Surface properties and crystallinity of Pinus taeda and Hymenaea stilbocarpa treated at low temperatures in different grain directions
2020
dos Santos, S. N. C. | de Almeida, T. H. | Sardela, M. R. | Lahr, F. A. R. | Gonçalves, D.
Nondestructive methods were employed to characterize longitudinal (L) and transverse (T) sections of Pinus (Pinus taeda) (softwood) and Hymenaea (Hymenaea stilbocarpa) (hardwood) treated at room temperature (25 °C) to 100 °C, 140 °C, and 180 °C. Changes in color were verified upon mild heating, regardless of cut direction, with Hymenaea exhibiting the darkest tan. Relatively high values of contact angles were obtained (120°) in water implying that surface wetting decreased even at relatively low temperatures, e.g., 100 °C. Differences in heat-treated woods were more noticeable after calculating the surface free energy and its components, with the polar component contributing significantly to the total energy. Crystallinity varied mostly in terms of a meridional pattern in (T) samples. The techniques used in this study seem promising for characterizing anisotropy in woods treated at temperatures lower than 180 °C, i.e., before thermal degradation reactions to be likely significant.
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