(402c) Investigation of Sub-Micron Milling Process of Poorly Water Soluble Products Using Factorial Design

The objective of this work was to investigate the mechanisms of very fine grinding in a wet ball milling set-up as a function of the product properties and process parameters. The ball mill used was a Dynomill and the grinding media consisted of zirconium oxide beads. The grinded powder was a poorly water-soluble product. The particle size distribution of the initial powder ranged from 1 to 100 um. Laser diffraction techniques were used to analyze the particle size distributions.

During grinding the average particle diameter of a particulate product is reduced to a minimum size. The grinding experiments showed that for a specific product this minimum size is a fixed constant within the range of tested operating conditions.

The grinding parameters (rotation speed of the mill, the grinding media size and pH) are being further investigated to be able to control the grinding process (grinding time and wear of the set-up) and to reach the desired particle attributes (minimizing size and degradation).

The experimental results showed that pH had a very limited effect on both the grinding process and the particle properties. The grinding time was strongly dependent on the grinding media size and on the rotation speed in a second order of importance. The grinding process becomes faster when both parameters increase. The wear of the set-up, and therefore the contamination of the final product strongly increased with the rotation speed. The same occurred to a lesser extend with an increase of grinding media size. The degradation of the product was not significant in the range of grinding parameters studied.