Link:  Pharm/Biotech Resources

Title:  Polymer emulsion preservation using cationic compounds

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.

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 1,2-benzoisothiazolin-3-ones.

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 hydrochloride.

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 Acetobacter aceti.

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 formaldehyde.

Poly(vinyl alcohol) used in this invention, generally, has a weight average molecular weight (M_w) 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 microbicidal activity.

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 weight.

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 by weight.

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 (M_w) 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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