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

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.