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The following holds for the viscosity/temperature shift factor aT in general:

Equation 3.8

aT = η(T) / η(Tref)

The dimensionless factor aT is the ratio of the two viscosity values at the temperature T and at the reference temperature Tref. For polymers, this relation is only valid for the values of the zero-shear viscosity η0. The following holds for the temperature shift factor according to Arrhenius (with T in [K]):

Equation 3.9

The semi-logarithmic, so-called Arrhenius plot presents the temperature shift factor aT on the y-axis on a logarithmic scale versus the reciprocal temperature 1/T on the x-axis (with the unit: 1/K).

In order to estimate viscosity values at temperatures at which no measuring values are available, proceed as follows:

1 Select Tref (e. g. a temperature, at which an η-value is available).

2 Calculate the shift factor aT for another available η(T)-value (using Equation 3.8).

3 Calculate the flow activation energy value EA (using Equation 3.9).

4 Calculate the shift factor aT for the desired η(T)-value (using Equation 3.9).

5 Result: Calculate the desired η(T)-value (using Equation 3.8).

Table 3.5: Temperature-dependent viscosity values, see the example of Chapter 3.5.4b
T [°C]	50	60	70	80
T [K]	323	333	343	353
η [Pas]	2.00	1.55	1.26	1.00