Flow-induced crystallization of high-density polyethylene: the effects of shear and uniaxial extension

Abstract

The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of high-density polyethylene (a metallocene and a ZN-HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed at temperatures below and well above the peak melting point of the polyethylenes in order to characterize their flow-induced crystallization behavior at rates relevant to processing (elongational rates up to 30 s −1 and shear rates 1 to 1,000 s −1 depending on the application). 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, Bull Akad Sci USSR, Class Sci, Math Nat 1:355-359, 1937) proposed by Tanner and Qi (Chem Eng Sci 64:4576-4579, 2009) was used to describe the crystallization kinetics under both shear and elongational flow at different temperatures.

Flow-enhanced nucleation of poly(1-butene): Model application to short-term and continuous shear and extensional flow

“…Both Derakhshandeh and Hatzikiriakos (2012) and White et al (2012) also observed the viscosity upturn at constant strain in extensional flow. Derakhshandeh and Hatzikiriakos (2012) performed experiments on two grades of high-density polyethylene of which Ansari et al (2010) studied the rheology.…”

“…Derakhshandeh and Hatzikiriakos (2012) performed experiments on two grades of high-density polyethylene of which Ansari et al (2010) studied the rheology. As the onset of the terminal regime is not shown, we are not able to estimate the longest relaxation times.…”

“…The time at which this happens is a measure for the crystallizationenhancing effect of flow. These types of experiments have been performed in rotational flow [Acierno et al (2008); Hadinata et al (2005)] as well as extensional flow [Derakhshandeh and Hatzikiriakos (2012); Hadinata et al (2007); White et al (2012)]. Flow times are typically higher than for short-term flow experiments, which at high-shear rates might result in destruction of the sample.…”

Designing polymer crystallinity: An industrial perspective

“…Next to shear, also extension in flow has been shown to be capable of generating first higher nuclei and—at higher stresses—oriented structures both for PP and for HDPE . In contrast to the rheological concept of “weak” (shear‐dominated) and “strong” (extension‐dominated) flows, comparable levels of work input to a system were found to give comparable effects in shear and extension by Stadlbauer .…”

Flow-induced crystallization studied in the RheoDSC device: Quantifying the importance of edge effects

“…Such studies have been performed on, for example, isotactic polypropylene (iPP) (Housmans et al 2009;Ma et al 2011;Lamberti et al 2007;Vleeshouwers and Meijer 1996), polyethylene (PE) (Carrot et al 1993;Derakhshandeh and Hatzikiriakos 2012), isotactic poly(1-butene) (iP1B) (Acierno et al 2008;Hadinata et al 2007;Hadinata et al 2005;Roozemond and Peters 2013), and poly(lactic acid) (PLA) (Fang et al 2013), either using the short-term shear protocol (Liedauer et al 1993), cf. refs.…”