Effect of structural change of pitch on the thermal conductivity of epoxy-based composites filled with heat-treated pitch

Petroleum‐based pitches were used as filler materials to study the effects of heat‐treatment‐induced changes in pitch structure on the thermal conductivity of epoxy‐based composites. The heat treatment was performed in two steps: the first involved heating the pitch to 250 °C in order to remove the low‐molecular‐weight compounds from the pitch, and the second involved heating the pitch to either 430 or 450 °C. There was no significant difference in the curing behavior of the diglycidyl ether of bisphenol A (DGEBA)/pitch composites, regardless of the heat‐treatment temperature. However, the thermal conductivity of the DGEBA/pitch composites improved with increasing heat‐treatment temperature, and the epoxy composite prepared with pitch heat‐treated at 430 °C exhibited the maximum thermal conductivity. This can be attributed to structural changes in the pitch, such as the distance between adjacent planes (d‐spacing), crystallite height (Lc) and crystallite width (La). Although Lc of the pitch increased with increasing heat‐treatment temperature, the d‐spacings and La decreased. These results suggest that the heat treatment of the pitch led to a well‐stacked crystalline structure. However, compared with the pitch heat‐treated at 430 °C, that heat‐treated at 450 °C exhibited lower thermal conductivity in the DGEBA/pitch composite because of the low La, resulting in the loss of basal carbon as a consequence of in situ gasification, and pyrolysis of the low‐molecular‐weight compounds in the pitch. © 2013 Society of Chemical Industry The crystal phase structure of pitch was improved with heat treatment, but the three‐dimensional graphite structure did not form in spite of the heat treatment, resulting in low carbonization temperature.