US2676871A - Bleaching of wool - Google Patents

Description

Patented Apr. 27, 1954 \in tiCH Mu BLEACHING OF WOOL John J. McGovern, Wilmington, Del., asslgnor to E. I. du Pont de Ncmours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 7, 1950, Serial No. 172,611

3 Claims.

This invention relates to the bleaching of wool with alkaline peroxide solutions and more particularly to a method whereby wool may be bleached with such solutions with minimum damage resulting.

Wool is commonly bleached with alkaline peroxide solutions. Solutions of low peroxide concentrations are generally employed at relatively low temperatures and for relatively long times in order to avoid excessive oxidative degradation of the wool. Wool is readily damaged by alkaline peroxide solutions and the extent of such damage is indicated by the alkali solubility of the wool. If badly damaged, the bleached wool will not satisfactorily withstand even mild washing with soap and water.

It is an object of the invention to provide a method of bleaching wool with alkaline peroxide solutions with minimum damage to the wool resulting. A further object is a method whereby wool may be bleached rapidly and at relatively high temperatures with alkaline peroxide solutions without excessive degradation of the wool. Still further objects will be apparent from the following description.

It is known that formaldehyde will combine loosely with wool. It is also well known that formaldehyde reacts readily with alkaline peroxide. This reaction proceeds rapidly and quantitatively to destroy both formaldehyde and hydrogen peroxide and to produce sodium formate,

water and hydrogen according to the following equation:

The Blank and Finkenbeimer (Ber. 31, 2979 (1898)) method of formaldehyde analysis is based on this reaction. In view of the loose nature of the combination of formaldehyde with wool and the ease and rapidity with which formaldehyde reacts with hydrogen peroxide, it would have been expected that alkaline peroxide solutions would remove formaldehyde from its combination with wool and destroy it with resultant consumption of peroxide, and that, therefore, no substantial beneficial action would result from the treatment of wool with formaldehyde prior to bleaching with alkaline peroxide solutions. On the contrary, it would have been expected that peroxide consumption would be excessive, which would be disadvantageous.

Contrary to expectations it has been discovered that in the bleaching of wool with alkaline aqueous hydrogen peroxide solutions, substantial advantages result from the pretreatment of the W001 with formaldehyde, provided such pretreatment is carried out under such conditions that the combined formaldehyde content is at least 0.3% and preferably 0.5 to 1%, based on the weight of the wool, and that when so pretreated, wool may be rapidly bleached at elevated temperatures without excessive peroxide consumption and with minimum damage to the wool resulting. In accordance with the invention, the wool which is to be bleached is treated with an aqueous formaldehyde solution under such conditions as will effect a combined formaldehyde content of at least 0.3% and preferably from 0.5 to 1%, after which the wool is bleached with an alkaline hydrogen peroxide solution.

In present wool bleaching methods using alkaline peroxide solutions, temperatures above about -130 F. are generally avoided in order to avoid excessive degradation of the wool. At such temperatures 6 to 16 hours are usually required to obtain a satisfactory bleach. It has been discovered that when wool has been pretreated so as to contain at least 0.3% and preferably 0.5 to 1% of combined formaldehyde, it may be bleached successfully at substantially higher temperatures in much shorter times without excessive degradation of the wool. Thus at F. good bleaching can be effected in 1 hour or less with minimum of damage to the wool.

The combined formaldehyde content should be at least 0.3% in order to provide worth while protection against damage by the alkaline peroxide. In order to effect combination of that amount of formaldehyde, the wool should be contacted with a formaldehyde solution having a pH of about 2 to 10 and a concentration of at least about 0.1% CHzO. The preferred pH is about 4 to 9. The use of solutions of concentrations above about 5% offers no particular advantage and concentrations of about 0.3 to 2% are preferred. The time of treatment will depend chiefly on the concentrations and temperatures used, the higher the concentration or temperature the shorter the time required to obtain the desired amount of formaldehyde combined with the wool. At concentrations within the preferred range and at temperatures of 120-180 R, which are preferred, treating times of from about 2 to 30 minutes, and generally about 5 to 15 minutes, are adequate and result in combined formaldehyde values of from around 0.5 to 1.0%. Larger amounts of formaldehyde can be combined with the wool, but they offer no advantages over the preferred amounts.

The invention is illustrated by the following examples.

