Effect Of Coagulation Bath Conditions On The Structure And Properties Of PVDF Composite Membrane

Clean water is an important resource for human life and ecosystems.However,due to population growth and the rapid development of economy and urbanization,the pressure on the shortage of water resources is increasing,which urgently requires cost-effective water treatment technology to produce high-quality clean water.According to the actual needs of this paper,based on the research of the hydrophilic modification of PVDF membrane by introducing hydrophilic ionic liquid through in-situ polymerization,PVDF composite membrane was prepared by immersion precipitation phase inversion method.In this paper,the mambrane structure is adjusted by changing the conditions of the coagulation bath.The specific research contents are as follows:(1)By changing the content of ethanol in the coagulation bath(ethanol:deionized water=0:100,15:85,30:70,45:55,60:40,wt%),explore the structure and properties of the PVDF composite films were studied.The addition of ethanol in the coagulation bath caused the delayed phase separation of the copolymer during the film formation and reduced the film formation speed,thereby changing the internal microstructure of the film.Through scanning electron microscopy and other testing methods,it was found that the structure of the fracture surface of the composite membrane has changed,and the average pore size and porosity increased,resulting in the pure water flux of PVDF composite membrane increased to 718.6 L/m~2h.At the same time,the addition of 1-butyl-3-vinylimidazole(ILs)ionic liquids makes the membranes hydrophilic.The separation rate of bovine serum albumin(BSA)and orange G dye reached a high rejection rate,the rejection rate of rhodamine 6G can reach 100%,and the dye flux recovery rate can reach up to 98%.This shows that the antifouling ability of the membrane has been improved.However,when the ethanol content in the coagulation bath reached 60%,the higher flux caused the retention effect of the membrane to begin to decrease,which was not conducive to the improvement of the membrane's anti-fouling performance.(2)The effects of different coagulation bath temperatures(0°C,10°C,20°C,30°C,40°C)on the comprehensive performance of PVDF composite membrane structure and anti-fouling ability were studied.By controlling the temperature of the coagulation bath,the surface and internal pore diameters of the PVDF composite membrane were changed.As the temperature of the coagulation bath decreases,the porosity of the membrane increases and the pure water flux increases,the flux which can reach 853.3 L/m~2h.The dense cortex can effectively trap pollutants.The retention rate of BSA and Orange G dye can reach 98%,and the maximum rejection of Rhodamine 6G dye is 100%.Through the circulating filtration of the dye,the flux recovery rate has also reached a good level,which has improved the anti-pollution performance of the PVDF composite membrane.