Mechanical properties of polyurethane films prepared from liquefied wood with polymeric MDI

Sugi (Cryptomeria japonica D.Don) wood was liquefied using glycerol–PEG#400 co-solvent as reaction reagent in the presence of sulfuric acid for 75 min, at 150°C. The liquefied woods (LWs) obtained comprised of 9.6–29.8% dissolution wood and had a hydroxyl number of 329.1–278.7 mg KOH/g and viscosity of 0.33–31.6 Pa s at 25°C. Polyurethane (PU) films were prepared by a solution-casting technique after co-polymerization of the obtained LWs and polymeric methylene diphenylene diisocyanate (PMDI) in dichloromethane. FT-IR spectra, weight loss in acetone, and tensile properties were studied as functions of the isocyanate/hydroxyl group ([NCO]/[OH]) ratio and of wood content in PU film. The increase of wood content at a [NCO]/[OH] ratio of 1.0 significantly enhanced the Young’s modulus, and reduced the maximum elongation of LW–PU film. The rigid mechanical properties were due to the increase of dissolved wood fragments.