In situ X-ray diffraction investigation of thermal decomposition of wood cellulose

The kinetics of thermal decomposition of crystalline cellulose in spruce wood (Picea abies [L.] Karst.) was studied by in situ X-ray diffraction using synchrotron radiation. Fiber diffraction patterns resulting from the crystal lattice of native cellulose arranged in oriented microfibrils were collected as a function of heat treatment time for various temperatures from 300 to 360 °C. Sample heating was performed using a specially designed in situ pyrolysis furnace based on halogen lamps with elliptical-shaped reflectors. The variations of the cellulose microfibril size were analyzed by calculating the Scherrer size from equatorial and meridional diffraction peaks. By quantitatively analyzing the kinetics for different temperatures it is found that thermal decomposition of crystalline cellulose in wood occurs mainly via a thermally activated decrease of the fibril diameter and an estimate for the activation energy is obtained. A simple scheme about the structural degradation of cellulose is presented.