Dry-jet wet spinning technique

Semipermeable membranes and hollow fibers are produced from cellulose acetate. Dry-jet wet-spinning techniques are described to provide asymmetric and homogeneous hollow fiber membranes. Manipulation of spinning conditions leads to morphologies that permit higher rejection and higher fluxes. The excellent balance of the hydrophobic-hydrophilic characteristics for cellulose acetate makes this polymer useful for reverse osmosis [89-93]. Cellulose acetate membranes and hollow fiber membranes are commercially available for hemopurification. [94], for ultrafiltration [95], and for other commercial separation processes. 

In addition, dual layer hollow fibers have been manufactured by a dry jet-wet spinning technique [81]. Two different polymers, i.e., PAI and poly(ether sul-fone), were used as the selective layer on the outer side and the porous support layer on the inner side, respectively. The dual layer substrates were subsequently modified crosslinking followed by multilayer polyelectrolyte depositions in order to get a nanofiltration skin on the outer layer. 

Wu et al. (1992) treated the surfaces of the hydrophilic porous membranes, such as cellulose acetate, by radiation graft polymerization of styrene to increase their hydrophobicity and to reach the MD membrane characteristics. Kong et al. (1992) employed a cellulose nitrate membrane modified via plasma polymerization of both vinyltrimethylsilicone and carbontetrafluoride and octafluorocyclobutane for the preparation of MD membranes. Fujii et al. (1992) prepared tubular membranes from PVDF polymer dopes by using the dry-jet wet-spinning technique. Ortiz de Zarate et al. (1995) and Tomaszewska (1996) reported on PVDF flat-sheet membranes prepared for MD by the phase inversion method. 

Since PPT melts with decomposition at ca 560°C (36), melt spinning cannot be employed. Thus, solution spinning techniques (31) must be used to prepare fibers. Although dry, wet, and dry jet-wet spinning methods have all been used to... 

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