Sustainable waterborne polyurethane/lignin nanoparticles composites: Durability meets degradability

Abstract

Optimizing the durability and degradability of polymers is essential for prolonging their useful life and minimizing their environmental footprint post-use, contributing to a sustainable world; however, durability in many cases conflicts with degradability. In this context, we developed lignin-based waterborne polyurethane (WPU) composites that bypass this dichotomy. Lignin nanoparticles (LNP), derived from enzymatic hydrolysis lignin (EHL), were synthesized using the anti-solvent method and incorporated into WPU emulsions through solution blending. The introduction of 5 wt% LNP notably improved the tensile strength of WPU composites, increasing it from 21.5 MPa to 29.7 MPa, a surge of up to 38 %. Moreover, 5 wt% of LNP significantly enhanced the durability of WPU by reducing creep strain (under a stress of 1 MPa for 3000 s) from 606 % to 70 % with an 88 % decrease, and by increasing molecular weight retention rate from 11 % to 87 % after 15 days of UV exposure. Concurrently, LNP notably accelerated the alkaline degradability of WPU/LNP composites, with weight loss rate increasing from 38 % to 92 % (a 142 % increase) and molecular weight loss from 17 % to 44 % (a 159 % increase), compared to pure WPU. The strategy employed in this study leverages the inherent properties of LNP to offer a promising approach to enhancing polymer sustainability, presenting an effective solution to the significant end-of-life challenge.