Optimization of Cassava Starch–CMC–Glycerol Formulations for Enhanced Water Resistance of Biofilms

Biodegradable films from natural polymers offer a sustainable alternative to synthetic plastics, with water resistance being a critical property. This study examined the effects of cassava starch (5 g, 10 g, 15 g), carboxymethyl cellulose (CMC: 1%, 2%, 3%), and glycerol (6 mL, 9 mL, 12 mL) on biofilm water resistance, producing 27 formulations. Water resistance was measured through immersion tests by assessing weight changes due to absorption and swelling. Results showed that starch concentration strongly influenced matrix formation, where higher starch content (15 g) produced denser and more stable films with greater resistance. CMC reduced water resistance because of its hydrophilic nature, while glycerol acted as a plasticizer with dual effects: moderate amounts improved flexibility and minimized cracks, but higher levels increased water uptake. Among all formulations, only the film with 15 g starch, 1% CMC, and 6 mL glycerol met the Indonesian National Standard (SNI), achieving 103.3% water resistance. These findings highlight the importance of optimizing starch, CMC, and glycerol composition to produce biofilms with strong barrier properties for biodegradable packaging applications.