Development of dynamic mechanical methods to characterize the cure state of phenolic resole resins

We are interested in using dynamic mechanical analysis (DMA) to measure the degree of cure achieved by aqueous phenol‐formaldehyde (PF) resole resins as a result of previous exposures to various temperature‐humidity‐time regimes. We developed procedures that permit the obtaining of data that properly characterize and quantify the DMA behavior of these aqueous systems. Particularly important factors are substrate selection, sample clamping geometry, and sample humidification prior to analysis. In this report, we illustrate the problems encountered and the steps that we adopted to resolve them. We also present preliminary DMA data that illustrate some approaches for measuring the degree of cure achieved during previous resin exposures. One especially promising approach employs the area under the tan delta curve during isothermal scanning as an inverse measure of precure.