(688g) Exploiting Capillary Forces in Filled Plastics: Electrically Conductive Plastics By Bonding Copper Filler with Molten Solder

We test whether the electrical conductivity of copper-polystyrene composites can be improved by adding a metal solder alloy during blending. Copper-in-polystyrene composites prepared by melt-blending have poor electrical conductivity. Addition of a flux (a compound commonly used in soldering) during blending is found significantly to improve the conductivity. A further large increase in conductivity was obtained by adding molten solder during composite preparation. The mechanism of this improvement is that the solder bonded the copper particles together into large aggregates that percolated throughout the sample. We examined the effects of the volume ratio of solder to copper particles on electrical conductivity and the composite morphology. If sufficient solder was added, the copper particles become welded together by the solder to form a self-supporting metal network, and a conductivity of ~500 S/m was realized at a metal loading of only 20 vol%. With insufficient solder, large but non-percolating structures of solder-bound copper particles appeared, and the corresponding blends had lower conductivity. While most of the samples were prepared by hand-blending, we verify that the same approach of improving conductivity can be applied using a Brabender batch mixer.