Adhesion strength of cellulosic varnish coated wood species as function of their surface roughness

Abstract

The objective of this study was to evaluate adhesion strength of four wood species, namely, beech (Fagus orientalis Lipsky), alder (Alnus glutinosa subsp. barbata Yalt.), spruce (Picea orientalis L. Link), and fir (Abies nordmanniana subsp.) coated with cellulosic varnish. Samples were prepared in tangential and radial grain orientations from the above species. Surface quality of the specimens was also measured employing stylus type equipment after samples of all four types of species were sanded with 80- and 180-grit sandpaper prior to coating process. Surface roughness of the specimens sanded with 80-grit sandpaper resulted in significantly higher mean peak-to-valley height (R z) values based on the measurement employing stylus type profilometer. The highest adhesion strength values of 2.39 N/mm2 and 2.03 N/mm2 were found for beech and alder samples, respectively. It appears that overall higher roughness characteristics of the specimens exhibited enhanced adherence between substrate and varnish resulting in higher adhesion strength values.