Abstract
Crosslink density measurement considering carbon black fraction was performed to study the thermo-oxidative ageing behaviours of a radiator hose made of carbon black filled EPDM (ethylene-propylene diene monomer) rubber. The crosslink density and the strength of the skin part of the rubber specimens decreased slightly in the initial stage at 125℃, but increased with increasing the ageing time. The elongation at break considerably reduced showing no similarity to the behaviours of the cross-link density. This might be due to the formation of rigid sulphoxide crosslinks as well as to additional crosslinks made by the reaction of unvalcunized sulfurs. A high temperature ageing of rubber specimens at 180℃ caused only a slight increase in crosslink density, but it caused a large decrease in tensile strength and elongation particularly showing a rapid increase of microhardness accelerated in the surface skin region. The formation of carbonyl groups in EPDM molecule chain and the formation of rigid sulphoxide crosslink, in comparison with the crosslink density variation, had a large influence.
Keywords: cross-link density measurement, thermal oxidative ageing, rubber hose, ethylene-propylene diene monomer (EPDM), mechanical analysis