Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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REINFORCED NETWORKED POLYMERICLAY ALLOY COMPOSITE
FIELD OF THE INVENTION
The present invention relates to absorbent materials. More specifically, the
invention
relates to a reinforced networked polymer/clay alloy composite useful, for
example, in
containment applications such as landfill liners or covers, reservoir liners,
underground
storage tank liners, secondary containment liners, and man-made bodies of
water, or
personal care absorbent articles, including diapers, training pants, feminine
hygiene
products such as sanitary napkins, incontinence devices and the like.
BACKGROUND DISCUSSION
There are a number of commercial applications for absorbent materials,
including,
without limitation, in containment applications as landfill liners or covers,
reservoir liners,
underground storage tank liners, secondary containment liners, and man-made
bodies of
water, or personal care absorbent articles, including diapers, training pants,
feminine
hygiene products such as sanitary napkins, incontinence devices and the like.
While the
applications are diverse, there is need for a material having improved water
absorbency
and/or fluid barrier properties.
2o For example, in waste containment applications, hydraulic barriers can
reduce the
escape or leakage of harmful leachates into surface and ground waters. In man-
made
bodies of water, a hydraulic barrier acts to contain the water within an
enclosure or defined
impoundment area.
In one type of liner, hydraulic barriers are often formed from bentonite.
Specifically,
bentonite is admixed with the soil forming the water-holding area. Upon
contact of the
bentonite with water, the bentonite swells and thereby fills up the voids
found in the soil.
However, the water absorption capacity of bentonite alone may not be
sufficient for the
containment of some water-soluble wastes.
US 3,949,560 (Clem, April 13, 1976) is directed to a soil sealant composition
dry
mixed with soil. The soil sealant composition consists of bentonite, a water-
soluble
dispersing agent and a pre-formed water-soluble polymer. The water-soluble
dispersing
agent is a phosphoric acid salt, sulfate of ROS03X (R is a C8-C32 hydrocarbon,
X is an
alkaline metal or ammonium) or a leonardite salt. The pre-formed water-soluble
polymer is
polyacrylic acid, water-soluble salts of polyacrylic acid, hydrolyzed poly-
acrylonitrile,
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polyvinyl acetate, polyvinyl alcohol, copolymers of the foregoing or a
copolymer of acrylic
acid and malefic anhydride. A water containing enclosure is formed from the
soil/soil sealant
mixture and contacted with water to hydrate the bentonite. The resulting
hydrated enclosure
is used for containing water contaminated with industrial waste. No
reinforcing agent is
used with the soil/soil sealant mixture.
US 4,048,373 (Clem, September 13, 1977), US 4,103,499 (Clem, August 1, 1978)
and US 4,139,588 (Clem, February 13, 1979) all describe a water barrier panel
or moisture
impervious panel comprised of a soil sealant sandwiched between two paperboard
sheets.
More particularly, the panel is formed of a corrugated paperboard carrier or
form including a
1o pair of spaced paperboard facing sheets interconnected by a paper
corrugated strip to form
a plurality of voids. The voids are filled with the soil sealant composition
described in US
3,949,560 and the edges of the panel may be sealed with wax, tape or water-
soluble gum.
When contacted with water, moisture passes through the paperboard sheets to
the soil
sealant composition, where the bentonite swells.
15 More recently, so-called geosynthetic clay liners ("GCL") have become
relatively
widely accepted for use as hydraulic barriers. A GCL has a layer of bentonite
supported by
a geotextile or a geomembrane material, mechanically held together by
needling, stitching
or chemical adhesives.
An example of a GCL prepared with a chemical adhesive is provided in US
20 4,467,015 (Clem, August 21, 1984). This patent describes a waterproofing
structure or
water impervious sheet material comprised of layers of flexible carrier sheets
coated with a
water swellable composition. The water swellable composition is clay or a dry
granular
mixture of clay, a pre-formed water-soluble polymer, such as polyacrylic acid,
and a water-
soluble salt. The composition is secured by using an adhesive, whether water-
soluble or -
25 insoluble or a solvent-soluble or -insoluble adhesive. A disadvantage of
this type of
laminate is that clays in the GCL may still migrate away from the GCL with the
leachate
percolating through the liner, albeit very slowly.
Similarly, US 4,810,573 (Harriet, March 7, 1989) describes a laminated
composite
article with a clay composition adhered to a water-impermeable sheet. The clay
composition
30 is an intimate mixture of water swellable clay and a pre-formed elastomer,
such as
polypropylene and/or polybutene. The intimate clay/elastomer mixture is
produced by
blending clay with pre-formed elastomers in a sigma blender to masticate the
elastomer.
The clay composition is adhered to the water-impermeable sheet by rolling to
form a
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laminate. US 5,580,630 (Byrd, December 3, 1996) describes a multi-layer
article using the
same clay composition as Harriet.
As indicated above, rather than using a chemical adhesive, the layers of the
GCL
may be mechanically held together by other means such as stitching and needle
punching.
For instance, US 4,565,468 (Crawford, January 21, 1986) described a moisture
impermeable barrier comprised of two fabric layers quilted together. A top
sheet member is
positioned over a base sheet member having a layer of bentonite resting on its
upper
surface. The top sheet member is secured to the base sheet member by stitches
extending
therebetween. The stitching forms either quilted compartments or elongated
corrugated
compartments containing the bentonite therein.
DE 3704503 A1 (Heerten et al.) discloses an article having two fabric layers
sandwiching a bentonite clay layer, wherein the two fabric layers are needle
punched
together. US 5,174,231 (White, December 29, 1992) describes a multi-layer
article
including an intermediate layer of a water-swellable colloidal clay sandwiched
between two
layers of flexible material or fabric sheet. The two layers are structurally
interconnected
through the intermediate clay layer, such as by needle punching, sewing,
quilting, or needle
looming, to interconnect fibers of one fabric layer to the other fabric layer
at spaced
locations over essentially the entire surface areas of both layers.
Thus, in these GCLs, the clay particles are either adhered onto the geotextile
or
2o geomembrane or are physically confined by opposing layers of geotextile or
geomembrane.
The opposing layers of geotextile or geomembranes are mechanically held
together by
means such as sewing, quilting and needle punching, which limits the movement
of clay
particles therebetween. However, the clay particles in granular bentonite used
in these
applications are typically a couple of micrometers or less in diameter.
Further, the void
spaces in the geotextiles or geomembranes and the spacing of the stitching or
needle
punching tend to be greater than the size of the clay articles. Thus, it is
still possible for the
clay particles in the GCL to migrate out of the liner, particularly when
placed under a
hydraulic pressure gradient, albeit slowly.
It is commonly known that bentonite swells well in fresh water but poorly in,
water
containing salts and/or metals, such as saltwater, seawater, acid mine
drainage, and the
like. Thus, while GCL's are effective barriers for fresh water, they are
ineffective barriers to
water with high salt and dissolved metals concentrations.
Another problem with GCL's is that the bentonite is typically dry and,
therefore, until
the bentonite swells, waste water can flow through the GCL. Accordingly, GCL's
must first
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be pre-hydrated after installation. This pre-hydration step can take up to 48
hours, for
example.
Yet another problem with GCL's is their weight. Typically, a GCL weighs more
than
kg/m2. Because of its weight, transportation and installation costs are
significant.
Accordingly, there is a need for an absorbent material for containment
applications,
especially environmental containment applications, which is salt water and
contaminant
resistant. Also, there is a need for a barrier liner that is lighter than GCL,
but having
substantially comparable or improved barrier properties versus GCL. Moreover,
there is a
need for an absorbent material having intimately integrated components that do
not disperse
o and/or migrate from the product, particularly when exposed to or immersed in
water, and
can effectively absorb water containing salt and/or metals.
SUMMARY OF THE INVENTION
According to the invention, there is provided a process for producing a
reinforced
networked polymer/clay alloy composite, comprising the steps of: (a) preparing
a
monomer/clay mixture by mixing at least a monomer, clay particles, a cross-
linking agent,
and a mixing fluid in a vessel; (b) contacting the monomer/clay mixture and a
reinforcing
agent; (c) exposing the monomer/clay mixture to a polymerization initiator
means; and (d)
polymerizing the monomer/clay mixture in the presence of the reinforcing agent
so that a
reinforced networked polymer/clay alloy composite is formed.
According to the invention, there is also provided a product produced by the
process
described above.
According to the invention, there is further provided a reinforced networked
polymer/clay alloy composite comprising a networked polymer/clay alloy,
wherein the alloy is
a chemically integrated composition of polymer and clay, and the alloy is
intimately
integrated with a reinforcing agent so that, when the composite is immersed in
deionized
water, at a temperature in a range of from about 20°C to about
30°C, the alloy swells with
substantially no clay separating from the composite.
According to the invention, there is provided the method of using the
reinforced
networked polymer/clay alloy composite as an absorbent material for a personal
care
product or as a fluid barrier in a confining stress range of from about 0 kPa
to about 10000
kPa, wherein, when placed under a zero confining stress, the barrier has a
deionized water
flux less than about 1 x 10$ m3/m2/s.
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BRIEF DESCRIPTION OF THE DRAWINGS
The reinforced networked polymer/clay alloy composite and the process for
producing the reinforced networked polymer/clay alloy composite of the present
invention
will be better understood by referring to the following detailed description
of preferred
embodiments and the drawings referenced therein, in which:
Fig. 1 is a schematic of one embodiment of an apparatus for use in producing
one
embodiment of the reinforced networked polymer/clay alloy composite;
Fig. 2 is a schematic of another embodiment of an apparatus for use in
producing
one embodiment of the reinforced networked polymer/clay alloy composite;
1o Fig. 3 is a schematic of a further embodiment of an apparatus for use in
producing
one embodiment of the reinforced networked polymer/clay alloy composite;
Fig. 4 is a graphical representation of the results of the flux test in
Example 6 for
3.5% (wt.) NaCI solution and the minimum flux for conventional GCL under
similar salt water
conditions indicated by the dotted line;
Fig. 5 is a graphical representation of the results of the flux test in
Example 6 for
artificial seawater and the minimum flux for conventional GCL under similar
salt water
conditions indicated by the dotted line;
Fig. 6 is a scanning electron microscope (SEM) micrograph of a top plan
perspective
of the reinforcing agent used in Example 7, at a magnification of 140X;
Fig. 7 is an SEM micrograph of a hydrated polymer used for comparison in
Example
7, at a magnification of 7000X;
Fig. 8 is an SEM micrograph of a cross-section of a reinforced networked
polymer/clay alloy composite produced in Example 7, at a magnification of 50X;
Fig. 9 is an SEM micrograph of a cross-section of a reinforced networked
polymer/clay alloy composite produced in Example 7, at a magnification of
270X;
Fig. 10 is an SEM micrograph of a cross-section of a water-swelled reinforced
networked polymer/clay alloy composite produced in Example 7, at a
magnification of 500X;
Fig. 11 is an SEM micrograph of a cross-section of a water-swelled reinforced
networked polymer/clay alloy composite produced in Example 7, at a
magnification of
4500X;
Fig. 12 is an SEM micrograph of a cross-section of a water-swelled polymer,
without
clay, at a magnification of 650X;
Figs. 13A and 13B are drawings based on photographs taken of Sample A in
Example 8 prior to immersion (13A) and after 3 hours immersion in deionized
water (13B);
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Figs. 14A and 14B are drawings based on photographs taken of Sample D in
Example 8 prior to immersion (14A) and after 3 hours immersion in deionized
water (14B);
and
Figs. 15A and 15B are drawings based on photographs taken of Sample G in
Example 8 prior to immersion (15A) and after 3 hours immersion in deionized
water (15B).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Definitions
"Monomer" is an organic molecule that can combine with a number of the same or
different molecules to form a large molecule having repeating monomeric units,
wherein the
repeating monomeric units have a similar chemical architecture and atom
composition as
the monomeric units.
"Polymer" is a large molecule built from the same or different repeating
monomeric
units and typically has a molecular weight in a range from about 10,000 to
about
20,000,000. Polymer, as used herein, also includes any polymer made from two
or more
different repeating units, such as copolymers (i.e., comprising two different
monomeric
units), terpolymers (i.e., comprising three different monomeric units),
tetrapolymers (i.e.,
comprising four different monomeric units) and so on. Moreover, the repeating
monomeric
units can alternate in a sequential pattern (e.g., A-B-A-B), block pattern
(e.g., A-A-
2o B-B), random pattern (A-B-B-A-B-A) or combinations thereof.
"Oligomer" is also built from the same or different repeating monomer units
but is a
smaller molecule than a polymer and typically has a molecular weight in a
range of from
about 200 up to about 9,000.
