Environmentally friendly mixed Tannin/Lignin wood resins

We obtained lignin-based wood adhesives satisfying the requirements of relevant international standards for the manufacture of wood particleboard. These were based on two different low-molecular-mass lignins. These lignin-based wood adhesives did not use any formaldehyde in their formulation; formaldehyde was substituted with a nonvolatile nontoxic aldehyde, namely, glyoxal. The last formaldehyde present, contributed by a fortifying synthetic phenol-formaldehyde resin, was also eliminated by the substitution of the phenol-formaldehyde resin with a natural, vegetable polyflavonoid tannin extract to which no aldehyde was added. This substitution brought the total content of natural material up to 80 wt % of the total adhesive. The adhesives yielded good internal bond strength results of the panels, enough to pass relevant international standard specifications for interior-grade panels. (C) 2007 Wiley Periodicals, Inc.