Porous granules by freeze granulation of Pickering emulsions stabilized with halloysite particles

Pickering emulsions stabilized with a natural silicate mineral, halloysite, were dried by freeze granulation in order to prepare porous granules. Different formulations were studied, by varying the pH of the suspension, the ionic strength and with the addition of organic binders (poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG)). To get a better understanding and control on the process, the objective was to correlate the formulation and the emulsion behavior to the morphology and size of the granules. This study highlights the predominant role of electrostatic interactions on the emulsions. Their stability is improved if the dispersion of solid particles in the continuous phase is relatively limited, with medium zeta potential absolute values. Freeze granulation of emulsions prepared at different ionic strength and pH led to similar granules, with an internal porosity attributed to the low solid fraction. The addition of organic additives PVA and PEG led to a better conservation of the structure, with fewer broken fragments and a larger porosity, attributed to a higher cohesion of these emulsions during the spray freezing and the lyophilisation steps.