"Polymerization Initiator Means" is a chemical substance, gamma ray
irradiation, X-
ray irradiation, irradiation by high energy sub-atomic particles, each type of
radiation having
a wavelength less than about 10 nm, (collectively, high energy irradiation)
and combinations
thereof that can increase the reactivity of a monomer so that a polymerization
or
oligomerization chain reaction between monomers is initiated and a polymer or
oligomer is
formed. At the appropriate temperature, certain chemical substances become
either an
ionic or free radical species that can react with a monomer alone to produce
an ionic or free
radical monomeric species, which can, in turn, react with another monomer,
thereby
initiating a polymerization reaction. Also, high energy irradiation can be
used to produce an
ionic or free radical monomeric species from a monomer and/or a chemical
substance other
than a monomer to initiate a polymerization reaction.
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"Cross-linking Agent" is a chemical substance, photons produced from a
radiation
source and combinations thereof that assist in forming a bridging moiety
between two or
more backbone structures formed by multiple monomeric units (e.g., oligomeric
or polymeric
units). Thus, a cross-linking agent can bridge oligomeric or polymeric species
either during
or after their formation.
"Networked Polymer" is a very large polymer molecule formed by cross-linking
multiple oligomers and/or polymers to form an interconnected polymeric
network. A
networked polymer can have cross-linking moieties between oligomers and/or
polymers,
where the moieties are formed from either the cross-linking agent itself,
branches attached
to the backbone of each oligomer and/or polymer or combinations thereof.
"Networked Polymer/Clay Alloy" ("NPC Alloy") is a chemically integrated
composition
of polymer and clay. Clay particles form a unique chemical association with
the networked
polymer as it is formed. The chemical association may be, for example, without
limitation,
through hydrogen bonding, ionic bonding, Van der Waal's/dipole bonding,
affinity bonding,
covalent bonding and combinations thereof.
"Reinforcing Agent" is a material having a sufficiently porous or permeable
structure
so that a networked polymer, and/or an NPC alloy can form around and/or in the
material's
structure, thereby providing additional support and/or strength to the
aforementioned
networked polymer or polymer/clay compositions.
"Reinforced Networked Polymer/Clay Alloy Composite" ("Reinforced NPC Alloy
Composite") is a macroscopic combination comprising a reinforcing agent and an
NPC alloy.
There is an intimate three-dimensional integrated association between
composite
components, as opposed to a simple two-dimensional laminate composite, where
there is
no integration along a third dimension.
General Discussion
A reinforced NPC alloy composite of the present invention is an absorbent
material
useful, for example, without limitation, in containment applications such as
landfill liners or
covers, reservoir liners, underground storage tank liners, secondary
containment liners, and
liners for man-made bodies of water, or personal care absorbent articles,
including diapers,
training pants, feminine hygiene products such as sanitary napkins,
incontinence devices
and the like.
In containment applications, the composite material preferably absorbs water
to form
a barrier, which then has a relatively low permeability to water, oil and
other liquids. In
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personal care articles, the composite material preferably has a high water
absorbency
capacity. As discussed more fully below, the properties of the reinforced NPC
alloy
composite can be adjusted depending on the application.
The reinforced NPC alloy composite of the present invention has improved
resistance to chemical, electromagnetic radiation and biological degradation
in surface and
subsurface conditions. By improved resistance to chemical degradation, we mean
that the
composite has improved resistance to, for example, without limitation, salt
water and
drainage fluids with high heavy metal content and/or acidic pH. By improved
resistance to
electromagnetic degradation, we mean that the composite has an improved
resistance to
ultraviolet (UV) and other potentially detrimental electromagnetic radiation.
By improved
resistance to biological degradation, we mean that the NPC alloy would be more
resistant to
bacterial attack after installation, as compared with a polymer without clay.
For example, the permeability of a liner produced with the reinforced NPC
alloy
composite is not significantly affected by salt water, or other aqueous
solutions with heavy
~5 metals and/or acidic pH. Thus, the composite represents an improvement over
a
conventional GCL liner, which typically loses its effectiveness on exposure to
salt water.
As another example, polyacrylamide is stable at surface and sub-surface
conditions.
However, it is susceptible to chemical and UV degradation. The clay reduces
degradation in
the NPC alloy by protecting the polymer. Also, the NPC alloy is more resistant
to biological
degradation than, for example, polyacrylic acid alone.
When used in barrier applications, the reinforced NPC alloy composite weighs
less
than a conventional GCL per unit area. Also, the reinforced NPC alloy
composite can be
used without pre-hydration, as is often required for conventional GCL's.
A reinforced NPC alloy composite is produced by intimately distributing a
mixture of
monomer, clay particles, a cross-linking agent and a mixing fluid (i.e., an
MCX mixture) in,
on and/or among a reinforcing agent, such as a porous substrate or non-
aggregated fibers.
By "intimately distributing", "intimate distribution" or "intimately
distributed", we mean that an
MCX mixture is distributed throughout the porous substrate or non-aggregated
fibers so that
a substantial portion of the surfaces, voids and interstitial spaces of and/or
between the
3o fibers or substrate is covered and/or occupied with the MCX mixture.
Preferably, the MCX
mixture is intimately distributed substantially through the thickness of the
reinforcing agent.
After the MCX mixture is intimately distributed in, on and/or among the
reinforcing
agent, the MCX mixture is polymerized. The clay particles are chemically
associated with
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the networked polymer as it is formed to produce an NPC alloy. Because of the
intimate
MCX mixture distribution, the NPC alloy is intimately integrated with the
reinforcing agent.
The polymer and clay in the NPC alloy cooperate physically and chemically
(i.e.,
physicochemically) to contribute to the reinforced NPC alloy composite's water
absorbency.
Thus, the composite can swell substantially as an integrated unit while only
negligible
amounts of clay, if any, (i.e., substantially no clay) separate from the
composite when it is
immersed in deionized water at temperatures in a range of from about 1
°C to about 60°C.
MonomerlClay Mixture
The monomer/clay mixture used in making the NPC alloy includes, without
limitation,
a monomer, clay particles, a cross-linking agent and a mixing fluid. For
brevity, we may
refer to the mixture of monomer, clay, cross-linking agent and mixing fluid as
"MCX."
The monomer is at least partially soluble in the mixing fluid. A monomer
soluble in
the mixing fluid may be mixed with other monomers that are soluble or
insoluble in the
mixing fluid. Preferably, at least one water-soluble monomer has the following
general
formula:
R' R3 R O
C C CH C X
n
R2
wherein X is selected from the group consisting of OM, OR4 and NRSR6, M is an
alkali or
alkaline earth metal ion or NH4+, R', R2, R3, R5, R6 and R' are independently
selected from
the group consisting of H, CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CH2CH2CH2CH3, and
CN,
and OR4 is selected from the group consisting of OH, OCH3, OCH2CH3,
OCH2CH2CH3,
OCH(CH3)2, OCH2CH2CH2CH3, OCH2CH20H and (OCH2CH2)mOH, n= 0 to about 10 and m=
1 to about 10.
More preferably, the monomer is selected from the group consisting of acrylic
acid
(where R'=H, R2=H, R3=H, n=0, X=OR4, R4=H), acrylamide (where R'=H, R2=H,
R3=H, n=0,
X=NR5R6, R5=H, R6=H), sodium acrylate (where R'=H, R2=H, R3=H, n=0, X=OM,
M=Na),
potassium acrylate (where R'=H, R2=H, R3=H, n=0, X=OM, M=K), methacrylic acid
(where
R'=H, R2=H, R3=CH3, n=0, X=OR4, R4=H), N-isopropylacrylamide (where R'=H,
R2=H,
R3=H, n=0, X=NR5R6, R5=CH(CH3)2, Rs=H), and combinations thereof.
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An example of a monomer that can be co-polymerized with a monomer of the above
general formula are vinyl esters, such as vinyl acetate. Vinyl acetate is
readily co-
polymerized and may be retained as a vinyl acetate moiety or subsequently
hydrolyzed to
the corresponding vinyl alcohol.
The clay particles may be swelling or non-swelling clays. Suitable swelling
clay
particles include, without limitation, montmorillonite, saponite, nontronite,
laponite, beidellite,
iron-saponite, hectorite, sauconite, stevensite, vermiculite, and combinations
thereof.
Suitable non-swelling clay particles include, without limitation, kaolin
minerals (including
kaolinite, dickite and nacrite), serpentine minerals, mica minerals (including
illite), chlorite
1 o minerals, sepiolite, palygorskite, bauxite, silica and combinations
thereof.
Preferably, the clay is a swelling clay such as, for example, smectite and
vermiculite
type clays. More preferably, the clay is a smectite type clay. Examples of
suitable smectites
are, without limitation, montmorillonite (sometimes referred to as bentonite),
beidellite,
nontronite, hectorite, saponite, sauconite and laponite. Bentonite is an
example of a
naturally-occurring combination of clay particles. Bentonite is a rock rich in
montmorillonite
and may also comprise other smectites as well as other non-clay mineral
constituents.
Consequently, montmorillonites or their mixtures with other smectites are
often referred to
simply as bentonite. Bentonite clays are fine crystals or particles, usually
plate-like in shape,
with a lateral dimension up to 2 Nm and a thickness in a range of a few to
tens of
nanometers (nm).
Swelling clays have the ability to absorb water and are less expensive than
monomer. Accordingly, the reinforced networked polymer composite of the
present
invention is less expensive than one produced without clay. Moreover, clay
particles are
resistant to degradation in long-term environmental applications, while still
providing water
absorbency for long periods of time.
Non-swelling clays would provide increased resistance to salt water for the
reinforced NPC alloy composite. Also, non-swelling clays, like swelling clays,
are less
expensive than monomer and would reduce the composite's cost.
Preferably, the weight ratio of clay to monomer in the MCX mixture is in a
range of
3o from about 0.05:1 to about 19:1. More preferably, the weight ratio of clay
to monomer in the
MCX mixture is in a range of from about 0.5:1 to about 3:1.
Suitable chemical substances for use as cross-linking agents include, without
limitation, N,N'-methylene bisacrylamide, phenol formaldehyde,
terephthalaldehyde,
allylmethacrylate, diethyleneglycol diacrylate, ethoxylated trimethylolpropane
triacrylate,
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ethylene carbonate, ethylene glycol diglycidal ether, tetraallyloxyethane,
triallylamine,
trimethylolpropanetriacrylate, and combinations thereof.
As a general rule, depending on the selected polymerization reaction time and
temperature, a higher ratio of cross-linking agent to monomer will generally
produce a lower
concentration of residual monomer, but the networked polymer's water
absorption capacity
(WAG) may drop if the ratio gets too high. The weight ratio of the cross-
linking agent to the
monomer is preferably in a range of from about 0.05:100 to about 1.5:100. More
preferably,
the weight ratio of the cross-linking agent to the monomer is in a range of
from about
0.05:100 to about 0.7:100. Most preferably, the weight ratio of the cross-
linking agent to the
monomer is in a range of from about 0.1:100 to about 0.5:100.
The mixing fluid is a polar solvent. Examples of suitable mixing fluids
include,
without limitation, water, alcohol, oxygen-containing organic solvents, and
combinations
thereof, in which the monomer can be at least partially dissolved. Examples of
suitable
oxygen-containing organic solvents include, without limitation, alcohols,
glycols, polyols,
sulfoxides, sulfones, ketones and combinations thereof. Preferably, the mixing
fluid is
water, alcohol or a combination thereof. Most preferably, the mixing fluid is
water.
Preferably, the amount of mixing fluid in the MCX mixture is in a range of
from about
30% to about 90% by weight. More preferably, the amount of mixing fluid in the
MCX
mixture is in a range of from about 40% to about 80% by weight. Most
preferably, the
amount of mixing fluid in the MCX mixture is in a range of from about 40% to
about 60% by
weight.
Additionally, the MCX mixture preferably comprises one or more additives.
Buffering
agents and/or neutralizing agents may be used as additives to maintain the pH
of the
mixture in a predetermined range and/or neutralize acidic and/or basic
monomers.
Also, metal complexing agents may be used as additives to form metal
complexes,
thereby sequestering metal ions that might otherwise interfere with forming
the NPC alloy.
For example, acrylamide monomer is typically manufactured with cupric salts as
a stabilizer
(e.g., to inhibit polymerization during shipment or in storage). Thus, a metal
complexing
agent, such as a sodium carbonate or ethylenediaminetetracetic acid (EDTA),
can be added
to the MCX mixture to complex the metal ion and thereby sequester the metal.
