U.S. patent number RE37,701 [Application Number 09/542,864] was granted by the patent office on 2002-05-14 for integral composite membrane.
This patent grant is currently assigned to W. L. Gore & Associates, Inc.. Invention is credited to Bamdad Bahar, Alex R. Hobson, Jeffrey A. Kolde, Robert S. Mallouk.
United States Patent |
RE37,701 |
Bahar , et al. |
May 14, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
Integral composite membrane
Abstract
A composite membrane is provided which includes a base material
and an ion exchange resin. The base material has a microstructure
characterized by nodes interconnected by fibrils, or a
microstructure characterized by fibrils with no nodes present. The
ion exchange resin substantially impregnates the membrane such that
the membrane is essentially air impermeable.
Inventors: |
Bahar; Bamdad (Elkton, MD),
Mallouk; Robert S. (Chadds Ford, PA), Hobson; Alex R.
(Elkton, MD), Kolde; Jeffrey A. (Baltimore, MD) |
Assignee: |
W. L. Gore & Associates,
Inc. (Newark, DE)
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Family
ID: |
27500186 |
Appl.
No.: |
09/542,864 |
Filed: |
April 4, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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245496 |
Feb 4, 1999 |
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404853 |
Mar 15, 1995 |
5547551 |
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245496 |
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339425 |
Nov 14, 1994 |
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Reissue of: |
561514 |
Nov 21, 1995 |
05599614 |
Feb 4, 1997 |
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Current U.S.
Class: |
442/171; 204/296;
210/500.36; 210/505; 210/507; 210/508; 428/305.5; 428/308.4;
428/311.51; 428/316.6; 428/422; 521/27; 429/494; 429/524;
429/532 |
Current CPC
Class: |
H01M
8/1023 (20130101); B01D 67/0088 (20130101); H01M
8/1067 (20130101); H01M 50/411 (20210101); H01M
8/1051 (20130101); H01M 8/1062 (20130101); H01M
8/1048 (20130101); B01D 69/141 (20130101); B32B
5/18 (20130101); H01M 8/106 (20130101); C25B
13/08 (20130101); C08J 5/2281 (20130101); C08J
5/225 (20130101); H01M 8/1039 (20130101); Y02E
60/10 (20130101); C08J 2361/06 (20130101); Y10T
428/249954 (20150401); Y10T 442/2918 (20150401); Y10T
428/249958 (20150401); Y10T 428/31544 (20150401); Y02E
60/50 (20130101); Y10T 428/249981 (20150401); C08J
2327/18 (20130101); Y10T 428/249964 (20150401) |
Current International
Class: |
B32B
5/18 (20060101); C08J 5/20 (20060101); C08J
5/22 (20060101); B01D 67/00 (20060101); C25B
13/00 (20060101); B01D 69/14 (20060101); B01D
69/00 (20060101); C25B 13/08 (20060101); H01M
2/16 (20060101); H01M 8/10 (20060101); B32B
005/14 (); B32B 005/16 (); B32B 033/00 (); C25B
013/08 () |
Field of
Search: |
;442/171 ;204/296
;210/500.36,505,507,508 ;428/305.5,308.4,316.6,422,311.51 ;429/33
;521/27 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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51-71888 |
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Jun 1976 |
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JP |
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62-240627 |
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Sep 1987 |
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JP |
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95/16730 |
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Jun 1995 |
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WO |
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Other References
"Ion Transporting Composite Membranes," Lui et al., J. Electrochem.
Soc., vol. 137, No. 2, The Electrochemical Society, Inc. pp.
510-515, Feb. 1990.* .
"Ion Transporting Composite Membranes," Penner et al, Journal
Electrochem. Soc., vol. 132, No. 2, pp. 514-515, Feb. 1985.* .
"Composite Membranes for Fuel-Cell Applications," Verbrugge et al.,
AIChE Journal, vol. 38, No. 1, pp. 93-100, Jan. 1992..
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Primary Examiner: Copenheaver; Blaine
Attorney, Agent or Firm: Morgan & Finnegan, LLP
Parent Case Text
.Iadd.This is a continuation of Reissue U.S. Ser. No. 09/245,496,
filed Feb. 4, 1999, now abandoned, which was a Reissue application
based on U.S. Pat. No. 5,599,614 (issued on Feb. 4, 1997) which was
U.S. Ser. No. 08/561,514, filed Nov. 21, 1995, which
.Iaddend..[.This.]. is a continuation in part of application Ser.
No. 08/404,853, filed on Mar. 15, 1995, now U.S. Pat. No.
5,547,551; .Iadd.said U.S. Ser. No. 08/561,514 is also a
continuation-in-part of U.S. Ser. No. 08/339,425, filed Nov. 14,
1994, now abandoned..Iaddend.
.Iadd.OTHER RELATED APPLICATIONS
Above mentioned U.S. Ser. No. 08/404,853, filed on Mar. 15, 1995,
now U.S. Pat. No. 5,547,551, is currently being subject to Reissue
in U.S. Ser. No. 09/137,515, filed on Aug. 20, 1998, which will
issue as RE37307 on Aug. 7, 2001. Above mentioned U.S. Ser. No.
08/339,425, filed Nov. 14, 1994, which was abandoned in favor of
continuation application Ser. No. 08/903,844, filed Jul. 31, 1997,
which was abandoned in favor of continuation application Ser. No.
09/209,932, filed Jul. 8, 1998, now U.S. Pat. No.
6,254,978..Iaddend.
Claims
Having described the invention, what is claimed is:
1. A composite membrane .[.comprising.]. .[.n.]. .Iadd.t least one
.Iaddend.expanded polytetrafluoroethylene membrane having a porous
microstructure of polymeric fibrils .Iadd.and having a thickness of
80 microns or less.Iaddend.; and
(b) a.[.n.]. .Iadd.t least one .Iaddend.ion exchange material
impregnated throughout the .Iadd.porous microstructure of the
expanded polytetraafluoroethylene .Iaddend.membrane .Iadd.so as to
render an interior volume of the expanded polytetrafluoroethylene
membrane substantially occlusive.Iaddend., the impregnated expanded
polytetrafluoroethylene membrane having a Gurley number of greater
than 10,000 seconds.[., wherein the ion exchange material
substantially impregnates the membrane so as to render an interior
volume of the membrane substantially occlusive.]. .Iadd.; wherein
optionally the at least one ion exchange material is complimented
by powder, non-ionic polymer, or a combination
thereof.Iaddend..
2. The composite membrane of claim 1, wherein the .Iadd.expanded
polytetrafluoroethylene .Iaddend.membrane .[.comprises.].
.Iadd.consists essentially of .Iaddend.a microstructure of nodes
interconnected by .Iadd.the .Iaddend.fibrils.
3. The composite membrane of claim 1, wherein the .Iadd.at least
one .Iaddend.ion exchange material is selected from a group
consisting of: perfluorinated sulfonic acid resin, perfluorinated
carboxylic acid resin, polyvinyl alcohol, divinyl benzene,
styrene-based polymers, and metal salts.
4. The composite membrane of claim 1, wherein the .Iadd.at least
one .Iaddend.ion exchange material is .[.comprised.].
.Iadd.complimented .Iaddend..[.at least in part of a.]. .Iadd.by
.Iaddend.powder.
5. The composite membrane of claim 4, wherein the powder is at
least in part carbon.
6. The composite membrane of claim 4, wherein the powder is at
least in part a metal.
7. The composite membrane of claim 4, wherein the powder is at
least in part a metal oxide.
8. The composite membrane of claim 1, wherein the ion exchange
material is a perfluorosulfonic acid/tetrafluoroethylene copolymer
resin derived from a solvent solution selected from a group
consisting .[.essentially.]. of water, ethanol, propanol, butanol,
and methanol.
9. The composite membrane of claim 1, wherein the ion exchange
material is .[.at least in part a.]. .Iadd.complimented by
.Iaddend.non-ionic polymer..Iadd.
10. The composite membrane of claim 9, wherein the non-ionic
polymer is thermoplastic resin..Iaddend..Iadd.
11. The composite membrane of claim 9, wherein the non-ionic
polymer is a thermoset resin..Iaddend..Iadd.
12. The composite membrane of claim 9, wherein the non-ionic
polymer is polyolefin or fluoropolymer..Iaddend..Iadd.
13. The composite membrane of claim 4, wherein the powder is finely
divided..Iaddend..Iadd.
14. The composite membrane of claim 4, wherein the powder is an
organic powder..Iaddend..Iadd.
15. The composite membrane of claim 4, wherein the powder is an
inorganic powder..Iaddend..Iadd.
16. The composite membrane of claim 4, wherein the powder is
selected from the group consisting of carbon black, graphite,
nickel, silica, titanium dioxide, and platinum
black..Iaddend..Iadd.
17. The composite membrane of claim 4, wherein the powder is carbon
black..Iaddend..Iadd.
18. The composite membrane of claim 4, wherein the powder is
graphite..Iaddend..Iadd.
19. The composite membrane of claim 4, wherein the powder is
silica..Iaddend..Iadd.
20. The composite membrane of claim 4, wherein the powder is
titanium dioxide..Iaddend..Iadd.
21. The composite membrane of claim 4, wherein the powder is
platinum black..Iaddend..Iadd.
22. The composite membrane of claim 1, wherein the thickness of the
expanded polytetrafluoroethylene membrane is 60 microns or
less..Iaddend..Iadd.
