AUTOCONDENSATION-BASED, ZERO-EMISSION, TANNIN ADHESIVES FOR PARTICLEBOARD

Interior grade particleboard prepared with tannin adhesives to which no aldehyde hardener was added were prepared. The hardening of the tannin adhesive was induced by the reaction of autocondensation tannins undergo when catalyzed by a lignocellulosic substrate or by a weak Lewis acid as alkali dissolved silica. The more alkaline the tannin extract solution the higher the ceiling internal bond strength that the particleboard bonded with it can reach. Differences between four commercial tannins are discussed. Pecan nut tannin and pine tannin need only lignocellulosic induced autocondensation to give excellent interior grade particleboard. Slower reacting tannins such as mimosa need instead both the catalytic effect of the substrate as well as that of a weak Lewis acid such as silica. Only pecan nut tannin appears at this stage to be able to give boards of acceptable dry internal bond strength at industrially significant pressing times.