INDUSTRIAL A N D ENGINEERING CHEMISTRY
316
Vol. 21, No. 4
Further oxidations have been carried out on floridin tars obtained from the three crude oils. These tars were dissolved in non-oxidizing oil and the solutions oxidized during 3 hours a t a temperature of 150" C. and under 15 atmospheres of oxygen. The asphaltene contents after these oxidations were as follows: Grosny, 27.5; Emba, 16.2; Balakhany, 5.28; and American cylinder oil, 20.60 per cent. These data show that both crude oils and their floridin tars give different amounts of asphaltenes under the same conditions of oxidation. Since when subjected to oxidation asphaltenes turn into carbenes, the amounts of coke obtained from these oils will be different after oxidation and, as may be seen, do not correspond to the data obtained with Conradson's apparatus. T a b l e V-Asphalt
Formation a n d Conradson Carbon Oxidation of Lubricating Oils
undissolved in the oil) and the Conradson carbon residue obtained from each oil after oxidation are shown in Table V. A comparison of the amounts of asphalt obtained after oxidation with the Conradson carbon residue values proves that the latter data are far from being true. It is interesting to note that the data obtained by oxidation of cylinder oils derived from Balakhany and Emba crude oils correspond to the data resulting from the oxidation of these crude oils and their tars. American filtered cylinder oil (No. 3) whose floridin tar has given 20.6 per cent of asphaltenes after oxidation also gives a large amount of asphalt through oxidation. Russian cylinder oils (8 and 10) give much coke in steamengine cylinders; oils 7, 11, and 12 do not give any coke in steam machines working with superheated steam. Russian dark cylinder oil (13) can be very well applied in steam maR e s i d u e on chines working with saturated steam (no higher than 12 CONRADSON atmospheres pressure).
ASPHALTS KINDO F CARBON 200' e. 250' c. SBDIMENT' RESIDUE Per cent Per cent Per cent American airplane ... 0.12 .... 1.43 American filtered cylinder .. 0.00 .... 1.92 American filtered cylinder . , 5.17 Grainy 2.33 American dark cylinder .. 2.21 Grainy 4.63 Russian airplane, filtered ... 0.09 . .. , 0.86 Russian refined cylinder 0.75 0.46 Grainy 2.20 Russian refined cylinder ... 0.31 .... 2.61 Russian refined cylinder 1.43 1.82 Grainy 2.89 Russian refined cylinder .. 5.60 Grainy 1.26 Russian refined cylinder 3.02 Grainy 1.64 Russian refined cylinder Traces 1,30 .... 3.94 Russian refined cylinder Traces Traces .... 5.56 0.81 3.50 Grainy 3,49 Russian dark cylinder 0 Not diluted with petroleum ether.
LUBRICATING OIL
1 2 3 4 5 6 7 8 9 10 11 12 13
..
.
.
I n order to further prove these conclusions, several lubricating oils were oxidized for 3 hours a t temperatures of 200" and 250" C. and under 15 atmospheres of air. The percentage of asphalts (asphaltenes, carbenes, and some high molecular acids
Conclusions
1-Under the conditions of the Conradson carbon residue test the carbonization of oils depends on the amounts of asphaltenes and tars present in the given oil. Colorless oils and paraffins do not give appreciable amounts of coke when evaporated in the Conradson apparatus. 2-The carbonization values of Conradson are not representative of the carbonization of oils in service. .+-More reliable information can be obtained by determining the stability of the oils with regard to sludge formation. This method is based on the oxidation of oils by oxygen or air under high temperatures and pressures. 4-Different crude oils, lubricating oils, and their tars give different amounts of sediment or sludge under the same conditions of oxidation.
Effect of Antioxidants in Typical Rubber Stocks' Marion C. Reed T H E B. F. GOODRICH COMPANY, AKRON,OHIO
NUMBER of valuable papers have appeared from time to time concerning the use of antioxidants in rubber goods. I n most of these papers tensile strength and elongation before and after varying periods of aging in the Geer oven2 or the Bierer-Davis bomb3 have been the criterion of merit of different antioxidants. Recognizing the value of these tests, the writer wishes to point out certain additional evidence of the usefulness of antioxidants in the rubber industry as shown by other tests as well as by tensile strength and elongation. While antioxidants are of value in a great variety of rubber goods, only a few typical examples are given as illustrating the effects of antioxidants in factory production stocksnamely, tire treads, inner tubes, dry-heat-cured goods, specification stocks, and sponge rubber. I n these examples AgeRite resin was the antioxidant used, since this was the first non-accelerating antioxidant available for use in this plant. After nearly five years of production use, a sufficient background of experience has been obtained to judge the value of this antioxidant in practice. Where available, natural aging results are presented along with artificial aging results.
