due to the lower mass and volume of materials required for initial

186 RECYCLED PLASTICS IN INFRASTRUCTURE use, and expansion of the breadth of polyolefin chemical structures (beyond HDPE, low-density polyethylene [LDPE], polypropylene) to various archi- tectures and compositions of LLDPE and copolymers, which may produce incompatibilities in recycled materials streams, complicating separations, and driving need for compatibilizers (Eagan et al. 2017; Xu et al. 2018). A second example is the development of polydiketoenamines and their breakdown via hydrolysis, an emerging chemistry, with promise to enable fully and infinitely chemically recyclable materials, as reported recently from work ongoing at several international government and academic institutions (Demarteau et al. 2022). These two examples were selected as representative and disparate systems to illustrate this approach. Many others exist. Next Generation: Sustainably Sourced Plastics with In-Built Recyclability/ Degradability Many new, next-generation, recyclable polymer types derived from sus- tainably sourced feedstocks are under development. Here, too, some have been commercialized. Examples include a series of polymers that have been developed to pivot away from the health and environmental concerns of bisphenol A (CHE 2023; NIH 2023; USEPA 2023), while maintaining the engineering plastics properties of bisphenol A–based polycarbonates. For instance, Mitsubishi has developed DURABIOTM, an isosorbide-containing polycarbonate (Mitsubishi Chemical Group 2022), and SK Chemicals has commercialized ECOZEN as an ecofriendly biocopolyester that also in- cludes isosorbide as a naturally sourced comonomer building block (SK Chemicals 2022). However, relevance of such materials to plastics recycling for the purpose of infrastructure applications is limited by their small-scale production, collection, and availability for recycling. Next Generation: Upcycling of Current Petrochemical Plastics and Hybridized Upcycling with Incorporation of Sustainable Building Blocks Upcycling of plastic materials may involve either physical blending or chemical modification. Chemical upcycling has included direct transfor- mations of polymer chains through chemical reactions that install new chemical functionalities or that transform an initial polymer into value- added products or materials, as reviewed by Jehanno et al. (2022). There is also early-stage research being undertaken to explore the incorpora- tion of biomass-derived constituents during the upcycling process (see Figure 8-2). Many such studies are premature for plastics recycling into infrastructure applications currently, but they may be useful for future developments.

PLASTICS REDESIGN FOR RECYCLING 187 CAVEATS, RISKS, UPSTREAM/DOWNSTREAM REALITY CHECKS, AND POTENTIAL ADVERSE EFFECTS OF NEXT-GENERATION PLASTICS The introduction of any next-generation plastic material, regardless of for- mulation and enhanced recyclability, will involve obstacles to acceptance and impacts to the plastics production, use, and reuse system. These chal- lenges merit as much preconsideration as possible. Not all of the system impacts will be predictable. As is the case for most new materials, pilot testing and evaluation will be needed. Life-cycle economic and environmen- tal assessments will be important components of preproduction planning. Some of the issues to be considered in this planning are described here. Production of any new polymer material will have capital requirements. Some new-generation plastics may be able to be produced with modifica- tions to existing facilities, while others will require completely new produc- tion facilities. While a next-generation plastic may have significantly enhanced po- tential for recycling, economically feasible collection of the material will require the availability of a sufficient quantity of the material. As discussed in preceding chapters, the lack of sufficient collection and recycling infra- structure is a primary impediment to material availability for recycling of plastics waste in the United States and globally, even for LDPE, HDPE, and polyethylene terephthalate, the most recycled of the plastic materials. New polymers may use different resources, the production of which will have different impacts on the environment and society. The production of biopolymers in great quantity, for example, will have implications for FIGURE 8-2 Chemical upcycling with combination of petrochemically derived plastics and biomass to create new polymers. SOURCES: Adapted from slide from Gregg Beckham’s presentation to the study committee on July 29, 2022. Biobased building blocks graphic from Rorrer et al. (2019).

