Compactibility - Analyses of powders

| Home | | Pharmaceutical Drugs and Dosage | | Pharmaceutical Industrial Management |

Chapter: Pharmaceutical Drugs and Dosage: Powders and granules

In the manufacture of the most common pharmaceutical dosage forms, tablets, and capsules, powders and granules are compacted into solid masses of a given dosage unit.


Compactibility - Analyses of powders

In the manufacture of the most common pharmaceutical dosage forms, tablets, and capsules, powders and granules are compacted into solid masses of a given dosage unit. This process of compaction involves application of pressure on a fixed quantity of the powder within a die using stainless steel punches. The ability of a powder to form a compact on application of pressure is important for the ability to manufacture tablets.


Compressibility, compactibility, and tabletability

As illustrated in Figure 19.2, the ability of a powder to form a compact on application of pressure can be defined in terms of three parameters:

·           Compressibility is defined as the ability of material to reduce in vol-ume under applied pressure and can be measured by plotting tab-let porosity as a function of compression pressure. Tablet porosity is measured by the solid fraction of the compact.

·           Compactibility represents the ability of material to produce tablets with sufficient strength under the effect of densification. Compactability can be measured by plotting the mechanical strength of the compact (tensile strength) as a function of its porosity.

·           Tabletability is the ability of powder material to be transformed into tablets of a specified strength under compaction pressure. Tabletability is measured by plotting the mechanical strength of the compact (tensile strength) as a function of the compaction pressure used.


Figure 19.2 An illustration of the interrelationship between the concepts of compactibility, compressibility, and tabletability.


Importance of compactibility

The ability of a powder blend to form a strong and physically stable com-pact depends on its interparticle adhesion characteristics, and the balance of plastic deformation and elastic recovery under mechanical stress. Plastic deformation refers to the ability of a powder blend to permanently deform under pressure. Elastic recovery, on the other hand, represents the percent expansion of the compact from its most consolidated state under pressure.

Under compressive stress, powder particles may maintain their size but only deform in shape (plastic deformation, e.g., microcrystalline cellulose) or may break into several smaller particles (brittle fracture, e.g., dibasic calcium phosphate). Such material behavior can affect bonding between dif-ferent components of the powder and affect adhesion of the powder blend. For example, lubricated powder particles—where the surface has been coated with hydrophobic magnesium stearate—show better interparticle bonding for materials that exhibit brittle fracture due to particle breakage and exposure of new uncoated surfaces upon compression compared to the materials that undergo plastic deformation.

Powder blends that show high elastic recovery or lack of adhesive bonding with other components of the powder tend to form physically unstable com-pacts. Such compacts tend to show problems such as capping and lamination of the tablets. Capping refers to breakage and separation of one layer of tablet close to the edge, whereas lamination refers to breakage in the middle.


Determination of compaction characteristics

During pharmaceutical development, compactibility of a powder blend is estimated using simulated tableting equipment, such as Presster® tab-let press simulator or a compaction simulator. These equipments apply well-defined and controlled compression pressure within a defined period of time on the powder blends. They allow the study of a powder blend’s compaction characteristics under a range of compression pressures, dwell times (duration of time for which the blend is subjected to the compression pressure), and compaction speeds (speed of compaction of powder as deter-mined by the speed of punch movement during compression).


Factors affecting compactibility

Compactibility of a powder is a function of its intrinsic mechanical behavior, such as plastic deformation or brittle fracture, and surface interac-tions with other powder particles. Compactibility of a powder can also be affected by its particle size and moisture content, which act by impacting particle packing and interparticle interactions, respectively.

In pharmaceutical operations, usually powder blends are used for tablet-ing. The pharmaceutical unit operations, such as granulation, and the use of excipients in the dosage form can adjust the compaction characteristics of a powder blend. The compactibility of a blend is a result of the compac-tion behavior of its individual components, which can be influenced by changing the composition of the blend.

Contact Us, Privacy Policy, Terms and Compliant, DMCA Policy and Compliant

TH 2019 - 2023 pharmacy180.com; Developed by Therithal info.