Study On Structure And Properties Of Carbon Nanotubes Filled PC Composites

In this dissertation, using multi-walled carbon nanotube (MWNTs) as fillers, polycarbonate (PC) as matrix, conductive polymer composites were produced by a torque rheometer, and then hot compression-molded into a sheet. The effects of contents, aspect ratios and surface treatment of fillers on micro-structure and electrical conductivity properties were investigated. Particular attentions has been paid on the effect of filler structure and surface character on conductive network formation of the composites, and a thermodynamic percolation model was proposed to fit the kinetics of the conductive network formation under electric field.The room volume resistivity of MWNT, s-MWNT and MWNT-COOH filled PC composites showed percolation clearly. The percolation threshold of PC/MWNT, PC/s-MWNT, PC/MWNT-COOH were 1.66vol%, 3.58vol% and >3.48vol%, respectively, due to the large aspect ratio of MWNT resulting in the very low percolation threshold in PC/MWNT composites. The classical percolation theory was used to fit the room temperature resistivity of conductive filler content, and analysised with MATLAB software, the result showed that the whole curve fitted well with the classical percolation theory.An in-situ method, named as dynamic percolation, was used to study the kinetics of conductive formation of the composites in the non-electric field conditions. The results showed that the percolation time, characterized at a certain annealing time where the electrical resistivity started to decrease drastically, decreased with the increase of both the filler concentration and the annealing temperature. The activation energy of conductive network formation (Ec) for PC/MWNT, PC/MWNT-COOH and PC/s-MWNT was 116, 123 and 98kJ/mol, respectively. The Ec was related to the structure and the interfacial interaction of MWNT-polymer. Furthemore, based on the classical percolation theory and modified thermodynamic percolation model, a new model was proposed to predict the electrical resistivity at the different annealing time. The predicted data fitted the experimental results very well.Electric field induced alignment and conductive network formation of s-MWNT and s-MWNT-COOH in the PC melt were investigated by in-situ tracing the time dependence of electrical resistivity during isothermal treatment. The results showed that the percolation time for PC/fillers composites decreased sharply with increasing the electric field, indicating that aggregation of fillers to form conductive network was greatly accelerated duo to the field induced filler alignment. Based on the Arrhenius equation, the classical percolation theory and modified thermodynamic percolation model, a new model was proposed to predict the zero-shear-rate viscosity at the different temperatures. Furthemore, the contrast of studies in LDPE/CB, LDPE/s-MWNT, PC/CB and PC/s-MWNT composites present that activation energy of conductive network formation under various electric fields was mainly affected by the shape of conductive fillers, rather than the characteristic of matrix. Finally, based on the classical percolation theory and modified thermodynamic percolation model, a new model was proposed to predict the electrical resistivity at the different annealing time under electric field. The predicted data fitted the experimental results very well.