Propriedades tecnológicas da madeira densificada de eucalipto submetida ao tratamento em óleo vegetal

Abstract

Densification is relevant in the timber industry. Since it makes it possible to increase the use of wood less valued by the market. However, densified wood shows high dimensional instability. In order to minimize this problem, a post-treatment using the oil heat treatment (OHT®) was performed. In view of the above, the present research aims to evaluate the technological properties of densified wood of the eucalipto submitted to treatment in vegetable oil. The methodology consisted in the use of wood of E. grandis, E. dunnii, E. cloeziana and E. tereticornis that were submitted to the process of densification and post-treatment in vegetable oil. Twenty-four treatments were performed, consisting of different species, densification temperatures and post-treatment. For the characterization of the produced wood based material, physical, mechanical, chemical and superficial tests were carried out. For the statistical analysis, the 4 x 6 qualitative factorial arrangement was used, with four species and six treatments, compared by the Tukey test. The main results showed that densification increases distinctly in the basic density (ρb) among the evaluated species, which shows that the increase of ρb by densification is conditioned to its initial value. In the case of wood dimensional stability it was observed that the densification caused a reduction in this property in relation to the control. However, in the treatments in which the post-treatment in oil was applied, there was a decrease of more than 30% in the dimensional instability, caused by the relaxation of the stresses stored during the compression, through the partial hydrolysis of the hemicelluloses. As for the hygroscopicity of the wood, it was observed that the densification using the temperature of 140 °C showed an increase in the water absorption after 24 hours of immersion, caused by the reopening of the flattened vessels. However, when the wood was submitted to the post-treatment, there was a reduction of the hygroscopicity caused by the thermal degradation and the presence of oil in the cell lumens. In wettability it was identified that the only densified wood presented a hydrophilic character. However, when submitted to post-treatment it has become hydrophobic. Mechanical strength showed the most satisfactory results in densified wood at 140 °C without post-treatment, obtaining increases in all properties and species evaluated. However, with the post-treatment application there was an average decrease of 20% in the mechanical strength of the treated wood. In the analysis of Infrared Spectrometry it was verified that there was a greater chemical alteration after the application of the post-treatment, obtaining degradation of hemicelluloses and amorphous cellulose, which provided proportional increase of crystalline cellulose and lignin. For the colorimetric parameters, it was identified that the post-treatment presented the greatest changes in the color of the wood, causing the wood of the four species to gain a tropical tone (dark brown), which is feasible for the application of aesthetic purposes.