Thermoplastic composites reinforced with long fiber thermotropic liquid crystalline polymers for fused deposition modeling

This work is concerned with preliminary studies on developing thermoplastic composites for use in fused deposition modeling (FDM). Polypropylene (PP) strands reinforced with thermotropic liquid crystalline polymer (TLCP) fibrils were generated in a novel dual extruder process. The process allowed the reinforcement of PP with a melting point (Tm) of 165°C with continuous fibrils of a high melting (283°C) TLCP (Vectra A950). The strands were then re‐extruded in a capillary rheometer forming monofilaments to simulate piston actuated FDM. The effects of the thermal and deformation histories on the mechanical properties of the re‐extruded strands were evaluated. It was found that tensile properties of the strands improved with draw ratio and that the maximum modulus of the composite strands was similar to that predicted by composite theory. Strands were consolidated uniaxially via compression molding at temperatures just above the melting point of the matrix to determine the effect of thermal history. This resulted in a ∼20% reduction in tensile modulus relative to the modulus of the strands. Monofilaments were extruded from a capillary rheometer in which long fiber strands were used as feedstock to study the effects of deformation history on the tensile properties. It was found that the tensile properties of the monofilaments were dependent on capillary diameter, capillary L/D, and apparent shear rate due to fibril alignment.