The rheological behavior of carbon nanofiber-reinforced thermoplastic composites

A rheological study of the thermoplastic HDPE filled with vapor grow carbon nanofiber (VGCNF) has been performed with a RheoStress 150 Tester. VGCNF having average 50 nm diameter were used. These nanofibers were purified to provide for an open network of high purity nanofibers. A rheomixer was used to disperse the nanofibers uniformly in the polyethylene matrix because of shear working conditions. The influence of fiber loading, frequency and temperature on the rheology was investigated. Studies were carried out in the temperature range of 160 to 210°C and frequency range of 0.062 to 628.3 rad/s. The rheological measurements show that the composites behave as pseudoplastic. Viscosity of the system decreased with increase of temperature. Significant modulus enhancement occurs at low temperature range due to stiffness imparted by the fiber and efficient stress transfer at the interface between nanofiber and matrix. The viscosity difference between composite and pure polyethylene drops steeply when frequency goes higher than 628.3 rad/s which shows that the difficulty of processing advanced electrical products with VGCNFs is not an issue at higher shear rates. In the mean time, it has been realized that the rheological behavior of VGCNF reinforced polymer system cannot be modeled by an existing single mathematical model.