Plastics in the US: toward a material flow characterization of production, markets and end of life

The starting point for plastic production and use by major markets in North America is the survey-based industry data compiled for the American Chemistry Council (ACC) through an independent third party [16]. These data are limited to plastics manufacturers that participate in the survey, but covers an expected 95%–100% of the total US production for the materials reported. We use these data as provided, noting limitations here. The geographic boundaries for the data from ACC reflect the production locations of survey participants and are inconsistent (e.g. production of polyethylenes represents US and Canada, whereas polypropylene and polystyrene represents US, Canada & Mexico) and disaggregation by country is unavailable. We offer scaling estimates based on both the relative national gross domestic product (GDP) and population to provide context for the US component of this North American data. In addition to North American production, resin sales can include imports by resin manufacturers. Further, only the dominant thermoplastics (LDPE, LLDPE, HDPE, PP, PS, EPS, PVC) are disaggregated and detailed, requiring supplemental data from disparate sources on other important resins such as PET. While the ACC data may include imports, it does not account for all imports. Likewise, reported exports represent sales by resin manufacturers to foreign buyers, but do not capture additional exports by brokers or other third party sales. This makes reconciliation with international trade data challenging. We include US imports of primary form plastics as well as formed plastics (rods, sticks, sheets, films, plates, caps, etc) based on US trade data for 2017 [17], acknowledging that some double-counting can not be avoided and that some discrepancies may be introduced due to trade between N. American countries. These imports are detailed in the supplementary information (available online at stacks.iop.org/ERL/15/094034/mmedia). Imports of plastics also occur as finished consumer goods. The plastics contained in imported finished goods (foods, apparel, footwear, computers and electronics, appliances, automobiles, furniture, medical supplies, athletic goods, toys) and their packaging were estimated using the monetary value of net imports into the US, averaged over three years (2016–2018) combined with sector-level estimates of plastic content per unit of revenue [18]. Details are contained in the supplementary information. Resin composition of these imported finished goods is unspecified. While material flow estimates reliant on monetary value is less desirable than physical bases, in the absence of higher quality data on the quantity of plastics in imported and exported finished goods, we offer these as rough initial estimates.

The US EPA maintains national level data on the characterization and management of municipal solid waste (MSW) in the US [19]. These data are used to define the majority of post-use flow of plastics, based on the year of 2017. Plastics in the US MSW stream are estimated by US EPA using material flow methodologies, but rely on the industry data from ACC as the primary source of plastic generation, with sales data that include Canada being reduced by the ratio of Canada/US population [20]. In the US EPA method, containers and packaging are assumed to be discarded in the same year that the products they contain are purchased. Non-durable goods are those that generally last less than three years and the plastic-containing non-durables include plastic plates and cups, trash bags, disposable diapers, clothing and footwear, and other miscellaneous products. Durable goods have assumed lifetimes of three years or more, and include items such as major and small appliances, furniture, carpets, and consumer electronics; specific plastic-containing durable goods are poorly defined. Appearance of durable and non-durable goods in the MSW stream reported by US EPA is temporally lagged based on modeling of the product's useful life [20]. In other words, inclusion of these materials in MSW represents disposal in 2017 of products manufactured in previous years.

The End of life (EOL) disposition of plastics contained in MSW is also informed by data from US EPA [19]. Recovery of plastics in that report is also primarily based on industry-sourced surveys [21–24]. Data on recovery of plastics from durable goods is limited. After accounting for recovery, disposal of plastics in MSW is distributed between combustion with energy recovery and landfill based on average national rates. Note that, per US EPA methods, combustion without energy recovery is included as landfill.

Recycling of post-industrial plastic waste is not explicitly detailed in our analysis. These materials—non-conforming parts, runners and trim waste from processing—are generally clean and of high demand and therefore have high recycling rates, often within the same manufacturing facility.

Additional plastics-containing waste streams not captured in US EPA's definition of MSW include construction and demolition (C&D) waste and automotive shredder residue (ASR). Estimates of the plastics contained in these waste flows are included using available data [25, 26]. Plastics represent a very small fraction (<2%) of total C&D generation in the US; packaging materials likely form the bulk of plastics recovered by C&D recyclers [25]. Plastics in ASR are estimated based on the number of end of life vehicles disposed annually in the US, a representative weight, and the fraction of plastics in automobiles in 2003 (i.e., assuming models retired in 2017 are 14 years old) [26]. Landfill disposal of ASR is most common and assumed in this assessment.

