Environmental-friendly Soy Protein Isolate Blend Films

Soy protein isolate (SPI)-based films have been extensively studied as a potential replacement for petroleum-based plastic films. Blending is an effective method for the modification of polymers because of the strong economic incentives for the use of polymer blends: this method can endow polymers with enhanced properties by conventional processing techniques. In this thesis, SPI-based blend films were fabricated and their properties were investigated to ensure these films could be applied in packaging, edible packaging and drug release fileds.Blend films from nature soy protein isolates (SPI) and synthetical poly (vinyl alcohol) (PVA) compatibilized by glycerol were successfully fabricated by a solution-casting method in this study. XRD tests confirm that the SPI/PVA films were partially crystalline materials and the addition of glycerol will insert the crystalline structure and destroy the blend microstructure of SPI/PVA. The tension tests show that SPI/PVA films exhibit both higher tensile strength and percentage elongation at break point. Thermogravimetric analysis and water solubility tests show that SPI/PVA blend polymer has more stable stability than pure SPI. Heat-sealing test results showed that both of PVA and glycerol contents greatly affected the melting behaviors and heat of fusion (Hf) of SPI/PVA blends; these blend films had a higher melting temperature (Tm) than pure SPI films. Peel strength and tensile strength tests indicated that the long molecular of PVA had the main function to enhance the mechanical properties above the melting temperature. Crosslinking between glycerol molecules and SPI reduced the interstitial spaces in the protein matrix, thus decreasing the rate of diffusion of water molecules through the films. Moisture adsorption and sorption isotherm data of SPI/PVA/glycerol were mathematically fitted to the GAB model. With increasing PVA content, the equilibrium moisture content (EMC) of film samples clearly decreased. Photo-oxidative degradation and biodegradation behaviors test results showed that PVA could dilute the yellow color and make the SPI-based films less darkness in application and the transparency of SPI/PVA films at various stages of degradation was improved.Another blend films based on carboxymethyl cellulose (CMC) and SPI compatibilized by glycerol were prepared by solution casting. The effects of CMC content on blend structure, thermal stability, water solubility and water sorption, and mechanical properties were systematically investigated. FTIR spectra showed that Maillard reactions occurred between CMC and SPI, and XRD scans indicated that the Maillard reactions greatly reduced the crystallinity of SPI. According to DSC analysis, CMC/SPI blends had a single Tg between 75oC and 100oC, indicating that CMC and SPI form one phase blends. Increasing the CMC content improved the mechanical properties and reduced the water sensitivity of blend films. The results indicate that the structure and properties of SPI edible films were modified and improved by blending with CMC.SPI/PVA blend films crosslinked by ferulic acid (FA) were successfully fabricated by a solution-casting process, and salicylic acid was carried by in-suit method. The results showed that FA could make the SPI/PVA forming crosslinked structure. The crosslinked structure would achieve the max. value using at lest 150mg/100g FA. The crosslinked structure enhanced the thermal stability and mechanical properties. By in-vitro release study,a higher amount of FA resulted in a lower salicylic acid release rate.And the release mechanism changed from anomalous diffusion to non-Fick diffusion.