THE ELASTIC RELAXATION DURING TABLETTING

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

The ejection and strength of binary iron-cellulose powder compacts

In this study, the ejection stage during the densification process and the mechanical strength of green (unsintered) compact were studied for the binary powder compact of iron and micro crystalline cellulose (MCC). The mass percentage of MCC powder were varied between 0% to 60% of the total mass composition of the iron and MCC mixture. Three different compaction load of 30kN, 60 kN and 90 kN were applied during the compaction process. The tensile strength of the green compact was determined by conducting diametral compression test where the green compact was loaded until fracture. From the compaction experiment, green compact with 60% MCC and 40% iron is the least friable which leads to coherent and well compactable powder. This composition also results in the green compact with the highest tensile strength

Interfacial elastic relaxation during the ejection of bi-layered tablets

The predilection of a bi-layered tablet to fail in the interface region after its initial formation in the compaction process reduces its practicality as a choice for controlled release solid drug delivery system. Hence, a fundamental appreciation of the governing mechanism that causes the weakening of the interfacial bonds within the bi-layered tablet is crucial in order to improve the overall bi-layered tablet mechanical integrity. This work has shown that the occurrence of the elastic relaxation in the interface region during the ejection stage of the compaction process decreases with the increase in the bi-layered tablet interface strength. This is believed to be due to the increase in the plastic bonding in the interface region. The tablet diametrical elastic relaxation affects the tablet height elastic relaxation, where the impediment of the tablet height expansion is observed when the interface region experiences a diametrical expansion

Characteristics of tableted roselle (Hibiscus sabdariffa Linn.) with addition of sodium starch glycolate

The focus of this research is to study the characteristics of tablets produced from the binary powder mixture of Roselle (Hibiscus sabdariffa Linn.) and sodium starch glycolate (SSG) powders. The experimental parameters studied were the compaction pressure and the mass composition. The findings indicated that the increase of compaction pressure increased the tensile strength of tablets until a limiting value was reached. On the other hand, as the compaction pressure increased, the porosity of tablets decreased to a minimum value. The elastic recovery of tablets slightly decreased in some results. The increase in compaction pressure also increased the dissolution time of tablets up to a maximum value. The increase of SSG composition decreased the tensile strength of tablets to a certain amount. The dissolution time of tablets also reduced when the percentage of SSG increased. Subsequently, under the same compaction conditions, the increase of SSG composition increased the porosity and the elastic recovery of tablets until the limiting values were achieved

Physical properties of Liberica coffee (Coffea liberica) berries and beans

Liberica coffee is the most important coffee species grown in Malaysia. However, there is little or no research at all conducted on coffee berries and green coffee beans since the plant itself is a low income crop in Malaysia. Therefore, research on Malaysian Liberica coffee can help to increase the knowledge of coffee farmers and coffee manufacturers in the processing and handling of the coffee. Physical properties of Liberica coffee berries and beans were investigated the current study. The properties investigated include the size, mass, density, coefficient of friction, angle of repose, fracture force and colour. In comparison to Arabica and Robusta coffee, Liberica coffee has the biggest size, mass, true density and fracture force values but were lower in bulk density in both berries and beans. The Liberica berries and beans were found to be orange-ish and yellowish colour respectively. Angle of repose was low and approximately similar in berries and beans while jute fibre gave the highest friction to both Liberica berries and beans

Drying, colour and sensory characteristics of ‘Berangan’ banana (Musa accuminata) flesh dried using a microwave oven

The drying characteristics of ‘Berangan’ banana flesh dried under microwave heating were studied in this work. The produced microwave banana chip was then compared with the conventional deep oil fried banana chip in terms of colour and sensory characteristics.‘Berangan’ banana slices with 3 mm thickness were dried using microwave at three power levels of 100, 440 and 1000 W. Shorter drying times were obtained when higher microwave power was applied during drying, where the drying times were found to be 30, 7, 4 min at 100, 440 and 100W. Three different drying models were used to describe the resulting drying curves. The drying rate constant increased from 0.298, 0.4211 and 0.2977 min-1 to 1.8717, 1.9956 and 1.8936 min-1 for the Newton, Page and Henderson and Pabis models when the microwave power used was increased from 100W to 1000W. The best model to represent the drying data obtained in this work was found to be the Page model. In terms of colour, fried banana had a browner, duller colour than microwave dried banana. For sensory evaluation, dried banana chips using microwave at a power level of 440W was the most preferable. It can be concluded microwave dried banana chips showed better results than fried banana chips in terms of colour and sensory characteristics in the range tested in this study