23. The composite membrane of claim 1, wherein the thickness of the
expanded polytetrafluoroethylene membrane is 40 microns or
less..Iaddend..Iadd.
24. The composite membrane of claim 1, wherein the thickness of the
expanded polytetrafluoroethylene membrane is 20 microns or
less..Iaddend..Iadd.
25. The composite membrane of claim 1, wherein the thickness of the
expanded polytetrafluoroethylene membrane is at least 1.5
microns..Iaddend..Iadd.
26. The composite membrane of claim 1, wherein the thickness of the
expanded polytetrafluoroethylene membrane is at least 13
microns..Iaddend..Iadd.
27. A composite membrane according to claim 1, wherein the
impregnated membrane has an ionic conductance of at least 8.5
mhos/cm.sup.2..Iaddend..Iadd.
28. A composite membrane according to claim 1, wherein the
impregnated membrane has an ionic conductance of at least 22.7
mhos/cm.sup.2..Iaddend..Iadd.
29. A composite membrane according to claim 1, wherein the
impregnated membrane has been heated to a temperature of 60.degree.
C. to 200.degree. C..Iaddend..Iadd.
30. A composite membrane according to claim 29, wherein the
impregnated membrane has an ionic conductance of at least 8.5
mhos/cm.sup.2..Iaddend..Iadd.
31. A composite membrane according to claim 30, wherein the
thickness of the expanded polytetrafluoroethylene membrane is 20
microns or less and the ion exchange material is perfluorinated
sulfonic acid resin..Iaddend..Iadd.
32. A composite membrane according to claim 31, wherein the
impregnated membrane is prepared by impregnation of at least two
sides of the expanded polytetrafluoroethylene membrane with the ion
exchange material..Iaddend..Iadd.
33. A composite membrane according to claim 32, wherein the
impregnation is carried out by multiple impregnations of the at
least two sides of expanded polytetrafluoroethylene
membrane..Iaddend..Iadd.
34. A composite membrane according to claim 29, wherein the
impregnated membrane has an ionic conductance of at least 22.7
mhos/cm.sup.2..Iaddend..Iadd.
35. A composite membrane according to claim 1, wherein the
impregnated membrane has been heated to a temperature of
120.degree. C. to 200.degree. C..Iaddend..Iadd.
36. A composite membrane according to claim 1, wherein the
impregnated membrane has been heated to a temperature of
140.degree. C. to 200.degree. C..Iaddend..Iadd.
37. A laminate of composite membranes consisting essentially of at
least two composite membranes laminated to each other, wherein the
at least two composite membranes each consist essentially of:
(a) an expanded polytetrafluoroethylene membrane having a porous
microstructure of polymeric fibrils and having a thickness of 80
microns or less; and
(b) an ion exchange material impregnated throughout the porous
microstructure of the membrane so as to render an interior volume
of the expanded polytetrafluoroethylene membrane substantially
occlusive, the impregnated membrane having a Gurley number of
greater than 10,000 seconds..Iaddend..Iadd.
38. A laminate according to claim 37, wherein each of the
impregnated polytetrafluoroethylene membranes have been heated to a
temperature of at least 60.degree. C. and each of the impregnated
membranes have an ionic conductance of at least 22.7 mhos/cm.sup.2
; wherein the thickness of each of the impregnated membranes is 20
microns or less; wherein the ion exchange material is
perfluorinated sulfonic acid resin; wherein each of the impregnated
membranes are prepared by multiple impregnations of two sides of
the expanded polytetrafluoroethylene membrane with ion exchange
material..Iaddend..Iadd.
39. A laminate according to claim 38, wherein the thickness of the
laminate is 40 microns or less..Iaddend..Iadd.
40. A laminate according to claim 38, wherein at least two of the
impregnated membranes are impregnated with ion exchange material
before lamination to form the laminate..Iaddend..Iadd.
41. A laminate according to claim 37, wherein the thickness of the
laminate is 40 microns or less..Iaddend..Iadd.
42. A laminate according to claim 37, wherein at least two of the
impregnated membranes are impregnated with ion exchange material
before lamination to form the laminate..Iaddend..Iadd.
43. A laminate according to claim 37, wherein the laminate is
prepared by (i) impregnation of at least one first unimpregnated
expanded polytetrafluoroethylene membrane with ion exchange
material to form a first impregnated membrane, (ii) lamination of
the first impregnated membrane with a second unimpregnated expanded
polytetrafluoroethylene membrane, and (iii) impregnation of the
second unimpregnated expanded polytetrafluoroethylene to form a
second impregnated membrane which is laminated to the first
impregnated membrane..Iaddend..Iadd.
44. A laminate according to claim 37, wherein lamination is carried
out with heat..Iaddend..Iadd.
45. A membrane comprising:
(a) at least one expanded polytetrafluoroethylene membrane having a
porous microstructure of polymeric fibrils; and
(b) at least one ion exchange material impregnated throughout the
porous microstructure of the membrane so as to render an interior
volume of the expanded polytetrafluoroethylene membrane
substantially occlusive, the impregnated expanded
polytetrafluoroethylene membrane having a Gurley number of greater
than 10,000 seconds, wherein powder is included with the at least
one ion exchange material..Iaddend..Iadd.
46. A membrane according to claim 45, wherein the thickness of the
expanded polytetrafluoroethylene membrane is 80 microns or
less..Iaddend..Iadd.
47. A membrane according to claim 45, wherein the thickness of the
expanded polytetrafluoroethylene membrane is 20 microns or
less..Iaddend..Iadd.
48. A membrane according to claim 47, wherein the impregnated
membrane has an ionic conductivity of at least 8.5
mhos/cm.sup.2..Iaddend..Iadd.
49. A membrane according to claim 47, wherein the impregnated
membrane has an ionic conductivity of at least 22.7
mhos/cm.sup.2..Iaddend..Iadd.
50. A membrane according to claim 45, wherein the impregnated
membrane has an ionic conductivity of at least 8.5
mhos/cm.sup.2..Iaddend..Iadd.
51. A membrane according to claim 45, wherein the impregnated
membrane has an ionic conductivity of at least 22.7
mhos/cm.sup.2..Iaddend..Iadd.
52. A membrane consisting essentially of:
(a) at least one expanded base membrane having a porous
microstructure of polymeric fibrils and having a thickness of 80
microns or less; and
(b) at least one ion exchange material impregnated throughout the
porous microstructure of the expanded base membrane so as to render
an interior volume of the base membrane substantially occlusive the
impregnated expanded base membrane having a Gurley number of
greater than 10,000 seconds..Iaddend..Iadd.
53. A membrane according to claim 52, wherein the impregnated
membrane has a thickness of 20 microns or less and an ionic
conductivity of at least 8.5 mhos/cm.sup.2..Iaddend..Iadd.
54. A membrane according to claim 52, wherein the impregnated
membrane has an ionic conductivity of at least 22.7
mhos/cm.sup.2..Iaddend..Iadd.
55. A membrane according to claim 54, wherein the impregnated
membrane is heated to between 120.degree. C. and 200.degree.
C..Iaddend..Iadd.
56. A composite membrane consisting essentially of:
(a) at least one expanded polytetrafluoroethylene membrane having a
porous microstructure of polymeric fibrils and having a thickness
of 80 microns or less; and
(b) at least one ion exchange material impregnated throughout the
porous microstructure of the expanded polytetrafluoroethylene
membrane so as to render an interior volume of the expanded
polytetrafluoroethylene membrane substantially occlusive, the
impregnated membrane not allowing for fluid
percolation..Iaddend..Iadd.
57. A composite membrane according to claim 56, wherein the ionic
conductivity of the impregnated membrane is at least 8.5
mhos/cm.sup.2 and the impregnated membrane is heated to between
120.degree. C. and 200.degree. C..Iaddend..Iadd.
58. A composite membrane according to claim 56, wherein the
thickness of the composite membrane and the thickness of the
impregnated expanded polytetrafluoroethylene membrane are
substantially the same..Iaddend..Iadd.
59. A composite membrane according to claim 56, wherein a side of
the composite membrane is laminated to a support structure, and the
ion exchange material is impregnated throughout the porous
microstructure of the expanded polytetrafluoroethylene membrane
from a side opposite to side laminated to the support
structure..Iaddend..Iadd.
60. A composite membrane according to claim 56, wherein the ion
exchange material is impregnated throughout the porous
microstructure of the expanded polytetrafluoroethylene membrane by
simultaneous treatment of both sides of the expanded
polytetrafluoroethylene membrane..Iaddend..Iadd.
61. A composite membrane according to claim 56, wherein the ion
exchange material is uniformly impregnated throughout the porous
microstructure of the expanded polytetrafluoroethylene membrane,
and the composite membrane has no porous surfaces exposed..Iaddend.
Description
FIELD OF THE INVENTION
An integral composite membrane is provided which is useful in
electrolytic processes and other chemical separations.
BACKGROUND OF THE INVENTION
Ion exchange membranes (IEM) are used in polymer electrolyte fuel
cells as solid electrolytes. A membrane, located between a cathode
and an anode of such a fuel cell, transports protons formed near
the catalyst at the hydrogen electrode to the oxygen electrode,
thereby allowing a current to be drawn from the fuel cell. These
polymer electrolyte fuel cells are particularly advantageous
because they operate at lower temperatures than other fuel cells.
