Implementation of powders - Humid granulation: bases and theory

The term "granulation" includes any process in which fine solid particles, dispersed in a gaseous or liquid medium, are assembled to form larger particles. The latter, in which it is still possible to identify the original particles, are called granules or agglomerates. This assembly is made possible by the inter-particle bonding forces created and/or intensified during granulation. Depending on the process used, the size of the granules can generally vary between 0.1 and 50 mm. The purpose of this operation may be purely commercial, as the resulting product has a better appearance, or strictly technical, as granulation of a powder enables, among other things:

• to ensure easier handling;

• reduce dust emissions during handling;

• to make it more pourable;

• reduce the risk of explosion or caking;

• to obtain a more homogeneous mixture;

• to obtain intermediate products for compression;

• to obtain calibrated particle sizes.

Granulation mechanisms are varied and complex. Although some cohesive powders can agglomerate spontaneously by physical forces naturally present in the medium, in most cases granulation requires the addition of a binder in liquid or dry form.

There are two main granulation methods:

• dry granulation. In this category, granulation is carried out without the presence of a binder or with the aid of a dry (starch, gelatins, sugars, cellulose derivatives, etc.) or liquid (beet and cane molasses, for example) binding agent. The granules are obtained by compression and their mechanical strength is ensured by the combined effect of reducing the spacing of the particles and increasing their contact surface;

• wet granulation. In this method, a liquid, very often an aqueous solution of a suitable binder, is used to ensure the preliminary bonds between the particles, and no compression is applied.

This file presents the basic principles of wet granulation, with basic theoretical notions [J 2 253] . The following folder