Uniform encapsulation of fine inorganic powder with soapless emulsion polymerization

Abstract

AbstractThe encapsulation of inorganic powder of submicron sizes was attempted with soapless emulsion polymerization of methyl methacrylate in water in the presence of the powder. The powders used were barium sulfate and calcium carbonate. The polymerizations were initiated by potassium persulfate and by sodium bisulfite‐oxygen redox reaction. The encapsulation state of the powder with the polymer formed varied considerably with the initiators used. With potassium persulfate initiator the powder surface was partially or totally covered by polymer particles, while with redox initiator under air atmosphere the powder surface was well encapsulated with a film‐like polymer layer. From the differences in the encapsulation states, an encapsulation mechanism is suggested for each initiator system. Based upon this mechanism, a new encapsulation process capable of covering uniformly fine powders with a film polymer is proposed. An important factor in the new process is the addition of an extremely small quantity of a surfactant into the reaction system prior to the polymerization.