Note: Descriptions are shown in the official language in which they were submitted.
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HIGH-PERFORMANCE FIBROUS PRODUCTS
RELATED APPLICATION
100011 This application claims the benefit of U.S. Provisional Application No.
61/450,407 filed March 8, 2011. The entire teachings of the above application
are
incorporated herein by reference.
FIELD OF APPLICATION
[0002] This application relates generally to high-performance fibrous
products.
BACKGROUND
[0003] Filtration applications require that the media being used have
durability and
dimensional stability under the operating conditions for the product. For high
performance applications, the filtration media can encounter extreme
conditions, such as
high temperatures, contact with oil or other solvents, or exposure to oil or
water under
high pressure. Most filtration media used for demanding applications such as
intake
filters, in-line fluid filters, engine oil filters and the like, are nonwoven
products made
using cellulose in combination with synthetic fibers. Such composites make use
of the
inexpensive cellulose fibers with strong synthetic fibers to impart desired
functionalities.
Desired functionalities include properties like wet or dry strength of the
nonwoven
product, durability, dimensional uniformity and stability, and consistently
engineered
thickness, fiber, and pore size. Such functionalities are desirable in other
high-
performance fibrous products as well.
[0004] Nonwoven composites comprising natural and synthetic fibers can be
formed
cost-effectively by traditional papermaking processes. When traditional
papermaking is
used to form natural-synthetic composites, though, performance limitations can
be
introduced. Synthetic fibers that are added to cellulosic fibers during
traditional
papermaking can bunch up in the headbox, interfering with the intimate mixing
and
fiber-fiber attachment needed to produce a durable web. In addition, the
different surface
energies of the two fiber populations (i.e., natural and synthetic) can
prevent them from
attaching to each other. Therefore, the typical combination of natural and
synthetic fibers
in a fibrous composite can perform poorly in filtration.
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[0005] To enhance the strength and solvent resistance of the high-performance
nonwoven product, as may be used for filter applications, these media can be
impregnated
with synthetic polymer solutions capable of curing during the wet-web drying
to provide
additional strength and solvent resistance. Thermosetting high temperature
polymers
such as phenol-formaldehyde resins are one such example of impregnating resins
currently being used. Many polymeric resin systems used in impregnation are
not water
soluble and hence require organic solvents to enable them to coat the fibers.
These
impregnation processes also poorly control the thickness of polymeric coating
deposited
on the fibers, leading to variability and imprecision in pore sizing.
Moreover, the solvent
systems used for depositing the polymeric resins are typically flammable,
hazardous to
health, costly, and require specialized disposal.
[0006] A need exists in the art, therefore, for high-performance products made
from
fibrous webs using traditional papermaking techniques, where the product is
strong and
resistant to heat and oils. Such a product can be useful, for example, in
filtration media.
A need also exists for a coating process adaptable to nonwoven fibrous
products that
imparts desirable properties to the product, such as fire resistance,
consistent pore size
and stable dimensionality. Such a coating process desirably would comprise an
aqueous
system, so that the detrimental features of the solvent-based system would be
avoided.
SUMMARY
[0007] Disclosed herein, in embodiments, are formulations for coating a
fibrous web,
comprising an emulsion capable of deposition on the fibrous web, the emulsion
comprising an aqueous continuous phase and a discontinuous internal phase
comprising a
surface-modifying agent. In embodiments, the fibrous web comprises a
population of
fibers that are pretreated with a pretreatment polymer. The pretreatment
polymer can be a
polycation. In embodiments, the fibrous web comprises cellulose fibers. In
embodiments, the fibrous web comprises two populations of dissimilar fibers.
In
embodiments, the surface-modifying agent comprises a polymeric system that
forms a
coating polymer on fibers of the fibrous web following evaporation of the
aqueous
continuous phase of the emulsion. The surface-modifying agent can further
comprise an
additive. The additive can impart properties to the fibrous web such as fire
resistance,
flame retardation, lubricity, hydrophobicity, and plasticity. In embodiments,
the
polymeric system comprises a polymeric precursor. In embodiments, the surface-
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modifying agent comprises a crosslinking agent that crosslinks the coating
polymer. In
embodiments, the pretreatment polymer has an affinity for the coating polymer.
