Spinning Variables for Hollow Fibers

In addition to the above, there are other variables unique to the spinning process which offer additional handles for controlling fiber permeability and re-tentivity. 

In general, an increase in the spinning solution velocity and the air-gap will result in tighter fibers with lower permeability and increased retentivity. An increase in the coagulating fluid velocity will have the opposite effect, leading to more open fibers of higher permeability and reduced retentivity. 

The alignment of polymer chains in shear flow through the spinneret may explain why hollow fibers generally have lower permeabilities than flat-sheet membranes with the same retention rating. 

On the other hand, an increase in the velocity of the coagulating fluid through the inner tube tends to counteract the elongation of pores in the skin the increased pressure in the fiber lumen tends to expand itsdiameter and thereby enlarge the width of the elongated pores. The result is a more open fiber with increased permeability and decreased solute rejection. 

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