The evolution of pellet size and shape during spheronisation of an extruded microcrystalline cellulose paste

Abstract

The process by which cylindrical rods of soft solid paste extrudate are converted into round pellets on a spheronsier (Marumeriser) plate was studied by interrupting spheronisation tests and measuring the size and shape of the pellets. Batches of 20 identical rods (20 mm long, 3 mm diameter) generated by ram extrusion of 47 wt% microcrystalline cellulose/water paste were spheronised at rotational speeds, , between 1200 rpm and 1800 rpm on a laboratory spheroniser. The time to complete spheronisation was found to scale with  -3.6 , which was close to the  -3 dependency predicted by a simple collision model. Breakage occupied the first 10% of the process duration: rounding off was the rate determining step. The evolution of pellet shape was classified into five stages, the duration of which was found to scale with spheronisation time. Pellet shape, quantified by aspect ratio, circularity, shape and angularity factors presented by Sukumaran and Ashmawy (Géotechnique, 2001, Vol 51, 1-9), showed similar behaviour for all  studied. A phenomenological model is proposed which identifies different routes for small and large rod breakage products.

Stages in spheronisation: Evolution of pellet size and shape during spheronisation of microcrystalline cellulose-based paste extrudates

“…Lau et al [11] performed spheronisation tests starting with the same number (20) of identical extrudates, stopping tests after different times in order to measure the number of pellets, their size and shape. With this relatively small number of extrudates, collisions were dominated by wall-pellet events.…”

“…This paper employs the approach taken by Lau et al [11] to investigate the spheronisation of a simple microcrystalline cellulose (MCC)/water paste. The E-S formulations of water-tolerant active pharmaceutical ingredients (APIs) regularly incorporate MCC as an excipient, as this 'gold standard' material [10] provides the paste with good water retention properties and ductility.…”

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The stages of extrudate breakup and rounding to form spheroidal pellets were investigated for MCC/water pastes and some MCC/water/calcium carbonate pastes using the interrupted technique reported by Lau et al (2014). A new quantitative parameter, named 'dumb-bellity', was developed to monitor the formation and disappearance of 'dumb-bell' shaped pellets in the early stages of the rounding process.

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Influence of extruder screws speed and process temperature on the extrudate shape changes of the maize-spelt blends

“…The introduction of quick vision based analysis with the use of specialist software is, consequently, the subject of numerous studies related to the production process of not only extruded products, but also many other foods [12,13,14]. Not only do studies in this area cover investigations into the external shape of products, but also into the shape of pores making up the internal product structure.…”

Study of the widely used ethylcellulose polymer as film forming and matrix former agent

“…It has plastic properties, thus it provides the cohesiveness of the wetted mass, which was suitable for extrusion andspheronization. MCC has a large surface area and high internal porosity, therefore introduces the liquid into the matrix to provide a faster liberation of the API [67,68]. Moreover, in consequence of its large surface area and high internal porosity, it is able to absorb and retain a large quantity of water thereby facilitating extrusion, improving the wetted mass plasticity and enhancing spheronization [33,69].…”