188 RECYCLED PLASTICS IN INFRASTRUCTURE land and water consumption, as is the case for biofuel production (NRC 2008, 2011). Furthermore, large-scale biopolymer production could pos- sibly result in competition for land and other resources for production of biofuels, food, lumber, and other materials. FINDINGS • Plastics waste management could benefit from the development of new plastics formulations and product designs that are easily recyclable (i.e., less complex to sort, clean, and separate during re- cycling processing) and are driven by the chemical and mechanical properties needed to meet functionality and performance specifica- tions of new products. • The designs of existing or next-generation plastics can be modi- fied or developed to help mitigate the complexities in the recycling process. Solutions involve learning from the limitations and chal- lenges of the recycling process and implementing product designs that avoid, for example, additives that represent contaminants for recycling or mixing plastics within one product. • Innovative R&D for next-generation plastics is already ongoing to meet the challenge of decreasing the inherent complexity of plastic recycling. USEPA contributes to, supports, and incentivizes these efforts. Other federal agencies also have ongoing R&D efforts in next-generation plastics chemistry and engineering. The develop- ment of new plastic formulations also presents the opportunity to enhance the performance of plastics to meet improved functionality in consumer, industrial, and infrastructure applications. • In addition to having to be functionally and aesthetically suitable for product manufacturing, new plastic formulations and designs have to be economically competitive and have acceptable environ- mental and social impacts to be adopted. • As described in Chapter 4, life-cycle economic and environmental assessments are needed to avoid overlooking important burdens or benefits from plastic products. As next-generation plastics are developed, it will be important to fully consider their production processes, uses, expected life, and potential degradation under intended or extreme conditions. Such life-cycle assessments also need to evaluate potential upstream and downstream risks, adverse effects, and competition for other societal needs. • In the design of next-generation plastics, material characteristics and interplays among sustainability, durability, degradability, re- cyclability, and upcyclability need careful consideration.

PLASTICS REDESIGN FOR RECYCLING 189 • Guiding principles for the design of next-generation plastics and plastic products include correlation between plastic durability, conditions, and lifetime. As next-generation plastics and plastic products are designed, it would be beneficial to create guidance on selective routes for their mechanical recycling, chemical recycling, mechanical upcycling, chemical upcycling, and/or (bio)degrading. • Wide deployment of new plastic formulations—in infrastructure, consumer, and industrial products—will create demand pathways for scalable production. REFERENCES Ames National Laboratory. 2023. Institute for Cooperative Upcycling of Plastics. https:// www.ameslab.gov/institute-for-cooperative-upcycling-of-plastics-icoup Arriola, D. J., Carnahan, E. M., Hustad, P. D., Kuhlman, R. L., and Wenzel, T. T. 2006. Catalytic production of olefin block copolymers via chain shuttling polymerization. Sci- ence 312:714-719. Awoyera, P. O., and Adesina, A. 2020. Plastic wastes to construction products; Status, limita- tion and future perspectives. Case Studies in Construction Materials 12:e00330. https:// doi.org/10.1016/j.cscm.2020.e00330 Bio-Optimized Technologies to Keep Thermoplastics Out of Landfills and the Environment (BOTTLE) Consortium. 2022. About BOTTLE. https://www.bottle.org/about.html Chemical & Engineering News. 2015. Heroes of Chemistry Award in 2015. https://cen.acs. org/articles/93/i38/Heroes-Chemistry.html –––. 2022. Heroes of Chemistry Award in 2022. https://cen.acs.org/people/awards/ ACS-celebrates-2022-Heroes-Chemistry/100/i43 Chum, P. S., and Swogger, K. W. 2008. Olefin polymer technologies—history and recent prog- ress at the Dow Chemical Company. Progress in Polymer Science 33:797-819. Collaborative for Health & Environment (CHE). 2023. Bisphenol A. https://www.healthand environment.org/environmental-health/environmental-risks/chemical-environment- overview/bpa Demarteau, J., Epstein, A. R., Christensen, P. R., Abubekerov, M., Wang, H., Teat, S. J., Seguin, T. J., Chan, C. W., Scown, C. D., Russell, T. P., Keasling, J. D., Persson, K. A., and Helms, B. A. 2022. Circularity in mixed-plastic chemical recycling enable by variable rates of polydiketoenamine hydrolysis. Science Advances 8:eabp8823. Dow. 2016. Dowlex polyethylene resin breathable back sheets. https://s3.amazonaws.com/ entecpolymers.com/v3/uploads/003-20601-01-dow-solutions-for-strong-breathable-back- sheets.pdf Duke University. 2022. Do Voluntary Corporate Pledges Help Reduce Plastic Pollution? https:// nicholas.duke.edu/news/do-voluntary-corporate-pledges-help-reduce-plastic-pollution Eagan, J. M., Xu, J., Di Girolamo, R., Thurber, C. M., Macosko, C. W., LaPointe, A. M., Bates, F. S., and Coates, G. W. 2017. Combining polyethylene and polypropylene: En- hanced performance with PE/iPP multiblock polymers. Science 355:814-816. https://doi. org/10.1126/science.aah5744 Ellen MacArthur Foundation. 2023. Plastics and the Circular Economy. https://archive. ellenmacarthurfoundation.org/explore/plastics-and-the-circular-economy European Chemicals Agency (ECHA). 2020. Chemicals Strategy for Sustainability, European Chemicals Agency. https://echa.europa.eu/hot-topics/chemicals-strategy-for-sustainability

