Studies on electrically conductive composites of ethylene propylene diene monomer rubber and steel fibers

Electrically conductive composites comprised of ethylene propylene diene monomer (EPDM) rubber and steel fibers were prepared by an open mill mixing method. Fibers of two distinctly different lengths (5 mm and several meters) were used and the influence of these fibers on electrical conductivity, mechanical, thermal, and physical properties of the composites was investigated. Composites with different compositions were prepared by varying the loading levels of fibers from 20–100 phr (parts per hundred parts of rubber). Homogeneity of the composites was determined using scanning electron microscopy. Further analysis included the measurement of resistance, hardness, tensile strength, tear strength, rebound resilience, etc. The results of the analysis revealed that the addition of steel fibers rendered conductivity to the otherwise insulating EPDM rubber even at small loading levels, however, the length appears to have negligible effect on conductivity. In case of short fibers, the resistance of composites was observed to decrease from > 40 MΩ (Initial value of EPDM rubber) to 25 KΩ at a loading level of 20 phr with a further significant decrease of the order of 10³, that is around 18 Ω at 100 phr. Composites with long fibers exhibited resistance in the range of 15 kΩ–70 Ω at loading levels between 30 and 100 phr. The conductivity of the sample is observed to be altered negligibly on ageing. Mechanical properties such as hardness, tensile, and tear strength were observed to be enhanced in case of composites except resilience which decreased by 29 % in comparison to EPDM rubber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011