Analysis of Whitening Phenomenon of EPDM Article by Humid Aging

An ethylene-propylene-diene terpolymer (EPDM) article used for a car component was aged in 80 degrees C humid air (60% relative humidity) for 30 days and in 80 degrees C tap water for 7 days. The aged sample surfaces were changed to white. The aged sample surfaces were analyzed using GC/MS, image analyzer, SEM, EDX, and ATR-FTIR. Calcium stearate was found on the aged sample surface. To confirm the whitening phenomenon, three sulfur-cured EPDM composites with different reinforcing systems (talc/carbon black, calcium carbonate/carbon black, and clay/carbon black) and one resole-cured EPDM composite were prepared and aged in 90 degrees C tap water for 7 days. The sulfur-cured EPDM composites contained stearic acid, whereas the resole-cured EPDM composite did not contain stearic acid. Whitening occurred in the sulfur-cured EPDM samples irrespective of the filler systems but the aged resole-cured EPDM composite surface was not changed. The whitening was due to the formation of calcium stearate as a result of reaction between calcium cation and stearic acid. The calcium cation came from humid air and tap water, while the stearic acid came from the sulfur-cured EPDM samples. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2451-2457, 2012