Study On Modification Of Soy Protein/Poly(Hydroxyalkanoate) By Macromolecular Assembly

Soy protein (SP), poly(3-hydroxybutyrate) (PHB), the polymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid (PHBV) are natural biodegradable polymers. But hydrogen-bonding, self-assembly in SP macromolecules and its hydrophilic property result in low water resistance or moisture resistance and unstable mechanical properties of SP. Moreover, britlleness of PHB and PHBV is high for their high degrees of crystallinity. In the study, based on characteristics of SP, PHB and PHBV, macromolecular assembly was formed to some extent or the states of macromolecular assembly was modified by blending or copolymerization. Resultingly, the properties of SP were improved.Firstly, a soy protein isolate (SPIG) with rich 11S was prepared by the difference in solubility of 7S and 11S in water at relatively low temperature. The water sorption of SPIG is lower than other SP products by the study on it.Secondly, SPIG/PHB, SPIG/PHBV and SPIG/LPHB (the PHB with low molecular-mass) were prepared by blending them respectively. Effects of PHB, PHBV and LPHB on improving properties of SP were researched. Mechanism of the improvement of the properties was proposed. Effects of glycol, glycerol, xylitol, epoxidized soy oil and triolein on SPIG/PHB were investigated. A SPI-co-PHB copolymer was prepared by solution-polymerization. Effect of the copolymeration on improving properties of SP was studied. The morphology and properties of all of the blends prepared here and the SPI-co-PHB were characterized by DSC, DMA, FTIR, SEM, PLM, 13C solid-NMR, the test of strength, BIC Particle Sizing, SDS-PAG, water sorption test and biodegradation rate test.It is revealed that hydrogen-bonds formed between SP and PHB, PHBV, LPHB, respectively, conversely, rigid self-assembling structures of SP, PHB, PHBV and LPHB privately were partly altered into intermacromolecular assembly, resulting in that PHB and PHBV could not assembled into big spherulites, or only formed lamellar-beams distributed in SP. The secondary crystallization of PHB and PHBV was inhibited also. Mechanical properties, water and moisture resistance and the stability of mechanical properties of the blends based on SP were improved because hydrophobic PHB and PHBV assembled to hydrophilic groups of SP and constructed a layer of film round the hydrophilic groups. It is indicated that toughness of SPIG/PHB was enhanced by glycol, glycerol, xylitol, epoxidized soy oil and triolein. However, high hydrophilicity of the former three additives decreased slightly water resistance of their blends. Conversely, hydrophobic nature of the farmer two additives increased lightly water resistance of the blends added the farmer. It is exhibited that PHB may copolymerize with SP. The self-assembly of SP and PHB privately was changed in the copolymerization. The strength and roughness of the copolymer based on SP were improved by copolymerization. Water resistance of the copolymer is high for copolymerizing PHB. It is indicated that the SP/PHA blends have higher biodegradation rates than pure SP. The biodegradation rate of SPI-co-PHB is near to pure SP.