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.

摘要 为降低人类对石油基材料的依赖，已有诸多研究开展相关工作，该思路可应用于木材胶黏剂与木制品领域。本研究旨在评估采用蓖麻油基聚氨酯（castor oil-based polyurethane）与间苯二酚甲醛（resorcinol formaldehyde）胶黏剂、不同施胶量（grammage）制备的巴西橡胶树（Hevea brasiliensis）单板层积材（laminated veneer lumber, LVL）板材。本研究选取6株树龄12年、胸径（diameter at breast height, DBH）＞25 cm的橡胶木，采伐后制备规格为500 mm（长）×500 mm（宽）×2 mm（厚）的单板用于板材生产；采用无损脉冲激振法（non-destructive impulse excitation method）结合Sonelastic系统（Sonelastic system）对单板进行预分级。每块LVL板材由7块沿同一纹理方向排布的单板压制而成，两种胶黏剂分别采用240、280及320 g·m⁻²的施胶量进行施胶。本研究对板材的体积膨胀率、干态、湿态及沸煮后工况下的胶层剪切强度，以及平置与边置工况下静弯曲试验的刚度与强度进行了评价，同时通过光学显微镜对胶层形貌进行观测。结果显示，采用240 g·m⁻²施胶量的两种胶黏剂制备的板材均表现出最高的体积膨胀率；当施胶量从240 g·m⁻²提升至280 g·m⁻²时，间苯二酚甲醛胶黏剂板材的体积膨胀率降低32.53%，蓖麻油基聚氨酯胶黏剂板材则降低21.42%。采用植物基聚氨酯胶黏剂制备的板材胶层剪切强度表现最优，不同胶黏剂配比间的静弯曲性能无显著统计学差异。研究结果表明，采用植物基聚氨酯胶黏剂粘接的橡胶木具备制备LVL板材的潜力，可替代石油基胶黏剂。