UPGRADING OF PROTEIN GLUE BY COMPLEXATION WITH TANNINS - CONDITIONS FOR THE FORMATION OF GELATIN-TANNIN COMPLEX

The water-resistant properties and bonding strengths of plywoods bonded with animal glue and tannin combinations were investigated. Gelatin was used as a model compound for animal glue. Tannins used were mimosa (Acacia mearnsii) tannin (MT), tannic acid (TA), and persimmon (Diospyros kaki Thunb.) juice tannin (PJ). The optimum tannin/gelatin ratios, by weight for insoluble product formation, and index of the water-resistant property were 4/6 for MT and TA and 6/4 for PJ. The optimum pH values for insoluble material production were 4.5 for MT and PJ and pH 5.5 for TA. The bonding strengths and water-resistant properties of plywoods made using the cold-press method (honeymoon-type adhesion), in which the tannin and gelatin solutions were spread individually on the surfaces of separate veneers, were not improved because solidified products were formed at the contact-interfaces of the tannin and gelatin solutions and these two reactants were not mixed homogeneously. On the other hand, the water-resistant property of plywood made using the hot-press method, in which the gelatin-powder was scattered on the veneer surface spread with the tannin solution, was improved markedly because the melting of the gelatin by heat and water and the mixing of the two reactants by high temperature occurred. The waterproof properties of the adhesives produced as a result of tanning-gelatin complex were best when persimmon juice was sued as the tannin source, being superior to both mimosa tannin and tannic acid.