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Browsing by Subject "plastic deformation"

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  • Koskela, Jaana (2015)
    Mechanofusion is a dry coating method in which the high shear forces cause a mechanochemical reaction between the processed particles. With the approach it is possible to improve flowability of a host cohesive powder when the guest particle forming the coating is magnesium stearate. Applying mechanofusion in tablet formulations could make poor flowing large dose drug substances suitable for direct compression. However, it is well known that magnesium stearate decreases mechanical strength of the tablets and prolongs disintegration and dissolution time of tablets. A previous study, however, showed that it is possible to compress tablets from a formulation dry coated with magnesium stearate without reducing the dissolution rate. Dry coating with magnesium stearate and its effect on a plastic material, known to be sensitive for the negative effects of magnesium stearate, has not been studied previously. The aim of the study was to examine the effect of mechanical dry coating with magnesium stearate on the physical qualities and compression behaviour of a plastic material. The effect was studied by dry coating four grades of microcrystalline cellulose with different magnesium stearatecon centrations. The approach was to find an optimum between the flowability and compressibility of the powders by using different process parameters. Microcrystalline cellulose with median particle size of 23 and 78 µm were also mechanofused without magnesium stearate in order to examine whether mechanofusion itself has an effect on the properties of microcrystalline cellulose. Pure raw materials and Turbula-mixed magnesium stearate and microcrystalline cellulose blends were studied as references. Dry coating with magnesium stearate improved the flow properties of microcrystalline cellulose with D50 value less than 78 µm. Powders with D50 value greater than 144 µm, however, break down under the shear during the process and hence their flow properties were decreased. This suggests, that mechanofusion as a process is more suitable for the small particle size microcrystalline cellulose powders which, based on the results, can withstand the high-shear forces better. Mechanofusion of plain microcrystalline cellulose (D50 78 µm) revealed that the moisture content of the powder increased and stronger tablets could be compressed. Mechanofusion may cause changes to the microstructure of microcrystalline cellulose particles and to its ability to adsorb moisture. Dry coating with magnesium stearate was very effective even with short processing times and relatively low blade speeds, and it was challenging to compress hard tablets from the mechanofused mixtures. Plastic material was found to be sensitive for the negative effects of magnesium stearate, and better flow properties of a mechanofused powder resulted in weaker compressed tablets.
  • Ikonen, Jasmina (2016)
    In tablet compression the objective is to obtain a durable tablet. The main deformation mechanism of substance affects how good tablet is obtained. The pharmaceutical powders is often divided into two categories with respect to their principal deformation mechanism: plastic and fragmented. Good tablet formulation requires its components to deform with both of these mechanisms. It is possible to examine in many ways, whether material is plastic or fragmented. These include force-time graphs and indentation methods, as well as different compression equations such Heckel equation. Examination and identification of the deformation mechanisms is important in order to design a formulation which provides the most durable tablet. The aim of experimental work in this study was to test the new compression device and method, and to compare the results of the device shown in the earlier literature results. Comparison with previous research, new in this study was compression rate and without a motor acting compaction system. In this study, there was two compression method developed, dynamic and static. Data from a dynamic method were analysed by time-travel - and force-displacement -curves. Results were parameterized, and on the basis of these parameters the behaviour of various materials was evaluated and compared to the earlier literature. Relaxation study was also performed in this research. The results of these measurements were analysed with the parameterized function fit, after which the results were compared with earlier results presented in the literature. The results of this work in dynamic measurements are cosistent with the research results received earlier. In terms of almost all parameters investigated, substances were divided into two groups in the same way as in the previous literature on the basis of the main deformation mechanism. The results obtained in static measurements, however, were quite inconsistent with previous research. Based on the results it can be stated that the method makes it possible to get consistent results with the literature. However, the method still requires development, and possible error sources and the choice of analytical method should pay special attention.