Preparation Of PVC/PU Blend Ultrafiltration Membrane And Separation Of The Astragalus

PVC is a widely used and low-cost membrane material, forming spontaneously wrinkle-prone and relatively brittle membrane. PVC membrane has a stronger repelling force on saccharide compounds, but its hydrophilicity is poor, whereas polyurethane(PU) has strong hydrophilicity and good flexility,and membrane-forming is porous structure. In order to prepare ultrafiltration membranes which can effectively separate polysaccharide, and have the high-throughput, low cost, and have the certain separation properties and difficult blocking , we select membrane material that blended the PVC and a small amount PU, the blending can complement the performance of the two materials. Thereby the blended membrane have many characteristics, such as the low-cost, the excellent film-forming properties, not very strict requirement of conditions,the chemical stability,the good mechanical properties, the high water flux and good performance.By the experiments, to prepare PVC/PU blended membrane, and to study the factors how impacted the capabilities of PVC/PU blended membrane in the process, the results showed that the polymer concentration, the blending ratio, coagulation bath has a greater influence on membrane water flux and pore size. Low polymer concentration can make the casting solution’s viscosity too low, scraping out the membrane toughness is low and more vulnerable, not conducive to forming a more detrimental to industrial applications. However, when the concentration is too high, will make the casting solution’s viscosity too high, forming a compact structure, and the membrane flux declined sharply.By a comprehensive comparison, in preparation of PVC/PU blend membrane, the concentration of casting solution as 16%, in the polymer PU ratio of 20%, coagulation bath temperature is 22℃, under the conditions we can make the good water flux, interception rate porous membrane. The most water flux of the membrane can reach to 388.6 L/m2·h, The porosity and the retention rate are 75.8% and 91.7%.Adding SiO2 to the casting solution can increase the blend membrane water flux effectively, when the SiO2 as the solid in the casting solution accounts for 10%, the water flux can reach to maximum 428.6 L/m2·h, but the retention rate is 74.1%. However when the SiO2 as the solid in the casting solution accounts for 6%, the retention rate can reach to maximum 84.3%.The results showed that we can make the better blend membrane by adopting the suitable mixing ratio, temperature of coagulation bath, the proper additive. With the subject of self-made PVC / PU blend membrane separate Astragalus polysaccharide, Membrane pollution using hydraulic reverse wash, and the flux recovery rate is 90%.