Correlating Die-Filling Performance with Powder Properties - Pharmaceutical Technology

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Correlating Die-Filling Performance with Powder Properties
The author explains how to gain an understanding of the relationships between powder characteristics and process performance to match filling-machine geometry to the demands of specific formulations.


Pharmaceutical Technology
Volume 35, pp. s24-s28

Correlating process performance with powder properties


Figure 2: Correlations between filling-performance Cpk in configuration A and various powder properties.
Figures 2 and 3 show correlations between filling performance and four powder properties for configurations A and B. Data are shown for all four formulations for configuration A, and for S1, S2, and S4 for configuration B. S3 was not intended to be processed on configuration B during production, and data for this combination are therefore unavailable.


Figure 3: Correlations between filling performance Cpk in configuration B and various powder properties.
The results indicated that for configuration A, less cohesive materials were more compatible than cohesive materials. High basic flowability energy, aeration ratio, and flow function, along with low cohesion, were correlated to improved processing performance. All of these features indicated low cohesiveness. The findings suggested that for this configuration, the powder's ability to flow freely into the feed channel and pocket determined process performance. The small feed diameter of the configuration made this design more susceptible to the powder arching and to the discontinuous flow that can occur with cohesive materials, which could have a dramatic effect on processing performance.

The results for configuration B showed different behavior. For this configuration, cohesive formulations (i.e., those with low basic flowability energy, aeration ratio, and flow function) performed better. This suggested that with the wider feed channel, the ability of the powder to flow freely under gravity was less important. Further research would be required to fully understand the mechanisms that gave rise to the observed behavior, but it is worth reiterating that the filling process involves more than simply filling the pocket. Successful transfer of the extracted volume as the wheel rotates is also essential. The wide feed channel may have encouraged successful pocket filling for all formulations, regardless of cohesiveness, but as the wheel rotates, less cohesive materials may have been lost more easily, thus compromising dose weight. The types of powders that were optimal for configuration A clearly were suboptimal for configuration B, and vice versa.

Conclusion

To succeed in matching filling-machine geometry to the demands of a specific formulation, it is critical to gain a good understanding of the relationships between powder characteristics and process performance. The results presented in this article suggest that the optimal powder property set depends on machine geometry. Although free-flowing formulations are preferable for certain geometries, as might be expected, cohesive formulations perform better for other geometries.

The data indicated that certain types of geometry were better suited to cohesive materials, thus highlighting the importance of studies such as these for personnel who develop filling solutions. Equally important, the data suggested that new, free-flowing formulations will not necessarily perform better on an existing unit than previous products. Appropriate powder testing holds the key to achieving a compatible powder–geometry match that delivers efficient operation over the long term.

Tim Freeman is director of operations at Freeman Technology, Boulters Farm Centre, Castlemorton Common, Welland, Worcestershire, WR13 6LE, UK, tel. +44 0 1684 310860, fax +44 0 1684 310236,
.

References

1. S. Kotz and N.L. Johnson, Process Capability Indices (Chapman and Hall, London, 1993).

2. R. Freeman, Powder Technol. 174 (1–2), 25–33, (2007).


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