(389bw) A Multi-Scale Computational Study of Hydrolytic Degradation of PET Under Working Condition

Polyethylene terephthalate (PET) exhibits limited hydrolysis under ambient conditions, but in processes operating at elevated temperatures (400 K–600 K) and in water-rich environments, significantly higher water uptake occurs. Despite the industrial relevance of such settings—ranging from subcritical hydrolysis to advanced chemical recycling—water absorption and its impact on the hydrolytic pathway have not been thoroughly examined under these conditions. This study addresses this gap by combining multi-scale molecular simulations and kinetic modeling to elucidate PET–water interactions, water diffusion, and ester bond cleavage under intensified hydrolysis scenarios.

To capture equilibrium water uptake at 400 K–600 K, we utilize a statistical mechanics-based sorption approach that calculates the chemical potential of water in contact with PET. These simulations reveal a pronounced increase in water content within the polymer matrix at higher temperatures, in contrast to ambient humidity conditions under room temperatures. Subsequent molecular dynamics simulations are employed to the local arrangement and mobility of absorbed water and reactive simulations are also further performed to examine the chain scission involved in the hydrolysis mechanism. In addition, the macro-scale kinetic model is improved to represent PET hydrolysis as governed by temperature and water concentration. Unlike conventional approaches with fixed diffusivity or unlimited water supply, our revised ordinary differential equation (ODE) system explicitly incorporates: (1) A temperature-dependent saturation limit for water uptake, and (2) Concentration-dependent diffusivity, reflecting enhanced water mobility as local polymer domains become hydrated. By coupling the multi-scale simulation results to the kinetic ODE system, we study the trade-off between diffusion-limited (at moderate temperatures and partial water pressure) and reaction-limited (higher temperature, where even deeper ingress can be achieved). This refined framework captures the interplay of water transport, chain mobility, and reactive pathways, offering a robust predictive tool for scenarios where PET is exposed to pressurized, high-temperature water.

Our findings underscore that PET degradation dynamics cannot be fully understood without accounting for the heightened water uptake and accelerated diffusion at 400 K–600 K. The simulations highlight how these conditions influence ester cleavage, while the improved kinetic model more accurately forecasts time-to-failure or monomer recovery. Such insights can guide reactor design for chemical recycling of PET, enabling optimization of temperature and water partial pressure to achieve efficient depolymerization

Ultimately, this work bridges atomistic-scale reactivity with engineering-scale kinetics, establishing a comprehensive approach to evaluate PET hydrolysis at conditions relevant to both advanced recycling processes and high-temperature applications. By moving beyond ambient assumptions about limited moisture uptake, we illuminate previously underappreciated factors that critically influence PET’s degradation pathway, paving the way for more effective and sustainable industrial treatments.