Note: Descriptions are shown in the official language in which they were submitted.
CA 2929446 2017-10-03
FILTRATION MEMBRANE COMPRISING COATED MICROPOROUS MATERIAL OF
POLYOLEFIN AND PARTICULATE SILICA
FIELD OF THE INVENTION
[0001] The present invention relates to coated microporous materials useful in
filtration
and adsorption membranes and their use in fluid purification processes.
BACKGROUND OF THE INVENTION
[0002] Accessibility to clean and potable water is a concern throughout the
world,
particularly in developing countries. The search for low-cost, effective
filtration materials
and processes is ongoing. Filtration media that can remove both macroscopic,
particulate
contaminants and molecular contaminants are particularly desired, including
those that
can remove both hydrophilic and hydrophobic contaminants at low cost and high
flux rate.
[0003] It would be desirable to provide novel membranes suitable for use on
liquid or
gaseous streams that serve to remove contaminants via both chemisorption and
physisorption.
SUMMARY OF THE INVENTION
100041 The present invention is directed to microfiltration and
ultrafiltration membranes
comprising a microporous material. The microporous material comprises:
(a) a polyolefin matrix present in an amount of at least 2 percent by
weight,
(b) finely divided, particulate, substantially water-insoluble silica
filler distributed
throughout said matrix, said filler constituting from about 10 percent to
about 90 percent
by weight of said coated microporous material substrate,
(c) at least 20 percent by volume of a network of interconnecting pores
communicating
throughout the coated microporous material, and
(d) at least one coating composition applied to at least one surface of the
membrane
to adjust the surface energy of the membrane.
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DETAILED DESCRIPTION OF THE INVENTION
[0005] Other than in any operating examples, or where otherwise indicated, all
numbers
expressing quantities of ingredients, reaction conditions and so forth used in
the
specification and claims are to be understood as being modified in all
instances by the
term "about." Accordingly, unless indicated to the contrary, the numerical
parameters set
forth in the following specification and attached claims are approximations
that may vary
depending upon the desired properties to be obtained by the present invention.
At the
very least, and not as an attempt to limit the application of the doctrine of
equivalents to
the scope of the claims, each numerical parameter should at least be construed
in light
of the number of reported significant digits and by applying ordinary rounding
techniques.
[0006] Notwithstanding that the numerical ranges and parameters setting forth
the broad
scope of the invention are approximations, the numerical values set forth in
the specific
examples are reported as precisely as possible. Any numerical value, however,
inherently contain certain errors necessarily resulting from the standard
deviation found
in their respective testing measurements.
[0007] Also, it should be understood that any numerical range recited herein
is intended
to include all sub-ranges subsumed therein. For example, a range of "1 to 10"
is intended
to include all sub-ranges between (and including) the recited minimum value of
1 and the
recited maximum value of 10, that is, having a minimum value equal to or
greater than 1
and a maximum value of equal to or less than 10.
[0008] As used in this specification and the appended claims, the articles
"a," "an," and
"the" include plural referents unless expressly and unequivocally limited to
one referent.
[0009] The various embodiments and examples of the present invention as
presented
herein are each understood to be non-limiting with respect to the scope of the
invention.
[0010] As used in the following description and claims, the following terms
have the
meanings indicated below:
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[0011] By "polymer" is meant a polymer including homopolymers and copolymers,
and
oligomers. By "composite material" is meant a combination of two or more
differing
materials.
[0012] As used herein, "formed from" denotes open, e.g., "comprising," claim
language.
As such, it is intended that a composition "formed from" a list of recited
components be a
composition comprising at least these recited components, and can further
comprise
other, nonrecited components, during the composition's formation.
[0013] As used herein, the term "polymeric inorganic material" means a
polymeric
material having a backbone repeat unit based on an element or elements other
than
carbon. For more information see James Mark et al., Inorganic Polymers,
Prentice Hall
Polymer Science and Engineering Series, (1992) at page 5. Moreover, as used
herein,
the term "polymeric organic materials" means synthetic polymeric materials,
semisynthetic polymeric materials and natural polymeric materials, all of
which have a
backbone repeat unit based on carbon.
[0014] An "organic material," as used herein, means carbon containing
compounds
wherein the carbon is typically bonded to itself and to hydrogen, and often to
other
elements as well, and excludes binary compounds such as the carbon oxides, the
carbides, carbon disulfide, etc.; such ternary compounds as the metallic
cyanides,
metallic carbonyls, phosgene, carbonyl sulfide, etc.; and carbon-containing
ionic
compounds such as metallic carbonates, for example calcium carbonate and
sodium
carbonate. See R. Lewis, Sr., Hawley's Condensed Chemical Dictionary, (12th
Ed. 1993)
at pages 761-762, and M. Silberberg, Chemistry The Molecular Nature of Matter
and
Change (1996) at page 586.
[0015] As used herein, the term "inorganic material" means any material that
is not an
organic material.
[0016] As used herein, a "thermoplastic" material is a material that softens
when exposed
to heat and returns to its original condition when cooled to room temperature.
As used
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herein, a "thermoset" material is a material that solidifies or "sets"
irreversibly when
heated.
[0017] As used herein, "microporous material" or "microporous sheet material"
means a
material having a network of interconnecting pores, wherein, on a coating-
free, printing
ink-free, impregnant-free, and pre-bonding basis, the pores have a volume
average
diameter ranging from 0.001 to 0.5 micrometer, and constitute at least 5
percent by
volume of the material as discussed herein below.
100181 By "plastomer" is meant a polymer exhibiting both plastic and
elastomeric
properties.
[0019] As noted above, the present invention is directed to microfiltration
and
ultrafiltration membranes comprising a microporous material. Microporous
materials
used in the membranes of the present invention comprise a polyolefin matrix
(a). The
polyolefin matrix is present in the microporous material in an amount of at
least 2 percent
by weight. Polyolefins are polymers derived from at least one ethylenically
unsaturated
monomer. In certain embodiments of the present invention, the matrix comprises
a
plastomer. For example, the matrix may comprise a plastomer derived from
butene,
hexene, and/or octene. Suitable plastomers are available from ExxonMobil
Chemical
under the tradename "EXACT".
[0020] In certain embodiments of the present invention, the matrix comprises a
different
polymer derived from at least one ethylenically unsaturated monomer, which may
be used
in place of or in combination with the plastomer. Examples include polymers
derived from
ethylene, propylene, and/or butene, such as polyethylene, polypropylene, and
polybutene. High density and/or ultrahigh molecular weight polyolefins such as
high
density polyethylene are also suitable.
[0021] In a particular embodiment of the present invention, the polyolefin
matrix
comprises a copolymer of ethylene and butene.
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[0022] Non-limiting examples of ultrahigh molecular weight (UHMW) polyolefin
can
include essentially linear UHMW polyethylene or polypropylene. Inasmuch as
UHMW
polyolefins are not thermoset polymers having an infinite molecular weight,
they are
technically classified as thermoplastic materials.
[0023] The ultrahigh molecular weight polypropylene can comprise essentially
linear
ultrahigh molecular weight isotactic polypropylene. Often the degree of
isotacticity of
such polymer is at least 95 percent, e.g., at least 98 percent.
[0024] While there is no particular restriction on the upper limit of the
intrinsic viscosity of
the UHMW polyethylene, in one non-limiting example, the intrinsic viscosity
can range
from 18 to 39 deciliters/gram, e.g., from 18 to 32 deciliters/gram. While
there is no
particular restriction on the upper limit of the intrinsic viscosity of the
UHMW
polypropylene, in one non-limiting example, the intrinsic viscosity can range
from 6 to 18
deciliters/gram, e.g., from 7 to 16 deciliters/gram.
