Resolving Mobility-Diffusion-Reaction Coupling in Thermoset Chemical Recycling Through In-situ Dielectric Spectroscopy with DRT Analysis

Closing the material loop for end-of-life thermoset composites demands efficient solvolysis recycling, yet the coupled action of solvent diffusion into the crosslinked network, plasticization that unlocks chain-segment mobility, and catalytic bond cleavage remains poorly understood at the mechanistic level. In this work, in-situ dielectric spectroscopy combined with distribution of relaxation times (DRT) analysis is established as a real-time strategy for resolving the coupled mobility, diffusion, and reaction contributions during the chemical recycling of anhydride-cured epoxy resin. An interdigital electrode sensor embedded beneath the epoxy layer enables continuous dielectric acquisition throughout the solvolysis process, which is further considered to be different modes resolved by DRT. An orthogonal perturbation design assigns these modes to segmental mobility and catalytic bond cleavage. Dedicated swelling and thin-film degradation schemes provide the intrinsic diffusion and reaction parameters of a quantitative coupled kinetic framework. Assembling these parameters into a coupled kinetic framework with three local state variables produces a quantitative description of the simultaneous evolution of mobility, solvent penetration, and bond cleavage. The framework identifies a dual-gated positive-feedback mechanism in which both a mobility threshold and a concentration threshold must be exceeded before bond cleavage proceeds, after which two positive feedback loops accelerate degradation from the surface inward. The coupled model reproduces the in-situ response across conditions withheld from calibration, providing a general experimental and theoretical framework for resolving coupled transport-reaction processes in thermoset chemical recycling and for guiding the design of greener, energy-efficient solvolysis processes for thermoset waste valorization.