AU4942996A - Dry cleaning system using densified carbon dioxide and a surfactant adjunct - Google Patents

Description

DRY CLEANING SYSTEM USING DENSIFIED CARBON DIOXIDE

AND A SURFACTANT ADJUNCT

Field of the Invention

The invention pertains to a dry cleaning system utilizing densified carbon dioxide and a surfactant adjunct. The invention also pertains to a method of dry cleaning fabrics utilising densified carbon dioxide and a surfactant

adjunct.

Background of the Invention

Densified, particularly supercritical fluid, carbon dioxide has been suggested as an alternative to halo-carbon

solvents used in conventional dry cleaning. For example, a dry cleaning system in which chilled liquid carbon dioxide is used to extract soils from fabrics is described in U.S. 4,012,194 issued to Maffei on March 15, 1977.

Supercritical fluid carbon dioxide provides a nontoxic, inexpensive, recyclable and environmentally acceptable solvent to remove soils in the dry cleaning process. The solvent has been shown to be effective in removing nonpolar stains such as motor oil, when combined with a viscous cleaning solvent, particularly mineral oil or petrolatum as described in US S/N 715,299, filed June 14, 1991, assigned to The Clorox Company and corresponding to EP 518,653.

Supercritical fluid carbon dioxide has been combined with other components, such as a source of hydrogen peroxide and an organic bleach activator as described in US S/N 754,809, filed September 4, 1991 and owned by The Clorox Company, corresponding to EP 530,949. The solvent power of densified carbon dioxide is low relative to ordinary liquid solvents and the carbon dioxide solvent alone is less effective on hydrophilic stains such as grape juice, coffee and tea and on compound hydrophobic stains such as lipstick and red candle wax, unless

surfactants and solvent modifiers are added.

A cleaning system combining particular anionic or nonionic surface active agents with supercritical fluid CO₂ is described in DE 39 04 514 A1 published August 23, 1990.

These anionic and nonionic agents, such as alkylbenzene sulfates and sulfonates, ethoxylated alkyl phenols and ethoxylated fatty alcohols, were particularly effective when combined with a relatively large amount of water

(greater than or equal to 4%). The patented system appears to combine the detergency mechanism of conventional agents with the solvent power of supercritical fluid carbon dioxide.

It has been observed that most commercially available surfactants have little solubility in supercritical fluid carbon dioxide as described in Consani, K.A., J. Sup.

Fluids, 1990 (3), pages 51-65. Moreover, it has been observed that surfactants soluble in supercritical fluid carbon dioxide become insoluble upon the addition of water. No evidence for the formation of water-containing reversed micelles with the surfactants was found. Consani supra .

Thus, the dry cleaning systems known in the art have merely combined cleaning agents with various viscosities and polarities with supercritical fluid CO₂ generally with high amounts of water as a cosolvent. The actives clean soils as in conventional washing without any synergistic effect with the CO₂ solvent.

The formation of water-containing reversed micelles is believed to be critical for the solubility and removal of hydrophilic stains. Studies of the interaction of surfactants in supercritical carbon dioxide with water, cosurfactants and cosolvents led to the conclusion that most commercially available surfactants are not designed for the formation of reversed micelles in supercritical carbon dioxide as described in McFann, G., Dissertation, University of Texas at Austin, pp. 216-306, 1993.

Therefore, the problem of developing an effective dry cleaning system utilizing supercritical fluid carbon dioxide to clean a variety of consumer soils on fabrics has remained unsolved until the present invention. Summary of the Invention

It is therefore an object of the present invention to provide a dry cleaning system utilizing an environmentally safe, nonpolar solvent such as densified carbon dioxide, which effectively removes a variety of soils on fabrics. Another object is the design of effective surfactants for use in supercritical fluid carbon dioxide.

Another object of the invention is to provide a dry

cleaning system of solvent, surfactant, enzyme and bleach for the total cleaning of fabrics using

densified/supercritical fluid carbon dioxide that gives results equivalent to the cleaning demonstrated by

conventional dry cleaning solvents.

In one aspect of the present invention, the dry cleaning system used for cleaning a variety of soiled fabrics comprises densified carbon dioxide and about 0.001% to about 5% of a surfactant in supercritical fluid carbon dioxide. The surfactant has a supercritical fluid CO₂-philic functional moiety connected to a supercritical fluid CO₂-phobic functional moiety. Preferred CO₂-philic moieties of the surfactant include halocarbons such as

fluorocarbons, chlorocarbons and mixed fluorochlorocarbons, polysiloxanes, and branched polyalkylene oxides. The CO₂-phobic groups for the surfactant contain preferably polyalkylene oxides, carboxylates, C_1-30 alkyl sulfonates, carbohydrates, glycerates, phosphates, sulfates and C_1-30 hydrocarbons. The dry cleaning system may also be designed to include a modifier, such as water, or an organic solvent up to only about 5% by volume; enzymes up to about 10 wt.% and a bleaching agent such as a peracid. In a second aspect of the invention, a method for dry cleaning a variety of soiled fabrics is provided wherein a selected surfactant and optionally a modifier, an enzyme, bleaching agent or mixtures thereof are combined and the cloth is contacted with the mixture. Densified carbon dioxide is introduced into a cleaning vessel which is then pressurized from about 700 psi to about 10,000 psi and heated to a range of about 20°C to about 100°C. Fresh densified carbon dioxide is used to flush the cleaning vessel.

Brief Description of the Drawing

Figure 1 is a diagrammatic flow chart of the supercritical fluid carbon dioxide dry cleaning process according to the invention.

Detailed Description of Preferred Embodiments

The invention provides a dry cleaning system which replaces conventional solvents with densified carbon dioxide in combination with selected cleaning surfactants.

Optionally, modifiers, enzymes, bleaching agents and mixtures thereof are combined with the solvent and

surfactant to provide a total cleaning system.

For purposes of the invention, the following definitions are used: "Densified carbon dioxide" means carbon dioxide in a gas form which is placed under pressures exceeding about 700 psi at about 20°C.

