Study On Hydrophilic Modification Of PTFE Flat Membrane By Post-cross-linking Method

The Polytetrafluoroethylene?PTFE?micropores flat membrane is widely used in membrane separation technology due to its high porosity,suitable and uniform pore size and high chemical stability.However,the application of PTFE membrane in the waste water is limited by the strong hydrophobicity of PTFE materials owing to the high C-F bonding energy and symmetrical molecular structure of PTFE molecules.Therefore,to improve the hydrophilicity of the PTFE flat membrane is extremely important.In this paper,the post-crosslinking modification method was used to modify the PTFE flat membrane via selecting different crosslinking agents with Polyacrylic acid?PAA?as the hydrophilic agent.The surface chemical functional groups and morphology of PTFE flat membranes were investigated by X-ray photoelectron spectroscopy?XPS?,Field-Emission Scanning Electron Microscope?FESEM?and Attenuated total reflection Fourier transform infrared spectroscopy?ATR-FTIR?.The effects of reactant concentration and reaction condition on the hydrophilicity of modified PTFE flat membrane were studied systematically.The main research contents are as follows:?1?A trifunctional Trimethylolpropane-tris[3-?2-methylaziridinyl?propionate]?for short Sac-100?and PAA were selected and reacted under acidic conditions.The PTFE flat membrane was modified by the method of post-cross-linking,and then the surface of the modified membrane was ionized by soaking with saturated sodium bicarbonate solution to enhance the hydrophilicity of the modified flat membrane.The experimental results show that the surface of the modified PTFE flat membrane was wrapped with a layer of hydrophilic material,and no clogging phenomenon occurs;The new elements N,O and Na were found on the surface and cross section of the modified membrane;Hydrophilic groups such as carbonyl?C=O?,hydroxyl?-OH?and carboxylic ion?-COO^-?were observed on the surface of modified membrane;The water flux of the modified membranes were first increased and then decreased and the surface water contact angle?WCA?were first rapidly decreased and then slowly increased with the increase of PAA concentration;The water flux of the modified membranes were first rapidly increased and then slowly decreased and the surface WCA were gradually with the increase of Sac-100 concentration;The water flux of the modified membranes were increased first and then rapidly decreased and the surface WCA were first decreased and then rapidly increased with the increase of pH;The best reaction condition:PAA concentration is 2%,Sac-100 concentration is 0.4%and the reaction pH is 5;The water flux of the modified membrane was 5084kg·m^-2·h^-1,the surface WCA was decreased from the original membrane136°to 23.41°;Bovine serum albumin?BSA?adsorption test showed that the prepared hydrophilic PTFE flat membrane had strong anti-pollution.The stability test of the modified flat membrane showed that the modified membrane can be used in water,weak acid,weak base.?2?The double-amino organosilicone?for short 9300?was chosen as another cross-linking agent and PAA in acidic conditions for the reaction of PTFE flat membrane hydrophilic modification.The experimental results show that the surface of the modified PTFE flat membrane was wrapped with a layer of hydrophilic material,and a bit micro-particle are found;The new elements N,O and Si were found on the surface and cross section of the modified membrane;The water flux of the modified membranes were first increased and then decreased and the surface WCA were first decreased and then slowly stabilized with the increase of 9300concentration;The water flux of the modified membranes were first increased and then decreased and the surface WCA were first decreased and then increased with the increase of PAA/9300?mass ratio?;The water flux of the modified membranes were first increased and then stabilized and the surface WCA were first decreased and then stabilized with the increase of reaction temperature and time;The best reaction condition:9300 concentration is 2g/L,PAA:9300 mass ratio is 15:1,the reaction temperature is 80?and reaction time is 6h;The water flux of the modified membrane was 4300.32kg·m^-2·h^-1,the surface water contact angle was decreased from original membrane 136°to 30.35°;The results show that the turbidity removal rate of the modified membrane is 99.1%for the crystal grinding wastewater;The stability of the modified membrane showed that the modified membrane was not resistance strong alkali,but the hydrophilicity of the membrane is reduced under strong acid conditions;it is stable in weak alkali,EtOH and water.