It should be
understood that some additives can be used to satisfy multiple functions. For
example,
sodium carbonate (Na2C03) and sodium bicarbonate (NaHC03), could function as
both a
buffering agent (i.e., maintaining pH) and a neutralizing agent (i.e.,
neutralizing acidic
monomers), while also working as a metal complexing agent. Therefore, it will
be apparent
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to those skilled in the art that one or more additives can be used for forming
an NPC alloy
depending on the monomer and cross-linking agent used, type of stabilizing
agent mixed
with the monomer, type of polymerization reaction and the desired reaction pH
and
temperature.
Examples of buffering agents and/or neutralizing agents include, without
limitation,
sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate,
sodium
bicarbonate, potassium carbonate, potassium bicarbonate, oxylate-containing
compounds,
sulfate-containing compounds, phosphate-containing compounds, and combinations
thereof.
Examples of metal complexing agents include, without limitation, sodium
carbonate,
sodium bicarbonate, potassium carbonate, potassium bicarbonate,
ethylenediaminetetraacetic acid (EDTA), EDTA salts, orthophosphate,
pyrophosphate,
metaphosphate, hydrogen phosphate, and combinations thereof.
Each of the components of the MCX mixture may be added in any order.
Preferably,
however, the mixing fluid and monomer are mixed with any other desired
component,
followed by adding a chemical initiator and then adding the clay. Also,
caution should be
exercised in mixing any mixture components to avoid any significant exotherms.
Otherwise,
any significant exotherm should be allowed to cool. A large exotherm from
mixing
components might otherwise lead to premature polymerization shortly after the
initiator is
added, but before the mixture is intimately distributed in, on and/or among
the reinforcing
agent and heated under a controlled condition.
The MCX mixture forms a slurry type mixture, which should be mixed until it is
substantially homogeneous.
Reinforcing Agent
The reinforcing agent may comprise non-aggregated fibers or a substrate having
a
porous structure. Examples of porous substrates include knitted, woven and non-
woven,
natural and synthetic fibers. Suitable synthetic fibers for either type of
reinforcing agent
include, for example, without limitation, polypropylene, polyester, polyamide,
polyethylene
fibers, and combinations thereof. Examples of suitable natural fibers include,
without
limitation, wood pulp, cotton, hemp, flax and asbestos fibers, and
combinations thereof.
Preferred porous substrates for landfill applications include geotextile
materials.
Examples of suitable non-woven geotextiles are, without limitation,
PETROMATT"" 4597
(Amoco), AMOCO 4551 T"", AMOCO 4553T"", AMOCO 4506T"", GEOTEX~ (Synthetic
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Industries, Inc., Chattanooga, TN, U.S.A.) and TERRAFIX~ 2708-A (Terrafix
Geosynthetics
Inc., Toronto, Ontario, Canada). Preferred geotextiles have a unit weight in a
range of from
about 0.1 to 0.8 kg/m2.
Another preferred porous substrate is a geotextile bonded to a geomembrane.
Presently, one type of geotextile-geomembrane laminate is commercially
available from
Vernon Plastics, Haverhill, MA, USA.
Alternatively, the geotextile-geomembrane laminate could be formed in a
continuous
process by bonding a geomembrane material to a geotextile. For example,
without
limitation, suitable geomembrane materials are high density polyethylene
(HDPE), polyvinyl
1 o chloride (PVC), very flexible polyethylene (VFPE), flexible polypropylene
(fPP),
chlorosulfonated polyethylene (CSPE), and combinations thereof. Preferably,
the
geomembrane is substantially non-porous. The geomembrane may be bonded to the
geotextile, for example, without limitation, by heat, adhesive, and
combinations thereof.
The geomembrane material can be applied to the porous substrate material
either
15 before or after the substrate material is mixed with the polymer/clay alloy
mixture to form the
NPC alloy composite. Preferably, however, the polymer/clay alloy mixture is
dispersed in
the substrate material using a roller or piston.
The use of a geotextile-geomembrane laminate as a reinforcing agent is
particularly
advantageous in some applications, for example land-fill applications, where
it is desired to
20 use both a primary liner (often a geomembrane) and a secondary liner (for
example, a GCt-).
By using a geotextile-geomembrane laminate as a reinforcing agent, a
reinforced NPC alloy
composite can be installed in one step.
In certain applications, for example, as landfill liners and covers, it may be
desirable
to use a reinforcing agent that is resistant to biodegradation. In other
applications, for
25 example, personal care absorbent articles, it may be desirable to use a
reinforcing agent
that will biodegrade within a selected time period.
Whether the reinforcing agent is a porous substrate or non-aggregated fibers,
the
inventive process produces a non-laminated, but intimately integrated,
composite between
the reinforcing agent and the NPC alloy. Preferably, the reinforcing agent is
dispersed
30 homogeneously throughout the NPC alloy. However, a portion of NPC alloy may
be formed
that is substantially free of reinforcing agent (i.e., non-reinforced NPC
alloy). Typically, a
contiguous portion of non-reinforced NPC alloy is integrally connected with
the reinforced
NPC alloy and is formed on one side of the composite, usually its topside. To
the extent the
composite is made with a contiguous portion of non-reinforced NPC alloy layer,
the non-
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reinforced contiguous portion is preferably less than about 2.5 mm deep. More
preferably,
the non-reinforced contiguous portion is less than about 1 mm deep and most
preferably, it
is less than 0.5 mm deep.
Also, the portions of non-reinforced NPC alloy formed may also be non-
contiguous.
In that case, however, the percentage of non-contiguous non-reinforced
portions should be
limited so that the overall structural integrity needed for composite's
specific application is
not compromised.
When the reinforcing agent comprises a substrate having a porous structure,
the
MCX mixture is added to the porous substrate so that an intimate distribution
of the mixture
1o in and/or on the substrate is achieved. When the MCX mixture is
polymerized, a layer of
NPC alloy may be formed on top of the substrate. But, because the MCX mixture
is
intimately distributed in and/or on the substrate, the layer on top of the
substrate is also an
integral part of the NPC alloy in the substrate and, therefore, an integral
part of the
composite.
When the reinforcing agent comprises non-aggregated fibers, the reinforcing
agent is
mixed into the MCX mixture. The MCX/fiber mixture is then distributed into a
mold prior to
polymerization. Alternatively, non-aggregated fibers may be distributed in a
mold and the
MCX mixture is poured over the fibers. The mold may be such so as to produce a
sheet-like
material or another suitable shape for other applications. The MCX/fiber
mixture may be
2o distributed in a mold, for example, without limitation, vibration,
hydraulic loading, pressure,
and combinations thereof.
The MCX mixture may be intimately distributed in and on the porous substrate
by, for
example, without limitation, vibration, rolling, scrubbing, spraying,
hydraulic loading,
pressure, vacuum and combinations thereof.
It will be understood that if a pre-formed geosynthetic dual liner is used or
if the
geomembrane is fused prior to polymerization, that intimate distribution
means, other than a
vacuum, will be used to intimately distribute the MCX mixture in and on the
porous
substrate.
Polymerization
After the MCX mixture is intimately distributed in, on and/or among the
reinforcing
agent, the polymerization process begins while the cross-linking agent, acting
in concert
with the polymerization process, helps to form a networked polymer/clay alloy
structure that
is intimately integrated with the reinforcing agent. Polymerization of the MCX
mixture is
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initiated by a polymerization initiator means for generating an ionic or free
radical
monomeric species. Initiation may be accomplished by adding a suitable
chemical
substance to the MCX mixture. Also, electromagnetic radiation having a
wavelength of 10
nanometers (nm)or less may be used alone or in combination with a chemical
initiator.
Suitable chemical substances for initiating polymerization include, without
limitation,
free radical initiators, carbanions, carbonium ions, and combinations thereof.
Examples of free radical initiators include, without limitation, thermal
initiators, and
redox systems, which are typically two or more chemicals, which are added
simultaneously
as different solutions.
Examples of thermal initiators include, without limitation, (1 ) alkali metal
salts of
sulfite, bisulfite, persulfate, benzoyl peroxide, and combinations thereof,
(2) ammonium salts
of sulfite, bisulfite, persulfate, benzoyl peroxide, and combinations thereof,
(3) 2,2'-azobis(2-
amidino-propane)-dihydrochloride, (4) 2,2'-azobis(4-cyanopentanoic acid), and
combinations
thereof.
The desired polymerization temperature for forming an NPC alloy composite is
primarily dependent on the type and concentration of initiator means selected.
For example,
lower polymerization temperatures may be used where a thermal initiator prone
to forming
free radicals at a lower temperature (e.g., about 40°C to about
50°C) is used. Thus, where
the polymerization reaction used for making the NPC alloy is initiated with a
thermal initiator,
2o the reaction is preferably at a temperature in a range of from about
40°C to about 95°C.
More preferably, however, the reaction temperature is at a temperature in a
range of from
about 60°C to about 85°C and most preferably, in a range of from
about 65°C to about 80°C.
Also, where a high energy radiation source, such as gamma ray radiation is
used, the
polymerization reaction may be conducted as low as about ambient temperature,
for
example about 20°C.
The polymerization reaction time is also primarily dependent on the type of
initiator
means used and its concentration. However, other factors affecting the desired
reaction
time include the type of monomer and its concentration, the depth of the MCX
mixture and
the amount of reinforcing agent (e.g., MCX mixture thickness as applied on the
substrate or
volume of non-aggregated fibers in the MCX mixture). Also, once a
polymerization reaction
is initiated, typically, it will not terminate in response to a sharp
temperature drop. For
example, once the MCX mixture is exposed to the desired initiation
temperature, the
polymerization reaction will proceed for some time thereafter, depending on
the reaction
temperature selected, the time period that the MCX mixture is exposed to the
selected
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temperature (i.e., heat exposure period) and the composite's heat retention.
Also, we have
discovered that higher initiator concentrations generally produce residual
monomer
concentrations of about 200 ppm or less. However, these higher initiator
concentrations are
more likely to promote premature polymerization unless the temperature is kept
sufficiently
below 40°C. Accordingly, it is important to maintain the MCX mixture
below 40°C before the
mixture is distributed in, on and/or among the reinforcing agent so that the
mixture's
viscosity is sufficiently low to ensure the mixture is intimately distributed
in, on and/or among
the reinforcing agent.
The time period that the MCX mixture is exposed to the selected reaction
1o temperature may be in a range from as low as about 1 minute to as high as
about 24 hours.
For example, where an MCX mixture having a clay to monomer ratio of about 2:1
is pressed
into a porous substrate to a depth of about 2-3 mm, potassium persulfate is
used as a
thermal initiator and the selected temperature is about 80°C, the
duration of the heat
exposure period is preferably in a range of from about 2 minutes to about 60
minutes. More
preferably, under similar conditions, the heat exposure period is in a range
of from about 2
minutes to 45 minutes and, most preferably, in a range from about 3 minutes to
about 30
minutes.
Examples of redox systems include, without limitation, persulfate/bisulfite,
persulfate/thiosulfate, persulfate/ascorbate, hydrogen peroxide/ascorbate
couples, and
combinations thereof. Typically, additional heat is not required when using a
redox systems
initiator because the reactions are often exothermic, so such systems can work
effectively at
temperatures in a range of from about the freezing point of the MCX mixture to
the boiling
point of the mixing fluid. Typically, the temperature is ambient, about
20°C.
Alternatively, polymerization may be initiated by electromagnetic radiation
having a
wavelength below about 10 nm such as, for example, without limitation, by
gamma rays, X-
rays, or high energy sub-atomic particles. In such a case, the polymerization
reaction is
typically conducted at ambient temperatures. However, the temperature can be
higher or
lower.
However, it is well known to those skilled in the art that UV radiation, with
wavelengths ranging from about 200 nm to 390 nm is not suitable for
polymerization
initiation of the MCX mixture because the clay will interfere with UV light's
ability to penetrate
into the sample, and thereby initiate the polymerization reaction, even with a
photo-initiator
present. More specifically, it is believed that the clay preferentially
absorbs the UV light,
thereby inhibiting the UV light's effectiveness as an initiator means.
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Optionally, once polymerized, all or a portion of the mixing fluid remaining
in the
reinforced NPC alloy composite product may be removed, for example by
desiccating at
room temperature or oven-drying. If oven-dried, the composite should be dried
at a
temperature that does not adversely affect the properties or characteristics
of the product,
for example, at a temperature less than about 110°C.
The moisture content of the reinforced NPC alloy composite product is
dependent on
the application and other factors. For example, a higher moisture content
composite
provides greater flexibility and a lower initial permeability. But a lower
moisture content
composite can have reduced transportation costs. Consequently, the desired
moisture
1o content will be determined by the environment in which the composite
product will be used
and maximum acceptable transportation costs.
