A Study of the Effect of Mixing Method and Particle Size on Polymer Composites

In this study three mixing methods, mechanical, melt and solution, are directly compared when making carbon nanotube (CNT)/ polymethyl methacrylate (PMMA) composites. The samples were characterized using impedance spectroscopy and micrography. The effect of particle size is also explored using nano-, micron-, and whisker silicon carbide (SiC) with a PMMA matrix using the mechanical mixing method. Results show that mechanical mixing provides the lowest percolation threshold (0.05 wt% CNT) and lowest resistivity (0.237 Ωcm @ 0.249 wt% CNT), close to that of pure CNT. With the SiC composites, the nano-SiC composites achieved the lowest percolation (1.96 wt% SiC). With both the CNT and SiC composites, mechanical mixing formed a grain-like microstructure with the filler particles going into the grain-like boundaries. Melt mixed samples formed dispersed microstructures, and solution mixed samples formed agglomerated microstructures. Further analysis was done by fitting the electrical data to equivalent circuits and attributing each component to a part of the circuit.