Base-Mediated Depolymerization of Amine-Cured Epoxy Resins

Carbon fiber-reinforced epoxy composites are used in multiple industries, including aerospace, automotive, and wind energy applications, due to their excellent strength-to-weight ratios and tunable material properties. Fortunately, recycling strategies for carbon fiber-based composites are emerging, with the primary focus on the recovery of fibers due to the cost and energy intensity in their production. In addition to fiber recovery, there is an opportunity to recycle the epoxy components such that ideal recycling strategies would yield both fibers and epoxy monomers for reuse. To that end, here we examine potassium tert-butoxide-mediated cleavage of C-O and C-N bonds in amine-cured epoxy resins. We accomplish this via developing model compounds that reflect both C-O and C-N linkages in amine-cured epoxy composites before expanding to both model linear thermoplastics and thermosets. We obtain excellent yields of both phenol (up to 97% molar yield) and amine products (up to 99 mol %) from aromatic and/or aliphatic amine-based model compounds. This system enables up to a quantitative yield of bisphenol A and up to 58% molar yield of aniline from model thermoplastic epoxy amines and 71% molar yield of BPA from a reaction with a thermoset substrate. These data correspond to a 15% mass recovery of BPA from a commercial epoxy thermoset.