Creep and glass transition behaviour of fractionated petroleum pitches: the influence of molecular weight and its distribution

Abstract

The dependence of viscoelastic properties on the molecular weight of fractionated and and blended petroleum pitches was examined in relation to the creep and glass transition behaviour. The steady-state viscosity,η, as a measure of energy dissipation, and the steady-state creep compliance,J e 0 , as a measure of elastic stored energy, were empirically related to the glass transition point,T g. The values ofη showed a steep dependence on the number average molecular weight,¯M n (ηf ¯M n 42 ). It was proved that the molecular weight dependence ofη andJ e 0 manifest through the dependence ofT g on¯M n (T gf 1/¯M n). Discussion of the blending laws to elucidate the effect of molecular weight distribution has revealed that Inη,J e 0 , andT g are expressed additively by using the mole fraction of each pitch component with different molecular weights.