[0008] Further disclosed herein, in embodiments, are methods for modifying the
surface
of fibers in a fibrous web, comprising the steps of: providing a plurality of
fibers capable
of being arranged in a fibrous web, coating the plurality of fibers with an
emulsion
comprising a continuous aqueous phase and a discontinuous phase comprising a
surface-
modifying agent, wherein the surface-modifying agent comprises a polymeric
system
capable of depositing a polymer on a fiber surface, arranging the plurality of
fibers to
form the fibrous web before, during, or after the step of coating the fibers,
evaporating the
continuous aqueous phase of the emulsion, coalescing the discontinuous phase
to form an
even coating disposed on the fiber surface of the plurality of fibers, and
engaging the
polymeric system to deposit the polymer on the fiber surface of the plurality
of fibers,
thereby modifying the fiber surface. In embodiments, the polymeric system
comprises a
polymer precursor and the step of engaging the polymeric system comprises
activating
the polymer precursor to form the polymer to be deposited on the fiber
surface. In
embodiments, the surface-modifying agent further comprises an additive that
interacts
with the polymer on the fiber surface. In embodiments, the method further
comprises the
step of crosslinking the polymer on the fiber surface. In embodiments, the
method further
comprises an initial step of pretreating some or all of the plurality of
fibers, to be
performed before the step of providing the plurality of fibers.
DETAILED DESCRIPTION
[0009] Disclosed herein, in embodiments, are systems and methods for surface-
modification of fibers based on the use of aqueous oil-in-water emulsions to
deposit the
surface-modifying agents on fibrous structures or fibrous webs. As used
herein, the term
"fibrous structure" or "fibrous web" refers to any arrangement of individual
fibers or
filaments that are interlaid with one another. In some embodiments, the
fibrous structure
or web has a nonwoven character. In some embodiments, the fibers or filaments
form a
disorganized pattern (e.g., a substantially random formation or structure
whose
organization has little discernable pattern). Some techniques for fabricating
fibrous
structures are known in the art, including papermaking techniques and other
techniques
for making nonwoven materials.
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[0010] As used herein, the term "fiber" can refer to any filamentous entity,
whether
natural or synthetic, that possesses a large aspect ratio (e.g., a dimensional
length much
larger than its cross-sectional dimension (e.g., a diameter)). For instance,
in
embodiments, the aspect ratio of the fibers can be larger than about 10, 20,
30, 50, or 100.
The term "fiber" comprises larger fibers and microfibers. A microfiber is
identified by
having a small cross-sectional width (i.e., diameter), of no more than 100
microns in
some embodiments. In embodiments, a microfiber may have an average cross-
sectional
width between 0.5 and 50 microns. In other embodiments, a microfiber may have
an
average cross-sectional width between 4 and 40 microns. In embodiments, a
microfiber
may have an average cross-sectional width less than 30 microns. The size of
the
microfibers can also be characterized in terms of denier units. In some
embodiments, the
microfibers, on average, are less than about 10 denier, or less than about 5
denier, or less
than about 2 denier, or less than about 1 denier. Fibers larger than
microfibers can be
called "larger fibers." As used herein, the term "larger fiber" refers to any
synthetic or
natural fiber that is longer and/or broader (i.e., having a larger cross-
sectional length) than
a microfiber. In some embodiments, larger fibers have a cross-sectional length
(e.g.,
diameter) of 3-50 microns, 7-70 microns, or 150-600 microns, when used with
smaller
microfibers. One example of larger fibers is the cellulosic fiber associated
with typical
wood pulp formulations. In some embodiments, the ratio of the average cross-
section
dimensions (e.g., diameters) of the larger fibers to the microfibers can be
greater than
about 5, 10, 20, 50, 100, 500, 1000, 5000, or 10000. Fibers can have a
plurality of fibrils
(i.e., fibrillated fibers), which can potentially be separated. A fibrillated
fiber can be
produced from a fiber during fiber processing, where a precursor fiber is
abraded or
otherwise mechanically distressed. For example, processes (e.g., papermaking)
can
increase the internal and external fibrillation of a cellulosic pulp. A
fibrillated fiber can
include portions having a cross-sectional width less than about 100 microns,
though the
unfibrillated fiber may have a cross-sectional width larger than about 100
microns.
Fibrils can have a nanofiber structure, e.g., exhibiting an average cross-
sectional width
between about 1 nm and 1 micrometer, or between about 50 nm and about 500 nm.
