MELT-SPUN POLYSULFONE SEMIPERMEABLE MEMBRANES AND METHODS FOR MAKING THE SAME

MEMBRANES SEMI-PERMEABLES POLYSULFONES FILEES PAR FUSION ET LEURS PROCEDES DE FABRICATION

English Abstract

The present invention discloses, inter alia, a composition useful for
producing a homogeneous, semipermeable membrane, the composition comprising
(1) a polysulfone compound, (2) a solvent, such as sulfolane, antypyrine,
.delta.-valerolactam, diethyl phthalate, and mixtures thereof, and (3) a non-
solvent, such as poly(ethylene glycol), di(ethylene glycol), tri(ethylene
glycol), glycerol, and mixtures thereof. Another aspect of this invention
discloses methods for fabricating semipermeable membranes by homogeneously
mixing the composition of the polysulfone compound, solvent, and non-solvent,
melting the composition, and melt-spinning the molten composition. Another
aspect of the present invention includes homogeneous, melt-spun, semipermeable
membranes useful for liquid separation processes, such as, but not limited to,
microfiltration, ultrafiltration, dialysis, and reverse osmosis.

French Abstract

L'invention concerne, en premier lieu, une composition qui permet de fabriquer une membrane semi-perméable homogène. Ladite composition comprend (1) un composé polysulfone, (2) un solvant, tel que sulfolane, antipyrine, .delta.-valérolactam, diéthyl phtalate et des mélanges de ces produits, et (3) une substance non solvante, telle que poly(éthylène glycol), di(éthylène glycol), tri(éthylène glycol), glycérol et des mélanges de ces produits. Selon un autre aspect, la présente invention concerne des procédés permettant de fabriquer des membranes semi-perméables en mélangeant de façon homogène la composition de composé polysulfone, le solvant et la substance non solvante, en faisant fondre ladite composition et en filant par fusion la composition fondue. Selon un autre aspect encore, la présente invention concerne des membranes semi-perméables, homogènes et filées par fusion, particulièrement utiles pour les procédés de séparation de liquide, tels que, mais pas exclusivement, la microfiltration, l'ultrafiltration, la dialyse et l'osmose inverse.

Claims

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CLAIMS:
1. A composition useful for making a polysulfone semipermeable membrane, the
composition comprising a mixture of:
a polysulfone compound; and
a solvent for the polysulfone compound.
2. The composition of claim 1, wherein the polysulfone compound is a
polyarylsulfone
compound.
3. The composition of claim 1, wherein the polysulfone compound is selected
from the
group consisting of bisphenol A polysulfone, polyether polysulfone, polyphenyl
polysulfone, and
mixtures thereof.
4. The composition of claim 1, wherein the solvent is selected from the group
consisting
of tetramethylene sulfone, antipyrine, .delta.-valerolactam, diethyl
phthalate, and mixtures thereof.
5. A composition useful for making a polysulfone semipermeable membrane, the
composition comprising a mixture of:
a polysulfone compound;
a solvent for the polysulfone compound; and
a non-solvent for the polysulfone compound.
6. The composition of claim 5, wherein the non-solvent is selected from the
group
consisting of 1,1-diethylurea, 1,3-diethylurea, dinitrotoluene, 1,2-ethane
diamine, diphenylamine,
toluenediamine, o-toluic acid, m-toluic acid, toluene-3,4-diamine, dibutyl
phthalate, piperidine,
decalin, cyclohexane, cyclohexene, chlorocyclohexane, cellosolve solvent,
n,n-dimethylbenzylamine, paraffin, mineral oil, mineral wax, tallow amine,
triethanol amine, lauryl
methacrylate, stearic acid, di(ethylene glycol), tri(ethylene glycol),
ethylene glycol, poly(ethylene
glycol), tetra(ethylene glycol), glycerin) diethyl adipate, d-sorbitol,
chlorotriphenyl stannane,
resorcinol, 2-methyl-8-quinolinol, quinaldine, 4-phenylpyridine,
phosphorothioic acid, o,o-diethyl
o-(p-nitrophenyl) ester, N,N-dimethyl-p-phenylene diamine, 2,6-
dimethoxyphenol,
4-allyl-2-methoxyphenol, phenanthridine, 2-naphthylamine, 1-naphthylamine, 1-
naphthol,
2-naphthalenethiol, 1-bromonaphthalene, levulinic acid, phenyl pyrrol-2-yl
ketone, phenyl 4-pyridyl
ketone, isothiocyanic acid, m-nitrophenyl ester, 2-methyl-1H-indole, 4-methyl
imidazole,
imidazole, 1,7-heptanediol, 9H-fluoren-9-one, ferrocene, 2,2',2"-
nitrilotriethanol,
2,2'-iminodiethanol, dibenzofuran, cyclohexaneacetic acid, cyanamide,
courmarin, 2,2'-bipyridine,
benzoic acid, benzenepropionic acid, o-dinitrobenzene, 9-methyl-9-
azabicyclo(3.3.1)nonan-3-one,
chlorodiphenylarsine, antimony bromide, p-anisidine, o-anisaldehyde,
adiponitrile, p-amino
acetophenone, monoacetin, diacetin, triacetin, pentoxane, 4-benzoylbiphenyl,
methyl oleate,
triethylphosphate, butyrolactone, terphenyl, tetradecanol, polychlorinated
biphenyl, myristic acid,
methacrylic acid, dodecyl ester, isocyanic acid, methylenedi-p-phenylene
ester,
2-((2-hexyloxy)ethoxy) ethanol, 4-nitro biphenyl, benzyl ether,
benzenesulfonyl chloride,
2,4-diisocyanato-1-1-methyl benzene, adipic acid, diethyl ester, 2'-nitro-
acetophenone) 1'-

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acetonaphthone, tetradecanone, (dichlorophenyl)trichlorosilane,
dichlorodiphenyl silane,
phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester, phosphoric acid,
tri-o-tolyl ester,
phosphoric acid, triphenyl ester, phosphoric acid, tributyl ester, phenyl
phosphorous dichloride,
p-nitrophenol, isocyanic acid, methyl-m-phenylene ester, 2,2'-iminodiethanol,
N-(2-aminoethyl)-
N'-(2-((2-aminoethyl)amino)ethyl) 1,2-ethanediamine, 2,6-di-tert-butyl p-
cresol, chloro biphenyl,
4-biphenylamine, benzyl ether, benzenesulfonyl chloride, 1,2-(methylenedioxy)-
4-propenyl
benzene, 2,4-diisocyanato-1-methyl benzene, chlorodinitro benzene (mixed
isomers), hexahydro
2H-azepin-2-one, 4,4'-methylenedianiline, 1'-acetonaphthone, mercapto acetic
acid, acetanilide,
glycerol, and mixtures thereof, wherein the solvent and non-solvent are
present in the composition
in a ratio sufficient to form a semipermeable membrane useful for liquid-
separation processes.
7. The composition of claim 5 having a viscosity, at a temperature in which
the
composition is a homogeneous mixture, sufficient to allow melt-extrusion of
the composition to
form a semipermeable polysulfone membrane.
8. The composition of claim 5, wherein the polysulfone compound is a
polyarylsulfone
compound.
9. The composition of claim 5, wherein the polysulfone compound is selected
from the
group consisting of bisphenol A polysulfone, polyether polysulfone, polyphenyl
polysulfone, and
mixtures thereof.
10. The composition of claim 8, wherein the polysulfone compound comprises
bisphenol
A polysulfone.
11. The composition of claim 5, comprising between about 8 and about 80
percent by
weight polysulfone compound.
12. The composition of claim 5, comprising at least about 25 percent by weight
polysulfone compound.
13. The composition of claim 5, wherein the solvent is selected from the group
consisting
of tetramethylene sulfone, 3-methyl sulfolane, benzophenone, n,n-
dimethylacetamide,
2-pyrrolidone, 3-methylsulfolene, pyridine, thiophene, o-dichlorobenzene, 1-
chloronaphthalene,
methyl salicylate, anisole, o-nitroanisole, diphenyl ether, diphenoxy methane,
acetophenone,
p-methoxyphenyl-2-ethanol, 2-piperidine, antipyrine, .delta.-valerolactam,
diethyl phthalate, diphenyl
sulfone, diphenyl sulfoxide, phthalic acid, dioctyl ester, phthalic acid,
dimethyl ester, phthalic
acid, diethyl ester, phthalic acid, dibutyl ester, phthalic acid, bis(2-
ethylhexyl) ester, phthalic
acid, benzyl butyl ester, phenyl sulfide, and mixtures thereof.
14. The composition of claim 5, wherein the solvent is selected from the group
consisting
of tetramethylene sulfone, antipyrine, .delta.-valerolactam, diethyl
phthalate, and mixtures thereof.
15. The composition of claim 5, wherein the solvent comprises tetramethylene
sulfone.
16. The composition of claim 5, wherein the solvent and non-solvent are
present in a ratio
of about 2:1 to about 10:1.

