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Flow-induced crystallization of high-density polyethylene : the effects of shear, uniaxial extension and temperature Derakhshandeh, Maziar


The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of two high-density polyethylenes (a metallocene and a Ziegler-Natta HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed at temperatures below and well above the peak melting point of the polyethylene’s in order to characterize their flow-induced crystallization behavior at rates relevant to processing. Generally, strain and strain rate found to enhance crystallization in both shear and elongation. In particular, extensional flow was found to be a much stronger stimulus for polymer crystallization compared to shear. At temperatures well above the melting peak point (up to 25°C), polymer crystallized under elongational flow, while there was no sign of crystallization under simple shear. A modified Kolmogorov crystallization model (Kolmogorov AN (1937) On the statistics of the crystallization process on metals. Bull Akad Sci. USSR, Class Sci, Math Nat. 1:355–359) proposed by Tanner (Tanner RI (2009) Stretching, shearing and solidification, Chem Eng Sci, 64:4576-4579) was used to describe the crystallization kinetics under both shear and elongational flow. The model was found to predict the FIC behaviour under low deformation rates and various temperatures well; however the predictions for the higher rates were not satisfactory.

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