Particle size-based segregation of pharmaceutical powders in a vertical chute with a closed bottom: An experimental evaluation

• Large particles are accumulated at the bottom and small at the top of the sediment.
• Local accumulation threshold size limit was established as 0.46 of D(0.9) value.
• Segregation was most pronounced at the beginning and end of material flow.
• Visualization of flow structures facilitated explanation of segregation.
• Chute flow induced segregation was correlated with certain powder bulk properties.

Vertical chute transport is a common and widespread means of transporting powders and powder blends in the pharmaceutical industry; conversely, it is also a ready source of segregation. All components of powder mixtures (i.e., active pharmaceutical ingredients, as well as excipients) are subjected to particle size-based segregation, and therefore all properties of the final product, which depend on the particle size of its constituents, may be affected (e.g., compressibility, dissolution rate, API content, and content uniformity). Segregation of single-component pharmaceutical powders with continuous size distributions (excipients or model API) based on particle size was experimentally investigated. Single-component pharmaceutical powders were subjected to fall in a laboratory-scale vertical chute with a closed bottom, and powder samples from various powder bed heights were collected and analysed for particle-size distributions. The results show particle size-based segregation in all materials tested, and the segregation extent and pattern are material-specific. Certain segregation effects were explained with the flow patterns of falling powder and powder bulk properties. An interesting finding is that less cohesive materials with better flowability exhibit increased segregation of smaller sized-D(0.1) particles, which has been attributed to the vertical chute system with a closed, airtight bottom. The size limit, below which particles concentrate at the top of the sediment, and above which particles concentrate at the bottom of the sediment, seems to be universal at 0.46 of D(0.9) value for tested materials.

Gravity driven flow of granular material in vertical chutes (pipes) is commonly used for bulk powder transport and is a known source of segregation. Particle size-based segregation of single-component pharmaceutical powders was measured; segregation was linked to powder flow and potential impact on final dosage form performance was discussed.Figure optionsDownload as PowerPoint slide