Ultrafiltration membranes from Winicet
The proces of formation, structure and transport properties of ultrafiltration membranes from Winicet, a copolymer of vinyl chloride and vinyl acetate (VC/VAC) manufactured by the Oświęcim Chemical Works wih the trade name of Winicet, has been investigated. A process for the formation of planar membranes by the phase inversion method has been elaborated. As solvent in the preparation of film-forming solutions dimethylacetamide (DMAC) and as non-solvent — water has been used. By changing Winicet oncentration in the film-forming solution membranes of different compactness have been prepared. The porous structure of membranes has been characterized by electron microscopy and by the bubble method. Membranes are asymmetric and the acroporous base has voids in the form of oblong droplets (finger-like structure). The distribution of pore radii in the skin layer is wide and the mean radius of pores is in the range of 290 to 320 nm. The transport and separation properties of membranes have been determined by measuring the volume stream of water and coefficients of retention of water- -soluble polymers. The dependence of the volume stream of water, Ju, on pressure, AP, is described by a power function Jw = Au.(dP)b. The membrane permeability, Aw, decreases with an increase in concentration of film-forming solution of Winicet in DMAC (in the range of 14—18%) and the power exponent b is independent of the value of this concentration and changes in the range of 0.5—0.6. Winicet membranes are impermeable for dextrans, proteins and poly(oxyethylene glycols) with molecular weight above 20,000.
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