Flow activation energies

Table 1. Activation energies and ratios of the preexponential factors to the radiative rate constants (A/kp) for the photoisomcrization of BMPC in several solvents. Solvent dielectric constants at room temperature, e [65], and viscous flow activation energies, Eri [66], are shown too.

Fig. 9.11 Flow activation energy of pure PLA and various PLA-based nanocomposites as a function of MMTcontent. Reprinted from [47], 2003 Wiley-VCH Verlag GmbH Co.

Figure 9.11 represents the MMT content-dependent (wt%) flow activation energy (Ea) of pure PLA and various PLANCs obtained from an Arrhenius fit of the master curves [47]. It is clearly observed that the Ea value increases significantly for the nanocomposite containing 3 wt% MMT and then is almost unchanged with increasing MMT content. This result indicates that, in the presence of MMT, it is very difficult for the materials to flow. This behavior is also ascribed to the formation of a spatially linked structure in the nanocomposite in the molten state. 

Table 11.5 shows the flow activation energies, a, for PET, PTT and PBT [68], PTT has a higher a compared to PET but similar to that of PBT. The change in its melt viscosity is therefore less sensitive to temperatures changes than PET. However, due to the higher degradation rate, increased melt processing temperatures can have deleterious effect on the melt viscosity and IV. 

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

Molecular Weights, Flow Activation Energies and Type of Catalyst for a Series of Polyethylenes Examined for Long Chain Branching. 

Polymer "B" is an ethylene-l-hexene copolymer by design. A flow activation energy of 9.6 kcal/mol suggests that long chain branching may be present. The C-13 NMR spectrum, however, is complicated by the presence of butyl branches as in the case of... 

R is the gas constant and Ea the flow activation energy. The latter is a material-specific factor that is not dependent on the molar mass of the polymer and for thermorheological simple polymers also is not dependent on the shear stress. The activation energy Ea for polymer melts varies between 25 and 80 kj/mol. It can be determined from the slope of the line in the Arrhenius plot. 

The approximated lines at the right side of Fig. 3.14 correspond to an Arrhenius activation energy of approximately 120 kj/mol, which is significantly higher than the flow activation energy of the semi-crystalline polyolefin melts shown in Fig. 3.13. The temperature dependence of the melt viscosity for amorphous thermoplastics is substantially higher than that of semi-crystalline polymers and increases dramatically as the temperature approaches the glass transition temperature. 

Figure 5-1 Values of the Flow Activation Energy ( a) of Concentrated Apple and Grape Juices are Exponentially Dependent on their °Brix Values.

Nakajima, N., G. A. Tirpak, and M. Shida Branching and flow activation energy of conventional high pressure process polyethylene. J. Pol5rmer ScL 3B. 1089 (1965). 

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. 

Another key feature of the fluid is the design parameter B (see Table 3), obtained by differentiation of the Falcher-Tamman equation [3], which is proportional to the viscous flow activation energy ... 

Additive content increase in the compositions results in a regular increase in the value of Bt and the values of the viscous flow activation energy at 20 °C (see Table 3). 

Thus, the conducted research showed that absolute reaction rate theory is not applicable to the explanation of the composition s viscosity-temperature relationship. It was found that the fi e volume theory allows us to describe the viscosity-temperature relationship with satisfactory accuracy within the studied temperature range from nunus -20 to 50 C. Parts of the fi ee fluctuation volume and viscous flow activation energy values determining fluids properties were calculated. 

A regression fit to the bulk viscosity as a function of temperature, provided AE = 34.7kJ/mol) and A5 , = 9.87J/mol-K. The flow-activation energy is close to that reported for bulk Zdol with a molecular weight of 3100 in Refs. . A positive value for the flow activation entropy of bulk Zdol means that the entropy of the flow unit increases on going into the flow-activated state. 

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