Effect of Supercooling on Crystallization of Polyamide 11

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Abstract

The crystallization rate of polyamide 11 has been quantified in a wide temperature range between 320 and 450 K, using fast scanning chip calorimetry and differential scanning calorimetry. Different mechanisms of crystal nucleation/growth have been identified at temperatures below and above 370 K, causing a bimodal distribution of the crystallization rate as a function of temperature. Crystallization at low supercooling is connected with formation of triclinic α-crystals of lamellar morphology and ringed/banded spherulites. At high supercooling, formation of pseudohexagonal δ′-mesophase is observed. Because of the high nucleation density at low temperature, growth of the δ′-mesophase is nonspherulitic. The δ′-mesophase transforms on heating to α-crystals without affecting the superstructure. The study is completed by quantification of the cooling conditions to allow δ-crystal formation at low supercooling, δ′-mesophase formation at high supercooling, and complete vitrification of the melt. The interplay between nucleation density and mesophase formation according Ostwald’s rule of stages is discussed as a consequence of immobilization of the amorphous phase/formation of a rigid amorphous fraction.

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