Crystal self-nucleation in polyamide 11 of different semicrystalline morphology

Abstract

Self-nuclei supported recrystallization of the crystal-free melt of polyamide 11 (PA 11) of qualitatively different initial semicrystalline morphology, either containing nodular crystals or spherulitically grown lamellar crystals, has been investigated by fast scanning chip calorimetry, optical microscopy and atomic force microscopy. Melt-recrystallization of PA 11 initially containing a large number of nodules of high surface-to-volume ratio and strong coupling to the surrounding amorphous structure, as confirmed with the detection of significant amount of rigid amorphous fraction, is distinctly faster than melt-recrystallization of PA 11 initially containing lamellae and spherulites, caused by a lower number of self-nuclei in the latter system. Moreover, the temperature range of survival of self-nuclei above the respective melting temperature of nodular and lamellar crystals is larger for PA 11 initially containing nodules. The melt-residence time, within the assessable time-range before onset of melt-recrystallization, has no effect on the self-nuclei number. Enhanced self-nucleation in PA 11 containing nodules, compared to spherulitically crystallized PA 11, is suggested being caused by the distinctly larger initial number of individually grown crystals. A possible effect of the rigid amorphous fraction, forming during nodular crystallization, on hindering relaxation of the melt is discussed.