Ultra-robust polyurethane/lignin elastomers based on multiscale structural orientation induced by pre-stretching

This work focuses on a simple approach for designing polyurethane elastomers with ultra-robust properties. Initially, polyurethane/lignin elastomers were synthesized using polytetramethylene ether glycol (PTMG) as a soft segment, hexamethylene diisocyanate (HDI) with 4,4'-dihydroxydiphenyl ether (DO) as hard segments, and lignin nanoparticles (LNP) as a biomacromolecular crosslinker. Subsequently, the resulting elastomers were pre-stretched at certain ratios (λ), and surprisingly, the pre-stretched polyurethane/lignin elastomer (at the ratio of λ = 14) displayed significant improvement in mechanical properties, while the tensile strength and toughness values were sharply enhanced from 32.4 MPa and 298.7 MJ m^-3 to 116.2 MPa and 501.3 MJ m^-3, respectively. This improvement can be attributed to the obtainment of dense cross-linked networks due to the combined effect of pre-stretching on both multiscale structural orientation and stress-induced crystallization (SIC). The interphase distance (d_p) decreased from 15.708 to 14.612 nm, 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.