Particle–particle coating in a cyclomix impact mixer

Abstract

Dry particle coating can be used to create new-generation materials by combining different powders exhibiting different physical and/or chemical properties. In such processes relatively large particles (host particles) are mechanically coated with fine particles (guest particles), without using solvents and subsequent drying, to create new functionalities or to improve initial characteristics. The coating of a host powder by guest particles can be performed in many different ways ranging from simple stirring of two components, to high energy impact coating. The purpose here is to examine the use of a Cyclomix high shear mixer granulator for the surface modification of silica particles by dry coating with magnesium stearate, and of cornstarch dry coated with hydrophilic or hydrophobic fume silica. Several powder characterisation methods have been used to study the physico-chemical properties of the coated particles. These include: Observation by environmental scanning electron microscopy (ESEM), Characterization of cohesion and flowability by tap density measurements, Determination of wettability by measurements of the contact angle between the coated particles and water. Measurement of moisture adsorption-desorption isotherms of uncoated and coated particles, and Tribo-electrification characteristics of the powders. The results show that the surface properties of the two host particles are changed, and that the Cyclomix can be used for dry particle coating to modify the properties of silica gel and cornstarch powders.