(65ae) Nanocomposites of An Engineering Plastic, Poly(ether ether ketone) with Carbon Nanofibers

Engineering plastics must provide excellent mechanical properties at elevated temperatures for myriad applications, especially in automotive and aerospace industries. PEEK is an engineering polymer which is widely used because of its superior mechanical properties, high melting temperature (380 °C) and excellent resistance to chemical corrosion. Carbon nanofibers (CNFs) are novel three-dimensional reinforcements, formed when graphene sheets are assembled into cone or tube-like structures. Polymer composites with small concentrations of CNFs generally exhibit significant increases in mechanical properties, as well as electrical and thermal conductivity. Incorporating CNFs into PEEK thus has the potential to generate nanocomposites with improved mechanical properties while conserving high melting point and chemical resistance. This improvement is due to a variety of potential factors, including the reinforcement effect of the CNFs forming a network structure, increased crystallinity caused by CNFs acting as a nucleating agent, or by thermal crosslinks forming within the polymer structure. In this investigation, PEEK CNF nanocomposites were prepared by two separate methods (melt mixing and dissolution processes), and at varying CNF concentrations (0.5 to 2% by weight). Linear viscoelastic properties of the molded PEEK/CNF nanocomposite specimens were characterized using both tensile and torsional oscillatory deformations. Furthermore, differential scanning calorimetry and X-ray diffraction were employed to determine the percent crystallinity and crystal size of the PEEK as functions of CNF concentration and processing method. The results suggest that improvements in mechanical properties can only occur under favorable dispersion conditions for the CNFs and in the absence of the thermal degradation of the PEEK.