Generalized kinetic analysis of heterogeneous PET glycolysis: Nucleation-controlled depolymerization

Abstract

The kinetics of poly(ethylene terephthalate) depolymerization by glycolysis has been commonly modeled as a second-order reaction. However, the occurrence of an activation stage and anomalous kinetic behavior does not fit into this reaction model. Utilizing the concept of reference theoretical master plots, we show in terms of generalized kinetics that the chain depolymerization can be controlled by a nucleation-based kinetic behavior. We associate the reported anomalous "activation" stage and chain scission-induced recrystallization in PET glycolysis with the induction period and chain reordering processes during polymer nucleation and growth. The kinetic profile and microscopic images of the polymer surface during degradation support the mechanism of sporadic nucleation and lamellar thickening. Using the matching nucleation-based conversion function we obtained an activation energy of 29 kJ/mol, the closest value reported so far to the experimental and simulated activation energy of thermal and glycolytic breakage of a PET ester bond.