Title: Polymer emulsion preservation using cationic
United States Patent: 6,890,969
Issued: May 10, 2005
Inventors: Rabasco; John Joseph (Allentown, PA); Sagl;
Dennis (Fogelsville, PA)
Assignee: Air Products Polymers, L.P. (Allentown, PA)
Appl. No.: 997599
Filed: November 29, 2001
This invention is directed to a method of preserving colloid-stabilized
polymer emulsions against microbial attack and spoilage using selected
cationic compounds. It is also directed to compositions containing
colloid-stabilized polymer emulsions and cationic compounds that are
resistant to contamination with biodeteriogenic microbes. It has been
discovered that specific cationic compounds are particularly effective
against biodeteriogenic microbes in preserving polymer emulsions that have
been stabilized with protective colloids, such as poly(vinyl alcohol).
Examples of suitable microbicidal cationic compounds are: substituted
pyridinium salts, substituted guanidine salts, tetrasubstituted ammonium
salts, and polymeric cationic compounds.
Description of the Invention
BACKGROUND OF THE INVENTION
Water based polymer emulsions (latex emulsions) are susceptible to
microbial contamination resulting in product spoilage. Polymer emulsions are
dispersions of fine organic polymer particles in water. These polymer
particles are suspended and stabilized in an aqueous environment with
additional organic substrates, such as surfactants and protective colloids.
Surfactants, protective colloids, such as poly(vinyl alcohol) and
hydroxyethyl cellulose, thickeners and other additives, and the polymer
itself all provide a supply of carbon nutrition for microorganisms to
metabolize. Polymer emulsions are therefore susceptible to spoilage due to
microbial attack and propagation. Standard industrial practices combat such
product biodeterioration by the addition of various industrial biocides
(antimicrobial agents) directly after the manufacturing process. Examples of
commonly used industrial biocides are: 1,2-benzisothiazolin-3-one (BIT), and
a blend of 5-chloro-2-methyl4-isothiazolin-3-one (CIT) and
2-methyl-4-isothiazolin-3-one (MIT). Examples of other biocides commonly
used for polymer emulsion preservation include 1,2-dibromo-2,4-dicyanobutane
(DBDCB), 2,2-dibromo-3-nitrilo-propionamide (DBNPA),
2-bromo-2-nitro-1,3-propanediol (BNPD), aldehyde derivatives, formaldehyde
releasing agents, hydantoins, and chlorinated aromatics.
These commonly used biocides are usually adequate to preserve various types
of polymer emulsions against most industrial spoilage from bacteria and
fungi. However, polymer emulsions stabilized with protective colloids, such
as poly(vinyl alcohol) or hydroxyethyl cellulose, and/or nonionic
surfactants, pose additional strains and challenges to many preservative
systems. In general, it has been found that this class of polymer emulsion
products is more susceptible to spoilage than other polymer emulsions by
certain types of microbes. For example, biodeteriogenic microbes that can
survive in acidic environments and/or that metabolize alcohols, such as
Gluconoacetobacter liquefaciens (GABL), have begun to emerge and thrive
in polymer emulsions, even in the presence of commonly used industrial
biocides. Biodeteriogenic microbes include bacteria and fungi that can
adversely affect the commercial value of products and materials. Some
biodeteriogenic microbes have become so well adapted to the environment
present in these emulsions, such as poly(vinyl alcohol)-stabilized
poly(vinyl acetate-co-ethylene) copolymer emulsions, that the standard
industrial biocides are inadequate to prevent product spoilage by this
species over the entire product shelf life period; e.g., 6 to 12 months. A
significant rise in polymer emulsion biodeterioration problems has resulted
in a need to identify more effective preservative systems.
It is known that VOC's (volatile organic compounds), such as unreacted
monomers, in polymer emulsions exert some level of a bacteriostatic, if not
bacteriocidal, effect, which can inhibit the growth of biodeteriogenic
microbes. Recent developments in polymer emulsion technology, in response to
regulatory issues and environmental concerns, have lead to reductions in
residual VOC and residual monomer levels. Such VOC reductions impact polymer
emulsions in many ways. For example: 1) it creates an emulsion environment
more conducive to microbial growth, 2) it may permit the emergence of new
microorganisms that find the new emulsion environment more hospitable, 3) it
poses additional challenges to current preservative technologies, and 4) it
creates the need for new preservation methods to prevent biodeterioration
over the product's shelf life.
