UV-IRRADIATED HOLLOW FIBER MEMBRANES

Abstract

The present invention relates to porous hollow fiber membranes suitable for hemodialysis, hemodiafiltration or hemofiltration of blood and processes for their production involving UV irradiation of the membrane.

Claims

1. A continuous process for treating a porous hollow fiber membrane comprising i) polysulfone, polyethersulfone or polyarylethersulfone; and ii) polyvinylpyrrolidone; the process comprising continuously feeding the porous hollow fiber membrane through a zone in which the membrane is irradiated with UV radiation at a dose of from about 200 to about 800 mJ/cm.sup.2, wherein the UV radiation has a wavelength of about 254 nm and wherein the UV radiation is generated by low-pressure mercury-vapor lamps.

2. The process of claim 1, wherein the porous hollow fiber membrane is wetted with water during irradiation.

3. The process of claim 1, wherein the porous hollow fiber membrane is submerged in water during irradiation.

4. The process of claim 1, wherein the porous hollow fiber membrane is asymmetric.

5. The process of claim 4, wherein the porous hollow fiber membrane has a sponge structure.

6. The process of claim 4, wherein the porous hollow fiber membrane comprises a layer having a finger structure.

7. The process of claim 1, wherein the porous hollow fiber membrane is prepared by a process comprising a) dissolving at least one polysulfone, polyethersulfone (PES), or polyarylethersulfone (PAES), optionally in combination with polyamide (PA), and at least one polyvinylpyrrolidone (PVP) in at least one solvent to form a polymer solution; b) extruding the polymer solution through an outer ring slit of a nozzle with two concentric openings into a precipitation bath; simultaneously c) extruding a center fluid through the inner opening of the nozzle; and d) washing the hollow fiber membrane obtained.

8. The process of claim 1, wherein the porous hollow fiber membrane is dried subsequent to irradiation.

9. The process of claim 8, wherein the porous hollow fiber membrane is sterilized subsequent to drying.

10. The process of claim 9, wherein the porous hollow fiber membrane is steam-sterilized at a temperature of at least 121 C. for at least 21 minutes.

11. The process of claim 2, wherein the porous hollow fiber membrane is asymmetric.

12. The process of claim 3, wherein the porous hollow fiber membrane is asymmetric.

13. The process of claim 2, wherein the porous hollow fiber membrane is prepared by a process comprising a) dissolving at least one polysulfone, polyethersulfone (PES), or polyarylethersulfone (PAES), optionally in combination with polyamide (PA), and at least one polyvinylpyrrolidone (PVP) in at least one solvent to form a polymer solution; b) extruding the polymer solution through an outer ring slit of a nozzle with two concentric openings into a precipitation bath; simultaneously c) extruding a center fluid through the inner opening of the nozzle; and d) washing the hollow fiber membrane obtained.

14. The process of claim 3, wherein the porous hollow fiber membrane is prepared by a process comprising a) dissolving at least one polysulfone, polyethersulfone (PES), or polyarylethersulfone (PAES), optionally in combination with polyamide (PA), and at least one polyvinylpyrrolidone (PVP) in at least one solvent to form a polymer solution; b) extruding the polymer solution through an outer ring slit of a nozzle with two concentric openings into a precipitation bath; simultaneously c) extruding a center fluid through the inner opening of the nozzle; and d) washing the hollow fiber membrane obtained.

15. The process of claim 4, wherein the porous hollow fiber membrane is prepared by a process comprising a) dissolving at least one polysulfone, polyethersulfone (PES), or polyarylethersulfone (PAES), optionally in combination with polyamide (PA), and at least one polyvinylpyrrolidone (PVP) in at least one solvent to form a polymer solution; b) extruding the polymer solution through an outer ring slit of a nozzle with two concentric openings into a precipitation bath; simultaneously c) extruding a center fluid through the inner opening of the nozzle; and d) washing the hollow fiber membrane obtained.

16. The process of claim 5, wherein the porous hollow fiber membrane is prepared by a process comprising a) dissolving at least one polysulfone, polyethersulfone (PES), or polyarylethersulfone (PAES), optionally in combination with polyamide (PA), and at least one polyvinylpyrrolidone (PVP) in at least one solvent to form a polymer solution; b) extruding the polymer solution through an outer ring slit of a nozzle with two concentric openings into a precipitation bath; simultaneously c) extruding a center fluid through the inner opening of the nozzle; and d) washing the hollow fiber membrane obtained.

17. The process of claim 6, wherein the porous hollow fiber membrane is prepared by a process comprising a) dissolving at least one polysulfone, polyethersulfone (PES), or polyarylethersulfone (PAES), optionally in combination with polyamide (PA), and at least one polyvinylpyrrolidone (PVP) in at least one solvent to form a polymer solution; b) extruding the polymer solution through an outer ring slit of a nozzle with two concentric openings into a precipitation bath; simultaneously c) extruding a center fluid through the inner opening of the nozzle; and d) washing the hollow fiber membrane obtained.

