Note: Descriptions are shown in the official language in which they were submitted.
i31373~
-- 1 --
RELATED APPLICATIONS
This application is related to U.S. Pa~ent
No. 4,473,474 issued September 25, 1984, entitled
"Charge Modified Microporous Membrane, Process for
Charge Modifying Said Membrane and Process for
Filtration of Fluid", to Ostreicher.
This application is also related to
United S~a~es Pa~ent iYo. 4,473,475 issued September
25, 1984, entitled "Charge Modified Microporous
Membrane, Process for Charge Modifying Said Membrane,
and Process for Filt a~ion of Fluid", to Barnes,
~r. et al.
This application is further related
to U.S. Patent No. 4,604,208 issued August 5,
1986, entitled "Anionic Charge Modified Microporous
Membrane, Process for Charge Modifying Said Micro-
porous Membrane and Fil~ration of Fluid", to
Chu et al.
- This application is a division of Canadian Application
No. 455,077 filed October 10, 1984.
13137~
BACKGROU~'D OF ~HE INVENTION
.
l. Field of the Invention
This invention relates to microporous membranes,
and more particularly to surface modified microporous mem-
branes suitable for the filtration of aqueous fluids, such
as biolo~ical liquids.
2. Prior Art
Micro~orous membranes are well known in the art.
For example, U.S. Patent ~o. 3,876,738 to Marinaccio et al.
(1975) describes a process for preparing a microporous mem-
brane, for e~a.~ple, by quenching a solution of a film forming
polymer in a non-solvent system for the polymer. European
Patent Application O OOS 536 to Pall (1979) describes a
similar process.
Commercially available microporous membranes, for
example, made of nylon, are available from Pall Corporation,
Glen Cove, New York under the trademark ULTIPOR N65". Such
membranes are advertised as useful for the sterile filtration
of pharmaceuticals~ e.~. removal of microorganisms.
Various studies in recent years, in particular Wall-
hausser, Journal o~ Parenteral Drug Association, June, 1979,
Vol. 33, ~3, pp. 156-170, and Howard et al, Journal of the
Parenteral Drug Association, March-April, 1980, Volume 34,
~2, pp. 94-102, have reported the phenomena of bacterial
bre~kthrough in filtration media, in spite of the fact that
the media had a low microrneter rating. For example, commer-
clally available membrane filters for bacterial removal are
ty~ically rated as havin~ an effective micrometer rating for
~he microreticulate membranes structure of 0.2 micrometers
or less, yet such mem~ranestypically have only a 0.357 effec-
tive micrometer rating for spherical contaminant particles,
even when rated as absolute for Ps. diminuta, the conven-
Iional tes~ for bacterial retention. This problem of pas-
s~ge Or a few microorganisms under certain conditions have
~een rendered more severe as the medical uses of filter
~nembranes has increased.
.
1 313~3~
One method of addressing this problem is to prepare
a ti~hter fllter having a sufficiently small effective pore
dimension to capture microorganisms, etc., by mechanical
sieving. Such microporous membranes of 0.1 micrometer rating
or less may be readily prepared but flow rates at conventional
~ressure drops are prohibitively low. Increasing the pressure
dro~ to provide the desired flow rate is not ~enerally feasi-
ble because pressure drop is an inverse function of the
fourth power of pore diameter.
It has lon~ been recognized that adsorptive effects
can enhance the capture of particulate contaminants. For
example, Wen~, "Electrokinetic and Chemical Aspects of ~Yater
Filtration", Filtration and Separation, May/June 1974, indi-
cates that surfactants, pH, and ionic strength may be used
in various ways to improve the efficiency of a filter by mo-
difyin~ the char~e characteristics of either the suspension,
filter or both.
It has also been sug~ested that adsorptive seques-
tration (particle capture within pore channels), may some-
times be more important in sterile filtration than bubble
point characterization of internal geometry (representing
tne "lar~est pore"). See, e.g., Tanny et al, Journal of the
Parenteral Dru~ Association, November-December 1978, Vol.
~1, #6, pp. 258-267 and January-February, 1979, Vol. 33,
~1, p~. 40-51 and Lu~aszewicz et al, Id., July-August, 1979,
Vol. 33, ~4, pp. 187-194.
Pall et al, Colloids and Surfaces 1 (1980), pp.
~35-256, indicates that if the zeta potential of the pore
walls of a melnbrane, e.g. nylon 66, and of the particles are
bolh low, or if they are oppositely charged, the particles
wlll tend to adhere to the pore walls, and the result will
~e removal of particles smaller than the pores of the filter.
Pall et al su~est the use of membranes of substantially
smaller pore size to increase the probability of obtaining
microbial sterillty in filtering fluids.
- : .
1313~3~ `
Zierdt, Applied and Environmental Microbiology, Dec.
1979, pp. 1166-1172, found a stron~ adherence by bacteria, yeast,
erythrocytes, leukocytes, platele~s, spores and polystyrene spheres
to membrane materials during filtration through membranes with
pore-size diame~ers much larger than the particles themselves.
Zierdt found that cellulose membranes adsorbed more bacteria, blood
cells and other particles than did polycaxbonate filters. Of
lesser adsorptive capacity were vinyl acetate, nylon, acrylic and
TeflonTM membranes. Zierdt additionally found that solvent cast
membrane filter materials, e.g. nylon, had strong surface cha ges,
whereas ordinary fibrous cellulose materials which are not solvent
cast do not.
Attempts to increase the short life of filter media due
to pore blockage and enhance flow rates through filter media having
small pores have been made by charge modifying the media by various
means to enhance capture potential of the filter. For example,
U.S. Patents 4,007,113 and 4,007,114 to Ostreicher, describe the
use of a melamine formaldehyde cationic colloid to charge modify
fib.ous and particulate filter elements; U.S. Patent No. 4,305,782,
to Ostreicher et al describes the use of an inorganic cationic
colloidal silica to charge modify such elements. None of these
references teaches or suggests charge modifying a synthetic organic
polymeric microporous membrane, nor do any of the filtration media
described therein, e.g. fiber and/or particulate, provide the
advantages of such a membrane.
Similarly, U.S. Patent No. 3,242,073 (1966) and 3,352,424
(1967) to Guebert et al, describe removal of microorganisms from
fluids by passage through a filter medium of conventional anionic
type filter aid, e.g. diatomaceous earth,
,
~3~37~
~a~er filter pulp, fullers earth, charcoal, etc., having an
adsor~ed cationic, organic, polyelectrolyte coating. The
coated filter aid media is said to possess numerous cationic
sites which are freely available to attract and hold parti-
cles bearin~ a ne~ative surface charge.
U.S. Patent No. 4,178,438 to Hasset et al (1979)
describes ~ process for the purification of industrial efflu-
ent using cationically modified cellulose containing material,
e.O., bleached or unbleached pine sulphite cellulose, kraft
sul~hate cellulose, paper, card~oard products, textiles
fibers made of cotton, rayon staple, jute, woodfibers, etc.
The cationic substituent is bonded to the cellulose via a
~roupin~ -0-C~2-N- , where the nitrogen belongs to an amide
grou~ of the cationic part and the oxygen to the cellulose
part.
There are numerous references which describe the
treatment of porous membranes for various objects. U.S.
Patent No. 3,556,305 to Shorr (1971) describes a tripartite
~embrane for use in reverse osmosis comprising an anisotropic
~orous substrate, an ultra-thin adhesive layer over the
porous substrate, and a thin diffusive membrane formed over
the adhesive layer and bound to the substrate by the adhesive
layer. Such a~isotropic porous membranes are distinguished
from isotropic, homogeneous membrane structures used for
microfiltration whose flow and retention properties are in-
dependent of flow direction and which do not function properly
when subs~i_u-'~ed in the invention of ~x~-~.
U.S. Patent ~o. 3,556,99 to .~assuco (1971) describes
another anisotro~ic ultra-filtration membrane having thereon
an adhering coating of irreversibly compressed gel.
U.S. Patent No. 3,808,305 to Gregor (1974) describes
a charged membrane of ~.acrosco~ic homogeneity prepared by pro-
vidin~ a solution containin~ a matrix polymer, polyelectro-
lytes (for charge) and a crosslinking agent. The solvent is
1313~
evaporated fron~ a cast film which is then chemically cross-
linked. The membranes are used for ultrafiltration.
U.S. Patent No. 3,944,485 (1976) and 4,045,352 (1977)
to Rembaum et al describe ion exchange hollow fibers produced
by introducing into the wall of the pre-formed fiber, poly-
merizable liquid monomers ~hich are then polymerized to form
solid, insoluble, ion e~;chan~e resin particles embedded
within the wall of the fiber. The treated fibers are useful
as membranes in ~rater treatment, dialysis and generally to
separate ionic solutions. See also U.S. Patent No. 4,014,798
to Rembaum (1977).
