Cause and Remedy for Wet Screening

Wet screening in the pharmaceutical industry for wet mass is the process of separating wet granules into different size fractions using a series of screens with different mesh sizes. It is a common step in the wet granulation process, which is used to produce granules that are suitable for tableting, capsule filling, and other dosage forms.

The granules that are smaller than the mesh size of the screen will fall through to the next screen below. This process continues until the granules reach the bottom screen, which has the smallest mesh size. The granules that are too large to pass through the bottom screen are collected as the oversize fraction.

Wet screening is used to achieve a number of goals in the wet granulation process, including:

1. To remove oversize granules: Oversize granules can cause problems in downstream processing, such as tableting and capsule filling. Wet screening can be used to remove oversize granules and ensure that the final product has a consistent particle size distribution.
2. To produce granules with a desired particle size: The particle size of the granules can affect their flowability, compressibility, and dissolution rate. Wet screening can be used to produce granules with a desired particle size for the intended dosage form.
3. To wash the granules: Wet screening can be used to wash the granules to remove surface contaminants, such as binder solution or residual solvents. This helps to improve the purity and quality of the final product.

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Wet screening is a relatively simple and straightforward process, but it is important to optimize the screening parameters to achieve the desired results. The factors that can affect the wet screening process include:

• The mesh size of the screens: The mesh size of the screens should be selected based on the desired particle size of the final product.
• The type of liquid used to suspend the wet mass: The type of liquid can affect the flowability of the wet mass and the blinding of the screens.
• The vibration frequency and amplitude of the screens: The vibration frequency and amplitude can affect the movement of the wet mass across the screens and the efficiency of the screening process.

By optimizing the wet screening parameters, manufacturers can improve the quality and consistency of their products.

Cause and Remedy for Wet Screening

Problem	Cause	Remedy
Screen clogging	Doughy or sticky wet mass	Avoid oscillating granulator. Use extrusion-type granulator or Fitz Mill® without screens. Reduce granulation time. Add 5% to 20% Avicel® PH-101 (gives less sticky or doughy mass, easier to screen).
	Too much water in mass	Reduce water content; add water gradually and mix well after each addition
	Mass sensitive to water content	Incorporate 5% to 20% Avicel® PH-101 (allows a wider range of solvent volume)
	Gummy binder	Change binder
	Component or active ingredient	Use diluted or anhydrous ethyl or isopropyl alcohol (if latter, determine acceptable residual solvent level by GC or other appropriate method); change binder

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