I
826
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INDU~TRIALAND ENGINEERING CHEMISTRY
VOL. 30, NO. 7
.I.
mer predicted for the polymerization of 3-methyl-1-butene with 2-methyl-1-propene. These examples show that reasonably reliable predictions of the polymerization products of the lower olefins can be made by means of the rules formulated. The scheme of rules presented is not held out as having an established theoretical basis or as being complete and final. It is, however, believed to be in good agreement with all the known facts. How far, if at all, it can be extended to cover polymerization of other unsaturated types such as diolefins, olefins with electronegative substituents like methyl allyl chloride, cyclic olefins such as cyclohexene, or aromatic olefins of the type of styrene is not known a t present.
Literature Cited (1) Birch, Pim, and Tait, J.SOC.Chem. Ind., 55,335T (1936). (2) Brooks, J. Am. Chem. SOC.,56,1998 (1934). (3) Carothers, Chem. Rev.,8, 392,399 (1931). (4) Church, Whitmore, and McGrew, S. Am. Chem. SOC.,56. 176 (1934). (6) Drake, Kline, and Rose, Ibid., 56,2076 (1934). (6) Drake and Veitch, Ibid., 57,2623 (1935). (7) Henze and Blair, Ibid., 55,685 (1933). (8) Ipatieff, “Catalytic Reactions a t High Pressures and Tempera-
tures,” New York, Macmillan Go., 1936; Ipatieff, Pines, and Schaad, S.Am. Chem. Sor., 56,2696 (1934). (9) Kharasch and Flenner, Ibid., 54,674 (1932). (10) Kline and Drake, J. Research Natl. B u r . Standards, 13, 705 (1934). (11) Kondakov, J. Russ. Phys. Chem. Soc., 24, 309 (1893); J. prakt. Chem., [2]54,442,454 (1896). (12) Lebedev and Orlov, J. Gen. Chem. (U. S. S. R.), 5, 1589 (1935). (13) McCubbin, J. Am. Chem. Soc., 53,357 (1931). (14) McKenna and Sowa, Ibid., 59,470(1937). (15) Morikawa, Trenner, and Taylor, Ibid., 59, 1103 (1937). (16) Norris and Joubert, Ibid., 49,873 (1927). (17) Norris and Reuter, Ibid., 49,2624 (1927). (18) Pauling, Ibid., 54, 3570 (1932). (19) Whitmore, IND.ENG.CHEM.,26,94 (1934). (20) Whitmore and Church, J . Am. Chem. Soc., 54,3710 (1932). (21) Whitmore and co-workers, Ibid., 55,406, 812, 1106,1119,3428, 3721,3732,4194(1933); 56,176 (1934). (22) Whitmore and Herndon, Ibid., 55, 3428 (1933); Whitmore and Homeyer, Ibid., 55,4194 (1933). (23) Whitmore and Laughlin, Ibid., 55, 3732 (1933). (24) Whitmore, Laughlin, Matuszeski, Crooks, and Fleming, paper presented before Div. of Organic Chemistry at 9Znd Meeting , of Am. Chem. SOC.,Pittsburgh, Pa., Sept. 7 to 11,1936. (25) Whitmore and Mixon, Ibid., 90th Meeting, San Francisco, ‘L Calif., Aug. 19 to 23, 1935. (26) Whitmore and Rothrock, J. Am. Chem. Soe., 55, 1106 (1933). RECEIVBD March 14, 1938.
Extraction of Water-Soluble Accelerators in Water Cure J. W. MAcKAY Monsanto Chemical Company, Nitro, W. Va. Eight-hour extraction with 160 liters of water did not remove any measurable quantity of the 5 grams of piperidine cyclopentamethylene dithiocarbamate or the 10 grams of sodium mercaptobenzothiazole from 1000 grams of rubber film. A similar quantity of 0.1 per cent sodium hydroxide solution did not remove any measurable quantity of the 1 gram of sodium pentamethylene dithiocarbamate or the 10 gramsof sodium mercaptobenzothiazole from the rubber. The extraction removed water-soluble nonrubber constituents, giving a softer rubber film. The water-soluble accelerators tested had a selective solubility for rubber which is many times their solubility in water.