In
some embodiments, the microfibers are embodied as nanofibers, which can
originate
from fibrils of a microfiber.
[0011] The term "fiber" can refer to a synthetic fiber or a natural fiber. As
used herein,
the term "synthetic fibers" include fibers or microfibers that are
manufactured in whole or
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in part. Synthetic fibers include artificial fibers, where a natural precursor
material is
modified to form a fiber. For example, cellulose (derived from natural
materials) can be
formed into an artificial fiber such as Rayon or Lyocell. Cellulose can also
be modified
to produce cellulose acetate fibers. These artificial fibers are examples of
synthetic
fibers. Synthetic fibers can be formed from synthetic materials that are
inorganic or
organic. As used herein, the term "natural fiber" refers to a fiber or a
microfiber derived
from a natural source without artificial modification. Natural fibers include
vegetable-
derived fibers, animal-derived fibers and mineral-derived fibers. Vegetable-
derived fibers
can be predominately cellulosic, e.g., cotton, jute, flax, hemp, sisal, ramie,
and the like.
Vegetable-derived fibers can include fibers derived from seeds or seed cases,
such as
cotton or kapok. Vegetable-derived fibers can include fibers derived from
leaves, such as
sisal and agave. Vegetable-derived fibers can include fibers derived from the
skin or bast
surrounding the stem of a plant, such as flax, jute, kenaf, hemp, ramie,
rattan, soybean
fibers, vine fibers, jute, kenaf, industrial hemp, ramie, rattan, soybean
fiber, and banana
fibers. Vegetable-derived fibers can include fibers derived from the fruit of
a plant, such
as coconut fibers. Vegetable-derived fibers can include fibers derived from
the stalk of a
plant, such as wheat, rice, barley, bamboo, and grass. Vegetable-derived
fibers can
include wood fibers. Animal-derived fibers typically comprise proteins, e.g.,
wool, silk,
mohair, and the like. Animal-derived fibers can be derived from animal hair,
e.g., sheep's
wool, goat hair, alpaca hair, horse hair, etc. Animal-derived fibers can be
derived from
animal body parts, e.g., catgut, sinew, etc. Animal-derived fibers can be
collected from
the dried saliva or other excretions of insects or their cocoons, e.g., silk
obtained from silk
worm cocoons. Animal-derived fibers can be derived from feathers of birds.
Mineral-
derived natural fibers are obtained from minerals. Mineral-derived fibers can
be derived
from asbestos. Mineral-derived fibers can be a glass or ceramic fiber, e.g.,
glass wool
fibers, quartz fibers, aluminum oxide, silicon carbide, boron carbide, and the
like.
[0012] In embodiments, the surface-modifying agents for fibers disclosed
herein
comprise polymers or polymeric precursors (e.g., monomers, comonomers,
oligomers,
etc.) and mixtures thereof The term "polymeric system" shall refer to the
polymers,
polymeric precursors or mixtures thereof that can be used to coat fibers in a
fibrous web
with a polymeric coating. In embodiments, the polymeric system can be carried
in the
internal phase of an emulsion. As used herein, the term "emulsion" refers to a
heterogeneous system comprised of two immiscible liquids, where one of the
liquids is
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intimately dispersed in the other liquid in the form of droplets. The emulsion
matrix is
termed the external or continuous phase of the emulsion, and the phase
comprised of the
dispersed small droplets is called the internal or discontinuous phase. An
emulsion can
be stabilized or destabilized by the presence of surface-active agents called
emulsifiers or
demulsifiers. As an example, an emulsifying agent can form interfacial films
around the
droplets in the dispersed phase to create a barrier that interferes with the
coalescence of
the emulsified droplets. If an emulsion is destabilized, the droplets tend to
coalesce into
larger sizes, causing the phases to separate by gravitational settling.
Conversely, in a
stable emulsion, the two components remain admixed. As described herein, an
aqueous
lo continuous phase of an emulsion supports a discontinuous phase bearing
the surface-
modifying agents, (e.g., the polymeric system (monomers, comonomers,
oligomers,
polymers, and the like, and initiators (free radical, ionic, etc.)) for
coating the fibers. The
discontinuous oil phase can contain a variety of other surface-modifying
agents, such as
plasticizers (e.g., polyols), fire-retardants (e.g., brominated or phosphate
molecules),
crosslinkers (bifunctional or multifunctional), and the like.
