The purpose of dry granulation is generally to improve the fluidity of materials, eliminate the degradation caused by wet granulation to improve product stability, prevent stratification between materials, and increase bulk density.

Compared with the more mature wet granulation technology, dry granulation technology has many advantages, but there are also some problems. Let’s take a look at the advantages and disadvantages of dry granulation technology.

  1. Advantages of dry granulation

Dry granulation is an agglomeration process. Choosing the dry granulation process has both product advantages and process advantages.

In general, a major advantage of dry granulation over wet granulation is that it does not require water or any organic solvent. Therefore, this method is particularly suitable for some drugs, because some drugs are sensitive to moisture or heat. In addition, the dry granulator is environmentally friendly, with no exhaust emissions, reducing environmental pollution. And dry granulation technology is an efficient and easy-to-automate process, which is easy to scale up, simple to operate, and low in cost. The particle size of the finished product after dry granulation is uniform, the bulk density is increased, the fluidity is improved, and the disintegration degree can be controlled, and it is convenient for subsequent processing, storage and transportation.

Dry granulator can be used for drugs or excipients that are poorly fluid or sensitive to heat or moisture. However, there are also some technical problems in dry granulation technology. Let’s take a look at the problems and solutions in the process of dry granulator.

2. Disadvantages of dry granulation technology and their solutions

(1) Uncompacted material or fine powder leakage

First, use concave rolls for sealing, as leaks between the roll-side seals can create uncompacted material. Second, the material can be re-granulated after recovery, but if the composition of the leaked fines is different from the overall composition, this will result in non-uniformity of the final product. In addition, multiple rolling of the material can negatively affect the compressibility of the material. Third, vacuum around the equipment to prevent powder from splashing.

(2) Material compressibility loss

Loss of material compressibility is a common problem in dry granulator and is more pronounced at higher roller pressures. The loss of material compressibility occurs mainly in plastic materials, but also in brittle materials. Usually, the roller pressure is high during dry granulation to achieve the required particle characteristics, but the roller pressure should be reduced as much as possible under the premise of satisfying the product quality to avoid the loss of material compressibility. Excessive compression can lead to discoloration, overheating, severe cracking, or plasticization of material strips.

(3) Material sticking roller

Lubricant can be added to control the moisture content of the material within the optimal range. The auxiliary materials such as dextrin and maltodextrin with higher Tg can be selected. Cooling water can be used to effectively reduce the surface temperature of the roller, and the appropriate roller pressure and production can be controlled. Ambient relative humidity to avoid sticking rollers.

(4) Pressed strip layering

Control the consistency of particle size distribution, density and other properties of materials to reduce stratification.