The Application of Structural Adhesives in Glulam Beams: A Comparative Study

This study aimed to evaluate the adhesion behavior of wood from an E. urophylla × E. grandis clone using the application of melamine–urea–formaldehyde (MUF), resorcinol–formaldehyde (RF), and polyurethane (PUR) adhesives in test samples obtained from 12 glulam beams. Adhesives were characterized by their pH, viscosity, density, and solid content. The wood–adhesive interface was assessed through the shear strength, percentage of wood failure, delamination, and photomicrograph analysis. A microdensitometer with X-rays and a resistograph were used to determine the material density and drilling resistance of the elements. Adhesive pH values ranged from 6.35 to 9.05. MUF exhibited the highest viscosity (1169 cP), while the adhesive density varied between 1.29 and 1.67 g cm−3. No statistically significant difference in results was obtained for the shear strength in dry conditions. The MUF adhesive showed a lower percentage of wood failure compared to PUR and RF. In the delamination test, the wood beams glued with RF yielded the best results. Photomicrographs revealed the adhesive’s penetration into the wood’s anatomical structure. Densitometry and resistograph profiles accurately represented the beam balancing configuration. The adhesives PUR, RF, and MUF demonstrated suitability for producing glulam beams with the Eucalyptus clone wood evaluated in this study.