Study On The Control Method Of Microstructure Of Chlorinated Polyvinyl Chloride Ultrafiltration Membrane

As a cost-effective separation technology,ultrafiltration has been widely applied in various modern industrial fields.The development of novel ultrafiltration membranes and the regulation of membrane structure have always been the focus for membrane preparation and the urgent demands of membrane application research.It has been found that chlorinated polyvinyl chloride(CPVC)with excellent performance and moderate price has a good application prospect as membrane material.And the properties of CPVC membranes obtained by immersion precipitation phase separation had significant advantages over the other methods.However,the structure uniformity and the separation performance of CPVC membrane are still to be improved.For the above problems,this study introduced the single and compound additive into casting solution,and by controlling the phase transformation process of casting film to obtain CPVC membranes with highly selective permeability.The mechanism of various additives on CPVC membranes was discussed via the characterization of membrane structure and properties.The study first discussed the effects of commonly used hydrophilic small molecules(propylene glycol,PEG 400,PEG 200)and amphiphilic additives(Pluronic PE6400,Tween-20)on the structure and properties of CPVC membranes.The results showed that when 8 wt.%hydrophilic small molecules was added to casting solution,the pure water flux of CPVC membranes was up to 327.1 L·m-2·h-1,BSA rejection was 98.8%,and high mechanical strength could be maintained;when the ratio of amphiphilic additives was 10 wt.%,the pure water flux of CPVC membranes was prominently increased to 818.7 L·m-2·h-1(which was nearly 10 times the original membrane flux),BSA rejection dropped to 85.7%and mechanical properties had a partial loss.We founded that the improvement of membrane penneability by hydrophilic small molecules was much lower than that of amphiphilic additives;while the amphiphilic additives significantly reduced the skin layer thickness of CPVC membranes,the separation performance decreased obviously,and the mechanical properties were more lost.The limitations of single-component additives hinder the further development and application of CPVC membranes.Therefore,the propylene glycol(PG)and Tween-20 with better performance in the two types of additives were made into a total amount of 10 wt.%by weight of the compound additive and introduced into the casting solution.Moreover,we adjusted the ratio of two components,and the effect of compound additives on casting solution system and the morphology and properties of CPVC membranes was studied by series characterization.The results showed that compound additive could give full play to the advantages of each component.The casting solution could form a homogeneous system with lower thermodynamic stability,and the instantaneous liquid-liquid phase separation and rapid precipitation could work together on phase inversion process.The pore size of membrane surface was increased and the pore size distribution was more uniform.The selectivity and permeability of CPVC membranes were simultaneously improved.When PG/Tween-20 = 3/7 in the compound additive,the most probable pore size of membrane top surface reached 24.3 nm,the pore size distribution frequency was 86.7%,the pure water flux was increased to 955.2 L·m-2·h-1,and BSH rejection reached 95.5%.Meanwhile,the loose gradient top layer led to membrane with high mechanical strength and good surface chemical stability,and increased the flux recovery rate to 73.3%.