The Preparation Of PNAGA Gel Modified PVDF Membrane And Its Anti-fouling Performance

Polyvinylidene fluoride(PVDF)ultrafiltration(UF)membranes are widely used in water treatment due to their good thermal stability,chemical stability and excellent mechanical properties.However,PVDF membranes are easily contaminated,which limits the further application of the PVDF membrane.The hydrophobicity of membrane surfaces is considered as the leading factor of fouling.In this work,three-dimensional cross-linked hydrogel based on multi-hydrogen bond self-assembly was used to modify the membranes,which can combine and store more water molecules and result in a stable hydration layer.Acryl-glycinamide(NAGA)has dual amide group,and corresponding polymer can form hydrogel by intra-and intermolecular hydrogen bonding without adding any chemical crosslinking agent,which will enhance the strength of the gel layer and helps to the long time filtration of separation membrane.In addition,the absence of a chemical crosslinker reduces the risk of introducing toxicity and is beneficial for the applications of the separation membranes in biotechnology,medicine and oily wastewater.Firstly,it was verified by molecular dynamic simulation that PNAGA has better hydrophilicity than traditional anti-fouling material PEG,then PNAGA microgel was synthesized,at last,it was blended with PVDF powder in solvent and the blending membrane was made through phase separation method.In the phase separation process,the microgel will segregate to surface,and enrich on the surface of the membrane as well as in the pores of the membrane,thereby achieving hydrophilic modification of the separation membrane.The contact angle test showes that the contact angle of the PVDF/PNAGA microgel blend membrane is 78±30.Bovine serum albumin(BSA)is used as a protein model to test its anti-protein-fouling ability.The results show that the flux recovery rate is 96%and keep stable in three-cycle filtration.In order to obtain a separation membrane having more excellent hydrophilicity,the above PNAGA was directly grafted onto the surface of the PVDF membrane under ultraviolet irradiation.Water contact angle of PNAGA modified membranes reduces from 55.2±1.1° to 00°within 11 s,illustrating a superior hydrophilicity.Ultrasonic 30 min and 7 days pure water filtration tests indicate that the PNAGA hydrogel layer has good stability.The results from anti-fouling test show that,when the pH is 7.0,the flux recovery rate of modified membrane maintains at 99%,the total fouling rate is as low as 30%,and the irreversible fouling rate is only 1.2%.Furthermore,the fouling mechanism investigation shows that fouling layers are not easy to form on the anti-protein-fouling PNAGA hydrogel grafted membranes.The anti-oil-fouling properities of PNAGA modified PVDF membrane were further studied.The contact angle test shows that the underwater oil contact angle is 160±40,which has excellent underwater superhydrophobic performance.The results from anti-oil fouling test show that the rejection rate of the oil droplets is up to 91.4%,and the flux recovery rate is 98%.Considering that the waste water containing oil which produce in life and industry has more co,mplicated system,the filtration performance of the modified membrane to the oil-water emulsion containing BSA is also tested.The results show that the flux recovery rate of the modified membrane is still as high as 98%,and the flux recovery rate of the original membrane is only 57%.This shows that the modified membrane still has superior anti-fouling ability when filtering the solution of the complex system.