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Rheological behavior of cycloolefin copolymer/graphite composites



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