US2265033A - Method of purifying textile materials - Google Patents

Description

,called continuous process.

Patented Dec. 2, 1941 METHOD OF PURIFYING TEXTILE MATERIALS Louis S. Fryer, Harvey A. Schwartz, and Emerson B. Helm, Cleveland, Ohio, assignors to Industrial Rayon Corporation, Cleveland, Ohio, a

corporation of Delaware No Drawing. Application March 12, 1940,

Serial No. 323,630

11 Claims.

This invention relates to the purification of textile materials; i. e., fabrics, threads, filaments, fibers, etc., of which some or all of the component elements have been produced by the viscose process.

In the viscose process, the thread is formed by the extrusion of a solution of sodium cellulose xanthate (viscose) into an aqueous coagulating bath which contains sulphuric acid, together with certain of itsmetallic salts. By the action of the coagulating bath, the cellulose content of the viscose is regenerated, so that the resulting thread is made up largely of hydrated cellulose. Sulphur is formed in 'and upon the thread by the regeneration reaction, in consequence whereof it usually becomes necessary to desulphurize it. If it is desired to produce a particularly lightcolored or white product, a bleaching operation is performed to eliminate organic and even some inorganic impurities which tend to give the thread an undesirable color.

In the prior art, either or both of these purification operations may be performed separately upon the thread; either or both, upon the fabric formed of the thread; or one may be performed upon the thread and the other upon the fabric. Similarly, the desulphurizing and bleaching operations may be performed upon the thread either in the course of one of the usual discontinuous processes of manufacturing thread; e. g., upon thread in skein form, or as a part of the so- Although difiering from the prior art in respects hereinafter to be pointed out, the present invention embraces to the same extent as the prior art these alternative ways of performing the operations in question.

In the after-treatment of freshly spun multiple filament viscose artificial silk thread, it is the usual procedure to wash the thread thoroughly to free it of acid and then desulphurize it by subjecting it to the action of an alkaline desulphurizing liquid; e. g., sodium sulphide. The thread is then washed free of desulphurizing medium, after which it is usually bleached. In the ordinary case, the bleaching treatment is followed by an anti-chlorination treatment to remove any residual bleaching material which, in time. might damage the thread; thereafter, the thread is once again washed and finally dried.

A similar sequence of operations has been followed heretofore in processing fabrics; that is, the fabric is desulphurized, washed free of the desulphurizing agent, bleached, subjected to the action of an anti-chlorination agent, and washed again before being dried.

According to one embodiment of the present invention, previously untreated material; e. g., thread still wet with acid carried therewith from the coagulating bath, is subjected first to a bleaching operation and then to a desulphurizing operation without interposing any washing, antichlorination or drying steps between the bleaching and desulphurizing operation. The one and only washing operation performed upon the material may be, and preferably is, deferred until after the bleaching and desulphurizing operations have been completed. If desulphurization is not desired, the material may be bleached and dried without the intervention between the bleaching and drying operations of a Washing operation, an anti-chlorination operation or both.

The preferred procedure is to bleach freshly spun multiple filament viscose artificial silk thread soon after its formation, desulphurize it immediately after performance of the bleaching operation, and wash it after the desulphurization operation has been completed. Such preferred procedure makes it possible to eliminate at least two washing treatments, performing the remaining washing treatment only after the thread has been bleached and desulphurized. This procedure not only results in economies made possible by the elimination of the usual washing operations, but, notwithstanding the omission of steps formerly considered necessary, gives rise to a thread of superior physical and physico-chemical properties.

In the practice of the invention, the bleaching agent may conveniently be a halite, preferably a chlorite, of a metal selected from a class comprising -the alkali and alkaline-earth metals. For example, an aqueous solution of sodium chlorite (NaClO2) rendered somewhat acidic by the addition of a weak organic acid such as acetic acid; i. e., having a hydrogen ion concentration corresponding to a value of pH 5 or less, constitutes a satisfactory bleaching medium. Efficient bleaching action is obtained by'the use of such a bleaching medium even if the material being bleached is a freshly formed thread which has not been washed free of the acid carried over by the thread from the coagulating bath.

