TABLETING
PREVENTING
Robert Sedlock describes the cause of tablet capping during production and reveals how to prevent it from occurring
TABLET CAPPING
T
he term “capping” in tablet manufacturing refers to a break across the horizontal plane that is found when performing a breaking
force or friability test. Many factors can contribute to capping, including a formulation’s blend characteristics, the material’s deformation properties, and the mechanical confi guration of the tablet press/tooling. Pharmaceutical manufacturers commonly discover capping during manufacturing. It’s preferable to identify problems in the developmental stage, because changing formulation after a product has moved to full-scale manufacturing can be challenging.
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BLEND CHARACTERISTICS Formulators can identify a potential
capping problem by characterising a formulation’s permeability, which is a fundamental property aff ecting the tableting process. Entrapped air in a powder blend can reduce interparticle bonding and the tablet’s fi nal tensile strength, both of which can lead to tablet failures like capping. If a formulation’s permeability is high, less air entrapment will occur, resulting in fewer tablet defects. Permeability tests can be conducted using a lab-scale powder rheometer, which measures the powder’s resistance to airfl ow. Using a vented piston under a range of applied normal stresses, air is passed
through the powder bed. T e relative diff erence in the air pressure between the bottom and top of the powder column represents the powder’s permeability.
DEFORMATION PROPERTIES A compaction simulator or emulator is a single-punch tablet press that measures applied forces and punch displacement data under conditions similar to that of a production-scale rotary tablet press. T e simulator allows an analysis of the force displacement curves (work curves) that show the formulation’s elastic recovery after an applied load is released. T ese tools allow users to select the appropriate excipients to develop a robust formulation
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