Product Fact Sheet
Waterborne Epoxy Resin Systems
for Use as Binders in Nonwovens and Textiles
SC: 2429 Re-issued: August 2005
By
Glenda C. Young
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SC: 2429 Waterborne Epoxy Resin Systems for Use as Binders in Nonwovens and Textiles Page 2
Abstract EPI-REZ鈩? epoxy resin dispersions are one of the most versatile classes of resins. These
formaldehyde-free waterborne polymers are used in a wide variety of industrial end uses
and are well known for their balance of mechanical, chemical, and adhesive properties. EPI-
REZ epoxy resin dispersions can be used alone or they can be thermoset when mixed with
curing agents or with reactive latexes.
This paper describes the formulation of EPI-REZ epoxy resin dispersions for use as binders
in the nonwoven and textile industry. Methodology and property sets will be described for
EPI-REZ dispersion systems as modifiers for conventional latex emulsions for increased
performance and handling ease.
Introduction General
Epoxy resins are one of the most versatile classes of reactive thermosets. These
formaldehydefree polymers are used in a wide variety of industrial end uses and are well
known for their balance of mechanical, chemical, and adhesive properties. Epoxy resins
have historically been used as neat liquids or solids, or they have been used in solvent
solutions. More recently, with the increasing concerns over solvent use and effluent
release, water dispersions of epoxy resins (EPI-REZ waterborne resins available from
Resolution Performance Products) have been made. These products have increased the
number of markets that can access the high performance of epoxies because they can now
be delivered in water. One such area is binders for nonwovens and textiles.
Chemistry and Formulation with Epoxy Resins
The class of epoxy resins that have proved most useful to industrial processes are the epoxy
resins based on bisphenol A. The majority of epoxy resin types from this group are
difunctional having two reactive groups per molecule, and can be made at varying
molecular weights. A generalized representation of this family of resins can be depicted by
the structure below.
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Introduction, cont. By varying the backbone length of this molecule and by the addition of reactive diluents,
resins can be produced ranging from low viscosity liquids of 5 to 10 poise to friable solids
with molecular weights from less than 500 to greater than 3000, respectively. Multifunctional
(more than two reactive groups per molecule) epoxy resins based on bisphenol A are also
available. They provide higher crosslinked matrixes leading to improved heat and chemical
resistance.
Epoxy resins based on bisphenol A, either difunctional or multifunctional, provide broad
latitude in formulating useable compositions. Also, they can be cured, or reacted with
several other families of materials to produce a variety of thermoset polymers.
Water dispersions of epoxy resins can be produced without altering the functional epoxy
end groups. Non-ionic surfactants are used that coat the resin particles and suspend them
in water. The resultant dispersions, unlike ionic dispersions or emulsions, are not pH
sensitive since the surfactant efficiency is not related to ionic charge. The particle size of
such dispersions usually ranges from 0.5 to 2.0 microns. Dispersions of low molecular weight
epoxies contain no organic co-solvents, while the dispersions of high molecular weight
epoxies have small amounts of high boiling co-solvents to aid in particle coalescence upon
water release. These epoxy dispersions, called EPI-REZ waterborne resins, are
mechanically and chemically stable for long periods of time.
Formulating and curing EPI-REZ waterborne resin dispersions can be accomplished in much
the same way as curing conventional epoxies and epoxy solutions. One major difference,
however, is the incorporation of the curing agent into the water dispersion. The major
requirements of the curing agent are that it be water soluble or dispersible and stable in the
water, and the curing agent must be mixed with the dispersed resin particle at the proper
time. Selection of the proper curing agent is essential to the successful use of epoxy resin
dispersions in conventional epoxy processes.
