INDUSTRIAL AND ENGINEERING CHEMISTRY
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expansion. The extent of this expansion is illustrated by comparing the record of 1938, the last normal prewar year, with that of 1941. In 1938 domestic deliveries of potassium chloride t o chemical industries amounted to 25,000 tons KC1 and in 1941 to 83,000 tons. Imports of potash chemicals during the first nine months of 1941 amounted t o only 162 long tons, exclusive of bitartrate, a by-product of the wine industry. In 1938 we imported in excess of 6000 long tons of the chlorate and perchlorate alone. With the cessation of imports, expansion in this field received immediate and effective attention. These chemicals and their derivatives enter into innumerable peacetime applications and into the every-day lives of most of us. It suffices to mention only the chlorates, essential constituents of the modern match. Expansion in production to supply these normal peacetime uses had to be further increased to provide for military requirements. Among the compounds officially listed as of military importance are potassium bromide, chloride, chlorate, perchlorate, dichromate, chrome sulfate, hydroxide, nitrate, and sulfate. When their specific uses can be discussed publicly it is t o be hoped that the desirability will be stressed of maintaining these manufactures as permanent sources of essential chemicals in accordance with the lessons taught by two world wars. Quoting from “The Mineral Industry during 1940”: “From the standpoint of the present
VOl. 34, No. 12
emergency perhaps one of the most $ratifying developments in recent years has been the establishment of facilities for the production of essential potash chemical compounds in quantities sufficient to satisfy domestic needs.” From the former problem of what to do with our surpluses, we have changed overnight to how t o make out with inadequacies, Priorities, allocations, rationing, pricefixing, and other devices to regulate supplies with maximum benefit to the mar effort and minimum derangement of private lives are the order of the day. By contrast with a situation affecting what superficially appears to be most other commodities, potash is conspicuous as an outstanding exception. To date, federal war agencies have taken the position that only minor problems exist with respect to potash supplies and publicly have expressed gratification in that fact. Official satisfaction must be multiplied many times by that of the agricultural public whose operations in this emergency are not being disrupted as they were in World War I. Foresight born of that experience has resulted in this present state of adequacy of potash supplies from our own mines and refineries. Equal foresight must be exercised if that state of independence is to be perpetuated for the benefit of future generations. PRESENTED as part of the Symposium on Potash before the Division of Fertilizer Chemistry a t the 104th Meeting of the A ~ I ~ R I C CHEMICAL AN SOCIETY, Buffalo, N,
Y.
Methyl Ethyl Ketone J
J
Extraction of Rubber LA VERNE E. CHEYNEY The Goodyear Tire & Rubber Company, Akron, Ohio
An attempt has been made to substitute methyl ethyl ketone for acetone in the standard extraction procedure employed for rubber samples. The extract values are higher with methyl ethyl ketone than with acetone and are highest in samples which have been subjected to severe oxidative breakdown. The higher ketone is believed to exert a direct solvent action upon the sol fraction of the rubber. H E extraction of rubber samples with acetone as an analytical procedure is a classical method; its origin is almost lost in antiquity, a t least from the viewpoint of the rubber technologist. It is a valuable procedure, not only for practical evaluation of rubber samples, but from theoretical considerations as well. Acetone is commonly regarded as a polar “nonsolvent” for rubber, although some slight swelling action on rubber samples has been reported (6,11, SO). Various investigators have carried out the extraction under differing conditions (1, 8, 8, 9,29, SS), and the results have been shown to vary somewhat with the treatment of the sample (8, 9, 99). The procedure as commonly employed
T
today is well standardized (I), and great reliance is placed by rubber chemists upon the analytical data obtained thereby. The standard procedure, however, suffers from one serious drawback-the length of time necessary to obtain the desired data. With a large number of samples this factor is enormously magnified. When applied to plant control determinations, the disadvantage is too readily apparent. One possible method of reducing this difficulty would be the substitution for acetone of some other solvent, perhaps of higher boiling point, which a t the temperature of extraction would have a greater solvent action upon the nonrubber constituents. It should therefore accomplish the desired extraction in a shorter time. A solvent which suggested itself for this purpose was the next member of the ketone series, methyl ethyl ketone. Its solvent action is, in general, similar to that of acetone, and its boiling point (79.6” C.) is sufficiently low so that any undesirable thermal effects upon the rubber sample should be minimized. At the same time, the boiling point of methyl ethyl ketone is enough higher than the boiling point of acetone that its solvent power a t the temperature of reflux might be expected to be considerably greater. Only limited data are available concerning the solvent action of methyl ethyl ketone on rubber. This condition is probably due to the fact that only recently has this solvent become obtainable in large commercial quantities. Whitby (88) mentions that methyl ethyl ketone exerts a little swelling
December, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
1427
a constant value for the acetone extract, which served as AIRBAG REC LA1M
P
“ I
a
control for the results with methyl ethyl ketone. The experimental results are summarized in Table I and plotted in Figures 1 and 2. An experimental result given aa Sw. indicates that the sample had been swollen enough by the liquid to render the extract figures valueless. I n most cases the sample swelled to the point where it burst the filter paper thimble and then clogged shut the siphon tube in the extraction cup. When this point was reached, the determination was abandoned.
TfRE RECLAIM
Swelling Effects
II O
-
-
O
F
0
0
FLAT BARK CREPE
5’
lo TIME IN HOURS
15
EXTRACTS OF SAMPLESSTUDIED FIGURE 1. ACETONE
action on raw rubber, more so than acetone, and that diethyl ketone is a solvent for rubber. Bloomfield and Farmer (9) mention that the dialkyl ketones possess some “interesting solvent properties” for rubber, but they likewise give no data and do not mention methyl ethyl ketone specifically.
Extraction Procedure Three types of samples were included in this study: (a) three samples of raw rubber-a smoked sheet, a pale crepe, and a flat bark crepe; (b) three samples of vulcanized rubber, and (c) two samples of reclaimed rubber. These samples were sheeted and otherwise treated according to the A. S. T. M. standard method (1). The methyl ethyl ketone was distilled over anhydrous potassium carbonate before use. The acetone extractions were carried out under the conditions specified in the standard procedure, except as otherwise noted. The methyl ethyl ketone extractions were adjusted to the same rate of reflux and, except for the variations noted, were otherwise treated exactly the same as the acetone extractions. I n order to eliminate the effects of other variables, all the extractions carried out under a given set of conditions were run side by side a t the same time. Two types of extraction were employed with methyl ethyl ketone-continuous and discontinuous. It has been previously shown that discontinuous extraction with acetone gives higher results than continuous extraction, presumably due to oxidation caused by the removal of the natural antioxidant by the acetone (8, 28). The samples were completely enclosed in filter paper and therefore not directly exposed to light. No difficulty was experienced in obtaining
The most outstanding result for crude rubber is the marked difference in rate of extraction of the flat bark crepe sample, which has the lowest extract with acetone but is swollen fairly rapidly by methyl ethyl ketone. The 4-hour methyl ethyl ketone extracts for the pale crepe and smoked sheet samples ate only slightly greater than the corresponding acetone extracts. With longer extraction, however, the samples swell; the pale crepe swells more rapidly with discontinuous extraction and the smoked sheet more rapidly with continuous extraction. This swelling characteristic, which agrees with the observations of Whitby, is evidently concerned with the sol-gel equilibrium (9,16,26,S7,28). The first action of the methyl ethyl ketone is probably to remove the same nonrubber constituents as the acetone, after which it starts to swell the sol fraction of the rubber. Because of its polar character, i t might be expected to exert a depolymerizing effect upon the rubber molecule. It probably also removes the natural antioxidant and thus tends to shift the equilibrium toward the sol phase, as i t has been clearly demonstrated that oxygen plays a major role in promoting this shift (3,6, 7, 10, 12, 16, 22, ,24, ,26). I n this light the flat bark crepe, because of ita variable history, might be expected to give higher extract values, since it would undoubtedly be subjected to more oxidation and depolymerization influences during its previous treatment. The vulcanized samples show the same general trend, although the swelling tendency is repressed, as would be expected. The differences between continuous and discontinuous extraction are less pronounced. The tread stock is the only one of the three which seems to approach a value which is fairly constant for both continuous and discontinuous extraction. The experimental results for the reclaim samples are even more interesting. Both samples show large extract values, which increase even more rapidly with discontinuous extraction than do any of the samples previously noted. The methyl ethyl ketone extract at the end of 2 hours is larger for either sample than the acetone extract after repeated extraction. These unusually high values recall the behavior of reclaim with chloroform, as noted by Stafford (26)and studied in more detail by Weber, Winkleman, and others (16-,21, 29,91, 84).
