INDUSTRIAL AND ENGINEERING CHEMISTRY
218
grams of extracted tissues mixed with filter aid and fragments of filter paper. After the ascorbic acid was stirred into the residue, the extractant was added and the suspension was placed in the Blendor. The procedure was then the same as described for the extraction of fresh material. The degree of completeness of extraction of added ascorbic acid was similar t o that of the first extraction of naturally occurring ascorbic acid. The total percentage recovered varied from 90 to 101 per cent. Boiled cabbage tissue residue gave about the same percentage recovery of added ascorbic acid as the unboiled residue. A recovery of 99 per cent was made when ascorbic acid was added t o t h e extractant containing
Vol. 34, No. 2
no plant tissue and the motor was run a t high speed for 10 minutes. Much time and effort may be saved by this procedure, because a large number of workers have been making the ascorbic acid assay by the chemical method.
Literature Cited (1) Ballentine, R.8 1x0. ENG.CHEM.9 ANAL.ED.,13, 89 (1941). (2) Davis, W. B.,IND. ENG.CHEM.,NEWSED., 17, 752 (1939). (3) King, C. G., IND.ENG.CHEX.,ANAL.ED.,13, 228 (1941). (4) Menaker, M. H., and Guerrant, N. B., Ibid., 10, 25 (1938). ( 5 ) Thornton, N. C.,Contrib. Boyce Thompson Inst , 9,273 (1938). CovTRiBuTroN 37 f r o m t h e Division of Agricultural
Chomioal Research.
Effect of Reinforcing Pigments on Rubber Hydrocarbon F. S. THORNHILL AND W. R. SMITH Godfrey L. Cabot, Iiic., Boston, Mass.
The unsaturation values and amount of combined sulfur at various states of vulcanization for a number of rubber compounds have been studied. While the anticipated loss in unsaturation of the rubber hydrocarbonwas noted in stocks containing nonreinforcing fillers, no such loss in unsaturation could be detected in rubber compounds containing reinforcing channel blacks. It is suggested that this alteration in the mechanism of sulfur vulcanization may be mostly responsible for the physical characteristics of reinforced rubber stocks. It has not been possible to detect any effect of carbon black on the unsaturation value of natural rubber. Calculation indicates that, while such an effect would not be detected in the present case with the analytical method employed, such an effect, if present, should be detectable with carbon blacks of greater surface area than those employed in the present investigation.
EVERAL investigators (20)have established that sulfur
S
vulcanization of rubber involves chemical combination of sulfur and rubber hydrocarbon. A definite decrease in unsaturation of the rubber hydrocarbon as vulcanization progresses has been generally noted (S, 10, 18). While it has often been concluded that a double bond is saturated for each atomic equivalent of combined sulfur (10, 18), recent work by Brown and Hauser (3, 7 ) demonstrates that this conclusion cannot be applied in all cases. I n certain compounds they found the loss in unsaturation with extent of vulcanization to be considerably less than anticipated on the above basis. Their results indicated that stocks reaching optimum cure with the least loss of unsaturation possessed the greatest tensile strength. Although a considerable amount of work has been done on this problem, we have not found a published account of simi-
lar investigations performed on stocks containing significant loadings of reinforcing fillers. Since, as pointed out below, the nature of the bonding between such fillers and the rubber molecule has not been clearly defined, one is not justified in applying previous results obtained on stocks containing no reinforcing fillers t o those bearing appreciable loadings of such substances. Accordingly one portion of the present investigation was concerned with determining the effect of various. fillers on the course of sulfur vulcanization, as judged from combined sulfur and unsaturatioii values. Aa pointed out by Gehman and Field (S), it is undoubtedly true that the black particle in a carbon-black-reinforced rubber stock is firmly attached to the rubber molecule. The nature of the bonding between the black and rubber has not been clearly defined. Some investigators (4, 8, 14, 17) maintain that the association is physical and involves dcfinitc forces of adhesion or adsorption; othcrs ( I S ) have suggested formation of primary valence linkages with the rubber hydrocarbon. The opinion of the present autho& is that if such linkages are formed, the ethylenic bonds of the rubber molecule would probably beinvolved. If this latter view is correct, then a specific loss in unsaturation of the rubber hydrocarbon, due to the reinforcing filler, should occur. Thus the second objective of the present study was to determine whether it was possible by chemical means t o detect such a linkage. If measurable, this effect, together with the surface area determinations reported previously (15), would be particularly valuable in estimating the reinforcing value of various fillers.
