Abstract: Films was cast from a mixture of soy protein isolate (SPI) and calcium stearate (CaSt2) containing glycerol as a plasticizer. The structure and properties of the plastics were investigated using attenuated total reflectance-Fourier transform infrared, X-ray diffraction, thermal properties, tensile properties and water vapor permeability. The results showed that CaSt2 existed in two structural forms, in which the ions form as the main structure. The crystallinity of modified SPI film increased by 70.4%, and then the internal structure was more compact. The thermal analysis indicated that thermal stability of modified SPI film enhanced. As the concentration of CaSt2 was increased, the values of water vapor permeability decreased, when the content of 12 %, the capacity of water vapor barrier increased by 40 %; the elongation at break increased by 67.63 %.

Key words: soy protein isolate, calcium stearate, film, modification