Tunable Dynamic Covalent Networks from Mechanochemical Depolymerization of Post-Consumer Aliphatic Polyesters

Abstract

Aliphatic polyesters such as poly(lactic acid) (PLA) and poly(hydroxyalkanoates) (PHAs) are inherently biodegradable, therefore these materials are typically collected and composted at end of life which results in products that prevent recycling and repurposing into new materials. Chemical recycling presents an orthogonal method for the depolymerization of polyesters and their packaging formats (e.g., multilayer flexible packaging), but this process can produce significant chemical waste in the form of solvents and excess reagents. Using ball mill grinding (BMG) to overcome the limitations of conventional ester aminolysis, we demonstrate an operationally simple mechanochemical depolymerization of PLA, PHAs, and biodegradable multilayer flexible film packaging. Maintaining a focus on sustainable materials, we then demonstrate the synthesis of tunable αlipoic acid (αLA)-based resins for photopolymerization to disulfide covalent adaptable networks (CANs) from the depolymerized polyesters in one-pot. Investigation into structure-property relationships reveals a range of mechanical properties-producing significantly softer materials relative to the initial polyester film packaging. Additionally, we demonstrate degradation via disulfide cleavage of the αLA-based materials under conditions that mimic low oxidation-reduction potential (ORP) environments. Ultimately, this work further solidifies the utility of BMG mechanochemistry for mild and sustainable depolymerizations and demonstrates metamorphosis of the depolymerized monomers into bio-based CANs with unique properties while maintaining degradability.