DETERMINATION OF GLASS-TRANSITION TEMPERATURE BY INTERNAL-FRICTION MEASUREMENTS

Internal friction measurements at constant frequency are useful in determining the liquid–glass transition of non‐crystalline materials that devitrify easily or when the number of available configurations are entropically not sufficiently high to develop a neat endotherm at Tg. This method is applied to oxide glasses and organic polymer samples of different thermal histories and is shown to be particularly of interest for studies of the glass transition in semi‐crystalline polymers. Theoretical justification for the method is given and it is shown that the temperature dependence of mechanical loss can be expressed by a parameter μ whose variation is similar to the corresponding one obtained from DSC and dilatometric measurements. On the basis of a theory for the rheology of non‐crystalline materials, it is shown that internal friction is finally related to the thermodynamic behavior near Tg. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA