US3416879A - High temperature bleaching with peracetic acid - Google Patents

Description

United States Patent 3,4163% HIGH TEMPERATURE BLEAHTNG WTTH PERACETEC ACllD Arnold M. Soolrne, Silver Spring, and Charles A. Rader, Laurel, Md, assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed June 30, 1965, Ser. No. 468,601 2 Claims. (Cl. 8--l15.5)

ABSTRACT 0F THE DISCLOSURE Cellulosic fabrics are bleached by impregnating the fabric with an aqueous medium containing peracetic acid which is essentially free of mineral acids and hydrogen peroxide and thereafter contacting the impregnated fabric with saturated steam at about one atmosphere for no more than 30 minutes, preferably to 10 minutes.

This invention is concerned with a novel method for bleaching textile fabrics with peracetic acid. More particularly, this invention relates to a method for bleaching cellulosic fabrics with peracetic acid at elevated temperatures.

Today almost all large-scale bleaching of textiles, particularly cotton, is done with hydrogen peroxide. Although hydrogen peroxide bleaching is generally superior to the previously employed chlorine bleaching processes, it nevertheless suffers from several disadvantages. In the conventional process the fabric is padded with an aqueous hydrogen peroxide solution and the wet fabric is stored at elevated temperatures, generally about 100 C., and c0ntacted with steam for from /2 to about 2 hours. For a continuous process this requires large bleaching chutes, which occupy considerable floor space and require large amounts of steam. Further, to obtain optimum bleaching with hydrogen peroxide, the aqueous pad bath must be at an alkaline pH, generally about 11.5, which is normally maintained by including sodium silicate in the pad bath. The silicate can adversely affect the hand of the bleached fabric, tends to accumulate in the bleaching chutes and often complicates dyeing of the bleached fabric by silicate rub marks or rope streaks.

It has been suggested that if peracetic acid was substituted for hydrogen peroxide, sodium silicate would be unnecessary and thus the associated problems would be eliminated. However, reported attempts to effect bleaching with peracetic acid have indicated that long times, about one hour, are necessary for optimum bleaching, and that the results are poorer than those obtained with hydrogen peroxide. See for example, Rosch, Deutsche Textiltechnik, 10, 191-5 (1960).

It is an object of this invention to provide a process for bleaching textile materials, especially cotton, with peracetic acid.

This and other objects of this invention are accomplished by impregnating the fabric to be bleached with an aqueous medium containing peracetic acid substantially free of hydrogen peroxide and mineral acids, thereafter contacting the impregnated fabric with saturated steam at atmospheric pressure for a period of time not exceeding 30 minutes and thereafter cooling the fabric to below about 100 C. .and washing the fabric. By operating in this manner we are able to obtain a degree of bleaching equivalent to that obtained with hydrogen peroxide for longer periods of time without serious fabric deterioration.

The reasons for applicants improved results over those of the prior art, particularly Rosch, are not fully understood, but .are believed to be (1) the absence of mineral acids, which are present in the peracetic acid employed by Rosch, and (2) the avoidance of long times at elevated temperatures.

The aqueous medium employed in the process of this invention contains peracetic acid free from mineral acids and hydrogen peroxide and has a pH of from about 3 to about 7. It is preferred that the bath also contains a wetting agent to ensure uniform contact of the bath with the fabric and a sequestering agent or a compound capable of complexing with heavy metal ions.

As has been pointed out above, the peracetic acid should be free of mineral acids. Thus, peracetic acid prepared by the acid-catalyzed reaction of acetic anhydride and hydrogen peroxide should not be employed because of the difliculty of removing unreacted hydrogen peroxide and the mineral acid employed as the catalyst. One suitable source for the peracetic acid is via the oxidation of acetaldehyde as disclosed in -U.S. Patent No. 2,804,473 to B. Phillips et al.

The amount of peracetic acid employed in the bath is not highly critical, but should be suflicient to provide from about 0.2 to about 3 weight percent of peracetic acid, based upon dry fabric. Thus, the amount of peracetic acid depends upon the quantity of aqueous medium with which the fabric is impregnated. For example, if the fabric is padded to about percent wet pick-up, the peracetic acid concentration should be from about 0.2 to about 3 weight percent. Lower degrees of wet pick-up require higher peracetic acid concentrations and vice versa. Preferred concentrations at 100 percent wet pick-up are in the range of from about 1 to about 2.5 weight percent.

The bath should be at a pH of from about 3 to about 7, with a pH of from about 4.5 to about 6.5 being preferred and a pH of about 5.5 being optimum. The desired pH is obtained in any desirable manner, preferably by the addition of suitable amounts of an alkali metal hydroxide, for example, sodium hydroxide or potassium hydroxide. The aqueous peracetic acid solution normally has a pH of 3. To obtain a pH of about 5.5, sodium hydroxide is added in a weight ratio to peracetic acid of about 0.2: 1.