After being bleached in a solution of this type. the material is not subjected to an anti-chlorination treatment or washing, but is subjected immediately to a desulphurizing treatment. A dilute alkaline solution of sodium sulphite (NazSOz) will be found to act very satisfactorily; however. other desulphurizing media which may be employed are solutions of alkali or alkaline-earth rial is desulphurized immediately after bleaching without intermediate treatment, no harmful results occur when it is desulphurized, not withstanding the fact that it is subjected to the action of an alkaline desulphurizing liquid while still containing the residual acidic bleaching liquid.

Once the material being treated has been bleached and desulphurized, it may be washed free of desulphurizing liquid, after which it may be dried. For these purposes, washing and drying operations of the ordinary kind may be employed. The resulting product is whiter and has a more pleasing appearance than that obtainable if sodium hypochlorite is employed for bleaching as in prior purification practices. The tensile strengths are equal to or greater than those of materials treated by prior practices, es-

pecially those in which desulphurization precedes bleaching of the material.

Although the invention may be practiced in various ways, preferred methods are given in the following examples:

Example I In the spool-spinning process of making multiple filament viscose artificial silk thread, viscose is extruded into a coagulating bath containing approximately 8% H2504, Na2SO4, and 1% 211804. on a spool which, after it has been filled, is placed in a wash box of the conventional kind. Air is drawn into the interior of the spool through the package of thread for a period of approximately five minutes. The thread on the spool in the wash box is then bleached by subjecting it for three hours to treatment by a sodium chlorite bleaching solution heated to about 60 C.

The bleaching solution preferably comprises a .3% aqueous solution, by weight, of commercial sodium chlorite. The latter is a flaky, crystalline, whitish powder comprising, by weight, NaClOz 83.4%, M10103 1.9%, NaCl 6.8%, NaOH 2.7 and H 5.2%. The acidity of the solution is adjusted to pH 3.3 with acetic acid before it is employed to bleach the thread. The NaClOz,

the active bleaching constituent, yields a high proportion of available chlorine as compared with most bleaching agents and yet does not deleteriously afiect the tensile strength of the treated material.

At the end of the three-hour period, the bleaching solution is drained from the wash box, after which air is again drawn through the thread package for approximately five minutes. The package of thread on the spool is then treated in the same wash box for a period of two hours with a .5% aqueous solution of sodium sulphite maintained at approximately 60 C. During this period, the rather considerable amount of sulphur remaining in the thread after completion of the bleaching operation is taken may be dried; The drying opera'tioniis performed. we 9m wa hi th ihr e ie vw The thread is collected in package form 2,265,033 sulphides, sulphites and silicates. If the matethe spool. The dried thread is characterized by a clear white color and an extremely low sulphur content; indeed, the sulphur content runs well below .05%, based on the dry weight of the thread. The thread also has excellent tensile properties and dyeing qualities.

Example II Fabric formed of unbleached, undesulphurized thread is boiled for one hour in an aqueous solution comprising .1%, by weight, of the bleaching agent described in Example I, which solution has previously been rendered acid (in this case, to pH 3.0-3.5) by the addition of acetic acid. The

ratio of weight of solution to weight of cloth is preferably 25 to 1. After such boiling, the fabric is squeezed to remove excess bleaching liquid and is then subjected for two hours to treatment with a .5% solution of sodium silicate at 30 C., whereby it is desulphurized. The fabric is then washed for the first time for one hour with water at C. Thereafter th bleached desulphurized cloth is dried in the usual manner. The resulting fabric is characterized by a pleasing white color, low residual sulphur content, and excellent physical properties.

