May, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
515
Notes on the Viscosity of Cotton Cellulose' By J. 0. Small HBPCUZBS POWDBX Co., WILYINGTON, DEL.
into the digester decreases the ultimate consumption of variation in the viscosity of different cotton cellulose caustic soda per pound of finished product, and when lower materials, and even in the same fiber the cellulose is grade fibers are being utilized this is most important. Bleaching when properly conducted causes but a slight probably in varying degrees of molecular complexity. The viscosity a t this point is influenced by the species of the reduction in viscosity and under these conditions a product cotton plant, its age or growth, the conditions under which having but a small proportion of material soluble in 7.14 it ripens, and the locality where grown. There exist numerous per cent sodium hydroxide or 10 per cent potassium hydroxide varieties of the cotton plant, and a t the present time it is results. On the other hand, it is possible to effect enormous impossible to make a definite biological classification or to reductions in viscosity by bleaching a t high temperatures, ascertain definitely the ultimate affect on viscosity of the age but this is always accompanied by the formation of oxidation products of the cellulose. of the plant or of conditions Low-viscosity products obunder which it has matured. tained in this manner have There is a growing tendency The use of cotton cellulose as a raw material for a doubtful value. among those who use cotton many industries has become widely extended and, from The control of viscosity cellulose for chemical a practical point of view, viscosity is its most important during the p u r i f i c a t i o n manufacturing purposes to physical property. A brief outline is given of factors treatment has assumed conrestrict their raw material that are believed to influence viscosity from the growth siderable importance in reto that from a single locality, of the cotton plant until the purification treatment cent years, part(icu1arly to in order to obtain a more has been completed. A method is described which has manufacturers of artificial uniform product, since the been used for determining the viscosity of cotton celsilk and of nitrocellulose, conditions of growth in so lulose in cuprammonium solution. Although it is and it is now customary to far as they affect viscosity understood that colloidal solutions such as are formed purchase purified cotton cannot be controlled. by cellulose in cuprammonium do not have viscosities cellulose on definite visSpecification as to source independent of the rate of shear, the latter factor can It cosity specifications. can be made only after conbe neglected, for it is too small to be significant in inwould appear that the first siderable e x p e r i m e n t a1 dustrial application. step in the control of viswork, and in the case of cosity should be the deterlinters sharp lines of demination of viscositv of the marcation cannot be drawn for the several empirical geographical divisions, because raw material prior to the digestion treatment. This can cottonseed is sometimes transferred from one locality to be readily done with fibers of the better grade by making approximately 1 per cent solutions in cuprammonium and another for purposes of removing the linters. determining the viscosity as later described. The imporPurification Treatment tance of blending thoroughly the raw material before digesDuring the purification of the cotton cellulose its viscosity tion treatment cannot be overestimated and provision should is affected by (1) temperature (pressure) of digestion, (2) be made also for blending the material after digestion if a time of digestion, (3) strength of caustic solution, and (4) uniform viscosity is desirable. method of bleaching. Of these factors, the temperature of Estimation of Viscosity of Purified Material digestion exerts the greatest influence. I n recent years The importance of viscosity in selecting cotton cellulose comparatively high temperatures have become necessary, owing partly to the more extensive use of cheaper and more for the manufacture of nitrocellulose for the arts has been impure cotton fibers. For the low-viscosity types required realized for some time, and until recently it has been the pracin pyroxylin varnishes and similar products longer periods tice of certain manufacturers to nitrate samples of the puriof digestion are often required than were used in purifying fied cellulose on a small scale and determine the viscosity value cotton cellulose for smokeless powder. Naturally, the cost when the nitrocellulose had been dissolved in suitable solvents. of material prepared in this manner is relatively high owing This method was more or less unreliable because of the many to the effect of such drastic treatment upon yields, and a steps involved. It was desirable, therefore, to develop a method applicable to several types of cotton cellulose matefruitful field is offered here for economies. The strength of caustic solution employed in the digestion rials in order to control properly the viscosity of resultant prodtreatment depends upon the grade of raw cotton cellulose ucts. Ost2 describes a method for determining the viscosity of being purified and also upon the purpose for which it is to be used. For instance, when dealing with a low grade of lin- various forms of cellulose such as cotton, wood pulp, etc., ters or with hull fiber, it is necessary to use a higher concen- in cuprammonium solution. This solvent was made by distration of caustic solution than with a high-grade linter solving specially prepared basic copper sulfate in ammonia. having a much larger proportion of cellulose. It is gen- A subsequent study of this method of preparationJ showed erally accepted that lower viscosities result from the use of that accurate control of the copper and ammonia content stronger solutions during the digestion treatment. Any was difficult and for this reason duplicate determinations reduction in the amount of noncellulose material introduced could not be made. Ost refers to progressive changes taking place in the cellulose-cuprammonium solution during solution I Presented before the Division of Cellulose Chemistry a t the 67th
I
T IS generally understood that there is a considerable
Meeting of the American Chemical Society, Washington, D. C., April 21 to 26, 1924.
