Development of polar phases in poly(vinylidene fluoride-co-hexafluoropropylene)/expanded graphite composites during 3-D printing as revealed by “operando” small and wide angle X-ray scattering

Here we present a research work about the crystallization of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and of one PVDF-HFP composite with expanded graphite (EG) as nanoadditive during 3D printing Fused Filament Fabrication (FFF). Simultaneous Small and Wide Angle X-ray Scattering experiments (SAXS and WAXS) were performed “in situ” under “ operando ” conditions. The X-ray experiments clearly reveal the presence of a polar phase in the PVDF-HFP/EG while for PVDF-HFP its presence is not obvious. Complementary Fourier Transform Infrared Spectroscopy experiments corroborate the presence of the polar phase for both materials. For PVDF-HFP crystallization is faster at the interfaces (polymer-air and polymer-polymer) than in other points within a printed line, being the crystallinity lower at the interfaces. However, for the PVDF-HF composite, neither crystallization rate nor crystallinity is dependent on position. The effect of EG, acting as nucleating agent, has been discussed as being the reason for this behavior. • The crystallization PVDF-HFP and of one its composites with expanded graphite has been investigated by operando X-ray scattering 3D printing Fused Filament Fabrication (FFF). • The X-ray experiments clearly reveal the presence of a polar phase in the PVDF-HFP/EG while for PVDF-HFP its presence is not obvious while Fourier Transform Infrared Spectroscopy experiments corroborate the presence of the polar phase for both materials. • The presence of the polar phase suggests that 3D printing could be integrated in the fabrication process for energy density capacitors.