Agglomeration and coating

Solid particles are not readily wettable when air is entrapped because the contact angle widens. Hydroscopic (or water-miscible) materials such as glycerin, alcohol, and glycol penetrate the spaces occupied by air and displace it. During the dispersion process, the hydroscopic materials separate the agglomerates and coat the particles so that water can flow into and wet the particles. 

These agglomeration and coating technologies, which are established and well experienced in the pharmaceutical area, have been extended to other areas such as food and agricultural industries. However, the current fluidization technology has a limit in the size of the particles that can be processed. The extension of the size limit to a smaller range will lead to the wider applications. From practical aspects, the fluidized bed processes will be described below. 

Tmchiuli C. and Dumoulin E., 2013a. Chapter 14 Aroma encapsulation in powder by spray drying, and fluid bed agglomeration and coating. In Advances in Food Process Engineering Research and Applications. Eds. S. Yanniotis, P. Taoukis, N.G. Stoforos, and T. Karathanos, Springer, New York, pp. 255-265. 

Later, Fisher and Israelachvili showed the same result for mica surfaces even down to vapor pressures of 0.1, where only the odd molecular layer is condensed. Much more condensation is needed for rougher surfaces where it is necessary to fill the gaps. However, once the particles are too wet, then the capillary force drops and adhesion diminishes. These results are highly significant for agglomerating and coating granules. It is clear from these examples that the presence of contamination at the interface is a key issue in adhesive hysteresis. 

Smith s recommendation was that the best way to avoid agglomerates was to prevent their formation in the first place [8]. In dispersing powders, they must be wetted by the matrix to displace air from polymer clusters such as agglomerates and coat each particle. This is more easily achieved by the comparatively low viscosity of paints than the high viscosities of molten plastic. However, the former requires higher standards of dispersion. Further requirements are the removal of water, air and other impurities at the particle-polymer interface and the subsequent establishment of a firm bond between the two phases [12]. Smaller particles also contribute to a higher colour value. 

FIG. 20-71 Classification of agglomeration processes by agitation intensity and compaction pressure. Relative density is with respect to primary particle density and equals (1 — e) where e is the solid volume fraction. Reprinted from Granulation and Coating Technologies for High-Value-Added Industties, Ennis and Litster (1996) with permission of E G Associates. All rights reserved. 

The RDX thus coated and presumed to be 3% waxed RDX or a 97/3 RDX/wax mixt, is hand rolled to crush agglomerates and hand blended before use... 

Despite the importance of fluidized bed granulafion wifhin the food indusfry, fhere is relafively little published literature on the operation of fluidized beds used for agglomeration, instantising, coating or encapsulation of food materials and consequently very little... 

Soils containing more than 10% water can cause the soil/solvent slurry to form emulsions and either agglomerate or coat the walls of the process vessels. As a result, the solvents do not adequately contact the soil for effective contaminant extraction. The vendor claims to have solved this problem by adding a small amount of a proprietary reagent to the soil in the initial process step. 

In order to coat each particle in a discrete manner and avoid agglomeration, the coating fluid must often be atomized more finely and in a more controlled manner than in the case where tablets are coated in a typical pan process. 

As the plastic material is introduced into the reactor, it melts onto the sand particles and coats them. The vigorous cyclic movement of the particles can prevent agglomeration problems. Temperature is measured by means of three thermocouples placed at different radial positions in the reactor and provided with free vertical movement. Bed isothermic-ity is noteworthy, which is attained due to the vigorous particle circulation. 

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