Evaluation of Electromagnetic Shielding Effectiveness of Carbon Black Composites Prepared from Local Materials

Electromagnetic interference shielding is increasingly important as electronic devices proliferate in industrial and medical environments, yet high-performance shielding materials remain expensive and largely imported in Nigeria. This study evaluates the electromagnetic shielding effectiveness of composite materials prepared by incorporating locally sourced carbon black from palm kernel shell pyrolysis into natural rubber matrices at different loading levels of 5, 10, 20, and 40 parts per hundred rubber. Composite sheets of 2 mm thickness were compression molded and characterized for mechanical properties, electrical conductivity, and shielding effectiveness. Shielding effectiveness measurements were performed in the frequency range of 100 MHz to 3 GHz using the coaxial transmission line method with a calibrated vector network analyzer. Results indicate that shielding effectiveness increased monotonically with carbon black loading, reaching a maximum of 28 dB at 40 parts per hundred rubber and 1 GHz, satisfying the minimum 20 dB commercial shielding standard. Electrical conductivity measurements show a percolation threshold near 15 parts per hundred rubber, above which conductivity increases rapidly due to formation of a continuous conductive network. The palm kernel shell carbon black produced by slow pyrolysis at 500 degrees Celsius shows higher graphitic character as confirmed by Raman spectroscopy, contributing to enhanced conductivity relative to commercial carbon black. The study presents a cost-effective, locally sustainable shielding composite pathway relevant to Nigerian electronics manufacturers. Keywords: electromagnetic shielding, carbon black, palm kernel shell, composite material, electrical conductivity