High lignin, light-driven shape memory polymers with excellent mechanical performance

With the gradual global standardization of carbon emission policies, the development of renewable resources to replace traditional fossil resources is assuming increasing importance. Lignin is the most abundant natural source of aromatic compounds and has the potential to replace petroleum-based aromatic hydrocarbons. In this work, the rigid benzene ring structure and excellent photothermal properties of lignin were exploited to produce light-driven lignin-based shape memory polymers (ELEPs) that contain high proportions of lignin and have good mechanical properties. Enzymatically hydrolyzed lignin (EL), epoxy soybean oil (ESO) and polyethylene glycol (PEG 400) were copolymerized and cured to form ELEPs, which have a disordered three-dimensional network. An increase in the proportion of EL from 40 to 60 wt% enhanced the mechanical properties, as reflected by an increase in tensile strength from 11.3 to 30.8 MPa and in the glass transition temperature (Tg) from 93 to 115.7 °C. Under simulated solar irradiation (2000 W m-2), ELEP50, which contains 50 wt% lignin and has a Tg of 105 °C, reached a surface temperature as high as 105 °C and achieved shape memory within 20 s. The shape fixation ratio (Rf) and shape recovery ratio (Rr) were stably >98 % and >97 %, respectively, over eight cycles in a bending-recovery experiment. The unique light-driven shape memory properties of ELEPs provide a method for high value utilization of EL, and the design strategy offers new ideas for producing novel intelligent materials.