Chemical Delinting of Cottonseed and Industrial Utilization of the Lint B. T. ARDASHEV,Cotton T r u s t of Middle Asia, Tashkent, U. S. S. R.
C
OTTONSEED after ginning and removal of first-cut linters is still covered with linters-a short-staple interfelted fiber amounting to about 10 per cent of the weight of the seeds. This fiber, chemically nearly pure cellulose, is at present not utilized in U. S. S. R. and is a nuisance, as it hampers the sifting out of the seeds, leads to losses of oil in pressing, and detracts from the value of the hull as fodder. If it were removed from the seed, it could be used in industry as cellulose. A removal of 8 per cent could yield 85,000 tons of linters annually, based on the 1931 crop in Middle Asia. These linters when purified and with a yield of 80 per cent would become 68,000 tons of cellulose. Attempts to remove cotton linters were made a t the beginning of the World War in Germany. One type of machine, represented by the Ragsvel gin and the DeSegundo defibrator, was developed to remove the linters from seed; another type, represented by the Mink gin, removes linters from hull. With neither type of machine were the results entirely satisfactory. If the seeds were to be kept from injury, the removal was not good; if the linters were removed a t all effectively, the seeds were injured and the linters soiled with oil and particles of hull. Mechanically removed linters do not constitute pure enough cellulose for the manufacture of artificial silk. (The chemical purification of such linters is the basis of the American cotton cellulose industry.) The delinting of hull has the further drawback that in such a process it is impossible to realize the advantages of denuded seeds for oil pressing or sowing. A further fault of the mechanical removal of linters is the large power requirement. First-cut delinting with a Karver machine, according to Dynzhev (IO) requires 12.5 h. p. at 750 r. p. m. for a maximum yield of 4.6 tons of raw material per day, and the removal of the residual linters would be expected to consume even more power. As a result of the comparatively poor efficiency of linters gins and the desire to remove the fiber from the seeds as completely as possible, the Cotton Trust in planning its giant cotton plants is compelled to furnish each gin with a series of successive linters machines. The linters last removed-the fourth and fifth grades-are not utilized for spinning and are usually used for the manufacture of cellulose (32). A solution of the linters problem which would permit removing all of the fiber unsuitable for textile purposes a t a single stroke would therefore effect a great saving in the number of linters gins to be installed and operated. For a number of years the mechanical delinting of cottonseed has appeared uneconomical in the face of a number of new proofs of its value, such as the convenience of storing and transporting of delinted seeds (12,3.4, the increase of oil output (9),the improvement of the feeding qualities of the delinted hull, and the better chance that the seeds can be used for the production of furfural. I n addition, there are many experimental data to indicate the favorable influence of delinting on germination (6, 34, 37). A very important advantage of delinted seeds is the feasibility and cheapness of sowing. Unlike pubescent seeds,
they can be sown with ordinary corn-sowing machines such as are used for rice and maize. In 1931 one firm in Texas saved more than $1000 by sowing 800 acres with delinted seeds. A given quantity of delinted seed will sow an area two and a half to three times as large as an equal quantity of pubescent seed.
CHEMICAL METHODSOF DELINTING The advantages of delinting and the disadvantages of mechanical delinting make the problem of finding new ways of delinting attractive to scientific thought. One new way is the chemical method which has lately begun to be applied in America. Experiments passed the laboratory stage and field tests were begun in 1921, but even now they cannot be considered as complete. There are two processes, one using sulfuric acid and the other gaseous hydrochloric acid. According to the former method the seeds are covered with technical sulfuric acid of a t least 90 per cent strength and stirred continuously for 15 to 20 minutes until the linters are removed. Then they are transferred to a large funnel, drained, and washed with water. Finally the seeds are spread on a floor for drying. At present there are in America several machines that accelerate the process and make it less dangerous than treatment in an open vessel (8). I n the second method the seeds are treated in closed rotating vessels whereupon the lint becomes brittle and is easily removed by friction as a powdery substance averaging 80 to 100 kg. per ton of seed. Chemical delinting has all of the advantages of any kind of delinting as far as sowing and oil production are concerned, and has the further feature (important for sowing) of disinfecting the seeds. The seeds can also be sorted during the operations (21). The sulfuric acid method was the first to appear. As it is simple to operate, even on a large scale, it has found considerable application in America (8, 21). This year the chemical laboratory of the Cotton Trust (formerly Investigation Institute for Cotton Culture) has investigated the industrial feasibility of delinting sowing seeds with sulfuric acid throughout Middle Asia and of producing alcohol from the solutions obtained. I n April, 1932, about 4800 kg. of cottonseed were run through the semiplant equipment. The solutions after delinting contained 16 to 20 per cent glucose. The experiments on fermentation to alcohol have not yet been completed. The germination of the seeds proved to be better than that of check pubescent seeds. The sulfuric method, with its favorable effect on germination, combined with disinfection and sorting, is clearly superior to mechanical delinting for the purpose of sowing. Nevertheless, it has drawbacks. The acid consumption is about 30 per cent of the weight of the seeds. Special packing and equipment are necessary to transport the acid. The acid solution of the linters is comparatively unstable, and it is difficult to recover the theoretical quantity of alcohol. Also, a valuable chemical substance, cellulose, is transformed to a less valuable, glucose. The disadvantages mentioned are avoided by the more recent hydrochloric acid delinting process. This method
