Natural rubber/ethylene propylene diene blends for high insulation iron crossarm

Abstract

This research studied composition and behavior of natural rubber (NR) and ethylene propylene diene (EPDM) blends at carbon black concentrations (0-30 phr) in terms of electrical resistivity, dielectric breakdown voltage testing, and physical properties. The blends having the electrical properties suitable for application in high insulation iron crossarms were selected for investigation of compatibility and increased physical properties. Effect of the homogenizing agent concentration on improvement of compatibility of blends was studied by scanning electron microscopy, pulsed-nuclear magnetic resonance spectroscopy, rheology techniques, and mechanical properties, such as, tensile strength, tear strength, elongation at break, and hardness. Effect of the NR/EPDM blends filled with a fixed concentration of silica was investigated for ozone resistance. The carbon black content as high as 10 phr is still suitable for insulation coating material, which can withstand electrical voltage at 10 kVac. Addition of the homogenizing agent of 5 phr can increase the mechanical properties of blends as evidenced by the positive deviation of shear viscosity of the rubber blend, as resulting from the calculated shear viscosity being higher than that of experimental data. Moreover, the pulsed NMR results indicated that spin-spin- relaxation (T2) of all three components of the rubber blend was compressed upon the addition of the homogenizing agent. The ratio of NR/EPDM blend, which resists the ozone gas is 80/20 by the addition of silica of 30 phr into the blend. Besides that, the filled NR/EPDM with silica decreased the change of thermal and mechanical properties of blends after thermal ageing. The synergistic effect of silica content and high NR content (80) in 20 phr EPDM could improve antioxidation by ozone in the absence of normal antioxidant for natural rubber.