Pyrolytic performance and kinetics study of epoxy resin in carbon fiber reinforced composites: Synergistic effects of epoxy resin and carbon fiber

Abstract

Pyrolysis is recognized as a sustainable approach for recycling carbon fiber reinforced polymers (CFRP), ensuring enhanced process efficiency and resource utilization. To unveil the pyrolysis mechanism of epoxy resin and its synergistic interaction with carbon fiber in different scenarios, we conducted pyrolysis experiments on pure epoxy resin diglycidyl ether of bisphenol A cured with 4,4'-Diaminodiphenylmethane (C-epoxy), as well as three kinds of carbon fiber-resin mixtures, using TG and Py-GC/MS techniques. Isoconversional analysis (Friedman method) of C-epoxy degradation revealed three reaction stages within the temperature range of 280–540 °C, each corresponding to activation energies of 158 kJ/mol at α = 5%, 179–190 kJ/mol at the plateau of α = 10–60%, and 190–236 kJ/mol for α values surpassing 60%. The multi-Gaussian distributed activation energy model (DAEM) aptly characterized C-epoxy’s thermal decomposition, featuring two Gaussian peaks with similar contributions of 0.58 and 0.42, and activation energy distributions of 217.76 ± 3.92 kJ/mol and 233.36 ± 21.42 kJ/mol, respectively, which are close to the activation energies from isoconversional analysis at α = 10–60% and α > 60%, respectively. The presence of carbon fiber significantly influenced the kinetic parameters of epoxy resin pyrolysis, with the extent of change linked to the mixing methodology applied. Notably, carbon fiber decreased the activation energy of the reaction while accelerating the rate of weight loss. However, the synergistic effects vary depending on different synergistic scenarios. By analyzing the product distribution obtained through an analytical pyrolyzer coupled with a gas chromatography–mass spectrometry set-up (Py-GC/MS), we proposed a pyrolysis mechanism for epoxy resin, encompassing three key stages: cleavage of N–C and NC–COH bonds, phenolic O–C and vicinal C–C bonds, and disruption of the isopropylidene bridge on bisphenol A. The influence of carbon fiber on epoxy resin pyrolysis product distribution was relatively modest, manifesting predominantly within the mixture obtained by premixing before curing. Here, carbon fiber exhibited a dual effect, inhibiting oxygen-containing diphenyl products while promoting oxygen-containing monophenyl products. Ultimately, our study provides essential kinetic data for multidimensional simulation and theoretical guidance pertaining to the pyrolysis recycling of widely used carbon fiber-reinforced epoxy resin composites.