U.S. Patent ~o. 4,005,012 to Wrasidlo (1977) describes
a process for producing a semi-permeable anisotropic membrane
useful in reverse osmosis processes. The membranes are pre-
pared by for~ing a polymeric ultra-thin film, possessing semi-
permeable properties by contacting an amine modified polyepi-
halohydrin with a polyfunctional agent and depositing this
film on the external surface of a microporous sllbstrate.
Preferred semi-permeable membranes are polysulfone, polysty-
rene, cellulose butyrate, cellulose nitrate and cellulose
acetS~te.
U.S. ~atent No. 4,125,462 to Latty (1978) describes
a coated semi-permeable reverse osmosis membrane having an
external layer or coating of a cationic polyelectrolyte pre-
ferably poly(vinylimidazoline) in the bi-sulfate form.
U.S. Patent No. 4,214,020 to ~'ard et al (1980) de-
scribes a novel method of coating the e~teriors of a bundle
of hollow-fiber semi-permeable membranes for use in fluid
separations. Typical polymers coated are polysulfones, poly-
st~renes, polycarbonates, cellulosic polymers, polyamides
and polyimides. Numerous depositable materials are listed,
see col. 10, lines 55 - col. 12, for example, poly(epichlor-
hydrin) or polyamides.
U.S. Paten~ No. 4,239,714 to Spar~s et al (1980)
descri~es a method of modifyin~ the pore size distribution
131 37~ `
of a separation media to provide it with a sharp upper cut-off of a
preselected molecular size. This is accomplished by effectively
blocking the entrances to all of the pores larger than a pre-
selected desired cut-off size, but leaving unchanged the smaller
pores. The separation media may be in the form of polymeric
membranes, e.g. cellulose acetate, cellulose nitrate, poly-
carbonates, polyolefins, polyacrylics, and polysulfones. The pores
are filled with a vola~ile liquid which is evaporated to form voids
at the pore entrances and a concentrated solution of a cross-
linkable or polymerizable pore blocking agent, such as protein,
enzyme, or polymeric materials is then applied to the surface of
the membrane.
U.S. Patent No. 4,250,029 to Kiser et al (1981) describes
coated membranes having two or re external coatings of
polyelectrolytes with at least one oppositely charged adjacent pair
separated by a layer of material which is substantially charge
neutralized. Kiser et al is primarily directed to the use of
charged membranes to repel ions and thereby prevent passage through
the membrane pores. The coated membranes are described as ordinary
semi-permeable membranes used for ultrafiltration, reverse osmosis,
electrodialysis or other filtration processes. A microscopic
observation of the coated membranes shows microscopic hills and
valleys of polyelectrolyte coating formed on the original external
smooth skin of the membrane. The mmbranes are particularly useful
for deionizing aqueous solutions. Preferred membranes are organic
polymeric me~branes used for ultrafiltration and reverse osmosis
processes, e.g., polyimide, polysulfone, aliphatic and aromatic
nylons, polyamides, etc. Preferred membranes are anisotropic
hollow fiber membranes having an apparent pore diameter of from
about 21 to about 480 angstroms.
Charge modified microporous filter membranes are
disclosed in Canadian Patent No. 1,044,537 of Ostreicher, issued
1 3 ~ 3 r~ ~ ~
December 19, 1978, (corresponding to Japanese Patent No. 923,649).
As disclosed therein, an isotropic cellulose mixed ester membrane,
was treated with a cationic colloidal melamine-formaldehyde resin
to provide charge functionality. The membrane achieved only
marginal charge modification. Additionally, the membrane was
discolored and embrittled by the treatment, extractables exceeded
desirable limits for certain critical applications, and the
membrane was not thermally sanitizable or sterilizable. Ostreicher
also suggests such treatment for the nylon membranes prepared by
the methods described in U.S. Patent No. 2,783,894 to Lovell (1957)
and U.S. Patent No. 3,408,315 to Paine (1968). It has been
demonstrated that nylon microporous membranes treated according to
said Ostreicher reference would also demonstrate marginal charge
modification, high extractables and/or inability to be thermally
sanitizable or sterilizable.
The aforesaid Ostreicher U.S. Patent No. 4,473,474
(published as European 0050804 on May 5, 1982) generally describes
a novel cationic charge modified microporous membrane comprising a
hydrophilic organic polymeric microporous membrane and a charge
modifying amount of a primary cationic charge modifying agent
bonded to substantially all of the internal microstructure o$ the
membrane. The primary charge modifying agent is a water-soluble
organic poly~ner having a molecular weight greater than about 1,000
wherein each monomer thereof has at least one epoxide group capable
of bonding to the surface of the membrane and at least one tertiary
amine or quaternary ammonium group. Preferably, a portion of the
epoxy groups on the organic polymer are bonded to a secondary
charge modifying agent selected from the group consisting of:
i) aliphatic amines having at least one primary amino or
at least two secondary amino groups; and
9` 13i3~3~`
ii) aliphatic amines having at least one secondary amino
and a carboxyl or hydroxyl substituent.
The membrane is made by a process for cationically charge modifying
a hydrophilic organic polymeric microporous membrane by applying to
the membrane the aforesaid charge modifying agents, preferably by
contacting the membrane with aqueous solutions of the charge
modifying agents. The preferred microporous membrane is nylon, the
preferred primary and secondary charge modifying agents are,
respectively, polyamido-polyamine epichlorohydrin and tetraethylene
pentamine. The charge modified microporous membrane may be used
for the filtration of fluids, particularly parenteral of biological
liquids. The membrane has low extract~bles and is sanitizable or
sterilizable.
m e aforesaid Chu et al U.S. Patent No. ~,604,208
generally describes a novel anionic charge ~odified microporous
m~mbrane comprising a hydrophilic organic polymeric microporous
membrane and a charge modifying amount of anionic charge modifying
agent bonded to substantially all of the membrane microstructure.
m e anionic charge modifying agent is preferably a water-soluble
polymer having anionic functional groups, e.g. carboxyl, phos-
phonous, phosphonic and sulfonic groups. The charged n~mbrane is
made by a process of applying the anionic charge modifying agent to
the membrane, preferably by contacting the membrane with aqueous
solutions of the charge modifying agent.
The just described Patents describe a comparatively
complex treatment of a preformed membrane requiring treatment,
rinse and drying steps which involve complicated equipment and
expensive capital inves~nent.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to provide a process
for surface ncdifying a hydrophilic organic polymeric
131373~
micro~orous me!~brane so as to provide a novel surface modi-
fied micro~orous membrane, part cularly suitable for the
microfiltralion of biolo~ical or parenteral liquids.
It is another object of this inventon to provide an
isotropic, surface modified microporous membrane which pre-
ferably has low extractables suitable for the microfiltration
of biolo~ical or parenteral liquids.
It is yet another object of this invention to pre-
pare a sanitizable or sterilizable microporous membrane for
the efficient removal of bacteria, viruses and pyrogen from
contaminated liquids.
A still further object of this invention is to pro-
vide a process for enhancing the filtration, adsorptive
and/or capacity of microporous membranes without affecting
the internal microreticulate structure.
It is still a further object of this invention to
provide a process for producin~ a microporous membrane cap-
a~le of capturin~ anionic or cationic particulate contaminant
o~ a size smaller than the effective pore size of the membrane.
These and other objects of this invention are attained
by a process for surface modifying a hydrophilic organic poly-
meric microporous membrane by forming the membrane from a
composition con~æinin~ surface modifying agents. The pre-
ferred microporous membrane is nylon, the preferred surface
modifyin~ agents are polyamido-polyamine epichlorohydrin,
e~hylene diamine ~etraacetic acid, carbon, silica and other
cnromato~raphic additives, poly (styrene sulfonic acid) and
~oly (acrylic acid).
The surface modified microporous membrane produced
by tnis invention may be used for the microfiltration of
fluids, particularly parenteral or biological liquids.
3RIEF DESCRI?TION OF T~E FIGUP.ES
Figure 1 is a time vs. transmittance graph of mem-
~ranes described in E~ample V.
ll 131373`'~
DETAIT.F.l- DESCRIPTION OF T~IE INVENTlON
-
m e process of -this invention produces a hydrophilic
surface modified organic polymeric microporous membrane.
