Novel degradable acetal-linkage-containing epoxy resins with high thermal stability: synthesis and application in carbon fiber-reinforced plastics

Two novel types of degradable acetal-linkage-containing epoxy resins were synthesized through the addition reaction of 2,2bis(4-hydroxycyclohexyl)propane (HBA) or 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane (HOBA) with cyclohexane dimethanol vinyl glycidyl ether (CHDMVG). The thermal decomposition temperatures (T-d) of the cured HBA-CHDMVG (283 degrees C) and HOBA-CHDMVG (319 degrees C) epoxy resins indicated that they were more thermally stable than several previously reported acetal-linkage-containing epoxy resins. The Charpy impact test results demonstrated that the toughnesses of the HOBA-CHDMVG-based epoxy resin sheets and HOBA-CHDMVG-based carbon fiber-reinforced plastics (CFRPs) were higher than those of conventional bisphenol-A-based epoxy resin sheets and CFRPs. The HOBA-CHDMVG-based epoxy resin sheets were completely decomposed via hydrolysis under acidic conditions, and the hydrolysis products were soluble in a tetrahydrofuran-H2O mixed solvent. Furthermore, the carbon fibers of the HOBA-CHDMVG-based CFRPs were recovered via the decomposition of the matrix epoxy resin. In contrast, when H2O was the only solvent for the acid treatment, the HOBA-CHDMVG-based epoxy resin sheets and CFRPs did not undergo any changes. Therefore, we developed novel degradable epoxy resins, which easily decomposed in the presence of organic solvents, were stable in the absence of organic solvents and exhibited high thermal stability and remarkable toughness.