Hollow fibers of cuprammonium cellulose and a process of the manufacture of same

Abstract

An improved dialyzing hollow fiber of cuprammonium regenerated cellulose, showing a substantially similar network structure of fine gap passage routes having a max. gap size of 200 A when seen observed at its any cross-section and logitudinal longitudinal section, having skinless structure at its inside and outside surface of the hollow fiber and representing a superior water permeability.

Description

stressly notedthe manufacturing the novel fiber and process according to the present invention will be described hereinbelow in detail.

Numeral 10 represents a spinneret unit which is formed with an inside chamber 9 adapted for provisionally accumulating a spinning liquor to be described more fully hereinafter, said the liquor being supplied under pressure from a reservoir by a conventional spinning pump, not shown, through an inlet pipe 1 detachably attached to the housing at 6 of the unit 10, although not specifically shown, said chamber 9 being formed in the interior space of said the housing as shown.

A second inlet pipe 2 adapted for introducing noncoagulating liquid for the spinning liquor is mounted concentrically at the interior space of said the housing 6, said the inlet pipe being connected through a proper piping to a pressurized supply source, although not shown.

The lower end of the chamber 9 is sealingly closed by a nozzle plate 7 having centrally positioned a duplicate orifice 4 and kept fixedly in position by an internally threaded ring fixture 8 which is detachably attached to the lower end portion of said housing 6. The duplicate orifice 4 consists of an outer ring orifice 20 kept in fluid communication with the chamber 9, and a concentric core orifice 21 which is formed by the reduced tip end part of said second inlet pipe 2 vertically passing through the unit 10. The upper part of inlet pipe 2 projects from the upper end of the housing 6 and is flanged at 2a for being mounted mounting thereon, said the pipe 2 being firmly held in position by an internally threaded ring cap 5 which is detachably attached to the reduced and male threaded upper part of the housing 6. At an intermediate level within the chamber 9, there is provided a perforated rectifier ring 18 which is fixedly mounted between the inside wall surface of the housing 6 and the outer tubular suface of the middle part of the second inlet pipe 2.

The spinning liquor supplied through first inlet pipe 1 is introduced into the upper part of the chamber 9 arranged above rectifier plate 18 and then into the lower part of the same chamber positioned below the latter, upon passage therethrough. The spinning liquor is then extruded downwards substantially at a constant pressure through the outer ring-shaped outlet orifice 20.

On the other hand, the non-coagulating liquid fed through second inlet pipe 2 is extruded through the central core orifice 21 in a concentric arrangement with the outer spinning liquor, thus forming the core medium relative thereto. The thus jointly extruded composite core-and-sheath liquid string is substantially freely dropped through an open atmospheric space at 11 to be fully extended in its length by gravity action after leave from exiting the composite orifice 4.

The thus extended composite liquid filament is then supplied to and processed in a coagulating and after-treating unit 100 positioned at a lower level from the spinneret unit 10 and comprising coagulating bath 13, first rinsing bath 14, regenerating bath 15 and second rinsing bath 19. Thus, the extruded composite liquid filament is introduced firstly into the coagulating bath 13 positioned directly below the orifice 4 and fitted with a stationary or rotatable guide bars 12 which are so arranged that the vertically introduced and at least partially coagulated filament is deflected in its travelling direction from vertical to horizontal by means of these guide bars 12 dipped in the coagulation bath liquid 13 consisting of aqueous NaOH-solution NaOH soltuion as referred to hereinbefore. By passage of the filament or fiber through the bath 13, it is completely coagulated as shown at 17 and then led to pass successively through a first water-rinsing bath 14, a diluted surfuric sulfuric acid bath 15 adapted for regeneration, and a second water-rinsing bath 19. The thus coagulated and regenerated filament is passed through a conventional drier, not shown, and wound up on a winding roll 16.

