EFFECT OF PARTICLE-SIZE AND POROSITY ON PARTICLE FILM COATINGS

This paper is concerned with work carried out to establish the influence of particle size and porosity on the encapsulation of inorganic particles. Particles were film coated with a polymer latex in a 20-cm diameter fluidised bed with draft tube. Scanning electron microscopy, release measurements and mercury porosimetry were used to determine the quality of the coated particles. Equations were derived to predict coating thickness for both spherical and non-spherical encapsulates. The experiments showed that the smaller particles captured more coating than the larger particles, but due to their higher specific surface area, had thinner coatings. Coating quality of the porous particles was poor and was attributed to polymer wicking into pores during the coating process. Ideally, for film coating the core particles should be spherical, of high density and of zero porosity to both minimise the amount of coating material required and improve encapsulation.