A
1 Presented before the Division of Rubber Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928. Geer and Evans, Rubber Age (London), I,308 (1921). Bierer and Davis, IND. Eac. CHEM..16, 711 (1924).
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Tire Treads
The effects of 1 per cent of antioxidant on the recipe in a blooming tread stock are shown in Table I. The stocks used in these tests were mixed and cured in the laboratory, making presssheets 15 x 20 x 0.25 cm. (6 X 8 x 3/32inch). The cure was controlled to approximate the actual heat treatment that a tread using the same compound received in the factory. Strips of these stocks were aged in the Geer oven, in sunlight, and in dark boxes in a storeroom. I n the sunlight one set of strips was exposed without tension at 45 degrees from the horizontal, facing south, during ,June to September, 1924. Another set of strips was flexed while exposed to sunlight. After 3 weeks' flexing in sunlight the stock containing antioxidant showed slight surface cracks, while the stock without antioxidant was cracked much worse. Sections of two 30 x 3]/? inch tires were obtained. One using the above tread compound without antioxidant was cured in November, 1923. The other section WRS cured in February, 1924, and carried a tread compound the same except for the substitution of 0.44 part antioxidant for an equal weight of rubber in 100 parts of stock. Other conditions of manufacture and storage were identical. After nearly three years of storage in a fairly dark sample room, the stock without antioxidant was weak as shown by "bite" and hand tests. The stock containing antioxidant was
INDUSTRIAL AND ENGIATEERINGCHEMISTRY
April, 1929
markedly stronger. After nearly five years of storage the difference between the two stocks was even greater. Antioxidants have shown a similar effect in maintaining resistance to tear when aged in the Geer oven and in the Bierer bomb, or in storage in the dark. Abrasion tests after varying periods in the Geer oven have shown the lasting properties of tread stock to be better when containing antioxidant. Table I-Effect of Antioxidants on Tire Tread Stock Rubber 53, zinc oxide 15, gas black 20, and sulfur 3 per cent Accelerator-hexamethylenetetramine
1 yo ANTIOXIDANT
No ANTIOXIDANT
TREATMENT
Kg.1 250 87 49 208 177 159
Lbs./ sq. rn. 3550 1240 700 2960 2520 2260
184
2620
sq. cm.
Original Geer oven 7 days Geer oven 14 days Sunlight 6 weeks Sunlight 10 weeks Sunlight 14 weeks In dark 2 years, 5 months
Kg./
LbsJ
sq. tn.
Yo
690 440 240 600 570 530
sp. cm. 254 167 87 232 221 216
3610 3380 1240 3300 3150 3070
700 560 430 670 610 560
520
219
3120
570
%
Inner Tubes
I n high-gum inner tubes tensile strength is probably not so important as resistance to tear. Inner tubes 29 X 4.40 inches were made up in the factory from two stocks identical except that in one case 0.75 part of antioxidant was substituted for an equal part of rubber in 100 parts of the compound, while the other stock contained no antioxidant. One tube of each compound was run approximately 2000 miles on the dynamometer and tested. Tear was determined on crescent-shaped strips having nicks cut on the concave side. Jaws were fastened to the ends of the crescent and were separated a t the rate of 50.8 cm. (20 inches) per minute. The figures represent pounds per 0.1 inch thickness and are averages of transverse and longitudinal tear. The results of these tests are shown in Table 11. It is noteworthy that resistance to tear after running on the dynamometer decreased when antioxidant was not used. Table 11-Blooming
I
TREATMENT
1
Inner T u b e (80 Per Cent Rubber)
No ANTIOXIDANT
Tensile strength
Kg./ Lbs./ sq. cm.sq. rn. Original-new tube 147 2090 Original-used tube 153 2180" Geer oven 4 daysc 129 1840 Geer o\'en 7 days 119 1690 Geer oven 10 days 95 1360 Geer oven 14 days 53 750 2 days oxygen bomb, 70' C., 300 Ibs. per sq. in. (21 kg. per sq. cm.) 43 610 4 days oxygen bomb 70' C. 300 1s;. per sq. i n y l . .
1 11 .
b c
..
0.75y0 ANTIOXIDANT
IElongation at Teal break
% 730 1 9 . 2 715a 1 3 . 4 ' 665 6.8 600 5.7 565 5.0 465 3.7
475
.
... .,
Kg./ L b s , / q. cm. sq. an. 161 2290 170 2420b 165 2350 167 2370 185 2630 165 2350
% 750 1 8 . 5 6 9 3 18.6b 700 1 6 . 1 700 9.1 620 7.8 605 7.4
172
2440
695
..
