Abstract
Empirical correlations have been developed to relate experimentally determined starch nanoparticle size obtained in a solvent–antisolvent precipitation process with key hydrodynamic parameters of a spinning disc reactor (SDR). Three different combinations of dimensionless groups including a conventional Reynolds number (Re), rotational Reynolds number (Reω) and Rossby number (Ro) have been applied in individual models for two disc surfaces (smooth and grooved) to represent operating variables affecting film flow such as liquid flowrate and disc rotational speed, whilst initial supersaturation (S) has been included to represent varying antisolvent concentrations. Model 1 featuring a combination of Re, Reω and S shows good agreement with the experimental data for both the grooved and smooth discs. For the grooved disc, Re has a greater impact on particle size, whereas Reω is more influential on the smooth disc surface, the difference likely being due to the passive mixing induced by the grooves irrespective of the magnitude of the disc speed. Supersaturation has little impact on particle size within the limited initial supersaturation range studied. Model 2 which characterises both flow rate and disc rotational speed through Ro alone and combined with Re was less accurate in predicting particle size due to several inherent limitations.
Highlights
Nanoparticles are incredibly small particles with sizes ranging between 1 and 100 nm
The results indicated a change in morphology of the starch nanoparticles from fibrous structures to spherical nanoparticles at increased antisolvent concentrations, as well as a reduction in particle size
Previous work involving the solvent–antisolvent precipitation of starch nanoparticles in a spinning disc reactor has demonstrated that starch nanoparticle size is influenced by flow rate, disc rotational speed, and antisolvent to solvent ratio [28]
Summary
Nanoparticles are incredibly small particles with sizes ranging between 1 and 100 nm. Previous work involving the solvent–antisolvent precipitation of starch nanoparticles in a spinning disc reactor has demonstrated that starch nanoparticle size is influenced by flow rate, disc rotational speed, and antisolvent to solvent ratio [28]. The study indicated a reduction in particle size with an increase in flow rate and disc rotational speed This was attributed to the increase in shear as either flow rate or disc rotational speed were increased, leading to enhanced micromixing between the solvent/solute and the antisolvent, and generating supersaturation at a faster rate. An increase in antisolvent to solvent ratio demonstrated a reduction in particle size, caused by an increase in supersaturation The interactions of these three single variables have been further analysed in the present work through empirical correlations consisting of the relevant dimensionless numbers derived to predict starch nanoparticle size for smooth and grooved discs. Besides relating the operating parameters to starch nanoparticle size obtained in the SDR, the aim of such a model is to highlight the significance of each of the parameters for optimisation, process control and scale up
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