EXAMPLE 1 Skeins of Wool weighing 45 g. each were scoured by immersion for 10 minutes in water at 120 F. containing 1 g. of soap and 1 g. of 28% NHrOH per liter. The skeins were then washed thoroughly and divided into two groups. The skeins of the first group were bleached in peroxide bleach baths under the conditions indicated in Table 1. Comparative bleaching tests were run on the second group of skeins after they had first been soaked for 30 minutes in 1 liter of Water containing 4.5 g. CH2O and having a pH of 6.5 and a temperature of 120 F., then rinsed thoroughly with water to remove uncombined formaldehyde. This pretreatment with formaldehyde resulted in a combined formaldehyde content of about 0.8%. All bleaching tests in both series were carried out using 1 liter of bleach solution having a pH of 9.6 and containing g. sodium pyrophosphate as a stabilizer for the peroxide. Following bleaching, the alkali solubilities and degree of whiteness of the wool samples were determined.

the formaldehyde-pretreated sample was relatively high because the bleaching time was much longer than necessary. However, it will be noted that the corresponding sample which had not been pretreated with formaldehyde had a solubility of 52%, or almost three times as high.

EXAIWPLE 2 Samples of scoured skeins of wool each weighing 45 g. were treated for various times and at various temperatures in formaldehyde solutions. Each treatment was carried out using 45 g. of wool and 1 liter of formaldehyde solution containing 4.5 g. CHzO at a pH of 4-5. The formaldehyde solutions were analyzed before and after the treatments to determine the amount of formaldehyde which had combined with the wool in each instance, after which the samples were thoroughly rinsed to remove uncombined formaldehyde. The samples so treated were then bleached at 180 F. for 1 hour in peroxide solutions containing 3 g. H202 and 5 g. sodium pyrophosphate per liter at a pH of 9.6. The results of these tests are shown in Table 2.

able 2 Table 1 Formaldehyde Percent Alkali Solubility Percent Treatment Percent Alkali Bleaching Conditmns (percent) whiteness Test Combined Soluble fiig Test omo after 9 ess Min. F. Bleach g. H1O: Temp. Time No Pre- Pre- No Pre- Preperl. (F.) (Hi-s.) treat. treat. treat. treat.

. l9 3 120 8 l8 10 70 67 10 150 0. 83 14 3 120 28 28 14 71 68 2 150 0. 79 14 69 6 120 8 13 7 5 180 0. 97 10 69 6 1g 6 74 73 2 180 0. 79 11 69 3 none 2 3 180 1 33 15 72 69 7 70 G Blank (scour only) 11 54.5 EXABH LE 3 The alkali solubilities were determined by treat ing the wool sample for 1 hour at 65 C. (149 F.) with 0.1 N NaOI-I solution using a 1:1000 wool: liquor weight ratio. The wool was then recovered on a Biichner funnel, washed with 2 liters of distilled water, dried to constant Weight at 105 C. (221 C.) and weighed. The percent weight loss based on the dry weight of the original sample was then calculated. The alkali solubility thus represents the weight percent of the wool which is dissolved by 0.1 N NaOH under the conditions described.

The "percent whiteness is a measure of the degree of bleaching obtained. It is determined by a Hunter multipurpose reflectometer. The use of this machine for measurements of this type is fully described in Bureau of Standards Research Paper RP 1345.

It will be noted from Table 1 that the efiectiveness of the bleach at any given temperature was about the same whether or not the wool was pretreated with formaldehyde. On the other hand, the alkali solubilities after bleaching were outstandingly lower for all samples which had been pretreated with formaldehyde than for those which had not been pretreated. Furthermore, the alkali solubilities of the bleached samples which had been pretreated with formaldehyde were, with one exception, but slightly higher than the corresponding value for the blank sample which had been scoured only, showing that wool which has been pretreated with formaldehyde can be effectively bleached with alkaline peroxide without substantial increase in alkali solubility resulting. In test D, the alkali solubility (19%) of Scoured skeins of wool were soaked for varying periods of time at 180 F. in a 0.9% formaldehyde solution having a pH of 4-5, employing 225 g. of wool for each liter of solution. The amount of combined formaldehyde was determined in each case as indicated in Example 2. Each 45 g. skein was rinsed thoroughly to remove excess formaldehyde then bleached for 1 hour at 180 F. in 1 liter of a solution containing 3 g. H202 and 5 g. sodium pyrophosphate. The alkali solubilities of the bleached samples were then determined and are shown in Table 3 along with the values for percent combined formaldehyde.

The time required in the formaldehyde pretreatment to obtain a combined formaldehyde value of at least 0.3% will depend on the concentration of formaldehyde in the treating solution as well as upon the temperature. Thus,

treatment of wool at F. with a 0.045% solution for 10 and 30 minutes resulted in combined formaldehyd values of 0.09 and 0.11%, respectively, whereas a value of 0.5% was obtained in 10 minutes at the same temperature using a 0.36% solution.

