Desenvolvimento de bioadesivos para madeira utilizando misturas de taninos e lignina Kraft

Abstract

The smaller supply of wood, such as logs with large diameters and high quality, makes the use of reconstituted wood increasingly common. However, these products are usually manufactured using petroleum-based adhesives formulated with formaldehyde, a chemical known to be carcinogenic. The use of hexamethylenetetramine as a substitute for formaldehyde is an excellent option, because in the presence of tannins, it produces wood panels with zero formaldehyde emission. Thus, the use of phenolic compounds of biological origin, such as tannins and lignin, are a promising alternative to these adhesives. Adhesives produced with tannins-formaldehyde are considered low emission, whereas lignin, due to its high annual production and its similarity to phenolic derivatives of petroleum, makes this macromolecule promising in the formulation of adhesives for wood. The objective of this work was to formulate and evaluate Kraft tannin-lignin based adhesives and to verify the influence of the substitution of paraformaldehyde for hexamine as a hardener in the adhesives. Tannins were extracted from the bark of Stryphnodendron rotundifolium Mart. ex Benth. Fabaceae family, the adhesives were produced at a concentration of approximately 50% of total solids, the adhesive formulations were Tannins-Formaldehyde (TF) and Tannins-Hexamethylenetetramine (TH), Kraft lignin will be used as a partial substitute for tannins in the formulations TF and TH (10, 20 and 30%). Commercial Phenol-Formaldehyde (FF) adhesive was used as a control. The physical/chemical properties of the adhesives were evaluated. Subsequently, glued boards were made to evaluate the shear strength of the glue line, following the ASTM D 2339-98 standard (ASTM, 2000), the evaluation was carried out in two states, after acclimatization and after being immersed in water for 24 hours. Tannins, Kraft lignin and TF-lignin, TH-lignin and FF adhesives were characterized by Fourier transform infrared spectroscopy (FTIR). The adhesives formulated in this work showed good qualities for application on wood. Due to its physical/chemical properties, which under certain conditions even favored its application on wood, in addition to the shear strength values in dry and wet conditions that were similar to those of commercial FF adhesive. The results demonstrate that the use of barbatimão tannins and Kraft lignin in the production of adhesives for wood can be performed, but the use of hexamine as a hardener improves the characteristics of the adhesives and returns the best results of shear strength under dry and wet than paraformaldehyde. This work is expected to demonstrate the possibility of using underutilized natural resources for the production of wood adhesives.