Therefore, for a composite product with at least some flexibility, the
moisture content
is preferably in a range of from about 25% to about 75% by weight.
Reinforced NPC Alloy Composite
In use, the NPC alloy swells on contact with water as the alloy absorbs water.
The
expanded NPC alloy swells in and/or around the reinforcing agent. It is
believed that the
alloy swells and expands into any interstitial spaces that were not occupied
by the NPC alloy
when the composite was formed. Also, it is believed that the alloy expands
around the
reinforcing agent itself. Consequently, the composite swells substantially as
an integrated
unit while only negligible amounts of clay, if any (i.e., substantially no
clay), separate from
the composite when it is immersed in water at a temperature in a range of from
about 1 °C to
about 60°C, whether the water is saline or not.
It will be understood by those skilled in the art that the degree to which the
NPC alloy
is networked will affect the alloy's capacity to absorb water. Of course, if
insufficient cross-
linking agent is used, the NPC alloy may become water soluble under certain
conditions and
the clay could then substantially separate from the alloy. On the other hand,
if excessive
amounts of cross-linking agent are used, the NPC alloy may be so inflexible
that it is unable
to absorb sufficient amounts water and thereby reach either the desired fluid
permeability
and/or water absorption performance.
In containment applications, the reinforced NPC alloy composite product is
often
under a confining stress due to overburden. Under a standard effective
confining stress of
20 kPa or 2.9 psi, the flux (i.e., the rate water travels at the specified
pressure) of the
composite is about 10$ m3/m2/s or less, as measured by ASTM 5887-95. As the
confining
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stress increases with additional overburden, the hydraulic conductivity of the
composite will
decrease because the composite will become compressed.
Cover Sheet
A cover sheet is advantageously used to (1 ) assist in MCX mixture
distribution, for
example, when using a vacuum, (2) reduce evaporation and/or boiling of mixing
fluid or
other components in the MCX mixture during polymerization, and/or (3) assist
in handling,
for example rolling, and storage of the composite.
In one embodiment, a cover sheet can be contacted with the MCX mixture either
during or shortly after the mixture is contacted with the reinforcing agent.
Moreover, the
cover sheet may be applied to one or both sides of the reinforcing agent
contacted with the
MCX mixture. But preferably, the cover sheet is applied to one side, and more
preferably,
the cover sheet is applied to the side opposing the side on which the means
for distributing
the MCX mixture (e.g., vacuum, roller, pressure, etc.) is applied. Most
preferably, the cover
sheet is concurrently contacted with the MCX mixture and reinforcing agent,
while a vacuum
is applied to the opposing side and thus the mixture is intimately distributed
in, on and/or
among the reinforcing agent.
In another embodiment, the cover sheet may be applied to one or both side of
the
reinforced NPC alloy composite after polymerization. If desired, the cover
sheet may be
self-adhering to the composite or may be adhered to the composite, for
example, without
limitation, by heat bonding or an adhesive.
Examples of suitable cover sheets include, without limitation, polyethylene
film,
sulfite and sulfate papers, kraft papers, groundwood papers, filter papers,
woven and non-
woven natural and synthetic fabrics, fiberglass, and combinations thereof. The
cover sheet
may be removed after polymerization or left in place, depending on the
composite's ultimate
application.
Illustrative Process
Figs. 1-3 illustrate a process for producing a reinforced NPC alloy composite
10. A
reinforcing agent, in this case a porous substrate 12, is fed onto a conveyor
26, using feeder
rollers 28, 30.
An MCX mixture 14 is prepared in vessel 16, by mixing at least a monomer, clay
particles, a cross-linking agent and a mixing fluid until the mixture is
substantially
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homogeneous. Preferably, the MCX mixture 14 is maintained in the vessel 16 at
a
temperature less than about 40°C, to reduce premature polymerization of
the monomer.
The MCX mixture 14 is metered from the vessel 16 and contacts the porous
substrate 12 as it moves along the conveyor 26. A cover sheet 24 is placed on
top of the
MCX mixture 14 using a guiding roller 36.
In the embodiment illustrated in Fig. 1, the porous substrate 12 is contacted
with the
MCX mixture 14, using a roller 18, until the mixture 14 is distributed in and
on the substrate
12.
In the embodiment illustrated in Fig. 2, the porous substrate 12 is contacted
with the
MCX mixture 14, using a piston 20, until the mixture 14 is intimately
distributed in and on the
substrate 12. Piston 20 may be a mechanical or gas piston.
In the embodiment illustrated in Fig. 3, the porous substrate 12 is contacted
with the
MCX mixture 14, using a vacuum means 32, until the mixture 14 is intimately
distributed in
and on the substrate 12.
In all the illustrated embodiments, after the MCX mixture 14 is intimately
distributed
in and/or on the porous substrate 12 , the mixture 14 is, in accordance with
the above
discussion, polymerized within and on the substrate 12 by heating the combined
substrate
12 and mixture 14 in a heating zone 22 to form the reinforced NPC alloy
composite 10. The
reinforced NPC alloy composite 10 can be rolled and packaged for subsequent
handling and
transport, if desired.
The following non-limiting examples of embodiments of the present invention
that
may be made and used as claimed herein are provided for illustrative purposes
only.
EXAMPLE 1
Effect of Clay to Monomer Ratio on Water Absorption Capacity
NPC Alloy Preparation
Seven MCX mixtures were prepared in the amounts shown in Table 1. Clay to
monomer weight ratios ranged from 0.1 to 9.62 in the seven MCX mixtures. The
clay used
in the MCX mixtures was NATURAL GELT"", a natural swelling clay often referred
to as
Wyoming bentonite, commercially available from American Colloid. The monomer
was
acrylamide, obtained from Cytec, West Paterson, NJ. A Control sample was made
using
acrylamide monomer without added clay.
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Water, sodium hydroxide (NaOH), sodium bicarbonate (NaHC03), EDTA,
acrylamide, N,N'-methylene bisacrylamide (NBAM) and potassium persulfate
(K2S208) were
mixed in a 250-mL HDPE bottle. The aqueous solution was mixed well, prior to
addition of
clay. Clay was added and mixed again to form a homogeneous MCX mixture. All
MCX
mixtures were viscous but fluid before polymerization.
Table 1
Sam
1e
ComponentControl1 2 3 4 5 6 7
Water 79.98 72.5 98.778 74.4 291.15374.4 151.23 91.91
NaOH 3.768 3.108 3.904 2.28 7.498 1.891 1.563 0.506
NaHC03 0.931 0.802 0.931 0.60 0.204 0.468 0.323 0.105
EDTA 0.109 0.09 0.116 0.08 0.217 0.06 0.042 0.025
Ac lamide25.073 21.02824.871 15.00 50.00 7.72 10.042 2.294
NBAM 0.057 0.05 0.058 0.04 0.123 0.028 0.022 0.012
K2S208 0.21 0.183 0.217 0.132 0.418 0.085 0.088 0.032
Cla -- 2.121 8.368 7.502 50.22 15.389 30.00 22.029
Total 110.12899.882137.243100.034399.833100.041193.31 116.913
Clay:
Monomer 0 0.10 0.34 0.50 1.00 2.00 3.00 9.60
Ratio
wt
The Control and MCX mixtures were left in an oven overnight at
65°C for
polymerization. After polymerization, the Control and NPC alloys were
transferred to glass
dishes and dried at 105°C for 48 hours.
Water Absorption Capacity (WAC) of NPC Alloys
Approximately 1 gm of each NPC alloy and the Control was placed in a 500 mL
HDPE bottle with 400 ml distilled water. After 48 hours, free water was
decanted off the
swollen NPC alloy using a 115 mesh screen.
The swollen NPC alloy was weighed and the water absorption capacity (WAG) was
calculated according to the following equation:
(H20 Swollen NPC Alloy Mass - Dried NPC Alloy Mass)
WAC =
Dried NPC Alloy Mass
A projected WAC, WACpr~, based on the Control WAC and clay content was also
calculated according to the following equation:
Parts Monomer x Contro + Parts Cla x Max. Est.
WACP~ _ (Total Parts Monomer + Clay WAC ~ Total Parts Monomer + Clay Clay WAC)
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where the Control WAC = 352 and the Maximum Estimated WAC for clay = 10. For
example, where a 1:3 clay to monomer ratio is used to produce the NPC alloy,
the NPC
alloy's WACP~~ is [(3/4) x 352] + (1/4)10 =266. Likewise, where a 2:1 clay to
monomer ratio is
used, the NPC alloy's WACP~ is [(1/3) x 352] + (2/3)10 = 124.
Finally, the monomer WAC (WACm) was also calculated to determine the water
absorption capacity based on the amount of monomer used to produce the
polymer/clay
alloy sample being tested. The WACm was calculated according to the following
equation:
(H20 Swollen NPC Alloy Mass - Dried NPC Alloy Mass)
WACm
Mass of Monomer used to produce NPC Alloy
1 o The results are tabulated in Table 2.
Table 2
Sam Control1 2 3 4 5 6 7
1e
ID
Cla 0.00 0.10 0.34 0.50 1.00 2.00 3.00 9.61
:
Monomer
Ratio
WAC g H20 per 352 339 332 213 207 _134 83 14
g
WACP~~polymer/clay 321 266 238 181 124 96 42
alloy
WACm g H20 per 421 441 472 364 414 403 349 250
g
monomer
in
polymer/clay
alto
As shown in Table 2, the WAC for NPC alloy Samples 1 and 2 is 339 and 332,
respectively. This means that the NPC alloy absorbs 339 and 332 times its own
weight in
water for these two samples, respectively, versus a 352 WAC for the clay-free
Control.
Bentonite clay typically has a paste-like consistency up to a water absorption
of 5 to 10
times its weight, after which the clay becomes dispersed in water to form a
slurry.
Consequently, because bentonite clay is not known as being highly water-
absorbent on a
per unit mass basis, as compared with a water-absorbent polymer, the drop in
WAC shown
in Table 2 with increasing clay to monomer ratio was a surprising and
unexpected result.
For example, at a 1:1 ratio, those skilled in the art might have projected a
WAC of
just slightly more than 0.5 x the Control's WAC because only half of the NPC
alloy is
networked polymer. So, taking into account the water absorption for clay alone
(i.e., about
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5-10), a 1:1 clay to monomer ratio in an NPC alloy would have been expected to
be, at best,
about 1/2 the Control's WAC (i.e., 176) plus 5 for the clay's expected water
absorption for a
WACP~ of 181. But Sample 4, with a 1:1 clay to monomer ratio, has a 207 WAC,
which is
14.4% greater than expected. Similarly, a 2:1 clay to monomer ratio has a
WACP~ of about
124, while Sample 5 produced a 134 WAC, which is 8.1% greater than expected.
The
general trend is that WAC, across a broad range of clay to monomer ratios, is
substantially
comparable, if not slightly improved versus the clay-free Control until a
significantly high clay
loading in the NPC alloy is reached. At a significantly high clay loading, it
appears that the
polymer loading is so low that the clay's inherent WAC is dominant.
This is a surprising and unexpected result, particularly at high clay to
monomer ratios
of 2:1 and 3:1. Ogawa et al ("Preparation of Montmorillonite- Polyacrylamide
Intercalation
Compounds and the Water Absorbing Property" Clay Science 7:243-251; 1989)
suggest on
pg. 250 that clay acts as a cross-linking agent. Thus, Ogawa et al suggest
that clay would
act in concert with a cross-linking agent in an MCX mixture to severely
constrain a polymer
formed from that mixture. Moreover, the results in Example 2 illustrate that a
cross-linking
agent concentration as low as about 0.1 wt.% can over cross-link a polymer,
thereby
substantially reducing its water absorption capacity. Thus, the sensitivity of
WAC to excess
cross-linking agent and Ogawa et al suggest that increasing the clay content
would produce
a highly constrained NPC alloy with inhibited WAC. Consequently, it is
surprising and
unexpected that using an MCX mixture with both a cross-linking agent and clay,
for
example, at a 2:1 clay to monomer ratio, would produce an NPC alloy with
comparable or
slightly better performance than the clay-free Control.
When calculated on the basis of an equivalent amount of acrylamide monomer
used
to produce an alloy, the WACm of the polymer/clay alloys Samples 1-5 is
similar to that of
the Control sample. As mentioned above, monomers are more costly than clay.
Thus, the
WACm results demonstrate the economic advantages of the NPC alloy.
