Combined effect of hybrid carbon fillers on the physical and rheological properties of polyvinylidene fluoride composites

Three different types of carbon materials [carbon nanotubes (CNTs), carbon black (CB), and carbon fibers (CFs)] were incorporated into polyvinylidene fluoride (PVDF) as single fillers or hybrid fillers (CNT/CB and CNT/CF) via solution blending. The physical properties of the hybrid filler systems such as the electrical, thermal, morphological, and rheological properties were compared to those of the single filler systems. Images of the PVDF composites containing hybrid fillers obtained by a field-emission scanning electron microscope showed that CB appeared to be embedded between highly entangled nanotubes, promoting their debundling in the PVDF matrix. The hybrid filler systems of CB and CF with 0.5 wt% nanotubes were electrically conductive from the corresponding content of 1 wt%, showing maximum values from 5 wt% CB and 10 wt% CF. In the hybrid filler systems, the extent of the increase in crystallization temperature (Tc) in the presence of CB or CF was more prominent at a lower CNT content of 0.5 wt%. In the hybrid systems of CB with 0.5 wt% nanotubes, the melting peak for the β phase was generated from 1 wt% CB and its intensity increased with CB content. On the contrary, the hybrid filler systems of CF with nanotubes did not provide a new peak. Regarding the rheological properties, the complex viscosity (η*) of PVDF/CNT0.5/CB increased with CB content, a pattern similar to that of the single filler system of CB. On the contrary, the presence of CF with 0.5 wt% nanotubes slightly increased η* with CF content, while that with 1 wt% nanotubes notably increased η*, exhibiting a sharp increase at 10 wt%.