Modification Of Porous Membranes By Blending With Triblock Copolymers PEG-PB-PEG

High density polyethylene (HDPE) and poly (vinylidene fluoride)(PVDF) are generally found membrane materials used in filtration and battery separator because of their excellent physicochemical property, thermal stability and mechanical performance. However, HDPE and PVDF membranes tend to be fouled in separation process because of their intrinsic hydrophobicity. It’s common knowledge that the increase in membrane’s hydrophilicity would improve the fouling resistance of membranes. To endow membranes with improved performance and hydrophilicity, the PVDF and HDPE blend membranes were fabricated by blending with amphiphilic copolymer in this paper.Triblock amphiphilic copolymers PEG-b-PB-b-PEG had been synthesized via esterification, where poly(ethylene oxide)(PEG) was hydrophilic with molecular weight of1,900or5,000g/mol, while polybutadiene(PB) was hydrophobic with molecular weight of about9,000g/mol. The structure, composition, molecular weight and thermal stability of the copolymer were characterized by FTIR,1H NMR, GPC, TGAand DSC. The successful synthesis of the copolymer had been confirmed.In thermally induced phase separation process (TIPS) of preparation of HDPE membranes, the phase behavior of ternary system of HDPE/PEG-b-PB-b-PEG/LP had been studied by DSC、WAXD、optical microscope. XPS, contact angle and so on. The results indicated that PEG-b-PB-b-PEG was incompatible with HDPE, and aggregates (or micelles) formed in HDPE matrix. The influence of experimental conditions on structure and properties of HDPE membranes was researched in depth. It was found that PEG-b-PB-b-PEG obviously enriched in the outer surface of membranes. As a result, the water contact angle of modified HDPE membrane decreased to82°and the water flux of the blend membrane was simultaneously improved. The fouling resistance of modified membranes was also promoted, for the absorption of proteins on membrane surface decreased and the flux recovery was reached to79%. Moreover, the water flux had little changed though the blend membranes had been suffered from a thermal treatment in a water bath of60℃for30days, which indicated the permanent hydrophilicity and stable modification efficiency were confirmed by this method.The blend membranes PVDF/PEG-b-PB-b-PEG were prepared via non-solvent induced phase separation method. The effects of the amphiphilic copolymer on the membrane morphologies and performance also had been investigated. SEM images indicated that pore diameter and structure had been obviously influenced when the PEG-b-PB-b-PEG was introduced. The water contact angle of modified PVDF membrane could decrease to85.1°, compared to104°of pure PVDF membranes. The water fluxes of the blend membranes were also greatly promoted. Moreover, the blend membranes had been washed for over15days in a thermostat water bath at60℃to investigate the persistence of the modification effects.