The isothermal crystallization process from the melt in nylon-6,6 was followed in situ by X-ray diffraction. At all the crystallization temperatures studied, the samples crystallized into the pseudohexagonal (hexagonally packed) Brill structure, which transformed into the triclinic structure on subsequent cooling to room temperature from the crystallization temperature. This transition occurs about 40°C lower than the respective crystallization temperature. Also the transformation temperature (TB) displays a hysteresis effect on heat cycling, with Ts being higher on heating than on cooling. These findings affirm the first-order transition character of TB, contrary to some previous suggestions. They also imply gradation in perfection and/or crystal size while in the Brili structure. It follows further that any difference in structure and property, as determined at room temperature, must reside in the Brill structure at the stage of formation and can only be reflected indirectly by the transformed structures observed at room temperature. With reference to spherulites, the latter has important implications for the arrangement of hydrogen bonding within the Brill structure. On the other hand, crystallization directly into the triclinic Bunn structure remains a possibility for crystallization from solution, awaiting confirmation by X-ray diffraction
Посилання на статтю:
Studies on the crystallization and melting of nylon-6,6: 1. The dependence of the Brill transition on the crystallization temperature / C. Ramesh* and A. Kellert // Polymer. – 1994. – Vol 35. – P. 2483-2487.