WO1993006293A1

WO1993006293A1 - Process for bleaching textiles with hypochlorite solutions

Info

Publication number: WO1993006293A1
Application number: PCT/US1992/006432
Authority: WO
Inventors: Harry Stitzel; Richard C. Ness; James P. Brennan
Original assignee: Olin Corporation
Priority date: 1991-09-16
Filing date: 1992-08-05
Publication date: 1993-04-01
Also published as: AU2414692A; MX9204768A

Abstract

A process for bleaching textiles by treating the textiles with an aqueous solution of formic acid to prepare clean textiles and contacting the clean textiles with an aqueous hypochlorite solution to provide the textiles with an available chlorine concentration of at least 0.5 percent.

Description

PROCESS FOR BLEACHING TEXTILES WITH HYPOCHLORITE SOLUTIONS

This invention relates to a process _for bleaching textiles with hypochlorite solutions.

Bleaching processes are generally performed to remove naturally occurring colors, tints or other foreign materials such as oil or stains from natural fibers such as cotton, wool, flax and the like. Also, bleaching is used on man-made polymeric fibers to remove coloring matter which is inherent in the chemicals or which occurs as colored impurities produced during the chemical synthesis and manufacture of such fibers.

Bleaching is generally understood to mean the chemical destruction of chromophores in organic or inorganic compounds. Usually the aim is to increase the brightness by weakening or removing the color of the material being bleached. Industrially decolorization is often combined with cleaning. Scouring, a common textile pre-bleaching, involves the treatment of a fabric or fiber with alkali (generally caustic soda) at high temperatures. The prime functions of the caustic scour are to soften motes and to emulsify waxes and oils making the fabric absorbent to bleaching chemicals. After scouring, the fabric is ready for bleaching. During bleaching chemical components that affect material quality, handling properties or marketability of a product are removed. This is especially important for natural products which almost always contain impurities. For example, cotton is contaminated with residual seed capsule parts, wax, fatty constituents and inorganic compounds. Bleaching cotton simultaneously removes impurities and increases brightness.

Historically sodium hypochlorite first was used in the textile industry to bleach linen. When cotton came into wide use, it too was bleached with hypochlorite. Today, hypochlorite is still used for some bleaching in the United States, but it is used more extensively in Europe. In a continuous process, about 2.5-5 g/L of available chlorine is used for about 0.25-0.5 h at 40-50°C. The hypochlorite treatment is followed by an antichlor treatment (sodium bisulfite, sulfur dioxide or hydrogen peroxide) to prevent color reversion (formation of chloramines) . Hypochlorite solutions previously used in textile bleaching, however, caused undesirable corrosion of equipment. In addition the hypochlorite solution products had low concentrations of HOCl and contained impurities which substantially reduced the stability. As a result, the bleaching of textiles such as cotton is primarily done with peroxide solutions.

In the peroxide bleaching process, following the removal of sizing materials, the textile form is immersed in a caustic soda solution heated with steam for a period of time long enough to cook out the motes etc.

The caustic scoured textile form is then treated with peroxide bleach solutions, containing various additives such as silicates, at elevated temperatures for extended periods of time to bleach the textiles. It is an object of the present invention to provide a process for bleaching textiles which substantially reduces energy requirements.

Another object of the present invention is to provide a process for bleaching textiles which minimizes bleaching time and increases productivity.

An additional object of the present invention is to provide a process for bleaching textiles which significantly increases the penetration of the bleach solution.

A further object of the present invention is to provide a process for bleaching textiles which reduces corrosion of bleaching equipment.

A still further object of the present invention is to provide a process for bleaching textiles which measurably reduces the amounts of chemicals employed.

These and other improvements are achieved in a process for bleaching textiles with a hypochlorite solution which comprises treating the textiles with an aqueous solution of formic acid and bleaching the treated textiles with a hypochlorite solution to provide the textile with an available chlorine concentration of at least about 0.5%.

The novel process of the present invention can be used in bleaching textiles produced from natural fibers such as cotton, as well as synthetic fibers, including those of cellulose acetate, cellulose triacetate, rayon, viscose and polyesters.

In a preferred embodiment, cotton textiles, including cotton polyester blends, are bleached by the process of the present invention. The textiles to be bleached may be in various forms, including ropes, fabrics, fluffs, ribbons, etc. Prior to bleaching, greige fabric may be washed in at least one standard rope or open width washer using water having a temperature of at least 70^βC. After washing, in the process of the present invention, the fabric is cooled to ambient temperatures, i.e. temperatures below about 33°C, and preferably in the range of from about 20^βC to about 30^βC.

