High Temperature Thermal Treatment (HTTT) is generally made in order to improve both the technological performances of the raw material and its aesthetical appearance; as a matter of fact, wood modification by HTTT is well known as an interesting solution for improving the dimensional stability, the durability and the uniformity of the colour of the solid wood of coniferous species with limited decreasing of the mechanical properties (Jämsä and Viitaniemi, 2001). At present in Italy the aim of the HTTT is to reach more interesting and remunerative uses of low quality hardwood, with potential applications for solid wood panels, flooring, furniture and cabinets or other uses in indoor conditions. The paper reports a preliminary evaluation on the effects of HTTT carried out on two Italian hardwoods (European walnut and cherry) in terms of modification of some technological properties of wood, such as surface hardness, durability against insects and dimensional stability. Surface hardness of treated wood has been compared applying the standards EN 1534 (Brinell method) and ISO 3350 (Janka method). Tests of durability against insects referred to EN 350-1, EN 20-1 and EN 46-1 standards and EN 335 for use class of wood assortments. All treated materials have also been characterised in terms of bonding quality by verifying the strength of the wood-to-wood joint when glued with polyvinyl acetate emulsions belonging to the D2 and D3 class of durability of the standard EN 204. Dimensional and shape stability have then been evaluated according to EN 1910, measuring the linear variations and warping of treated wood between dry (20°C, 30 % RH) and wet conditions (20°C, 80 % RH). Cherry and walnut sawnwoods treated with high temperature have displayed notably changes in their properties. Hygroscopicity was reduced, and results also revealed an oven dry density reduction, a bending strength decreasing, a modulus of elasticity increment in treated wood and an increasing in surface hardness. After one month from the beginning of tests, the durability of cherry and walnut against insects was not modified by the thermal treatment. The HTTT in walnut reduced the quality of gluing with PVAc-dispersed products belonging to D3 and D2 classes of durability of EN204, but the application of acetone appreciably increased the performance of the D2-class adhesive. Finally, the thermal treatment stabilized the wood, and the varnish layer could contribute in the same way. The HTTT seems to be a good solution to reach more interesting and remunerative uses of the examined timber material and a method worthy of further studies.
Thermal treatment of hardwood species from Italian plantations: preliminary studies on some effects on technological properties of wood
Brunetti M;Palanti S;Pizzo B;
2007
Abstract
High Temperature Thermal Treatment (HTTT) is generally made in order to improve both the technological performances of the raw material and its aesthetical appearance; as a matter of fact, wood modification by HTTT is well known as an interesting solution for improving the dimensional stability, the durability and the uniformity of the colour of the solid wood of coniferous species with limited decreasing of the mechanical properties (Jämsä and Viitaniemi, 2001). At present in Italy the aim of the HTTT is to reach more interesting and remunerative uses of low quality hardwood, with potential applications for solid wood panels, flooring, furniture and cabinets or other uses in indoor conditions. The paper reports a preliminary evaluation on the effects of HTTT carried out on two Italian hardwoods (European walnut and cherry) in terms of modification of some technological properties of wood, such as surface hardness, durability against insects and dimensional stability. Surface hardness of treated wood has been compared applying the standards EN 1534 (Brinell method) and ISO 3350 (Janka method). Tests of durability against insects referred to EN 350-1, EN 20-1 and EN 46-1 standards and EN 335 for use class of wood assortments. All treated materials have also been characterised in terms of bonding quality by verifying the strength of the wood-to-wood joint when glued with polyvinyl acetate emulsions belonging to the D2 and D3 class of durability of the standard EN 204. Dimensional and shape stability have then been evaluated according to EN 1910, measuring the linear variations and warping of treated wood between dry (20°C, 30 % RH) and wet conditions (20°C, 80 % RH). Cherry and walnut sawnwoods treated with high temperature have displayed notably changes in their properties. Hygroscopicity was reduced, and results also revealed an oven dry density reduction, a bending strength decreasing, a modulus of elasticity increment in treated wood and an increasing in surface hardness. After one month from the beginning of tests, the durability of cherry and walnut against insects was not modified by the thermal treatment. The HTTT in walnut reduced the quality of gluing with PVAc-dispersed products belonging to D3 and D2 classes of durability of EN204, but the application of acetone appreciably increased the performance of the D2-class adhesive. Finally, the thermal treatment stabilized the wood, and the varnish layer could contribute in the same way. The HTTT seems to be a good solution to reach more interesting and remunerative uses of the examined timber material and a method worthy of further studies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.