Physical Cross Links in Amorphous PET, Influence of Cooling Rate and Ageing

Abstract

A Continuous Cooling Transformation (CCT) procedure can be used to distinguish the initial “state” of the amorphous PET samples produced upon solidification from the melt at different cooling rates. The material frozen at this stage behaves as a rubber when brought above the T_g due to the onset of physical cross links. The rubber is not a stable network, however, since physical cross links may eventually dissolve. Their size distribution, and possibly their number, depend on cooling rate and ageing. Some may be even stable above the glass transition and act as nuclei for further crystallization from the glass. Upon increasing cooling rate, size distribution becomes smaller and stability of physical cross links decreases. Ageing may give rise to the onset of further physical cross links or may affect the stability of the ones already set in depending on cooling rate, i.e. on how is constrained the initial network structure.