Effect on the physico-chemical properties of liberica green coffee beans under ambient storage

Green coffee beans are stored for a certain period and under certain conditions until they are finally utilized. The storage period may depend on customer demand while the storage conditions depend on where the coffee beans are stored. Thus, this research emphasizes the physico-chemical changes that occur in Liberica coffee beans during storage under the Malaysian climate (average temperature and relative humidity of 29.33ºC and 71.75% respectively). The changes in the physico-chemical (coffee size, mass, densities, colour, proximate analysis, sucrose, chlorogenic acid content) and microbiological (yeast and mould count) properties were evaluated during eight months of storage. After the storage, the physical properties of the coffee changed as the coffee beans expanded in size, reduced in mass and density and became brighter in colour. Changes in the chemical properties were also detected where the moisture decreased and the ash content increased. In addition, the sucrose level was found to decrease with a corresponding increase in chlorogenic acid. During storage, the counts of yeast and mould were reduced. Model equations describing the changes in the properties were developed. The overall conclusion was that the coffee beans reduced in quality during storage

Effect of drying methods on phenolic contents of neem (Azadirachta indica) leaf powder

The medicinal quality of plant parts is affected due to the thermal decomposition of the active ingredients during the drying process. Additional processing such as grinding will also influence the composition and extraction of active ingredients. Neem (Azadirachta indica) leaves dried under shade, oven-dried at 45°C and at 70°C varied in final moisture content, color, and crispness and in their phenolic contents. Grinding depended upon the crispness of the dried leaves, where finer particle sizes were obtained from crisper leaves. The phenolics contents were higher in powder obtained from shade-dried leaves compared to the oven-dried leaves at 45°C or at 70°C. There was no difference in total phenolics in extracts from finer-sized (250 μm) particles in the case of oven-dried leaves at 45°C. However, the extracts from finer particle sizes (250 μm) from oven-dried leaves at 70°C and shade-dried leaves respectively

Deformation and Mechanical Characteristics of Compacted Binary Mixtures of Plastic (Microcrystalline Cellulose), Elastic (Sodium Starch Glycolate), and Brittle (Lactose Monohydrate) Pharmaceutical Excipients.

This work studies the tensile strength, coherence, elastic, and plastic energy of single and bi-component compacted tablets consisting of (i) microcrystalline cellulose (MCC) PH 102 as a plastic material, (ii) (SSG) as an elastic material, and (iii) alpha lactose monohydrate as a brittle material by direct compression. Compacted tablets were studied with various mass ratios formed at an ultimate compaction stress of 150 MPa. The loading and unloading stages of the compaction process for the single and binary tablets were evaluated based on the energies derived from the force-displacement data obtained. The resulting tablet quality was measured in terms of the tensile strength. Material that exhibit predominantly plastic deformation (MCC) shows a dominant property over elastically deforming sodium starch glycolate (SSG) and brittle (lactose) materials during the loading and unloading stages of the compaction process. In conclusion, the tensile strength of the formed tablets depends directly on the plastic energy and indirectly on the elastic energy and is negatively affected by the presence of a brittle material

Effect of raw material variation, process variables and device stability on drying process of rambutan (Nephelium lappaceum L.) seed

This study was conducted to determine the influence of raw material variation, equipment process variables and device stability on the drying process of rambutan seed using oven and microwave drying equipments. The raw material variations studied were skin colour (yellow and fully red), storage period (fresh and stored) and seed mass (5 and 10 g). The important equipment process variables studied were oven temperature (40 and 60°C) and microwave power (250 and 1000 W).The output power and drying distribution in the drying chamber were studied to examine the device stability. Results indicated that the seed mass, oven temperature and microwave power influenced the drying time. The skin colour and storage period were negatively correlated with drying time due to drying time speculate to relay on time required for moisture removal that associated to initial moisture content and seed mass. It is also observed that the drying time will be shorten if the sample was located at the central of the microwave drying chamber. In contrast, the oven exhibited higher stability compared to microwave due to its ability to provide similar level of heating at each location in the drying chamber. This information will aid researchers and industrial operators to design an effective drying process using microwave and oven thus reducing cost and time