Any suitable means of cooling the textiles may be used, including applying cold solutions of pre-bleaching agents or the hypochlorite bleach solution. Suitable pre-bleaching agents include formic acid, alkyl aryl sulfonates such as alkyl benzene sulfonate, and mixtures thereof.

These solutions contain from about 0.1 to about 5 and preferably from about 0.5 to about 2 percent by weight of pre-bleaching agents. In one embodiment, an aqueous solution of formic acid is used which is at a pH in the range of from about 1 to about 5. In alternative embodiment, an aqueous solution of alkyl benzene sulfonate is used. An additional embodiment employs a mixture of formic acid and alkyl benzene sulfonate. The solution of pre-bleaching agents may also contain as an additive, a biodegradable, nonionic linear alcohol alkoxylate. Pre-bleaching treatment of the greige fabric generally takes from about 1 to about 10 minutes, after which the fabric is squeezed to remove the solution.

The textiles are then bleached by contacting them with an aqueous hypochlorite solution, for example, by immersing the textiles in the aqueous solution. To increase the rate of penetration of the hypochlorite bleach into the textile, a wetting amount of a biodegradable, nonionic linear alcohol alkoxylate may be used. Suitable nonionic linear alcohol alkoxylates include those illustrated by the formula:

CH₃ RO-(CH₂-CHO)_χ-(CH₂-CH₂0)_yH

wherein R represents a linear alkyl group having from about 6 to about 10 carbon atoms, and x + y are from about 3 to about 25.

Alkyl alcohols which are alkoxylated include primary and secondary alcohols having linear chains and containing from about 6 to about 10 carbon atoms. Examples of these alkyl alcohols include hexanol, heptanol, methyl-1-heptanol, octanol, isoctanol, nonanol, decanol and mixtures thereof. The number of alkoxy groups is preferably in the range of from about 4 to about 20. Biodegradable, nonionic linear alcohol alkoxylates are exemplified by Poly-Tergent® SL-42, SL-62, SL-92 and mixtures thereof (Olin Corporation, Stamford, Connecticut). Preferably mixtures of Poly-Tergent® SL-42, SL-62, SL-92 are employed. As the wetting amount, any suitable concentration of the nonionic linear alcohol alkoxylates may be used which, for example, increases penetration of the hypochlorite bleaching solution into textiles during bleaching. For example, wetting amounts in the range of from about 0.1 to about 1, preferably from about 0.1 to about 0.7, and more preferably from about 0.2 to about 0.5 percent by weight of the solution. The solution of hypochlorite bleaching agent and linear alcohol alkoxylate penetrates the textile form and permits substantial reductions in the contact or holding time required to bleach the textile. Surprisingly, the bleaching takes place at ambient temperatures, i.e. those below about 33^βC and preferably in the range of from about 20° to about 30°C. Thus the process provides a substantial reduction in energy requirements for the bleaching step. Textiles are held in contact with the aqueous hypochlorite solution for a period of time sufficient to provide the materials with the desired degree of bleaching. Suitable bleaching times include those from l to about 20 minutes and, preferably, from 5 to about 10 minutes. The aqueous hypochlorite solutions contain amounts of hypochlorite ion which provide the textiles with at least 0.5% of available chlorine and preferably from about 1 to about 3% of available chlorine on the weight of the goods.

Following bleaching, the textiles may be washed in water. If it is necessary to remove or destroy residual chlorine the bleached textiles may be treated with solutions of an "antichlor" such as sodium thiosulfite or sodium bisulfite. It has been discovered that formic acid solutions may be used to remove residual chlorine and aqueous solutions containing from about 0.5 to about 2% by weight of HCO-H may be employed. Hypochlorite solutions suitable for use in the bleaching process of the invention include aqueous solutions of hypochlorous acid and alkali metal hypochlorites such as lithium hypochlorite, sodium hypochlorite and potassium hypochlorite. The hypochlorite solutions employed are at a pH in the range of from about 9 to about 13.

To simplify the treatment of effluent solutions from the bleaching process by reducing the cost, volume and particularly the total dissolved solids content. the hypochlorite solutions are preferably those which contain reduced amounts of impurities. Recently, a process has been developed which produces pure hypochlorous acid containing high concentrations of HOCl.

The method for producing high purity concentrated HOCl solutions is that in which gaseous mixtures, having high concentrations of hypochlorous acid vapors and chlorine monoxide gas and controlled amounts of water vapor are produced, for example, by the process described by J. P. Brennan et al in U.S. Patent No. 4,147,761.

