Preparation And Performance Study On Thermo-responsive Ultrafiltration Membrane Of PVDF/PVDF-g-PNIPAAm/GO

Temperature sensitive ultrafiltration membrane is a new type of membrane which is sensitive to temperature and self regulating to temperature.The structure and pore size of the temperature sensitive ultrafiltration membrane changes with the temperature,which changes the pure water flux and the permeability of the membrane.At present,temperature sensitive ultrafiltration membrane becomes the most important research object in smart membranes.Amphiphilic graft copolymers with poly(vinylidene fluoride)(PVDF)backbones and poly(N-isopropylacrylamide)(PNIPAAm)side chains were synthesized through graft polymerization pre-treated by alkaline.The structure of the copolymer was characterized by IR,1H-NMR and TG.The results showed that PNIPAAm was successfully grafted onto the PVDF backbone,the grafting ratio of PNIPAAm increased with increasing monomer concentration and increasing polymerization time,the optimum mass ratio of PVDF and NIPAAm in alkali treatment is 1:1,and the optimum polymerization time is 24 h in ATRP method.The PVDF/PVDF-g-PNIPAAm thermo-responsive membrane was prepared by immersion precipitation phase transformation.The effects of different grafting rates on the properties of the thermo-responsive membrane was investigated.The results show that the membranes exhibit obvious temperature sensitive property above the lowest critical solution temperature(LCST,32?),which is due to the PNIPAAm chain conformational change from stretching to contraction.When the grafting ratio of PNIPAAm in the alkali treatment method is 8.3%,the temperature sensitive property of the blend membrane is remarkable,25?,40? water flux ratio J40/J22 reached 1.98,bovine serum protein rejection rate was 84.7%.Compared with the thermo-responsive property,its hydrophilicity,anti fouling and mechanical properties are not outstanding,the water flux recovery rate is 55.96%,the hydrophilicity is weak,the water contact angle is 64.12°,and the mechanical properties are decreased,the elastic modulus is 71.40 MPa.The modified thermo-responsive membrane was prepared by doping GO into PVDF/PVDF-g-PNIPAAm casting solution.The temperature sensitivity,permeability,hydrophilicity,mechanical properties and surface morphology of the membranes were testedrespectively by water flux,rejection rate,porosity,water contact angle,elastic modulus,and scanning electron microscopy.It was found that the hydrophilicity,anti fouling and mechanical properties of the membranes were improved while maintaining the significant thermo-responsive properties when the GO doping content was 0.5 wt%.The rejection rate of bovine serum albumin was 90.2%,and the thermo-responsive properties of PVDF-g-PNIPAAm ultrafiltration membrane were not changed,and J40/J22 was 2.12.The water contact angle was as low as 54.1°,the recovery rate of water flux was 90.52% and the elastic modulus was 93.35 MPa.