Effect of plasticizers and cross-linking degrees on the physical properties of modified pullulan films

The increasing consumer interests in convenience and food quality has encouraged more and more researches about the applications of natural polymers (i.e. polysaccharides) in packaging technology. This study aimed to investigate the feasibility of plasticized glutaraldehyde cross-linking pullulan films as packaging. Pullulan film has good tensile strength and oxygen barrier property; however, its poor water resistance puts a drawback of using it as packaging materials. In this study, the weakness of pullulan films was improved by cross-linking with various degrees of glutaraldehyde and different plasticizers including glycerol, sorbitol, and xylitol. Moreover, the mechanical properties, FTIR, water resistance, water vapor permeability (WVP), swelling ratio, and surface morphology of them were determined. Films were obtained by casting method. At the same time, the cross-linking reaction happened at 80 ^oC. With 2.5% (w/w) of glutaraldehyde cross-linking, the tensile strength of the films were 5-fold to pure pullulan one, and the water resistance were also improved. The incorporation of plasticizers resulted in more flexible, storable, and higher WVP in both pure and cross-linking films. The tensile strength of films plasticized with glycerol was higher than sorbitol- and xylitol-plasticized films. Water vapor permeability of films increased with increasing plasticizer content and storage relative humidity.