3. Electronic Theses and Dissertations (ETDs) - All submissions
Permanent URI for this communityhttps://wiredspace.wits.ac.za/handle/10539/45
Browse
1 results
Search Results
Item Determination of the effect of different blade speeds and mixing times on the homogeneity of mixtures containing different ratios of two powders(2015-04-16) Van Wyk, ElzaanAim The first step in a wet granulation process is dry mixing. This step has the objective of ensuring that all the raw materials are mixed such that the end product is homogeneous. Dry mixing in a high shear mixer instead of a blender saves cost. However, the mixing parameters have not been well researched. Dry mixing parameters that are currently used, have been established through experience, trial and error and in-process testing. Alexander and Muzzio (2006) confirms this by stating that there are currently no mathematical techniques to predict blending behaviour of granular components without prior experimental work; therefore, blending studies start with a small-scale, try-itand- see approach. Even though they are referring to blending, the same is also true for dry mixing. Both processes are the mixing of powders. Therefore the aim of this research was to develop parameters for dry mixing, based on experimental work. Methods Using a Saral rapid mixer and wet granulator (Saral Engineering Company, India), experiments were performed according to a 24 two-level Plackett-Burman Design method, to determine the effects of different blades (mixer/impeller and chopper) speeds and mixing times on the homogeneity of the mixtures containing different ratios of two powders that have different densities and particle sizes. One of the powders mixed, was enalapril maleate. This was chosen as it can be assayed. Samples were taken from the bowl and tested for assay. The mix for a specific experiment is homogeneous if the results of all 7 assayed samples are within 10 % of the target % w/w value and the % Relative Standard Deviation (% RSD) of the 7 results is less than or equal to 5,0 %. The outcome was being measured in % RSD. A lower % RSD indicates a more homogeneous mix. The parameters developed, will be beneficial to pharmaceutical companies as it can assist them to improve accuracy, consistency and quality of granular mixes. The experimental method used can serve as an example for future experiments. Results The results indicated that impeller blade mixing speed and mixing time are the two factors that have the biggest impact on the homogeneity of a mix in a high shear mixer. Chopper blade speed was also found to be significant, but less than the above two parameters mentioned. Optimal parameters were predicted. Conclusion As there are many parameters to be controlled during dry mixing in a high shear mixer, a statistical design method is suitable to establish the parameters that would have the most impact on the end result. Statistically it was found that mixing speed of the main impeller and chopper blades and overall mixing time are the three factors that have the biggest impact on the homogeneity of a mixture. The mixing time and impeller blade speed have proven to be more significant than the chopper blade speed. Concentration was found to be insignificant. For our experiments and for the specific granulator used the following optimal parameters could be deduced: Impeller blade set at 191 rpm, chopper blade set at 2002 rpm and mixing time set at 3.01 minutes.