PhD Research Project: Continuous Granulation: Powder caking
Powders are an important part of our day to day life, they come in various forms; milk powder, instant coffee granules and medicinal and detergent granules and tablets. There is ever increasing demand for the use of powder particles with micron size, providing very high specific surface area, in order to increase the dissolution rate (reduction in dissolution time). This is important to powder processing industries including pharmaceutical when achieving the maximum effect of the products. For pharmaceutical industry, micronized drugs (active pharmaceutical ingredients) attain higher efficacy in minimum dose. However, handling and processing of such submicron size powders is challenging. One of the greatest difficulties is the increase in the cohesiveness leading to sticking/caking during processing viz., granulation. Granulation is a process of particle size enlargement in which powder particles are agglomerated while retaining the integrity of the original particles. In pharmaceutical industry, there are two common granulation approaches, namely wet and dry granulation. The dry granulation is normally carried out using the roller compactor. In roller compaction, powder is compressed at high pressure using two counter rotating rollers to produce ribbon. The ribbons are milled to produce granules which are subsequently compressed into tablets. One of the most common issue in roller compactor is the sticking and caking of submicron, cohesive powder in the compression zone (point where powder is forced by the screws into the compression zone between the two rollers) and on the rollers. This increase the wastage of expensive powders and lowers the efficiency of the process.
Therefore, there is a need to study the mechanism involved in sticking/caking of powders in the compression zone and rollers and develop methods to minimize it. This project aims to develop the key scientific understanding of how and why the powders interact with a target substrate; stainless steel at micro-scale. It will cover particle-particle (adhesion) and particle-wall (cohesion) interactions in static state using specially built Micromanipulation Particle Tester device as well as Atomic Force Microscopy in a controlled environment (temperature and relative humidity). These techniques will allow the direct measure the effect of processing conditions on particle interactions (adhesion and cohesion) during dry granulation. The real time monitoring of change in the physical (size, shape) and mechanical (deformation/flattening kinetics) properties will also be carried out. In the second stage the powders will be granulated at varying process variables (varying speed, pressure, gap of the rollers) using roller compactor and the extent of caking will be monitored. The optimum; ‘no sticking/caking’ conditions will be deduced from the experiments. In the final stage the findings from the stage 1 and 2 will be correlated to develop mechanistic understanding of the sticking/caking of powders in solid target surface in roller compactor. This will allow to develop approaches to troubleshoot and minimise the sticking/caking during roller compaction of powders.
The DTG provides funds for studentships (fees + stipend for UK applicants, fees only for EU students) on a competitive basis. Applications are welcome up until the closing date. Overseas applicants will not qualify for DTG funding but self funded/externally funded applications are welcome
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