Characterization of polyurethane wood adhesive prepared from liquefied sawdust by ethylene carbonate

Abstract

Polyols, which are important compounds of polyurethane adhesives (PU), were prepared in this work from renewable sources. Beech wood sawdust was liquefied using ethylene carbonate as a new solvent and sulfuric acid as a catalyst in the two phases. The first phase of the liquefaction process was carried out at temperatures 110 to 160 °C, and the catalyst content was studied in the second phase. The biopolyol was used for two types of polyurethane adhesive by blending two types of isocyanate, poly4,4′- diphenyl methane diisocyanate (PMDI) and toluene diisocyanate (TDI), in different NCO/OH ratios for the preparation of polyurethane adhesives. Liquefaction temperature had a great influence on the characteristics of polyol such as acid and hydroxyl numbers and yield. Moreover, the polyol obtained at 130°C and 120 min with yield 85% was found to be a suitable polyol for preparing polyurethane adhesives. By increasing the molar ratio (NCO/OH) to 1.7, the lap shear strength was increased. The optimal lap shear strengths in PU PMDI and PU TDI were 1.64MPa and 1.46MPa, respectively. FTIR results showed that due to the presence of hydroxyl groups (OH), beechwood sawdust can be a source of polyol. Urethane bonds can form between the polyol and isocyanate in polyurethane adhesives.