US2116210A - Regenerated cellulose structures and method for preparing same - Google Patents

Description

Patented May 3, 1938 REGENERATED CELLULOSE STRUCTURES AND METHOD FOR PREPARING SAME Edward R. McKee, Hermitage, Tenn, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application October" 21, 1936,

Serial No. 106,821

4 Claims.

This invention relates to the manufacture of regenerated cellulose structures, such as yarns,

filaments,-threads, horsehair, straw, film, caps.

bands;tubes and the like. More particularly, this invention relates to the process of purifying regenerated cellulose structures produced from viscose and especially to that step in the purification procedure known as bleaching.

In the manufacture of regenerated cellulose structures from viscose, the freshly formed structures contain large quantities of impurities and reaction products, most of which are objectionable and must be removed. The usual purification treatments comprise washing the freshly produced regenerated cellulose structures to remove the acid and other water soluble compounds, then treating the structures with a desulfuring solution to remove,the sulfur and sulfur compounds and finally bleaching to remove coloring matter and the like which have resisted removal in the prior treatments.

Complete and uniform removal of the impurities and reaction products requires careful manipulation because the regenerated cellulose structures are easily degraded by too severe chemical'treatments, or by repeated handling or mechanical treatments, especially when an artificial silk thread constitutes the cellulosic structure. Generally, the purifying treatment of thread is carried out in the form of skeins which is not only a long, tedious operation, but results in degradation of the yarn both from mechanical handling and severe chemical treatment. such as bleaching.

I1. application Serial No. 683,896 to Fonda and Filson, filed August 5, 1933, there is disclosed a package bleaching process which comprises treating cakes of regenerated cellulose thread prepared by the viscose process with chlorinated water which contains, for instance. from 3--100 parts per million of chlorine and which is substantially neutral, having a pH between 6.0 and 8.0. This process is a decided improvement over earlier prior art processes for the very dilute solution of chlorine in water eflec'tively bleaches reenerated cellulose structures and in the case of hard, compact packages of yarn, such as may be produced by collecting freshly formed thread incentrifugal spinning buckets rotating at high speeds,'good penetration and uniform bleaching is obtainedbecause the solution does not swell the thread which would tend to close up the interstices between the thread windings.

It has been found, however,. that when rayon packages are bleached'in accordance with the Fonda and Filson application just previously referred to and dried in the usual manner, the yarn layers on the outside of the cake tend to darken due to a trace of hydrogen sulfide in the air that is circulated through'the drier and which probably reacts with a trace of lead or lead compounds contained in or on the yarn.

It is therefore an object of this invention to provide a modified chlorinated water bleaching solution which will not only eiiectiveiy bleach compact packages of rayon, but will also eliminatesubstantial darkening of the outer layers of the thread package after the yarn is dried in the usual manner. Other objects of the invention will appear hereinafter.

The objects of the invention may be accomplished, in general, by'treating the regenerated 'cellulose structures to be bleached with a bleachingsolution containing 3-100 parts of.chlorine per million parts of water and which has a pH value of between 2.0 and 4.0.

The bleaching solution of the present invention has substantially the same chlorine concentration as that disclosed in the above-mentioned Fonda and Filson application. The latter bleaching solution is maintained substantially neutral, having a pH value of between 6.0 and 8.0, whereas the bleaching solution of this invention is decidedly acidic having a-pH value of between 2.0 and 4.0. The pH value of the bleaching solution will be obtained by the addition of an acid, preferably a strong mineral acid such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid or the like. Obviously the amount of any acid to be added to obtain the desired pH value can be readily determined after ascertaining the alkalinity of the water. The use of a bleaching solution having a pH value of 2.0 to 4.0 will su :tantlally prevent the formation of dark stains on the outer surface of a yarn cake or other regenerated cellulose structure without deleteriously affecting the physical properties of the yarn.

