Preparation and application of polyurethane adhesives made from polyhydric alcohol liquefied Taiwan acacia and China fir

Taiwan acacia (Acacia confusa) and China fir (Cunninghamia lanceolata) were liquefied in polyethylene glycol (PEG)-glycerol cosolvent, with sulfuric acid (H2SO4) as a catalyst. The liquefied woods were blended with three kinds of isocyanate, such as poly-4,4'-diphenylmetliane diisocyanate (PMDI), Desmodur L (adduct of toluene diisocyanate with trimethylol propane), and Desmodur N (trimer of hexamethylene diisocyanate), to prepare polyurethane (PU) resins. From the results, China fir had better liquefaction effect than Taiwan acacia. Those PU resins prepared from liquefied wood blending with isocyanate could cure at room temperature. Their gel property was influenced by the type of isocyanate, the molar ratio of the functional group of isocyanate to liquefied wood [NCO/(OH+COOH)], and the rate of catalyst added. PU resins prepared from Desmodur L had an appropriate gel time for processing. But those prepared from PMDI had too short gel time to process. Contrary, the PU resins prepared from Desmodur N would take a longer time to gel. However, addition of catalyst could shorten the gel time significantly. FT-IR analysis showed that a urethane bond had formed between the liquefied wood and isocyanate. When these PU resins were used as wood adhesives, liquefied wood blended with Desmodur L had better dry and wet bonding strength than others. Increasing the molar ratio of NCO/(OH+COOH) could increase the bonding strength. On comparing liquefied Taiwan acacia and China fir, the former had better bonding strength than the latter. (C) 2008 Wiley Periodicals, Inc.