Circularity in Mixed Plastics Chemical Recycling Enabled by Variable Rates of Polydiketoenamine Hydrolysis

Abstract

<div>Footwear, carpet, soft furnishings, automotive interiors, and multi-layer packaging are examples of products manufactured from several types of polymers whose inextricability poses significant challenges for recycling at end-of-life. Here, we show that chemical circularity in mixed-polymer recycling becomes possible by controlling the rates of depolymerization of polydiketoenamines (PDKs) over several orders of magnitude through molecular engineering. Stepwise deconstruction of mixed-PDK composites, laminates, and assemblies is chemospecific, allowing a prescribed subset of monomers, fillers, and additives to be recovered in pristine condition at each stage of the recycling process. We provide a theoretical framework to understand PDK depolymerization via acid-catalyzed hydrolysis and experimentally validate trends predicted for the rate-limiting step. The control achieved by PDKs in managing thermal and materials entropy points to new opportunities for pairing circular design with sustainable manufacturing.</div>

Strong and Tough Supramolecular Covalent Adaptable Networks with Room‐Temperature Closed‐Loop Recyclability

“…Furthermore, CRM could enable the removal of additives from the recycled monomers/polymers, and also the recycling of the polymers from mixed polymer wastes. [ 26–28 ] Therefore, the development of closed‐loop chemically recyclable plastics (CCRPs) provides a fundamental solution to the unsustainable generation of plastic waste.…”

Closed‐Loop Recycling of Poly(Imine‐Carbonate) Derived from Plastic Waste and Bio‐based Resources

“…The high purity and chemical integrity of the recovered monomers was confirmed by 1 H NMR spectroscopy (Figures 5C and S8), thus rendering them ideal for producing fresh polymer samples and closing the recycling loop. In addition, the chemical recycling and separation of recycled materials from the heterogeneity and wide range of compositions in plastic waste streams are key points toward a sustainable economy [12, 13, 39, 54] . Thus, the depolymerization of CL‐P(ImC)‐TREN and monomer recovery from mixed plastic waste were examined (Figure 5D).…”

“…Due to the dynamic character of these polymeric networks, CANs are considered sustainable alternatives to non‐recyclable polymers. The introduction of reversible chemical linkages facilitates in certain cases the chemical depolymerization of thermosets back into original monomers [12, 16, 38, 39] …”

Lower-Cost, Lower-Carbon Production of Circular Polydiketoenamine Plastics

“…Although this fluff would be very difficult to handle in a mechanical recycling process because of the levels of contamination from mixed plastics and metals, prior experimental work has demonstrated the ability to chemically recycle PDK resins when metals, glass, adhesives, and other polyolefins are present, suggesting that PDKs could successfully be recovered from these heterogeneous ASR mixtures. 14 Three different scenarios were envisaged over a 60-year timespan: either (A) 99% or (B) 44% of the virgin PDK has been recycled and (C) 99% of the circular PDK has been recycled. In scenarios A and B, virgin PDK must first be introduced into the market and later recovered to begin increasing the fraction of recycled PDK in circulation.…”