Issue link: https://www.e-digitaleditions.com/i/648486
Tablets & Capsules March 2016 27 T powder characterization Tracking bulk density to maximize tablet production Vinnie Hebert Brookfield Ametek Maintaining the correct bulk density is critical to manufactur- ing on-spec tablets. This article outlines the benefits of shear cell testing to measure the bulk density of powders and granulations. o a layperson, manufacturing tablets must look simple. A powder flows into dies, gets compressed between two punches, and out pops a tablet. The process is more com- plex than that, of course, and a good deal of that complex- ity stems from the fickle nature of powders. Even small changes in their properties can affect how they behave on a tablet press. That's why it's important to measure the char- acteristics of powders and granulations during production. Once you see a change, you can adjust the powder and/or the process to maximize uptime and maintain yield. Whether your tablets are pharmaceuticals, dietary sup- plements, or something else, the process to make them doesn't differ much. Nor does the goal: Produce high- quality products at high rates. After all, maximum produc- tion at maximum speed equals maximum profit. Yet each product's starting powder has unique characteristics, includ- ing flow properties, so they all need to undergo accurate, quick, and repeatable flow tests during production. This article explores the flow problems associated with tablet making and how to conduct precise QA/QC tests that ensure maximum production while maintaining on- spec tablet weight and hardness. One test method, shear cell testing, can reveal your powder's flow metrics and sup- port all facets of the tablet making process. The tabletting process Most readers need no explanation of the tabletting process, but if you're new to tablet making, it's important to understand this fact about it: The tablets you make must remain within the specified weight range, but the press itself operates without reference to weight. Instead, it depends on being fed a powder of consistent and uniform bulk density to fill the fixed volume of its dies. That's how—presuming the press is set up correctly—the tablets meet the weight specification. In practice, however, things change and we must adjust for those changes to ensure we get a good product. Plus, because tablet presses can make hundreds of thousands of tablets per hour, just one misstep can lead to the production of a lot of inferior tablets in a very short time. Factor in the high value of today's active pharmaceutical ingredients (APIs)—perhaps millions of dollars per kilogram—and it becomes obvious that it's worth your time to prevent poor flow, changes in bulk density, segregation, or a jammed feeding system from upsetting production. What's in a tablet In addition to the API, tablets comprise a variety of excipients, including binders, disintegrants, flavorings, gli- dants, and lubricants. Ideally, we would blend these ingredi- ents, send them to the press, and make good tablets. In real- ity, each ingredient can differ in particle size, size distribution, shape, density, and many other ways. Those differences can cause segregation, creating a nonuniform, poorly flowing powder. To avoid that problem, powder blends often undergo a wet or dry granulation process that increases homogeneity. Wet granulation is the traditional and perhaps most pop- ular method. It is extremely reliable and improves not only the flow but the compaction properties of powders. Typically, it entails combining the dry powder blend with a liquid binder inside a high-shear mixer. The material is then dried and milled to create particles of uniform size, density, and composition. With dry granulation, the API-excipient