Studying the grammage in lvl panels glued with castor oil-based polyurethane adhesive: a possible alternative to formaldehyde releasing adhesives

Abstract

Efforts have been done in order to decrease the human dependence on petroleum materials. This idea can be applied for 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 in different grammages. Six rubber tree (12 years old) with diameters at breast height (DBH) > 25 cm were harvested to generate veneers (500 x 500 x 2 mm; length, width, and thickness, respectively) for the panels production. The veneers were pre classified by a non-destructive impulse excitation method (Sonelastic system). Seven veneers were arranged in the same grain direction to produce each LVL. 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 glue line was evaluated by optical microscopy. The panels with grammages of 240 g.m-² had the highest volumetric swelling for both adhesives. As the grammage increased from 240 to 280 g.m-², 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 shear strength in the glue line. No significant statistical differences were found between the compositions for static bending. The results indicate that rubber wood glued with vegetal polyurethane has the potential to be used for production of LVL panels and consequently replace the petroleum based adhesives.