Adhesive bond strength of end grain joints in softwood with varying density

Abstract Norway spruce wood specimens covering a wide density range, including density samples between 300 kg m-3 (low density wood) and 750 kg m-3 (high-density compression wood), were joined at end grain surfaces and tested in tension perpendicular to the bonded surface to estimate the effect of mechanical interlocking on the adhesive bond strength. It was hypothesised that the higher the density of the specimens the lower will be the mechanical interlocking of the adhesive joints due to a reduced penetration of the adhesive into the cell cavities. An increase of tensile strength was observed with increasing density. These results demonstrate that in the specific case investigated here the cross-sectional cell wall area available for adhesive bonding, which correlates with density, is probably more important than mechanical interlocking.

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