190 RECYCLED PLASTICS IN INFRASTRUCTURE European Commission. 2018. A Sustainable Bioeconomy for Europe: Strengthening the Connection Between Economy, Society and the Environment. https://eur-lex.europa.eu/ legal-content/EN/TXT/?uri=CELEX%3A52018DC0673 –––. 2022. Plastics. https://environment.ec.europa.eu/topics/plastics_en 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. Hundertmark, T., Mayer, M., McNally, C., Simons, T. J., and Witte, C. 2018. How Plastics Waste Recycling Could Transform the Chemical Industry. McKinsey & Company. https://www.mckinsey.com/industries/chemicals/our-insights/how-plastics-waste- recycling-could-transform-the-chemical-industry Jehanno, C., Alty, J. W., Roosen, M., De Meester, S., Dove, A. P., Chen, E. Y.-X., Leibfarth, F. A., and Sardon, H. 2022. Critical advances and future opportunities in upcycling com- modity polymers. Nature 603:803-814. Lange, J. P. 2021. Managing plastic waste—sorting, recycling, disposal, and product redesign. ACS Sustainable Chemistry & Engineering 9(47):15722-15738. https://doi.org/10.1021/ acssuschemeng.1c05013 Marquis, C. 2022. Beyond plastics: The myths and truths about recycling, and potential solutions. Forbes. https://www.forbes.com/sites/christophermarquis/2022/07/12/beyond- plastics-the-myths-and-truths-about-recycling-and-potential-solutions/?sh=40fd6169c30c Mehta, A. 2023. Plastics Need a complete redesign to make them easier to recycle, research- ers argue. Chemistry World. https://www.chemistryworld.com/news/plastics-need-a- complete-redesign-to-make-them-easier-to-recycle-researchers-argue/4016931.article Mitsubishi Chemical Group. 2022. DURABIOTM. https://us.mitsubishi-chemical.com/ product/durabio National Institutes of Health (NIH). 2023. Bisphenol A (BPA). https://www.niehs.nih.gov/ health/topics/agents/sya-bpa/index.cfm National Renewable Energy Laboratory (NREL). 2022. U.S. Department of Energy’s BOT- TLE Consortium. https://www.nrel.gov/manufacturing/bottle.html National Research Council (NRC). 2008. Water Implications of Biofuels Production. Wash- ington, DC: The National Academies Press. https://doi.org/10.17226/12039 –––. 2011. Renewable Fuel Standard: Potential Economic and Environmental Effects of U.S. Biofuel Policy. Washington, DC: The National Academies Press. https://doi. org/10.17226/13105 National Science Foundation (NSF). 2021. Engineering the Elimination of End-of-Life Plastic Waste. https://www.nsf.gov/news/news_summ.jsp?cntn_id=303230&org= ENG&from=news Nodehi, M., and Taghvaee, V. M. 2022. Applying circular economy to construction indus- try through use of waste materials: A review of supplementary cementitious materials, plastics, and ceramics.  Circular Economy and Sustainability  2:987-1020. https://doi. org/10.1007/s43615-022-00149-x Office of Science and Technology Policy (OSTP). 2022. Request for information: Sustain- able chemistry, Office of Science and Technology Policy. Federal Register 87:19539. https://www.federalregister.gov/documents/2022/04/04/2022-07043/request-for- information-sustainable-chemistry Rizzuto, P. 2022. White House to define “sustainable chemistry” as EU demands it. Bloomberg Law, April 1. https://news.bloomberglaw.com/environment-and-energy/ white-house-to-define-sustainable-chemistry-as-eu-demands-it Rorrer, N., Nicholson, S., Carpenter, A., Biddy, M., Grundl, N. and Beckham, G. 2019. Combining reclaimed PET with bio-based monomers enables plastics upcycling. Joule 3. https://doi.org/10.1016/j.joule.2019.01.018