Wetting agents which can be employed in the process of this invention are known to the art, and include alkali metal sulfates of long chain alcohols, alkali metal sulfonates of ethylene oxide adducts of acohols, alkali metal sulfonates of alkylphenols and the like. While not essential to this invention, they are desirably employed in amounts of from about 0.1 to about 1 weight percent.

sequestering agents, although not essential, are desiraby present in the bath in amounts of from about 0.05 to about 1 weight percent. Suitable sequestering agents are known to the art, and include alkali metal salts, preferably sodium salts, of condensed phosphates, such as sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate and the like.

After impregnation with the aqueous medium, the fabric is contacted with saturated steam at atmosheric pressure, i.e., at about 100 C. for a period of not more than 30 minutes. Times in excess of 30 minutes cannot be employed because of the serious fabric deterioration resulting from such extended times. Times of from about 5 to about 10 minutes are preferred.

The bleached fabric is then cooled to below about 100 C., Washed to terminate the bleaching action of the peracetic acid, and then dried.

The following example is illustrative. In the example, the bleached fabrics were evaluated by the following techniques.

(1) Refleczance.Determined with a Hunter Multipurpose Reflectometer employing green, blue and amber filters, with the reflectometer calibrated to read 100% reflectance from a magnesium oxide block. Green and blue reflectances are reported as percents of the reflectance 3 from a magnesium oxide block. Whiteness was calculated by the equation:

Whiteness: (4 blue reflectance) (3 X green reflectance) Yellowness index was calculated by the equation:

amber reflectanceblue reflectance green reflectance (2) Fluidity.A.A.T.C.C. Standard Test Method 82- 1961 as modified by H. C. Lindley, Rapid Dispersion of Cellulose in Cuene, Textile Res. 1., pp. 2867, February 1951.

Ycllowness= Example 1 A piece of 80-inch by 80-inch scoured cotton printcloth was padded to about 100 percent wet pick-up with an aqueous solution having a pH of 5.5 and containing 2.37 weight percent peracetic acid, 0.5 weight percent sodium lauryl sulfate as a wetting agent, 0.2 weight percent sodium hexametaphosphate as a stabilizer and 1.25

as Run 1.

TABLE I Run No.

Control Time, min 5 10 20 Blue reflectance. 37v 8 88. 6 90. 2 90. 0 (i5. 2 Green reflectance 90. 6 91. 0 92. 2 92. 6 72. 1 whiteness 70. 2 81. ti 80. 2 84. 8 44. Yellowncss index 0. 04 0. 03 0. 03 0. 0L. 0. l2 Fluidity, rhes 1. 05 3. 27 0. 70

As is readily seen, the process of this invention provides a high degree of bleaching in from 5 to 10 minutes (Runs 1 and 2) with some additional improvement being obtained at a time of about 20 minutes (Run 3). Little further bleaching occurs on heating for longer times, such as one hour (Run 4), and the main effect of this additional heating is to promote oxidative degradation of the cotton, as is indicated by the approximate doubling in fluidity in going from 20 minutes to minutes.

What is claimed is:

1. In the method for bleaching a cellulosic fabric which comprises impregnating the fabric with an aqueous medium containing peracetic acid and thereafter heating said impregnated fabric at elevated temperatures, the improvement of (1) employing an aqueous medium essentially free of mineral acids and hydrogen peroxide, and (2) contacting the impregnated fabric with saturated steam at about atmospheric pressure for a period not in excess of 30 minutes and thereafter washing said fabric.

2. In the method for bleaching a cellulosic fabric which comprises impregnating the fabric with an aqueous medium containing peracetic acid and thereafter heating said impregnated fabric at elevated temperatures, the improvement of (1) employing an aqueous medium essentially free of mineral acids and hydrogen peroxide, and (2) contacting the impregnated fabric with saturated steam at about atmospheric pressure for a period of from about 5 to about 10 minutes and thereafter washing said fabric.

References Cited UNITED STATES PATENTS 2,347,434 4/1944 Richert et al. 8111.5 XR 2,442,332 6/1948 Haney et a1 8111.5 XR 2,590,856 4/1952 Greenspan et al. 8111.5 XR 2,804,473 8/1957 Phillips 260-502 FOREIGN PATENTS 901,687 7/1962 Great Britain.

OTHER REFERENCES Roesch, Darstellung und annending von Peressivesaure in der Bleicherei. Deutsche Textiletchnik 10 (1960), pp. 191-195. Use of Peracetic Acid for Bleaching Nylon Textiles, The Textile Manufacture, January 1955, pp. 4243.

NORMAN G. TORCHIN, Primary Examiner.

I. P. BRAMMER, Assistant Examiner.

U.S. Cl. X.R. 8-1 15