US1547138A - Bleaching process - Google Patents

Description

Patented July 21, 1925.

UNITED STATES PATENT OFFICE.

'JOHN R. MAeMILLAN, or LA SALLE, NEW YOR AssIeNbR 'ro NiAGARA ALKALI COMPANY, or IAGARA FALLS, NEW YORK, A OORPORATION or NEW YORK.

BLEACHING- PROCESS N'o Drawing.

, To all whom z'tmwy con/am:

Be it known that I, JOHN R. MAOMiLLAN,

a citizen of the United States, residing at La Salle, in the county of Niagara and State of New York, have invented certain new and useful Improvements in Bleaching Processes, of which the following is a specification. t

This invention relates to bleaching processes; and 'it relates to a method of bleaching fiber wherem such fiber is treated with it has of course long been the ractice totreat the fiber with a bleaching iquor containing a 'hypochlorite; this bleaching liquor containing hypochlorite of calcium, of 1 sodium, or of potassium as the case may be. A solution of bleaching powder (which contains calcium h pochlorite) is often used. Sometimes bleaclilng liquoris made by chlo- 3 rinating a caustic soda solution. Afterwards the fabric is washed, etc., and is, in some cases, treated with an antichlor. This method of bleaching has beefi known and used for 'many years. For some purposes, as in bleaching paper pulp, it has been found more convenient to use a preliminary treatment with chlorin before treating with the regular bleaching liquor; .Part of the bleaching is done by the chlorin and the rest by the bleaching liquor.

With many fibers thereis a practical limit to the extent to which bleaching can becarried in these ways, this being particularly true with fibers, like jute, rich in lignin. With such fibers production of a full white or complete bleaching is attended with too much loss in weight or too much tendering; that is weakening of the fiber.

I have found that much better results can be obtained'by a special method of bleaching whereby it is possible toobtain an equal degree of bleaching with considerably less bleaching agent or, 1n using the same amount of bleaching agent a much greater bleaching result can be attained, and with the furlignin, that the extra effects are due to re- Application filed September 6, 1924. Serial No. 736,282.

' ther unexpected result of a lessening in the usual loss of weight and tendering, thereby making it possible to secure a full bleach in some fibers, like jute, usually regarded as too refractory for a white bleach. Furthermore in this special method several other results are accomplished which do not follow from the use of the ordinary methods; these results being a diminution in the total ash of the fiber and a diminution in the amount of ether extract-the latter representing fats, resins, etc. Why these results'should follow I cannot say and content myself with noting the results without speculation as to the-reason. Sometimes the reduction in ash and ether content by the new method is astonishingly great. In one particular case a jute with about 14 per cent total -ash, bleached by the ordinary methods still carried 10 per cent ash while when treated by the present'method and completelybleached it carried but two per cent; From the facts, it appears that although ordinary bleaching agents (chlorin and. bleaching liquog are used in my method and an unusually e ective bleach is secured, the agents are doing something more than bleaching and since the extra effects are particularly noteworthy with fibers rich in action with non-cellulosic components of the fiber other than lignin. Whatever the reason the facts are as stated.

