A fast and mild closed-loop recycling of anhydride-cured epoxy through microwave-assisted catalytic degradation by trifunctional amine and subsequent reuse without separation

Abstract

The recycling of thermoset polymer wastes has been challenging due to their stable three-dimensional network structure. Current methods have the problems of long time of the reaction process, harsh conditions and complex separation. Herein, we developed a facile and mild approach for high-efficiency recycling and reuse of thermoset epoxy. First, the epoxy resin was pretreated with dichloromethane to obtain a loose and porous structure, and then degraded by microwave-assisted catalysis of diethylenetriamine (DETA). DETA in the system functions as a catalyst, a reactant and a solvent. The degradation degree of the epoxy resin reached 99% at 130 °C only in 50 min. The degradation products were characterized by FTIR, NMR, SEM, GPC, TGA and elemental analysis and the degradation mechanism was proposed. During the reaction, the ester bonds in the cross-linked structure were selectively cleaved by the amination of DETA, and the epoxy resin was fully converted to oligomers that contained multifunctional reactive groups. The degradation liquid containing oligomers and unreacted DETA can be used as a curing agent and is directly mixed with the uncured epoxy to obtain recycled epoxy resin with high modulus and high thermal stability.