[0025] For purposes of the present invention, intrinsic viscosity is
determined by
extrapolating to zero concentration the reduced viscosities or the inherent
viscosities of
several dilute solutions of the UHMW polyolefin where the solvent is freshly
distilled
decahydronaphthalene to which 0.2 percent by weight, 3,5-di-tert-buty1-4-
hydroxyhydrocinnamic acid, neopentanetetrayl ester [CAS Registry No. 6683-19-
8] has
been added. The reduced viscosities or the inherent viscosities of the UHMW
polyolefin
are ascertained from relative viscosities obtained at 135 C using an
Ubbelohde No. 1
viscometer in accordance with the general procedures of ASTM D 4020-81, except
that
several dilute solutions of differing concentration are employed.
[0026] The nominal molecular weight of UHMW polyethylene is empirically
related to the
intrinsic viscosity of the polymer in accordance with the following equation:
M=5.37 x 104 [rj]1.37
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[00271 wherein M is the nominal molecular weight and [ri] is the intrinsic
viscosity of the
UHMW polyethylene expressed in deciliters/gram. Similarly, the nominal
molecular
weight of UHMW polypropylene is empirically related to the intrinsic viscosity
of the
polymer according to the following equation:
M=8.88 x 104 [rfir.25
wherein M is the nominal molecular weight and [rj] is the intrinsic viscosity
of the UHMW
polypropylene expressed in deciliters/gram.
100281 A mixture of substantially linear ultrahigh molecular weight
polyethylene and lower
molecular weight polyethylene can be used. In certain embodiments, the UHMW
polyethylene has an intrinsic viscosity of at least 10 deciliters/gram, and
the lower
molecular weight polyethylene has an ASTM D 1238-86 Condition E melt index of
less
than 50 grams/10 minutes, e.g., less than 25 grams/10 minutes, such as less
than 15
grams/10 minutes, and an ASTM D 1238-86 Condition F melt index of at least 0.1
gram/10
minutes, e.g., at least 0.5 gram/10 minutes, such as at least 1.0 gram/10
minutes. The
amount of UHMW polyethylene used (as weight percent) in this embodiment is
described
in column 1, line 52 to column 2, line 18 of U.S. Patent 5,196,262. More
particularly, the
weight percent of UHMW polyethylene used is described in relation to Figure 6
of U.S.
5,196,262; namely, with reference to the polygons ABCDEF, GHCI or JHCK of
Figure 6.
[0029] The nominal molecular weight of the lower molecular weight polyethylene
(LMWPE) is lower than that of the UHMW polyethylene. LMWPE is a thermoplastic
material and many different types are known. One method of classification is
by density,
expressed in grams/cubic centimeter and rounded to the nearest thousandth, in
accordance with ASTM D 1248-84 (Reapproved 1989). Non-limiting examples of the
densities of LMWPE are found in the following Table 1.
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TABLE 1
Type Abbreviation Density, 9/cm3
Low Density LDPE 0.910-0.925
Polyethylene
Medium Density MDPE 0.926-0.940
Polyethylene
High Density HDPE 0.941-0.965
Polyethylene
[0030] Any or all of the polyethylenes listed in Table 1 above may be used as
the LMWPE
in the matrix of the microporous material. HDPE may be used because it can be
more
linear than MDPE or LDPE. Processes for making the various LMWPE's are well
known
and well documented. They include the high pressure process, the Phillips
Petroleum
Company process, the Standard Oil Company (Indiana) process, and the Ziegler
process.
The ASTM D 1238-86 Condition E (that is, 190 C. and 2.16 kilogram load) melt
index of
the LMWPE is less than about 50 grams/10 minutes. Often the Condition E melt
index is
less than about 25 grams/10 minutes. The Condition E melt index can be less
than about
15 grams/10 minutes. The ASTM D 1238-86 Condition F (that is, 190 C. and 21.6
kilogram load) melt index of the LMWPE is at least 0.1 gram/10 minutes. In
many cases
the Condition F melt index is at least 0.5 gram/10 minutes such as at least
1.0 gram/10
minutes.
[0031] The UHMWPE and the LMWPE may together constitute at least 65 percent by
weight, e.g., at least 85 percent by weight, of the polyolefin polymer of the
microporous
material. Also, the UHMWPE and LMWPE together may constitute substantially 100
percent by weight of the polyolefin polymer of the microporous material.
[0032] In a particular embodiment of the present invention, the microporous
material can
comprise a polyolefin comprising ultrahigh molecular weight polyethylene,
ultrahigh
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molecular weight polypropylene, high density polyethylene, high density
polypropylene,
or mixtures thereof.
[0033] If desired, other thermoplastic organic polymers also may be present in
the matrix
of the microporous material provided that their presence does not materially
affect the
properties of the microporous material substrate in an adverse manner. The
amount of
the other thermoplastic polymer which may be present depends upon the nature
of such
polymer. In general, a greater amount of other thermoplastic organic polymer
may be
used if the molecular structure contains little branching, few long side
chains, and few
bulky side groups, than when there is a large amount of branching, many long
side chains,
or many bulky side groups. Non-limiting examples of thermoplastic organic
polymers that
optionally may be present in the matrix of the microporous material include
low density
polyethylene, high density polyethylene, poly(tetrafluoroethylene),
polypropylene,
copolymers of ethylene and propylene, copolymers of ethylene and acrylic acid,
and
copolymers of ethylene and methacrylic acid. If desired. all or a portion of
the carboxyl
groups of carboxyl-containing copolymers can be neutralized with sodium, zinc
or the like.
Generally, the microporous material comprises at least 70 percent by weight of
UHMW
polyolefin, based on the weight of the matrix. In a non-limiting embodiment,
the above-
described other thermoplastic organic polymer are substantially absent from
the matrix of
the microporous material.
[0034] The microporous materials used in the membranes of the present
invention further
comprise finely divided, particulate, substantially water-insoluble silica
filler (b) distributed
throughout the matrix.
[0035] The particulate filler typically comprises precipitated silica
particles. It is important
to distinguish precipitated silica from silica gel inasmuch as these different
materials have
different properties. Reference inthis regard is made to R. K. Iler, The
Chemistry of Silica,
John Wiley & Sons, New York (1979). Library of Congress Catalog No. QD
181.S6144.
Note especially pages 15-29, 172-176, 218-233, 364-365, 462-465, 554-564, and
578-
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579. Silica gel is usually produced commercially at low pH by acidifying an
aqueous
solution of a soluble metal silicate, typically sodium silicate, with acid.
The acid employed
is generally a strong mineral acid such as sulfuric acid or hydrochloric acid
although
carbon dioxide is sometimes used. Inasmuch as there is essentially no
difference in
density between gel phase and the surrounding liquid phase while the viscosity
is low,
the gel phase does not settle out, that is to say, it does not precipitate.
Silica gel, then,
may be described as a nonprecipitated, coherent, rigid, three-dimensional
network of
contiguous particles of colloidal amorphous silica. The state of subdivision
ranges from
large, solid masses to submicroscopic particles, and the degree of hydration
from almost
anhydrous silica to soft gelatinous masses containing on the order of 100
parts of water
per part of silica by weight.
100361 Precipitated silica is usually produced commercially by combining an
aqueous
solution of a soluble metal silicate, ordinarily alkali metal silicate such as
sodium silicate,
and an acid so that colloidal particles will grow in weakly alkaline solution
and be
coagulated by the alkali metal ions of the resulting soluble alkali metal
salt. Various acids
may be used, including the mineral acids, but the preferred acid is carbon
dioxide. In the
absence of a coagulant, silica is not precipitated from solution at any pH.
