US2011227A - Method of treating cellulosic solutions - Google Patents

Description

Patented Aug. 13, 1935 UNITED. STATES METHOD OF TREATING CELLULOSIC sotUTIoNs Robert W. Maxwell, Wilmington, DeL, assignor to Du Pont Rayon Company, New York, N.,Y., a corporation of, Delaware t i No Drawing. Application Apri1a'19s4, r 7 Serial No. 7183877 Y "aoc aims. (01. 106-40 tThis invention relates tothe' treatment of cele lulosic solutions, and, in particular, itpertains to amethod for controlling the degreeof ripening of viscose.

5 'r- In the-manufacture of'filaments, wrapping tissues and other articles from viscose, it is essential for'successful commercial operation to control the degree of ripening of viscose so as to produce, after coagulation and regeneration, filaments, sheets. and the like, having satisfactory physical characteristics. h ---,Ihe, rate of ripening of viscose is quite rapid, and unless properly allowed for or controlled, causes great difficulty in producing products hav ingi uniform and otherwise satisfactory physical characteristics. Thus, by way of example, in the production of artificial threads, viscose is introduced. into and is passed through the spinning room through a. long series of pipes, and ordiu narily will pass through more pipe in being delivered to one spinning machine than to another. In addition, after being delivered to a spinning machine, the viscose will 'have a different length of travel for'the different spinnerettes, e. g.,' the viscose delivered to the spinnerettes at one end of the spinning machine may travel farther than that delivered to the spinnerettes at the other end of the machine. The viscose necessarily travels at a rather slow rate of speed through the pipes, and its temperature in passing through the spinning room is moderately high. Both of these factors increase the degree of ripening of the viscose.- f

The art has long been concerned "with this problem and a large number of mate-rials have been suggested for use as inhibitors to control viscose ripening. Of the materials suggested for .useas inhibitors, only a small number, to wit, sodium sulfite, and/to a lesser degree, sodium .arsenitejha've shown promise. One object of the invention pertains to an emcient method for controlling viscose ripening. Another object of the invention comprises a method for slowing down the" normal rate of viscose ripening. A further object relates to the substantial inhibition of viscose ripening. :A further object of the inventionis concerned with the inhibition of the ripening of viscose during its conduction to the forming devices. Other objects of theinvention will appear hereinafter.

It hasbeenfound in accordancewith the presentinventionthat water-soluble cyanides and, particularly, alkali metal cyanides, can be used in very small amounts to successfully control or inhibit the 'ri'pening of viscose. The following examples which are intended to be illustrative only indicate specific applications of the invention:

Example I.0.25 pounds of sodium cyanide are mixed with 1000 pounds of a viscose containing 7% cellulose and 6% sodium hydroxide just prior to the introduction of the viscose into the spinning room. The viscose assumes a pinkish cast almost immediately and the rate of ripening is reduced two-thirds as measured by the rate of change in the salt index.

\ Example II.This is the same asExample I except that'the same amount of sodium cyanide is added in the form of a 7% aqueous solution. The rate of viscose ripening is reduced very substantially as in Example I.

Example III .'-To. 1000 pounds of partially mixed viscose inthe mixer is added 0.5 pounds of potassium cyanide. If desired, the cyanide can be addedin the mixing caustic solution. The resultingviscoseripens at about one-third the usual rate as 'measured by the rate of change in salt index. p

Example IVA-This." example is the same as Example III. except that 0.25 pounds of hydrocyanic acid is added in-plac'e of the potassium cyanide; A substantialdecrease in the rate of viscose ripening occurs. i

Although I do not wish to be limited to theory, the inhibiting effect of the alkali cyanides is believedito bedue 'to the fact that they react with persulfi'des (which have an accelerating effect on the ripening of viscose and which are present in normal viscose) to'form thiocyanate and the corresponding sulfide. As a general rule, the alkali metal cyanides need. be added only in that quantity necessary to. destroy the persulfide. This amount will vary depending upon the particular type of viscose to be treated, the use to which the viscoseis to be put, i. e., whether it is to be used to make sheets or filaments, and thatpoint of ripening at which the inhibitor is incorporated in the viscose. The amount of inhibitor used may, for example, be varied between 0.1% or lower up to 2% or higher, based on the cellulose content of theviscose. In the ordinary commercial viscose used in the spinning of rayon filaments, and where the inhibitor is introduced in the viscose when it has reached that state of ripening at which it is to be spun, i. e.,at the spinning index, 0.35% sodium cyanide, based on the cellulose content of the viscose, is suificient to reduce the rate of ripening to about one-third of its original value.

