Studies On Processing And Properties Of Soy Protein Isolate Plastics

Soy protein isolate(SPI) plastics are typically completely biodegradable plastics. And soy protein, a by-product of the production of soy bean oil is a kind of widespread and abundant natural polymers. But, the brittleness, water-sensitivity and complexity of SPI plastics restricted their research and development. The main objective of this thesis was to prepare SPI plastics by physical modification and to improve the processibility, mechanical properties and water-resistivity of SPI plastics. The main achievements of this thesis are:1. Effectively improve the processibility, brittleness and water resistance of SPI plastics after a simple physical modification.2. Bring up that glycerol plasticized SPI plastics have glycerol-rich micro domain and protein-rich micro domain, and analysis the SPI plastics relationship between property and structure. Specific work list as follows:1. Researched the effect of plasticizer on the structure and properties of SPI plastics. The mechanical properties and water resistance of glycerol plasticized SPI plastics were good. With the increase of glycerol content, tensile strength decreased and elongation at break increase, water absorption also increased. With the increase of water content, tensile strength decreased, and elongation increased first, but then decreased. It had little effect on its water absorption. By XRD and DMTA analysis, the glycerol plasticized SPI plastics had glycerol-rich micro domain and protein-rich micro domain. With the increase of glycerol content, the glass transition temperature of glycerol-rich micro domain shifted to lower temperature. Through the experiment of torque, glycerol and water can significantly reduce the SPI processing torque, improve its mobility.2, Na2SO3 reduced the tensile and impact strength of SPI plastics, and increased their water absorption, but the products became more and more light. XRD and DMTA analysis showed that adding Na2SO3, their crystallinity increased a little, and the glass transition temperature of glycerol-rich micro domain shifted to higher temperature. The appropriate alkali treatment will improve the tensile and impact strength properties of SPI plastics. However, with the increase of NaOH content, the water absorption increased, and products became more and more black, opaque. XRD showed that the peak of SPI plastics treated by alkali at 21.4°was at almost disappeared. DMTA shows that with the enhancement of alkaline, the glass transition temperature of glycerol-rich micro domain is gradually shifted to higher temperature. TG showed that the alkali treatment mainly affects the tertiary structure of SPI.3, Successfully prepared SPI/PVA plastics. PVA significantly improved the tensile strength of SPI/PVA plastics, but had a certain impact on the toughness of SPI/PVA plastics. The addition of PVA can significantly drop water absorption of SPI/PVA plastics. XRD and DMTA showed that the addition of PVA can significantly damage crystalline structure in glycerol-rich micro domain, and shift the glass transition temperature in glycerol-rich micro domain to higher temperature. DSC showed the addition of PVA can shift the SPI/PVA plastics melting peaks to higher temperature, but when PVA content was too many, it would occur reunion and affect its property.