Lignin: a sustainable photothermal block for smart elastomers

Remote controllable photothermal elastomers can realize precise non-contact control through the photothermal conversion effect, highlighting a new routine for light energy utilization and a promising direction for smart materials. Developing biomass-based photothermal materials is an important strategy to promote the realization of carbon neutrality and improve the environmental friendliness of photothermal elastomers. In this work, green biomass lignin was demonstrated as an efficient photothermal agent for preparing smart elastomer composites with versatile functionalities, owing to the fact that the conjugated structures in lignin could effectively promote electron transitions from low-energy orbitals to high-energy states and the visible and near-infrared (NIR) light energy absorbed by lignin was mainly released in the form of non-radiative transition. A high photothermal conversion efficiency of 53.7% was obtained for low molecular weight alkaline lignin with the photothermal temperature exceeding 280°C under NIR irradiation (808 nm, 1.25W cm−2). Under the stimulation of NIR light, the alkaline lignin/polyethylene elastomer (POE) composite exhibited a good light-triggered shape memory effect, excellent light-controlled self-repairing properties with the self-repairing efficiency as high as 98.2% (808 nm, 1.25W cm−2, 20 min), and strong photothermal bactericidal activity. Meanwhile, a series of functional applications were demonstrated based on the excellent photothermal effect of lignin, such as photothermal engines, photothermal generators and photothermal switches, which endowed lignin-based elastomer composites with considerable application prospects in smart materials for precise remote driving of robots, machines, sensors, sterilization and self-repairing equipment, etc., promoting the sustainable development and high-value utilization of biomass lignin.