Synthesis of wood-based epoxy resins and their mechanical and adhesive properties

Wood-based epoxy resins were synthesized from resorcinol-liquefied wood. Wood was first liquefied in the presence of resorcinol with or without a sulfuric acid catalyst at high temperature. Because of the hydroxyl groups, the resorcinol-liquefied wood was considered as a precursor for synthesizing wood-based epoxy resin. Namely, the phenolic OH groups of the liquefied wood reacted with epichlorohydrin under alkali condition. By the glycidyl etherification, epoxy functionality was introduced to the liquefied wood. The epoxy functionality of the resins was controlled by the concentration of phenolic OH groups in the liquefied wood, which would be a dominant factor for crosslink density and properties of the cured epoxy resins. The flexural strength (150-180 MPa) and the modulus of elasticity (3.2 GPa) of the highly crosslinked wood-based epoxy resin were equivalent to those of the commercially available epoxy resin, diglycidyl ether of bisphenol A (DGEBA). Also, the shear adhesive strength of the wood-based epoxy resin was higher than that of DGEBA when plywood was used as the adhesive substrates. The mechanical and adhesive properties suggested that the wood-based epoxy resins would be well suited for matrix resins of natural plant-fiber reinforced composites. (c) 2006 Wiley Periodicals, Inc.