Effect of grafting method on the physical property and antioxidant potential of chitosan film functionalized with gallic acid

Chitosan (CS) was functionalized with gallic acid (GA) by three different grafting methods including free radical initiation, carbodiimide coupling and tyrosinase catalysis. The obtained GA grafted CSs (GA-g-CSs) were further characterized and developed into films by casting. For the first time, effect of grafting method on the physical property and antioxidant potential of GA-g-CS films was investigated. Different grafting methods resulted in varied grafting ratios (41.80-125.88 mg/g). Three GA-g-CSs presented different ultraviolet (UV) and infrared spectra, indicating GA was conjugated with CS by different linkage patterns. CS and three GA-g-CS films had similar thicknesses and elongation at break. Among different films, GA-g-CS film obtained through carbodiimide coupling method showed the highest water vapor barrier property, tensile strength, thermal stability and 2,2-diphenyl-1-picrylhydrazyl radical scavenging ability; whereas GA-g-CS film prepared by tyrosinase catalysis exhibited the darkest color and the highest UV light barrier property and opacity. Besides, three GA-g-CS films presented rougher surfaces and cross-sections than CS film. Our results suggested the physical property and antioxidant potential of GA-g-CS films were significantly affected by the grafting method and grafting ratio.