Also, these polymer electrolyte fuel cells do not contain any
corrosive acids which are found in phosphoric acid fuel cells. In
these type fuel cells, there is a need to eliminate the bulk
transfer of reactants from one electrode to the other, i.e. fluid
percolation.
Ion exchange membranes are also used in chloralkali applications to
separate brine mixtures to form chlorine gas and sodium hydroxide.
For best performance, it is preferred that the membrane selectively
transport the sodium ions across the membrane while rejecting the
chloride ions. Also, the ion exchange membrane must eliminate bulk
transfer of electrolytic solution across the membrane, i.e. fluid
percolation.
Additionally, IEMs are useful in the areas of diffusion dialysis,
electrodialysis and in pervaporation and vapor permeation
separations. IEMs may also be used for selective transport of polar
compounds from mixtures containing both polar and non-polar
compounds.
IEMs must have sufficient strength to be useful in their various
applications. Often, this need for increased strength requires that
an IEM be made relatively thick in cross section, or that the IEM
be reinforced with woven fabrics (macro-reinforcements), both of
which decreases the ionic conductance of the IEM. Additionally,
conventional IEMs exhibit inherent dimensional instability due to
the absorbance of solvents, such as water, for example. Such
dimensional instability renders conventional IEMs substantially
ineffective for many commercial applications.
U.S. Pat. No. 3,692,569 relates to the use of a coating of a
copolymer of fluorinated ethylene and a sulfonyl-containing
fluorinated vinyl monomer on a fluorocarbon polymer that was
previously non-wettable. The fluorocarbon polymer may include
tetrafluoroethylene polymers. This coating provides a topical
treatment to the surface so as to decrease the surface tension of
the fluorocarbon polymer. U.S. Pat. No. 3,692,569 provides for a
fluid percolating structure.
U.S. Pat. No. 4,453,991 relates to a process for making articles
coated with a liquid composition of a perfluorinated polymer,
having sulfonic acid or sulfonate groups in a liquid medium, by
contacting the polymer with a mixture of 25 to 100% by weight of
water and 0 to 75% by weight of a second liquid component, such as
a low molecular weight alcohol, in a closed system. Such a process
provides for a multi-layered structure.
U.S. Pat. No. 4,902,308 relates to a film of porous expanded
polytetrafluoroethylene (PTFE) having its surfaces, both exterior
and internal, coated with a metal salt of perfluoro-cation exchange
polymer. Such a composite product is permeable to air. The air flow
of such a structure, as measured by the Gurley densometer ASTM
D726-58, is about 12 to 22 seconds. Therefore, this structure
provides for fluid percolation.
U.S. Pat. No. 5,082,472 relates to a composite material of a
microporous membrane, such as porous expanded PTFE, in laminar
contact with a continuous ion exchange resin layer, wherein both
layers have similar area dimensions. Surfaces of internal nodes and
fibrils of the expanded PTFE may be coated, at least in part, with
an ion exchange resin coating. The expanded PTFE layer of this
composite membrane imparts mechanical strength to the composite
structure. However, the interior of the expanded PTFE membrane is
unfilled so as to not block the flow of fluids. Therefore, U.S.
Pat. No. 5,082,472 provides for fluid percolation.
U.S. Pat. No. 5,094,895 and 5,183,545 relate to a composite porous
liquid-permeable article having multiple layers of porous expanded
PTFE, which are bonded together, and which have interior and
exterior surfaces coated with an ion exchange polymer. Such a
composite article is particularly useful as a diaphragm in
electrolytic cells. However, diaphragms are inherently percolating
structures.
Japanese Patent Application No. 62-240627 relates to a coated or an
impregnated membrane formed with a perfluoro type ion exchange
resin and a porous PTFE film to form an integral structure. The
resulting composite is not fully occlusive. Furthermore, the
teachings of this application do not provide for permanent adhesion
of the ion exchange resin to the inside surface of the PTFE
film.
There remains a need for a strong, integral composite ion exchange
membrane, having long term chemical and mechanical stability.
SUMMARY OF THE INVENTION
The present invention is an advancement over presently known ion
exchange membranes. In one embodiment of the present invention,
this is accomplished by providing a composite membrane comprising
an expanded polytetrafluoroethylene (PTFE) membrane having a porous
microstructure of polymeric fibrils. The composite membrane is
impregnated with an ion exchange material throughout the membrane.
The impregnated expanded polytetrafluoroethylene membrane has a
Gurley number of greater than 10,000 seconds. The ion exchange
material substantially impregnates the membrane so as to render an
interior volume of the membrane substantially occlusive.
The expanded PTFE membrane may comprise a microstructure of nodes
interconnected by fibrils.
The ion exchange material may be selected from a group consisting
of perfluorinated sulfonic acid resin, perfluorinated carboxylic
acid resin, polyvinyl alcohol, divinyl benzene, styrene-based
polymers, and metal salts with or without a polymer. The ion
exchange material may also be comprised of at least in part a
powder, such as but not limited to, carbon black, graphite, nickel
silica, titanium dioxide, and platinum black.
A purpose of the present invention is to provide an improved
alternative to the macro-reinforcement of ionomer materials.
Another purpose of the present invention is to provide an ion
exchange membrane having a single integral structure that does not
allow for fluid percolation.
The foregoing and other aspects will become apparent from the
following detailed description of the invention when considered in
conjunction with the accompanying drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-section of a composite membrane of the
present invention that is fully impregnated with an ion exchange
material.
FIG. 2 is a schematic cross-section of the composite membrane of
the present invention that is fully impregnated with an ion
exchange material and which includes a backing material attached
thereto.
FIG. 3 is a photomicrograph, at a magnification of 2.5 kX, of a
cross-section of an expanded PTFE membrane that has not been
treated with an ion exchange material.
FIG. 4 is a photomicrograph, at a magnification of 5.1 kX, of a
cross-section of an expanded PTFE membrane impregnated with an ion
exchange material, such that the interior volume of the membrane is
substantially occluded.
FIG. 5 is a photomicrograph, at a magnification of 20.0 kx, of a
cross-section of an expanded PTFE membrane, comprised substantially
of fibrils with no nodes present, which has not been treated with
an ion exchange material.
DETAILED DESCRIPTION OF THE INVENTION
As best illustrated by FIG. 1, a composite membrane is provided
which includes a base material 4 and an ion exchange material or
ion exchange resin 2. The base material 4 is a membrane which is
defined by a porous microstructure characterized by nodes
interconnected by fibrils (FIG. 3), or a porous microstructure
characterized substantially by fibrils (FIG. 5). The ion exchange
resin substantially impregnates the membrane so as to render the
interior volume substantially occlusive. The ion exchange resin is
securely adhered to both the external and internal membrane
surfaces, i.e. the fibrils and/or nodes of the base material.
The composite membrane of the present invention may be employed in
various applications, including but not limited to, polarity-based
chemical separations; electrolysis; fuel cells and batteries;
pervaporation; gas separation; dialysis separation; industrial
electrochemistry, such as chloralkali production and other
electrochemical applications; use as a super acid catalyst; or use
as a medium in enzyme immobilization, for example.
The composite membrane of the present invention is uniform and
mechanically strong. As used herein, the term "uniform" is defined
as continuous impregnation with the ion exchange material such that
no pin holes or other discontinuities exist within the composite
structure. The membrane should be "occlusive", meaning that the
interior volume of the porous membrane is impregnated such that the
interior volume is filled with the ion exchange material and the
final membrane is essentially air impermeable having a Gurley
number of greater than 10,000 seconds. A fill of 90% or more of the
interior volume of the membrane should provide adequate occlusion
for purposes of the present invention.
A preferred base material 4 is an expanded polytetrafluoroethylene
(ePTFE) which may be made in accordance with the teachings of U.S.
Pat. No. 3,593,566, incorporated herein by reference. Such a base
material has a porosity of greater than 35%. Preferably, the
porosity is between 70-95%. Preferably the thickness is between
0.06 mils (0.19 .mu.m) and 0.8 mils (0.02 mm), and most preferably
the thickness is between 0.50 mils (0.013 mm) and 0.75 mils (0.019
mm). This material is commercially available in a variety of forms
from W. L. Gore & Associates, Inc., of Elkton, Md., under the
trademark GORE-TEX.RTM.. FIG. 3 shows a photomicrograph of the
internal porous microstructure of an embodiment of such an expanded
PTFE membrane. As seen therein, the porous microstructure comprises
nodes interconnected by fibrils which define an interior volume of
the base material 4. Alternatively, the base material 4 may
comprise an ePTFE material having a porous microstructure defined
substantially of fibrils with no nodes present.