p In the present invention, the fiber is first treated with a small amount of bleaching solution, this bleaching solution being made from bleaching powder in the'ordinar way or in any other way as by leading c Orin into a solution of alkali. The liquor is, asis usual with bleaching liquors, slightly alkaline. The amount used on the fiber is usually around 10 per cent of the total amount of bleaching liqgior which would be required I to effect a su stantial commercial bleaching action; in other words the amount here used 100 is, from the bleaching standpoint, extremely small. As soon as the bleaching liquor is incorporated into the pulp I treat at once with gaseous chlorin; blowing it into the pulp .or otherwise contacting it with the 1 fiber to be treated, In working with pulped fiber I ordinarily take a 3' to 5 per cent pulp, stir the required amount of bleaching liquor into'this and then blow chlorin into the. pulp for the time necessary to effect the 0 action desired-say about 10 to 15 minutes with a slow introduction of chlorin. In operating in this way, the material is attacked practically simultaneously by an alkaline bleaching liquor and by a solution of chlorin; this solution being, in large part, of chlorin as such. Chlorin on contact with water does not hydrolyze into hypochlorous and hydrochloric acids at once but remains for a time as a solution of chlorin itself. And when hydrolysis occurs, it goes to a balance or a dynamic equilibrium between unhydrolyzed chlorin and its hydrolyzed reaction products, hypoehlorous and hydrochloric acids. In the presence of hypochlorite (added as bleaching liquor) this hydrolysis is correspondingly retarded. The net result in the present process is that for a time the fiber is exposed both to the action of a hypochlorite, hypochlorous acid, and to that of chlorin itself; something which seems to be necessary in accomplishing the present results. In these actions which I am now discussing while bleaching occurs, the nonfibrous constituents, etc., which encrust the fibers are attacked and either oxidized or rendered water soluble or alkali soluble. After the requisite amount of chlorin has been introduced, this amount being, usually equal to about 50 per cent of the total bleaching agent required, the fiber is washed, in certain cases, the slight amount of hydrochloric acid present is neutralized with caustic soda or lime, and the fiber is finally put through the usual bleach with bleaching liq nor; the amount of bleach used bein diminished however to allow for the bleaching agent used in the two prior stages. For an equal degree of bleaching, the total amount of bleaching agent used in the three bleaching steps of the present process is consider ably less than by either of the older methods hereinbefore described; or, for an equal amount of bleaching agent considerably more bleaching is effected. And in some cases, and particularly with ligniferous fi bers, as with the jute mentioned, with kraft pulp, etc., bleaclnng results can be accomplished which are impossible by any of the known methods; that is without undue loss of weight and tendering.

Most vegetable fibers contain cellulose and in addition the bodies which collectively are known as lignin; the proportion of lignin and cellulose varying from fiber to fiber. Some fibers, like cotton, contain very little lignin while others, like jute, are rich in lignin and relatively poor in cellulose. Lignin is considerably more reactive chemically than is cellulose; a. fact which is re.- sponsible both for the loss of weight and the tendering occurring in any drastic bleaching of fibers rich in lignin. Chlorin attacks lignin forming products soluble in alkaline solution and the lignin is moreover susceptible to oxidation. In the usual methods, using chlorin any attempt to secure far-going bleaching of jute results in a great loss of fiber, in tendering, etc. But on the other hand although chlorin is used in the present method the loss of fiber with fibers rich in lignin is not greater than in usual methods of treating fibers poor in lignin such as cotton, sulfite pulp and the like and the bleaching action is sufiicient while there is no tendering or weakening of the fiber. Bleaching liquor and chlorin acting together in very dilute solution, as is the case in my method of bleaching,.for some reason do not exercise the deleterious effects of either as is the case at the higher bleaching concentrations usually employed. The activity of this combination of reagents is great but it specifically attacks the coloring matter and encrustants which are relatively more susceptible to their action rather than the cellulose or the fiber structure. For this reason the bleaching action is more effective than when either is used separately at the higher concentrations usually employed.

lVhat I claim is 1. In bleaching fiber the process which comprises treating the fiber with bleaching liquor and with chlorin, followed by another treatment with bleaching liquor.

2. In bleaching fiber the process which comprises treating fiber simultaneously with bleaching liquor and with chlorin and subsequently treating with bleaching liquor.

3. In bleaching fiber the process which comprises treating the fiber with bleaching liquor and with chlorin, washing and following by another treatment with bleaching liquor.

4. In bleaching fiber the process which comprises treating fiber simultaneously with bleaching liquor and with chlorin, washing with an alkaline wash and subsequently treating with bleaching liquor.

In testimony whereof,.I have hereunto afiixed my signature.

JOHN R. MACMILLAN.