The coagulant
used to effect precipitation may be the soluble alkali metal salt produced
during formation
of the colloidal silica particles, it may be added electrolyte such as a
soluble inorganic or
organic salt, or it may be a combination of both.
100371 Precipitated silica, then, may be described as precipitated aggregates
of ultimate
particles of colloidal amorphous silica that have not at any point existed as
macroscopic
gel during the preparation. The sizes of the aggregates and the degree of
hydration may
vary widely.
[0038] Precipitated silica powders differ from silica gels that have been
pulverized in
ordinarily having a more open structure, that is, a higher specific pore
volume. However,
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the specific surface area of precipitated silica as measured by the Brunauer,
Emmet,
Teller (BET) method using nitrogen as the adsorbate, is often lower than that
of silica gel.
[0039] Many different precipitated silicas may be employed in the present
invention, but
the preferred precipitated silicas are those obtained by precipitation from an
aqueous
solution of sodium silicate using a suitable acid such as sulfuric acid,
hydrochloric acid,
or carbon dioxide. Such precipitated silicas are themselves known and
processes for
producing them are described in detail in the U.S. Pat. No. 2,940,830 and in
West German
Offenlegungsschrift No. 35 45 615, including especially the processes for
making
precipitated silicas and the properties of the products.
[0040] The precipitated silicas used in the present invention can be produced
by a
process involving the following successive steps:
(a) an initial stock solution of aqueous alkali metal silicate having the
desired
alkalinity is prepared and added to (or prepared in) a reactor equipped with
means for
heating the contents of the reactor,
(b) the initial stock solution within the reactor is heated to the desired
reaction
temperature,
(c) acidifying agent and additional alkali metal silicate solution are
simultaneously
added with agitation to the reactor while maintaining the alkalinity value and
temperature of the contents of the reactor at the desired values,
(d) the addition of alkali metal silicate to the reactor is stopped, and
additional
acidifying agent is added to adjust the pH of the resulting suspension of
precipitated
silica to a desired acid value,
(e) the precipitated silica in the reactor is separated from the reaction
mixture,
washed to remove by-product salts, and
(f) dried to form the precipitated silica.
[0041] The washed silica solids are then dried using conventional drying
techniques.
Non-limiting examples of such techniques include oven drying, vacuum oven
drying,
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rotary dryers, spray drying or spin flash drying. Non-limiting examples of
spray dryers
include rotary atomizers and nozzle spray dryers. Spray drying can be carried
out using
any suitable type of atomizer, in particular a turbine, nozzle, liquid-
pressure or twin-fluid
atomizer.
[0042] The washed silica solids may not be in a condition that is suitable for
spray drying.
For example, the washed silica solids may be too thick to be spray dried. In
one aspect
of the above-described process, the washed silica solids, e.g., the washed
filter cake, are
mixed with water to form a liquid suspension and the pH of the suspension
adjusted, if
required, with dilute acid or dilute alkali, e.g., sodium hydroxide, to from 6
to 7, e.g., 6.5,
and then fed to the inlet nozzle of the spray dryer.
[0043] The temperature at which the silica is dried can vary widely but will
be below the
fusion temperature of the silica. Typically, the drying temperature will range
from above
50 C to less than 700 C, e.g., from above 100 C, e.g., 200 C, to 500 C.
In one aspect
of the above-described process, the silica solids are dried in a spray dryer
having an inlet
temperature of approximately 400 C and an outlet temperature of approximately
105 C.
The free water content of the dried silica can vary, but is usually in the
range of from
approximately 1 to 10 wt.%, e.g., from 4 to 7 wt.%. As used herein, the term
free water
means water that can be removed from the silica by heating it for 24 hours at
from 100
C to 200 C, e.g., 105 C.
[0044] In one aspect of the process described herein, the dried silica is
forwarded directly
to a granulator where it is compacted and granulated to obtain a granular
product. Dried
silica can also be subjected to conventional size reduction techniques, e.g.,
as
exemplified by grinding and pulverizing. Fluid energy milling using air or
superheated
steam as the working fluid can also be used. The precipitated silica obtained
is usually
in the form of a powder.
[0045] Most often, the precipitated silica is rotary dried or spray dried.
Rotary dried silica
particles have been observed to demonstrate greater structural integrity than
spray dried
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silica particles. They are less likely to break into smaller particles during
extrusion and
other subsequent processing during production of the microporous material than
are
spray dried particles. Particle size distribution of rotary dried particles
does not change
as significantly as does that of spray dried particles during processing.
Spray dried silica
particles are more friable than rotary dried, often providing smaller
particles during
processing. It is possible to use a spray dried silica of a particular
particle size such that
the final particle size distribution in the membrane does not have a
detrimental effect on
water flux. In certain embodiments, the silica is reinforced; i.e., has a
structural integrity
such that porosity is preserved after extrusion. More preferred is a
precipitated silica in
which the initial number of silica particles and the initial silica particle
size distribution is
mostly unchanged by stresses applied during membrane fabrication. Most
preferred is a
silica reinforced such that a broad particle size distribution is present in
the finished
membrane. Blends of different types of dried silica and different sizes of
silica may be
used to provide unique properties to the membrane. For example, a blend of
silicas with
a bimodal distribution of particle sizes may be particularly suitable for
certain separation
processes. It is expected that external forces applied to silica of any type
may be used
to influence and tailor the particle size distribution, providing unique
properties to the final
membrane.
[0046] The surface of the particle can be modified in any manner well known in
the art,
including, but not limited to, chemically or physically changing its surface
characteristics
using techniques known in the art. For example, the silica may be surface
treated with
an anti-fouling moiety such as polyethylene glycol, carboxybetaine,
sulfobetaine and
polymers thereof, mixed valence molecules, oligomers and polymers thereof and
mixtures thereof. Another embodiment may be a blend of silicas in which one
silica has
been treated with a positively charged moiety and the other silica has been
treated with
a negatively charged moiety. The silica may also be surface modified with
functional
groups that allow for targeted removal of specific contaminants in a fluid
stream to be
purified using the microfiltration membrane of the present invention.
Untreated particles
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may also be used. Silica particles coated with hydrophilic coatings reduce
fouling and
may eliminate pre-wetting processing. Silica particles coated with hydrophobic
coatings
also reduce fouling and may aid degassing and venting of a system.
[0047] Precipitated silica typically has an average ultimate particle size of
1 to 100
nanometers.
[0048] The surface area of the silica particles, both external and internal
due to pores,
can have an impact on performance. High surface area fillers are materials of
very small
particle size, materials having a high degree of porosity or materials
exhibiting both
characteristics. Usually the surface area of the filler itself is in the range
of from about 125
to about 700 square meters per gram (m2/g) as determined by the Brunauer,
Emmett,
Teller (BET) method according to ASTM C 819-77 using nitrogen as the adsorbate
but
modified by outgassing the system and the sample for one hour at 130 C. Often
the BET
surface area is in the range of from about 190 to 350 m2/g, more often, the
silica
demonstrates a BET surface area of 351 to 700 m2/g.
[0049] The BET/CTAB quotient is the ratio of the overall precipitated silica
surface area
including the surface area contained in pores only accessible to smaller
molecules, such
as nitrogen (BET), to the external surface area (CTAB). This ratio is
typically referred to
as a measure of microporosity. A high microporosity value, i.e., a high
BET/CTAB
quotient number, is a high proportion of internal surface¨ accessible to the
small nitrogen
molecule (BET surface area) but not to larger particles - to the external
surface (CTAB).
