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Title: Roller compaction : effect of morphology and amorphous content of different types of lactose
Author: Omar, Chalak S.
ISNI:       0000 0004 5991 6865
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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Roller compaction is a dry granulation process in which high stresses are applied on the powder using two counter-rotating rollers to produce compacts which can then be milled into granules. Roller compaction is a complex process and very sensitive to the primary powder properties. The process is not fully understood due to the diversity of materials properties which could be different even for similar materials. For example, particles of lactose (an important material in food and pharmaceutical industries) can be found in different morphologies as well as different amorphous contents. This thesis aims to understand the behaviour of various types of lactose (with different morphologies and amorphous contents) during roller compaction at different humidity conditions and process parameters, and attempts to improve the quality of ribbons using various approaches. Three types of lactose powders were used: anhydrous SuperTab21AN, spray dried SuperTab11SD which are agglomerated forms of lactose, and a-lactose monohydrate 200M which is non-agglomerated. The morphology of the particle was found to have a significant effect on single particle strength. The strength of a single particle of the nonagglomerated type of lactose (200M) was higher in comparison with the agglomerated types (21AN and SD). The lowest strength was shown by particles of spray dried (SD) lactose due to its agglomerated structure. During the roller compaction experiments, an online thermal camera was used to record the temperature of ribbon which was considered as a key factor to describe the behaviour of powder undergoing roller compaction. It was found that the morphology and amorphous content of the powder have a significant effect on the ribbon properties. The agglomerated type of lactose (21AN and SD) showed better binding capacity compare to the non-agglomerated type (200M). The best binding capacity was shown by the agglomerated types of lactose which contain the highest percentage of the amorphous form. It was found that there is a relationship between the tensile strength of the produced ribbon and the strength of a single particle of the starting powder. The stronger the primary particle of the initial powder the weaker the ribbon after roller compaction. It was also found that there is a relationship between the surface temperature of the ribbon during production and its resultant tensile strength: the higher the temperature of the ribbon during production the higher the ribbon tensile strength. This means that the temperature of the ribbon may be used to predict the tensile strength of the produced ribbon, regardless of the type of lactose. The changes in the relative humidity (RH) conditions during powder storage were shown to have a significant effect on powder and ribbon properties. It was found that powders conditioned at different RH values exhibited different behaviours in the compaction zone which was evident by the PIV (Particle Image Velocimetry) experiments. The optimum storage conditions for all three types of lactose were found to be in the range of 20% - 40% RH. Within this range, wider ribbons with a minimum amount of fines were produced. The online thermal imaging was found to be a useful technique to describe the difference in ribbon properties at different process parameters. The process parameter of the roller compactor (roller speed, roller gap and the feeder screw speed) was shown to have a significant effect on the ribbon properties. The results showed that ribbons with homogeneous properties (e.g. porosity and strength) along the width can be obtained using a new roller with a novel curved design. The curved roller was able to apply a more uniform stress on the powder along the width of the roller surface and resulted in a significant reduction in the percentage of fines in the product. This approach can be used in different industries to overcome the non-uniformity of ribbon properties across the width and reduce the undesirably large amount of fines which have a negative impact on the final product.
Supervisor: Salman, Agba D. ; Hounslow, Michael J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available