Polyhydroxybutyrate laminated trilayer films with enhanced barrier and mechanical properties for active food packaging

Polysaccharides such as starch and chitosan have been explored for biodegradable food packaging films. However, their inherent hydrophilicity and brittleness cause poor water vapor barrier performance and limited mechanical properties. To address these issues, starch was first functionalized with acetoacetate groups and subsequently blended with chitosan. Dynamic cross-linking occurred between the acetoacetate groups and the primary amine groups of chitosan, forming vinylogous urethane linkages that reduced the water solubility of the films while preserving high mechanical strength. With 30 wt% of glycerol as a plasticizer, the resulting films showed a tensile strength of up to 24.68 MPa and an elongation at break of up to 83.96%. To improve the barrier properties, poly(3-hydroxybutyrate) (PHB), plasticized with 5-15 wt% epoxidized vegetable oil, was laminated on top of the chitosan/modified starch films, resulting in a significantly reduced water vapor transmission rate (WVTR) of 66%. Additional components, such as food colors like β-carotene were incorporated into this layer to make UV-protective films. A third layer of PHB without active additives was then coated to further reduce WVTR by 99%. Therefore, this multilayer lamination strategy effectively enhanced the barrier and mechanical properties of the polysaccharide-based packaging films.