"Supercritical fluid carbon dioxide" means carbon dioxide which is at or above the critical temperature of 31°C and a critical pressure of 71 atmospheres and which cannot be condensed into a liquid phase despite the addition of further pressure. The term "densified carbon dioxide-philic" in reference to surfactants R_nZ_n, wherein n and n' are each independently 1 to 50, means that the functional group, R_n- is soluble in carbon dioxide at pressures of 500-10,000 psi and

temperatures of 0-100°C to greater than 10 weight percent. Preferably n and n' are each independently 1-35. Such functional groups (R_n-) include halocarbons, polysiloxanes and branched polyalkylene oxides.

The term "densified carbon dioxide-phobic" in reference to surfactants, R_nZ_n,, means that Z_n,- will have a solubility in carbon dioxide at pressures of 500-10,000 psi and

temperatures of 0-100°C of less than 10 weight percent.

The functional groups in Z_n,- include carboxylic acids, phosphatyl esters, hydroxys, C_1-30 alkyls or alkenyls, polyalkylene oxides, branched polyalkylene oxides,

carboxylates, C_1-30 alkyl sulfonates, phosphates,

glycerates, carbohydrates, nitrates, substituted or

unsubstituted aryls and sulfates. The hydrocarbon and halocarbon containing surfactants

(i.e., R_nZ_n,, containing the CO₂-philic functional group, R_n-, and the CO₂-phobic group, Z_n,-) will have an HLB of less than 15, preferably less than 13 and most preferably less than 12. The polymeric siloxane containing surfactants, R_nZ_n,, also designated MD_xD*_yM, with M representing trimethylsiloxyl end groups, D_x as a dimethylsiloxyl backbone (C_O2-philic functional group) and D*_y as one or more substituted methylsiloxyl groups substituted with CO₂-phobic R or R' groups as described in the Detailed Description Section will have a D_xD*_y ratio of greater than 0.5:1, preferably greater than 0.7:1 and most preferably greater than 1:1. The term "nonpolar stains" refers to those which are at least partially made by nonpolar organic compounds such as oily soils, sebum and the like.

The term "polar stains" is interchangeable with the term "hydrophilic stains" and refers to stains such as grape juice, coffee and tea.

The term "compound hydrophobic stains" refers to stains such as lipstick and red candle wax.

The term "particulate soils" means soils containing

insoluble solid components such as silicates, carbon black, etc. Densified carbon dioxide, preferably supercritical fluid carbon dioxide, is used in the inventive dry cleaning system. It is noted that other densified molecules having supercritical properties may also be employed alone or in mixture. These molecules include methane, ethane, propane, ammonia, butane, n-pentane, n-hexane, cyclohexane, n-heptane, ethylene, propylene, methanol, ethanol,

isopropanol, benzene, toluene, p-xylene, sulfur dioxide, chlorotrifluoromethane, trichlorofluoromethane,

perfluoropropane, chlorodifluoromethane, sulfur

hexafluoride and nitrous oxide. During the dry cleaning process, the temperature range is between about 20°C and about 100°C, preferably 20°C to 60°C and most preferably 30°C to about 60°C. The pressure during cleaning is about 700 psi to about 10,000 psi, preferably 800 psi to about 7,000 psi and most preferably 800 psi to about 6,000 psi.

A "substituted methylsiloxyl group" is a methylsiloxyl group substituted with a CO₂-phobic group R or RM R or R' are each represented in the following formula:

-(CH₂)_a(C₆H₄)_b(A)_d— [(L)_e(A')_f]_n- (L')_gZ(G)_h wherein a is 1-30, b is 0-1, C₆H₄ is substituted or

unsubstituted with a C_1-10 alkyl or alkenyl and A, d, L, e,

A', F, n L', g, Z, G and h are defined below, and mixtures of R and R'.

A "substituted aryl" is an aryl substituted with a C_1-30 alkyl, alkenyl or hydroxyl, preferably a C_1-20 alkyl or alkenyl.

A "substituted carbohydrate" is a carbohydrate substituted with a C_1-10 alkyl or alkenyl, preferably a C_1-5 alkyl.

The terms "polyalkylene oxide", "alkyl" and "alkenyl" each contain a carbon chain which may be either straight or branched unless otherwise stated.

Surfactant Adjunct

A surfactant which is effective for use in a densified carbon dioxide dry cleaning system requires the combination of densified carbon dioxide-philic functional groups with densified carbon dioxide-phobic functional groups (see definitions above). The resulting compound may form reversed micelles with the CO₂-philic functional groups extending into a continuous phase and the CO₂-phobic functional groups directed toward the center of the micelle.

The surfactant is present in an amount of from 0.001 to 10 wt.%, preferably 0.01 to 5 wt.%.

The CO₂-philic moieties of the surfactants are groups exhibiting low Hildebrand solubility parameters, as

described in Grant, D. J. W. et al. "Solubility Behavior of Organic Compounds", Techniques of Chemistry Series, J.

Wiley & Sons, NY (1990) pp. 46-55 which describes the

Hildebrand solubility equation, herein incorporated by reference. These CO₂-philic moieties also exhibit low polarizability and some electron donating capability allowing them to be solubilized easily in densified fluid carbon dioxide.

As defined above the CO₂-philic functional groups are soluble in densified carbon dioxide to greater than 10 weight percent, preferably greater than 15 weight percent, at pressures of 500-10,000 psi and temperatures of 0-100°C.

Preferred densified CO₂-philic functional groups include halocarbons (such as fluoro-, chloro- and fluorochlorocarbons), polysiloxanes and branched polyalkylene oxides.

