Polyolefine blends of ethylene-propylene-diene terpolymer (EPDM) and polypropylene(pp) have been studied. Blends were prepared in a laboratory internal mixer where EPDM phase was cured under shear with dicumyl peroxide(DCP) at different shear conditions(Blend-cure). Blends were also prepared for comparison from EPDM which has been dynamically cured in the absence of PP(Cure-blend).
The effect of DCP concentration, shear intensity of the mixing, and rubber/plastic composition were studied. The melt viscosity was measured by a capillary rheometer. The rate of crystallization and the degree of crystallinity were determined by differential scanning calorimetry. The tensile tests were done according to ASTM D 1708.
In Blend-cure, the melt viscosity increased with increasing DCP concentration at 75% EPDM and decreased with increasing DCP concentration at 75% PP for EPDM/PP blends. In Cure-blend, however, the melt viscosity increased with increasing DCP concentration for all compositions. The melt viscosity decreased with shear intensity of mixing presumably due to the formation of the segregated microdomain of the crosslinked EPDM gels for both cases.
The crystallization rate was higher in EPDM/PP blends than PP homopolymer. The crystallization rates for various blending conditions were also compared.
In Blend-cure, the tensile strength decreased with increasing DCP concentration for 50/50 and 25/75 EPDM/PP blends, and increased for 75/25 EPDM/PP blend. But, tensile strength increased with DCP concentration in Cure-blend for 50/50 and 25/75 EPDM/PP blends.
Increasing shear intensity of the mixing, significant changes in mechanical properties were not observed. But, the melt viscosity decreased with increasing shear intensity. It will give a good processability in a crosslinked EPDM blends.
