Strain-induced disorder–order crystalline phase transition in nylon 6 and its miscible blends

This study deals with the structural modifications of a polyamide 6 (PA6) and a miscible blend of this PA6 with an amorphous semi-aromatic copolyamide (PA6/aPA) under tensile drawing. By combining X-ray diffraction and FTIR spectroscopy, the crystalline phase transitions have been investigated as a function of drawing temperature and strain for both systems. A mechanically induced β–α transition has been clearly identified for PA6 at 100°C and above, whereas the PA6/aPA blend undergoes the same evolution at 130°C. These threshold temperatures are very close to the upper limit of the glass–rubber transition of the two systems. This is evidence that the amorphous chain mobility plays a major role on the reorganization capability of the crystalline phase towards its stable form. Further discussion is made regarding the physical origin of this phenomenon.