Study On Nano-Silica Polyvinylidene Fluoride Composite Membrane For Separation Of Chinese Yam Polysaccharide

Till now, membrane separation technology has been applied to chemistry industry, food processing and medicine technology widely. Its operation process is simple, costing is inexpesive and it can be used at room temperature. So it can be used to deal with materials sensitive to heat. Membrane materials include natural materials, organo-polymer materials and inorganic marerials. Now membrane material is one of the most important matters in membrane technology and the properties of the membrane correlate to its material closely.Polyvinylidene fluoride (PVDF) is a good membrane material and it has good chemical stability and heat stability. A marked characteristic of PVDF membrane to other membrane material is that it has good hydrophobic property, so it can be fouled easily. The resistance is great and the flux is small when it is used to deal with water-based liquor. The problem that how to enhance the property of resisting fouling of PVDF by the method of hydrophilization process and reduce the power energy in membrane operation is the most needed resolved.First, all factors in PVDF membrane preparation were examined and the optimal condition of membrane preparation was gotten. The content of PVDF was wt.16%, PEG was wt.8% and the coagulating bath temperature was 30℃.Then a composite membrane was made by adding nano-SiO₂ to PVDF. It has the properties of resisting high temperature, good machine property, good chemical stability and good hydrophilic property. To prevent the agglomeration of nano-SiO₂,γ-aminopropylthriethoxysilane was used to modify it. The experiment results showed that the effect of infiltration and separation was optimal when the mass of nano-SiO₂ added was twice of the coupling reagent and the hydrophilic property of the composite membrane was optimal when the mass of PVDF was four times of the modified SiO₂.At one time, the composite membrane was used to separate Chinese yam polysaccharide. The optimal methodology condition of separating Chinese yam polysaccharide by composite membrane was gotten by examining every factor which affected the property of the composite membrane. The yield of polysaccharide could reach 74.7% in this operation condition.Besides, the mechanism of resisting fouling of the composite membrane was discussed and the problem how to enhance the membrane's hydrophilic property and improve its property of resisting fouling by adding SiO₂ to it was expounded.