Evaluation Of Varnish Coating Performance For Two Surfacing Methods On Sugar Maple Wood
Keywords:Planing, sanding, wetting properties, roughness, varnishing, sugar maple
AbstractThe understanding of adhesion mechanisms on wood surfaces is essential in order to extend service life of film-forming coatings. Pull-off adhesion test and accelerated aging were used to assess adhesion and performance of a high-solids polyurethane coating on sugar maple wood. Two surfacing processes were employed prior to coating: peripheral knife planing and sanding. Planing produced surfaces and subsurfaces virtually free of damage, which provoked a higher coating penetration. However, this was not sufficient to promote good adhesion. Sanding offered better wetting properties of wood surface even though superficial crushing of cells hindered coating penetration. Wetting was facilitated in the direction of abrasive scratches. Stronger pull-off adhesion and better aging-resistance of films on sanded surfaces were mainly associated to the presence of torn-out micro-fibrils, which promoted a better mechanical anchorage and offered a greater actual surface available to coating and wood interactions. Surface roughness, wetting properties and film aging-resistance were significantly correlated with pull-off adhesion.
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