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Savvas G. Hatzikiriakos - One of the best experts on this subject based on the ideXlab platform.
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Melt Fracture of linear low density polyethylenes die geometry and molecular weight characteristics
Physics of Fluids, 2018Co-Authors: Marzieh Ebrahimi, Tanja Tomkovic, Guochang Liu, Antonios A Doufas, Savvas G. HatzikiriakosAbstract:The Melt Fracture phenomena of three linear low-density polyethylenes are investigated as a function of die geometry (capillary, slit, and annular) and molecular weight and its distribution. The onset of Melt Fracture instabilities is determined by using capillary rheometry, mainly studying the extrudate appearance using optical microscopy. It is found that the onset of flow instabilities (Melt Fracture phenomena) is significantly affected by die geometry and molecular weight characteristics of the polymers. Use of annular die eliminates the stick-slip transition (oscillating Melt Fracture) and delays the onset of sharkskin to higher values of shear rate and shear stress. Moreover, it is shown that the molecular weight characteristics of the polymers are well correlated with critical conditions for the onset of flow instabilities based on a criterion proposed in the literature [A. Allal et al., “Relationships between molecular structure and sharkskin defect for linear polymers,” J. Non-Newtonian Fluid Mech. 134, 127–135 (2006) and A. Allal and B. Vergnes, “Molecular design to eliminate sharkskin defect for linear polymers,” J. Non-Newtonian Fluid Mech. 146, 45–50 (2007)].
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the role of microstructure on Melt Fracture of linear low density polyethylenes
Polymer Testing, 2018Co-Authors: Mahmoud Ansari, Tanja Tomkovic, Antonios A Doufas, Maziar Derakhshandeh, Savvas G. HatzikiriakosAbstract:Abstract The effects of molecular characteristics on the rheology and Melt Fracture of several linear and branched low-density polyethylene (LLDPE and LDPE) resins in capillary extrusion were studied as functions of molecular weight, polydispersity and the level of long chain branching (LCB). The level of LCB in the resins was found qualitatively by using several rheological methods which in general agree. These are based on the zero-shear viscosity versus molecular weight relationship, the energy of activation, the linear viscoelastic properties and the characteristic shapes of the flow curves. A previously proposed criterion (critical shear stress versus plateau modulus) for the onset of sharkskin Melt Fracture (Allal et al., J. Non-Newtonian Fluid Mech., 134 (2006) 127–135) was tested and found to give reasonable predictions for the sharkskin instability of the polyethylenes considered in this work.
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Melt Fracture of polyisobutylenes
Polymer Testing, 2017Co-Authors: Marzieh Ebrahimi, Emmanouil Chatzigiannakis, Manfred H Wagner, Savvas G. HatzikiriakosAbstract:Abstract The processability of different grades of polyisobutylene (PIB) was investigated using a capillary rheometer. Direct focus was given to the occurrence of Melt Fracture phenomena, such as sharkskin and gross Melt Fracture (GMF). The influence of molecular weight (MW) of PIB, temperature and die entrance angle on Melt Fracture was examined in detail. Due to their highly elastic nature, high MW PIBs were found to exhibit gross Melt Fracture instability even at low shear rates, rendering their processing an impossible task. An increase in temperature resulted in postponing both instabilities (sharkskin and gross) to higher shear rates, thus making their processing easier. Finally, decreasing the entrance angle below a critical value resulted in postponing the onset of GMF to higher shear rates.
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biodegradable polymers wall slip Melt Fracture and processing aids
6th International Conference on Novel Trends in Rheology, 2015Co-Authors: Norhayani Othman, Bashar Jazrawi, Parisa Mehrkhodavandi, Nazbanoo Noroozi, Laurel L Schafer, Savvas G. HatzikiriakosAbstract:The wall slip and Melt Fracture behaviour of several commercial polylactides (PLAs) and poly(e-caprolactone), (PCLs) have been investigated. PLAs with molecular weights greater than a certain value were found to slip, with the slip velocity to increase with decrease of molecular weight consistent with wall slip data reported in the literature for other systems. 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. Similarly, sharkskin and gross Melt Fracture was observed for the case of PCLs depending on the molecular characteristics of the resins and the geometrical details of the capillary dies. It was also found that the addition of a small amount of PCL (typically 0.5 wt.%) into the PLA and vice versa is effective in eliminating and delaying the onset of Melt Fracture to higher shear rates in the capillary extrusion of PLA and PCL respectively. This is due to significant interfacial slip that occurs in the presence of PCL or PLA as well as to the immiscibility of the PLA/PCL blend system at all compositions.
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rheology and Melt Fracture of poly lactides
70th Annual Technical Conference of the Society of Plastics Engineers 2012 ANTEC 2012, 2012Co-Authors: Norhayani Othman, Bashar Jazrawi, Parisa Mehrkhodavandi, Savvas G. HatzikiriakosAbstract:The wall slip and Melt Fracture behaviour of several commercial polylactides (PLAs) have been investigated. 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 onset of Melt Fracture for the high molecular weight PLAs was found to occur at around 0.2 to 0.3 MPa, depending on the geometrical characteristics of the dies. Addition of 0.5wt% of a poly(e-caprolactone) (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.
