Cold Plasma Modification of Cassava Starch–Gelatin Blend Films for Enhanced Mechanical Strength and Water Resistance in Sustainable Packaging

A cold plasma-treated cassava starch–gelatin blended film (CS-GL) was developed to enhance the mechanical, thermal, and physical properties of biopolymer films for sustainable packaging applications. Cassava starch and gelatin were blended at an 80:20 ratio and treated using a cold plasma jet at 7 W with exposure times of 5–45 min and at plasma powers of 4–13 W for 15 min. Plasma treatment at moderate power and duration promoted structural interactions between starch and gelatin chains, as supported by FTIR by FT-IR and 1H-NMR, while excessive power and prolonged exposure caused depolymerization of the polymer chains. The tensile strength of the CS-GL films increased from 30 to 42 MPa at 7 W for 15 min, whereas the elongation at break decreased from 7.62% to 5.42%. The TGA results showed that the residual content increased with plasma power up to 10 W and with exposure time up to 45 min but decreased to 13 W owing to chain scission. DSC analysis showed an increase in the endothermic transition temperature under moderate plasma conditions and a broader transition with a larger amorphous fraction under excessive treatment. Plasma treatment increased the water contact angle while reducing swelling and solubility owing to the consumption of hydroxyl groups and network densification. SEM images showed surface smoothing and densification at moderate plasma power and surface roughening at high power owing to chain scission. The optimal conditions were identified as 7 W for 15 min, which provided the best balance between mechanical strength, thermal stability, and structural homogeneity. A moderately higher dose further improved water resistance. Cold plasma is an effective and controllable green modification technique for tailoring the mechanical and water-resistance properties of starch–gelatin biopolymer films, offering a promising basis for future development toward biodegradable packaging industry, pending further evaluation of migration safety, packaging regulation, biodegradation behavior, and storage stability.