I N D U S T R I A L A N D ENGI,YEERING CHEMISTRY
December, 1926
Ripening of Viscose
A freshly prepared solution of cellulose xanthate appears to have characteristics somewhat similar to those of a true solution. Upon standing it undergoes certain changes gradually assuming properties of a colloidal solution. This transition, which may be accelerated by increased temperatures or exposure to air, has been termed “ripening.” Ripening may be accelerated by addition of certain salts which will react with sodium h y d r 0 ~ i d e . l ~Upon prolonged standing the cellulose hydrate separates out spontaneously 3rd contracts gradually according to the concentration of cellulose in viscose. Freshly prepared xanthates are sc1uL)le in strong alcohol and in salt solutions, but become insoluble upon standing. The solubility seems to be influenced by the composition and proportion of the by-products. l o E’ur.thermore, decomposition of the xanthate is materially iiifluenced by the conditions attending its preparation. There seems to be no evidence supporting the separation and re-aggregation of CGor larger units during ripening. Various theories have been advanced to interpret and explain such changes.’G Some of the reactions during ripening may be represented as f ~ l l o w s . ’ ~ /OCeHsOn /O(CeHoOa)zOH 4C=S 2H1.0 = 2 C d SNa \S?*Ta /O(CsHsOa)zOH /O(CsHoOa)r(OH)s 2c=s HzO = C=S \SNa \SNa
/OH
+ 2c=3
‘
+
+
+
18
17
Coagulation of Viscose
Technically, viscose is coagulated in a bath consisting chiefly of sulfuric acid and sodium sulfate. Numerous reactions, some of uncertain character, take place with the subsequent regeneration of cellulose or probably cellulose hydrate. The following equations represent regeneration in its simplest form: /OC6HeO4 C=S HzS04 = NaHSOa -I- CSz
+
+ c=:;
(b)
\sNa (C)
+ NazCSs 4- HzS + Hz0 + 3HzS
+ CsHloOr
\SNa
Monocellulose /O(CsHsOa)r(OH)r HzS04 C=S \SNa
+
-
NaHSO4
Tetracellulose
+ CSz + 4CeH1oOr Regenerated cellulose
When coagulated in masses viscose effloresces with the formation of minute crystals which reduce the transparency of the mass.lg Sodium silicate is ordinarily added to prevent this. Technical Application
(d)
(e)
I n (a) the monocellulose xanthate is not precipitated by alcohol or sodium chloride. However, the solubility diminishes rapidly, the dicellulose derivative being insoluble in these reagents. ,4ccording to (a) and ( b ) the xanthate 15
units rrgrow” by taking up of water. During hydration the ratio E a : S remains the same and the cellulose increases. For instance, after 24 hours the ratio of S a : S: cellulose is 1 . 2 : 2 ;after seyeral days, 1:2:4.18
\SNa /OH
+
C d g H = NaOH CSz \SNa 2CS2 4NaOH = NazCOs 3Hz0 = NazCOs NazCSs
(a)
1259
Massot, Z. angew Chem., 26, 261 (1913). Herzog, KoZloid.Z., 35, 193-S(1924). Die Kunstserde, August, 1925, p. 169.
Viscose may be used in the manufacture of rayon, cellophane, viscose caps, viscoid, artificial wool, horsehair, and straw; Vistra, sizing material for paper, dyeing, printing, and finishing of cellulose textiles. It must be understood that some of these uses have not yet been developed commercially. The many uses of rayon are generally known. Cellophane, which is essentially a resistant transparent film, is extensively used as a wrapper for candy and bakery goods, in novelties and millinery. Viscose caps are being made on a large scale, while artificial wool and Vistra are rapidly making a place for themselves in textile circles. 18 19
Heuser, Zoc. c i t . , p 68 Waite, U. S. Patent 689,337 (1901).
The Viscosity of Cuprammonium Solutions of Cotton Cellulose’” By F. C. Hahn and H. Bradshaw E. I.
DU
PONTDE NEWOURS & Co., HENRYCLAY,WILMINGTON, DEL.
