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Ih'DUSTRIAL A S D ESGI.VEERING CHEMISTRY
62'5 X 100 -
= 3125. If in this new process only 4 pounds 2 of steam are condensed, 4000 B. t. u.'s are released for heating and there is a vast difference between removing 30 odd pounds of water and a matter of 4 pints, most, if not all, of which may itself evaporate on release of pressure. As a matter of fact, fewer heat units need be added to the bag because of reduced thickness required as compared with general hotwater practice. It was recently stated2 that if heat were transmitted equally to two sides of a rubber slab '/z inch thick it would take 15 minutes for the center of the slab to reach the impressed temperature (in this case 280" F.), but if the slab were 1 inch thick an hour would be required. This emphasizes the advantage of the relatively thin bag that may be used in the new process and its bearing on the rate of heat transfer. A further important fact is that the conductivity of a mixture of one-third gas and two-thirds steam is much greater than that of static water. The uniformity of heat transfer compares favorably with the hot-water process. Pressure being supplied by steam, * Blaker and Shade, India Rubber World, 76, 313 (1927)
Vol. 20, No. 3
considerable leakage may exist without affecting the cure, whereas with a liquid medium a small leak will cause pronounced change in pressure conditions. I n the hot-water process owing to change in water density during progress of cure, there is a marked difference in the temperature of the water a t different points in the bag, while a t the top there is a variable pocket of air and steam. In the new process temperature conditions are practically constant, owing to rapid diffusion of gases mixed under conditions of curing temperature and pressure, and if the particular conditions applied call for a large addition of heat units it is simple to secure a continuous movement of the steam-gas mixture circumferentially. Advantage i n Manufacture of Molded Tubes
Molded tubes are now being cured by this process with a 25 per cent reduction in curing time and without any moisture remaining in the tube. The quality of molded tubes cured with carbon dioxide and steam is outstanding as compared with tubes cured by any other process. Under the severe treatment accorded molded tubes by the busses, this superior quality is a factor of first importance.
Chemical Unsaturation of Rubbers Vulcanized with Polynitro Compounds and Benzoyl Peroxide, and Its Possible Bearing on Vulcanization' Harry L. Fisher* and A. E. Gray* THEB. F. GOODRICH COMPANY, AKRON,OHIO
TUDIES on the chemical unsaturation of ordinary vulcanized rubber show that vulcanization has caused no change in the unsaturation of the rubber hydrocarbon beyond that which can satisfactorily be accounted for by the chemical combination of sulfur on the basis of one atomic equivalent of sulfur to a C5Hs group.4 If such is the case with sulfur vulcanization, it becomes very desirable to know whether there is any change in the unsaturation when rubber is vulcanized with substances other than sulfur-namely, polynitro compounds and benzoyl peroxide. Do these substances or their decomposition products also add to the olefin bonds and thus similarly reduce the unsaturation of the rubber hydrocarbon, or do they simply act in a catalytic fashion and change the rubber hydrocarbon without changing its unsaturation? I n an effort to throw some light on this interesting and intricate problem, samples of rubber were vulcanized with dinitrobenzene, trinitrotoluene, and benzoyl peroxide, and the unsaturation was determined by the Kemp-Wijs method with iodine ~ h l o r i d e . ~These samples dissolved with consid.erable difficulty, but a modified procedure, in which each sample cut into very thin pieces was allowed to swell in the solvent for many hours, worked very well. The results so far obtained are not so complete as
S
1 Presented before the Rubber Division at the 73rd Meeting of the American Chemical Society, Richmond, Va., April 11 to 16, 1927. Received October 25, 1927. 2 Present address, U. S. Rubber Co., 561 West 58th S t . , N e w York, N. Y. 8 Present address, Lehigh Unibersity, Eeth!ehem, Pa. 4 Spence and Scott, Kolloid-Z.. 8, 308 (1911); also private communication from Kemp, author of the Kemp-Wijs method for the determination of the rubber hydrocarbon, Ind. Eng. Chem., 19, 531 (1927); and unpublished work of the writers. 6 Ostromislenski, J. Russ. Phys. Chcm. Soc., 47, 1462, 1885 (1915); C . A . , 10, 1943, 3177 (1916).
