Encapsulation of calcium carbonate by styrene polymerization

Abstract

In order to obtain composites of calcium carbonate (CaCO3) encapsulated by polystyrene (PS), soapless polymerization of styrene (S) in aqueous phase in the presence of CaCO3 was carried out. Influences on the encapsulation and on monomer conversion were studied. Results showed that monomer conversion higher than 52% can be achieved by increasing the stirring speed of polymerization to 1000 rpm. In order to remove the polymer adsorbed on the surface of the inorganic powder, the crude PS/CaCO3 composite obtained was treated by Soxhlet extractor, and the PS/CaCO3 ratio after the extraction was measured and defined as the real encapsulation ratio. A maximum real encapsulation ratio of 6.4% was obtained regardless of variations in experimental conditions such as monomer/CaCO3 ratios, monomer and initiator concentrations. The presence of PS on the surface of CaCO3 was tested by scanning electron microscopy and zeta potential (ξ) measurement of CaCO3 particles encapsulated by PS. With an increase in monomer conversion, ξ approached the value obtained from particles of pure PS prepared by soapless emulsion polymerization in the absence of CaCO3 powder. © 1999 John Wiley & Sons, Ltd.