Conducting carbon black filled EPDM vulcanizates: assessment of dependence of physical and mechanical properties and conducting character on variation of filler loading

The effects of incorporation of different extents of extra conducting carbon black as filler on some selected physical and mechanical properties, aging behavior and DC electrical conducting character of vulcanizates of ethylene-propylene diene monomer (EPDM) based compounds have been studied. Increasing carbon black loading caused a monotonic increase in density and hardness and in tensile strength with a leveling off trend for carbon black filler loading >40 phr. Elongation at break of the initial EPDM vulcanizates, however, passes through a maximum corresponding to 20 phr carbon black loading; the position of the maximum shifts to 30 phr carbon black loading on aging of the vulcanizates at 135°C for 7 days. DC electrical conductivity measurements of the filled EPDM vulcanizates indicate a percolation concentration range over 15–30 phr of conducting carbon black loading. Trends of change in voltage (V) developed with increase in the current (I) applied for the carbon black filled EPDM vulcanizates at different temperatures commonly indicate ohmic behavior for application of current up to a critical level. Beyond the critical current (IC), the developed voltage becomes practically insensitive to large enhancements in the applied current; the filled vulcanizates, thus, exhibit non-ohmic character for I>IC. An attempt has been made to analyze and interpret the observed effects. Electromagnetic interference (EMI) shielding effectiveness (SE) generally increases on increasing the carbon black loading. Vulcanization substantially contributes to enhancement in the EMI SE of the filled EPDM compounds.