Recyclable Lignin-Based Light-Driven Shape Memory Epoxy Resins with Excellent Mechanical Performance

The use of biomass raw materials as replacements for traditional fossil resources is becoming increasingly important, both to reduce pressure on nonrenewable resources and to reduce environmental pollution. The abundant natural polymer lignin is still not used effectively, and it would be a win-win strategy to develop lignin-based light-driven shape memory polymers, especially if the polymers could be recycled. In this work, recyclable lignin-based light-driven shape memory polymers (EELDs) that respond to heat and light were designed by combining the rigid structure of lignin with dynamic ester bonds. EELD31 (where 31 represents the mass ratio of enzymatic lignin epoxy resin to dithiodibutyric acid) had good overall mechanical properties and could be easily recycled, with 90.8% of the original tensile strength retained after recycling. The maximum tensile strength achieved with the EELDs was 45.2 MPa (EELD31), the maximum elongation at break exceeded 100% (EELD21), and the fracture energy was as high as 15.7 J cm(-3) (EELD21). The EELDs also have good thermal stability and excellent shape memory properties. The shape fixation rate of EELD31 was as high as 99.0%, and the shape recovery rate was as high as 97.9%. Under 2 sun radiation, EELD31 showed a marked photothermal effect, reaching a temperature of 88 degrees C. Recycled EELD31 showed only a slightly reduced photothermal effect, reaching a temperature of 82 degrees C under the same conditions. EELD31 completed shape recovery in similar to 85 s under 2 sun radiation. The excellent mechanical and light-driven shape memory properties of the EELDs, combined with their good recyclability, provide new ideas for the development and utilization of lignin-based light-driven shape memory polymers.