To manufacture an ePTFE membrane having a porous microstructure
defined substantially of fibrils with no nodes present, a PTFE that
has a low amorphous content and a degree of crystallization of at
least 98% is used as the raw material. More particularly, a
coagulated dispersion or fine powder PTFE may be employed, such as
but not limited to FLUON.RTM. CD-123 AND FLUON.RTM. CD-1 available
from ICI Americas, Inc., or TEFLON.RTM. fine powders available from
E. I. DuPont de Nemours and Co., Inc. (TEFLON is a registered
trademark of E. I. DuPont de Nemours and Co., Inc.) These
coagulated dispersion powders are lubricated with a hydrocarbon
extrusion aid, preferably an odorless mineral spirit, such as
ISOPAR K (made by Exxon Corp.) (ISOPAR is a registered trademark of
the Exxon Corporation). The lubricated powder is compressed into
cylinders and extruded in a ram extruder to form a tape. The tape
is compressed between rolls to an appropriate thickness, usually 5
to 10 mils. The wet tape is stretched traversely to 1.5 to 5 times
its original width. The extrusion aid is driven off with heat. The
dried tape is then expanded longitudinally between banks of rolls
in a space heated to a temperature that is below the polymer
melting point (approximately 327.degree. C.). The longitudinal
expansion is such that the ratio of speed of the second bank of
rolls to the first bank is from about 10-100 to 1. The longitudinal
expansion is repeated at about 1-1.5 to 1 ratio. After the
longitudinal expansion, the tape is expanded traversely, at a
temperature that is less than about 327.degree. C., to at least 1.5
times, and preferably to 6 to 15 times, the width of the original
extrudate, while restraining the membrane from longitudinal
contraction. While still under constraint, the membrane is
preferably heated to above the polymer melting point (approximately
342.degree. C.) and then cooled. This ePTFE membrane is
characterized by the following properties:
(a) average pore size between 0.05 and 0.4 micrometers, and
preferably less than 0.2;
(b) a bubble point between 10 and 60 psi;
(c) a pore size distribution value between 1.05 and 1.20;
(d) a ball burst strength between 0.9 and 17 pounds/force;
(e) an air flow of between 20 Frazier and 10 Gurley seconds;
(f) a thickness between 1.32 .mu.m and 25.4 .mu.m; and
(g) a fiber diameter of between 5 and 20 Nm.
Suitable ion exchange materials 2 include, but are not limited to,
perfluorinated sulfonic acid resin, perfluorinated carboxylic acid
resin, polyvinyl alcohol, divinyl benzene, styrene-based polymers
and metal salts with or without a polymer. A mixture of these ion
exchange materials may also be employed in treating the membrane 4.
Solvents that are suitable for use with the ion exchange material,
include for example, alcohols, carbonates, THF (tetrahydrofuran),
water, and combinations thereof. Optionally, ion exchange materials
may be complemented by finely divided powders or other (non-ionic)
polymers to provide final composites. Such a finely divided powder
may be selected from a wide range of organic and inorganic
compounds such as, but not limited to, carbon black, graphite,
nickel, silica, titanium dioxide, platinum black, for example, to
provide specific added effects such as different aesthetic
appearance (color), electrical conductivity, thermal conductivity,
catalytic effects, or enhanced or reduced reactant transport
properties. Examples of non-ionic polymers include, but are not
limited to, polyolefins, other fluoropolymers such as
polyvinylidene (PVDF), or other thermoplastics and thermoset
resins. Such non-ionic polymers may be added to aid occlusion of
the substrate matrix, or to enhance or reduce reactant transport
properties.
A surfactant having a molecular weight of greater than 100 is
preferably employed with the ion exchange material 2 to ensure
impregnation of the interior volume of the base material 4.
Surfactants or surface active agents having a hydrophobic portion
and a hydrophilic portion may be utilized.
A most preferred surfactant is a nonionic material, octylphenoxy
polyethoxyethanol having a chemical structure: ##STR1##
where x=10 (average),
and is known as Triton X-100, which is commercially available from
Rohm & Haas of Philadelphia, Pa.
As best seen by reference to FIG. 4, the final composite membrane
of the present invention has a uniform thickness free of any
discontinuities or pinholes on the surface. The interior volume of
the membrane is occluded such that the composite membrane is
impermeable to non-polar gases and to bulk flow of liquids.
Optionally, and as shown schematically in FIG. 2, the composite
membrane may be reinforced with a woven or non-woven material 6
bonded to one side of the base material 4. Suitable woven materials
may include, for example, scrims made of woven fibers of expanded
porous polytetrafluoroethylene; webs made of extruded or oriented
polypropylene or polypropylene netting, commercially available from
Conwed, Inc. of Minneapolis, Minn; and woven materials of
polypropylene and polyester, from Tetko Inc., of Briarcliff Manor,
N.Y. Suitable non-woven materials may include, for example, a
spun-bonded polypropylene from Reemay Inc. of Old Hickory,
Tenn.
The treated membrane may be further processed to remove any
surfactant which may have been employed in processing the base
material as described in detail herein. This is accomplished by
soaking or submerging the membrane in a solution of, for example,
water, isopropyl alcohol, hydrogen peroxide, methanol, and/or
glycerin. During this step, the surfactant, which was originally
mixed in solution with the ion exchange material, is removed. This
soaking or submerging causes a slight swelling of the membrane,
however the ion exchange material remains within the interior
volume of the base material 4.
The membrane is further treated by boiling in a suitable swelling
agent, preferably water, causing the membrane to slightly swell in
the x and y direction. Additions swelling occurs in the
z-direction. A composite membrane results having a higher ion
transport rate that is also strong. The swollen membrane retains
its mechanical integrity and dimensional stability, unlike the
membranes consisting only of the ion exchange material. Also, the
membrane maintains desired ionic transport characteristics. A
correlation exists between the content of the swelling agent within
the membrane structure and transport properties of the membrane. A
swollen membrane will transport chemical species faster than an
unswollen membrane.
Although the membrane has excellent long term chemical stability,
it can be susceptible to poisoning by organics. Accordingly, it is
often desirable to remove such organics from the membrane. For
example, organics can be removed by regeneration in which the
membrane is boiled in a strong acid, such as nitric or chromic
acid.
To prepare the integral composite membrane of the present
invention, a support structure, such as a polypropylene woven
fabric, may first be laminated to the untreated base material 4 by
any conventional technique, such as, hot roll lamination,
ultrasonic lamination, adhesive lamination, or forced hot air
lamination so long as the technique does not damage the integrity
of the base material. A solution is prepared containing an ion
exchange material in solvent mixed with one or more surfactants.
The solution may be applied to the base material 4 by any
conventional coating technique including forwarding roll coating,
reverse roll coating, gravure coating, doctor coating, kiss
coating, as well as dipping, brushing, painting, and spraying so
long as the liquid solution is able to penetrate the interstices
and interior volume of the base material. Excess solution from the
surface of the membrane may be removed. The treated membrane is
then immediately placed into an oven to dry. Oven temperatures may
range from 60.degree.-200.degree. C., but preferably
120.degree.-160.degree. C. Drying the treated membrane in the oven
causes the ion exchange resin to become securely adhered to both
the external and internal membrane surfaces, i.e., the fibrils
and/or nodes of the base material. Additional solution application
steps, and subsequent drying, may be repeated until the membrane
becomes completely transparent. Typically, between 2 to 8
treatments are required, but the actual number of treatments is
dependent on the surfactant concentration and thickness of the
membrane. If the membrane is prepared without a support structure,
both sides of the membrane may be treated simultaneously thereby
reducing the number of treatments required.
The oven treated membrane is then soaked in a solvent, such as the
type described hereinabove, to remove the surfactant. Thereafter
the membrane is boiled in a swelling agent and under a pressure
ranging from about 1 to about 20 atmospheres absolute thereby
increasing the amount of swelling agent the treated membrane is
capable of holding.
Alternatively, the ion exchange material may be applied to the
membrane without the use of a surfactant. This procedure requires
additional treatment with the ion exchange resin. However, this
procedure does not require that the oven treated membrane be soaked
in a solvent, thereby reducing the total number of process steps. A
vacuum may also be used to draw the ion exchange material into the
membrane. Treatment without surfactant is made easier if the water
content of the solution is lowered. Partial solution dewatering is
accomplished by slow partial evaporation of the ion exchange
material solution at room temperature followed by the addition of a
non-aqueous solvent. Ideally, a fully dewatered solution can be
used. This is accomplished in several steps. First, the ion
exchange material is completely dried at room temperature. The
resulting resin is ground to a find powder. Finally, this powder is
redissolved in a solvent, preferably a combination of methanol and
isopropanol.
Because the composite membrane of the present invention can be made
thinner than a fabric or non-woven reinforced structure, it is
possible to transport ions at a faster rate than previously has
been achieved, with only a slight lowering of the selectivity
characteristics of the membrane.
The following testing procedures were employed on samples which
were prepared in accordance with the teachings of the present
invention.
TEST PROCEDURES
TENSILE TEST
Tensile tests were carried out on an Instron Model 1122 tensile
strength tester, in accordance with ASTM D 638-91. Machine
parameters were set as follows:
Cross head speed: 0.423 cm/sec.
Full Scale load range: 222.4N
Humidity (%): 50
Temperature: 22.8.degree. C.
Grip Distance: 6.35 cm
Specimens were stamped out to conform with Type (II) of ASTM D638.
The specimens had a width of 0.635 cm, and a gauge length of 2.54
cm.
THICKNESS
Thickness of the base material was determined with the use of a
snap gauge (Johannes Kafer Co. Model No. F1000/302). Measurements
were taken in at least four areas of each specimen. Thickness of
the dried composite membrane was also obtained with the use of the
snap gauge. Thicknesses of swollen samples were not measurable with
the snap gauge due to the compression or residual water on the
surface of the swollen membrane. Thickness measurements of the
swollen membranes were also not able to be obtained with the use of
scanning electron microscopy due to the interferences with the
swelling agents.
MOISTURE VAPOR TRANSMISSION RATE (MVTR)
A potassium acetate solution, having a paste like consistency, was
prepared from potassium acetate and distilled water. (Such a paste
may be obtained by combining 230 g potassium acetate with 100 g of
water, for example.) This solution was placed into a 133 ml.
polypropylene cup, having an inside diameter of 6.5 cm, at its
mouth. An expanded polytetrafluoroethylene (ePTFE) membrane was
provided having a minimum MVTR of approximately 85,000 g/m.sup.2
-24 hr. as tested by the method described in U.S. Pat. No.