Experimental Procedure The unsaturation of the rubber stocks was determined b y addition of iodine chloride. The procedure followed was essentially Kemp’s technique (9, 11) as modified by Blake and Bruce ( 9 ) : A 0.1-gram sample of stock was dissolved in boiling p-dichlorobenzene. This usually required from 2 to 3 hours. Solution became more difficult with well cured compounds. This was over
-
February, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
219
This village built for carbon plant employees of the Cabot Company at Kermit is located in arid, sparsely populated West Texas. Accordingly it wasnecessary forthe company tobuild acompletevillagefor the plant employees. Thousands of tons of top soil were imported to make possible the lawns and growing trees.
come by freezing the sample with solid carbon dioxide and sectioning on a microtome. These finely shaved sections dissolved readily and no further difficulty was encountered. When the sample had dissolved, it was allowed to cool and was then taken up in carbon disulfide and further cooled to 0" C. Twenty-five cubic centimeters of 0.2 N iodine chloride were then added, and the reaction was allowed to progress for 2 hours at 0' C. Ten cubic centimeters of 1.2 N potassium iodine and 25 cc. of ethanol were added and the iodine liberated from the excess iodine chloridewastitrated with 0.1 N sodium thiosulfate. A blank was run, and from the difference the amount of iodine chloride combined was calculated. Kemp (10) showed that cyrbon black, glue, cellulose, and inorganic compounding ingredients have no effect on the determination. In agreement with Kemp (10) we found that, while a reinforcing channel black removes about 11 per cent iodine chloride from a 0.2 N solution, it is only physically adsorbed, as evidenced by the fact that the entire 11per cent could be titrated back with sodium thiosulfate. The other pigments emplo ed were similarly shown to be chemically inert toward io&e chloride. The fillers employed in the present investigation included a standard rubber-reinforcing channel black with a surface area of 110 A12 per gram, a German reinforcing black (CK-3) with a surface of 98 M a er gram, and kaolin with a surface of 20 M 2 per gram. A singk supply of wmhed pale crepe was used throu hout the entire invest1 ation. Combined sulfur was determined%y first extracting the free sulfur with acetone and then oxidizing the extracted stock with concentrated nitric acid and potassium chlorate, according to A. S. T. M. procedure D 297 (1): The combined sulfur was precipitated and weighed as barium sulfate. The rubber stocks were mixed on a 12-inch (30.5-cm) laboratory open mill a t 140" F. (00"C.). After 3 hours of coolin they were remilled and, with the exception of the 10 per cent suffur stocks, cured a t 274" F. (134.4' C.) on a laboratory steampress. The 10 er cent sulfur stocks were qured at 300' F. (148.9 C.). %e iodine values reported in Table I are based on 100 grams of rubber. The per cent unsaturation was calculated by comparison with the value 372.8 rams of iodine added per 100 grams of ure rubber hydrocarbon f2, 11). The iodine values reported in 8able I11 for the compounded stocks are as determined per 100 grams of compound. From the known composition of the stocks,
the iodine value per 100 rams of rubber was computed and the per cent unsaturation cafculated by comparison with the value 372.8.