By the use of the term "microporous membrane" as used
herein is meant a skinless ("symmetric"), isotropic or anisotropic
porous membrane having a pore size of at least .05 microns or
larger, or an initial bubble point (IBP), as that term is used
herein, in water of less than 120 psi. A maximum pore size useful
for this invention is abou~ 1.2 micron or an IBP of grea-~er ~han
about 10 psi. By "isotropic" it is meant that the pore structure
is substantially the same throughout the cross-sectional structure
of the membrane. By "anisotropic" is meant tha~ the pore size
differs from one surface to the other. m ere are a nu~ber of
commercially available membranes not encompassed by the tenm
"microporous membrane~ or ~microfiltration membrane" such as those
having one side formed with a very light thin skin layer (skinned,
i.e. asymmetric) which is supported by a much more porous open
structure which are typically used for reverse osmosis, ultra-
filtration and dialysis. Thus, by the term "microporous membrane"
or "microfiltration membrane" are meant membranes suitable for the
re val of suspended solids and particulates from fluids and which
do not function as ultrafiltration or reverse osmosis membranes but
which may have adsorptive and/or sequestration capacity.
By "surface modified microporous membranes" are meant
microporous membranes which provide surface adsorption and/or
sequestration effects in addition to the microfiltration effects of
the membranes per se. By adsorptive surface, it is meant a surface
that has controlled molecular geometry and/or surface functionality
that allows species to be attacned to the surface by means of
ionic, covalent, hydrogen and/or Van Der Walls bonding and/or
molecular geometric effects, e.g. ionic exchange, affinity,
frontal, size exclusion and the like.
1313~
By Ihe use of the term `'hydrophilic" in describing
tne microporous membrane, it is meant a membrane which ad-
sorbs or a~sor~s water. Generally, such hydrophilicity is
~roduced by a sufficienl amount of hydroxyl (OH-), carboxyl
( 2)~ (-C-NH-), and/or similar functional
~rou~s on the surface of the membrane. Such groups assist
in the adsor~tion and/or absorption of the water onto the
membrane. Such hydrophilicity of the membrane and internal
~icrostructure of the surface modified membrane of this
invention is preferred in order to render the membrane more
useful for the treatmen~ of aqueous fluids.
Preferred microporous membranes are produced from
nylon. The term "nylon" is intended to embrace film forming
~olyamide resins includin~ copolymers and terpolymers which
include the recurrin~ amido groupin~.
While, ~enerally, the various nylon or polyamide
resins are all copolymers of a diamine and a dicarbo~ylic
acia, or homopolymers of a lactam of an amino acid, they
v~ry widely in crystallinity or solid structure, meltin~
~oint, and other physical properties. Preferred nylons for
use in this invention are copolymers of hexamethylene dia- -
mine and adipic acid (nylon 66), copolymers of hexamethylene
diamine and se~acic acid (nylon 610) and homopolymers of
poly-o-ca~rolactam (nylon 6).
Alternatively, these preferred polyamide resins
have a ratio of methylene (CH2) to amide (~HCO) ~-oups
within the ran~e about 5:1 to about 8:1, most preferably
acout 5:1 to about 7:1. ~ylon 6 and nylon 66 each have a
ratio of 6:1, whereas nylon 610 has a ratio of 8:1.
The nylon polymers are available in a wide variety
of ~rades, which vary a~reciably with respect to molecular
wel~ht, within the ran~e from about lS,OOO to about a2,000
and in otner characteristics.
13 1 3 ~ 3 7 3ll '
The highly preferred species of the unites composing the
polymer chain is polyhexamethylene adipamide, i.e. nylon 66, and
molecular weights in the range above about 30,000 are preferred.
To the extent that commercially available polymers
contain additives such as antioxidants and the like, such additives
are included within the term "polymer" as used herein.
The membrane substrates can be produced by modifying the
method disclosed in U.S. Patent No. 3,876,738 to Marinaccio et al
or described in European Patent ~pplication No. 0 005 536 to Pall.
I`he Marinaccio et al process for producing membrane
develops a unique fine internal microstructure through the quench
technique described therein, offering a superior substrate for
filtration. Broadly, Marinaccio et al produces micropor~us films
by casting or extruding a solution of a film-forming polymer in a
solvent system into a quenching bath comprised of a non-solvent
system for the polymer. Although the non-solvent system may
comprise only a non-solvent, the solvent system may consist of any
combination of materials provided the resultant non-solvent system
is capable of setting a film and is not deleterious to the formed
film. For example, the non-solvent system may consist of materials
such as water/salt, alcohol/salt or other solvent-chemical
mixtures. The Marinaccio et al process is especially effective for
producing nylon films. More specifically, the general steps of the
process involve first forming a solution of the film-forming
polymer, casting the solution to form a film and quenching the film
in a bath which includes a non-solvent for the polymer.
The nylon solutions which can be used in the Marinaccio
et al process inciude solutions of certain nylons in various
solvents, such as lower alkanols, e.g., methanol,
131373(~
ethanol and butanol, including mixtures thereof. It is known
that other nylons ~ill dissolve in solutions of acids in which
they ~ehave as a polyelectrolyte and such solutions are useful.
Re~resentative acids include, for example, formic acid, citriG
acid, acetic acid, maleic acid and similar acids which react
~ith nylons throu~h pro~onation of nitrogen in the amide group
characteristic of nylon.
The nylon solutions after formation are diluted with
non-solvent for nylon and the non-solvent employed is miscible
with the nylon solution. Dilution with non-solvent may,
accordin~ to Marinaccio et al, be effected up to the point
of incipient precipitation of the nylon. The non-solvents
are selected on the basis of the nylon solvent utilized.
For example, when water-miscible nylon solvents are employed,
water can oe employed. Generally, the non-solvent can be
methyl forma~e, aqueous lower alcohols, such as methanol and
ethanol~ polyols such as ~lycerol, glycols, polyglycols and
ethers and esters thereof, water and mixtures of such com-
~ounds. Moreover, saits can also be used to control solu-
tion pro~erties.
The 4uenchi~0 bath may or may not be comprised of
the same non-solvent selected for preparation of the nylon
solution and may also contain small amounts of the solvent
em~loyed in the nylon solulion. However, the ratio of sol-
vent to non-solvent is lower in the quenching bath than in
the polymer solu~ion in order that the desired result be
o~tained. The o,uenchin~ bath may also include other non-
solvents, e.g. WQter,
The formation of the polymer film can be accomplished
~y any of the recognized methods familiar to the art. The
~referred method is casting using a knife edge which controls
tne thickness of the cast film. The thickness o the film
will be dictated by the intended use of the microporous
~roduc~. In ~eneral, the films will be cast at thicknesses
in the range of from about 1 mil to about 20 mils, prefer-
a~ly from about 1 to about 10 mils.
.
~3~37~
Preferably, the polymer solution is cast and simul-
ta~eously 4uenched, although it may be desirable to pass the
cast film throu~h a short air evaporation zone prior to the
quench bath. This la~ter technique is, however, not pre-
ferred.
After the polymer solution is cast and quenched, it
is removed from the quench bath and preferably washed free
of solvent and/or non-solvent. Subsequently the film can be
at least partially dried.
Pall's aforementioned European Patent Application
No. 0 005 536 describes another similar method for the con-
version of polymer into microporous membrane which may be
used. Broadly, Pall provides a process for preparing skin-
less hydrophilic alcohol-insoluble polyamide membranes by
~re~arin~ a solution of an alcohol-insoluble polyamide resin
in a polyamide solvent. ~ucleation of the solution is in-
duced by the controlled addition to the solution of a non-
solvent for the polyamide resin, under controlled conditions
of concentration, tem~erature, addition rate, and degree of
agitation to obtain a visible precipitate of polyamide resin
~articles (which may or may not partially or completely re-
dissolve) ~hereby forminJ a casting solution.
The castin~ solution is then spread on a substrate
to form a thin film. The film is then contacted and diluted
with a mixture of solvent and nonsolvent liquids containing
a substantial proportion of the solvent liquid, but less
tnan the proportion in the casting solution, thereby preci-
~itatinO polyamide resin from the casting solution in the
form of a ~hin skinless hydrophilic membrane. The resulting
mem~rane is then washed and dried.
In Pall's preferred embodiment of the process, the
sol~ent for the polyamide resin solution is formic acid and
tne nonsolvent is water. The polyamide resin solution film
is contact~d with the nonsolvent by immersing the film, car-
ried on the substrate, in a bath of nonsolvent comprising
water containing B substantial proportion of formic acid.
i313~
16
The nylon membranes described in Marinaccio et al and
Pall are characterized ~y hydrophilic isotropic stl~cture, having a
high effective surface area and a fine internal microstructure of
con-trolled pore dimensions with narrow pore size distribution and
adequate pore volume. For example, a representative 0.22
nucrometer rated nylon 66 men~rane (polyhexarnethylene adiparnide)
exhibits an initial bubble point (IBP) of about 45 to 50 psid, a
foam all over point (FAOP) of about 50 to 55 psid, provides a flow
of from 70 to 80 ml/min of water at 5 psid (47 mm. diameter discs),
has a surface area (BET, nitrogen adsorption) of about 13 m2/g and
a thickness of about 4.5 to 4.75 mils.