4,862,730 to Crosby. The ePTFE was heat sealed to the lip of the
cup to create a taut, leakproof, microporous barrier containing the
solution.
A similar ePTFE membrane was mounted to the surface of a water
bath. The water bath assembly was controlled at 23.degree.
C..+-.plus or minus 0.2.degree. C., utilizing a temperature
controlled room and a water circulating bath.
Prior to performing the MVTR test procedure, a sample to be tested
was allowed to condition at a temperature of 23.degree. C. and a
relative humidity of 50%. The sample to be tested was placed
directly on the ePTFE membrane mounted to the surface of the water
bath and allowed to equilibrate for 15 minutes prior to the
introduction of the cup assembly.
The cup assembly was weighed to the nearest 1/1000 g. and was
placed in an inverted manner onto the center of the test
sample.
Water transport was provided by a driving force defined by the
difference in relative humidity existing between the water in the
water bath and the saturated salt solution of the inverted cup
assembly. The sample was tested for 10 minutes and the cup assembly
was then removed and weighed again within 1/1000 g.
The MVTR of the sample was calculated from the weight gain of the
cup assembly and was expressed in grams of water per square meter
of sample surface area per 24 hours.
PEEL STRENGTH
Peel strength or membrane adhesion strength tests were conducted on
membrane samples prepared with reinforced backings. Test samples
were prepared having dimensions of 3 inches by 3.5 inches (7.62
cm.times.8.89 cm). Double coated vinyl tape (type--#419 available
from the 3M Company of Saint Paul, Minn.) having a width of 1 inch
(2.54 cm) was placed over the edges of a 4 inch by 4 inch (10.2
cm.times.10.2 cm.) chrome steel plate so that tape covered all
edges of the plate. The membrane sample was then mounted on top of
the adhesive exposed side of the tape and pressure was applied so
that sample was adhesively secured to the chrome plate.
The plate and sample were then installed, in a horizontal position,
within an Instron tensile test machine Model No. 1000. An upper
crosshead of the tensile test machine was lowered so that the jaws
of the test machine closed flat and tightly upon the sample. The
upper crosshead was then slowly raised pulling the membrane sample
from the reinforced backing. When the membrane detached from the
reinforced backing, the test was complete. Adhesion strength was
estimated from the average strength needed to pull the membrane
from the reinforced backing.
IONIC CONDUCTANCE
The ionic conductance of the membrane was tested using a Palico
9100-2 type test system. This test system consisted of a bath of 1
molar sulfuric acid maintained at a constant temperature of
25.degree. C. Submerged in the bath were four probes used for
imposing current and measuring voltage by a standard "Kelvin"
four-terminal measurement technique. A device capable of holding a
separator, such as the sample membrane to be tested, was located
between the probes. First, a square wave current signal was
introduced into the bath, without a separator in place, and the
resulting square wave voltage was measured. This provided an
indication of the resistance of the acid bath. The sample membrane
was then placed in the membrane-holding device, and a second square
wave current signal was introduced into the bath. The resulting
square wave voltage was measured between the probes. This was a
measurement of the resistance due to the membrane and the bath. By
subtracting this number from the first, the resistance due to the
membrane alone was found.
DIMENSIONAL STABILITY
Reverse expansion in the x and y direction upon dehydration was
measured using a type Thermomechanical Analyzer 2940, made by TA
Instruments, Inc., of New Castle, Del. This instrument was used to
apply a predetermined force to a sample that had been boiled in
water for 30 minutes. A quartz probe placed in contact with the
sample measured any linear changes in the sample as it dried. A
sample was placed in a holder and then dried at 75.degree. C. for
greater than 10 min. The change in dimension (i.e., the shrinkage)
was recorded as a percentage of the original weight.
WEIGHT LOSS WITH TEMPERATURE
A high resolution TGA 2950, Thermogravimetric Analyzer, made by TA
Instruments (Newcastle, Del.) was used to determine the weight loss
of samples with respect to temperature. This weight loss is an
indication of the water content of the ionomer sample.
SELECTIVITY
Two solutions of KCl, having concentrations of 1 molar and 0.5
molar, respectively, were separated using the membranes of the
present invention. Two calomel reference electrodes (available from
Fischer Scientific, Pittsburgh Pa., catalog number 13-620-52) were
placed in each solution, and the potential difference across the
membranes was recorded using a digital multimeter (available from
Hewlett Packard, Englewood Calif., catalog number HP34401A). The
values obtained correspond to the difference of chloride ion
activity across the membrane and are reduced by the rate of anion
migration across the membranes. Therefore the obtained values
provide an indication of the membrane selectivity. The higher the
measured voltage, the better the membrane selectivity.
BUBBLE POINT TEST
Liquids with surface free energies less than that of stretched
porous PTFE can be forced out of the structure with the application
of a differential pressure. This clearing will occur from the
largest passageways first. A passageway is then created through
which bulk air flow can take place. The air flow appears as a
steady stream of small bubbles through the liquid layer on top of
the sample. The pressure at which the first bulk air flow takes
place is called the bubble point and is dependent on the surface
tension of the test fluid and the size of the largest opening. The
bubble point can be used as a relative measure of the structure of
a membrane and is often correlated with some other type of
performance criteria, such as filtration efficiency.
The Bubble Point was measured according to the procedures of ASTM
F316-86. Isopropyl alcohol was used as the wetting fluid to fill
the pores of the test specimen.
The Bubble Point is the pressure of air required to displace the
isopropyl alcohol from the largest pores of the test specimen and
create the first continuous stream of bubbles detectable by their
rise through a layer of isopropyl alcohol covering the porous
media. This measurement provides an estimation of maximum pore
size.
PORE SIZE AND PORE SIZE DISTRIBUTION
Pore size measurements are made by the Coulter Porometer.TM.,
manufactured by Coulter Electronics, Inc., Hialeah, Fla. The
Coulter Porometer is an instrument that provides automated
measurement of pore size distributions in porous media using the
liquid displacement method (described in ASTM Standard E1298-89).
The Porometer determines the pore size distribution of a sample by
increasing air pressure on the sample and measuring the resulting
flow. This distribution is a measure of the degree of uniformity of
the membrane (i.e., a narrow distribution means there is little
difference between the smallest and largest pore size). The
Porometer also calculates the mean flow pore size. By definition,
half of the fluid flow through the filter occurs through pores that
are above or below this size. It is the mean flow pore size which
is most often linked to other filter properties, such as retention
of particulates in a liquid stream. The maximum pore size is often
linked to the Bubble Point because bulk air flow is first seen
through the largest pore.
BALL BURST TEST
This text measures the relative strength of a sample by determining
the maximum load at break. The sample is challenged with a 1 inch
diameter ball while being clamped between two plates. The material
is placed taut in the measuring device and pressure applied with
the ball burst probe. Pressure at break is recorded.
AIR FLOW DATA
The Gurley air flow test measures the time in seconds for 100 cc of
air to flow through a one square inch sample at 4.88 inches of
water pressure. The sample is measured in a Gurley Densometer (ASTM
0726-58). The sample is placed between the clamp plates. The
cylinder is then dropped gently. The automatic timer (or stopwatch)
is used to record the time (seconds) required for a specific volume
recited above to be displaced by the cylinder. This time is the
Gurley number.
The Frazier air flow test is similar but is mostly used for much
tinner or open membranes. The test reports flow in cubic feet per
minute per square foot of material at 0.5 inches water pressure.
Air flow can also be measured with the Coulter Porometer. In this
test, the operator can select any pressure over a wide range. The
Porometer can also perform a pressure hold test that measures air
flow during a decreasing pressure curve.
BACKGROUND OF EXAMPLES
As may be appreciated by one skilled in the art, the present
invention provides for an integral composite membrane. No porous
surfaces are exposed in the present invention.
The integral composite membrane of the present invention can be
advantageously employed in electrolytic processes and chemical
separations. In a plate-and-frame type electrodialysis unit, the
membrane of the present invention would take the place of existing
cation exchange membranes. This membrane could be of the type which
is laminated to a spacer screen in accordance with a specific
application. Due to the higher conductance of this membrane
feasible with thinner membranes, an electrodialysis unit could
employ less membrane to achieve a given flux rate, thereby saving
space and cost. If equipment is retrofitted with this membrane, the
voltage requirements would be reduced at a given current, or higher
current could be run at a given voltage. Also, in a diffusion
dialysis system, a given unit employing the membrane of the present
invention would provide a higher flux.
A fuel cell, utilizing the membrane of the present invention,
operates at a higher voltage for a given current density due to the
improved ionic conductance of thinner versions of the membrane of
this invention.
Due to improved water transport across the membrane of the present
invention, high limiting current may be achieved with less fuel gas
humidification, as compared to membranes which have been employed
heretofore. For example, the membrane of the present invention has
a resistance of 0.044 ohm-sq cm. At a current density of 1
A/cm.sup.2, this causes a voltage drop of about 44 mV, or about a
99 mV improvement in cell voltage compared to NAFION 117 membranes
which have a resistance of 0.143 .OMEGA.-cm.sup.3. (NAFION is a
registered trademark of E. I. DuPont de Nemours and Co., Inc.). As
used herein, NAFION 117 means a membrane having a thickness of 7
mils made from perfluorosulfonic acid/tetrafluoroethylene
(TFE)/copolymer. This may reduce losses by about 99 mW/sq cm at
this operating condition for resistance. If the cell operating
voltage increased from 500 mV to 599 mV, the cell voltage
efficiency would increase from 41% to 49% of the theoretical 1.23
V. The decrease in the internal resistance of the cell allows the
design of smaller or more efficient cells.