The CO₂-phobic portion of the surfactant molecule is obtained either by a hydrophilic or a hydrophobic

functional group which is less than 10 weight percent soluble in densified CO₂, preferably less than 5 wt. %, at a pressures of 500-10,000 psi and temperatures of 0-100°C. Examples of moieties contained in the CO₂-phobic groups include polyalkylene oxides, carboxylates, branched acrylate esters, C_1-30 hydrocarbons, aryls which are

unsubstituted or substituted, sulfonates, glycerates, phosphates, sulfates and carbohydrates. Especially preferred CO₂-phobic groups include C_2-20 straight chain or branched alkyls, polyalkylene oxides, glycerates,

carboxylates, phosphates, sulfates and carbohydrates. The CO₂-philic and CO₂-phobic groups may be directly

connected or linked together via a linkage group. Such groups include ester, keto, ether, amide, amine, thio, alkyl, alkenyl, fluoroalkyl or fluoroalkenyl. Surfactants which are useful in the invention may be selected from four groups of compounds. The first group of compounds has the following formula:

[(CX₃(CX₂)_a(CH₂)_b)_c(A)_d—[(L)_e—(A-)_f]_n—(L')_g]₀Z(G)_h (I) wherein X is F, Cl, Br, I and mixtures thereof, preferably F and Cl;

a is 1 - 30, preferably 1-25, most preferably 5-20; b is 0 - 5, preferably 0 - 3;

c is 1 - 5, preferably 1 - 3;

A and A' are each independently a linking moiety representing an ester, a keto, an ether, a thio, an amido, an amino, a C_1-4 fluoroalkyl, a C_1-4 fluoroalkenyl, a

branched or straight chain polyalkylene oxide, a phosphato, a sulfonyl, a sulfate, an ammonium and mixtures thereof; d is 0 or 1;

L and L' are each independently a C_1-30 straight

chained or branched alkyl or alkenyl or an aryl which is unsubstituted or substituted and mixtures thereof;

e is 0-3;

f is 0 or 1;

n is 0-10, preferably 0-5, most preferably 0-3;

g is 0-3;

o is 0-5, preferably 0-3;

Z is a hydrogen, a carboxylic acid, a hydroxy, a phosphato, a phosphato ester, a sulfonyl, a sulfonate, a sulfate, a branched or straight-chained polyalkylene oxide, a nitryl, a glyceryl, an aryl unsubstituted or substituted with a C_1-30 alkyl or alkenyl, (preferably C_1-25 alkyl), a carbohydrate unsubstituted or substituted with a C_1-10 alkyl or alkenyl (preferably a C_1-5 alkyl) or an ammonium;

G is an anion or cation such as H⁺, Na⁺, Li⁺, K⁺, NH₄ ⁺ Ca⁺², Mg⁺²; Cl-, Br-, I-, mesylate, or tosylate; and h is 0-3, preferably 0-2.

Preferred compounds within the scope of the formula I include those having linking moieties A and A' which are each independently an ester, an ether, a thio, a

polyalkylene oxide, an amido, an ammonium and mixtures thereof;

L and L' are each independently a C_1-25 straight chain or branched alkyl or unsubstituted aryl; and Z is a

hydrogen, carboxylic acid, hydroxyl, a phosphato, a

sulfonyl, a sulfate, an ammonium, a polyalkylene oxide, or a carbohydrate, preferably unsubstituted. G groups which are preferred include H⁺, Li⁺, Na⁺, NH⁺ ₄, Cl-, Br- and tosylate.

Most preferred compounds within the scope of formula I include those compounds wherein A and A' are each

independently an ester, ether, an amido, a polyoxyalkylene oxide and mixtures thereof; L and L' are each independently a C_1-20 straight chain or branched alkyl or an unsubstituted aryl; Z is a hydrogen, a phosphato, a sulfonyl, a

carboxylic acid, a sulfate, a polyalkylene oxide and mixtures thereof; and

G is H⁺, Na⁺ or NH₄ ⁺ .

Non-limiting examples of compounds within the scope of 'formula I include the following: Compounds of formula I are prepared by any conventional preparation method known in the art such as the one

described in March, J., "Advanced Organic Chemistry", J. Wiley & Sons, NY (1985).

Commercially available fluorinated compounds include compounds supplied as the Zonyl™ series by Dupont.

The second group of surfactants useful in the dry cleaning system are those compounds having a polyalkylene moiety and having a formula (II). wherein R and R' each represent a hydrogen, a C_1-5 straight chained or branched alkyl or alkylene oxide and mixtures thereof;

i is 1 to 50, preferably 1 to 30, and

A, A', d, L, L', e f, n, g, o, Z, G and h are as defined above.

Preferably R and R' are each independently a hydrogen, a C_1-3 alkyl, or alkylene oxide and mixtures thereof. Most preferably R and R' are each independently a hydrogen, C_1-3 alkyl and mixtures thereof. Non-limiting examples of compounds within the scope of formula II are:

Compounds of formula II may be prepared as is known in the art and as described in March et al., Supra . Examples of commercially available compounds of formula II may be obtained as the Pluronic series from BASF, Inc.

A third group of surfactants useful in the invention contain a fluorinated oxide moiety and the compounds have a formula:

[(CX₃(XO)_r(T)_s)_c(A)_d-[(L)_e-(A')_f-]_n(L')_g]₀Z(G)_h (III) wherein XO is a halogenated alkylene oxide having C_1-6 straight or branched halocarbons, preferably C_1-3,

r is 1-50, preferably 1-25, most preferably 5-20, T is a straight chained or branched haloalkyl or haloaryl,

s is 0 to 5, preferably 0-3,

X, A, A', c, d, L, L', e, f, n, g, o, Z, G and hare as defined above.

Non-limiting examples of halogenated oxide containing compounds include:

Examples of commercially available compounds within the scope of formula III include those compounds supplied under the Krytox™ series by DuPont having a formula:

wherein x is 1- 50 .

Other compounds within the scope of formula III are made as known in the art and described in March et al., Supra.