[0050] It has been suggested that the structure, i.e., pores, formed within
the precipitated
silica during its preparation can have an impact on performance. Two
measurements of
this structure are the BET/CTAB surface area ratio of the precipitated silica
noted above,
and the relative breadth (y) of the pore size distribution of the precipitated
silica. The
relative breadth (y) of pore size distribution is an indication of how broadly
the pore sizes
are distributed within the precipitated silica particle. The lower the y
value, the narrower
is the pore size distribution of the pores within the precipitated silica
particle.
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[0051] The silica CTAB values may be determined using a CTAB solution and the
hereinafter described method. The analysis is performed using a Metrohm 751
Titrino TM
automatic titrator, equipped with a Metrohm Interchangeable "Snap-In" 50
milliliter buret
and a Brinkmann Probe Colorimeter Model PC 910 equipped with a 550 nm filter.
In
addition, a Mettler Toledo HB43 or equivalent is used to determine the 105 C
moisture
loss of the silica and a Fisher Scientific CentrificTm Centrifuge Model 225
may be used for
separating the silica and the residual CTAB solution. The excess CTAB can be
determined by auto titration with a solution of Aerosol OT until maximum
turbidity is
attained, which can be detected with the probe colorimeter. The maximum
turbidity point
is taken as corresponding to a millivolt reading of 150. Knowing the quantity
of CTAB
adsorbed for a given weight of silica and the space occupied by the CTAB
molecule, the
external specific surface area of the silica is calculated and reported as
square meters
per gram on a dry-weight basis.
100521 Solutions required for testing and preparation include a buffer of pH
9.6, cetyl
[hexadecyl] trimethyl ammonium bromide (CTAB), dioctyl sodium sulfosuccinate
(Aerosol
OT) and 1N sodium hydroxide. The buffer solution of pH 9.6 can be prepared by
dissolving 3.101 g of orthoboric acid (99%; Fisher Scientific, Inc., technical
grade,
crystalline) in a one-liter volumetric flask, containing 500 milliliters of
deionized water and
3.708 grams of potassium chloride solids (Fisher Scientific, Inc., technical
grade,
crystalline). Using a buret, 36.85 milliliters of the IN sodium hydroxide
solution was
added. The solution is mixed and diluted to volume.
100531 The CTAB solutibn is prepared using 11.0 g 0.005 g of powdered CTAB
(cetyl
trimethyl ammonium bromide, also known as hexadecyl trimethyl ammonium
bromide,
Fisher Scientific Inc., technical grade) onto a weighing dish, The CTAB powder
is
transferred to a 2-liter beaker and the weighing dish rinsed with deionized
water.
Approximately 700 milliliters of the pH 9.6 buffer solution and 1000
milliliters of distilled or
deionized water is added to the 2-liter beaker and stirred with a magnetic
stir bar. The
beaker may be covered and stirred at room temperature until the CTAB powder is
totally
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dissolved. The solution is transferred to a 2-liter volumetric flask, rinsing
the beaker and
stir bar with deionized water. The bubbles are allowed to dissipate, and the
solution
diluted to volume with deionized water. A large stir bar can be added and the
solution
mixed on a magnetic stirrer for approximately 10 hours. The CTAB solution can
be used
after 24 hours and for only 15 days. The Aerosol CT (dioctyl sodium
sulfosuccinate,
Fisher Scientific Inc., 100% solid) solution may be prepared using 3.46 g
0.005 g, which
is placed onto a weighing dish. The Aerosol OT on the weighing dish is rinsed
into a 2-
liter beaker, which contains about 1500 milliliter deionized water and a large
stir bar. The
Aerosol OT solution is dissolved and rinsed into a 2-liter volumetric flask.
The solution is
diluted to the 2-liter volume mark in the volumetric flask. The Aerosol OT
solution is
allowed to age for a minimum of 12 days prior to use. The shelf life of the
Aerosol OT
solution is 2 months from the preparation date.
[0054] Prior to surface area sample preparation, the pH of the CTAB solution
should be
verified and adjusted as necessary to a pH of 9.6 0.1 using 1N sodium
hydroxide
solution. For test calculations a blank sample should be prepared and
analyzed. 5
milliliters of the CTAB solution are pipetted and 55 milliliters deionized
water added into
a 150-milliliter beaker and analyzed on a Metrohm 751 Titrino automatic
titrator. The
automatic titrator is programmed for determination of the blank and the
samples with the
following parameters: Measuring point density = 2, Signal drift = 20,
Equilibrium time =
20 seconds, Start volume = 0 ml, Stop volume = 35 ml, and Fixed endpoint = 150
mV.
The buret tip and the colorimeter probe are placed just below the surface of
the solution,
positioned such that the tip and the photo probe path length are completely
submerged.
Both the tip and photo probe should be essentially equidistant from the bottom
of the
beaker and not touching one another. With minimum stirring (setting of 1 on
the Metrohm
728 stirrer) the colorimeter is set to 100 %T prior to every blank and sample
determination
and titration initiated with the Aerosol CT solution. The end point can be
recorded as
the volume (ml) of titrant at 150 mV.
CA 2929446 2017-10-03
[0055] For test sample preparation, approximately 0.30 grams of powdered
silica was
weighed into a 50-milliliter container containing a stir bar. Granulated
silica samples,
were riffled (prior to grinding and weighing) to obtain a representative sub-
sample. A
coffee mill style grinder was used to grind granulated materials. Then 30
milliliters of the
pH adjusted CTAB solution was pipetted into the sample container containing
the 0.30
grams of powdered silica. The silica and CTAB solution was then mixed on a
stirrer for
35 minutes. When mixing was completed, the silica and CTAB solution were
centrifuged
for 20 minutes to separate the silica and excess CTAB solution. When
centrifuging was
completed, the CTAB solution was pipetted into a clean container minus the
separated
solids, referred to as the "centrifugate". For sample analysis, 50 milliliters
of deionized
water was placed into a 150-milliliter beaker containing a stir bar. Then 10
milliliters of
the sample centrifugate was pipetted for analysis into the same beaker. The
sample was
analyzed using the same technique and programmed procedure as used for the
blank
solution.
10056] For determination of the moisture content, approximately 0.2 grams of
silica was
weighed onto the Mettler Toledo HB43 while determining the CTAB value. The
moisture
analyzer was programmed to 105 C with the shut-off 5 drying criteria. The
moisture loss
was recorded to the nearest + 0.1 /0.
[0057] The external surface area is calculated using the following equation,
(2V0
CTAB Surface Area (dried basis) [m2/g] = - V) x (4774)
(VOW) x (100- Vol)
wherein,
Vo = Volume in ml of Aerosol OT used in the blank titration.
V = Volume in ml of Aerosol OT used in the sample titration.
W = sample weight in grams.
Vol = % moisture loss (Vol represents "volatiles").
16
CA 2929446 2017-10-03
[0058] Typically, the CTAB surface area of the silica particles used in the
present
invention ranges from 120 to 500 m2/g. Often, the silica demonstrates a CTAB
surface
area of 170-280 m2/g. More often, the silica demonstrates a CTAB surface area
of 281-
500 m2/g.
[0059] In certain embodiments of the present invention, the BET value of the
precipitated
silica will be a value such that the quotient of the BET surface area in
square meters per
gram to the CTAB surface area in square meters per gram is equal to or greater
than 1Ø
Often, the BET to CTAB ratio is 1.0-1.5. More often, the BET to CTAB ratio is
1.5-2Ø
[0060] The BET surface area values reported in the examples of this
application were
determined in accordance with the Brunauer-Emmet-Teller (BET) method in
accordance
with ASTM D1993-03. The BET surface area can be determined by fitting five
relative-
pressure points from a nitrogen sorption isotherm measurement made with a
Micromeritics TriStar 3000 TM instrument. A flow Prep-O6OTM station provides
heat and a
continuous gas flow to prepare samples for analysis. Prior to nitrogen
sorption, the silica
samples are dried by heating to a temperature of 160 C in flowing nitrogen
(P5 grade)
for at least one (1) hour.
