Читать книгу The Rheology Handbook - Thomas Mezger - Страница 235

Creep and creep recovery tests are used to analyze the viscoelastic (VE) behavior performing two shear stress steps. This method is mostly used to examine chemically uncrosslinked and unfilled polymers (melts and solutions), but it is also suitable to evaluate the behavior of chemically crosslinked polymers, gels and dispersions showing a physical-chemical network of forces.

In industrial practice, however, creep tests have lost of importance since rheometers with air bearings are meanwhile available enabling the user to directly preset very low rotational speeds. Previously, creep tests have been the only way to produce very low shear rates, even if indirectly and therefore to obtain information about the behavior of uncrosslinked polymers in the

zero-shear viscosity range, for example, to determine the average molar mass. Today however, with modern rheometers measurements with direct shear rate control are possible as well in the low-shear range. For these reasons since around 1995, creep tests are mostly carried out by scientists only, especially to achieve results under the extreme low-shear conditions of γ ̇ < 10-3 s-1.