Synthesis of Wood-Based Epoxy Resins and Their Mechanical and Adhesive Properties Hajime Kishi, Akira Fujita, Hikaru Miyazaki, Satoshi Matsuda, Atsushi Murakami Graduate School of Engineering, Himeji Institute of Technology, University of Hyogo, 2167, Shosha, Himeji, Hyogo 671-2201, Japan Received 3 December 2005; accepted 16 March 2006 DOI 10.1002/app.24433 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: 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 cata- lyst 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 epichlorohy- drin 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 sub- strates. 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. Ó 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2285–2292, 2006 Key words: biopolymers; resins; strength; adhesives; com- posites INTRODUCTION It is essential that industrial systems respect anti- global-warming restrictions. An effective use of plant biomass should be an ideal replacement for fossil- fuel resources. Moreover, in contrast to fossil-fuel resources, plant biomass is a renewable resource, which is another advantage. Therefore, much effort has been devoted to utilizing disposed biomass as a valuable resource for polymers and chemicals. The liquefaction of wood in the presence of phe- nols or alcohols has been intensively studied by Shiraishi et al. 1–6 Liquefied wood has a high reactiv- ity due to the large amount of phenolic OH groups and alcoholic OH groups. Using these functional groups, liquefied wood can be converted to phenolic resins and polyurethane forms. 7–10 Liquefied wood has further potential and may be used as a resource for other valuable biomass-based materials. The epoxy-resin family has good mechanical and adhesive performances, and is widely used in various fields, for example, as adhesives, coatings, and matrix resins of composites. The first objective of this study is to synthesize wood-based epoxy resins using lique- fied wood as the precursor of the resin. The second objective is to evaluate the mechanical and adhesive properties of the wood-based epoxy resins in order to clarify the potential of further applications. EXPERIMENTAL Materials The wood sample used was 20–80 mesh wood meal from German spruce (Picea abies). Resorcinol, epi- chlorohydrin, and all other chemicals for liquefaction of wood and synthesis of wood-based epoxy resins were of reagent grade (from Wako Pure Chemical Industries, Ltd., Osaka, Japan), and were used with- out further purification. A mixture of diglycidyl ether of bisphenol A oligomers [Ep828 : Ep1001 ¼ 7 : 3 in weight ratio; both grades were produced by Japan Epoxy Resin Inc. (Tokyo, Japan)] was used as a reference epoxy resin. The resins were cured with a stoichiometric amount of 4,4 0 -diamino diphenyl methane (DDM). Synthesis of wood-based epoxy resins Liquefaction of wood Wood-based epoxy resins were attained via the fol- lowing two steps. The first step was the liquefaction of the wood and the second step was the synthesis of epoxy resins from the liquefied wood. Two methods, namely, the noncatalyzed method and the acid-catalyzed method, were used for the Correspondence to: H. Kishi (kishi@eng.u-hyogo.ac.jp). Journal of Applied Polymer Science, Vol. 102, 2285–2292 (2006) V V C 2006 Wiley Periodicals, Inc.