Vapor grown carbon fiber (VGCF) is a new class of highly graphitic carbon nanofiber and offers advantages of economy and simpler processing over continuous-fiber composites. VGCF used in this work (Pyrograf® III) is grown by means of gas phase catalyst synthesis. The diameter of this fiber ranges from 60 and 200 nanometers and the length varies from 50 to 100 micrometers. There are several issues that must be resolved before VGCF can be a suitable reinforcement. The VGCF must be dispersed in the polymer matrix, a good interface with matrix must be obtained, and the VGCF must be aligned in a specific direction.
The object of this study is the extrusion of VGCF/nylon composites. To produce the composite, VGCF and nylon 6 were premixed, and then extruded by twin-screw extruder. An annular converging die was used to produce different volume fractions of VGCF/nylon 6 composite in the form of a continuous strand. SEM analysis and X-ray diffraction results showed that VGCF is well dispersed, wetted, and aligned in the nylon 6 matrix.
The tensile strength and modulus for extruded VGCF/nylon 6 composites increased as VGCF volume fraction increased, whereas the ductility decreased. For composite strands subjected to additional extension by drawing, it was seen that both the tensile strength and modulus of composites were increased as draw ratio increased.
The theoretical strength prediction performed in this study is a combination of a strength prediction model based on fiber alignment, a model for fiber rotation in the polymer melt, and POLYFLOW simulation, which are sequentially correlated. The theoretical prediction was comparable with experimental results when fiber orientation was evaluated by x-ray diffraction; but the theory overestimated composite strength when fiber rotation was incorporated with the model.