All calcium carbonates have inherently poor compressibility, so are not directly compressible. They cannot simply be mixed with the tablet excipient, other binders and ingredients and put in a tablet press. Even if a tablet could be formed this way, it would have poor hardness and other mechanical properties. This is a fundamental property of calcium carbonate, no matter the type. All calcium carbonates to be used in tablets must be granulated.
Proper granulation is critical to producing tablets with adequate strength for handling and shipping while also being able to disintegrate and dissolve quickly in the stomach. USP requirements for calcium carbonate tablets require disintegration within 10 minutes for an antacid, 30 minutes for a calcium supplement, and dissolution within 30 minutes for both.
Granulation involves mixing the calcium carbonate with some binder such as maltodextrin, starch or acacia gum, usually at a 5 to 10 percent binder level, and then agglomerating to a larger, easier to handle particle, much like sand. Granulations can be prepared using dry or wet techniques. A high shear, wet granulation method is commonly used for calcium carbonates.
During this process, liquid, usually water, is gradually added to the calcium carbonate powder, which begins to absorb the liquid, and form clumps or agglomerates. At first the powder/liquid mixture forms a pendular agglomerate, one where the particles in the agglomerate are held together by small amounts of liquid, and the liquid connects the particles as thin liquid rings with large air voids inside. This state tends to exist until about 25 percent of the required liquid has been added.
As more liquid is added, the funicular agglomerate state is reached, where the powder particles are covered by liquid, and there is enough liquid to form a continuous network, but one still with air voids inside. This exists while about 25 to 80 percent of the total liquid has been added. Finally the capillary stage is reached, where all the particles are fully covered by liquid, which also fills all voids between the particles. This is the granulation endpoint, where the critical pigment concentration of the mixture is reached. The agglomerate is then dried to form a free-flowing granulation that can be formed into tablets.
The particle size, particle size distribution, and particle shape, or morphology, are key properties of a calcium carbonate that have a major impact on its behavior during the granulation process, as well as on the physical properties and tableting performance of the final granulation. In developing tablet formulations containing calcium carbonate, it is important to understand how the choice of type and grade of calcium carbonate will affect final product properties and the ability to achieve desired targets.
Specialty Minerals Calcium Carbonate Granulation Study
To understand the effect of a calcium carbonate’s particle size, particle size distribution, and particle shape on the processing behavior and tableting performance, the Specialty Minerals Inc. (SMI) Healthcare Laboratory carried out a study on a range of precipitated and ground calcium carbonates in a maltodextrin granulation.
Click here to read the details of this study.
- SMI calcium carbonates for nutritional supplements and pharmaceuticals
- SMI minerals used in consumer products
- What is Precipitated Calcium Carbonate? A mineral introductory webpage
- What is Precipitated Calcium Carbonate (PCC) for Healthcare? A downloadable information sheet
- Granulation Study webpages
- Resources and useful Information for Formulators: Downloadable information sheets on bioavailability, economics of formulating with calcium carbonate, effect of particle size and shape on supplement properties, and California Proposition 65 / lead levels.
- Osteoporosis: Anyone Can Be At Risk—Even You! A downloadable information sheet
- About Specialty Minerals Inc.