November, 1929
I1liDUSTRIA.L AhTDENGINEERING CHEMISTRY
and sometimes even in cotton and rubber; therefore, they are a fruitful cause of unexpected deterioration.
1019
Therefore, the use of antioxidants is the practical answer to the aging problem. Acknowledgment
Conclusion
I n view of the many variables involved in accelerated and shelf aging, and of the fact that the correlation between the two is only qualitative, it is believed that there are two practical answers to the aging problem. One is incessant care. If the stock is properly balanced, if certain impurities are absent, and if the state of vulcanization is correct, good aging will be obtained. The other answer, which seems to he safer, is to use antioxidants. A certain antioxidant has always improved the aging of all sorts of stocks under all conditions; prohahly other antioxidants will 110 as well.
The author desires to express his indebtedness to J. \V. Temple and RI. W. Mead for their valuable assistance in the preparation of this paper, and to J. F. Reid for a portion of the data. Literature Cited Bierer and Davis, IND. END.CHEX.,16, 711 (1924). Bierer and Davis, Zbid.. 17, 860 (1925). Geer and Evans, India Rubber W o v l d , 64, 887 (1921). McKee and Depew. IND. ENG.CHEM.,20, 484 (1928). ( 5 ) Reed, fbid., 21, 316 (1929). (6) Stevens, India Rubber J . , 61, 310 (1921). ( 7 ) Tener, Smith, and Holt, Bur. Standards, Tech. PaPcr 342 (1927). (1) (2) (3) (4)
Correlation between Geer Oven and Natural Aging of Selected Tire Compounds A. H. Nellen and H. M . Sellers LEE TIRE & R U R R B RC O R P O R
HE Geer oven used was the standard equipment with circulating air, and tests were made a t 70" C. The samples for the natural or shelf-aging tests were placed one upon the other on shelves at ordinary room temperature which varied from 65" to 90" F. (18" to 32" C.) depending on the season. An attempt was made to correlate these Geer tests with shelf-aging tests in a broad way, but all generalizations which suggested themselves were open to serious objections. For instance, the shelf-aged results showed that certain carcass and tread compounds accelerated with a n aldehyde-amine type of accelerator aged considerably better than similar compounds accelerated with a guanidine. These same compounds when aged in the Geer oven do not show the same relative deterioration. Since this difference is due solely to the accelerator used, it is evident that a n accurate comparison between oven- and shelf-aged tests can be made only when the same accelerator is used throughout the test. The writers therefore selected stocks accelerated with phenyl-otolylguanidine, which had been oven-aged 4, 8, and 12 dayc, and shelf-aged 1, 2, and 3 years, and confined themselve. to two standard tread compounds and three standard carcass compounds as follows: ( a ) all-rubber tread compound (sp. gr. 1.30), (b) 10 per cent shoddy tread compound (sp. gr. 1.13), (e) pure-gum carcass compound, (d) 5 per cent shoddy carcass compound, and ( e ) 30 per cent shoddy carcass compound. The inodulus a t 300 per cent for tread compounds, the modulus a t 500 per cent for carcass compounds, also the elongation. tensile strength, and tensile product were tabulated for each compound and cure. To give quantitative expression to the test data, each result was calculated as a percentage of the original result for each of the four criteria. For example, if the modulus at 300 per cent on a tread stock was 1000 pounds per square inch (70.5 kg. per sq. cm.) for 25minute cure a t 290" F. (143" C ) on the 1-year natural test and the niodulus for the original test was 850 pounds per square inch (59.9 kg per sq. cin.), the result would be expressed in percentage of the original, or 117.8 per cent. These percentages were then averaged and these averages are given in the accompanying table. On ( a ) and (b) twenty tests were used for the 1- and 2-year tests, and also for the 4and 8-day teqt., whilc ten tests r e r e U S P ~for the 3-yPar and
T
ITION,
CONSHOHOCKEN, PA.
12-day tests. For the carcasb stocks, ( e ) , ( d ) , and ( e ) , tmentytwo results were used for the 1- and 2-year and 4- and 8-day tests. For the 3-year and 12-day tests six tests were compared. The ratio percentages below each figure were obtained by dividing the oven percentages by the natural percent ages. The range of cures a t 290' I?. (143" C.) was 25 to 100 minutes for the tread compounds and 15 to 35 minutes for the carcass compounds. These included under cures, optimum, and over cures on all compounds. Comparison of Natural a n d Oven Aging of Tread a n d Carcass Compounds (Calculated as percentage of original result)
TEWILE TENSILE ~ I O D U L U S ELONGATION STRENGTH PRODVCT KISD O F
.%GIh.G
Tread
Tread
FZs- Tread&: :
Tread
% I 7 %4 . 2
c;:
7 0 %
$ 7 0
120.6 144 9 131.4 1 2 2 . 8 108.9 84.7
90.7 9 3 . 6 88.1 9 9 . 4 97.1 106.2
8 2 . 6 101.5 81.5 9 6 . 4 9 8 . 6 95.0
91.1 7 2 . 2 92 1 9 7 . 3 101.1
Satural, 2 years 157.9 148.5 Oven, S days 1 2 4 . 0 111.9 Ratio 78.5 75.3
78.3 9 2 . 5 1 0 9 . 2 105.6
7 1 , 7 87.6
65.5 77.4 59.7 8 0 . 4 91.1 104.0
46.5 68.8 4 7 . 6 74.6 1 0 2 . 3 108.4
A-atural, 3 pears 139.5 109.4 Oven, 12 days 119.7 9 2 . 0 Ratio 85 8 8 4 . 1
6 6 . 8 89.6 63.2 82.5 94.6 9 2 . 0
45.2 5 6 . 8 39.3 36.1 86.9 63.5
30.8 51.8 25.8 2 9 . 5 83.7 58.9
Satural, 1 yPar Oven, 4 days Ratio
%
JIoDvLvs-It will be seen that under shelf-aging conditions for carcass and tread compounds the modulus stiffens in 1and 2-year tests and then softens in the third year. I n the oven aging the modulus stiffens in 4 days and softens in 8 and 12 days. The effect of the heat of the oven is quite marked. ELomATIox-The I-. 2-, and 3-year natural-aged tests
