Rheological behavior of cycloolefin copolymer/graphite composites

Abstract In this study, morphological and rheological properties of cycloolefin copolymer (COC)/graphite composites prepared in a twin screw extruder by using various amounts of graphite (G) and expanded graphite (EG) were investigated in detail. Rheological behaviors of the samples were measured in a dynamic oscillatory rheometer in the melt state. Rheology data were analyzed in different ways in order to quantify the microstructural features which indicate the solid‐state physical properties of the composite materials. In the linear viscoelastic region, increasing of storage modulus ( G ′) with the filler amount and the van Gurp‐Palmen plots were used to determine the percolation threshold which is the critical filler amount for the physical network formation by the G sheets. Percolation threshold values were found to be about 21.5 phr and 3.8 phr for the G‐ and EG‐loaded samples, respectively. Microstructures of the samples which include quite higher amount of filler than the percolation were observed in a scanning electron microscopy. It was found that the sheets of pristine G maintained their original stack form while the EG was successfully dispersed in the COC phase and formed three dimensional house‐of‐card structures without a compatibilizer. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers