Modification and characterization of sodium alginate-zein composite films by cold plasma at different voltages

Cold plasma (CP) is an innovative non-thermal technology with potential applications in the modification of macromolecular complexes. In this study, sodium alginate–zein composite (SA-ZC) solutions were treated with CP at different voltages (0, 40, 100, and 160 kV), and changes in the properties of SA-ZC solutions and their films were analyzed. The results indicated that CP treatment significantly increased the viscosity and particle size of the SA-ZC solution while reducing the electronegativity, free sulfhydryl and amino group contents, suggesting enhanced intermolecular interactions. Notably, 100 kV treatment significantly enhanced the film's mechanical properties, hydrophilicity, and thermal stability (with degradation temperature increasing from 214.43 to 217.01 °C). FTIR, XRD, and AFM analyses revealed that the formation of hydrogen bonds, increased orderliness and crystallinity, and surface roughness were the primary reasons for the improved performance. However, CP treatment had no significant effect on film transparency or on antibacterial and antioxidant activities. These findings demonstrate that CP treatment enhances intermolecular interactions including disulfide and hydrogen bonds in the SA-ZC solution, ultimately improving the resultant film's performance. This provides fundamental insight into CP's mechanism and suggests promising avenues for developing modification applications.