A novolak-based hydroxymethylated resorcinol coupling agent for wood bonding

A hydroxymethylated resorcinol (HMR) coupling agent was previously shown to enhance the exterior durability of epoxy and one-part polyurethane bonds to wood and of phenol-resorcinol-formaldehyde bonds to southern pine treated with chromated copper arsenate. In its original state of development, HMR is not user friendly. It has essentially no shelf life, and the resorcinol and formaldehyde components must be mixed and reacted for a few hours before being applied. By using less formaldehyde, we made a novolak-type pre-polymer that produces a liquid material stable in storage. Prior to applying this compound to wood, additional formaldehyde is added to the novolak to make the HMR usable immediately and up to 7 hours after formaldehyde addition: The new form of HMR is as good a coupling agent as the original HMR, producing epoxy bonds to wood that pass delamination requirements when exposed to the three accelerated aging cycles of ASTM D2559.