US2072665A - Bleaching process - Google Patents

Description

iii-11B g FIP8309 GR 213721665 "l U? ill/\HLLO an i mum,

Patented Mar. 2, 1937 UNITED STATES PATENT OFFICE BLEACHING PROCESS Boy P. London, to E. I. du Pont Del., a

corporation of Delaware No Drawing. Application September 25, 1934, Serial No. 745,452

13 Claims.

This invention relates to a method of bleaching and more particularly to a process for bleaching g attle hair f ur or any dark animal fiber in order to produce" a product of satisfactory light color and undamaged texture.

One of the objects of this invention is to employ satisfactorily in the bleaching of dark animal fiber, such as cattle hair or fur which usually contains a residual depilatory, an alkaline hydrogen peroxide solution or an alkaline solution yielding hydrogen peroxide under the conditions of use. Another object of this invention is to include as a pre-treatment step in the bleaching operation a treatment which will remove dark inorganic coloring, such as that caused by iron, from an animal fiber as cattle hair which may be stained a reddish or dark brown color as a result of iron present therein. Still another object of this invention is to convert these iron compounds present in an animal fiber such as cattle hair into a condition in which they may be removed readily therefrom before subjecting the cattle hair to the subsequent alkaline peroxide bleach.

Ordinarily, cattle hair contains residues from the depilatory agent which has been employed to remove the hairs from the body of the animal. The most usual depilatory agents are calcium compounds, such as calcium sulfide and calcium hydroxide. We have found that when hydrogen peroxide or a compound yielding hydrogen peroxide is employed as the bleaching agent, and cattle hair is introduced into the bleach bath without preliminary treatment of any sort, the bleaching cost is very high. After considerable experimentation, we have found that the presence of iron and calcium in the cattle hair or other animal fiber being treated, conjointly act as a catalytic agent of high efficacy for the decomposition of hydrogen peroxide. Thus, when animal fiber containing residues of the depilatory agents and iron is introduced directly into an alkaline peroxide bleach bath, a large part of the peroxide loss is caused by the catalytic action of the elements mentioned and but little of the chemical is used up in effecting the bleaching. An object of this invention, therefore, is to develop a process which will give the most satisfactory degree of whiteness for a given chemical cost. Previously, the same degree of whiteness attained by the use of our process has been obtainable, but only by the use of much larger quantities of hydrogen peroxide, and a consequent increased chemical cost. These and still other objects of our invention will be apparent from the procedure hereinafter described which is the best method known to us for satisfactorily bleaching such materials as cattle hair and other animal fibers by the use of an alkaline hydrogen peroxide bleach without the chemical cost running beyond that expense which is economical in commercial bleaching.

The animal fiber is first subjected to the action of a reducing agent, such as sodium bisulphite, NaI-ISOz, for the purpose of converting any iron compounds present therein or thereon which may cause part of the. reddish or dark coloration thereof and which are very undesirable because of their catalytic effect in decomposing hydrogen peroxide with consequent losses of peroxide, from the ferric state to the ferrous state. oxide may be used to accomplish this reaction but we prefer to use the sodium-hydrogen salt of sulfurous acid, sodium bisulfite. Preferably, the animal fiber, whether it be cattle hair or some other dark colored fiber, is steeped in a bath comprising from two to eight pounds of sodium bisulphite per one-hundred gallons of bleaching solution. To the bath, dilute sulfuric acid in concentration equivalent to 0.25% or less is also added, as the salt exerts its reducing action preferably in acid media. If desired, sodium hydrosulfite, NazszOi, in equivalent amount may be used as a reducing compound and this salt acts best in alkaline solutions. The time of treatment may vary from 15 minutes to 1 hour, although We have found 30 minutes to be a most satisfactory time for the usual commercial cattle hair. The temperature may be room temperature or may be an elevated temperature, preferably not higher than 180 F. Above this temperature, sulfur dioxide is freely evolved from the sodium bisulfite and besides escaping into the atmosphere may also have a deleterious effect on the fiber being bleached. The presence of an excess of S02 may cause harshening of the fiber, especially in those cases in which the total quantity of S02 evolving materials is large. We prefer that the temperature be maintained at about 140 F. as we have found that temperature most suitable for our preferred bleach bath which contains two pounds of sodium bisulfite per one-hundred gallons of bleaching solution and enough sulfuric acid to render the acid concentration in the bleach bath approximately 0.25%.

