The Application And Research Of Hydrophilic Modification Of Poly (Vinyl Chloride)(PVC) Membrane By The Additive Of Cellulose Acetate (CA)

The separation technology of membrane is often applied in treatting wastewater these year because it has a lot of advantages,such as lower energy consume, high separation efficiency,no second pollution, low operation expenses and small equipment size,and so on. But its development is seriously obstructed by its disadvantages, such as lower output, easier to be polluted, higher construct price contrast with traditional wastewater treatment technologies. This paper prepared a new polymer membrane, PVC/CA blend membrane, which is low price, high water flux, high intension and not easy to be polluted.The design of this research and its main content are showed as follows:(1) The miscibility of PVC/CA blending system was investigated by the method of shear viscosity, intrinsic viscosity, dynamic thermomechanical analysis(DMA). The curve of the viscosity-constitute of the PVC/CA blending system was nonlinear or look like S, which indicated that PVC and CA were partly miscible. Then the quantitatively research for the compatibility of the blending system was discussed by intrinsic viscosity method, and the results showed that,when PVC/CA=9/1,8/2,7/3,3/7,2/8,1/9,the blending system was compatible. The conclusions from DMA agreed with the result of intrinsic viscosity.(2) The permeability and mechanical properties of the blend membrane were investigated with the changes of the polymer concentration and the blending ratio in the casting solution, and the best blending ratio and the best polymer concentration were confirmed. The results showed that, the optimum blending ratio of the casting solution is7/3, and with the conditions of that the polymer concentration of the casting solution was17%, the blending membrane would have the best performance.(3) By measuring the water contact angles of PVC/CA blend membrane, the wettability of membrane surfaces were estimated. The results showed that, the water contact of pure PVC membrane is70.69, then when the polymer CA was added to it, the water contact angles decreased sharply, for example, the water contact angle is55.57for the PVC/CA=7/3blend membrane. This results proved that PVC membranes with blending with CA are more hydrophilic than the neat PVC membrane. X-ray photoelectron spectroscopy(XPS) analysis confirmed the enrichment of CA on the PVC membrane surfaces due to surface segregation for lowing of interface free energy. The shift of C11s binding energy from285.7ev to284.98ev indicated that there are interactions between PVC and CA.(4) The permeability and mechanical properties of the blend membrane were investigated with the changes of the temperature of the casting solution. The temperature of the casting solution were90℃,75℃,60℃,45℃and30℃,respectively. The result confirms that, the permeability and mechanical properties of the blend membrane were good, when the temperature of the casting solution is45℃。So the optimum temperature of the casting solution is45℃。The permeability and mechanical properties of the blend membrane were investigated with the changes of volume percentage of DMAC in the coagulation bath. The volume percentage of DMAC in the coagulation bath were0%,10%,20%,30%,40%and50%,respectively. The result confirms that, the addition of DMAC in the coagulation bath, has a little impact to the mechanical properties of the blend membrane, but the pure water flux is low sharply. So the optimum coagulation is pure water.(5) The properties of blend membrane were investigated with the additive of PEG,which has different molecular weight, and PVP-k30. The result confirms that,all of the PEG make the pure water flux of the blend membrane decrease sharply, so all of them are not suitable additive for the PVC/CA membrane.PVP-k30also make the pure water flux of the blend membrane decrease,but the retention rate is improved,so it is the suitable additive.The influence of nano SiO2on the Pure Water Flux and the hydrophilic of blend membrane was investigated. The results show that a moderate amount of nano SiO2to join can improve the Pure Water Flux blend membrane, but too much of it will make the Pure Water Flux decreases. The best content of the additive, nano SiO2is3%. Finally, the hydrophilic modification of nano SiO2on the Pure Water Flux of blend membrane was investigated, it is indicated that the polymer CA than nano SiO2on blend membrane hydrophilic modification effect is good.