The alpha-relaxation of a coal tar pitch has been experimentally illustrated through typical G' and G " isotherms steps and tan(delta) peak isochrone. This phenomena has been identified by means of its non-Debye (m similar to 1, n similar to 0.5) and non-Arrhenius behaviours. It has been characterized in terms of its relaxation temperature T-alpha and relaxation time tau(a) and compared to A240 petroleum pitch and amorphous polymers leading to a strong similarity between these materials. Moreover, experimental density data have been investigated in the temperature range of 25 to 400 degrees C for both petroleum and coal tar pitches using the Archimedean method. The obtained results were in very good agreement with published data based on dilatometry. The density effect on the time-temperature superposition standard procedure has been analysed in terms of reduced loss modulus and shift factors deviations. Temperature-density and temperature-viscosity data have been used for calculation of theoretical shift factors which have been compared with success to empirical ones. (C) 1998 Elsevier Science Ltd. All rights reserved. References: 20
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