Symmetrical microfiltration membrane made of aromatic polyamide and process for their preparation

摘要

Prodn. of a symmetrical microfiltration membrane based on aromatic polyamide (I) involves dissolving (I) in solvent(s) in the presence of LiCl, casting the soln. on a smooth substrate to form a membrane, contacting this with humid air until it become turbid and then completing consolidation by immersion in water. The novel features are that: (a) the soln. is treated with polyvinyl-pyrrolidone (PVP) with a mol. wt. of over 50000 and with ethylene glycol or glycerol as non-solvent (II) for (I); and (b) the cell structure and pore size of the membrane are regulated by the dwell in humid air. The membrane is claimed per se. The membrane has cells with a dia. of 1-10, pref. 3-7, microns, and has an elongation at break of 30-50% in the moist state. The casting soln. contains DMF, DMA and/or NMP, esp. a mixt. of DMA/DMF or DMA/NMP, as solvent, up to 25, esp. 8-20 wt.% (I), 0.2-5 wt.% PVP, LiCl in an amt. of 5-100% w.r.t. (I) and 5-25, esp. 10-15 wt.% (II). It has a viscosity of 15-30 Pa.s. The membrane is contacted with air having at 80-100% RH and 15-30, esp. 20-28, more esp. 20 deg C for 5-15 min. The soln. is cast in a thickness of 50-300, esp. 80-150, more esp. 100, microns.