The fourth group of surfactants useful in the invention include siloxanes containing surfactants of formula IV

MD_xD*_yM (IV) wherein M is a trimethylsiloxyl end group, D_x is a dimethylsiloxyl backbone which is CO₂-philic and D^* _y is one or more methylsiloxyl groups which are substituted with a CO₂-phobic R or R' group,

wherein R and R' each independently have the following formula:

(CH₂)_a(C₆H₄)_b(A)_d-[(L)_e╌(A')_f-]_n-(L')_gZ(G)_h wherein a is 1-30, preferably 1-25, most preferably 1-

20,

b is 0 or 1,

C₆H₄ is unsubstituted or substituted with a C_1-10 alkyl or alkenyl, and

A, A', d, L, e, f, n, L', g, Z, G and h are as defined above and mixtures of R and R' thereof. The D_x:D*_y ratio of the siloxane containing surfactants should be greater than 0.5:1, preferably greater than 0.7:1 and most preferably greater than 1:1. The siloxane compounds should have a molecular weight ranging from 100 to 100,000, preferably 200 to 50,000, most preferably 500 to 35,000.

Silicones may be prepared by any conventional method such as the method described in Hardman, B. "Silicones" the

Encyclopedia of Polymer Science and Engineering, v. 15, 2nd Ed., J. Wiley and Sons, NY, NY (1989).

Examples of commercially available siloxane containing compounds which may be used in the invention are those supplied under the ABIL series by Goldschmidt.

Suitable siloxane compounds within the scope of formula IV are compounds of formula V:

the ratio of x:y and y' is greater than 0.5:1,

preferably greater than 0.7:1 and most preferably greater than 1:1, and

R and R' are as defined above.

Preferred CO₂-phobic groups represented by R and R' include those moieties of the following formula:

(CH₂)_a(C₆H₄)_b(A)_d-[(L)_e-(A')_f-]-(L')_gZ(G)_h wherein a is 1-20,

b is 0,

C₆H₄ is unsubstituted,

A, A', d, L, e, f, n, g, Z, G and h are as defined above, and mixtures of R and R'.

Non-limiting examples of polydimethylsiloxane surfactants substituted with CO₂-phobic R or R' groups are:

Enzymes

Enzymes may additionally be added to the dry cleaning system of the invention to improve stain removal. Such enzymes include proteases (e.g., Alcalase^®, Savinase^® and Esperase^® from Novo Industries A/S); amylases (e.g.,

Termamyl^® from Novo Industries A/S); lipases (e.g.,

Lipolase^® from Novo Industries A/S); and oxidases. The enzyme should be added to the cleaning drum in an amount from 0.001% to 10%, preferably 0.01% to 5%. The type of soil dictates the choice of enzyme used in the system. The enzymes should be delivered in a conventional manner, such as by preparing an enzyme solution, typically of 1% by volume (i.e., 3 mls enzyme in buffered water or solvent). Modifiers

In a preferred embodiment, a modifier such as water, or a useful organic solvent may be added with the stained cloth in the cleaning drum in a small volume. Preferred amounts of modifier should be 0.0% to about 10% by volume, more preferably 0.0% to about 5% by volume, most preferably 0.0% to about 3%. Preferred solvents include water, ethanol, acetone, hexane, methanol, glycols, acetonitrile, C_1-10 alcohols and C_5-15 hydrocarbons. Especially preferred solvents include water, ethanol and methanol.

Peracid Precursors

Organic peracids which are stable in storage and which solubilize in densified carbon dioxide are effective at bleaching stains in the dry cleaning system. The selected organic peracid should be soluble in carbon dioxide to greater than 0.001 wt . % at pressures of 500-10,000 psi and temperatures of 0-100°C. The peracid compound should be present in an amount of about 0.01% to about 5%, preferably 0.1% to about 3%. The organic peroxyacids usable in the present invention can contain either one or two peroxy groups and can be either aliphatic or aromatic. When the organic peroxyacid is aliphatic, the unsubstituted acid has the general formula: where Y can be, for example, H, CH₃, CH₂Cl, COOH, or COOOH; and n is an integer from 1 to 20.

When the organic peroxy acid is aromatic, the

unsubstituted acid has the general formula: wherein Y is hydrogen, alkyl, alkylhalogen, halogen, or COOH or COOOH.

Typical monoperoxyacids useful herein include alkyl

peroxyacids and aryl peroxyacids such as:

(i) peroxybenzoic acid and ring-substituted

peroxybenzoic acid, e.g. peroxy-α-naphthoic acid;

(ii) aliphatic, substituted aliphatic and arylalkyl monoperoxy acids, e.g. peroxylauric acid, peroxystearic acid, and N,N-phthaloylaminoperoxycaproic acid (PAP); and

(iii) amidoperoxy acids, e.g. monononylamide of either peroxysuccinic acid (NAPSA) or of peroxyadipic acid (NAPAA).

Typical diperoxy acids useful herein include alkyl diperoxy acids and aryldiperoxy acids, such as:

(iii) 1,12-diperoxydodecanedioic acid;

(iv) 1,9-diperoxyazelaic acid;

(v) diperoxybrassylic acid; diperoxysebacic acid and diperoxyisophthalic acid;

(vi) 2-decyldiperoxybutane-1,4-dioic acid;

(vii) 4,4'-sulfonylbisperoxybenzoic acid; and

(viii) N,N'-terephthaloyl-di(6-aminoperoxycaproic acid) (TPCAP).

Particularly preferred peroxy acids include PAP, TPCAP, haloperbenzoic acid and peracetic acid.

