Biodegradable and High-Performance Poly(butylene adipate-co-terephthalate)–Lignin UV-Blocking Films

Renewable and biodegradable UV-blocking films are in high demand for the increasing need of sustainable environment. Lignin can offer significant UV absorption, but it deteriorates the mechanical properties of films at a high content. In this effort, biobased 10-undecenoic and oleic acids were successfully grafted on soda lignin via solvent- and catalyst-free processes, as confirmed by 31P and 1H NMR and Fourier transform infrared (FTIR). The resulting lignin ester derivatives and neat lignin were then melt-blended with a biodegradable poly(butylene adipate-co-terephthalate) (PBAT) to prepare UV-protective films. The incorporation of the modified lignins into the PBAT matrix exhibited good dispersion of lignin particles with almost unaffected tensile properties as well as good thermal stability for up to 20 wt % loading of lignin derivatives. The resulting films showed excellent UV-barrier property with 10 wt % lignin loading, having full protection in the whole UV-irradiation range (280–400 nm). The UV protection of prepared films proved persistent even after UV irradiation for 50 h, and their transparency was evidently enhanced. This work demonstrates a very promising procedure to produce high-performance and biodegradable PBAT–lignin UV-blocking films.