Sequence of enthalpy relaxation, homogeneous crystal nucleation and crystal growth in glassy polyamide 6

The sequence of densification/enthalpy relaxation, crystal nucleation and crystal growth in glassy polyamide 6 has been quantified using fast scanning chip calorimetry. The melt was vitrified by fast cooling, and then the glass was annealed as a function of temperature and time, covering a time scale of six orders of magnitude, required to separate the individual relaxation/ordering processes. During annealing of the glass, there is first observed enthalpy relaxation, and only after its completion there is detected crystal nucleation followed by crystal growth. A homogeneous nucleation mechanism is suggested. In such case, the characteristic relaxation time of the glass to attain metastability, that is, of its densification, has been shown theoretically (Gutzow and Schmelzer, 2013) to be as a rule much shorter than the characteristic time of nucleus formation.