| The polyamide reverse osmosis composite membrane prepared by the interfacial polymerization method is usually composed of a support membrane and an ultra-thin functional layer.Because the two parts are not the same material,and the preparation method is different,they can be controlled and improved independently.The separation performance of the composite membrane is determined by the interaction of the support and the polyamide functional layer.Up to now,the research on the support has mainly focused on improving its characteristics,and the material of the support is usually PS material.It is difficult to interfacial polymerize on the surface of the PVDF support with good chemical stability and high mechanical strength to form a complete dense polyamide layer due to its relatively hydrophobic nature.In this work,low-temperature plasma technology is mainly used to investigate the effect of plasma treatment conditions on the separation performance of the prepared composite membrane by direct irradiation treatment and initiation of graft polymerization.And the feasibility of the PVDF membrane as the support of the reverse osmosis composite membrane was explored,and the process parameters of interfacial polymerization were also discussed.First,based on the previous work of the research group,the influence of four time factors of the interfacial polymerization process,namely water immersion time,water drying time,reaction time and standing time,on the formation of polyamide functional layer and the separation performance of reverse osmosis composite membrane were discussed.The optimal time parameters of the interfacial polymerization process were obtained by single factor experimental analysis:the immersion time of water phase was 10min,the drying time of water phase was 20min,the reaction time was 60s,and the standing time was 4min.The rejection rate of the composite membrane prepared by interfacial polymerization was finally96.40%,and the flux was 13.47L/m~2·h.Second,the effect of separation performance of the prepared reverse osmosis composite membrane based on direct plasma treatment of the support was investigated.The influence of four factors such as support material,gas atmosphere,discharge duration and discharge current on the separation performance of reverse osmosis composite membrane prepared by interfacial polymerization after direct treatment of support by low temperature plasma was investigated through orthogonal test design.Through the range analysis and analysis of variance experimental results,the significance of each factor and the optimal combination result are consistent.Taking the rejection rate of the composite membrane as the decisive index,the optimal schemes are obtained:base material(PS),gas atmosphere(air),discharge duration(4min),discharge current(5.5A).Through the test of the contact angle of the support and the adhesion performance of the composite membrane,it is found that the direct treatment of the support by nitrogen and air plasma can improve the hydrophilicity of the support,the adhesion performance and separation performance of the composite membrane,and the more hydrophobic the support is,the more obvious the improvement effect is.The direct treatment of the support by argon plasma can reduce its contact angle,but the effect on the separation performance and adhesion performance of the composite film is not obvious.Finally,the influence of low temperature plasma on the separation performance of the composite membrane prepared on the surface of the support after graft polymerization was investigated.By comparing the separation performance of the composite membrane prepared by grafting four monomers containing hydroxyl group,carboxyl group,amino group and amide group on PS support by argon low temperature plasma,the best graft monomer was determined to be AA containing carboxyl group.The uniform test design was used on PS and PVDF support respectively to investigate the effects of discharge current,discharge duration,grafting duration,and grafting concentration on the separation performance of the reverse osmosis composite membrane prepared by graft modification of the support membrane.The optimal process conditions of grafting AA monomer on the two supports were obtained by quadratic polynomial stepwise regression analysis.The optimal grafting process conditions on the PS support are:discharge current 5A,discharge time 11min,grafting time 30min,graft concentration 30%.The rejection rate of the reverse osmosis composite membrane prepared by the optimal process is 97.86%,and the flux is 13.71L/m~2·h,which is slightly improved compared with the composite membrane prepared on the unmodified support.The optimal process conditions of low temperature plasma graft modification on PVDF support are:discharge current 5A,discharge time 11min,grafting time 50min,graft concentration 30%.The experimental results showed that the rejection rate of the reverse osmosis composite membrane prepared by the optimal process is 86.32%,which is 56.32%higher than that of the composite membrane on unmodified support,and the flux is 22.79L/m~2·h,which is 38.12%lower than that of the composite membrane on unmodified support.Low temperature plasma grafting of AA monomer can improve the hydrophilicity of the support membrane,increase the adhesion between the support and the functional layer,improve the separation performance of the composite membrane.The hydrophilicity of the support membrane and the separation performance of the reverse osmosis composite membrane prepared by interfacial polymerization on the modified support can be improved effectively by direct irradiation treatment of low temperature plasma and the initiation of graft polymerization.This paper provides a reference for expanding the selection range of the support membranes for the preparation of reverse osmosis composite membrane by interfacial polymerization,and also has a certain reference significance for improving the separation performance of reverse osmosis composite membranes. |
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