2 8
Z. angew. Chem., 24, 1892 (1911). Gibson, Spencer, and McCall, J . Chem. So6 (London), 117,470T(1920).
516
INDUSTRIAL A N D ENGINEERING CHEMISTRY
and up to the time of determining the viscosity. Later work has shown this to be due to exposure to air and light. During the war an extensive study was made of methods for making cellulose viscosity determinations with the aim of developing control methods for the production of propellant explosives. Gibson, Spencer, and RIcCal13 describe the method finally adopted. The solvent was prepared by dissolving copper hydroxide, * prepared by Dawson's method,4 in aqueous ammonia. Solutions were prepared using 1 and 2 per cent cellulose and viscosity determinations made both by using a hydrogen capillary viscometer and by the falling sphere method. However, Gibson's method frequently gave widely varying results on the same cotton, the solvent was comparatively difficult to duplicate, and air had to be admitted to the solution just before filling the viscosity tube. Joyner reinvestigated the subject of cellulose viscosities in cuprammonium and published an account of his work showing the effect on viscosity produced by varying the concentration of cellulose, copper, and ammonia, and a design for an apparatus for measuring viscosity without exposure of the solution to air.5 A modified form of this method hns been found to give more reliable results. In order to obtain a solution with sufficiently high viscosity to be determined by a falling sphere when some of the lower viscosity types of cotton linters were used. a solvent containing approximately 3 per cent copper was required. Attempts were made to obtain this by dissolving copper hydroxide in aqueous ammonia, but the variation in the physical nature of the copper hydroxide and the impossibility of obtaining high copper concentrations by this method made it necessary to prepare the solvent in a manner similar to that used by manufacturers of cuprammonium artificial silk. This involves the oxidation of copper _ - in the presence of ammonia. It was accomplished in the laboratory by bubbling air throuih a glass column filled with clean copper turnings and C. P. 28 per cent ammonia in which were dissolved 10 grams of sucrose per liter. The sucrose increases the viscosity of the solution somewhat, but it stabilizes the solvent and facilitates the preparation of cuprammonium by keeping the surface of the copper clean. Four hours' bubbling through a 61-cm. (2-foot) column produces a solution containing approximately 3 per cent copper and 17 per cent ammonia. As the copper concentration approaches 4 per cent the solution becomes unstable a t room temperature. A-Storage bulb for cuprammonium The solvent should contain 3 * solution B-Bulb for dissolving cellulose 0.2 per cent copper, 165 * 1.2 C-Viscosity tube grams ammonia per liter, and 10 grams sucrose per liter. It was prepared by diluting the solution from the towers with aqueous ammonia of the proper strength containing 1 per cent sucrose. The solution thus prepared, if kept in a dark bottle below 28" C., will remain unchanged for 3 or 4 weeks, except for an increase in nitrites which does not materially affect the viscosity. Careful preparation of the sample by thorough blending and tearing apart by hand is necessary to obtain consistent results. An apparatus identical to that described by Joy-
