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

•Spheronisation of cylindrical extrudates is probed by interrupted experiments.•The time to spheronise small batches is proportional to rotational speed−3.6.•Rod breakage is followed by rounding, with rounding taking ∼85% time.•Small pellets round off: large particles pass through a dumb-bell stage....

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Bibliographic Details
Published in:Chemical engineering research & design 2014-11, Vol.92 (11), p.2413-2424
Main Authors: Lau, C.L.S., Yu, Q., Lister, V.Y., Rough, S.L., Wilson, D.I., Zhang, M.
Format: Article
Language:English
Subjects:
Breakage
Cellulose
Evolution
Extrusion
Extrusion–spheronisation
Granulation
Mathematical models
Microcrystalline cellulose
Pastes
Pellet
Pellets
Rods
Rounding
Shape
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Summary:•Spheronisation of cylindrical extrudates is probed by interrupted experiments.•The time to spheronise small batches is proportional to rotational speed−3.6.•Rod breakage is followed by rounding, with rounding taking ∼85% time.•Small pellets round off: large particles pass through a dumb-bell stage.•X-ray microtomography indicates a variation of porosity in pellets. The process by which cylindrical rods of soft solid paste extrudate are converted into round pellets on a spheroniser (Marumeriser™) plate was studied by interrupting spheronisation tests and measuring the size and shape of the pellets. Batches of 20 identical rods (20mm long, 3mm diameter) generated by ram extrusion of 47wt% microcrystalline cellulose/water paste were spheronised at rotational speeds, ω, between 1200rpm and 1800rpm on a laboratory spheroniser. The time to complete spheronisation was found to scale with ω−3.6, which was close to the ω−3dependency 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 (2001), showed similar behaviour for all ω studied. A phenomenological model is proposed which identifies different routes for small and large rod breakage products.
ISSN:0263-8762
1744-3563
DOI:10.1016/j.cherd.2014.01.018