Testing the validity of comparisons between the rheological and the calorimetric glass transition temperatures.

Dynamic mechanical techniques are used increasingly in the investigation of vitrification phenomena in biological materials, thus posing the question of whether the rheological T(g) should be compared with the established practice of obtaining T(g) values from differential scanning calorimetry. The nature of the rheological T(g) is discussed and its frequency dependence is established with a view to facilitating comparisons with calorimetric data. Despite claims made in the literature, results on high sugar-kappa-carrageenan mixtures, hydrated gelatin films, and thermoset epoxy resins demonstrate that there is no clear reference point for comparison of the glass transition temperatures derived with the two techniques. Furthermore, the structure-forming ability of kappa-carrageenan and other biopolymers impacts primarily upon the mechanical manifestation of vitrification and contributes to the state of complexity of comparisons between thermal and mechanical data.