Leakage of plastics to aquatic and other environments has arisen as a major concern due to their persistence and potential impacts on organisms and ecosystems. Here we include estimates of macro- and microplastic losses in the N. American region from a recent UN Environment report [12]. As such, this should be an overestimate of the environmental leakage in the US specifically. In this UN Environment assessment, losses of plastic to the environment from mismanaged waste treatment—a major concern in other regions—is assumed negligible in N. America. In addition, a number of other sources of leaked plastics deemed of low to medium importance were not included in the UN Environment report estimates due to inadequate quantitative knowledge (see table 19 in [12]).

Geyer et al estimate that roughly 30% of all the plastics ever made globally are currently in-use stock: that is, still contained in products that have not yet been disposed [3]. Applying the product lifetime distributions reported by Geyer et al [3] to US sales and captive use of all plastics going back to 1973, we estimate that the plastics existing as in-use stock in 2017 are on the order of 400 Mt, eight times the quantity of plastics manufactured in 2017 (details of estimate in supplementary information). These plastics exist in durable applications including houses and buildings, automobiles, appliances and electronics, as well as shorter lifetime 'non-durable' applications such as clothing, housewares, and reusable containers.

As plastic packaging represents a large fraction of plastic use and because of its short-lived and pervasive nature, efforts to improve the circularity of the plastics economy and reduce the impact of inappropriate disposal and environmental leakage have focused on packaging [11, 41]. In theory, most of the thermoplastics used in packaging have very high recyclability, and the short lifespan and high volume of single-use plastic packaging makes it attractive for recapturing its material value. Current low recycling rates can often be traced to market issues including inexpensive virgin feedstocks, combined with material quality aspects that are inherent in the current system, either due to product design (choice of: materials and combinations of materials, colors, additives, formats, labels) or use and handling (contamination with dust, soil, organics, incomplete separation of recycling streams) [42]. For example, the PET recycling rate of 29% reported in [19] reflects the recovery or collection of PET bottles in 2017. 16% of the total bottles collected were exported out of the US, and only 67% of the recovered PET bottles purchased by US reclaimers in 2017 became clean flake available for reuse as recycled PET [21]. Combined with expected utilization rates of exported bottles, the utilization rate (i.e. amount of clean flake produced divided by bottles available in the US market) was 20.9%. The discrepancy between the recycling (or recovery) rate and the utilization rate is attributed to non-PET contamination in recyclate bales, the prevalence of smaller, lighter containers which require more processing per pound of material, and design for recyclability issues such as difficult-to-remove labels, barrier layers added to PET for added packaging function, and metal integrated into PET packages [21]. As PET bottles are among the easier plastic materials to recycle and have a reliable recycled market, this exemplifies the myriad challenges faced in improving the circularity of plastic materials. The market drive to innovate has led to tremendous diversity in the materials (polymers, additives, colors) and formats (bottles, tubs, bags, films) present in today's plastic packaging, which has limited the technical and economic ability to recycle these materials. There is now growing recognition that improving recyclability, especially of single-use plastics, will require a systemic approach across the value chain that coordinates material and application design with collection, sorting and reprocessing innovation [11, 41]. Key strategies could include: innovations in reusable packaging models for both consumer products and business-to-business logistics; converging to a few key materials used across the market and eliminating less common materials from packaging such as PVC, PS and EPS to reduce cross-contamination and improve value of recycle streams; addressing the challenges of multi-material layered packaging via material innovation or reprocessing strategies; promoting minimum recycled content in packaging and products to build reliable markets for recycled plastics [11]; and development of next-generation plastic resins, such as poly(diketoenamine)s, that permit easy depolymerization, re-manufacture and re-use in a closed loop fashion [43]. Significant challenges exist in implementing and institutionalizing these strategies, including replicating or overcoming the need for the diverse performance characteristics offered by less common plastic materials. Still, such strategies offer important guideposts for innovations in plastic packaging.

After years of tightening restrictions on the purity of plastics imports, China implemented its 'National Sword' program in January, 2018, banning the imports of nearly all plastic waste into the country and greatly disrupting material flows in the global recycling industry [44]. Between 1992 and 2016, China imported 106 Mt of plastic waste, representing 45% of all global imports. Combined with Hong Kong, which largely serves as an entry port into China, the two countries imported 72% of all plastics waste [45]. In 2016, the US exported 0.7 Mt of plastic waste to China, making it the third ranking exporter after Hong Kong and Japan [45]. Then in 2018, China's waste plastic imports dropped by 99.1% [44]. Exports from the US and other developed countries shifted to Southeast Asian countries including Malaysia, Vietnam, Indonesia and Thailand, which have also begun to implement regulatory policies on plastic waste imports [46]. These importing countries often lack sufficient infrastructure to properly manage plastic waste [47], increasing the likelihood of leakage. These dramatic changes in the global recycling markets are not reflected in the material flow data presented here.

