HWAHAK KONGHAK, Vol.26, No.1, 66-73, February, 1988
Poly(vinylidene fluoride ) 다공성막의 제조;한외여과성능에 미치는 제막용매의 효과
Preparation of Porous Poly (vinylidene fluoride) Membranes; The Effect of Casting Solvents on the Ultrafiltration Performances
초록
기계적 강도가 좋고 제막성능이 우수하며 화학적으로 안정한 Poly（vinylidene fluoride）(PVDF)를 사용하여 습식응고방법에 의해 한외여과막을 제조하였다. 막의 구조는 유체역학적인 저항을 줄이기 위해 비대칭구조로 제조하였으며 막두께를 200 ㎛ 이하로 조절하였다. 막의 성능 및 구조에 미치는 용매의 영향을 검토하기 위하여 dimethyl formamide(DMF), dimethyl sulfoxide(DMSO) 및 dimethyl acetamide(DMAc)를 제막용매로 사용하였으며 제막용액에 휘발성 난용매인 acetone을 첨가하여 그에 따른 효과도 검토하였다. 사용된 용매의 조성은 (a) 단일용매계 ; DMF, DMSO 및 DMAc, (b) 2성분 용매계 ; DMSO/DMF, DMF/DMAc 및 DMAc/DMSO, (c) 2성분용매/난용매계 : DMF/Aceton, DMAc/Acetone, DMSO/Acetone 등이다. 한외여과막의 성능을 평가하기 위하여 polyethylene glycol(PEG, 평균분자량 1,500∼20,000)수용액을 사용하여 배제율과 투수성을 측정하였으며 시차주사전자현미경으로 막의 단면을 관찰하였다. 실험결과로부터 PVDF한외여과막은 2 기압하에서 10∼200(l/㎡h)의 투수량을 나타냈음을 알았다. DMF를 용매로 사용한 막의 배제율이 매우 우수한 반면 투수성이 떨어지며 DMSO를 사용하였을 때는 배제율도 비교적 크고 물투과성도 좋은 것을 알 수 있었다. 2 성분용매계에서는 DMSO/DMF(1/1)의 경우 PEG 7,500의 배제율이 9.5 %이며 PEG 20,000은 93.5 %의 배제율을 나타내어 매우 우수한 분획성능을 가짐을 알 수 있었으며 투수량도 89.4(l/㎡·h)로 매우 우수한 한외여과성능을 나타내었다.
Poly（vinylidene fluoride）(PVDF) was prepared for the ultrafiltration membranes because of its good film forming ability, high mechanical strength, and chemical resistance to solvents. Membranes were prepared by solvent casting method on a glass plate. To investigate the effect of casting solvents on the membrane performances dimethyl formamide(DMF), dimethyl sulfoxide(DMSO), and dimethyl acetamide(DMAc) were used as casting solvents. The solvent composition of casting solution was selected from one of followings; (A) homosolvent system of DMF, DMSO or DMAc, (B) binary solvent system of DMSO/DMF, DMF/DMAc or DMAc/DMSO, and (C) binary solvent system of solvent and volatile nonsolvent such as acetone.
Ultrafiltration experments were carried out with 0.2 % aqueous solution of polyethylene glycol（PEG, average molecular weight of 1,500-20,000）. Water flux and rejection were measured, and the cross-sectional structures of membranes were observed by a scanning electron microscope. From the result of water permeation, it was revealed that most of all the PVDF membranes had the water flux 10∼200(ℓ/㎡·hr) at 2 atm. Membranes prepared by DMF solvent DMF solvent system had the high rejection values inspite of poor water fluxes in comparison with other membranes. DMAC and DMF solvent systems showed the sharp slope of rejection curves with the increase of molecular weight of solute, and especially, membranes prepared by DMSO had good performances for ultrafiltration.
Ultrafiltration experments were carried out with 0.2 % aqueous solution of polyethylene glycol（PEG, average molecular weight of 1,500-20,000）. Water flux and rejection were measured, and the cross-sectional structures of membranes were observed by a scanning electron microscope. From the result of water permeation, it was revealed that most of all the PVDF membranes had the water flux 10∼200(ℓ/㎡·hr) at 2 atm. Membranes prepared by DMF solvent DMF solvent system had the high rejection values inspite of poor water fluxes in comparison with other membranes. DMAC and DMF solvent systems showed the sharp slope of rejection curves with the increase of molecular weight of solute, and especially, membranes prepared by DMSO had good performances for ultrafiltration.