Kinetics of homogeneous crystal nucleation of polyamide 11 near the glass transition temperature

Abstract

© 2020 Wiley Periodicals LLC In this work, the kinetics of formation of homogeneous crystal nuclei of polyamide 11 (PA 11) near the glass transition temperature (Tg), which is slightly above ambient temperature, has been analyzed using fast scanning chip calorimetry (FSC), employing Tammann's two-stage crystal nuclei development method with non-isothermal and isothermal nucleation and growth stages. The critical cooling rate above which formation of an ordered phase (crystals or mesophase) is suppressed is around 1000 K/s. Formation of nuclei, in contrast, can only be prevented by cooling the melt faster than about 30,000 K/s to far below Tg. The temperature of fastest formation of crystal nuclei is about 10–15 K higher than Tg, with first detection of nuclei within less than a millisecond. As such, the onset-time of nuclei formation is about one order of magnitude shorter than the time of first observation of crystals/mesophase. Furthermore, annealing experiments performed below Tg revealed glass-crystallization, with the stability of the formed ordered phase limited to temperatures near Tg. Since rapid cooling and solidification of the melt of PA 11 at low temperatures often occurs in processing of this material, this work provides new insights into processing-controlled structure formation, eventually being beneficial for tailoring the property profile.