EXAMPLE 1

A conventionally prepared cuprammonium cellulose spinning solution, cellulose content 10.0 wt. %, ammonium content 7.0 wt. % and copper content 3.6 wt. %, viscosity: 2,000 poises, was extruded through an outer ring-shaped orifice, 5 mm diameter, of the duplicate style as was referred to hereinbefore in connection with FIG. 1 at a delivery rate of 20 ml/min.

At the same time, perchloroethylene was extruded through a central core orifice, 1 mm diameter, of the same duplicate nozzle at a delivery rate of 5 ml/min, so as to fill the core space of the ring-shaped liquid string.

This sheath-and-core composite string was let permitted to fall under gravity by a vertical length of 300 mm in an open air atmosphere, the outside diameter of said composite liquid string being thereby reduced to 600μ under the influence of the gravity stretch. The liquid string was then introduced vertically into a coagulation bath comprising an aqueous NaOH-solution NaOH solution of 11 wt. % concentration kept at 25°C and extending horizontally for a length of 8 m. The traveling speed of the filament through the coagulation bath was set to 100 m/min. The degree of the normannrization normannization amounted to about 30%.

The thus coagulated hollow fiber of or filament was taken out on a revolving hank frame, not shown, and kept thereon for about 2 hours. The hank was suspended from a bar and sufficiently rinsed with fresh water by means of a shower. Then, the hank was treated in a diluted sulfuric acid bath, of 3 wt. % concentration, for the regeneration purpose, and rinsed with fresh water. The thus treated hank was suspended from a moving frame and passed through a tunnel drier for drying in a hot air atmosphere, 130°C The hank was finally and mechanically cut into proper lengths for recovery of the contained core liquid solvent and kept in a calm room at normal temperature for several hours.

The thus obtained hollow fibers represented an outer diameter of 290μ with a wall thickness of 25μ which was found substantially precisely constant at any cross-section along the axis of each of the hollow fibers.

These hollow fibers were swollen with water and observed under an electron microscope,×20,000 times, showing a network structure of even gap passage routes structure, being substantially similar at the cross-section as well as the longitudinal section of the fiber, representing gaps of max. 200 A. It was amazingly observed that at each cross-section, there is no skin formation. The fine gap network was of highly uniform distribution throughout the whole mass of the hollow fiber, when seen in the cross-section, as well as longitudinal section.

At a further observation of the sections of the hollow fiber, at a magnetification magnification of 8,000 times, under an electron microscope, almost no undulations were found on the inside and outside wall surface surfaces of the hollow fiber and further, no deposits of hemi-cellulose particles deposited on the inside wall surface of the hollow fiber, thus representing a highly smooth surface on the inside wall of the hollow fiber even by review inspection thereof under an electron microscope.

Comparative test data of the novel hollow fiber and a representative dialyzing conventional one, made of cellulose triacetate, are given in the following Table 1, concerning their structure, tensile strength and tensile elongation.

TABLE 1
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Item         Unit       Conv.   Inventive
______________________________________
O.D.         μ       285     290
Wall Thickness
μ       25      25
Tensile Str. (wet)
g          23.0    103.2
Elongation (wet)
%          27.3     32.7
Tensile Str. (dry)
g          92.0    277.4
Elongation (dry)
%          14.4     24.3
______________________________________

As is clear from the foregoing data, the hollow fiber according to this invention represents about three times higher tensile strength than that of the conventional one.

In the following Table 2, comparative test data in model liquid dialysis are shown, especially of the removal

TABLE 2
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Item          Unit      Conventional
Inventive
______________________________________
Main Sizes of Sample
O.D.          μ      285        290
Wall Thickness
μ       25         25
Effective Filtering Area
m2      1.0        1.0
Dialyzing Conditions
Length of Hollow Fiber
mm        135        135
Blood Passage Rate
ml/min    200        200
Buffer Passage Rate
ml/min    500        500
Press Differential
mm Hg     -200       -200
Dialyzing Performance
Removal of Urea
%           63.5       64.2
Removal of Albumin
%          0          0
Ultra-Filtration
Treating Condition
mm Hg     +400       +400
(Pressure)
Filtration Rate
ml/m2 Hr
430        1020
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rate of albumin and urea and those of untrafiltration ultrafiltration velocity.