18. The process of claim 4, wherein the hollow fiber membrane is dried subsequent to irradiation.

19. The process of claim 6, wherein the hollow fiber membrane is dried subsequent to irradiation.

20. The process of claim 7, wherein the hollow fiber membrane is dried subsequent to irradiation.

Description

[0050] An exemplary device for irradiating a hollow fiber membrane is depicted in FIGS. 1-4.

[0051] FIG. 1 shows a perspective view of the device.

[0052] FIG. 2 shows a side view of the device.

[0053] FIG. 3 shows a front view and a front cross-sectional view of the device.

[0054] FIG. 4 shows a cross-sectional top view of the device (roller 3 not shown). Dimensions are given in mm.

[0055] The reactor comprises a stainless steel container 1. The container 1 is largely box-shaped and has a tapered bottom which facilitates discharge of fluid from the container 1. The container 1 has a height of 1019 mm, a width of 302 mm, and a depth of 479 mm. As shown in FIG. 4, Reflector boards 2 comprised of PTFE (polytetrafluoroethylene) are arranged within the container 1 and define a rectangular compartment having a width of 287 mm and a depth of 359 mm.

[0056] The device features two rollers 3 and 4 which guide the hollow fiber membrane 5. Roller 3 has a diameter of 100 mm. Its axis is positioned 178 mm above the container 1 and 71 mm left of the center plane. Roller 4 is positioned inside the container 1 and has a diameter of 50 mm. Its axis is positioned 1095 mm below and 123.5 mm to the right of the axis of roller 3.

[0057] Ten low pressure amalgam lamps 6 are arranged within the container 1 as shown in FIG. 3. Each lamp 6 (type UVX 60; UV-Technik Speziallampen GmbH, 98704 Wolfsberg, Germany) has a length of 435 mm, an arc length of 359 mm, and a diameter of 15 mm. Lamps 6 each have 60 W power input and 18 W total power output of UV radiation at 254 nm, corresponding to 0.18 mW/cm.sup.2 at 1 m distance. The spacing between the centers of the lamps 6 is 95 mm. Each lamp 6 is positioned within a quartz tube having an outer diameter of 23 mm and a wall thickness of 1.4 mm. The quartz tubes protect the lamps 6 from contact with fluid present in container 1. The quartz tubes can be flushed with pressurized air to cool the lamps 6.

[0058] A cover lid 7 seals the container 1. An UV sensor 8 (SiC-based UV sensor having an entry window for UV radiation with diameter 6.0 mm and 30 opening angle; UV sensor SUV 13 A1, UV-Technik Speziallampen GmbH, 98704 Wolfsberg, Germany) is provided on the lid 7 for measuring UV radiation intensity within the container 1. The UV sensor 8 is positioned inside the compartment defined by the PTFE reflector boards 2, 217.75 mm from the plane defined by the axes of lamps 6 and 10 mm from the back wall of the compartment.

EXAMPLES

Analytical Methods

i) Dynamic Viscosity

[0059] The dynamic viscosity of the polymer solutions was determined according to DIN ISO 1628-1 at a temperature of 22 C. using a capillary viscosimeter (ViscoSystem AVS 370, Schott-Gerte GmbH, Mainz, Germany).

ii) UV Irradiation Dose

[0060] Average irradiance E.sub.av (in mW/cm.sup.2) on the fiber within container 1 was determined from the intensity I (in arbitrary units) of UV radiation in container 1 measured by UV sensor 8 according to formula 1:

E.sub.av [mW/cm.sup.2]=29 mW/cm.sup.2*(I/217)(1)

[0061] The UV irradiation dose H (in mJ/cm.sup.2) was calculated from the average irradiance E.sub.av and the residence time t.sub.R (in seconds) of the fiber in the container 1.

H [mJ/cm.sup.2]=E.sub.av [mW/cm.sup.2]*t.sub.R [s](2)

iii) Residual Content of Extractable PVP

[0062] Fibers were cut into pieces having a length of about 5 cm and about 1 g of cuttings were transferred to an Erlenmeyer flask. RO water was added (80 ml of water per g of fiber) and the cuttings were extracted for 20 hours at 90 C. The extract was filtered through a filter paper. 1000 l of the extract was transferred to a cuvette. 500 l 2M citric acid solution and 200 l 0.006 N KJ.sub.3 solution were added. The cuvette was sealed with a stopper and shaken to mix the contents. PVP content of the extract was determined by quantitative UV/VIS spectroscopy of the iodine complex of PVP at 470 nm. At each measurement, standards having a PVP concentration of 5 mg/l and 25 mg/l, respectively, were used as controls. From the measured PVP concentration, the content of extractable PVP in the fiber, relative to fiber dry weight, was calculated.

