Effect of processing on the properties and morphology of MWCNT-polymer networks

Abstract The objective of this study was to determine the effect of processing on the electrical properties and microstructure of MWCNTs/PMMA nanocomposites made by compression molding. Three different mixing methods were used: mechanical, solution, and melt mixing of the same starting materials. The composite microstructures were found to be segregated, agglomerated, and randomly distributed respectively. Electrical property measurements indicate that the mechanically mixed composites have the lowest percolation threshold of 0.05 phr (0.028 vol% MWCNT). Melt mixed composites have the highest percolation threshold of 4 phr (2.161 vol% MWCNT) while solution mixed composites have a percolation threshold of 2 phr (1.102 vol% MWCNT). These results indicate that the segregated microstructure allows for the CNTs to form a percolated network through the composite more easily than the other two methods. Fitted equivalent circuits to the measured impedance spectra show that after percolation the CNTs dominate the electrical properties as represented by an increase in the number of inductance circuit elements. Before or at percolation, the presence of PMMA plays a stronger role in the circuit. This article is novel in that this is the first study where direct comparison of the properties and microstructure of composites fabricated utilizing three different mixing methods using the same source materials can be made.