23 janvier 2016 ~ 0 Commentaire

Foam Granulation part 2

extrusion systems

The aqueous foamed binder used 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 large foaming activity and become binders along the way. Many approved nonionic, polymeric excipients are also suitable foaming agents. The foam liquid may include additives given that they do not hinder its preparation. Semirigid foams characteristically exhibit closely packed bubbles or a polyhedral morphology based on the gas-quantity fraction although a minimum of 64% gas is necessary for the foam to display some extent of rigidity. The volume fraction of gas present in foam is often referred to as its foam quality. For granulation, FQ is normally kept in a range of 75-95%. Foams that are too wet absence adequate stability to pass on well and often just collapse on the floors of processing equipment. Very dry foams occupy large volumes of space; exhibit high inherent viscosities; and more collapse in the presence of shear than wetter foams readily.

Continuous foam granulation with a twin-screw extruder was introduced on a case study comparing the strategy to the conventional liquid addition method. An effective methodology to metering such foam into the machine expected recognizing its solid-like behavior and using approaches commonly employed for feeding bulk solids rather than liquids. An auxiliary device, known as a area stuffer to the extrusion industry, was found suitable for feeding foam. The side stuffer commercially is readily available, and the physical setup and control software of most extruders could be configured to accommodate it. The side stuffer is normally a miniature, twin-screw auger that mounts aside of the main extruder and conveys materials right into a specified zone of the process. Due to the drag-flow actions of the rotating screws in the relative side feeder, foam is forced in to the moving formulation within the main 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 unit proposed in a recently available publication was based on how foams well prepared from liquids of distinctive viscosities and having numerous FQ collapsed and drained under distinct shear conditions as well as how they influenced granule homes from the extruder. A pressure-driven wetting stage is considered to occur at the true point of entry where the foam enters the procedure, with stiffer foams showing greater level of resistance to collapsing upon contacting the non-wetted formulation immediately. The remaining, uncollapsed foam pushes the powder to form a layer preceding aside. The subsequent shear-driven wetting stage looks governed by the response of foam to shear; layers of stiffer foam collapse more readily under mechanical shear to wet the powder beneath while wetter foams display greater tolerant collapse under mechanical shear by establishing more stable morphologies made up of smaller bubbles.

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 certainly steadily saturated with the binder over a much larger area of get in touch with than in direct liquid addition, which minimizes the binder’s local focus in the porous matter. The lubricating feature of foam granulation, in which the foam coating isolates the powders from the barrel wall until uniformly wetted, can be an important point to be stressed for extrusion processing. The lubricity of conveyed solids impacts both electricity consumption by the machinery plus the exiting temperature of granules.

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