A robust experimental model to explore the three-dimensional printing of polylactide parts: Solution versus melt extrusion

Three-dimensional (3D) printing is a simple and versatile process for producing parts of complex geometries. Although the process possesses several manufacturing advantages, such as rapid prototyping, customization, and complexity, the optimization of the 3D printing procedure remains a challenge. Here we explore the influences of various processing conditions on the mechanical properties of melt extrusion- and solution extrusion-printed polylactide (PLA) products by adopting a robust experimental design model. In addition to the commercially available melt extrusion 3D printer, a novel solution-type 3D printer has been exploited especially for this study, which consists of a solution-type plunger-actuated feeding system, stepper motors and motion components, a power supply unit, a print bed, a user interface, and connectivity. The effects of various parameters were investigated by adopting a robust experimental design. We compared the parts printed using the melt extrusion and solution extrusion methods and found that, in the melt extrusion printing, the print speed and fill density were the principal parameters affecting product quality, while in the solution extrusion printing, oven temperature, fill density, and PLA/dichloromethane (DCM) ratio were the key parameters. By scanning electron microscopy, we found that the melt extrusion-printed parts exhibit a strip-like microstructure and the solution extrusion-printed parts show a fused surface morphology. Due to the addition of solvent, the solution-printed PLA material show a different thermal profile in the differential scanning calorimeter analysis, which in turn affects the mechanical behaviour of printed parts.