US3756774A

US3756774A - Aqueous bleach bath

Info

Publication number: US3756774A
Application number: US00182158A
Authority: US
Inventors: U Kirner
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1970-09-25
Filing date: 1971-09-20
Publication date: 1973-09-04
Anticipated expiration: 1990-09-04
Also published as: FR2107961B1; CH1187771A4; ATA829771A; IT939451B; AT327148B; FR2107961A1; CH539721A; DE2047289A1; DE2047289B2

Abstract

AQUEOUS ACIDIC BLEACH BATH BASED ON HYDROGEN PEROXIDE AND ORGANIC CYANIDES.

Description

3,756,774 Patented Sept. 4, 1973 hce 3,756,774 AQUEOUS BLEACH BATH Uwe Kirner, Bobenheim-Roxheim, Germany, assignor to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany No Drawing. Filed Sept. 20, 1971, Ser. No. 182,158 Claims priority, application Germany, Sept. 25, 1970, P 20 47 289.3 Int. Cl. D06l 3/02 US. Cl. 8111 6 Claims ABSTRACT OF THE DISCLOSURE Aqueous acidic bleach bath based on hydrogen peroxide and organic cyanides.

This invention relates to an aqueous bleach bath based on hydrogen peroxide with which bleaching may be carried out in an acid medium, particularly bleaching of cellulosic textile materials.

The bleaching of cellulosic fibrous materials has hitherto been carried out with aqueous alkaline hydrogen peroxide solutions because alkaline hydrogen peroxide is notable for a particularly strong oxidizing action. Moreover, the fabric is hydrophilic and shows excellent whiteness after a single bleaching step.

In order to prevent unduly rapid decomposition of the hydrogen peroxide, sodium silicate or sodium-pyrophosphate is added to such bleach baths. These chemicals form undesirable deposits on parts of the machines, on the padding equipment or on the textile material being treated, particularly in continuous operation.

Another disadvantage is that all types of cellulose may not be advantageously bleached under alkaline conditions, as alkalis frequently effect a change in the structure of cellulose.

Attempts have therefore been made to carry out bleaching under acid conditions, mainly in order to stabilize the hydrogen peroxide by means of acids so that the addition of silicates or similar substances would no longer be necessary. The main difiiculty in this case, however, resides in the fact that, under acid conditions, the rate of decomposition of the hydrogen peroxide is so low that the bleaching elfect produced by a simple hydrogen peroxide bleach does not come up to the desired standard. Moreover, the cellulose fibers are chemically attacked by the acid, particularly at elevated temperatures, giving rise to the risk of an excessive fall in the average degree of polymerization after such a bleaching operation.

Greater success has been achieved in the field of acid bleaching at pHs of about 5 to 6 not with hydrogen peroxide itself but with one of its organic derivatives, peracetic acid, produced in the bleach bath by the addition of acetic anhydride and hydrogen peroxide. This method was carried out for a period on a commercial scale but was found to be too dangerous, since the second peroxidic compound produced as a co-product of the aforementioned reaction, diacetyl peroxide, was often the cause of violent explosions. At relatively high concentrations, diacetyl peroxide can, on account of its relatively poor solubility in water, separate out in the solid form and then decompose explosively.

For this reason, attention was soon redirected to possibilities of bleaching under alkaline conditions (at pHs greater than 9), attempts being made to replace the silicate by other stabilizers or activators, as taught, for example, in US. Pat. 3,350,161. In that specification, use is made of an adduct of hydrogen peroxide and urea. This peroxide/urea adduct decomposes in aqueous solution to form urea and hydrogen peroxide. This process may be carried out at pHs between 9 and 13. Its drawback is that it is frequently necessary to improve the bleaching action by adding further bleaching agents such as sodium chloride or buffers and/or other organic stabilizers. In other words, the unduly rapid consumption of the peroxide must be compensated for by the addition of further bleaching agents.

German published application DAS 1,018,181 also teaches a bleaching method which, according to the examples, may be carried out under alkaline conditions (pH=about 9). In this case, the problem has been tackled with the use of nitriles and it is stated in said application that the addition of nitriles greatly accelerates the liberation of oxygen. However, to obtain better results using this method, it is still necessary to add stabilizers such as sodium silicate, which is understandable from the fact that nitriles accelerate the liberation of oxygen from hydrogen peroxide.

Thus there is still an unfulfilled industrial need for a method of bleaching under acid conditions. It is an object of the invention to provide an aqueous bleach bath with which the fabric is adequately bleached and the fibers are not substantially damaged.

It is another object of the invention to enable bleaching of textile materials and in particular of cellulosic textile materials such as cotton or cotton blended with synthetic fibers to be carried out with the use of nitriles and hydrogen peroxide.

It is yet another object of the invention to provide a method of bleaching cellulosic textile materials without parts of the equipment being coated with deposits of additives such as silicates or other inorganic precipitates.

