Untersuchungen zur - OPUS - Universität Würzburg

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SUMMARY
At a further increase in blending tim e the flow properties of the binary m ixtures becom e
worse as already observed for mixtures with corn starch. The mixtures with SIPERNAT ® 350
again show different flow beha viour. Even after several ho urs of m ixing there was no reincrease
in tensile strength observed.
By the evaluation of scanning electron m icroscopic im ages of DATEM particles it was
demonstrated that the loss of the flow regulating properties is due to a change of the profile of
the guest particles which becom e too sm all and too flat to act as g lidants. Mixtures with
SIPERNAT ® 350 however maintain larger silica adsorbates on the host particles’ surface even
after longer mixing times which results in unchanged low tensile strength values.
Special attention was p aid to the q uestion if guest particles becom e embedded in the surface
of the soft DATEM particles during m ixing. By means of transm ission electron microscopic
images of a cross section of DATEM particle s th is hypo thesis was d isproved. It becam e
obvious that the silica coating beco mes m ore co mpact in the course of m ixing but is no t
pressed into the surface of the host particles. Larger hos t particles m ight accelerate the
flattening of the adsorba tes which re sults in a f aster re-increase in tens ile strength compared
to corn starch.
The results of this thesis demonstrate that the properties of a certain powder always have to be
taken into account when choosing a suitable g lidant because the ratin g of the potential of
different flow aids depends on the respective po wder. Especially the particle distribution and
hardness have to be considered. A comparison with already tested substances might be a point
of reference. W hen blending di fferent powder com ponents special attention needs to be paid
to the energy input of t he available m ixing apparatus. High shear m ixers can accelerate the
required blending tim e to devel op the flow regulating properties of a glidant. However, one
has to be careful not to exceed mixing time until a loss of flowability occurs.