The first step to prepare starch for extrusion was to modify
starch by glycerin. For this purpose Intensive Mixer manufactured
by Maschinenfabrik Gustav Eirich (Germany) was used (Fig. 1).
In the Eirich intensive mixers 90% of the energy is used for mixing
the mass in the range of the high-speed agitator, which rotates
in the opposite direction to the direction in which the mixer pan
rotates. The movement of the material in the device also runs at
the level parallel to the axis of the rotor. Components of any consistence
can be mixed in the device.
The intensive mixer enables to realize the mixture homogenization
and granulation process during one technological operation.
Such a granulation procedure is an innovative method for preparation
of powders for further processing.
The way in which the material moves in the mixer and the mixer’s
construction enable homogenous distribution of the additives
in the whole volume of the mixed material. Granulation in the
intensive mixer is a process which gives the mass the form of dense
and stable granules, as the result, a dense and at the same time
granulated material with required shape and size and good stability
parameters is obtained. The homogeneity degree of the mixture
decides about the level of quality and influences the repeatability
and the properties of the respective material batches. Homogeneity
is of a particular significance in case when small amounts of the
introduced additives (i.e. binding substances – in this case glycerine)
are used, which have to be homogenously distributed in the
total material volume in order to efficiently influence the composition
properties. High mixing degree also means higher stability of
the granulates at a given content of the binder. Granulation in the
intensive mixer enables to control the grain size distribution,
ensures their high density and gives the granulate surface
properties which are beneficial for the rheological properties.