Pine wood retification : relationships between lignin structural alterations and wood performances.
Résumé
Retification (thermal treatment of wood in an inert atmosphere between 200 and 260°C) noticeably increases both the wood resistance towards fungal degradation and the wood dimensional stability. To better understand the molecular basis of these improved performances, pine wood simples were retified in various conditions of severity. The structural alterations of lignins were investigated in relation with the wood properties. While very little change in lignin structure was observed when pine samples were treated under inert atmosphere up to 230°C, lignin structure was substantially altered when wood was heated 5 minutes at 240°C. These experimental conditions happen to correspond to those allowing to significantly improve pine wood dimensional stability and fungal resistance without detrimental loss of mechanical properties. When higher temperature (250°C) or longer thermal treatment (45 minutes) were applied to the pine samples further alteration of lignin structure, relative to the sample treated at 240°C for 5 minutes, occurred only to a moderate extent while the mechanical properties were dramatically reduced.