EPI-REZ dispersions are useful in non-conventional epoxy end uses. The fact that the epoxy
is now in an aqueous form renders it compatible with materials that historically could not be
used with liquid or solution epoxy resins. One category of materials that can be used
successfully with epoxy resin dispersions is conventional latex emulsions. EPI-REZ
waterborne resin dispersions are compatible with most types of latex emulsions including
acrylic, urethane, styrene-butadiene, vinyl chloride, and polyvinyl acetate emulsions. The
epoxy dispersion can be used as a modifier to these emulsions to alter handling and
application characteristics such as emulsion rheology, pH sensitivity, wetting properties,
and coating coalescence. They can also be reacted into the latex resin either by reacting
the epoxy with a functionalized latex or by use of an epoxy with a co-reactant. In the former
case, the epoxy will react with the latex slowly at room temperature. This is a two package
system; the system is processed within days of mixing. In the latter case, the epoxy and
curing agent will form a cross-linked matrix within the latex matrix. Latent epoxy curing
agents can be used in this case to produce one package systems that will be stable for
months. In some cases, both reaction of the epoxy with the curing agent and the latex can
be accomplished simultaneously. Using any of these chemistries, the formulator can
combine the properties of both the latex
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Introduction, cont. polymer and the epoxy polymer. This results in binders that have better handling
characteristics and/or better water and chemical resistance. With proper choice of the latex
emulsion, the systems will also be formaldehyde-free.
EPI-REZ dispersions are compatible with latex emulsions in all proportions and can be
poured directly into the latex with mixing. As stated earlier, pH changes do not affect the
epoxy resin dispersion stability or its performance. However, pH changes caused by the
addition of epoxy dispersions into latexes may cause problems with an ionically dispersed
latex polymer. In such cases, the pH of the epoxy dispersion can be adjusted to the
specifications of the latex emulsion being used before mixing.
Experimentation Methodology and Systems
One method of assessing the properties of a waterborne binder is to measure the tensile
properties of the binder on a porous substrate. In this study, Whatman #4 chromatography
paper was saturated by pan dipping with binder systems using a 15 percent weight water
solution. The final dry resin add-on to the paper was controlled to 22 +/- 2.0 percent weight.
The water was flashed from the saturated papers at 150 掳F for 15 minutes in a forced draft
oven. The papers were then cured at 300 掳F for 10 minutes. Five 18 x 18 centimeter papers
per system were prepared. Four of the five specimens were immersed in water, boiling
water, methyl ethyl ketone, or isopropyl alcohol respectively. The papers were tested
according to ASTM D 882 on an Instron tensile testing instrument after a 10 minute
immersion period. A dry paper specimen was tested as a control. All tensile testing was
carried out at 77 掳F and 50 percent relative humidity.
Latex Systems
Five latex binders that are used for nonwoven and textile applications were received from
two different manufacturers. The latex emulsions were classed as low or formaldehyde-free
polymers and are designated in this text and described by their manufacturers as: aliphatic
urethane - a high solids water-borne aliphatic urethane dispersion; aromatic urethane 鈥? an
aqueous colloidal dispersion of an aromatic urethane; acrylic 1 - an anionic acrylic; acrylic 2
- an aqueous, low particle size acrylic copolymer; vinyl chloride - a carboxyl-modified
anionic polyvinyl chloride copolymer.
Each emulsion was thinned with water to yield a 15 percent weight solids solution.
Saturated paper specimens were prepared, cured, and tested according to the above
methodology.
Two Package Latex-epoxy Systems
Two package latex-epoxy systems were formulated using EPI-REZ 3515-W-60, a dispersion
of a low molecular weight difunctional epoxy having a weight per epoxide of 250. The epoxy
dispersion was added to each emulsion to yield a latex to epoxy weight ratio of 90 to 10
based on polymer solids. A tertiary amine, EPI-CURE* Curing Agent 3253, was added to the
system to accelerate the reaction of the epoxy with the latex. The EPI-CURE Curing Agent
3253 was added at 0.5 percent weight based on total system solids. The dispersions were
thinned to yield 15 percent weight final polymer solids. The mixed systems were applied to
the paper, cured and tested as above.
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Experimentation Similar systems were also prepared using EPI-REZ 5003-W-55, a multifunctional epoxy
(cont.) dispersion. The resin dispersion has an average functionality of three epoxy groups per
molecule and a weight per epoxide of 205.
The stability of each solution was measured by following Brookfield viscosity with time. The
viscosities were measured using an RVT viscometer with #4 spindle at 100 RPM.
