Synthesizing Phenol-Formaldehyde Resins for Controlled Dryout Resistance

A novel method for the synthesis of phenol formaldehyde resin adhesives having controlled resistance to gluing dryout is described and evaluated. The concept involves preparation of essentially linear and non-crosslinking alkaline novolac prepolymers and their co-reaction with essentially non-linear and crosslinking resole prepolymers to form a copolymer having combined properties. Preliminary tests suggested that resins formed from approximately equal weight percentages of the alkaline novolac and the resole prepolymers were useful for developing improved dryout resistance in resins for in gluing southern pine veneer. Further tests indicate that single stage and multi-stage synthesis procedures will work. Comparative evaluation with examples of the then current commercial dryout resistant resins was favorable for several of the developmental A/B resin formulations. In several cases, reduced glue spread rates seem to be possible while maintaining good dryout resistance.

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