0
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17. A composition useful for making a polysulfone semipermeable membrane, the
composition consisting of:
a polysulfone compound; and
a solvent for the polysulfone compound.
18. The composition of claim 17, wherein the polysulfone compound is a
polyarylsulfone
compound.
19. The composition of claim 17, wherein the polysulfone compound is selected
from the
group consisting of bisphenol A polysulfone, polyether polysulfone, polyphenyl
polysulfone, and
mixtures thereof.
20. The composition of claim 17, wherein the solvent is selected from the
group
consisting of tetramethylene sulfone, 3-methyl sulfolane, benzophenone, n,n-
dimethylacetamide,
2-pyrrolidone, 3-methylsulfolene, pyridine, thiophene, o-dichlorobenzene, 1-
chloronaphthalene,
methyl salicylate, anisole, o-nitroanisole, diphenyl ether, diphenoxy methane,
acetophenone,
p-methoxyphenyl-2-ethanol, 2-piperidine, antipyrine, diethyl phthalate,
diphenyl sulfone, diphenyl
sulfoxide, phthalic acid, dioctyl ester, phthalic acid, dimethyl ester,
phthalic acid, diethyl ester,
phthalic acid, dibutyl ester, phthalic acid, bis(2-ethylhexyl) ester, phthalic
acid, benzyl butyl
ester, phenyl sulfide, and mixtures thereof.
21. A process for making a polysulfone semipermeable membrane, the process
comprising the steps of:
(a) forming a composition including a polysulfone compound, a solvent for the
polysulfone compound, and a non-solvent for the polysulfone compound, the
solvent and
non-solvent being present in the composition in a ratio sufficient to form a
semipermeable membrane
useful for a liquid separation process;
(b) heating the composition to a temperature at which the composition is a
homogeneous
liquid;
(c) extruding the homogeneous liquid to form an extrudate; and
(d) quenching the extrudate to form a semipermeable membrane.
22. The process of claim 21, wherein the solvent is selected from the group
consisting of
tetramethylene sulfone, 3-methyl sulfolane, benzophenone, n,n-
dimethylacetamide, 2-pyrrolidone,
3-methylsulfolene, pyridine, thiophene, o-dichlorobenzene, 1-
chloronaphthalene, methyl
salicylate, anisole, o-nitroanisoie, diphenyl ether, diphenoxy methane,
acetophenone.
p-methoxyphenyl-2-ethanol, 2-piperidine, antipyrine, .delta.-valerolactam,
diethyl phthalate, diphenyl
sulfone, diphenyl sulfoxide, phthalic acid, dioctyl ester, phthalic acid,
dimethyl ester, phthalic
acid, diethyl ester, phthalic acid, dibutyl ester, phthalic acid, bis(2-
ethylhexyl) ester, phthalic
acid, benzyl butyl ester, phenyl sulfide, and mixtures thereof.
23. The process of claim 21, wherein polysulfone compound is a polyarylsulfone
compound.

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24. The process of claim 21, wherein the polysulfone compound is selected from
the
group consisting of bisphenol A polysulfone, polyether polysulfone, polyphenyl
polysulfone, and
mixtures thereof.
25. The process of claim 21, wherein the non-solvent is selected from the
group
consisting of poly(ethylene glycol), di(ethylene glycol), tri(ethylene
glycol), glycerol, and
mixtures thereof.
26. The process of claim 21, wherein the step of quenching the extrudate
comprises
passing the extrudate through a quench zone, the quench zone comprising a
fluid selected from
the group consisting of air, water, glycerol, tetramethylene sulfone, and
mixtures thereof.
27. The process of claim 21, further comprising the step of drawing the
semipermeable
membrane.
28. The process of claim 21, further comprising the step of storing the
semipermeable
membrane in a liquid for a period of about 4 hours to about 15 days.
29. The process of claim 28, further comprising the step of passing the
semipermeable
membrane through a leach bath.
30. The process of claim 28, wherein the leach bath comprises a non-solvent
for the
polysulfone compound.
31. The process of claim 28, wherein the leach bath comprises water.
32. The process of claim 29, further comprising the step of passing the
semipermeable
membrane through a rinse bath.
33. The process of claim 32, wherein the rinse bath comprises water.
34. The process of claim 32, further comprising the step of passing the
semipermeable
membrane through a replasticization bath.
35. The process of claim 34, wherein the replasticization bath comprises an
aqueous
glycerol solution.
36. The process of claim 35, wherein the aqueous glycerol solution comprises
less than
about 50 percent glycerol by weight.
37. The process of claim 34, further comprising the step of drying the
semipermeable
membrane.
38. The process of claim 37, wherein the semipermeable membrane is dried in an
oven.
39. A process for making a polysulfone semipermeable membrane useful for a
liquid
membrane separation process, the process comprising the steps of:
(a) forming a composition including a polysulfone compound, a solvent for the
polysulfone compound, and a non-solvent for the polysulfone compound, wherein
the solvent and
non-solvent are present in a ratio sufficient to form a semipermeable membrane
useful for a liquid
separation process;
(b) heating the composition to a temperature at which the composition is a
homogeneous
liquid;

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(c) forcing the homogeneous liquid through a strand die to produce solid
strands;
(d) pelletizing the strands to a particle size readily fed to an extruder;
(e) remelting the particles; and
(f) extruding the melted pellets to form a semipermeable membrane.
40. The process of claim 39 wherein the solvent is selected from the group
consisting of
tetramethylene sulfone, 3-methyl sulfolane, benzophenone, n,n-
dimethylacetamide, 2-pyrrolidone,
3-methylsulfolene, pyridine, thiophene, o-dichlorobenzene, 1-
chloronaphthalene, methyl
salicylate, anisole, o-nitroanisole, diphenyl ether, diphenoxy methane,
acetophenone,
p-methoxyphenyl-2-ethanol, 2-piperidine, antipyrine, diethyl phthalate,
diphenyl sulfone, diphenyl
sulfoxide, phthalic acid, dioctyl ester, phthalic acid, dimethyl ester,
phthalic acid, diethyl ester,
phthalic acid, dibutyl ester, phthalic acid, bis(2-ethylhexyl) ester, phthalic
acid, benzyl butyl
ester, phenyl sulfide, ~-valerolactam, diethyl phthalate, and mixtures
thereof.
41. The process of claim 39 wherein the non-solvent is selected from the group
consisting
of 1,1-diethylurea, 1,3-diethylurea, dinitrotoluene, 1,2-ethane diamine,
diphenylamine,
toluenediamine, o-toluic acid, m-toluic acid, toluene-3,4-diamine, dibutyl
phthalate, piperidine,
decalin, cyclohexane, cyclohexene, chlorocyclohexane, cellosolve solvent,
n,n-dimethylbenzylamine, paraffin, mineral oil, mineral wax, tallow amine,
triethanol amine, lauryl
methacrylate, stearic acid, di(ethylene glycol), tri(ethylene glycol),
ethylene glycol, poly(ethylene
glycol), tetra(ethylene glycol), glycerin, diethyl adipate, d-sorbitol,
chlorotriphenyl stannane,
resorcinol, 2-methyl-8-quinolinol, quinaldine, 4-phenylpyridine,
phosphorothioic acid, o,o-diethyl
o-(p-nitrophenyl) ester, N,N-dimethyl-p-phenylene diamine, 2,6-
dimethoxyphenol, 4-allyl-2-
methoxyphenol, phenanthridine, 2-naphthylamine, 1-naphthylanune, 1-naphthol,
2-naphthalenethiol, 1-bromonaphthalene, levulinic acid, phenyl pyrrol-2-yl
ketone, phenyl 4-pyridyl
ketone, isothiocyanic acid, m-nitrophenyl ester, 2-methyl-1H-indole, 4-methyl
imidazole,
imidazole, 1,7-heptanediol, 9H-fluoren-9-one, ferrocene, 2,2',2"-
nitrilotriethanol,
2,2'-iminodiethanol, dibenzofuran, cyclohexaneacetic acid, cyanamide)
courmarin, 2,2'-bipyridine,
benzoic acid, benzenepropionic acid, o-dinitrobenzene, 9-methyl-9-
azabicyclo(3.3.1)nonan-3-one,
chlorodiphenylarsine, antimony bromide, p-anisidine, o-anisaldehyde,
adiponitrile, p-amino
acetophenone, monoacetin, diacetin, triacetin, pentoxane, 4-benzoylbiphenyl,
methyl oleate,
triethylphosphate, butyrolactone, terphenyl, tetradecanol, polychlorinated
biphenyl, myristic acid,
methacrylic acid, dodecyl ester, isocyanic acid, methylenedi-p-phenylene
ester, 2-((2-
hexyloxy)ethoxy) ethanol, 4-nitro biphenyl, benzyl ether, benzenesulfonyl
chloride,
2,4-diisocyanato-1-1-methyl benzene, adipic acid, diethyl ester, 2'-nitro-
acetophenone,
1'-acetonaphthone, tetradecanone, (dichlorophenyl)trichlorosilane,
dichlorodiphenyl silane,
phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester, phosphoric acid,
tri-o-tolyl ester,
phosphoric acid, triphenyl ester, phosphoric acid, tributyl ester, phenyl
phosphorous dichloride,
p-nitrophenol, isocyanic acid, methyl-m-phenylene ester, 2,2'-iminodiethanol,
N-(2-aminoethyl)-
N'-(2-((2-aminoethyl)amino)ethyl) 1,2-ethanediamine, 2,6-di-tert-butyl p-
cresol, chloro biphenyl,