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INDUSTRIAL AND ENGINEERING CHEMISTRY
has not passed beyond the semiplant stage in America on account of difEiculties in operating it on an industrial scale. The method was developed for improving sowing seed and only as an accessory feature (21): "The seed hulls or linters are obtained as a powder-like cellulose substance which, being pressed, has a density of about 25 pounds per cubic foot. This material can be applied for manufacturing artificial silk and other products made of cellulose." Cheapness and convenience of sowing, the possibilities of covering large areas in sowing, improvement of germination, and the disinfection of the seed are also claimed for the process. The method of removing lint from cottonseed by the action of hydrochloric acid is not new, as a method of determining the pubescence of cottonqeed is based on the use of aqueous hydrogen chloride. The industrial application of the idea, however, is undoubtedly new and worthy of serious thought. The procedure need not be on a wet basis; the present investigation is on the dry process. The expenditure of acid is insignificant, as only 2 to 3 per cent of acid as sulfuric is required in the gaseous hydrochloric acid process, compared with 30 per cent in the sulfuric acid process. The calculation is made on the basis of sulfuric acid, since it is more expedient to prepare the hydrochloric acid on the spot from sulfuric acid and sodium chloride which is found everywhere, and in abundance in Middle Asia. The powdery product obtained is readily transported or stored, whereas in the sulfuric acid method the product is an unstable liquid; this is no insignificant advantage. The industrial utilization of the product requires further investigation of its composition, and experimental study of its application to various industries. Even in the least favorable case (that of saccharifying and fermenting to alcohol), this product must be of greater economic importance than the unstable sulfuric acid solutions obtained in the sulfuric process. I n order to solve the problem of the industrial application of the lint, it is necessary to consider these things: (1) the most complete and easiest way of mechanically removing the chemically treated lint, (2) the quality of lint obtained, (3) the amount of seeds after the removal of the lint available for sowing or oil production. This paper is concerned with the second consideration, the fundamental one.
DELINTING WITH HYDROCHLORIC ACID Preliminary experiments to determine the effect of hydrogen chloride concentration and time and temperature of the reaction were run in the apparatus shown in Figure 1. Gaseous hydrogen chloride generated in flask A was passed through Tischenko flasks a to be dried and to remove entrained acid, and into the gas-holder B previously filled with kerosene saturated with hydrochloric acid. To determine the concentration of hydrochloric acid in the gas-holder, a measured volume of the gas was passed through 0.1 N sodium hydroxide in an Erlenmeyer flask closed with a rubber stopper provided with two glass tubes. The excess sodium hydroxide was titrated with 0.1 N hydrochloric acid. Hydrochloric acid was passed from the gas-holder into a 3-liter flask, C , containing the seeds to be treated. This flask was placed in an aqueous bath, D. Thermometers TIand Ta measured the temperatures of the bath and flask, respectively. The flask was connected by means of a glass cock to a series of absorbing flasks containing 0.1 N alkali solution. Air-dr cottonseeds were used containing 7 to 10 per cent moisture. T i e seeds had previously been ginned and carefully blended to assure a uniform material. The gas-holder was filled with the highest concentration of hydrochloric acid available under the conditions, 1.4 to 1.5 grams per liter. In ex eriments 1 and 3, the seeds were treated twice with 1.5 liters ofgas, 15 minutes each treatment or 30 minutes in all. In experiments 2 and 4,2 liters of the gas were passed in 10 minutes. In experiment 5, 3 liters were passed in 10 minutes. After an experiment, the gas was sucked away with a water pump, passing through the absorption train containing standard sodium
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hydroxide solution. From the amount of hydrochloric acid taken from the gas-holder and the amount collected in the absorption train, determined by titration, the hydrochloric acid adsorbed by the seeds was determined. The results of the experiments are given in Table I; this shows that the concentration does not exert a marked influence on the character of the absorption of hydrochloric acid and that the limit of the absorption by the seeds a t a given temperature is 2 per cent of the weight of the seeds even when a considerable excess of hydrochloric acid was passed. For this reason, in later experiments where the absolute amount of hydrochloric acid consumed was not important, the gas-holder was disconnected and continuous flow was used. TABLEI. EFFECTOF HYDROCHLORIC ACID CONCENTRATION ON COTTONSEED (200 grams of cottonseed of 7.6 per cent moisture content treated in each experiment at 40' C.) DURAHCI HCI NEUTRAL- HC1 ABSORBED EXPT. TION CONCN. IZED B Y SEEDS % of weight Minutes Grams/liter Grams Grama of seeds 1 30 0.73 0.29 3.91 1.96 2 30 0.98 1.9 4.02 2.01 3 30 0.73 0.47 3.73 1.87 4 20 0.95 1.9 3.91 1.96 5 20 1.4 4.6 3.84 1.92
.