Without intending to limit the scope of the present invention, the
apparatus and method of production of the present invention may be
better understood by referring to the following examples. All
samples of ePTFE provided in the following examples were made in
accordance with the teachings of U.S. Pat. No. 3,593,566. More
particularly, the ePTFE had the following material properties:
TYPE 1 TYPE 2 Gurley (sec.) 3.3 0.9 Bubble Point (psi) 28.3 32.6
Mass/Area (g/m.sup.2) 6.1 4.4 Density (g/cc) 0.65 0.77 Longitudinal
Maximum Load (lbs.) 1.76 2.18 Transverse Maximum Load (lbs.) 2.33
1.31
As may be appreciated by one skilled in the art, ePTFE membranes
can be made with a wide range of physical property values, with
ranges far exceeding the two examples given above.
EXAMPLE 1
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm), was mounted on a 6 inch diameter wooden embroidery hoop.
An ion exchange material/surfactant solution was prepared
comprising 95% by volume of a perfluorosulfonic
acid/tetrafluoroethylene copolymer resin solution (in H+ form,
which itself is comprised of 5% perfluorosulfonic
acid/tetrafluoroethylene copolymer resin, 45% water, and 50% a
mixture of low molecular weight alcohols, commercially available
from E. I. DuPont de Nemours, Inc. under the registered trademark
NAFION.RTM. type NR-50 (1100 EW) hereinafter "NR-50") and a 5% of a
nonionic surfactant of octylphenoxy polyethoxyethanol (Triton
X-100, commercially available from Rohm & Haas of Philadelphia,
Pa.). This solution was brushed on both sides of the membrane to
impregnate and substantially occlude the interior volume of the
membrane. The sample was then dried in the oven at 140.degree. C.
for 30 seconds. The procedure was repeated two more times to fully
occlude the interior volume. The sample was then soaked in
isopropanol for 5 minutes to remove the surfactant. After rinsing
with distilled water and allowing the sample to dry at room
temperature, a final coat of the ion exchange material/surfactant
solution was applied. The wet membrane was again dried in the oven
at 140.degree. C. for 30 seconds and soaked in isopropanol for 2
minutes. The membrane was finally boiled in distilled water for 30
minutes under atmospheric pressure to swell the treated membrane.
Gurley numbers for this material are summarized in Table 3. Ionic
conductive rates are summarized in Table 4. The tensile strength
may be found in Table 2. Percent weight change of this sample may
be found in Table 6. The swollen membrane was later dried to a
dehydrated state in an oven at 140.degree. C. for 30 seconds. The
thickness of the dried composite membrane was measured and found to
be approximately the same thickness as the base material.
EXAMPLE 2
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
placed on top of a netting of polypropylene obtained from Conwed
Plastics Corp. of Minneapolis, Minn. The two materials were bonded
together on a laminator with 10 psig pressure, a speed of 15 feet
per minute and a temperature of 200.degree. C. No adhesives were
used. The reinforced membrane sample was then placed on a 6 inch
wooden embroidery hoop. A solution was prepared of 96% by volume of
a perfluorosulfonic acid/TFE copolymer resin in alcohol, and 4% of
the nonionic surfactant Triton X-100. This solution was brushed
only on the membrane side to substantially occlude the interior
volume of the membrane. The sample was dried in an oven at
130.degree. C. This procedure was repeated three more times to
fully occlude the interior volume of the membrane. The sample was
then baked in an oven at 140.degree. C. for 5 minutes. The sample
was soaked in isopropanol for 5 minutes to remove the surfactant.
The membrane was then boiled in distilled water for 30 minutes
under atmospheric pressure causing the treated membrane to swell.
Gurley numbers for this material are summarized in Table 3.
This sample was tested for its peel strength in accordance with the
method described above. The linear bond strength was found to be
2.06 lb./sq. in. (1450 kg/m.sup.2).
EXAMPLE 3
A TYPE 2 ePTFE membrane, having a thickness of 0.5 mils (0.01 mm),
was mounted on a 6 inch diameter wooden embroidery hoop. A solution
of 100% by volume of NR-50 was brushed onto both sides of the
membrane, without the addition of any surfactants, to substantially
occlude the interior volume of the membrane. The sample was then
placed in an oven at 140.degree. C. to dry. This procedure was
repeated four more times until the membrane was completely
transparent and the interior volume of the membrane was fully
occluded. The sample was then boiled in distilled water for 30
minutes at atmospheric pressure causing the membrane to swell.
Gurley numbers for this material are summarized in Table 3.
EXAMPLE 4
A TYPE 2 ePTFE membrane, having a thickness of 0.5 mils (0.01 mm),
was mounted onto a 6 inch diameter wooden embroidery hoop. A
solution was prepared of 95% by volume NE-50 and 5% of the nonionic
surfactant, Triton X-100. The solution was brushed on both sides of
the membrane with a foam brush and the excess was wiped off. The
wet membrane was dried in an oven at 140.degree. C. for 30 seconds.
Three additional coats of solution were applied to the membrane in
the same manner to fully occlude the interior volume of the
membrane. The membrane was then soaked in isopropanol for 2 minutes
to remove the surfactant. The membrane was rinsed with distilled
water and allowed to dry at room temperature. A final treatment of
the solution was applied. The wet membrane was dried in the oven at
140.degree. C. for 30 seconds, and then soaked in isopropanol for 2
minutes. Finally, the membrane was boiled in distilled water for 5
minutes. Moisture vapor transmission rates for the treated membrane
were measured and are summarized in Table 1.
EXAMPLE 5
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm), was mounted onto a 6 inch diameter wooden embroidery
hoop. The Gurley Densometer air flow for this membrane was 2-4
seconds. A solution was prepared of 95% by volume NR-50 and 5%
Triton X-100. The solution was brushed on both sides of the
membrane with a foam brush and the excess was wiped off. The wet
membrane was dried in the oven at 140.degree. C. for 30 seconds.
Three additional coats of solution were applied in the same manner.
The membrane was then soaked in isopropanol for 2 minutes. After
rinsing with distilled water and allowing to dry at room
temperature, a final coat of the solution was applied. The wet
membrane was dried in the oven at 140.degree. C. for 30 seconds,
then soaked in isopropanol for 2 minutes. This material was not
boiled. No swelling other than the minor swelling during the
surfactant removal occurred. The ionic conduction rate for this
material is presented in Table 4.
EXAMPLE 6
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm), was mounted onto a 5 inch diameter plastic embroidery
hoop. The Gurley Densometer air flow for this membrane was 2-4
seconds. A solution was prepared of 95% NR-50 and 5% Triton X-100.
The solution was brushed on both sides of the membrane with a foam
brush and the excess was wiped off. The wet membrane was dried in
the oven at 140.degree. C. for 30 seconds. Two additional coats of
solution were applied in the same manner to fully occlude the
interior volume of the membrane. The membrane was then soaked in
isopropanol for 2 minutes. After rinsing with distilled water and
allowing to dry at room temperature, a final coat of the solution
was applied. The wet membrane was dried in the oven at 140.degree.
C. for 30 seconds, and then soaked in isopropanol for 2 minutes to
remove the surfactant. The sample was rinsed and dried at room
temperature.
This sample was weighed before it was mounted on the 5 inch plastic
hoop. Following treatment, it was removed from the hoop and weighed
again. The ion exchange polymer content was directly calculated by
determining the weight change before and after treatment. The ion
exchange content for this sample was found to be 98.4 mg or 7.77
grams per square meter of membrane.
EXAMPLE 7
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
placed on top of a netting of polypropylene which was obtained from
Applied Extrusion Technologies, Inc. of Middletown, Del. The two
materials were bonded together on a laminator with 10 psig
pressure, a speed of 15 feet per minute and a temperature of
200.degree. C. The reinforced sample was then mounted on a 6 inch
diameter wooden embroidery hoop. A solution was prepared consisting
of the following: 95% by volume NR-50, containing 5% by weight
perfluorosulfonic acid/TFE copolymer resin in a solvent mixture of
less than 25% water, preferably 16-18% water, and the remainder a
mixture of isopropanol and normal propanol: and 5% of Triton X-100
non-ionic surfactant. The solution was brushed on both sides of the
membrane with a foam brush and the excess was wiped off. The wet
membrane was dried in an oven at 140.degree. C. for 30 seconds.
Three additional coats of solution were applied to the membrane in
the same manner to fully occlude the interior volume of the
membrane. The membrane was then soaked in isopropanol for 2 minutes
to remove the surfactant. The membrane was rinsed with distilled
water and allowed to dry at room temperature. A final treatment of
the ion exchange material/surfactant solution was applied. The wet
membrane was dried in the oven at 140.degree. C. for 30 seconds,
then soaked in isopropanol for 2 minutes. Finally, the membrane was
boiled in distilled water for 5 minutes.