PLASTICS REDESIGN FOR RECYCLING 191 SK Chemicals. 2022. ECOZEN. https://www.skchemicals.com/en/products/ECOZEN.aspx The SustainAbility Institute. 2023. Creating a Circular Economy for Plastics. ERM.com. https://www.sustainability.com/thinking/creating-a-circular-economy-for-plastics University of Delaware. 2023. Center for Plastics Innovation: A Hub for Transformative Chemical Conversion Strategies and Enabling Cross-Cutting Tools. https://cpi.udel.edu University of Minnesota. 2023. Transforming How Plastics Are Made, Unmade, and Remade. https://csp.umn.edu U.S. Department of Energy (USDOE). 2020. Plastics for a Circular Economy Workshop: Sum- mary Report. December 11-12, 2019. Golden, Colorado. https://www.energy.gov/sites/ prod/files/2020/07/f77/beto-plastics-wksp-rpt-final.pdf –––. 2022. DOE Invests $13.4 Million to Combat Plastic Waste, Reduce Plastic Indus- try Emissions. https://www.energy.gov/articles/doe-invests-134-million-combat-plastic- waste-reduce-plastic-industry-emissions –––. 2023. Strategy for Plastics Innovation. https://www.energy.gov/entity%3Anode/4394292/ strategy-plastics-innovation U.S. Environmental Protection Agency (USEPA). 2022a. America Recycles Pledge. https:// www.epa.gov/recyclingstrategy/forms/america-recycles-pledge –––. 2022b. Green Chemistry. U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics. https://www.epa.gov/greenchemistry –––. 2022c. Green Engineering. U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics. https://www.epa.gov/green-engineering –––. 2022d. Greener Products and Services. U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics. https://www.epa.gov/greenerproducts –––. 2022e. Green Chemistry Challenge. Office of Pollution Prevention and Tox- ics, U.S. Environmental Protection Agency. https://www.epa.gov/greenchemistry/ information-about-green-chemistry-challenge –––. 2022f. Green Chemistry Challenge—Winners. Office of Pollution Prevention and Toxics, U.S. Environmental Protection Agency. https://www.epa.gov/greenchemistry/ green-chemistry-challenge-winners –––. 2023. Risk Management for Bisphenol A (BPA). https://www.epa.gov/ assessing-and-managing-chemicals-under-tsca/risk-management-bisphenol-bpa Xu, J., Eagan, J. M., Kim, S.-S., Pan, S., BoLee, B., Klimovica, K., Jin, K., Lin, T.-W., Howard, M. J., Ellison, C. J., LaPointe, A. M., Coates, G. W., and Bates, F. S. 2018. Compatibiliza- tion of isotactic polypropylene (iPP) and high-density polyethylene (HDPE) with iPP–PE multiblock copolymers. Macromolecules 51(21):8585-8596. https://doi.org/10.1021/acs. macromol.8b01907

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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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