When the hydrochloric acid had been sucked away for 20 to 30 minutes, the lint was removed from the seeds manually with a brush made of rough bristle or card. The lint treated for 5 minutes remained white and did not peel off the seed easily. After 10 minutes it was slightly yellow. After 15 minutes it was distinctly yellow and came off relatively easily, partly as fine short fibers and partly as a powder. After 30 to 40 minutes it was light brown and came off easily. The lint brushed off was removed from hull particles and other impurities by screening. Table I1 shows that a more prolonged treatment of the seeds under given conditions lowers the baryta resistance of the lint and the yield of technical cellulose, but even for a 40-minute sample the change is not great. For this reason in the industrial application of the method the time should be reduced to a minimum consistent with easy and complete removal of the lint. WITH GASEOVS TABLE11. EFFECTOF TIME OF TREATMENT HYDROCHLORIC ACID ON COTTONSEED
(200 grams of cottonseed of 7.8 per cent moisture content treated in each experiment with continuous flow of hydrochloric acid.) BARYTA RESISTANCE COPPER YIELD OF: LOSB No. OF GLUCOSE TECHNI-TechLint CAL nical washed beIN UNIN DURA-AQUEOUS WABHED WATER CELLU- cellu- fore neutral RXPT TEMP.TION EXTRACTLINT EXTRACT LOSE lose reaction ._ * C. .-. M i n .. "/, % % % % ._ 76.69 93.95 85.60 9.6 1.48 1 20 5 13.69 69.1 93.95 1.48 13.96 10.44 52.48 10 2 21 1.43 68.15 58.17 13.5 10.61 81.65 3 20 15 61.14 87.37 80.00 1.90 13.64 11.2 4 20 30 61.21 86.93 81.20 13.68 11.06 1.48 5 21 40
__
~
I"
OF TREATMENT WITH TABLE111. EFFECTOF TEMPERATURE GASEOVS HYDROCHLORIC ACID ON COTTONSEED
(200 grams of cottonseed of 7.8 per cent moisture content treated in each experiment with continuous flow of hydrochlorlc acid for 7 rmnutes) BARYTA RESISTANCB COPPER OB: No. OF GLUCOSEYIELDOF TechLint washed beI N TECHNICAL nical LOSBIN UNAQUEOUSWAUHED AQUEOUSCELLU- ceUu- fore neutral EXPT.TEMP.EXTRACT LINT EXTRACT LOBE lose reaction 1 2 3 4
OC.
%
40
10.31 13.1 13.04 13.67
60
73 82
11.06 12.28 13.16 13.01
%
%
%
%
1.2 2.2 2.1 3.06
52.73 52.13 54.40 66.63
95.10 96.86 95.37 97.76
76.1 75.6 74.6 74.3
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INDUSTRIAL AND ENGINEERING CHEMISTRY
577
Three products were obtained, differing in appearance. Changes of temperature have a greater effect on the product than changes of time (Table 111). As the temperature Lint K1 was represented by small fibers which were brittle rises, the yield of technical cellulose decreases, the amount and slightly dusty. It had a yellowish tint which was hardly of glucose in the aqueous extract increases, and even the color visible and contained some hull particles. After washing of the lint (which is yellow a t 40°, light brown a t 60°, and and drying, the sample was almost free of powdery material. Lint hiz had a r a t h e r d i r t y b r o w n a t 70' d i r t y color and was C.) i n d i c a t e d m o r e more dusty. Lint s i g n if i c a n t changes Na was a fine powder in its structure. The of dirty yellow color insignificant increases in which no h u l l of technical-cellulose p a r t i c l e s were to be yield observed a t 70" seen. The hulls had and 82" C. may be accrumbled to dust c o u n t e d f o r b y the in t h e t r e a t m e n t . carbonization of part The product was of the lint. s e p a r a t e d from t h e I n t h e a n a l y s i s of seeds by sifting t h e l i n t i t will be through large Buchner noted that, in place of funnels. the usual alpha-cellulose d e t e r m i n a t i o n , The c o n d i t i o n s of t h e baryta resistance treatment are recorded (24) was used, since, in Table IV, but the changing factor of the owing t o t h e g r e a t swelling of the powdery duration of treatment material in the strong i s n o t significant f o r FIGURE1. DIAGRAM OF APPARATUS sodium hvdroxide soht h e s e exDeriments tion, it could not be filtered. For comparison, the baryta owing to variability of the flow of hydrochloric acid. Thus resistance determination was also carried out on a less de- in the first experiment hydrochloric acid was passed for graded material-short-staple linters. 1 hour and 10 minutes before the solution with methyl orange in a check flask turned color. In the second experiment, 2 hours and 15 minutes, and in the third 2 hours and 30 minutes TABLEIV. CONDITIONS OF TREATMENT OF COTTOXSEED WITH GASEOUS HYDROCHLORIC ACID were required. (8 kg. of cottonseed treated in each experiment with weak flow of hydrochloric acid at 20" C.) TIMEOF TR~ATMENT Before methyl After methyl orange reddens orange has EXPT. in check vessel reddened YIELDOF LINT^ Min. Min. % . _ of . wt. of seed 1 70 20 7.8 2 135 45 9.0 10.6 3 160 90 At end of delinting, small losses due to pulverication of product were not taken into account.