TABLEI. UNSATURATION OF NATURAL AND SYNTHETIC RUBBERS Gram Iodine/100 Grams Rubber CrHs (theoretical) Pale crepe Pale crepe milled) Pale crepe {cold-extracted) Smoked sheet
372.8 359 359 367 357
Hycar OR Vistanex
191
Per Cent Unsaturatiori 100 96.3 96.3
98.3 95.7
2.5
Results Table I contains unsaturation values for the pale crepe employed in the present investigation, which are in agreement with previously reported values (2, 9, 11). The nearly complete saturation of Vistanex is in agreement with its recognized resistance t o deterioration, as well as its inability to vulcanize with sulfur (1.2, 16). Similarly the lower unsaturation value for Hycar OR is in agreement with its compounding properties (6). Table I1 describes the rubber compounds employed in the present investigation. All recipes are described on a weight basis. The data collected are presented in Tables I11 and IV. Compound A,consisting simply of 100 parts by weight of pale crepe and 45 parts by weight of black, shows no significant alteration in unsaturation on heating at 274" F. for the times indicated. Compound C, consisting of 3 parts of sulfur and
220
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 34, No. 2
( L e f t ) Residue gas, the raw materia1 for carbon black, is collected from various wells in the oil field and conducted to the plant b y pipe line. (Below) Inside the “hot house”, blaclrproducing flames are shown impinging on collecting channels. (Lower L e f t ) The carbon black is conveyed from the hot house by screw- conveyors to these centrifugal separators. The light fluffy black spirals upward; the denser foreign material descends and is collected at the bottom of the separator.
I N D U S T R IBA L
Yebruary, 1942
HEMISTRY
100 of pale crepe, shows a definite loss in unsaturation with time of cure. As Figure 1 shows', this loss in unsaturation is accompanied by a n increase in the amount of combined sulfur. However, the loss in unsaturation is considerably greater than can be accounted for by assuming that one sulfur atom satu\rates a single double bond. I n this low sulfur compound only .about 12 per cent of the available sulfur has combined a t the longest cure. I n order to study the relationship a t concentrations of combined sulfur approaching those encountered i n commercial tread stocks, compound E was prepared containing 10 parts of sulfur to 100 of rubber. The results for cures up to 120 minutes are presented graphically in Figure 2. I n this case nearly 50 per cent of the total sulfur has combined in 120 minutes a t 300" F. The data indicate one sulfur atom saturating between one and two double bonds. The next compound studied, I, was a typical accelerated tread stock recipe with the usual 45 parts of reinforcing agent omitted. It was cured for 30, 60, and 90 minutes. After a 60-minute cure, over 90 per cent of the sulfur has combined and the unsaturation drops rapidly (Figure 3). Hauser and Brown (7) noted this loss in unsaturation after most of the sulfur in the stock had combined. They suggest that it may be due to polymerization of the rubber. Our data on compound A indicate that on prolonged heating some loss of unsaturation of rubber may occur in the absence of sulfur. The effect, however, is small and may not be real. I n any case it is too slight to account for the anomalous drop in unsaturation on overcure, shown by sulfur-bearing compound I. This, however, does not mean that the possibility of extended polymerization on overcure in sulfur-bearing stocks is excluded, since the presence of a definite amount of combined sulfur may be essential for the initiation of such a reaction.
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TABLE 11. COMPOUNDS INVESTIGATED Pale crepe Zinc oxide Bulfur Pine tar Captax Gtearic acid Agerite Hipar Filler Channelblack Kaolin CK-3 black
A B C 100 100 100
D E F G H I 100 100 100 100 100 100
J 100
.................. 5 5 5 5 ... .. .. .. .. ..3.. .. ..3.. .. .10 . .. .. .10 . .. .. ..10.. 0 . 933 0.933 0.933 0.933 .................. 4 4 4 4 .................. 1 1 1 1 45 45 ... 45 . . . . . . 45 . . . . . . . . . . . . . . . . . . . . . . . . 45 ... 45 . . . . . . ........................... 45
Before the sudden drop of unsaturation on overcure, the data for compound I indicate a loss of somewhat less than one double bond for every atom of combined sulfur. To certain of the above compounds various fillers were added, as shown in Table 11. Unsaturation and amount of combined sulfur were again determined for various times of cure, as recorded in Tables 111and IV. From Figure 1 it is evident that the addition of 45 parts of channel black to compound C has not greatly altered the unsaturation-combined sulfur ratio. [The accelerating effect of carbon black on cure, as pointed out by Wiegand (IO),is evident in compounds B and C . Compound G, on the other hand, shows the familiar retarding effect experienced with stocks containing added organic accelerators. ] The amounts of combined sulfur found in compound B were only B tenth those normally found for similar cures in accelerated tread stock compounds. Accordingly compound D was prepared with 10 parts of sulfur in order t o obtain com1 I n Figures 1 through 5, the curves are all displaced slightly so that the per cent unsaturrttion for the uncured stock is 100 per cent in each case. The deviations from this value, shown in the complete data in Table.111. are due t o experimental errors in compounding and analysls.
