Curing behavior and adhesion properties of epoxy resin blended with phenol-liquefied Cryptomeria japonica

Epoxy resin is one of the most important thermosetting polymers. Most of the commercial epoxy resins are prepared by reacting bisphenol A with epichlorohydrin. However, epoxy resins have the drawback of being expensive. How to reduce manufacturing cost is an important issue. Solvent liquefaction is an effective method to convert biomass from solid to liquid. Phenol-liquefied wood contains a large amount of phenol structure which has the potential to react with the epoxide group of epoxy resin. In this study, wood of Cryptomeria japonica was liquefied in phenol with HCl and H2SO4 as a catalyst and named as LW-C and LW-S, respectively. These phenol-liquefied woods were mixed with epoxy resin to prepare blended resins. The curing behavior, thermal properties and wood bonding performance of blended epoxy resins with different weight mixing ratios were investigated. The results show that the gel time of blended resins can be shortened when compared with the neat epoxy resin, especially for those mixed with LW-S. DSC analysis shows blended epoxy resin prepared by mixing with LW-C has a heat flow variation similar to that of neat epoxy resin but a lower peak temperature with less heat released. Blended epoxy resins mixed with LW-C can be used as a wood adhesive to achieve a dry bonding strength similar to that of neat epoxy resin. These results indicated liquefied wood has the potential to prepare epoxy resin. However, the wet bonding strength is still necessary to further improve.