Hydrodynamic difference between inline and batch operation of a rotor-stator mixer head - A CFD approach

Continuous Production of Water-Based UV-Curable Polyurethane Dispersions Using Static Mixers and a Rotor-Stator Mixer

UV-curable polyurethane dispersions (UV-PUDs) have applications in coatings for a variety of materials. Historically, the neutralization and dispersion steps of the UV-PUD production process have been performed in batch. However, continuous processing might reduce capital and operating costs, improve the dispersion characteristics, and facilitate scale-up. Static mixers and inline high-shear mixers are able to provide the necessary shear forces to obtain miniemulsions. The production of a UV-PUD is therefore studied in a continuous setup, whereby the neutralization step is performed in static mixers and the dispersion step is performed either in static mixers or in a high-shear mixer. The influence of the prepolymer temperature, mixing energy, and feed flow rate on the particle size and stability of the UV-PUD particles in water is explored. The results show that the neutralization step is mixing-sensitive, and the temperature of the neutralized prepolymer influences the particle size in the dispersion process. The amount of shear force applied during the dispersion step has a limited effect on the particle size. UV-PU dispersions with an average particle size below 80 nm and PDI below 0.1 are obtained with static mixers or in an inline rotor-stator mixer, at flow rates of 5.2 and 7.2 L/h, respectively. This research demonstrates that continuous processing using static mixers and high-shear mixing is a viable option for the neutralization and dispersion of UV-PUDs.

Emulsion Formation by Homogenization: Current Understanding and Future Perspectives

Emulsion formation by homogenization is commonly used in food production and research to increase product stability and to design colloidal structures. High-energy methods such as high-pressure homogenizers and rotor–stator mixers are the two most common techniques. However, to what extent does the research community understand the emulsion formation taking place in these devices? This contribution attempts to answer this question through critically reviewing the scientific literature, starting with the hydrodynamics of homogenizers and continuing by reviewing drop breakup and coalescence. It is concluded that although research in this field has been ongoing for a century and has provided a substantial amount of empirical correlations and scaling laws, the fundamental understanding is still limited, especially in the case of emulsions with a high-volume fraction of the disperse phase, as seen in many food applications. These limitations in the current understanding are also used to provide future perspectives and suggest directions for further investigation.