LARQE-SCALE TREATMENT
A complete analysis of a product to be used industriallypurified cellulose-is of importance. It is likewise desirable to know the relation of the purification treatment to certain constants-e. g., viscosity, as has been shown by many writers (20). Freiberger (14) even suggests the determination of the viscosity in cuprammonia solution as a test for degree of purity. However, not much could be deduced from a single product. To obtain enough material for analyses and to make the treating conditions approach industrial conditions, a special apparatus was used in which 700 to 1000 grams of lint could be obtained a t one time. The main part, of the apparatus consisted of a cylindrical copper drum lined with tin and set horizontally. The drum had small fins inside and could hold as much as 10 kg. of seeds. It rotated a t 45 r. p. m. Hydrochloric acid entered and left the apparatus through hollow axles. A manhole which could be tightly closed was used for loading and unloading the seeds. A water pump drew the hydrochloric acid from the generating flask through the drum. A Tischenko flask between the drum and the pump served to regulate the flow of gas. Delinting was carried out by brushing with a rough brush, and the lint was separated from the denuded seeds by screening. The yield of lint was 7.8 to 10.5 per cent of the weight of the seeds (Table IV).
ANALYSISOF RAW LINT Lint obtained after the separation of seeds was immediately washed with water to neutral reaction and dried first in air, then in an oven at 50" to 60" C. to an air-dry state. The samples of lints N1, N z , Na were then analyzed. The product examined visually contained some admixture of hull, especially Nz. In the raw product, moisture, copper number, baryta resistance, and loss of weight in boiling in 7.14 per cent solution of sodium hydroxide were determined. Lynch (23) indicates the importance of degree of division of cellulose in alkali treatment. His data are shown in Table V. TABLEV. EFFECTOF FINE DIVISIONON SOLUBILITY OF aCELLULOSE IN COLD AND HOTSODIUM HYDROXIDE (According to Lynch, 2'3) ~SOLEBILITYIn cold In hot DIFFERENC~ 17.5% 7.14% IN SAMPLE PULP0 a-CmLLuLom NaOH NaOH SOLEBILITY % % % % 1 Cotton 98.6 1.5 1.8 0.3 2 Cotton cut with shears 2.1 98.4 1.6 0.5 2.1 3 Cotton: ground in mill 97.9 4.7 2.6 4 Lintera 99.4 0.6 2.3 1.7 0.7 5 Linters. cut with shears 99.3 2.4 1.7 6 Linters, ground in mill 99.1 0.9 3.5 2.6 a AU cotton and linters samples were from same Iota of materials, respectively.
For a comparison with the products made in this laboratory, a sample of hydrocellulose was prepared by Girard's method (24) by treating cellulose with 3 per cent sulfuric acid for 3 hours a t 70" C. The material was then wrung out and dried a t 50" to 60' C. Such hydrocellulose may be used for acetylation (36), though it is not a good raw material since the acetate made from it has a low viscosity
578
INDUSTRIAL AND ENGINEERING CHEMISTRY
in organic solvents and yields brittle films (19). The raw material of this hydrocellulose was third-grade linters which were obtained from the oil mill a t Kanncha and carefully washed (sample N4). The analyses reported in Table V I have been calculated to the dry basis. The copper number of the lint increases in direct proportion to the degree of treatment with hydrochloric acid, the number being considerably greater for the product N3 than for the other samples.
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(28). The same results were obtained by Galperin and Tumarkin in an investigation of the chemical properties and viscosities of cotton linters from different regions of U. S. S. R. (16).
