The predictability and control afforded by PDKs in multistage chemical recycling suggest that a common infrastructure may be used to recycle complex products that would normally be considered nonrecyclable. At each stage of the thermally controlled recycling process, we recover specific monomers, additives, and fillers from PDK resins in either mixed-PDK blends, laminates, or assemblies that are indistinguishable from the associated primary feedstocks and reusable in closed-loop material life cycles ( Fig. PDK resins are deconstructed as solids in the presence of metals and glass, obviating the high-cost melt filtration step required for recycling commodity plastics. Here, we show that chemospecificity in mixed-polymer recycling is enabled through molecular engineering of polydiketoenamines (PDKs) ( 24, 25), where fast- and slow-to-depolymerize PDK chemistries incorporated into either mixed-polymer or mixed-material products allow each PDK variant to be selectively deconstructed in space and time simply by varying the depolymerization temperature under acidic conditions ( Fig. The control achieved by PDK resins in managing chemical and material entropy points to wide-ranging opportunities for pairing circular design with sustainable manufacturing.
We provide a theoretical framework to understand PDK depolymerization via acid-catalyzed hydrolysis and experimentally validate trends predicted for the rate-limiting step. Stepwise deconstruction of mixed-PDK composites, laminates, and assemblies is chemospecific, allowing a prescribed subset of monomers, fillers, and additives to be recovered under pristine condition at each stage of the recycling process. Here, we show that chemical circularity in mixed-polymer recycling becomes possible by controlling the rates of depolymerization of polydiketoenamines (PDK) over several orders of magnitude through molecular engineering.
Footwear, carpet, automotive interiors, and multilayer packaging are examples of products manufactured from several types of polymers whose inextricability poses substantial challenges for recycling at the end of life.
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