Lignin‐Based Type I Macromolecular Photoinitiator for Fabricating UV‐Blocking Films

ABSTRACT As the largest renewable source of aromatic feedstock in nature, lignin has good thermal stability, strong ultraviolet (UV) absorption, and mechanical reinforcing property. In this study, a lignin‐based Type I macromolecular photoinitiator (macro PI) named DAL‐11ene‐TPO is designed and synthesized through covalently grafting 10‐undecenoyl chloride (11ene) and 2,4,6‐trimethylbenzoyl‐ethoxy‐phenylphosphine oxide (TPO‐L, a commercial small molecular PI) into dealkaline lignin (DAL) skeleton. A series of characterizations were performed to prove that DAL‐11ene‐TPO was synthesized successfully, including 1 H NMR, FTIR, UV–vis, 31 P NMR, GPC (gel permeation chromatography). The formed active free radicals were monitored by electron spin resonance (ESR). DAL‐11ene‐TPO can high‐efficiently initiate the monomers polymerization upon the irradiation of 405 nm LED. The resulting polymer films showed strong UV‐blocking performance and good visible light transmittance. Moreover, the elongation at break of the polymer film containing 0.5% DAL‐11ene‐TPO is improved by 50% compared with that of TPO‐L control group. Furthermore, DAL‐11ene‐TPO has polymerizable groups, which can be bonded into the network of the polymers, resulting in a high biosafety of the end products. The results indicate that DAL‐11ene‐TPO can be used as a high‐efficient bio‐based macro PI for preparing high performance UV‐blocking films.