I n the work of Birtwell, Clibbens, and Geake on the properties of hydrocellulose (6) the writers show the existence of a relation between tearing strength and viscosity of the 2 per cent cuprammonia solution of cellulose as determined by the method of Farrow and Neale (11). TABLEVI. CONSTANTS OF LINT REMOVED FROM COTTONSEED The viscosity is a measure of the micellar size of the celluBY GASEOUS HYDROCHLORIC ACID lose. It has been shown that the micellre of cotton celluSUM OF lose are in general larger than those of wood cellulose (19). BARYTA REThe presence of hydrocellulose or oxycellulose can confuse B A R Y T A SOLY. I N HOT IIBTANCE A N D COPPEB RESIST7.14% SOLY. I N 7.14% this relation. A low viscosity may be due to a mixture of LINT MOI~TURE No. ANCE NaOH NaOH high viscosity of the fiber interior and low viscosity of the % % % % .. 8.29 1.33 90.5 N1 superficial portion of the fiber due to treatment. The vis21.34 111.39 6.12 1.91 82.72 N2 32.05 114.77 cosity does not necessarily indicate the alpha-cellulose conN3 5.62 4.10 77.35 45.03 122.38 N4' 6.12 1.41 91.2 18.12 109.37 tent, because some treatments, such as mercerization, can Girsrd's hydrocellulose from washed linters. increase the alpha-cellulose content and lower the viscosity. Treatment a t high temperature or with acid lowers the visAccording to the literature (7) a hydrocellulose with a cosity (29). To obtain low-viscosity cellulose, one heats copper number (determined by Braidy's method) higher cellulose to 80-85' C. with 0.5 per cent sulfuric acid (16). than 1.5 should have a high solubility in alkalies. The copper It is known that for different cellulose compounds used for number of products N2 and N3 is higher than that of hydro- the manufacture of artificial silk, smokeless powder, laccellulose N4, the solubility in 7.14 per cent sodium hydroxide quer, etc., viscosity in certain solvents is one of the most is higher, and the baryta resistance is lower. Lint N1 agrees important properties, and the related cuprammonia viscosity fairly well with the hydrocellulose, particularly if allowance is made a specification of bleached linters used in the prepais made for the increased solubility due to its fine division ration of the cellulose compounds. Many writers have tried to find a relation between the (,??3), but its copper number is lower. In all cases the sum of the baryta resistance and the solubility in 7.14 per cent viscosity and the chemical constants of cellulose by which sodium hydroxide is more than 100 per cent, which is easy control testing of cellulose and its derivatives could be simto understand in view of the h e division of the product plified. Thus Ost, investigating the viscosity and copper number of celluloses, came to the conclusion that there was (Table V) and the previous treatment with alkali (24). no relation between them (87). Nikitin says that there is a certain relation which holds for celluloses of the same oriTHEORETICAL BASESOF CONSTANTS SELECTED FOR gin but does not hold for celluloses from different sources on DESCRIBING PRODUCTS account of differences in their micellar sizes. For example, I n the purified materials, moisture, alpha-cellulose, copper the following results were obtained for fir cellulose on sulfite number, and viscosity were determined. The alpha-cellulose cooking (84): determination is essentially a random test since not only CVPRAMMONlA COPPER No. the hemicelluloses, pentosans, and hexosans, but also some VISCOSITY (STADD AND GRAY) 233 1.5 of the cellulose itself, are dissolved, Nevertheless, experience 183 1.65 has shown that the capacity of the cellulose to be esterzed, 170 1.66 1.75 145 etc., is well indicated by the alpha-cellulose determination. 2.05 90 The copper number may be an indication of the effect of The investigation of another variety of iir by the present acid on cotton; the extent of degradation of hydrocellulose prepared in the usual way may be judged by the copper author gave these figures (4): numbers. Birtwell, Clibbens, and Geake studied the proper16 3.045 ties of hydrocellulose prepared by the action of acids on cot84 1.446 ton. Their data show that the copper number (Braidy Rogovin (31) thinks that such a dependence is improbable, method) increases by 50 per cent when the time of treatment is doubled. Between 20' and 100' C. the copper number since the copper number is not a sufficiently reliable index increases by 2.3 for every 10' C . rise in temperature. From of the disaggregation of cellulose, and its variations depend these rules they were able to compute with satisfactory ac- largely both on the character of the reagents with which curacy the copper numbers of hydrocelluloses prepared by the cellulose has been treated and on the conditions of the treatment of cotton with hydrochloric or sulfuric acid a t copper number determinations itself. I n fact, many invarious concentrations, times, and temperatures (6). The vestigators doubt that the copper number is worth deterviscosity of cellulose has been made the subject of a number mining (SO). The present author holds that, if cellulose is treated by of works. According to Small (99) and Hahn and Bradshaw ( l 7 ) , American factories have established viscosity deter- some definite method, a connection may exist between visminations as important tests of the quality of cellulose. cosity and copper number. This is confirmed by the work Purely chemical tests do not always allow conclusions to be of Birtwell, Clibbens, and Geake, where the problem is disdrawn about the technical value of material studied. For cussed in detail for their hydrocelluloses made from cotton instance, the present authors were unable to draw conclu- yarn and fabric by two methods. I n the one method the sions from their examination of the chemical composition material was immersed in acid solutions, washed in distilled of Turkestan cottons from different regions and hybrid water, and wrung in a centrifuge until i t was airdry. I n cottons (4) because the chemical compositions were very the other method the cotton fabric was washed with a large similar. The viscosities were different, however, and the amount of acid solution and wrung between India rubber varieties with the higher viscosities had better properties rolls to a double air-dry weight, dried overnight in air, and
May, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
heated in an electric oven a t different temperatures for different times. Results on seventy hydrocelluloses prepared with acid concentrations of 0.05 to 700 grams per liter, temperatures of 20" to 100" C., and times of treatment of 0.25 to 960 hours showed a relation between tearing strength and viscosity and also a relation between copper number and tearing strength. The loss of 10 per cent of the strength corresponds to an increase of copper number by Braidy's method of 0.25, and the loss of 80 per cent of the strength raises the copper number 3.5. As the test shows, the change of the copper number is more evident in acid digestion when the loss in strength lies between 50 and 100 per cent, whereas viscosity changes more rapidly in the earlier stages of the treatment when the loss in strength does not exceed 20 per cent (6). This fact emphasizes once more the importance of the viscosity determination in printing works where the loss in strength of the cloth after several chemical treatments is within the above range. The author has found that, in spite of the most diverse conditions of manufacture, there is a definite correlation between viscosity and copper number which can be formulated by the equation Arcu V* = 2.6
where
Ncu = copper number V = logarithm of relative viscosity = log q/qo
where
hydroxide solubility has been determined, as this test is much used by nitrators of cellulose (23). This test often yields results corresponding to alpha-cellulose content but frequently the sum of the alpha-cellulose and sodium hydroxide-soluble material exceeds 100 per cent (29). High solubility in 7.14 per cent sodium hydroxide is accompanied by high copper number, though alpha-cellulose also may be high; that is, cotton or wood cellulose with high alphacellulose content may yield hydro- or oxycellulose having high solubility in 7.14 per cent sodium hydroxide and high copper number without a fundamental change in the alphacellulose (29).
