Study of Dryout Resistance of Phenolic Copolymer Resins for Pine Plywood Glues–Part I

Closed assembly time tolerances and dryout resistances of several phenol-alkylated phenol copolymer resins were evaluated and compared between copolymer resins and a commercial phenolic resin. The copolymer resins synthesized included one which had a 20 percent (mole basis) replacement of phenol by a predominantly 3,4-xylenol alkylated phenol isomer blend, and it showed outstanding dryout resistance and assembly time tolerance. Panels using the higher spread rates of glue mix based on this resin (i.e. 80-85 and 95-100 lbs./MDGL) maintained vacuum-pressure wood failure averages of close to 90 percent, even to the maximum closed assembly time level. Panels with the lower spread rate of 60-65 lbs./NDGL maintained vacuum-pressure wood failures of 80 percent or better to the maximum closed assembly time level. The next best copolymer resin was one involving 20 percent (mole basis) replacement of phenol with p-cresol. However, it did not seem to out-perform the commercial control, and certainly seemed to lack the properties of the resin based predominantly on replacement with 3,4-xylenol. A press time study was also carried out, and the copolymer resins tested seemed to cure at least as rapidly as the commercial phenolic control resin. The combined factors of long assembly time tolerance under dry-out intensifying conditions and reasonable cure speed suggest that the use of partial substitution by selected alkylated phenols may hold promise in developing better resins for use in southern pine plywood manufacture. Additional work is underway, on the evaluation of other isomers and alternate resin preparation procedures, and it is felt that this will produce even further improvements.

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