Facile recycling of anhydride-cured epoxy thermoset under mild conditions with multifunctional hydrazine hydrate

Abstract

Environmental economics is accelerating the urgency to develop recycling technologies for the ever-growing quantity of discarded thermoset polymers. Herein, we developed a mild and energy-saving process for high-efficiency degradation and reuse of anhydride-cured epoxy thermoset with the aid of hydrazine hydrate. The degradation degree of the epoxy resin reached 99.6% at 120 °C within a short time of 60 min. During the reaction, the ester bonds in the cross-linked network were selectively cleaved by the amination of hydrazine hydrate, and the epoxy resin was fully converted to new monomers that contained hydrazide and hydroxyl groups, respectively. Moreover, the degradation mechanism of the epoxy resin in hydrazine hydrate was studied and a nucleation model was utilized to predict the actual degradation behavior of the system. Finally, the degradation products can be directly mixed with epoxy precursor to prepare a new waterborne epoxy coating with good comprehensive properties. This work not only demonstrates a new way to realize the efficient degradation of epoxy resins, but also provides a facile and efficient recycling protocol for thermosets.