Hydrophilic Modification Of PTFE Microfiltration Flat Membrane By Cross-linking Method

Water pollution and purification have become a worldwide problem.Insufficient supply of potable water resources and severe water pollution have prompted scientists to develop efficient technologies for wastewater reclamation and seawater desalination.Polytetrafluoroethylene(PTFE)is widely used in aerospace,automotive machinery,textile and environmental protection due to its excellent chemical resistance,thermal stability,self-lubricity,aging resistance and electrical insulation properties.PTFE microfiltration flat membrane is considered to be one of the most important membrane materials in separation technology owing to its excellent chemical stability.However,the application of PTFE microfiltration flat membrane is limited because of its hydrophobicity.It is extremely susceptible to contaminating during filtration and difficult to be repaired,reducing its long-term performance properties.Therefore,the hydrophilization modification of the PTFE microfiltration flat membrane is urgent.In this paper,glutaraldehyde(GA)was used as a cross-linking agent,hydrophilic layer was coated on the PTFE microfiltration flat membrane fibers by cross-linking reaction with different hydrophilic agents to enhance its hydrophilicity.The effect of reagent concentration and reaction time on the properties of modified membrane were investigated.This method is convenient,low toxic and endowed excellent the PTFE microfiltration flat membrane with excellent hydrophilicity and anti-fouling properties.The research was mainly divided into the following two contents:(1)Crosslinking polyethylenimine(PEI)which contains a large amount of amino group and O-carboxymethyl chitosan(OCMCS)by GA to enhance the hydrophilicity of PTFE microfiltration flat membrane.The results indicated that the average pore size of the OCMCS/PEI-GA PTFE microfiltration flat membrane was reduced from 0.183?m to 0.17?m compared with the original membrane.The fibers of the OCMCS/PEI-GA PTFE microfiltration flat membrane were coated with hydrophilic layer;carbon-oxygen double bond,carbon-nitrogen double bond,N,O and Na element appeared on the surface of OCMCS/PEI-GA PTFE flat membranes.The results indicated that OCMCS and PEI were successfully introduced into the OCMCS/PEI-GA PTFE microfiltration flat membrane.The hydrophilicity test of the modified membrane showed that with the increase of OCMCS concentration,the pure water flux increased in the beginning and then decreased,the corresponding surface contact angle decreased in the beginning and then increased;with the decrease of OCMCS:PEI,the pure water flux decreased and the corresponding surface contact angle increased;with the increase of GA concentration,the pure water flux increased in the beginning and then decreased,finally reach a stable value,corresponding surface contact angle decreased in the beginning and then increased.The optimal concentration of OCMCS,mass concentration of OCMCS:PEI,concentration of GA and reaction time were 5g/L,4:1,5g/L and 12h respectively.Compared with the PTFE original membrane,the pure water flux of the OCMCS/PEI-GA PTFE flat microfiltration membrane increased from 0 to 5220±200 L/m2h(test pressure is 0.1MPa),water contact angle decreased from 119°±2.4° to 69°±3°.Both static bovine serum albumin adsorption experiments and dynamic cross-flow fouling experiments showed that OCMCS/PEI-GA PTFE microfiltration flat membrane was endowed with excellent antifouling properties.The stability test result showed that the hydrophilicity of the modified membrane was reduced under strong acid or strong alkali conditions,stronger the acidity or alkalinity was,more the hydrophilicity decreased.The long-term operational experiment indicating that the modified membrane was endowed with excellent long-term operational stability.(2)Crosslinking PEI which containing a large amount of amino group and carboxymethyl cellulose(CMC)by GA to enhance the hydrophilicity of the PTFE microfiltration flat membrane.The results indicated that the average pore size of the CMC/PEI-GA PTFE microfiltration flat membrane was reduced from 0.183?m to 0.16?m compared with the original membrane.The fiber of the CMC/PEI-GA PTFE microfiltration flat membrane was coated with a hydrophilic layer.There was no pore blocked on the surface of the membrane.The hydrophilicity test of the modified membrane showed that with the increase of CMC concentration and GA concentration,the pure water flux increased in the beginning and then decreased,the corresponding surface contact angle decreased in the beginning and then increased;with the decrease of CMC:PEI,the pure water flux decreased and the corresponding surface contact angle increased.The optimal react conditions are as follows:concentration of CMC,mass concentration ratio of CMC and PEI,concentration of GA and reaction time is 5 g/L,4:1,5g/L and 6h,respectively.Compared with the PTFE original membrane,the pure water flux of the CMC/PEI-GA PTFE microfiltration flat membrane increased from 0 to 4485± 187.4L/m2h(test pressure is 0.1MPa),water contact angle decreased from 119°±22.4° to 45.6°±2°.The oil-in-water emulsion separation experiment showed that the CMC/PEI-GA PTFE microfiltration flat membrane was endowed with good anti-fouling property.The stability test results showed that the hydrophilicity of the modified membrane decreased under strong acid condition,stronger the acidity was,more the hydrophilicity decreased,but it was stable under strong alkali conditions.The long-term operational experiment indicating that the modified membrane was endowed with excellent long-term operational stability.