Tensile, electrical and thermal properties of vapor grown carbon fibers composites

摘要

This chapter presents a study of the DC electrical resistivity and thermal conductivity of VGCF filled polypropylene (PP). The electrical resistivity exhibits a characteristic percolating behavior. Because of the low degree of graphite perfection, the fraction of VGCF required to achieve percolation was higher than expected. Also non-linear I-V characteristics and time dependent electrical resistivity effects were observed. The thermal conductivity of the composites agrees with the predictions of the effective medium theory. To enhance both the mechanical and transport properties an alternative technique must be used. It is well known that most crystalline polymers can be self-reinforced by forming a fibrilar structure, if stretched at high temperature. However, the production of carbon fiber reinforced composites in fibrilar form is not easy. In fact, the dimensional characteristics of the fibrilar structure are much smaller than the average fiber length in a composite. Due to their small dimensions, sub-micron VGCF could be suitable fillers to incorporate in such a structure. Hence, the feasibility of processing highly oriented thermoplastic composites reinforced with VGCF is also studied herein. The mechanical behavior of these composites, as well as their DC response over a wide range of applied electrical fields, are reported, showing that this technique offers good prospects for property enhancement.