The Effects of Processing Conditions on Thermoplastic Prototypes Reinforced with Thermotropic Liquid Crystalline Polymers

by Gray, Robert Williamson

This work is concerned with preliminary studies on developing thermoplastic composite materials suitable for use in fused deposition modeling (FDM). Polypropylene (PP) strands reinforced with continuous thermotropic liquid crystalline polymer (TLCP) fibrils were generated in a novel dual extruder process. Strands were then re-extruded to form short fiber composite monofilaments that were used as feed stock in the FDM 1600 rapid prototyping system. Prototypes containing 40 wt% Vectra A were shown to have tensile properties twice those of parts built using acrylonitrile butadiene styrene copolymer (ABS), a commercially available material used in the FDM 1600 rapid prototyping system. It was also shown that the final mechanical properties of a composite prototype can be tailored to a specific application by adjusting the lay-down pattern, increasing the functionality of the prototype. In order to obtain the maximum tensile properties in these composite prototype, additional studies were performed to determine the effects of thermal and deformation histories on the mechanical properties of monofilaments that were re-extruded from long fiber TLCP reinforced strands. Strands were consolidated uniaxially at temperatures just above the melting point of the matrix in order to determine the effects of thermal history, and an approximate 20% reduction in tensile modulus relative to the modulus of the strands was observed. Monofilaments that could be used as feed stock in FDM were extruded from long fiber TLCP reinforced strands using a capillary rheometer in order to study the effects of capillary diameter, capillary L/D, and apparent shear rate on the tensile properties.