Dry Cleaning Process

A process of dry cleaning using densified carbon dioxide as the cleaning fluid is schematically represented in Figure 1. A cleaning vessel 5, preferably a rotatable drum, receives soiled fabrics as well as the selected surfactant, modifier, enzyme, peracid and mixtures thereof. The cleaning vessel may also be referred to as an autoclave, particularly as described in the examples below. Densified carbon dioxide, such as supercritical fluid carbon dioxide, is introduced into the cleaning vessel from a storage vessel 1. Since much of the CO₂ cleaning fluid is recycled within the system, any losses during the dry cleaning process are made up through a CO₂ liquid supply vessel 2. The CO₂ fluid is pumped into the cleaning vessel by a pump 3 at pressures ranging between 700 and 10,000 psi, preferably 800 to 6000 psi. The CO₂ fluid is heated to its supercritical range of about 20°C to about 60°C by a heat exchanger 4. During operation, the densified CO₂ is transferred from the supply vessel 2 to the cleaning vessel 5 through line 7 for a dry cleaning cycle of between about 15 to about 30 minutes. Before or during the cleaning cycle, surfactants, modifiers, enzymes, peracid and mixtures thereof as discussed above are introduced into the cleaning vessel, preferably through a line and pump system connected to the cleaning vessel.

At the end of the dry cleaning cycle, dirty CO₂, soil and spent cleaning agents are transferred through an expansion valve 6, a heat exchanger 8 by way of a line 9 into a flash drum 10. In the flash drum, pressures are reduced to between about 800 and about 1,000 and psi and to a

temperature of about 20°C to about 60°C. Gaseous CO₂ is separated from the soil and spent agents and transferred via line 11 through a filter 12 and condenser 13 to be recycled back to the supply vessel 2. The spent agents and residue CO₂ are transferred via line 14 to an atmospheric tank 15, where the remaining CO₂ is vented to the

atmosphere.

Other processes known in the art may be used in the claimed dry cleaning system such as those described in Dewees et al., US Patent No. 5,267,455, owned by The Clorox Company, herein incorporated by reference. The following examples will more fully illustrate the embodiments of the invention. All parts, percentages and proportions referred to herein and in appended claims are by weight unless otherwise indicated. The definition and examples are intended to illustrate and not limit the scope of the invention.

Example 1

Hydrocarbon and fluorocarbon containing surfactants useful in the invention must exhibit a hydrophilic/lipophilic balance of less than 15. This example describes the calculation of HLB values for various surfactants to determine their effectiveness in supercritical carbon dioxide. This calculation for various hydrocarbon and fluorocarbon surfactants is reported in the literature¹ and is represented by the following equation:

HLB = 7 + Σ (hydrophilic group numbers) - ∑(lipophilic group numbers)

The hydrophilic and lipophilic group numbers have been assigned to a number of common surfactant functionalities including hydrophilic groups such as carboxylates, sulfates and ethoxylates and lipophilic groups such as -CH₂, CF₂ and PPG's.¹ These group numbers for the functional groups in surfactants were utilized to calculate the HLB number for the following hydrocarbon or fluorocarbon surfactant:

The conventional surfactants (Nos. 14-18) exhibit an HLB value of greater than 15 and are not effective as dry cleaning components in the invention. Example 2

Supercritical fluid carbon dioxide only as a cleaning medium was used to dry clean several hydrophobic stains on cotton and wool fabrics.

The stained fabrics were prepared by taking a two inch by three inch cloth and applying the stain directly to the cloths. The cloths were allowed to dry.

The stained fabrics were then placed in a 300 ml autoclave having a gas compressor and an extraction system. The stained cloth was hung from the bottom of the autoclave's overhead stirrer using a copper wire to promote good agitation during washing and extraction. After placing the cloth in the autoclave and sealing it, liquid CO₂ at a tank pressure of 850 psi was allowed into the system and was heated to reach a temperature of about 40°C to 45°C. When the desired temperature was reached in the autoclave, the pressure inside the autoclave was increased to 4,000 psi by pumping in more CO₂ with a gas compressor. The stirrer was then turned on for 15 minutes to mimic a wash cycle. At the completion of the wash cycle, 20 cubic feet of fresh CO₂ were passed through the system to mimic a rinse cycle. The pressure of the autoclave was then released to

atmospheric pressure and the cleaned cloths were removed from the autoclave. To measure the extent of cleaning, the cloths were placed in a Reflectometer^® supplied by

Colorguard. The R scale, which measures darkness from black to white, was used to determine stain removal.

Cleaning results were reported as the percent stain removal according to the following calculation:

% stain removal = stain removed = cleaned cloth reading - stained cloth reading × 100%

stain applied unstained cloth reading - stained cloth reading The cleaning results for the cotton and wool cloths dry cleaned with supercritical fluid carbon dioxide alone are in Table 1 below.

The results confirm what was known in the art: that hydrophobic stains are substantially removed with

supercritical fluid carbon dioxide alone. However, the lipstick stain, which is a compound hydrophobic stain with pigment particulates, was removed only to the extent of its waxy components. The colored portion of the stain fully remained.

Example 3

The hydrophilic stain, grape juice, was dry cleaned using supercritical fluid carbon dioxide, a polydimethylsiloxane surfactant, water as a modifier and mixtures thereof according to the invention.

Two inch by three inch polyester cloths were cut and stained with concentrated grape juice which was diluted 1:10 with water. The grape juice stain was then dried and was approximately 2 wt.% and 7 wt.% grape juice stain after drying. The cloths were then placed in the autoclave as described in Example 2, except these experiments were run at a pressure of 6,000 psi.

Two different polydimethylsiloxane surfactants were used alone or in combination with 0.5 ml of water and

supercritical fluid carbon dioxide. The control was supercritical fluid carbon dioxide alone.

The water was added directly to the bottom of the autoclave and not on the stain itself and the surfactant was applied directly to the stain on the cloth. After the wash and rinse cycles, cleaning results were evaluated and the results are reported in Table 2 below.

It was observed that the combination of water as a modifier with the selected polydimethylsiloxane surfactants improved dry cleaning results in supercritical fluid carbon dioxide. In fact, none of the three components alone removed

substantially any of the grape juice stain.

Example 4

As a comparison with the prior art, a conventional alkane surfactant was used alone or in combination with a modifier and supercritical CO₂ to dry clean the hydrophilic stain, grape juice, on polyester, as described in Example 3 above.

