Taninos de Mimosa tenuiflora (Willd.) Poir. submetidos à hidrólise ácida e adição de microfibras de celulose para produção de adesivos para madeira

Abstract

The use of vegetable tannin-based adhesives is an alternative to the environmental problems involved in the use of synthetic adhesives, besides being a way to reduce costs in the production process of wood panels and glued wood. The limitations inherent to the use of tannins, such as high viscosity and low moisture resistance, can be solved through the chemical modification of tannins and the addition of products that alter their characteristics. In this context, this work aimed to evaluate tannin-based adhesives extracted from the bark of jurema-preta trees subjected to acid hydrolysis and with the addition of cellulose microfibers. The rheological properties of the produced adhesives, the bonding quality through the evaluation of shear strength and percentage of failure in wood of bonded joints, and the physical-mechanical quality of particleboard panels were evaluated. The adhesives presented rheological properties suitable for use in wood bonding. The glued joints presented high percentage of wood failure and the acid hydrolysis favored the penetration of the adhesive into the wood, generating good quality of glue line. For the wood panels, the addition of cellulose microfibers increased the density of the panels, influenced the water absorption and the swelling in thickness, and all the mechanical properties evaluated presented satisfactory results and within the limits established by the regulatory standards. As for formaldehyde emission, tannic adhesives showed significantly lower results than ureaformaldehyde, as well as in treatments where 20% of urea was replaced by tannins. In general, the modified tannin-based adhesives showed satisfactory quality for wood bonding and production of particleboard.