Abstract
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.
Highlights
The flavonoid compounds, which have been used commercially, are tannins derived from barks and woods
This study showed that bark particle adhesives and fibrillated bark adhesives both gave excellent bonding qualities which satisfy the requirements of the Japanese Agricultural Standard for Plywood (JAS) for exterior use of plywood, despite the fact that they contained low total solids contents
This study revealed for the first time that the gluability of fibrillated bark adhesives, which were formulated with PF resin, fibrillated bark and water only, gave excellent results despite optimum gluing conditions not being used
Summary
The flavonoid compounds, which have been used commercially, are tannins derived from barks and woods. As reported in the early history of Australia, Acacia mearnsii bark was first identified in 1814 as one of the excellent sources of tannins for the tanning of leather and a textile factory was opened at Botany Bay in New South Wales in 1815 with a tannery established before 1820 [3]. The use of wattle tannin in leather tanning commenced in the early 1820s, the commercial use of wattle tannin as a major component in the Unlike the rapid industrial acceptance and the largescale commercial use of wattle tannin adhesives for more than 50 years, the commercial use of tannin adhesives derived from radiata tannin, which is extracted from the bark of radiata pine Don), has not been realized, except for a small industrial particleboard and medium-density fiberboard (MDF) production and trials in Chile lasting approximately 15 years [4]
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