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

Abstract

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 °C. Recycled EELD31 showed only a slightly reduced photothermal effect, reaching a temperature of 82 °C under the same conditions. EELD31 completed shape recovery in ∼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.

Elaboration of Biobased Nonisocyanate Polyurea Materials with Shape-Memory Properties

“…Finally, the mechanical properties of shape memory materials vary widely in the literature depending on the chemical nature of the polymer network. Our materials have properties specific to their chemical and morphological nature and are within the range of properties reported in the literature. − ,,,,,− …”

“…This reaction enables the rearrangement of the cross-linked network and the fixation of the new permanent shape, S2 (ε S2 ), with a shape fixation ratio, R S2f , of 84.6%. Interestingly, when the temporary shape fixation and recovering procedure was applied on S2, the material continues to exhibit good shape fixation ( R s3f = 88.3%) and recovery ( R s3r = 108.1%) rates, demonstrating a very good combination between shape reconfiguration (plasticity) and shape memory (elasticity) properties. − ,,,,,− …”

“…Shape memory polymers (SMPs) have the unique ability to be fixed into temporary shapes and then return to their original shape when they are triggered by heating. SMPs play a crucial role in various applications, including aerospace, intelligent actuators, and sensors. − SMPs can be broadly categorized into thermoplastic and thermosetting types based on their thermal processing characteristics. Thermoplastic SMPs are easily processed and reshaped, but they often exhibit inferior solvent resistance, mechanical properties, and dimensional stability compared with thermosetting SMPs.…”

Covalent Adaptable Networks Containing Nitrogen-Coordinated Boronic Ester and Imine Bonds

“…Despite these achievements, most epoxy CANs lose their excellent initial mechanical performance because of the relative weak chemical bonds, i.e., dynamic covalent bonds, present in them. 9,14,21,22 both excellent mechanical performance and good reprocessing ability.…”

“…The obtained epoxy resins exhibited excellent mechanical strength over 97.6 MPa. Despite these achievements, most epoxy CANs lose their excellent initial mechanical performance because of the relative weak chemical bonds, i.e., dynamic covalent bonds, present in them. ,,, Therefore, there still remains a challenge to fabricating epoxy CANs with both excellent mechanical performance and good reprocessing ability.…”