Grafting Polymerization of Long-Chain Hydrophobic Acrylic Monomer onto Lignin and Its Application in Poly(Lactic Acid)-Based Wholly Green UV Barrier Composite Films

The development of low-cost and high-performance bio-basedcompositesderived from forestry waste lignin and polylactic acid has emergedas a topic of central attention. However, the weak compatibility betweenlignin and polylactic acid often resulted in high brittleness of thecomposites. Graft copolymerization is not only the most effectiveway to modify lignin but also can significantly improve the compatibilityof lignin and polylactic acid. In this study, bio-based monomer laurylmethacrylate was grafted onto lignin by feasible radical polymerizationto prepare lignin graft copolymers with excellent thermal stabilityand hydrophobicity, which are expected to improve the compatibilitywith polylactic acid. Wholly bio-based composites were prepared bycompounding this graft copolymer with polylactic acid. The resultsshowed that the crystallization ability of the composite was improved,and the highest crystallinity was increased from 6.42% to 17.46%.With addition of LG-g-PLMA lower than 9%, the thermal stability ofthe composites was slightly improved. At 5% copolymer addition, theelongation at break and tensile toughness of the composites increasedby 42% and 36%, respectively. Observation of the frozen fracture surfaceof the composite by SEM found that wire drawing and ductile deformationappeared when a small amount of LG-g-PLMAwas added. The thus prepared composites also showed excellent UV barrierproperties. This approach provides a new idea for the high-value applicationof lignin.