Effect of the spatial distribution of metallic fibers on the electromagnetic shielding of thermoplastic composites

In this work the effect of the morphology of fiber-filled thermoplastic composites has been studied. Two molds with the same thickness and different filling configurations have been used for the preparation of the samples that afterwards have been tested to obtain their electromagnetic Shielding Effectiveness (SE). The selected molds produce two completely different patterns of filling. In one of them, the pattern is mainly radial, as the gate is located in the center of the mold. In the other one, there are two entrances in a side of the mold, and this produces a weld line in the center of the plate. The effect of the radial distribution and the existence of a weld line has been studied against the shielding effectiveness, measured using a device formed by a stainless-steel cube with an opening in one of the faces to allow the SE measurement of representative plates. It has been observed from the shielding results that the main parameter to consider is the even and high-density distribution of the fibers, measured both by discreet methods (i.e. TGA and density measurements) and a continuous method like the grey scale analysis of tomography scans. It is finally concluded that the material's density distribution and not the existence of a weld line in the plate is the key factor to take into consideration when analyzing the shielding characteristics of fiber-filled thermoplastic composites. • A novel method to measure the density of filled thermoplastic materials using grey scale analysis from tomographies is used. • The effect of a welding line in the EMI shielding characteristics of steel fibers reinforced PP has been studied. • The effect of the use of two molds with different filling patterns has shown a small difference in the shielding characteristics. • The existence of welding lines has shown not to be an issue in the shielding performance of steel fiber reinforced PP.