Recycling Benzoxazine–Epoxy Composites via Catalytic Oxidation

Abstract

Carbon fiber-reinforced polymers (CFRPs) are structural composites used in the aerospace and sporting goods industries. Their chief appeal lies in their high specific properties, which generally outperform metallic counterparts. There is a contemporary need for viable methods for recycling CRFPs at the end of their lifecycles and for utilizing the considerable production waste (ca. 30%) of CFRP part manufacturing. The cost associated with these waste streams is a principal economic driver inhibiting the penetration of CRFPs into larger-scale manufacturing, particularly in the automotive industry. Reported techniques for CRFP degradation involve pyrolysis or mechanical grinding of the CFRP, processes which are outlawed in some jurisdictions and can reduce the thermomechanical properties of the recycled products. In this study, we report a conceptually different approach to degrading a commercial blended benzoxazine/epoxy resin under mild, oxidative conditions. The thermosetting resin is polymerized, characterized, and then catalytically depolymerized via hydride abstraction with a ruthenium catalyst. These results demonstrate a concept for sustainable recycling of CFRP composites.

Current status of carbon fibre and carbon fibre composites recycling

“…A catalytic oxidation method was demonstrated to recycle the most thermally stable benzoxazines under mild conditions. The thermoset matrix was catalytically depolymerized through hydride abstraction with a ruthenium catalyst [46]. Hou's group has developed an effective chemical recycling method by using AlCl 3 /CH 3 COOH as a catalyst to realise selective cleavage of the tertiary carbon-nitrogen bond [47].…”

A structural chemistry look at composites recycling

“…39 An analogous strategy was successfully utilized in depolymerizing benzoxazine-epoxy composites by abstracting a hydride atom alpha to an aniline nitrogen center using a high valent ruthenium species (Scheme 3, top). 40 Another method is to use an inexpensive peroxide, like hydrogen peroxide, as an oxygen atom transfer agent to form an amine oxide, or N-oxide (Scheme 3, bottom). 41,42 We have previously reported the formation of imines from N-oxides via NMR spectroscopy in our degradation studies of small molecule analogues of amine-cured epoxies.…”

Studies on Recycling Silane Controllable Recovered Carbon Fiber from Waste CFRP

“…As such, material recovered in this way is usually made into powder for filling or as a reinforcing material. (2) Chemical recovery: separate CFs from the matrix resin [2,9,[31][32][33][34][35][36][37][38]. The damage to recovered CFs is minimal, but the cost of chemical agents is high and this technology is still very much in its infancy.…”