When more EPDM or R-EPDM was
added to the natural rubber, the compatibility between the
blends decreased. EPDM and R-EPDM are highly saturated
elastomers due to their saturated backbones and low diene
content. The blending of EPDM or R-EPDM with highly
unsaturated natural rubber resulted in a cure rate
mismatch in the rubber phases. The difference in the molar
concentrations of double bonds in each elastomer resulted
in differences in the polarity, number of allylic sites for
sulphur vulcanisation and reactivity of the crosslink sites