Tablet processing fragmentation

It is suggested that four mechanisms are basically involved in the process of compression of particles deformation, densification, fragmentation, and attrition. The process of compression is briefly described as follows small solid particles are filled in a die cavity and a compression force is applied to it by means of punches and then the formed monolithic dosage form is ejected. The shape of the tablet is dictated by the shape of the die while the distance between the punch tips at the point of maximum compression governs the tablet thickness, and the punch tip configuration determines the profile of the tablet. The compression cycle in a conventional rotary tablet press will be described in detail in this chapter and is illustrated in Figure 1. 

The general tablet compaction process normally is described by a number of sequential phases rearrangement, deformation (elastic, plastic) of initial particles, fragmentation, and deformation of fragments. Particle-surfaces are brought into close proximity and interparticulate attraction or bonds will be formed. Similar conditions will prevail with the effervescent tablets. 

The deformation properties of the drug substance and excipients will have a direct influence on the strength of the tablets that are produced by direct compression. The type of deformation that occurs will depend upon the material s inherent properties and the amount of force being applied. Deformation can be described in three main ways elastic, plastic, and brittle fragmentation, but it is important to realize that these are idealized deformation mechanisms— most real materials are some combination of two or all three mechanisms. Processes such as wet granulation, melt extrusion, and roller compaction can be used to improve compaction properties and reduce formulation sensitivity to changes in raw material quality. 

Fragmentation (the creation of new clean surfaces) continues at the same time at which bonding and den-sification occur. A high quality tablet can be formed only when the process of bonding and densification exceeds fragmentation. The rates at which these functions occur are dependent upon the rate at which the forces are applied. 

The consolidation of a powder bed into a tablet is a process of porosity reduction and the formation of an intact compact. During compression, the structure of the powder bed changes and consolidation is brought about mainly by particle rearrangement, plastic deformation, and fragmentation. The compression of powdered or granular material into a cohesive mass is a complex and irreversible dynamic process. 

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