Although there are a significant number of biocides that can kill
microorganisms effectively and can provide very good preservation for
polymer emulsions and other industrial products, only a limited number of
these exhibit acceptably low toxicity to higher organisms, e.g., humans. The
choice of effective biocides that can be added to polymer emulsions becomes
even more limited when United States Food and Drug Administration (FDA)
clearances are required for the polymer emulsion end use. Many polymer
emulsions are used to manufacture consumer goods, such as adhesives and
papers for food packaging, diapers, paper towels, baby wipes, and feminine
hygiene products. As a result of such contact with skin and indirect contact
with foods, the polymer emulsions used in these applications must have the
appropriate FDA clearances. These FDA clearances are based on favorable
toxicological profiles, including no skin sensitization. In order for a
polymer emulsion to receive the necessary FDA clearances, all of its
constituents, including the preservative technology, must meet FDA's
rigorous toxicological criteria when used at concentrations required for
satisfactory performance in the polymer emulsion. FDA-approved biocides have
use level restrictions. In some cases, the minimum biologically effective
concentration is greater than the maximum allowable use level. Typically,
this results in premature product biocontamination and biodeterioration.
Additionally, microorganisms continue to evolve and new microorganisms are
beginning to appear that exhibit resistance to some of the more common
industrial biocidal agents, particularly at the allowable use level. A
tightening regulatory environment, specific consumer good manufacturing
specifications, public concern, and product liability, further complicates
biocide selection and use. For example, isothiazolinones are widely used
antimicrobial agents for many consumer products, but their known skin
sensitization property causes concern among many consumer goods
manufacturers. Such health concerns and microbial resistance are leading to
a search for preservation alternatives and new preservation approaches.
Cationic compounds, such as quaternary ammonium compounds, are well known in
the antimicrobial art and are widely used as disinfectants for surfaces. For
example, they are used to disinfect floors, walls, countertops, equipment
surfaces, food contact surfaces, and the like in hospitals, schools, nursing
homes, restaurants, and residential homes. Furthermore, combinations of
detergents with cationic compounds are widely used formulations for cleaning
and disinfecting or sanitizing such surfaces with a single product. Cationic
compounds are also used to inhibit the growth of algae and microorganisms in
water, such as in swimming pools. Cationic compounds have been utilized on a
limited basis for the preservation of industrial products and to prevent
microbial growth in aqueous systems.
GB 1,091,049 (1967) discloses the preparation of bacteriostatic tissue paper
by incorporating alkylated guanidine salts during the tissue paper
manufacturing process. The guanidine salt is introduced into the paper pulp
slurry prior to sheet formation.
U.S. Pat. No. 3,970,755 (Gazzard et al., 1976) discloses biocidal
compositions for aqueous systems comprising lauryl benzyl dimethyl ammonium
chloride or cetyl trimethyl ammonium chloride, and
U.S. Pat. No. 4,661,503 (Martin et al., 1987) discloses a synergistic
biocide composition of n-dodecylguanidine hydrochloride (DGH) and a mixture
of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one
for treating industrial process waters to prevent the growth of gram
negative bacteria and fungi.
U.S. Pat. No. 4,725,623 (Whitekettle et al., 1988) discloses a bactericidal
composition for aqueous systems comprising a synergistic aqueous mixture of
2-bromo-2-nitropropane-1,3-diol and n-dodecylguanidine.
U.S. Pat. No. 4,906,385 (Lyons, et al., 1990) discloses the use of water
soluble C8-C18 alkyl guanidine salts, especially n-dodecylguanidine
hydrochloride, for controlling macroinvertebrate biofouling of industrial
cooling water system.
U.S. Pat. No. 5,041,463 (Whitekettle et al., 1991) discloses a bactericidal
composition for aqueous systems, such as pulp and paper mill systems,
comprising a combination of glutaraldehyde and dodecylguanidine
U.S. Pat. No. 5,457,083 (Muia et al., 1995) discloses synergistic
antimicrobial compositions containing polyether polyamino methylene
phosphonates (PAPEMP) and one or more non-oxidizing biocide, such as didecyl
dimethyl ammonium chloride, dodecylguanidine hydrochloride, methylene
bisthiocyanate, and 5-chloro-2-methyl-4-isothiazolin-3-one. The combination
is reported to be useful in aqueous systems in a variety of industrial
applications, such as papermaking, paints, adhesives, latex emulsions, and
joint cements. Examples show that addition of PAPEMP to a non-oxidizing
biocide improves bacterial kills in an aqueous system over 24 hour period.
