New Approach to Recycling of Epoxy Resins Using Nitric Acid: Regeneration of Decomposed Products through Hydrogenation

Abstract

Due to the increase in the amount of produced epoxy resin waste, it is desirable to recycle this material to reduce the burden on the environment. Despite many studies focusing on recovering fibers from composites, few studies have focused on recycling the resin itself. In this study, we developed a new approach for recycling the decomposed amine-cured epoxy resin as an amine curing agent. Following the decomposition of the epoxy resin in nitric acid, a nitrated and decomposed resin product was extracted from the nitric acid solution. The resulting extract was then hydrogenated to convert the nitro group into amino group, and the hydrogenated extract was incorporated into the epoxy resin by replacing a portion of the original curing agent. The obtained recycled resin exhibited a higher tensile strength and comparable tensile modulus compared to the virgin resin due to the presence of aromatic amino groups. Moreover, when 20 mass% of the curing agent was replaced with the hydrogenated extract, the recycled resin with the optimized formulation exhibited tensile strength comparable to that of the virgin one. This approach demonstrates a novel recycling method for creating a closed loop of amine-cured epoxy resins.

Itaconic acid-based hyperbranched polymer toughened epoxy resins with rapid stress relaxation, superb solvent resistance and closed-loop recyclability

“…The hydrogenated extract can replace 20 wt% of the conventional amine curing agent in amine-cured epoxy resins. 55 Ma et al used glacial acetic acid/H 2 O 2 solution to degrade amine-cured epoxy resins, and employed the recovered products as the catalyst and filler for anhydride-cured epoxy resins. 56 Xu et al reported that microwave-assisted catalysis was capable of degrading dichloromethane treated anhydride-cured epoxy resins at 130 °C.…”

Progress in Chemical Recycling of Carbon Fiber Reinforced Epoxy Composites

“…Recently, the same group treated the DP obtained from the depolymerization of an aliphatic amine cured BPA epoxy in nitric acid by hydrogenation which converted the –NO 2 group of DP to amine groups. [ 88 ] The treated DP was used as a curing agent and replaced 10 wt.% of the original amine curing agent, and the resulting product exhibited comparable tensile properties to that of the virgin resin. Although this method is interesting, the hydrogenation treatment would significantly add cost to the recycling process, limiting its practical application.…”

A mild and efficient oxidative degradation system of epoxy thermosets: full recovery and degradation mechanism

“…12,13 In comparison, oxidative degradation has significant advantages in energy efficiency which can be performed at atmospheric pressure with a temperature lower than 90 °C. [14][15][16][17][18][19][20][21][22][23][24][25] Use of common oxidants or catalysts has been reported for the degradation of EP including hydrogen peroxide, 14,16,25 nitric acids, 18,21,22,24 ruthenium trichloride, 15 sodium hypochlorite, 19 potassium permanganate, 20 and so on. Among these, hydrogen peroxide is preferred because of its high redox potential and clean process with water as the only by-product.…”