Contribution of printing parameters to the interfacial strength of polylactic acid (PLA) in material extrusion additive manufacturing

The strength of polymer parts made by material extrusion additive manufacturing is weaker than injection-molded parts attributed to the existence of interfaces among the strands in the matrix structure. Interfacial strength is an indicator of the mechanical properties of 3D-printed polymers. In this study, a commercial polylactic acid (PLA) filament for material extrusion processing was used to print samples for interfacial strength tests. Two printing parameters were studied: plate temperature (30 and 160 °C) and air gap size (0 and − 0.04 mm). Differential scanning calorimetry (DSC) indicated that higher plate temperature imparted components with higher crystallinity. Mechanical tests showed that higher plate temperature resulted in weaker interfacial strength of the PLA parts. More shrinkage induced by higher crystallinity of the PLA pre-stressed the interfaces resulting in lower interfacial strength. A negative air gap size was able to ameliorate the shrinkage caused by processing at the higher plate temperature. Scanning electron microscopy (SEM) showed that a negative air gap size generated smaller voids inside the PLA parts made by material extrusion, however, the reduction in air gap size created rougher surfaces.