| How to effectively regulate the microstructure and surface properties of polyvinylidene fluoride(PVDF)porous membranes to obtain PVDF porous membranes with excellent separation(high flux,high selectivity)and antifouling performance has always been the key problems in PVDF porous membrane research.In this paper,the blending modification of PVDF porous membrane with PVDF-based amphiphilic copolymer with different hydrophilic chain length to improve the separation and antifouling performance of PVDF porous membranes.In order to overcome the shortcomings of increasing membrane pore size and decreasing membrane mechanical properties in blending modification,a novel strategy to reconstruct the pore channels of porous membrane via confined-region swelling effect is reported,which lays a foundation for the development of high-performance PVDF porous membranes.This paper uses PVDF-based amphiphilic macromolecules to modify the membrane,and focuses on exploring the regulation mechanism of the hydrophilic chain length in the amphiphilic macromolecules on the pore size and pore size distribution of the membrane surface and internal pores.The results show that the increase of hydrophilic chain length in amphiphilic macromolecules promote the exchange rate between solvent and non-solvent.Finally,the liquid-liquid phase separation and gelation occurs at low polymer concentration,which is conducive to the formation of the surface pore.The larger the length of the hydrophilic chain segment,the more water bound,the more favorable to the formation of macropore structure.This also leads to the increase of pore size and the widening of pore size distribution.Finally,the flux of membrane was increased from 670 L/(m~2·h)to 867 670 L/(m~2·h),and the hydrophilicity and antifouling property of membrane were significantly improved.Aiming at the common problems of increasing membrane pore and decreasing membrane strength in the blending modification of PVDF membrane,a novel strategy to reconstruct the pore channels of porous membrane via confined-region swelling effect is reported.The results indicated that the average pore size significantly decreased from 164.2 nm to 73.5 nm and the maximum pore size decreased from 199.6nm to 101.5 nm after the swelling treatment.Meanwhile,the ovalbumin rejection increased from 50%to 98%.This method can avoid the large pore formed in conventional blending method,which leads to the decrease of membrane rejection.Besides,while the pore size decrease through confined-region swelling strategy,the membrane flux increased from 670 L/(m~2·h)to 1298 L/(m~2·h).After the reconstruction of membrane pore channels by the confined-region swelling effect,the hydrophilicity and antifouling properties of the porous membrane were maintained excellently.Meanwhile,for crystalline polymer porous membrane,the confined-region swelling effect only occurs in amorphous regions,which will not change the structure of crystalline region.Therefore,the mechanical strength of membrane did not decrease.In view of the advantages of confined-region swelling in preparing high-flux PVDF porous membranes with small pore size,the mechanism of confined-region swelling was further revealed by exploring the swelling temperature,time and molecular size of swelling reagents that affect confined-region swelling effect on regulating pore size.The results interpreted that the confined-region swelling method for the reconstruction of membrane pores is mainly due to the volume expansion of hydrophilic chains in the swelling reagent,which drives the movement of PVDF molecular segments to achieve the reconstruction of membrane pore.The average pore size decreased from 164.2 nm to 37.1 nm and membrane flux increased from 747L/(m~2·h)to 1398.6 L/(m~2·h)after the swelling of glycerol.The regulation of solvent surface tension on membrane pore structure and properties was investigated.When ethanol was used as solvent,the membrane had the smallest pore size(33.9 nm)and the largest flux(1518.8 L/(m~2·h)). |
PDF Full Text Request