WO1994011481A1

WO1994011481A1 - Polyacrylamide acid compositions

Info

Publication number: WO1994011481A1
Application number: PCT/US1992/009755
Authority: WO
Inventors: Timothy E. Janota; James A. Krogh; John C. Miller
Original assignee: Tomah Products, Inc.
Priority date: 1992-11-10
Filing date: 1992-11-10
Publication date: 1994-05-26
Also published as: AU3133893A

Abstract

An acid composition comprising an acid having a pKa1 value greater than or equal to about 0.5, a polymer having the repeating monomeric structure -CH(R)C(R')(CONR''R''')-, and water in an amount sufficent to provide the composition a viscosity of about 50-20,000,000 centipoise. The polymer of this invention may be utilised at concentration levels much lower than previously thought possible and acts synergistically in the presence of surfactants and/or biocides to thicken acids.

Description

Title: POLYACRYLAMIDE ACID COMPOSITIONS

Field of the Invention

This invention is related generally to viscous acid solutions and, more particularly to acid compositions thickened with acrylamide polymers.

Background of the Invention

Acidic compositions have found wide utility in a variety of household and industrial settings, as cleaning agents for everything from coffee urns to well-drilling equipment. In many applications, it is desirable to prolong contact time to enhance cleaning efficiency. Not unexpectedly, vertical and sloped surfaces induce a "run¬ off" condition, thereby presenting unique formulation challenges.

Early concerns over undesirable run-off fostered the use of thickening agents such as xanthan, locust bean. and guar gums, cellulose, and the like. To a certain extent, these vegetative thickeners prolonged contact time, but created other problems. They are relatively- expensive and significantly increase the overall cost of the acid composition. Low water-solubility presents formulation problems, and the solutions, once obtained, are unstable over time and across a useable temperature range. Furthermore, thickeners of this type are generally incompatible with many additives commonly found in acid compositions. For instance, the presence of quaternary amine biocides exacerbates the inadequate solubility and stability.

The search for an efficient, effective acid thickener meeting the requirements outlined above has been an on-going concern in the art. One approach, which has been used with certain success, involves use of synthetic polymers. In particular, water-soluble homopolyacids and their alkali and alkaline earth metal salts have been employed with mineral or carboxylic acids and, in some applications, are used instead of vegetative thickeners.

However, the prior art has associated with it a number of significant problems and deficiencies. Most are related to inadequate and/or unacceptable viscosity and stability parameters, and result from the polymers currently used.

One major problem relates to the fact that polymeric thickeners represent a significant portion of the overall cost of an acid composition, and must be used at relatively-high concentrations to provide adequate viscosities. In addition, there is little correlation between polymer concentration and viscosity. As a result, cost and efficiency are compromised as the viscosity obtained often exceeds that appropriate for a given application.

Another significant concern is that certain polymers of the prior art are unstable over time and upon prolonged exposure to high-temperature conditions, resulting in decreased viscosities. Incompatibility with surfactants, biocides, and perfumes/dyes further destabilizes the acid composition. Another significant deficiency of the prior art is the required incorporation of a low molecular weight alcohol to achieve optimal viscosity. Alternatively, high viscosities may require mixing the polymer with a vegetative thickener. The presence of a volatile alcohol component is often undesirable from both a formulation and application perspective, while the drawbacks of using gums and the like are as noted above. Furthermore, addition of either increases the overall cost of the resulting acid composition. In summary, a considerable number of drawbacks and problems exist in the art relating to acid cleaners. There is a need for a thickener which maximizes the function and utility of such compositions.

Objects of the Invention

It is an object of this invention to provide a thickened acid cleaning composition, overcoming some of the problems and shortcomings of the prior art.

Another object of this invention is to provide a thickener which is efficient, effective, and may be utilized in lower relative concentrations.

Another object of this invention is to provide a thickener such that the compositional viscosities desired may be achieved through control of polymer concentration, affording compositions which lend themselves to a greater range of applications.

Another object of this invention is to provide a thickener which maintains stable viscosities over time and upon prolonged exposure to high temperature conditions. Another object of this invention is to provide a thickener which is compatible with surfactants, biocides, perfumes, dyes, and other such components which are typically present in acid compositions. Another object of this invention is to provide a thickener which will give optimal viscosity and stability without addition of low molecular weight alcohols or vegetative thickeners.

