Flow-induced Crystallization of Nylon 6/6

When a semi-crystalline polymer melt is subjected to intense flow before crystallization, the crystallization kinetics are accelerated and the crystal morphology is changed from isotropic spherulites to smaller anisotropic structures, which is termed flow-induced crystallization (FIC). In this study, FIC of Nylon 6/6 was characterized using rheology and polarized optical microscopy. Using a rotational rheometer, a wide range of specific works (10 ~ 10^7 Pa) was imposed prior to crystallization (Ts=270 ^oC) above the melting temperature (Tm=265 ^oC). Small amplitude oscillatory shear was then used to monitor the acceleration of crystallization kinetics at a lower crystallization temperature (Tc=245 ^oC). When the imposed specific work increased from 10 to 10^7 Pa before crystallization, the onset time of crystallization was accelerated from 628 to 26 s. The shear-induced structures were directly observed through a polarized optical microscope equipped with a hot stage under nitrogen. With a Nylon 6/6 disc, which was sheared at 10 s^-1 between two parallel plates, large spherulites were observed at the center (~0 s^-1), while a mixture of smaller spherulites and anisotropic cylindrites were observed at the edge (~10 s^-1).