Enhanced electrical properties of graphite/ABS composites prepared via supercritical CO₂ processing

Highly conductive graphite/acrylonitrile–butadiene–styrene copolymer (ABS) composites were prepared via foaming with supercritical carbon dioxide (scCO₂), followed by de-foaming with an open mixing mill. This processing technique decreased the direct current resistivity of the composites by about 1 order of magnitude. The alternating current (AC) resistivity results demonstrated that an insulator-semiconductor transition occurred upon increasing the graphite content. In analyzing the AC impedance, it was shown that the response characteristics changed from capacitive to resistive at significantly lower graphite loading levels for composites processed with scCO₂. The dispersion of graphite in the copolymer matrix was characterized by scanning electron microscopy (SEM), rheometry and dynamic mechanical analysis. SEM of graphite/ABS composites revealed that the graphite was very well-dispersed. The sample treated with scCO₂ processing showed higher storage modulus and complex viscosity than those processed conventionally. Additionally, the T _g was increased by 2–3 °C after the scCO₂ processing treatment. This approach to composites processing with scCO₂ represents an attractive method for preparing electrically conductive composites with well-dispersed fillers.