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.

Thermal modifications alter the physical properties and improve the natural durability of wood without using chemical impregnation processes being an environmentally friendly alternative; these improvements could be made due to changes in the internal wood structure. In this investigation, changes caused to the chemical composition and microstructure of wood Pinus oocarpa by thermal modification at 170 and 190 °C were evaluated. The thermal treatment was carried out in a prototype chamber operated during the modification steps under a steam atmosphere, with a continuous flow without pressure. The evaluation of chemical changes was performed following the TAPPI standards. Using Fourier transform infrared spectroscopy (FTIR) and optical microscopy, the wood microstructure was characterized. The results showed a decrease in holocellulose contents by 7% at 170 °C and by 9% at 190 °C; lignin contents increased at 170 °C (6%) and at 190 °C (8%) and extractives were increased by 8% (170 °C) and 13% (190 °C); the changes obtained by the spectra were related to the C-H deformation in cellulose and hemicelluloses and the complex bonds of lignin carbohydrates of the -CH3 (lignin) and CH2 (carbohydrates) groups and organic acids released during thermal modification. Thickness of tracheid walls decreased in earlywood 8% (170 °C) and 22% (190 °C) and in latewood 11% (170 °C) and 14% (190 °C); lumen diameters increased in earlywood to 170 °C (14%) and 190 °C (48%) and in latewood in 14% (170 °C) an in 20% (190 °C). At 190 °C, the cell alterations were higher. Pinus oocarpa was thermally modified at 170 °C showing better wood quality in its internal structure.

La presente investigación se desarrolló con la madera Pinus oocarpa Schiede ex Schltdl. Var. Ochoterenai de plantación forestal de Colombia, especie que ha presentado inconvenientes importantes que han limitado su uso, debido a su inestabilidad dimensional y baja resistencia mecánica. Los tratamientos con impregnación de polímeros han permitido reducir las deformaciones, y mejorar las propiedades físicas y mecánicas. El objetivo de esta investigación fue evaluar el efecto de la impregnación de polietilenglicol con peso molecular 600 y 1500, alcohol polivinílico y adición de zeolita, sobre la densidad, estabilidad dimensional, flexión estática y compresión paralela al grano. Las muestras se impregnaron con baño caliente a 95 °C, durante 8 horas, y luego impregnados a temperatura ambiente, por 16 horas. La evaluación de la madera se llevó a cabo bajo las Normas Técnicas Colombianas NTC 290, 663, 784 y otros estándares de la literatura. Los mejores resultados se obtuvieron con la impregnación de polietilenglicol 1500; la densidad aumentó entre el 21 % y 24 %; la eficiencia anti-hinchazón fue de 60 %; en flexión estática aumentó el módulo ruptura 20 %, el módulo de elasticidad 39 % en compresión paralela al grano aumentó 8 %. El tratamiento con polietilenglicol 600 proporcionó una menor eficacia anti-hinchazón (14 %), y menor mejora en densidad (8 %) y en las propiedades mecánicas (1 % a 7 %). La impregnación con polímeros evidenció madera con mayor estabilidad dimensional y mejores propiedades físicas y mecánicas Palabras claves: Densidad, eficiencia anti-hinchazón, flexión estática, módulo de elasticidad, Pinus oocarpa, polímeros, tratamiento químico de madera.