Comparative study of filled and unfilled polylactic acid produced via injection molding and 3d printing

This study investigates the impact of two different processing methods, Injection molding (IM) and 3D printing (3Dp), on neat/unfilled polylactic acid (NPLA) and the short carbon fibers (SCFs) filled polylactic acid (SPLA). Furthermore, the resulting processing conditions and the influence on mechanical properties, such as tensile, flexural, notched Charpy impact test, and heat deflection temperature (HDT), along with the process-induced effects, such as fiber length distribution and voids, were studied. The process-induced voids were evident in all the computed tomography (CT) scans, 3Dp specimens have higher void volume fraction compared to no visible voids in IM specimens. Similarly, the mechanical test results such as tensile, flexural and notched Charpy impact test follow the trend for 3Dp SPLA and IM SPLA. On the contrary, 3Dp 0° and ±45° NPLA tensile test results are comparable to IM NPLA, whereas 3Dp 0° NPLA has the highest impact resistance compared to injection molded NPLA and SPLA as well as 3Dp SPLA specimens, indicating the annealing effect induced by the heated 3D printing bed along with increased void volume fraction. Furthermore, the HDT study indicates the maximum serviceable temperature of both NPLA and SPLA remained comparable regardless of the processing method. Moreover, the change in fiber length distribution for SPLA injection molded and extruded filament specimens were negligible.