Moisture content of granulation

Schaefer T, Worts O. Control of fluidized granulation III, Effects of the inlet air temperature, and liquid flow rate on granule size and Size distribution. Control of Moisture Content of Granules in the Drying Phase. Arch Pharm Chem Sci Ed 6. 1978 1 1-13. 

Moisture content of Granules, Amount of residual solvent... 

Pitkin C Carstensen JT. Moisture content of granulations. J Pharm Sci 1973 62(7) 1215. Kunii D, Levenspiel O. Fluidization Engineering, 2nd ed. Boston, MA Butterworth-Heinemann, 1991. 

Schaefer T, V0rts O. Control of fluidized bed granulation. III. Effects of inlet air distribution. Control of moisture content of granules in the drying phase. Arch Pharm Chem Sci Ed 1978 6 1. 

The range of 15-45% crystallinity has been reported for various starches (Zobel, 1988). However, the value of crystallinity varies with the method of determination, moisture content of starch granules, and starch source. 

Influence of machine variables on particle sizes and moisture content of the granulations ... 

Determine the moisture content of the nongranulated product with the granulated product. 

Rantanen J, Antikanen O, Mannermaa JP, Yliuusi J. Use of near-infrared reflectance method for measurement of moisture content during granulation. Pharm Dev Technol 2000 5(2) 209-217. 

These studies point towards the need to optimize moisture content of the wet mass and extrudate by careful selection of formulation ingredients and type of extruder. A basket or gear/roll extruder is preferred for a very dense and moist wet mass, as it generates little shear and rise in temperature, while an axial or radial screw extruder which increases granule density and hardness is desirable for a wet mass which is less cohesive with poor binding. 

After scale-up into production, it was determined that an increase in moisture content would improve the formulation stability for a high dose wet granulated product. It was decided to use the Presster to predict the results that would be obtained in production when the moisture content of the final blend was increased. Blends with three moisture levels were compressed at two forces. As shown in Figure 5, as moisture content increases, tablet hardness increased. The dissolution profiles for the tablets with different moisture levels were compared and found to be within specification, indicating that raising the moisture content in the final blend should result in acceptable tablets in production. 

On the other hand, it has been experimentally proved that, at the temperature of the air coming out of the second zone being in excess of 80 °C, the moisture content of the granulated material is below 1.2% by mass, while the content of methylol groups is less than 8.8 %. With such characteristics, the material may not flow and, thus, cannot be processed into articles. 

Hence, the temperature of the material in the second zone of the drier should be maintained within, 58-62 °C with a view to obtaining quality granulated material having a residual moisture content of 1.5 to 3.5% (which corresponds to 8.8-9.2% content of methylol groups in the given material). The temperature of the air coming out of the second zone is within 68-75 °C. 

Moisture content of dried granulation Loss on drying (LOD) can be used to determine whether or not the granulation solvent has been removed to a sufficient level during the drying operation (usually less than 2% moisture). 

The optimal moisture content of the dried granulation needs to be determined. High moisture content can result in (1) tablet picking or sticking to tablet punch surfaces and (2) poor chemical stability as a result of hydrolysis. An overdried granulation could result in poor hardness and friability. Moisture content analysis can he performed using the conventional loss-on-drying techniques or such state-of-the-art techniques as near infrared (NIR) spectroscopy. 

Fig. 8 shows examples of unit energy input for the increase of particle consolidation in the granules (a decrease of mean granule porosity) for a selected material (D5), at variable moisture content of the feed. 

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