Chitosan-based composite films with good biodegradability, biocompatibility, and sustainability are extensively employed in the field of food packaging. In this study, novel chitosan/tannic acid (CTA) and chitosan/oxidized tannic acid (COTA) composite films with excellent mechanical and antibacterial properties were prepared using a tape casting method. The results showed that, when 20% tannic acid (TA) was added, the tensile strength of the CTA composite film was 80.7 MPa, which was 89.4% higher than that of the pure chitosan (CS) film. TA was oxidized to oxidized tannic acid (OTA) with laccase, and the phenolic hydroxyl groups were oxidized to an o-quinone structure. With the addition of OTA, a Schiff base reaction between the OTA and CS occurred, and a dual network structure consisting of a chemical bond and hydrogen bond was constructed, which further improved the mechanical properties. The tensile strength of 3% COTA composite film was increased by 97.2% compared to that of pure CS film. Furthermore, these CTA films with significant antibacterial effects against Escherichia coli (E. coli) are likely to find uses in food packaging applications.
In order to reduce the threat of 'plastic pollution' and reduce or eliminate some traditional polymer packaging materials, in this study, soybean protein isolate (SPI) composite film, a biodegradable natural polymer film, was prepared by tape casting method with Thyme (Thy) and mangosteen peel extracts (MPE) as antibacterial agents. The antibacterial rates of the composite films against E. coli and S. aureus were 95.79% and 92.63%, respectively, and the DPPH free radical scavenging rate was 70.28%. The composite film had good UV-visible barrier properties. Compared with the pure SPI film, the tensile strength of the composite film was improved, the water absorption, water solubility, and water vapor permeability were reduced, and the contact angle was improved. The maximum thermal decomposition temperature of the composite film increased and the thermal stability increased.
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