Efeito da temperatura na anatomia das madeiras de Eucalyptus urophylla e Corymbia citriodora em processo de carbonização

Abstract

Heat treatments are frequently used to improve wood properties. However, elevated temperatures can degrade the material, leading to anatomical deformations such as collapse of the vessels and thermal degradation of the fibers, especially with temperatures near 400oC. Despite the knowledge that the carbonization process causes elevated volumetric shrinkage, the influence that the temperature causes over the anatomical structure of the cellular components of the wood and charcoal is not yet clear. The objective of the present work was to evaluate the influence of applying temperatures from 100oC to 450oC over the the anatomical structure and integrity of Corymbia citriodora and clones of Eucalyptus urophylla hybrid woods under process of carbonization. To do this, we removed bolts along the stems for samples production. Heat treatments with temperatures of 100oC, 250oC, 350oC and 450oC were conducted in order to evaluate the chemical and anatomical components in relation to the increase in temperature. From the results we verified a higher length of the fiber of clone MN463, with 0.97 mm long, C. citriodora presented thicker fiber wall, with 6.56 μm thick. There is a tendency for the increase of these traits in the pith-bark direction. After carbonization, C. citriodora and the clone VM4 showed the highest carbon content. With the analyses conducted at the scan electron microscope, it was possible to verify that the increase in temperature considerably reduces the fiber width. When comparing the control sample to the carbonized at 450oC, the reduction was of approximately 40% for both the VM4 and MN463 clones and near 36% for C. citriodora. The MN463 and VM4 clones presented reduction in fiber wall thickness higher to 75%; for C. citriodora, cell wall thickness reduced 65%.