PACMO/PMMA Amphiphilic Block Polymer Blending Modified PVDF Membrane And Performance Research

PVDF is a commonly used polymer membrane material.However,due to its own strong hydrophobicity,membrane fouling severely limits its application in water treatment and other fields.It is an important strategy to improve the membrane fouling resistance by improving the hydrophilicity of the membranes.Based on the characteristic of surface segregation of amphiphilic polymers during phase inversion,poly(methyl methacrylate)(PNMMA)has a good compatibility with PVDF and was selected as the hydrophobic segment.Non-toxic,biocompatible,highly hydrophilic,and electrically neutral poly(acryloylmorpholine)(PACMO)acted as a hydrophilic segment.Amphiphilic triblock copolymers,PACMO-b-PMMA-b-PACMO(PAMA),were prepared by reversible addition-fragmentation chain transfer activity/"controlled" free radical polymerization(RAFT).A series of PVDF/PAMA blend membranes were prepared by non-solvent phase inversion.(1)The PVDF content in the casting solution is the most important factor affecting the physicochemical structure and properties of the blend membranes.Firstly,the effects of different PVDF contents on the hydrophilicity,mechanical properties,permeability and anti-fouling properties of the membranes were studied under the condition of a certain PAMA modifier concentration.The results showed that the pure water flux of PVDF-1 0/1.0 membrane was 236 L·M-2·h-1,which was 21.8 times higher than that of PVDF-10/0,and the BSA rejection was 98.3%.Additionally,98.2%flux recovery rate indicated that PVDF-10/1.0 was the better proportion in the PVDF/PAMA casting solution system.Studies have shown that the moderate increase of polymer concentration in the casting solution and the introduction of modifiers were beneficial to construct a small pore size,high-flux separation membranes with anti-fouling and high BSA rejection.(2)Secondly,the effect of PAMA with different hydrophilic segment lengths on the structure and properties of PVDF/PAMA blend membrane under the condition of certain PVDF content in casting solution was studied.It was found that with the increase of length of hydrophilic segment,the contact angle of the membranes became smaller,the surface pore size and porosity increased,and the pure water flux increased remarkably.When the ratio of polymerization degree of PACMO to PMMA was 1:1,the surface of the membrane had the highest hydrophilic substance coverage,and the pure water flux was 109 L·m-2·h-1,which was 3.2 times that of the pure membrane.The flux recovery rate was 99.3%,the BSA rejection was 97.1%,and the optimal anti-fouling effect was obtained.The pure water flux of the modified membranes was monitored for 30 days,and the flux did not change significantly,indicating that the modified membranes had excellent performance.(3)Finally,the studies optimized the structure and surface segregation behavior of the blend membranes by adjusting the content of PAMA and PVDF in the casting solution.Studies have shown that the increase in the percentage of modifier accelerated the phase separation rate and promoted the increase of surface pore size and porosity.When the modifier content was 2%(membrane PVDF-9.5/1.5),the hydrophilic segments on the surface of the modified membrane had the largest coverage on the surface of the membrane,which improved the hydrophilicity and fouling resistance of the membranes.The surface pore size was 14,1 nm,the pure water flux was 239 L·m-2·h-1,which was 8 times the flux of unmodified membrane,while maintaining high BSA rejection(97.7%)and excellent anti-fouling performance(flux recovery rate was greater than 97%).