THE ELASTIC RELAXATION DURING TABLETTING
Author(s)
Anuar, Mohd Shamsul
Type
Thesis
Abstract
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.
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.
Date Issued
2009-06
Date Awarded
2009-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
License URL
Advisor
Luckham, Paul
Briscoe, Brian
Sponsor
Ministry of Higher Education Malaysia, Universiti Putra Malaysia
Creator
Anuar, Mohd Shamsul
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)