One Package Latex-epoxy Systems
One package latex-epoxy systems were prepared using the same latexes and epoxy resin
dispersions. A latent epoxy curing agent, dicyandiamide, was dissolved in water and added
to the EPI-REZ 3515-W-60. The dicyandiamide was added to yield 6 parts of curing agent per
100 parts of epoxy resin solids. An accelerator, 2-methyl imidazole, was added to the mix at
0.1 percent weight on the epoxy solids. This mix was then added to the latex. Likewise,
similar mixes were prepared with EPI-REZ 5003-W-55. In each system the epoxy/curing
agent mixture was added to the latex to yield a 90 to 10 ratio of latex solids to epoxy/curing
agent solids. Each system was thinned with water to yield 15 percent weight polymer solids.
The systems were applied to paper, cured, and tested.
A second set of latex-epoxy systems were prepared as above with EPI-REZ 3515-W-60, but
the latex to epoxy/curing agent ratio was changed to 80 to 20 based on resin solids. This set
of experiments was included in the study to determine the effect of increasing epoxy
modification on final cured state properties.
The stability of these solutions was measured by following Brookfield viscosity with time. A
Brookfield RVT viscometer was used with a #4 spindle at 100 RPM.
Latex Handling Characteristics
One important handling characteristic of a binder system for use in nonwovens and textiles
is the foaming tendency of the polymer in water. The four latexes in this study were
screened for their tendency to foam. One hundred milliliters of latex emulsion was agitated
with a high speed disperser at 600 RPM for twenty minutes. The resulting volume of latex
and foam was recorded. Similar tests were conducted using the two package latex/epoxy
systems containing the EPI-REZ 3515-W-60.
Results In all the epoxy-modified latex blends tested, the addition of the epoxy did not significantly
affect the final dry tensile strength of the Whatm谩n #4 paper samples. However, after
immersion, the retention of tensile strength was significantly better for several of the epoxy-
modified systems than the unmodified systems. Immersion in room temperature water
showed no significant change in tensile strength for modified on unmodified systems. The
retention of tensile strength after immersion in boiling water was significantly better for
epoxy-modified systems, especially for the urethane latexes and acrylic 2, as shown in
Figures 3 and 5. Immersion of the paper samples in methyl ethyl ketone was significantly
better for the epoxymodified systems (Figures 4 and 6). The samples immersed in isopropyl
alcohol showed similar trends to the MEK systems but were much less severe.
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Results (cont.) Two Package Latex-epoxy Systems
Figures 1 and 2 show the retention of strength of the two package latex-epoxy systems after
immersion in water and in methyl ethyl ketone. The bars in the foreground are the retention
of tensile strength after immersion in the same media using the five different unmodified
latex binders. In all the formulations, addition of the difunctional EPI-REZ 3515-W-60 to the
latex binder increased retention of strength after immersion in water. In the case of the
aliphatic urethane and acrylic 2, the retention of strength was increasedon the order of
100%. With acrylic 1, the improvement in retention was smaller (10%). This illustrates that
the latex chemical composition is very important to final cure state properties just as it is in
the unmodified latexes. The addition of the multifunctional epoxy dispersion, EPI-REZ 5003-
W-55 increased the wet strength retention of the latex even more than the difunctional EPI-
REZ 3515-W-60. This is as expected assuming that the multifunctional nature of the resin has
increased the crosslink density of the final cured resin matrix.
Figure 1 / Retention of Tensile Strength After Immersion in Boiling Water for
10 Minutes. Epoxy Cured with Latex Functionality.
Figure 2/Retention of Tensile Strength After Immersion in Methyl Ethyl Ketone.
Epoxy Cured with Functionality on Latex.
General
Information
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Results (cont.) Figure 2 shows the retention of strength of the same systems when immersed in methyl ethyl
ketone. The improvement of retention of strength in this media was substantial. Most
systems improved more than 100%. Again, the improvement of retention of tensile in this
media is greater in the formulations containing EPI-REZ 5003-W-55.
Figure 3 is a plot of Brookfield viscosity of the two package systems containing EPI-REZ
3515-W-60 with time. The useable pot life of the systems tested is limited to between one
and four weeks. The tertiary amine present in these formulations needed for reaction of the
epoxy with the latex causes reaction at room temperature and an increase in binder
viscosity. Usable shelf life is also related to change in physical properties of the finished
cured binder. Using that criteria, the actual shelf life may be shorter than what is depicted
by viscosity change alone.
Figure 3 / Brookfield Viscosity in Centipoise versus Time in Weeks.