NUMBER of valuable papers have been published on this subject in recent years, and the method as a control method is now under investigation by a standardization committee of the Division of Cellulose Chemistry. In the writers’ opinion the most important paptrs are those of Joyner,3 Farrow and Neale,4 and SmalL5 Even with the precautions for the exclusion of air prescribed by Joyner, the writers did not find the method satisfactory for testing cotton that has been only slightly degraded by the purification process. They, therefore, about two years ago, undertook to investigate the applicability of the method to this type of cotton, using extreme
A
Presented before the Midwest Regional Meeting and a t the Meeting of the Division of Cellulose Chemistry of the American Chemical Society, Madison, Wis., May 27 to 29. 1926. Contribution No. 3 from the d u Pout Experimental Station. 8 J. Chem. SOC.(London), 121, 1511 (1922). 4 J. Terlrle Inst. 16, “157 (1924). 8 THISJOURNAL, 17, 515 (1925). f
precautions to exclude air. Soon after the work was started, the paper by Farrow and Neale came to their attention, and they also had the benefit of Small’s results prior to the publication of his paper. They found it particularly advantageous to use the mercury displacement method of removing air, and to use a glass ball in the viscometer because of its better visibility in the dark blue solution. Both of these ideas were obtained from Small. It was considered very important, however, to replace the air with an inert gas, preferably purified nitrogen. When a vacuum is maintained in the tube it is very difficult to prevent inward leakage of air, and a very little oxygen is extremely harmful. The cuprammonium solution was the same as that used by Small, containing 3 per cent copper and 16.5 per cent ammonia, together with 1 per cent sucrose. The high copper concentration is important because it facilitates the dissolving of high-viscosity cotton. For more easily soluble cottons, also, it permits d‘issolving a larger quantity. Using the
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1260
above conditions and precautions, it was not difficult to obtain reproducible results on any sample of purified cotton. Extreme care is justified even on cotton of fairly low viscosity, because of the greater uniformity of results.
Xot only are the figures for the linters samples higher than those for the long staple cotton, but there also seems to be a progressive rise in viscosity from low-grade second-cut to high-grade mill-run linters, and then a drop to first-cut linters, and a further drop to long staple cotton. This interesting point should be further investigated, and a study should be made of the effect of aging of cotton on viscosity. The writers are not yet quite convinced that the above results are representative, because they are exactly the opposite of what was expected, but similar low viscosities have been obtained for solutions of cop waste, and no reason has been found for questioning the reliability of the results. All of the solutions, or rather dispersions, appeared to be complete, with not more than a trace of fibrous material remaining. 1 Viscosity m poises I-Low- Viscosily Linters
-
Gramdl00 cc. solvent
Test
1 2 3 4 5 6 7 8
9 10 11
12
Time of fall-seconds
Grade of cotton
(1) 224 291 392 490 381 343 260 280 163 85 113
Low-grade second-cut linters Very good second-cut linters Average mill-run linters High-grade mill-run linters Ordinary first-cut linters Medium grade first-cut linters Good grade first-cut linters Very high grade first-cut linters Long-fiber cotton Long-fiber cotton Long-fiber cotton Sea Island cotton
80
(2) 232 289 363 477 377 331 260 297 165 92 116 90
0.0151 10 0.0188 4 0.0255 2 0.0457 1 0.0749 0.667 2.4057 0.167 3.8185 0.160 II-High-Viscosity Linters 1.75 2.000 10.20 1.333 48.30 1.000 169.00 0.800 460.00 0.667
0.10 0.25 0.50 1.0 1.5 6.0 6.25
Figure 1-Relation b e t w e e n Viscosity a n d Concentration of C u p r a m m o n i u m S o l u t i o n s of Low Viscosity Linters
In applying the method to a number of samples of cotton we obtained a very unexpected result-namely, a higher viscosity for linters than for long staple cotton. The tests were made on a representative series of different grades of linters and on four distinct samples of long staple cotton, as follows:
0.5 0.75 1.00 1.25 1.50
GI.
I
I
,
log
5
14.771 6.131 3.382 1.835 1.310 0.438 0.405 0.471 0.345 0.280 0.243 0.2197
ting l/log
:
against l / m , where n and n1 are the viscosities
of the solution and the solvent, respectively, and m is the concentration in grams per 100 cc. This method frequently gives a straight line where a curve would be obtained by plotting log
n 5
against m. The results on two samples of
I-Low-viscosity
$03
1 -
The results have been plotted in accordance with the method proposed by Farrow and Neale-namely, plot-
The ,-gures represent the time of fall of a glass -311 of 3.3 mm. diameter through 15 cm. of a solution of 1 gram of cotton in 100 cc. of solvent a t 25" C . The samples were purified by boiling 4 hours in a 2 per cent solution of caustic soda, carefully excluding air during both the boiling and the subsequent washing. The results given are duplicate determinations, and each is the average of a t least two times of fall with different balls. Although with high-viscosity
04
Vol. 18, No. 12
Figure 3 linters 11-High-viscosity
linters
cotton are shown both in tabular form and as graphs. Sample I is a digested cotton linters of fairly low viscosity. Sample I1 is a high-grade second-cut linters, purified a t atmospheric pressure. The viscosity of the solvent was determined in an Ostwald pipet as 0.01292 poise. The results are expressed as poises for convenience in plotting. The conversion factor was obtained by standardizing against a sample of castor oil of known viscosity. It is understood, of course, that these figures are not absolute viscosities, and that they might be appreciably different if calculated in the same way from the times of fall of steel b a l k 6 The third graph shows the results for both cottons, omitting the two lower concentrations of Sample I. It is interesting to note that for the higher concentrations the linear relationship does not hold. Presumably this is due to the increasingly plastic nature of the dispersions. 6
Carver and Folts, J A m . Chcm. Soc., 47, 1430 (1925).
