Surface Functionalization Of PVDF Flat Membranes With Polydopamine And Sulfonated Chitosan

Poly(vinylidene fluoride)(PVDF)has become greater concern as a membrane material due to its outstanding chemical resistance,oxidation resistance,thermal stability,mechanical strength,and high hydrophobicity properties compared with other membrane materials.and it has a very good property of membrane forming.But as membrane materials,the PVDF exhibits hydrophobocity.so it was easily polluted in practical application of process,especially in protein separation process.Therefore,to improve the hrdrophicity of PVDF membrane has become a hot spot in separation membrane filed,In this paper,dopamine(DA)and chitosan(CTS)were chosen as modifier to improve the hydrophilicity and antifouling properties of PVDF membrane by surface modification.Firstly,DA was used to improve hydrophicity of PVDF membrane by surface coating due to the advantage of DA super strong adhesion and easily self polymerization to form polydopamine(PDA).The effect of PDA deposition time on the performance of’ PVDF ultrafiltration membrane and anti protein(BSA)pollution properties were investigated.The results showed that PDA layer was successfully deposited on the surface of PVDF ultrafiltration membrane,and the surface hydrophicity and anti-protein properties were improved.The initial contact angle of’PVDF membrane was decreased to about 52.4°from 95°for pure membrane.The static adsorption mass of BSA decreased to 60.32 μg/cm2,the rejection ratio of BSA protein reached about 95%and the flux recovery rate(FRR)was 43.26%for pure PVDF ultrafiltration membrane increased to 77.73%.The modified membranes exhibited relatively stable antifouling properties.In addition,in this paper.PDA layer was used as an intermediate layer of PVDF ultrafiltration membrane to secondary functionlization.The aim is to further improve the hydrophilicity and pollution resistance of PVDF membranes.Firstly,2-N-propyl sulfonated chitosan(PCS)was synthesized using ring opening polymerization method.Then the PCS was immobilized on the surface of the PVDF membrane by Schiff or Michael addition crosslinking reaction.The effects of different reaction time of PCS on the performance of PVDF ultrafiltration membrane and antifouling properties were investigated.The secondary functionalized PVDF ultrafiltration membrane showed better hydrophilicity and antifouling properties.The initial contact angle of the membranes modified with PCS was decreased to 42.8°,the permeability of PVDF membrane can be promoted.The pure water flux can reach to 120.56 L(m-2 h-1).The rejection ratio of the modified membranes reached 93.45%(BSA)and 83.65%(LZM),respectively.After BSA and LZM protein pollution,the FRR of the modified membranes reached 88.89%(BSA)and(LZM)79.93%,respectively.Irreversible fouling(Rir)of modified PVDF membranes decreased to 7.28%and 11.24%,respectively.Therefore,the secondary functionalized PVDF ultrafiltration membrane possesses a better hydrophilicity and antifouling properties.