Highly stiff and strong fiber reinforced core-shell composites for 3D printing

A novel core-shell continuous polymeric fiber reinforced composite with excellent mechanical performance was prepared using a dual-extrusion process. Continuous pumping of a thermotropic liquid crystalline polymer (TLCP) into polyamide 6 (PA6) via dual-extrusion equipped with a core-shell circular die enabled the generation of continuous fiber reinforced composite filaments with core-shell structure. Microscopic analysis confirmed the composition of the composite and the core-shell macroscopic morphology where the TLCP core was surrounded by a polyamide shell. The core-shell structure exhibited a strong weld-strength of 3D printed parts with improved tensile properties which was attributed to the strong inter-diffusion and entanglement of polyamide chains across the printed layers. The average tensile strength of 3D printed core-shell TLCP-polyamide material was measured to be 132.7 MPa, which is an improvement of about 50% compared to its “sea-island” TLCP-polyamide counterparts prepared using the same dual extrusion process with added static mixers. A comparison between the printed core-shell 20 wt% TLCP-PA6 and continuous traditional glass-fiber reinforced composite revealed that the printed core-shell 20 wt% TLCP-PA6 exhibited a tensile modulus (~12 GPa) approximately 300% higher than that of its 20 wt% glass-fiber/polyamide counterpart. The continuous TLCP composite filament can be printed with a generic extrusion-based 3D printer without requiring any modification, and the presence of continuous TLCP fibers in the filament core has no adverse effect on the printability. Notably, sharp turns (e.g., 180° changes in printing direction) can be achieved during the printing without creating fiber-less regions in the printed parts which overcomes one of the major limitations of printing continuous glass or carbon-fiber reinforced composites. By leveraging the core-shell morphology with TLCP's lightweight and reinforcement properties, we successfully fabricated high strength and stiff additively manufactured parts with enhanced interlayer bonding. Highlights: Prepared core-shell fiber reinforced polyamide using dual-extrusion technology. 3D printed continuous fiber reinforced composite filaments. Significant improvements in mechanical properties of polyamide. Higher modulus than conventional 3D printed glass fiber composite.