The thermal expansion of cellulose, hemicellulose, and lignin

Abstract

Abstract 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.