As will be apparent from the foregoing description, both
the Marinaccio and Pall processes involve the fonnation of a nylon
polymer solution or dope which is then diluted with a non-solvent,
cast on a suitable su~strate surface and contacted ~ith additional
non-solvent to cause precipitation of the polyamide resin from the
dope solution in -~he fonn of a thin skinless hydrophilic m~nbrane.
In thc aforementioned Patents to Ostreicher et al, Barnes et al and
Chu et al, the res~llting melllbrane is charge modified by contacting
the formed membrane with a charge modifying amowlt of a charge
modifying agent. In the present invention, the surface modifying
agent (which can be a cationic or anionic charge modifying agent)
is incorporated into the polymer solution or dope before the
membrane is precipitated. The men~rane can thereafter be fonned by
the casting technique described in Marinaccio et al and Pall or
alternatively, the dope can be introduced into the quenching bath
of the non-solven-t under shear to produce fibers of the surface
modified n~mbrane which can be formed into a sheet material
similarly to the fonnation of paper from fibers, e.g. as described
in U.S. Patent 4,309,247 to ~lou et al (1982) or made into hollow
fibers to produce surface modified hollow fibers.
i3~ 3~
17
The surface modifying agent is bound to the internal
microstructure, preferably substantially all of the internal
microstructure, of the microporous membrane. By the use of the
term "bound" is meant that the surface modifying agent is
sufficiently attached to or incorporated into the membrane so that
it will not be significantly extracted under the intended
conditions of use. By the use of the term "substantially all of
the internal microstructure" as used herein, is meant substantially
all of the external surface and internal pore surfaces. ~`ypically
by this is meant the surfaces which are wetted by a fluid, e.g.,
water, passing through the membrane or in which the membrane is
immersed .
The term "surface difying agent" means a compound,
material or composi-tion which when bound to ~he m~nbrane, alters
its capacity to remove a desired entity from a fluid being filtered
and which is compatible with the dope. By the use of the term
"charge modifying agent", is meant a compound or composition that
when bound to the microporous filter membrane alters the "zeta
potential" of the membrane (see Knight et al, "Measuring the
Electrokinetic Properties of Charged Filter Media," Filtration and
Separation, pp. 30-34, Jan./Feb. 1981).
The cationic charge modifier is a compound or composition
which is capable of being bound to the membrane microstructure and
provides a more positive zeta potential 'co the membrane micro-
structure. Preferably, such cationic charge modifier is a
water-soluble compound having substituents capable of binding to
the membrane and substituents which are capable of producing a more
positive "zeta potential" in the use enviroml~nt (e.g. aqueous) or
cationic functional groups. Most preferably, the agent may be a
water-soluble organic polymer capable of becoming a non-extractable
constituent of the membrane.
1~3 131373~x
The cationic charge modifying agent can also be
cross-linked ~o itself or to the membrane polymer through a
cross-linking agent, for example, an aliphatic polyepoxide having a
m~lecular weight of less than about 500.
The cationic charge modifying agent may have either a
high or low charge density, or anything between these extremes,
however, high charge density is preferred.
The preferred cationic charge difier is selected from
the class of polyamido-polyamine epichlorohydrin cationic resins,
in particular, those described in the following U.S. patents:
2,926,116 to Keim;
2,926,154 to Keim;
3,224,986 to Butler et al;
3,311,594 to Earle, Jr.;
3,332,901 to Keim;
3,382,096 to Boardman; and
3,761,350 to ~lunjat et al.
Broadly, these preferred charge modifiers (hereinafter
"polyamido-polyamine epichlorohydrin") are produced by reacting a
long chain polyamide with epichlorohydrin, i.e. 1 - chloro-2,3
epoxypropane having the formula:
~.
2 CH CH2Cl
The polyamide may be derived from the reaction of a
polyalkylene polyamine and a saturated aliphatic dibasic carboxylic
acid containing from abou-t 3 to 10 carbon atoms. The polyamide
produced is water-soluble and con~ains the recurring groups:
-NH(CnH2nHN)X-CORCO-
~3~3~
19
where n and x are each 2 or more and R is the divalent hydr~-
carbon radical of the dicarboxylic acid. This polyamide is
then reacted with epichlorohydrin to form the preferred
wa~er-soluble charge modifiers used in its invention.
The dicarboxylic acids which may be used in preparing
the polyaMides are the saturated aliphatic dicarboxylic acids
containing from 3 to 10 carbon atoms each as malonic, succinic,
glutaric, adipic, azelaic and the like. Blends of two or more
of the saturated carboxylic acids may also be used. -
A variety of polyalkylene polyamines including poly-
ethylene polyamines, polypropylene polyamines, polybutylene
polyamides and so on may be employed. More specifically,
the polyalkylene polyamines are polyamines containing two
primary amine groups and at least one secondary amine group
in which the nitrogen atoms are linked together by groups of
the formula - CnH2n_, where n is a small integer greater
than unity and the number of such groups in the molecule
ran~es from two up to about eight. The nitrogen atoms may
be attached to adjacent carbon atoms in the group -CnH2n_ or
to carbon atoms further apart, but not to the same carbon
atom. Polyamines such as diethylenetriamine, triethylene-
tetramine, tetraethylene-pentamine, dipropylenetriamine, and
the li~e, and mixtures thereof may be used. Generally,
these yolyalkylene polyamines have the general formula:
H2[(CnH2n)NH]yCnH2nNH2
wherein n is an integer of at least 2 and y is an integer of
1 to 7.
In carrying out the reaction of the polyalkylene
polyamine with tbe acid, it is preferred to use an amount of
dicarboxylic acid sufficient to react substantially completely
witn the primary amine groups of the polyalkylene polyamine
but insufficient to react with the secondary amine groups to
any subst~ntial extent. The polyamide produced is then re-
acted with Ihe epichlorohydrin to form the preferred poly-
amido-polyamine epichlorohydrin charge modifying agent.
1313~
Typically, in the polyamide-epichlorohydrin reaction it is
preferred to use sufficient epichlorohydrin to convert all of the
secondary amine groups to tertiary amine groups, and/ox quaternary
ammonium groups (including cyclic structures). Generally, however,
from about 0.5 mol to about 1.8 moles of epichlorohydrin for each
secondary amine group of -the polyamide may be used.
The epichlorohydrin may also be reacted with a polyamino-
ureylene containing tertiary amine nitrogens to produce the primary
charge modifying agents which may be utilized in this invention
(see for example the aforementioned Earle, Jr.).
Other suitable charge modifying agents of the foregoing
type may be produced by reacting a heterocyclic dicarboxylic acid
with a diamine or polyalkylene polyamine and reacting the resultant
product with epichlorohydrin (see for example the aforementioned
Munjat et al.)
The polyamido-polyamine epichlorohydrin cationic resins
are available commercially as Polycup 172, 1884, 2002 or S2064
(Hercules; Cascamide Resin pR-420 (Borden); or Nopcobond 35
(Nopco). Most preferably, the polyamido-polyamine epichlorhydrin
resin is Polycup 1884 or Hercules R4308, wherein the charged
nitrogen atom forms part of a heterocyclic grouping and is bonded
through methylene to a depending, reactive epoxide group. The
terms Polycup, Cascamide, Nopcobond and Hercules are all trade-
marks.
13~373~ ` `
21
. Each monomer grou~ in R 4308 has the general formula:
r~
L 2 ~~
~ CH2_ CH CH .~
'.
CH2 CH2
~+
. . `~ Cl-
_ . i CH3 CH2-CH-CH2
O __
Polycup 172, 2002 and 1884, on the other hand, have
J~onomer groups of the general formula:
R C1- ~'
(C~2)4 --- CNHCH2 -- CH2 -- NCH2 -- CH2NH
0 0 CH
CH -- CH2
!_ O
wherein R is methyl or hydrogen (Polycup 172 and 2002, R=H;
and Polycup 1884, R=CH3).
A secondary charge modifying agent may be used to
enhance the cationic charge of the primary charge modifying
agent and/or enhance the bonding of the primary charge modi-
fying a~en~. The secondary charge modifying agent may be
selecled from the group consisting of:
~ i) aliphatic amines having at least one pri-
mary amino or at least two secondary amino groups;
and
.- .
131373 `~
(ii) aliphatic amines having at least one
secondary amine and a carboxyl or hydroxyl sub-
stituent.
Preferably, ~he secondary charge modifying agent is
a polyamide havin~ the formula:
H
H2N-(Rl-N-)~-R2-NH2
wherein Rl and R2 are alkyl of 1 to 4 carbon atoms and ~
is an integer from O to 4. Preferably, Rl and R2 are both
ethyl.
