US3063782A - Bleaching cellulosic materials - Google Patents

Description

n-iutsat Virginia No Drawing. Filed Feb. 29, 1960, Ser. No. 11,488 6 Claims. (Cl. 8-108) This invention relates to improvements in bleaching using aqueous solutions of chlorites.

In the bleaching of cellulosic textiles, an acid solution of a chlorite gives maximum bleaching with minimum degradation and the production of goods of high whiteness and full strength. A typical bleach bath contains, for example, approximately one gram per liter of sodium chlorite. Sutficient acid is added to the bath with or without buffering to bring the pH to the desired value, generally to a pH of about 3.5 for cotton goods. Acetic acid is the preferred acid for achieving the pH of 3.5 and formic acid is the preferred acid for solutions of lower pH. Mineral acids, including sulfuric acid and phosphoric acid, are also frequently used as acidifying agents. Buffer salts, for example, Na i-IP NaH PO or NHJ-IF can be added. In addition, wetting agents which are effective under acid conditions, for example, the Igepons (salts of acylalkyl taurides) are commonly added. Bleaching baths of these compositions are commonly used at elevated temperatures, for example, 180 F. to 195 F.

Under these conditions of use, the bleaching solutions generate chlorine dioxide rather rapidly, as evidenced by the development of a yellow color in the solution and by the evolution of chlorine dioxide as a gas from the surface of the solution. This generation of chlorine dioxide is objectionable in that the gas lost from the solution represents a loss in bleaching power. It is also objectionable as a health hazard when sufficient chlorine dioxide is evolved to affect workers deleteriously. Chlorine dioxide is an irritating gas and requires removal, for example by means of hoods, from the working space. Furthermore, acid chlorite solutions, particularly when chlorine dioxide is being evolved in the range of pH 2 to pH 4, are corrosive to stainless steels and other metals. These metals become pitted and then corrode at a faster rate than the original highly polished surfaces. In addition, the corrosion products in the solution frequently stain the textile and accelerate further decomposition of the chlorite to chlorine dioxide. Thus, it is necessary, for the most economical and eflicient bleaching, to acidify the bleaching bath to form chlorous acid and/or chlorine dioxide at a rate matching the demand on the solution by the textile being bleached and, at the same time, to avoid producing an excess of chlorine dioxide which would saturate the solution and be evolved as a gas.

Fine adjustment of the pH of the bleaching bath is difficult, and by itself, is inadequate to provide sufiicient chlorine dioxide, as opposed to too much chlorine dioxide. Control of the rate of formation of chlorine dioxide has been attempted by starting the bleach at a moderate temperature, such as 160 F. and a moderate pH of about 4 and adding acid and increasing the temperature during the bleaching period to activate the remaining chlorite more strongly. But such procedures require constant manual attention and it is more desirable, in any event, to add sufficient acid at the beginning for the entire process and to maintain constant temperature.

Considerable control of the corrosion aspect of the excessive chlorine dioxide production problem can be effected by addition to the bleaching bath of nitric acid as the acidifying agent or the addition to the bleaching SEARCH RUOiiti Ere bath of inorganic nitrates up to a molar ratio of 0.5:1 or more of nitrate to chlorite. For some fabrics, such as Dacron (polyethylene terephthalate fiber), the use of nitric acid or nitrates has been specified by the manufacturer when chlorite bleaching is employed. Many textile plants, however, regard nitric acid as dangerous to handle. Moreover, control of pH using nitric acid is difiicult, since it has no buffering action. Consequently, some mills have preferred to add nitrate salts, e.g., sodium nitrate, to the bath along with the other ingredients and to employ acetic acid as the acidifying agent. Acetic acid has a pronounced and useful bufiering action, tending to hold the pH value somewhat constant or, at least, minimizing its rise as the bleach bath is used. The addition of sodium nitrate or other nitrate salts to the bath does not interfere with the buffering action. However, there is .a limit to the ability of nitrates to retard corrosion of stainless steel in acidified chlorite solutions; to reduce the amounts of corrosion products, particularly iron compounds which cause the decomposition of the chlorite and the production of chlorine dioxide; and to overcome the adverse eifects of, for example, iron which may be introduced into the bleach bath from other sources.

One method for lessening the corrosiveness of chlorite baths is to activate the chlorite with formaldehyde, for example, as described in Hampel, US. Patent 2,367,771. In this way the bleaching can take place at pH of 5 or higher and the corrosion of stainless steel equip-- ment becomes negligible. Although the bath is less acid when formaldehyde is used for activation there is considerable chlorine dioxide evolution because the formaldehyde catalyses its formation. For this reason formaldehyde activation has not met with commercial acceptance in spite of its low cost and effectiveness in bleaching.

