Water-Network-Triggered Breakdown: Multiscale Theoretical Insights into PET Hydrolysis under Working Conditions.

Polyethylene terephthalate (PET) undergoes depolymerization in the presence of active water, a principle that is widely utilized in innovative chemical-recycling reactors. However, the intertwined effects of water sorption, nanoscale reconfiguration, and the energetics of ester bonds remain predominantly unquantified. Here, a multiscale workflow is developed that links sorption thermodynamics to reaction kinetics by combining molecular simulations with density functional theory (DFT). Simulations quantify PET water uptake, swelling, and water mobility under reactor-relevant conditions and reveal a clear hydration threshold in the polymer phase: when hydration remains below this level, water access is limited and chain scission events are rare; once hydration exceeds it, interconnected water clusters form and hydrolysis accelerates sharply. Above the threshold, end-initiated "peeling" becomes dominant, rapidly producing MHET/BHET and ultimately terephthalic acid (TPA) and ethylene glycol (EG) as reactions proceed within these active water domains. DFT further explains this rate jump: extended hydrogen-bond networks in clustered water enable proton-relay assistance, which stabilizes the tetrahedral intermediate and lowers the hydrolysis barrier compared with attack by an isolated water molecule. Incorporating these barrier reductions together with simulation-derived, loading-dependent water mobility into a kinetic model reproduces both the acceleration at high water availability and the slowdown as water is depleted, clarifying when uptake, transport, or intrinsic chemistry is rate-determining. Overall, the results provide a quantitatively predictive, theory-based description of PET hydrolysis under realistic reactor conditions and translate directly into design principles for tunable, high-efficiency polyester depolymerization.