[0013] In embodiments, for example, a polymeric system can deposit a coating
on fiber
surfaces that conveys advantageous properties to a fibrous web formed
therefrom. For
example, a polymeric system comprising a reactive monomer/initiator or a
monomer/crosslinker or oligomers/crosslinker or a polymer/crosslinker can be
emulsified
in water using an appropriate surfactant/emulsifier. The surface-modifying
agents
contained in the emulsion can include other materials besides the polymeric
system, i.e.,
additives that cooperate with the polymeric system or otherwise interact with
the fibers to
impart desirable properties. For example, the emulsion can contain a polymeric
system
comprising monomers and comonomers as the predominant species, followed by
curing
agents or crosslinking agents mixed with various additives that can impart
different
finishes to the web such as hydrophobicity, fire retardancy etc. These
ingredients can all
be mixed with a small amount of surfactant and added to water under high
agitation. The
resulting stable emulsion, comprising the polymeric system and the other
additives, is
then applied to the fibrous web.
[0014] After the emulsion is applied to the web, it coats the fibers
relatively
homogenously. As the web is processed through the dryer, the combination of
shear and
heat cause the aqueous phase of the emulsion to evaporate, leaving behind
residual
droplets of the oil phase. These same forces over time urge the droplets to
coalesce. As
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the droplets coalesce, the polymeric system becomes engaged. As it is engaged,
the
polymeric system provides for the intact coating polymers that coat the fibers
of the
fibrous web. Engaging the polmeric system may involve merely depositing intact
coating
polymers that are already contained in the emulsion droplets on the fiber
surface.
Engaging the polymeric system may involve initiating and propagating
polymerization
from polymeric precursors, so that coating polymers are formed on the fiber
surface.
[0015] As the polymeric system within the oil phase is affected by the high
temperature
of the drying unit, the polymeric system cures, forming the coating polymer
and
incorporating the additives (such as lubricant, fire retardant,
hydrophobicizer, and the
like) that are present in the oil phase droplets. The result is a continuous
application to
the web fibers of a cured polymeric system comprising the coating polymer and
the
additives. The cure completes during the drying process and incorporates into
the coating,
all the additives that are present in the droplet.
[0016] In certain embodiments, the candidate fibers can be pretreated before
the
application of the surface-modifying agents, for example, so that the fibers
carry a
positive charge. Pretreatment can be carried out, for example, with a
polycation. As used
herein, the term "polycation" may include any polymer (e.g., copolymer) having
a net
positive charge, such as a polyamine. As used herein, the term "polyamine" may
include
any polymer or copolymer that has at least a portion of its repeat units
containing an
amine (quaternary, ternary, secondary, or primary). In embodiments, the
polyamine may
desirably contain some repeat units with primary amines due to the reactivity
of a primary
amine. The polymers (e.g., polycations) as used herein can have an average
molecular
weight which can range from 1,000 up to 10,000,000 but it is preferable to be
between
10,000 to 500,000.
[0017] In embodiments, a polyamine useful as a pretreatment may be a polymer
comprising chitosan or polyethyleneimine. In embodiments, a chitosan polymer
may
comprise a certain portion of higher molecular weight chitosan, i.e., chitosan
with a
viscosity of at least 800 cp when in a 1% acetic acid solution. In
embodiments, the
amount of higher molecular weight chitosan may be greater than 10%, greater
than 20%,
or greater than 30%. Those of skill in the art will appreciate that for
certain polymers,
e.g., chitosan, an exact molecular weight may not be available, because such
structures
are defined by viscosity rather than molecular weight.
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[0018] As an example of pretreatment, a polycation, such as a polyamine, or
some other
binder or wet strength component, can be added directly to a mixture of the
fibers
dispersed in a slurry. The polycation can be attached to the fiber by covalent
bonding, or
through electrostatic, hydrogen bonding, or hydrophobic interactions, or it
can
spontaneously self-assemble onto the fiber surface, for example, or it can be
precipitated
onto the surface. Chitosan, for example, may be precipitated onto the fiber
surfaces.
Because chitosan is only soluble in an acidic solution, it may be precipitated
onto the
fibers or microfibers in a solution by adding base to a polyamine-
fiber/microfiber
dispersion until the chitosan precipitates onto the fibers that will form the
fibrous web.