The new process of this invention avoids the use of corrosive, acid activated chlorite baths and the unstable, chlorine dioxide-evolving, formaldehyde activated baths described by the prior art. According to this invention, the cellulosic textile is impregnated with an aqueous solution containing a reaction product of formaldehyde and certain organic acid hydrazides. Suitable hydrazides have the formulas: (CONHNH R(CONHNH R(CONHNH and R(CONHNH wherein R is selected from the group consisting of hydrogen, saturated hydrocarbon chains and hydroxyl-substituted hydrocarbon chains, R is a saturated hydrocarbon chain interrupted by an oxygen atom and R" is a saturated hydrocarbon chain interrupted by a sulfur atom. Each of the R groups should have less than about 9 carbon atoms. In the formulas, x is a whole number less than 4. Examples of some suitable hydrazides include those of formic, acetic, glycolic, adipic, oxalic, diglycolic, tartaric and citric acids. The use of hydrazides of acids with a higher molecular weight than about that of suberic acid is hampered by water insolubility. However, any organic acid hydrazide which is soluble in water to the extent required can be used. It is surprising that only a very small amount of formaldehyde, in comparison to amounts used in the past, is efiective when used in combination with these hydrazides. The reaction of formaldehyde with the hydrazides goes quickly in aqueous solution to produce compounds whose composition is not definitely known. However, they are water soluble, colorless and stable when used in the dilute solutions of this invention.

The textile containing the aqueous formaldehydehydrazide reaction product is then bleached with the aqueous alkali metal or alkaline earth metal chlorite solution containing from about 0.05% to 2% by weight of the chlorite and enough weak acid, such as acetic,

Parts by weight Water 100 Formaldehyde 0.005 to 0.1. Hydrazide 2 to times the formaldehyde weight.

The textile is then squeezed or dried by gentle warming until it contains about 30% to 80% by weight of the liquid from the bath. In this damp condition the textile is passed into a chlorite bath. The bleaching can be done by heating the chlorite bath to 80 to 100 C. while the cloth resides therein for about 1 to 2 hours, or the cloth can be passed through the chlorite bath at room temperature, squeezed until it no longer drips and then bleached by heating it in a stream box or other suitable apparatus which provides a hot, humid atmosphere, substantially saturated with water vapor, for 1 to 2 hours. Alternatively, the cloth first can be partially impregnated with the chlorite solution, further impregnated with the hydrazide formaldehyde solution and then heated in the steam box or other apparatus.

The method of this invention can be used to bleach textiles which are blends of different fibers, for example cotton-rayon or cotton-dacron blends; especially those having 50% or more of cellulosic material. The term celulosic textile as used in this specification and claims is meant to include cotton, linen, regenerated cellulose (rayon) and textile blends containing non-cellulosic fibers but having about 50% or more of cellulosic fibers.

The following examples further illustrate this invention:

Example I A section of white cotton poplin was passed through an aqueous solution containing 1% by weight of the hydrazide of diglycolic acid O(CH CONHNH and 0.2% by Weight of formaldehyde. It was then squeezed between rollers until it contained 82% by weight, based on its own weight, of the solution. The textile was then partially dried to a moisture content of about 30% by weight based on the weight of the cloth, by heating it at 210 F. for 2 minutes. The cloth was then put into an aqueous solution containing about 1.6 grams per liter of sodium chlorite and enough acetic acid to bring the pH to 6.0. After one hour in the bath at 96 C., the cloth was removed, rinsed and dried. During this time the solution gave off no chlorine dioxide. It had an initial reflectance, as measured with a photovolt brightness meter, of 58.4 units and a final reflectance of 82.3. With the brightness scale used, a difference of 2 units is discernible by the unaided eye. A second piece of the cloth bleached in a similar manner, but with no hydrazide-formaldehyde pretreatment, showed a reflectance of only about 70 units.

Example 11 A section of white cotton poplin was passed through an aqueous solution containing 0.21% by weight of the hydrazide of diglycolic acid and 0.04% by weight of formaldehyde. It was then squeezed between rollers until it contained 83%, based on its own weight, of the solution. The cloth was partially dried to a moisture content of about 30% by weight based on the weight of the cloth, by heating it at 210 F. for 2 minutes. The cloth was then put into an aqueous solution coni taining about 1.6 grams per liter of sodium chlorite and enough acetic acid to bring the pH down to 6.0. After one hour in the bath at 96 C. the cloth was removed, rinsed and dried. It has a reflectance of 83.0 after the bleaching and only 58.6 before.

Example III An aqueous solution containing 0.6% by Weight of thiodiglycolic hydrazide, S(CH CONHNH and 0.2% formaldehyde was padded onto linen to the extent that the cloth retained 70% by Weight, based on its own weight, of the solution. The cloth was then passed into a solution containing 1.9% by weight of magnesium chlorite and enough acetic acid to bring the pH down to 5.1 at room temperature. The cloth picked up 65% by weight of the bleach solution based on the dry cloth weight. The linen was put into a steam box wherein the temperature was maintained at 97 C. for 2 hours. After removing the linen from the box, rinsing and drying it, the brightness obtained was 72 compared to an original value of 48.