The sodium bisulfite treatment or treatment with any other reducing agent, such as sulfur dioxide, is essentially for the purpose of reducing the ferric compounds present in the material to the ferrous state, in which state they may be Sulfur direadily removed by means of an acid. We prefer to use for this purpose an inorganic mineral acid, and preferably hydrochloric acid, although organic acids may be used. Concentrations from 0.5% to 5% by weight, made up by using c. p. hydrochloric acid of specific gravity of 1.18, are most suitable. Hydrochloric acid is perhaps the cheapest of the mineral acids and we have found our process to give results of entire satisfaction with a solution of that acid of 2% concentration. The treatment time may vary from to 30 minutes but we have found that under most conditions, onequarter of an hour of treatment is all that is necessary to remove substantially all of the iron. Here again, an elevated temperature may be used and in general, any temperature from room temperature to 140 F. has been found suitable. Under certain conditions, the acid may be boiled with the animal fiber, as when cattle hair is being treated, but ordinarily, boiling will not be necessary unless the fiber is extremely discolored. This treatment also removes any lime compounds which may be present on the hair or fibers, which is very desirable, for as previously pointed out, iron and lime together constitute an agent for catalytic decomposition of hydrogen peroxide which is of far superior action to that of compounds of either element when present alone.

Following the acid treatment for the removal of iron from the animal fiber, which iron has preferably been converted to the ferrous state, in which condition it is more readily removed, the next step in our process involves neutralizing the acid. For this purpose, we prefer to treat the-cattle hair with a solution containing from two to six pounds of sodium carbonate, NazCOs, per one-hundred gallons of solution, although other alkalining agents, such as caustic alkali or sodium silicate, may be used. We prefer a solution containing four pounds per one-hundred gallons of solution for the usual commercial cattle hair. The treatment period necessary ranges from 15 minutes to 1 hour with /1 hour being the preferred time of treatment. Here again, either room temperature or an elevated temperature up to 140 F. may be employed and in general, we prefer to use a temperature of 120 F.

After neutralizing the acid, the cattle hair is then treated with an additional amount of sodium carbonate for the purpose of scouring the fiber. This treatment also serves to remove the suint or waxy and oily residue caused by animal perspiration and deposited on the fiber. This solution should preferably consist of from two to four pounds of sodium carbonate per one-hundred gallons of solution, two pounds having been found most suitable for ordinary commercial cattle hair. The treatment time should range from 15 minutes to 1 hour, one-half hour being preferred; the temperature may be either room temperature or an elevated temperature such as 140 F. The temperature of 120 F. has been found most generally suitable.

In place of the sodium carbonate, a soap may be used which will also effectively scour the fiber and remove suint. Ordinarily, it may be more advantageous in commercial bleacheries to use both sodium carbonate and a soap in the scouring bath for the removal of suint.

The treatment for the neutralization of the acid and that for the purpose of scouring the fiber may also advantageously be combined into one treatment, under some circumstances, by the use of an increased amount of sodium carbonate or other suitable alkalining agent. We have found it most satisfactory in general, however, first to neutralize the acid by the use of an alkalining agent and then to complete the scouring by the use of a separate treatment step and a fresh solution containing sodium carbonate and/or a soap. One reason for this is that otherwise inert salts formed by neutralization of the acid will be present in the treating solution and may interfere with successful scouring. However, the chief reason is that ordinarily if both steps are carried out in a single operation, i. e., the step of neutralization and the step of scouring, the concentration of hydroxyl ion in the solution will become so high as to produce deleterious effects usually termed harshening on the fiber being treated. Consequently, we prefer to carry out each operation separately although in commercial bleacheries, expediency may sometimes dictate the use of single operation even at the risk of some minor damage resulting to the fiber.

After the removal of the iron and scouring of the fiber to remove suint and other material readily removable by means ofan alkaline or soapy scouring treatment, the fiber is in condition for bleaching with hydrogen peroxide or any material yielding hydrogen peroxide, such as an alkali metal peroxide. We have found an alkaline bleaching solution more suitable than an acid bleaching bath and in general, we have found most desirable alkaline solutions which contain stabilizing and buffering agents, such as sodium pyrophosphate, sodium silicate, and borax. In general, we have found alkaline bleaching solutions made up as follows and containing hydrogen peroxide as the active bleaching agent most suitable:

Solution A 2 lbs. of borax per 100 gals. of solution.

