Experimental Study of the Segregation Tendency of Minor Ingredients in the Formulated Bulk Particulate Products

Segregation, the separation of particles during handling, transportation and storage
of powders, is a phenomenon that nearly all industrial sectors dealing with powders
encounter. A good example is detergent industry where segregation of the
formulated powder mixtures and in particular the minor components such as enzyme
granules could have significant economic as well as health and safety impacts. Most
industrial processes aim to achieve a homogenous mixture as the inhomogeneities
caused by segregation could contribute to significant effects on the economics of
production.
In this research, a broad literature review on segregation of powders was carried out
to understand the main segregation mechanisms and popular measurement techniques
for the segregation evaluation. The literature review revealed that despite
considerable reported research on particle segregation, there is a lack of in-depth
work on the evaluation of segregation mechanisms and minimization of minor
ingredients (less than 2 wt %), particularly in multicomponent powder mixtures
during processes such as heap formation and vibration. In addition, robust
measurement methods for quantifying the segregation of such ingredients must be
investigated.
The aim of this research project is to investigate the segregation of the main
constituents of laundry detergent powders (Blown Powder (BP),
Tetraacetylethylenediamine (TAED) and enzyme granules). Specific attention is
given to the segregation analysis of the minor ingredient enzyme granules as it is
highly prone to segregate during heap formation and vibration. For the evaluation of
the segregation propensity of minor ingredient, image processing technique is simple
but it lacks the assessment of segregation in the mixture of powders with similar
particle colours. On the other hand, differentiation of particles with similar colour
could be achieved using spectroscopic techniques. In this work, two interesting areas
of research are investigated: firstly, reliable measurement of the component fractions
particularly for low level ingredients using both image processing and Near-Infrared
spectroscopy technique is explored and secondly, segregation reduction approaches (by particle surface coating and modification) for the low-content level ingredient in
the mixture of laundry detergent powders are examined.
The results have demonstrated that powder segregation analysis of the components
can be successfully achieved using the proposed Near-Infrared spectroscopy
instrument. In addition, different spectral pre-processing (to remove the effect of
varying physical properties of the components) have been compared and the optimum
spectral treatment technique is introduced for the accurate quantification of minor
ingredient.
Study of the segregation of powder mixture during heap formation and vibration
(representing the conditions encountered during box filling and transportation) has
shown that enzyme granules are prone to extensive segregation towards the centre of
the heap due to their higher density and the push-away effect as compared to other
components. Segregation of enzyme granules in the ternary powder mixtures was
shown to be reduced noticeably by applying a thin layer of a sticky liquid on the
granules, due to the interlocking effect arising from the surface coverage of enzyme
granules by fine particles. Optimum coating level has been found for this purpose to
reduce the segregation of enzyme granules without compromising the flowability of
the materials. Segregation of enzyme granules is further evaluated by modifying their
surface properties to analyse its effects on density driven segregation. Granulation
technique has been used for modifying the structural properties of enzyme granules.
It is shown that surface modification of dense enzyme granules could hinder the
push-away effect.