Toward Predictive Structure–Depolymerization Relationships in Polyesters

• Ian Hegge, Chemical Engineering, University of Delaware

• Thomas Epps, Chemical and Biomolecular Engineering, University of Delaware

Plastics account for a significant portion of the world’s total waste, yet only a small portion is reused or recycled. This waste introduces pollution and greenhouse gas emissions into the environment and needs to be mitigated. Polyesters are one of the most widely used classes of plastics due to their mechanical strength and flexibility. Additionally, polyesters have the potential to be chemically recycled; however, high temperatures, long times, and harsh solvents are often required. To address these challenges, Lewis acids have emerged as promising depolymerization catalysts because they enable depolymerization at lower temperatures and with milder chemical reagents. To optimize the recycling process, it is necessary to gather a better understanding of how this depolymerization is impacted by intrinsic polymer properties such as molecular weight and viscosity. In this work, the depolymerization of polycaprolactone (PCL), a polyester with a cyclic monomer, is conducted with a series of solvents and catalysts. Initial characterization determined the molecular weight and molecular weight distribution of the PCL, along with the glass transition, melting, and thermal degradation temperatures, as well as the volatility of the chosen solvents. The reactive distillation experiments were performed at various times and temperatures to maximize depolymerization and monomer yields. Varying molecular weights of PCL and other polyesters (to assess the impact of chemical structure) will enable a deeper understanding of the chemical recycling of polyesters, resulting in the determination of deconstruction rate constants based on polymer properties and ultimately, more effective recycling.