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VALUESFOR FIQURES 1 TO 5. UNSATURATION THE VARIOUS COMPOUNDS
parisons with accelerated compounds a t about equal concentrations of combined sulfur. As Figure 2 shows a definite effect of the carbon black is now apparent. For a given amount of combined sulfur the black-bearing stock D shows considerably less loss in unsaturation than the pure gum stock E.
222
Vol. 34, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
indicated in Figure 3 for the 30-minute cure is probably experimental error, since no further A B C D E decrease could be detected with increasing Time of Cure, 12 % I2 % I2 % I2 % I2 % amounts of combined sulfur. The method Min. value unsatn. value unsatn. value unsatn. value unsatn. value unsatn. of manufacture and raw material used in the 0 258 100 257 101.8 360 237 99.0 335 99 preparation of these two reinforcing carbon 20 ... . . . . . . . . . . . . 99.5 . . . . . . . . . . . . . 30 260 101 . . . . . . ... . . . . . . . . . . . . . blacks are quite different, yet their effect in 40 ... . . . . . . . . . ... GO 260 101 239 94.8 367 98:s 23i 94:s 307 90:6 preventing loss of unsaturation of the rubber 76 . . . . . . . . . ... stock on vulcanization is the same. Accordgo 233' 98.5 237 92.8 332 9i:o iii 9i:o ibi 8817 120 ... .., 234 9 2 . 5 343 94.8 212 88.2 290 85.5 ingly, this effect is not peculiar to channel F G H I J blacks prepared from natural gas but appears to be general for reinforcing pigments. 0 238.5 99.2 229 99.2 230 99.5 315 98.9 232 100.3 229 99.2 ... 20 ... . . . . . . . . . Various grades of channel blacks with dif30G 96:s 2i9 96' 30 ... ... 228 99.0 ... 99:2 40 ... ... , .. 229 fering processing and curing characteristics are GO 222 92.5 230 99.5 ... .. 302 94:s iii 99' 75 ... . . . . . . . . . 226 98 available to the rubber industry. The present 90 215 90.7 229 99.2 297 93:4 22i 99' investigation was extended t o include some 120 209 SG.S . . . . . . zis:; 93:o . . . . . . . . . . . of them. Detailed results are not included here since over the range of commercial rubber blacks studied no essential differences were The next stock studied was a typical accelerated tread noted from those obtained with the grade 6 black reported in stock, G, containing 45 parts of channel black. The results Table 111. are plotted in Figure 3, together with stock I from which the All the pigments so far studied exert a definite reinforcing black was omitted. The effect of reinforcing carbon black in effect in rubber, and in each case during vulcanization no real this compound is most striking. As Figure 3 shows, no sigloss in unsaturation was observed with increasing amounts of nificant loss in unsaturation of the carbon-black-bearing combined sulfur. I n order to observe whether this effect was stock could be detected over any of the cures studied. This characteristic only of reinforcing pigments, the latter experiis in striking contrast to compound I, which contains no rements were repeated with compounds F and H in which equal inforcing agent and which shows a marked drop in unsaturation loadings of kaolin were substituted for the reinforcing black. over the same range of cures. This range, as is evident from As Table V shows, kaolin has little reinforcing ability in the present compounds. I n Figure 4 the data for compound F Table V, includes all cures of technical significance. I n compound J, 45 parts of the German naphthalene black show that the loss of unsaturation with increasing amounts CK-3 were substituted for the channel black. As Table V of combined sulfur is unaltered by the presence of this pigment. The same conclusions apply to 45 parts of clay in a shows, CK-3 has compounding properties approaching those of American channel black. The slight drop in unsaturation typical tread stock (compound H) as shown in Figure 5 . Accordingly, the present data indicate that nonreinforcing fillers have little effect on the course of vulcanization, as judged from the combined sulfur-unsaturation values, in contrast with the marked effect of reinforcing fillers noted above. TABLE 111. UNSATURATION VALUES
