Thanks all. Because I was referring the boiling point of a single mixture based on ASHRAE results. I had the same idea when I got similar results for all samples.
Thermal Stability of both the components is different as shown in TGA curve. First stage is refereed to dehydration where water evaporates nearly 100-120 degree Celsius. The weight loss in second stage is attributed to degradation of EG by escaping of volatile components like CO2, H2O, etc.,