Modeling the Effect of the Curing Conversion on the Dynamic Viscosity of Epoxy Resins Cured by an Anhydride Curing Agent

Published curing profiles of epoxy resins mixed with an anhydride curing agent and subsequently crosslinked were reanalyzed with a modified sigmoidal model to describe the dynamic viscosity accompanying resin curing. The sigmoidal analysis yielded two kinetic parameters, one relating to the induction time required to observe meaningful viscosity changes and one relating to the rate of viscosity rise in the rapidly polymerizing zone. Both of these kinetic factors decreased with increasing polymerization temperature. The analysis also led to the interpretation of the upper limit in viscosity in the model that correlated with a higher network density at higher temperatures. The initial viscosity was fixed in our model. The sigmoidal analysis led to a closer representation of the dynamic viscosity data than the Williams-Landel-Ferry (WLF)-based analysis presented with the original data sets and, although from a more semiempirical basis, might be both easier and more adaptable for incorporating into other flow models. As a final observation, the induction time identified by the log-sigmoidal model correlated closely with the gelation time identified with a modified-WLF-based model by Ivankovic et al. (J Appl Polym Sci 2003, 90, 3012); this suggested a similar activation energy threshold for curing advancement. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1671-1674, 2010