Surface process effect on PVAc glued joints

The changes in glueline shear strength on sugar maple, American beech, paper birch wood bonded with polyvinyl acetate (PVAc) adhesive were evaluated. The wood species had different surface properties as the result of across and along to the grain helical planing and sanding with three grit size sandpapers (g.s.p.). The specimens prepared to determine the effect of the variables on bond performance were subjected to shear test in an universal test machine. Surface roughness and wetting properties of wood were measured; microscopic analysis allowed to reveal damages on wood surface. Sugar maple specimens were also subjected to an accelerated aging treatment. The most effective surfacing methods were the helical planing process along and across the grain and sanding process with 150 g.s.p., all able to obtain the best surface for gluing, reaching a peak stress of 22,5 N/mm2. Among the different species studied, sugar maple gave the best gluing performance, followed by American beech, and paper birch. Sanding with 60 and 100 g.s.p. produced the roughest surfaces, showing compressed parenchyma rays and torn fibres. Among the studied species paper birch showed the roughest surfaces followed by American beech and sugar maple. Sugar maple sanded with 100 g.s.p. had the highest contact and equilibrium angles, sugar maple sanded with 120 g.s.p. had the lowest.