INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1923
819
The Chemical Properties of Cotton Linters’I2 By William F. Henderson MELLON INSTITUTE OF
INDUSTRIAL
RESEARCH, PITTSBURGH, PA.
a
EXTRACTION WITH SOLHE purpose of this B y treating cotton linters with strong acids it was found that vEms-Extractions wer e investigation was to the copper numbers were increased considerably as long as the acid made on linters, using for obtain more definite concentrations were low. but very rapidly when the acid concensolvents, water, chloroform, information concerning the trations were high. With weak. acids the change in copper numbers and ethyl alcohol. A Soxhchemical reactions of cotton was slight for all concentrations. When the linters were treated let apparatus was employed linters. Although the quanwith alkalies, the copper numbers remained practicaUy constant. and the solvent afterwards tity of linters produced is Various methods for preparing viscose from linters were tried. was distilled and the resisubject to wide variation, Preliminary acid treatment of the linters produced a marked effect due weighed. the amount of this material upon the viscosity of the viscose solutions. The effect upon the Samples dried at 105” to which is available is large. oiscosity was much more pronounced than that on the copper numbers. 110” C. were used in each The Deak of the annual case. The results of the prodiction was reached in 1916, when over a million and a quarter of the 500-lb. extractions were as follows: Per cent bales were produced. That the supply is fairly large and the Extract SOLVENT cost of production low has been recognized to some extent, Water ................................... 0.310 Chloroform. ............................. 0.415 and large quantities of linters are used in the paper and nitroEthyl alcohol.. ........................... 0.575 cellulose industries. Other industries use linters in considerable quantities, and doubtless there will be many addiASH-The material showed a low percentage of ash, the tional opportunities for application. It has been the au- average of several determinations giving 0.230 per cent. thor’s aim to discover some of the properties of linters which Bleached cotton, according to S ~ h w a l b eshould ,~ give on the will make possible further applications of this type of average about 0.5 per cent of ash, although Cross and Bevan5 material. found the ash content to range from 0.1 to 0.4 per cent. COPPERNUMBER-The copper number, or copper index, PHYSICAL CHARACTERISTICS is a value based on the reduction of copper in Fehling’s soluUnder the microscope linters show the same character- tion. The standards of comparison are purely arbitrary, istics as ordinary cotton fibers. They are colorless, trans- and consistent results depend entirely upon well-controlled, parent, and present a flattened, ribbon-like appearance. uniform conditions for all the determinations to be made. The fibers are hollow, the lumen showing up very plainly The method used by the author was very similar to that in unstained preparations. A characteristic twisting is recommended by Schwalbe.6 revealed, just as in the case of long cotton fibers. The An oven-dried sample, weighing from 1 t o 2 grams, was covered linters differ from long-fiber cotton apparently only in length. with 250 cc. of water and the mixture brought t o boiling. Fifty cubic centimeters of each part of Fehling’s solution were boiled, The linters used for this research were almost pure white in color, but when compared with a sheet of white paper t h e two parts mixed, and the mixture added t o t h e water conthe cellulose. The whole was boiled exactly 15 minutes, a faint yellow tint could be detected, due to the presence of taining with stirring, in a n all-glass reflux apparatus. After filtration a small amount of iron salts on the fiber. When immersed through a Bdchner funnel (diatomaceous earth was unnecessary), for a few minutes in strong hydrochloric acid, this iron t h e linters were washed with hot water until the filtrate showed dissolved out, imparted a yellow color to the acid, and am- no copper when tested with ferrocyanide. The linters were with 7 per cent nitric acid, warmed, and filtered. After monium thiocyanate showed the presence of iron in the acid treated rinsing they were treated with dilute ammonia water, warmed, solution. When washed free from this acid solution, pure filtered, and then treated again with dilute nitric acid, and finally washed free from copper. The filtrates and washings were conwhite fibers remained. centrated and the copper determined by titration with thioANALYTICAL CHARACTERISTICS sulfate. The copper determined by this method represents the “total MoIsTuRE-Linters are hygroscopic, and when dried in copper,” which consists of t h a t which is precipitated as cuprous air mill retain from 5 to 6 per cent of their own weight of oxide during the reduction, and also the trace of unreduced copper water. Determinations of the moisture content were made which cannot be removed from the fibers by washing with hot In order t o determine the amount of copper reduced, by noting the loss in weight when the air-dried samples water. this small amount of unreduced copper which adheres so tenmere heated for 2 hours at 110” C. and the material cooled aciously t o the linters must be determined and the amount subin a desiccator. The following data are typical for the type tracted from t h e total copper. The unreduced copper was determined by treating the linters with cold Fehling’s solution. of linters used: MOISTURE
Air-dried.. .............................. Saturated air.. ..........................
