Rheological flow activation energies

Table 11.5 Rheological flow activation energies ( a) of PET, PTT and PBT melts [68]...

Rheological properties of the oligoethylsiloxane-based compositions with additives are of vital importance for the selection of maintenance conditions of various items, but they have not been studied yet. No data on such composition-fluidity relationships (unconfined fluctuating free volume and viscous flow activation energy values) are available. 

As shown in Table 4, introduction of 1-hexadecene as comonomer has a similar influence to hydrogen on the rheological properties of the polyethylene the tj o = 0.02 rad s ) and G values were lowered, indicating suppression of the LCB. The flow activation energy value, a remained almost unchanged due to two opposite effects at play simultaneously. For flow E, two different effects of the comonomer incorporation are present an increase in the comonomer content in a linear polymer will increase E, but for the LCB, a decrease in the LCB content would decrease the E value. 

Rheology. Both PB and PMP melts exhibit strong non-Newtonian behavior thek apparent melt viscosity decreases with an increase in shear stress (27,28). Melt viscosities of both resins depend on temperature (24,27). The activation energy for PB viscous flow is 46 kj /mol (11 kcal/mol) (39), and for PMP, 77 kJ/mol (18.4 kcal/mol) (28). Equipment used for PP processing is usually suitable for PB and PMP processing as well however, adjustments in the processing conditions must be made to account for the differences in melt temperatures and rheology. 

Caustic Waterflooding. In caustic waterflooding, the interfacial rheologic properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior, and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration, and aging time. The interfacial viscosity drastically... 

For a nematic polymer in a transition region from LC to isotropic state, maximal viscosity is observed at low shear rates j. For a smectic polymer in the same temperature range only a break in the curve is observed on a lgq — 1/T plot. This difference is apparently determined by the same reasons that control the difference in rheological behaviour of low-molecular nematics and smectics 126). A polymeric character of liquid crystals is revealed in higher values of the activation energy (Ef) of viscous flow in a mesophase, e.g., Ef for a smectic polymer is 103 kJ/mole, for a nematic polymer3 80-140kJ/mole. 

Table 5-N Rheological Properties of Egg Products, and Activation Energies of Flow (Rao. 1977)...

Therefore, the study of rheological properties, the determination of the activation energy of viscous flow, composition-fluidity relationships, and key factor effects of the lubricity-promoting additive on the fluidity of oligoethylsiloxane-based compositions were of interest. 

The multiplicity of rheological phenomena observed in BC is related to sensitivity of the melt structure to independent molecular and rheological variables. For example, for styrene-butadiene-styrene (SBS), the activation energy of flow AE = 80 or 160 kJ/mol for compositions containing less or more that 31 vol% of styrene. The difference originates in the structure it is dispersed below 31 % and interconnected above [Arnold and Meier, 1970]. 

Of all the physico-chemical properties, it is the rheology which shows the strongest temperature dependence. For instance, the decrease in apparent viscosity at a fixed shear rate is well represented by the Arrhenius-type exponential expression the pre-exponential factor and the activation energy are then both fimctions of shear rate. It is thus customary to denote the temperature dependence using rheological constants such as the power-law consistency coefficient and flow behaviour index. It is now reasonably well established that the flow behaviour index, n, of suspensions, polymer melts and solutions is nearly independent of temperature, at least over a range of 40-50°C, whereas the consistency coefficient exhibits an exponential dependence on temperature, i.e. 

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