Open- and Closed-Loop Recycling of Polyesters and Post-Consumer Waste Under Industrially Relevant Conditions Using...

With the increasing demand for sustainable plastic materials, the implementation of a circular plastics economy starting from designing environmentally friendly polymers and including effective recycling strategies is of the utmost importance. The biobased and biodegradable polyester polylactide (PLA) is a promising candidate for a sustainable, circular plastics economy. Polyesters can be chemically recycled to obtain monomers or value-added chemicals following either a closed- or open-loop recycling approach. However, the requirements for catalysts applicable in post-consumer waste recycling are high: Besides a high activity, robustness and scalability of the catalyst are important factors. We studied highly active, robust bisguanidine organocatalysts for the depolymerization of the polyesters polycaprolactone, polyethylene terephthalate, and PLA. Focusing on PLA, we investigated the structure-reactivity relationship of the length of the aliphatic linker between the guanidine functionalities to identify the most active catalyst: Bis(N,N,N',N'-tetramethylguanidino)ethane (TMG₂e) depolymerizes PLA completely via alcoholysis within minutes under mild reaction conditions. The bisguanidine shows excellent activity for the alcoholysis of the investigated polymers, the ability to depolymerize binary and ternary plastic mixes, and robustness against additives, plasticizers, and other impurities in different post-consumer waste samples. Thus, TMG₂e has promising properties to be an asset for the implementation of a sustainable, circular plastics economy.