synopsisThe thermal degradation of samples of cellulose, hemicellulose, and lignin have been investigated using the techniques of thermogravimetric analysis (TGA) and differential thermal analysis (DTA) between room temperature and 600°C. The results calculated from static and dynamic TGA indicated that the activation energy E for thermal degradation for different cellulosic, hemicellulose, and lignin samples is in the range 36-60, 15-26, and 13-19 kcal/mole, respectively. DTA of all the wood components studied showed an endothermic tendency around 100°C in an atmosphere of flowing nitrogen and stationary air. However, in the presence of flowing oxygen this endothermic effect was abseiit. In the active pyrolysis temperature range in flowing nitrogen and stationary air atmospheres, thermal degradation of Avicel cellulose occurred via a sharp endothermic and a sharp exothermic process, the endothermic nadir and exothermic peak being at 320' and 360"C, respectively. In the presence of oxygen, combustion of Avicel cellulose occurred via two sharp exothermic processes. DTA studies of different cellulose samples in the presence of air showed that the shape of the curve depends on the sources from which the samples were prepared as well as on the presence of noncellulosic impurities. Potassium xylan recorded a sharp exothermic peak at 290°C in a nitrogen atmosphere, and in a stationary air atmosphere it yielded an additional peak at 410°C, while in the presence of oxygen the curve showed two sharp exothermic peaks. DTA traces of periodate lignin in flowing nitrogen and air were the same and showed two exothermic peaks a t 320" and 41OoC, while in the presence of oxygen there were two exothermic peaks in the temperature range 200"-500'C.

The thermal expansion of wood constituents has been measured dilatometrically both in the dry and the water‐swollen state. Dry measure meats were made with mercury as the confining liquid on samples pressed into dense pellets at elevated temperatures and pressures. Between −30 and 30°C, the thermal expansion coefficients for various celluloses and hemicelluloses ranged from 5.1 to 6.0 × 10−4 ml./g./°C. For lignin, the coefficient increased to about 10 × 10−5 ml./g./°C. A second order transition was noted in all samples at 19–33°C. A further transition at 8G‐110°C. was detected for the dioxane lignin, periodate lignin, and Avory cellulose. All transitions in the dry state produced an increase in the expansion above the transition temperature. In the water‐swollen state, samples were in the form of powders or broken pellets, with distilled water as the confining liquid. The thermal expansion coefficients of the water‐swollen samples were several times as great as the expansion coefficients measured in the dry state. The second order transition near 20°C. persisted, but in water the transition was negative with expansion decreasing above the transition temperature. Analogous results were obtained for glucose and cellobiose, both in the dry state and in solution. The transition in the dry state is attributed to increased thermal motion caused by the rupture of weak hydrogen bonds. The large and interesting discrepancy found in the expansion of the water‐swollen materials is interpreted as arising from the perturbation of the water structure by the hydrophilic surfaces of woody macromolecules, and a quantitative assessment of this effect is attempted.

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