[0019] In embodiments, a pretreatment that provides functionalization of the
fibers
before exposure to a surface-modifying emulsion can be performed with cationic
agents
having specific properties. For example, the surface chemistry of the
cellulosic and
synthetic fibers can be changed by attaching selected polymers to the fiber
surface to
make them more hydrophilic or hydrophobic (e.g., chitosan analogs). For
filtration
membranes and other applications where low protein binding is necessary (such
as
biological applications and medical applications), synthetic and natural
fibers can have
further surface modifications, using, for example, polymers that contain PEG-
like
moieties (Jeffamines, Pluronics, Tectonics, chitosan analogs, and the like).
[0020] Following the functionalization of the fibers with the polycation, the
fibrous web
can be impregnated with an emulsion carrying the surface-modifying agents
(i.e., the
polymeric system and any desirable additives) stabilized with an anionic
surfactant.
Anionic surfactants familiar to those of skill in the art can be used, for
example,
surfactants such as sodium laureth sulfate, sodium dodecylbenzenesulfonate,
sodium
lauroyl sarcosinate, sodium lauryl sulfate, sodium myreth sulfate, sodium
palmate,
sodium pareth sulfate, sodium stearate, and the like. The electrostatic
attraction between
the emulsion droplets and the fibers allows the deposition of the emulsion on
the fibers in
a uniform manner, ensuring a uniform coating of the web. The emulsion droplets
that
flow along the fiber length result in the deposition of the polymeric system,
which then
forms a thin and uniform coating upon drying due to the combination of
shearing and the
drying process.
[0021] In embodiments, crosslinking agents contained in the emulsion droplets
can be
activated during the drying, or during a heat-curing phase. Crosslinking is
advantageous
because it helps retain the dimensional stability of sheets produced from the
fibrous web,
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and also helps retain the pore dimensions of a consistent and unchanging size,
along with
providing additional durability to the fibrous web. For example, a polymeric
system
comprising acrylate monomers can include multifunctional comonomers such as
CN975
hexafunctional urethane acrylate (Sartomer LLC, Exton PA), to provide high
crosslinking
density and thereby abrasion resistance to the coatings.
[0022] In embodiments, the polymeric system (e.g., a monomer/crosslinker
system) in
the emulsion drops can be engineered to provide different functionalities to
the fibrous
web, such functionalities being derived from the crosslinking behavior or the
characteristics of the polymeric system itself As an example, multifunctional
monomers
could be chosen for the polymeric system, such that the resulting coating is
hard, solvent
and scratch resistant, and adapted for high temperature environments. In
applications
requiring high temperature resistance, such aromatic reactive compounds can be
incorporated into the fibrous web. Such resonance-stabilized aromatic
structures (e.g.,
aromatic acrylates such as CN2601 (Sartomer LLC, Exton PA)) provide high
temperature
stability and solvent resistance. In another embodiment when pliability of the
coating is
required, a reactive polyol could be used to provide the flexibility to the
coated fibrous
web. In another embodiment, brominated aromatic acrylates (Sartomer LLC, Exton
PA)
can be used as comonomers with acrylate monomers in a polymer system suspended
in
the aqueous emulsion to impart both high temperature resistance and fire
retardancy in
one step. In embodiments, resonance-stabilized aromatic structures that impart
advantageous properties (e.g., high temperature resistance and/or fire
retardancy) can be
incorporated into a crosslinked network. In other embodiments, such structures
can be
incorporated into the cured polymer itself, initiated to polymerize with a
majority
monomer by free radical initiation, for example.
[0023] In certain embodiments, the internal phase of the emulsion can contain
other
additives that produce additional desirable properties beyond those imparted
by the
polymeric system itself For example, the emulsion droplets can contain fire
retardants as
additives that can be incorporated into the cured coating layer. As another
example, the
emulsion droplets can contain biocidal agents to kill targeted organisms, to
remove them
from the solutions being filtered, or to preserve the longevity of the filters
in settings
where microorganisms can grow on the fibers.
[0024] A polymeric system carried in an aqueous emulsion can comprise reactive
silicones, especially if hydrophobicity is desired for the fibrous web. For
example, the
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polymeric system can comprise peroxide-cured or platinum-cured silicone
monomers or
oligomers.
