Abstract: The lignin-based polyurethane (PU) films were prepared from wheat straw alkali lignin by solution casting with polyethylene glycol (PEG) 300 or 1000 and polymeric phenyl methane-diisocyanate (PAPI) in the solvent of N,N-dimethylformamide (DMF). The mechanical performance of PU films was improved by adjusting the ratios of PEG 300 to PEG 1000. The mechanical performance including Young's modulus, tensile strength, elongation at break and tear resistance were tested for PU films. The results showed that by the way of altering the molar ratio of PEGs of different molecular weight in the system of reaction, the tear resistance behavior of PU films was outstandingly enhanced. Under the following conditions: NCO:OH=2.5, lignin coutent 20% and PEG 1000:PEG 300=2.0, the Young's modulus, tensile strength, elongation at break and tear resis-tance of PU film were 1.49 GPa, 36.5 MPa, 12.7% and 8460 mN, respectively, Meanwhile, its moulding film performance was better under the above conditions.

Key words: wheat straw alkali lignin, PEG, PAPI, polyurethane film, compatibilization