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4-biphenylamine, benzyl ether, benzenesulfonyl chloride, 1,2-(methylenedioxy)-
4-propenyl
benzene, 2,4-diisocyanato-1-methyl benzene, chlorodinitro benzene (mixed
isomers), hexahydro
2H-azepin-2-one, 4,4'-methylenedianiline, 1'-acetonaphthone, mercapto acetic
acid, acetanilide,
glycerol, and mixtures thereof
42. The process of claim 39, wherein the polysulfone compound is a
polyarylsulfone
compound.
43. The process of claim 39, further including the step of quenching the
extrudate by
passing the extrudate through a quench zone, the quench zone comprising a
fluid selected from
the group consisting of air, water, glycerol, tetramethylene sulfone, and
mixtures thereof.
44. The process of claim 39 further comprising the step of drawing the
semipermeable
membrane.
45. The process of claim 39, further comprising the step of storing the
semipermeable
membrane in a liquid for a period of about 4 hours to about 15 days.
46. The process of claim 39, further comprising the step of passing the
semipermeable
membrane through a leach bath.
47. The process of claim 46, wherein the leach bath comprises a non-solvent
for the
polysulfone compound.
48. The process of claim 46, wherein the leach bath comprises water.
49. The process of claim 39, further comprising the step of passing the
semipermeable
membrane through a rinse bath.
50. The process of claim 49 wherein the rinse bath comprises water.
51. The process of claim 39, further comprising the step of passing the
semipermeable
membrane through a replasticization bath.
52. The process of claim 51 wherein the replasticization bath comprises an
aqueous
glycerol solution.
53. The process of claim 52 wherein the aqueous glycerol solution comprises
less than
about 50 percent glycerol by weight.
54. The process of claim 39, further comprising the step of drying the
semipermeable
membrane.
55. The process of claim 54, wherein the semipermeable membrane is dried in an
oven.
56. A semipermeable polysulfone membrane made by the process of claim 21.
57. A semipermeable polysulfone membrane made by the process of claim 39.
58. A melt-spun, substantially homogeneous, semipermeable polysulfone membrane
useful
for liquid separation processes.
59. The semipermeable polysulfone membrane of claim 58 having an in vitro
water flux
value of at least about 9 mL/(hr~mmHg~m2).
60. The semipermeable polysulfone membrane of claim 58 comprising a hollow
fiber
having a lumen and an average K ov for sodium chloride of at least about 0.5 x
10 -2 centimeters

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per minute at a solution flow rate through the fiber lumen of about 0.02
milliliters per minute per
fiber.
61. A dialyzer comprising the semipermeable polysulfone membrane of claim 58.
62. An extracorporeal blood treatment device comprising the semipermeable
polysulfone
membrane of claim 58.
63. A liquid-separation device comprising the semipermeable polysulfone
membrane of
claim 58.

Description

CA 02272364 1999-OS-19
WO 98!29478 PCT/LTS97/24087
MELT-SPUN POLYSULFONE SEMIPERMEABLE MEMBRANES
AND METHODS FOR MAKING THE SAME
FIELD OF THE INVENTION
The present invention concerns poiysulfone semipermeable membranes and methods
for
making the same. More particularly, the invention pertains to melt-spun
polysulfone
semipermeable membranes.
BACKGROUND OF THE INVENTION
Contemporary semipermeable membranes are available in a variety of forms such
as
sheets, tubes, and hollow fibers. A "hollow fiber" is generally a hollow
cylindrical structure in
which the wall functions as a permeable, non-permeable, or semipermeable
(i.e., selectively
permeable) membrane depending upon the application. Generally, hollow fibers
are used as
cylindrical membranes that permit selective exchange of materials across the
walls.
Liquid-separation processes utilizing membranes having selective
permeabilities, such
processes including ultrafiltration) microfiltration, dialysis ) reverse
osmosis, or the like, require a
variety of materials adapted for diversified applications. For example,
semipermeable membranes
are currently favored for use in extracorporeal blood treatments including
hemodialysis,
hemofiltration, and hemodiafiltration. In such cases ) the membranes typically
comprise hollow
fibers bundled together and assembled in a casing in a manner allowing blood
to flow
simultaneously in a parallel manner through the lumina of the fibers while a
blood-cleansing
liquid is simultaneously passed through the casing so as to bathe the exterior
surfaces of the
hollow fibers with the liquid.
Compounds utilized for selectively permeable membranes have included polymers,
such as
cellulose, cellulose acetate, polyamide) polyacrylonitrile) polyvinylalcohol,
polymethyl
methacrylate, polysulfone) polyolefin, or the like) depending upon the use of
the membranes.
Polysulfone compounds are of particular interest as they have, inter alia)
excellent physical and
chemical properties, such as resistance to heat, resistance to acids,
resistance to alkali, and
resistance to oxidation. Polysulfone compounds have been found to be
biocompatible, capable of
forming excellent pores and interstitia, and chemically inert to such
compounds as bleach)
disinfectants) and salt solutions. Polysulfone compounds can be sterilized by
a number of
methods, such as ethylene oxide (Et0)) gamma irradiation, steam autoclave, and
heated citric
acid. Additionally, polysulfone compounds possess sufficient strength and
resistance to wear to
withstand repeated use and sterilization cycles.
Conventionally) polysulfone hollow fibers have been formed by solution-
spinning
techniques. Producing polysulfone hollow fibers by solution-spinning
techniques typically
involves dissolving a polysulfone compound in a relatively large amount of an
aprotic solvent and
a non-solvent, then extruding the solution through a spinneret. For solution
spinning, a "solvent"
is a compound in which the polysulfone compound substantially dissolves at the
membrane-

CA 02272364 1999-OS-19
WO 98129478 PCTIUS97/24087
-2-
fabrication temperature (i.e., ambient temperature). For solution spinning, a
"non-solvent" is a
compound in which the polysulfone compound is substantially insoluble at the
membrane-
fabrication temperature. For solution-spinning techniques, the solvents must
be sufficient to
substantially dissolve the polysulfone compound and produce a homogeneous
liquid at ambient
S temperature (membrane fabrication temperature).
The solvents and non-solvents utilized for solution-spinning techniques
require that the
membranes be extensively leached and rinsed after fabrication, as even
residual amounts left in
the membranes can cause unacceptable contamination of fluids treated using the
membranes.
Avoiding such contamination is particularly important in membranes used for
the treatment of
blood by dialysis or the desalination of water by reverse osmosis. When
fabricating hollow-fiber
membranes utilizing solution spinning techniques, removal of the core liquid
used to form the
fiber lumen is especially difficult. Following removal of the solvents, non-
solvents) and core
liquid, a non-volatile, water-soluble compound must then be added to preserve
the membrane
pore structure prior to drying the membrane. The non-volatile material also
serves as a surfactant
for later rewetting of the membranes. Such a process is known as
"replasticization. "
Solution-spinning techniques require the inclusion of large amounts of
solvents and non-
solvents many of which are generally toxic and can be difficult to extract
from the resulting
polysulfone fiber. Moreover, the significant amount and high level of toxicity
of certain solvents
and non-solvents removed from the fibers may create a hazardous waste-disposal
problem.
Moreover, conventional solution-spinning techniques produce asymmetric
polysulfone
membranes (i.e.) non-homogeneous membrane porosity progressing through the
thickness
dimension of the membrane). That is, a non-homogeneous membrane has a dense
skin or micro-
porous barrier layer on one (or both) of the major surfaces of the membrane.
The dense skin or
micro-porous barrier layer comprises a relatively small portion of the
membrane but contributes a
disproportionally large amount of control on the permeability characteristics
of the membrane.
Accordingly, there is a need for a polysulfone composition and simple method
for the
production of polysulfone semipermeable membranes which composition and method
minimizes
toxic waste by-products. Additionally) there is a need for a method for the
production of
polysulfone semipermeable membranes wherein the solvents, non-solvents, and
processing aids
used in the manufacture of the membranes are easily removed from the membranes
after
fabrication andlor are of relatively low toxicity. There is also a need for
polysulfone
semipermeable membranes having a more uniform structure throughout the
thickness dimension
(i.e.) a homogeneous polysulfone membrane) so that the entire thickness
dimension controls the
permeability of the membrane.
SUMMARY OF THE INVENTION
In general, the present invention provides, inter alia, a novel method and
polysulfone
composition for preparing a homogeneous, semipermeable polysulfone membrane by
melt-spinning. The polysulfone composition comprises a liquid mixture of a
polysulfone
_......~__

