Miriyala, Sethu M. (2009-05). Effect of composite microstructure on electrical and mechanical properties of poly(vinyl acetate) composites with carbon black and clay.. Master's Thesis.
Thesis
The electrical and mechanical behavior of carbon black filled poly(vinyl acetate) latex-based and solution-based polymer composites was examined. A set of experiments were performed to distinguish composites with a segregated network (emulsion-based) from those with random dispersion (solution-based) of the filler. The percolation thresholds for the emulsion-based composites were near 1.2 vol% carbon black, while the solution-based composites were around 8.2 vol% carbon black. This difference is due to the segregated network formation, which leads to excluded volume effects in emulsion-based systems. This excluded volume created by the solid polymer particles forces the carbon black particles into conductive pathways at low concentration. In the solution-based case, fully solvated polymer results in a random dispersion of carbon black. The segregated network composite also shows significant improvement in both electrical conductivity and storage modulus with low carbon black loading, while the solution-based composite achieves significant property enhancements at higher carbon black loading because of the greater percolation threshold. The effect of clay in both emulsion and solution-based composites with carbon black was also studied by preparing composites with three clay concentrations (0.2, 0.4 and 2 wt%). In emulsion-based composites, low clay concentration reduced the percolation threshold from 1.2 vol% to 0.8 vol% carbon black, but with solution-based composites clay increased the percolation threshold from 8.2 vol% to 11.7 vol% carbon black. It is assumed that clay helps to force the carbon black particles into the conductive pathways in the emulsion-based composites. In solution-base composites, clay improves the dispersion of carbon black, thereby destroying the carbon black network and reducing conductivity and storage modulus. The storage modulus in emulsion-based composites improved with 0.2 wt% clay but greater clay concentration resulted in a drop in modulus due to porosity from excess excluded volume effects.
