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3.11 Viscosity calculation
Concerning the calibration of a viscometer, please read the sheet with the heading "Viscometer within
quality assurance systems" which is enclosed with each SI Analytics GmbH viscometer.
Viscosity is a "classical" parameter of liquids. The result obtained using capillary viscometry is kinematic
viscosity, measured in the unit of mm²/s (formerly Centistokes, cSt). Considering that viscosity is highly
depending on temperature, the measurement temperature has to be maintained accurately and included
in the result (± 0.02 K).
The number of seconds identified for the various capillaries in the tables for Hagenbach corrections have
to be subtracted from the determined flow time. Intermediate values may be interpolated.
ln the case of absolute measurements the corrected flow time will directly result in kinematic viscosity in
(mm²/s) by multiplying the corrected flow time by the constants identified on the viscometer (determined at
23 °C).
Relative viscosity is the quotient of the viscosities of a solution and the pure solvent. It is especially of ma-
jor importance in the food industry and the evaluation of large polymers. After Staudinger detected the
contexts between the average chain length and viscosity, polymers were increasingly evaluated using vis-
cosity determlnation. ln practice, relative viscosity is used for the calculatory derivation of further parame-
ters, such as specific and inherent viscosity and the viscosity J number and the k-value.
3.12 Evaluation example
Ubbelohde viscometer type no. 532 10, calibrated for automatic measurements.
Caplllaries no. I
Constant
Flow time (averaged)
Hagenbach correction for 180.00 ∆t
Kinematic viscosity
Initial operation
ν = K (t-∆t
H
=
0.009987
=
180,00 s
=
0.30 s (→ correction - table in viscometer operating instruct-
H
ions)
ν
=
K (t-∆t
)
H
=
0.009987 • (180.00 – 0.30)
1.795 mm2/s
)
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