Rheology of Ziegler–Natta and metallocene high-density polyethylenes: broad molecular weight distribution effects

Ansari, Mahmoud; Hatzikiriakos, Savvas G.; Sukhadia, Ashish M.; Rohlfing, David C.

doi:10.1007/s00397-010-0503-4

Cited by 73 publications

(47 citation statements)

References 60 publications

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“…7 as a function of angular frequency (G * ≡ √ G 2 + G 2 versus ω), which represents the flow curve of the polymers under no slip. The diameter dependency of the flow curves or deviation of the flow curves from the curve indicated as LVE (failure of the Cox-Merz rule) implies wall slip (Ansari et al 2011). In fact, such deviations from the LVE curve and diameter dependence has been obtained for the three PLAs (see Fig.…”

Section: Wall Slipmentioning

confidence: 93%

Wall slip and melt fracture of poly(lactides)

et al. 2011

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The wall slip and melt fracture behaviour of several commercial polylactides (PLAs) as well as their rheological properties under shear and extensional have been investigated. The PLAs have had weight-average molecular weights in the range of 10 4 -10 5 g/mol and studied in the temperature range of 160-200 • C. The solution properties and linear viscoelastic behaviour of melts indicate linear microstructure behaviour. PLAs with molecular weights greater than a certain value were found to slip, with the slip velocity to increase with decrease of molecular weight. The capillary data were found to agree well with linear viscoelastic envelope once correction for slip effects was applied. The onset of melt fracture for the high molecular weight PLAs was found to occur at about 0.2 to 0.3 MPa, depending on the geometrical characteristics of the dies and independent of temperature. Addition of 0.5 wt.% of a polycaprolactone (PCL) into the PLA that exhibits melt fracture was found to be effective in eliminating and delaying the onset of melt fracture to higher shear rates. This is due to significant interfacial slip that occurs in the presence of PCL.

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Section: Wall Slipmentioning

confidence: 93%

Wall slip and melt fracture of poly(lactides)

et al. 2011

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“…Differences in crystallization behavior were proposed as the reason for this observation. The rheology of these HDPEs has been studied in detail by Ansari et al (2010). A Shimadzu DSC-60 calorimeter with air as heating flow was used to study the thermal behavior of the highdensity polyethylene samples.…”

Section: Methodsmentioning

confidence: 99%

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

Derakhshandeh

Hatzikiriakos

2011

Rheol Acta

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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.

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“…More details on the swell measurements can be found elsewhere [27]. Capillary extrusion experiments using dies of various length-to-diameter ratios (L/D = 5, 16, and 33, with D=0.79 mm) and diameters (such as D=0.43, 0.79, and 2.11 mm with L/D=16) were carried out to apply all the necessary corrections such as Bagley, Rabinowitsch, and slip (Mooney analysis) to the raw data [28,29].…”

Section: Extrudate Swell Measurementsmentioning

confidence: 99%