The rheology of the rheotens test

Wagner, Manfred H.; Bernnat, A.; Schulze, V.

doi:10.1122/1.550907

Cited by 84 publications

(49 citation statements)

References 20 publications

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“…He also noticed a decrease in melt strength and an increase in melt elongation of PLA with increasing PEG content. From the fitted parameters of the analytical model, the elongational viscosity can be calculated according to Wagner et al [31]. Figure 8 shows the apparent elongational viscosity of externally plasticized CA as a function of the extension rate.…”

Section: Influence Of Plasticizer Content On Shear Viscosity and Elonmentioning

confidence: 99%

“…Information on melt strength at low strain rate is important for polymer foaming. Therefore, extensional viscosities were calculated from the Rheotens curves according to an analytical model developed by Wagner et al [31]. To gain further information on the extensional deformation at low strain rate, the initial slope of the stress curve σ(V) at low draw ratio V was studied in dependence of plasticizer content.…”

Section: Measurementsmentioning

confidence: 99%

“…Figure 7a shows the drawdown force as a function of draw ratio. The Rheotens curves were successfully fitted using an analytical model developed by Wagner et al [31] and a Levenberg-Marquardt procedure. Figure 7b shows the mean melt strength (mean drawdown force F mid ) and the maximum drawdown velocity as a function of TEC content.…”

Section: Influence Of Plasticizer Content On Shear Viscosity and Elonmentioning

confidence: 99%

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Extensional Flow Properties of Externally Plasticized Cellulose Acetate: Influence of Plasticizer Content

et al. 2013

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Elongational flow properties of polymer melts are very important for numerous polymer processing technologies such as blown film extrusion or foam extrusion. Rheotens tests were conducted to investigate the influence of plasticizer content on elongational flow properties of cellulose acetate (CA). Triethyl citrate (TEC) was used as plasticizer. Melt strength decreases whereas melt extensibility increases with increasing plasticizer content. Melt strength was further studied as a function of zero shear viscosity. The typical draw resonance of the Rheotens curve shifts to higher drawdown velocity and the amplitude of the draw resonance decreases with increasing TEC content. With respect to foam extrusion, not only are melt strength and melt extensibility important but the elongational behavior at low strain rates and the area under the Rheotens curve are also significant. Therefore, elongational viscosity as well as specific energy input were calculated and investigated with respect to plasticizer content. Preliminary foam extrusion tests of externally plasticized CA using chemical blowing agents confirm the results from rheological characterization.

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Section: Influence Of Plasticizer Content On Shear Viscosity and Elonmentioning

confidence: 99%

Section: Measurementsmentioning

confidence: 99%

Section: Influence Of Plasticizer Content On Shear Viscosity and Elonmentioning

confidence: 99%

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Extensional Flow Properties of Externally Plasticized Cellulose Acetate: Influence of Plasticizer Content

et al. 2013

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“…All these extensional flows have simple velocity field, which make them standard flow for rheological measurements. Typical uniaxial extension can be found in fiber spinning (53) and contraction flow (54)(55)(56)(57)(58). It can be represented by extension in one direction and simultaneous contraction in the other two directions.…”

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confidence: 99%

Rheological Measurements

2013

Encyclopedia of Polymer Science and Technology

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Rheology is the science to study the flow and deformation of matter. It becomes an important field in material science and engineering, food, biotechnology, and so on. The objects in rheological study are not the ideal solid and ideal fluid, which can be described by the Hookean elastic model and the Newtonian viscous model, respectively. Instead, the rheological study often focuses on materials that can exhibit viscous, elastic, and plastic behavior under different flow conditions. They are often termed as complex fluids or soft matter, which include polymers, gels, suspensions, emulsions, biofluids, foods, inks (1). In contrast to hydrodynamics, which often accounts for the complex flow behavior of simple fluids, simple geometry is utilized in rheological measurements to understand the rather complicated relationship between the mechanical input and output of complex fluids. The real flow fields encountered in many applications (such as polymer extrusion, injection molding, blow molding, fiber spinning, inkjet printing, coating) are rather complicated (2). It becomes a problem whether the rheological measurements that performed under simple flow fields are useful in understanding the complicated flow behaviors of complex fluids. Fortunately, it has been proved in many examples that the properties determined from simple rheological measurements are sufficient to quantify the material parameters in various constitutive equations, which have been used widely and successfully to simulate the flow behaviors in polymer processing (3-11). The most frequently used simple flow fields are simple shear flow and simple extensional flow.The simplest geometry that defines the simple shear is two infinite parallel plates separated by a distance h. The liquid is set between two plates with one plate moving parallel to the other (Fig. 1). In reality, when the length L and the width B are much larger than the gap h, the flow in the center regime resembles the flow between two infinite plates. It means that the edge effects are ignored in most experimental shear geometries. In rheological measurements, the flow between two plates should be laminar. Moreover, it is usually assumed that the velocity across the gap satisfies a linear profile. As shown in Fig. 1, if the bottom plate is fixed and the upper plate moves horizontally with the velocity V, the fluid velocity varies linearly from 0 at the bottom plate to V at the upper plate if the no-slip boundary condition is satisfied. The linear velocity profile generates a constant velocity gradient, which is known as the shear rate. Then, the flow field between two parallel plates is homogeneous in the shear rate. The homogeneous assumption is nontrivial in the rheological tests since the actual velocity

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“…The blend with fibril structure shows a significant increase of tensile force, which means an increase of melt strength. 18,19 Since PBT fibrils entangle and have many physical networks, they induce significant resistance against extension, leading to the enhancement of tensile properties without losing ductility. This suggests that the melt strength can be enhanced by morphology control.…”

Section: Resultsmentioning

confidence: 99%

Morphology development of PBT/PE blends during extrusion and its reflection on the rheological properties

Hong

Kim

Ahn

et al. 2005

J of Applied Polymer Sci

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ABSTRACT:In this study, we have investigated morphology evolution of polymer blends during extrusion. By choosing two polymers, high density polyethylene (PE) and poly (1,4-butylene terephthalate) (PBT), having a large difference in melting temperature, we could control the viscosity ratio of the blend as well as the morphology. The morphology of the dispersed phase evolved from film to fibril and to droplet structure depending on thermal and deformation history. We could maintain the film or fibril structure in a final product by keeping the dispersed phase deformable and rigid enough to avoid the relaxation that is related with instability originating from the interfacial tension. The anisotropic structures (film and fibril) were found to enhance the rheological properties significantly, but in different manners under shear and extensional flow fields. This study shows that diverse morphology can be obtained by controlling processing conditions, and the rheological properties can be dramatically enhanced by morphology control.

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The rheology of the rheotens test

Cited by 84 publications

References 20 publications

Extensional Flow Properties of Externally Plasticized Cellulose Acetate: Influence of Plasticizer Content

Extensional Flow Properties of Externally Plasticized Cellulose Acetate: Influence of Plasticizer Content

Rheological Measurements

Morphology development of PBT/PE blends during extrusion and its reflection on the rheological properties

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