These and other objects and advantages of the invention are achieved by bleach baths based on hydrogen peroxide and organic cyanides and containing from 0.1 to 2.0% by weight of 100% hydrogen peroxide and from 0.05 to 1.2% by weight of an organic cyanide, based on the weight of the bath, and which have hydrogen ion concentrations corresponding to pH 4 to pH 7.

Suitable cyanides for the bleach baths of the invention are any compounds or mixtures of compounds containing at least one cyano group. We prefer to use cyanides which are soluble in water or readily dispersible therein. Examples are cyanides of from 3 to 6 carbon atoms, particularly aliphatic cyanides of from 3 to 6 carbon atoms, these not only being particularly suitable for the bleach bathof the invention but also being readily available. The cyanides, which are also referred to below as nitriles, may, for example, be aliphatic, aromatic or cycloaliphatic and they may contain hetero atoms.

It is convenient to use nitriles which boil above C. and which show no or only very little tendency to distil with steam. Specific examples are phthalonitrile, malonamidonitrile, propionitrile, butyronitrile, malononitrile, succinonitrile, adiponitrile, cyanamide, dicyanodiamide or mixtures thereof.

The hydrogen peroxide may be used in any of the commercially available concentrations. Successful results have been obtained by adding hydrogen peroxide to the bleach bath of the invention such that the concentration of hydrogen peroxide in the bath is from 0.1 to 2.0% by weight and preferably from 0.2 to 1.0% by weight, equivalent to a concentration-of active oxygen in the bath of from 0.5 to 10.0 g./l. and preferably from 1 to 5 g./l.

The organic cyanides are added in concentrations of from 0.05 to 1.2% and preferably from 0.1 to 0.7% based on the weight of the bath, the ratio of hydrogen peroxide to cyanide groups then being in the range 1:0.1 to 1:1 and preferably the range 1:0.15 to 1:05, without the activity of the bleach bath being substantially reduced.

The bath containing the hydrogen peroxide and organic cyanide must have a hydrogen ion concentration equivalent to a pH of from 4 to 7 and preferably from 5 to 6.5. This hydrogen ion concentration is obtained by using the substances commonly employed for pH adjustments or by using bulfer mixtures, which also prevent a fall in pH during bleaching. Specific examples of such substances are alkali metal and ammonium carbonates, bicarbonates, carbamates, and hexamethylene tetramine, primary, secondary and tertiary alkali metal phosphates, polyphosphates and/or mixtures of said substances. We prefer to use mixtures of primary and tertiary phosphates, of primary phosphates and bicarbonates or of bicarbonates and polyphosphates, the proportions being such that the resulting bleach baths have the specified pH.

Alkali metal formates or acetates, urea or formamide may be added to the baths and, other components commonly used in such baths may also be added, for example optical brighteners or surface active agents or mixtures thereof, particular examples being anionic and non-ionic wetting agents and detergents.

The bleach bath is generally prepared at room temperature or slightly elevated temperatures of up to about 40 C. It is possible to use higher or lower temperatures but this usually has no added advantage.

The effect of the bleach baths of the invention is surprising, as it could not be foreseen that such acidic baths would increase the activity of hydrogen peroxide whilst causing substantially no harm to the fibers without any need for the addition of stabilizers. In the pH range 4 to 7 the organic cyanide apparently has a double function. At pHs below 7.5 the reaction of hydrogen peroxide with the cyanide forms a peroxy carboximide according to the equation:

R-CEH E 0, R-l'J-OOH but on the other hand the organic cyanide does not act as an accelerator in the liberation of oxygen from the hydrogen peroxide (as is the case under alkaline conditions according to the teaching of German published application DAS 1,018,181 for example), as otherwise the fabric would be attacked to a much greater extent in acid medium.

At a pH of between 4 and 7 the peroxy carboximide appears to be relatively stable and to have a similar property to that exhibited by hydrogen peroxide systems stabilized by sodium silicate under alkaline conditions.

To effect bleaching, the bath prepared in the manner indicated above may be heated to from 70 to 100 C., and the fibrous material to be bleached may be immersed in the bath before or after the desired temperature has been reached. Alternatively, the fibrous material may be impregnated with the bleaching liquor and then heated to the bleaching temperature in known manner, for example by steaming. By high pressure steaming temperatures of for example up to 130 C. are obtainable. The liquor ratio may be from 1:1 to 50:1 depending on the bleaching process used. The treating time should be sufficient to effect bleaching. Bleaching is complete under the specified conditions over periods ranging from a few minutes, for example 1 to 5 minutes (high-pressure steaming) to 3 hours (pad-roll or J-box bleaching). Yet another alternative is to impregnate the fibrous material and heat it for a few seconds, for Example 5 to 15 seconds, at from about 100 to 130 C. and then leave it for a number of hours, for example up to 24 hours, in the cold impregnated state, by which method the cellulosic material often achieves even higher DP values.

