2.13. Differential Scanning Calorimetry (DSC)

DSC (differential scanning calorimetry) measurements were carried out under air (20 mL·min⁻¹) on a Q2000 differential scanning calorimeter (TA Instruments Inc., New Castle, DE, USA) while applying a heating rate of 10 K·min^–1. The sample mass was 2 mg. The melt enthalpy ΔH_m and melting peak temperature T_m,p were determined from the heat flow–temperature curves, as well as the glass-transition temperature T_g. One measurement per sample was carried out using the 1st heating cycle only, for both the granules and the fiber samples. This is because the second heating cycle gives no information on the history of the material and because the (re-)crystallization of PEF is very slow and therefore not displayable by DSC measurements.

The degree of crystallinity χ_c was calculated by standardizing the melt enthalpy to the standard melt enthalpy ΔH_m,0, as shown by Equation (1).

The standard melt enthalpy ΔH_m,0 used was 137 J·g⁻¹ according to the literature [9].