As the model liquid use was made of an aqueous solution containing 0.1 wt. % of albumin and 0.167 N of urea in these tests.

From the data shown in the foregoing Table 2, the inventive hollow fiber has superior performance for removal of protein (albumin) and for allowing the passage of urea, comparative to bests compared to the best of conventional comparative hollow fibers. It should be stressed, however, that the novel hollow fiber has a 2.5 times or still higher ultra-filtration ultrafiltration velocity than those of conventional comparative fibrous products.

In addition, it may be seen that the novel fiber represents a substantially superior water permeability over conventional fibers.

According to our test results, it was found that there is are no pin holes on 50,000 novel hollow fibers according to this invention, each being of 135 mm.

EXAMPLE 2

Hollow fibers, O.D. 285μ, wall thickness 11μ, were prepared in the similar way as before.

The spinning liquor was extruded at a rate of 13 ml/min, and trichloroethylene was extruded at a rate of 5 ml/min, the length of the free falling zone extending for a length of 310 mm.

The sectional structures of each of the thus prepared hollow fibers were similar to those of the foregoing hollow fibers obtained in the foregoing Example 1, when observed under an electron microscope.

The dialyzing power of the present hollow fiber carried out by use of a model liquid of the similar kind as before was such as :

removal rate of albumin 0%;

removal rate of urea 71%.

Thus, the performance was superior as before.

The wall thickness of 11μ corresponds generally to about one-half of that of conventional cellulose hollow fiber. From this reason, the ultrafiltration velocity showed a remarkably high value of 1,250 ml/m². Hr under the condition of (live atmospheric pressure plus 400 mm Hg ).

EXAMPLE 3

Hollow fibers were prepared under similar conditions as employed in the foregoing Example 1, O.D. 350μ, wall thickness 20μ, at a winding speed of 120 m/min. The extrusion rate of the spinning liquor was 25 ml/min and that of the core benzene solvent was 7 ml/min.

The falling distance was 270 mm. Coagulation, regeneration, rinsing and drying steps were similar as to those employed in Example 1.

The sectional representations of the hollow fiber were similar to those observed in Example 1.

The dialyzing performance of the hollow fiber by use of model test liquid was as follows:

removal rate of albumin 0%;

removal rate of urea 71%.

thus, showing superior results as before.

The ultrafiltration velocity amounted to 980 ml/m². Hr at the treating condition of (live atmospheric pressure+400 mm Hg), thus being superior as before.

EXAMPLE 4

Hollow fibers were prepared under similar conditions as before. O.D. 800μ, wall thickness 70μ. Winding speed: 100 m/min. The extrusion rate of spinning liquor was set to 62 ml/min, while that of the core solvent, normal hexane, amounted to 12 ml/min.

The extruded liquid state sheath-and-core composition was led to fall along a vertical distance of 300 mm and then introduced into a coagulation bath consisting of aqueous NaOH-solution NaOH solution, of 15 wt. %. The coagulated filament was passed through a diluted aqueous H₂ SO₄ -solutionH₂ SO₄ solution bath of 7 wt. % concentration and finally wound on a hank frame.

The hank was enough sufficiently rinsed and gradually dried up at 130°C The core of the hollow fiber represented an elliptical cross-section. The cross-section structure was similar to that as seen in the Example 1.

COMPARATIVE TEST

Hollow fibers were prepared under similar conditions as to those employed in Example 1. The concentration of the aqueous NaOH-solution NaOH solution was, however, set to a concentration of 40 wt. %. The sheath-and-core liquid composition was immersed to a full degree, so as to attain a 100%-normannrizing 100%-normannizing.

When observed the thus prepared hollow fiber was observed under an electron microscope, a disadvantageous skin core structure was found. The ultrafiltration velocity in this case amounted under similar test conditions as mentioned in Example 1 to 400 ml/m². Hr., thus being substantially inferior value.

