Flexural strength of the sandwich-structured parts made of polylactic-acid and thermoplastic-polyurethane fabricated by using extrusion-based multi-material additive manufacturing

Polylactic-acid (PLA) and thermoplastic-polyurethane (TPU) have become two promising polymeric materials that can be processed in combination with multi-material additive manufacturing (MMAM) approach owing to their high rigidity and flexibility, respectively. This approach enables the realization of a printed PLA/TPU multi-material product with tailorable mechanical properties, suitable for a wide range of applications including soft robotics and biomedical devices. However, the applications of such a printed, combined PLA/TPU material are often restricted by failures in the form of layer delamination and disintegration between these two dissimilar materials. In this research, a three-point bending test was used for determining the flexural strength as well as establishing possible failure mechanisms of this combined two materials once constructed in a sandwich structure and prepared with material extrusion additive manufacturing. The results of this research generally showed that the flexural strengths of the sandwich-structured PLA/TPU multi-material parts were laying between those of the monolithic parental materials. Obviously, the sandwich configuration determined the flexural strength of the printed PLA/TPU multi-materials. In this case, the printed PLA/TPU part with PLA layers distributed evenly over the body of the printed part exhibited a higher flexural strength compared to the others having each PLA and TPU layers printed independently and then joined together. The raster configurations also influenced the flexural strength of PLA/TPU-printed parts. It is reported from this study that the use of bidirectional raster orientations could enhance the flexural strength up to 25.7 from the ones printed unidirectionally owing to the mechanical interlocking mechanism operating at the interface between the adjacent PLA and TPU layers. The findings of this research also align with the results obtained from tensile tests in earlier work on the same sandwich-structured PLA/TPU multi-material system. In conclusion, the material extrusion printing shows its potential to be used for preparing PLA/TPU multi-material with sandwich structures. Nonetheless, careful attention should be given to the low interfacial bonding strength between these dissimilar materials. © The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2024.