Journal ArticleDOI
The different capillary flow regimes of entangled polydimethylsiloxane polymers : macroscopic slip at the wall, hysteresis and cork flow
N. El Kissi,J.M. Paiu +1 more
TLDR
In this paper, a master curve was shown for the sliding friction properties of the polymer under consideration, and the existence of the master curve for variations in average velocity vs. wall stress, during flow with macroscopic slip at the wall.Abstract:
Polymers, melted at room temperature, have been extruded through capillary dies using either a controlled pressure system or an automatic capillary rheometer in which the rate of flow is controlled. When the polymer is highly entangled, macroscopic slip is observed at the wall. However, flow curves differ: for controlled pressure conditions, slip appears simultaneously with a sudden increase in the rate of flow, an dflow curves exhibit a hysteretic regime. For controlled flow conditions, slip is accompanied by oscillations of the rate of flow and pressure head around a mean value, as a result of polymer compressibility. The succession and evolution of the different flow defects are clearly identified. As the flow regime increases, scratches appear first. Then, beyond a critical value of wall shear stress in the exit region, cracks are formed just at the exit of the capillary die. These cracks are accompanied by the formation of “rings”, which are more easily observed as the molecular weight increases. At high flow rates, when macroscopic slip appears at the wall, the aspect of the extrudate depends on the system used. For controlled pressure conditions, the polymer is ejected in the form of an opaque, irregular jet, where swelling is quasi-non-existent. For controlled flow conditions, cork flow is observed. At higher flow regimes the extrudate becomes chaotic. The existence of a master curve was also shown for variations in average velocity vs. wall stress, during flow with macroscopic slip at the wall. It is important to note that this curve represents the sliding friction properties of the polymer under consideration.read more
Citations
More filters
Journal ArticleDOI
Instabilities in viscoelastic flows
TL;DR: In this article, the authors present a review of the latest developments as well as earlier work in this area, organized into the following categories: Taylor-Couette flows, instabilities in cone and plate-and-plate flows, parallel shear flows, extrudate distortions and fracture, Instabilities in shear flow with interfaces, extensional flows, and thermohydrodynamic instabilities.
Journal ArticleDOI
Extrusion Instabilities and Wall Slip
TL;DR: In this paper, the authors explore the evidence for slip, the possible mechanisms of slip, and the relation between slip and extrusion instabilities, and show that extrusion melts exhibit extrusion instability at sufficiently high levels of stress.
Journal ArticleDOI
Wall slip of molten polymers
TL;DR: In this paper, the two physical mechanisms of slip are discussed and validated on the basis of published experimental data and their significance on the rheology and flow simulations of molten polymers is discussed.
Book ChapterDOI
Surface-Anchored Polymer Chains: Their Role in Adhesion and Friction
TL;DR: In this article, the role played by surface-anchored polymer layers in adhesion and friction is discussed, and the degree of interdigitation between the surface layer and the bulk polymer system is analyzed to determine the optimum enhancement in the adhesion energy between the solid wall and an elastomer.
Journal ArticleDOI
Migration of macromolecules under flow: the physical origin and engineering implications
TL;DR: In this article, the authors review the experimental evidence, especially the anomalous experimental observations of interest to engineers, concerned with enhancement (which is sometimes rather dramatic) in heat, mass and momentum transfer during the flow of such sliding fluids.
References
More filters
Journal ArticleDOI
Wall Slip in Viscous Fluids and Influence of Materials of Construction
TL;DR: In this paper, the question of slip and the influence of materials of construction on the observed extrudate irregularities are examined for high viscosity molten polyethylenes. But the assumption of "no slip at the rigid boundary" is generally not valid for polyethylene above a critical shear stress of approximately 0.1-0.14 MPa, when either surface or gross irregularities are present in the extrudates.
Journal ArticleDOI
Instabilities in polymer processing
C. J. S. Petrie,Morton M. Denn +1 more
TL;DR: The experimental observations and the extent of theoretical understanding of the instabilities in shear and extensional flows in polymeric liquids are discussed in this paper, where the experimental observations are compared with theoretical understanding.
Journal ArticleDOI
Wall Slip and Extrudate Distortion in Linear Low‐Density Polyethylene
TL;DR: In this paper, the onset of extrudate distortion (sharkskin) in linear low-density polyethylene is shown to coincide with the failure of adhesion at the polymer/metal interface.
Journal ArticleDOI
Cone-and-plate rheometry of yield stress fluids. Study of an aqueous gel
Albert Magnin,Jean-Michel Piau +1 more
TL;DR: In this paper, the authors focus on the rheometric study of a physical gel exhibiting a yield stress and show how the determination of shear rheological properties can be affected by anomalous phenomena such as fracture and slip at the wall.
Journal ArticleDOI
Numerically stable finite element techniques for viscoelastic calculations in smooth and singular geometries
TL;DR: In this article, a restructured version of the constitutive equation of motion, called the Explicity Elliptic Momentum Equation (EEME), is used for viscoelastic flow analysis.