The surfactant, linear alkylbenzene sulfonate is a solid and has an HLB value of 20. The LAS was added to the bottom of the autoclave with varying amounts of water. The following cleaning results were observed and are reported in Table 3 below.

It was observed that LAS was only effective in a larger amount of water (6 ml). When the modifier was reduced from 6 ml to 0.5 ml, the stain only wicked up the cloth and was not removed.

It is noted that DE 3904514 describes dry cleaning using supercritical fluid carbon dioxide in combination with a conventional surfactant. The publication exemplifies cleaning results with LAS. The experimental conditions in the examples state that the stained cloth has only minimal contact with supercritical fluid carbon dioxide, namely a 10 minute rinse only. It appears that the cleaning obtained with LAS and the large amount of water is similar to spot or wet cleaning, since the cloth remains wet at the end of the process. There appears to be little to minimal

influence of the supercritical fluid carbon dioxide on spot removal under these conditions.

Additionally, in a dry cleaning process, the use of LAS with supercritical fluid carbon dioxide would not be possible with water-sensitive fabrics such as silks and wools since such large amounts of water are necessary.

Example 5

A hydrophilic stain, namely grape juice, was dry cleaned using polydimethylsiloxane surfactants with water and supercritical fluid carbon dioxide according to the

invention.

Polyester cloths were stained with 7% grape juice stain as described in Example 3 above. Two different

polydimethylsiloxane surfactants were used with varying amounts of water and supercritical fluid carbon dioxide. In comparison, LAS, the conventional surfactant, used with the same amounts of water was used to remove the grape juice stains. The cleaning results for the two types of surfactants are reported in Table 4 below.

It was observed that the modified polydimethylsiloxane surfactants according to the invention are more effective in the presence of less water (0.5 ml vs. 6.0 ml) as cleaning was reduced from 50% to 40% when the water levels were increased. The opposite effect was observed with LAS, as stain removal increased from 0% to 75% as the water levels were increased to 6.0 ml. Thus, the claimed siloxane surfactants provide better cleaning results with less water which is beneficial for water sensitive fabrics.

Example 6

Polydimethylsiloxanes having varying molecular weights and alkyl substituted moieties were tested as surfactants with supercritical fluid carbon dioxide in the inventive dry cleaning process. Various types of stained cloths were tested under the dry cleaning conditions described in

Example 2 above.

A compound hydrophobic stain, red candle wax, was placed on both cotton fabrics as follows. A candle was lit and approximately 40 drops of melted wax were placed on each cloth so that a circular pattern was achieved. The cloths were then allowed to dry and the crusty excess wax layer was scraped off the top and bottom of each stain so that only a flat waxy colored stain was left.

Red candle wax was placed on the wool cloth by

predissolving the red candle in hexane and then pipetting an amount of the hexane solution onto the fabric. The fabric was dried and the resulting fabric contained about 10 wt.% stain.

As stated above, the pressure of the autoclave during the washing cycle was 6000 psi at a temperature of 40°C with a 15 minute cycle. Twenty cubic feet of supercritical fluid carbon dioxide was used for the rinse cycle.

Five types of modified polydimethylsiloxanes having formula V:

wherein x:y and y' ratio is ≥ 0.5:1 and R and R' are each independently a straight or branched C_1-30 alkyl chain were prepared. The compound formula is represented as MD_X

D*_yM(C_z) wherein M represents the trimethylsiloxyl end groups, D_x represents the dimethylsiloxane backbone (CO₂- philic), D*_y represents the substituted methylsiloxyl group (CO₂-phobic) and (C_z) represents the carbon length of the alkyl chain of R.

Molecular weights of the siloxanes ranged from 1,100 to 31,000. The polydimethylsiloxanes straight chain alkyl group ranged from C₈ to C₁₈ carbons. The red wax stained cloths were cleaned and the cleaning results were observed and are reported in Table 5 below. No modifier was used.

Example 7

A glycerated siloxane surfactant having a formula MD_xD*_yM wherein D*_y is substituted by -(CH₂)₃OCH₂CH(OH)CH₂OH was used to dry clean a grape juice stain on a polyester cloth under the dry cleaning conditions described in Example 2 above. About 0.2 gram of the surfactant was combined with 0.5 ml. water. The glycerated siloxane is a polydimethylsiloxane with a glycerol side chain having a molecular weight of 870 and prepared as described in Hardman, Supra.

It was observed that the glycerated siloxane removed 33% of the grape juice stain.

Example 8

Various fluorinated surfactants, either alone or with water, were used with supercritical fluid carbon dioxide to clean several types of stained fabric under the dry

cleaning conditions described in Example 2.

Specifically, the pressure in the autoclave was 4000 psi and the temperature was 40°C to 45°C.

Cotton stained with red candle wax and polyester stained with grape juice were cleaned with the fluorinated

surfactants and the following cleaning results were

observed as reported in Table 6 below.

It was observed that all of the fluorinated surfactants equalled or improved dry cleaning of the tested stains over the use of supercritical fluid carbon dioxide alone. It was further observed that the fluorinated nonionic

surfactants (FSO-100 and FSN) were more effective than the fluorinated nonionic having a lithium carboxylate salt (FSA).

Example 9

Various bleaching peracids were combined with supercritical fluid carbon dioxide to dry clean stained fabrics.

The bleaching peracids tested include m-chloroperbenzoic acid (m-CPBA), p-nitroperbenzoic acid (p-NPBA) and 6-phthalimidoperoxy hexanoic acid (PAP) in an amount of about 0.2 to 0.5 grams each. Cotton stained with red candle wax was cleaned as described in Example 5. The wash cycle of the dry cleaning system was run at 6000 psi and 45°C as described in Example 2. The coffee stains were applied to polyester and wool cloths.

At the end of the cleaning cycle, the stained cloths were evaluated and the results are reported below in Table 7.

The results show that the three peroxides tested

significantly improved stain removal on the two types of stains cleaned over supercritical fluid carbon dioxide alone.