These and other important objects will be apparent from the descriptions of this invention which follow.

Summary of the Invention

This invention is an acid composition useful for a variety of household and industrial cleaning applications. It overcomes certain well-known problems and deficiencies, including those outlined above. An important aspect of this invention is a water-soluble polyacrylamide which is admixed with the acid to be thickened. The inventive thickener is less expensive than those of the prior art and may be used effectively at lower concentrations, resulting in a two-fold decrease in the overall cost of the acid composition.

(For the purpose of this discussion, the term "polymer" is used generally and, unless otherwise indicated, includes homo- and copolymers. Likewise, the term "acryla ide", unless otherwise indicated, includes C- and N-alkyl-substituted acrylamide compounds. Therefore and as used herein, the term "polyacrylamide" encompasses polymers prepared from any number or combination of acrylamide monomers, as defined above.)

This invention is a composition including: (1) an acid having a pK,¹ value greater than or equal to about

0.5, in an amount sufficient to provide the composition a pH of greater than or equal to about 1.0 and less than about 7.0; 2) a polymer having the repeating monomeric structure -CH(R)C(R') (CONR' 'R' ^■ •)-, wherein R, R', R'',and R' • ' are selected from the group consisting of hydrogen and alkyl; and (3) water in an amount sufficient to provide the composition a viscosity of about 50 - 20,000,000 centipoise.

In preferred embodiments, R, R¹, R¹¹, and R¹ • • are hydrogen, the polymer has a molecular weight of about

500,000 - 50,000,000, and the polymer is about 0.01 to 10 percent by weight of the composition. In highly preferred embodiments, the polymer (R, R', R" ' , and R' • * are hydrogen) has a molecular weight of about 5,000,000 - 25,000,000 and is about 0.2 to 1.0 percent by weight of the composition.

In preferred embodiments, the acid component of the composition is about 0.5 to 20 percent by weight of the composition, whereas in highly preferred embodiments, it is about 2.0 - 5.0 percent by weight of the composition. This invention may further comprise an additive selected from the group consisting of biocides, surfactants, and mixtures thereof which function with the polymer component to synergistically thicken the composition. Cationic, anionic, amphoteric, or neutral surfactants and quaternary amine biocides may be used. When present, the additive is about 0.1 to 5.0 percent by weight of the composition and, preferably, a biocide and surfactant mixture. Alternatively, the polyacrylamide is a copolymer of the preferred monomer where R, R¹, R¹¹, and R¹ ' • are hydrogen and another monomer where R, R¹', and R' • • are hydrogen and R' is methyl.

The preferred polyacrylamide thickener is commercially available from a number of sources including Allied Colloid Corporation of Suffolk, Virginia, and Delta Chemical Corporation of Baltimore, Maryland. Alternatively, the monomeric precursor may be obtained from a variety of sources and polymerized by methods well-known to those skilled in the art. Methacrylamide (R, R'¹, and R¹ ' ' are hydrogen and R^» is methyl) may be obtained from Rohm-Tech, Inc. of Maiden, Maryland. Regardless, to achieve the preferred high molecular weights, care must be taken to rigorously exclude the presence of molecular oxygen and iron impurities which would otherwise prematurely terminate polymerization. As stated above, in highly-preferred embodiments, the polyacrylamide has a molecular weight of about 500,000 - 50,000,000. Through observation, it has been found that at a molecular weight within this range the polymers disclosed herein provide excellent viscosities at concentrations much lower than otherwise thought possible. Typically, within this molecular weight range, thickener concentrations are on the order of about four times lower than that needed through use of prior art polymers. As a result, acid compositions may be thickened more economically and efficiently. At concentrations below this range, viscosities required for most applications are not achieved. Beyond the upper limit, the polyacrylamide tends to become too dense and water-insoluble, creating a variety of handling and related process difficulties.

As shown more explicitly in the examples which follow, polyacrylamides afford acid compositions with excellent, effective viscosities immediately upon preparation and which remain essentially undiminished over time. In contrast, the vegetative and polymeric thickeners of the prior art are specifically formulated to account for a steady decrease in viscosity. As a further indication of the benefits available thorough use of these inventive compositions, stabilities of the prior art are measured in days; comparable parameters of this invention are referenced by months, even at elevated temperatures.

