Abstract
ABSTRACT To evaluate the adhesive efficiency on the union of glued joints in a particular temperature and humidity conditions for a specified time the adhesive must be submitted to specific load tests, such as shear in the glue line. The objective of this study was to evaluate the shear strength in the glue line of Eucalyptus sp and Pinus sp.woods. Five adhesives (castor oil, sodium silicate, modified silicate, , PVA and resorcinol-formaldehyde), three weights (150 g/m2, 200 g/m2, and 250 g/m2) and two species (Eucalyptus sp. and Pinus sp.) of wood were used. Twelve specimens were obtained from each repetition per treatment, corresponding to 108 specimens that were conditioned at a temperature of 23 ± 1°C and relative humidity of 50 ± 2%. The interaction between the weight and type of adhesive was significant for the shear strength in the glue line of eucalyptus wood. However, no interaction between the weight and the adhesive was found for pinus, only the isolated from the adhesive effect. Chemical bonds originated in the polymerization of resorcinol-formaldehyde adhesives and castor bi-component conferred upon these adhesives the greatest resistance in the glue line. Castor and resorcinol-formaldehyde adhesives showed the highest shear strength values in the line of glue and wood failure. Castor adhesive presented satisfactory performance for bonding of eucalyptus and pine woods.
Highlights
In the wood-glue line system, the tensions generated in the bonded product are extremely important in the overall balance of the strength
Weight and adhesive type interaction was significant for the shear strength in the glue line of eucalyptus wood in dry condition
A significant effect was found for the interaction between weight and type of adhesive for failure in eucalyptus wood, which was not found in pinewood, with only the isolated effect of the adhesive type, that is, no effect of weight was observed
Summary
In the wood-glue line system, the tensions generated in the bonded product are extremely important in the overall balance of the strength. Tensions generated in the glue line are manifested through shear stresses in the adhesive bonding plane and perpendicular to it (PINTO, 2011). To evaluate the adhesive efficiency on the union of bonded joints under a particular temperature and humidity conditions during a specific time, the adhesive must be evaluated by means of specific loading tests, such as shear in the glue line. The resistance of the unions of the wood pieces per adhesive depends upon the strength of each element involved in the union. The adhesive has the function of establishing chemical bond between the pieces of wood (CARNEIRO, 2010)
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