TABLE IV. Time of Cure, A h . 20
30 40
GO 75 90 120
.4MOUN'T O F C O M B I N E D SULFUR AT VARIOUS OF CURE
Grams Combined Sulfur/100 Grams Rubber C D E F G H I J . . . . . . . . . . 0.71 . . . . . . . . . . 1:;3 2:oo 1165 1:25 o : i 4 o:io a : i i i:k7 1154 2 : i o _ . 2:73 2 : 4 i 2.48 0:42 0:25 3:4G 3:iZ 2 : i 3 2198 3102 2174 0.46 0.32 5.12 4.38 3.67 ,. 3:Ol ,. ,,
TABLEV.
B
STRESS-STRAIN DATAOF COMPOUNDS STUDIED
Compound
Cure, Min.
D
GO 90 120
r'
G
Carbon black storage silo with a capacity of 3,000,000 pounds
2400
2780
Hardness GO 63 66
610
680
850
120
670
870
50 52 54
30
4370
620 560 500
1990
63
2760
70 72
90
4500
4370 2210
3560 3380
660 670 650
90
3100 3440 3370
20 40 75
4070 4530 4360
20 40
75
J
hlodulus a t 400y0 Lb./Sq. Ih. 1800
630
60
I
Tensile Elongation a t Break, Strength % Lb./Sq. Ih. 3140 550 3880 540 3900 510
1780 2750 2920
GO
90 H
TIma
30
GO
2960
640 880
930
58
720 680 670
400 530
54
520
6G
650
1710 2500 2970
580 620
55
GO G5
68
February, 1942
INDUSTRIAL A N D ENGINEERING CHEMISTRY
223
Carbon black plant at Bowers, in the Texas Panhandle, with a capacity of 30,000,000 pounds a year
Association between Rubber and Carbon Black From the present data it has not been possible to detect any appreciable loss of unsaturation that could be attributed to association of carbon black at the double bonds of the rubber hydrocarbon. Yet there is some body of opinion to the effect that unsaturation is essential for reinforcement. These views are substantiated in part by the difference in physical behavior of reinforcing pigments in unsaturated natural and synthetic rubber, as contrasted with their behavior in saturated rubberlike polymers of the polyisobutylene (Vistanex) type (18). The argument can be raised that only a few chemical bonds, of the type suggested above, are essential for reinforcement. The net effect on the total unsaturation would thus be very slight and possibly beyond detection by the present chemical methods. This line of reasoning is somewhat substantiated by the following calculation: If the assumption is made that only those ethylenic linkages within 3 A. of the carbon black particle are able to form a true bond with the particle, then it can be shown that the total “saturating” effect of the carbon black is actually quite smal!. The average diameter of a reinforcing channel black is 300 A. Assuming the black particle t o be spherical and combination to occur only within 3 1.of the surface‘of the particle, then each carbon black particle will possess a “reactive volume” of 8.5 X lo6 cubic d. Since there are about 3.75 x 10’6 of the above particles per gram of carbon black, tbe total “reactive volume” per gram is 3.2 X loz2 cubic A. From a density of 0.93 for smoke sheet, the total volume of 2 grams of rubber is 2.15 X loz4cubic 1. Thus in a compound of 50 parts of black to 100 parts of rubber, only 1.5 per cent of the total rubber hydrocarbon is able to come within the required 3 1.“reaction distance” of the black particle. Therefore, according to this result, the maximum loss in unsaturation due to carbon black could not exceed 1.5 per cent in the compounds studied. This figure approaches the experimental error in our analytical technique. Accordingly, we must conclude from our data that if a chemical saturation of ethylenic linkages by carbon black does occur, it cannot invoke more than one or two double bonds out of every hundred.