Table 2 demonstrates that good WAC results were obtained for the composition
described in Table 1 in a clay to monomer ratio of about 0.3 to about 3Ø The
optimal clay
to monomer ratio will depend on the intended use of the compositions falling
within the
scope of the claimed invention. For instance, beyond adjusting the clay to
monomer ratio,
as discussed more fully under Example 2, the cross-linking agent to monomer
ratio can also
be adjusted to increase or decrease the WAC to the desired level.
For example, as a landfill liner, a WAC for the reinforced NPC alloy composite
only
needs to be high enough to ensure that the NPC alloy swells sufficiently to
occupy any
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interstitial spaces that were not occupied by NPC alloy when the composite was
formed.
This degree of swelling will ensure that the composite has sufficiently low
permeability to
water and other fluids. For example, the WAC for an NPC alloy used in a
landfill liner
composite could be as low as about 5. Of course, a higher WAC up to about 500
could also
be used in a landfill liner composite. However, a WAC significantly much
higher than 50
could reduce the structural integrity of the composite due to excess water.
Consequently, in personal care type applications, where the composite's
structural
integrity is likely to be a factor as well, a WAC in a range of from about 20
to about 100
would be most likely desired for the composite.
1o Accordingly, the above data illustrates that the unique polymer/clay alloy
can provide
effective water absorption for a reinforced NPC alloy composite. As well, the
clay
component in the NPC alloy provides a cost effective means to make a
reinforced NPC alloy
composite while delivering the water absorbing and/or permeability property
performance
desired for the intended use.
EXAMPLE 2
Effect of Cross-Linking Agent to Monomer Ratio on WAC
NPC Alloy Preparation
Three MCX mixtures were mixed in the amounts shown in Table 3. The cross-
linking
agent to monomer weight ratios ranged from 1.10 x 10-3 to 9.41 x 10-3 in the
three MCX
mixtures. The clay to monomer weight ratio was held constant at about 1:1. The
clay used
in the MCX mixtures was NATURAL GELT~". The monomer was a 1:4 (wt) mixture of
acrylic
acid (Aldrich) and acrylamide (Cytec).
Water, NaOH, sodium carbonate (Na2C03), acrylic acid, acrylamide, NBAM and
K2S208 were mixed in the proportions shown in Table 3 in a 2-L Erlenmeyer
flask. The
aqueous solution was mixed well, prior to addition of clay. Clay was added and
mixed again
to form a homogeneous MCX mixture. All MCX mixtures were viscous but fluid
before
polymerization.
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Table 3
Sam 1e
Component 8 9 10
Water 1000 1000 1000
NaOH 10 10 10
Na2C03 12 12 12
Ac lic Acid 20 20 20
AA
Ac lamide 80 80 80
AM
NBAM 0.941 0.303 0.11
K2S208 0.6 0.6 0.6
Cla 99 105 105
Total 1222.541 1227.903 1227.71
NBAM/(AA+AM) 9.41 3.03 1.10
Wt Ratio x
103
The MCX mixtures were left in an oven overnight at 65°C for
polymerization. After
polymerization, the NPC alloys were transferred to glass dishes and dried at
105°C for 48
hours.
Water Absorption Capacity (WAC) of PolymerlClay Alloys
Approximately 1 gm of NPC alloy Sample 8 was placed in a 500 mL HDPE bottle
with 400 ml distilled water. After 48 hours, free water was decanted off the
swollen NPC
1 o alloy using a 115 mesh screen.
The swollen NPC alloy was weighed and the water absorption capacity (WAC) was
calculated as described in Example 1. Samples 9 and 10 were treated in the
same manner.
The results are tabulated in Table 4.
The monomer WAC (WACm) was also calculated to determine the water absorption
capacity based on the amount of monomer used to produce the NPC alloy sample
being
tested. These results are also tabulated in Table 4.
Table 4
Sam 8 9 10
1e
NBAM/(AA+AM) 9.41 3.03 1.10
Wt
Ratio
x
103
WAC g H20 per 145 281 281
g
polymer/clay
alto
WACm g H20 per 324 641 640
g
monomer
in
polymer/clay
alto
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As shown in Table 4, the NPC alloy's WAC increases as the cross-linking agent
to
monomer ratio decreases from 9.41 x 10-3 to 3.03 x 10-3. However, it is
believed that a
further significant decrease in cross-linking agent to monomer ratio (e.g., to
about 0.10 x
10-3) would sufficiently reduce the mechanical strength of the NPC alloy's
networked
polymer and thereby limit NPC alloy's ability to absorb and retain water.
Of course, to the extent the polymer is not cross-linked, the polymer will
dissolve in
water. Also, at low levels of cross-linking, the polymer may fracture and
become water-
soluble. However, if the degree of cross-linking is too high, there is too
much constraint on
the polymer and its water absorption capacity is reduced.
Accordingly, the above data illustrates that the unique NPC alloy can provide
effective water absorption for a reinforced NPC alloy composite. As well,
controlling the
cross-linking agent to monomer ratio, alone or in combination with the clay to
monomer
ratio, provides a means for designing the water absorbing and/or permeability
property
performance desired for the composite's intended use.
EXAMPLE 3
Hydraulic Conductivity of
Reinforced Networked Polymer Clay Alloy Composite
MonomerlClay Mixture Preparation
Two MCX mixtures were prepared in the amounts shown in Table 5. The clay to
monomer weight ratios were 1:1 and 2:1 in Samples 11 and 12, respectively. The
clay used
in the MCX mixtures was NATURAL GELT"'. The monomer was acrylamide.
Water, NaOH, NaHC03, EDTA, acrylamide, NBAM and K2S20a were mixed in the
proportions shown in Table 5 in a 2-L Erlenmeyer flask. The aqueous solution
was mixed
well, prior to addition of clay. Clay was added and mixed again to form a
homogeneous
MCX mixture. The MCX mixtures were viscous but fluid before being contacted
with the
reinforcing agent.
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Table 5
Component 11 12
Water 291.153 74.4
NaOH 7.498 1.891
NaHC03 0.204 0.468
EDTA 0.217 0.06
Ac lamide 50.00 7.72
NBAM 0.123 0.028
K2S208 0.418 0.085
Cla 50.22 15.389
Total 399.833 100.041
Clay to Monomer 1.00 1.99
Ratio
wt
Reinforced NPC Alloy Composite Preparation
PETROMATT"" 4597 and AMOCO 4551 T"" (Amoco) geotextiles were used as
reinforcing agent. These commercially available geotextiles are nonwoven
fabrics
comprising polypropylene fibers. The unit weight for PETROMATT"~ 4597 and
AMOCO
4551 T"" is 0.14 kg/m2 and 0.2 kg/m2, respectively. The geotextiles were about
1-3 mm thick.
The thickness typically varies in a non-woven geotextile and it is difficult
to measure
because of the fibers.
0 Reinforced Sample A1 was prepared by pouring Sample 11 MCX mixture in a
thickness of about 2.5 mm thickness onto a 20 cm x 20 cm piece of PETROMATT"~
4597
geotextile, representing a loading of about 2.5 kg/m2. The MCX mixture was
intimately
distributed in and on the geotextile material using a wooden rolling pin.
Reinforced Sample A2 was prepared in the same manner as Sample A1 using
Sample 12 MCX mixture and AMOCO 4551 T"" geotextile.
Reinforced Sample A3 was prepared using Sample 11 MCX mixture and two layers
of AMOCO 4551 T~" geotextile. The MCX mixture was poured onto one layer of
geotextile
(i.e., bottom layer) and then covered with the second layer of geotextile
(i.e., top layer). The
MCX mixture was intimately distributed in and on both layers using a wooden
rolling pin,
though the mixture was primarily substantially embedded throughout the bottom
layer.
The reinforced MCX mixture samples was placed between two glass plates and put
into an oven at 75°C for 2 hours for polymerization. Spacers were
placed between the glass
plates so that the polymerized samples would be of substantially uniform
thickness, without
added pressure during polymerization. The glass plates also reduced
evaporation of MCX
mixture components during polymerization.
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Reinforced Samples A1 and A2 were dried in an oven at 80°C overnight.
Sample A3
was not dried, but was stored in a polyethylene bag directly after
polymerization. Though
Samples A1 and A2 were dried, it is preferable to use the reinforced NPC alloy
composite in
an non-dried state, as in Sample A3.
Hydraulic Conductivity Test
The rate of water flow through a layer of the reinforced NPC alloy composite
samples
under a hydraulic gradient was measured using ASTM 5887-95.
ASTM 5887-95 is a standard method to measure the flux or flow of water per
unit
area through the sample. The test specimen was set up in a flexible wall
permeameter,
subjected to a total stress of 550 kPa and a back pressure of 515 kPa for a
period of 48
hours. Flow of deionized water was initiated by raising the pressure on the
influent side of
the test specimen to 530 kPa. This places an effective confining stress on the
specimen of
approximately 20 kPa. All samples were tested at 20 kPa, except Sample A2,
which was
tested at 120 kPa. The flux was determined when inflow and outflow were
approximately
equal.
Because the sample's thickness has an influence on its hydraulic conductivity,
the
flux determined by the ASTM 5887-95 test was used to calculate hydraulic
conductivity
based on each sample's different thickness. The hydraulic conductivity results
in Table 7
were calculated as follows:
k/~ _ (Q/A) (DUOp)
K = P9 (ww)
where k is permeability, ~ is fluid viscosity, (Q/A) is flux, (DU4p) is the
reciprocal of the
pressure gradient, which accounts for variations in the sample's thickness and
thereby
normalizes k/~ and hence K, K is hydraulic conductivity, p is fluid density
and g is a
gravitational constant.
In addition, the change in specimen thickness was measured and used to
calculate
the percentage of swelling during the test.
The results of the hydraulic conductivity tests are tabulated in Table 7.
BENTOMATT~'
3o ST (CETCO, Arlington, Illinois) was used as a comparative sample.
BENTOMAT'~' ST is a
GCL consisting of a sodium bentonite layer (approximately 4.9 kg/m2) between
woven and
non-woven geotextiles, which are needle-punched together.
The initial and final thicknesses are shown in Table 7 as To and T,,
respectively. The
unit weight shown in Table 7 for Samples A1 and A2 is on a moisture-free
basis. Sample
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A3 was not dried after polymerization and, therefore, the exact loading on a
moisture-free
basis is not known. However, it is estimated that the unit weight on a
moisture-free basis is
less than 0.75 kg/m2.
For convenience, the MCX mixture and geotextile used in each sample is
summarized in Table 6.
Table 6
Sample Reinforcing Monomer/Clay
Agent Mixture
A1 PETROMAT 11
4597
A2 AMOCO 4551 12
A3 Double AMOCO 11
4551
ComparativeBENTOMAT ST NIA
~
Table 7
Sample WeightT Tf Swell6effectiveFlux K (cm/s)
(kg/m2)(mm) (mm) (%) kPa (m3/m2/s)
A1 0.64 1.08 4.80 344 20 4.8 x 1.5 x
10- 10-
A2 0.96 1.70 2.19 29 120 3.7 x 5.1 x
10- 10-
A3 <0.75 3.89 6.92 78 20 1.6 x 7.2 x
10~ 10-
Com arative4.90 6.20 8.68 40 20 3.2 x 2.0 x
10- 10-
The water flux through Samples A1 and A3 was similar to the flux through the
comparative sample at an effective confining stress of 20 kPa. Even at this
very low NPC
alloy loading (as little as 0.64 kg/m2, where the weight of the NPC alloy is
calculated on a
water-free basis), the reinforced composite is as effective as GCL with 4.9
kg/m2 bentonite.
The average hydraulic conductivity (K) for Samples A1 and A3 of 1.1 x 10-9
cm/s, which is
about a 50% improvement versus the comparative sample's K of 2.0 x 109 cm/s.
This
improved K value is particularly significant since hydraulic conductivity
tends to increase as
the confining stress approaches zero, as discussed more fully in Example 5.
However, this
data demonstrates the composite's surprising and unexpected ability to deliver
relatively
consistent hydraulic conductivity performance under both lower confining
stress and higher
confining stress conditions.
The flux through Sample A2 was tested at a confining stress of 120 kPa to
determine
the effect of the confining stress on flux and corresponding hydraulic
conductivity. The flux
through Sample A2 was similar to the flux through Samples A1 and A3 and the
hydraulic
conductivity was similar to Sample A3. Accordingly, there was little change
when the
confining stress was increased from 20 kPa to 120 kPa.