(>
4 J. Chen. Soc (London), 96, 370 (1909). S I b i d . , 121, 1511 (1'922).
Vol. 17, No. 5
ner is used, but instead of evacuating by a vacuum pump the bulb into which the sample of cotton cellulose is placed is connected with a reservoir of mercury. The air is forced out of the bulb by the mercury when the reservoir is raised, and a partial vacuum is then produced by lowering the reservoir. I t was found that check results could be obtained more readily in this manner. Five grams of the blended sample after having been dried with air a t 80" C. are placed in the bulb and the mercury reservoir is adjusted so that the bulb containing the sample is under about 61 * 12 cm. (24 * 5 inches) vacuum. A definite quantity (97 cc.) of the standard cuprammonium solution is then drawn in, and the bulb after having been closed tightly is placed in a shaker for 17 hours a t a temperature range of 15" to 28" C. The degree of shaking is standardized by fastening the bulbs radially on the face of a disk 46 em. (18 inches) in diameter rotating one revolution per minute. Although it is possible to use black bulbs and thus protect the solution from light during preparation, it must be exposed when the viscosity determination is made. Since the reducing effect of light may not be the same on all viscosities of cellulose-cuprammonium solution, it was thought best to use transparent bulbs. However, a t no time are the bulbs exposed to direct sunlight and viscosity determinations are made after a definite time of standing. When the time of shaking has elapsed the cellulose-cuprammonium solution is transferred by means of air from the bulb to a glass tube and the viscosity determined by causing a glass sphere 3.3 mm. in diameter to fall through 20 cm. of the solution a t 25" C. in a tube 1.5 cm. in diameter and 30 cm. long. Joyner has shown that the use of air in transferring the solution from the bulb does not seriously affect the accuracy of the result. The method outlined above is particularly applicable to the lowest ranges of viscosity in use a t this time. For higher viscosities, such as used in the manufacture of artificial silk, the weight of the original sample must be reduced from 5 grams to 2.5 grams or even 1 gram. Relation of Viscosity in Cuprammonium to Nitrocellulose Viscosities
Aibrief study was made to determine whether a definite relation exists between viscosity results as obtained in this manner and the viscosity of the corresponding nitrocellulose prepared under standard conditions in the laboratory. I n the latter case viscosity was determined in a pyroxylin solution using the falling sphere method. All the samples were of purified, bleached linters of the type generally employed in making nitro cotton for "dopes." They represent a variety of raw materials and methods of manufacturing, and were selected with regard to viscosity only. All the check determinations on cuprammonia viscosities are given to illustrate the deviation that can be expected. Sample
A-In Cuprammonium (1) (2) (3) .4v. 12.2 12.8 11.9 14.4 2 6 . 3 27.6 27.5 29.0 25.5 26.9 27.4 27.7 79 97.4 54 163 161 156 152 154 232 222 236 192 156 146 166 473 461 489 422
B-Nitrocellulose solution 9 29 49 83 153 178 IS? 533
Ratio B:A 0.70 1.05 1.82 0.85 0.98 0.80 1.20 1.16
From the table it is evident that consistent results can be obtained on the viscosity of cellulose by the method here outlined and the values so determined can be used to control the viscosity of the nitrated product. It is interesting to note that Sample 3, which consisted almost entirely of hull fiber, gave a high ratio. The KaOHsoluble on this sample was 10 per cent. Other results on a plant scale have since been obtained which tend to confirm
I N D U S T R I A L A S D EAYGIAI-EERINGCHE.UISTRY
May, 1923
this higher ratio when dealing with a linter with high SaOHsoluble. This is reasonable since it is known that the SaOHsoluble portion of linters is low in viscosity. The cuprammonia viscosity is lowered by the presence of the SaOH-
517
soluble portion to a much greater degree than the nitrocellulose viscosity, because a large portion of the KaOH-soluble part of the lint dissolves during nitration and purification of the nitrocelldobe.
Apparatus for Determining the Specific Gravity of Aggregates' By F. H. Tucker B U R E A U OF
ENTOMOLOGY, T . 4 L L U L A H , LA
A n apparatus has been developed by which the specific gravity of aggregates separated from bituminous mixtures can be determined, without separation into grades, to a n accuracy of 2 per cent and better. I t is adaptable to the gravity determination of fine materials, as Portland cement and sand, comparing favorably with the LeChatelier flask in results obtained, and requiring one-third as much time per determination. Although it has not been used for the apparent gravity of porous materials, there is nothing in its construction or operation t h a t would prohibit its use in the same way as any apparatus used for t h a t purpose. The essential features of the apparatus are (1) the special overflow tube, which produces a sharp cut-off of the overflowing liquid and responds to as small a n increase in
volume as 20 cc. or less; (2) the special lid and funnel combined, which effectually reduces flotation of fine material by introduction beneath the surface of the liquid, and prohibits air inclusions and splashing by providing for the spreading of the material and control of the speed a t which the material enters the liquid; (3) the glass jar, which permits the observation of behavior of the material in the liquid and is very easily and quickly cleaned. For aggregates abstractly considered, absorption, adsorption, and relative solution, are problems for investigation. The unoccupiable pore space in the aggregate material is constant for both the compressed bituminous mix and the aggregate after separation, and affects their respective densities in proportion to the relative percentages by weight.
