Effect of Thermal Modification Treatment on Some Physical and Mechanical Properties of Pinus oocarpa Wood

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 2.39% and 3.34% 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.

Correlation of Studies between Colour, Structure and Mechanical Properties of Commercially Produced ThermoWood® Treated Norway Spruce and Scots Pine

“…Won et al [93] observed increased values for thermal treated Pinus densiflora compared to untreated samples. Herrera-Builes et al [91], using specimens of 410 × 25 × 25 mm (L x R x T), found an increase in MOR of about 47 and 22% after thermal modification of wood at 170 and 190 • C, respectively, whereas MOE increased by 4 and 10%, respectively. The authors mentioned that the increase in mechanical properties might have been due to the condensation reactions in lignin and the rearrangement and crystallinity increase of cellulose, which may have acted as a "hardener" [91,94].…”

“…The results indicate that higher treatment temperature resulted in greater colour changes, with the ∆E* values being about 24 for Thermo-S and about 33/31 for Thermo-D Norway spruce and Scots pine wood. A ∆E* value higher than 6 is classified as a major colour change [90,91].…”

“…that the increase in mechanical properties might have been due to the condensation reactions in lignin and the rearrangement and crystallinity increase of cellulose, which may have acted as a "hardener" [91,94].…”

Influence of the Thickness of Scots Pine (Pinus sylvestris L.) Veneers on Selected Properties of Flooring Materials

“…Thus, this kind of research is focused on testing the properties of the top layer and is conducted on separated face layers material (without base layer) or on the face layer as a part of flooring. The research may include exposition to temperature and humidity [7], hardness [8][9][10], strength [11], top-layer examination after material modifications [12][13][14], or in situ polymerization of active monomers [15]. The study of entire flooring materials focuses on connection with heating systems [16][17][18][19][20] or using individual wood species or quality for flooring applications.…”

Water Absorption Properties in Transverse Direction of Heat-Treated Chinese Fir Wood Determined Using TD-NMR

“…Heat treatment is a method of exposing wood to an almost oxygen-free environment under high temperature conditions and causing changes in the chemical structure of the wood substance [4,5]. Hemicellulose first degrades during the heat treatment process, including acid hydrolysis and decarboxylation reactions [6].…”