ANALYSISOF BLEACHED LINT For purification of the lint and Girard hydrocellulose the American standard method (18) was used, which had been utilized previously in this laboratory for the purification of cotton (g8). For the sake of comparison, several samples of cotton were subjected to the same purification and investigated. TABLEVII. RESULTSOF ANALYSEBOF REFINEDLINTS VIECOSITY OF: 0.5% 1% CUcupram- pramO N RE- a-CmL- COPPBRmonia monia EXPT. PULP F I N I N Q ~LULOBE No. soln. 8oln.b 7" 7" 5,7" qr, .1 Lint N1 67.14 96.4 0.33 11.9 23.7 2 Lint N 3 51.5 89.32 1.86 8.84 3 Girard'a hydrocellulose 74.8 89.1 0.38 13.4 4 American bleached cellulose from cottonseed 55.68 hullsc 6 Bleached lint obtained from hulls by boiling 98.07 0.16 in alkalid 33.4 6 Same a6 5C,d 97.4 0.37 7 Cotton, Navrotsky ... 88.25 99.21 0.115 166 variety 8 "Pima" Egyptian longstaple, specimen 94.9' 99.23 0.088 361 N180 9 Same as 8, specimen N190 93.2 99.35 0.088 299 10 Guza cotton, common blend 92.4 99.11 0.089 346 0 According t o American standard method (18). b Viscosity of solvent, 6.1 8ec. e Method of refining these samplea unknown. d Viscosity determined by method of Moscow Institute for Artificial Fiber: sample N4, 115.8; sample N5, 65. YIELD
I-
q ~0
absolute viscosity of 2% cuprammonia soh. of cellulose by Farrow and Neale's method, poises = abs. viscosit of Schweitzer's reagent, a constant the logarit%m of which is -1.82. Therefore, V = log q 1.82
=
+
For hydrocelluloses with copper numbers between 0.4 and 3, the product N c u P is fairly constant, the average value for forty-two preparations being 2.6. When the copper number is greater than 3, the product becomes less than 2.6. This is not very important industrially since the copper number of 3 corresponds to a loss in strength of 15 to 75 per cent. The relation above holds only for hydrocelluloses. For oxycelluloses prepared with hypochlorous or chromic acid on the same material, the product NcuVz lies between 4 and 5.5. The above relation appears as a possible way of distinguishing oxycellulose from hydrocellulose, although the constancy of the relation is to some extent approximate. When hydrocellulose is prepared by wringing material soaked in acid and subsequently drying it, the above relation between copper number and viscosity holds, provided that the temperature of preparation has not been above 70" C. The accuracy is somewhat less, because of the difficulties of preparing entirely uniform material by this method. However, if the temperature has been above 70" C., the relation N C U Vis no longer a constant. The above considerations show the value of the copper numbers and viscosities as a means of identifying hydrocellulose in a comparatively simple and exact way. I n describing the lint stock, the author used instead of alpha-cellulose the baryta resistance and solubility in 7.14 per cent sodium hydroxide for the reason mentioned above. According to Nikitin, barium hydroxide a t the boiling point extracts from cellulose only the products of decomposition, leaving the cellulose itself unchanged. Cotton of 98 per cent alpha-cellulose has a baryta resistance of 97 per cent. Moreover, experience has shown that the baryta resistance can be used as an index of the qualities of technical cellulose. For celluloses containing oxy- and hydrocelluloses, the difference between alpha-cellulose and baryta resistance increases, especially if the cellulose has not undergone alkaline treatment. For this reason the 7.14 per cent sodium
579
.-
.. .
...
... ... ... ...
... ...
... ...
...
... ...