2 lbs. of sodium pyrophosphate per 100 gals. of solution.

2 lbs. of sodium silicate per 100 gals. of solution.

3 to 12 gals. of 100-volume hydrogen peroxide per 100 gals. of solution.

(Preferably, 5 gals. of 100-volume H202 per 100 gals. of solution are used for the ordinary commercial cattle hair.)

Solution B 2 lbs. of borax per 100 gals. of solution.

4 lbs. of sodium pyrophosphate per 100 gals. of solution.

3 to 12 gals. of 100-volume hydrogen peroxide per 100 gals. of solution.

(Preferably, 5 gals. of 100-volume H202 per 100 gals. of solution are used for the commercial cattle hair ordinarily encountered).

The treatment time may vary from. 8 to 24 hours and usually, the longer the fiber is immersed in the bleaching solution, the better will be the degree of whiteness produced. The temperature may range from room temperature to an elevated temperature, such as 140 F. as a maximum and ordinarily, a higher temperature up to 140 F. produces an enhanced bleaching action without deleterious effect on the cattle hair or other fiber.

By the use of our process, it is possible to produce a bleached animal fiber of lighter color than was formerly obtainable by any of the whiteness, formerly it was not possible ecoaction of a dilute mineral acid, neutralizing, -5 nomically to utilize hydrogen peroxide in the scouring the fiber with an alkaline scour, and bleaching of these fibers. Our process permits finally bleaching the fiber with a dilute alkaline the obtainment of a satisfactory lightened color solution of hydrogen peroxide. with animal fiber, such as cattle hair, at a chemi- '7'. A process of bleaching animal fiber which cal cost which is well within the limits permitted comprises t ep o at t unb ea 10 in commercial bleaching operations. fiber first with a solution of a reducing agent As will be apparent, our improved process reselected from the group which consists of sodium sults from the elimination of iron and/or calulfi d Sodi y su fi then adding a cium compounds from the fiber previous to mineral acid, neutralizing any acid on the fiber,

bleaching which compounds previously destroyed treating said fiber With an alkaline $001.11, and 15 a large amount of hydrogen peroxide by reason fi y treating Said fi e W y o peroxide of their catalytic action with a consequent infor the pu p f bleaching said f r in a d lut crease in the amount of peroxide essential to alkaline active oxygen bleach bathbleach the fiber, thereby resulting in an increased A process of bleaching a imal fi r which chemical cost. The procedures a d a t comprises the steps of treating the unbleached 20 given above are to be considered as illustrative fiber With Sodium bisulfite, adding yd ch r and not as restrictive, and various changes may acid to dissolve out the undesired diseolorihg be made in the precise temperatures, times and compounds, n utralizing, adding Sodium a b amounts without departing from the spirit of ate for the p p of scouring the fiber, a d

20 our invention. In short, changes may be made nelly add hyd n p oxide t said s lutio which will not employ the precise amounts and thereby effecting bleaching of t e animal fibe conditions specified but will still fall within the in a d lu e alkaline hydrogen peroxide bleaching scope of our invention as defined by the appended sOlutionclaims. 9. A process of bleaching animal fiber which Wherever, in th following 1m hydrogen comprises the steps of treating unbleached fiber 0 peroxide is referred to, we intend to include in h d m bisulfite, subject the fi e o t the scope of that term any material or materials action of hydrochloric acid, Showing e fi e which, under the conditions of the process, will with e scouring s l o ontaining sodium caryield hydrogen peroxide or a solution thereof. b011ate,and Subsequently bleaching t e fiber with We claim: a dilute alkaline solution of hydrogen peroxide.