Example 10

Protease enzyme was used in supercritical carbon dioxide to clean spinach stains from cotton cloth. Three (3) mls of protease enzyme (Savinase supplied by Novo, Inc.) was added to buffered water to form a 1% solution and then added to each cloth. The cloths were then washed and rinsed as described in Example 2 above. The cleaning results

observed and calculated are as shown in Table 8 below:

These results show enhanced cleaning of the spinach stain over supercritical carbon dioxide alone when the enzyme is added to the system. Example 11

Lipolase enzyme (1% enzyme solution of 3 mls in buffered wear) was used in supercritical carbon dioxide to clean red candle wax stains from rayon cloth. The procedure used was identical to that of Example 10. The results are

summarized in Table 9 below.

The results in Table 9 show enhanced cleaning of the red candle wax stain when lipolase is used in conjunction with supercritical carbon dioxide, on both rayon and cotton cloths.

Example 12

Amylase enzyme (1% enzyme solution of 3 mls enzyme in buffered water) was used to dryclean starch/azure blue stains on wool cloth in supercritical carbon dioxide. The blue dye is added to make the starch stain visible so that its removal may be detected by the reflectometer. The drycleaning procedure used was identical to that of example 10, and the results are presented in Table 10 below.

The results in Table 10 show that the Termamyl enzyme is effective at cleaning the starch stain from wool cloth in supercritical carbon dioxide.

Example 13

Dry cleaning of grape juice stain was conducted on cloths other than polyester fabric. The experiments on rayon and silk cloth were conducted using the same procedure as in Example 3, using cloths with 2 wt. % grape juice stains with water as a modifier at pressures of 6000 psi and 4000 psi as noted in Table 11.

These results show significantly enhanced cleaning of the grape juice stain on rayon and silk when the

polydimethylsiloxane surfactant Abil 88184 is added to the supercritical carbon dioxide dry cleaning system.

Example 14

Dry cleaning of red candle wax stains was conducted on several different types of fabric, using an alkyl modified polydimethylsiloxane surfactant, MD_15.3D^* _1.5M (C₁₂), having a molecular weight of 1475 g/mole. The surfactant was synthesized as described in Hardman, Supra. The dry cleaning procedure used was the same as that used in example 5, and the cleaning results are presented in the following table.

The dry cleaning results show significantly enhanced cleaning of the red candle wax stain on all fabrics except for rayon, which shows no cleaning enhancement from addition of the surfactant. The cleaning results for the silk cloth are especially high, giving a cloth which looks very clean to the eye.

Example 15

Dry cleaning of grape juice on polyester cloth and of red candle wax on cotton cloth was investigated at different pressures to determine the effect of the pressure of supercritical carbon dioxide on the cleaning effectiveness of the system. The dry cleaning procedures used were the same as those used in examples 3 and 6 except for the variations in pressure, and the results are presented in the following table.

The results presented in the table show that the cleaning of red candle wax stains diminishes between 3000 and 2000 psi, while the cleaning of grape juice stains diminishes between 4000 and 3000 psi.

Example 16

Further dry cleaning experiments were conducted on

polyester stained with grape juice using other ethylene oxide/propylene oxide modified polydimethylsiloxane

surfactants. The cleaning efficacy of these surfactants was compared to that of the Abil 88184 surfactant, whose cleaning results are presented in example 3. The dry cleaning procedure used was that same as that in example 2. Water (0.5 ml) was applied to the stained cloth before each experiment was conducted. The results are presented in the following table.

Example 17

The following tables show dry cleaning results on grape juice stains made on polyester cloth where the stained cloths were prepared by dipping the entire cloth in the staining solution. The cloths are prepared with 2 wt. % stain, and otherwise, the drycleaning procedure is

identical to that of Example 3, including the use of 0.5 ml water on each cloth prior to cleaning.

The dry cleaning results presented in this table show that the synthesized surfactants (entries 2 and 3) are just as effective at cleaning as Abil 88184. In addition, the new surfactants are just as effective at 4000 psi as they are at 6000 psi, although their cleaning ability diminishes somewhat at 3000 psi.

Example 18

These experiments comprised the cleaning of both red candle wax and grape juice stains simultaneously in the high pressure autoclave. One of each stained cloth was used with its respective surfactant and modifier (i.e. water added to the grape juice stained cloth). The grape juice stained cloth was prepared by the dipping method. Dry cleaning was conducted as described in example 2 and 5, at 6000 psi and 43-45°C, and the results are presented in the following table.

The results in the table show that the surfactants provide compatible amounts of cleaning of both stains, except for the combination of Krytox^(R) with Abil 88184, (entry 2), where the effectiveness of the Abil 88184 at cleaning the grape juice is diminished. The cleaning ability of the Krytox on red candle wax is actually enhanced somewhat in combination with polydimethylsiloxane surfactants.

Claims (15)

1. A dry cleaning system for removing stains from fabrics comprising: a. an effective amount of densified carbon dioxide; b. 0.001% to 10% by weight of a surfactant

which is soluble in the densified carbon

dioxide and which is represented by a

formula wherein R_n- is a densified CO₂-philic functional group, R is a halocarbon, a polysiloxane, or a branched polyalkylene oxide and n is 1-50, and Z_n,- is a densified CO₂-phobic functional group, and n' is 1-50 and at pressures of 500-10,000 psi and temperatures of 0-100°C, the R_n- group is soluble in the densified carbon dioxide to greater than 10 wt. percent and the Z_n'- group is soluble in the densified carbon dioxide to less than 10 wt. percent, and wherein R of the surfactant is the halocarbon or the branched polyalkylene oxide the surfactant has an HLB value of less than 15 and wherein R is the polysiloxane, the surfactant has a ratio of dimethyl siloxyl to substituted methyl siloxy groups of greater than 0.5:1;

c. 0 to about 10% by volume of a modifier;

d. 0 to 3% by weight of an organic peracid; and e. 0 to 10% by weight of an enzyme solution,

to substantially dry clean stains from fabrics.

