The macromolecular states of solvent-swollen and dry coal

Abstract

Improved understanding of the physical state of coal is needed to better characterize, modify and utilize this abundant source of energy. In spite of extensive research in this area for well over half a century, the level of understanding has been poor. Here, new substantive evidence clarifying the macromolecular states of coal is presented. The approach involved studying changes in the optical anisotropy of raw and solvent-swollen thin section samples of a bituminous coal. It was found that the natural optical anisotropy was completely relaxed on immersion of the coal in pyridine. From changes in the optical anisotropy induced by pressure, the solvent-swollen coal was determined to be a cross-linked rubber and its macromolecular chain segments were found to have substantial mobility. It appears that pyridine and some other good swelling agents relax essentially all of the secondary bonding in the coal. On the other hand, raw coal and coal immersed in water, various hydrocarbon solvents and other poor swelling agents were determined to be macromolecular plastics.