Via the New York Times, this article on recycling plastic and mass balance:
...To grasp what mass balance accounting entails, you first have to know a bit about the two methods of plastic recycling.
The first, which has been around for decades, involves sorting, washing, shredding and melting down plastic waste and reshaping it into pellets. Much of the recycled plastic produced by this method, called mechanical recycling, is of lesser quality than the original. And only certain types of plastics can be recycled mechanically.
The second, newer method, chemical recycling, is an energy-intensive process that typically uses high temperatures, pressurization and chemical solvents or other chemical processes not to simply melt plastic but to break it down into its chemical building blocks. The recycled chemicals are then mixed with all sorts of other materials, including fossil-fuel-derived virgin plastic, to make new products.
This year, Eastman began operating one of the largest chemical plastic recycling plants in the world. Near the company’s headquarters in Tennessee, the plant uses methanol, heat and pressure to transform plastic waste. It takes plastics not accepted in most curbside recycling programs, like clamshell containers, colored plastics used in food and beverage packaging, and plastic fibers used in carpets and textiles.
Eastman wants to be able to market as recycled the products made with this material. But while it’s theoretically possible to physically track plastic pellets from recycled water bottles to a new life as plastic lawn furniture, it’s virtually impossible to trace basic chemicals dissolved from plastic waste and mixed with other materials to any particular batch of plastic products...
I think the criticisms of the mass balance calculations are reasonable (i.e. is there a good reason that Eastman should be trusted? Not really?) That said, if Eastman is truly hiding something and the material isn't being recycled, it will definitely start piling up or their landfill bills will start increasing. A thorough and public accounting of their warehouses (to be fair, the inputs and outputs of their plastic recycling system) would seem to me to be the only way that you could independently verify that mass balance is a reasonable way to calculate chemical recycling content.
If they’re going basic feedstocks, there’s no reason to expect they’d even end up back in plastic and not on a shelf in a teaching lab or in an API.
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