The gaseous mixture is then converted to a concentrated hypochlorous acid solution as described in WO 90/05111 published May 17, 1990 by J.K. Melton, et. al.

The concentrated hypochlorous acid solutions produced have a concentration in the range of from about 35 to about 60, and preferably from about 40 to about 55 percent by weight of HOCl. The solutions are substantially free of ionic impurities such as chloride ions and alkali metal ions and have low concentrations of dissolved chlorine. For example, concentrations of the chloride ion are less than about 50 parts per million and the alkali metal ion concentration is less than about 50 parts per million. The dissolved chlorine concentration in the hypochlorous acid solution is less than about 2 percent, and preferably less than about 1 percent by weight. Alkali metal hypochlorite solutions can be prepared from the high purity concentrated hypochlorous acid solutions by reaction with alkali metal hydroxides. Preferably, the alkali metal hydroxide solutions are those having minimal amounts of ionic impurities. These solutions can be produced, for example, in electrolytic processes employing membrane cells or mercury cells. Sodium hypochlorite solutions, a preferred embodiment of hypochlorite bleach solution, can be produced having concentrations up to about 35% by weight of NaOCl, and preferably at concentrations of from about 15 to about 35% by weight of NaOCl. These concentrated bleach solutions are highly stable as they have very low concentration of ionic impurities such as chloride and chlorate ions. For example, the sodium chloride concentration is less than about 2% by weight. Effluents produced during the bleaching process have greatly reduced concentrations of dissolved solids. The novel process of the present invention permits substantial increases in bleaching rates for textiles by reducing the contact or holding time during the bleaching step. Further, energy requirements are significantly reduced by operating the cleaning and the bleaching steps at ambient temperatures.

To further illustrate the invention the following examples are provided without any intention of being limited thereby. All parts and percentages are by weight unless otherwise specified and temperatures are in degrees Celsius.

-9-

EXAMPLE 1

From a roll of greige 100% cotton terry cloth that had been previously desized in a hot water wash a sample was was cut and weighed (42 grams). The cloth was first saturated at room temperatures with a sour solution containing 0.5 percent formic acid and 0.2% of a 50/50 blend of Poly-Tergent SL 42 and Poly-Tergent SL 62 and then squeezed in a set of rollers to minimize solution pick up. The cloth was next saturated with a NaOCl bleach solution containing 2 percent available chlorine also at room temperature and padded to obtain approximately 140% pick up. This resulted in approximately 1.5% available chlorine on the weight of the goods. After 20 minutes retention time the cloth was washed in hot deionized water and dried. The bleached cloth was measured on a spectrophotometer and found to have a brightness value of 96.53 and a yellow value of 1.57 compared to the original greige fabric values of 85.46 and 10.45.

EXAMPLE 2

An 33 gram sample was cut from the roll of greige 100% cotton terry cloth that had been previously desized in a hot water wash, a sample was cut and weighed (33 grams). The cloth was saturated in a room temperature bleach solution of NaOCl (2% available chlorine by weight) containing 0.2% of a 50/50 blend of Poly-Tergent SL 42 and Poly-Tergent SL-62 and was padded to obtain approximately 140 percent pick up of the solution. This resulted in approximately 2.6% available chlorine on the weight of the goods. After 20 minutes the fabric was washed in hot deionized water and dried. Using a spectrophotometer the sample was found to have a brightness of 93.64 and a yellow value of 2.65 compared to the original greige fabric values of 85.46 and 10.45. In addition, the brightness and yellow values of the same greige fabric used in the examples were measured at 95.82 and 2.09 respectively after it had been production bleached on standard hydrogen peroxide bleaching range. Compared to this production prepared fabric the process of the invention achieved higher brightness and a lower yellow value.

EXAMPLE 3

A sample of greige 100% cotton terry cloth that had been previously desized in a hot water wash was saturated in a solution at room temperature containing 0.5 percent formic acid. The treated cloth was placed in an extractor and spun dry to a moisture content of about 40%. The cloth was next saturated for 20 minutes in a bleach solution of NaOCl (2% available chlorine by weight, HYPURE^N, Olin Corporation, Stamford, Connecticut) and 0.2% of a 50/50 blend of Poly-Tergent SL 42 and Poly-Tergent SL 62 and was padded to obtain a 68.3% pick up of the solution (approximately 1.37% available chlorine on the weight of the goods).