92
1300
600
..
i t does not occur in steam cures or cures in dry carbon dioxide. Surface tack is greatly diminished or eliminated by the proper use of antioxidants, especially AgeRite resin. Many stocks now in use could not be handled without antioxidant. Antioxidants also greatly improve resistance to cracking when flexed in sunlight. Specification Stocks
I n many rubber goods artificial aging specifications are imposed. In these cases antioxidants have proved to be of considerable value, often permitting the use of cheaper compounds. The amount of antioxidant to be used in these cases must be determined by the nature of the specifications. In certain cases a minimum acetone extract is specified which will not permit the use of more than a very small amount of antioxidant. A steam hose cover was considerably improved, as indicated by the rack test, by the addition of 0.5 per cent antioxidant on the recipe. Sponge Rubber
A very spectacular example of the value of antioxidants was in black sponge rubber. Samples were taken from factory production, both before and after substitution in to the recipe of 0.5 per cent of antioxidant for an equal amount of rubber. These samples were aged in the Bierer bomb a t 70" C. and 300 pounds per square inch (21 kg. per sq. cm.) oxygen pressure for two days. Without antioxidant the sponge became so brittle in some places it could not be bent without cracking, while the sample with antioxidant was quite live and flexible. Similar results were obtained yith a poorer grade of sponge rubber made in the laboratory and stored in the dark without artificial aging tests. Effect of High Temperatures
In order to get some measure of the value of antioxidants in stocks subjected in service t o high temperatures in the presence of air, a 90" C. air oven test was investigated. Since a short heating a t a very high temperature is known to depolymerize or otherwise adversely affect rubber, it was thought that perhaps long heating a t 90" C. might produce the same effect. A day in air a t 90" C. was found to cause nearly as much deterioration of rubber as a week in air a t 70" C. Aging a t 90" C. in an oven through which commercial nitrogen was passed gave in several trials almost the same results as aging in air a t the same temperature. If, however, the strips were sealed in vacuum or in a small container in purified nitrogen, very little deterioration took place. While long heating a t 90" C. in the absence of oxygen produces overcure in some stocks, heating in the presence of air or an inert gas containing a very small concentration of oxygen causes vastly more deterioration. Table 111-Effect of Heat a n d of Oxygen o n Tire Tread Stock Rubber 53, zinc oxide 15, gas black %O, and sulfur 3 per cent Cured 45 minutes at 146 C. in press Accelerator-hexamethvlenetetramne
1
No ANTIOXIDANT
-
TREATMENT
Tensile strength
Tube run 2113 miles on dynamometer Tube run 1857 miles on dynamometer. All oven and bomb tests are on tubes run on dynamometer.
Stocks Cured in Dry Air
Much footwear and a number of specialty stocks are cured in dry air. It is often a very difficult problem to get stocks to cure properly in dry heat, without becoming tacky and a t the same time not to cure so quickly as to scorch in handling. This surface tack in dry-heat-cures- is due t o oxidation, since
317
KQ./
cm. 269
sq.
Original 7 days in vacuum at 900 c. 2 days in commercial nitrogen at 90' C. 2 days in air a t 90' C 7 days in Geer oven a t 70' C.
Lbs.1
Elonga tion at break
0.5% ANTIOXIDANT ON RECIPE Tensile strength
sq. tn.
%
3830
633
Kg./ sq. cm. 262
Lbs./
Elongation a t break
-
sq. m.
%
3730
633
238
3380
530
241
3430
565
77 71
1100 1010
353 300
102 99
1450 1410
423 400
133
1890
473
190
2700
662
.
318
t
IND IlSTRIAL A N D ENGINEERING CHE;IfISTRY
I n the stocks tested, and probably in all well-balanced stocks that are not highly accelerated, the effect of temperatures up to 90" C. in the absence of oxygen is insignificant as compared a t these temperatures. Similar by Jones,4 who found that three d almost no change in tensile and C. in a vacuum but were markame period in air at 70" C.
of H e a t a n d of Oxygen on Low Zinc Oxide T u b e Stock Rubber 82, zinc oxide 18, sulfur 2.3, and di-o-tolylguanidine 0.5 per cent.
Table V-Effect
TREATMENT
TREATMENT
'
Tensile strength
1
Original
7 days pure nitrogen
at 90' C. 2daysinairat90'C. 3 days in air a t 90' C. 4davsinairat90°C.
1
190 168
1%
2700 2390
;%
1 'EAt *!Onga-
I
593 653
-1
Tensile strength
1 %: 1
2810 3060 2750 2340
E1onga-
%$:'
600 660
4
Jones, IND. ENG.CHEM.,17, 871 (1925).
j
Tensile strength
Kg./ cm. 225
sq. zn.
