Poly(lactic acid)/lignin films with enhanced toughness and anti-oxidation performance for active food packaging

In this study, grafting of star-like lignin microparticles (LMP) onto PLA (LMP-g-PLA) was successfully realized by ring open polymerization of l-lactide, initiating from the hydroxyl groups on LMP surface. After that, various amount of LMP-g-PLA were melt blended with neat PLA and ethylene–vinyl acetate–glycidyl methacrylate (NPG) to prepare different PLA composites films, by exploiting the interfacial reactions between epoxy groups of NPG and carboxyl and hydroxyl groups of both LMP-g-PLA and PLA. Mechanical test results show that the addition of LMP-g-PLA made a significant contribution to the toughness of PLA/NPG blend, as the elongation at break increased up to 236% in PLA/NPG/1LMP sample. Although the addition of NPG and LMP-g-PLA hindered the crystallization capacity of PLA, good dispersion of LMP-g-PLA and compatibility between LMP and PLA acted as longer tortuous paths, consequently reducing the water vapor transmission rate. Meanwhile, the UV–Vis spectroscopy results showed that PLA/NPG/LMP films have excellent UV resistance behaviour without sacrificing too much the transparency. Results from overall migration tests and testing of anti-oxidant behaviour demonstrated that PLA films blended with NPG and lignin can be used as competitive materials in active food packaging industry.