Foam Granulation part 1 As a total consequence of changing philosophies towards continuous production, new equipment has been introduced into pharmaceutical production facilities. The twin-screw extruder is an exemplory case of such equipment for work with in wet granulation. The authors review developments in wet granulation using a twin-screw extruder; lay out the presssing problems with wetting in this machine; and introduce a novel strategy, foam granulation, that uses the twin-screw extruder to fully satisfy the unique desires of granulation. The twin-screw extruder provides highly consistent granulates due to its continuous operation and closely confined flow path, which requires that all particles experience a similar shear history. The intensive blending of the twin-screw extruder allows lower optimum liquid concentration for granulation while making 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 may be significantly reduced with usage of this machinery in solid oral-dosage production. plastic compounding machines The binding liquid in wet granulation has 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 concerns to be solved when it comes to presenting liquids into this type of machinery to obtain rapid and uniform wetting of excipients so that the process exhibits balance in operation, boundaries become quickly lubricated to reduce equipment wear and granule heating, and top quality granulates are obtained. A basic variant of extruder used for granulation may be the fully intermeshing, co-rotating twinscrew extruder. Differences between vendors are largely based on the available internal level of the machine plus the screw diameter, both of which can substantially affect granulate properties in both granule size and intragranular porosity. The machine is modular highly, making it a flexible platform for constant manufacturing of different products during its duration of services to a company. The intermeshing location between your two screws creates a self-wiping actions that minimizes material accumulation within the machine but also offers a complex flow path for powders to combine and consolidate. For wet granulation, the die end of the extruder is generally open to collect granules without abnormal consolidation. Wet granulation inside the co-rotating twin-screw extruder is a starve-fed process, and therefore the available internal volume of the machine is by no means completely filled with material during procedure. This modus operandi is essential to extrusion since it minimizes dissipative heating buildup in conveyed medicine formulations as it limitations compression against the barrel wall, it decouples the parameters of output screw and rate speed to give formulators considerably more control over their method, and it more readily enables the downstream addition of supplies because the system is not pressurized aside from small mixing regions. The zones of the screws that are starved knowledge dominant drag flow, in which powders will be pushed by the rotating flights of conveying-type elements downstream. These screw elements have already been seen to contribute little to granule growth. Actually, screw designs using only conveying elements show inadequate distribution of the binding liquid within exiting solids. It really is rare, however, that a screw design is completely comprised of conveying elements or that the complete amount of the machine is ever totally starved. Significant granule development necessitates the inclusion of pressure-driven mixing zones, which are totally filled as powders are squeezed through these sections necessarily. Kneading
blocks and comb elements are types of mixers commonly used in sparing numbers across 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 level is probably the most crucial parameters influencing the extent of granule expansion, with larger outputs producing greater granules. The effect is induced by the bigger volumes of powder that build-up in front of pressure-powered mixing zones as stream rate increases, producing much larger axial compressive forces on the contaminants present. In fact, it's been proven that the dispersion of binder within poorly wetted mass could be improved for granulation if the screw design and flow fee are adjusted to supply ideal compressive forces. The affect of flow price on granule growth, however, is not often observed in smaller extruders or highly starved processes. Increasing screw speed has less effect on granule size but generally increases the number of chopping events provided by mixing zones to lessen the occurrence of oversized contaminants. For a set flow rate, raising the screw speed shall reduce the volume of powder that fills the conveying screw elements, resulting in lower power usage by the process. Among the published research for wet granulation, an essential point that is rarely mentioned, yet recognized to the pharmaceutical industry widely, is the problems of wetting a formulation in an extruder uniformly. The problem arises due to the earlier mentioned closely confined space inside the extruder, which benefits in the liquid injection port staying in instant proximity to the powder movement. This confinement prevents atomization of the binder choice into micro-sized droplets ahead of contacting the powder solids, as is done in high-shear batch mixers. Consequently, regions of the powder become oversaturated while some remain dry virtually. This presssing concern was highlighted in the industrial-oriented article by Shah, who reported procedure surging, though electric motor overload events are normal also. Shah demonstrated several strategies related to screw design and the sequential addition of smaller liquid quantities in to the process as means to minimize surging occurrences. Such changes greatly raise the complexity of functioning the extruder and do not get rid of the root cause of the problem. Alternatively, a fresh solution called foam granulation uses the unique behavior of aqueous foam to cause fast spreading of the binding liquid over a big section of the powder during wetting.
Published on Jan 26, 2016