Ductile, High-Lignin-Content Thermoset Films and Coatings

Although lignin is a highly abundant and renewable polymer with very interesting properties, the preparation of high-lignin-content materials is challenging due to the brittleness and poor reactivity of lignin. Herein, high lignin content films and coatings were prepared by a simple and efficient method. A glyoxylic acid lignin (GA lignin), rich in carboxylic acid groups and hence highly reactive towards epoxy cross-linkers, was reacted with poly(ethylene glycol) diglycidyl ether and glycerol diglycidyl ether cross-linkers to achieve freestanding films containing up to 70 wt% lignin, and covalently attached surface coatings containing up to 90 wt% lignin. These films and coatings, potentially 100% biobased, show high antioxidant activity and UV barrier property, still maintaining good visible transparency. They hence are promising for application as sustainable food packaging films.