Influence of pH on the structure and properties of soy protein/montmorillonite nanocomposite prepared by aqueous solution intercalating

Abstract The soy protein isolate (SPI)/montmorillonite (Mt) nanocomposites were successfully prepared in aqueous media with different pH values. And then, the SPI/Mt composite plastics with glycerol as plasticizer were obtained via a compression molding process. The electrostatic surface potential has been calculated to investigate the surface charge distribution of the soy protein subunits. The results revealed that the structure of the SPI/Mt nanocomposites was strongly depended on the pH environment during the preparation process. The intercalated nanocomposites were obtained at pH = 1, 4.6 and 12.5, whereas exfoliated ones were prepared at pH = 3 and 10, indicating a significant influence of the solution pH values. The heterogeneous distribution of the surface positive charge caused the positive-charge-rich domains for soy protein bearing net negative charge to anchor into the interlayer space of Mt The mechanical strength of the SPI/Mt plastics was significantly improved as a result of the strong interaction and the fine dispersion of the Mt layers in the SPI matrix.