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ABSTRACTS AND R E V I E W S 253 differential thermal analyses show that the pyrolysis of lignin is more strongly exothermic than that of cellulose, this is consistent with the data from two sets of experiments with bulk samples of wood which suggest that g=â800 J/g for hgmn and g= â80 J/g for cellulose, and that hgmii contributes 65% of the exother- mic heat of reaction of pyrolyzing wood Data from other experiments in which bulk samples of wood are heated to temperatures greater than 320''C give reason- ably consistent values of g= â(160-240) J/g Where the maximum temperature achieved is less than 320°C, the value obtained for the heat of reaction is highly dependent on conditions and may rise to â1700 J/g The role of primary and secondary pyrolysis reactions in determimng the overall heat of reaction and the influence of the physical structure of the wood are discussed Shafizadeh, F . (Department of Chemistry and School of Forestry, Umversity of Montana, Missoula, Montana) "Thermal Behavior of Carbohydrates," J Polymer Sn-Parte, 21 (1971) Section: H Subjects: Carbohydrates, Thermal degradation, Thermal analysis, Wood, Pyrol- ysis, ESR, NMR, Kinetics of pyrolysis, Calonmetry Author's Synopsis Thermal analysis of a hardwood reflected the pyrolysis of its main components including xylan and cellulose Thermal properties of these components were in- vestigated with model compounds consisting of a-D-xylose, substituted phenyl j9-D-xylopyranosides, /3-D-glucopyranosides and a-D-arai>ino-hexopyranosides and 1,6-anhydro-j8-D-glucopyranose At the lower temperatures these molecules displayed anomerization, loss of water and phase change, which were studied \vith a variety of physical methods Calorimetric and wide-line NMR measurements showed that l,6-anhydro-/3-D- glucopyranose and related anhydro sugars undergo plastic crystalline transition, involving reorientation of the molecules about their centers of gravity, and self- diffusion before melting At more elevated temperatures the above compounds showed cleavage of the glycosidic group, polymerization of the sugar moiety, decomposition and evapora- tion of the pyrolysis products This involved some heterolytic reactions, which could be catalyzed by acid or alkaline materials Kinetics of the pyrolysis process, including the rates and energies of activa- tion were determined by thermal analysis and ESR spectroscopy These data mdicated that cleavage of the glycosidic bond is directly influenced by variation of its electron density and constitutes the rate determimng step in pyrolysis of the carbohydrate compounds
