Ultra-flexible, UV shielding, and flame-retardant gelatin films modified by lignin from a pilot-scale microwave fractionation platform

Pure gelatin film (GEL) is extremely brittle, combustible as well as poor UV shielding. In this study, nano-lignin (ML) was fractionated from a pilot-scale microwave separation platform for preparation of lignin modified gelatin films. The addition of ML endowed the pure gelatin film excellent UV shielding ability by preventing 100 % of ultraviolet light. ML also transformed the films from combustibility to flame-retardancy as the limiting oxygen index of the GEL/ML₁₁ film reached 31.45 %. The introduction of ammonium polyphosphate (APP) into the GEL/ML matrix further improved the flame-retardant performance of the film with minimal effect on the UV shielding and transparency. The limiting oxygen index increased to be 52.9 % when 20 % of APP was added. Moreover, the addition of APP also dramatically improved the elongation at break of the film. The elongation at break of films with 20 % of APP was more than three times that of pure gelatin film and GEL/ML film, transforming the film from brittle material to ultra flexible material. Results in this study provided a reference approach for the production of ultra-flexible, UV-shielding and flame-retardant gelatin films.