Mass balance accounting: Considerations for circular polymers.

While plastic packaging and products have greatly benefitted civilization, the current and historical approaches to design, use, and end‐of‐life management have resulted in significant challenges, particularly in recovering and retaining the economic value of the materials and preventing plastic pollution. The dominant route for recycling plastic in the United States and elsewhere has been mechanical recycling, which is effective for select polymer types and package designs and has potential for growth. However, several regulatory, technical, and economic challenges will ultimately cap the fraction of plastic waste recovered by mechanical recycling technologies, and as a result, chemical recycling―processes that either break covalent bonds or otherwise exploit fundamental chemical processes to return molecules to early or mid‐stage chemical production―has great appeal, especially for plastic products most challenging for mechanical recycling. Due to the nature of some chemical recycling technologies, specifically that molecules derived from chemically recycled polymers become indistinguishable from primary feedstocks and thus not traceable or measurable in the process, the mass balance (MB) accounting chain of custody model has been proposed as a tool to track, trace, and certify circular polymers. While MB certification standards have an extensive history in other commodity sectors, they have only recently been considered in the polymers sector in part due to recent technology advances and incentives to expand chemical recycling. Here we discuss the roll of MB in polymer circularity, including controversial aspects, and provide technical examples to describe its potential applicability. We further provide recommendations for the effective use of MB to certify circular polymers. This article is categorized under:Climate and Environment > Pollution PreventionClimate and Environment > Circular EconomyEmerging Technologies > Materials [ABSTRACT FROM AUTHOR]