Abstract
This study deals with the effect of heat treatment on Pinus oocarpa specimens from forest plantations in Colombia. The effects of two heat treatments at 170 and 190 °C for 2.5 h in saturated vapor were evaluated based on the color, dimensional stability, air-dry and basic densities, modulus of elasticity (MOE), and modulus of rupture (MOR) in static bending of samples. The evaluations were carried out following the Colombian Technical Standards NTC 290 and 663, and the color changes resulting from heat treatments were monitored using the CIE-Lab, as well as other standards from the literature. The results show that there was 2.4% and 3.3% mass loss of wood modified at 170 and 190 °C, respectively. The air-dry and basic densities were higher in 170 °C treatment than after 190 °C treatment, and the thermal modifications applied increased the dimensional stability of the treated wood. After treatment at 170 and 190 °C, the lightness to darkness (L*) was reduced by 10% and 22%; the a* coordinate increased by 11% and 26%, causing redness in the treated wood; the b* coordinate increased by 14% and 17%; and the values of the wood color saturation (c*) increased by 14% and 18%, respectively. The general color change (ΔE*) increased gradually with the increase in the treatment temperature, resulting in a high color change to a very different color. The bending strength of thermally modified wood was improved and significantly increased to values higher than those of unmodified Pinus oocarpa wood. The high air-dry and basic densities, improved dimensional stability and resistance to bending, and attractive appearance of the treated wood indicate that thermal modification is a promising alternative for the transformation of Pinus oocarpa wood into a raw material with a high added value.
Highlights
As a result of the increasing need to reduce environmental pollution, lumber producers around the world have gradually begun to reduce the amount of chemicals used to improve wood properties [1]
At 170 ◦ C, the air-dry density increased by 5%, but at 190 ◦ C, it decreased by
On the other hand, the samples modified at 170 ◦ C increased by 20%, but the wood treated at 190 ◦ C did not improve, obtaining values similar to those obtained in the unmodified wood, which presented statistically significant differences
Summary
As a result of the increasing need to reduce environmental pollution, lumber producers around the world have gradually begun to reduce the amount of chemicals used to improve wood properties [1] For this reason, thermal modification is an environmentally friendly alternative that can be applied to wood [2]. Among the benefits of thermally modifying the wood, it was found that the dimensional stability of the wood increases [7,8,9], presenting low values of shrinkage and swelling [8], owing to the changes in the polymeric components of the cell wall This prevents the bonding between water molecules and the cellulose structure [4,9,10,11,12], which decreases the hygroscopic property of the treated wood [13]. The darkening of the wood obtained during the thermal modification by the degradation of hemicellulose and lignin—as well their conversion into extractive chromophores—provides improvements in the aesthetic properties of the treated wood [14,15,16,17,18,19]
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