Preferred polyamines are:
Ethylene diamine H2N-(cH2)2-NH2-NH2
~iethylenetriarnine H2N-(cH2)2-NH-(c~2)2-NH2
Triethylenetetrarnine H2N-(CH2-CH2-NH)2-CH2-CH2-NH2
Tetraethylenepen'amine H2N-(CH2-C~2-N~)3-CH2-CH2-NH2
The hi~hly preferred polyamine is tetraethylene pentamine.
Alternatively, aliphatic amines used in this inven-
tion may have at least one secondary amine and a carbo~yl or
hydroxyl substituent. Exemplary of such aliphatic amines
are gamlna-amino-butyric acid (H2NCH2CH2CH2COOH) and 2-amino-
ethanol (H2Nc~2c~2oH).
The secondary charge modifying agent is bonded to
~he micro~orous membrane by bondin~ to a portion of the epo~ide
substituents of the polymeric primary charge modifying agent.
Tne amount of primary and secondary cationic charge
modifyin~ a~ens utilized is an amount sufficient to enhance
the electropositive c~p~ure potential of the microporous
membrane. Such an amount is ni~hly dependent on the speci-
fic charge modifying~ ents utilized. For general guidance,
nowever, it has been Iound that a weight ratio of primary to
secondary char~e modi~yin~ agenl of from about 2:1 to about
5~:1, preferably from about 20:1 to about 75:1 is generally
sufficient.
In another embodiment of the present invention, the
foregoinD "secondary" charge mod~fyin~ a~ent can be used as
,
~3137~
23
tne cnar~e modifyin~ agent by the cojoint employment of an
aliyhatic yolyepoxide crosslinking agent having a molecular
weight of less than about 500. Preferably, the polyepoxide
is a di- or tri- epoxide having a molecular weight of from
about 146 ~o about 300. Such polyepo~ides have viscosities
(undiluted) of less than about 200 centipoises at 25C. Due
to the necessity of the epo~ide to act as a crosslinking
a~ent, monoepo~ides, e.g. glycidyl ethers, are unsuitable.
Similarly, it is theorized that a polyepo~ide offerin~
~reater than three epoxy ~roups offers no benefit and in
fact may limit the couplin~ reactions of the polyepoxide by
steric hindrance. Additionally, the presence of unreacted
eyoxide grouys in the cationically charge modified micropor-
ous membrane may be undesirable in the finished product.
Highly preferred yolyepo~ides have the formula:
'- R(0-CH2-CH~cH2)n
wherein R is an alkyl of 1 to 6 carbon atoms and n is from 2
to 3. The limitation that the number of carbon atoms in the
non-e~o~ide portion --(R)-- be less than 6 is so that the
polyeyoxide will be soluble in water or ethanol-water mix-
tures, e.g. uy to 20~ ethanol. While higher carbon content
materials are functionally suitable, their application would
involve the use of polar organic solvents with resulting
~roblems in to~icity, flammability and vapor emissions.
The anionic charge modifying agent is a compound
or cornyosition which is capable of bonding to the membrane
microstructure without substantial pore size reduction or
yore blockage and provides an anionic charge or negative
zeta yotential to the membrane microstructure. ?referably,
such anionic charge modifier is a water-soluble compound
havin~ substituents capable of binding to the membrane and
substituents which are capable of producing a more negative
"zet~ potential" in the use environrnent (e.g. aqueous) or
anionic functional grou~s.
13137~
24
Preferred anionic functional groups may be carboxyl,
phosphonous, phosphonic and sulfonic. Preferably, the anionic
charge modifying agent may be a water-soluble organic polymer or
polyelectrolyte having a molecular weight greater than about 2,000
and less than about 500,000 and capable of becoming a non-
extractable constituent of the membrane.
m e anionic charge modifying agent may have either a high
or low charge density, or anything between these extremes, however
high charge density is preferred. Specific preferred anionic
charge modifying agents useful herein are poly (styrene sulfonic)
acid, poly (toluene sulfonic) acid, poly (vinyl sulfonic) acid and
poly (acrylic) acid. Other anionic charge modifying agents are
poly (methacrylic acid), poly (itaconic acid), hydrolyzed poly
(styrene/maleic anhydride) and poly (vinyl phosphonic acid).
Additionally, the alkali and alkaline earth m~al salts of all of
the foregoing may be utilized.
Highly preferred anionic charge modifying agents are poly
(styrene sulfonic) acids having a molecular weight between 2,000
and 300,000 and poly (acrylic acid~ having a molecular weight
between 2,000 and 300,000.
The anionic charge modifying agent may also be cross-
linked to the microporous membrane structure or itself in the same
manner as the cationic agents using the same aliphatic polyepoxi~e
cross-linking agent having a molecular weight of less than about
500. In addition to the preferred polyepoxides described above,
certain diglycidyl ethers of aliphatic diols,
Cl-l -CH_C~2-O-R-o-cH2-cH~H2
b o
may be used. Examples are 1,2-ethanediol, 1,3-propanediol, and
1,4-butanediol. 1'he preferred diglycidyl ether of 1,4-butanediol
is commercially available from Ciba-Geigy, Inc. as RD-2 and from
Celanese Corp. as Epi-Rez 5022 and Polyscience. The terms RD-2,
Epi-Rez and Polyscience are trademarks.
13~3~3`~ `
~ ther higher carbon diglycidyl ethers may be used
as the polyepoxide cross-linkin~ a~ent, for example 5-pen-
tauediol di~lycidyl ether. However, the appropriate polar
or~anic solvents must be used for diluting such polyepoxides.
Tri~lycidyl ethers, i.e. tri-epoxides may also be
utilized as the polyepoxide cross-linking agent. The tri-
eyoxides have the followin~ formula:
C~2-CH-CH2_0_CH2_CH_CH2_0_CH2-CH-CH2
o
C~2 . .
CH
~ O
CH2
The tri~lycidyl ether of glycerol is available from Shell,
Inc. as Epon 812 and Celanese Corp. as Epi-Rez 5048.
Another prei'erred cross-linkin~ agent is ~ethylated
urea formaldehyde resin, commercially available from American
Cyanalnid; i'or examplé, Beetle 65, and melamine formaldehyde,
e.~., Cymel 303 from American Cyanamid.
Other water-soluble polymers havinO polar groups
can also be employed in this invention as the charge modi-
f~in~ a~ent. E~amples include sodium alginate, ethylene
diamine tetraacetic acid, diethylene triamine tetraacetic
acid, tetraethylene pentamine tetraacetic acid, quaternized
~olyethylenei~ine, quaternized vinyl pyridine, quaternized
diethylaminoethylmethacrylate and the like. The molecular
weight of the char~e modifyin~ agent does not appear to be
sl~nificant so lon~ as the agent is soluble in the polymer
"~o~e". Thus, sodium alginate which has a molecular weight
above lO,OOV and ethylene diamine tetra acetic acid which
nas a molecular wei~ht below 10,000 are equally employable.
Tne ~olyamido-polyamine epichlorohydrin cationic resins
enerally have a molecular wei~ht above 10,000. For example,
Polycu~ 18~4 has a molecular wei~ht of about 300,000 and
~4308 has ~ molecular wei~ht of about 530,000.
13137~`~
26
Other surface modifying agents which are soluble or
suspendable in aqueous solvents are such materials as carbon,
diatornaceous earth, barium ferrite, iodine, aluminum, alumina,
silica, kaolin, molecular sieves, carbohydrates, perlite, clays,
vermiculite, asbestos, bentonite, casein and the like.
Broadly, the process of this invention is directed to
surface modifying a hydrophilic organic polymeric rnicroporous
men~rane, e.g. nylon. The process comprises forrning a dope
solution of nylon polymer, water-soluble or water-suspendable
membrane surface modifying agent and a solvent, diluting the
resulting dope solution with a miscible non-solvent for the nylon
polyrner and contacting the diluted dope solul:ion with sufficient
non-solven. for the nylon polyrmer ~:o precipitate said nernbrane
therefrom. The dilution of the dope solution is preferably carried
out up to the point of incipient precipitation of the nylon but
should any precipitation occur, the solids can be eliminated by
filtration or can be redissolveâ by adding additional solvent to
the diluted dope solution. ~en cast films are prepared, the
diluted dope solution is spread on a substrate surface prior to
contact with the non-solvent for precipitation. When fibers are
being prepared, the contacting step is conducted by extruding the
dope into a quenching bath and/or with the application of shear.
Ln order to provlde the surface modifying amount of
surface rnodifying agent ~o the rnembrane, it is preferred tha-t the
polyrner dope solution contain at least about 0.0196 surface
modifying agent, by ~eight of total solids. The rnaximum amount of
surface modifying agent in the solution is limited by economic and
solubility-suspendability lirnitations. For example, an excess of
rnodifying agent which does not becorne bonded to the microporous
membrane will not be economically utilized and will constitute an
undesirable extractive from the membrane. It has been found that
the amount of surface modifying agen~ in the dope should not exceed
about 75~6 by weight of total solids
13137~
27
After the microporous membrane has been prepared, it is
then dried and cured, preferably in a restrained condition to
prevent shrinkage.