COSTEJIPLATED study of compressed bituminous road materials involved the specific gravity determination of aggregates separated by extraction in order to determine the theoretical maximum or voidless density of bitumincius mixtures. A search of the literature and examination of laboratory practice revealed the need of an apparatus adaptable to the gravity determination of such aggregate?. Acccirding to the type of mix, aggregate. vary in size of particle from that passing a 200-mesh sieve to that retained on a 4.4-cm. (1.i5-inch) mesh. Common practice is to separate the coarse from the fine material and separately det'ermine the grayities by use of apparatus adaptable to the grades. It is highly desirable to eliminate this waste of time and increased chance for error by a single grayity determination of the aggregate as a whole.
tion between apparent and true specific gravity is dependent upon the absorption factor of the material and that i t is not practical to determine the apgarent gravity of fragments smaller than 0.5 inch diameter by any of the methods studied. For larger materials the Goldbeck, Chapman wire basket, and HubbardJackson methods were found to be equally reliable. The Bureau of Standards' modification of the LeChatelier apparatus was pronounced more convenient and rapid than the Jackson apparatus for fine materials with diameters less than 0.5 inch. Rea' described a method depending on the difference in specific gravity and the nonmiscihility of water and kerosene, to measure the displaced volume of the aggregate, including any pores that the particles may contain.
A
History Buckly' pointed out the faulty practice in the methods for specific gravity determinations of building stone, and recommends a procedure for determining porosity. Thorner3 proposed a method for determining the pore space in building materials, determining the true specific gravity by a Schumaunschen apparatus, and the apparent specific gravity by a device designed by himself, which is essentially a glass jar fitted with a ground-glass top containing an overflow tube and a vertical measuring tube connected to a tube sealed into the lower part of the wall of the jar. Seger and Gramendemployed the Thorner principle, but simplified the apparatus and procedure. Hilleh a n d 5 has a noteworthy discussion pertaining to the importance of correction for absorption by porous materials in the specific gravity determination of rocks. Hubbard and Jackson,6 after a comparative study of seven methods for the specific gravity determination of aggregates, concluded that an appreciable variaI 2 J
4
5
Received August 4 , 1924. K i s . Geol. S a t . H i s f S u r u e y Auli. 4, 63, 70 (1895) Chern. Ztg., 29, 744 (1905). I b i d . , 29, 884 (1905). U . S . Geoi. Survey. Bull. 422, 43. Proc. A m . So>. T e s t i n g M a t e r i a l s , 1 6 , 380 (1916).
Apparatus The method whereby the displaced volume is measured or weighed outside the parent volume and container was chosen as being in all probability the most practical. The apparatus hitherto used in this method is inadequate for the gravity determination of aggregat'es. In designing such an apparatus the following physical principles had t'o be considered: (1) A liquid such as kerosene is necessary as a medium of comparison and the surface tension of the liquid must be taken into account. The nature of the material determines the liquid to be used and the physical properties of the liquid the form of overflow tube required for an accurate displacement. (2) The material must be introduced beneath the surface of the liquid in order to diminish flotation of fine material. (3) Spreading of the material when entering the liquid is essential to air exclusion. (4). Control of the speed of introduction of the material into the liquid minimizes disturbances, splashing, and air inclusions.
Preliminary gravity determinations were made upon aggregates separated from bituminous pavements, using a liter side-tube flask with tube extended and bent down and a sleeve to introduce the aggregate beneath the surface of the liquid. Reasonably concordant results were obtained for displacements of 200 cc. or more. 7
Proc. A m . SOC.T e s l i n g M a t e r i a l s , 17, 2 5 i (1917').
