Agglomeration tendency during top-spray fluidized bed coating with gums

Abstract Top-spray fluidized bed coating of glass beads with gums leads to an `all or nothing' side-effect agglomeration in the case of locust bean gum, carboxymethylcellulose (CMC), and sodium alginate, meaning that it appeared very drastically when a critical spray rate was exceeded. By contrast, a continuous sticking of the particles onto the reactor wall was observed for κ-carrageenan. It was illustrated that wet film properties instead of solution properties determine agglomeration tendency since locust bean gum, high and low viscosity CMC show a comparable agglomeration tendency. The glass transition concept offers some relevant explanation as to why κ-carrageenan permits working at considerably higher spray rates than sodium alginate, although both biopolymers show similar hygroscopical and rheological characteristics. Glass transition phenomena also seem to influence the magnitude of coating imperfections: coatings consisting of locust bean gum and κ-carrageenan appear to have a surprisingly uniform structure.