Detecting reorganization in semicrystalline polymers during heating: Insights from Fast Scanning Chip Calorimetry coupled with real-time optical microscopy

Abstract

Thermal behavior of semicrystalline polymers is notoriously complex due to the metastable nature of polymer crystals. This complexity is evidenced in the multiple melting endotherms frequently observed in the heating traces of various plastics, a phenomenon known as ‘multiple melting behavior’. Extensive research indicates that calorimetric analysis alone may not suffice to fully elucidate the processes occurring during thermal experiments. In this study, we introduce an experimental setup that integrates Fast Scanning Chip Calorimetry, or nanocalorimetry, with real-time polarized optical microscopy. This combination enables in-situ morphological observations during rapid heating/cooling experiments. The setup not only complements thermal analysis but also rivals the capabilities of fast in situ X-ray scattering experiments conducted at synchrotron sources. Our findings show that the obtained data help in identifying melting/recrystallization processes and, therefore, enable the determination of the critical heating rate above which reorganization processes during heating are kinetically bypassed. This ensures that the thermal events detected in calorimetric curves are exclusively due to the initial sample structure, without being influenced by any reorganization that may occur during the heating process.