Analysis of nitric acid decomposition of epoxy resin network structures for chemical recycling

Epoxy resin is an essential material for the society, although it poses challenges for recycling because of its cross-linked three-dimensional (3D) structure. Nitric acid decomposition is an effective recycling method for such a 3D network resin; this process can be performed at low temperature (80 °C) and normal pressure compared to other recycling methods. However, no systematic investigation on the relationship between the decomposition and chemical structure of raw epoxy resin is available. In this study, various types of epoxy resins which consist of bisphenol F-type epoxy resin and typical amine curing agent are prepared and decomposed using nitric acid. This is the first study to have systematically investigated the epoxy resin decomposition using nitric acid. Our results reveal that the chemical structure around the C–N bond and the ring structure of the curing agent strongly affect the epoxy resin decomposition, which is the first such report in the existing literature on such processes. The findings of this study are applicable for improving the nitric acid decomposition method employed for chemical recycling and to identify epoxy resins suitable for such recycling.