Twin-screw granulation: Understanding the mechanical properties from powder to tablets

Granulation is a technique commonly used before tabletting because it solves powder handling problems and ensures uniform filling of the compression dies. However, granulation can have an adverse impact on powder transformation into a tablet; i.e. tabletability.

The aim of this work is to examine the effect of continuous wet granulation using twin-screw granulator (TSG) on the tabletability of the granulated materials. Also, the study investigates the mechanisms that dictate the change in tabletability after wet granulation using TSG.

Granules and tablet properties were characterised using a range of mechanical and X-ray analysis techniques. It was found that wet granulation using TSG has an impact on the tabletability of the granulated pharmaceutical excipients. The presented work suggests that there is a correlation between the yield pressure, plastic and elastic work of the primary powder and the percentage of change in tabletability after granulation. The study found that plastically deformable materials like microcrystalline cellulose (MCC) experience a significant reduction of tabletability (up to 67%) when granulated compared with the direct compression of its powder. On the other hand, brittle materials like crystalline mannitol C160 or calcium phosphate dibasic anhydrous maintain their tabletability after twin-screw granulation.

The presented results show that the granule size of microcrystalline cellulose and mannitol 100 SD does not affect tabletability for the range studied. However increasing the strength of granules was found to cause reduction of the tabletability. On the other hand, the granule size of mannitol C160 and calcium phosphate dibasic anhydrous did affect its tabletability.