CA 02272364 1999-OS-19
WO 98/29478 PCT/US97/24087
-3-
compound) a solvent and) optionally, a non-solvent that are relatively non-
toxic and that
preferably do not deleteriously affect the environment.
The solvent may be selected from the group consisting of tetramethylene
sulfone
("sulfolane"); 3-methyl sulfolane; benzophenone; n,n-dimethylacetamide; 2-
pyrrolidone; 3-
methylsulfolene; pyridine; thiophene; o-dichlorobenzene; 1-chloronaphthalene;
methyl salicylate;
anisole; o-nitroanisole; Biphenyl ether; diphenoxy methane; acetophenone; p-
methoxyphenyl-2-
ethanol; 2-piperidine; antipyrine; diethyl phthalate; Biphenyl sulfone;
Biphenyl sulfoxide; phthalic
acid, dioctyl ester; phthalic acid, dimethyl ester; phthalic acid, diethyl
ester; phthalic acid, dibutyl
ester; phthalic acid, bis(2-ethylhexyl) ester; phthalic acid, benzyl butyl
ester; and phenyl sulfide.
Especially good results have been achieved when the solvent comprises
sulfolane, 2,3-
dimethyl-1-phenyl-3-pyrazolin-5-one (antipyrine), 2-piperidine (b-
valerolactam) diethyl phthalate,
or a mixture thereof.
The non-solvent may be selected from the group consisting of polyethylene
glycol),
di(ethylene glycol)) tri(ethylene glycol), glycerol, 1,1-diethylurea; 1,3-
diethylurea; dinitrotoluene;
1,2-ethane diamine; diphenyiamine; toluenediamine; o-toluic acid; m-toluic
acid; toluene-3,4-
diamine; dibutyl phthalate; piperidine; decalin; cyclohexane; cyclohexene;
chlorocyclohexane;
"cellosolve" solvent; n,n-dimethylbenzylamine; paraffin; mineral oil; mineral
wax; tallow amine;
triethanol amine; lauryl methacrylate; stearic acid; ethylene glycol;
tetra(ethylene glycol); diethyl
adipate; d-sorbitol; chlorotriphenyl stannane; resorcinol; 2-methyl-8-
quinolinol; quinaldine; 4-
phenylpyridine; phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester; N,N-
dimethyl-p-
phenylene diamine; 2,6-dimethoxyphenol; 4-allyl-2-methoxyphenol;
phenanthridine; 2-
naphthylamine; 1-naphthylamine; 1-naphthol; 2-naphthalenethiol; 1-
bromonaphthalene; levulinic
acid; phenyl pyrrol-2-yl ketone; phenyl 4-pyridyl ketone; isothiocyanic acid,
m-nitrophenyl ester;
2-methyl-1H-indole; 4-methyl imidazole; imidazole; 1,7-heptanediol; 9H-fluoren-
9-one; ferrocene;
2,2',2"-nitrilotriethanol; 2,2'-iminodiethanol; dibenzofuran;
cyclohexaneacetic acid; cyanamide;
courmarin; 2,2'-bipyridine; benzoic acid; benzenepropionic acid; o-
dinitrobenzene; 9-methyl-9-
azabicyclo(3.3.1)nonan-3-one; chlorodiphenylarsine; antimony bromide; p-
anisidine; o-
anisaldehyde; adiponitrile; p-amino acetophenone; monoacetin; diacetin;
triacetin; pentoxane; 4-
benzoylbiphenyl; methyl oleate; triethylphosphate; butyrolactone; terphenyl;
tetradecanol;
polychlorinated biphenyl ("Aroclor 1242"); myristic acid; methacrylic acid,
dodecyl ester;
isocyanic acid) methylenedi-p-phenylene ester; 2-((2-hexyloxy)ethoxy) ethanol;
4-nitro biphenyl;
benzyl ether; benzenesulfonyl chloride; 2,4-diisocyanato-1-1-methyl benzene;
adipic acid) diethyl
ester; 2'-nitro-acetophenone; 1'-acetonaphthone; tetradecancne;
(dichlorophenyl)trichlorosilane;
dichlorodiphenyl silane; phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl)
ester; phosphoric
acid, tri-o-tolyl ester; phosphoric acid, triphenyl ester; phosphoric acid,
tributyl ester; phenyl
phosphorous dichloride; p-nitrophenol; isocyanic acid) methyl-m-phenylene
ester; 2,2'-
iminodiethanol; N-(2-aminoethyl)-N'-(2-((2-aminoethyl)amino)ethyl) 1,2-
ethanediamine; 2,6-di-
tert-butyl p-cresol; chloro biphenyl; 4-biphenylamine; benzyl ether;
benzenesulfonyl chloride; 1,2-

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(methylenedioxy)-4-propenyl benzene; 2,4-diisocyanato-1-methyl benzene;
chlorodinitro benzene
(mixed isomers); hexahydro 2H-azepin-2-one; 4,4'-methylenedianiline; I'-
acetonaphthone;
mercapto acetic acid; and acetanilide. Especially good results have been
achieved when the non-
solvent comprises polyethylene glycol)) di(ethyIene glycol), tri(ethylene
glycol), glycerol, or a
mixture thereof.
The solvent and non-solvent are present in a ratio useful to form a
semipermeable)
polysulfone membrane useful for performing liquid-separation processes.
According to another aspect of the invention) a "melt-spinning" or "melt-
extrusion"
method is provided for producing semipermeable, polysulfone membranes. The
melt-spinning
method includes the steps of: ( 1 ) forming a composition comprising a
polysuIfone compound, a
solvent selected from the foregoing group of candidate solvents and preferably
selected from the
group consisting of tetramethylene sulfone, antypyrine, d-valerolactam,
diethyl phthalate) and
mixtures thereof, and, optionally, a non-solvent selected from the foregoing
group of candidate
non-solvents and preferably selected from the group consisting of polyethylene
glycol),
di(ethylene glycol), tri(ethylene glycol)) glycerol, and mixtures thereof; (2)
heating the
composition to a temperature at which the composition becomes a homogeneous
liquid (i.e.) a
temperature greater than ambient); (3) extruding the composition through an
extrusion die (such
as a single or multi-holed hollow-fiber die (termed a "spinneret"); and (4)
passing the extrudate
through a quench zone in which the extrudate gels and solidifies, thereby
forming the membrane.
According to another aspect of the present invention, melt-spun,
semipermeable)
polysulfone membranes are provided having a uniform structure throughout the
thickness
dimension of the membrane (i.e., a "homogeneous" membrane structure) useful
for liquid
separations, such as, but not limited to, microfiltration) ultrafiltration,
reverse osmosis, and
dialysis.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 illustrates a preferred embodiment of the process for fabricating
homogeneous
polysulfone hollow fibers (as a representative membrane configuration)
according to the present
invention.
Fig. 2 illustrates an alternative process for fabricating homogeneous
polysulfone hollow
fibers according to the present invention.
Fig. 3 is a three-component diagram showing the proportions of polysulfone
compound)
solvent, and non-solvent which are combined in representative melt-spin
compositions according
to Lhe invention.
Fig. 4 is a scanning electron microscope photograph of a representative
homogeneous,
polysulfone hollow fiber according to the present invention.
Fig. 5 is a schematic diagram of a hemodialyzer including homogeneous
polysulfone
hollow-fiber membranes of the present invention.
."~ . ,r , . . .. _ _ .

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-5-
DETAILED DESCRIPTION
This invention encompasses, inter alia, compositions useful for forming, by
melt-spinning)
polysulfone semipermeable membranes. The compositions comprise a polysulfone
compound, a
solvent and, optionally, a non-solvent. In the composition, the solvent and
optional non-solvent
are present in a ratio useful to form a semipermeable membrane useful for
performing liquid
separation processes. Membranes that are melt-spun using such compositions are
homogeneous.
That is, the melt-spun membranes are symmetric such that the membranes have a
substantially
uniform structure throughout the thickness dimension of the membranes, as
illustrated in the
scanning electron microscope photograph in Fig. 4 of a hollow fiber made using
such a
composition. As defined herein, a "homogeneous" polysulfone membrane is a
membrane in
which each portion or section of the membrane contributes its substantially
proportional share to
the permeability characteristics of the membrane.
Polysulfone compounds and their synthesis are well-known in the art. Preferred
polysulfone compounds useful in this invention satisfy the formula:
R,-SOz-R2
wherein R, and Rz (which can be the same or different) are groups such as
alkanes, alkenes,
alkynes, aryls, alkyls, alkoxys, aldehydes, anhydrides) esters, ethers, and
mixtures thereof, each
such group having fifty or fewer carbon atoms and including both straight-
chained and branched-
chained structures. Preferred polysulfone compounds useful in this invention
have a melt flow
index (MFI) in a range of from about 1.7 dg/min to about 9.0 dg/min as
measured according to
the American Standard Test Method (ASTM) for Flow Rates of Thermoplastics by
Extrusion
Plastometer, ASTM D 1238-94a. Good results have been achieved when the
polysulfone
compounds have a MFl of from about 2.0 dglmin to about S.0 dg/min. Preferred
polysulfone
compounds useful in this invention include) but are not limited to
polyarylsulfones, for example,
bisphenol A polysulfone, polyether sulfone, polyphenyl sulfane) and mixtures
thereof. Especially
good results have been achieved utilizing bisphenol A polysulfone.
A "solvent for the polysulfone compound" is defined herein as a compound
having the
following characteristics: a boiling point of at least about 150°C, a
solvating power to dissolve
from about 8 weight percent to about 80 weight percent of the polysulfone
compound at a
temperature in a range from about 50°C to about 300°C. The
solvent preferably can dissolve
from about 8 weight percent to about 80 weight percent of a polyarylsulfone.
Candidate solvents useful in this invention include, but are not limited to,
tetramethylene
' 35 sulfone; 3-methyl sulfolane; benzophenone; n,n-dimethylacetanude; 2-
pyrrolidone; 3-
methylsulfolene; pyridine; thiophene; o-dichlorobenzene; 1-chloronaphthalene;
methyl salicylate;
anisole; o-nitroanisole; diphenyl ether; diphenoxy methane; acetophenone; p-
methoxyphenyl-2-
ethanol; 2-piperidine; antipyrine; diethyl phthalate; diphenyl sulfone;
diphenyl sulfoxide; phthalic