Since lint is much lower in viscosity than cotton, there was taken for closer comparison an American cellulose prepared from cottonseed hulls and two samples of linters, from the Moscow Institute for Artificial Cellulose, obtained from hulls by means of boiling in alkali. The American hull cellulose had the appearance of thin bleached cardboard. The samples from Moscow were also bleached pressed material with short-staple fibers, which produced a little dust when rubbed. The results are recorded in Table VII. The yield of purified lint N 1 is nearly 70 per cent compared with 90 to 93 per cent for cotton, which is quite acceptable. It must be noted, however, that the lint was not sufficiently purified; even the color was not quite white, especially in the case of N3. The constants are typical of the degree of refining. One more boiling with rosin soap was originally planned, but this was not carried out since it could scarcely raise the viscosity markedly, and prolonged treatment is uneconomical industrially. Alpha-cellulose figurea show that cotton is well purified by this treatment. The copper number of the lint was much reduced from that of the raw lint, as it should have been (7, I S ) . The absolute value of the copper number is quite acceptable from the production point of view. Thus, for artificial silk, cellulose having copper numbers as high as 2.5 may be used (IS). The constants of the Girard hydrocellulose indicate that this
5 80
INDUSTRIAL AND ENGINEERING CH-EMISTRY
material is similar to lint N 3 except for the copper number, even though a good yield was obtained after boiling in rosin soap. The low yield of the lint can no doubt be accounted for in part by its fine state of division. The low viscosity of the Girard hydrocellulose casts doubt on the suitability of hydrocellulose so prepared for acetylations, which is advised by Zhirmundsky (36). The viscosity of the lint is very low. A significant formation of hydrocellulose seems to have occurred, but alphacellulose content in lint K1 permits the assumption that this product can be used industrially. The viscosity of several cotton varieties shown in Table VI1 tends to decrease as the tearing strength falls off. According to the data of the technological laboratory of the Cotton Trust, samples N180 and XI90 have tearing strengths 47.84 and 41.38 kg./per mm., respectively. Data for the other samples were unfortunately not available. It is hard to believe that the Navrotsky variety of cotton widely cultivated in Middle Asia is as poor compared to other cottons as its viscosity would indicate. It is probable that the sample tested was not representative.
Vol. 25, NO.5
From the viscosity of the lint, i t would seem most suitable for preparation of lacquers for metals in the manufacture of which nitrocellulose of minimum viscosity is used, since as much as 15 per cent of it is put into the lacquer. The greatest defect of such lacquers-their brittleness-is avoided by the addition of vulcanized oils (2). I n America, where linters viscosities range between 3 and 1000 seconds by the American standard method, linters of the lowest viscosity are used for making nitrocellulose for lacquers. An exact comparison of the present method and the American standard method is difficult on account of different concentrations of copper, ammonia, and cellulose in the solutions used, and also because the American method uses the falling sphere while that used here is an outflow method ( I ) . The question of the fitness of the lint for nitration will be intensively studied. The principal objection to nitrating highly degraded cellulose is the solution of the material in the nitrating acid which leads to low yields of nitrocellulose and contamination of the acid (16). Assuming that the lint is waste and that, according to Galperin and Tumarkin, cotton having a viscosity greater than 8 can be nitrated by the American method, it is thought that TABLEVIII. RESULTSOF ANALYSESOF HYDROCELLELOSERO the question must interest the scientific and research orFROM STANDARD YARNN70 ganizations of industry. LOQOF As for artificial silk, hydrocellulose of such properties as VISGOGOF COSITY I N K.ELAlint is hardly to be used, since the low viscosity usually indiCUPRAMTIVE VIScates a thread with reduced firmness (19). It may become MOmA COSITY, PREPARA-HzSO4 DURACOPPER SOLN ? - v PRODECT possible to improve the delinting method so as not to reduce TION CONCN. TION TEMP.NO.,Ncu Log ; - A'cuV~ the viscosity so much. It may also be possible to apply the Qroms/liter Hours C. 200 24 20 0.31 present product for such purposes as acetate lacquers, etc., St 1B 0.91 2.76 2.4 0.36 2.59 2.4 100 96 20 0.77 S t 12 since it is known that hydrocellulose acetylates more readily 50 24 20 1.76 1.38 1.20 2.5 St 23 1.74 1.19 2.5 4.9 1 100 1.37 S 14 than cellulose (86). 