Light scattering approach to the in situ measurement of polymer crystallization during 3D printing: A feasibility study

Fused filament fabrication (FFF) is among the most accessible and rapidly developing additive manufacturing (AM) technologies. Even though amorphous thermoplastic polymers are the elected materials in FFF, semicrystalline polymers would enhance the strength and durability of 3D printed parts. The properties of the products depend on the crystalline structure and on the morphology, which develops during the printing process. However, to date, polymer crystallization during 3D printing is still largely unexplored. Then, fundamental knowledge of the crystallization process in realistic printing conditions is necessary to pave the way to semicrystalline polymers in FFF. This work focuses on the implementation of a simple optical setup to follow the crystallization process in situ. The new setup exploits light scattering generated during filament deposition and cooling. To this purpose, the beam scattered by a growing 3D printed wall geometry is collected on a semi-transparent screen during the deposition for both amorphous polylactide and a semicrystalline polyamide copolymer. While the amorphous polymer scatters light anisotropically and generates a vertical scattering pattern, the semicrystalline polyamide produces isotropic scattering. Moreover, the kinetics of scattering intensity increase follows closely that of deposition in the case of polylactide. Instead, it strongly deviates from that for the semicrystalline polyamide. These pieces of evidence suggest that simple light scattering measurements, which are quickly and cost-effectively implemented on a lab-scale, can be further developed to allow a better understanding of polymer structuring phenomena in the highly non-equilibrium conditions of 3D printing.