Drying of the membrane under restraint is described in
the Assignee's defensive publication T 103,602 to Repetti,
published ~ovember 1, 1983. Generally, any suitable restraining
technique may be used while drying, such as winding the membrane
tightly about a drying surface, e.g. a drum. Biaxial control is
preferred and tensioning the membrane on a stretching frame is
considered the most preferred. Preferably, the restraining imposed
effects no reduction in dimensions.
Final drving and curing temperatures should be to dry and
cure the treated membranes, preferably from abou~ 120& to 140C
for minimization of drying times wi~hou~ ernbrittlement or other
detrimental effects to the membrane.
m e completed membrane may be rolled and stored for use
under ambient conditions. It will be understood that the treated
membrané may be supplied in any of the usual commercial fonns, for
example, as discs or pleated cartridges.
The present invention provides an integral, coherent
microporous membrane of retained internal pore geometry. m e
surface modified membrane has an improved effective filtration
rating relative to the untreated micro-reticulate polymer
structure.
For so-called sterile filtrations involving biological
liquids, the filter is sanitized or sterilized by autoclaving or
hot water flushing. Accordingly, the surface modified mernbrane
rnust be resistant to this type treatrnent, and must retain its
integrity in use. Any modification to the filter structure,
especially brought about by chemical agents which m~y be unstable
under conditions of treatment and use, rnust be scrutinized with
care to minimize the prospect of extractables contaminating the
filtrate, interfering
13i373`~.
28
with analyses and potentially introducing harmful toxins to a
patient. Specifically, any such filter must meet the test
standards in the industry, e.g. ASTM D 3861-79, and generally prove
less than S mg. of extractables in 250 ml solvent (water at 80C.i
35~ ethanol at room temperature) for a 293 mm diameter disc.
Biological liquids as that term is employed in the
specification and claims, is a liquid system which is derived from
or amenable to use with living organisms. Such liquids are
ordinarily handled and processed under sanitary-or sterile
conditions and therefore require sanitized or sterilized media for
filtration. Included within such term are isotonic solutions for
intermuscular (im) or intravenous (iv) administration, solutions
designed for administration per os, as well as solutions for
topical use, biological wastes or other biological f~uids which rrlay
comprise filterable bodies such as impurities, e.g., bacterial,
viruses or pyrogens which are desirably isolated or separated for
examination or disposal by i D bilization or fixation upon or
entrapment within filter rnedia.
Filter rnembranes in accordance with this invention may be
er~ployed alone or in combination with other filter media to treat
pharmaceuticals such as antibiotics, saline solutions, dextrose
solutions, vaccines, blood plasma, serums, (e.g. to remove hormones
or toxins), sterile water or eye washesi beverages, such as
cordials, gin, vodka, beer, scotch, whiskey, sweet and dry wines,
champagne or brandy; cosmetics such as mouthwash, perfume, sham~oo,
hair tonic, face cream or shaving lotion; food products such as
vinegar, vegetable oils; chemical such as antiseptics, insecti-
cides, photographic solutions, electroplating solutions, cleaning
compounds, solvent purification and lubrication oils, cutting oils
for r~noval of me,allic fines (e.g. where the ferrite modifying
agent has been magnetized); and the like for retention of
submicronic particles, removal of bacterial contaminants and _
1313~
2~
resolution of colloidal hazes. Illustratively, in hospital
usage, membrane filters are employed to concentrate abnormal
exfoliated cells from a vaginal rinse, to isolate blood
~arasites from peripheral blood, or bacteria from serum or
leucocytes and casts from urine.
In the case of ~re~aration for use in sterile fil-
tration, the membrane is thermally sterilized or~sanitized
as by treatment in an autoclave at 121C. under 15 psig. for
1 hour, or hot water flushing at 85F. for l hour.
The membranes and fibers, etc. of this invention
can also be used to provide a bactericide (e.g. where the
modifying agent is iodine) or bacteriostatic treatment to
fluids, to remove contaminants such as chlorine or phenol
from fluids, in molecular separation columns, in bioreactors
where cells, etc. are immobilized thereon, as cigarette
fllters, and for many other uses.
Havin~ now generally described this invention, the
s~me will become better understood by reference to certain
s~ecific eamples, which are included herein for the purposes
of illustration only and are not intended to be limiting of
the invention.
EXAMPLES
The following are the measurement and test procedures
utilized in all the Examples.
Thickness
The dry me~brane thickness was measured with a l/2
inch (1.27 cm) diameter platen dial indicator thickness gauge.
Gauge accuracy was +O.OOOOa inches (+.05 mils).
Initial Bubble Point (IBP) and
Foam-All-_ver-Point (FAOP) Tests
A 47 mm diameter disc of the membrane sample is
~laced in a special test holder which seals the edge of the
disc. Above the membrane and direc~ly in contact with its
u~er face, is a perforated stainless steel support screen
which prevents the membrane from deforming or rupturing when
.
~3~373l~
air ~ressure ~s ap?lied tO its bottom face. Above the mem-
brane and support screen, the holder provides an inch
deep cavity into which distilled water is introduced.
~ re~ulated air pressure is increased until a first stream
of air bubbles is emitted by the water wetted membrane into
quiescent pool of water. The air pressure at which this
first stream of air bubbles is emitted is called the Initial
bubble Point (IBP) of the lar~est pore in that membrane
s~mple - see AST~I D-2499-66T.
Once the Initial Bubble Point pressure has been
determined and recorded, the air pressure is further in-
creased until the air flow throu~h the wetted membrane sam-
ple, as measured by a flow meter in the line between the
re~ulator and the sample holder, reaches 100 cc/min. The
air pressure at this flow rate is called the Foam-All-Over-
Point (FAOP), and is directly proportional to the mean pore
diameter of the sample mem~rane. In this series of tests,
these two parameters (IBP and FAOP) are used to determine if
any chan~e has occurred in the maximum or mean pore size of
the mem~rane sample as a result of the charge modifying
process utilized.
Flow Rate Test
A 47 mm diameter disc of the membrane sample is
placed in a test housin~ which allows pressurized water to
flow through the membrane. Prefiltered water is passed
through the membrane sample at a pressure differential of 5
psid. A graduate cylinder is used to measure the volume of
water passed by the membrane sample in a one minute period.
In this series of tests this parameter is used in conjunction
with the IBV and FAOP to determine if any reduction in pore
size or ~ore blockage has occurred as a result of the charge
modif~ing process utilized.
Dye Adsor~tion Test
A 47 mm diameter disc of the membrane sample is
placed in a test housin~ which allows pressurized water flow
31 i~37~
through the m~nbrane. The challenge solution consists of distilled
water at a pH of 7.0, and Metanil Yellow dye (color index CI#13065:
CAS587-98-4) for cationically charged membranes and methylene blue
(color index CI#52015: CAS61-73-4) for anionically charged
membranes. The dye inlet concentration is adjusted to produce a 76
percent transmittance at a waveleng~h of 430 nm, as measured on a
Perkin-Elmer Model 295 Spectrophotometer for cationic membranes or
34 percent at 660 nm as measured on a Bausch & L~nb Spectronic 710
Spectrophotometer for anionic membranes. By means of a peristaltic
pump the challenge solution is flowed through the me~brane sample
at a flow rate of 28 ml/min. m e transmittance of the effluent is
measured by passing it through a constant flow cell in the
aforementioned spectrophotometer. The effluent transmittance and
pressure drop across the membrane is measured and recorded as a
function of time. m e test is terminated when the effluent
transmittance increases to 85 percent for cationic membranes or 45
percent for anionic membranes of the inlet transmittance. In this
series of tests, the length of time that it takes to reach the 85
or 45 percent, ~ransmittance in the effluent is called the
"breakthrough" time. Since the Metanil Yellow and methylene blue
are low molecular weight charged dyes incapable of being mechan-
ically removed (filtered) by the membrane, -~his breakthrough time
is proportional to the charge adsorptive capaci-~y of the membrane
sample. This test is therefore used to determine the effectiveness
of the charge modification technique.
Extractables (ASTM D-3861-79)
Extractables were determined by ASTM D-3861-79. l`he
quantity of water-soluble extractables present in the membrane
filters was determined by immersing the preweighed membrane in
boiling reagent grade water for an extended time and then drying
and reweighing the membrane. A control membrane was employed to
eliminate weighing errors caused by balance changes or changing
moisture content of the membrane in the weighing procedures.
Weight changes of the control
131373~
membrane were ~plied as a correction factor to the weight
change of the test membrane filters.
