High Modulus, Strength, and Toughness Polyurethane Elastomer Based on Unmodified Lignin

Lignin-based polyurethane elastomers (LPUe) with high stiffness, strength, and toughness were facilely prepared by direct cross-linking of unfunctionized lignin as hard segments and poly(propylene glycol) tolylene 2,4-diisocyanate terminated (PPGTDI) as soft domains. The effects of lignin molecular weight (3600 and 600 g mol –1 ) and weight fraction (5–40 wt %) on the thermal and mechanical properties of LPUe were studied. With an increase in lignin content, LPUe exhibited improved thermal stability, and the glass transition temperature ( T g ) also increased, especially for LPUe derived from lignin with low lignin molecular weight of 600 g mol –1 (600-LPUe). Furthermore, LPUe also exhibits excellent mechanical properties. For 600-LPUe with 40 wt % of lignin, the Young’s modulus, tensile strength, and strain at break reach 176.4 MPa, 33.0 MPa, and 1394%, respectively, which could be attributed to better dispersion of low molecular weight lignin in elastomers as evident from DSC, SEM, and TEM studies. Our results demonstrate the potential application of unmodified lignin in developing biobased high-performance PU materials. This is in contrast to many current studies of LPUe systems that need lignin modification to prepare PU materials.