Direct observation of alkaline and enzymatic Poly(Ethylene Terephthalate) hydrolysis via neutron Reflectivity: Kinetics and mechanistic insights

Abstract

One of the challenges in achieving industrial enzymatic depolymerization of poly(ethylene terephthalate) (PET) is the rapid loss of catalytic activity leading to incomplete polymer hydrolysis. While there are several possible explanations for this phenomenon, there is a lack of methods that can measure polymer hydrolysis directly, which makes it challenging to reliably infer mechanistic details. Here, we introduce neutron reflectivity of polymer thin films as a method that allows for direct assessment of the hydrolysis rate of polymers like PET. Through matching and variation of the isotopic contrasts, one can directly observe the reaction kinetics, while simultaneously obtaining structural information on the polymer/enzyme/water system. We show that the Michaelis-Menten theory describes well the enzymatic chain scission kinetics, whereas the alkaline one follows a (pseudo)-first order kinetics. At the concentrations used in the experiments, the areal density of enzymes at the polymer surface is very low, ruling out surface passivation or overcrowding as inhibition mechanisms.