Graphite‐rich PVDF composite foams prepared by supercritical CO 2 foaming: Role of temperature and hybrid carbon fillers on their morphology, electrical and mechanical properties

Abstract This study examines the combined effects of foaming temperature and carbon fillers on the morphology, porosity, electrical resistivity, and compressive properties of polyvinylidene fluoride (PVDF)‐based composite foams. PVDF/graphite (GR) composites containing 60 wt.% carbon fillers were modified by partially replacing GR with carbon fibres (CF), carbon black (CB), or a CF/CB system. The reference PVDF/GR (40/60 wt.%) composite was foamed using supercritical CO 2 at 210, 220, and 230°C to identify the best foaming condition. Foaming at 210°C yielded limited cell development, attributed to restricted PVDF chain mobility, whereas 230°C promoted pore coalescence and partial structural collapse. The best cellular structure was obtained at 220°C, reaching 20% porosity and in‐plane resistivity of 0.14 Ω · cm. At this temperature, secondary fillers further improved porosity and electrical performance. CF increased porosity to 24% and promoted conductive bridging, while CB increased porosity to 30% and reduced interparticle resistance. The CF/CB system exhibited the strongest synergistic effect, achieving 32% porosity and the lowest in‐plane resistivity of 0.03 Ω · cm. Improved electrical performance was accompanied by reduced compressive properties. Supercritical CO 2 foaming combined with hybrid filler design therefore produces highly conductive PVDF‐based foams, although optimization remains necessary to balance electrical conductivity and mechanical integrity for proton exchange membrane fuel cell (PEMFC) bipolar plates. The novelty lies in elucidating the foaming‐driven redistribution of a graphite‐rich, multiscale CF/CB/graphite network within the PVDF matrix and its coupled effects on porosity, through‐plane and in‐plane resistivities, and compressive behaviour.