Drycleaning With Hydrogen Peroxide

Abstract

Drycleaning of white garments is carried out by including, in conventional solvent-detergent baths, hydrogen peroxide, water, and sufficient volatile alkali (e.g. ammonia) to make the water phase slightly alkaline, using limiting ratios of the ingredients to insure adequate bleaching without damage to the fabric.

Description

BACKGROUND OF THE INVENTION

For cleaning garments and other articles, two standard methods are in general use-- washing with detergents in water, and drycleaning with detergents in an oil solvent such as petroleum distillate or, more recently, in a halogenated solvent such as trichloroethylene, perchloroethylene or trichlorotrifluorethane. Drycleaning is more expensive and difficult, and is generally restricted to cleaning where the particular textiles involved are susceptible to damage by washing in water, or where oil-soluble stains must be removed.

Typically, a modern drycleaning bath contains about 0.5 to 5.0 percent of a suitable detergent, and a very low level of water-- usually about 0.02 to 1.12 percent dispersed in a petroleum distillate, perchloroethylene or other highly halogenated solvent. About five times as much solvent bath is used as weight of fabric to insure proper cleaning; more is advantageous, but of course adds to the cost. Cleaning is generally carried out at room temperature, and for times of the order of 20 minutes or less, for economic reasons. Oil solubilization by the solvent, and dispersion of other soil by the water and detergent, result in pickup of moisture and dirt from the fabrics being cleaned. The insoluble dirt and most of the excess moisture are removed by filtration, and the bath can be reused several times. When the filtered bath becomes too dirty from soluble dirt, it is distilled to produce clean solvent, which is again reformulated into a cleaning bath by adding water and detergent.

One of the major problems in drycleaning is that it is relatively ineffective with white and light-colored garments, particularly those containing cotton, linen or rayon, alone or blended with synthetics. In conventional washing, use is made of chlorine or peroxygen bleaches, so that the tendency to yellowing induced by the washing operation is corrected by the bleach. The bleaches tend to degrade cellulose somewhat, but careful control produces effective washing and bleaching while holding the degradation within acceptable limits. In drycleaning, on the contrary, no bleaching is ordinarily carried out, and white fabrics tend to yellow markedly when compared with whites which have been bleach laundered.

The art has recognized the problem, and attempts have been made to introduce bleaches-- particularly volatile bleaches such as hydrogen peroxide into the drycleaning system. However, none of the attempts has been really successful. The principal problem has been that the art has been unable to bleach with hydrogen peroxide in drycleaning systems without producing undue degradation of cellulose. Because drycleaning is essentially a room temperature operation, and contact times are short-- typically 15 to 20 minutes-- rather high bleach concentration is necessary, while excessive fabric degradation occurs at hydrogen peroxide concentrations well under those necessary for bleaching.

STATEMENT OF THE INVENTION

We have discovered that, despite the experience of the art, it is indeed possible to get acceptable whitening of white fabrics, approaching and equaling that of typical laundering with bleach, without damage to the fabric, in drycleaning operations employing a solvent and detergent, by using hydrogen peroxide, water and a volatile alkali in controlled proportion relative to the weight of fabric being cleaned (expressed as percent w.o.f.). To get these results, it is essential to use in the drycleaning bath between about 0.25 and 2.5percent w.o.f. of hydrogen peroxide, most preferably 0.5 to 1.5 percent and preferably 2.0 to 10.0 percent w.o.f. of water, using at least twice as much water as hydrogen peroxide; at least 2.0 percent w.o.f. of water plus peroxide; and sufficient volatile water-soluble alkali to bring the aqueous phase to a pH of preferably 8.5 and at least 7.0, generally equivalent to about 0.004 to 0.025 percent w.o.f. of 100 percent NH.sub.4 OH. Within these limits, reasonably good bleaching is obtained, approaching or equaling that of commercial laundering within the preferred limits, and with less damage to the cellulosic fabrics being cleaned than obtained in typical launderings.

DETAILED DESCRIPTION OF THE INVENTION

In the practice of the present invention, we start with conventional dry cleaning baths consisting of a petroleum distillate, or a halogenated solvent and a detergent. We have worked with stoddard solvent, trichloroethylene, perchloroethylene and trichlorotrifluoroethane, with similar results. Any detergent which is soluble in the solvent and does not react with hydrogen peroxide under the conditions of use is satisfactory. A wide range of nonionic and anionic surfactants can be used.

Suitable anionics are alkylaryl sulfonates in which the alkyl substituent varies from C.sub.8 through C.sub.18 carbon atoms and in which the aryl substituent may be phenyl or naphthyl, such as dodecylbenzene sodium sulfonate manufactured under the trademark Santomerse; sodium alkyl sulfates in which the alkyl substituents may vary from C.sub.8 through C.sub.18 carbon atoms, such as sodium lauryl sulfate manufactured under the trademark Duponol P.C.; alkyl sulfonates in which the alkyl substituent may vary from C.sub.8 through C.sub.18 carbon atoms such as sodium dodecyl sulfonate manufactured under the trademark MP-189; aryl sulfonates in which the aryl substituents may be phenyl or naphthyl such as sodium tetrahydronaphthalene sulfonate sold under the trademark Alkanol S; alkali metal salts of fatty acids having a carbon content of C.sub.8 through C.sub.18 carbon atoms such as sodium stearate; alkali metal lignosulfonates such as Polyfons, and phosphate esters of long-chain alcohols.

