Enhancing water resistance of interface between starch films and acrylated epoxidized soybean oil coating

Starch-based materials are a promising biobased polymer for packaging applications. To improve the water resistance of starch films, composite systems consisting of hydrophobic acrylated epoxidized soybean oil (AESO) coating and oxidized starch were prepared. To enhance the interfacial bonding between the starch film and AESO coating (AC), surface modification of oxidized starch with polyethyleneimine (PEI) was carried out. PEI modified AC coated oxidized starch films demonstrated significantly reduced water adsorption at the exposed cross-section, while only marginal improvement was observed when unoxidized starch AC coated with PEI treatment was used. Lap shear experiments demonstrated that the surface treatment of PEI on oxidized starch resulted in more than 650% improvement of bonding strength with AESO coating compared to untreated oxidized starch. This improvement of interface adhesion and water resistance is due to the new interface created through the formation of ionic bonds between PEI and oxidized starch, as well as the chemical bonds between the hydrophobic AESO and PEI molecules.