Soy protein isolate films with improved property via a facile surface coating

Abstract A facile surface coating approach was explored, in this paper, for soy protein isolate (SPI) films to overcome their drawbacks of high stiffness and low water resistance. Scanning electron microscope images confirmed the formation of polyurethane (PU)-coated SPI films with variable thickness of PU coating layer from 2.46 to 14.54 μm. The optical transmittance and appearance of the coated films were maintained well compared with the neat SPI film owing to the low thickness of PU layer. The surface hydrophobicity of SPI film was greatly increased after being coated with PU, and the neat and coated SPI films showed exponential and linear decline profiles of contact angle with time, respectively. The water resistance, water vapor barrier, and mechanical properties of the neat SPI film were enhanced upon coated with PU, and the properties can be well modulated controlling the thickness of coating layer. Furthermore, good interfacial interactions were existed between the matrix and coating layer, suggesting of durability of the resultant trilayer films. The results indicated that coating SPI with a polymer with good water barrier property and toughness was an effective manner for fabrication of SPI-based materials with improved properties.