ON THE CHEMISTRY, BEHAVIOR, AND CURE ACCELERATION OF PHENOL-FORMALDEHYDE RESINS UNDER VERY ALKALINE CONDITIONS

The curing acceleration by organic esters of alkaline phenol-formaldehyde (PF) resins can be explained by two different mechanisms. In the course of the work, the unexpected curing behavior of PF resins alone, under very alkaline conditions, was observed, which diverged from past assumptions. PF resins curing, which is supposed to be accelerated by the formation of phenate ions, is instead markedly slowed down by increasingly alkaline pHs and accelerates in the presence of esters. The mechanism of ester acceleration of PF resins curing was clarified and the effect of different esters was quantified and was related to the pK(a) and quantity of the acid forming the ester. A second mechanism, which appeared also to explain the peculiar slowing down at increasing pH of PF resin curing, could not be confirmed; some evidence appeared to point to this second mechanism's existence, while other evidence appeared clearly to deny it. The impossibility of isolating an Na+ phenol ring complex, theorized by other authors and other evidence, indicates that this second mechanism is unlikely to occur. (C) 1993 John Wiley & Sons, Inc.