IMPROVEMENTS OF TANNIN RESIN BY THE USE OF THE OXIDATIVE COUPLING REACTION OF PHENOLS

For the purpose of improving the water-resistant properties and the neutralization of the pH of the decoctions of cured tannin adhesives by the use of the oxidative coupling reaction of phenols, the raw tannins were given various kinds of pretreatments. The water-resistant properties of the cured resins were improved by the treatments which removed contaminants, such as sugars from the water-soluble parts of the commercial tannin powders. However, in these treatments or in the preoxidizing treatments of tannin, although the water-resistant properties were improved, the pHs of the decoctions from the cured resins were about 1.5 to 2.5, and were not to be neutralized. On the other hand, the cured resins of the iodine-treated tannins, which were obtained by the reaction between tannin and iodine in an alkaline solution, were the resins which had great water-resistant properties even at pH values around neutrality.