Determination and review of specific heat capacity measurements during isothermal cure of an epoxy using TM-DSC and standard DSC techniques

摘要

The technique normally used to measure C_p during isothermal cure is Temperature Modulated-Dynamic Scanning Calorimetry TM-DSC. It is however not standardised, experimentally complicated and quite time intensive. As will be shown, C_p may also be estimated during isothermal cure just from using dynamic heating experiments on a fully cured sample. Such values are often sufficient for isothermal heat transfer models that otherwise employ a constant C_p value obtained from the fully cured epoxy. Secondly, the results from dynamic heating experiments provide a quick means, in comparison to isothermal TMDSC measurements, of estimating C_p variation during cure as well as providing a good estimate value for C_p towards the end of isothermal cure. As will be shown, such values obtained from a standardised measurement procedure are very helpful in setting up TMDSC experiments that are more sensitive to experimental error influenced by factors such as sample weight and geometry. The DSC results illustrate that the measured heat capacity C _p for a fully cured epoxy over a temperature range are very similar to values for samples partially cured at corresponding isothermal temperatures, under the prerequisite that vitrification takes place. In such cases the primary influence on C_p is specific measurement temperature and not degree of cure. For isothermal cure temperatures investigated between 150 and 200 °C, the total change of C_p during cure is nearly constant and correlates well with values published by authors on other epoxy based systems. Taking C_p variation as constant, it is possible from just dynamic heating experiments on the cured epoxy to estimate C_p for the uncured epoxy system at specific cure temperatures. The next step would be to estimate the full C_p profile during isothermal cure, however, in such cases, the time to vitrification would also be needed as additional information.