Alkylated lignin with graft copolymerization for enhancing toughness of PLA
Abstract A green modification method for effectively enhancing toughness of PLA was established. Herein, alkaline lignin (LG) was firstly alkylated with dodecane, and then grafted with lactide (LA). The alkylated lignin-lactide graft copolymer (GLG-g-LA) was obtained via ring-opening polymerization (ROP). GLG-g-LA copolymer can be utilized as a functional filler to toughen polylactic acid (PLA) packaging film. The 31P-NMR of alkylated lignin (GLG) demonstrated that the peak of phenolic hydroxyl groups disappeared completely, while the relative peak intensity of carboxyl hydroxyl groups decreased significantly. The grafting rate of GLG-g-LA copolymer was improved more than twice times compared with lignin-lactide graft copolymer (LG-g-LA). Then LG-g-LA and GLG-g-LA copolymer were mixed with PLA to prepare different PLA composite films via casting method, respectively. Particularly, the elongation at break of PLA/GLG-g-LA2 composite film increased to 41.98%, which was more than 20 times higher than PLA. In general, PLA/GLG-g-LA composite film with toughness, excellent UV barrier, water resistance and controllable gas permeation could be used as high-performance and biodegradable materials in packaging field.