Roller compaction process

High-energy processes (milling, lyophilisation, granulating, drying) can introduce certain amounts of amorphicity into otherwise highly crystalline material [20]. As has been previously indicated, enhanced levels of amorphicity lead to increased local levels of moismre, and increased chemical reactivity in these areas. Hancock and Zografi [49] reported on the impact of a roller-compaction process on the water vapour sorption of a sample of aspirin. They speculated that... 

Table 8 Powder Properties from Non-Roller Compacted Formulation and Powder Properties from Vector Freund Lab and Pilot Roller Compaction Processes...

The Bib and BI are defined as shown below in Equations (2) and (3), respectively. Both indices describe the bonding ability of the tablets by using the ratio of tensile strength and indentation hardness. However, Bib is determined at low-indentation speed (Hq) and BIw is determined at high speed (Hio). Hence, BI is considered more indicative of actual tableting conditions, whereas Bib relates to slower compactions speeds typical of development or roller compaction processes. 

As shown in Figure 27, it is apparent that when the roller compaction force was scaled-up, the compactibility curve of the tablets shifted downward. Ideally, a formulator would prefer a 60 N hardness window of acceptable force. In this example, the flat part of the curve had no effect on friability and dissolution and thus could be processed. The example does show that for a roller compaction process, a scale-up factor must be considered for the roller compaction force early on in development. Factors that affect the tablet compactibility curve at scale-up include the roller compaction force and strain-rate sensitivity of the compact. 

Miller, R.W., The use of near infrared technology to map roller compaction processing applications, Proceedings Institute for Briquetting and Agglomeration, Biennial Conference (2000), 1999, 26, 17-26. 

Critical variables may be characteristic of the materials and/or the process. Materials properties have already been discussed briefly and of course the equipment variables for the unit operations will depend upon differences in the raw materials. However, there are general relationships between the roller compaction process variables and the properties of the resulting ribbons and granules that can aid in process design. 

The type of roll surfaces has a marked effect on the overall production throughput of a roller compaction process (Fig, lO). A variety of roll surfaces and configurations are available depending on the compaction behavior of the material. For instance, powders that tend to stick or cling to the roll surface requires the use of smooth or circumferential grooved surfaces, while materials that release cleanly from the roil after compaction may be pressed with one of the pocketed design or rolls with grooves in the axial direction. 

Gupta also showed that for a given set of milling conditions in a Comil the post milled particle size distribution is related to the tensile strength of the ribbon (Fig. 17). This is a key in designing and controlling a roller compaction process as will be discussed later in the monitoring section. 

Johanson JR. A rolling theory for granular solids. Trans ASME J AppI Mcch 1965 32 842-8. Turkoglu M, Aydin I. Murray M, Sakr A. Modeling of a roller-compaction process using neural networks and genetic algorithms. Eur J Pharm Biopharm 1999 48(3) 239-45. 

This type of simulation has been reported to be effective in mimicking a roller compaction compression cycle as shown in Figure 12 (4). When / =0, the punches begin their travel towards one another and compress the powder at the same strain rate as in the real roller compaction process. The crest of the sine wave correlates to the point at which the punches (or roller points) reach their minimum. separation and can be used to target the thickness of the simulated ribbons. Once the punches reach their minimum separation, they retract to decompress the ribbon before it is ejected by the lower punch to the die surface. This simulation utilizes a batch process to mimic a continuous one. As such, it does not account for roller compaction variables associated with continuous... 

It is clear that the particle size of MBP can influence the downstream processing as well as performance of the final product. This is illustrated in Fig. 12.7 that shows the effect of MBP particle size on the particulate properties (bulk density and particle size) of the densitied material, following the roller compaction process. 

The selection of the downstream processing itself strongly depends on the bulk density of the obtained material. In case of sufficiently high bulk density, a direct compression approach could be used, otherwise it is recommended to increase the bulk density using a roller compaction process. 

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