Mechanically robust, recyclable lignin-reinforced photothermal shape memory polymers containing dynamic boronic ester bonds

To address the growing demand for sustainable smart materials, a novel strategy was used to design lignin-reinforced photothermal shape memory polymers (ELBEs) incorporating dynamic boronic ester bonds. 1,4-Benzenediboronic acid serves as a dual functionality crosslinker that covalently bridges enzymatic lignin and poly(ethylene- co -vinyl alcohol) through boronic ester bonds. The resulting dynamic covalent networks reinforce and toughen the ELBEs, without complex chemical modifications. The ELBEs have an excellent balance of toughness and strength, with tensile strength, fracture strain and Young's modulus as high as 50.1 MPa, 102 % and 636.3 MPa, respectively. This comprehensive performance exceeds that of most existing lignin-containing shape memory materials. The dynamic boronic ester bonds confer rapid stress relaxation, water-assisted room temperature self-healing and solvent cycling performance, while intrinsic photothermal conversion by lignin confers excellent light-controlled shape memory performance. To illustrate utility, an optimized ELBE was successfully used as a photo-responsive circuit protection device. The superior photothermal properties of the optimized ELBE also allow generation of electricity when the material is incorporated into a thermoelectric generator, highlighting its excellent light-thermal-electricity conversion. Despite the relatively low proportion of EL in ELBE materials (ranging from 2 to 8 wt%), its high functional efficiency significantly enhances various properties of the system. This work not only provides a novel paradigm for the development of recyclable smart materials suitable for use in flexible electronics and green energy generation, but also offers a new strategy for high-value utilization of lignin.