Avaliação do ângulo microfibrilar da madeira de Dipteryx odorata (Aubl.) Willd - cumaru em função da variação de umidade na madeira

Abstract

The microfibrilar angle - MFA has an effect on a wide range of properties of the fiber and, consequently, of the wood it composes. However, little is known about the changes that occur in MFA due to the variation in wood moisture. The objective of this work was to estimate the MFA at the fiber saturation point - FSP at 12% and 0% moisture contente and to compare them with measurements made by polarized light microscopy for Dipteryx odorata (Aublet.) Willd wood, (cumaru). For this purpose, three trees were felled, cuting five discs along the trunk of each tree for the sampling. From each disc, three across pith-to-bark samples were cut. MFA were estimated by the X-ray diffraction method (XRD) and measured by polarized light microscopy (PLM). The average MFAXRD was equal to 9.0 degrees, while the MFAPLM was equal to 8.5 degrees. The MFA did not differ statistically in relation to the two methods used. The average microfibrilar angle estimated by XRD was higher in wood at the fiber saturation point and lower in wood at 12% moisture content. The microfibrilar angle increased from 0% to 100% of commercial height. For the pith bark variation in the trunk, there was no uniform behavior of MFA by X-ray diffraction. Under the conditions in which the study was carried out, it was not possible to estimate the microfibrilar angle by polarized light microscopy as function of X-ray diffraction.