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acid) dioctyl ester; phthalic acid, dimethyl ester; phthalic acid, diethyl
ester; phthalic acid) dibutyl
ester; phthalic acid, bis(2-ethylhexyl) ester; phthalic acid, benzyt butyl
ester; phenyl sulfide.
Especially preferred solvents useful in this invention include, but are not
limited to,
tetramethylene sulfone ("sulfolane"), antipyrine, b-valerolactam, diethyl
phthalate, and mixtures
thereof. Especially good results have been achieved utilizing tetramethylene
sulfone as the
solvent.
A "non-solvent for the polysulfone compound" is defined herein as a compound
having the
following characteristics: a boiling point of at least about 150°C, a
solvating power sufficiently
low to dissolve less than about 5 weight percent of the polysulfone compound
at a temperature in
a range from about 50°C to about 300°C.
Candidate non-solvents useful in this invention are 1,1-diethylurea; 1,3-
diethylurea;
dinitrotoluene; 1,2-ethane diamine; diphenylamine; toluenediamine; o-toluic
acid; m-toluic acid;
toluene-3,4-diamine; dibutyl phthalate; piperidine; decalin; cyclohexane;
cyclohexene;
chlorocyclohexane; "cellosolve" solvent; n,n-dimethylbenzylamine; paraffin;
mineral oil; mineral
wax; tallow amine; triethanol amine; lauryl methacrylate; stearic acid;
di(ethylene glycol);
tri(ethylene glycol); ethylene glycol; polyethylene glycol); tetra(ethylene
glycol); glycerin; diethyl
adipate; d-sorbitol; chlorotriphenyl stannane; resorcinol; 2-methyl-8-
quinolinol; quinaldine; 4-
phenylpyridine; phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester; N,N-
dimethyl-p-
phenylene diamine; 2,6-dimethoxyphenol; 4-allyl-2-methoxyphenol;
phenanthridine; 2-
naphthylamine; 1-naphthylamine; 1-naphthol; 2-naphthalenethiol; 1-
bromonaphthalene; levulinic
acid; phenyl pyrrol-2-yl ketone; phenyl 4-pyridyl ketone; isothiocyanic acid)
m-nitrophenyl ester;
2-methyl-1H-indole; 4-methyl imidazole; imidazole; 1,7-heptanediol; 9H-fluoren-
9-one; ferrocene;
2,2',2"-nitrilotriethanol; 2,2'-iminodiethanol; dibenzofuran;
cyclohexaneacetic acid; cyanamide;
courmarin; 2,2'-bipyridine; benzoic acid; benzenepropionic acid; o-
dinitrobenzene; 9-methyl-9-
azabicyclo(3.3.1 )nonan-3-one; chlorodiphenylarsine; antimony bromide; p-
anisidine; o-
anisaldehyde; adiponitrile; p-amino acetophenone; monoacetin; diacetin;
triacetin; pentoxane; 4-
benzoylbiphenyl; methyl oleate; triethylphosphate; butyrolactone; terphenyl;
tetradecanol;
polychlorinated biphenyl ("Aroclor 1242"); myristic acid; methacrylic acid)
dodecyl ester;
isocyanic acid) methylenedi-p-phenylene ester; 2-((2-hexyloxy)ethoxy) ethanol;
4-vitro biphenyl;
benzyl ether; benzenesulfonyl chloride; 2,4-diisocyanato-1-1-methyl benzene;
adipic acid, diethyl
ester; 2'-vitro-acetophenone; I'-acetonaphthone; tetradecanone;
(dichlorophenyl)trichlorosilane;
dichlorodiphenyl silane; phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl)
ester; phosphoric
acid, tri-o-tolyl ester; phosphoric acid) triphenyl ester; phosphoric acid,
tributyl ester; phenyl
phosphorous dichloride; p-nitrophenol; isocyanic acid, methyl-m-phenylene
ester; 2,2'-
iminodiethanol; N-{2-aminoethyl)-N'-(2-{(2-aminoethyl)amino)ethyl) 1,2-
ethanediamine; 2,6-di-
tert-butyl p-cresol; chloro biphenyl; 4-biphenylamine; benzyl ether;
benzenesulfonyl chloride; 1,2-
(methylenedioxy)-4-propenyl benzene; 2,4-diisocyanato-1-methyl benzene;
chlorodinitro benzene
(mixed isomers); hexahydro 2H-azepin-2-one; 4,4'-methylenedianiline; 1'-
acetonaphthone;

CA 02272364 1999-OS-19
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mercapto acetic acid; and acetanilide. Especially preferred non-solvents
useful in this invention
include, but are not limited to, polyethylene glycol}) di(ethylene glycol),
tri(ethylene glycol),
glycerol, and mixtures thereof.
The concentrations of the components in the composition may vary and are
dependent upon
variables many of which can be readily worked out with simple bench
experiments. For
example) miscibility of the composition at the melt-extrusion temperature is
one factor to be
considered in determining a suitable component concentration. Miscibility of
polysulfone
compound solutions can be readily determined empirically by methods known in
the art.
(Whether or not the components of a composition are miscible is readily
apparent.) The end use
of the membrane is another factor in determining the appropriate blend
composition because the
preferred pore size of the membrane and transport rate of liquids and solutes
through the
membrane vary depending upon the intended fiber end use.
In the case of membranes useful for microfiltration of liquids, the
concentration of the
polysulfone compound is preferably at least about 8 weight percent, more
preferably at least about
12 weight percent. The concentration of the solvent is preferably at least
about 40 weight
percent, more preferably at least about 60 weight percent. The concentration
of the non-solvent)
if present, is preferably at least about 1 weight percent) and more preferably
at least about 5
weight percent.
In the case of membranes useful for ultrafiltration or dialysis, the
concentration of the
polysulfone compound is preferably at least about 18 weight percent) more
preferably at least
about 25 weight percent. The concentration of the solvent is preferably at
least about 40 weight
percent, more preferably at least about 45 weight percent. Concentration of
the non-solvent, if
present, is preferably at least about 1 weight percent, more preferably at
least about S weight
percent.
If the non-solvent is present) solvent to non-solvent ratios (i.e., a solvent
to non-solvent
ratio "sufficient to form a semipermeable membrane useful for liquid
separation processes") are
preferably about 0.95:1 to about 80:1, and more preferably about 2:1 to about
10: I . For
example, as shown in Fig. 3) for a three-component composition (for melt-
spinning polysulfone
hollow fibers) comprising bisphenol A polysulfone, sulfolane (the solvent),
and polyethylene
glycol) (the non-solvent), acceptable amounts of the polysulfone compound,
solvent, and non-
solvent lie within the area bounded by the extremes of each component which
generate the area
A, B, C. Any of the specific compositions consisting of an amount of each of
the three
' components within the area A, B, C of Fig. 3 are suitable for melt spinning
into hollow-fiber
membranes.
In the case of membranes useful for reverse osmosis of liquids, the
concentration of
polysulfone is preferably at least about 30 weight percent, more preferably at
least about 35
weight percent. The concentration of the solvent is preferably at least about
12 weight percent,

