Responsive lignin for shape memory applications
Here, we analyze thermally unstable lignin linkages that generate reactive sites and promote crosslinking reactions during thermal annealing at 180 °C. This results in significantly enhanced glass transition temperature (Tg). We use these characteristics of lignin to enhance interfacial reactivity of a lignin-based multiphase polymer synthesized by a dynamic shear process. An approximately 18 °C increase in Tg and more than 230% increase in storage modulus (E') are achieved by thermally annealing the 50 wt% hardwood lignin-nitrile rubber composite for 5 h at 180 °C. Tunable chemical and physical crosslinks within lignin and rubber resulted in shape programmability demonstrating excellent strain recovery of the synthesized renewable materials. The substantial improvement of the elastic work density of the lignin-based elastomers allows a broader applicable stress window for stress/strain sensing. The renewable materials also exhibit a better strain recovery after thermal annealing.