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Title: The elastic relaxation during tabletting
Author: Anuar, Mohd Shamsul
ISNI:       0000 0004 2687 2309
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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The process of pharmaceutical tabletting involves the application of stress onto the powdered drug ingredients contained within a rigid die. This compaction process will cause the powder to densify and form a tablet, which is then ejected from the die cavity. In reality, the tablet will incur some elastic strains during the compaction process and the tablet dimensional changes resulted due to the elastic relaxation of the tablet in the subsequent processing stages undermine the final tablet mechanical integrity. The ejection stage, where the tablet is extruded from the die, has not been studied extensively and is an important stage where any tabletting defects are immediately visible. It is then the purpose of this Thesis to experimentally elucidate the behaviour of the tablet elastic relaxation and its influence on the tablet mechanical integrity during the ejection, the final stage of the compaction process. The Thesis starts with highlighting the existence of the tablet elastic relaxation during the ejection stage that has been successfully studied on-line by the novel use of accurate laser sensors to record the tablet dimensional changes, with particular emphasis on the interrelationship of the tablet elastic relaxation with the observed ejection force and the tabletting defects of the Paracetamol tablet. The use of a lubricated die has also been shown to reduce the tablet elastic relaxation and the tabletting defects of the Paracetamol tablets. In terms of the time-dependent nature of the elastic relaxation, subtle time-dependent elastic relaxation behaviour has been observed and eludicated for the chosen time-dependent Starch material. A brief, but detailed and comprehensive material comparison consisting Aspirin, microcrystalline cellulose (Avicel) and Paracetamol is presented in terms of the elastic relaxation during the ejection stage. The observed tablet elastic relaxation is then interrelated with the tablet strength, which is determined by an indirect tensile test (Brazilian) and a direct tensile test. Finally, the presence of a localized elastic relaxation occurring at the interface of an Avicel bilayered tablet has been shown to undermine the strength of the bilayered tablet, where the extent of the interface weaknesses is clearly dependent upon the behaviour of the localized elastic relaxation. In conclusion, the Thesis has successfully demonstrated and elucidated the tablet elastic relaxation behaviour during the ejection stage and the consequences on the final tablet mechanical integrity.
Supervisor: Luckham, Paul ; Briscoe, Brian Sponsor: Ministry of Higher Education Malaysia ; Universiti Putra Malaysia
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral