Résumé
Thermal treatment of wood is, besides other wood modification system, used to improve the decay resistance and dimensional stability. However, the chemical changes that are caused by treatment process are still difficult to quantify, characterize and control. Previous studies have shown that thermodesorption coupled to GC-MS is an attractive tool to characterize and quantify products formed during wood thermal degradation and determine energies of activation of these volatile products during thermal treatment. Simultaneous Thermal Analysis (STA) is a laboratory method which has been investigated in recent years. In STA, the recording of DSC curves allows to detect the endothermic peaks and determine the caloric value during thermal degradation. The aim of this study is to give better insights on wood thermal degradation during wood heat treatment with special emphasis on the kinetics of thermal degradation. For this purpose, one hardwood species (beech), one softwood species (Silver fir) and their respective holocellulose and Klason lignin fraction have been subjected to thermal treatment directly, in a TG STA under helium atmosphere at different temperatures from 180 to 280°C and for different times ranging from 15 to 60 minutes. The results showed that mass losses generated from thermal degradation and calorific values as a function of thermal treatment intensity were depending on time and temperature. A higher DSC value during thermal treatment could be shown for softwood compared with hardwood, in the same conditions. DSC values were corresponding to the necessary energy to begin the wood thermal degradation and it also correlated to elemental composition and colour changes after heat treatment.