Synergistic material extrusion 3D-printing using core-shell filaments containing polycarbonate-based material with different glass transition temperatures and viscosities

The application of 3D printing of thermoplastics by Material Extrusion (MatEx) has commonly been limited by their poor mechanical strength that results from voids and weak interfaces between printed layers. Here, we demonstrate that core-shell structured filaments made of polycarbonate-based thermoplastics can achieve synergistic improvement in their interfacial bonding from the combination of high-glass transition temperature (T g)/high-viscosity core and low-T g/low-viscosity shell. Tensile strength along the printing direction was enhanced with the core-shell filaments. Layer-interfacial bonding strength as determined by Izod impact tests of the 3D printed parts is significantly improved by using filaments either with only a core-shell T g mismatch or both T g/viscosity core-shell mismatch. The mechanical behavior can be rationalized in terms of improved inter-layer molecule diffusion by a low T g/viscosity shell, better printability at higher temperature due to the core with higher melt strength, and better bulk mechanical strength of high-viscosity/T g core.