El-Zayat and Omran, "Disinfectants Effect on the growth and Metabolism of
Acetobacter aceti" (Egypt J-Food-Sci., 11(1-2), 1983, pages 123-128)
evaluate quaternary ammonium compounds, such as cetyl trimethylammonium
bromide, as disinfectants against the growth and metabolism of
Handbook of Biocide and Preservative Use, Edited by H. W. Rossmore,
Blackie Academic & Professional, 1995, pages 361-362, describes biocidal
surfactants for preservation of cosmetics and toiletries. Quaternary amines
are reported to be potent antimicrobial substances.
A need remains for a method of protecting polymer emulsions, especially
those stabilized with hydroxyl-containing protective colloids and those with
low VOC's, against product biodeterioration by microbes. There is also a
need for polymer emulsion compositions which are resistant to
biodeterioration over their shelf life (about 6 to 12 months).
BRIEF SUMMARY OF THE INVENTION
This invention is directed to a method of preserving colloid-stabilized
polymer emulsions against biodeteriogenic microbe attack and spoilage using
selected cationic compounds. It is also directed to compositions containing
colloid-stabilized polymer emulsions and cationic compounds that are
resistant to spoilage by biodeteriogenic microbes. A method for preventing
biodeteriogenic microbe contamination in protective colloid-stabilized
polymer emulsions involves mising an effective amount of the cationic
compound with the polymer emulsion. Examples of specific cationic compounds
that are particularly effective in preserving polymer emulsions that have
been stabilized with protective colloids, such as poly(vinyl alcohol),
against biodeteriogenic microbes are: substituted pyridinium salts,
substituted guanidine salts, tetrasubstituted ammonium salts, and polymeric
cationic compounds, in which the substitution can be an alkyl, a cycloalkyl,
and/or an aryl group of 2 to 18 carbons. The cationic compounds are also
particularly effective in preserving polymer emulsions with low VOC's (i.e.
less than 1000 ppm VOC).
These cationic compounds are effective as stand-alone preservatives,
exhibiting a broad spectrum of microbicidal activity against bacteria and
fungi for an extended period of time, or can also be used in combination
with other biocides, such as isothiazolinone derivatives.
The cationic compounds are particularly effective in polymer emulsions
containing little or no anionic comonomers, anionic surfactants, or other
anionic constituents. The preservative efficacy and potency of the cationic
compounds can be diminished in the presence of high surface area polymer
particles and/or free aqueous phase nonionic surfactant.
The polymer emulsion compositions of this invention can be blended and
formulated with other raw materials for use in preparation of adhesives,
architectural coatings, paper coatings, nonwoven binders, etc.
DETAILED DESCRIPTION OF THE INVENTION
Polymer emulsions of this invention are dispersions of synthetic polymers
and copolymers in aqueous media. The basic raw materials used to manufacture
the polymer emulsions are monomers, initiators, and stabilizers. Examples of
monomers include vinyl acetate, ethylene and other olefins, diolefins such
as butadiene, various alkyl acrylates, various alkyl methacrylates, styrene,
vinyl chloride, vinyl esters, acrylamides, methacrylamides, N-methylolacrylamides,
maleates, and others known in the art. Examples of polymer emulsions for
purposes of this invention include emulsions of poly(vinyl acetate),
poly(vinyl acetate) copolymers such as poly(vinyl acetate-co-ethylene) (VAE),
poly(vinyl acetate-acrylics) such as poly(vinyl acetate-butyl acrylate) and
poly(vinyl acetate-(2-ethyl)hexyl acrylate), polyacrylics, polymethacrylics,
poly(styrene-acrylics), wherein acrylics can include C3-C10
alkenoic acids, such as acrylic acid, methacrylic acid, crotonic acid and
isocrotonic acid and their esters, other polystyrene copolymers, poly(vinyl
chloride-co-ethylene) copolymers, and the like. These polymer emulsions can
be stabilized with various surfactants known in the art or with protective
colloids, such as hydroxyethyl cellulose or poly(vinyl alcohol), and others
known in the art. Polymer emulsions particularly suitable for this invention
are stabilized with hydroxyl-containing protective colloids, especially
poly(vinyl alcohol). When anionic or nonionic surfactants are used, polymer
emulsions must be augmented with a sufficient concentration of cationic
compound to compensate for the antagonistic effect of the surfactants.