Viscosity control is yet another advantage realized through use of the present invention. While viscosities of prior art compositions appear to bear no direct relation to the amount of thickener present, the compositional viscosities documented herein are a function of polyacrylamide concentration. As a result, the polyacrylamides are extremely versatile and lend themselves to a greater range of use applications. Acid compositions may now be formulated economically, incorporating only that amount of thickener required for a desired viscosity.

Stability of the inventive compositions is not adversely affected by the presence of quaternary amine biocides or surfactants (amphoteric, neutral, cationic, or anionic) . Whereas prior art thickeners exhibit solubility and related deficiencies when such ingredients are introduced, the inventive polyacrylamides perform without significant loss of composition viscosity, even under prolonged high-temperature conditions. In fact, quite unexpectedly and as illustrated below, the presence of various biocides and surfactants induces a positive synergistic effect on viscosity at all temperatures tested.

Unlike the prior art, polyacrylamides do not require addition of low molecular weight alcohols to achieve optimal composition viscosities. Indeed, comparative data shows compositions thickened with polyacrylamides remain essentially unchanged when prepared with isopropyl alcohol. These additives are thought to function via a complexation mechanism and actually increase viscosity by inducing thickener precipitation, thereby compromising the benefits to be gained through use of a soluble system. Resorting to such measures invariably presents formulation problems not otherwise incurred and increases the overall cost of the acid composition. Furthermore, the volatility associated with many such alcohols is undesired in many applications.

This invention also permits access to highly viscous compositions without addition of vegetative co- thickeners. When used in such compositions, various gums and/or the hydroxyalkylether derivatives thereof must be present in amounts approaching the weight percents of their polymeric counterparts. Increased cost and formulation problems are the consequence and, as discussed above, the resulting compositions are further destabilized when surfactant and biocide additives are included therein. Utilization of the inventive polyacrylamides completely avoids such alcohol and gum- related problems and affords process and economic benefits previously unavailable through the prior art. The acids used in conjunction with this invention generally include those water-soluble organic and inorganic acids which have a pK_t-value greater than or equal to 0.5. Polybasic acids having a pK^-value greater than or equal to 0.5 may also be employed. Stronger acids tend to hydrolize polyacrylamides to the corresponding polyacrylic acids, which do not exhibit thickening properties in acidic media. Within these parameters, useful acids include, but are not limited to, acetic, butyric, chloroacetic, chloropropionic, citric, hydroxyacetic, maleic, malonic, oxalic, phosphoric, propionic, and sulfanilic. The amount of acid added to the composition is that required to provide the pH desired for a given application, without inducing conditions detrimental to composition performance and integrity. Polyacrylamides would not seem appropriate for use as acid thickeners. These polymers are reported to hydrolyze at high temperatures and precipitate in the presence of alkali or alkaline earth metal ions, necessitating the use of quaternary ammonium hydolysis- suppression agents. However, the compositions of the present invention maintain excellent viscosity over a variety of deleterious conditions without use of suppression agents. Furthermore, at the molecular weights preferred herein, polyacrylic acid does not thicken aqueous acidic media, presumably due to a high degree of inter- and/or intramolecular hydrogen-bonding. Inasmuch as amides also exhibit hydrogen-bonding, the excellent thickening properties observed were quite unexpected and contrary to the prior art. The fact that viscosity remains essentially unchanged over time in the presence of alcohols suggests a fundamental and unanticipated chemical and/or structural distinction between the polyacrylamides and the polymeric thickeners of the prior art.

Careful observation shows that, within the preferred molecular weight range, the polyacrylamides induce a somewhat-striated effect as the acid composition slowly proceeds across a sloped surface. While not wanting to be bound by theoretical considerations, it may be that the high molecular weights employed herein are responsible for a fiber-like consistency observed and the fact that lower thickener concentrations and composition viscosities are required to achieve a desired cleaning effect. The striations may operate in such a way as to control the release of the acidic component and prolong contact time with the surface to be cleaned.

