Study On Preparation And Performance Of PVC Modified Ultrafiltration Membrane

Polyvinyl chloride (PVC) has a wealth of production, good acid and alkali resistance and wear resistance. So it has been widely used in the area of ultrafiltration. But the poor heat resistance, mechanical strength and hydropHilicity of PVC membrane greatly restrict its application.No complete and mature membrane-forming mechanism can be referenced, so the preparation of PVC membrane and its characteristics must be explored in the first place. In this paper, polymer concentration, additive content, evaporation time and the gelation temperature were used to study in order to get the optimal preparation process conditions of PVC ultrafiltration membrane. Then the modification of PVC UF membrane was studied. Organic blending and inorganic-organic blending modification were used. And the following conclusions were got.The optimal preparation technological parameters of PVC ultrafiltration membrane were determined as follows:the polymer concentration 18wt.%, anhydrous lithium chloride 6wt.%, PEG400 2wt.%, water bath temperature 0℃ and evaporation time of membrane 1min in the casting solution. PVC ultrafiltration membranes were prepared under above technology, which good separating performances were as followed:pure water flux 630 L·m-2·h-1, rejection to above 96% of BSA. And there are good surface shape and cross section structure. The Flory-Huggins equation is used to calculate the PVC ternary membrane system pHase diagram. And calculation results agree well with experimental data.PS and ABS were selected to study organic blending modification for PVC UF membrane. The experiment shows that the immiscible ratio of PS and kinds of inorganic salt is lower. And the compatibility of PVC and PS is poor, unable to blend.The compatibility of PVC and ABS is good. So the PVC/ABS blend ultrafiltration membranes were prepared by special compatibility, which good separating performances were as followed:pure water flux 340 L·m-2·h-1, rejection to above 95% of BSA. The blend membranes were used under the high pressure and high temperature for a long time. The results shows rejection rate of blend membrane is still a decline. But compared with pure PVC UF membrane, the declining rate of rejection rate tends to slow down.The calcium silicate was selected to study inorganic-organic blending modification for PVC UF membrane as inorganic material. The experiment shows that the blend membrane of 5wt.%calcium silicate content has good mechanical strength, thermal stability and alkali corrosion resistance. The blend membranes were used under the o.4 MPa for 5h, the rejection rate still maintained above 96%to BSA. And it were used under the 50 ℃ temperature for 5h, the rejection rate still maintained above 94% to BSA. Blend membranes was soaked in alkali solution (pH=13) for 24h. The membrane surface did not show damage, and the rejection rate still remained at above 96% to BSA. Another was used to soak in acid solution (pH=2) for 24h. The membrane surface showed obviously damage, and the rejection rate dropped significantly to BSA. And Blend membrane structure adjustment is accomplished by controlling the membrane preparation process. Its intercept molecular weight range is expanded from 2000～67000, which make it have more practical value.