Qualidade de painéis compensados produzidos com adesivos tânicos de Anadenanthera peregrina, extraídos em diferentes concentrações de bissulfito de sódio

Abstract

To increase the extraction yield and improve the properties of tannic adhesives in the bonding of plywood panels, different concentrations of salts can be applied and this process is called sulfitation. This study aimed to evaluate the quality of plywood panels produced with tannic adhesives from the bark of Anadenanthera peregrina (red angico), extracted at concentrations of 0, 3, 5% of sodium bisulfite (NaHSO3), in relation to the dry mass of the shell. The extracts were taken in a water bath at a temperature of 70°C for 2 hours, then filtered through a 200 mesh sieve and into a number 2 porosity crucible, in order to retain fine particles. Then, they were placed in a refractory and taken to an oven with forced air circulation at 40°C. After this process, the material obtained was macerated in a mortar and pestle to turn it into powder. Subsequently, the adhesives were produced with a solids content of 45% and 6% paraformaldehyde. The adhesives were tested on plywood panels, produced in triplicate, with 30x30x10cm sheets. Analyzes of tannins, adhesives and panels were carried out. The gravimetric yield of tannins was performed to evaluate its use as an adhesive. FTIR and TGA analyzes of tannins extracted at different concentrations of NaHSO3 were also performed. The adhesives were characterized in terms of viscosity, gel time, solids content and pH. The panels were evaluated in the following aspects: humidity on a dry basis, apparent density, total water absorption, modulus of rupture and elasticity to static bending (parallel and perpendicular to the grain of the layer), dry shear test in the glue line and microscopy scanning electronics (SEM). The tannins extracted from the bark of Anadenanthera peregrina, under different concentrations of NaHSO3, reached high Stiasny Indexes and the adhesives produced, presented good physical-chemical properties, and the viscosity of the adhesives reduced as the concentration of bisulfite increased. However, for the properties of plywood panels, the best results were for tannic adhesives extracted in 0 and 3% NaHSO3, thus making them a promising alternative to replace commercial adhesives.