[0061] The filler particles can constitute from 10 to 90 percent by weight of
the
microporous material. For example, such filler particles can constitute from
25 to 90
percent by weight of the microporous material, such as from 30 percent to 90
percent by
weight of the microporous material, or from 40 to 90 percent by weight of the
microporous
material, or from 50 to 90 percent by weight of the microporous material and
even from
60 percent to 90 percent by weight of the microporous material. The filler is
typically
present in the microporous material of the present invention in an amount of
50 percent
to about 85 percent by weight of the microporous material. Often the weight
ratio of silica
to polyolefin in the microporous material is 0.5:1 to 10:1, such as 1.7:1 to
3.5:1.
Alternatively the weight ratio of filler to polyolefin in the microporous
material may be
greater than 4:1.
17
CA 2929446 2017-10-03
[0062] The microporous material used in the membrane of the present invention
further
comprises a network of interconnecting pores (c) communicating throughout the
microporous material.
[0063] On an impregnant-free basis, such pores can comprise at least 15
percent by
volume, e.g. from at least 20 to 95 percent by volume, or from at least 25 to
95 percent
by volume, or from 35 to 70 percent by volume of the microporous material.
Often the
pores comprise at least 35 percent by volume, or even at least 45 percent by
volume of
the microporous material. Such high porosity provides higher surface area
throughout
the microporous material, which in turn facilitates removal of contaminants
from a fluid
stream and higher flux rates of a fluid stream through the membrane.
[0064] As used herein and in the claims, the porosity (also known as void
volume) of the
microporous material, expressed as percent by volume, is determined according
to the
following equation:
Porosity=100[1-di /d2]
wherein di is the density of the sample, which is determined from the sample
weight and
the sample volume as ascertained from measurements of the sample dimensions,
and d2
is the density of the solid portion of the sample, which is determined from
the sample
weight and the volume of the solid portion of the sample. The volume of the
solid portion
of the same is determined using a Quantachrome stereopycnometer (Quantachrome
Corp.) in accordance with the accompanying operating manual.
[0065] The volume average diameter of the pores of the microporous material
can be
determined by mercury porosimetry using an Autopore TM Ill porosimeter
(Micromeretics,
Inc.) in accordance with the accompanying operating manual. The volume average
pore
radius for a single scan is automatically determined by the porosimeter. In
operating the
porosimeter, a scan is made in the high pressure range (from 138 kilopascals
absolute to
227 megapascals absolute). If approximately 2 percent or less of the total
intruded
volume occurs at the low end (from 138 to 250 kilopascals absolute) of the
high pressure
18
CA 2929446 2017-10-03
range, the volume average pore diameter is taken as twice the volume average
pore
radius determined by the porosimeter. Otherwise, an additional scan is made in
the low
pressure range (from 7 to 165 kilopascals absolute) and the volume average
pore
diameter is calculated according to the equation:
d = 2 [ ri/wi + v2r2/w2] / [vi/ Wi + v2/ w2]
wherein d is the volume average pore diameter, vi is the total volume of
mercury intruded
in the high pressure range, v2 is the total volume of mercury intruded in the
low pressure
range, ri is the volume average pore radius determined from the high pressure
scan, 12
is the volume average pore radius determined from the low pressure scan, wi is
the
weight of the sample subjected to the high pressure scan, and w2 is the weight
of the
sample subjected to the low pressure scan. For ultrafiltration membranes, the
volume
average diameter of the pores (mean pore size) is typically less than 0.1
micrometers
(microns), and can be in the range of from 0.001 to 0.70 micrometers, e.g.,
from 0.30 to
0.70 micrometers. For microfiltration membranes, the mean pore size is
typically greater
than 0.1 micrometers (microns),
[0066] In the course of determining the volume average pore diameter of the
above
procedure, the maximum pore radius detected is sometimes noted. This is taken
from
the low pressure range scan, if run; otherwise it is taken from the high
pressure range
scan. The maximum pore diameter is twice the maximum pore radius. Inasmuch as
some
production or treatment steps, e.g., coating processes, printing processes,
impregnation
processes and/or bonding processes, can result in the filling of at least some
of the pores
of the microporous material, and since some of these processes irreversibly
compress
the microporous material, the parameters in respect of porosity, volume
average diameter
of the pores, and maximum pore diameter are determined for the microporous
material
prior to the application of one or more of such production or treatment steps.
[0067] To prepare the microporous materials of the present invention, filler,
polymer
powder (polyolefin polymer), processing plasticizer, and minor amounts of
lubricant and
19
CA 2929446 2017-10-03
antioxidant are mixed until a substantially uniform mixture is obtained. The
weight ratio of
filler to polymer powder employed in forming the mixture is essentially the
same as that
of the microporous material substrate to be produced. The mixture, together
with
additional processing plasticizer, is introduced to the heated barrel of a
screw extruder.
Attached to the extruder is a die, such as a sheeting die, to form the desired
end shape.
[0068] In an exemplary manufacturing process, when the material is formed into
a sheet
or film, a continuous sheet or film formed by a die is forwarded to a pair of
heated calender
rolls acting cooperatively to form continuous sheet of lesser thickness than
the continuous
sheet exiting from the die. The final thickness may depend on the desired end-
use
application. The microporous material may have a thickness ranging from 0.7 to
18 mil
(17.8 to 457.2 microns), such as 0.7 to 15 mil (17.8 to 381 microns), or 1 to
10 mil (25.4
to 254 microns), or 5 to 10 mil (127 to 254 microns), and demonstrates a
bubble point of
to 80 psi based on ethanol.
[0069] Optionally, the sheet exiting the calendar rolls may then be stretched
in at least
one stretching direction above the elastic limit, depending on whether the
membrane
being formed is to be for microfiltration or ultrafiltration. Stretching may
alternatively take
place during or immediately after exiting from the sheeting die or during
calendaring, or
multiple times, but it is typically done prior to extraction. Stretched
microporous material
substrate may be produced by stretching the intermediate product in at least
one
stretching direction above the elastic limit. Usually the stretch ratio is at
least about 1.5.
In many cases the stretch ratio is at least about 1.7. Preferably it is at
least about 2.
Frequently the stretch ratio is in the range of from about 1.5 to about 15.
Often the stretch
ratio is in the range of from about 1.7 to about 10. Usually the stretch ratio
is in the range
of from about 2 to about 6. However, care should be taken that stretching does
not result
in pore sizes too large for ultrafiltration.
[0070] The temperatures at which stretching is accomplished may vary widely.
Stretching
may be accomplished at about ambient room temperature, but usually elevated
CA 2929446 2017-10-03
temperatures are employed. The intermediate product may be heated by any of a
wide
variety of techniques prior to, during, and/or after stretching. Examples of
these
techniques include radiative heating such as that provided by electrically
heated or gas
fired infrared heaters, convective heating such as that provided by
recirculating hot air,
and conductive heating such as that provided by contact with heated rolls. The
temperatures which are measured for temperature control purposes may vary
according
to the apparatus used and personal preference. For example, temperature-
measuring
devices may be placed to ascertain the temperatures of the surfaces of
infrared heaters,
the interiors of infrared heaters, the air temperatures of points between the
infrared
heaters and the intermediate product, the temperatures of circulating hot air
at points
within the apparatus, the temperature of hot air entering or leaving the
apparatus, the
temperatures of the surfaces of rolls used in the stretching process, the
temperature of
heat transfer fluid entering or leaving such rolls, or film surface
temperatures. In general,
the temperature or temperatures are controlled such that the intermediate
product is
stretched about evenly so that the variations, if any, in film thickness of
the stretched
microporous material are within acceptable limits and so that the amount of
stretched
microporous material outside of those limits is acceptably low. It will be
apparent that the
temperatures used for control purposes may or may not be close to those of the
intermediate product itself since they depend upon the nature of the apparatus
used, the
locations of the temperature-measuring devices, and the identities of the
substances or
objects whose temperatures are being measured.
