Viscosity Differences

There appears to be no rules for real situations [2], but it is not at all difficult to inject a liquid into the downstream regions of an extruder and produce a fine spray of the liquid around an extruded strand as it emerges from the die, e.g., white oil added to polystyrene. It is evident that the liquid can form a durable lubricating layer between the molten polymer and both barrel and die surfaces even when mixing elements are used. Fortunately there are ways of avoiding these problems. 

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Paraffinic white oils from the same source but varying in molecular weight as indicated by their viscosity differences. 

A comparison of values of yield stress for filled polymers of the same nature but of different molecular weights is of fundamental interest. An example of experimental results very clearly answering the question about the role of molecular weight is given in Fig. 9, where the concentration dependences of yield stress are presented for two filled poly(isobutilene)s with the viscosity differing by more than 103 times. As is seen, a difference between molecular weights and, as a result, a vast difference in the viscosity of a polymer, do not affect the values of yield stress. 

Continuous polymerization processes for PA-6,6 have been reported for over 30 years.5,6,28 Prepolymerization in tubular (Fig. 3.21) or baffled reactors is particularly well suited to continuous polymerization. The polymerization of prepolymers to high-molecular-weight materials in a continuous process is more difficult to control as small differences is molecular weights result in large differences in viscosities. Viscosity differences result in different hold-up times in die reactor and thus nonhomogeneous products. 

Thus, the measurements of integral flow characteristics, as well as mean velocity and rms of velocity fluctuations testify to the fact that the critical Reynolds number is the same as Rccr in the macroscopic Poiseuille flow. Some decrease in the critical Reynolds number down to Re 1,500— 1,700, reported by the second group above, may be due to energy dissipation. The energy dissipation leads to an increase in fluid temperature. As a result, the viscosity would increase in gas and decrease in liquid. Accordingly, in both cases the Reynolds number based on the inlet flow viscosity differs from that based on local viscosity at a given point in the micro-channel. 

This approach leads to a model of a liquid other than water that has a calculated viscosity different from water but that may be all that is needed for a particular study. It should be noted that the vapor pressure presents a similar... 

X 10 cm by measuring molecularly dispersed water in toluene and by correcting for local viscosity differences between toluene and these microemulsions [36]. Values for Dfnic were taken as the observed self-diffusion coefficient for AOT. The apparent mole fraction of water in the continuous toluene pseudophases was then calculated from Eq. (1) and the observed water proton self-diffusion data of Fig. 9. These apparent mole fractions are illustrated in Fig. 10 (top) as a function of... 

Sample-to-sample viscosity differences Use internal standards... 

Viscosity differences-. Different sample vial temperatures create different viscosities, and thus different amounts injected. To reduce the effect, use the instrument temperature control (see Section IV). However, often the sample and buffer vials reside outside the temperature-controlled area. The effect of this might vary depending on the climate system in your lab and how the lab temperature varies over the year. Besides temperature control, it is important to match samples and standards in terms of viscosity and conductivity. 

The standards should match the samples in order to accurately determine the latter. Viscosity differences result in injected volume differences. If a compound is determined in the presence of high concentrations of other compounds in the sample, these can influence the migration time and peak shape by electromigration dispersion (EMD), and should therefore be present in the standards as well (Figure 1). ... 

The FDEMS sensor-controlled run significantly reduced the time lag and viscosity difference between the center ply and the tool surface ply. The amount of flow as measured by the magnitude of the viscosity minimum was greater in the FDEMS sensor-controlled run. The approach of ds"/dt to zero was used to determine cure completion. The total cure time of 200 min in this FDEMS controlled run is 40 min less than the conventional cure cycle. 

Zlokarnik M. Influence of density and viscosity differences on mixing time in the homogenisation of liquid mixtures (in German). Chem Ing Tech 1970 42 1009-1011. 

These two formulas for the viscosity differ by only the leading multiplicative constants, which are within 2% of one another. 

For synthetic rubbers, the mill homogenization is generally omitted, although it is specified as an alternative where the appropriate evaluation procedure requires it before measuring Mooney viscosity. Different conditions are given for specific polymers. The mill method of ISO 248 for determining volatile matter is specified but the oven method may be substituted if the material sticks to the mill rolls. Regardless of which volatile matter method is used, the mill procedure is required to dry samples for any chemical tests needed - unless this is not possible. To the uninitiated at least, this is not a model of clarity. Vulcanization characteristics are determined for synthetic rubbers, but not plasticity retention index. 

The Delta Mooney (A Mooney) test is an extension of the Mooney used on empirical grounds as a general indication of processibility for non-pigmented oil extended emulsion styrene/butadiene rubber. It quantifies the changes that occur in Mooney viscosity with time, either as the difference between viscosities recorded at two specified times or as the difference between the minimum viscosity recorded immediately after the commencement of the test and the subsequent maximum viscosity. Several alternative Delta Mooney values are defined depending on the times, whether minimum/maximum viscosity difference is used and whether or not the sample has been massed on a mill. Procedures for Delta Mooney are standardised in ISO 289-341, BS 903 Part A58-142 and in ASTM D334643. 

In Table 11, photopolymerization speeds were measured by step-wedge exposure in film-based compositions containing MB and a triacrylate monomer. The comparison, largely for amine-type activators and enolates, shows only a 5x variation in viscous films compared to approximately 20x for similar activators in solution. The absolute loss in system photospeed on changing from solution to film composition is estimated to be near 60x for NPG and TBBS. This loss of reactivity is presumed to be caused by viscosity differences between the two media reflected in lower overall sensitization efficiency in films as a result of increased competition of dye radiationless decay relative to bimolecular quenching. 

VL = 1 Wj), partial inversion. In the first case, N = 0 corresponds to a CSTR and N to a plug-flow reactor. It is shown that the best chemical conversion is obtained with complete flow inversion. The RTD in a Kenics mixer comprising 8 elements could be represented by this model with N = 3 and complete mixing. Static mixers could be used as chemical reactors for specific applications (reactants having large viscosity differences, polymerizations) but the published data are still very scarce and additional information is required for assessing these possibilities. 

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