Abstract
For a radiator hose made of carbon black filled EPDM(ethylene-propylene diene monomer) rubber, a measuring method of crosslink density was established to analyze the aging behaviors under thermooxidative stresses. The crosslink density of the rubber specimens decreased slightly in the initial stage, but increased with increasing the aging time. Such variation was similar to that of tensile strength. This might be due to the formation of sulphoxide crosslinks as well as to additional crosslinks made by the reaction of unvalcunized sulfurs. A high temperature aging of rubber specimens at 180 caused a slight increase in crosslink density while it did a large decrease in tensile strength and elongation. In this case, the formation of carbonyl groups in EPDM molecule chain and formation of sulphoxide crosslink, rather than the crosslink density variation, had a large influence. Particularly, on the surface skin area a rapid degradation was observed. This implies that internal structure factors causing the changes in cross-link density and mechanical properties due to degradation are significantly different depending on the temperature.
Keywords: cross-link density measurement, thermal oxidative aging, rubber hose, EPDM(ethylene-propylene dine monomer)