Thermoplastic interpenetrating polymer networks(TP IPN's) were prepared using ethylene-propylene-diene terpolymer(EPDM), high density polyethylene(HDPE), and dicumyl peroxide(DCP) in a laboratory internal mixer. A conventional thermoset blend was also prepared for comparison by curing in a press.
The effect of DCP concentration, shear intensity of the mixing, and rubber/plastic composition were studied. The melt viscosity was measured by an Instron capillary rheometer, and the tensile tests were done according to ASTM D 1708. The degree of crystallity and rate of crystallization were measured by differential scanning calorimetry(DSC). The melt viscosity increased with increasing DCP concentration, and decreased with shear intensity of the mixing presumably due to the formation of the segregated microdomain of the crosslinked EPDM gels. The crystallinity decreased with increasing DCP concentration and slightly increased with increasing shear intensity of the mixing. The crystallization rate was higher in a dynamically cured sample than in a press cured.
Increasing DCP concentration, the tensile strength increases and elongation at break has a maximum at some concentration. Dynamic cure gives lower tensile strength and elongation at break than press cure. But dynamically cured blends have better processability and superior mechanical properties than linear EPDM/HDPE blends.
