Abstract
Spinning disc technology is capable of achieving intensified micromixing within thin liquid films created through large shear rates, typically of the order of 103 s−1, generated by means of fast disc surface rotation. In this study the effect of the high shear on solvent–antisolvent mixing and starch nanoparticle precipitation is reported. Rheological studies of starch solutions at 2% w/v and 4% w/v have demonstrated their shear-thinning behaviour at the large shear rates experienced on the spinning disc surface. The effect of such high shear rate on starch nanoparticle precipitation is investigated alongside solute concentration and several other operating parameters such as flow rate, disc rotational speed, and solvent/antisolvent ratio. A reduction in nanoparticle size has been observed with an increase in starch concentration, although agglomeration was found to be more prevalent amongst these smaller particles particularly at larger flow rates and disc rotational speeds. Micromixing time, estimated on the basis of an engulfment mechanism, has been correlated against shear rate. With fast micromixing of the order of 1 ms observed at higher shear rates, and which are practically unaffected by the starch concentrations used, micromixing is not thought to be influential in determining the particle characteristics highlighted in this work.
Highlights
Starch is a polysaccharide molecule made up of straight chained amylose and branched amylopectin polymers, it is found in sources such as corn, rice, and potato
With the exception of the author’s previous publication [14], starch solvent–antisolvent precipitation has only been conducted through semi-batch processes using a dropwise or low flow rate addition of the antisolvent
The Z-average is the intensity-weighted mean hydrodynamic size of the particles, and the associated polydispersity index (PdI) quantifies the overall width of the size distribution, which is constituted of a primary peak and a secondary agglomeration peak
Summary
Starch is a polysaccharide molecule made up of straight chained amylose and branched amylopectin polymers, it is found in sources such as corn, rice, and potato. With the exception of the author’s previous publication [14], starch solvent–antisolvent precipitation has only been conducted through semi-batch processes using a dropwise or low flow rate addition of the antisolvent The reason behind this is that due to the high viscosity of the starch solution, stirred tank systems are not able to allow sufficient mixing between the starch–solvent mixture and the antisolvent [12,15,16,17,18]. The study demonstrated the production of small nanoparticles with narrow particle size distributions This was attributed to the high shear generated by the disc that creates instabilities within the thin liquid film, intensifying micromixing between the solute–solvent and the antisolvent. This previous study primarily entailed precipitation using a single concentration of 2% w/v starch in a sodium hydroxide solution. The current work focused on the rheology of the starch solutions at the high shear rates present in the spinning disc reactor and the implications it has on the solvent–antisolvent precipitation of starch nanoparticles at different concentrations of starch solution
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