EXA~IPLE I
A. reparation of ~licroporous Membrane
A re~resentative nylon 66 membrane of 0.22 micrometer
nominal ratin~, having a nominal surface area of about 13 m2/g,
an Initi~l Bubble Point of about 47 psi, a Foam-All-Over-Point
of about 52 ~si was prepared by the method of Marinaccio et al,
U.S. Patent 3,87~,738, utilizing a dope composition of 16 per-
cent ~y weight nylon 6~ (Monsanto Vydyne 66B), 7.1~ methanol
and 76.9~ formic acid, a quench bath composition of 25Z metha-
nol, 75~ water by volume (regenerated as required by the method
of Kni~ht et al, U.S. Patent 3,928,517) a casting speed of
24 inches/minute (61 cm/min), and a quench bath temperature
of 20C. The membrane was cast just under the surface o~
the quench bath by a~plication to a casting drum rotating in
the bath (9 to 10 mils as cast wet, to obtain 4.5 to 5.5
mils dry) and allowed to separate from the drum about 90 of
arc from the point of application, the self-supporting mem-
brane forming a shallow catenary to takeup. A portion of
the uniform opaque film was dried (in restrained condition
to resist shrinka~e) in a forced air oven at 89-90C. for 30
mi nu tes.
B. Preparatior. of Charge Modified
MicroDorous Membrane - Post-Treatment
1. Membrane samples (dried and undried) were dipped
in a bath of ~ercules 1~4 polyamido-polyamine epichloro~ydrin
resin (4~ solids by weight), and allowed to attain adsorption
e~uilibrium. The treated membrane samples were washed to re-
rnove e~cess resin and dried in restrained condition on a drum
at a tem~erature of 110~C. for a period of about 3 minutes.
The Ireated memr)rane samples were compared for flow
and bubble point characteristics as follows, and found to be
essenlially identical for treated and untreated samples,
evidencing retention of pore and surface geometry. The
results are set forth in Table I.
13~73~
TABLE I
Control (No Undried Dried
Treatment~ Membrane Membrane
Thickness (mils) 4.25 4.58 4.83
Initial ~u~ble Point (psi) 43.7 44.7 44.7
Foam-All-Over-Point (psi)55.0 54.0 54-7
Thlckness Normalized Flow
Rate (cc. mil/min. cm2 psi) 7.1 7.2 7.0
BET, N2 adSorption 13.12 - 13.58
Thus, in terms of the morphological and hydrodynamic
parameters that control mechanical sieving,the filtration charac-
teristics of the treated membrances were essentially identical
with the untreated nylon membrane.
2. Similar characterizations were conducted on an-
other membrane sample, similarly prepared, but treated with 2~o
~ercules K4308 resin (a free radical polymerized resin based
u~on diallyl nitrogen-containing materials, reacted with epi-
chlorohydrin) in a bath adjusted to pH 10.5, overcoated with
V.lZ tetraethylene pentamine, dried, cured, washed and redried.
The results are set forth in Table II.
TABLE II
Control
(No Treatment~ Dried Membrane
Tensile Stren~th (Dsi)
Wet S28 6~5
Vry 860 960
Elon~ation (Z)
Wet 140 100
~ry 95 40
Surface area of the treated and untreated membranes
remained essentially unchan~ed; tensile stren~th increased
with treatment with some loss in elon~ation. The treated
.
- .
-~ '
.
,~
13137~
34
sneet was mor~ flexible; creasing of the untreated sheet
resulted in crac~ing and splitting.
C. Filtration Tests
The ~ercules 1884 treated membrane samples (Example
I.B.l.) were subjected to the filtraton tests indicated below:
Pyro~en Removal
Purified E. coli endotoxin was added to a 0.9~ NaCl
solution, pH 6.7 and passed through test filters mounted in
a 25 mm diameter stainless steel holder. Inlet and effluent
endotoxin levels were determined by standard L.A.L. analysis.
Results are set forth in Table III.
TABLE III
Inlet Endotoxin Effluent Endotoxin Level (pg/ml)
Filter Level (~g/ml) 10 ml. 50 ml 100 ml
Dried, treated
llembrane 15000 1000 lOC0 1000
Control -
Untreated 15000 10000 10000 10000
(Pg is "picogram")
Virus Xemoval
~ S-2 bacleriophage was added to ~ouston Texas (U.S~A.)
zay waler to produce a concentration of 3.4 x 105 ?FU/ml (PFU
is "Plaque Forming Unit"), and 10 ml was passed through each
of the test filters mounted in a 25 mm diameter stainless
steel holder. Effluents were analyzed for viral content by
standard ~echni~ues. Results are set forth in Table I~':
TABLE IV
- Total Viral PFU Virus Removal
Filter in Filtrate Efficiency t~o)
~ried, trealed
~lembrane 100 99.997
Control - un~reated 250000 26.4
~onodis~erse Latex Filtration
The test filters were challenged with a 10 ~TU dis-
~ersion (NTU is "nephlometric turbidity units") of 0.109
13137~
micrometer monodisperse latex (~DL) particles at a flow rate
of 0.5 ~m/ft.2 (.002 lpm/cm2), pH 7.0, R=21000-ohm-cm.
Effluent turbidities (~TU) were monitored and filtration
efficiencies were calculated from equilibrium effluent tur-
bidities. Results are set forth in Table V.
TABLE V
Filter MDL Removal Efficiency
Undried, treated 97.3
Control-untreated 10%
Dye Removal Efficiency
The test filters were challenged with a solution of
~lue food coloring dye (FD ~ C ~o. 1). The solution had a
light transmittance of 62.5~ at 628 nm. The light trans-
mittance of the effluent was monitored and removal ef~icien-
cies determined (based on distilled water light transmit-
tance - 100Z). Results are-set forth in Table VI.
TABLE VI
Throughput (litres) to 90X
Transmittance
Undried, treated 1.99
~ried, treated 1.76
Control-untreated o
EXA~PLE II
The cationically charged microporous membrane of
Example I.B. 1. is prepared by repeating the procedure of
Example I.~. and incorporating the Hercules 1884 resin into
the do~e composilion.
EXAMPLE III
A nylon dope solution was prepared containin~ 10
nylon, 85.3~ formic acid and 4.7~ methanol. About 28~ of
~ercules 1884 resin based on the wei~ht of the nylon was
introduced into the dope solution. The resulting dope solu-
tion ~as extruded throu~h an orifice which was in near proxi-
13137~ .~
36
mity tO a recirculating quench bath stream of about 25~ v/va~ueous ~ethanol. The recirculating strearn produces a mo-
derate shear on the dope solution entering the bath, thereby
producin~ fine fibrils from the dope solution. The resulting
fibers were blended at a ratio of 1:1 with coho cellulose
fi~er and 4.3 ~rams of the resulting mi~ture was felted into
pads. The electrokinetic status of the pad was determined
usin~ streamin~ potential techniques (~night and Ostreicher,
Measurin~ the Electrokinetic Properties of Charged Filter
.~edia, Filtration and Separation, January/February, 1981,
pp. 30-34). The pad had a slope Mv/Ft H2O of -6.8, an in-
tercept of -90.70 and an a~parent zeta potential of +0.33.
EXAI~IPLE IV
Approximately 1 litre of a mixture of methanol and
formic acid in a weight ratio of 0.04 was prepared and allowed
tO equilibriate for 1 hour. Then to four separate flasks,
150 ml of the solution was added. Thereafter, Hercules resin
1~84 (35~ solids) were added in amounts of 1, 5, 10 and 15
millilitres and allowed to equilibriate in a water bath at
4UC. for one hour with a~itation.
A sufficient quantity of nylon was added to bring
the wei~ht percentage of the nylon to 8~ based on the weight
of the methanol and acid and the flasXs were shaken in a
water bath at 40C. until the nylon dissolved. The composi-
tions of tAe resultin~ doped solutions were:
_ Percentage
~lethanol 4.1 4.1 4.0 4.0
Formic .~cid 87.887.2 86.4 85.7
~ylon 8 7.9 7.8 7.8
1~4 0.2 0.9 1.8 2.5
Cationically modified microporous membranes are pro-
duced repeating the procedure of Example I. A.
131373 '~
EXAMPLE V~
Four dope compositions containin~ 39 grams of Nylon
6~ and the following other ingredients were prepared:
Do~e Fonmic Acid Grams Water Grams 4308 Resin Grams Pentamine Gra~s
1 231.36 ~.6~ 0 0
2 231.36 16.916 10.263 2.46
3 231.36 4.~3 20.526 4.92
4 231.36 24.719 0 4.92
Dope 2 contains one equivalent wei~ht of 4308 Resin
and triethyler.epentamine per weight nylon, formulation 3
contains two equivalent weights of both resin and pentamine
per wei~ht nylon Pnd dope 4 contains two equivalent weights
of the pentamine alone. The dopes were placed in a jar mill
roller bath at 20C. until full dissolution. Following the
procedure of EXAMPLE I. A., two membranes were cast from
each do~e just under the surface of a quench bath (30~ meth-
anol, ~ water by volume) by application to a casting drum
rotatin~ in the bath usin~ an 8 mil blade to drum depth.
