Fast advancement and hardening acceleration of low condensation alkaline phenol-formaldehyde resins by esters and copolymerized urea. II. Esters during resin reaction and effect of guanidine salts

Guanidine carbonate is shown to be an accelerator of phenol-formaldehyde (P F) resins that while yielding slightly slower gel times than triacetin when added to a PF resin glue mix, is also capable of giving glue-mix pot lives on the order of several days. Hence, this is long enough to be premixed wi th the resin long before use. Both triacetin and guanidine carbonate used a s simple glue-mix additives are shown to increase the ultimate strength of the resin bond, whatever the length of the curing time used for the purpose . This is shown by thermomechanical analysis and the application to wood pa rticleboard. Triacetin is shown to be usable during PF resin preparation ra ther than just being added to the glue mix, yielding better resins capable of giving higher bond values without a great acceleration of the geling of the resin itself. The mechanisms involved in the acceleration of PF resins introduced by both compounds appears to be based on facilitating reactions of crosslinking involving carbonic acid ions present in the resin solution. (C) 2000 John Wiley & Sons, Inc.