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Accordingly, the reinforced NPC alloy composite provides a hydraulic
conductivity
performance at least comparable to, if not better than, conventional GCL, but
weighing
substantially less than GCL and having a dramatically improved clay retention
capacity
versus GCL when exposed to water. In turn, this contributes significantly to
the composite's
long-term hydraulic conductivity performance, which will remain relatively
stable over long-
term and persistent water exposure in the environment. Meanwhile, under
similar
environmental conditions, the hydraulic conductivity for GCL will deteriorate
over time as
clay particles migrate through the GCL fabric layer as discussed more fully
under Example
8.
EXAMPLE 4
One Alternative Preparation of
Reinforced Networked Polymer Clay Alloy Composite
Reinforced NPC Alloy Composite Preparation
Reinforced Samples B1 and B2 were prepared in the same manner as Reinforced
Sample A3 in Example 3 using Sample 11 MCX mixture (see Example 3) and 2
layers of
AMOCO 4551 T"" geotextile. The geotextile material was intimately contacted
with the MCX
mixture using a TEFLONT"" coated piston, with pressure applied by hand, until
the mixture
was substantially distributed throughout the material. It appeared that the
MCX mixture was
more evenly distributed using the piston, as compared with the wooden rolling
pin used in
Example 3.
The reinforced MCX mixture samples was placed in an oven at 65°C for 2
hours for
polymerization.
The reinforced samples were stored in a polyethylene bag directly after
polymerization.
Hydraulic Conductivity Test
The test procedures for hydraulic conductivity measurement were the same as
those
in Example 3. The results are tabulated in Table 8 with the results for the
same comparative
sample used in Example 3.
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Table 8
Sample Weight T Swell6effectiveFlux K (cm/s)
(kg/m2)(mm) (%) kPa (m3/m2/s)
B1 <0.75 3.61 112 20 2.7 1.4 x
x 10- 10-
82 <0.75 3.67 114 20 3.0 1.6 x
x 10~ 10-
Comparative4.90 6.20 40 T20 ( 3.2 ~ 2.O
x 109 x 10-9
The water flux and K through samples B1 and B2 was similar to the flux and K
through the comparative sample at an effective confining stress of 20 kPa.
Even at this very
low NPC alloy loading (<0.75 kg/m2, where the weight of the NPC alloy is
calculated on a
water-free basis), the reinforced composite is as effective as GCL with 4.9
kg/m2 bentonite
(dry weight).
Accordingly, the reinforced NPC alloy composite provides a hydraulic
conductivity
performance at least comparable to, if not better than, conventional GCL, but
weighing
substantially less than GCL and having a dramatically improved clay retention
capacity
versus GCL when exposed to water. In turn, this contributes significantly to
the composite's
long-term hydraulic conductivity performance, which will remain relatively
stable over long-
term and persistent water exposure in the environment. Meanwhile, under
similar
environmental conditions, the hydraulic conductivity for GCL will deteriorate
over time as
clay particles migrate through the GCL fabric layer as discussed more fully
under Example
8.
EXAMPLE 5
Flux at Zero Confining Stress
Sample Preparation
Samples were prepared using the following MCX mixture having a clay to monomer
ratio of 2:1:
100.8 g (1.52 wt.%) acrylic acid
400.5 g (6.04 wt.%) acrylamide
55.1 g (0.83 wt.%) NaOH
51.5 g (0.78 wt.%) Na2C03
1.62 g (0.02 wt.%) NBAM
12.8 g (0.19 wt.%) potassium persulfate
1000.8 g (15.09 wt.%) clay
5009.9 g (75.53 wt.%) water
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Reinforced NPC alloy composites were prepared using the MCX mixture and
TERRAFIX~ 2708-A geotextile.
Samples were prepared in a semi-continuous process, as discussed above and
illustrated in Fig. 3, to distribute the MCX mixture in the geotextile and
form the composite.
The MCX mixture was applied to the geotextile as described below for each set
of samples.
A polyethylene film cover sheet was placed on top of the MCX mixture and a
vacuum was
applied to the sample from the geotextile's opposing side. The MCX mixture was
intimately
distributed in and on the geotextile material by applying the vacuum. The
cover sheet
reduced channeling through the sample and the MCX mixture was more evenly
distributed
through the geotextile, as compared with a sample prepared without a cover
sheet.
For Samples 13 and 14, the MCX mixture was poured in a thickness of about 3.5
mm onto a 0.95 m x 0.97 m piece of geotextile. A second layer of the
geotextile was placed
on top of the MCX mixture. A polyethylene film cover sheet was placed on top
of the
second geotextile layer and a vacuum pressure of about 20 kPa was applied to
the
opposing side of the first geotextile layer.
For Samples 15 and 16, the MCX mixture was poured in a thickness of about 2.5
mm onto a 0.95 m x 0.50 m piece of geotextile. A polyethylene film cover sheet
was placed
on top of the MCX mixture and a vacuum pressure of about 16 kPa was applied to
the
geotextile's opposing side.
Samples 17 and 18 were prepared substantially the same as Samples 15 and 16,
but using a vacuum pressure of about 15 kPa, instead of 16 kPa.
All samples were heated in the semi-continuous process using a CATA-DYNET""
infrared heater (placed about 500 mm above the sample) at a temperature of
about 80°C for
10 minutes to form the reinforced NPC alloy composite.
Samples were cut into 9.0 cm discs using a high speed drill cutter and
weighed. The
results are presented in Table 9.
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Table 9
Sample Unit Weight
k /m2
13 3.47
14 2.92
15 2.73
16 2.90
17 2.42
18 ~ 2.46
Hydraulic Conductivity Tests
The hydraulic conductivity tests used to evaluate Samples 13-18 were based on
a
modified ASTM 5887-95 test. The apparatus used for the test was a Baroid
filter press.
Compressed air was used to apply pressure through a pressure manifold. Unlike
ASTM
5887-95, under this hydraulic conductivity test, no confining stress was
applied to the
sample. As mentioned previously, the hydraulic conductivity of a liner will
generally
decrease with increased confining stress. Accordingly, the hydraulic
conductivities
illustrated in this example, with zero confining stress applied, represents a
"worst case
scenario" where the liner may, at least early in its life, be exposed to
confining stresses that
are low or near zero.
The samples were placed at the bottom of the filter apparatus followed by a
rubber
gasket, cell and cap. The assembly was inserted into the support stand, sealed
by
tightening a "T" screw and then connected to the pressure manifold. The test
fluid was then
introduced to the cell and the sample was pre-soaked in the test fluid for 2
hours at
atmospheric pressure.
After 2 hours, a flow pressure of 15 kPa was applied. Effluent was weighed, at
an
interval of minutes at the beginning of test and several hours thereafter.
2o The amount of effluent was used to calculate the flux through the sample,
using an
effective flow area of 7.7 cm diameter.
In this example, deionized water was used as the test fluid.
The water flux through the samples was measured at 48 hours. These water flux
results are presented in Table 10.
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Table 10
Sample Water Flux @ 48 Pro'ected H draulic
hours Conductivit Based
on
(m3/m2/s) 2 mm Thickness 6 mm Thickness
13 4.87 x 10' 6.36 x 10- 1.91 x 10-
14 6.44 x 10- 8.41 x 10- 2.52 x 10-
15 5.59x10- 7.31 x10- 2.19x10'
16 4.78 x 10- 6.24 x 10~ 1.87 x 10-
17 3.85 x 10' 5.03 x 10- 1.51 x 10-
18 5.86x10- 7.65x10- 2.30x10-
As demonstrated in Table 10, the water flux through Samples 13 through 18
using
deionized water at zero confining stress are similar to the results for the
reinforced NPC
alloy composite samples tested in Example 6 (salt water, zero confining
stress), Example 3
(deionized water, 20 kPa and 120 kPa confining stress) and Example 4
(deionized water, 20
kPa confining stress).
In contrast, the hydraulic conductivity for water through conventional GCL's
is
significantly increased as the confining stress is reduced. Moreover, as
mentioned in the
1 o discussion in Example 6, the salt water flux through GCL is known to be
much greater than
1 x 108 m3/m2/s. Several conventional GCL's were tested with fresh water in a
paper by
D.E. Daniel ("Geosynthetic clay liners, part two: hydraulic properties"
Geotechnical Fabrics
Report 14:5:22; June-July, 1996). At a confining stress range from 100 to 1000
kPa,
conventional GCL's have a hydraulic conductivity range from 3 x 10-'°
to 1 x 10-9 cm/s. The
hydraulic conductivity increases to a range from 6 x 10-'° to 6 x 10-9
cm/s when the confining
stress ranges from 10 to 100 kPa. Only one data point was provided for a
confining stress
under 10 kPa. The hydraulic conductivity was 2 x 109 cm/s for a confining
stress of 7 kPa.
The data was extrapolated to show a hydraulic conductivity range of from 6 x
10-9 cm/s to
about 1 x 10-' cm/s, when the confining stress is decreased to 1 kPa.
Accordingly,
2o conventional GCL's have a hydraulic conductivity at least 1 x 10-' cm/s or
greater, thereby
making the composite hydraulic conductivity test results of about 2.5 x 10-9
cm/s, at zero
confining stress, particularly surprising and unexpected.
EXAMPLE 6
Salt Water Flux Tests
One problem, among others, with conventional barrier liners, such as GCL, is
that
their hydraulic barrier properties diminish with exposure to salt water,
particularly salt water
having a salt concentration about 3 wt.% or greater. For example, a
conventional GCL has
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a flux of about 1 x 10$ m3/m2/s, using tap water. However, salt water flux
through GCL is
known to be much greater than 1 x 10$ m3/m2/s, for example from about 1 x 10-'
m3/m2/s to
about 1 x 10~ m3/m2/s. This example demonstrates how a reinforced NPC alloy
composite
substantially maintains its low permeability on exposure to salt water.
Sample Preparation
Samples 19 and 24 were prepared using the following MCX mixture (2:1 clay to
monomer ratio) applied in the semi-continuous process described in Example 5:
100.8 g (1.52 wt.%) acrylic acid
400.5 g (6.04 wt.%) acrylamide
55.1 g (0.83 wt.%) NaOH
51.5 g (0.78 wt.%) Na2C03
1.62 g (0.02 wt.%) NBAM
12.8 g (0.19 wt.%) potassium persulfate
1000.8 g (15.09 wt.%) clay
5009.9 g (75.53 wt.%) water
Samples 20 to 23 were prepared using the following MCX mixture (2:1 clay to
monomer ratio), which is substantially similar to Samples 19 and 24 but in a
smaller batch
2o size and applied in a batch type process described below:
50.9 g (1.54 wt.%) acrylic acid
200.5 g (6.05 wt.%) acrylamide
27.55 g (0.83 wt.%) NaOH
25.8 g (0.78 wt.%) Na2C03
0.81 g (0.02 wt.%) NBAM
6.48 g (0.19 wt.%) potassium persulfate
500 g (15.09 wt.%) clay
2502 g (75.50 wt.%) water
Reinforced NPC alloy composites were prepared using the MCX mixtures described
above and TERRAFIX~ 2708-A geotextile, a non-woven polypropylene fiber
geotextile,
having a thickness of about 2.0-2.5 mm.
For Samples 20-23, a 2 mm thickness MCX mixture was poured onto a 120 mm
diameter piece of the geotextile. A polyethylene film cover sheet was placed
on top of the
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MCX mixture and a vacuum pressure in the range of from about 16 to about 30
kPa was
applied to the sample from the opposing side of the geotextile. The MCX
mixture was
intimately distributed in and on the geotextile material by applying the
vacuum. The cover
sheet reduced channeling through the sample and the MCX mixture was more
evenly
distributed through the geotextile, as compared with a sample prepared without
a cover
sheet.
The samples were heated using two 320 W infrared lamps (placed about 250 mm
above the sample) at a temperature of about 80°C for 10 minutes to
polymerize the MCX
mixture.
Samples 19 and 24 were similarly prepared. However, the vacuum process was
applied in the semi-continuous process, described in Example 5 and then passed
under the
CATA-DYNET"" infrared heater.
Samples were cut into 9.0 cm discs using a high speed drill cutter and
weighed. The
results are presented in Table 11.
Table 11
Sample Weight Unit Weight
k /m2
19 13.6 2.14
19.06 3.00
21 15.01 2.36
22 23.26 3.66
23 19.4 .05
3
_
24 15.6 _
2.45
Hydraulic Conductivity Tests
The hydraulic conductivity tests were based on the ASTM 5887-95 test,
described in
20 Example 5.
Flux was tested using two different solutions. The first solution was a 3.5
wt.% NaCI
solution. The second solution was an artificial seawater having the following
composition:
0.46 M NaCI, 0.035 M MgCl2, 0.028 MgS04, and 0.01 M KCI. The artificial
seawater
composition is similar to a natural seawater composition suggested in
Introduction to
Geochemistry (K.B. Krauskopf, McGraw-Hill, pg. 324; 1967).