the writers would like to have them, because each one changed his business connection before the full plans could be realized. However, the results appeared so satisfactory that it has seemed worth while to publish the work as far as it has gone. Experimental
(A) In a preliminary set of experiments with the two polynitro compounds the pale crepe used was not previously analyzed for its unsaturation. The value for the rubber hydrocarbon (CsH8)used was an average value, 91.7 per cent. The solution method was used in all these analyses, after acetone extraction and drying i n vacuo over concentrated sulfuric acid. Experiment ( 1 ) RATIO 100 9.5 10.5 3.0
Pale crepe Litharge Gas black m-Dinitrobenzene
BATCH Grams 400 38 42 12
492
Vulcanized 60 minutes at 141" C., 15 by 20 by 0.2 cm. (6 by 8 by 2!/3 inch) sheet; tensile, 200.50 kg. per sq. cm. (2852 Ibs. per sq. in.) ; elongation, 613 per cent.
Experiment ( 2 ) Pale crepe Litharge Trinitrotoluene
Grams 100 8 4s
112
Mixed on a small laboratory mill; vulcanized as gravity disks, 20 minutes at 135" C. 8
Stevens, J. Soc. Chem. Ind., 36, 107 (1917).
I N D U S T R I A L A N D ELVGINEERINGCHEMISTRY
March, 1928
Unsaturation Tests CsHs
DIFFE;RENCE
Per cenl (1) Calculated Found (2) Calculated Found
Per cent
74.55 75.24 81.86 82.73
+0.69 +I).
87
(B) A neTv set of experiments was therefore run using an analyzed lot of palelcrepe which, after acetone extraction, showed in two separate determinations, 91.77 and 91.79 per cent’CjHs. The samples were all vulcanized as 15 by 20 by 0.2 em. (6 by 8 by 3/’32 inch) sheets between tin in a press for the times specified. The highest and best cures were then acetoneextracted for 48 hours, dried in vacuo over concentrated sulfuric acid for 72 hours, and analyzed by allowing very thin strips to swell in carbon bisulfide for 24 hours and then letting the reagent act upon them in this condition for 24 hours more a t 0” C. in the dark. The calculated values all refer to the original weights before the acetone extraction. ’
Experiment ( 3 ) Same recipe as (1). C V R E(135” C.)
.Il~?iutes
EWKGATICIS
TENSILE Kg.js1. cm. Lbs./sq. in.
197,40 190.37 165,63
45 60 75
2808 2708 2356
Pev ceid 670 (sample analyzed) 635 610
Experiment ( 4 ) Same recipe as ( 2 ) ,but using 400 grams of the pale crepe. Kg./sq. cm. 4.64 13.64 27 00
Jliniiles 1(1
20
ELONCATIOK
T E I*‘s I I. E
CUKE(135’ C.)
Lbs./sq. itt. 66 194 384
Per cent 785 830 905 (sample analyzed)
Experiment ( 5 ) Grams 400
Pale crepe Benzoyl peroxide6
27
_.
