Vitrification during the isothermal cure of thermosets: Comparison of theoretical simulations with temperature-modulated DSC and dielectric analysis

Abstract

Vitrification during the isothermal cure of a thermoset, which is monitored by dynamic techniques such as temperature-modulated differential scanning calorimetry (TMDSC) or dielectric analysis (DEA), is analyzed in terms of its dependence on frequency. A simulation was used to obtain the vitrification time as a function of frequency, considering it as the time when the (frequency-dependent) glass transition temperature, Tg, of the curing system reaches the cure temperature. Simulations were carried out at different cure temperatures. Other parameters, such as the exponents (reaction orders) in the Kamal equation, λ in the DiBenedetto equation (controlling the dependence of Tg on the degree of cure), and the activation energy for the frequency dependence of Tg, were also considered. The results are compared with those obtained experimentally by a TMDSC technique at low frequencies and by DEA at high frequencies. From the simulations it is found that the vitrification time decreases nonlinearly with log(frequency) in the low frequency range but approaches a linear dependence at high frequencies, in agreement with experimental data. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.