Plasticized/graphite reinforced phenolic resin composites and their application potential

Abstract Plasticized graphite (PG)/phenolic resin composites are candidates for positive temperature coefficient resistivity (PTCρ) thermistors, which are used for self‐recoverable elements that provide protection from overcurrents, gasoline sensors, and electrostatic charge and electromagnetic wave shielding in many kinds of electrical devices. The morphology and network structure of PG/phenolic resin composites have been characterized with scanning electron microscopy and with measurements of the crosslinking density, bound resin content, degree of crystallinity, viscosity, surface energy, thermal conductivity, enthalpy, and glass‐transition temperature. In addition, mechanical properties such as the tensile strength, Young's modulus, Shore A hardness, and elongation at break for resins filled with PG have been studied. The electrical properties of the composites have been measured to relate the PG volume fraction to the electrical conductivity. A large PTCρ value has been observed for all samples. The mechanism of the PTCρ effect in the materials is related to the thermal expansion and highest barrier energy of the composites. Switching behaviors of the current and voltage for all samples have been observed. The applicability of PG/phenolic resin composites for temperature controllers and gasoline gas sensors has been examined. The antistatic charge dissipation and dielectric constant as functions of the PG content have been studied. Finally, the experimental electromagnetic interference of the PG/phenolic composites has been investigated in the frequency range of 1–15 GHz and compared with a theoretical model. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 697–709, 2007