inconclusivener48 - Blog
Jan
23
2016

Foam Granulation part 2

The aqueous foamed binder found in foam granulation is made up of a high volume of gas dispersed within a liquid containing foamable excipients, thus forming an unstable, semi-rigid structure. Effective excipients for pharmaceutical granulation happen to be cellulose-ether species that promote high foaming activity and become binders in the process. Many approved nonionic, polymeric excipients are likewise suitable foaming agents. The foam liquid might include additives as long as they do not interfere with its preparation. Semirigid foams characteristically exhibit closely packed bubbles or a polyhedral morphology based on the gas-quantity fraction although at the least 64% gas is required for the foam to show some extent of rigidity. The volume fraction of gas present in foam is referred to as its foam quality sometimes. For granulation, FQ is generally kept in a variety of 75-95%. Foams which are too wet lack adequate stability to pass on well and often simply collapse on the floors of processing equipment. Very dried out foams occupy very large volumes of space; exhibit very high inherent viscosities; and more readily collapse in the presence of shear than wetter foams.

Continuous foam granulation with a twin-screw extruder was introduced on a case study comparing the technique to the conventional liquid addition method. An effective methodology to metering such foam in to the machine needed recognizing its solid-like behavior and using approaches commonly useful for feeding mass solids instead of liquids. An auxiliary device, known as a side stuffer to the extrusion industry, was found suitable for feeding foam. The medial side stuffer commercially is readily available, and the physical setup and control software of most extruders could be configured to support it. The relative area stuffer is normally a miniature, twin-screw auger that mounts to the side of the primary extruder and conveys materials into a specified area of the process. As a result of drag-flow action of the rotating screws in the relative side feeder, foam is forced in to the passing formulation within the primary extruder and partially collapses upon get in touch with, as the remaining foam forms a layer between your extruder and powder barrel. The mechanism of foam wetting inside the extruder is under study still. A two-stage model proposed in a recently available publication was predicated on how foams prepared from liquids of different viscosities and having unique FQ collapsed and drained under different shear conditions as well as how they damaged granule homes from the extruder. A pressure-driven wetting level is considered to occur at the true point of entry where in fact the foam enters the procedure, with stiffer foams showing greater resistance to collapsing upon contacting the non-wetted formulation immediately. The remaining, uncollapsed foam pushes the powder apart to form a layer above. The next shear-driven wetting stage shows up governed by the response of foam to shear; layers of stiffer foam collapse more easily under mechanical shear to wet the powder beneath while wetter foams exhibit greater tolerant collapse under mechanical shear by establishing extra stable morphologies comprised of smaller bubbles.

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These observations are usually related to the two-stage wetting mechanism previously described, which causes the powder to be isolated from the barrel wall by way of a layer of foam immediately, at least until it is very well wetted. The powder in cases like this is without question steadily saturated with the binder over a much larger area of call than in immediate liquid addition, which minimizes the binder's local focus in the porous matter. The lubricating characteristic of foam granulation, where the foam layer isolates the powders from the barrel wall until uniformly wetted, can be an important indicate be stressed for extrusion processing. The lubricity of conveyed solids affects both electricity consumption by the machinery in addition to the exiting temperatures of granules.

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