1. A process of bleaching m m fiber which 10. A process of bleaching cattle hair which comprises the steps of treating the unbleached comprises the Steps of adding mbisulfite to fiber with a reducing t, capable of evolving a solution containing the cattle hair suspended sulfur dioxide, then subjecting the fiber to the therein for the purpo e of reducing iron comaction of an acid solvent for the soluble reduced pounds Present in Saidca'ttle him, adding a dllhte 40 compounds resulting from the action of the re mineral acid to Said quor for the purpose of disducing agent, and finally subjecting the fiber to Solving out said reduced compounds formed as a the action of a dilute alkaline bleaching solution result of the treatment Wlth h agent, of hydrogen peroxide, neutralizing said solution, adding sodium car- 2. A process of bleaching animal fiber hi onate thereto and heating for the purpose of 45 comprises the steps of treating the unbleached scouring the Cattle a r, and Subsequently addfiber with a reducing agent, capable of evolving ing hydrogen peroxide to said honor for the pursulfur dioxide, then subjecting the fiber to the Pose of bleaching said h hall m a mute action of a dilute acid and subsequently bleachkalihe active oxygen ylehhhg bathing the fiber with dilute hydrogen peroxide 11. A process of bleaching cattle hair which 50 bleaching solution, comprises subjecting the cattle hair to the ac- 3. A process of bleaching animal fibe hi h tion of a sodium bisulfite solution having aconcomprises the steps of treating the unbleached cehtratioh of at a tempirature Wlthm r fiber with a reducing agent capable of evolving the range, h temperature to 130 ri- Sulfur dioxide, then subjecting th fiber to the 0d of 15 minutes to 1 hour, thensub ectmg the action of a mineral acid, and finally bleaching cattle hair to the action of P hydro the fiber with a dilute l ti f hydrogen chloric acid of a concentration ranging from oxide. 1 A, %-5% at a temperature ranglng from room 4. A process of bleaching animal fiber which temperature to 180 F. for a period of 15 to 30 comprises the steps of treating the unbleached minutes, then subjecting the cattle hair to the 0 fiber with a reducing age t 1 t fmm the action of a solution of sodium carbonate ranging group which consists of sodium bisulfite and in concentration from 0.25% to 0.75% for a perisodium hydrosulfite, then subjecting the fiber to 0d of 15 minutes to 1 hour at a temperature rangthe action of a mineral acid, and subsequently from room temperature to 140 t bbleaching with a dilute hydrogen peroxide solujecting said cattle hair to the action of a solu- 5 tion. tion of sodium carbonate ranging in concentra- 5. A process of bleaching animal fiber which tion "from 0.25% to 0.50% o 15 es to 1 comprises the steps of treating the unbleached hour at a temperature a gi g from room temfiber with a reducing agent selected from the perature to 140 F., and finally bleaclnng said group which consists of sodium bisulfite and cattle hair in a dilute alkaline solution of hydro- 70 sodium hydrosulfite, then subjecting the fiber gen peroxide which contains stabilizing agents. to the action of a mineral acid, neutralizing any 12. A process of bleaching cattle hair which acid present on the fiber, and subsequently comprises treating said cattle hair with a solubleaching with a dilute solution of hydrogen tion of sodium bisulfite of approximately 0.25%

peroxide. concentration forhalf an hour at a temperature 75 how known methods having approximately the same chemical costs. While it is possible with the expenditure of considerable bleaching agent to produce an animal fiber of a high degree of 6. A process of bleaching animal fiber which comprises the steps of treating the unbleached fiber with a reducing agent, capable of evolving sulfur dioxide, then subjecting the fiber to the of substantially 120 F., then treating the cattle hair with a solution of hydrochloric acid of approximately 2% concentration at room temperature for approximately 15 minutes, then treating the cattle hair with a solution of sodium carbonate of approximately 0.5% concentration for 30 minutes at a temperature of approximately 120 F., then treating said cattle hair with a solution of sodium carbonate of approximately 0.25% concentration for half an hour at a temperature of substantially 120 F., and then bleaching said cattle hair with a dilute alkaline solution of hydrogen peroxide.

13. A process of bleaching cattle hair which comprises subjecting said cattle hair to the action of a reducing agent selected from the group which consists of sodium bisulfite and sodium hydrosulfite, subjecting said cattle hair to the action of a dilute mineral acid, subjecting said cattle hair to the action of an alkaline scour, and then bleaching said cattle hair in a dilute solution of hydrogen peroxide.

DONALD J. CAMPBELL. LE ROY P. LONDON.