Wim Van Saarloos - One of the best experts on this subject based on the ideXlab platform.
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weakly nonlinear subcritical instability of visco elastic poiseuille flow
arXiv: Statistical Mechanics, 2003Co-Authors: Bernard Meulenbroek, Cornelis Storm, Wim Van Saarloos, Alexander MorozovAbstract:It is well known that the Poiseuille flow of a visco-elastic polymer fluid between plates or through a tube is linearly stable in the zero Reynolds number limit, although the stability is weak for large Weissenberg numbers. In this paper we argue that recent experimental and theoretical work on the instability of visco-elastic fluids in Taylor-Couette cells and numerical work on channel flows suggest a scenario in which Poiseuille flow of visco-elastic polymer fluids exhibits a nonlinear "subcritical" instability due to normal stress effects, with a threshold which decreases for increasing Weissenberg number. This proposal is confirmed by an explicit weakly nonlinear stability analysis for Poiseuille flow of an UCM fluid. Our analysis yields explicit predictions for the critical amplitude of velocity perturbations beyond which the flow is nonlinearly unstable, and for the wavelength of the mode whose critical amplitude is smallest. The nonlinear instability sets in quite abruptly at Weissenberg numbers around 4 in the planar case and about 5.2 in the cylindrical case, so that for Weissenberg numbers somewhat larger than these values perturbations of the order of a few percent in the wall shear stress suffice to make the flow unstable. We have suggested elsewhere that this nonlinear instability could be an important intrinsic route to Melt Fracture and that preliminary experiments are both qualitatively and quantitatively in good agreement with these predictions.
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experimental evidence for an intrinsic route to polymer Melt Fracture phenomena a nonlinear instability of viscoelastic poiseuille flow
Physical Review Letters, 2003Co-Authors: Volfango Bertola, Bernard Meulenbroek, Cornelis Storm, Christian Wagner, Wim Van Saarloos, Alexander Morozov, Daniel BonnAbstract:The production rate of polymer fibers by extrusion is usually limited by the appearance of a series of instabilities ("Melt Fracture") that lead to unwanted undulations of the surface. We present both qualitative and quantitative experimental evidence that-in addition to previously known polymer-specific scenarios-there is an intrinsic route towards Melt Fracture type phenomena: a nonlinear ("subcritical") instability of viscoelastic Poiseuille flow.
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intrinsic route to Melt Fracture in polymer extrusion a weakly nonlinear subcritical instability of viscoelastic poiseuille flow
Physical Review Letters, 2003Co-Authors: Bernard Meulenbroek, Cornelis Storm, Volfango Bertola, Christian Wagner, Daniel Bonn, Wim Van SaarloosAbstract:As is well known, the extrusion rate of polymers from a cylindrical tube or slit (a "die") is in practice limited by the appearance of "Melt Fracture" instabilities which give rise to unwanted distortions or even Fracture of the extrudate. We present the results of a weakly nonlinear analysis which gives evidence for an intrinsic generic route to Melt Fracture via a weakly nonlinear subcritical instability of viscoelastic Poiseuille flow. This instability and the onset of associated Melt Fracture phenomena appear at a well-defined ratio of the elastic stresses to viscous stresses of the polymer solution.
Younggon Son - One of the best experts on this subject based on the ideXlab platform.
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anomalous rheological behavior of polyethylene Melts in the gross Melt Fracture regime in the capillary extrusion effect of long chain branching
Journal of Applied Polymer Science, 2008Co-Authors: Hwiyong Lee, Dong Hak Kim, Younggon SonAbstract:During a capillary extrusion with several different polyethylenes, we observe an abnormal rheological behavior. The nominal viscosity of some polyethylene Melt in the gross Melt Fracture regime does not change with the temperature. Several metallocene-catalyzed linear low density polyethylene are investigated. Among them, polyethylenes, which have long-chain branches in their main chain, show this abnormal rheological behavior. By capillary extrusion experiments with various dies of different L/D ratios, it is inferred that the abnormal rheological behavior is originated in the die land, not die entrance nor die exit. From various experiments, we notice that this abnormal phenomenon may be used to detect long-chain branch of PE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
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anomalous rheological behavior of polyethylene Melts in the gross Melt Fracture regime in the capillary extrusion
Polymer, 2006Co-Authors: Hwiyong Lee, Dong Hak Kim, Younggon SonAbstract:During the capillary extrusion with several different polyethylenes, we observe an abnormal rheological behavior. The nominal viscosity of polyethylene Melt in the gross Melt Fracture regime does not change with a temperature. All polyethylenes tested show same behaviors. More interestingly, the nominal viscosity in the gross Melt Fracture regime shows even no molecular weight dependency when PEs have similar molecular structures (degree of branching and co-monomer content). From various experiments, we conclude that this abnormal phenomenon is relevant to the structural change with the Melt temperature.