Per cent 5.56 14.89
For oydinary cotton fiber the water content usually ranges from 6 t o 8 per cent. In a saturated atmosphere, Wiesnera found a water content of 20.99 per cent for cotton cellulose. 1 Presented before the Division of Cellulose Chemistry a t the 64th Meeting of the American Chemiqal Society, Pittsburgh, Pa., September 4 to 8, 1922. ’Abstract of a thesis submitted t o the University of Pittsburgh in partial fulfilment of the requirements for the degree of Doctor of Philosophy. SWiesner, “Die Rohstoffe des Pfanzenreiche,” 2nd ed., 2, pp. 181 and 250; Matthews, “Textile Fibers,” 3rd ed., p. 174.
The removal and determination of the copper were accomplished in the manner described above. This copper has been termed “correction” in the data concerning copper numbers in this paper.
The linters used in this research gave the following results for copper number determinations, calculated on the basis of 100 grams of oven-dried material: Per cent
........................... 1 . 0 3 0.46 ...............0 . 5 7
Total copper.. Correction. .............................. Reduced copper (difference). “Chemie der Cellulose,” p. 34. “Cellulose,” 2nd ed., p. 3. 6 “Chemie der Cellulose,” p. 025. 4
6
880
INDUETRIAL A N D ENGINEERING CHEMISTRY
'
SUMMARY OF PROPERTIES-A resume of the preliminary treatment given the linters'duringthe course of manufacture, with the analytical figures determined, points very clearly to the fact that these linters are cellulosic material of exceptional purity. Preliminary Treatment: (1) Dirt dusted out (2) Boiled 5 hours in 1 per cent NaOH (3) Bleached with very weak hypochlorite (4) Dried a t low temperature Analytical Constants: (1) Moisturr, 5.5 per cent (2) Extracted material, 0.31 t o 0.57 per cent (3) Ash, 0.13 per cent (4) Copper reduction, 0.57 per cent
formic, and acetic. The concentrations ranged from 10 to 100 per cent, depending upon the acid. The time of exposure in most cases was 18 hours. The temperature was 25' C. in all cases. The results are given in the accompanying table and in Fig. 1. The results for sulfuric acid are plotted as representative of the action of strong acids on linters. EFFECTS OF ACIDS O N COPPER NUMBERSO P LINTSRS Aqueous Sulfuric A c i d , 16 H 7 s ( F i g . I ) Per cent Total Copper Correction Copper Acid Per cent Per cent Number 10 20 40 45 50 55 60
--r--r--
10 15 20 25 30 34
_I---~
Vol. 15, No. 8
10 20 30 34
10 20 30 40 50 60 70 10 30 60 70 80
0.88 1.33 2.64 3.16 3.59 5.10 6.88
0.44 0.49 0.34 0.34 0.29 0.20 0.14
Aqueous Hydi-ochloric A c i d , 20 Hrs.* 2.01 2.48 3.86 5.66 6.94 7.35
0.47 0.42 0.40 0.34 0.31 0.25
1.75 1.88 3.46 4.17
0.56 0.39 0.35 0.37
Aqueous Nilric A c i d , 18 Hrs. 0.46 0.41 0.42 0.40 0.39 0.44 1.21
1.00 1.32 1.61
2.10 3.51 10.53 26.99
ACID C O N C E N T R A T I O N , 1-COPPER
.'CTIOX
OF
CERTAIY HALOGEN
COMPOUNDS ON
FOR
LINTERS
PHOSPHORUS OXYCHLORIDE-Phosphorus oxychloride reacts with linters in the cold, and after several hours shows a marked tendency to disintegrate the fibers. The action is ~7erysimilar to that produced by hydrochloric acid, which is discussed below. YELENIVM OXYCHLORIDE-cold selqnium oxychloride produced no visible change in oven-dried linters after 24 hours. When warmed to approximately 75" C. the linters softened, disintegrated, and finally the mixture became a deep b r o f n liquid. A small amount of hydrogen chloride was evolved during the process. One hundred and fifty cubic centimeters of anhydrous ethyl ether were added to the cooled solution and a pale cream-colored, amorphous precipitate settled out. This substance quickly decomposed in the presence of a trace of moisture, turning bright red (selenium) and evolving hydrogen selenide.
