Tensile, electrical conductivity and EMI shielding properties of solid and foamed PBT/carbon fiber composites

In this study, we investigated the effects of carbon fiber loading on the electrical conductivity, EMI shielding effectiveness (SE) and mechanical properties of solid and foamed poly butylene terephthalate (PBT)/carbon fiber composites. The composites were prepared through compounding using twin-screw extrusion as a master batch containing 13 wt % fibers. The final composite samples containing 1, 3, 5, 8, and 13 wt % fibers were manufactured during solid and foamed injection molding process through the addition of fibers to PBT. As the carbon fiber loading increased, the tensile strength also increased; however, the increasing trend leveled off at fiber loading of 8 wt % both for solid and foamed composites. In the conductivity examinations, the electrical conductivity increased when the fiber content increased. The conductivity examinations were performed at three different locations: on the surface and at 0.3 and 1.5 mm below the surface. This examination indicated an increase in the conductivity in the positions below the surface. The SEM micrographs showed accumulation of more fibers on the PBT matrix farther from the sample surface. No EMI shielding effectiveness for carbon fiber loading less than 13 wt % was observed; therefore, the fiber content was increased to 20, 25, and 30 wt %. When the fiber loading was increased from 20 to 30 wt %, the EMI shielding effectiveness value also increased. Overall, the foamed composites revealed better electrical conductivity and EMI shielding properties than those of solid materials.