Development of bark-based adhesives for plywood: utilization of flavonoid compounds from bark and wood. II

Although many conventional adhesives for plywood are formulated with tannins (polyflavanoid compounds) extracted from bark or wood, adhesives using tannin directly without extraction from the bark have also been made. In 2003, the first bark particle (< 63 μm) adhesive was developed from radiata pine bark. In this present study, the quality of the bark adhesive has been improved by fibrillating the bark. Finely ground bark was fibrillated using a disc mill and formulated into plywood adhesives, which consisted of fibrillated bark, phenol–formaldehyde (PF) resin and water in different ratios. The gluability of the fibrillated bark adhesives was evaluated according to the Japanese Agricultural Standard for Plywood (JAS) and was found to be excellent. These bark adhesives have a number of advantages in that there is no tannin extraction, there is a total use of the bark, a low-level requirement of PF resins, no other components required and there is a high glue bond quality. Considering that very small amounts of fibrillated bark adhesives produced high-quality wood bonding, the bark components such as tannin, hemicellulose, lignin, cellulose nanofibers and other components may well be contributing to produce such a good bonding.