Example 1

[0063] A polymer solution was prepared by dissolving polyethersulfone (Ultrason 6020, BASF Aktiengesellschaft) and polyvinylpyrrolidone (K30 and K85, BASF Aktiengesellschaft) and distilled water in N-methyl-2-pyrrolidone (NMP). The weight fraction of the different components in the polymer spinning solution was:

PES:PVP K85:PVP K30:H.sub.2O:NMP=14:2:5:3:76.

[0064] The viscosity of the polymer solution was 5,210 mPa.Math.s.

[0065] A bore liquid was prepared by mixing distilled water and N-Methyl-2-pyrrolidone (NMP). The weight fraction of the two components in the center fluid was:

H.sub.2O:NMP=54.5 wt %:45.5 wt %.

[0066] A membrane was formed by heating the polymer solution to 50 C. and passing the solution as well as the bore liquid through a spinning die. The temperature of the die was 58 C. and of the spinning shaft was 56 C. The liquid capillary leaving the die was passed into a water bath (ambient temperature). The distance between the die and the precipitation bath was 100 cm.

[0067] The hollow fiber membrane formed was drawn off from the water bath at a speed of 55 m/min (=spinning speed) and subsequently washed by guiding it through 5 water baths having temperatures in the range of 40 to 80 C.

[0068] Downstream of the fifth water bath, the fiber was fed to the irradiation device via roller 3. Container 1 of the irradiation device held 8 l of water, so that the fiber was rewetted with water when passing roller 4.

[0069] UV irradiation dose on the fiber was varied between the individual runs by changing the number of enlacements of the fiber on rollers 3 and 4. In order to establish a reference value for the content of extractable PVP in the fiber, one run was conducted without UV irradiation.

[0070] After leaving the irradiation device via roller 3, the fiber was fed to an online-dryer and the dried fiber was wound onto a winding wheel. The dry hollow fiber membrane had an inner diameter of 190 m and an outer diameter of 260 m and a fully asymmetric membrane structure. The active separation layer of the membrane was at the inner side. The active separation layer is defined as the layer with the smallest pores.

[0071] Fiber bundles were cut from the winding wheel and steam-sterilized at 121 C. for 21 minutes. The amount of extractable PVP (in mg PVP per g of dry fiber) in the fibers after sterilization was determined as described above.

[0072] Seven runs were conducted, each with a different UV irradiation dose on the fiber. The number of enlacements, the UV irradiation dose in mJ/cm.sup.2, and the content of extractable PVP of the final fiber, both in mg per g of dry fiber and relative to the unirradiated fiber, are summarized in Table 1.

TABLE-US-00001 TABLE 1 Extractable UV Dose PVP Run Enlacements [mJ/cm.sup.2] [mg/g] [%] 1.1* 1 3.56 100 1.2 8 513 2.42 68 1.3 7 447 2.44 .sup.68.sub.5 1.4 6 375 2.64 74 1.5 5 312 2.76 .sup.77.sub.5 1.6 4 250 2.88 81 1.7 3 192 2.96 83 *comparative example

Example 2

[0073] Example 1 was repeated using a spinning speed of 50 m/min instead of 55 m/min. Five runs were conducted, each with a different UV irradiation dose on the fiber. The number of enlacements, the UV irradiation dose in mJ/cm.sup.2, and the content of extractable PVP of the final fiber, both in mg per g of dry fiber and relative to the unirradiated fiber, are summarized in Table 2.

TABLE-US-00002 TABLE 2 Extractable UV Dose PVP Run Enlacements [mJ/cm.sup.2] [mg/g] [%] 2.1* 1 4.35 100 2.2 7 635 2.20 .sub.50.sub.5 2.3 6 559 2.25 52 2.4 5 472 2.20 .sub.50.sub.5 2.5 4 382 2.50 .sub.57.sub.5 *comparative example

Example 3

[0074] Example 2 was repeated with the container 1 of the irradiation device being completely filled with water. Six runs were conducted, each with a different UV irradiation dose on the fiber. The number of enlacements, the UV irradiation dose in mJ/cm.sup.2, and the content of extractable PVP of the final fiber, both in mg per g of dry fiber and relative to the unirradiated fiber, are summarized in Table 3.

TABLE-US-00003 TABLE 3 Extractable UV Dose PVP Run Enlacements [mJ/cm.sup.2] [mg/g] [%] 3.1* 8 3.90 100 3.2 8 578 2.10 54 3.3 7 520 2.10 54 3.4 6 451 2.15 55 3.5 5 382 2.30 59 3.6 4 310 2.50 64 *comparative example