Quantifying the Microstructure-Properties Relationship of Material-Extrusion-Based 3d-Printed Thermoplastic Elastomers

Abstract

Material-extrusion-based (MEX) printing of polymer melts is a kind of layer-wise 3D prototyping technology that is prevalently employed to produce thermoplastics and elastomers owing to its low cost and high efficiency. However, the MEX-printed polymeric parts exhibit unsatisfactory mechanical properties which is lack of a comprehensive mechanism that are commonly disregarded in studies, especially for those MEX-printed elastomers. In this study, therefore, the structure–properties relationship of MEX-printed thermoplastic elastomers is specifically quantified to provide an in-depth understanding of their intrinsic mechanical dependence. MEX 3D printing of thermoplastic polyurethane is employed to fabricate tensile specimens with the expected microstructure. The effect of mechanical anisotropy is studied by measuring the actual microstructure characteristics and monitoring their evolution during the tensile process. To assist with this, a series of samples with different interface configurations are prepared by varying the layer thickness. These samples have varied bead contour shapes, interface contacting areas, internal void shapes, and bonding groove angles at their surfaces, which causes them to exhibit different responses to tensile stress. Insight into the observed mechanical anisotropy or deterioration of the printed samples is provided to address the lack of a convincing description. It is concluded that the observed tensile anisotropy can be explained by the bead-spring model and the effect of the stress concentration induced by the groove angle. In addition, it is determined that sharp angles in internal voids and surface grooves are obtained when the layer thickness is high, leading to a decrease in the tensile strength. This study can be used to optimize novel printing strategies for elastomers.

Keywords: Additive manufacturing, Melt-extrusion-based 3D printing, Microstructure, Mechanical Properties, Thermoplastic Elastomer.