Industrial Thermowood®and Termovuoto thermal modification of two hardwoods from Mozambique

The study aimed at treating metil ( Sterculia appendiculata K. Schum) and neem ( Azadirachta indica A. Juss) timber from Mozambique under industrial conditions by steam [Thermowood ® (TW)] and vacuum [Termovuoto (TV)] thermal modifications (TM). Matched boards were treated identically and wood alterations in chemistry, colour, mass loss (ML), mechanical properties and durability were compared. The applied vacuum partly removed the acetic acid that causes carbohydrate degradation, i.e. heat applied under vacuum was less destructive. TM under vacuum generated a lighter colour than that caused by steam treatment. ML was significantly higher after the TW process namely, 14.1 vs. 9.9% after thermo-vacuum treatment for metil and 14.2 and 12.1% for neem. Colour and ML changes correlated with the decrease in shear strength, rupture and elasticity moduli and increase in wood decay resistance. Metil wood is more permeable and demonstrated significant differences between the treatments; the thermo-vacuum process was less destructive but led to less improvement of durability compared to TW treatment.