Preparation Of Reverse Osmosis Composite Membrane By Low Temperature Plasma Modification And Interfacial Polymerization

At present,the main product of reverse osmosis membrane is polyamide reverse osmosis composite membrane.The support membrane and the functional skin layer of the reverse osmosis composite membrane are two different materials,and the performance of the composite membrane can be improved by optimizing each part separately.In this paper,the properties of support membrane and the preparation conditions of functional layer were taken as the starting point.The effects of support membrane properties and interfacial polymerization parameters on the performance of reverse osmosis membrane were investigated.The properties of reverse osmosis composite membranes were improved by optimizing the properties of support membranes and interfacial polymerization conditions.Firstly,reverse osmosis composite membranes were prepared by direct interfacial polymerization on polysulfone(PS)support membranes.The effect of interfacial polymerization process parameters on the performance of reverse osmosis composite membrane was investigated.The orthogonal design method was used to design the experiment,and the influencing factors of interfacial polymerization were selected as follows:concentration of water monomer,concentration of oil monomer,concentration of additives,pH,reaction time,post-treatment temperature,post-treatment time.Combined with variance analysis,the effect of each factor was obtained by using salt rejection rate and flux of composite membranes as indicators.The optimum conditions were determined as follows:concentration of water monomer(1.5%),concentration of oil monomer(0.15%),concentration of additives(0.15%),pH(10),reaction time(40s),post-treatment temperature(70?),post-treatment time(15min).The flux of the reverse osmosis composite membrane prepared by the optimal solution was 20.34(L/m~2·h),and the rejection was 92.78%.Secondly,reverse osmosis composite membranes were prepared by interfacial polymerization of acrylic acid(AA)modified by low temperature plasma initiated liquid phase graft copolymerization on polysulfone(PS)and polyvinylidene fluoride(PVDF)support membranes to study the effect of support membrane modification on the properties of reverse osmosis composite membranes.The experiment was designed by uniform design method to determine the experimental factors and modification conditions on the performance of the composite membrane:the effects of discharge current,discharge duration,grafting solution concentration and grafting time.Combining with regression analysis,the inversion contour map is drawn to optimize the equation and select the best factor level.The optimum modification conditions were determined as follows:(1)PS support-discharge current(4A),discharge time(7 min),concentration of grafting solution(70%),grafting time(180 min).The experimental results show that the reverse osmosis composite membrane rejection rate is 95.83%and the flux is 23.84(L/m~2·h).(2)PVDF support-discharge current(4A),discharge duration(2min),concentration of grafting solution(70%),grafting time(180min).The experimental results show that the reverse osmosis composite membrane rejection rate is 83.65%and the flux is 25.62(L/m~2·h).Finally,the interception rate and flux of modified and unmodified reverse osmosis composite membranes were compared and analyzed,and combined with the morphology of membrane surface by scanning electron microscopy(SEM).Comparative analysis of the SEM images revealed that the surface of the support exhibited a"ridge valley"structure after interfacial polymerization,indicating that the polyamide functional layer was formed on the surface of the support.After modification,the"ridge valley"structure of the polyamide layer on PS support membrane appears to be connected,while the composite film on PVDF support membrane appears to be connected with flaky structure.The results showed that the hydrophilicity of the modified basement membrane was improved,the water phase spread was more uniform,and the crosslinking degree of the polyamide layer was higher.In this paper,the influence factors of interfacial polymerization and the properties of support on the performance of reverse osmosis composite membrane were investigated.The performance of reverse osmosis composite membranes prepared by using PS as the support was improved by plasma modification.The modification of PVDF support membranes by low temperature plasma also provides a feasibility study of hydrophobic support membranes for preparing reverse osmosis composite membranes,and provides a way to expand the selection range of base membranes for reverse osmosis composite membranes.