CA 02272364 1999-OS-19
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_g_
more preferably at least about 20 weight percent. If present, the
concentration of the non-solvent
is preferably at least about 1 weight percent, more preferably at least about
5 weight percent.
The compositions of this invention may be used to fabricate polysulfone
semipermeable
membranes useful for "liquid-separation processes." As defined herein) such
processes include,
but are not limited to) microfiltration) ultrafiltration, dialysis) and
reverse osmosis. Fig. S shows
a representative liquid-separation device configured for use as an
extracorporeal blood treatment
device, specifically a hemodialyzer. The hemodialyzer 10 comprises an outer
casing 12, end
caps 14, a dialysate inlet 16, a dialysate outlet 18, a blood inlet 20) a
blood outlet 22) and a
bundle of fibers 24 potted in the outer casing. The outer casing defines a
dialysate compartment,
and the lumina of the fibers form a blood compartment. As blood flows through
the lumina of
the fibers in a parallel fashion, dialysate flows counter-currently through
the dialysate
compartment.
Membranes of the present invention may be fabricated by alternative method
schemes as
iliustrated in Figs. 1 and 2. A number of method schemes may be followed
depending upon the
optional method steps chosen to develop the desired polysulfone membrane.
In one preferred method according to the present invention, a polysulfone
composition of
polysulfone compound, solvent, and optional non-solvent is precompounded in a
high-shear
mixer, melted) extruded (as hollow fibers), quenched (Fig. 1)) and then wound
on cores or reels
using any number of commercially available winders, such as Leesona winders.
In such a
method, adequate care should be taken to maintain a slight tension on the
hollow fibers during
winding. In another preferred method according to the present invention) the
polysulfone
composition is precompounded in a high-shear mixer, melted, extruded through a
strand die (to
form solid strands)) cooled) pelletized) remelted, extruded (to form hollow
fibers), quenched, and
then wound (Fig. 2). In still another preferred method according to the
present invention, the
polysulfone composition is precompounded, melted, extruded (as hollow fibers),
quenched)
wound, held dry for a period of time, soaked in a liquid that is substantially
a non-solvent for the
polysulfone compound and stored in the soaking liquid for up to 15 days (Fig.
1). In yet another
preferred method according to the present invention, a polysulfone composition
is precompounded
in a high-shear mixer, melted, extruded (as hollow fibers), quenched) wound,
soaked, leached,
rinsed, replasticized, and then dried in an oven (preferably a convection
oven) (Fig. 1). In
another preferred method according to the present invention, the polysulfone
composition is
precompounded, melted, extruded (as solid strands), cooled, pelletized,
remelted) extruded (as
hollow fibers), quenched, wound) and then held dry in air followed by soaking
in a liquid that is
substantially a non-solvent for the polysulfone compound (Fig. 2). In yet
another preferred
method according to the present invention, a polysulfone composition is
precompounded, melted,
extruded (as solid strands), cooled, pelletized) remelted) extruded (as hollow
fibers)) quenched,
wound, soaked, leached, rinsed, replasticized, and dried (Fig. 2).
._..,r.. . ..__ .-. ~ _ ~..._._ _._

CA 02272364 1999-OS-19
WO 98!29478 PCT/US97124087
_g_
The components of the composition (i.e., the polysulfone compound, solvent,
and optional
non-solvent) to be extruded are combined and homogenized prior to extrusion by
mixing in a
convenient manner with conventional mixing equipment, as for example, a high-
shear mixer, such
as a compounding twin-screw extruder. The components of the extrusion
composition may also
be combined and homogenized directly in a meltpot provided with suitable
agitation of the molten
liquid. Alternatively, a polysulfone extrusion composition may be homogenized
by extruding a
molten composition through a strand die) cooling the global extrudate, and
grinding or pelletizing
the extrudate to a particle size readily-fed to a heated ) single-screw or
twin-screw extruder.
Alternatively ) other heating/homogenizing methods known to those skilled in
the art may be
utilized to produce a homogeneous, molten liquid for extrusion (termed a
"melt")
The melt is heated to a temperature that facilitates preparation of a
homogeneous liquid
possessing a viscosity suitable for extrusion. The temperature should not be
so high as to cause
significant degradation of the polysulfone, the solvent, or the non-solvent.
The temperature
should not be so low as to render the liquid too viscous for extrusion. For
example, when the
melt comprises bisphenol A polysulfone, the extrusion temperature is
preferably at least about
50°C, more preferably at least about 75°C. The extrusion
temperature is preferably less than
about 300°C) more preferably less than about 220°C.
The viscosity of the melt should not be so high as to be too viscous to be
extruded at
temperatures that do not deleteriously affect the polysulfone compound. The
viscosity, however,
of the melt must not be so low that the extrudate cannot maintain a desired
shape upon exiting the
extrusion die. The melt may be extruded in a variety of shapes such as, but
not limited to,
hollow-fibers, tubes, sheets, and hollow-fibers with fins. The extrudate may
be aided in retaining
its desired shape upon extrusion by cooling.
For making hollow-fiber membranes, the melt is extruded through a hollow-fiber
die
(spinneret). The spinneret typically is multi-holed and, thus, produces a tow
of multiple hollow
fibers. The spinneret typically includes a means for supplying a fluid (gas or
liquid) to the core
or "lumen" of the extrudate. The core fluid is used to prevent collapse of the
hollow fibers as
they exit the spinneret. The core fluid may be a gas, such as nitrogen) air,
carbon dioxide) or
other inert gas) or a liquid which is a non-solvent for the polysulfone
compound, such as, but not
limited to, water, polyethylene glycol), di(ethylene glycol)) tri(ethylene
glycol), glycerol, and
mixtures thereof. Mixtures of solvents and non-solvents may be used as long as
the mixture is
not a solvent for the polysulfone compound. Alternatively) the melt may first
be extruded as
solid strands through a single or multi-holed strand die and the resulting
solid strands cooled and
pelletized to a particle size readily fed to a single-screw or twin-screw
extruder (Fig. 2). In this
alternative method of production) the particles are remelted and then extruded
through a single-
holed or mufti-holed spinneret to form hollow fibers ) as described above.
The extrudate exiting extrusion die enters one or more quench zones. The
environment of
a quench zone may be gaseous or liquid. Within the quench zone, the extrudate
is subjected to

CA 02272364 1999-OS-19
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-10-
sufficient cooling to cause gelation and solidification of the membrane. In an
embodiment of the
method of the present invention, the time period beginning after the extrudate
exits the die and
extending to before the membrane is wound onto a core or reel, is important to
attain the desired
permeability of the membrane. During this time period, for a given
composition, the
permeability of the membrane is determined largely by the cooling rate to
which the extrudate is
subjected. Permeability is increased by rapid quenching of the extrudate)
compared to the
permeability obtained from a less drastic quench or slower gelling of the
extrudate. Increasing
permeability of the membranes) which results from more rapid quenching,
normally affects the
ability of the membranes to transport water) or other liquids and compounds
across the thickness
dimension of the membranes. Thus) the extrudate cooling rate (as affected by
the temperature
and composition of the cooling medium employed) may be varied to modify the
permeability of
the resulting membrane.
In one method according to the present invention, a polysulfone hollow-fiber
extrudate is
quenched in air. Within the quench zone, the hollow fibers gel and solidify.
The temperature of
the air-quench zone is preferably less than about 27°C) more preferably
less than about 24°C.
The hollow fibers are held in the air zone for preferably less than about 180
minutes, more
preferably less than about 30 minutes.
In another preferred method according to the present invention, the hollow-
fiber extrudate
is quenched in a liquid that is substantially a non-solvent for the
polysulfone compound, such as
water, polyethylene glycol)) di(ethylene glycol), tri(ethylene glycol),
glycerol, or a mixture
thereof. A mixture of solvents) and non-solvents) alternatively may be used so
long as the
mixture remains substantially a non-solvent for the polysulfone compound. When
a liquid quench
comprises water and one or more other components, the ratio of water to the
other components is
preferably from about 0.25:1 to about 200:1. The temperature of the liquid
quench zone is
preferably less than about SO°C, more preferably less than about
25°C) and more preferably less
than about 10°C. The advantage of a liquid quench is that it offers
less resistance to the transfer
of heat from the extrudate to the cooling medium than is present in an air
quench and, thus,
results in a more rapid removal of heat from the extrudate as the membrane
forms. The rapid
removal of heat modifies the permeability of the resulting membrane and can be
used to tailor
membrane permeability for the intended end use
Hollow fibers are, optionally, drawn using godet rollers or other conventional
equipment
to the appropriate fiber diameter. More specifically, drawing or stretching
the fiber may be
accomplished by passing the hollow fiber over a series of rollers. The desired
degree of
stretching may be obtained by control of the rate of rotation of the second
roller or second group
of rollers relative to the first roller encountered by the fiber. Line speeds
are generally not
critical and may vary over a wide range. Preferred line speeds are at least
about 10 feet per
minute and less than about 1000 feet per minute.

