Design of Lightweight and Conductive Segregated Polymer Composites Using Expanding Microspheres

ABSTRACT This study presents a design‐driven strategy for fabricating lightweight and electrically conductive polymer composites with a segregated architecture formed via foam‐induced cellular morphology. A wax‐modified styrene–butadiene–styrene matrix was used as the polymer phase, while graphite, carbon fiber, and nickel were employed as conductive fillers. Thermally expandable microspheres were employed as blowing agents to simultaneously reduce density and promote filler segregation by facilitating localized redistribution during cell growth. Among all bulk formulations, the highest electrical conductivity was observed in carbon fiber‐filled samples (1.5 × 10 −3 S/cm at 50 phr), followed by graphite‐filled samples. In contrast, nickel‐filled bulk composites showed negligible conductivity due to the high density and poor connectivity of spherical particles. Upon expansion, graphite‐filled foamed composites exhibited the highest conductivity (1.3 × 10 −4 S/cm at 75 phr), even surpassing their bulk counterparts, indicating the effectiveness of foam‐induced segregation for plate‐like graphite particles. In contrast, foamed carbon fiber composites exhibited reduced conductivity (up to 3 × 10 −5 S/cm), suggesting a more efficient segregation mechanism in the case of graphite.