26 janvier 2016 ~ 0 Commentaire

Foam Granulation part 1

As a result of changing philosophies towards continuous manufacturing, new equipment is being introduced into pharmaceutical production facilities. The twin-screw extruder can be an exemplory case of such equipment for employ in wet granulation. The authors evaluate advancements in wet granulation using a twin-screw extruder; lay out the presssing issues with wetting in this machine; and introduce a novel approach, foam granulation, that uses the twin-screw extruder to fulfill the unique desires of granulation fully.

The twin-screw extruder provides highly consistent granulates due to its continuous operation and closely confined flow path, which requires that all particles experience an identical shear history. The intensive blending of the twin-screw extruder allows lower ideal liquid focus for granulation while developing denser granules for both placebo formulations and highly dosed drugs compared to a high-shear batch mixer. As a total result, drying and milling operations could be reduced with use of this machinery in solid oral-dosage production significantly.

The binding liquid in wet granulation includes a profound influence on product granule properties and affects the friction between conveyed powders and the barrel wall in the extruder, which affects power consumption and the exiting temperature of granules. There are crucial issues to be solved in regards to presenting liquids into this sort of machinery to obtain rapid and uniform wetting of excipients so that the process exhibits stability in operation, boundaries become immediately lubricated to lessen equipment wear and granule heating, and high quality granulates are obtained.

A regular variant of extruder useful for granulation is the intermeshing fully, co-rotating twin-screw extruder. Differences between vendors are largely in line with the available internal level of the machine along with the screw diameter, both of which can affect granulate houses in both granule size and intragranular porosity significantly. The machine is highly modular, rendering it a flexible platform for continuous manufacturing of different products during its duration of service to a company. The intermeshing area between your two screws creates a self-wiping action that minimizes material accumulation within the machine but also offers a complex flow route for powders to combine and consolidate. For wet granulation, the die end of the extruder is normally open to collect granules without substantial consolidation.

Wet granulation in the co-rotating twin-screw extruder is a starve-fed method, meaning that the available internal volume of the machine is by no means completely filled up with material during procedure. This modus operandi is essential to extrusion because it minimizes dissipative high temperature build-up in conveyed medicine formulations as it restrictions compression against the barrel wall, it decouples the parameters of output amount and screw speed to give formulators considerably more control over their procedure, and it more easily permits the downstream addition of products because the system isn’t pressurized aside from small mixing regions. The zones of the screws which are starved experience dominant drag flow, in which powders are pushed downstream by the rotating flights of conveying-type elements. These screw elements have already been observed to contribute tiny to granule growth. Actually, screw designs only using conveying elements show inadequate distribution of the binding liquid within exiting solids. It is rare, however, a screw design is totally comprised of conveying factors or that the entire amount of the machine is ever completely starved. Significant granule expansion necessitates the inclusion of pressure-driven mixing zones, which are fully filled as powders are squeezed through these sections necessarily. Kneading blocks and comb elements are examples of mixers commonly used in sparing numbers along the screw length to produce granule growth along with minor attrition. Keeping these mixing elements nearer to the ultimate end of the extruder reduces attrition.

Powder flow price is probably the most crucial parameters influencing the degree of granule development, with higher outputs producing greater granules. The effect is caused by the higher volumes of powder that build up in front of pressure-powered mixing zones as move rate increases, producing greater axial compressive forces on the particles present. In fact, it’s been demonstrated that the dispersion of binder within badly wetted mass can be better for granulation if the screw design and flow pace are adjusted to provide appropriate compressive forces. The affect of flow fee on granule growth, even so, is not observed in smaller extruders or highly starved functions often. Increasing screw speed has less effect on granule size but generally escalates the number of chopping events supplied by mixing zones to lessen the occurrence of oversized contaminants. For a fixed flow rate, increasing the screw speed will certainly reduce the volume of powder that fills the conveying screw elements, leading to lower power intake by the process.

screw extruders

Among the published studies for wet granulation, an essential point that’s rarely mentioned, yet widely known to the pharmaceutical industry, is the difficulty of uniformly wetting a formulation within an extruder. The problem arises due to the previously mentioned confined space inside the extruder closely, which benefits in the liquid injection port becoming in quick proximity to the powder flow. This confinement prevents atomization of the binder method into micro-sized droplets ahead of contacting the powder solids, as is performed in high-shear batch mixers. Due to this fact, regions of the powder turn into oversaturated while some remain virtually dry. This presssing concern was highlighted in the industrial-oriented document by Shah, who reported procedure surging, though motor overload events are common also. Shah demonstrated several approaches related to screw design and the sequential addition of small liquid quantities in to the process as methods to minimize surging occurrences. Such alterations greatly raise the complexity of functioning the extruder and do not eliminate the root reason of the issue. Alternatively, a new solution called foam granulation uses the initial behavior of aqueous foam to cause quick spreading of the binding liquid over a big area of the powder during wetting.

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