The chemistry and development of tannin/urea–formaldehyde condensates for exterior wood adhesives

Novolak-like materials were prepared by condensation of urea–formaldehyde resins with resorcinol and/or resorcinolic A-rings of polyflavonoids such as condensed tannins. The copolymers formed were used as thermosetting and cold-setting exterior-grade wood adhesives. Condensation of tannins with small amounts of urea–formaldehyde resins can prevent the water deterioration normally experienced by the latter resins. Conversely, urea–formaldehyde resins improve crosslinking and strength of wood tannin–formaldehyde networks.