Liquid purification or separation – Filter – Material
Patent
1994-02-17
1996-04-09
Fortuna, Ana M.
Liquid purification or separation
Filter
Material
21050029, 21050035, 21050036, 210490, 264178R, 264199, 264200, 96 6, B01D 3321, B01D 3900
Patent
active
055058590
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Hollow cellulose fibers in which the cellulose is regenerated from cuoxam solutions are known for example from DE-A-23 28 853.
DE-C-29 06 576 teaches a method for spinning hollow fibers from regenerated cellulose for semipermeable membranes by extruding a cellulose-cuoxam solution through the annular slit of a hollow-fiber spinneret into an aqueous soda lye and extruding a cavity-forming fluid through the internal bore of the hollow-fiber spinneret and by conventional aftertreatment. Locating the hollow-fiber spinneret in the bottom of the coagulation tank is less favored because of technical problems in sealing and beginning spinning.
In order to avoid the known problems that can arise in using cavity-forming fluids to produce hollow fibers, it has already been proposed to use gases to form the internal cavity.
Thus, EP-B-0 076 442 teaches a method for manufacturing a hollow fiber from regenerated copper ammonium cellulose with an axially disposed cylindrical bore extending over the length of the fiber. The bore is filled exclusively with gas and contains no contaminants. EP-B-0 teaches a method with the following steps.
1) Extruding a spinning solution of copper ammonium cellulose through an annular opening, and forming a fiber extrudate with a bore, while gas is blown simultaneously into the fiber extrudate into the bore of the fiber through a blow tube located in the center of the annular opening;
2) Dropping the fibers in free fall in an air chamber and dipping them essentially perpendicularly to a depth of 2 to 20 mm, possibly also to a depth of up to 30 mm, below the surface of a coagulation bath only under the influence of a force directed downward and produced during free fall;
3) Guiding the fiber extrudate through the coagulating bath, producing a hollow fiber with an axially disposed cylindrical bore; and
4) Refining and drying the hollow fiber thus obtained.
The long air gap required for this purpose requires spinning solutions with a high viscosity. In addition, considerable difficulties arise in connection with the requirement of dipping the fiber in free fall up to 20 ml or possibly up to 30 ml deep in the coagulating bath. Dry elongation of such hollow fibers is approximately 40% and wet elongation is 70%, as is usual for conventionally spun hollow fibers as well.
Since the hollow fibers are produced from pure cellulose, the biocompatibility properties are much worse than for membranes that have been slightly modified for example. In addition, since materials that could be termed contaminating internal fluids under normal circumstances must not be present on the inside of the internal cavity, this rules out the possibility of improving biocompatibility by coating with suitable polymers usually ranked as contaminants. Substances that react with cellulose are likewise not provided according to this document.
DD-A-261 041 discloses a capillary hollow membrane made of regenerated cellulose (viscose) for liquid-phase permeation, with the internal cavity being formed by a gas or a liquid. Conventional viscoses with a high tendency to coagulate and the use of mildly coagulating precipitation baths characterizes the production of such hollow capillary membranes.
EP-A-0 135 593 teaches a hollow fiber for dialysis made of cuproammonium cellulose, which has a skin on the outside and no pores whatsoever on the inner surface. Elongation of such hollow fibers occurs in the range from +1.0 to -5.0%.
EP-B-0 175 948 describes the manufacture of nonstretched hollow fibers for dialysis by coagulating a cuproammonium cellulose solution with a cellulose concentration of 6.0 to 8.7 wt. % and a viscosity of 500-1300 poises (20.degree. C.), which has a film structure with a porosity of 15-25%, whose pores have a diameter of 25-40 .ANG., and whose ultrafiltration rate (UFR) is 3.0-5.5 ml/h.multidot.m.sup.2 .multidot.mmHg. The film structure must be essentially skin-free and essentially pore-free on the internal surface.
A major problem in dialysis is "biocompatibility," described below
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Baurmeister Ulrich
Breidohr Hans G.
Dunweg Gustav
Stein Uwe
Tilgner Hans G.
Akzo NV
Fortuna Ana M.
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