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The melting and recrystallization of yarns of polyamide 6 spun at different take-up velocities ranging from 3 500 to 5 600 m/min was investigated by means of wide-angle X-ray scattering (WAXS) employing synchrotron radiation and by differential scanning calorimetry (DSC). It was shown that the first peak in the double melting peak of the DSC-curves is caused by the melting of the y-crystals. The melting point is increased by approximately 5 "C when the take-up velocity is increased from 3 500 m/min to 5 600 m/min. The addition of calcium stearate to the material has no effect on the thermal stability of the crystals, but seems to have some effect on the crystallization rate.

Temperature‐reversible and ‐irreversible morphological events could be separated in the case of linear polyethylene during quasi‐isothermal crystallization by using simultaneous temperature‐modulated synchrotron SAXS and WAXD. Crystallization and subsequent annealing was followed at 126 °C for 90 min while applying a temperature modulation with an amplitude of 1 °C and a period of 2 min. The crystal growth rate associated with the irreversible part of the crystallization decreases with increasing temperature in a cycle. The crystalline lamellae irreversibly thicken with time. The actual crystallite thickness, however, exhibits a superimposed modulation out of phase with that of the temperature modulation. Melting was studied during heating at 1 °C/min after cooling at 10 °C/min. A temperature modulation was superimposed with an amplitude of 2 °C and a period of 3 min. Once again temperature‐reversible crystal thickness changes and irreversible crystal thickening could be observed.