Tannin extraction from heat-treated Pinus spp bark - application as an adhesive

The objective of the study was to identify the influence of heat treatment in obtaining condensable tannins compounds from Pinus spp bark residues for adhesive production. The heat treatments were: (a) bark without heat treatment (control); (b) bark exposed at 60 degrees C for 50 h dry; (c) bark exposed at 120 degrees C for 10 h in steam; (d) bark attached to the trunk exposed at 120 degrees C for 10 h in steam. For the chemical characterization of the material, the crust was ground and classified, the tannic compounds were extracted under reflux with distilled water for 2 h, and in addition, sodium carbonate and sodium sulphite salts were added, both at 5% in relation to dry mass. The properties of commercial tannin from Acacia mearnsii (acacia negra) were evaluated as the control. The tannin extraction process was carried out in an autoclave, and then used for the evaluation of properties such as viscosity, pH, gel formation time, solids content and density. It was determined that both the bark exposed at 120 degrees C for 10 h in steam and the bark adhered to the trunk (subjected to steam at 120 degrees C for 10 hours) for both salts, have higher tannin yields. Tannic extracts obtained from sodium carbonate have an alkaline structure, high viscosity, and shorter gel formation time. However, extracts obtained from sodium sulphite provide an acidic character and solids content close to those found in aqueous tannic extracts obtained from black acacia.