Modification Of PVDF Membrane By In-situ Cross-linking Method And Its Application

In recent years,membrane separation technology has developed rapidly and widely used in the field of sewage treatment due to its high separation efficiency and easy operation.PVDF membrane has excellent mechanical strength,chemical stability and weather resistance.It is a common material for preparing ultra/microfiltration membranes and has a good application prospect in water treatment applications.However,due to the hydrophobicity of the PVDF membrane itself,some problems are encountered in the application: on the one hand,the hydrophobicity of the membrane surface increases the membrane pressure,thereby reducing the filtration flux;on the other hand,the hydrophobicity of the membrane leads to its Poor anti-pollution properties,easy to be contaminated in the application,resulting in a sharp decline in flux and reduced membrane life.Therefore,hydrophilic modification of PVDF membranes is an effective way to solve these problems.In this paper,two different ways base on P(MMA-co-GMA)and PEI were used to improve the hydrophilicity of PVDF membrane by in-situ cross-linking blending method.The morphological structure,Wettability,mechanical strength,and membrane separation performance and anti-contamination properties of membranes prepared by different methods was systematically investigated.P(MMA-co-GMA)and PEI were blended with PVDF and subjected to in-situ cross-linking copolymerization to prepare superhydrophilic and underwater superoleophobic membrane for oil/water emulsion separation by immersion precipitation phase inversion method.P(MMA-co-GMA)acts as a crosslinking agent and crosslinks copolymerization with hydrophilic PEI,which can effectively reduce the loss of hydrophilic substances during membrane preparation process.The successful completion of these modifications was demonstrated by TGA,SEM,ATR-FTIR and XPS characterization.The prepared modified membrane has super hydrophilicity and underwater superoleophobicity,and also exhibits underwater oil stain resistance.With the increase of additive content,the hydrophilic and oleophobic properties of the membrane show an increasing trend.The water contact angle of the surface of pure PVDF membrane is 96°±3°,and it does not change much within 10 minutes.The surface water droplets of M30 and M40 can be Rapid penetrated.The underwater oil contact angle of the pure PVDF membrane is 128±3°,and the underwater oil contact angle of the M20 is 153±2°,and the oil droplets cannot adhere to the M30 and M40.The mixed PVDF membrane can retain oil droplets while allowing water to pass through,exhibiting excellent oil/water emulsion separation performance.In addition,due to the in-situ cross-linking strategy,blended PVDF membranes can withstand repeated use and long-term operation.After the tenth cycle,the rejection of all membranes was higher than 98.3%,and the underwater oil contact angle exceeded 150°.In order to further reduce the loss of hydrophilic substances in the membrane preparation process,ammonium bicarbonate was added as a porogen,and the film formation method was changed.After the solution was cast onto a cleaned glass plate,the modified film was placed in an oven at 60°.The gas and water generated by the decomposition of ammonium bicarbonate will form pores,to decrease the lose of the hydrophilic substance during the phase transform process in the water coagulation bath,and the amount of the additive lost in the AP40 is only 3% of the dosage.A series of characterizations of the prepared modified membrane(AP5-AP40)were carried out to investigate the relationship between the additive dosage and the hydrophilicity and anti-pollution performance of the membrane.