Degradable and Biobased Covalent Adaptable Networks for Light Controllable Switch

In this study, we successfully synthesized lignin-based covalent adaptable polyurethane networks containing lignin-graphite nanosheet composite particles with a light controllable positive temperature coefficient (LPTC) effect. The use of lignin facilitated the direct exfoliation of graphite, thus overcoming the challenge of achieving a uniform dispersion of conductive fillers in the polymer matrix. The exfoliated graphite had a thickness of approximately 3.0 nm, which was equivalent to three to five layers of graphene. By preparing lignin-based covalent adaptable polyurethane without graphite composite particles (LPU) and lignin-based covalent adaptable polyurethane with graphite composite particles (LPU-G), we achieved remoldable properties and a high LPTC intensity for LPU-G. LPU-60G (60 represents the mass fraction of lignin-graphite nanosheets in polyols) exhibited an excellent LPTC effect, with sharp increases in resistance under light, particularly under near-infrared light (NIR), enabling the control of the current in circuits. Additionally, both LPU and LPU-G demonstrated degradability by slowly degrading in a PBS solution while rapidly degrading in an alkaline solution. Overall, the LPU-G synthesized in this study displayed superior stability in the LPTC effect and possessed degradability, providing a promising avenue for the future development of smart materials.