STUDYING THE GRAMMAGE IN LVL PANELS GLUED WITH CASTOR OIL-BASED POLYURETHANE ADHESIVE: A POSSIBLE ALTERNATIVE TO FORMALDEHYDE RELEASING ADHESIVES

Abstract

Efforts are constantly done in trying to decrease dependence on petroleum materials. This idea has a strong application in wood adhesives and wood products. This study proposes to evaluate laminated veneer lumber (LVL) panels of Hevea brasiliensis produced with castor oil-based polyurethane and resorcinol-formaldehyde at different grammages. Six 12-year-old trees with diameters at breast height (DBH) > 25 cm were used. The veneers (500 x 500 x 2 mm) for panel production were generated in a rotary peeling lathe and were pre classified by a non-destructive impulse excitation method (Sonelastic system). The panels consisted of seven veneers arranged in the same grain direction. The following grammages were used for each adhesive type: 240, 280 and 320 g.m^-². The volumetric swelling of the panels, glue line strength under dry, wet and post-boiling conditions, and stiffness and strength in static bending tests in flatwise and edgewise positions were evaluated. The panels with grammages of 240 g.m^-² had the highest volumetric swelling for both adhesives. As the grammage increased, the panel volumetric swelling decreased 32.53% for the resorcinol-formaldehyde adhesive and 21.42% for the castor oil-based polyurethane adhesive. The panels glued with the vegetal polyurethane adhesive presented the best results for the three conditions tested for the shear strength tests at the glue line. For the static bending tests, there were no significant differences between the compositions. The results indicate that rubber wood glued with vegetal polyurethane has the potential for being used for production of LVL panels and consequently replace the petroleum based adhesives.