Polymer emulsions with less than 1000 ppm VOC's are also particularly
suitable for this invention. Among the VOC's present in polymer emulsions
are unreacted monomers, acetic acid, methanol, acetaldehyde, and
Poly(vinyl alcohol) used in this invention, generally, has a weight average
molecular weight (Mw) ranging from about 5,000 to 300,000,
preferably 10,000 to 200,000. Alternatively, the poly(vinyl alcohol) can
have a degree of polymerization of from 100 to 5,000, preferably 200 to
3500. Poly(vinyl alcohol) is made commercially by the hydrolysis of
poly(vinyl acetate) and typically has a hydrolysis level ranging from about
85% to greater than 99%. For this invention, the level of hydrolysis can
range from 70% to greater than 99%, preferably 85% to 98%. Mixed poly(vinyl
alcohol) grades, using combinations of poly(vinyl alcohol)s varying in
molecular weight and hydrolysis level, can also be employed. The molecular
weight and hydrolysis level are such that the poly(vinyl alcohol) is at
least partially soluble in an aqueous medium.
Microbial contamination of polymer emulsions can lead to a range of effects,
including color changes, odors, viscosity changes, pH changes, and visible
surface growth. It is known in the art that polymer emulsions are
susceptible to contamination by a broad range of biodeteriogenic microbes.
Examples of microorganisms found to contaminate polymer emulsions include,
Aeromonas hydrophilia, Alcaligenes faecalis, Corynebacterium ammoniagenes,
Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae, Pseudomonas
aeruginosa, Proteus vulgaris, Providencia rettgeri, Pseudomonas stutzeri,
Shewanella putrefaciens, Serratia liquefaciens, Acinetobacter baumannii,
Burkholderia cepacia, Chryseobacterium meningosepticum, Sphingobacterium
spiritivorum, Ralstonia pickettii, GABL, Geotrichum candidum,
Aspergillus species, Sporothrix species, Trichoderma viride,
Cladosporium species, Rhodoturula glutinis, Candida guillermondi,
Penicillium species, and Candida tropicalis.
Acceptable cationic compounds for the preservation of the polymer emulsions
of this invention include, substituted guanidine salts such as DGH,
substituted pyridinium salts such as cetylpyridinium chloride (CPC),
tetrasubstituted ammonium salts such as didecyldimethylammonium chloride and
alkyldimethyl benzalkonium chloride, biguanides, polymeric cationic
derivatives, and the like, in which the substitution is an alkyl, a
cycloalkyl, or an aryl group of 2 to 18 carbons. Preferred cationic
derivatives include, alkylguanidine salts and alkylpyridinium salts in which
the alkyl group contains 2 to 18 carbons. Alkylguanidine salts, especially
DGH, are most preferred.
The cationic compounds can be added to the polymer emulsion at any point
during the polymer emulsion manufacturing process; preferably, the cationic
compound is added to the polymer emulsion as the last additive in the
post-manufacturing process. The total amount or dosage of the cationic
compound that is added to a polymer emulsion for preservation against
microbial contamination can range from 10 ppm to 1 wt %, preferably 50 ppm
to 5000 ppm, based on the wet weight of the polymer emulsion.
The use of an alkylguanidine salt, specifically DGH, was unexpectedly found
to be very potent and effective for killing and inhibiting the growth of
biodeteriogenic microbes, such as GABL, that may contaminate poly(vinyl
alcohol) stabilized polymer emulsions, especially vinyl acetate-based
polymer emulsions. However, it has been unexpectedly discovered that slight
changes in the vinyl acetate-based polymer emulsion composition, such as
incorporation of anionic constituents, can have a dramatic influence on the
preservative efficacy and potency of alkylguanidine salts. Not intending to
be bound by theory, differences in DGH preservative efficacy can be
attributed to an unfavorable or competitive interaction of the cationic DGH
with the anionic surfactants and/or anionic components present in some of
these emulsions. Such interaction can serve to deplete the concentration of
the cationic compound in the aqueous phase where it is needed to exert its
The preservative efficacy of DGH can also be affected adversely by the
presence of nonionic surfactants. For example, the preservative efficacy of
DGH can be diminished in vinyl acetate-based polymer emulsions stabilized
with a combination of protective colloids and nonionic surfactants.
The cationic compounds are particularly effective in polymer emulsions
containing little or no anionic substituents, and little or no anionic or
nonionic surfactants. By little is meant nonionic surfactants below their
critical micelle concentration and anionic surfactants or substituents below
the molar concentration of the added cationic compound.
