Severs rheometer

ISO 4575 1985 Plastics - Polyvinyl chloride pastes using the Severs rheometer... 

It should be noted that the ASTM method is different than ISO standard. Severs rheometers of two different geometries are specified by ISO standard. They have a radius of orifice of 1.5 mm and its height either 45 or 22.5 mm depending on the model (dimensions of orifice are totally different than specified in ASTM). The use of several pressures is suggested to determine rheological properties of plastisols, since viscosity must be determined at different shear rates. Calculations are done from the equation [3.8]. 

ISO 3826 1993 Plastics collapsible containers for human blood and blood components ISO 4574 1978 Plastics — PVC resins for general use — Determination of hot plasticizer absorption ISO 4575 1985 Plastics — Polyvinyl chloride pastes — Determination of apparent viscosity using the Severs rheometer... 

Several rheometers do not subject the polymer to a steady rate of deformation but to an oscillatory deformation, usually sinusoidal simple shear. If the angular frequency is o, and the shear strain amplitude Yo. the shear strain y can be written as a function of time ... 

Figure 6.5.1 illustrates the very wide range of viscosity measurement possible on a stable suspension, eight decades in y, when one combines results from several rheometers. We see that concentric cylinders are typically used for the lowest shear rates, while capillaries provide high shear rate data. The increase in viscosity with shear rate is le and has been verified by tests with differ-... 

A number of mathematical models have been proposed for yield stress fluids, not all perfectly coherent however. If a shear thinning material is tested with one of several rheometers and the results plotted in terms of shear stress o vs. shear rate y (the so-called flow curve) using linear scales, one is nearly bound to the conclusion that there is a yield stress and that the best manner to model the observed behavior consists in considering the following equality 0 = 0,+ /(y). 

Dynamic mechanical properties also evolve gradually during the LST of polymeric systems. The gel point is reached when tan S becomes independent of frequency [58, 63, 65, 120, 149, 150] (see Eq. 4-12). Lines of tan 3(l) at several frequencies a>i, co2, co3, co4, co5, etc. decay gradually and intersect at the gel point (see Fig. 26). The method is very effective. The instant of gelation can be measured as precisely as the accuracy of the rheometer permits - a significant... 

Stress relaxation has been mentioned in the context of several plasticity instruments. ASTM D6048140 gives background information about techniques and theory of stress relaxation testing and interpretation of results. Mention is made of the Mooney and capillary rheometers. 

Recent advances in dynamic rotational rheometers are of growing importance in food analyses for several reasons. (1) The measurement minimizes the destruction of the material. (2) The time required for a measurement is reasonably short in comparison with chemical or physical changes in the material. (3) The viscoelasticity of gels is characterized by determining G and G" in the linear viscoelastic (LVE) region no other method gives dynamic moduli values. 

The crosslinking kinetics and the final state of cure are commonly studied with the aid of rheometers. NMR relaxation experiments can offer several advantages for the characterisation of the crosslinking kinetics in complex materials because of high method selectivity with respect to the rubbery chains/phases in polymer blends, filled and oil extended rubbers. 

Normally the coordinate system is chosen in such a way that T13 = T31 = T23 = T32 = 0 In general, use is made of normal stress differences, N1 and N2, because they do not include undetermined hydrostatic pressures that are always present but not affect the material properties (as long as they are not too high). In Table 15.1, also the possibilities to determine the normal stress differences or combinations are depicted. In the modem rheogoniometers also normal stress differences can be determined but. They follow from measurements of normal forces, Fn, or normal stresses, T22, as is also depicted in Table 15.1. For the measurements of the normal stresses T22 pressure gauges have to be mounted in the Couette cylinders, in the capillary of the capillary rheometer (in both cases quite difficult to mount) and in the plate of a cone and plate instrument at several distances from the axis (not that difficult). Sometimes use is made of a slit rheometer instead of a capillary rheometer, because pressure gauges are much easier to mount (Te Nijenhuis, 2007, Chap. 9.1.2). 

Acknowledgements. The author would like to acknowledge the M.S. research work of P.A. Drda and sharkskin measurements by Y.W. Inn that have been discussed here. Several more discussions were made possible due to the unpublished data on monodisperse PB melts by X. Yang. The author is grateful to H. Ishida for use of the instrumental Monsanto Capillary Rheometer to collect much of the experimental data discussed here. He thanks L. Leibler for pointing out the usefulness to evaluate the value of the critical stress for the stick-slip transition in terms of melt chain statistics. The financial support of the National Science Foundation (Grant No. CTS-9632466) and BP Chemicals is greatly appreciated. 

When using small deformation rheology there are several useful parameters that may be obtained to describe a material the complex modulus (G ), storage modulus (G ), loss modulus (G") and the tangent of the phase shift or phase angle (tan 5). These values must be taken from within the LVR, and are obtained using a dynamic oscillatory rheometer (Rao 1999). Outside the LVR, important information may be obtained such as the yield stress and yield strain. 

With automated rheometers it is relatively easy to obtain dynamic shear data than steady shear data. For this reason, the interrelationship between co and t) on one hand and y and t a on the other is of interest. The Cox-Merz rule, that is, equal magnitudes of i)a and if at equal values of y and co, respectively (Equation 5.17), was obeyed by several synthetic and biopolymer dispersions (Lopes da Silva and Rao, 1992). 

It is emphasized that rheological data described by Equations 8.41 and 8.42 of a STD cannot be predicted a priori and must be obtained experimentally. Because viscosities at > 95°C were severely affected by water evaporation in the rheometer (Yang and Rao, 1998a), for temperatures fi om 95 to 121°C (retort temperature) (C-D), the decrease in magnitudes of the rf with increase in temperature was assumed to follow an Arrhenius equation (Equation 8.43). 

As shown in Table 1, poly(isobutylene-co- -pinenes) containing up to 10 mole% -pinene are rubbery materials Tg< —53 ). In view of the structural similarity between our copolymer and butyl rubber, we decided to use conventional butyl rubber cure conditions (3) to prepare our vulcanizates (see Experimental). Figure 2 shows the curing rate of two copolymers containing 3 and 10 mole% fi-pi-nene units respectively, as determined by a Monsanto Rheometer at 160 C (320 F). As expected, the curing rate of the cr lymer containing 10 mole% unsaturation is several times hi r than that of the material with 3 mole% unsaturation level. 

In the study of the chemorheology of photopolymerizable systems, the use of a traditional rheometer is particularly difficult and the development of improved time resolution from several seconds to better than 1 ms has been noted, together with an increase in the intensity of initiating radiation that may be employed (Schmidt et al, 2005). The challenge is to gather data at the best possible SNR and then use the appropriate algorithm for recovery and analysis of the phase information and intensity to enable calculation of G and tan <5 (Schmidt et al, 2005, Chiou and Khan, 1997). These studies are often augmented by simultaneous real-time spectroscopic studies on the sample in the rheometer in order to provide conversion data as discussed in Section 3.3. 

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