THE MEASUREMENT OF THE GLASS-TRANSITION TEMPERATURE OF MESOPHASE PITCHES USING A THERMOMECHANICAL DEVICE

A thermomechanical analysis (TMA) technique is presented for the measu rement of the glass transition temperature (T-g) of glassy pitch mater ials. Pitches with varying mesophase content have been used for the T- g determination. In this technique, the linear expansion of a mesophas e pitch sample with respect to temperature is determined by means of a dilatometer. The change in the coefficient of thermal expansion (CTE) of the pitch materials was found to be significant at the glass trans ition temperature. Therefore, the measurement of the CTE of the specim en with respect to temperature revealed the glass transition temperatu re. This technique was Found to be very sensitive and easily executabl e. Results from the TMA technique show good agreement with those from differential scanning calorimetry (DSC). The TMA technique was found t o reproduce the T-g value for the mesophase pitch samples within +/-2 degrees C. In many cases, the value of T-g from the dilatometer was mu ch more definitive than that obtained from DSC, especially for the mes ophase pitch samples. A linear correlation for T-g as a function of Me ttler softening point temperature (T-s) is developed and compared with that in the literature. Copyright (C) 1996 Elsevier Science Ltd