According to the above interpretation, loss of unsaturation would be expected to increase with surface area of the black. Carbon blacks with surface areas considerably greater than those studied here are available (16). According to the above calculation a black with surface of 300 or 400 Ma per gram should, if the interpretation is correct, produce effects detectable by our present chemical means. Such experiments are now in progress.
Effect of Fillers on Vulcanization Reaction From Figures 4 and 5 it is evident that nonreinforcing fillers have no particular influence on the course of the vulcanization reaction. However, in the presence of reinforcing fillers, as shown in Figures 2 and 3, a marked influence is noted. This is particularly true in the latter case where we are dealing with accelerated tread stocks. The laboratory rubber tests on compounds G and 5 (Table V) show them to be well reinforced stocks, yet there is no significant loss in unsaturation with increasing extent of combined sulfur. The concentration of combined sulfur in these stocks is comparable with those of compound I from which filler was omitted and of compound H containing 45 parts of clay. These nonreinforced compounds, in contrast with those containing reinforcing pigments, show a marked loss in unsaturation as cure progresses. Compounds containing reinforcing pigments reach optimum cure with a minimum decrease in unsaturation. I n agreement with Hauser’s observation (S), they also show maximum stress-strain properties. The fact that the mechanism of rubber-sulfur combination during vulcanization appears to be markedly altered b y the presence of a reinforcing pigment suggests that some portion of the changes induced in rubber stocks by such pigments may be due to the initiation or enhancement of some particular type of sulfur-rubber linkage. Gehman and Field (6) have shown that there is a marked orientation of rubber molecules in the presence of reinforcing pigments. It may be t h a t as a consequence of this orientation certain portions of the rubber molecule are no longer available for reaction with sulfur, and consequently combination occurs at positions other
224
INDUSTRIAL AND ENGINEERING CHEMISTRY
than those involved in nonreinforced stocks where this orientation is less pronounced. The formation of this new type of rubber-sulfur linkage in the presence of reinforcing pigments may account for some of the characteristic properties of reinforced rubber stocks. At present we are not able to describe the nature of the sulfur-rubber combination induced by reinforcing pigments beyond the fact that they occur without loss of unsaturation of the rubber. While it is undoubtedly true that physical effects play an important role in reinforcement, the possibility that the course of the vulcanization process may be considerably altered by the presence of reinforcing pigments cannot be overlooked.
Acknowledgment We wish to thank Fred Amon for helpful advice and suggestions during the course of the investigation. We are also indebted to Almon Allard and Harold Offutt for the preparation and physical testing of the rubber stocks, and to Lotus Duerr for valuable aid in preparing the manuscript.
Vol. 34, No. 2
(4) Depew, H A., and Easley, >I. K., Ibicl., 26, 1157 (1934). (5) Garvey, B. S., Juve, A. E., and Sauser, D. E., I b i d , 33, 602 (1941). (6) (7) (8) (9) (10)
Gehman, S. D., and Field, J. F., Ibid., 32, 1401 (1940). Hauser, E. A., and Brown, J. R., Ibid., 31, 1225 (1939). Hock, L., and Schmidt, H., Rubber Chem. Tech., 7, 462 (1934). Kemp, A. R., IND.ENG.CHEM.,19,531 (1927). Kemp, A. R., Bishop, W. S., and Laokner, T. J., Ibid., 20, 427
(1925). (11) Kemp, A. R., and Mueller, G S., 1x1). EXG.CHmf., ANAL.ED., 6, 52 (1934). (12) Longman, S., Eubber Chem. Tech., 14, 356 (1941). (13) Naunton, W. J. S., and Waring, J. R. S., Trans. Inst. Rubber Ind., 14, 340 (1939). (14) Shepard, N. A., Street, J. N.. and Park, C. R., in Davis and Blake’s “Chemistry and Technology of Rubber”, A. C. 8. Monograph 74, pp. 408-9, Reinhold Pub. Corp., 1937. (16) Smith, W. R., Bray, R. I., and Thornhill, F. S., IND.ENO. CHEM., 33, 1303-7 (1941). (16) Sparks, W. J., et al., Ibid., 32, 731 (1940). (17) Spear, CoZZoid Symposicim Monograph, 1, 321 (1923). (18) Spenoe, D., and Scott, J. H., Ko[loid-Z., 8, 304 (1911). (19) Wiegand, W. B., and Snyder, J. W., Proe. Rubber Tech. Conf., London, 1938, 484.
