Polymer recycling has received increased attention of the past years to provide a necessary solution to solve the accumulation of post-consumer waste in the environment. For mechanical recycling, this often leads to downgraded plastics with different properties compared to the virgin plastic material. Chemical recycling on the other hand provides a viable solution to convert the polymer waste directly back into its original monomeric precursor. Biopolymers already provide a partial solution to the environmental problem. Poly(lactic acid) (PLA) is often considered to be one of the most promising solutions since it is both biobased and – in an industrial composting facility – biodegradable. Longer poly(lactones), e.g. poly(caprolactone) (PCL), recycled back into their monomeric equivalent using reversible ring-opening depolymerization. However, up until today, no clear chemical procedure has been found to convert PLA back into monomers, namely lactide. Here, we developed a new method to convert poly(lactones) into chemical building blocks using phosphonium ionic liquids (IL) as a solvent in combination with a bromine catalyst. Depending on the reaction time and applied temperature the PLA can be converted in either Lactides or Acrylic Acid (AA). Kinetic studies showed that after dissolution of the PLA in the IL, the Br-mediator allows for fast rearrangement to the lactide dimer intermediate (&gt;40% yield after 30 min). Under the applied reaction conditions, the lactide is converted further into AA as the final depolymerization end product. After optimization of the reaction parameters, we managed to obtain &gt;60% AA yield directly from (post-consumer) PLA with mass balances ranging from 80-95%. Other side-products are mainly lactic acid and ethylene from rehydration and decarboxylation of the AA, respectively. In addition, poly(caprolactone) could be converted to hexenoic acids (&gt;50% yield), which in their turn could be converted into pimelic acid as potential polyamide precursor. With this work we provide a green solution to the recycling of plastic waste converting into interesting platform chemicals for the polymer industry. The use of green, easily recyclable ionic liquids as both the catalyst and solvent makes this one of the most promising routes towards waste stream upcycling.

Catalytic depolymerization and upcycling of poly(lactones) into acrylic acid and other chemical building blocks.

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.