Multiresponsive shape memory photothermal elastomers based on unmodified and high-content lignin

Photothermal elastomers are intelligent soft materials that can rapidly and efficiently convert light energy into heat energy, and it is crucial to develop sustainable smart photothermal conversion materials using natural resources in the context of sustainable resources, carbon neutrality, and environmental protection. In this study, a high-content lignin-based polyurethane (LPU) photothermal elastomer was synthesized via a one-pot method by utilizing the unmodified membrane-filtered kraft lignin. The resulting LPU achieves high mechanical strength (25.6 MPa), toughness (51.8 MJ·m^-3) and Young's modulus (692.0 MPa) due to the combination of abundant hydrogen bonds, crosslinked network and microphase-separated structure. Additionally, the presence of phenolic groups and conjugated structures in lignin endows LPU with a combination of desirable properties, including dual-mode photothermal conversion (both Xenon cold light and near-infrared) and excellent thermoresponsive and photoresponsive shape memory performance (a shape recovery rate of up to 99.9 %), which further broaden the potential applications of LPU in photothermalelectirc generators, light-controlled programmable shape memory, smart labels, and photothermal energy harvesters. This work provides a facial and green method for synthesizing a high-content lignin-based polyurethane that have great prospects in photothermal fields.