No abstract

Last decades, wood was promoted as building material. Wood heat treatment by mild pyrolysis has been reported to improve biological durability and dimensional stability of the material and constitutes an attractive « non biocidal » alternative to classical preservation treatments. Previous studies have shown that conferred properties strongly depend on the heat treatment intensity. A quality control marker based on mass loss has been developed. For several years, the increased development of Tunisian wood industry provides a significant capacity of wood production and transformation. Forests in Tunisia consist essentially of coniferous species [Aleppo pine (Pinus halepensis), Radiata pine (Pinus radiata), Maritime pine (Pinus pinaster), Stone pine (Pinus pinea)], characterised by a weak natural durability. Improved durability and fungal resistance should allow the use of Tunisian species in the wood industry. Import limitation of European species and the use of local species allow the conservation of economic value added in the country and improve the economic balance. For this reason, several Tunisian softwood species (Aleppo pine, Radiata pine and Maritime pine) have been heat-treated under vacuum atmosphere at 230°C to obtain a thermal degradation with mass losses of approximately 8, 10 and 12%. The oven device allows recording the dynamic Mass Loss (ML) during the treatment and following the thermodegradation kinetic. The chemical composition of the studied wood samples was determined before and after heat treatment. For each wood species and treatment intensity, wood chemical and mechanical analyses were performed by measuring O/C ratio, bending and hardness tests. Afterward, tests of decay resistance were performed according to the EN 113 Standard, with different fungal attacks (Poria Placenta, Coriolus Versicolor) at 22°C and 70% of humidity for 16 weeks. Results were related to the mass loss. Furthermore, intensity of thermal degradation was evaluated by TD-GC-MS. Treated and untreated wood samples were maintained during 15 minutes at 230 °C under nitrogen in the thermodesorption tube in order to analyse and compare resulting from the wood thermodegradation volatile compounds.

Wood heat treatment is an attractive alternative to improve decay resistance of wood species with low natural durability. However, this improvement of durability is realized at the expense of the mechanical resistance. Decay resistance and mechanical properties are strongly correlated to thermal degradation of wood cells wall components. Mass loss resulting from this degradation is a good indicator of treatment intensity and final treated wood properties. However, the introduction of a fast and accurate system for measuring this mass loss on an industrial scale is very difficult. Nowadays, many studies are conducted on the determination of control parameters which could be correlated with the treatment conditions and final heat treated wood quality such as decay resistance. The aim of this study is to investigate the relations between kinetics of temperature used during thermal treatment process representing heat treatment intensity, mass losses due to thermal degradation and conferred properties to heat treated wood. It might appear that relative area of treatment temperature curves is a good indicator of treatment intensity. Heat treatment with different treatment conditions (temperature-time) have been performed under vacuum, on four wood species (one hardwood and three softwoods) in order to obtain thermal degradation mass loses of 8, 10 and 12%. For each experiment, relative areas corresponding to temperature kinetics, mass loss, decay resistance and mechanical properties have been determined. Results highlight the statement that the temperature curves' area constitutes a good indicator in the prediction of needed treatment intensity, to obtain required wood durability and mechanical properties such as bending resistance and Brinell hardness.

In order to evaluate their potential to be used as charcoal production by a new industrial thermal treatment process; the wood of seven trees of introduced species in the North eastern Tunisia (3 Eucalyptus, 4 Casuarina) and 1 local species (Tetraclinis) were selected. Physical properties of natural woods and Gravimetric yields in charcoal, ultimate composition, heating values measurements and combustion quality tests were performed before and after carbonization process. For the same thermal degradation intensity (550°C-4 h), Gravimetric yields in charcoal values were comprised between 41.1 and 45.3.9% for Casuarina wood species, 35.5 and 39.4% for Eucalyptus wood species and was 33.7% for Tetraclinis articulata wood. Elemental composition showed a significant difference between the selected species. It varies from 1.46 to 1.65 for H/C and 0.67 to 0.77 for O/C. Casuarina wood species showed the lowest values for the both ratios. The calorific values showed that the selected wood species have Heating Values ranged from 16.264to 20.798 MJ/kg and allow producing charcoal with heating values comprised between 23.871 and 30.943 MJ/kg. The best energetic improvement by carbonization process, in this work, concerns Eucalyptus and Tetraclinis woods, except for the Eucalyptus salmonophloia but the combustion quality showed that Casuarina wood species appears to be the wood species with the most optimal combustion, after undergoing a carbonization process.