Rheometer dynamic

J.L. Leblanc and A. Mongmel, A thorough examination of a commercial torsional dynamic rheometer with a closed oscillating cavity, Prog. Rubber Plast. TechnoL, 17, 162-185, 2001. 

J.L. Leblanc and C. de la Chapelle, Updating a torsional dynamic rheometer for Fourier transform rheometry on mbber materials. Rubber Chem. TechnoL, 76, 287-298, 2003. 

Dynamic rheometers have been widely used to study the viscoelastic characteristics of liquid, solid, and semi-solid foods. However, to our knowledge, very few studies on the rheological characteristics of potato flesh using dynamic rheometry have been carried out. The dynamic rheological behavior of potato tubers may be helpful to have a quick idea about potato texture and... 

Figure 4.2 is a plot of log(cr) versus log(viscosity) constructed from dielectric data of Figure 4.1 and measurements on a dynamic rheometer. The figure shows that at a viscosity less than 1 Pas (10P), a is proportioned to l/tj because the slope of log(n) versus log( j) is approximately — 1. The gel point of the polymerization reaction occurs at 90 min based on the crossover of G and G" measured at 40rad/s. This is very close to the time at which rj achieves 100 Pas, which is also often associated with gel. The region of gel marks the onset of a much more rapid change in viscosity than with a. This is undoubtedly due to the fact that as gel occurs the viscoelastic properties of the resin involve the cooperative motion of many chains, whereas the translational diffusion of the ions continues to involve motions over much smaller molecular dimensions. 

The four variables in dynamic oscillatory tests are strain amplitude (or stress amplitude in the case of controlled stress dynamic rheometers), frequency, temperature and time (Gunasekaran and Ak, 2002). Dynamic oscillatory tests can thus take the form of a strain (or stress) amplitude sweep (frequency and temperature held constant), a frequency sweep (strain or stress amplitude and temperature held constant), a temperature sweep (strain or stress amplitude and frequency held constant), or a time sweep (strain or stress amplitude, temperature and frequency held constant). A strain or stress amplitude sweep is normally carried out first to determine the limit of linear viscoelastic behavior. In processing data from both static and dynamic tests it is always necessary to check that measurements were made in the linear region. This is done by calculating viscoelastic properties from the experimental data and determining whether or not they are independent of the magnitude of applied stresses and strains. 

The power-law index, using either capillary or dynamic rheometers, or both ... 

The storage modulus and the loss modulus, using a dynamic rheometer and... 

The cone-and-plate and parallel-plate rheometers are rotational devices used to characterize the viscosity of molten polymers. The type of information obtained from these two types of rheometers is very similar. Both types of rheometers can be used to evaluate the shear rate-viscosity behavior at relatively low vales of shear rate therefore, allowing the experimental determination of the first region of the curve shown in Figure 22.6 and thus the determination of the zero-shear-rate viscosity. The rheological behavior observed in this region of the shear rate-viscosity curve cannot be described by the power-law model. On the other hand, besides describing the polymer viscosity at low shear rates, the cone-and-plate and parallel-plate rheometers are also useful as dynamic rheometers and they can yield more information about the stmcture/flow behavior of liquid polymeric materials, especially molten polymers. 

Figure 13 illustrates the influence of silanes in a silicar-rubber system. The graph shows data recorded with a dynamic rheometer, G being the elastic modulus and G" being the loss modulus as a function of dynamic strain. 

D IR spectrometer coupled with a dynamic rheometer capable of applying a small-amplitude mechanical perturbation [23],... 

With either pure, unfilled elastomers or slightly filled rubber compounds (typically filler volume fraction lower than 10 %) however, a Unear viscoelastic region is observable within the experimental window of most dynamic rheometers providing the strain amplitude does not exceed 10—20 %. 

Fig. 14 Strain sweep tests on a pure atactic polypropylene and an unfilled styrene-butadiene rubber compound using either an open-gap (VCOR) or a closed-cavity (RPA) torsional dynamic rheometer (authra- s experimental data)...

In order to overcome this problem, it was necessary to improve the frequency range for the dynamic rheological measurements. For this purpose a dynamic rheometer (HF rheometer) with a frequency range from 1 Hz up to 1 kHz was built. For samples with a high modulus (G 1 kPa) the measurements can even be extended to 2 kHz. 

Traditionally, polymer relaxation is characterized by a spectnun of multiple relaxation times corresponding to various modes of relaxation a polymer chain can undergo. The longest relaxation time corresponds to the relaxation of a whole chain, while the shorter ones correspond to the relaxation of short parts of the macromolecules. In this paper, we are particularly interested in the relaxation behavior at molecular chain level. Dynamic rheometers are the most used means for providing relaxation time spectrum of polymer melts [4-6]. However, since they only generate small scale melt deformation dming measurements, the relaxation time at macromolecular level... 

A torsion dynamic rheometer, Rheometric SCIENTIFIC RDA-II, was employed with a plate-plate fixture (i.e., 25 mm in diameter). Frequency sweep experiments were performed in the range 0.1 to 100 rad/s at 190°C in the linear viscoelastic range of the MDPE s. The tests were performed to obtained indirect evidences of the differences in molecular weights and molecular weight distribution of the samples. 

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