Untersuchungen zur - OPUS - Universität Würzburg

7 Summary
SUMMARY
In the present thesis different influences on the flow regulation of dry powders by the addition
of nanostructured m aterials were inv estigated. The test sub stances corn s tarch and D ATEM,
both representing cohesive powders, were characterized regarding particle size, agglomeration
tendencies and moisture content. Binary m ixtures of corn starch or DATEM respectiv ely and
different types of highly dispersed m aterials (AEROSIL ® , SIPERNAT ® and PRINTEX ® )
were prepared. A tensile strength tester was used to characterize flo w properties of the
powders. The optical characterization of the particles was performed by means of a scanning
electron microscope. An i mage analysis program was used to determ ine number and size of
the silica adsorbates on the surface of the corn starch.
Both test su bstances co nsist of sph erical pa rticles and their particle si ze distributions have
similar median values (corn starch: 17 µm; DATEM, batch I: 20 µm). However, the particle
size distribution of corn starch is co mparatively narrow whereas th e particle size distribution
of DATEM shows a broad dispersion of va lues. Among a large am ount of sm aller DATEM
particles there are also partic les present with diam eters up to 200 µm. In contrast to corn
starch, DATEM tends to agglomerate and therefore single particles are usually not present in
the powder. Due to the production process by means of a spray tower there are small DATEM
fragments sticking on the particles’ surface, whereas th e corn starch grains are m ainly even.
The DATEM fragm ents act as su rface roughn esses and thereby redu ce interparticle forces.
Larger particle and agglomerate diameters as well as the existence of small fragments result in
a smaller tensile strength value of DATEM (16.4 Pa) compared to corn starch (37.6 Pa).
An emphasis of this study was placed on the investigation of the influence of different mixing
conditions on the flow properties of binary powder mixtures. The powder m ixtures consisted
of native corn starch and 0.2 % of different highly disperse d flow regulators. A Turbula ®
shaker-mixer and a Som akon blade m ixer we re used for blending while the process
parameters mixing time and rotation speed were varied.
By the evaluation of scanning electron m icroscopic images it was demonstrated that a higher
rotation speed leads to a faster ads orption of the guest particles onto the hosts’ su rface. As
expected, the higher energy input of the Somakon blade mixer results in a faster comminution
and adsorption of the nanostructured materials by the host particles compared to the Turbula ®
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