100711 In view of the locations of the heating devices and the line speeds
usually
employed during stretching, gradients of varying temperatures may or may not
be present
through the thickness of the intermediate product. Also because of such line
speeds, it is
impracticable to measure these temperature gradients. The presence of
gradients of
varying temperatures, when they occur, makes it unreasonable to refer to a
singular film
temperature. Accordingly, film surface temperatures, which can be measured,
are best
used for characterizing the thermal condition of the intermediate product.
21
CA 2929446 2017-10-03
[0072] These are ordinarily about the same across the width of the
intermediate product
during stretching although they may be intentionally varied, as for example,
to
compensate for intermediate product having a wedge-shaped cross-section across
the
sheet. Film surface temperatures along the length of the sheet may be about
the same
or they may be different during stretching.
[0073] The film surface temperatures at which stretching is accomplished may
vary
widely, but in general they are such that the intermediate product is
stretched about
evenly, as explained above. In most cases, the film surface temperatures
during
stretching are in the range of from about 20 C to about 220 C. Often such
temperatures
are in the range of from about 50 C to about 200 C. From about 75 C to about
180 C is
preferred.
[0074] Stretching may be accomplished in a single step or a plurality of steps
as desired.
For example, when the intermediate product is to be stretched in a single
direction
(uniaxial stretching), the stretching may be accomplished by a single
stretching step or a
sequence of stretching steps until the desired final stretch ratio is
attained. Similarly, when
the intermediate product is to be stretched in two directions (biaxial
stretching), the
stretching can be conducted by a single biaxial stretching step or a sequence
of biaxial
stretching steps until the desired final stretch ratios are attained. Biaxial
stretching may
also be accomplished by a sequence of one of more uniaxial stretching steps in
one
direction and one or more uniaxial stretching steps in another direction.
Biaxial stretching
steps where the intermediate product is stretched simultaneously in two
directions and
uniaxial stretching steps may be conducted in sequence in any order.
Stretching in more
than two directions is within contemplation. It may be seen that the various
permutationes
of steps are quite numerous. Other steps, such as cooling, heating, sintering,
annealing,
reeling, unreeling, and the like, may optionally be included in the overall
process as
desired.
22
CA 2929446 2017-10-03
[0075] Various types of stretching apparatus are well known and may be used to
accomplish stretching of the intermediate product. Uniaxial stretching is
usually
accomplished by stretching between two rollers wherein the second or
downstream roller
rotates at a greater peripheral speed than the first or upstream roller.
Uniaxial stretching
can also be accomplished on a standard tentering machine. Biaxial stretching
may be
accomplished by simultaneously stretching in two different directions on a
tentering
machine. More commonly, however, biaxial stretching is accomplished by first
uniaxially
stretching between two differentially rotating rollers as described above,
followed by either
uniaxially stretching in a different direction using a tenter machine or by
biaxially
stretching using a tenter machine. The most common type of biaxial stretching
is where
the two stretching directions are approximately at right angles to each other.
In most
cases where continuous sheet is being stretched, one stretching direction is
at least
approximately parallel to the long axis of the sheet (machine direction) and
the other
stretching direction is at least approximately perpendicular to the machine
direction and
is in the plane of the sheet (transverse direction).
[0076] Stretching the sheets prior to extraction of the processing plasticizer
allows for
larger pore sizes than in microporous materials conventionally processed, thus
making
the microporous material particularly suitable for use in the microfiltration
membranes of
the present invention. It is also believed that stretching of the sheets prior
to extraction
of the processing plasticizer minimizes thermal shrinkage after processing.
[0077] The product passes to a first extraction zone where the processing
plasticizer is
substantially removed by extraction with an organic liquid which is a good
solvent for the
processing plasticizer, a poor solvent for the organic polymer, and more
volatile than the
processing plasticizer. Usually, but not necessarily, both the processing
plasticizer and
the organic extraction liquid are substantially immiscible with water. The
product then
passes to a second extraction zone where the residual organic extraction
liquid is
substantially removed by steam and/or water. The product is then passed
through a
forced air dryer for substantial removal of residual water and remaining
residual organic
23
CA 2929446 2017-10-03
extraction liquid. From the dryer the microporous material may be passed to a
take-up
roll, when it is in the form of a sheet.
100781 The processing plasticizer has little solvating effect on the
thermoplastic organic
polymer at 60 C, only a moderate solvating effect at elevated temperatures on
the order
of about 100 C, and a significant solvating effect at elevated temperatures on
the order
of about 200 C. It is a liquid at room temperature and usually it is
processing oil such as
paraffinic oil, naphthenic oil, or aromatic oil. Suitable processing oils
include those
meeting the requirements of ASTM D 2226-82, Types 103 and 104. Those oils
which
have a pour point of less than 22 C, or less than 10 C, according to ASTM D 97-
66
(reapproved 1978) are used most often. Examples of suitable oils include
Shellflex 412
and Shel!flex 371 oil (Shell Oil Co.) which are solvent refined and
hydrotreated oils
derived from naphthenic crude. It is expected that other materials, including
the phthalate
ester plasticizers such as dibutyl phthalate, bis(2-ethylhexyl) phthalate,
diisodecyl
phthalate, dicyclohexyl phthalate, butyl benzyl phthalate, and ditridecyl
phthalate will
function satisfactorily as processing plasticizers.
[0079] There are many organic extraction liquids that can be used. Examples of
suitable
organic extraction liquids include 1,1,2-trichloroethylene, perchloroethylene,
1,2-
dichloroethane. 1,1,1-trichloroethane, 1,1,2-trichloroethane, methylene
chloride,
chloroform, isopropyl alcohol, diethyl ether and acetone.
[0080] In the above described process for producing microporous material
substrate,
extrusion and calendering are facilitated when the filler carries much of the
processing
plasticizer. The capacity of the filler particles to absorb and hold the
processing plasticizer
is a function of the surface area of the filler. Therefore the filler
typically has a high surface
area as discussed above. Inasmuch as it is desirable to essentially retain the
filler in the
microporous material substrate, the filler should be substantially insoluble
in the
processing plasticizer and substantially insoluble in the organic extraction
liquid when
microporous material substrate is produced by the above process.
24
CA 2929446 2017-10-03
[0081] The residual processing plasticizer content is usually less than 15
percent by
weight of the resulting microporous material and this may be reduced even
further to
levels such as less than 5 percent by weight, by additional extractions using
the same or
a different organic extraction liquid.
[0082] The resulting microporous materials may be further processed depending
on the
desired application. In the present invention, a hydrophilic coating may be
applied to the
surface of the microporous material to adjust the surface energy of the
material. Though
not intending to be bound by theory, it is believed that components of the
coating interact
with the silica particles in the filler of the microporous material and adjust
the surface
energy, affecting wettability. Application of the coating may occur before,
during, or after
the stretching step described above, but is usually done simultaneously with
stretching to
maximize coating coverage on additional surface area created during the
stretching
process.
