Viscoelastic properties of coal in the thermoplastic phase

The viscoelastic properties of coals in the thermoplastic phase during carbonization were measured with dynamic mechanical oscillation instrumentation. The temperature and frequency dependence of the viscoelastic properties of the coals in the thermoplastic phase were similar to those of polymers and thermosetting resins. The storage modulus (G') and the loss modulus (G ") showed minimum (10(4)-10(5) Pa), the loss tangent (tan delta = G "/G') showed a peak, and the complex viscosity (eta*) also showed a minimum (10(4)-10(5) Pa s) near the temperature of maximum fluidity of coal. There was a close relationship between the caking characteristic parameters measured with conventional method and the rheological moduli obtained here. The complex viscosity (eta*) decreased as the frequency increased, which suggests that the conventional Gieseler plastometer overestimates the fluidity in the high fluidity range due to the high rotation speed. It proved promising to apply the dynamic viscoelasticity measurement technique to study the coal structural changes during the thermoplastic phase from analogy with polymers. (C) 1999 Elsevier Science Ltd. All rights reserved.