0.48 0.48 0.42 0.43 0.46
1.00 1.08 1.47 1.69 1.98
0.83 0.88 0 95 1 22 1.16
0.43 0.41 0 39 0 39 0.30
Aqueous Acelic Acid. 18 Hrs. 0.34 0.33 0.40 0.43 0.46
0.59 0.60 0.75 0.98
LkCTIOSO F
0.52 0.63 1.05 1,26 1.52 0.40 0.47 0.56 0 83 0 86 0.25 0.27 0.35 0.55 0.68
.
ALKALIES O N LINTERS
Experiments were conducted using alkalies with linters in a manner similar to that employed for acids. The alkalies used were sodium, potassium, and ammonium hydroxides. The following tables and Fig. 2 show the results of these experiments : Aqueous Sodium Hydvoxide, 18 Hrs., 25" C. Per cent Total Copper Correction Copper Alkali Per cent Per cent Number 10 15 20 30 50
1 10 1 81 2 06 2 03 2 14
0 57
1 12 1 37 1 34 1 36
0 53 0 69 0 69 0 69 0 78
These results agree with.the idea presented by Hibbert,' t h a t alkalies do not open u p one of the cellulose rings. The constancy of the copper reduction values bears out this observation. Aqueous Polasszum Hydvoyade, 18 H r s , 25' C. Per cent Total Copper Correction Copper Alkali Per cent Per cent NumheI
ACTIONOF ACIDSO N LIKTERS Linters were treated with different acids of varying concentrations fox several hours, and, after washing and drying, the copper numbers were determined. The acids used were sulfuric, hydrochloric, hydrobromic, nitric, phosphoric,
0.54 0.91 1.19 1.70 3.12 10.09 25.78
Aqueous Phosphoric A c i d , 18 N r s .
..
PER CENT
NUMBERS O F C O T T O N LINTERSTREATED W I T H H2SOa 16 HOURSA T 25' C.
1.19 1.49 3.11 3.80
1.14 When linters were treated for 18 hours with anhydrous ethyl ether, saturated with dry hydrochloric acid gas, a reaction somewhat similar to t h a t in aqueous solution was noted. The linters in this case gave copper values as follows: Per cent Total copper., . . . , . . . . . . . . . . . .I,3.29; 11, 3.17 Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.23 Correction.. . . . . . . . . . . . . . , . . , . . . . . . . . . . . . . 0.59 Copper nurhber.. . , , . . . . . . . . . . . . . . . . . . . . . . . 2.64
*
FIG.
20 40 60 80 100
1.54 2.06 3.46 5.32 6.63 7.10
Aqueous Hydrobromic A c i d , 18 Hrs.
Aqueous Fovmic A c i d , 18 H i s . 10 20 40 60 78
0.44 0.84 2.30 2.82 3.30 4.90 6.74
10 15 20 30 50 7
1.04 1.07 1.32 1.89 2.04
0.50 0.61 0.77 1.18 1.39
THISJOURNAL,18, 256, 334 (1921).
0.54 0.46 0.55 0.71 0.65
August, 1923
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Ammonium Hydroxide. Concentrated ammonium hydroxide, containing 28.3 per cent of ammonia, was tried with linters. The copper values were almost the same as were found ‘for untreated cellulose, being a$ follows: Total copper
Linters f NHa 1 10 0 49 0 61
Original Linters 1 03 0 46 0 57
It is evident that concentrated ammonium hydroxide at 25’ C has no appreciable effect upon the linters.
