Preparation and properties of hydrophobic soy protein isolate/carboxymethyl cellulose/gelatin composite films via phytic acid-induced dual crosslinking.

In this study, phytic acid (PA) was employed as a multifunctional crosslinking agent to fabricate dual-crosslinked composite films based on soy protein isolate (SPI) and carboxymethyl cellulose (CMC), with glycerol as a plasticizer and gelatin as a processing aid to improve film flexibility and processability, thereby overcoming the performance decline of conventional soy protein-based films under high-humidity conditions. The structural, mechanical, hydrophobic, thermal, and barrier properties of the films were systematically characterized. The results demonstrated that PA-mediated dual crosslinking significantly enhanced the overall performance of the composite films. The optimized formulation (SPI-0.5CMC-PA) exhibited a water contact angle of 106.91°, indicating substantially improved surface hydrophobicity. Meanwhile, the dual-crosslinking network simultaneously increased both tensile strength and elongation at break, reaching 13.22 MPa and 39.93%, respectively, accompanied by enhanced thermal stability. XRD and DSC analyses confirmed excellent compatibility components, revealing a more amorphous yet structurally intact network without phase separation. FTIR spectra further verified the formation of electrostatic salt bridges and hydrogen-bonding interactions within the PA-mediated dual-crosslinked network. Overall, this dual-crosslinking strategy yields a green, mechanically robust, and hydrophobic film, demonstrating significant promise for moisture-resistant food packaging while offering a new route to bio-based hydrophobic materials.