Tannin Formaldehyde Adhesive for Exterior Grade Plywood and Particleboard Manufacture

Tannin-formaldehyde adhesives were developed for the manufacture of exterior-grade plywood and particleboard. The sole resin component used was a commercial spray-dried tannin powder extracted from Acacia negra bark from plantations in southern Brazil. An experimental design was used in which a set of seven glue and process variables, involving two levels of treatment for each, were evaluated for their effect on glue bond quality in Virola sp. plywood. The statistical analysis of the results obtained from 512 three-ply test panels revealed that formaldehyde content in the glue, amount of glue spread, veneer moisture content, and assembly time had significant influences on glue bond quality in descending order of importance, respectively. Optimal results were obtained with 25 percent formaldehyde (37% by mass, 2 percent filler content, pH 5, 300 g/m2 (61 lb./Mft.2 double glueline) glue spread, 3 percent veneer moisture content, 10 minute assembly time, 150?c press temperature, 7 minute press time, and 12 kg/cm2 (171 lb./in.2) press pressure. A minimum of 80 percent wood failure was used as the only criterion for determining glue bond quality. Single layer particleboards were produced from a mixture of 36 tropical hardwood species from the Tapajos region in the Amazon basin on a weight-percent basis in accordance with their occurrence (volume/ha) in the forest. There is a strong indication that tannin adhesive bonded particleboards are water-resistant.

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