Anisotropic recrystallization of PCL/SBA-15 composites during 3D printing: a SAXS study of the influence of processing parameters

Abstract

Additive manufacturing represents nowadays one of the most disruptive technologies, both in academic and industrial fields. In this context, the design and 3D printing of biomimetic materials for tissue engineering and regenerative medicine applications have attracted a lot of attention. However, a key step that must be overcome in order to design and fabricate new functional materials is to have a better understanding about the effect of some process parameters on the final structure of materials. Recent works showed some interest in this area, and have investigated the structural evolution of PCL during 3D printing and the effect of particle alignment induced by extrusion-based 3D printing on final structural properties of 3D printed materials [1,2]. In the present work, mesoporous silica particles (SBA-15) were incorporated into a polycaprolactone (PCL) matrix through an extrusion-based process, to obtain a filament compatible with melt extrusion-based 3D printing systems. In order to study the effect of processing parameters and particle alignment on the polymer recrystallization, PCL and PCL/SBA-15 samples were printed using two different nozzle sizes, 0.25 mm and 0.40 mm. Structural characterization of PCL and PCL/SBA-15 3D-printed samples was performed by small-angle X-ray scattering (SAXS). Measurements were carried out using a Xeuss 2.0 (Xenocs, France) with a sample-to-detector distance of 1200 mm and λ = 0.154 nm which allowed us to study both the lamellar structure of PCL and the hexagonal pore structure of SBA-15. Analysis of 2D SAXS patterns showed that rod-like SBA-15 particles were aligned along the print direction, as expected. More interestingly, PCL presented anisotropic recrystallization, perpendicular to the print direction only in the presence of SBA-15 (anisotropic patterns were not observed when PCL samples were studied). Results indicate that melt extrusion-based 3D printing aligns high aspect ratio SBA-15 particles, which induces anisotropic recrystallization of PCL, and the alignment is dependent, for instance, on the nozzle size. To have a better understanding of the influence of processing parameters on the recrystallization and orientation of polymer crystals, we propose the use of CATERETÊ beamline at Sirius, in particular, the X-Ray Photon Correlation Spectroscopy (XPCS) facility. Since XPCS has proved to be an excellent technique to study polymer dynamics [3], we consider that this technique would shed some light on the anisotropic recrystallization of polymers in the presence of anisotropic particles.