Douglas Brenner

The macromolecular nature of bituminous coal

Abstract Considerable insight into the macromolecular state of coal has been obtained by examining the optical anisotropy of untreated solvent-swollen, and chemically derivatized thin sections of coal. From the effect of pressure on the optical anisotropy, and from the rate and degree of recovery after release of pressure, it was found possible to determine whether the coal is in a plastic or rubbery state, whether a rubbery state is cross-linked and how mobile the macromolecular chain segments are. The experimental technique utilized for this work was transmission optical microscopy in polarized light of uncontaminated thin sections of vitrinite from a bituminous coal. The study included in-situ microscopic examination of swollen coal immersed in pyridine, THF, toluene and several other solvents. Some samples were O -methylated to assess the impact of hydrogen bonding. New results and conclusions derived from this study include: (1) the vitrinite of raw bituminous coal is a plastic macromolecular substance; (2) coal swollen in pyridine (and some other ‘specific’ solvents) is a cross-linked rubber and its macromolecular chain segments have substantial mobility; (3) when pyridine-extracted coal dries, it reverts to a plastic; (4) the large discrepancies previously found between values of M c (molecular weight between crosslinks) measured by solvent-swelling and by stress-strain techniques is caused by differences in secondary interactions; (5) various solvents can, by their effect on secondary interactions, create appreciably different macromolecular structures in the coal; (6) different solvents, depending on their effect on secondary interactions in the coal, can be expected to extract chemically different molecules from a coal - rates of extraction and the ability of solvents to extract larger molecules should also differ; (7) O -methylated coal is a plastic, and thus, in addition to hydrogen bonding, other secondary interactions are of great importance; (8) it is likely that in their dry condition, solvent-treated coal and O -alkylated coal, as well as untreated coal, are in glassy states; (9) pyridine by itself appears to relax substantially all secondary interactions which are weakened by O -methylation, only permanent bonds are not relaxed; (10) previous measurements of M c can now be reassessed in view of these results.

Microscopic in-situ studies of the solvent-induced swelling of thin sections of coal

Abstract The swelling of thin sections of a high-volatile bituminous coal in certain solvents, studied in situ using transmitted light microscopy, was strikingly different from the highly destructive swelling normally observed with lump coal. Roughly a doubling of the volume occurred, with relatively few sizable cracks, and the shapes of the swollen samples closely resembled the original shapes, though there was more swelling perpendicular to the bedding plane. The regularity of swelling of thin sections demonstrates that the destructive swelling of lump coal is not caused by chemical breakdown of the coal structure but rather by mechanical stresses during swelling and shrinking. Repetition of swelling in n -propylamine vapour followed by drying in air gave samples which were extremely close replicas of the preceding swollen or shrunken samples. This high degree of reversibility is significant in relation to the application of thermodynamics to the swelling of coals. The rapid shrinkage on drying showed that the solvent was highly mobile within the coal structure and that most of the swelling was not caused by strong bonding of the liquid to the coal structure. Swollen samples were found to be substantially more flexible than the untreated or redried samples, indicating much greater macromolecular chain mobility and much lower ‘effective’ crosslink density, and suggesting that the elasticity of the solvent-swollen coal may be predominantly rubber-like.

In situ microscopic studies of the solvent-swelling of polished surfaces of coal

The swelling of polished surfaces of coal in a good solvent has been studied using a new in situ microscopic technique that enables detailed observations to be made during the swelling and shrinking of non-embedded, uncontaminated particles of coal. The swelling of particles, composed primarily of vitrinite, from a bituminous coal can be highly reversible if the swelling agent is removed early enough in the process. This reversibility establishes a closer analogy between the swelling properties of polymeric materials and coals, and lends support to the concept of coal as a macromolecular cross-linked structure. The further the swelling of coal is allowed to proceed, the less reversible it tends to become. This progressive irreversibility is attributed to fractures and distortions within the coal that occur when sufficiently high stresses are generated by uneven swelling. The most important cause of large stresses is the earlier swelling of the more accessible regions of the coal, which is constrained by the rigid underlying material. Another contributing cause is comprised by the differences in the swellability of the various microscopic subcomponents of the coal such as vitrinite, liptinite, fusinite and mineral matter. It appears that the destructive nature of the swelling of coals in good solvents is caused primarily by mechanical stresses from uneven swelling rather than by chemical reactions of the solvent with the coal.

Coal physical structure: porous rock and macromolecular network

Abstract This paper is a review of current knowledge of coal physical structure and the various new approaches used to investigate it. It is shown that in its native state coal is a porous solid, the pore structure being unstable in subbituminous and lower rank coals. Coals behave like cross-linked macromolecular networks, and can be swollen with appropriate organic solvents. Coal physical structure may be described as a porous macromolecular network having either plastic or elastic properties depending upon treatment.

Novel Flexible Foams Based On An Ionic Elastomer

The market for flexible foams is currently dominated by chemically crosslinked polymers, for example polyurethanes and sponge rubbers. The time required for curing these materials is costly and the resultant lack of melt reprocessibility can be a major handicap since many foaming operations generate up to 25% scrap. As an alternate approach to flexible foam systems without these disadvantages, we have explored novel flexible foams based