Nonionics suitable for use include alkylphenyl-ethylene oxide condensates in which the alkyl substituent may vary from C.sub.8 through C.sub.18 carbon atoms and the number of moles of condensed ethylene oxide units varies from 1 to 100 per mole of alkyl such as isooctylphenyl polyethoxy ethanol sold under the trademark Triton X or dodecylphenyl polyethylene glycol ether sold under the trademark Tergitol 12 P 12 ; polyoxyethylene thioethers such as STEROX SK; propylene oxide-ethylene oxide condensates such as Pluronics described in U.S. Pat. No. 2,674,619; fatty acid alkanolamides in which the fatty acid constituent may vary from C.sub.8 through C.sub.18 carbon atoms, such as lauric acid alkanolamide; alkyl poly-(ethyleneoxy) ethanols in which the alkyl radical may vary from C.sub.8 through C.sub.18 carbon atoms and the moles of condensed ethylene oxide may vary from 1 to 100 per mole of alkyl such as tridecyloxy poly-(ethyleneoxy) ethanol sold as Emulphogene BC-840, or the ethylene oxide condensate of stearyl alcohol containing about 10 moles of ethylene oxide per stearyl mole; and the polyhydroxyalkyl fatty acid esters such as glycerol monooleate or sorbitan stearate.

In a typical drycleaning bath, the solvent will contain 0.5 to 4.5 percent of the detergent, and a very small amount of water-- of the order of about 0.02 to 0.12 percent-- i.e., a maximum of about 0.6 percent w.o.f. in a typical operation where 5 pounds of bath are used per pound of fabric. For the practice of our invention, we use much higher concentrations of water-- from 1.0 to 15 percent, and for optimum results 2.0 to 10 percent w.o.f. With this, we combine 0.25 to 2.5 percent, most preferably 0.5 to 1.5 percent w.o.f., of hydrogen peroxide, using at least twice as much water as peroxide. Finally, it is essential to have present sufficient volatile alkali to bring the aqueous phase to a pH of at least 7.0 and preferably 8.5, generally equivalent to 0.015 to 0.004 percent w.o.f. and preferably to 0.024 to 0.001 percent of NH.sub.4 0.

Despite the relatively high concentration of hydrogen peroxide, these compositions will bleach fabric without significant deterioration of any cellulose contained therein. We believe this is due to the initial dilution of the peroxide with at least twice its weight of water, and the use of a volatile alkali to insure rapid reaction when it encounters a reactive site.

We believe that the failure of the prior art in combining peroxide with drycleaning baths has been due to the lack of realization that cellulose fibers will selectively adsorb water and hydrogen peroxide from drycleaning baths, so that the fabric is exposed not to very dilute peroxide, as is the case in aqueous bleaching, but to hydrogen peroxide in concentrations dependent only on the ratio of hydrogen peroxide to the water in the system; if the common 50 percent peroxide of commerce is added to the bath, it is 50 percent which is present on the fabric, and which acts on it.

To minimize this action, we use at least twice as much water as hydrogen peroxide in the bath, and sufficient volatile alkali to make the aqueous phase at least neutral, and preferably alkaline, so that the peroxide acts far more rapidly than when on the acid side. Since the pickup is not immediate, the fabric is in contact with at most 33 percent peroxide for a very brief period-- the loss of active oxygen in the bleaching action increases the amount of water, so that the peroxide becomes more and more dilute on the fabric during the operation; hence, fabric damage is minimized.

This is borne out by a series of tests run on swatches of cotton, and 65/35 polyester/cotton blends, using perchloroethylene containing 4 percent of an anionic detergent in a ratio of 15 parts by weight of solvent to 1 fabric. Tea-stained swatches are used, of the sort used in bleaching tests in aqueous wash systems to test bleaches, where a single wash with a good active oxygen bleach will give about 40 to 50 percent stain removal; fabric degradation was measured by AATC method 82-1961, with results measured in fluidity expressed as rhes, higher numbers expressing greater degradation. The results are shown in the following table: ##SPC1##

The results show that even at low concentrations of peroxide, insufficient to do any substantial bleaching, fabric damage is nonetheless marked. At fairly high concentrations, there is some bleach effect-- much below that of normal bleach laundering-- but fabric damage is still objectionable. Mere dilution of the peroxide gets somewhat improved bleach, still with more fabric damage than is desirable. But by inducing rapid bleach with volatile alkali, without increasing peroxide levels, we obtain both reduction in fabric damage to below that of a typical laundering, and bleach effectiveness approaching that of a typical laundering operation.

