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Thermoplastic Liquid-Crystal Polymer Filament for Fused Filament Fabrication of High-Strength Continuous-Fiber Composites

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Conference Abstract: Fused filament fabrication (FFF) is the most common form of 3D printing, enabling low cost fabrication of accurate, complex geometry thermoplastic parts. A limitation of these parts is their relatively low strength and stiffness, driven by the weak bonding between deposited layers and the limited mechanical properties of engineering thermoplastics. The polymer filaments that feed these printers may be reinforced with discontinuous carbon and glass fiber, but the resulting gains in mechanical properties are modest. Furthermore, inorganic fiber reinforcement can exacerbate interlayer bonding challenges and accelerate wear of print nozzles. Multiple academic studies have reported exceptional high trace-direction properties (e.g. 20-35GPa tensile modulus) by printing with thermotropic liquid crystal polymers (TLCP's), without addressing the very low inter-trace and inter-laminar properties associated with the use of TLCP’s in FFF.
This presentation will provide an overview of a new approach for FFF of TLCPs. A specialized feedstock has been developed, consisting of a combination of continuous TLCP reinforcement within a secondary, lower melting point polymer matrix. The filament can be printed using conventional desktop FFF printers, and results in continuous TLCP fiber reinforcement. Matrix chemistry, fiber volume fraction, surface treatments, and phase distribution have been tuned to improve system performance including bonding between traces and layers. Mechanical properties are sensitive to print conditions, with values as high as 219 MPa strength and 18.2 GPa modulus achieved to date.