Bicomponent melt-spinning of filaments for material extrusion 3D printing

In material extrusion (MEX) 3D printing, the layer-by-layer structure often presents challenges such as poor adhesion, void formation and rough surfaces, which can compromise the mechanical properties of printed parts and limit their applications. This study investigates whether 3D printing from bicomponent core-sheath filaments instead of printing from conventional monofilaments provides a potential solution to some of the described issues. Based on different material selections, various bicomponent filaments, comprising a rigid core and a soft sheath, were produced through co-extrusion and overcoating extrusion techniques. Tensile properties of 3D-printed specimens with different raster angles (0° vs 45°) from bicomponent filaments are compared to the properties of reference specimens printed from conventional monofilaments. While similar mechanical properties were observed for some 3D-printed specimens from bicomponent filaments (e.g., polylactic acid (PLA)-based), as compared to reference specimens, some core-sheath combinations of polyamide (PA) demonstrated a noticeable improvement of the mechanical properties of 3D-printed specimens, particularly for 45° raster angles. In particular, bicomponent filaments comprising a carbon fiber reinforced PA (PACF) core and a pure PA sheath exhibited improved processability and enhanced structural strength. Moreover, two overcoated filaments consisting of polyethylene terephthalate (PET) and polyphenylene sulfide (PPS) monofilament cores with a copolyester (CoPES) sheath were prepared for 3D printing. 3D-printed parts made from PET/CoPES overcoated filaments exhibited good compatibility and satisfactory results when printed at temperatures above the melting point of PET. These findings demonstrate the potential of bicomponent filaments to enhance both printability and mechanical performance of 3D-printed parts, offering new avenues for material selection and design optimization in various 3D printing applications.