EXAMPLES
[0025] MATERIALS
= Hexamethylenetetramine, Aldrich, USA
= D.E.N. 439 Epoxy Novolac Resin (Phenol, Formaldehyde Glycidyl Ether
Polymer),
Dow Chemicals, Midland, MI, USA
= Sodium Lauryl Sulfate, Spectrum Chemicals, NJ, USA
= Poly(Propylene Glycol) Diglycidyl Ether (Mn=640), Aldrich, USA
= Chitosan cg110, Primex, Siglufjodur, Iceland
= Poly(diallyldimethylammonium chloride) 20 wt% in Water, MW 400,000-
500,000,
Aldrich
= Arofene 8426-ME-63 Resin, Phenolic-formaldehyde resin in
Methanol/Ethanol,
Ashland Chemicals, Covington, KY, USA
[0026] Example 1: Cationic functionalization of fibrous web with polyDADMAC
[0027] A fibrous web comprising cellulose fibers can be functionalized with a
dilute
solution of Polydiallyldimethylammonium chloride (polyDADMAC). The inherently
ionic nature of the cellulose fibers can complex readily with the quaternary
amine groups
on the polyDADMAC, yielding a permanently cationic fibrous web.
[0028] Example 2: Preparation of paper comprising cationically modified
cellulose
fibers
[0029] A sheet of paper (650 grams per square meter) was dipped in a solution
containing 0.1% Chitosan solution in acidic water (pH 4). Once the paper was
completely saturated with the solution, 0.1M NaOH was dripped slowly while
monitoring
the pH to raise to pH 8. This enabled chitosan to precipitate out of the
solution and bind
to the cellulose papers. The paper was them removed from the solution, placed
between
absorbent couch sheets and pressed using a steel hand roll to remove excess
water and
then dried at 110 C on a speed dryer.
[0030] Example 3: Preparation of emulsions containing reactive polymers
(polymer
systems)
[0031] A phenol-formaldehyde resin reactive solution in methanol/Ethanol
(Arofene
8426-ME-63 Resin) was used as an impregnating solution. To this solution, was
added
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sodium lauryl sulfate solution in water at 10% concentration under agitation
until the
solution turned cloudy. The resulting cloudy solution was further diluted to
10%
consistency in water to prepare a water emulsion of the phenol formaldehyde
solution.
The emulsion droplets containing the reactive polymeric resin were now
stabilized and
provided with anionic charge in the water emulsion by the anionic surfactant.
[0032] Example 4: Preparation of reactive emulsion using epoxy modified
phenolic
resin
[0033] An Epoxy Novolac phenol formaldehyde resin (D.E.N. 439 Epoxy Novolac
Resin) was dissolved in methanol at 10% by weight. To this solution was added
crosslinker Hexamethylenetetramine , 3% by weight of the resin. To this
mixture was
added a 10% solution of Sodium Lauryl Sulfate under agitation till a cloudy
stable
suspension was observed. This emulsion was further diluted to 1% solution with
water.
The resulting emulsion was used as an impregnation solution. The emulsion
droplets
containing the reactive polymeric resin were now stabilized and provided with
anionic
charge in the water emulsion by the anionic surfactant.
[0034] Example 5: Preparation of reactive emulsion using plasticizing
crosslinkers
[0035] An Epoxy Novolac phenol formaldehyde resin (D.E.N. 439 Epoxy Novolac
Resin) was dissolved in methanol at 10% by weight. To this solution was added
crosslinker Hexamethylenetetramine, 3% by weight of the resin. To this
solution,
Poly(Propylene Glycol) Diglycidyl Ether was added as a plasticizer by 10% by
weight of
the resin. The resulting clear solution was emulsified by adding 10% solution
of Sodium
Lauryl Sulfate under agitation till a cloudy but stable emulsion was obtained.
The
emulsion droplets containing the reactive polymeric resin were now stabilized
and
provided anionic charge in the water emulsion by the anionic surfactant.
[0036] Example 6: Impregnation of paper using reactive solutions
[0037] Impregnating solutions and emulsions as prepared in Examples 3, 4 and 5
were
used for preparing paper/phenolic composites. For each experiment, a strip of
the
cationically modified paper prepared in accordance with Example 2 was dipped
into a
beaker containing the anionically modified reactive emulsion, pressed using a
steel hand
roller to remove excess emulsion and cured at 160 C for 120 s to obtain a
completely
cured composites. The reactive emulsions described in Examples 3 and 4 gave
rigid and
strong composites. The emulsion described in Example 5 resulted in a strong
but pliant
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composite due to the plasticizing action of Poly(Propylene Glycol) Diglycidyl
Ether
which had been incorporated in the cross-linked matrix.
