A Detailed Study on the Thermal Endurance of Kapton HN®i and Upilex S®

The purpose of this study was to evaluate the thermal endurance of two types of thermal control foils. This is an important parameter for selecting materials for inner solar system missions. Assessing the thermal endurance by isothermal testing in a thermogravimetric analyser (TGA) is a time-consuming method. A quicker method is to perform kinetic modelling on several decomposition curves. Four temperature scans at different heating rates were recorded with the TGA for two thermal control foils, Kapton HN (DuPont, USA) and Upilex S (UBE Industries, Japan). Two methods of kinetic modelling were used to calculate the activation energy, namely the ASTM E 1641 and the approach of model free kinetics (MFK). The first assumes a constant value for the activation energy whereas the latter calculates it as a function of the conversion. With the activation energy it is possible to make a lifetime prediction that indicates the mass loss that occurs at a certain temperature for a certain duration. The lifetime predictions are used to compare the two materials and also the two modelling methods. The modelling is verified by comparing the results to isothermal TGA tests and thermal ageing of samples in high vacuum chambers at 350'C for durations up to half a year and in combination with UV irradiation screening tests. All the experiments performed indicate that Upilex S has a better thermal endurance than Kapton HN. The results of the kinetic modelling were in good agreement with the isothermal experiments in the TGA and in the vacuum facilities. The MFK approach for kinetic modelling was found to be more adequate than the ASTM method.