Pretreatment of the wool as indicated permits the use of alkaline peroxide bleaching solutions at higher temperatures than would otherwise be possible without excessive damage to the wool resulting. Also, more alkaline solutions may be used. Generally, the alkalinity of the bleach solution will correspond to a pH of about 8.5 to 10.5 but is preferably about 9 to 10. While the pretreatment will afford worthwhile protection against damage during bleaching at any temperature, e. g., up to the boiling point of the bleach bath, bleaching will generally be sufiiciently rapid at temperatures of about 160- 190 R, which are preferred, so that higher temperatures seldom will be required. At the preferred temperatures the same degree of bleach may be obtained in but a fraction of the time required at the conventional lower temperatures and with no greater damage to the wool. Some degradation of the wool, of course, does result at such high temperatures but the amount thereof is slight providing the bleaching treatment is not prolonged beyond the relatively short period required to give the maximum bleach.

The concentration of peroxide in the bleach solution is not particularly critical and the concentrations usually employed in prior alkaline peroxide bleaching methods, e. g., about 0.1 to 2% and preferably 0.2 to 0.5%, are satisfactory. Hydrogen peroxide or any peroxygen type compound known to yield active oxygen under the conditions of use may be employed as the source "or active oxygen in the bleach bath. Examples of such compounds are the alkali metal peroxides, perborates, percarbonates and perphosphates; peracids such as peracetic acid and persulfuric acid; and the organic peroxygen compounds such as urea peroxide, tertiary butyl hydrogen peroxide and benzoyl peroxide. For economic reasons the use of hydrogen peroxide, sodium peroxide or sodium perborate is preferred. As is common practice in the use of alkaline bleach baths in which the active bleaching agent is a peroxygen type compound, a peroxide stabilizer will generally be added to the bath. Many stabilizers are known for this purpose such as the silicates, tin compounds, magnesium compounds and the like. The use of alkali metal pyrophosphates, particularly sodium pyrophosphate, is preferred.

I claim:

, 1. The method of bleaching wool comprising contacting the wool which is to be bleached with a solution consisting essentially of formaldehyde dissolved in water, said solution having a pH of 2xto 10 and a CHzO content of 0.1 to 5%; cont'nuing said contact until the combined formaldehyde content of said wool is at least 0.3%, based on the weight of the wool; then, without intermediate chemical treatment, bleaching the wool with an alkaline aqueous peroxide solution at a temperature of at least F.

22; The method of bleaching wool comprising contacting the wool which is to be bleached with an aqueous solution consisting essentially of formaldehyde dissolved in water, said solution having a pH of 4 to 9 and a CH2O content of 0.3 to 2%; continuing said contact at a temperature of 120 to 180 F. until the combined formaldehyde content of said wool is 0.5 to 1%, based on the weight of the wool; removing from the wool formaldehyde in excess of the combined content; then, without intermediate chemical treatment, bleaching the wool with an aqueous peroxide solution having a pH of 8.5 to 10.5 at a temperature of about -190 F.

3. The method of claim 2 wherein the bleaching step is carried out using a peroxide solution having a pH of 9 to 10 and containing 0.1 to 2% H202.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 787,923 Kann Apr. 25, 1905 1,713,641 Bohm May 21, 1929 1,978,800 Levy Oct. 30, 1934 2,077,103 Franz Apr. 13, 1937 2,220,426 Pratt Nov. 5, 1940 2,220,805 Pratt Nov. 5, 1940 2,422,586 Royer June 17, 1947 2,427,097 Kamlet Sept. 9, 1947 FOREIGN PATENTS Number Country Date 13,088 Great Britain 1911 181,698 Great Britain Sept. 24, 1923 28,115 Great Britain 1897 345,406 Great Britain Mar. 26, 1931 OTHER REFERENCES Technicus, Textile Finishing Faults, Textile Colorist, May 1944, pp. 201-203.

Claims (1)

1. THE METHOD OF BLEACHING WOOL COMPRISING CONTACTING THE WOOL WHICH IS TO BE BLEACHED WITH A SOLUTION CONSISTING ESSENTIALLY OF FORMALDEHYDE DISSOLVED IN WATER, SAID SOLUTION HAVING A PH OF 2 TO 10 AND A CH2O CONTENT OF 0.1 TO 5%; CONTINUING SAID CONTACT UNTIL THE COMBINED FORMALDEHYDE CONTENT OF SAID WOOL IS AT LEAST 0.3%, BASED ON THE WEIGHT OF THE WOOL; THEN, WITHOUT INTERMEDIATE CHEMICAL TREATMENT, BLEACHING THE WOOL WITH AN ALKALINE AQUEOUS PEROXIDE SOLUTION AT A TEMPERATURE OF AT LEAST 120* F.