Potassium bromite, potassium iodite, sodium bromite, sodium iodite, potassium chlorite, cal cium chlorite, barium chlorite and similar halites of the alkali and alkaline-earth metals may be regarded as equivalents of the sodium chlorite employed as the preferred bleaching agent in the foregoing examples of the practice of the present invention. Any suitable desulphurizing agents of the types already mentioned may be used in place of the particular desulphun'zing agents indicated in the examples; however, other alkaline solutions of alkali or alkaline-earth sulphides, sulphites or silicates; e. g., potassium sulphide, calcium sulphide, barium sulphide, potassium sulphite, calcium sulphite, barium sulphite, potassium silicate, ammonium sulphite, and ammonium sulphide, may be employed as desulphurizing agents.

The processes outlined above and described in the foregoing examples may be modified in various ways. As described or modified, they may be applied to the processing of materials other than those described. In general, they may, without departing from the spirit of the invention, be applied to any product of which part or all of the component elements have been made by the viscose process. It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty reside in the invention.

What is claimed is:

1. The method of purifying textile material comprising the steps of bleaching said material by treating it with an aqueous solution of sodium chlorite acidified with acetic acid; desulphurizing said material before the bleaching solution is washed therefrom, the desulphurizing step being performed by treating said material with an alkali-aqueous solution of sodium silicate; washing the desulphurizing solution from said material; and drying said material.

2. In a process of purifying textile material involving the steps of bleaching and desulphurizing the material, the method comprising treating the material with an acid-aqueous solution of a bleaching substance and, after completion of the bleaching treatment, treating the material with an alkali-aqueous solution of a desulphurizing substance without applying a washing treatment intermediate the bleaching and desulphurizlng treatment.

3. In a process of purifying textile material involving the steps of bleaching and desulfurizing the material, the method comprising bleaching the material with an aqueous solution of a halite of a metalfrom the group consisting of alkali and alkaline earth metals, said solution'being acidified with a weak acid; treating the material with an alkali-aqueous solution of a desulfurizing substance before the bleaching substance has been washed therefrom; washing the desulfurizing substance from the material; and drying the material.

4. The method set forth in claim 2 wherein the desulfurizing substance is sodium silicate.

5. The method set forth in claim 2 wherein the desulfurizing substance is a sulfide of a metal selected from a group consisting of alkali and alkaline-earth metals.

6. The method set forth in claim 2 wherein the desulfurizing substance is a sulfite of a metal selected from a group consisting of alkali and alkaline-earth metals.

'7. In a process of purifying a fabric formed of artificial silk thread which has been coagulated in an acidic medium involving the steps of bleaching and desulfurizing the fabric, the method comprising treating the fabric with an acidaqueous solution of a bleaching substance and, after completion of the bleaching treatment, treating the fabric with an alkali-aqueous solution of a desulfurizing substance, the desulfurizing treatment being performed without washing the fabric in the meanwhile.

'8. In a discontinuously performed process of purifying artificial silk thread which has been coagulated in an acidic medium involving the steps of bleaching and desulfurizing the thread,

the method comprising treating the thread with an acid-aqueous solution of a bleaching substance without employing a washing treatment following the step of forming the thread and, after completion of the bleaching treatment, treating the thread with an alkali-aqueous solution of a desulfurizing substance without washing the thread between the bleaching and desulfurizing treatments, the thread being in batch form at the time when the treating steps are performed upon it.

9. The method set forth in claim 2 wherein the bleaching substance is a halite of a metal selected from a group consisting of alkali and alkaline-earth metals.

10. The method set forth in claim 2 wherein the bleaching substance is sodium chlorite.

11. In a process of purifying continuous fila ment viscose artificial silk thread which has been coagulated in an acidic medium involving the steps of bleaching and desulfurizing the thread, the method comprising treating the thread with an acid-aqueous solution of a bleaching substance without employing a washing treatment following the step of forming the thread; treating the thread after the bleaching treatment with an alkali-aqueous solution of a desulfurizing substance without washing the thread intermediate the bleaching and desulfurizing treatments; treating the thread with a washing substance for the purpose of washing the desulfurizing substance from the thread; and drying the thread, the thread being in continuous filament form up to and including the time when the drying step is performed upon it.

LOUIS S. FRYER. HARVEY A. SCHWARTZ. EMERSON B. HELM.