Modification analysis of cellulose acetate on PVC/CPVC blended flat sheet membranes
Nowadays,polyvinyl chloride(PVC)is one of the commonly used membrane materials and it has good acid and alkali resistance and mechanical properties.However,the film-forming performance of PVC membranes is not very ideal currently,since the formed membrane has characteristics of strong hydrophobicity,low water flux,and poor toughness.Therefore,it is necessary to modify it to improve its hydrophilicity.Chlorinated polyvinyl chloride(CPVC)is obtained by deep chlorination of polyvinyl chloride,and it has better mechanical properties and thermal stability than PVC materials.Cellulose acetate is an acetate prepared by the reaction of cellulose with acetic anhydride mixture(or acetyl chloride).It has the advantages of excellent hydrophilicity and biocompatibility.Therefore,the blending modification of the three substances can improve the hydrophilicity and pollution resistance of the membrane,and provide certain toughness.PVC/CPVC/CA were prepared by phase transformation method,and the shear viscosity,infrared spectrum,surface morphology,cross section morphology,pure water flux,retention rate and flux recovery rate of the blend membranes at different blending ratios were studied.At the same time,the effect of esterification degree on the properties of the blended membranes was also studied.The results showed that the three materials had certain compatibility and could form a separation membrane with good performance when mixed in a certain proportion.The comprehensive performance was the best when the blending ratio of PVC/CPVC/CA was 70/10/20.Under this condition,when the pressure reached 0.1 Mpa,the water flux was 55.78 L/(m2·h),the retention rate for 0.1 g/L BSA solution was 64.67%,the flux recovery rate was 55.92%.And the comprehensive performance was the best when the blending ratio of PVC/CPVC/CDA was 65/10/25.When the pressure reached 0.1 MPa,the water flux was 91.21 L/(m2·h),the retention rate for 0.1 g/L BSA solution was 90.85%and the flux recovery rate was 56.93%.The results showed that the hydrophilicity and anti-pollution properties of the membranes were significantly improved.At present,there are few related studies on PVC blend membranes,and no study on PVC/CPVC/CA has been reported.In this paper,PVC/CPVC/CA were prepared by phase transformation method.The shear viscosity of casting solutions at different blending ratios was measured to analyze and discuss the film-forming properties.At the same time,the microstructure of the surface and cross section of the blend film were observed by field emission scanning electron microscopy(SEM).The hydrophilicity and separation performance of the membrane under different blending ratios were analyzed by water contact angles,pure water flux and retention rates.On this basis,the influence of esterification degree of cellulose acetate on the properties of the membrane was analyzed,which provides a certain choice for the modified materials of the PVC blend membrane and makes it have a broader market prospect in sewage treatment.
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