In its preferred form, the invention comprehends the treatment of viscose which is to be spun into filaments. -Without the use of an inhibitor, it is extremely difficult to deliver to all of the spinnerettes viscoseof a uniform degree of ripeness, since the viscose, in travelling through the spinhing room at a'moderately high temperature, continues to ripen at a fairly rapid rate in the pipes and is delivered to the different spinnerettes at difierent degrees of ripeness. When, however, a cyanide inhibitor is added to the viscose at that point of ripeness at which the viscose is ready to persulfides. The amount of inhibitor necessary to obtain the desired eiiect can be established roughly by determining the quantity necessary to bring out the pink color.

Temperature has a definite effect on the action of the cyanide 7 inhibitor. Thus, where ripening of the 'viscosetakes place at about 18 C., the effect of the inhibitor over the life of the viscose is approximately the same, whether the inhibitor is added during the mixing of the viscose or at a point close to the spinning index. Where the ripening takes place at higher temperatures, for instance, at about 30 0., the inhibitor tends todiminish in efficiency after a short time. For this reason, when the inhibitor is introduced into viscose at temperatures of the order of 30 C. or higher, the addition is preferably delayed until just before coagulation and/ or regeneration of the viscose. Where the inhibitor is introduced at some prior point, more inhibitor may be added over and above that which is sufficient when it is introduced just prior to coagulation and/or regeneration of the viscose.

The inhibitor can be added either in solution or as a solid, and it may be added to the viscose at the spinning index or in the mixer; as illustrated in Example IV, the cyanide inhibitor may be formed in the viscose by the introduction therein of hydrocyanic acid, thereby yielding sodium cyanide.

The use of cyanides as inhibitors of viscose ripening may be used wherever viscose is used, e. g., in the production of artificial thread, wrapping tissue, bottle caps and bands, artificial sponges, or other molded or cast articles. The inhibitor may be added at any point during the ripening of the viscose, depending on the degree of ripening desired.

In its broadest scope, the invention comprises the use of water-soluble cyanides as inhibitors of viscose ripening. The alkali metal cyanides have been found to be particularly efiicient. For the purposesof this invention, ammonium cyanide is intended to be included as an alkali metal cyanide.

Percentages referred to throughout the specification are percentages by weight.

Any variation or modification of the process as describedin the above specification and examples, which conforms to the spirit of the invention, is intended .to be included within the scope of the claims.

I claimi 1. A composition of matter comprising viscose which contains a water-soluble cyanide containing the negative radica1(CN-).

2. A composition of matter comprising viscose which contains an alkali metal cyanide containing the negative radical-(CN-).

3. A composition of matter comprising viscose which contains sodium cyanide.

4. A composition of matter comprising partially ripened viscose which contains a watersoluble cyanide containing the negative radical- 5. A composition of matter comprising partially ripened Viscose which contains an alkali metal cyanide containing the negative radical (CN-) 6. A composition of matter comprising partially ripened viscose which contains sodium cyanide.

The process which comprises adding to viscose a water-soluble cyanide containing the negative radical(CN) 8. The process which comprises adding to viscose an alkali metal cyanide containing the negative radical(CN-)'.

9. The process which comprises adding to viscose sodium cyanide.

10., The process which comprises adding to viscose a water-soluble cyanide in aqueous solution said; cyanide containing the negative radical-(CN) 11. The process which comprises adding to partially ripened.- viscose a water-soluble cyanide said cyanide containing the negative radical-(CN').

1-2. The process which comprises adding to partially ripened viscose an alkali metal cyanide said cyanide containing. the negative radical-KIN").

13. The process which comprises adding to partially ripened viscose, sodium cyanide.

14. The process which comprises introducing a Water-soluble cyanide into viscose which has been ripened to about the salt index at which it is to be coagulated said cyanide containing the negative radical(CN-) 15. The process which comprises introducing an alkali metal cyanide into viscose which has been ripened to about the salt index at which it is to be coagulated said cyanide containing the negative radical--(CN-) 16. The process which comprises introducing sodium cyanide into viscose which has been ripened to about the salt index at which it is to becoagulated.

17.. In the production of regenerated cellulose filaments from viscose, the step which comprises adding a water-soluble cyanide to the viscose just prior to its introduction into the spinning room said cyanidecontaining the negative radical- (CN-) 18. In the production of regenerated cellulose filaments from viscose, the step which comprises adding an alkali metal cyanide to the viscose just prior to its introduction into the spinning room said cyanide containing the negative radical v(CN 19. In the production of regenerated cellulose filaments from viscose, the step which comprises adding sodiumcyanide to the viscose just prior to its introduction into the spinning room.

20. In the production of regenerated cellulose filaments from viscose, the step which comprises adding sodium cyanide to the Viscose just prior to its introduction into the spinning room, the sodium cyanide being added in an amount of about 0.35% by weight, based on the cellulose content of the viscose.

ROBERT W. MAXWELL.