[0083] Hydrophilic coatings may comprise one or more of a polyoxazoline,
including
polyalkyloxazolines such as poly(2-ethyl-2-oxazoline), poly(2-methyl-2-
oxazoline), and
poly(2-methyliethy1-2-oxazoline); triblock copolymers based on poly(ethylene
glycol)-
poly(propylene glycol)-poly(ethylene glycol); polyethyleneimine; polyamide;
oxidized
polyethylene or its derivatives;
polyethyleneoxide; polyethyleneglycol;
polyvinylpyrrolidone; polyacrylic acid; polymethacrylic acid; polyethylene
glycol
derivatives; polypropylene oxide or its derivatives; a copolymer of
poly(ethylene glycol)
and polyethyleneoxide; polyvinyl alcohol; ethylene vinyl acetate; cellulose or
its
derivatives; polyimide; hydrogels such as collagen, polypeptides, guar and
pectin;
polypeptoids; poly(meth)acrylates such as poly(2-hydroxyethylmethacrylate);
poly(meth)acrylamide; polysaccharides; zwitterionic
polymers such as
poly(phosphorylcholine) derivatives, polysulfobetaines, and polycarbobetaines;
polyampholytes, and polyethylenimine. The hydrophilic coating preferably
comprises at
least one polymer having tertiary amine functional groups, such as poly(2-
ethyl-2-
oxazoline).
CA 2929446 2017-10-03
[0084] In certain embodiments, the coating compositions used in the methods of
the
present invention comprise one or more suitable surfactants to reduce surface
tension.
Surfactants include materials otherwise known as wetting agents, anti-foaming
agents,
emulsifiers, dispersing agents, leveling agents etc. Surfactants can be
anionic, cationic
and nonionic, and many surfactants of each type are available commercially.
Some
coating compositions include at least a wetting agent. Still other coating
compositions
may have additional surfactants to perform additional effects.
[0085] Other suitable surfactants may also be selected. The amount and number
of
surfactants added to the coating compositions will depend on the particular
surfactant(s)
selected, but should be limited to the minimum amount of surfactant that is
necessary to
achieve wetting of the substrate while not compromising the performance of the
dried
coating. In certain embodiments, the coating compositions comprise 0.01 up to
10 percent
by weight of surfactant, in some embodiments, 0.05 up to 5 percent by weight,
or, in yet
other embodiments, 0.1 up to 3 percent by weight of surfactant. The amount of
surfactant
present in the coating compositions can range between any combination of these
values
inclusive of the recited values. The use of coating compositions in the
membranes of the
present invention allows for their use in separation systems without the need
for pre-
wetting of the membrane such as with isopropanol.
[0086] The microporous material may be adhered to a support layer such as a
fiberglass
layer to provide additional structural integrity, depending on the particular
end use.
Additional optional stretching of the continuous sheet in at least one
stretching direction
may also be done during or immediately after any of the steps upon extrusion
in step (ii).
For example, in the production of an ultrafiltration membrane of the present
invention,
preparation of the microporous material may include stretching of the
continuous sheet
during calendering, to allow for pore sizes in the upper range of
ultrafiltration. Typically,
however, in the production of an ultrafiltration membrane of the present
invention,
preparation of the microporous material does not include stretching steps.
26
CA 2929446 2017-10-03
[0087] The microporous materials prepared as described above are suitable for
use in
the microfiltration and ultrafiltration membranes of the present invention,
capable of
removing particulates from a fluid stream ranging in size from 0.005 to 0.1
microns
(ultrafiltration) and capable of removing particulates from a fluid stream
ranging in size
from 0.05 to 1.5 microns (microfiltration). The membranes also serve to remove
molecular contaminants from a fluid stream by adsorption or by physical
rejection due to
molecular size.
[0088] The membranes of the present invention may be used in a method of
separating
suspended or dissolved materials from a fluid stream, such as removing one or
more
contaminants from a fluid (liquid or gaseous) stream, or concentrating desired
components in a depleted stream. The method comprises contacting the stream
with the
membrane, typically by passing the stream through the membrane. Examples of
contaminants include toxins, such as neurotoxins; heavy metal; hydrocarbons;
oils; dyes;
neurotoxins; pharmaceuticals; and/or pesticides. The fluid stream (such as a
water
stream, but it may be liquid or gas) is usually passed through the membrane at
a flux rate
of at least 1, for example, Ito 10000 gal/(ft2 day) (GFD), at 25 psi, without
the use of pre-
wetting agents. Ultrafiltration membranes may demonstrate a water flux rate of
greater
than 100 GFD, preferably greater than 150 GFD, and a molecular weight cut-off
of 100 to
500,000, while microfiltration membranes may demonstrate a water flux rate of
greater
than 300 GFD, preferably greater than 500 GFD. The membranes of the present
invention demonstrate a Gurley number of less than 2000 seconds.
[0089] Coated membranes comprising microporous material coated with
hydrophilic
coating compositions demonstrate a water contact angle less than 70 , often
less than
30 , more often less than 10 ,
EXAMPLES
In Part I of the following examples, the materials and methods used to prepare
the microporous sheet materials are described. In Part II, the methods and
conditions
27
CA 2929446 2017-10-03
used to stretch the microporous sheet materials are described. Part III
describes the
coating formulations and methods used to coat the microporous sheet materials.
The
physical properties of the Examples (coated) and Comparative Examples
(uncoated)
are presented in Part IV.
Part I ¨ Preparation of Microporous Sheet Materials
The dry ingredients of Example 1 were separately weighed into a FM-130D
Littleford plough blade mixer with one high intensity chopper style mixing
blade in the
order and amounts specified in Table 1. The dry ingredients were premixed for
15
seconds using the plough blades only. The process oil was then pumped in via a
double diaphragm pump through a spray nozzle at the top of the mixer over a
period of
about 45-60 seconds, with only the plough blades running. The high intensity
chopper
blade was then turned on, along with the plough blades, and mixing continued
for 30
seconds. The mixer was shut off and the internal sides of the mixer were
scraped down
to ensure all ingredients were evenly mixed. The mixer was turned back on with
both
the high intensity chopper and plough blades in use, and the mixing continued
for an
additional 30 seconds. The resulting mixture of dry ingredients was extruded
and
calendered into sheet form as follows. A gravimetric loss in weight feed
system (K-
tron model # K2MLT35D5) was used to feed the mix into a 27 millimeter twin
screw
extruder (Leistritz Micro-27 mm). The extruder barrel was comprised of eight
temperature zones and a heated adaptor to the sheet die. The extrusion mixture
feed
port was located just prior to the first temperature zone. An atmospheric vent
was
located in the third temperature zone. A vacuum vent was located in the
seventh
temperature zone.
The mixture was fed into the extruder at a rate of 90 grams/minute. Additional
processing oil also was injected at the first temperature zone, as required,
to achieve
the desired total oil content in the extruded sheet.
Examples 2 and 3 were prepared, extruded and calendered into final sheet form
using an extrusion system that was production sized. The version of the system
is
28
CA 2929446 2017-10-03
similar to the equipment and procedures described above for Example 1 except
for the
size of the equipment. The oil contained in the extruded sheet (extrudate)
being
discharged from the extruder is referenced herein as the extrudate oil weight
fraction,
which is based on the total weight of the sample. The arithmetic average of
the
extrudate oil weight fraction for all of the samples was 0.57.Residual oil in
each of
Examples 1, 2 and 3 was removed using a 1,1,2-trichloroethylene oil extraction
process.
Table 1: Formulation of the microporous membrane sheet
Example Example
Ingredient 1 2 Example 3
GUR 41501 1.44 144 136
FINA 12882 1.44 144 136
Hi-Si1C) 1353 5.00 500 500
SYNPRO 15804 0.05 4 4
IRGANOX 62156 0.03 4 4
TUFFLO 60566 8.39 835 835
lAn Ultra High Molecular Weight Polyethylene (UHMWPE), obtained commercially
from Ticona Corp and
reported to have a molecular weight of about 9.2 million grams per mole.
