Abstract
The shear rate in thin liquid film flow on a rotating disk is governed by the flow rate of the polymer solution and the rotation rate of the disk. Despite this fact we show that shear degradation is determined solely by the rotation rate, whereas a variation of the flow rate has no distinct effect. Also no significant influence of the polymer concentration in a range of 1–10 mg/ml could be observed. Threshold values of the rotation rate that cause shear degradation in different samples of dextran and purified polysaccharides of Viscum album L. berries are reported and changes in the molecular weight distributions of these samples are shown. Some of the polymers are presumably deformed in their geometrical shape under the influence of shearing. In gel permeation chromatography these polymers are eluted after polymers with lower masses, so that most probably the hydrodynamic radii of the deformed polymer particles are smaller while their molar masses are larger. A mathematical analysis of the light scattering data gives evidence to this assumption. Degradation rates of the dextran samples are compared with results of a previous study.
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