A cross-section of the hollow fiber is representatively and schematically shown at 22 in FIG. 3. The same reference numeral is shown in FIG. 2 to show the finishing position of such hollow fiber.

Claims

1. A dialyzing hollow fiber of cuprammonium regenerated cellulose having a smooth, skinless inner and outer wall surface and said wall having distributed throughout its thickness a netlike structure of passage routes, the routes having a diameter of not greater than 200, and said fiber having been prepared by the steps of extruding that in artificial kidney use causes substantially no clotting of blood and achieves an improved ultrafiltration rate obtained by a spinning process using a duplicate orifice, said process comprising extruding a spinning liquor of cuprommonium cuprammonium regenerated cellulose to form a hollow core extrudate through an outer ring-shaped orifice and simultaneously therewith passing extruding a non-coagulating organic solvent through the hollow core; passing the resulting extrudate through a gaseous atmosphere whereby the weight of said extrudate causes an inner concentric core orifice, stretching to substantially reduce the outer diameter thereof; the resultant extrudate, coagulating the hollow core extrudate by contacting said extrudate with in a solution containing aqueous sodium hydroxide to form a hollow core fiber having a smooth, skinless inner and outer wall;, regenerating the coagulated extrudate with an acid, and rinsing and drying the resulting hollow fiber , said hollow fiber having the following characteristics:

(1) a smooth skinless inner and outer wall surface,

(2) said wall having distributed throughout its thickness a network structure of passage routes,

(3) the said routes having a diameter of not greater than 200 Å,

(4) the outer diameter of the fiber being not greater than 1000μ,

(5) the wall thickness being not greater than 450μ; and

(6) the wall having substantially no pin holes.

2. The fiber of claim 1 wherein the outer diameter is no greater than 1,000μ.

3. The fiber of claim 1 wherein the wall thickness is not

greater than 450μ. 4. A process for the manufacture of a dialyzing hollow fiber having distributed throughout its thickness a net-like network structure of passage routes, said hollow fiber in artificial kidney use causing substantially no clotting of blood and achieving an improved ultrafiltration rate, which comprises the steps of

extruding a spinning liquor of cuprommonium cuprammonium regenerated cellulose to form a hollow core extrudate and simultaneously therewith passing a non-coagulating organic solvent through the hollow an outer ring-shaped orifice;

and simultaneously extruding a non-coagulating organic solvent through a concentric core orifice to form a composite core-and-sheath liquid string;

passing the resulting extrudate through a gaseous atmosphere whereby solely the weight of said extrudate causes stretching to substantially reduce the outer diameter thereof;

coagulating the hollow core extrudate by contacting said extrudate with a solution containing aqueous sodium hydroxide to from form a hollow core fiber having a smooth, skinless inner and outer wall;

regenerating the hollow fiber with an acid; and rinsing and drying the

resulting fiber. 5. The process according to claim 4 7 wherein the non-coagulating organic solvent is selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbon

hydrocarbons and halogenated hydrocarbons. 6. The process according to claim 4 7 wherein the sodium hydroxide

is present in the solution in an amount from 5% to 15% by weight. 7. The process of claim 4 wherein the fiber is dried at a temperature of up to 150°C 8. The fiber of claim 1, a wherein the fiber is dried at a temperature of up to 150°C 9. The fiber of claim 1 wherein the degree of polmerization of the cellulose ranges from 400 to 500. 10. The fiber of claim 8 wherein the concentration of aqueous sodium hydroxide solution is less than 20% by weight. 11. The fiber of claim 10, wherein the concentration of aqueous sodium hydroxide solution is between 5 and 15% by weight. 12. The fiber of claim 8 wherein the drying temperature ranges from 100°C to 140°C 13. The fiber of claim 10, wherein said contacting with a sodium hydroxde solution is for a time period short enough to avoid a skin core structure. 14. The process of claim 4, wherein the sodium hydroxide is present in the solution in an amount of less than 20% by weight, and said contacting with a sodium hydroxide solution is for a time period short enough to avoid a skin core structure.