427 CURE(135’ C.)
Minutes 10 15 20
TENSILE Lbs./sq. in. Kg./sq. cm. 751 52.80 542 38.10 792 55.68
ELONGATION Per cent 948 858 935 (sample analyzed)
All were clear, transparent, amber-colored sheets. Unsa tura tion Ana lyses EXPERIMENT CsHs AVERAGE DIFFERENCE Per cent (3)
Calculated Found
(4)
Calculated Found
74.84
74.56 74.00 81.92 81.80
Per cent
Per cent
74.27
-0.57
82.36 82.08 f0.16 Calculated 85.98 Found, 1 hour“ 39.06 2 hours 52.75 20 hours 86.12 86.12 +0.14 a Refers to time the sample, after having been swelled in the solvent, was in contact with the iodine chloride reagent. (5)
Discussion of Results
The preliminary set of experiments indicated that the change in unsaturation of the rubber hydrocarbon was not greater than 1 per cent. Since the unsaturation of different lots of pale crepe often varies 1 per cent, it seemed as if there were really no change in the vulcanized samples. The results of the analyzed lot of pale crepe calculated in terms of the percentage of C5He groups, varied from -0.57 to +0.16 per cent from the calculated amounts. Since a different reagent was used in each of the three cases-namely, dinitrobenzene, trinitrotoluene, and benzoyl peroxideand under different degrees of compounding, it does not seem
295
that such close agreement with the calculated value could be fortuitous. It must be concluded, therefore, that either there is no change in the unsaturation of the rubber hydrocarbon with these reagents, or, if there is, it is very small in amount. Ostromislenski, who discovered these methods of vulcanization without sulfur, believed that the reaction was due to oxidation. Molecular oxygen, so far as is known, does not vulcanize rubber as sulfur does. The products formed when rubber is t’reated with oxygen or allowed to stand in air are very different physically, and probably chemically. Of course, sulfur does not vulcanize rubber a t room temperatures except in the presence of a catalyst. Then, as, for example, with an ultra-accelerator, the air-cured, vulcanized rubber may contain as little as 0.5 per cent of combined sulfur.’ With a catalyst such as platinum black, oxygen is absorbed by the purified rubber hydrocarbon in solution until finally an amount is absorbed equivalent to the formation of a completely sat’urated compound ( C A O )z, and if perbenzoic acid is used, the same or similar compound-it has the same empirical formula-is obtained.* These reactions correspond in a general way to those with sulfur. Now oxygen is very closely related to sulfur chemically, and by analogy it ought to vulcanize rubber if the proper conditions could be found. If it does and the amounts correspond to those with sulfur, then using the 0.5 per cent of combined sulfur mentioned above, as a possible minimum, the equivalent of oxygen mould be just one-half (I6/a2) and the per cent bf oxygen would be 0.25. Perhaps the polynitro compounds and the benzoyl peroxide do oxidize the rubber hydrocarbon and t’hus cause vulcanization. If they do, and oxygen thus adds chemically as the sulfur does, then from the data given above, the amount added must be very low-less than 0.14 per cent, since this would be the amount equivalent to the greatest deviation, 0.57, which is approximately the same as the recognized error with the Kemp-Wijs method, 0.5 per cent of CsHs. The ratio of oxygen to C5He is 16:68 or 0.24. No reliable method for directly determining such a small amount of oxygen in chemical combination is known. The writers believe that the results herein given help to support the theoryg that ordinary vulcanization is an unknown or undetermined type of change in the hydrocarbon involving no change in the unsaturation, and that the chemical union of sulfur is a secondary reaction producing a further change which no doubt gives properties that are very important in the manufacture of rubber goods, but which is a change of degree only, not of kind. Acknowledgment
The authors express their thanks to The B. F. Goodrich Company for the opportunity to do this work and for permission to publish the results. 7 Cranor, I n d i a Rubber World, 61, 137 (1919), and unpublished observations of the senior writer. 8 Pummerer and Burkard, B n . , 66, 3458 (1922) 9 Compare Harries, “Untersuchungen uber die Natiirlichen und Kiinstlichen Kautschukarten,” p. 105 (1919).
Significance of the Word “Alum” A little brochure of ninety-three pages on “The Current Significance of the Word ‘Alum”’ has recently appeared, of which W. D. Richardson is the author. A great deal of space is devoted to a discussion of the significance of the word “alum,” its derivation and early history, as well as the modern definitions of the word. The book concludes with a bibliography divided into the broad headings of general literature, industrial literature, chemical literature, and medical literature. It is published by the Commonwealth Press of Chicago, from whom i t may be purchased for one dollar.