In order to more fully explain the nature of the invention, the following examples which are illustrative and in no waylimitative of the invention are given.-

E'mampie I I A relatively large dense package such as a freshly spun. acid cake of viscose'rayon is collected in-a bucket revolving at about 8,000 R. P. M., the bucket being the type disclosed in the copending application of S. W. Brainard, Serial No. 628,317. The cake so produced which con- 7 tains about 0.8 pounds of 150 denier-40 filament yarn is drip washed for 8-10 hours with soft water at. approximately 25 C. Thereafter, the cake is subjected to a desulfuring treatment which comprises drip washing with sodium carbonate solution at 00-100 C. for approximately 3-5 hours. The cake is then again washed with soft water by the drip method for 1 hour, after which the cake is treated or washed by the drip method for 10-14 hours with chlorinated water containing 20 parts per million of chlorine (0.002% a'nd having a pH value of 3.0 due to the addition of the required amount of sulfuric acid to the water prior to the chlorination thereof. The cake is again washed with soft water, using the drip method for 1 hour, after which it may be finished.

, A bobbin of viscose yarn which has been washed acid free, desulfured and dried to less than 20% moisture content is rewound with twisting upon a perforated bobbin in the manner set forth in U. S. Patent No. 2,004,153. This yarn is then subjected to a pressure washing treatment for 5-6 hours at 5-10 pounds pressure. depending upon the permeability of the package, (the flow through the package being about 6-10 gallons per hour). Soft water which has been acidulated slightly with nitric acid and then chlorinated to the extent of -40 parts per million of chlorine (0.003%-0.004% available chlorine) and with a final pH value of 2.0 to 4.0 is used at a temperature of approximately 30 C. At the end of the treatment, the bobbin of yarn is separately washed in chlorine free water for 15 minutes and then dried. Such bobbins of yarn may be wound directly into cones to be sold as bleached yarn.

Example III A freshly formed bucket cake of regenerated cellulose thread spun from viscose and collected in a normal or round centrifugal spinning bucket rotating at about 8,000 R. P. M. until a cake of about 0.8 pound is formed is wrapped in cheesecloth and then processed in the manner described in Example I. The solution contains sumcient nitric acid to bring the pH of the solution to between 3.0 and 4.0.. The cake so treated is uniformly bleached and shows no dark-stains on the surface.

It is obvious, of course, that other methods of applying the treating solution to the yarn packages may be used. such' as for instance, vacuum not appreciably swell the yarn, behaving in thisrespect the same as a substantially neutral solution. Thus, gel yarn, that is, yarn which has never been dried to equilibrium and which is more reactive than yarn which has once been dried and which is readily and largely swelled by the usual bleaching solutions which are alkaline, may be bleached satisfactorily in package form with solutions of chlorinated water having a pH from 2.0 to 4.0.

A pH of from 2.0 to 4.0 is preferred because the activity of the bleach is substantially as high as with a neutral solution. In scme cases a somewhat lower pH may be used to more readily effect a removal of the impurities in the yarn, in which case a higher concentration of chlorine is advisable to offset the lowering'of bleaching activity.

Though the invention in its preferred embodiment contemplates .treatingdense-packages of gel rayon produced by the viscose process, it is obvious that the invention is applicable to regenerated cellulose threads prepared from viscose in anyform and to other regenerated cellulose structures Obviously many changes and modifications canbe made in the above described procedure with-- out departing from the nature and spirit of the invention. It is therefore to be understood that the invention is not to be limited ekcept as set forth in the appended claims.

What is claimed is:

1. A bleaching solution suitable for use in the bleaching of regenerated cellulose structures comprising a solution containing between 3'and 100 parts chlorine per million parts water and having-a pH value of 2.0 to 4.0.

2. The method of bleaching regenerated'cellulose structures which comprises treating said structures 'with an aqueous solution of. chlorine having a pH value of less than 4.0.

3. The method of bleaching regenerated cellulose structures which comprises treating said structures with a solution containing between 3 and 100 parts chlorine per million parts water and having a pHjvalue of 2.0 to 4.0.

4. A bleaching solution suitable'for use in the bleaching of regenerated cellulose structures com- EDWARD R. MCKEE.