L
ATEX products are usually vulcanized at relatively low temperatures, below 212’ F. (100’ C.), because ultra-accelerators can be used without the danger of scorching. These low-temperature cures may be carried out in air or in water. The use of water-soluble accelerators in water cures has been subject to considerable controversy
inasmuch as it is believed that they are extracted in this type of cure. This paper is presented to show that the common and well-known water-soluble accelerators are not extracted from the rubber film during vulcanization in water. Since ultra-accelerators are very scorchy @), they were used in “split batches”; i. e., the sulfur and accelerator were mixed in separate stocks on the rubber mill. Vulcanization was effected either by mixing the two stocks on a mill immediately before use or by superimposing thin layers of these stocks upon each other. I n the latter method the vulcanization was entirely dependent upon the migration of sulfur and accelerator from one layer into the other. The split-batch rubber compound developed into the water cure where a rubber film containing sulfur, zinc oxide, etc., and no accelerator or a very slow accelerator was immersed in a hot water solution or dispersion of an ultra-accelerator. The water functioned as a carrier for the accelerator and as a medium supplying the heat necessary for rapid vulcanization. The accelerators used in this process were carbon disulfide reaction products of dimethylamine, piperidine, etc., and xanthates or their sodium or potassium salts, as well as tetramethylthiuram monosulfide, which are water soluble; water-insoluble accelerators were employed, such as the carbon disulfide reaction products of methylenedipiperidine, etc., or the metallic salts of dithiocarbamates, some of which are liquid and others solid at the water temperatures used. The vulcanization of latex products may be carried out by either of the methods outlined. Since no milling is necessary, scorching is eliminated and the complete formula containing
JULY, 1938
sulfur, zinc oxide, ultra-accelerator, etc., is prepared. Since latex is an aqueous dispersion of rubber, the use of watersoluble vulcanizing ingredients seems desirable because they remain in solution whereas insolubles tend to settle out from low-viscosity mixes. Consequently, the tolerances in the quantity of accelerator required to obtain a desired cure are very narrow. It is an accepted fact that an accelerator will migrate or dissolve into a rubber film which is immepsed into a n aqueous solution or dispersion of accelerator and will thus effect vulcanhation. However, it is possible that a vulcanizable film of rubber containing a water-soluble accelerator will have this accelerator partially extracted during water cure (6) and thus result in wide variations in the properties of the finished product. The water in this case is used only as a medium to supply the heat required for rapid vulcanization. The term "rubber a m " is used because a latex compound on the removal of substantially all of its water content is a rubber film, and the vulcanization of latex as latex is vulcanization in aqueous solution.
Extraction of Compounds The latex compounds given below were mixed and films were poured as described in a previous article (4): These 10 X 14 inch (25.4 X 35.6 cm.) rubber films were allowed to dry 8 hours under controlled humidity free from drafts until set, when the chamber was opened and air was circulated over their surface with an electric fan to accelerate drying. At the end of this period the rubber films were sufficiently dry to handle but were still opaque and suitable for extraction. A 20-liter container was fitted with a water inlet near the bottom and an overflow at approximately 18 liters capacity with water changing at approximately 20 liters per hour. This container was heated on a hot plate, and the temperature maintained at 105" F. * 2" (40"C,); this was the highest temperature that would not produce appreciable vulcanization in 8 hours in any compound employed. RVBBERAS bo? LATEX ZINC OXIDE SULFUR P@€RIDINE CYCLOPENTAMETHrLENE DITHIOG4RBAMATE (PIP-PIP)
100.0 1.0
rubber films were subjected to extraction at one time. The container was agitated with a paddle at least every 15 minutes to ensure thorough circulation. The rubber films, on removal from the extraction process, were placed on clean glass sheets in a cabinet at 70" F. (21" C.) and 80 to 90 per cent humidity to prevent their drying. On completion of the 8-hour extraction, all of the rubber films were suspended from a line to dry for 20 hours at 70" F. before being cured. These dry rubber films were cut into six pieces measuring 3.25 X 5.5 inches (8.25 X 13.9 cm.) each; a 3 X 14 inch (7.6 X 35.6 cm.) strip across the end was held for a check on prevulcanization or cure during the drying; period. Vulcanization or curing was carried out in water at 212 F. over a range of cures suitable for the respective acceleration. Water curing was preferred because the temperature is uniform and there is no lag as in dry-air cures. Each of the six 3.25 X 5.5 inch pieces had a hole punched in one end by means of which it was threaded on a glass rod. The rod kept the pieces submerged and made their individual removal convenient. Each set of six pieces from one period of extraction was cured in a 1500-cc. beaker containing approximately 1200 cc. of distilled water. The individual pieces were removed on com letion of the desired cure and laced on clean glass sheets untif the last iece had been cured? They were then all suspended from a yine to dry overnight at 70" F. before the preparation of dumbbell test pieces. Three dumbbell test pieces were cut from each stri by means of standard A. S. T. M. die and suspended on wires gwenty-one on each wire) for approximately 44 hours in a conditioning cabinet at zero per cent humidity and 70" F. before being tested. Twenty-one test pieces (one extraction) were removed from the conditioning cabinet a t one time and broken on the Scott tester (4). All the test pieces of one compound were broken by the same operator within 6 hours. The results as presented are the average results of the best two or, generally, all three test pieces from a given cure. I n order to simplify the presentation of the test data, the curves for tensile strength and modulus at 700 per cent elongation of the control stock, which is representative of the series, are given. The effect of extraction is shown graphically by taking the average results of tensile strength and modulus a t 700 per cent elongation for all seven cures for each period of extraction. The approximate solubilities of accelerators tested are as follows :
1.5
Parts Sol. in 100 Parts Solvent at 105" F. Water 0.10% NaOH
0.5
r-'
CONTROL
''%p
IN.