2. A system according to claim 1 wherein the Z of Z_n,- is a densified CO₂ phobic group having a functional moiety selected from the group consisting of a carboxylic acid, a hydroxyl, a phosphato, a phosphato ester, a sulfonyl, a C_1-30 alkyl sulfonate, a sulfate, an aryl which is unsubstituted or substituted with a C_1-30 alkyl or alkenyl, a branched or straight chained polyalkylene oxide, a nitro, a glyceryl, a C_1-30 straight chained or branched alkyl or alkenyl and a carbohydrate

unsubstituted or substituted with a C_1-10 alkyl or alkenyl.

3. A system according to claim 1, wherein the HLB value of the surfactant is less than 13.

4. A system according to claim 1, wherein n and n' are

each 1-35.

5. A system according to claim 1, wherein the modifier is selected from the group consisting of water, ethanol, methanol, hexane, acetone, glycol, acetonitrile, a C_1-10 alcohol, a C_5-15 hydrocarbon and mixtures thereof.

6. A system according to claim 5, wherein the modifier is present in an amount of 0.0% to about 4% by volume.

7. A system according to claim 1 wherein the organic

peracid is selected from the group consisting of PAP, TPCAP, a haloperbenzoic acid and peracetic acid.

8. A system according to claim 1, wherein the enzyme is selected from the group consisting of a protease, an amylase, a lipase, an oxidase and mixtures thereof.

9. A system according to claim 1 wherein the surfactant is a compound selected from the group consisting of i) compounds of formula I

[(CX₃(CX₂)_a(CH₂)_b)_c(A)_d—[(L)_e—(A')_f]_n—(L')_g]₀Z(G)_h (I) wherein X is F, Cl, Br, I and mixtures thereof;

a is 1 - 30;

b is 0 - 5;

c is 1 - 5;

A and A' are each independently a linking moiety representing an ester, a keto, an ether, a thio, an amido, an amino, a C_1-4 fluoroalkyl, a C_1-4

fluoroalkenyl, a branched or straight chain

polyalkelene oxide, a phosphate, a sulfonyl, a sulfate, an ammonium and mixtures thereof;

d is 0 or 1;

L and L' are each independently a C_1-30 straight chained or branched alkyl or alkenyl or an aryl which is unsubstituted or substituted and mixtures thereof;

e is 0-3;

f is 0 or 1;

n is 0-10;

g is 0-3;

o is 0-5;

Z is a hydrogen, a carboxylic acid, a hydroxy, a phosphato, a phosphato ester, a sulfonyl, a sulfonate, a sulfate, a branched or straight-chained polyalkylene oxide, a nitryl, a glyceryl, an aryl unsubstituted or substituted with a C_1-30 alkyl or alkenyl, a

carbohydrate unsubstituted or substituted with a C_1-10 alkyl or alkenyl or an ammonium;

G is an anion or cation such as H⁺, Na⁺, Li⁺, K⁺, NH₄ ⁺

Ca⁺², Mg⁺² , Cl-, Br-, I-, mesylate, or tosylate; and h is 0-3; ii) compounds of formula II

wherein R and R' each represent a hydrogen, a C_1-5 straight chained or branched alkyl or alkylene oxide and mixtures thereof;

i is 1 to 50;

A, A', d, L, L', e f, n, g, o, Z, G and h are as defined above, iii) compounds of formula III

[(CX₃(XO)_r(T)_s)_c(A)_d-[(L)_e-(A')_f-]_n(L-)_g]₀Z(G)_h (III) wherein XO is a halogenated alkylene oxide having a C_1-6 straight or branched halocarbon;

r is 1-30;

T is a straight chained or branched haloalkyl or haloaryl;

s is 0-5;

X, A, A', c, d, L, L', e, f, n, g, o, Z, G and h are as defined above,

iv) compounds of formula IV

MD_xD*_yM (IV) wherein M is a trimethylsiloxyl end group, D_x is a dimethylsiloxyl backbone which is CO₂-philic and D^* _y is one or more methylsiloxyl groups which are substituted with a CO₂-phobic R or R' group and mixtures of R and

R',

wherein R and R' are each independently defined in the formula

(CH₂)_a(C₆H₄)_b(A)_d-[(L)_e—(A')_f-]_n-(L')_gZ(G)_h wherein a is 1-30,

b is 0 or 1,

C₆H₄ is unsubstituted or substituted with a C_1-10 alkyl or alkenyl,

and A, A', d, L, e, f, n, L', g, Z, G and h are as defined above, and mixtures of compounds of formulas

I-IV.

10. A system according to claim 9 wherein the compounds of formulas I - IV are those wherein A and A' are each independently an ester, an ether, a thio, a polyalkylene oxide, an amido, an ammonium and mixtures thereof; Z is a hydrogen, a carboxylic acid, a hydroxyl, a phosphato, a sulfonyl, a sulfate, an ammonium, a polyalkylene oxide and an unsubstituted carbohydrate; and G is H⁺, Li⁺, Na⁺, NH₄ ⁺, Cl-, Br- and tosylate.

11. A system according to claim 10, wherein the

compounds of formulas I - IV are those wherein A and A' are each an ester, an ether, an amido, a polyoxyalkylene oxide and mixtures thereof; L and L' are each independently a C_1-20 alkyl or an

unsubstituted aryl, Z is a hydrogen, a phosphato, a sulfonyl, a carboxylic acid, a sulfate and a polyalkylene oxide; and G is H⁺, Na⁺ or NH₄ ⁺.

12. A system according to claim 9, wherein the

compounds of formula IV have a D_x:D*_y ratio of greater than 1:1.

13. A system according to claim 12, wherein the

compounds of formula IV have a molecular weight in a range of from 100 to 100,000.

14. A system according to claim 13, wherein the

molecular weight of the compounds of formula IV is from 200 to 50,000.

15. A system according to claim 1, wherein R of the R_n- group is the polysiloxane.