CA 02272364 1999-OS-19
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In another preferred method according to the present invention, as illustrated
in Fig. 2,
following quenching, the membrane is passed through at least one leach bath
containing a liquid
that is substantially a non-solvent for the polysulfone compound, such as
water or a mixture of
water and sulfolane and/or the non-solvent(s), or a mixture of water and the
solvent utilized in the
melt composition. Good results have been achieved when the leach bath is
water. The
membrane is leached to remove at least a portion of the solvent and the non-
solvent. The leach
bath need not remove all of the solvent and non-solvent from the membrane,
depending, at Least
in part, on the anticipated end use of the membrane.
The minimum temperature of the leach bath is such that removal of the solvent
and non-
solvent from the membrane occurs at a reasonable rate relative to production
rate demands. The
minimum temperature of the leach bath is preferably at least about
20°C, more preferably at least
about 40°C. The maximum temperature of the leach bath is below a
temperature at which the
integrity of the membrane is deleteriously affected. Accordingly) the
temperature of the leach
bath is preferably less than about 95°C.
By way of example, the residence time of a hollow-fiber membrane in the leach
bath is
preferably less than about 1200 seconds, more preferably less than about 300
seconds. The
hollow fiber may, optionally) be drawn to the desired size prior to entrance
into the leach bath,
during the residence time in the leach bath, subsequent to exiting the leach
bath, or during any
combination thereof.
Following immersion in the leach bath, the membrane may, optionally, be passed
through
a rinse bath containing water. The rinse bath removes residues in the membrane
from the leach
process. The rinse bath is preferably maintained at room temperature. For a
hollow fiber, the
residence time of the fiber within the rinse bath is preferably less than 1200
seconds, more
preferably less than 300 seconds.
After leaching) the membrane may then be subjected to a replasticization
process. For
hollow-fiber membranes to be used for dialysis, a replasticization bath is
used that preferably
contains less than about 50 weight percent glycerol and more preferably less
than about 45 weight
percent glycerol, with the balance being water. The minimum temperature of the
replasticization
bath is such that replasticization of the membrane occurs at reasonable rate
relative to production
demands. For example, the minimum temperature of a glycerol-containing
replasticization bath is
preferably at least about 20°C, more preferably at least about
35°C. The maximum temperature
of the replasticization bath is below a temperature at which the membrane
integrity could be
adversely affected. Accordingly, the maximum temperature of the
replasticization bath is
preferably less than about 100°C, more preferably less than about
50°C.
Following removal of the membrane from the replasticization bath) excess
liquid adhering
to the membrane may optionally be removed, preferably by use of a conventional
air knife
operating at a pressure of about 10 psig to about 60 psig. With hollow fibers,
good results have
been achieved when the air knife is maintained at a pressure of about 30 psig.

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The resulting polysulfone membrane may, optionally, be dried in an oven
(preferably a
convection oven). The oven is maintained at a temperature of from about
20°C to about 200°C.
With hollow fibers, good results have been achieved when the temperature of
the oven is about
70°C. In a convection oven the membrane is dried for a period of from
about 5 seconds to about
1200 seconds. With hollow fibers, good results have been achieved when the
fiber was dried for
at least about 140 seconds.
The semipermeable polysulfone membranes formed by the described methods may be
used
in liquid-separation processes such as, but not limited to, microfiltration,
ultrafiltration, dialysis)
and reverse osmosis. The specific fabrication method that is employed, within
the scope of
methods according to the present invention, is selected so as to tailor the
resulting membrane for
its anticipated end use. Such adaption is readily achieved by one skilled in
the art based upon the
teachings herein.
The following various examples are presented to illustrate the invention only
and are not
intended to limit the scope of the invention or the following claims.
EXAMPLE 1
A composition was prepared comprising about 36 weight percent Udel P1835NT11)
a
brand of bisphenol A polysulfone (available from Amoco Polymers, Inc. of
Alpharetta, Georgia)
about 44.3 weight percent anhydrous sulfolane (available from Phillips
Chemical Company of
Borger) Texas) and about 17.7 weight percent poiy(ethylene glycol) having an
average molecular
weight of about 1000 daltons (available from Dow Chemical Company of Midland,
Michigan).
The solvent to non-solvent ratio was about 4.5:1. The composition was
compounded in a
co-rotating twin-screw extruder at about 132°C. The extruded
composition was cooled) pelletized
using an RCP 2.0 pelletizer (available from Randcastle Extrusion Systems, Inc.
, of Cedar Grove,
New Jersey), and then remelted and extruded through a 30-hole hollow-fiber
spinneret at about
149°C using a single-screw extruder. The resulting hollow-fiber
extrudate was quenched in air at
about 21 °C for about 15 seconds, drawn from a first godet (rotating at
a surface speed of 172
feet per minute) to a second godet (rotating at a surface speed of 182 feet
per minute) to increase
the fiber's length by about 5.75 percent, wound on a core, and soaked in a
water bath at a
temperature of about 25°C for about four hours.
Following soaking in water, the hollow fiber was processed by unwinding the
fiber from
the core at a rate of about 30 ft/min and passing the fiber through a
37°C water bath for about
seconds. The fiber was then immersed in a room temperature water-rinse bath
for 139
seconds. Following the rinse bath, the fiber was replasticized by immersion
for 140 seconds in a
40-percent aqueous glycerol replasticization bath held at about 37°C.
After removing the fiber
35 from the aqueous glycerol bath, excess liquid was removed from the fiber
using an air knife
operating at about 30 psig. The processed hollow fiber was then dried in a
convection oven at
about 70°C for 155 seconds.

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The resulting hollow fiber had an average lumen diameter of 160 Vim, and an
average wall
thickness of 18 Vim. The hollow fiber was fabricated into a dialysis test unit
containing 150
fibers. The in vitro water flux of the device was 102.5 mL/(hrmmHg~mz) and the
average K°~
for sodium chloride was found to be 1.92 x 10'z centimeters per minute at a
solution flow rate
through the fiber lumina of about 0.02 milliliters per minute per fiber.
K°v is defined in the
following equation:
1 1 1
-_-+-
Kov _ Kb pin
where Kb is the resistance to mass transfer within the fluid present in the
lumen of the hollow
fiber, and Pm is the membrane permeability. it was not possible to determine
the membrane
permeability, Pm, alone using the test apparatus because the flow of solution
through an individual
fiber could not be made large enough to render Kb negligible.
This hollow-fiber membrane could be fabricated into a suitable device for use
as an
ultrafiltration cell for the removal of contaminants from water or aqueous
solutions.
EXAMPLE 2
A composition was prepared comprising about 36 weight percent Udel P1835NT11
polysulfone (Amoco Polymers, Inc. ), about 45 .7 weight percent anhydrous
sulfolane (Phillips
Chemical), and about 18.3 weight percent polyethylene glycol) having an
average molecular
weight of about 1000 daltons (Dow Chemical)) yielding a solvent to non-solvent
ratio about 2.5:1.
The composition was compounded in a co-rotating) twin-screw extruder at about
173°C. The
extruded composition was then pelletized, remelted) and extruded through a 30-
hole hollow-fiber
spinneret at about 178°C using a single-screw extruder. The resulting
hollow-fiber extrudate was
quenched in air at about 22 ° C for 7-8 seconds. The resulting hollow-
fiber membrane was wound
on a core at about 110 feet per minute, and held dry for about one hour. The
hollow fiber was
then placed in a water bath maintained at a temperature of about 25 °C
for a period of about 12-
15 hours.
The hollow fiber was then processed by unwinding from the core at about 30
ft/min and
passing the fiber through a 36°C water leach bath for about 40 seconds.
The fiber was immersed
in a room temperature water-rinse bath for 139 seconds. The fiber was
replasticized for 140
seconds in a 37 °C bath of about 40 weight percent aqueous glycerol.
After removing the fiber
from the aqueous glycerol bath, excess liquid was stripped from the fiber
using an air knife
operating at a pressure of about 30 psig. The processed fiber was then dried
in a convection
oven at about 70°C for 155 seconds.
The resulting hollow fiber had an average lumen diameter of about 142 ~cm, and
an
average wall thickness of about 31 pin. Dialysis test units each containing
150 of the hollow
fibers were fabricated. The average in vitro water flux of these devices was
68.0