The results of the flux tests for the 3.5% NaCI solution and the artificial
seawater
solution are presented graphically in Figs. 4 and 5, respectively.
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As shown in Figure 4, the 3.5 wt % NaCI solution's flux through Samples 19,
20, 21
and 22 dropped dramatically and rapidly within the first day of testing. In
fact, the first
several hours of test results produced the most dramatic decrease in flux.
Accordingly,
there are multiple data points shown near time zero for these samples.
However, the lowest
flux data points near time zero on the y-axis, in units of m3/m2/s, for
samples 19, 20, 21 and
22 are 1 x 10-6, 6 x 10-$, 4 x 10-' and 1.5 x 10-', respectively. As a
reference point, the
dotted line drawn at 1 x 10-' m3/m2/s indicates the lowest flux expected from
a conventional
GCL clay based liner when exposed to a similar salt solution. In fact, many
conventional
GCL's are reasonably expected to have a salt water flux significantly greater
than 1 x 10'
m3/m2/s, which is at least one order of magnitude greater than the average
salt water flux
shown for the composite samples of the invention after about 5 days of salt
water exposure.
This substantial disparity in the salt water flux performance between the
conventional GCL
compositions and the reinforced NPC alloy composite is both surprising and
unexpected.
Without being bound by theory, it is believed that the unique physicochemical
properties of
the NPC alloy may provide some synergistic interaction between the clay and
networked
polymer, which, as discussed more fully under Example 7, is preferably in a
naturally
hydrated state from date of manufacture and thereby accounts for the
composite's
precipitous flux drop in the first several hours as well as its at least one,
if not two, order of
magnitude improvement in long term salt water flux performance.
As shown in Fig. 5, the initial seawater flux results, in units of m3/m2/s,
for Samples
23 and 24 are 2 x 10-8 and about 2 x 10-9, respectively, which are
significantly less than for
Samples 19-22. Again, as a reference point, the dotted line drawn at 1 x 10-'
m3/m2/s
indicates the lowest flux expected from a conventional GCL clay based liner
when exposed
to a similar salt solution. This substantial disparity in the seawater flux
performance
between the conventional GCL compositions and the reinforced NPC alloy
composite is
both surprising and unexpected, for the reasons stated above.
EXAMPLE 7
SEM and X-Ray Analysis
The following SEM micrographs and X-ray analyses illustrate that (1 ) clay in
the NPC
alloy is chemically associated with the polymer, (2) clay does not become
dissociated from
the NPC alloy when the polymer is swollen, (3) NPC alloy is intimately
integrated with the
reinforcing agent in the reinforced NPC alloy composite, and (4) the
reinforced NPC alloy
composite can contain a significant amount of occluded water retained from
manufacture.
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MonomerlClay Mixture Preparation
An MCX mixture was prepared as shown in Table 12. The clay used in the MCX
mixture was NATURAL GELT"". The monomer was a 1:4 (wt) mixture of acrylic acid
(Aldrich) and acrylamide (Cytec).
Water, NaOH, NaHC03, acrylic acid, acrylamide, NBAM and K2S208 were mixed in a
10-L HDPE pail. The aqueous solution was mixed well, prior to addition of
clay. Clay was
added and mixed again to form a homogeneous MCX mixture. The MCX mixture was
viscous but fluid before polymerization.
Table 12
Com onent Amount
Water 5009.9
NaOH 55.1
NaHC03 51.5
Ac lic Acid 100.8
Ac lamide 400.5
NBAM 1.62
K2S20$ 12.8
Cla 1000.8
Total 6633.02
Clay to Monomer 2.00
Ratio
wt
Reinforced NPC Alloy Composite Preparation
The MCX mixture was poured in a thickness of about 1.5 mm onto a 0.95 m x 0.80
m
piece of TERRAFIX~2708-A geotextile, as a reinforcing agent. A polyethylene
cover sheet
was placed on top of the MCX mixture and a vacuum pressure in a range of from
about 16
to about 30 kPa was applied to the sample from the geotextile's opposing side.
The MCX
mixture was intimately distributed in and on the geotextile material by
applying the vacuum..
The reinforced MCX mixture sample was put under an infrared heater at
80°C for 8
minutes for polymerization. The moisture content of the reinforced NPC alloy
composite
was about 75%.
Scanning Electron Microscopy (SEM)
The reinforced NPC alloy composite was examined using a JEOL Model No. JSM
6301 FXV Scanning Electron Microscope (SEM, Japan Electron Optics Limited,
Japan) at
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the SEM Facility, Department of Earth & Atmospheric Sciences, University of
Alberta,
Edmonton, Alberta, Canada.
Samples were pretreated for SEM examination by placing the samples in a holder
and immersing them in liquid nitrogen (i.e., about -196°C). Once
frozen, the samples were
removed from the liquid nitrogen, using pliers or a knife, quickly torn or
cut, as indicated
below, to obtain a cross-sectional perspective of the sample. The samples were
then
quickly transferred to the SEM vacuum chamber, where they were warmed to -
40°C to
sublime any surface ice crystals. Next, the samples were placed in a coating
chamber
where a thin layer of gold was applied to the sample to increase electrical
conductivity. The
samples were then returned to the SEM vacuum chamber for examination. The
samples
were maintained at or near liquid nitrogen temperature during the gold coating
and
subsequent SEM examination. This was done so that the structure of the sample
would be
preserved. The samples contained considerable moisture and thus had to be
maintained in
a frozen state for the SEM to operate properly.
The sample in Figs. 8 and 9 was cut with a knife prior to mounting. Both
micrographs show the cut edges of fibers of the reinforcing agent. Particles
seen in Fig. 9
are fragments from the cutting step in preparing the sample for SEM
examination. The
sample in Figs. 10 and 11 was severed with a pair of pliers, instead of a
knife, prior to
mounting. Fig. 10 shows the fractured edges of fibers of the reinforcing agent
and other
fragments produced by fracturing. The SEM micrographs of Figs. 6 to 12 are
discussed in
Table 13.
Discussion of SEM Micrographs
In summary, the SEM micrographs illustrate that (1 ) clay in the NPC alloy is
chemically associated with the polymer, (2) clay does not become dissociated
from the NPC
alloy when the polymer is swollen, (3) NPC alloy is intimately integrated with
the reinforcing
agent in the reinforced NPC alloy composite and (4) the reinforced NPC alloy
composite can
contain a significant amount of occluded water retained from manufacture.
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Table 13
Fig. Magni-Description Observations
#
fication
6 140X Comparative. Top plan
perspective of reinforcing
a ent without NPC allo
.
7 7000X Comparative. Potassium Swollen polymer has crater-like
open-
acrylate cross-linked cell structure. The open cells
and were
polymerized without previously occupied by occluded
clay. No water,
reinforcing agent. Samplewhich was removed by SEM pre-
immersed in water for treatment procedures. It is
10 expected
minutes prior to SEM. that acrylamide/sodium acrylate
copolymer would behave in
a similar
manner.
8 50X Reinforced NPC alloy Illustrates NPC alloy intimately
composite. Sample driedintegrated with reinforcing
from agent. Also
the original 75 wt.% illustrates thin layer of
moisture NPC alloy (right-
to about 25-50wt.% withhand side of micrograph) integrated
with
ambient drying conditionsNPC alloy in reinforcing agent;
over i.e., not a
a 2 week period. The laminate structure.
NPC
alloy shrank around
the
reinforcing agent fibers.
The
shrinkage indicates
the volume
occupied by previously
occluded water.
9 270X Same as Fig. 8 No individual clay particles
can be seen
in the SEM micrographs, illustrating
that
the clay particles are chemically
associated with polymer in
NPC alloy,
even at cla to monomer ratio
of 2:1.
500X Reinforced NPC alloy Illustrates how swollen NPC
alloy
composite immersed in expands to conform to and
water substantially
for 10 minutes prior occupy interstitial spaces
to SEM. in reinforcing
a ent.
11 4500X Same as Fig. 10. Illustrates that clay particles
are
chemically associated with
polymer in
NPC alloy. No free clay particles
are
seen, therefore indicating
that the clay
does not dissociate from NPC
alloy
when water-swollen. Swollen
NPC alloy
has open-cell structure, similar
to
polymer without clay (Fig.
7). Also, the
degree of occluded water is
substantially similar to polymer
without
clay (Fig. 7), therefore indicating
that
clay even at high loading
does not have
a disproportionately detrimental
effect
on NPC alloy's swelling capacity
versus
a cla -free water absorbin
of mer.
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Fig. Magni-Description Observations
# fication
12 650X Comparative. Same Swollen polymer fills interstitial
spaces
monomer/cross-linking in reinforcing agent in same
agent manner as
mixture as used for NPC alloy in Fig.10. Open-cell
Fig. 10 structure
sample, but without of polymer without clay similar
clay. to that of
Immersed in water for the clay-based sample shown
10 in Fig. 10.
minutes prior to SEM. Comparison to Fig. 10 illustrates
how
the clay is (a) integrated
in the NPC
alloy and (b) does not have
a
disproportionately detrimental
effect on
NPC allo 's swellin ca acit
.
As shown more clearly in the comparison between Fig. 10 (reinforced NPC alloy
composite) and Fig. 7 (swollen polymer without clay) or Fig. 12 (swollen
polymer without
clay in reinforcing agent), the swollen NPC alloy open-cell structure is
similar to that of clay-
s free polymers. Accordingly, the clay does not constrain the NPC alloy's
water swelling
capacity. In view of Ogawa et al (discussed more fully in Example 1 ), which
suggests that
clay acts as a cross-linking agent for making water absorbent polymers, this
is a surprising
and unexpected result. Also, in view of the cross-linking agent results in
Example 2, which
illustrate that a cross-linking agent concentration as low as about 0.1 wt.%
can over cross-
link a polymer, thereby substantially reducing its water absorption capacity,
these results are
most particularly surprising and unexpected at a relatively high clay to
monomer ratio of 2:1.
X-Ray Analyses
The Energy Dispersive X-Ray (EDX) analysis device of the SEM collects signals
from an area of 1 ~m x 1 ~m at a penetration depth of about 1 ~,m. X-ray
analysis was
conducted at numerous sites on the sample in Fig. 11, including the NPC alloy
at the center
of Fig. 11. Consistently at each site, peaks appeared for gold (2.1, 8.5 keV),
silicon (1.74
keV), aluminum (1.49 keV), sodium (1.04 keV), magnesium (1.25 keV), and iron
(0.615, 6.40
keV). The gold peak was a result of the gold treatment for the SEM
examination. The
relative strengths and positions of the silicon and aluminum peaks in the EDX
spectra were
consistent with those expected for bentonite clay. All sites examined showed
the presence
of silicon, aluminum, sodium, magnesium and iron. This analysis shows that the
NPC alloy
is homogeneous throughout the sample, even at the 1 ~m3 level. Accordingly,
the clay in
the NPC alloy is chemically associated with the polymer.
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EXAMPLE 8
Clay Migration Tests
This example illustrates that, when the reinforced NPC alloy composite is
immersed
in water, the NPC alloy swells with substantially no clay separating from the
composite.
Reinforced NPC Alloy Composite
An MCX mixture was prepared by mixing 40.51 g acrylic acid with 500 g water.
36.6
potassium hydroxide and 0.624 g NBAM were then added with stirring. After the
potassium
hydroxide was in solution, 24.39 g potassium carbonate was dissolved, followed
by addition
of 160.33 g acrylamide, 4.83 g potassium persulfate and 500 g water. 594.07 g
of the
monomer mixture was blended with 199.79 g bentonite clay in a flood blender to
give a
creamy suspension.
A layer of the MCX mixture was poured onto a 2 cm x 2 cm piece of TERRAFIX~
2708-A geotextile. The MCX mixture was intimately distributed in and on the
geotextile
material by hand. The MCX mixture was polymerized in the reinforcing agent by
heating in a
75°C oven for 8 minutes.
This reinforced NPC composite was labeled as Sample A in the clay migration
tests.
Comparative Sample B - No Polymerization Initiator, No Cross-linking Agent
The monomer/clay mixture for Comparative Sample B was prepared by mixing 18.7
g acrylic acid, 6.1 g sodium hydroxide, 34.9 g clay and 18 g water to form a
viscous paste.