COMPARATIVE EXAMPLE A

The procedure of Example 3 was followed exactly with a terry cloth sample saturated at room temperature in a solution of 0.5 percent formic acid. The treated cloth was placed in an extractor and spun dry to a moisture content of about 40%. The cloth was next saturated for 20 minutes in a bleach solution of NaOCl (2% available chlorine by weight, HYPURE™N, Olin Corporation, Stamford, Connecticut) and 0.2% dioctyl sodium sulphosuccinate (Deceresol OT, American Cyanamid, Wayne, N.J.) and was padded to obtain a 49.4% pick up of the solution (approximately 0.99% available chlorine on the weight of the goods) .

Example 3 illustrates the improved penetration of the hypochlorite bleaching solution using the process of the invention.

EXAMPLE 4

A sample of greige 100% cotton terry cloth that had been previously desized in a hot water wash was saturated in a solution at room temperature containing 1 percent alkyl benzene sulfonate and 0.2% of a 50/50 blend of Poly-Tergent SL 42 and Poly-Tergent SL 62. The treated cloth was placed in an extractor and spun dry to a moisture content of about 40%. The cloth was next saturated for 20 minutes in a bleach solution of NaOCl (2% available chlorine by weight, HYPURE-^N, Olin Corporation, Stamford, Connecticut) and 0.2% of a 50/50 blend of Poly-Tergent SL 42 and Poly-Tergent SL 62 After 20 minutes the fabric was washed in hot deionized water and dried. Using a spectrophotometer the sample was found to have a brightness of 94.99 and a yellow value of 1.19 compared to the original greige fabric values of 85.46 and 10.45.

Claims

WHAT IS CLAIMED IS:

1. A process for bleaching textiles characterized by treating the textiles with an aqueous solution of formic acid to prepare clean textiles and contacting the clean textiles with an aqueous hypochlorite solution to provide the textiles with an available chlorine concentration of at least 0.5 percent.

2. The process of claims 1 or 12 characterized in that the aqueous hypochlorite solution is maintained at ambient temperatures.

3. The process of claim 1 characterized in that the aqueous hypochlorite solution employed is a solution of hypochlorous acid or alkali metal hypochlorite.

4. The process of claim 3 characterized in that the alkali metal hypochlorite is selected from the group consisting of sodium hypochlorite, potassium hypochlorite, or lithium hypochlorite.

5. The process of claim 1 characterized in that a wetting amount of a nonionic linear alcohol alkoxylate, represented by the formula:

CH₃ RO-(CH₂-CHO)_χ-(CH₂-CH₂0) H

wherein R represents a linear alkyl group having from about 6 to about 10 carbon atoms, and x + y are from about 3 to about 25, is added to the hypochlorite solution.

6. The process of claim 1 characterized in that the aqueous solution of formic acid is maintained at ambient temperatures.

7. The process of claim 4 characterized in that the hypochlorite solution is sodium hypochlorite.

8. The process of claim 1 characterized in that the aqueous solution of formic acid is maintained at ambient temperatures.

9. The process of claim 8 characterized in that the aqueous solution of formic acid contains an alkyl aryl sulfonate.

10. The process of claim 9 characterized in that the aqueous solution of formic acid contains a nonionic linear alcohol alkoxylate.

11. The process of claim 1 characterized in that the textiles are treated with an available chlorine concentration of at least 0.5 percent with an aqueous solution of formic acid to remove residual chlorine.

12 A process for bleaching textiles characterized by contacting the textiles with an aqueous hypochlorite solution and a wetting amount of a nonionic linear alcohol alkoxylate, represented by the formula:

CH₃ RO-(CH₂-CHO)_χ-(CH₂-CH₂0) H

wherein R represents a linear alkyl group having from about 6 to about 10 carbon atoms, and x + y are from about 3 to about 25, to provide the textiles with an available chlorine concentration of at least 0.5 percent.

13. The process of claim 12 characterized in that the textiles are contacted with the aqueous hypochlorite solution for from about 1 to about 20 minutes.

14. A process for bleaching textiles characterized by washing the textiles in water maintained at a temperature of at least 70^βC, cooling the washed textiles to a temperature below about 33°C, treating the cooled textiles with an aqueous solution of formic acid to prepare clean textiles and contacting the clean textiles with an aqueous hypochlorite solution to provide the textiles with an available chlorine concentration of at least 0.5 percent.

15. A process for treating greige cotton textiles characterized by contacting the greige cotton textiles with formic acid at a temperature below about 33°C.