209 179
2970 2550
sq.
Lbs,./
3200
1 *longa'EAt
1 1 1 I
;?:'!;IT
Tensile strength
Kg./
LbsJ
2 0
226
3220
625 773
219 230 212 197
3120 3270 3010 2800
I
I
.
2.57, ANTIOXIDANT
I I
I '% :%:I ii! I
sq.
cm. sq. zn.
break
1I 1
. 7 2 613 738 730 740 -
-. -
Conclusion
:i; -
The effect of air at 700 c. and Of air, 'ornmercia1 nitrogen, and vacuum at On a tread stock with and without antioxidant is shown in Table 111. Deterioration in 2 days in commercial nitrogen or air a t 90" C. was very great. Seven days a t 90" C. iii vacuum caused only a slight oie&u-e. The effects of purified nitrogen in 9. seaied flask and of air at 90" c. in a high zinc oxide tube stock, both without and
No ANTIOXIDANT
Original 7 days pure nitrogen at 90' C. 2 d a y s i n air at 90OC. 3 days in air at 90' C . 4 daysin air at 90OC. I
7, 603 198 215 193 163
I
1 1
1.57, ANTIOXIDANT
21, s o . 4
with 1.5 per cent antioxidant on the recipe, are shown in Table IV. Results of similar tests with a low zinc oxide tube stock are shown in Table V, in which 2.5 per cent antioxidant on the recipe was used.
TaYle IVLEffect of H e a t and of Oxygen on High Zinc Oxide T u b e # ,it I Stock
No ANTIOXIDANT
1701.
The results of these tests show that antioxidants are of value in stocks which become hot in service, such as bus tubes, belt frictions, and h e a w truck tire treads. It is believed that aging a t 90" C., both in air and in an inert gas free from oxygen, will be of assistance in separating the factors of oxidation and Overcure in designing rubber compounds for resistance to heat. Acknowledgment
The writer wishes to express his appreciation to friends for the use of data, and particularly to H. A. Winkehann for results on sunlight and Geer oven aging on tread stocks.
Some Characteristics of Amorphous Wax' Leo D. Jones and F. E. Blachly SHARPLES SPECIALTY COMPANY, PHILADELPHIA, PA.,
MAX B. MILLER& CO., INC.,NEWY O R K , N. Y.
Conditions Necessary for The various differences between crystalline wax and HE dewaxing of petroPrecipitation of Amoramorphous wax have been described, as well as the leum lubricating stock phous Wax in a various conditions whereby wax is precipitated by procedures involvcrystalline or amorphous state. A surface tension and T h e r e are several condi- . ing the use of centrifugal force colloidal theory has been proposed to account for the tions which must be fulfilled for the separation of the wax occurrence of amorphous Wax. in the DreciDitation of amorhas become of increasing corn- . phous wax in order that it, mercial importance in iecent years. The centrifugal process for the production of bright may be satisfactorily removed centrifugally from the liquid stock is in practically universal use in the United States. phase containing the lubricating stock. There must be a SUEConsiderable quantities of ('long residuum" are dewaxed cen- ciently complete precipitation of the wax and this precipitate trifugally and this procedure is extending rapidly into the must be coarse enough for its rapid and complete removal. These factors are controlled by the nature of the solvent used field of dewaxing heavier lubricating distillates. Since the centrifugal process is primarily adapted to the for diluting the lubricating stock, the amount of solvent used, dewaxing of those stocks containing wax that is precipitated and rate, extent and character of chilling. For the centrifuin the amorphous form, a study of the conditions affecting gal removal of precipitated wax from a liquid, it is essential the occurrence of amorphous wax and of theories as to its that there be a definite specific gravity difference between nature becomes desirable. Just as there are petroleum stocks the solid wax and the liquid phase in order that the centrifufrom which crystalline wax can be precipitated which is gal force may have something to act upon. This difference ideal for filter-pressing and sweating, and favorable technic in specific gravity is controlled primarily by the kind of for precipitation of the wax exists, so there are stocks from solvent employed and secondarily by the quantity of the which an amorphous wax can be precipitated most favorably solvent. A final and very important condition in the prefor centrifugal separation, and favorable technic for the pre- cipitation of wax for its centrifugal removal, and the one with which we are concerned in this paper, is that the wax, cipitation of amorphous wax exists. when separated from the liquid and compressed to a homo1 Presented before the Division of Petroleum Chemistry at the 76th geneous layer in the rotating bowi of the centrifuge, shall be Meeting of the American Chemical Society, Swampscott, Mass., September sufficiently amorphous t,o flow under the forces produced by 10 to 14, 1928.
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AND
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