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mL/(hr ~mmHg ~m2) and the average K°~ for sodium chloride was about
2.28 x 10-2 centimeters
per minute at a solution flow rate through the fiber lumina of about 0.02
milliliters per minute per
fiber. This hollow-fiber membrane is useful for ultrafiltration, such as for
use in an ultrafiltration
cell for the removal of contaminants from water or aqueous solutions.
EXAMPLE 3
A composition was prepared comprising about 38 weight percent Udel PI835NT11
potysulfone (Amoco Polymers, Inc.)) about 44.3 weight percent anhydrous
sulfolane (Phillips
Chemical), and about 17.7 weight percent polyethylene glycol) having an
average molecular
weight of about 1000 daltons (Dow Chemical), yielding a solvent to non-solvent
ratio of about
4.5:1. The composition was compounded in a co-rotating, twin-screw extruder at
about 99°C)
and extruded directly through a 30-hole hollow-fiber spinneret. The extrudate
was quenched in
air at about 26°C for about 6 seconds. The resulting hollow-fiber
membrane was wound on a
core at about 160 feet per minute, and placed immediately into a water bath
for a period of about
12-15 hours.
The hollow fiber was then unwound from the core at about 30 ft/min and passed
through a
37°C water leach bath for about 40 seconds. The fiber was then immersed
in a room-
temperature water rinse bath for about 140 seconds. The fiber was
replasticized for 140 seconds
in an aqueous glycerol bath containing about 40 weight percent glycerol, the
bath being held at
about 38°C. After removing the fiber from the aqueous glycerol bath)
excess liquid was removed
from the fiber by an air knife operating at a pressure of about 30 psig. The
fiber was then dried
in a convection oven at about 70°C for about I55 seconds.
The resulting hollow-fiber membrane had an average lumen diameter of 237 ~cm)
and an
average wall thickness of 35 ~,m. Dialysis test units each containing 150 of
the resulting fibers
were fabricated from this fiber. The average in vitro water flux of these
devices was 143.5
mL/(hr~mmHg ~m2) and the average K°~ for sodium chloride was found to
be 0.88 x 10-Z
centimeters per minute at a solution flow rate through the fiber lumina of
about 0.02 milliliters
per minute per fiber. This hollow-fiber membrane can be used in an
ultrafiltration cell for the
removal of contaminants from water or aqueous solutions.
EXAMPLE 4
A composition was prepared comprising about 38 weight percent Udel P1835NT11
polysulfone {Amoco Polymers, Inc.), about 45.7 weight percent anhydrous
sulfolane (Phillips
Chemical), and about 18.3 weight percent polyethylene glycol) having an
average molecular
weight of about 1000 daltons (Dow Chemical), yielding a solvent to non-solvent
ratio of about
2.5:1. The composition was compounded in a co-rotating twin-screw extruder at
about 143 °C,
and extruded directly through a 30-hole hollow-fiber spinneret. The extrudate
was quenched in
air at about 25 ° C for about 0.08 minutes, wound on a core at about
203 feet per minute, and held
dry for thirty minutes before being placed in a 25 °C water bath for
about three days.

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The hollow fiber was then unwound from the core at about thirty feet per
minute and
passed through a 38°C water-leach bath for about thirty seconds. The
fiber was immersed in a
room temperature water rinse bath for 148 seconds. The fiber was replasticized
for 149 seconds
in an aqueous glycerol bath containing about 40 weight percent glycerol, the
bath being held at
about 38°C. After removing the fiber from the aqueous glycerol bath,
excess liquid was removed
from the fiber using an air knife operating at a pressure of about thirty
psig. The processed
hollow fiber was dried in a convection oven at about 70°C for 147
seconds.
The resulting hollow-fiber membrane had an average lumen diameter of 192 ~.m,
and an
average wall thickness of 29.5 ~,m. Dialysis test units each containing 150 of
the resulting fibers
were fabricated. The average in vitro water flux of these devices was 141.2
mL/(hmmmHg ztt2)
and the average K°~ for sodium chloride was found to be 1.20 x 10-2
centimeters per minute at a
solution flow rate through the fiber lumina of about 0.02 milliliters per
minute per fiber. This
hollow-fiber membrane is useful in an ultrafiltration cell for the removal of
contaminants from
water or aqueous solutions.
EXAMPLE 5
A composition was prepared comprising about 34 weight percent Udel P1835NT11
polysulfone {Amoco Polymers, Inc.), about 54 weight percent anhydrous
sulfolane (Phillips
Chemical Company)) about 11 weight percent polyethylene glycol) having an
average molecular
weight of about 1000 daltons (Dow Chemical Company), and about 1 weight
percent glycerol
(VanWaters & Rogers, Inc., Seattle, Washington), yielding a solvent to non-
solvent ratio of about
4.5:1. The composition was compounded in a co-rotating twin-screw extruder at
about 144°C.
The extrudate was then cooled) pelletized, remelted, and extruded through a 30-
hole hollow-fiber
spinneret at about 134°C using a single-screw extruder. The resulting
extrudate was quenched in
air at about 20°C for about 0.08 minute, and wound on a core at about
200 feet per minute. The
entire wound core was immediately placed in a 25°C water bath for a
period of about 15-20
hours.
The hollow fiber was then processed by unwinding the fiber from the core at
about 30 feet
per minute and passing the fiber through a room-temperature water-leach bath
for 97 seconds.
The fiber was replasticized for 145 seconds in a bath containing about 40
weight percent aqueous
glycerol held at about 38°C. After removing the fiber from the aqueous
glycerol bath) excess
liquid was stripped from the fiber using an air knife operating a pressure of
about 30 psig. The
processed hollow fiber was dried in a convection oven at about 62°C for
151 seconds.
The resulting hollow-fiber membrane had an average lumen diameter of about 165
~cm,
and an average wall thickness of about 18 ~.m. Test units each containing
about 150 of the
resulting fibers were fabricated. The average in vitro water flux of these
devices was 67.2
mL/(hrmmHg ~mz) and the average K°~ for sodium chloride was found to be
2.19 x 10-Z
centimeters per minute at a solution flow rate through the fiber lumina of
about 0.02 milliliters
per minute per fiber.

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EXAMPLE 6
A composition was prepared comprising about 34 weight percent Udel P1835NT11
polysulfone (Amoco Polymers, Inc. ), about 54 weight percent anhydrous
sulfolane {Phillips
Chemical Company)) about 6 weight percent polyethylene glycol) having an
average molecular
weight of about 1000 daltons (Dow Chemical Company) and about 6 weight percent
tri(ethylene
glycol) (Aldrich Chemical Company, Inc., Milwaukee, Wisconsin), yielding a
solvent to non-
solvent ratio of about 4.5:1. The composition was compounded in a co-rotating,
twin-screw
extruder at about 153 °C. The extrudate was then cooled, pelletized,
remelted, and extruded
through a 30-hole hollow-fiber spinneret at about 137 °C using a single-
screw extruder. The
resulting hollow-fiber extrudate was quenched in air at about 20°C for
0.08 minute, and wound
on a core at about 200 feet per minute. The entire fiber core was immediately
placed in a 25 °C
water bath for a period of 15-20 hours.
The hollow fiber was then processed by unwinding the fiber from the core at
about 30 feet
per minute and passing the fiber through a room-temperature water-leach bath
for 95 seconds.
The fiber was then immersed in a room-temperature water-rinse bath for 134
seconds. The
hollow fiber was replasticized for 146 seconds in a bath of about 40 weight
percent aqueous
glycerol held at about 38°C. After removing the fiber from the aqueous
glycerol bath, excess
liquid was stripped from the fiber using an air knife operating at a pressure
of about 30 psig.
The processed hollow fiber was dried in a convection oven at about 70°C
for 150 seconds.
The resulting hollow-fiber membrane had an average lumen diameter of about 180
~,m,
and an average wall thickness of about 20 pm. Test units each containing about
150 of the
resulting fibers were fabricated. The average in vitro water flux of these
devices was 60.0
mLl(hr~mmHgzn2) and the average K°y for sodium chloride was found to be
2.17 x 10-2
centimeters per minute at a solution flow rate through the fiber lumina of
about 0.02 milliliters
per minute per fiber.
EXAMPLE 7
A composition was prepared comprising about 32 weight percent Udel P1835NT11
polysulfone (Amoco Polymers, Inc.)) about 53 weight percent anhydrous
sulfolane (Phillips
Chemical Company), and about 15 weight percent polyethylene glycol) having an
average
molecular weight of about 1000 daltons (Dow Chemical Company)) yielding a
solvem to non-
solvent ratio of about 2.5:1. The composition was compounded in a co-rotating
twin-screw
extruder at about 131 °C and extruded directly through a 30-hole hollow-
fiber spinneret. The
extrudate was quenched in water at about 7°C for about 6 seconds. The
resulting hollow-fiber
membranes were wound on a core at about 244 feet pr minute. The entire fiber
core was
immediately placed in a 25 °C water bath for a period of about 15-20
hours.
The hollow fibers were then processed by unwinding the fibers from the core at
about 30
feet per minute and passing the fibers through a room-temperature water-leach
bath for 97
seconds. The fibers were then immersed in a room-temperature water-rinse bath
for 135 seconds.
..._......

CA 02272364 1999-OS-19
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The fibers were replasticized for 146 seconds in a bath of about 40 weight
percent aqueous
glycerol, the bath being held at about 38°C. After removing the fibers
from the aqueous glycerol
bath, excess liquid was stripped from the fiber using an air knife operating
at a pressure of about
20 psig. The processed fibers were dried in a convection oven at about 45
°C for about 152
seconds.
The resulting hollow-fiber membranes had an average lumen diameter of about
203 ~.m,
and an average wall thickness of about 37 ~cm. Test units each containing
about 150 of the
resulting fibers were fabricated. The average in vitro water flux of these
devices was 9.1
mLl(hrmimHg~m2) and the average Ka~ for sodium chloride was found to be 1.76 x
10-2
centimeters per minute at a solution flow rate through the fiber lumina of
about 0.02 milliliters
per minute per fiber.
Having illustrated and described the principles of the invention with several
preferred
embodiments and multiple various examples, it should be apparent to those
skilled in the art that
the invention can be modified in arrangement and detail without departing from
such principles.
We claim all the modifications coming within the spirit and scope of the
following claims.

Representative Drawing