Читать книгу The Rheology Handbook - Thomas Mezger - Страница 75

Equation 3.4

η∞ = lim γ ̇ →∞ η( γ ̇ )

Infinite-shear viscosity is the limiting value of the shear rate-dependent viscosity function at an “infinitely high” shear rate.

End of the Cleverly section

Note: Degradation of polymer molecules

At these extreme shear conditions, there is always the risk of degradation of macromolecules. The polymer chains may be torn and divided into pieces, a process which might destroy their original chemical structure. However, this should be avoided when performing rheological tests. Using the previously highly sheared sample again, it is easy to check if degradation has really taken place by carrying out a second measurement at the same low-shear conditions of shear range 1 (see Figure 3.10). If the η0-value remains still unchanged, no effective degradation has taken place. If the occurring η0-value is significantly lower then, polymer molecules have been destroyed under the previously applied high shear load, thus, the value of the average molar mass is significantly lower now.