The Effects of Surface Roughness on Adhesion Strength of Coated Ash (Fraxinus excelsior L.) and Birch (Betula L.) Wood
Keywords:ash wood, birch wood, surface roughness, acrylic-polyurethane coating, adhesion strength, pull-off testing
AbstractFor the evaluation of surface roughness impact on adhesion properties, the samples of dried ash (Fraxinus excelsior L.) and birch (Betula L.) wood were used. Before wood finishing, the surfaces of the samples were sanded. In order to get different surface roughness the abrasive material of P80, P120, P150, P180, P220 and P240 grit was used. The parameters of surface roughness Ra, Rz and Rmax were measured in three directions: along the wood grain, across the grain and in the angle of 45º. Comparison of the results showed the non-linear dependency of roughness parameters. Afterwards the wood surface was coated with three different acrylic-polyurethane coating systems (1 layer of varnish without primer, 1 layer of primer and
1 layer of varnish, and 1 layer of primer and 2 layers of varnish). The adhesion strength was assessed using the pull-off method. Also the nature of the fracture was evaluated. It was determined that the peculiarities of surface roughness, coating system type and wood species signally results the values of the adhesion strength.
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