1649
V O L U M E 2 3 , NO. 11, NOVEMBER 1 9 5 1 severe action on natural rubber stocks, it is used to illustrate the extreme conditions that might be caused by material migration (Figure 7 and Table IV). Two of the last three stocks contain cupric oleate in conil1in:ition n-ith various quantities and
NIDUAL AGING
1
I
I
I
sulfur moves from one htwk to another. The differences in per cent sulfur obtained are small and therefore inconclusive. Additional precise testing is required. The question of methods of avoiding migration arises. An attempt was made to prevent migration during oxygen bomb aging by placing the different stocks in individual aluminum can? with lome-fitting lids within a single bomb. Data available but unreported shoir that aging in these containers is equivalent to group aging, without containers, and the results are significantly diffeient from those obtained by individual aging. It is concluded, therefore, that the use of this device is not the solution to the migration problem. The only adequate solution appears to be aging different stock? in separate bombs. All samples contained in a bomb at a given time must he of identical composition if results are to be reliable SUMMARY
0
2273" '2360
TENSILE (psi) Figure 7 . Effect of Migration of Cupric Oleate on Protected and Unprotected Stocks Aged as a group and aged alone
types of antioxidants. All three stocks melted when aged as a group, but when aged individually, stocks I and J showed a good retention of physical properties IDENTIFICATIOR OF .MIGRATING MATERIALS
I n the early experiments, the phenomenon being studied was assumed to be migration, although no confirming data were available. In order to confirm or deny the hypothesis of migration, qualitative chemical tests were run on samples after community aging in an attempt to detect the presence of a migrating material in a stock whei e originally none was present. The presence of antioxidants was confirmed by means of spot test identification ( I O ) . Stocks which originally contained no antioxidant showed a negative spot test, but after community aging gave positive tests for the presence of an antioxidant. This antioxidant was the same as that contained in one of the other stocks of the community group. Quantitative sulfur determinations ( I ) were performed to confirm the migration of sulfur from one stock to another. The results obtained were sufficient only to indicate that probably
It has been definitely established that various materials migrate and that the magnitude of resulting test error is significant Migration rvill take place whenever unlike stocks are aged together in a bomb. The most reliable test conditions prevail when separate bombs are used for individual stocks. It is reconimended that specifications for oxygen bomb aging be changed. The change should specify the use of individual bombs. ACKNOWLEDGMERT
The authors wish to express their appreciation to The Gates Rubber Co. for permission to publish this report, to Harold Thenhaus who prepared the graphs, and to other members of the staff for constructive criticism in preparation of this manuscript. LITERATURE CITED
(1) Am. SOC.Testing Materials, B.S.T.M. Designation D 297-43T. (2) Ibid., D 572-48. (3) Buist, J. hl., and Welding, G. S . , 7'7737~5. Iwt. Rubber I d . . 21, No. 2 , 60 (1945). (4) hlorgan and Ksunton, Rubber Chem. & Technol., 12, 235-60 (1945). (5) Neal, Bimnierman, and Vincent, Ibid., 16, 453-65 (1943). (6) Newton, R. G., and Scott, J. R., Ibid., 20, 760-8 (1947). (7) Schoch, M. G., and Juve, A. E., A.S.T.M. Symposium on Aging of Rubber, Chicago, Ill., March 2, 1949. (8) Shelton, J. R., and TT'inn, Hugh, Ind. Eng. C h m . , 39, 1133 (1947). (9) Vanderbilt Rubber Handbook. 9th od., p. 455, 1948. (10) I b i d . , p. 514.
RECEIVED March 2 , 19.51. Presented before the Division of Rubber Chemistry. AMERICAN c ~ ~ r 1 cS O. C4I E~T Y . Washington, D. C., March 2, 1951.
Nondestructive Aging Tests for Rubber l