The amounts of hydrogen peroxide which are used in accordance with this invention depend on the degree of bleach desired; at least about 0.25 percent w.o.f. is necessary if any really substantial bleach effect is to be obtained. From about 0.5 to 1.5 percent w.o.f. of hydrogen peroxide will give fair to good bleaching without unacceptable cellulose degradation. Somewhat better bleaching, with some but not excessive cellulose degradation, is obtained between 1.5 and 2.5 percent w.o.f. of peroxide; Above about 2.5 percent, cellulose degradation is, in our opinion, excessive. We prefer, therefore, to operate in the range of about 0.5 to 1.5 percent of peroxide.

We use at least 2 parts by weight of water per part of peroxide, using about 1.0 to 15 percent w.o.f., and preferably 2 to 10 percent w.o.f. Water plus peroxide should equal 2 percent w.o.f., or effective bleaching is not obtained; we believe this is due to the problem of effective distribution of bleach over the fabric.

With higher w.o.f. concentrations of water and peroxide larger ratios of bath to fabric than the ordinary minimum of 5 to 1 are desirable, since otherwise the bath may be unable to effectively keep the aqueous system properly dispersed.

The use of sufficient alkali to render the aqueous phase at lease neutral is essential for our desirable results, and preferably enough alkali is added to make the aqueous phase alkaline. Since hydrogen peroxide in water is acid, with pH depending on concentration, the amounts added will vary somewhat. Generally, we use from about 0.004 to 0.020 percent w.o.f. of NH.sub.4 OH (100 percent basis) or equivalent in other volatile alkali. While ammonium hydroxide is the cheapest and most readily available volatile alkali, we have successfully used various water-soluble volatile lower mono-, di-, and tri-alkyl amines. Water solubility and volatility are essential characteristics; unobjectionable odor is a desirable property, which many amines lack.

SPECIFIC EXAMPLES OF THE INVENTION

The following specific examples of the invention are given by way of illustration and not by way of limitation.

EXAMPLE 1

A 100 -pound load of naturally soiled garments was composed of 50/50 by weight of colored and white shirts and colored slacks in both 65/35 Dacron/cotton blends and 100 percent cotton. The drycleaning bath contained 500 pounds of solvent, in this case perchloroethylene, 4 pounds of detergent, in this case the isopropylamine salt of dodecylbenzene sulfonate, 2 pounds of 50 weight percent of aqueous hydrogen peroxide and 1 pound of 2.0 weight percent of aqueous NH.sub.4 OH.

The soiled garments were cleaned for a period of 15 minutes in a typical drycleaning machine and then forced hot air dried.

These garments were noticeably cleaner and colors brighter than comparable garments cleaned under similar drycleaning conditions but without the combination of hydrogen peroxide, water, and NH.sub.4 OH.

EXAMPLE 2

In this example, the conditions of testing were the same as those of example 1 except that 4 pounds of the sodium salt of a monophosphate ester of 1-dodecanol was used as the detergent in place of the isopropyl amine salt of dodecylbenzene sulfonate.

The garments cleaned in this example were also cleaner and brighter than those cleaned via conventional techniques.

EXAMPLE 3

In this example, the conditions of testing were the same as those of example 1 except that 500 pounds of stoddard solvent (saturated hydrocarbons) was used in place of perchloroethylene as the solvent.

The garments cleaned in this example again exhibited a cleaner, brighter appearance than those cleaned in a similar system but without hydrogen peroxide, water, and NH.sub.4 OH.

EXAMPLE 4

In this example, the conditions of testing were the same as those of example 1 except that 1 pound of 0.5 weight percent of aqueous NH.sub.4 OH was used in place of 1 pound of 2.0 weight percent of aqueous NH.sub.4 OH.

The garments of this example were of slightly poorer quality than those of example 1, but still superior to those cleaned via conventional practice.

EXAMPLE 5

In this example, the conditions of testing were the same as those of example 1 except that 5 pounds of water was added in addition to the other specified components.

The garments of this example were of approximately the same quality (cleanliness and brightness) as those of example 1, but noticeably cleaner than those cleaned in the absence of hydrogen peroxide, water, and NH.sub.4 OH.

In these examples, it was impossible to assess fabric damage, but none of the garments were damaged by the operation.

Obviously, examples could be multiplied without departing from the scope of the invention as defined in the claims.

Claims

We claim:

1. In the cleaning of textile fabrics in which they are treated with at least five times their weight of a fat solvent containing a small quantity of surfactant for a short period of time to remove dirt and stains, the improvement which comprises adding to the bath (a) from 0.25 to 2.5 percent weight of fabric of hydrogen peroxide; (b) between 1.0 and 15 percent weight of fabric of water, using at least twice as much water as hydrogen peroxide; (c) at least 2.0 percent weight of fabric of water plus peroxide; and (d) sufficient volatile water-soluble alkali to bring the pH of the water phase to at least 7.0.

2. The method of claim 1, in which the hydrogen peroxide content is between 0.5 and 1.5 percent, the water is between 2.0 and 10.0 percent, and the aqueous alkali is sufficient to bring the pH to 8.5.

3. The method of claim 1, in which the aqueous alkali is ammonium hydroxide.