Synthesis and properties of phenol/bisphenol A-liquefied Cryptomeria japonica wood-based epoxy resins and their glueability

Cryptomeria japonica Don. (Japanese cedar) was liquefied by a mixture of phenol and bisphenol A as the solvent under H ₂SO ₄ catalyst. The liquefied products could react with epichlorohydrin to prepare liquefied wood-based epoxy resin. The influence of different liquefied products on the properties of epoxy resins was investigated. GPC analysis showed that the average molecular weight of the liquefied woods and liquefied wood-based epoxy resins was between 864 and 1219, 1911 and 3450, respectively, with an increasing proportion of bisphenol A. DSC analysis illustrated that the isothermally cured resins could be further heated to promote post-cure. From DSC analysis, results showed that the enthalpy (ΔH) and the height of the exothermic peaks of LWER1, LWER2 and LWER3 resins were higher than those of the LWER4 resin, with the enthalpy of the LWER1 resin being the greatest. The latter can be attributed to the higher number of electron-withdrawing aromatic rings. TGA analysis showed that thermal degradation in all liquefied wood-based epoxy resins was different from the neat epoxy resin (ER), which indicated that the liquefied wood-based epoxy resins were a new copolymerized resin system. According to a glueability evaluation, the bonding strength of the phenol-liquefied wood-based epoxy resin (LWER1) was greater than that of the other resins. After a boiling water immersion test, the bonding performance of the phenol-liquefied wood-based epoxy resin (LWER1) was similar to that of the neat epoxy resin (ER). The results indicated that phenol-liquefied wood was a potential raw material for preparing BPA-free and biomass-based epoxy resins.