Valorization of organosolv lignin: Architectural strategy to enhance mechanical strength and UV protection in self-healing polymers

Altering the architecture of conventional self-healing polymers, from the original linear to a multiple-branched structure, has proved to be efficient in improving the mechanical properties. A novel strategy to achieve similar results is to utilize organosolv lignin, a renewable biopolymer with rigid aromatic backbone that has multiple active sites amenable for grafting heterogenous polymer units. In this study, a lignin-based triblock copolymer, namely lignin-grafted poly(diacetone acrylamide-co-2-hydroxypropyl acrylate) or LPDH, was successfully synthesized via ARGET-ATRP (activator regenerated by electron transfer-atom transfer radical polymerization) mechanism. The LPDH copolymers were found to exhibit higher ultimate tensile stress (≤6.3 ± 1.4 MPa) and Young's modulus (194.2 ± 46.1 MPa), as well as significant (86 %) recovery of tensile strength and extensibility. Moreover, the LPDH copolymers could absorb UV radiation. Since, a commercially available organosolv lignin was directly utilized to prepare the copolymer without any purification, it is suggested that LPDH has potential to be manufactured on an industrial scale for self-healing, anti-UV coating applications. It also is hoped that the proposed synthetic strategy will inspire the development of renewable biomass-based polymers with similar functions.