Measuring Flow-Induced Crystallization Kinetics of Polyethylene after Processing

The flow-induced crystallization of polymers is a pervasive aspect of processing where the effect of flow can dramatically alter end-use properties. Here we will describe development of a new methodology whereby the effect of flow on crystallization kinetics in polyethylene can be determined after an article is formed. The approach for rapidly crystallizing polyethylene was different than what has been done for other materials. Critically, an understanding of the self-nucleation and melt memory behavior as well as using thermal contact fluids with low kinematic viscosity was needed. With an optimized protocol, linear low-density polyethylene, LLDPE, can be heated to temperatures just above the melting point of the crystals using fast-scanning calorimetry and memory of the flow history can be maintained. As a result, the polymer can be melted many times without significantly changing the flow-induced crystallization kinetics. We demonstrate the ability to measure the flow-induced enhancement of crystallization kinetics on samples sheared using a parallel-plate rheometer or fabricated as blown film. Differences in crystallization rates between different classes of LLDPE blended with LDPE will also be discussed.