The membranes made ~rom each dope were separated from the
castin~ drum and rinsed in two successive wash baths of
distilled water. The membrane sheets were then doubled over
on top of themselves while wet and mounted in restrained
condition to resist shrin~a~e and placed in a forced draft
oven at 80C. for one-half hour. The membranes were then
subJected to .~.~etanil Yellow dye absorption tests, the results
of which are shown in Figure 1. Thereafter, the membranes
were subjected to flow, IBP and FOAP tests and the following
results obtained:
:: ~
'
.
.
:: : : . . .
i3i37~'~
38
Do~,e Sam~LeFlo~ (Ml/~lin) IBP (psi) FAOP (psi)
l 1 72 53.5 85
2 78 45.5 82.5
2 1 39 59 53.8
2 59.5 41.5 53
3 1 103 25 30
2 138 25 30
4 1 6 90+ 90+
2 11 85.5 90+
EXAllPLE VI
To 253.6 ~rams of a ~ylon 66 membrane dope for a
membrane of a 0.45 micron nominal rating containing 40.576
~rams of Nylon 66, methanol and formic acid (16~ solids) was
aaded 1.159 ~rams of Hercules 1884 resin (35% solids) to
~ive l~ resin based on the nylon and the resulting mixture
was a~itated urltil a clear solution was obtained. Membranes
were ~re~ared followin~ the procedure of E~ample I.A., using
the do~e witnout the 1884 resin and the dope with the resin.
The membranes were dried under restrained conditions for 30
minutes at 85C. and their properties were measured using
test water which had been prefiltered through a 0.2 micro-
meter nominal rating memorane. The results are shown in the
following table:
Flow cc/Min.-
b~embrane Thickness psi-cm2IBP (PSi) FAOP (Psi)
Do~e wit.~out resin 4.13 2.~7 41.3 47.5
~o~e wi~h resm 4.4 2.44 38.4 45.3
The membrane prepared with the dope which did not
contain the cationic 1884 resin had an IBP/FAOP ratio of
0.8~ wnile Ihe membrane prepared with the resin had a ratio
of 0.848. -
~ 3~373~
39
EXAMPLE VII
A membrane dope was prepared by combining 180S.5~arts of ~ylon 66 with 9479 parts of a mixture of methanol
an~l formic acid to obtain a 16~ solids nylon dope. The mix-
ture was heated with agitation at 30C. for about 4 hours.
A quantity of Polycup 1884 was added to the dope
in a qUanlity such that the concentration of the cationic
char~e modifyin~ resin was about laO based on the weight of
the nylon. Cast membranes were then prepared using the pro-
cedure described in Example I.A. A portion of the resulting
wet membrane was dried in restrained condition as a single
layer in an oven at 85C. for 1~ minutes. The resultin~
nominal 0.22 micrometer rated membrane had a thickness of
4.1 mils. Another portion of the ~vet membrane was folded
back onto i~self and dried under restrained conditions in
the 85C. oven for 60 minutes.- The resulting membrane was
7.8 mils thick. Prior to dryin~, the wet membrane had a
thickness of about 6.1-6.4 mils. The nominal pore size of
the membr~ne was 0.3 micron.
.
,
.
13~ 373l~
- EXAI~PLE VI I I
Followin~ ~he procedure of Example III, pads were
~roduced usin~ ~ther surface modifyin~ agents. The agent,
blend ratio, num~er of ~rams felted and electrokinetic status
Or the pads are shown in the following table:
Fiber to GramsSlope Apparent
A~ent COH0 Ratio Felted Mv/Ft H20Interce~t Zeta Pot
Alon 0.53 1.632.9 0.69 - 1.60
.4sbestosl 0.83 2.55.1 -32.90 - 0,25
Asbestos2 1.00 4.414.2 32.30 - 0.69
Asbestos3 1.00 3.625.1 -35.00 - 1,22
Asbestos4 0.97 2.917.4 -33.50 - 0.84
Casein 1.00 3.220.1 59.00 - 0.97
Silica 1.00 3.025.0 20.66 - 1.21
- Cabosil q~ 1.00 8.032.2 -53.50 - 1.56
Se~hadex (G-75)~1.00 5.56.3 -67.24 - 0.30
Bentonite 1.00 5.446.3 64.30 - 2.25
Diat~ ceous
Ear~h D.E. 215 1.00 5.0 27.9 26.65 - 1.35
~aolin 1.00 6.062.4 -70.~0 - 3.02
Na-Al,sinate 1.00 5.;: 18.5 -15.82 - 0.89
Aluminum 1.00 7.8-181.8 - 5.49 + 8.82
Carbon l.00 4.457.5 -10.14 - 2.78
Car~on/18~4 Resin 1.00 5.1 0.3 32.00 - 0.01
L)~215/1884 Resin 1.00 5.6 7.6 -26.30 - 0.37
Aluminum (1~) 1.00 3.6- 6.2 -50.99 1 0.30
1884/5A ,~lolecular
Sieve 0.67 2.0-29.2 -30.70 + 1.42
arium Ferrite1.00 8.653.2 -89.50 - 2.58
EL~rA l.OO 5.519.6 - 4.34 - 0.95
Loaine (Tinc~ ure) 1.00 4.3 33.1 50.03 - 1.60
~: :
.
,
.
131 373~
41
1: Arizona - not acid washed
2: Canadian - not acid washed
3: ~rizoua - acid washed
4: Canadian - acid washed
EXAMPLE IX
Followin~ the procedure of Example III, fibers were
pre~ared from a 60 ml dope solution containing 4.8g nylon
with and without lOg powdered activated carbon. The fibers
were exposed for 16 hours to 150 ml of distilled water which
had been chlorinated to 4~0 ppm chlorine. The chlorine con-
tent of the water was then determined to be 360 ppm for the
water treated with the non-carbon containing fibers and 0.4
ppm for the water treated with the carbon containing fibers.
EXAMPLE X
Anionically charged microporous membranes are prepared
by repeatin~ the procedure of Example I.A. and incorporating
the followin~ into the dope composition:
4~ polystyrene sulfonic acid and 2.7~ ethylene glycol
di~lycidal ether;
1.3~ polyacrylic acid;
0.88Z polyacrylic acid and 0.l2Z polyo~yethylene-
polyoxypropylene glycol;
3.6Z polyacrylic acid (mw 104,000) and 1.3Z he~a-
methoxy methylmelamine resin.
EXAMPLE XI
Into a polymer dope solution containin~ about 8Z
nylon 66, was suspended activated carbon (6?~Z of total solids).
The suspen~ion was allowed to flow by gravity into a 75Z/25Z
by volume waler/methanol non-solvent through a small orifice.
The resultin~ fibrils were harvested, washed and then tested
for chlorine and ~henol removal from water. In both cases,
: .
1~37~ ~
42
the ca~acity o~ the fibrils was about 90_95a of the particu-
l~te carbon per se and at equivalent mass transfer rates.
The fibrils did not manifest the same degree of problems
encountered with finely powdered carbon which has very poor
hydrodynamic characteristics, is difficult to retain and
tends to mi~rate.
EXAMPLE XII
Following the procedure of Example I, unmodified and
post-formation modified microporous membranes were prepared.
The post-formation modified microporous membranes were made
by dippin~ one of the unmodified membranes into a 2 wZ solu-
tion of ~ercules Polycup 172 resin (0.24~ solids). The same
dope was modified by the addition of 7 w~ of the Polycup 172
resin (0.84~ solids) and duplicate microporous membranes
prepared. When removed from the quench bath, the membranes
were air dried and then dried in a forced air oven at 40C.
for 1~ hours. The five membrane~ were analyzed for integrity
by determirlin~ bubble point, FOAP and then challenged with
~etanil Yellow dye. The results are shown in the following
table:
Bubble PSI Dye Ret. Time
`lembrane Poirt FOAP Initial Final (min.)
Unmodified 40 46 3.0 3.6 7
3~ 44 1.9 2.9 7
A,lodified -
Post Treatment 44 SO 3.9 5.0 ~4
.!~lodified Dope 31 52 3.9 12.0 77
31 53 4.3 14.0 73
Various changes and modifications can be made in
the process of the present invention witnout departing from
~ne s~irit and scope thereof. The various embodiments which
have been described herein were for the purpose of further
illustrating the invention but were not intended to limit it.
