Decomposition mechanism of epoxy resin in nitric acid for recycling

Bisphenol F type epoxy resin cured with 1, 8-p-menthanediamine was completely decomposed in specified immersion time in nitric acid solution due to its poor corrosion resistance to strong acid. By repolymerizing the decomposed products, an approach to chemical recycling of epoxy resin was proposed. Organic decomposed products of the resin in nitric acid with the highest yield were extracted by ethyl acetate from neutralized solution. The extract was repolymerized to prepare recycled resin, mixed with bisphenol F type epoxy resin and curing agent of phthalic anhydride. The mechanical properties of original resin and recycled resins were compared, as indicated that the recycled resin showed higher strength when the neutralized extract was used to substitute for a part of resin rather than curing agent. Furthermore, in order to investigate these behaviors, the decomposed products were analyzed in detail. The results of size exclusion chromatograph (SEC) and FT-IR showed the extract was mainly nitrated compounds which retained the main chain of epoxy resin, as explained the recycling mechanism that it could prepare recycled resin as quasi-monomer in place of part of epoxy resin