24 40 1.95 1.19 2.8 S 4A 200 1.37 Germination tests of delinted seeds were carried out by Obtained by acid treatment under various conditions, according to the controlling Seed Department of the Chemical Trust. Birtwell, Clibbens, and Geake. The best results were had with seeds that were not neuComparing the relation of. copper number to viscosity tralized but merely washed in water for 30 minutes. The for lint with data from Birtwell, Clibbens, and Geake (Table number germinated was the same as with pubescent seeds VIII), we see that, for two hydrocelluloses having copper and the germination energy was raised, since the denuded numbers equal to those of lints N 1 and N3, the ratio of the seeds sprouted earlier than the pubescent ones. Seeds delogarithms of relative viscosity is 2.67:1.2 = 2.2. For the linted a t temperatures above 60" C. had lowered germina11 9 8 84 tion (Table IX). lints we have log = 0.29 and log % = 0.161 (where viscosity of solvent = 6.1); therefore 0.29:0.161 = 1.8. TABLEIX. EFFECTOF TREATMENT AFTER DELINTING ON The agreement between 2.2 for hydrocellulose and 1.8 for GERMINATION OF DENUDED COTTONSEEDS lint is considered satisfactory when the errors of computa(At 23' C., continuous flow of hydrochloric acid gas) tion and of determination of viscosity by the different methods GERWIN.4- GERMINATION TREATMENT OF are considered. On account of the small number of experiEXPT.DURATION SEEDSAFTER DELINTING TION ENERGY ments run, the only conclusion to be drawn is that the lint Min. is hydrocellulose. An analogous comparison of lint N l and 1 30 Ammoniacal neutralization 42 21 Lime neutralization 4s 32 the Girard hydrocellulose tested is not drawn, because it Washing in water 81 74 Seeds not treated 57 47 has not much significance, since the starting materials were 2 20 Ammoniacal neutralization 42 31 different. It is hoped that the above-mentioned relation Lime neutralization 43 31 between copper number and viscosity will be substantiated Washing in water 85 75 Seeds not treated 58 48 by further experiments, because the methods of investigation Av. sample from seeds 84 52 and of analysis would be much simplified. For preparation of cellulose esters, raw material with high alpha-cellulose content is usually used; with wood cellulose METHODS OF ANALYSIS' the alpha-cellulose content should be 85 to 90 per cent (13), All data are referred to bone-dry materials. Determinaand with cotton not less than 98 per cent (16), but in America technically resistant nitrocellulose has been prepared from tions were run in duplicate and the averages put into the wood cellulose as well as from cellulose of other origin con- tables. Differences between duplicates did not exceed 1 to 2 per cent except for viscosities and high copper numbers, taining 80 or even 60 per cent alpha-cellulose (8). As seen from Table VII, the viscosities of lint, Girard where differences up to 5 per cent were encountered. The hydrocellulose, American hull cellulose, and cellulose pre- methods used were as follows: pared from hulls by boiling in alkali a t the Institute for Moistures were run in a Sha oshnikov apparatus. Artificial Fiber are values of the same order. The viscosity Water extracts were obtainet by stirring one gram of lint in of the cotton varies in a wide range, as in the Navrotsky 100 cc. of distilled water for 4 hours. and Guza varieties, but according to Galperin and Tumarkin Glucose in water extract was obtained by Max Mulier's method (56). (16) this is not important industrially. 0
~
Technical cellulose waa obtained by boiling in 2 per cent sodium hydroxide for 4 houm (17). Baryta resist.:mce was determined by the method of Schwalbe and Uecker (34). Alphn-cellulose was dotermined according to Buhek (34). The 7.14 ner rent sodium hvdroxide-soluble material was determined secoiding to Lynch (&). Copper number was deternrincd by the Braidy method @8). Viscosity N&S determined rtccording to Nikitm (26). The cuprrtmmonia solution contained 175 grnms pet liter of ammoni%, 12.5 prams per liter of capper, and less than 0.5 ~ m r per i liter of nitrous acid. The determiiiation was run a? 2 1 . 2 " C. CaNcLnsIoxs In ddinting cottonseeds by the gaseous hydrochloric acid process, complete removal of t.lie lint is accomplislied with hydrociiloric acid in qiiantity equal t o 2 per cent of the weight of the seed. The moisture present in the seeds, 7 to 10 per cent, is siificicnt. for carrying out the treatment. The treatnicrit of the seeds with g~seoushydrochloric acid under mild conditions, with subsequent renroval of the lint and washing of t.he seeds in water, does not ctiange their germination and increases the germination enerby. On the basis of seed germination, the optimum tenrperature is not above 60" C. Higher temperatures injure both the lint and the seeds. Using continuous flow of hydrochloric acid, from 15 t o 30 minutes are suficient at 20' and 7 minutes a t 40" to BO" C. for rendering tlie liut easily removable under tlie experimental conditions. The lint after treatment wit11 hydrocliloric acid is easily removed by brushing. It represents cellulose which is considerably degraded. Owing to its low viscosity, it may possibly be applied in the manufacture of Lacquers for metals. The poorest product may be used for alcohol production by hydrolysis and fermentatiori. A further study of the procedure is needed to stndy the use of the lint in esterification.
I,ITERATL'~E CITBD (in Xussiaii), No. 10, SA (1930). ( 2 ) Anonymous. J . Applied CbemislTw (in Ruasim), 4, l o . 1. l2U (1931). (3) Anonymous, . I , Chcm. I n d . (Moscow), Io. l l ~ - l 2 ,1141 (1931). (1) Anonymous, J . Arliricial Pilier
Rair. .J. E.. U . 8. Dept. Agr.. Bd1. 1219 (1924). Birtwell. CXilrbens, and Genke. J . 'lirtile Inst.. 17, 148 (1926). Zbid.. 19, 357 (1928). Ilmwn. J. G.. and Gibson. Fr'roderick, Uniu. &is. Agr. Expt. Sta.. Bull. 105 (1925). I>ynzliav, F. S..J . Coltoa Ind. (in Rusdan). No. 7-8, 56 (1922). Dvnrbev. I?. S..Trans. 1 s t Ai!-Llnion C o d . Enors. arid Teeh-
dmtcs;' p. 188 (Iaa2). Freibergor, h.1.. Vasa. 2.yon. and lihnig, I,.,J . .Sm I i ~ a i C'olows ids, 46, 111 (1930). Galnorin, D., and Tumorkin, I>., J . A m l i e d C6am (in Ihsaisn). 5;No. 1. a2 (1932). Galperin, D., &nilTumsrkin, I I . , J . ArIL.ficCai P'