The paste was then forced into a 2 cm x 2 cm piece of TERRAFIX~ 2708-A. The
monomer/clay mixture could not be embedded into the geotextile at 100kPa. So,
one of the
inventors, weighing about 80 kg, placed a piece of PLEXIGLAST"" on top of the
sample and
stood on it while rocking back and forth. About half of the monomer/clay
mixture was forced
into the fabric using this method. No polymerization initiator or cross-
linking agent was
added to the monomer/clay mixture.
The sample was dried in an oven at 75°C for one hour.
Comparative Sample C - No Polymerization Initiator
A monomer/clay mixture was prepared by mixing 79.89 g acrylamide, 20.56 g
acrylic
acid, 0.3 g NBAM as cross-linking agent, 9.995 sodium hydroxide, 9.962 g
sodium
carbonate, and 1000 g water. 552.8 g of the monomer mixture was blended with
100.55 g
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bentonite clay in a flood blender to give a creamy suspension. No
polymerization initiator
was added to the monomer/clay mixture.
A layer of the monomer/clay mixture was poured onto a 2 cm x 2 cm piece of
TERRAFIX~ 2708-A geotextile. The mixture was intimately distributed in and on
the
geotextile material by hand. The monomer/clay mixture was heated in a
70°C oven for 1
hour in the reinforcing agent.
This sample was labeled as Sample C in the clay migration tests.
Comparative Sample D - Pre-formed Oligomer (MW 2,000)
Comparative Sample D was prepared by mixing 6.5 g pre-formed polyacrylic acid,
1.6 g sodium hydroxide, 26 g water and 10.70 g clay. The polyacrylic acid,
having a
molecular weight of 2,000, was obtained from Aldrich Chemical Co.
A layer of the pre-formed oligomer/clay mixture was poured onto a 2 cm x 2 cm
piece
of TERRAFIX~ 2708-A geotextile. The pre-formed oligomer/clay mixture was
intimately
distributed in and on the geotextile material by hand. The sample was dried in
an oven at
75°C for one hour.
Comparative Sample E - Pre-formed Polymer (MW 450,000)
Comparative Sample E was prepared by mixing 4.74 g pre-formed polyacrylic
acid,
1.44 g sodium hydroxide, 96 g water and 11.52 g clay. The polyacrylic acid,
having a
molecular weight of 450,000, was obtained from Aldrich Chemical Co.
A layer of the pre-formed polymer/clay mixture was poured onto a 2 cm x 2 cm
piece
of TERRAFIX~ 2708-A geotextile. The mixture was intimately distributed in and
on the
geotextile material using a wooden rolling pin. The sample was dried in an
oven at 75°C for
one hour.
Comparative Commercial Products
Two commercial products were also tested for comparative purposes in the clay
migration tests.
GUNDSEAL~ (GSE Lining Technology, Inc., Houston, Texas) is a bentonite
clay/polyethylene geomembrane liner. Sodium bentonite is adhered to a
polyethylene
geomembrane using an adhesive at a loading of 1 Ib/ft2 (4.9 kg/m2). The sample
was about
3 mm thick. A 2.5 cm x 2.5 cm piece of GUNDSEAL~ was labeled as Comparative
Sample
F.
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BENTOMAT° DN (CETCO, Arlington, Illinois) is a geosynthetic clay liner
consisting
of a sodium bentonite layer between two layers of geotextile, which are needle-
punched
together. A 2.5 cm x 2.5 cm piece of BENTOMATT~'" DN was labeled as
Comparative Sample
G.
Clay Migration Test Procedure
Each of the samples was placed in a glass bottle. 100 mL deionized water at
room
temperature (about 20°C) were then poured into the bottle.
The bottle was left standing without disturbance at room temperature. The
sample
was observed at 3 hours and 22 hours after addition of water, as described in
Table 14.
Table 14
Sam 1e Descri tion of Sam 1e Observations
A MCX mixture: acrylamide, After 3 hours, the sample
sodium had swelled
acrylate, cross-linking considerably. After 22 hours,
agent, there was
persulfate polymerization some additional swelling of
initiator, the NPC
and clay. alloy. The swelled NPC alloy
was puffy
in appearance. Both the fabric
and clay
The MCX mixture was pressedremained as an integral part
into of the NPC
the fabric and polymerized alloy. (see Figs. 13A and
in a fabric 13B).
75C for 8 minutes. Substantially no clay separated
from the
NPC alloy after 22 hours of
immersion
time.
B Comparative. Monomer/clay After 3 hours, the acrylic
acid and
mixture: acrylic acid, NaOH,sodium acrylate dissolved
water in the water.
and clay. No polymerizationThe clay had migrated off
initiator the fabric and
or cross-linking agent was swelled at the bottom of the
used. test bottle.
There was no change after
22 hours.
The monomer/clay mixture
was
pressed into a fabric and
dried @
75C for one hour.
C Comparative. Monomer/clay After 3 hours, the acrylamide
and
mixture: acrylamide, acrylicsodium acrylate dissolved
acid, in the water.
NaOH, NBAM (cross-linking The clay had migrated off
agent), the fabric and
water and clay. No polymerizationdispersed in the water. There
was no
initiator was used. change after 22 hours.
The monomer/clay mixture
was
pressed into a fabric and
heated for
one hour 70C.
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Sam 1e Descri tion of Sam 1e Observations
D Comparative. A pre-formed After 3 hours, the polyacrylic
acid
polyacrylic acid (MW=2000) dissolved in the water. The
was clay
mixed with clay and pressedmigrated off the fabric and
into the dispersed in
fabric. the water. There was no change
after
22 hours. see Fi s. 14A and
14B
E Comparative. A pre-formed After 3 hours, the polyacrylic
acid
polyacrylic acid (MW=450,000)dissolved in the water and
was some clay
mixed with clay and pressedhad migrated off the fabric.
into a After 22
fabric. hours, the remaining clay
had migrated
off the fabric and swelled
at the bottom
of the bottle.
F Comparative. GUNDSEAL~ After 3 hours, the clay had
migrated off
the backing material and started
to
swell. After 22 hours, the
clay was
more swollen.
G Comparative. BENTOMAT~ DN After 3 hours, the clay had
migrated
from between the two geotextile
layers
and dispersed into the water.
The clay
had swelled and settled in
the bottom of
the bottle by 22 hours. (see
Figs. 15A
and 15B
Line drawings were prepared from some of the photographs taken during the clay
migration tests summarized in Table 14.
Sample A was a reinforced NPC alloy composite. Fig. 13A illustrates Sample A
prior
to immersion in deionized water. The NPC alloy is in the reinforcing agent 40.
Fig. 13B
illustrates the sample after 3 hours immersion in deionized water. The swelled
NPC alloy 46
had a puffy appearance. Substantially no clay separated from the composite.
Also, the
swelled NPC alloy 46 was still integrated with the reinforcing agent 40.
Fig. 14A illustrates Comparative Sample D prior to immersion in deionized
water.
The pre-formed polymer and clay mixture is in the reinforcing agent 40. Fig.
14B illustrates
the sample after 3 hours immersion in deionized water. The polymer had
dissolved in water
and the clay 44 migrated off the reinforcing agent 40 and dispersed in the
water. Some
settling of the clay 44 is observed at the bottom of the bottle.
Fig. 15A illustrates Comparative Sample G prior to immersion in deionized
water.
The sample has clay sandwiched between a first reinforcing agent 40 and a
second
reinforcing agent 42. Fig. 15B illustrates the sample after 3 hours immersion
in deionized
water. The clay 44 had migrated from between the two reinforcing agent layers
40, 42 and
dispersed into the water. The clay 44 of Sample G had settled more densely
than the clay
of Comparative Sample D, shown in Fig. 14B.
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The results in Table 14 and Fig. 13B illustrate how the clay is an integral
part of the
NPC alloy. Moreover, the results demonstrate how the NPC alloy is an integral
part of the
composite. In all of the comparative samples, clay migrates from the mixture
and/or the
reinforcing agent. Also, monomer and pre-formed polymer mixture migrate from
the
reinforcing agent. This is shown more clearly in Figs. 148 and 15B.
The reinforced NPC alloy composite remains substantially intact on exposure to
deionized water at about 20°C. Specifically, substantially no clay
separates from the NPC
alloy. Moreover, the composite is expected to exhibit substantially similar
performance in
deionized water in a temperature range of about 1 °C to about
60°C. This represents a
1o significant improvement over the conventional techniques.
EXAMPLE 9
Residual Monomer Content
One concern about using acrylamide as a monomer for preparing an NPC alloy is
the leaching of any residual monomer. The FDA limit for teachable acrylamide
in
polyacrylamide is 0.05% (500 ppm, 500 pg/g) when the polyacrylamide is used in
treatment
of potable water and for paper and paperboard for food contact applications
(EPA/600/X-
85/270 July 1985, PB88-170824).
This example provides residual monomer data for a polymer and an NPC alloy.
Generally, the amount of residual monomer is dependent on initiator
concentration, reaction
time, and reaction temperature. For example, residual monomer content
generally
decreases with increased temperature, increased reaction time and increased
initiator
concentration.
Sample Preparation
A monomer mixture was prepared by mixing 20 g acrylic acid, 80 g acrylamide,
10 g
sodium hydroxide, 12 g sodium carbonate, and 0.6 g potassium persulfate in
1000 mL
water. The monomer mixture was divided into three parts and NBAM was added as
a cross-
linking agent at 0.1 %, 0.3% and 0.9%, by weight, respectively. Each of the
three monomer
3o mixtures was sub-divided into three parts. Clay was added to some of the
mixtures in an
amount of about 1:1 monomer to clay or about 1:2 monomer to clay, as shown in
Table 15.
The MCX mixtures were blended in a food blender to produce a smooth,
homogeneous
mixture.
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Samples of the monomer and MCX mixtures were transferred to plastic beakers
and
placed in an 80°C oven for one hour for polymerization. The samples
were removed from
the oven and allowed to cool to room temperature. The samples were dried at
95°C for a
couple of days.
Residual Monomer Analysis
The residual acrylamide monomer was analyzed by EPA Method 8316 entitled
"Acrylonitrile, Acrylamide and Acrolein by High Performance Liquid
Chromatography
(HPLC)."
1o A weighed sample of dried polymer or polymer/clay alloy (1-2 g) was placed
in a
polyethylene beaker with about 200 mL water and allowed to stand overnight at
room
temperature (about 20°) overnight. The polymer and NPC alloy samples
swelled and
absorbed some of the water. The remaining water was decanted from each swollen
polymer and NPC alloy and analyzed for acrylamide content. The results are
presented in
Table 15.
Table 15
Sample Monomer Monomer:ClayLeached
Mixture (wt.) Acrylamide
(wt.) ppm
(N9/9
of mer
20%Ac lic 80% lamide,0.1 % No Cla 13.1
Acid, Ac NBAM
26 20%Ac lic 80% lamide,0.3% NBAMNo Cla 128
Acid, Ac
27 20%Ac lic 80% lamide,0.9% NBAMNo Cla 22
Acid, Ac
28 20%Ac lic 80% lamide,0.3% NBAM1:1 108
Acid, Ac
29 20%Ac lic 80% lamide,0.9% NBAM1:1 7596
Acid, Ac
20%Ac lic 80% lamide,0.3% NBAM1:2 90.1
Acid, Ac
The amount of leached acrylamide, leached by water from the dried polymer and
NPC alloy samples, was well below the FDA limit of 500 ppm for all samples
except one.
20 Sample 29 resulted in a very high leached acrylamide concentration. Because
of the
inordinately high residual monomer, it appears that Sample 29 did not
polymerize properly.
Thus, Sample 29 is an aberrant data point, especially in view of the Sample 28
result, based
also on a 1:1 MCX mixture, but with only 108 ppm residual acrylamide, and the
Sample 26
result, a clay-free, monomer, cross-linking agent mixture, but with only 128
ppm residual
25 acrylamide.
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It was expected that polymerization may not proceed as extensively and,
therefore,
the amount of leached acrylamide would be greater, for samples containing
clay, especially
at higher amounts of clay. Surprisingly, however, as shown in Table 15, the
amount of
leached acrylamide was similar for Samples 28 and 30 (0.3% NBAM, 1:1 and 1:2
monomer
to clay, respectively) and Sample 26 (0.3% NBAM, no clay). It is expected that
the residual
monomer contents will be similar for reinforced NPC alloy composite samples.
This and the other examples presented herein demonstrates the advantages of
the
reinforced NPC alloy composite over conventional GCL's used in fluid barrier
applications
and water absorbency applications.
Preferred compositions and processes for practicing the invention have been
described. It will be understood that the foregoing is illustrative only and
that other
embodiments of the process for producing a reinforced NPC alloy composite can
be
employed without departing from the true scope of the invention defined in the
following
claims.
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