Mahmoud Ansari - One of the best experts on this subject based on the ideXlab platform.
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the role of microstructure on Melt Fracture of linear low density polyethylenes
Polymer Testing, 2018Co-Authors: Mahmoud Ansari, Tanja Tomkovic, Antonios A Doufas, Maziar Derakhshandeh, Savvas G. HatzikiriakosAbstract:Abstract The effects of molecular characteristics on the rheology and Melt Fracture of several linear and branched low-density polyethylene (LLDPE and LDPE) resins in capillary extrusion were studied as functions of molecular weight, polydispersity and the level of long chain branching (LCB). The level of LCB in the resins was found qualitatively by using several rheological methods which in general agree. These are based on the zero-shear viscosity versus molecular weight relationship, the energy of activation, the linear viscoelastic properties and the characteristic shapes of the flow curves. A previously proposed criterion (critical shear stress versus plateau modulus) for the onset of sharkskin Melt Fracture (Allal et al., J. Non-Newtonian Fluid Mech., 134 (2006) 127–135) was tested and found to give reasonable predictions for the sharkskin instability of the polyethylenes considered in this work.
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Melt Fracture of hdpes metallocene versus ziegler natta and broad mwd effects
Polymer, 2012Co-Authors: Mahmoud Ansari, Ashish M. Sukhadia, Yong Woo Inn, Paul J Deslauriers, Savvas G. HatzikiriakosAbstract:Abstract The Melt Fracture of high-density polyethylenes (HDPEs) is studied primarily as a function of molecular weight and its distribution for broad molecular weight distribution metallocene and Ziegler–Natta catalyst resins. It is found that sharkskin and other Melt Fracture phenomena are very different for these two classes of polymers, although their rheological behaviors are nearly the same for many of these. Moreover, the metallocene HDPE shows significant slip at the die wall without exhibiting stick-slip transition. Important correlations are derived between the critical conditions for the onset of Melt Fracture and molecular characteristics.
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Melt Fracture of two broad molecular weight distribution high density polyethylenes
Polymer Engineering and Science, 2012Co-Authors: Mahmoud Ansari, Ashish M. Sukhadia, Savvas G. Hatzikiriakos, David C RohlfingAbstract:The Melt Fracture instabilities of two broad molecular weight distribution (MWD) high-density polyethylenes (one Ziegler–Natta and one metallocene HDPEs) are studied as functions of the temperature and geometrical details and type of die (cylindrical, slit, and annular). It is found that sharkskin and other Melt Fracture phenomena are distinctly different for these resins, despite their almost identical rheology. It is also found that the critical conditions for the onset of various Melt Fracture phenomena depend significantly on the type of die used for their study. For example, sharkskin Melt Fracture in slit and capillary extrusion was obtained at much small critical shear stress values compared with those found in annular extrusion. Moreover, the metallocene HDPE shows significant slip at the die wall in the sharkskin flow regime. On the other hand, the Ziegler–Natta HDPE has shown no sign of slip. These differences are discussed on the basis of differences in their MWDs that influence their Melt elasticity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Hwiyong Lee - One of the best experts on this subject based on the ideXlab platform.
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anomalous rheological behavior of polyethylene Melts in the gross Melt Fracture regime in the capillary extrusion effect of long chain branching
Journal of Applied Polymer Science, 2008Co-Authors: Hwiyong Lee, Dong Hak Kim, Younggon SonAbstract:During a capillary extrusion with several different polyethylenes, we observe an abnormal rheological behavior. The nominal viscosity of some polyethylene Melt in the gross Melt Fracture regime does not change with the temperature. Several metallocene-catalyzed linear low density polyethylene are investigated. Among them, polyethylenes, which have long-chain branches in their main chain, show this abnormal rheological behavior. By capillary extrusion experiments with various dies of different L/D ratios, it is inferred that the abnormal rheological behavior is originated in the die land, not die entrance nor die exit. From various experiments, we notice that this abnormal phenomenon may be used to detect long-chain branch of PE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
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anomalous rheological behavior of polyethylene Melts in the gross Melt Fracture regime in the capillary extrusion
Polymer, 2006Co-Authors: Hwiyong Lee, Dong Hak Kim, Younggon SonAbstract:During the capillary extrusion with several different polyethylenes, we observe an abnormal rheological behavior. The nominal viscosity of polyethylene Melt in the gross Melt Fracture regime does not change with a temperature. All polyethylenes tested show same behaviors. More interestingly, the nominal viscosity in the gross Melt Fracture regime shows even no molecular weight dependency when PEs have similar molecular structures (degree of branching and co-monomer content). From various experiments, we conclude that this abnormal phenomenon is relevant to the structural change with the Melt temperature.