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

Abstract 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.