Fluorescence method for monitoring isothermal curing and shelf life of an epoxy-anhydride system

A fluorescence technique with seven fluorescent probes was applied to monitor the curing and shelf life of an epoxy resin. As isothermal curing proceeded, the fluorescence emission bands of the probes exhibited blue shifts because of microviscosity and micropolarity changes, An intensity ratio method was applied in which ratios of the lowest and highest intensity changes in the emission bands were used to determine the degree of isothermal curing. A smooth and, in some cases, a linear correlation was found between the fluorescence intensity ratio and the degree of cure. This method enables the degree of cure to be monitored and allows comparable results from different types of probes to be monitored during the same curing process. The fluorescence technique and the ratio method offer the possibility of monitoring the precuring and the shelf life of the epoxy polymer. The method can be used to compare the kinetics of various monomers and resin formulations under constant curing conditions. Thus, the method would be useful for developing new resin formulations and technologies and could be applied to a variety of commercial and industrial uses of epoxy resins. (C) 2001 John Wiley & Sons, Inc.