Literature Cited
(20) Williams, Ira, in Davis and Blake’s “Chemistry and Technology of Rubber”, pp. 243-60 (1937).
(1) Am. SOC.Testing Materials, Standards, Part 111,p. 313 (1939). (2) Blake, J. T., and Bruce, P. L., IND. ENG.CHEM.,29, 866 (1937). (3) Brown, J. R., and Hauser, E. A., Ibid., 30, 129 (1938).
PRESENTED before the Division of Rubber Chemistry at the 102nd Meeting of the AVIRXOAN CREMICAL SOCIITY,Atlantic City, N. J.
Cellulose Content of Cotton and Southern Woods WEN-HSIEN WAN CHEN FRANK IC. CAMERON
AND
University of North Carolina, Chapel Hill, N. C .
w
X O L E cotton has been studied as a possible source of oil and cellulose adapted to commercial production. I n addition to the oil and alpha-cellulose there are present other celluloses, pentosans, lignin, waxes, proteins, colored products from the bark of stems and cusps, ash (mostly adhering soil), and water. Satisfactory methods of recovery of the oil and alpha-cellulose have been developed and subjected to critical scrutiny. The ash and water content need no special comment. The remaining complex mixture of components aggregates but a small content of the whole. Lacking a compelling motive, academic or practical, a cursory examination only has been given it. To determine distribution of cellulose in the different components of the cotton plant and to compare the data with the cellulose content of woods of southern origin were the objects of this study. As pulping agent a 5 per cent aqueous solution of nitric acid was used. It has the decided advantage for small-scale operations that the pulping can be done a t atmospheric pressure. Reid and Lynch (S) found that pulping with nitric acid gave results comparable with those from the procedure of Cross and Bevan. The alcoholic solution of nitric acid as suggested by Aronovsky and Lynch ( 1 ) has proved successful, and Macormac (2) found an even more dilute aqueous solution preferable to the standard alkaline media for pulping whole cotton. The procedure was as follows: Into a 5-liter flask, fitted
The distribution of cellulose in the different components of the cotton plant has been determined and compared with the cellulose content of some typical woods of southern origin. About 60 per cent of the alpha-cellulose in whole cotton comes from the lint, 30 per cent in about equal quantities from stems and from cusps. The alphacellulose content of whole cotton, generally, is higher than that of woods. The cellulose content of stems and of cusps is comparable to that of tree growths. with a long reflux condenser, there were introduced 100 grams of the solid to be pulped and 1000 cc. of the 5 per cent nitric acid solution. The mass was brought to a boil in about 20 minutes and the boiling continued for 3-10 hours, depending on the resistance of the solid. The solid residue was washed on a Buchner filter until the filtrate was neutral to litmus. The residue was then stirred into 500 cc. of a 2 per cent solution of sodium hydroxide and boiled for 45 minutes. It was again washed on the fdter to neutrality. I n color the pulps varied from light yellow to deep brown. They were bleached by seeping in a solution containing 3 grams of commercial bleaching powder t o 500 cc. of water. Washed free of chlorine, they were oven-dried at 100” C., cooled in a desiccator, and weighed as total cellulose.