ESTERFORMATION WITH LINTERS
82 1
The tribenzoate was produced and it was, completely soluble in chloroform, producing a very viscous solution. DITHIOCARBONATE-MOSt of the author’s research in regard to esters has been in connection with cellulose dithiocarbonate, or viscose, as it is usually called. This ester was discovered by Cross and Bevan, who patented their discovery in 1893.11 A description of the preparation of viscose and its properties has been given by these chemists in their book, “Cellulose,” and it has now become one of the important subjects in every general treatise on cellulose chemistry. The successful production of viscose depends upon the many factors which may b e classified in a general way as follows: (1) Preliminary treatment of the cellulose (2) Concentration of reagents employed ( 3 ) Temperature control (4) Time allowed for stages of the reaction
In the past twenty years an immense amount of work has been done with the esterification of cellulose. The formation of nitrates, acetates, benzoates, formates, lactates, etc., has been carefully studied, and almost iniiumerable patents have appeared covering the various methods of production.8 The author has not endeavored to add to this long list of methods, but has attempted the application of In general, the program carried out may be divided into a few of the well-tried processes to the preparation of esters three stages: from linters. During the war the formation of cellulose (1) Formation of alkali cellulose nitrates from linters was investigated thoroughly and carried ( 2 ) Combination of alkali cellulose with carbon disulfide out on an immense scale by the War Department. The ( 3 ) Solution of the ester in water author devoted his attention to the production of the benThe formation of the alkali cellulose is accomplished by zoate, and especially to the production of the dithiocarbonate, the interaction of cellulose and sodium hydroxide solution. commonly known as viscose. BENZOATE-The method most commonly used for the S o t only is the combination of cellulose with alkali to form formation of cellulose benzoate is one which proceeds accord- alkali cellulose necessary, but a process of “ripening” is also ing to the Shotten-Baumann reaction. The application of important. This process consists merely in allowing the this method to cellulose was investigated by Ost and Klein.g alkali cellulose to stand several hours before attempting to This method involved the use of benzoyl chloride with cellu- apply the carbon disulfide. I n a patentI2 granted to the discoverers of viscose, claim was made that the alkali and carbon disulfide could be applied simultaneously, but in the manufacture of viscose a t the present time the alkali cellulose is allowed to ripen before the carbon disulfide is applied. The ripening may be carried out in a closed vessel or it may be accomplished by exposing the alkali cellulose to the air. The temperature at which the ripening occurs has an important bearing on the quality of viscose produced. Carbon disulfide is added and the mixture sealed up to prevent loss of carbon disulfide vapor. The carbon disulfide vapor reacts with the alkali cellulose, and the whole mass becomes yellow and finally orange in color. If the reaction proceeds properly, the fibers eventually melt together into A.TOTALCOPPER, B. CORRECTION, moist, gelatinous masses. Here also the temperature affects C. REDUCED COPPER. the speed of the reaction. At 4” C. a t least 48 hours are necessary, while at 25” C. usually 18 hours are sufficient. When the combination of alkali cellulose with carbon diPOTASSIUM HYDROXI DE:sulfide is complete, any excess of cqrbon disulfide is removed by suction, and water and usually more sodium hydroxide are added to the cellulose ester. The dissolving of the ester is usually slow, due to the great viscosity of the solution. Frequent agitation is desirable. As the solution process is carried out the material is stored in a refrigerator, where it must be henceforth kept to prevent rapid decomposition. The quality of the various solutions is subject to wide variations unless great care has been exercised to control the condi0 to 20 30 40 50 60 tions under which these solutions have been prepared. A L K A L I CONCENTRATION,PER CENT Freshly prepared viscose must be subjected to another FIG 2-COPPER N U M B E R S O F C O T T O N L I N T E R S TREATED WITH ALKALIES ripening process if the product is to be used for producing FOR 18 HOURS A T 25’ C . threads or films. Cellulose dithiocarbonate is not a very lose in the presence of a base. The most successful prepara- stable substance and will decompose at room temperature tion of the tribenzoate of cellulose resulted when pyridine in the course of 2 or 3 days. This decomposition occurs was used as the base. The discussion of this reaction is given w r y slowly a t 4” C.; consequently, the preparations must be preserved in a refrigerator. The ripening consists in by Heuser.lo When this method was tried by the author, with linters, allowing this decomposition to proceed to the point where it was found that the esterification occurred very readily. the properties of the product are most suitable for the application in mind. 8 Wordan, “Technology of Cellulose Esters,” Vol. 1, p. 3088. 8 Z anrew. Chem., 26, 437 (1913). Brit. Patent 5700 (1893).
-
“Lehrbuch der Cellulose Chemie,” p. 5 6 .
U. S. Patent 520,770.
INDUSTRIAL A N D ENGINEERING CHEiMISTRY
822
A great many modifications of the methods described in general in the literature have been tried by the author of this paper, in the effort to discover the best conditions under which viscose could be produced from linters. It is generally recognized by workers in this field that viscose made from wood pulp is more readily dissolved in water than that made from very pure forms of cellulose, such as cotton. It is also generally known that viscose made from wood pulp produces films, or threads, which are not as strong as those produced from the purer forms of cellulose.
