Titanium dioxide nanoparticle coating in fluidized bed via supercritical anti-solvent process (SAS)

Abstract

A process to coat nanoparticle agglomerates has been developed and its critical operation parameters have been studied in this work. It consists on a fluidized bed where a supercritical anti-solvent process (SAS) takes place. Titanium dioxide (TiO2), used as model nanoparticle, has been coated with a polymer, Pluronic F-127, from an ethanolic solution. As main factors that can affect the coating process, the following process parameters were studied: the ratio between the velocity of carbon dioxide through the bed and the minimum fluidization velocity (umf), with values from 1.5 to 2.5 times the umf; the density of carbon dioxide, varying from 640 kg/m3 to 735 kg/m3 approximately; the flow rate of solution, within an interval between 0.5-2 mL/min; the concentration of the solution, from 0.030 mg/mL to 0.090 mg/mL and the mass ratio polymer-particle, 0.45-1.8 g/g. The process parameters were selected taking into account the values that increased the yield, defined as gram of coating material per gram of introduced polymer amount, and maintained a unimodal particle size distribution (PSD), with low increment in the mean particle size with respect to raw TiO2. All the samples were analyzed by four different methods, which showed the successful results of the experiments. The yield was analyzed gravimetrically, and the PSD was determined by laser diffraction. The presence of polymer on the surface of the nanoparticle agglomerates was verified by FT-IR spectrum and fluorescence microscopy, which also showed the quality and uniformity of the coating. Furthermore, the bulk density of the samples was measured showing a lineal variation with the mass ratio polymer-particle.