Foam Granulation part 2

The aqueous foamed binder used in foam granulation is made up of a high level of gas dispersed within a liquid containing foamable excipients, forming an unstable thus, semi-rigid structure. Effective excipients for pharmaceutical granulation happen to be cellulose-ether species that promote large foaming activity and act as binders along the way. Many approved nonionic, polymeric excipients are suited foaming agents also. The foam liquid might include additives as long as they do not hinder its preparation. Semirigid foams characteristically exhibit carefully packed bubbles or a polyhedral morphology depending on the gas-quantity fraction although at the least 64% gas is required for the foam to display some degree of rigidity. The quantity fraction of gas within foam is known as its foam quality frequently. For granulation, FQ is generally kept in a range of 75-95%. Foams which are too wet lack adequate stability to spread well and often merely collapse on the floors of processing equipment. Very dry foams occupy very large volumes of space; exhibit very high inherent viscosities; and more collapse in the presence of shear than wetter foams readily.

extruder dies

Continuous foam granulation with a twin-screw extruder was introduced on a case study comparing the strategy to the traditional 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 bulk solids rather than liquids. An auxiliary device, known as a aspect stuffer to the extrusion industry, was found ideal for feeding foam. The medial side stuffer is easily available commercially, and the physical control and setup software of most extruders could be configured to accommodate it. The relative part stuffer can be a miniature, twin-screw auger that mounts aside of the main extruder and conveys materials into a specified zone of the process. Due to the drag-flow actions of the rotating screws in the 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 the extruder and powder barrel. The mechanism of foam wetting in the extruder is under study still. A two-stage version proposed in a recently available publication was predicated on how foams ready from liquids of distinctive viscosities and having several FQ collapsed and drained under different shear conditions and also how they infected granule houses from the extruder. A pressure-driven wetting stage is thought 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 aside to create a layer above. The next shear-driven wetting stage appears 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 express greater tolerant collapse under mechanical shear by establishing extra stable morphologies comprised of smaller bubbles.

These observations are usually related to the two-stage wetting mechanism previously described, which in turn causes the powder to be isolated from the barrel wall by a layer of foam immediately, at least until it really is well wetted. The powder in this instance is usually steadily saturated with the binder over a much bigger area of contact than in direct liquid addition, which minimizes the binder's local focus in the porous matter. The lubricating feature of foam granulation, where the foam level 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 influences both power consumption by the machinery along with the exiting heat of granules.

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