The Effects of Ethylene Content and Mooney Viscosity of EPDM Polymers on the Mixing Efficiency and Physical Properties of EPDM/IIR Blends

EPDM rubber is widely used in blends with butyl rubber (isoprene-isobutylene rubber, IIR) in tire inner tube applications (automobiles, motor cycle, and bicycles) to improve the heat and ozone resistance of the compound. The choice of the EPDM is low ethylene, low diene and medium-low Mooney viscosity polymer according to tire manufacturers, The reasons given by them are that low Mooney, amorphous EPDM is easier to be blended into butyl rubber during mixing because no melting of the crystallites is necessary, thus requires shorter mixing time, and the low diene monomer of the EPDM is required to match the cure rate of butyl rubber and provide good heat resistance.

EPDM polymer samples of varying ethylene and polymer Mooney viscosity were evaluated to elucidate the effects of these molecular parameters on the mixing time required to produce homogeneous compound in blending with butyl rubber.  Physical and rheological tests were performed on each compound sample mixed at different length of time and the results will be discussed.