Searching for Rheological Conditions for FFF 3D Printing with Flexible Polymers

Abstract

Compounds based on PVC, typically employed to elaborate profiles, films, sheets and pond membranes by calendering, extrusion or injection processing methods, have been reformulated to obtain flexible materials apt to Fused Filament Fabrication (FFF) 3D Printing. Suitable filaments were obtained in Haake MiniLab extruder (Thermo Fisher Scientific) at a temperature of 140 °C. Since the occurrence of filament buckling depends on the ratio of the compression modulus, K, to the viscosity, η, the compounds were characterized under the premises of the printing temperatures and velocities. From the low K values found for the filaments it was inferred that buckling would arise during 3D Printing. However, FFF process was found to be perfectly feasible for selected samples. A rheological explanation of this unexpected and positive result was proposed considering the hypothesis of a plug flow in the nozzle.