Untersuchungen zur - OPUS - Universität Würzburg

SUMMARY
hydrophobicity and surface roughness gives rise to a flow regulation. C ompared to m ixtures
with hydrophilic materials the loss of flowability occurs delayed and is not as marked.
Tensile s trength m easurements of powders with dif ferent concentr ations of f low additiv es
also confirmed that a re-increase of tensile strength after longer mixing times is not caused by
an excessive coverage of the host particles’ surface. Concentrations of the flow aid of 0.1 or
0.2 % respectively are not sufficient to cover the host’s surface completely (cf. appendix. 8.2).
However, the lower the concentration of the fl ow aid is, the sooner a re-increase in tensile
strength occurs.
These results are also relevant in p ractice for the application of a “prem ix”. When preparing
those m ixtures it has to be considered that the agglom erates of the guest particles do not
become too sm all due to too long and intense m ixing since it is not possible to “reactivate”
their flow regulating effect by the addition of extra host partic les. A higher concentration of
the flow aid however d oes not have a negative effect. The tim e slot u ntil a re-increase of
tensile strength occurs can rather be extended.
Another emphasis of this study was placed on the investigation of the flow regulation of a
“soft” powder choosing the food emulsifier DA TEM as a test substance. W hen preparing
binary mixtures the adsorption of guest partic les by the DATEM host part icles is quite fast
compared to the soft powder Hoechst Wachs C Micropulver ® tested by Müller [81]. The high
adsorption rate of guest particles results in an immediate improvement in the flow properties
of DATEM. In spite of apparen tly soft material properties th e DATEM particle s are able to
act like b alls in a ball m ill and provide suf ficient ener gy in orde r to split u p large r
agglomerates of the host particles just like the corn starch grains.
All tested nanostructured substances get ad sorbed onto the host particles’ surface and
herewith significantly reduce the tensile strength of DATEM. However, the rating of the flow
regulating potential is q uite different from the results obtained with th e test substance corn
starch. While in binary mixtures with corn starch hydrophobic silicas always showed superior
effectiveness and efficiency com pared to hydr ophilic nanostructured m aterials for m ixtures
with DATEM this was not the cas e. The coarse ly structured silica SIPERNAT ® 350 which
turned out to be a rather poor gl idant in binary mixtures with corn starch causes the strongest
drop in tensile strength of DATEM. This is due to the wide particle distribution of DATEM
and the presence of larger particles which re quire larger surface roughnesses to achieve
minimum interparticle forces.
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