Investigation of the microwave attenuation performance and structure-property relationship for graphite-filled cyclo-olefin copolymer composites

This study examined the morphological, rheological, viscoelastic, electrical, and microwave attenuation properties (RADAR absorbent and EMI shielding) of cyclo-olefin copolymer (COC) composites prepared with the melt mixing method by using different amounts of graphite (0-75 phr). Rheological percolation threshold of the graphite was determined as similar to 38 phr. The RL analyses of the composites showed that the composites containing a moderate filler content (45 phr) exhibited the best radar absorption performance. Absorption bandwidth and minimum reflection loss (RL) value for the sample containing 45 phr of graphite were determined as 2.335 GHz (10.165-12.5 GHz) and -39.89 dB, respectively. Total shielding effectiveness (SET) values of the sample including 75 phr of graphite varied in the ranges of 30 to 47.5 dB for the sample thicknesses of 7 mm. The correlation of the microstructural parameters and microwave attenuation properties of the composites indicated that the minimum RL value could be obtained at a filler concentration close to the rheological and electrical percolation thresholds. However, it was also revealed that acceptable shielding effectiveness values for commercial applications could be obtained by the samples with higher filler concentrations than the electrical percolation threshold.