Full-factorial design for statistical planning of attritor milling parameters and evaluation of effects on particle size and structure of sodium-montmorillonite

Abstract

High-energy milling is the most widely used method in industry to achieve nanosized particles due to its low cost and potential to rapidly provide large-scale production. Using a top-down approach based on wet attritor milling, we investigated different combinations of the factors predicted from the 2 3 full-factorial design were investigated to process sodium-montmorillonite (Na-Mt). Statistical analyses were performed to determine the most suitable process conditions and to evaluate the factors influencing the response variable. Materials obtained from the different procedures were analyzed by energy dispersive x-ray spectroscopy, powder x-ray diffraction, nuclear magnetic resonance, Fourier transform infrared spectroscopy and dynamic light scattering. Particle surface, size and morphology were examined by scanning electron microscopy while the lamellar structure was observed by transmission electron microscopy. The results predicted using factorial design indicated that the milling time has a significant positive influence on the particle size of Na-Mt. The effect of rotation speed was nearly comparable and its impacts was similar to that of milling time. The interaction effects were significant at 99% confidence level (p<0.01). The optimal process conditions were: 3% Na-Mt concentration (w/v), 3 h of milling time and a rotation speed of 1867 rpm, resulting in a particle size of 282.23 nm. The proposed factorial model proved to be reliable and adequate (R 2 =0.9853, PredR 2 =0.9753 and AdjR 2 =0.9804). The wet attritor milling can be considered as an economical and effective alternative for the mechanical treatment of a wide variety of powders, aiming to achieve nanosized structures.