Macromolecular structure of coals: 2. Molecular weight between crosslinks from pyridine swelling experiments

Abstract

The effective macromolecular structure of ten coals was investigated by application of a modified Gaussian network equation to the results of equilibrium vapour-swelling studies using pyridine as the penetrant. Using data at 35 °C it was found that the effective number N of repeating units between crosslinks varied from 7.0 to 8.5, corresponding to a molecular weight M ̄ c between crosslinks of 990 to 1280, over the coal rank range 69.9–82.4 wt%C (dmmf). At 86.0 wt%C, N fell to 4.6, corresponding to a molecular weight between crosslinks of 780, and continued to decline to 2.2, corresponding to M ̄ c = 814 , at 91.5 wt%C. An increase in swelling temperature from 35 to 60 °C had little effect on the analysis; however, at 80 °C substantially increased equilibrium swelling values were obtained, which indicated a change in coal structure, increased thermodynamic interaction or attack on the hydrogen-bonded structure of the coal by pyridine.