Performance of solvent-borne coating on red oak wood prepared by two alternative surfacing processes

Abstract

The performance of varnishes applied to wood will depend on the way in which its surfaces have been prepared. Sanding has traditionally been used to prepare surfaces prior to coating. This process is one of the most expensive operations in woodworking, which produces a high level of wood dust. As a result, other surfacing processes are actually studied as alternatives to sanding for wood finishing. The effects of two alternative processes, oblique cutting and helical planing, on surface properties and coating performance of red oak wood were thus studied. Surfaces were prepared using three oblique angles (oblique cutting) and three wavelengths (helical planing) before application of an interior solvent-borne coating. Surface properties were examined by roughness parameters, scanning electron microscopy micrographs, wetting behavior, and surface energy. Coating performance was assessed by pull-off tests on aged and un-aged specimens. Oblique and helical planed surfaces at the highest oblique angle and wavelength, respectively, presented micro-torn grain, a certain level of micro-fuzziness, and higher roughness. Oblique-cut surfaces were more wettable than helical-planed surfaces. The wettability of machined surfaces decreased with increasing surface roughness within each process. Despite oblique samples had shown lower values of pull-off strength prior to aging treatment, these surfaces had statistically similar pull-off strength to those of helical-planed specimens after aging. As a result, the latter surfaces had higher loss in adhesion after accelerated aging. Results suggest that the use of oblique angles of 15° and 35° should provide a better coating performance in oblique-cut surfaces. On the other hand, no significant differences were detected between wavelengths during helical planing with respect to coating performance. Thus, a low (1 mm) or high wavelength (2.1 mm) could be used, depending on whether smoothness or productivity are required, in order to reduce sanding dependence for finishing red oak wood.