Preparation And Investigation Of Soy Protein Films Modified With Blending Polyamic Acid Salt

In this study, the conditions to prepare SPI films with glycerol as plasticizer were explored. The effects of glycerol amount, pH and bath temperature on the Tensile strength(TS), Elongation at break(E), Water vapor transmission rate(WVP) were researched. With TS and WVP as indicators, The best conditions for preparation were optimized by Response surface experiment. Then a novel biodegradable SPI material was prepared by blending Polyamic acid salt(PAS) and modified SPI solution. Microstructure and thermal Properties of the films were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Differential scanning calorimetry (DSC) analyses, Scanning electron microscopy (SEM). The effects of blending and PAS content on the structure were also discussed. Furthermore, a series of optical properties, water resistance, water vapor permeability and mechanical properties of the films were measured, and the effects of PAS content on the properties were discussed by correlation analysis. The main results obtained were as follow:Single factor experiment showed that glycerol amount, pH and bath temperature had great impact on the performance of SPI films. When the glycerol amount ranged from 1% to 4%, the TS first increased and then decreased, while E and WVP kept increase. When the pH ranged from 8 to 11, TS and E increased, WVP decreased. When bath temperature ranged from70℃to 90℃, TS and E increased, WVP decreased. But the upward trend of E is gentle.According to the Response surface experiment. The response model established with TS and WVP as indicater were significantly. The optimal process to prepare SPI films were as follow:the amount of glycerol was 3.44g, pH value was 9.75, bath temperature was 88.16℃. And the TS and WVP value of resultant SPI film were consistent with theoretical predictions. According to the analysis of three-dimensional surface plot, the effect of glycerol amount, pH and bath temperature on the TS were all significant, the effect of glycerol amount and pH on the WVP were significant. Furthermore, the interaction of glycerol and pH also had great impact on TS.The PAS/SPI films were prepared by the method of casting solution. The analysis of material structure confirmed that there exist strong molecular interactions between PAS and SPI. The Analysis of the performance of the films showed that, compared with SPI films, the TS and E of the SPI/PAS films increased by 54.98% and 61.23% respectively, transmittance increased from 3.23% to 5.67%, while the WVP decreased to 64%. In addition, the water resistance ability of them were good. Compared with films prepared by other methods, the PAS/SPI films also exhibited better light-transmitted, mechanical and water barrier property. After buried for 33 days, the mass loss rate (i.e. degree of degradation) of SPI/PAS films can up to 78.44%, showing good biodegradability. The correlation analysis showed that, the amount of PAS was significantly positively correlated with TS and E,and significantly negatively correlated with the WVP, which indicated that the addition of PAS can greatly improve the performance of SPI film. The studies above confirmed that the blending method was feasible, and the new PAS/SPI material had the potential to be used as biodegradable green packaging material.