The influences of moisture in un-crosslinked rubber on mechanical properties and crosslinking reaction were investigated in dicumyl peroxide (DCP)-crosslinked ethylene-propylene-diene terpolymer (EPDM), sulfur-crosslinked EPDM and sulfur-crosslinked natural rubber (NR).
The influences of water at the crosslinking reaction on mechanical and aging properties for DCP crosslinked EPDM and sulfur crosslinked EPDM were little. On the other hand, presence of water at the crosslinking reaction in the sulfur crosslinked NR made the crosslinking reaction progress excessively by shortening its scorch time, resulting in changing the properties such as mechanical strength and crosslink density, and deterioration of mechanical strength occured early. It was assumed that the water in un-crosslinked NR accelerated crosslinking reaction by promoting the formation of zinc stearate from stearic acid and zinc oxide, although the water in un-crosslinked NR at the crosslinking reaction did not directly react with NR molecule.