4000
827
INDUSTRIAL AND ENGINEERING CHEMISTRY
TENSILE
2000 fMoOULUS
%O.GM.
.
281.2
140.6
A T 700%
10 20 30 40 MINUTES CURE IN WATER AT212'F; (l00"C.)
50
4000
281.6
2000
140.6
10 . 2.0 4.0 6.0 0.0 HOURS WTRAGTION WmH WATERAT 105'E(rlO"d
FIGURE 1
The 10 x 14 inch rubber films, each weighing approximately 125 grams, were extracted 0.25, 0.50, 0.75, 1.0, 2.0, 4.0, and 8.0 hours except as noted in Figure 4. The rubber film for the 8hour extraction was removed from the glass plate, marked with a metal tag, and submerged by weights attached to one end in the 20-liter container. The film for the control stock was also placed in the container for 1 minute and then removed, and the 0.25-hour extraction was carried out. In this way only two
Piperidine cyclopentamethylene dithiocarbamate Sodium or potassium cyclopentamethylene dithiocarbamste ( 8 ) Sodium or potassium mercaptobenzothiazole (I) Zinc dibutyl dithiocarbamate (6)
8 100 100
None
100 100 100
None
Piperidine Cyclopentamethylene Dithiocarbamate A typical and well-known latex formula is shown in Figure 1. Physical tests were made on 5-, lo-, 15-, 20-, 30-, and 50minute cures in water a t 212O F. The tensile and modulus curves at 700 per cent elongation are shown in the upper part of Figure 1, and the lower part shows the effect of the extraction with water on this compound. The differences in average physical properties are negligible or well within the experimental error. The eight rubber films extracted had an approximate total weight of 1000 grams and would contain approximately 5 grams of accelerator. Over a period of 8 hours approximately 5 grams of accelerator were subjected to extraction in 160,000 grams of water (20 liters per hour for 8 hours), which is approximately three thousand times the quantity of water required to dissolve this accelerator. Therefore the accelerator (piperidine cyclopentamethylene dithiocarbamate) must have a selective solubility for rubber since there is no appreciable difference between the control and the 8-hour extraction. The possibility that as little as 0.05 per cent of the piperidine cyclopentamethylene dithiocarbarnate, based on the
VOL. 30, NO. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
828
film. Cures were made at 3, 5 , 10, 15, 20, and 40 minutes. The curves JUfFUR 1.5 P l F f R / D i N E GYGL OPENTAAM€TMYL€NE 0.I and results of extraction D/TH/OCARBdMATf (p/F-Pi@ /. 0 1.0 are shown in Figure 4. CONTROL A second control film w y !IN. CONTROL KGYW.CN. KYSO, CM which was not extracted 4000 201.2 is shown a t the extreme TENSIIE left. The water extraction softened the rubber 2000 Zoo0 140.6 as shown by the gradual MODULUS AT 700p .decrease in m o d u l u s ; I therefore, since the ac10 20 30 40 sa 10 20 30 40 50 celerator was insoluble MINUT€5 CUR€ IN WATER AT 2i2 'E (/OO*C) MINUTES CUAEIN WATER AT 211°F (I00"C ) and could not be extracted, this change must I 4000 have been due to the ac28i.2 4000 ZBt.2 t i o n of water, s o d i u m hydroxide, or both, on 2000 140.6 2000 140.6 the rubber film. Since the extraction of .sugars, p r o t e i n s , a n d 0 la 2.0 fo 6.0 0.0 o t h e r n o n r u b b e r con1.0 2.0 4.0 6.0 8.0 MOURS €XTRACTION IN 0./0%NOOM SOL N.AT /OS% (+O'CJ H O U R 5 EXTRACTION WITH WRTERAT 105%~30%.) stituents is possible, films FIGURE 2 FIGURE 3 were p r e p a r e d from a normal latex which has rubber content, was extracted in the first series of tests a maximum quantity of these water-soluble nonrubber conled to a second series, in which a small quantity of this stituents. Zinc dibutyl dithiocarbamate accelerator was accelerator was used as an .activator for a standard acused, and the accelerator and sulfur ratios were adjusted celerator. The test results of the water extractions are to approximate the cure in Figure 4. The results of the