Example IV A section of mercerized cotton broadcloth was passed through a bath containing 100 parts of water, 0.11 parts of sodium chlorite and enough acetic acid to bring the pH down to 5.3. It was squeezed until it contained 72% by weight, based on the cloth Weight, of the liquid. The cloth was then passed through a hath made by mixing 100 parts of water, 0.07 part of acetic hydrazide and 0.56 part of formaldehyde. It was again squeezed until the total weight of liquids on the cloth was 123%, again based on the cloth weight, and rolled up and placed in an oven where the temperature was 94 C. and the relative humidity about 98%. After 2 hours in the oven the cloth had a brightness or reflectance of 77 units compared to an original brightness of 62 units.

What is claimed is:

l. The process for bleaching cellulosic textiles comprising wetting the textile with two separate, aqueous solutions; one solution containing 0.05% to 2.0% by weight of a chlorite of a metal selected from the group consisting of alkali metal and alkaline earth metals, acidified to a pH of 5 to 7, and the other solution being prepared by admixing Water, formaldehyde and a hydrazide having a formula selected from the group: (CONHNH R(CONHNH R'(CONHNH and R"(CONHNl-I wherein R is selected from the group consisting of hydrogen, saturated hydrocarbon chains and hydroxyl substituted hydrocarbon chains, R is a saturated hydrocarbon chain interrupted by oxygen, R" is a saturated hydrocarbon chain interrupted by sulfur, each of said R, R and R having less than 9 carbon atoms, and x is an integer less than 4, the proportions by weight being 100 parts of water, 0.005 to 0.1 part of formaldehyde and an amount of hydrazide which is 2 to 10 times the weight of the formaldehyde; and then heating the textile at C. to C. while it is Wet with said solutions.

2. The process of claim 1 wherein the textile is partially impregnated with the chlorite solution, then as a second step further impregnated with the aqueous hydrazide-formaldehyde solution and then heated at 80 C. to 100 C. in an atmosphere substantially saturated with water vapor to effect bleaching.

3. The process of claim 1 wherein the textile is partially impregnated with the aqueous hydrazide-formaldehyde solution, then as a second step further impregnated with the chlorite solution and then heated at 80 C. to 100 C. to effect bleaching.

4. The process of claim 3 wherein the aqueous chlorite solution is at a temperature of 80 C. to 100 C. and the textile resides therein until bleaching is accomplished.

5. The process of claim 3 wherein the textile, while 5 wet with the solutions, is heated at 80 C. to 100 C.

in an atmosphere substantially saturated with water 2,430,674 Hampel Nov. 11, 1947 Vapor to effect bleaching. 2,430,675 Hampel Nov. 11, 1947 6. The process of claim 5 wherein the hydrazide is 2,893,819 Hawkins n July 7, 1959 diglycolic hydrazide and the chlorite is sodium chlorite. ,9 4,387 Holbrook et a1. Sept. 15, 1959 5 2,904,388 Holbrook et a1. Sept. 15, 1959 References Cited in the file of this patent 2,904,390 Holbrook et a1. Sept. 15, 1959 UNITED STATES PATENTS 2,947,700 Waibel A g- 2, 196

2,367,771 Hampel Jan. 23, 1945 IG ATENTS 2,429,317 Hampel O t. 21, 19 10 706,626 Great Britain Mar. 31, 1954

Claims (1)

1. THE PROCESS FOR BLENDING CELLULOSIC TEXTILES COMPRISING WETTING THE TEXILE WITH TWO SEPERATE AQUEOUS SOLUTION; ONE SOLUTION CONTAINING 0.05% TO 2.0% BY WEIGHT OF A CHLORITE OF A METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL AND ALKALINE EARTH METALS, ACIDIFIED TO A PH OF 5 TO 7, AND THE OTHER SOLUTION BEING PREPARED BY ADMIXING WATER, FORMALDEHYDE AND A HYDRAZIED HAVING A FORMULA SELECTED FROM THE GROUP: (CONHNH2)2, R (CONHNH2)X, R'' (CONHNH2)X AND R"(CONHNH2)X WHEREIN R IS SELECTED FROM THE GROUP CONSITING OF HYDROGEN, SATURATED HYDROCARBON CHAINS AND HYDROXYL SUBSTITUTED HYDROCARBONS CHAINS, R'' IS A SATURATED HYDROCARBON CHAIN INTERRUPTED BY OXYGEN, R" IS A SATURATED HYDROCARBON CHAIN INTERRUPTED BY SULFUR, EACH OF SAID R, R'' AND R" HAVING LESS THAN 9 CARBON ATOMS, AND X IS AN INTEGER LESS THAN 4, THE PROPORTIONS BY WEIGHT BEING 100 PARTS OF WATER, 0.005 TO 0.1 PART OF FORMALDEHYE AND AN AMOUNT OF HYDRAZIDE WHICH IS 2 TO 10 TIMES THE WEIGHT OF THE FORMALDEHYDE; AND THEN HEATING THE TEXILE AT 80*C, TO 100*C. WHILE IT IS WET WITH SAID SOLUTION.