Wettability and surface free energy on heat-treated Pinus sp. and Erisma sp. woods

Abstract

This study aims to investigate wettability, surface polarity, and mass loss in two reforestation woods, Pinus sp. (softwood) and Erisma sp (hardwood), after heat treatment. The wood samples were heated to 100 °C, 140 °C and 180 °C, meanwhile a control group was kept at a fixed temperature of 25 °C. Different test liquids were employed in order to obtain the contact angles (wetting angles) formed on the heat-treated sample surfaces. From such measurements, the values of surface free energy, in terms of its polar and dispersive components, were calculated by the Owens-Wendt-Rabel-Kaelble approach. Temperatures far below 180 °C proved to be high enough to yield hydrophobic samples, i.e., with relatively high wetting angles and low surface polarity, but without drastic visual and dimensional changes. The impact of heat treatment on the surface properties of Pinus sp. and Erisma sp. was also verified by fungal inoculation (Pycnoporus sanguineus). Compared to Pinus sp., heat-treated Erisma sp. showed improved properties, such as mass stability, surface polarity and wettability.