Wettability Variation of Unmodified and Thermally Modified Surfaces of Thinned Wood from a Hardwood Plantation

Abstract

The study of surface properties—particularly wettability—and how these vary from pith to bark in relation to changes in surface roughness, chemical composition and crystallinity is of importance to improve the use of wood that comes from thinning of a hardwood plantation. In this study, water wettability was assessed by measuring the contact angle using a drop shape analyzer, while surface roughness was evaluated with a confocal microscope. The chemical composition and crystallinity of the surface were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR). To minimize the influence of machining variables on surface properties, a consistent surface quality before and after thermal modification was ensured using computer-controlled cutting. The results revealed that, prior to thermal modification, the contact angle varied significantly from pith to bark. After modification, the contact angle increased, but the differences were no longer statistically significant, due to the homogenization of the chemical-structural characteristics caused by the thermal modification. Relative crystallinity and surface roughness tended to increase towards the bark, with the contact angle tending to decrease, before and after modification.