Abstract
The objective of this study was to evaluate the effect generated by a thermal treatment on the dimensional changes and compression behavior of three wood species from commercial plantations (Eucalyptus nitens, Tectona grandis and Gmelina arborea). To accomplish the goal, dilatometric and compression tests were performed in the three directions of wood. It was found a high anisotropy of the coefficient of linear thermal expansion (CTE) as well as of the compression strength of the woods. Higher values of CTE in the tangential direction than in the radial direction were measured, meanwhile in the longitudinal direction were null. In terms of mechanical strength, the longitudinal direction showed the highest strength. The radial strength was slightly higher than the tangential one. Thermal treatment increased the strength to compression and the resistance to deformation in the elastic region. The modulus of elasticity increased up to 30.9%, the stress at proportional limit up to 27.3% and the modulus of rupture up to 30.3%, in the longitudinal direction. The thermal treatment had a higher effect on the mechanical properties of the lowest density wood. On the contrary, the mass loss increased for these species, finding values around twice than those obtained for the denser wood.
Highlights
The demand of wood is increasing worldwide and it cannot always be obtained from natural forests
Along the plateau at this temperature, any dimensional change was detected. Another expansion is detected when the temperature increased up to 180°C, it is observed a shrinkage on the 180°C plateau, which is assumed to be caused by certain level of wood degradation due to high temperature exposure
The results show a characteristic mass loss at 180°C mainly caused by hemicellulose thermal degradation (Espinoza and Cloutier, 2009)
Summary
The demand of wood is increasing worldwide and it cannot always be obtained from natural forests. Due to its fast-growing, adaptability to different environments and low-temperature resistance, E. nitens, an Australian native species, is widely used for paper manufacturing and wood-based boards fabrication. T. grandis is the most widely planted tropical wood, with 74% of the total hardwoods plantations in the world (Keogh, 2009). It has been recognized as a high quality timber attributable to its excellent properties, becoming a very valuable wood (Bhat et al, 2001). Commercial forest plantations would help to solve the wood for paper and boards shortage, they produce a highly unstable material caused by the fast-growing of trees and their high proportion of juvenile wood, which may cause severe problems during their processing as lumber (Ananías et al, 2014). It is important to study these woods in order to have a better understanding of their behavior as primal matter
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