| Summary: | 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.
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