The grafting of styrene on soy protein isolate (SPI) in 8 moL/L urea aqueous solution initiated by ammonium cerous nitrate-potassium persulfate was studied.The grafted copolymers were characterized by NMR.The results indicated styrene had been grafted on the SPI.The films were prepared from aqueous solutions of soy protein and its grafted copolymer at different pH and various plastizer contents.The tensile strength (TS) and the elongation (E%) of these films were determined.The results indicated that TS values of SPI-g-PSt films were higher than those of SPI films,whereas E values of SPI-g-PSt films were lower than those of SPI films.The results also indicated TS and E of SPI-g-PSt and SPI increased with the increasing of pH and TS of SPI-g-PSt films increased with the increasing of graft percentage of copolymer.
A completely green pathway for the preparation of Ag nanoparticles was proposed, by using soy protein isolate （SPI） as stabilizer under UV irradiation and H2O as the environmentally benign solvent throughout the preparation. Transmission electronic microscopy （TEM） and zeta potential characterization results indicated that the Ag nanoparticles were stable and well dispersed with an average diameter about 13 nm, and X-ray diffraction （XRD） analysis of SPI/Ag composite nanoparticles confirmed the formation of metallic silver. UV-Vis spectrum showed that the Ag nanoparticles dispersion solution had the maximum absorbance at about 430 nm due to surface plasmon resonance of the Ag nanoparticles. Infrared spectroscopy confirmed that the polypeptide backbone of SPI was not cleaved during the conjugation process and that some active amino groups were oxidized. The SPI/Ag composite nanoparticles have excellent antibacterial activity against two representative bacteria, staphylococcus aureus （Gram positive） and escherichia coli （Gram negative） in the presence of SPI.
