Highly toughened blends of poly(lactic acid) (PLA) and natural rubber (NR) for FDM-based 3D printing applications: The effect of composition and infill pattern

Abstract In this study, the suitability of natural rubber (NR) toughened poly(lactic acid) (PLA)-based blends were investigated for additive manufacturing applications. Filaments for fused deposition modeling (FDM) were prepared with an NR concentration of 0 … 20 wt% using a twin-screw extruder. Subsequently, specimens were fabricated with a desktop 3D printer machine working on FDM principles. Besides the composition of PLA/NR blends, the effect of infill orientation was also analyzed by preparing two sets of specimens: i) one set prepared with an alternating raster angle of ±45° (3DGRID) and ii) another one with a linear infill parallel to the length of the specimens (3DPAR). Quasi-static and dynamic mechanical properties, morphology and thermal characteristics of the fabricated specimens were investigated. The tensile tests revealed that the presence of NR effectively enhances the ductility of PLA filaments, however, the achieved improvement was highly dependent on the applied infill pattern. Samples prepared using the 3DPAR infill exhibited an excellent deformability when paired with NR. On the other hand, the ones fabricated with the 3DGRID technique only showed a marginal improvement in elongation. Similarly, the Charpy impact tests indicated an outstanding impact resistance of NR-toughened 3DPAR specimens, while the 3DGRID types showed little to no improvement. Scanning electron microscopic analysis revealed a weaker interlayer adhesion in the specimens containing NR, which greatly contributed to the discrepancies observed between the mechanical properties of the samples prepared with different infill. The differential scanning calorimetry revealed an almost completely amorphous structure of 3D printed PLA due to the quite rapid cooling characteristic of the FDM technique, which was not affected by the embedded NR component.