[0038] Example 7: Impregnating a fibrous web using amine-reactive silicone
emulsions
[0039] An amine-functionalized fibrous web (prepared, for example, in
accordance with
Example 1 or 2) can be impregnated with emulsified epoxidized silicone
polymers. As
examples, both difunctional or the multifunctional Silmer EP C50, Silmer EPC
C50,
Silmer EP J10, Silmer EP Di-50, Silmer EP Di-100, Silmer EPC Di-50 epoxidized
silicones (SilTech Corp, Ontario, CA) can be emulsified with an anionic
surfactants such
as lauryl sulfate to create impregnating solutions. A fibrous web can then be
dipped into
lo a bath containing these silicones. The silicone-containing web can be
cured by drying to
initiate and complete crosslinking reaction between amines and epoxy,
resulting in an
extremely conformal nanocoating that resists water absorption.
[0040] Example 8: Impregnation of a fibrous web using reactive acrylate
emulsions
[0041] A fibrous web can be impregnated with an emulsified acrylate-terminated
silicone polymers mixed with a free radical initiator such as
azoisobutyronitrile, or a
peroxide such as benzoyl peroxide. The acrylate-functionalized silicones such
as Silmer
ACR D208, Silmer ACR D2, Silmer ACR Di-10, Silmer ACR Di-50, Silmer ACR Di-
1508 (SilTech Corp., Ontario, CA) can be emulsified with an anionic
surfactants such as
lauryl sulfate and a free radical initiator such as the peroxide initiator
Photostab 100 to
create impregnating solutions. The fibrous web can then be dipped into a bath
containing
the reactive silicones, followed by curing at the drying temperature of the
web (>170 C)
to complete crosslinking reaction between the acrylate groups. Alternatively
the web
coating can be cured by exposing the coating to an UV radiation source.
[0042] Example 9: Impregnation of a fibrous web with fire retardants
[0043] Phosphorus-based fire retardants such as phosphate esters, phosphonium
derivatives and phosphonates can be added to an aqueous-based emulsion
containing a
polymer system. These agents can be physically trapped in crosslinked
structures formed
by the polymeric system, thereby imparting fire retardancy. For example,
phosphate
esters such as triethyl or trioctyl phosphate, or triphenyl phosphate can be
used. The
dosage levels of fire retardants are usually in a few parts per hundred parts
of the solids in
the emulsion.
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[0044] Example 10: High crosslinking density
[0045] SR 9008 (Sartomer USA, Exton PA), a trifunctional acrylate ester, can
be used to
provide high crosslink density and high dimensional stability to the coating.
In a typical
composition, 25% SR 9008 can be mixed with EB767 polyirethane acrylate coating
resin
(UCB Chemical Corp, Smyrna GA) and appropriate initiator system to create an
acrylate
emulsion capable of having high cross link density. The SR 9008 content can be
varied
to alter the crosslink density of the resulting coating.
[0046] Example 11: Addition of plasticizer
[0047] SR 344 (Sartomer USA, Exton PA), a polyethyeleoxide acrylate reactive
plasticizer, can be mixed with EB767 polyirethane acrylate coating resin (UCB
Chemical
Corp, Smyrna GA) and appropriate initiator system to create a very flexible
coating for
applications requiring pliability.
EQUIVALENTS
[0048] As described herein, embodiments provide an overall understanding of
the
principles, structure, function, manufacture, and/or use of the systems and
methods
disclosed herein, and further disclosed in the examples provided below. Those
skilled in
the art will appreciate that the materials and methods specifically described
herein are
non-limiting embodiments. The features illustrated or described in connection
with one
embodiment may be combined with features of other embodiments. Such
modifications
and variations are intended to be included within the scope of the present
invention. As
well, one skilled in the art will appreciate further features and advantages
of the invention
based on the above-described embodiments. Accordingly, the invention is not to
be
limited by what has been particularly shown and described, but rather is to be
delimited
by the scope of the claims. All publications and references cited herein are
expressly
incorporated herein by reference in their entirety. The words "a" and "an" are
replaceable
by the phrase "one or more."
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