Metastability in polymer systems studied under extreme conditions: high pressure, scan-iso T-t ramps and high scanning rates

Laboratory measurements on polymer raw materials and products are often carried out (quasi-) isothermally, or at best at relatively slow cooling and heating rates. Such conditions differ greatly from those occurring during processing and during the product’s use in real life. During processing, high cooling rates and high pressures are common, the parameters of which have a major influence on the most important forming processes, namely vitrification and crystallisation. In addition, polymer systems are highly metastable: all kinds of changes are possible as a function of time and temperature, such as reorganisation (via recrystallisation and annealing), cold crystallisation, solidsolid transitions, and superheating. Reorganisation phenomena can be hindered by applying high heating rates. Therefore, not only high cooling rates are required, but also techniques enabling high heating rates would be very welcome. In this review article, we will comment on the metastability of polymers under extreme conditions: high-pressure DSC and X-ray at hundreds of MPa’s; scan-iso temperature (time ramps by DSC), and X-ray & high scanning rates as made possible by the recently developed High Performance DSC (HPer DSC). This is a generic name that encompasses quantitative measurement using controlled, linear scanning rates at hundreds of °C/min (high-rate DSC) in both the cooling and heating of (sub) milligram amounts of material. As such, it also facilitates high-throughput DSC.