Comparative study of the calculation techniques used for the determination of kinetic parameters of wood and cellulose degradation from T.G.A.

In a previous study, we had shown that the thermal degradation of wood could be described by a two-steps mechanism, the second step corresponding to the degradation of cellulose. This result had been obtained by using a simulation model taking into account several reactions to interpret the mass loss rates measured by thermogravimetric analysis (T.G.A.).When the classical techniques of calculation of the kinetic parameters from T.G.A. experiments are employed, it is generally assumed that only one overall reaction is needed to calculate the mass loss rate, at least for one part of the thermogram. In this work, we have checked whether these techniques are able to give for the second step of the thermal degradation of wood the values obtained with pure cellulose.Five techniques have been considered. It has been shown that the Freeman and Carroll's and the ratio methods lead to kinetic parameters common to wood and cellulose while three other techniques (maximum point, Coats and Redfern's, Broido's) give different results