Issue link: https://www.e-digitaleditions.com/i/819216
Tablets & Capsules May 2017 19 Key concentration of components in material after three distinct short-term fluidization events Concentration of API after three distinct short-term fluidization events 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 14% 12% 10% 8% 6% 4% 2% 0% Concentration Concentration Dimensionless height (h/Ht) Dimensionless height (h/Ht) 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 Material Segregation intensity (relative to mean) MCC/Lactose Mag stearate 40.18% Glycolate 54.86% API 4.22% 1.75% Material Segregation intensity (relative to mean) MCC/Lactose Mag stearate 40.18% Glycolate 54.86% API 4.22% 1.75% MCC/Lactose Mag stearate Glycolate API Ht h Ht h Mag stearate Glycolate API the material is transferred at least once from a blender to an empty vessel before it reaches the feed frame of the press and the die filling stations. Because mechanical con- straints make transferring the blend directly to the feed frame difficult, almost all tablet press feed systems have a small to medium size receiving hopper. This arrangement raises two important questions about the blend's segrega- tion behavior: 1. What type of behavior will be induced in the mater- ial when gas from an empty vessel attempts to vent up through the blender? 2. What segregation may occur as a pile forms when the blend is transferred to a receiving vessel or feed hopper? Gas fluidization of the blend Powder flowing from the blender into a sealed feed hopper or holding vessel will cause the gas pressure in the vessel being loaded to increase until it reaches a critical value, after which a void or bubble will form at its inlet. This will induce a short-lived fluidization event and cause a "burp" to rise up through the blender. This may happen several times, and segregation could occur if fine particles are carried up with the gas. Thus, one segregation test protocol is to form a column of material and expose it to several short-lived fluidization events. A variety of test methods can be used to determine whether a given mater- ial is sensitive to segregation in a fluidized environment. The standard protocol is to fluidize the blend using gas for a long period and then measure the segregation con- centrations. But that method wouldn't be effective in this case because the actual stimulus in the fill process is a very short-lived fluidization. Relying on the standard protocol would thus lead to erroneous conclusions. Consider the segregation behavior of the API in a blend that, as it discharges in a column, is exposed to three short- lived fluidization events (Figure 1). In this case, the con- centration profile of the blend was observed from the side of the column through a port after three fluidization Figure 1 Figure 2