TABLEI. ACETONE AND METHYL ETHYL KETONE EXTRACTIONS --Acetone
2 hr. Pale crepe Smoked sheet Flat bark crepe Tread Tube A Tube B Tire reclaim Air-bagreclaim
..
0:63 5.12 4.77 5.84 7.72 9.46
Extraction, %8 hr. 2 2 contmu2&.2 2 hr. ous 2.77 3.~17 3.40 2.70 2.73 2.76 0.98 1.20 1.20 5.72 6.10 6.22 5.02 5.32 5.45 6.02 6.22 6.30 7.78 8.11 8.20 16.71 17.22 17.64
++
-Methyl
2 hr. 1.84 1.86 1.73 5.96 6.18 7.62 12.42 23.62
Ethyl Ketone Extraction, %16 hr. 24 pr. 2 2 continu- contmu2&.2 2 hr. ous ous 2.71 6.16 3.72 4.77 2.50 3.09 4.93 8.62 3.10 4.68 Sw. Sw. 6.50 6.93 7.31 7.40 6.50 7.03 7.29 8.44 8.02 8.28 7.69 7.94 18.67 23.30 20.94 25.75 27.18 30.10 26.58 28.51
++
INDUSTRIAL AND ENGINEERING CHEMISTRY
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o SMOKED SHEET
PALE CREPE 0
/
CONT.
FLAT BARK C R E P E
Vol. 34, No. 12
As indicated by these results, especially when the entire set of data is considered together, it appears that the general solvent action of methyl elthy ketone is somewhat similar to that of chloroform. It apparently acts as a solvent for some of the lower molecular weight fractions. It also seems to act as a solvent for the antioxidants, both natural and added, so that discontinuous extraction results in a much greater oxidative depolymerization of the rubber and a shift toward the sol phase. This general selective solvent character of the methyl ethyl ketone for rubber fractions of certain molecular weight is in agreement with observed results with other high polymers. Vinyl chloride polymers of certain molecular weight ranges, for instance, are dissolved by methyl ethyl ketone, whereas the same fractions are insoluble in acetone. A study of these data in terms of the original problem indicates that methyl ethyl ketone could not be satisfactorily substituted for acetone in the classical extraction procedure, even though under certain conditions with a given sample the same values might be obtained. The results across a series of samples show too much variation. The data submitted in this report, however, indicate that methyl ethyl ketone may prove to be a useful research tool in studying the fractionation of rubber and similar problems.
l t
o v .0 .-
1
I
I
IO
20
MSCONT.
CONT.
I
o TUBE B
x W
0
TUBEA TREAD
I
I
AIRBAG- DISCONT.
Acknowledgment
la TIRE-
DISCONT.
