Maleic acid modified lignin for preparation of ultra-flexible and UV shielding gelatin/lignin films

Alkaline lignin and sodium lignosulfonate were chemically modified by using maleic acid for potential application on the production of ultra-flexible gelatin films. The comparison results in morphology and chemical structures of the two types of lignin before and after modification revealed that carboxyl and C=C groups were successfully grafted onto the lignin, resulting in the changes in physical-chemical properties. Compared to modified sodium lignosulfonate, modified alkaline lignin (MAL) was much more appropriate in the preparation of gelatin (GEL)/lignin films by endowing the films with transparency and excellent UV light shielding ability. Elongation at break of GEL/MAL films were more than two times that of the pure gelatin film, which greatly addressed the brittleness issues of the pure gelatin films during use, indicating that the modified alkaline lignin could be used as renewable additive with replacement of glycerol. The results in this study also gave evidence that the sources and structure of lignin affect its compatibility with gelatin solution. The higher weight loss rate and lower pyrolysis degradation temperature indicated that the gelatin/lignin films were much more easily thermal degradable at the end of service life. This research provided a potential and efficient approach on the production of renewable and biological films from gelatin and lignin.