In this example, DSC measurements* were carried out on an EVA film sample of approx. 7 mg with the DSC 204 F1 Phoenix® at heating rates of 10 K/min. These DSC experiments were performed at the Federal Institute for Materials Research and Testing ("BAM"), Germany.
In the 1st heating (blue curve), the glass transition temperature at -28°C (inflection point) is followed by an endothermic double peak between 50°C and 100°C. This melting behavior can be correlated to a lamellar thickness distribution. The exothermic peak at 158°C indicates the exothermic crosslinking reaction. Noticeable is the rather low reaction enthalpy (-14.15 J/g) in comparison to epoxy resins (typically between -400 J/g and -500 J/g).
In the 2nd heating (red curve), the glass transition occurred at almost the same temperature. The endothermic double peak between 40°C and 80°C
has changed to a broad shoulder with its maximum at 63°C. The higher the crystal thickness, the higher the melting temperature. Therefore, the change from a peak into a broad shoulder is an indication of a distribution of crystals with reduced thickness as a consequence of the thermal treatment in the 1st run. No exothermic reaction peak is present in the 2nd run, indicating that the crosslinking process was finished after the 1st heating.
*Our thanks to Dr. W. Stark and M. Jaunich from the Federal Institute for Materials Research and Testing ("BAM") in Berlin for the measurements and discussion. The results are published in Polymer Testing 30 (2011) 236-242.