Electrostatically assembled polyelectrolyte complex films from quaternized carboxymethyl chitosan and sulfated...

Biodegradable polysaccharide-based composite films were developed using quaternized carboxymethyl chitosan (QCMCS) and sulfated succinoglycan (SSG). Carboxymethyl chitosan (CMCS) was quaternized with glycidyltrimethylammonium chloride (GTMAC) to enhance water solubility and antibacterial activity, while succinoglycan (SG), an anionic extracellular polysaccharide produced by Sinorhizobium meliloti, was sulfated to introduce sulfate groups associated with antioxidant activity. Structural characterization using ¹H NMR, ¹³C NMR, FT-IR, and XRD confirmed the successful chemical modification of both polysaccharides. Composite films were fabricated through electrostatic interactions between the cationic quaternary ammonium groups of QCMCS and the anionic sulfate groups of SSG, forming polyelectrolyte complex (PEC) networks and a more compact internal film structure. The incorporation of SSG significantly improved the mechanical properties of the films, with tensile strength increasing from 7.13 MPa to 19.18 MPa. In addition, the composite films exhibited enhanced barrier performance, including a reduction in water vapor permeability of more than 50% and a decrease in UV transmittance at 254 nm from 22.46% to 5.78%. The films exhibited antioxidant activity from sulfated succinoglycan while maintaining antibacterial activity from the quaternized chitosan component. These improvements are attributed to enhanced intermolecular interactions and reduced free volume within the PEC-based film matrix, leading to more favorable structure-property relationships. Overall, this study demonstrates that electrostatic assembly between oppositely charged polysaccharide derivatives is an effective strategy for designing multifunctional biodegradable films with enhanced mechanical strength, barrier performance, and bioactive functionality. The developed films show strong potential as sustainable and multifunctional materials for biodegradable food packaging applications.