Hydrophobicity Strategies of Starch-Based Films: Recent Advances and Perspectives

The rapid accumulation of plastic waste and the depletion of fossil resources have intensified global efforts to develop biodegradable polymeric materials derived from renewable feedstocks. In this context, starch-based films have emerged as one of the most promising alternatives to conventional petroleum-based plastics, owing to their wide availability, low cost, biodegradability, and ability to form continuous films using simple and scalable processing techniques. Starch is a naturally occurring polysaccharide composed primarily of amylose and amylopectin, whose molecular structure is rich in hydroxyl (-OH) groups. These functional groups promote extensive intermolecular hydrogen bonding, enabling starch gelatinization and film formation in aqueous systems. However, the same hydroxyl-rich structure confers a pronounced hydrophilic character, resulting in high moisture sensitivity, poor water vapor barrier properties, and limited dimensional stability under humid. Consequently, improving the hydrophobicity of starch-based films remains one of the most critical challenges for their practical application in food packaging. This review aims to summarize and critically discuss the main strategies reported for improving the hydrophobicity of starch-based films. The review focuses on composition and processing approaches, including (i) chemical modification of starch, (ii) incorporation of hydrophobic additives, (iii) reinforcement with natural fibers and nanocellulosic materials, (iv) polymer blending and multilayer/gradient architectures, and (v) processing strategies, including film homogenization, shear treatment and aging conditions. Emphasis is placed on the mechanisms governing hydrophobicity enhancement, comparative performance indicators, and current limitations.