Viscosity flow activation energy

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. 

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. 

Low flow activation energies ( = temperature influence on viscosity variation)... 

Our purpose is to elucidate the correlation between the B and water structure from the viewpoint of the pressure effect. Some abnormal behaviors of water under high pressure have been observed in dynamical properties at room (or lower) temperature, such as the share-viscosity minimum, activation-energy minimum of viscous flow, and spin-lattice relaxationtime maximum of proton NMR. These phenomena suggest that the structural change of water by pressure is an important factor for the B as well as the change by temperature. 

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. 

For purposes of modeling the filling stage of the RIM molding operation, it is also generally desirable to quantify the increase in viscosity due to polymerization. Therefore, to correlate the viscosity with a developing polymer matrix, a conversion term was added to Equation 8, adapted from Castro and Macosko (lA). Since it has been shown that the flow activation energy does not necessarily remain constant with conversion (7), the expression became... 

From Figure 1.10, it can he seen that the plots of kinematic viscosity vs pressure at temperatures below 308 K have a minimum at 0—1973 atm, and the calculation indicated that the activation energy of viscous flow has a minimum at about 1973 atm. These decreases in viscosity and activation energy with increasing pressure on the low-pressure side of the minima were ascribed to a break of the bulky water structure like hydrogen-bonded tetra-hedra. However, when the pressure is increased to a value of higher than 2000 atm, a monotonic increase with further increasing pressure can be observed. The similar trend was observed not only for pure liquid water but also for several electrolyte solutions. ... 

Polyvinyl acetate Apparent viscosity, viscous flow activation energy Viscometry 128... 

It can be observed from both tests at constant shear stress and constant shear rate that the melt viscosity is reciprocal of temperature. The melt viscosity is relatively related to the structure and free volume, whereby the increase in temperature might result in the enhancement of free volume and the improvement of chain mobility. Thus, viscosity gradually decreased exponentially with rising temperature. It is well known that the value of flow activation energy reflects the temperature-sensitivity of viscosity so, higher E or Ea leads to higher sensitivity of the blends to temperature. It can be seen from the values of E and Ea that E. increases with increasing... 

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