Effect of Salicylic Acid on the Mechanical Properties and Water Resistance of Soy Protein Isolate Films

Soy protein composites films (SF) have been prepared using soy protein isolate (SPI), salicylic acid (SA) and glycerol as a plasticizer. To prepare water resistant soy protein composites films (SF-B), 2, 2-diphenyl-2-hydroxyethanoic acid (DPHEAc) was used. Different amounts of SA were added in both SF and SF-B films. The results showed that the SF-B films with 0.5% (wt) of SA had higher tensile strength and modulus with low water uptake than that of SF films at same amount of SA. Contact angle analysis also indicated that the SF-B films showed hydrophobic surface. Thus both lower levels of water uptake and hydrophobic surface indicated high water resistance of the materials. Higher transmittance value and increased intermolecular hydrogen bonding showed higher compatibility between SPI and SA. This work provided a new approach in the use of SA in water resistant soy protein films for enhancing the processing window.