From the results, it can be seen that the shielding increases with the content of stearic acid up to about 2 vol. % of stearic acid (i.e. about 2 wt. %) and then start to decrease. The optimised range is, therefore, ranging from 1.5 to 4.0 wt. % of component C based on the total weight of the composite material, with preference from 1.5 to 3.0 wt. %.
Example 3: Effect of Stearic Acid (Component C) on the Percolation Threshold and the Electrical Conductivity
The percolation threshold of the different electrically conductive fillers was studied in the absence or the presence of stearic acid. The results in the absence of stearic acid are reported in FIG. 8. From this figure, it can further be seen that the metal-coated particles tested (i.e. silver glass fibres) provide an electrical conductivity that is similar to the metal particle (i.e. tin particles) but with a lower percolation threshold. The carbon particle (i.e. CNT) shows lower electrical conductivity.
FIG. 9 shows the effect of the presence of stearic acid on the electrical conductivity of the composite material containing silver glass fibres. It can be seen that the percolation threshold is lowered and at the same time the electrical conductivity is enhanced. Since stearic acid has no properties of electrical conduction a synergetic effect is therefore shown. The same effect was observed with tin particles but not with the CNT, suggesting that the synergetic effect occurs with metal or metal-coated particles only.
Example 4: Mechanical Properties
Traction tests were performed on Injected PP AgGF 10 vol. %, stearic acid 2 vol. %. Composite made in internal mixer 200° C., 100 rpm.
