Ultra-robust polyurethane/lignin elastomer built on multiscale structure orientation induced by pre-stretching

This work focuses on a simple approach for designing the polyurethane elastomers with ultra-robust properties. Initially, polyurethane/lignin elastomers were synthesized using polytetramethylene ether glycol (PTMG) as soft segment, hexamethylene diisocyanate (HDI) along with 4,4'-dihydroxydiphenyl ether (DO) as hard segments, and lignin nanoparticles (LNP) as the biomacromolecule crosslinker. Subsequently, the resulting elastomer were pre-stretched at certain ratios (λ), and surprisingly, the pre-stretched polyurethane/lignin elastomer (λ=14) displayed significant improvement in mechanical properties, while the tensile strength and toughness were sharply enhanced from 32.4 MPa and 298.7 MJ/m3 to 120.2 MPa and 501.3 MJ/m3, respectively. The improvement can be attributed to the denser cross-linked networks combined with the multiscale structure orientation and stress-induced crystallization (SIC) effects induced by pre-stretching. The interphase distance (d_p) decreased from 15.708 to 14.612 nm, while the interplanar crystal distance (d_c) increased from 4.387 Å to 4.398 Å, and the Herman orientation factor (f) increased from -0.0066 to 0.0518. This work presents a novel strategy for preparing polyurethane elastomers with exceptional mechanical performance.