Ultrasound-Regulated Molecular Reorganization and Property Enhancement in Gelatin–Glycerol Films

The replacement of petroleum-based plastics with sustainable and biodegradable materials remains a critical challenge for food packaging and biomedical applications. Gelatin is an attractive natural biopolymer for film fabrication; however, its inherent brittleness, moisture sensitivity, and limited structural stability restrict practical use. In this work, for the first time, low-power direct-probe ultrasonication is introduced as a green and additive-free strategy to regulate molecular organization and enhance the performance of gelatin-glycerol composite films. Systematic variation in ultrasonic power and treatment duration revealed a strong dependence of film structure and properties on processing conditions. Low-power ultrasonication (20 W) promoted gelatin-glycerol interactions, induced a transition from loosely organized molecular arrangements to helix-like molecular packing at the nanometer scale, and produced smooth, compact microscale surface morphologies. As a result, these films exhibited enhanced hydrophilicity, reduced surface defects, and improved thermal stability. In contrast, high-power ultrasonication generated excessive cavitation, leading to large-scale porous structures and diminished thermal and surface performance. Therefore, this work identifies a distinct low-power ultrasonic window that enables controlled molecular reorganization and hierarchical structure formation in gelatin-glycerol systems. Structural and physicochemical analyses using SEM, FTIR, XRD, water contact angle measurements, and thermogravimetric analysis collectively elucidate the ultrasound-driven structure-property relationships within the gelatin-glycerol matrix. Overall, this study demonstrates that controlled ultrasonication enables precise tuning of gelatin-based film architecture and properties, offering a scalable and environmentally friendly route to high-performance biodegradable materials for sustainable packaging and biomedical applications.