Frequency dependent heat capacity in the cure of epoxy resins

Different temperature modulated differential scanning calorimetry (TMDSC) approaches were explored for studying the frequency dependence of the vitrification phenomenon during the cure of a thermosetting epoxy resin. All approaches show the expected decrease in vitrification time with increasing frequency. Light (heating) (temperature) modulated DSC (LMDSC), developed by Saruyama, offers the advantage that the frequency range for direct measurements is extended (from 0.01 to 1 Hz). However, at frequencies above 0.1 Hz, the results contain information about the changing thermal diffusivity (for samples above 100 μm thick). A complex saw-tooth modulation method, developed by Wunderlich, allows multiple frequencies (over almost one decade) to be measured in a single experiment, thus eliminating effects of sample reproducibility. For studying the frequency dependence during (chemical) transformations, such as cure, the desired invariance of the sample during at least one modulation period and thermal diffusivity effects (even for films of only 100 μm thick) limit a further extension of the frequency domain to lower and higher frequencies, respectively.