Glass transitions and enthalpy relaxation in coals

Differential scanning calorimetry was used to investigate the glass-to-rubber transition at 383 K of Illinois No. 6 coal dried at 383 K and thermally treated to 523 K. The intensity of the transition is 0.2 Jg−1 K−1, similar in magnitude to that for polypyrrole and polystyrene. The temperatures of the glass transitions in the coal and the polymers are also very similar. It is concluded that the glass transition of the coal represents a significant change in structure. Annealing experiments were conducted on the coal at temperatures just below the glass transition. Enthalpy relaxation occurred after thermal treatment to 553 K.