Thermogravimetric Analysis and Devolatilization Kinetics of Wood

Thermogravimetric curves have been measured at a heating rate of 5 K/min for several hardwoods (beech, alder, birch, and oak) and softwoods (Douglas fir, two pine species, redwood, and spruce), whose chemical composition varies within the usual standards. The analysis of the devolatilization characteristics is based on the introduction of several reaction temperatures. A comparison between hardwoods and softwoods shows that, in the latter case, the decomposition starts at lower temperatures, the hemicellulose shoulder is more delayed, and both the hemicellulose and cellulose zones are wider. Furthermore, the yields of char are higher. However, a devolatilization mechanism, consisting of three parallel reactions and the same set of activation energies for hemicellulose, cellulose, and lignin (100, 236, and 46 kJ/mol), can describe the high-temperature (>553 K) degradation behavior of all of the woods with a good accuracy. Modifications for the extension of the mechanism at lower temperatures are required only for species with significant extractive contents and consist of two further reactions (activation energies of 105 and 127 kJ/mol, respectively).