2A High Density Polyethylene (HDPE), obtained commercially from Total
Petrochemicals.
3A precipitated silica available from PPG Industries, Inc.
4Reported to be a calcium-zinc stearate lubricant, obtained commercially from
Ferro
5A processing and thermal stabilizing blend of antioxidants, obtained
commercially from BASF.
6A process oil, obtained commercially from PPC Lubricants.
Part ll ¨ Preparation of Stretched Sheet Microporous Materials
Stretching was conducted by Parkinson Technologies, Inc. using the Marshall
and Williams Biaxial Orientation Plastic Processing System. The Machine
Direction
Oriented (MDO) stretching of the material from Part II was accomplished by
heating the
microporous sheet of Examples 2 and 3 and stretching it in the machine
direction over a
series of rollers maintained at the temperatures listed in Table 2.
Transverse Direction Orientation (TDO) stretching was conducted after MDO
stretching by heating the resultant sheets according to the temperature
conditions listed
in Table 2, and stretching in the transverse (or cross) direction on a tenter
frame,
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,
consisting of two horizontal chain tracks, on which clip and chain assemblies
held the
material in place. The combination of MDO and TDO conditions provided biaxial
stretching of the material.
Table 2: Microporous sheet stretching conditions:
Example 4 5 6
Microporous sheet Ex. 2 Ex. 3 Ex. 3
material
Stretch roll ( C) 132 132 132
Anneal roll ( C) 141 141 141
Cooling ( C) 25 25 25
MOO Slow draw 10.4 10.4 10.4
speed, FPM
Fast Roll 35 35 40
Speed, FPM
Stretch ratio 2 3 NA
Preheat ( C) 132 132 NA
TDO
Stretching ( C) 132 132 NA
Anneal ( C) 141 141 NA
Part Ill ¨ Hydrophilic coating formulations:
a) Preparation of hydrophilic coatings:
The hydrophilic coating Examples A, B and C were prepared according to the
ingredients and quantities listed in Table 3. The first ingredient of the
corresponding
Example was dissolved in the specified quantity of deionized water with
vigorous
stirring. Upon complete dissolution, PluronicTM 17R2 was added, followed by
butoxyethanol. The coating solutions were stirred gently for a minimum of 30
minutes
before proceeding.
CA 2929446 2017-10-03
Table 3: Hydrophilic coating formulation
Example A
Polyethyleneoxazolinel (g) 7.5
Chitosan2 (g) 10
PVP-K903 (g) 5
Deionized Water (g) 457 480 480
PLURONIC 17R24 (g) 5 5 5
Butoxyethanol (g) 30 5 10
1Molecular weight 50,000, available from SigmaAldrich.
2Chitosan from shrimp shells, practial grade, available from SigmaAldrich.
3Polyvinylpyrrolidone with average Mw 360,000, available from SigmaAldrich
4Block copolymer surfactant, available from BASF Corporation.
b) Procedure for coating microporous materials:
The microporous materials described in the previous Examples were cut into
sheets 12 inches square. The hydrophilic coating compositions were applied by
dipping
the microporous materials of the previous examples into a Pyrex dish
containing sufficient
hydrophilic coating to completely submerge the sheet. The sheet was submerged
in the
hydrophilic coating for about 5 minutes. The sheet was then removed from the
solution
and excess coating solution was allowed to drip off. The coated microporous
material was
then clamped in an aluminum frame which was fitted with a gasket to prevent
the film
from shrinking during drying. The frame with film then was dried in an oven at
95 C for 15
minutes. The stretched microporous material of Example 4 was coated with each
of the
coating solutions of Examples A, B and C in this manner. The stretched
microporous
materials of Examples 5 and 6 and the unstretched microporous material of
Example 1
were coated with the coating formulation of Example A.
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Part IV ¨ Properties:
The stretched microporous materials of Examples 4, 5 and 6 and the unstretched
microporous material of Example 1 were tested for properties and water
permeability
with and without a hydrophilic coating applied.
Table 6 demonstrates the differences between the microporous material of
Example
4 with and without a hydrophilic coating composition. Tables 7 and 8
illustrate the water
permeability of various microporous materials with and without a hydrophilic
coating
composition. Properties were determined using the methods described below:
a) Thickness was determined by using an Ono Sokki thickness gauge EG-225. The
thickness reported is the average of 9 measurements.
b) Porosity was determined using a Gurley Precision Densometer, model 4340,
manufactured by GPI Gurley Precision Instruments of Troy, New York.
c) The maximum elongation or tensile energy to break the samples was
determined
following the procedure of ASTM D-882-02. Samples were tested oriented such
that the stress was applied in the machine direction ("MD") and the transverse
direction ("TD") as described in Part II.
d) Contact angle was measured on a VCA 2500XE video contact angle system,
available from AST Products, Inc. using 1 microliter of ultrapure water.
e) Water flux testing was carried out on a Sepa TM CF II cross flow test cell
apparatus provided by Sterlitech Corp, Kent WA at 20 psi and 25 C, with an
effective membrane area of 140cm2.
0 Water intrusion pressure was determined on a circular sample with an area of
90cm2. The sample was sandwiched in a dead end filter provided by Sterlitech
Corp, Kent WA. 100mL of water was placed on top of the sample. Pressure was
applied in 5 psi increments, holding 15 minutes between pressure increments.
The test pressure was recorded when the first drop water was visible passing
through the sample.
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g) Pore volume: The pore volume, expressed as percent by volume, is determined
according to the following equation
Porosity = 100(1 ¨ ¨d2)
Where, di is the density of the sample, which is determined from the same
weight and
the sample dimensions, and d2 is the density of the solid portion of the
sample, which is
determined from the sample weight and the volume of the solid portion of the
sample.
The volume of the solid portion of the same is determined using a
Stereopycnometer
(Quantachrome Corp.) in accordance with the accompanying operating manual.
Table 6: Physical properties of uncoated and hydrophilically coated
microporous
material
Example CE-4 4A
Microporous Material Example 4 Example 4
Hydrophilic coating None Example A
Thickness (micron) 110 115
Gurley (sec) 36 35
Contact angle >1000 <20
MD Maximum elongation 15 14
MD Maximum tension 3550 2970
TD Maximum elongation 63 85
TD Maximum tension 279 175
Table 7: Water permeability of uncoated microporous materials:
Comparative
CE-1 CE-4 CE-5 CE-6
Example
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Microporous
Ex. 1 Ex. 4 Ex. 5 Ex. 6
Material
Water flux @ 20ps1
<1* <1* <1* <1*
(GFD)
Water intrusion
>60 >40 >40 >45
pressure (psi)
Pore volume (%) >60 >80 >80 >80
* No detectable volume observed after 30 minutes @ 20psi.
Table 8: Water permeability of microporous materials with hydrophilic coating:
Example 1A 4A 4B 40 5A 6A
Microporous
Ex. 1 Ex. 4 Ex. 4 Ex. 4 Ex. 5 Ex. 6
Material
Hydrophilic
Ex. A Ex. A Ex. B Ex. C Ex. A Ex. A
Coating
Water flux @
283 884 990 1060 1308 707
20psi (GFD)
Water intrusion
<5 <5 <5 <5 <5 <5
pressure (psi)
Water wetable
<5 <5 <5 <5 <5 <5
time (sec)
Pore Volume
>60 >80 >80 >80 >80 >80
(%)
100901 Whereas particular embodiments of this invention have been described
above for
purposes of illustration, it will be evident to those skilled in the art that
numerous variations
of the details of the present invention may be made without departing from the
scope of
the invention as defined in the appended claims.
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