Rheological characteristic of impregnating pitch from modified pitch

Abstract

The refined pitch (1#) and impregnating pitch (2#) were obtained under certain conditions with the modified pitch as the raw materials. The data of viscosity and shear stress for each pitch have been tested by rotational viscometer. The flow activation energy and non-Newtonian index sample 1# and 2# have been calculated by Arrhenius equation and Saal equation. The results show that the flow activation energy of each sample was 109.13 kJ mol⁻¹ and 133.71 kJ mol⁻¹, and non-Newtonian index was 4.78 and 5.31, respectively. The processed data of Williams–Landel–Ferry (WLF) equation showed that the free volume of two pitches increased with increasing the temperature above the softening point. But impregnating pitch had a smaller free volume than refined pitch at the same temperature. What is more, the shear thinning phenomenon occurred under the shear rate of 40 s⁻¹ and temperatures of 108 °C and 150 °C for sample 1# and 2#, respectively. When the shear rate was less than 10 s⁻¹, temperatures were above 114 °C and 156 °C, and the shear thickening phenomenon has been taken place for pitch sample 1# and 2#, respectively. The impregnation temperature of samples 1# and 2# was 130 °C and 180 °C which is determined by viscosity–temperature curves. The power-law model and Robertson–Stiff model were applicable for describing the rheological characteristic of two pitches, and both pitches belonged to power-law fluid.