Surface properties and crystallinity of Pinus taeda and Hymenaea stilbocarpa treated at low temperatures in different grain directions

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.