Storage at Room Temperature, Two Package Latex-epoxy Systems.
One Package Latex-epoxy Systems
Figures 4 and 5 depict retention of tensile strength after immersion in water and methyl ethyl
ketone of the one package latex-epoxy systems. Again most of the epoxy modified systems
showed improvement in strength retention after immersion in water and methyl ethyl ketone.
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Results (cont.) Figure 4 / Retention of Tensile Strength After Immersion in Water.
Epoxy Plus a Curing Agent.
Figure 5 / Retention of Tensile Strength After Immersion in Methyl Ethyl
Ketone. Epoxy Plus a Curing Agent.
Figures 6 and 7 show the influence of increased amounts of epoxy modification on retention
of tensile strength of the one package latex modified systems using EPI-REZ 3515-W-60. In
some cases, increasing the epoxy content increases the tensile strength retention. In other
cases, the increases in epoxy did not substantially change or only marginally changed the
retention of tensile strength. Increasing the epoxy modification in the vinyl chloride systems
made a marked improvement in the methyl ethyl ketone resistance. This is noticeable
because improvements were marginal in the lower epoxy modification. In this instance, the
highly crosslinked matrix of the epoxy appears to be favored over the lightly crosslinked
vinyl chloride.
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Results (cont.) Figure 6 / Retention of Tensile Strength After Immersion in Boiling Water
Increasing Levels of Epoxy Modification.
Figure 7 / Retention of Tensile Strength After Immersion in Methyl Ethyl
Ketone Increasing Levels of Epoxy Modification.
Figure 8 is a plot of Brookfield viscosity of the one package systems using EPI-REZ 3515-W-
60 with time. The viscosities of all the systems did not change over a one month period
providing a prediction of handling stability. To adequately determine true shelf life of any
reactive material, a critical final cured state property should be measured.
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Results (cont.) Figure 8 / Brookfield Viscosity in Centipoise versus Time in Weeks.
Storage at Room Temperature, One Package Latex-epoxy Systems.
Resistance to Foaming
Figure 9 depicts the change in foaming characteristics of the modified versus the unmodified
latexes. In all cases, the epoxy resin dispersion significantly decreased the foaming
tendencies of the latexes tested.
Figure 9 / Volume of Foam Produced After Agitation for 20 Minutes at 600 rpm.
Milliliters Produced Using 100 Milliliters of Emulsion.
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Conclusions 1. EPI-REZ waterborne resin dispersions can be successfully formulated into latex
binders for nonwoven applications.
2. Modification of latex binders with EPI-REZ waterborne resins for nonwovens and
textiles can improve the wet and chemical strength of the final system up to 100
percent.
3. Formaldehyde-free systems can be formulated that are either one package or two
package. Formulation selection is dependent on the material handling, processing,
and final cure state properties required by the application.
4. The final cure state properties of a system are dependent on the latex selected for
formulation. The backbone and chemical functionality will affect epoxy reactivity
and thus, the final cure state properties of the binder system.
5. Improvements in wet and chemical strength of saturated paper can be increased
with increasing amounts of epoxy modification.
6. Epoxy modification of latex binder systems can improve other handling properties,
including resistance to foaming.
Summary EPI-REZ waterborne resin dispersions can be used as modifications for latex binders for use
in nonwoven and textile applications. EPI-REZ modified formulations offer improved handling
performance and wet and chemical strength advantages over unmodified formulations. The
property set described here was focused on two BPA-based epoxy dispersions. There are
many other types of EPI-REZ waterborne resin dispersions available including
multifunctional epoxies and epoxies of varying backbones. The broad range of available
latex polymers added to the wide range of EPI-REZ waterborne resin dispersions and curing
agents offer an endless latitude in formulation flexibility to provide improved performance
for nonwoven and textile products.
This document may contain starting point formulations which are not proven for use in the
user鈥檚 particular application, but are simply meant to demonstrate the efficacy of the
products and to assist in the development of the user鈥檚 own formulations. It is the user鈥檚
responsibility to fully test and qualify the formulation, along with the ingredients, methods,
applications, or equipment identified herein (鈥淚nformation鈥?), by the user鈥檚 knowledgeable
formulator or scientist, and to determine the appropriate use conditions and legal
restrictions, prior to use of any Information.
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