The advantages of the present method are obvious. It it now possible to bleach in a pH range in which cellulose fibers have hitherto been strongly attacked when bleaching with hydrogen peroxide. A particular advantage is that baths may be prepared which give rise to very clean working, since no inorganic deposits are found in the machines or on the squeezing rolls, and a degree of whiteness is obtained such as has hitherto only been possible when working under alkaline conditions and using silicates as stabilizers.

In the following examples the parts and percentages are by weight.

EXAMPLE 1 Desized and dried unbleached cotton cloth is impregnated with a solution of the composition:

0.5% of 100% hydrogen peroxide,

0.4% of adiponitrile,

0.2% of sodium tripolyphosphate,

0.02% of adipic acid and 0.4% of an adduct of 10 moles of ethylene oxide and 1 mole of nonyl phenol.

The pH of the liquor is 6.5.

The material treated with this solution is padded to a wet pickup of 100% and steamed for 3 hours at from to C. The material is then rinsed with warm water and then with cold water.

The bleached material is completely free from husks and has a whiteness of from 82 to 85% reflectance (as measured with an Elrephofotometer using filter R 46 T) depending on the quality of cotton used. Of particular note is the fact that the treated material is extremely hydrophilic.

Similar results are obtained when impregnation liquors of the following compositions are used:

0.5% of hydrogen peroxide,

0.6% of benzonitrile,

0.2% of sodium tripolyphosphate and 0.4% of the adduct of 10 moles of ethylene oxide and 1 1 mole of nonyl phenol.

pH adjusted to 7.0 with adipic acid.

0.5 of 100% hydrogen peroxide, 0.2% of adiponitrile,

0.4% of urea,

0.2% of primary sodium phosphate and 0.2% of sodium bicarbonate.

0.5 of 100% hydrogen peroxide, 0.2% of dicyanodiamide, 0.6% of urea, 0.2% of primary sodium phosphate and 0.2% of sodium bicarbonate. pH=6.5.

of 100% hydrogen peroxide,

of adiponitrile,

0.6% of sodium formate,

0.2% of sodium tripolyphosphate and 0.4% of the adduct 0f 10 moles of ethylene oxide and 1 mole of nonyl phenol.

EXAMPLE 2 Dry tubular knitted fabric of pure cotton is impregnated with a solution of the following composition:

The material treated with this solution is padded to a wet pickup of 100% and steamed at 100 C. for 45 minutes in a perforated conveyor steamer. Using this method, there is obtained a whiteness having a reflectance of 87 to 90% (Elrepho, filter R 46 T) depending on the quality of the cotton used.

EXAMPLE 3 Cotton terry cloth is treated on a winch vat (liquor ratio 20:1) with a bleach bath of the following composition:

0.15% of 100% hydrogen peroxide, 0.1% of succinonitrile,

0.08% of primary sodium phosphate, 0.02% of calcined soda and 0.3% of urea.

After 2 hours at from 90 to 95 C. a whiteness of from 86 to 88% reflectance (Elrepho, filter R 46 T) is obtained. The material has a soft handle and is extremely hydrophilic.

I claim:

1. A process for bleaching cellulosic textile material which comprises treating said material in an aqueous acidic bleach bath at a liquid ratio of from 1:1 to 50:1 and at a temperature of from 70 to 130 C. for a period sufficiently long to effect bleaching of said material, said bleach bath consisting essentially of water from 0.1 to 2% by Weight of 100% hydrogen peroxide and from 0.05 to 1.2% by Weight of an organic cyanide selected from the class consisting of cyanamide, dicyanodiamide, ben zonitrile, phthalonitrile and aliphatic nitriles of 3 to 6 carbon atoms, all percentages being based on the weight of the bath, and said bath having a hydrogen ion concentration equivalent to a pH of between 4 and 7.

2. A process as claimed in claim 1 wherein the hydrogen ion concentration is equivalent to a pH of from 5 to 6.5.

3. A process as claimed in claim 1 wherein the organic cyanide is a compound selected from the group consisting of phthalonitrile, malonamidonitrile, propionitrile, butyronitrile, malononitrile, succinonitrile, adiponitrile, cyanarni de, dicyanodiamide and mixtures thereof.

4. A process as claimed in claim 1 wherein the organic cyanide is a compound selected from the group consisting of dicyanodiamide, cyanamide and mixtures thereof.

5. A process as claimed in claim 1 wherein said bath additionally contains urea, formamide or sodium acetate.

6. A process as claimed in claim 1 wherein said bath also contained an additive selected from the group consisting of alkali metal and ammonium carbonates, bicarbonates, carbamates, hexamethylene tetramide, primary, secondary and tertiary alkali metal phosphates, polyphosphates and mixtures thereof for adjustment of the pH.

References Cited UNITED STATES PATENTS 2,927,840 3/1960 Dithmar et a1. 8-111 3,163,606 12/1964 Viveen et a1. 252-99 3,457,023 7/1969 Beloguin 81l1 3,345,303 10/1967 Schmid et a1 252-186 MAYER WEINBLATT, Primary Examiner U.S. Cl. X.R.