Caracterização de madeira de Eucalyptus urograndis e adesivo a base de óleos vegetais visando o emprego em peças de madeira laminada colada

Abstract

The wood gluing process is a very old technique, but also very complex, because it involves several variables, ranging from wood characteristics to the adhesive inherent properties. Satisfaction in the gluing process is linked to the glue line, which serves to predict the adhesive's performance when exposed to stresses. Following the world trend, companies search in forest options new alternatives to add value to the products, this way, the Eucalyptus genus appears as a potential option to be used. An alternative to conventional adhesives is the natural-based adhesives, usually polyurethanes, which are composed of a bicomponent polymer. With this, the present study aims to produce and test compressed parts made of glued laminated timber using 72-month-old Eucalyptus urograndis wood and vegetable oil-based bicomponent adhesive, in a 1:2 isocyanate and polyol, respectively. The wood was characterized to obtain its physical, chemical, and mechanical properties, and for the adhesive some physical, chemical, and thermal properties were analyzed. For the treatment models analyzed were considered specimens with square cross section of 5 cm side, with 15 cm length. The tests were carried out following the NBR 7190 (ABNT, 1997) and ASTM D 905 (ASTM, 1998) standards. Twelve specimens were assembled for each treatment model, being: solid, two wood veneers, three wood veneers and four wood veneers. Each specimen was individually tested until failure. For data analysis the resistance of the proposed models was evaluated in relation to the number of wood veneers. As a result, the species showed a basic density of 0.46g/cm3, total extractive content of 3.37%, total lignin of 31.5%, holocellulose of 64.5%, and fiber parallel compressive strength of 9.13 MPa. The adhesive had a solids content of 96%, a working time of 26 min, and a viscosity equal to 4,488.18 cp. The highest average values of shear strength were obtained in joints from the lowest weight of adhesive adopted. The tested adhesive weights showed significant differences in the results, with the 150 g/m2 adhesive showing higher efficiency. For the visualization of the wood-adhesive interface a photomicrographic analysis was used, in which it was possible to characterize the glue line produced by the bond between the adhesive and the wood, evidencing the efficiency of the glue weight adopted. For the analysis of the compressive strength of glued pieces, the number of veneers did not influence the strength of the piece. For characterization it was observed that the wood evaluated presented satisfactory results to be used in the manufacture of glulam.