Interfacial welding and reprocessing of engineering thermosets based on surface depolymerization

Welding and reprocessing of engineering thermosets are difficult for conventional techniques due to their permanently crosslinked networks. In this study, an interfacial welding method is developed for the anhydride-cured engineering epoxy based on surface depolymerization. The material is first soaked in an alcohol solvent mixed with the catalyst for bond exchange reactions. During the interfacial welding at high temperatures, the solvent molecules break the polymer chains into short segments, which leads to the surface materials being partially depolymerized. The chain segments subsequently disentangle from the network and reconnect on the interface. Assisted by a microscale chemomechanics model, the influences of various processing and material properties are investigated, including the soaking time, welding time, welding temperature, and catalyst content. The parametric studies also reveal welding domains that are respectively dominated by the welding time and soaking time, which provide guidelines to select optimal processing conditions for the practical engineering applications of the welding method. Finally, the welding method is extended to reprocess the epoxy scarps from the powder state. The reprocessed samples are shown to exhibit comparable mechanical properties as the unprocessed ones.