Probing structure development in Poly(vinylidene Fluoride) during “operando” 3-D printing by small and wide angle X-ray scattering

Abstract

We have investigated the crystallization of the thermoplastic polymer Poly(vinylidene Fluoride) (PVDF) during “operando” 3D printing Fused Filament Fabrication (FFF). The performance of the 3D printing set-up and the corresponding methodology for performing simultaneous SAXS/WAXS with synchrotron radiation have been discussed. Simultaneous SAXS and WAXS experiments were performed across the printed line with a resolution of 50 μm. The experiments indicate that crystallization is faster at the polymer-air interface than in other points within the printed line. The final crystallinity varies with position being lower at both the interfaces, i.e. polymer-air (13%) and welding zone (11%), while being higher (18%) in the middle part of the printed line. Orientation of the crystalline lamellae is higher at both interfaces, suggesting higher shear rate than in the bulk of the printed line where elongational flow is dominant. The final crystallinity levels in the different locations of the printed line are relatively low, as compared with reported values in melt pressed samples (≈30%), due to the extremely fast crystallization kinetics involved in the solidification of PVDF 3D printed lines. Therefore, it is expected that 3D printed PVDF pieces will exhibit significant structural modifications due to the potential crystallization that eventually will proceed during storage because the glass transition of PVDF is well below room temperature.