Two thirds of the plastic put into use in the US in 2017 went into markets other than packaging. These other sectors—consumer products, furniture and furnishing, electrical and electronics, transportation, buildings and construction—introduce unique challenges and opportunities. They include products with short- (disposable serviceware, trashbags, diapers), medium- (clothing, tools, electronics, furniture, small appliances), and long- (large appliances, automobiles, buildings) lifetimes. This means that materials retired from medium- and long-lifetime products were designed and manufactured 5–50 years or more in the past, and material and product innovations will not appear in the disposal stream until many years in the future. As with packaging, coordination and convergence are needed between design and end-of-life efforts, but currently retired products reflect design choices that may be decades old. In addition, these products typically involve combinations of materials—a great variety of plastics plus metals, wood, rubber, foam, textiles, etc, often joined together with adhesives, fasteners or other methods. Durable parts also come in a much wider variety of shapes and sizes than packaging, limiting the ability to use automated handling and detection systems. At the same time, with sufficient separation and cleaning, many of the plastics commonly used in durable products such as ABS and PC can have higher market value than packaging recylates. Where performance specifications will allow, durable products may represent a growing market for mechanically recycled plastics from packaging waste streams. Ongoing developments in chemical recycling methods, especially those effective with plastic mixtures, may ultimately offer preferred pathways for recovering materials and/or energy from plastics in durable goods [48–50]. In the following paragraphs, we identify unique challenges and opportunities of key product markets.

3.3.1. Building and construction

3.3.2. Transportation

3.3.3. E-waste

Waste to fuel and waste to energy are occasionally put forth as a wholesale solution to plastic waste. While these processes have unique technical challenges, it is useful to understand the scale of energy resources available from waste plastics. If the 32.1 Mt of plastics reported as generated in US MSW in 2017 were all combusted for energy, this would result in approximately 0.6 EJ (0.6 quads) of electricity (estimated via US EPA's WARM model [63]), which would be equivalent to 4% of total US electricity net generation [64]. Other potential air emissions notwithstanding, combustion of plastics typically results in greater CO₂ emissions than disposing plastics in landfill, even when the emissions associated with displaced electricity generation are taken into account [65–67]. Alternatively, converting all of the 28.2 Mt of landfilled plastics represented in figure 1 into fuel via pyrolysis could result in roughly 26 gigaliters (6.8 billion gallons) of liquid fuels [67], equal to ∼15% of the distillate fuel oil (diesel) consumed annually in the US [64]. Life cycle greenhouse gas emissions from plastic-derived diesel fuel are estimated to be 1%–14% lower than conventional diesel, and the plastic to fuel pathway also has lower emissions per tonne of plastic than conventional disposal (landfill and waste to energy) [67].

A wide array of policy options will be required to reduce plastic waste and improve the circularity of the plastic economy given the complex and systemic nature of plastic waste and recycling and the diversity of sectors and products. In addition, specific suites of policy instruments need to be tailored to the objectives and context of an implementing country. The Stockholm Convention and the Basel Convention may offer the best opportunities to address the impacts of plastics and plastic waste through a coordinated global policy framework, but will require notable strengthening to be applicable to the full life cycle of all plastic applications [68]. However, the US is not currently a party to the Basel Convention and remains an unratified signatory to the Stockholm Convention. Notable industry-led initiatives such as those through the New Plastics Economy Global Commitment [14] are likely to have significant impact on recyclability and recycled plastic markets, but these voluntary commitments will benefit from mandatory public policies instated (preferably) at the federal level. In addition to creating more favorable economic conditions, mandatory policy can add accountability, coordination and harmonization to voluntary industry efforts. A suite of policy tools aimed at reducing plastic packaging pollution and increasing plastic packaging recycling rates, identified in table 3, were recently analyzed to provide insights and recommendations to the advantages and disadvantages of each [40]. While that analysis focused specifically on packaging, the policy instruments—including recycled content standards, virgin resin taxes, and tradeable permits (similar in mechanism to 'cap and trade' schemes)—which aim to address discrepant market conditions between virgin and recycled plastics [8] and therefore develop plastic recycling end markets, should be sector independent and impact the full plastic economy. Regardless of instrument, development of new waste and recycling policies must take a systems-level, life-cycle approach to avoid burden shifting or promotion of less environmentally sustainable alternatives.