A systematic electrical and rheological characterization of percolation in commercial polydisperse polystyrene (PS) nanocomposites containing multiwall carbon nanotubes (MWCNTs) is presented. The MWCNTs confer appreciable electrical conductivities (up to ca. 1 S/m) to these nanocomposites at a concentration of 8 vol %. In addition to enhancing the electrical properties, even at small concentrations (ca. 2 vol %), MWCNTs significantly enhance the rheological properties of PS melts. At concentrations exceeding 2 vol %, a plateau appears in the storage modulus G‘ at low frequencies, indicating the formation of a percolated MWCNT network that responds elastically over long timescales. Network formation, in turn, implies a diverging complex viscosity vs complex modulus curve. A focus of this study is on the correlation between electrical and rheological properties at the onset of percolation. The experimental results indicate that the elastic load transfer and electrical conductivity are far more sensitive to the onset of percolation than the viscous dissipation in the nanocomposite. Sensitivity of the electrical and rheological percolations to two different solvents used in processing the nanocomposites has also been characterized.

Industrial production of nanocomposites could revolutionize the polymer industry. The NASA Goddard project Oriented Nanocomposite Extrusion (O.N.E.) is developing a process to produce desirable nanocomposites that can easily be scaled up and transferred to industry. This development uses a researchscale twin screw extruder (TSE) based at the University of Maryland. A major need for this process is a method for online characterization of the polymer composition.This project focuses on using pressure measurements, in combination with correlations for inferential, online characterization of the composition. Pressure measured near the entrance of the die is dependent on the temperature, flow velocity, and composition of the nanocomposite being produced. Since temperature and flow velocity can be directly measured, the correlation allows for online calculation of the composition of the polymer composite.A correlation was developed that related pressure to the flow velocity and screw speed. The temperature probe was found to be faulty, so the correlation used screw speed measurements as a substitute for the temperature of the polymer melt. Temperature of the melt is affected by viscous heating due to the rotating screws, enabling screw speed to be used as a possible substitute. During the research, major findings include the faulty temperature probe and a periodic variation in pressure. The periodic variation in pressure was caused by variations in the polymer flow rate that results in thickness variation of the extrudate on the order of 20% (+10%).Recommendations are made for investigations of the temperature probes, the feeder flow rate, and the installation of the pressure probe.