Production of Starch/Gelatin-Based Films Using Extrusion Method and Their in-Situ Hydrophobicity Enhancement

Biodegradable films based on corn starch and bovine gelatin were produced using a co-rotating twin screw extruder and water and sorbitol, both as plasticizers. To enhance hydrophobicity, two reactive methods were employed: one, chemical bonding of paraffin wax via maleic anhydride, and the other, acetylation through acetic anhydride. In both methods, the extruder served as a reactor. Next, biodegradable films were cast from binary starch/gelatin, and ternary starch/gelatin/paraffin-grafted starch, as well as starch/gelatin/acetic anhydride-grafted starch blends, with the same extrusion process. The films were evaluated and compared in terms of mechanical and barrier properties against moisture, contact angle, water absorption, and water vapor permeation. Results revealed that introducing paraffin-grafted starch into the starch/gelatin blend improved hydrophobicity according to three criteria: a 28° rise in water contact angle, a 9 percent decrease in water absorption, and a 4.2 percent lessening in water vapor permeation, while the mechanical properties were comparable to the binary starch/gelatin blend. On the other hand, in films from starch/gelatin/ acetic anhydride-grafted starch compared to starch/gelatin, the contact angle increased by 21° and water absorption decrease by 4.5 percent, but the mechanical properties were deteriorated, and water vapor permeation elevated by 3.5 percent.