Evaluating the effects of material extrusion 3D printing process parameters on shape-shifting of Poly-lactic acid 4D-printed structures

4D printing is a relatively new branch of 3D printing. Material extrusion, as one of the most common 3D printing processes, has been recently receiving increasing attention within this area of research. There are, however, many aspects of material extrusion-based 4D printing processes that are not yet well understood. In this study, we investigated the effects of different processing parameters including the activation parameters, printing parameters, and material parameters on the curvature of self-folding bilayer specimens. All the specimens were printed using three different types of Poly-lactic acid filaments. We found that the activation time and activation temperature, as well as the printing speed, have significant effects on the resulting curvature. Moreover, the shape-shifting behavior of the specimens depended to a great extent on the type of Poly-lactic acid filament used for their printing. Characterization of the filament materials showed no significant difference in terms of mechanical properties. However, considerable differences in thermal and thermomechanical properties of the different types of filaments were observed. According to the results of differential scanning calorimetry and dynamic mechanical analysis, the differences between the different types of filaments could be traced back to their compositions including the amounts and types of additives. The results of the current study have important implications for the design of material extrusion-based 4D printing processes.