EXAMPLES OF THE INVENTION Examples of the inventive compositions are provided below. The compositions may be prepared by dissolving the polyacrylamide in water, then admixing with acid to achieve a desired pH and viscosity. (The order of addition may be varied depending upon the composition components and the amounts used.) Where provided, viscosity measurements (cps) were obtained using a Brookfield viscometer operating at 100 rpm with a No. 4 spindle at the temperature indicated.

EXAMPLE 1 The compositions shown below are representative of those which may be used in accordance with this invention. Relative amounts of the acid and thickener components (weight percent of the total composition) are given, with the balance comprised of water. Acid Thickener

Citric (5.0%) Polyacrylamide (1.0%) Citric (5.0%) Polyacrylamide (0.75%) Hydroxyacetic (2.5%) Polyacrylamide (0.75%) Hydroxyacetic (2.5%) Polyacrylamide (0.50%) Oxalic (5.0%) Polyacrylamide (1.0%) Oxalic (2.5%) Polyacrylamide (0.10%) Oxalic (2.5%) Polymethacrylamide

(0.50%)

Acetic (5.0%) Polyacrylamide (0.10%) Acetic (5.0%) Polymethacrylamide

(0.50%) j) Acetic (2.5%) Acrylamide, copolymer with Methacrylamide

(0.50%) k) Propanoic (2.5%) Polyacrylamide (0.50%)

1) Propanoic (2.5%) Polymethacrylamide

(0.50%) m) Phosphoric (2.5%) Polyacrylamide (0.75%) n) Phosphoric (2.5%) Acrylamide, copolymer with Methacrylamide

(1.0%)

EXAMPLE 2 This acid composition (5.0% Citric Acid, 1.0% thickener) exhibited stable viscosity, at room tempera¬ ture over the time shown, as is typical through use of the polyacrylamides of this invention. The testing period employed mimics typical warehouse storage and/or household use conditions and demonstrates that excellent viscosity is maintained throughout.

Time (mo . ) Viscosity (cps)

0. 6 300

1. 6 300

2 . 6 294 EXAMPLE 3 The presence of a low-molecular weight alcohol has essentially no effect on the viscosities exhibited by compositions of this invention. A control (1.0% polyacrylamide in water) was compared to the same solution containing 8% isopropyl alcohol. (Viscosities were measured at 100 rpm, using a No. 3 spindle)

Viscosity (cps) Viscosity (cps) at 24 hr. at 96 hr.

Control 215 211

With 8% isopropyl alcohol 175 175

* * * As shown in Examples 4-9, below, the compositions contemplated by this invention include those containing surfactants and quaternary ammonium biocides. Composi¬ tions so formulated (water comprises the balance of each) exhibit suitable viscosities over time, even under prolonged exposure to high-temperature conditions. In Example 8, the stability study was conducted at 120 F, while viscosity measurements were recorded at ambient temperatures.

(Maquat is the tradename of a quaternary amine biocide available from Mason Chemical Company, Chicago, IL; Triton NlOl is the tradename of a cationic surfactant available from Union Carbide of Danbury, CT; Amphoteric-L is the tradename of an amphoteric surfactant available from the Tomah Products Division of Exxon Chemical Company, Milton, WI.)

EXAMPLE 4

Composition comprised of Citric Acid (2.5%), Polyacrylamide (0.50%), Maquat (1.0%), and Triton NlOl (1.0%) . Time (mo . ) Viscosity (cps)

0. . 1 84

0. . 8 82

1. , 8 83

2 . . 8 84

4 . . 8 83

EXAMPLE 5 Composition comprised of Citric Acid (5.0%), Poly¬ acrylamide (0.50%), and Amphoteric-L (1.0%).

Time (mo. ) Viscosity (CPS) 0.6 85 1.2 82 2.3 81 3.3 80 5.3 76

EXAMPLE 6 Composition comprised of Citric Acid (2.5%), Poly¬ acrylamide, 0.50%, and Triton NlOl (1.0%).

