3D printing of polyvinylidene fluoride composite films with enhanced electroactive beta-phase for flexible wearable pressure sensors

Following the notable rise of three-dimensional (3D) printing in recent years, its use for the fabrication of functional devices derived from piezoelectric polymers such as poly (vinylidene fluoride), PVDF, has become an active area of research. However, there is still a lot to understand about the structure–property-processing relationship regarding the 3D printing of PVDF-based polymers with an enhanced piezoelectric property, which is closely related to the β-phase crystal structure of the polymer. This paper presents the preliminary results of investigations into the extrusion-based 3D printing of poly(vinylidene fluoride-hexafluoropropylene), PVDF-HFP, a PVDF copolymer. Towards the enhancement of the β-phase content of this copolymer, the study analyzed the influence of two fillers in the form of barium titanate (BaTiO3) and untreated activated carbon (UAC) and considered the effect of two printing parameters on the piezoelectric crystalline structure of the PVDF-HFP. First, composite films of the PVDF-HFP with the fillers were formed via the solvent evaporation casting method. From the characterization of the solvent-cast samples using Fourier Transform Infrared Spectrum (FTIR), a composite consisting of 10.55 wt% BaTiO3 and 0.45 wt% UAC with the matrix of PVDF-HFP was found to produce a superior β-phase content (67%) and it was deployed for syringe-based extrusion-assisted 3D printing. Post-fabrication characterization of the extruded samples was carried out to examine the influence of the 3D printing conditions in the form of printing bed temperature (50, 75, 95) and extrusion speed (10, 15, 25). It was found that the combination of a higher printing bed temperature and a low printing speed further enhanced the β-phase content for the PVDF-HFP composites, yielding a β-phase content of 79.6%. Confirmation of the electromechanical/piezoelectric response of the unpoled strips of printed samples revealed a positive correlation between the externally applied pressure on the printed strips and generated voltage.