The cationic compounds of this invention can be used alone or together with
other known industrial biocides; for example, BIT, CIT, MIT, DBDCB, DBNPA,
DNPD, aldehyde derivatives, such as glutaraldehyde and formaldehyde,
formaldehyde releasing agents, such as dimethyloldimethyl hydantoin,
imidazolidinyl urea derivatives, polymethoxy bicyclic oxazolidine, and
1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane hydrochloride, hydantoins,
phenols, such as sodium o-phenyl phenylate, and chlorinated aromatics, such
as chlorhexidene, p-chloro-m-cresol, and chloroxylenol.
In addition, the polymer emulsion compositions of this invention can be
blended or formulated with other raw materials for use in preparation of
adhesives, architectural coatings, paper coatings, nonwoven binders, etc.,
provided that those raw materials do not impart sufficient anionic character
to inactivate the cationic biocides. For example, although the polymer
emulsion compositions of this invention may be used neat for adhesive
applications, such polymer emulsion compositions are often formulated
depending upon the specific end use.
When formulated for adhesive compositions, the polymer emulsion compositions
of this invention are typically present in the adhesive composition at
levels ranging from 60 to 90 parts by weight. Common additives used in the
formulation of adhesive compositions include, plasticizers, defoamers,
thickeners, dispersants, crosslinkers, humectants, tackifiers, poly(vinyl
alcohol), and fillers.
Representative plasticizers include glycols, such as dipropylene glycol,
dibenzoate types, such as dipropylene glycol dibenzoate and diethylene
glycol dibenzoate, phthalates, such as dibutyl phthalate, and liquid
polyesters, such as triethylene glycol polyester of benzoic acid and
phthalic acid, and others known in the water-based adhesion art. The
plasticizer is typically used at levels ranging from 2 to 30 parts by
Representative defoamers include silicon or hydrocarbon based materials. The
defoamer is typically used at levels of 0 to 1 part by weight.
Representative thickeners include, casein, fumed silica, guar gum, bentonite,
alginates, starches, hydroxyethyl cellulose, other cellulosics, polyether
polyols, and other thickeners known in the water-based adhesion art.
Thickeners are typically used at levels of 0 to 5 parts by weight.
Representative crosslinkers include dialdehydes, such as glutaraldehyde,
metals, such as zinc and zirconium, melamine formaldehyde resins, diepoxides
and epoxy resins. Crosslinkers are typically used at levels of 0 to 10 parts
Representative humectants include, calcium chloride, glycols, glycerine,
ureas, sorbitol, and others known in the water-based adhesion art.
Humectants are typically incorporated at levels of 0 to 20 parts by weight.
Representative tackifiers include, gum rosin, ester gum, hydrocarbon resins,
hydrogenated rosin, tall oil rosins, terpene resins, and others known in the
water-based adhesion art. Tackifiers are typically used in their dispersion
form and used at levels of 0 to 35 parts by weight in adhesive compositions.
Poly(vinyl alcohol) in the formulation can have a weight average molecular
weight (Mw) ranging from about 5,000 to 300,000, preferably
10,000 to 200,000. Alternatively, the poly(vinyl alcohol) can have a degree
of polymerization of from 100 to 5,000, preferably 200 to 3500. It is
typically used at levels of 0 to 10 parts by weight.
Representative fillers include, calcium carbonate, clay, mica, silica, talc,
and others known in the water-based adhesion art. Fillers are typically used
at levels 0 to 40 parts by weight.
Depending upon the level of formulation, it may be required to add
additional amounts of the cationic biocide to compensate for the dilution
from the formulation additives in order to produce a water-based adhesive
composition that is resistant to biodeteriogenic microbe contamination.
Claim 1 of 22 Claims
1. An aqueous polymer emulsion composition resistant to biodeteriogenic
microbe contamination comprising a poly(vinyl alcohol) stabilized aqueous
polymer emulsion combined with a cationic compound selected from the group
consisting of a substituted guanidine salt, a polymeric cationic compound,
and mixtures thereof, wherein the substituted guanidine salt is
substituted with an alkyl, a cycloalkyl, or an aryl group containing 2 to
18 carbons, said cationic compound in an amount effective for preventing
biodeteriogenic microbe contamination of said polymer emulsion, said
polymer emulsion containing little or no nonionic or anionic surfactants
and little or no anionic substituents.
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