EXAMPLE 8
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
mounted on a 6 inch diameter wooden embroidery hoop. A solution was
prepared consisting of the following: 95% NR-50, containing 5% by
weight perfluorosulfonic acid/TFE copolymer resin in a solvent
mixture of less than 25% water, preferably 16-18% water, and the
remainder a mixture being isopropanol and normal propanol; and 5%
of Triton X-100 non-ionic surfactant. The solution was brushed on
both sides of the membrane with a foam brush and the excess was
wiped off. The wet membrane was dried in an oven at 140.degree. C.
for 30 seconds. Three additional coats of solution were applied to
the membrane in the same manner. The membrane was then soaked in
isopropanol for 2 minutes to remove the surfactant. The membrane
was rinsed with distilled water and allowed to dry at room
temperature. A final treatment of the solution was applied. The wet
membrane was dried in the oven at 140.degree. C. for 30 seconds,
then soaked in isopropanol for 2 minutes. Finally, the membrane was
boiled in distilled water for 5 minutes.
EXAMPLE 9
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
mounted on a 6 inch diameter wooden embroidery hoop. The membrane
was first submerged in a solution consisting of 25% Triton X-100
non-ionic surfactant, 25% water, and 50% isopropyl alcohol. Next, a
solution of NR-50 was brushed on both sides of the membrane with a
foam brush and the excess was wiped off. The wet membrane was dried
in an oven at 140.degree. C. for 30 seconds. Three additional coats
of surfactant solution followed by a coat of NR-50 solution were
applied to the membrane in the same manner to fully occlude the
interior volume of the membrane. The membrane was then soaked in
isopropanol for 2 minutes to remove the surfactant. The membrane
was rinsed with distilled water and allowed to dry at room
temperature. A final treatment of the ion exchange
material/surfactant was applied to the membrane. The wet membrane
was dried in the oven at 140.degree. C. for 30 seconds, then soaked
in isopropanol for 2 minutes. Finally, the membrane was boiled in
distilled water for 5 minutes.
EXAMPLE 10
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
mounted on a 6 inch diameter wooden embroidery hoop. The membrane
was first submerged in a solution consisting of 25% Triton X-100
non-ionic surfactant, 25% water, and 50% isopropyl alcohol. Next, a
95% by weight NR-50 solution containing 5% by weight
perfluorosulfonic acid/TFE copolymer resin in a solvent mixture of
less than 25% water, preferably 16-18% water, and the remainder a
mixture of isopropanol and normal propanol, was brushed on both
sides of the membrane with a foam brush and the excess was wiped
off. The wet membrane was dried in an oven at 140.degree. C. for 30
seconds. Three additional coats of surfactant solution followed by
the NR-50 solution were applied to the membrane in the same manner
to fully occlude the interior volume of the membrane. The membrane
was then soaked in isopropanol for 2 minutes to remove the
surfactant. The membrane was rinsed with distilled water and
allowed to dry at room temperature. A final treatment of the NR-50
solution was applied. The wet membrane was fried in the oven at
140.degree. C. for 30 seconds, then soaked in isopropanol for 2
minutes. Finally, the membrane was boiled in distilled water for 5
minutes.
EXAMPLE 11
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
placed on top of a netting of polypropylene. The two materials were
bonded together on a laminator with 10 psig pressure, a speed of 15
feet per minute and a temperature of 200.degree. C. The reinforced
sample was then mounted on a 6 inch diameter wooden embroidery
hoop. The membrane was first submerged in a solution consisting of
25% Triton X-100 non-ionic surfactant, 25% water, and 50 %
isopropyl alcohol. Next, a solution of NR-50 was brushed on both
sides of the membrane with a foam brush and the excess was wiped
off. The wet membrane was dried in an oven at 140.degree. C. for 30
seconds. Three additional coats of the surfactant solution followed
by the NR-50 solution were applied to the membrane in the same
manner to fully occlude the interior volume of the membrane. The
membrane was then soaked in isopropanol for 2 minutes to remove the
surfactant. The membrane was rinsed with distilled water and
allowed to dry at room temperature. A final treatment of the NR-50
solution was applied. The wet membrane was dried in the oven at
140.degree. C. for 30 seconds, then soaked in isopropanol for 2
minutes. Finally, the membrane was boiled in distilled water for 5
minutes.
EXAMPLE 12
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
mounted on a 6 inch diameter wooden embroidery hoop. A solution
consisting 5% by weight of perfluorosulfonic acid/TFE copolymer
resin in a solvent mixture of less than 25% water, preferably
16-18% water, and the remainder a mixture of isopropanol and normal
propanol was allowed to evaporate slowly at room temperature. The
resulting resin was ground to a powder with a mortar and pestle.
This resin was then dissolved in methanol under low heat (less than
70.degree. C.). The final solution contained the original resin
content in a base solvent of methanol such that the resin content
of the solution was 5% by weight. The solution was brushed on both
sides of the membrane with a foam brush and the excess was wiped
off. The wet membrane was dried in an oven at 140.degree. C. for 30
seconds. Three additional coats of solution were applied to the
membrane in the same manner to fully occlude the interior volume of
the membrane. The membrane was boiled in distilled water for 5
minutes.
EXAMPLE 13
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
mounted on a 6 inch diameter wooden embroidery hoop. A solution
consisting of 5% by weight of perfluorosulfonic acid/TFE copolymer
resin, in a solvent mixture of less than 25% water, preferably
16-18% water, and the remainder a mixture of isopropanol and normal
propanol, was allowed to evaporate slowly at room temperature. The
resulting resin was ground to a powder with a mortar and pestle.
This resin was then dissolved in methanol under low heat (less than
70.degree. C.). The final solution contained the original resin
content in a base solvent of methanol such that the resin content
of the solution was 5% by weight. This solution was used to prepare
a new solution comprised of a 95% dewatered resin solution, and 5%
Triton X-100 non-ionic surfactant. The solution was brushed on both
sides of the membrane with a foam brush and the excess was wiped
off. The wet membrane was dried in an oven at 140.degree. C. for 30
seconds. Two additional coats of solution were applied to the
membrane in the same manner to fully occlude the interior volume of
the membrane. The membrane was then soaked in isopropanol for 2
minutes to remove the surfactant. The membrane was rinsed with
distilled water and allowed to dry at room temperature. A final
treatment of the resin/Triton X-100 non-ionic surfactant solution
was applied. The wet membrane was dried in the oven at 140.degree.
C. for 30 seconds, then soaked in isopropanol for 2 minutes.
Finally, the membrane was boiled in distilled water for 5
minutes.
EXAMPLE 14
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
mounted on a 6 inch diameter wooden embroidery hoop. A solution
consisting of 5% by weight of perfluorosulfonic acid/TFE copolymer
resin in a solvent mixture of less than 25% water, preferably
16-18% water, and the remainder a mixture of isopropanol and normal
propanol, was allowed to partially evaporate slowly at room
temperature. Before all the solvent evaporated, the viscous liquid
was mixed with methanol. The water content of the resulting
solution was estimated at 5%. The resin content of the solution was
5%. The solution was brushed on both sides of the membrane with a
foam brush and the excess was wiped off. The wet membrane was dried
in an oven at 140.degree. C. for 30 seconds. Three additional coats
of solution were applied to the membrane in the same manner to
fully occlude the interior volume of the membrane. The membrane was
boiled in distilled water for 5 minutes.
EXAMPLE 15
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
placed on top of a netting of polypropylene. The two materials were
bonded together on a laminator with 10 psig pressure, a speed of 15
feet per minute and a temperature of 200.degree. C. The reinforced
sample was then mounted on a 6 inch diameter wooden embroidery
hoop. A solution consisting of 5% by weight of perfluorosulfonic
acid/TFE copolymer resin in a solvent mixture of less than 25%
water, preferably 16-18% water and the remainder a mixture of
isopropanol and normal propanol, was allowed to partially evaporate
slowly at room temperature. Before all the solvent evaporated, the
viscous liquid was mixed with methanol. The water content of the
resulting solution was estimated at 5%. The resin content of the
solution was 5%. The solution was brushed on both sides of the
membrane with a foam brush and the excess was wiped off. The wet
membrane was dried in an oven at 140.degree. C. for 30 seconds.
Three additional coats of solution were applied to the membrane in
the same manner to fully occlude the interior volume of the
membrane. The membrane was boiled in distilled water for 5
minutes.
EXAMPLE 16
A TYPE 1 ePTFE membrane, having a nominal thickness of 0.75 mils
(0.02 mm) and a Gurley Densometer air flow of 2-4 seconds, was
mounted on a 6 inch diameter wooden embroidery hoop. A solution
consisting of 5% by weight of perfluorosulfonic acid/TFE copolymer
resin in a solvent mixture of less than 25% water, preferably
16-18% water and the remainder a mixture of isopropanol and normal
propanol, was allowed to partially evaporate slowly at room
temperature. Before all the solvent evaporated, the viscous liquid
was mixed with methanol. The water content of the resulting
solution was estimated at 5%. The resin content of the solution was
5%. This solution was used to prepare a new solution comprised of
95% of the low-water resin solution, and 5% of the nonionic
surfactant, Triton X-100. The new solution was brushed on both
sides of the membrane with a foam brush and the excess was wiped
off. The wet membrane was dried in an oven at 140.degree. C. for 30
seconds. Two additional coats of solution were applied to the
membrane in the same manner to fully occlude the interior volume of
the membrane. The membrane was then soaked in isopropanol for 2
minutes to remove the surfactant. The membrane was rinsed with
distilled water and allowed to dry at room temperature. A final
treatment of the new solution was applied. The wet membrane was
dried in the oven at 140.degree. C. for 30 seconds, then soaked in
isopropanol for 2 minutes. Finally, the membrane was boiled in
distilled water for 5 minutes.
