Modelización de la transición vítrea con relajación entálpica a partir de datos térmicos

Abstract

The aim of this work is to model the total heat flow curve obtained by standard differential scanning calorimetry (DSC) in the glass transition-enthalpy recovery range of temperature. To this aim, a mathematical model is proposed, which allows to estimate the reversing and non-reversing curves from the total heat flow curve obtained in a standard DSC test. The model is optimally fitted to the total heat flow curve by non linear regression techniques. Similarly to modulated temperature-DSC (MTDSC), the model allows for separation of the reversing and non-reversing processes, but with the important difference consisting in that, since only total heat flow data are involved in the calculation, the separated signals will not be affected by the modulation frequency. Taking these differences into account, the separation obtained by the model is compared to the one obtained by MTDSC, and an estimation of the frequency effect is also obtained. The possibility of applying this model is of great interest for the study of the physical aging of noncrystalline or partially noncrystalline materials, which when stored at temperatures below its glass transition temperature, evolve spontaneously toward a state of equilibrium, experiencing what is known as enthalpy relaxation. In those situations, the study of the glass transition by standard DSC is very complicated, unless the thermal history is previously erased, which would alter the material itself. It should be mentioned that the importance of the proposed model does not lie on the possibility of obtaining by standard DSC something similar to what is obtained by MTDSC, but on the fact that the obtained estimation of the glass transition temperature is free, differently than in the MTDSC case, from the frequency effect.