Time (mo.) Viscositv (CDS) 0.5 82 1.2 80 2.2 80 3.2 78 5.2 77 EXAMPLE 7 Composition comprised of Citric Acid (2.5%), Poly¬ acrylamide (0.50%), Maquat (1.0%) and Triton NlOl (1.0%)

Time (mo.) Viscosity (cps)

0.1 301

0.8 298

1.8 298

2.8 294 4.8 294

EXAMPLE 8 Composition comprised of Citric Acid (2.5%), Poly¬ acrylamide (1.0%), Maquat (1.0%) and Triton NlOl (1.0%)

Time (mo.) Viscosity (cps)

0.3 294 0.8 271

1.4 248

1.9 210

2.8 188

3.0 192 3.8 169

EXAMPLE 9 Composition comprised of Citric Acid (2.5%), Poly¬ acrylamide (1.0%) and Amphoteric-L (1.0%). Ti e (mo.) Viscosity (cps)

0.8 253

1.3 213 1.8 189

2.4 166

3.2 150

3.5 154

4.3 141

* * *

While the principles of this invention have been described in connection with specific embodiments, it should be understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention. For instance, the biocides which may be utilized through the compositions disclosed herein include benzenetrialkylammonium chlorides, present as ethanolic solutions or otherwise; iminopropanates, betaines, or imidazolines may be used as surfactants.

Various perfumes, dyes, and other non-active components are also anticipated. Likewise, the polyacrylamides which may be used are limited only by their water- solubility. As such, this invention also contemplates use of those polyacrylamides (both homo- and copolymers) commercially-available as latex-emulsions whereby the polymer may be dissolved in water through an inversion process upon introduction of aqueous surfactant.

Claims

CLAIMS :

1. A composition comprising:

- an acid having a pK,¹ value greater than or equal to about 0.5, in an amount sufficient to provide the composition a pH of greater than or equal to about 1.0 and less than 7.0;

- a polymer having the repeating monomeric structure

-CH(R)C(R') (CONR^{» »}R^« • ')- wherein R, R¹, R¹¹, and R* * • are selected from the group consisting of hydrogen and alkyl; and

- water in an amount sufficient to provide the composition a viscosity of about 50 - 20,000,000 centipoise.

2. The composition of claim 1 wherein R, R¹ , R¹', and R' ' • are hydrogen.

3. The composition of claim 2 wherein the polymer has a molecular weight of about 500,000 - 50,000,000.

4. The composition of claim 3 wherein the polymer has a molecular weight of about 5,000,000 - 25,000,000.

5. The composition of claim 4 wherein the polymer is about 0.01 - 10 percent by weight of the composition.

6. The composition of claim 5 wherein the polymer is about 0.2 - 1.0 percent by weight of the composition.

7. The composition of claim 1 wherein the acid is about 0.5 - 20 percent by weight of the composition.

8. The composition of claim 7 wherein the acid is about 2.0 - 5.0 percent by weight of the composition.

9. The composition of claim 8 wherein R, R' , R¹¹, and R' • ' are hydrogen.

10. The composition of claim 9 wherein the polymer has a molecular weight of about 500,000 - 50,000,000.

11. The composition of claim 10 wherein the polymer has a molecular weight of about 5,000,000 - 25,000,000.

12. The composition of claim 13 wherein the polymer is about 0.01 - 10 percent by weight of the composition.

13. The composition of claim 12 wherein the polymer is about 0.2 - 1.0 percent by weight of the composition.

14. The composition of claim 1 further comprising an additive selected from the group consisting of biocides, surfactants, and mixtures thereof to synergistically thicken the composition.

15. The composition of claim 14 wherein:

- the surfactants are selected from the group consisting of cationic, anionic, amphoteric, and neutral surfactants; and - the biocides are quaternary amine salts.

16. The composition of claim 14 wherein the additive is a biocide and surfactant mixture.

17. The composition of claim 16 wherein the additive is about 0.1 - 5.0 percent by weight of the composition.

18. The composition of claim 1 wherein the polymer is a copolymer.

19. The composition of claim 14 wherein:

-a monomer of the copolymer has the structure where

R, R' , R' ' , and R¹ • • are hydrogen; and -another monomer of the copolymer has the structure where R, R¹¹, and R' • ' are hydrogen, and R¹ is methyl.

20. The composition of claim 19 further comprising an additive selected from the group consisting of biocides, surfactants, and mixtures thereof to synergistically thicken the composition.