shown in Figure 2 where it is evident that no appreciable physical tests on these extractions are shown in Figure 5 quantity of either accelerator was removed by extraction. where a marked softening is evident during the first hour Piperidine cyclopentamethylene dithiocarbamate forms salts of extraction. Since the accelerator was insoluble, this of sodium or potassium readily, and these salts are very softening was due to the removal of nonrubber constituents soluble in water or dilute caustic solutions. Therefore, from the rubber film by the water extraction. a second series of extractions was carried out using 0.10 per cent sodium hydroxide as an extraction medium. The Effect of Extraction physical tests are shown in Figure 3 where a gradual softening or decrease in modulus is observed with no appreciable change I n the five series of extractions discussed, a gradual loss of in tensile. The removal of a small quantity of either or rigidity was observed in the dry rubber film with increasing both of these accelerators would produce a greater variation time of extraction before and after cure. In tests comparing in the physical properties. Therefore, this softening must ordinary centrifuged latex with latex centrifuged and dibe due to the saponification or removal of proteins and other luted two, three, or four times, a similar softening was observed. I n a study of the effect of humidity on the physical nonrubber codstituents from the rubber film. RUBBLR A5 So% LATEX ZINC OXIDE SULFUR PlPERlOlNE CYCLOPENTAMETHYLENE DITHIOCARBSMATE (PIP-PIP) SODIUM MERCAPTOBENZOTHIAZOLE
Zinc Dibutyl Dithiocarbamate T h e r e s u l t s of t h e three previous extractions indicated that the variations observed were due to the extraction of materials from the rubber film; therefore a new compound was prepared using zinc dibutyl dithiocarbamate (which is insoluble in water, 6) for the accelerator. The r e s u l t s a r e s h o w n in Figure 4. The sodium hydroxide was used t o verify the results obtained in Figure 3 and to ensure the presence of a small quantity of alkali thoroughly dispersed i n t h e r u b b e r
RU00€R AS 60%LATEX /00.0 ZINC OXIDE 1.0 sooiu,v ~ E , ~ C ~AOP~ E N Z O ~ M I AEZ O L/.o
100.0 1.0 1.5
'
RU00TR AS 60XLA?€X ZiNC M I D € SUl f UR Z/NC D/BUTYl DlTHiOCAR0AMAlL
HUBERAS #PLATEX ZINC O X I E SULFUR
/oo.o /. 0 /.5 0.5
TfNJifE
L
0.75 0.75
KGY?.C.cM.
CONTROL
I
QWO
/40.6
2000
1.0
ZINC D/'UTYLDI TU/C€ME4hMT?5 TH/CK€N€R/LOCUSTWGUMJ B3/5o./N:
4000
/oO.O /. 0
ZCW
I
3a IO
P(I
10
/O 20 30 40 50 fl/NUT€.S CURE i N WA TER kT Z/Z % (/OOZ,)
M/NUT€S CURE/N WAT€RAT Z/Z%//OO'C.l
FIGURE 4
FIGURE 5
I WOO
zoo0
50
JULY, 1958
INDUSTRIAL AND ENGINEERING CHEMISTRY
tests of latex rubber compounds (4) it was evident that the water cures adsorbed less moisture than the air cures of the same compound; this behavior indicated that the water removed solubles from the rubber film. This extraction or leaching out of water-soluble nonrubber constituents is well known and is general practice with the manufacturers of latex products. It is carried out before or after cure with equal success, and gives a softer and less water-adsorbent article. The tests discussed were carried out on semidry, uncured latex rubber films, and it is believed that bone-dry or even cured films will produce similar results. However, under no conditions should tests be attempted on latex rubber films which are so wet that they will disintegrate on immersion in water. In practice, latex products are trimmed and may have a bead rolled before vulcanization; in order to accomplish these operations, the film must be comparatively dry. The immersion of a too wet latex rubber film in water for vulcanization causes distortion which vulcanizes in this unnatural condition and is too evident in the finished product.
