Abstract
Extractable polyphenolics from certain woods and barks belong either to the so-called hydrolysable tannins or to condensed tannins. Reaction between formaldehyde and condensed tannins leads to cross-linked polymers, which can serve as a binder in particle- und fiberboards. Acacia bark and quebracho wood are the two main raw materials used commercially for extraction of condensed tannins. Recent results reveal that quebracho extract can be extended by extractives from spruce bark for production of particle- and fiberboards. Moreover, hydrolysed starch can also be used as a correactant for condensed tannins in particle- and fiberboard manufacture. On bonding wood chips with tanninformaldehyde resins different wood species have a significant influence on the physical-technological properties of the boards. According to results of recent investigations it is possible to use tannin as a binder even without adding any crosslinking agent.