The major portion of the experimental work was done a t the University of Akron while the author was a member of the staff of that institution. He is grateful for the opportunity thus afforded. Part of the experimental data was obtained by Karl Cullison, to whom thanks are due,
Literature Cited A. S. T. M. Standards on Rubber Products, D297-41T (1941). Asano, I n d i a Rubber J., 70, 307 (1925). Bloomfield and Farmer, Trans. Inst. Rubber Ind., 16, 69 (1940). Brown and Hauser, IND. ENG.CHEM.,30, 1291 (1938). Busse, Ibid., 24, 140 (1932). Cachtem, Gummi-Ztg., 43,2099 (1929). Cotton, Trans. Inst. Rubber Ind., 6,457 (1931). (8) Dawson and Porritt, “Rubber-Physical and Chemical Properties”, Croydon, England, 1935. (9) Endo, J . $00. Chem. I n d . J a p a n , 10,Suppl. Binding, 514 (1935). (10) Fisher and Gray, IND.ENG.CHEM.,18, 414 (1926). (11) Flusin, Ann. chim. phys., [8]13,450 (1908). (12) Fry and Porritt, Trans. Inst. Rubber Ind., 3, 203 (1927). (13) Hauser and Brown, IXD.ENQ. C ~ n x .31, , 1225 (1939). (14) Hauser and Sse, J . Phw. Chem., 46, 118 (1942). (15) Kemp and Peters, Ibid., 43,923, 1063 (1939). (16) Kirchof, Kautschuk, 11, 115 (1935). (17) Lindmayer, Ibid., 4,278 (1928). (18) Loewen, Ibid., 5, 81 (1929). (19) Miller, IND.ENG.CHEM.,20, 1165 (1928). (20) Palmer and Kilbourne, Ibid., 32, 512 (1940). (21) Palmer, Miller, and Brothers, Ibid., 23, 821 (1931). (22) Park, Carson, and Sebrell, Ibid., 20, 478 (1928). (23) Rouxeville, Rev. ghn. caoutchouc, 6,No. 48, 15 (1929). (24) Shacklock, Trans. Inst. Rubber Ind., 6,259 (1930); 7,354 (1932). (25) Smith and Saylor, J . Research Natl. Bur. Standards, 13, 453 (1934). (26) Stafford, I n d i a Rubber J., 71, 59 (1926). (27) Staudinger, “Die hochmolekularen organischen VerbindungenKautschuk und CeIIuIose”, Berlin, Julius Springer, 1932. (28) Stevens, J. SOC.Chem. Ind., 38,1941 (1919). (29) Stevens and Rowe, Proc. Rubber Tech. Conf., London, 1938,281. (30) Tompkins, “Physics and Chemistry of Colloids and Their Bearing on Industrial Questions”, 1921. (31) . . Weber, “Chemistry of Rubber Manufacture”, London, Chas. Griffin & Co., 1926. (32) Whitby, Colloid Symposium Monograph 4, 203 (1926). (33) Whitby and Winn, J . $00. Chem. Ind., 41, 3361‘ (1923). (34) Winklsman, IND.ENG.CHIPM., 18,1163 (1926). (1) (2) (3) (4) (5) (6) (7)
ob
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I
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TI%E IN HOURS FIQURE2. METHYL ETHYLKETONEEXTRACTS OF RAW RUBBER SAMPLES,VULCANIZEDSAMPLES, AND RECLAIM SAMPLES
These investigators have well established the postulate that the chloroform extract consists chiefly of depolymerized rubber. It was further s h o w that there is a definite distribution of the combined sulfur, most of it remaining in the chloroform-insoluble portion. As shown by the work of Hauser and co-workers (4, IS,14), vulcanization to optimum cure apparently takes place with a minimum loss of unsaturation. The portion of the molecule which has combined with sulfur is then insoluble in chloroform, whether because of this combination or simply because the sulfur linkage provides i t with a higher molecular weight. The uncombined portion is still unsaturated and hence susceptible of oxidation. The action of oxygen would depolymerize it and increase the solubility.
PRESENTED before the Division of Rubber Chemistry a t the 104th Meeting of t h e AMERICAN CHEMICAL SOCIETY, Buffalo, N. Y.