EXAMPLE 17
A thermoplastic frame was cut and a membrane of ePTFE was placed at
a center location of the frame. The ePTFE membrane was heat sealed
to the frame. The membrane was then treated in accordance with
Example 1. Alternatively, a fluoroionomer membrane made in
accordance with Example 1 was secured mechanically within a
frame.
This "framed" fluoroionomer composite has utility, by providing a
unitary construction which can be placed in a device, which beyond
serving as an ion exchange medium, can also serve as a sealant
between various components of a cell assembly.
EXAMPLE 18
TEFLON.RTM. fine powder was blended with ISOPAR K mineral spirit at
a rate of 115 cc per pound of fine powder. The lubricated powder
was compressed into a cylinder and was ram extruded at 70.degree.
C. to provide a tape. The tape was split into two rolls, layered
together and compressed between rolls to a thickness of 0.030 inch.
Next, the tape was stretched transversely to 2.6 times its original
width. The ISOPAR K was driven off by heating to 210.degree. C. The
dry tape was expanded longitudinally between banks of rolls in a
heat zone heated to 300.degree. C. The ratio of speed of the second
bank of rolls to the first bank of rolls was 35:1 and the third
bank of rolls to the second bank of rolls was 1.5:1, for a total of
52:1 longitudinal expansion producing a tape having a width of 3.5
inches. This tape was heated to 295.degree. C. and transversely
expanded 13.7 times in width, while being constrained from
shrinkage and then heated at 365.degree. C. while still
constrained. This process produced a web-like membrane having a
porous microstructure composed substantially of fibrils in which no
nodes were present.
EXAMPLE 19
An ePTFE membrane, having a nominal thickness of 2.2 mils (0.6 mm)
and a Gurley Densometer air flow of 6-9 seconds, was mounted on a 6
inch diameter wooden embroidery hoop. A solution consisting of 5%
by weight of ionomer, such as perfluorosulfonic acid/TFE copolymer
resin in a solvent such as methanol, was brushed on both sides of
the membrane with a foam brush and the excess was wiped off. The
wet membrane was dried in an oven at 140.degree. C. for 30 seconds.
Three additional coats of solution were applied to the membrane in
the same manner to fully occlude the interior volume of the
membrane.
EXAMPLE 20
An ePTFE membrane, having a nominal thickness of 3 mils (0.8 mm)
and a Gurley Densometer air flow of 6-9 seconds, was mounted on a 6
inch diameter wooden embroidery hoop. A solution consisting of 5%
by weight of ionomer, such as perfluorosulfonic acid/TFE copolymer
resin in a solution such as methanol, was brushed on both sides of
the membrane with a foam brush and the excess was wiped off. The
wet membrane was dried in an oven at 140.degree. C. for 30 seconds.
Three additional coats of solution were applied to the membrane in
the same manner to fully occlude the interior volume of the
membrane.
EXAMPLE 21
An ePTFE membrane, having a nominal thickness of 0.75 mils (0.02
mm) and a Gurley Densometer air flow of 2-4 seconds, was mounted on
a 6 inch diameter wooden embroidery hoop. A solution consisting of
5% by weight of ionomer, such as perfluorosulfonic acid/TFE
copolymer resin of 1100 EW in a solvent such as methanol, was
brushed on both sides of the membrane with a foam brush and the
excess was wiped off. The wet membrane was dried in an oven at
140.degree. C. for 30 seconds. Three additional coats of solution
were applied to the membrane in the same manner to fully occlude
the interior volume of the membrane. A second composite membrane
prepared in the same manner, however using a 950 EW
perfluorosulfonic acid/TFE copolymer in a solvent such as ethanol.
The two membranes were then combined (laminated) by use of heat and
pressure. For example, at 190.degree. C. (375.degree. F.) @ 100 psi
for 1 minute in a heated press or a comparable arrangement in a
heated roll.
EXAMPLE 22
An ePTFE membrane, having a nominal thickness of 0.75 mils (0.002
mm) and a Gurley Densometer air flow of 2-4 seconds, was mounted on
a 6 inch diameter wooden embroidery hoop. An alcohol solution
consisting of 5% by weight of ionomer, and a finely divided powder,
such as carbon black (10%), was brushed on both sides of the
membrane with a foam brush and the excess was wiped off. The wet
membrane was dried in an oven at 140.degree. C. for 30 seconds.
Three additional coats of solution were applied to the membrane in
the same manner to fully occlude the interior volume of the
membrane. The final composite had a dark appearance.
EXAMPLE 23
An ePTFE membrane, having a nominal thickness of 0.75 mils (0.002
mm) and a Gurley Densometer air flow of 2-4 seconds, was mounted on
a 6 inch diameter wooden embroidery hoop. A solution consisting of
5% by weight of ionomer, was brushed on both sides of the membrane
with a foam brush and the excess was wiped off. The wet membrane
was dried in an oven at 140.degree. C. for 30 seconds. Three
additional coats of solution were applied to the membrane in the
same manner to fully occlude the interior volume of the membrane.
This composite membrane was then combined (laminated) to another
ePTFE membrane having a nominal thickness of 0.75 (0.002) mm and a
Gurley Densometer air flow of 2-4 second, by use of heat and
pressure (for example 190.degree. C. [375.degree. F.] @ 100 psi)
using a heated press or a comparable arrangement.
A solution consisting of 5% by weight of ionomer, such as
perfluorosulfonic acid/TFE copolymer resin in a solvent such as
methanol, was brushed on the ePTFE membrane side of the membrane
with a foam brush and the excess was wiped off. The wet membrane
was dried in an oven at 140.degree. C. for 30 seconds. Three
additional coats of solution were applied to the membrane in the
same manner to fully occlude the interior volume of the ePTFE
membrane. A thicker integral composite membrane was thus
formed.
Comparative Samples
NAFION 117, a perfluorosulfonic acid cation exchange membrane,
unreinforced film of 1100 equivalent weight commercially available
from E. I. DuPont de Nemours Co., Inc., having a quoted nominal
thickness of 7 mils (0.18 mm) was obtained. The samples, originally
in the hydrated swollen state, were measured in the x- and
y-directions and weighed.
Without intending to limit the scope of the present invention, data
collected from testing the ion exchange membranes made in
accordance with the procedures of the foregoing examples are
summarized in the following tables. As may be appreciated by one
skilled in the art, these tables reveal that the ion exchange
membrane of this invention has superior ionic conductance and
exceptional dimensional stability compared to known ion exchange
membranes. Furthermore, this inventive membrane has good mechanical
strength in the unswollen state and retains much of its mechanical
strength in the swollen state, whereas conventional membranes are
substantially weakened upon hydration.
TABLE 1 Moisture Vapor Transmission Rates (MVTR) Sample ID* MVTR
(grams/m.sup.2 -24 hrs.) 4 25.040 NAFION 117 23.608 *Measurements
were obtained on samples in their swollen state.
TABLE 2 Tensile Test (Avg) Normalized Stress @ Max Load (psi)
Sample ID M-Dir XM-Dir Example 1 4706 2571 NAFION 117* 2308 1572
Example 6 4988 3463 NAFION 117*** 4314 3581 *sample was boiled in
distilled water for 30 minutes. ***sample was tested as received
from E. I. DuPont de Nemours, Inc.
TABLE 2 Tensile Test (Avg) Normalized Stress @ Max Load (psi)
Sample ID M-Dir XM-Dir Example 1 4706 2571 NAFION 117* 2308 1572
Example 6 4988 3463 NAFION 117*** 4314 3581 *sample was boiled in
distilled water for 30 minutes. ***sample was tested as received
from E. I. DuPont de Nemours, Inc.
TABLE 2 Tensile Test (Avg) Normalized Stress @ Max Load (psi)
Sample ID M-Dir XM-Dir Example 1 4706 2571 NAFION 117* 2308 1572
Example 6 4988 3463 NAFION 117*** 4314 3581 *sample was boiled in
distilled water for 30 minutes. ***sample was tested as received
from E. I. DuPont de Nemours, Inc.
TABLE 2 Tensile Test (Avg) Normalized Stress @ Max Load (psi)
Sample ID M-Dir XM-Dir Example 1 4706 2571 NAFION 117* 2308 1572
Example 6 4988 3463 NAFION 117*** 4314 3581 *sample was boiled in
distilled water for 30 minutes. ***sample was tested as received
from E. I. DuPont de Nemours, Inc.
TABLE 2 Tensile Test (Avg) Normalized Stress @ Max Load (psi)
Sample ID M-Dir XM-Dir Example 1 4706 2571 NAFION 117* 2308 1572
Example 6 4988 3463 NAFION 117*** 4314 3581 *sample was boiled in
distilled water for 30 minutes. ***sample was tested as received
from E. I. DuPont de Nemours, Inc.
TABLE 7 Transverse Direction Machine Direction Example 1 2.95%
2.90% NAFION 117 11.80% 10.55%
Although a few exemplary embodiments of the present invention have
been described in detail above, those skilled in the art readily
appreciate that many modifications are possible without materially
departing from the novel teachings and advantages which are
described herein. Accordingly, all such modifications are intended
to be included within the scope of the present invention, as
defined by the following claims.
* * * * *