Utilizing Liquid Crystalline Polymers as a Reinforcement Phase in the Fused Filament Fabrication with Conventional Polymers

Abstract

Using thermotropic liquid crystalline polymers (LCP) in fused filament fabrication (FFF) facilitates the production of highly anisotropic parts that exhibit a high tensile strength and Young´s modulus in the printing direction. This work investigates, for the first time, an approach where the LCP (reinforcing phase) and a conventional polymer (matrix) are printed using two separate printer nozzles. This contrasts with the existing approach in literature, where both components are blended during filament extrusion and subsequently printed with a single printer nozzle. A polyamide 6/66 copolymer (CoPA), a polycarbonate (PC), and a polyetherketoneketone (PEKK) serve as conventional matrix polymers. Due to their chemical structure, a good compatibility is expected between each of these polymers with the LCP. Composite tensile samples are printed with 14, 23, and 30 vol.% LCP and subsequently characterized by uniaxial tensile testing. The highest Young's modulus of 6.8 GPa is achieved in PC/LCP samples with 30 vol.% LCP. In contrast, the highest tensile strength of 126 MPa is obtained in PEKK/LCP tensile samples with 30 vol.% LCP, after an additional thermal annealing at elevated temperatures. The main failure mechanism for all composites is an LCP pull-out, indicating a poor adhesion between the LCP and the matrix polymers.