Sensitivity of Polymer Crystallization to Shear at Low and High Supercooling of the Melt

Flow-induced crystallization (FIC) is a dominant mechanism of polymer self-assembly, but the process is poorly understood at high supercooling and under fast cooling conditions because of structural rearrangements that occur during slow heating and cooling conditions typically used for investigation. Incorporating fast-scanning chip calorimetry techniques, the influence that specific amounts of shear flow have on the subsequent crystallization of polyamide 66 over a wide range of temperatures, 85-240 degrees C, is determined. At high temperatures, heterogeneous nucleation dominates and crystallization rate increases with increasing shear. Low-temperature crystallization, driven by homogeneous nucleation, is not influenced by previous shear flow, but sheared samples are able to crystallize via the heterogeneous nucleation route at temperatures 15 K lower than unsheared materials. The magnitude of previous shear flow also dictates alpha-/gamma-crystalline phase development and crystallization during cooling at rates below 200 K/s. This approach provides a route to develop important thermodynamic and kinetic insights that describe the crystallization behavior of many important polymers to enable the advanced engineering of polymer processing and injection molding applications, where practical cooling rates typically range between 10 K/s and 1000 K/s.