Measurements of first and second normal stress differences in a polymer melt

Jensen, Erik Appel; Christiansen, Jesper de Claville

doi:10.1016/j.jnnfm.2007.04.011

Cited by 29 publications

(19 citation statements)

References 23 publications

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“…Since the diameter is measured aer cooling, a correction factor is employed in order to normalize all swell data at the extrusion temperature rather than room temperature. 67 Thus, the ratio of the extrudate diameter (D 2 ) to the die diameter (D 1 ) is multiplied by a density correction factor of: r s r m…”

Section: Capillary Rheometry Measurementsmentioning

confidence: 99%

Development of nanofibrillar morphologies in poly(l-lactide)/poly(amide) blends: role of the matrix elasticity and identification of the critical shear rate for the nodular/fibrillar transition

et al. 2018

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Bio-based poly(L-lactide)/poly(amide-11) blends (PLA/PA11, 80/20 w/w) and poly(L-lactide)/poly(amide-6) blends (PLA/PA6, 80/20 w/w) are processed by twin-screw extrusion followed by injection-moulding and key rheological parameters controlling their morphologie are investigated. The same work is done using the same PLA modified by a multi-step reactive extrusion route with an epoxy-based chain extender to obtain modified poly(lactide)/poly(amide-11) (PLA-j/PA11 80/20 w/w) blends. The morphologies of the extruded materials and of the injection moulded parts are characterized by SEM and their formation is deeply discussed via rheological investigation to highlight the contribution of viscosity, elasticity and interfacial tension. The existence of a critical shear rate related to the transition from nodular to fibrillar morphology is highlighted and the results are in good agreement with the condition of fibrillation Ca/Ca (crit) $ 4. Interestingly, with the exception of PLA/PA6 specimens, all blends obviously display uniform thin-thread fibrillar morphologies after injection-moulding. Compared with pure PLA, a drastic increase of the ductility was observed in the blends exhibiting a fiberlike structure without meanwhile sacrificing the stiffness. This study confirms that, through the appropriate choice of blend components (viscosity and elasticity ratio, flow conditions, interfacial tensions) the in situ fibrillation concept provides access, at a reasonable cost, to new materials with improved thermomechanical performances, without sacrificing weight and ability to be recycled.

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Section: Capillary Rheometry Measurementsmentioning

confidence: 99%

Development of nanofibrillar morphologies in poly(l-lactide)/poly(amide) blends: role of the matrix elasticity and identification of the critical shear rate for the nodular/fibrillar transition

et al. 2018

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“…Therefore, it is possible to determine N 2 of material by combining the data from cone plate and parallel plate (67)(68)(69)(70). Furthermore, optical and electromagnetic device can be readily installed on the parallel plate, which helps to perform other tests simultaneously with the rheological test.…”

Section: Rotational Rheometermentioning

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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“…Before all rheological testing, the samples were vacuum dried at 110°C during 16 h. Measurements of the steady state shear viscosity $\eta (\mathop \gamma \limits^ \cdot )$ , where $\mathop \gamma \limits^\cdot$ is the shear rate and first normal stress difference $N_1 (\mathop \gamma \limits^ \cdot ) = - (\tau _{11} - \tau _{22} ),$ where 1 is the direction of the fluid velocity, 2 is the direction of velocity variation, τ 11 the normal stress along the direction of the fluid velocity, and τ 22 the normal stress along the direction of velocity variation [44, 45] were made in a controlled strain ARES rheometer, from Rheometric Scientific, using a 25 mm parallel‐plate fixture, gap of 1 mm, at 250°C, under nitrogen atmosphere; the Rabinowitsch correction on the shear stress τ 12 ( $\tau _{12} = \tau _{{\rm measured}} \cdot ((3 + n)/4)$ , where n = power law index) was also done. Regarding N 1 , it must be pointed out that this parameter is usually measured by cone and plate geometry, among other techniques [46, 47]; however, when the nanocomposites were tested on this geometry, they displayed an extremely high elastic behavior, developing extremely high normal forces (or high N 1 ), beyond the equipment limits, and no constant gap was attained. Therefore, N 1 − N 2 was measured by parallel plates, assuming the Weissenberg hypothesis ( N 2 = second normal stress difference = 0); thus, its interpretation was only qualitative.…”

Section: Methodsmentioning

confidence: 99%

Influence of shape and surface modification of nanoparticle on the rheological and dynamic‐mechanical properties of polyamide 6 nanocomposites

Marini

Bretas

2012

Polymer Engineering & Sci

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Nanocomposites of polyamide 6 (PA6) with different concentrations of silane‐treated, organic‐treated, and nontreated nanoparticles of halloysite (HNT) and montmorillonite (MMT) had their microstructure and melt and solid state rheological behavior analyzed. The microstructure analysis was done using transmission electron microscopy (TEM) and wide angle X‐ray diffraction (WAXD); the effectiveness of the silanization was studied by thermogravimetric analysis (TGA) and Fourier transform infrared. It was found that exfoliation occurred in the organic‐treated MMT, but not in the silane‐treated MMT and that silanization was small in the HNT nanoparticles (due to its low amount of surface hydroxyls groups). Steady state shear, small amplitude oscillatory, and transient tests also indicated that: (i) only the nanocomposites with organic‐treated MMT, at concentrations above the theoretical percolation threshold developed a percolated network; (ii) the silane treatment increased the shear elastic modulus (G) of the PA6/HNT nanocomposites in the solid state, but not of the PA6/MMT; (iii) the organic‐treated MMT formed composites with the highest G, as expected. Thus, it was concluded that the HNT nanoparticles had a high potential as nanofiller for PA6, but further research on more efficient compatibilizers for HNT is still needed. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.

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Measurements of first and second normal stress differences in a polymer melt

Cited by 29 publications

References 23 publications

Development of nanofibrillar morphologies in poly(l-lactide)/poly(amide) blends: role of the matrix elasticity and identification of the critical shear rate for the nodular/fibrillar transition

Development of nanofibrillar morphologies in poly(l-lactide)/poly(amide) blends: role of the matrix elasticity and identification of the critical shear rate for the nodular/fibrillar transition

Rheological Measurements

Influence of shape and surface modification of nanoparticle on the rheological and dynamic‐mechanical properties of polyamide 6 nanocomposites

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