Study On Hydrophilic Modification And Oxidation Resistance Of PVDF Membranes

Although,poly(vinylidene fluoride)membrane(PVDF)has a good filtration performance,the hydrophobicity of PVDF limits its wide applications.Many people use a variety of hydrophilic substances to improve the hydrophilicity of PVDF.However,it is also necessary to clean the membranes use a variety of chemical reagents to prolong the life-time of the membranes and reduce the cost of operation.In this paper,PVA modified PVDF membrane and PVA/GO modified PVDF membrane were prepared by poly(vinyl alcohol)(PVA)and graphene oxide(GO),and the antioxidation performance of PVA modified PVDF membrane was evaluated.The results are showed as follows:Firstly,commercial PVDF membranes were modified by dip-coating and crosslinking hydrophilic PVA on the membrane surface.And then the changes of the permeability.rejection,and hydrophility of the modified membranes were explored.The results showed that PVA was cross-linked to PVDF membrane successfully.The contact angle of pure water of PVDF membrane decreased from 106° to 28°.The rejection of ink increased from 70.5%to 95.4%and the average pore diameter of membrane decreased slightly after the modification.Secondly,the antioxidation performance of the modified PVDF membranes was evaluated.The measurements showed that some of PVAs coated on the membrane surface could be oxidized and peeled slightly after the modified membranes were treated with NaCIO or KMnO4 for 30 days.Hence.larger PVDF area was exposed and the content of O element was decreased when a small amount of PVA was coated on the surface.Conversely,the content of O element was increased when a large amount of PVA was coated on the surface due to the oxidation of PVA.In addition,PVA was oxidized more severely by KMnO4 than by NaCIO.The tests indicated the permeability and hydrophilicity were essentially remained and only the rejection was slightly decreased after the modified membranes were oxidized.Finally,the properties of PVA/GO modified PVDF membrane were evaluated,the test results showed that PVA/GO was successfully coated on the surface of PVDF.and the contact angle of pure water of modified PVDF membrane dropped from 118° to 75°.The average pore size was smaller,the ink rejection increase from 70.5%to 99.9%,and the rejection of PEG-20000 up to 80.5%.The results showed that the membrane performance reached the level of ultrafiltration.Pure water flux test showed that the membrane has a certain pressure response.The same film under the same pressure,the positive and negative water flux difference of up to 10 times.