ACID CONCENTRATION
IN PRELIMINARY TREATMENT
FIG.%-COMPARATIVE
VISCOSITY OF S O L U T I O N S OF VISCOSE M A D E FROM C O T T O N L I N T E R S TREATED WITH NITRIC ACID
Experiments were conducted in which the conditions of formation of the alkali were tried, and both temperature and time of exposure were varied. The conditions under which the alkali cellulose was ripened were varied and the effects noted. In many of these preparations the alkali reaction was not complete and the resulting xanthogeiiate would not dissolve in water. In others the alkali reaction had gone too far and, while complete solubility of the ester often resulted, the viscosity of the solution was very low. A method suggested by &fits~herling~~ for the production of viscose from cotton was tried out with linters. This method was briefly as follows: One hundred grams of linters were treated with 750 grams of 20 per cent sodium hydroxide for 20 minutes a t 25" C. Alkali was pressed out under pressure and the pressed alkali cellulose weighed 360 grams. This was exposed to air for 44 hours at 25" C. It was then placed in a bottle, 50 grams of carbon disulfide added, and the bottle sealed. The mixture was allowed to stand a t 25" C. for 18 hours.l4 Fifty grams of sodium hydroxide were dissolved in a liter of water and this solution was added to the xanthogenate. The whole was made up to 2000 grams. The solution was practically complete, but the product was thin and watery, and very unsatisfactory for most applications. This very low viscosity of the product just described reminded the author of a series of viscose preparations 1s Paper presented before the Section of Cellulose Chemistry a t the 62nd Meeting of t h e American Chemical Society, New York, N. Y.. September 6 t o 10, 1921. 1 4 Mitscherling proposed t h e use a t this point of sodium hydroxide equal t o t h e weight of the original cellulose.
Vol. 15, No. 8
whiah he had made earlier from partially hydrolyzed linters. These preparatibns were likewise low in viscosity. In a series of experiments in which the method suggested by Mitscherling's paper was modified, it was found that by shortening the time of exposure of the alkali cellulose to air (ripening) the viscosity of the product became much greater. When the time was shortened to 5 hours, a product of high viscosity and other fine qualities was produced. Reference was made earlier in this discussion to the effect on viscose of preliminary treatment of the cellulose. Herein apparently lies the reason for the difference in properties of wood-pulp viscose and cotton viscose. The treatment through which wood pulp goes in order to free the cellulose from lignin, etc., is more drastic than that through which cotton is put. The effect is noticed in the more rapid solution of viscose made from wood pulp than that made from cotton, and at the same time the production of weaker threads or films by the former when compared with those from the latter. This was borne out by a series of experiments performed by the author. Samples of linters were treated for varying lengths of time with hydrochlnric acid and afterwards washed until neutral. Viscose was made from these acid-treated linters, and in every case very thin watery products were formed. The cellulose was rendered much more reactive by the acid treafment, but the products made from the viscose possessed very little strength. The final piece of work in connection with this research consisted in the preparation of viscose from samples of linters which had been treated with increasing concentrations of nitric acid. Thirty-gram samples of linters were treated with nitric acid solutions ranging from 10 to 70 per cent, for 18 hours a t 25' C. After washing thoroughly, until free from acid, these samples were dried at room temperature. Each sample was converted into viscose, using identical conditions for all. A blank (untreated fibers) was run for a comparative test. The blank test gave viscose which possessed the highest viscosity of all the samples, and in the acid-treated samples the viscosity fell with great rapidity. A Stormer viscometer was used to gain some idea of the comparative viscosities. The results of these tests were as follows: Per cent Acid Used for Preliminary Treatment 0 10 20
30
40 50 60
70 Water
Number of Seconds for 100 Revolutions 3300 1500 900 420
178 50 27
7 6
The greatest diminution of viscosity occurred when the Iowest concentration of acid was used. This is readily seen when the figures are plotted, as in Fig. 3.
ACKNOWLEDOME NT The author wishes to express his appreciation to W. A. Hamor, of Mellon Institute, and to Alexander L o w , of the University of Pittsburgh, for many helpful suggestions during the course of this research. Zanetti Appointed on Committee of League of N a t i o n s J. Enrique Zanetti has been appointed t o a committee of the League of Nations which will investigate the whole question of chemical warfare. Associated with Dr. Zanetti, who is now in England on leave of absence from Columbia during the next academic year, will be a group of chemists representing other countries, among whom will be Sir William Jackson Pope, of Cambridge University, England, and Charles Moureu, of the University of Paris.