829
Conclusions No measurable quantity of the water-soluble accelerators tested was extracted from the rubber during the water extraction. Therefore, these accelerators will not be extracted during vulcanization in water. The softening action observed in water-cured latex products is due to the extraction of watersoluble nonrubber constituents from the rubber film. The water-soluble accelerators tested have a selective solubility for rubber which is many times greater than their solubility in water.
Literature Cited (1) Du P o n t d e Nemours, E . I., & Co., Inc., "Properties of Du Pont Rubber Chemicals," p . 7, May 25, 1937. (2) Ibid., p. 9. (3) Ibid., pp. 15 and 16. (4) MaoKay, IND.ENG.CHEM.,Anal. E d . , 10, 57 (1938). (5) Vanderbilt News, 4, No. 5, 21 (1934) : 7, No. 6, 6-10 (1937). R ~ C E I V EApril D 2, 1938. Presented before the meeting of the Division of Rubber Chemistry of the American Chemical Society, Detroit, Mich.. March 28 and 29, 1938.
Viscosity of Hydrocarbon Solutions' Viscosity of Liquid and Gaseous Propane B. H. SAGE AND W. N. LACEY California Institute of Technology, Pasadena, Calif.
The effect of pressure upon the vis(Pressures r e p o r t e d are absoHE viscosity of fluids is cosity of liquid and gaseous propane has lute-) Useful in calculating the The viscosity of hydrocareneru changes attending been determined at five temperatures bebon gases in the vicinity of attheir flow by use of the Reynolds tween 100"and 220" The work includes m o s p h e r i c pressure has been criterion. Data of this nature measurements throughout the superstudied by a number of investiare of special importance in heated gas region and the condensed gators. Vogel (27) measured laminar or s t r e a m l i n e flow the viscosity of m e t h a n e a t such as it; often found in the liquid region at pressures up to 200 32" F. and atmospheric presm o v e m e n t of homogeneous pounds per square inch. sure. This work was substanh y d r o c a r b o n f l u i d s in the tiated by Rankine and Smith porous strata of natural petro(16) and later by Ishida (11). Day (5) studied the effect of leum reservoirs. Numerous studies have been made of the pressure upon the viscosity of n-pentane and isopentane, from effect of temperature upon the viscosity of hydrocarbon approximately 2 pounds per square inch to vapor pressure a t liquids and gases in the vicinity of atmospheric pressure, and 77" F. Trautz and Kurz (26) measured the viscosity of prothe effect of changes in pressure and composition upon the pane a t atmospheric pressure from 83" to 550" F. The visviscosity 'of such liquids has been ascertained to a lesser decosity of air was measured by Harrington (7) by the rotating gree, Until recently the influence of pressure upon the viscylinder method a t 73.4"F. and atmospheric pressure. Kellcosity of hydrocarbon gases has received little attention, but strom's recent elaborate investigation (12) of the viscosity of the investigations reported indicate that the effect of pressure air under these same conditions is probably the most accurate may be as great as that of temperature within the range of constudy of the viscosity of any gas so far reported. ditions encountered in petroleum production. Because of the The effect of pressure upon the viscosity of gases has not scarcity of this type of information, a study was made of the been as extensively investigated as the effect of temperature effect of pressure and temperature upon the viscosity of at atmospheric pressure. Phillips (15) studied the influence liquid and gaseous propane. The data reported cover the of pressure upon the viscosity of carbon dioxide at temperasingle-phase regions from atmospheric pressure to 2000 tures near its critical point. Stakelbeck (23) recently depounds per square inch at temperatures from 100" to 220" F. termined the viscosity of gaseous carbon dioxide and included * Previous papers in this series appeared in 1935 (page 954) and 1937 measurements in the same range of temperature and pressure (page 858).
T
