Encapsulation of nanometer CaCO₃ by polymer network

Stearic acid coated nanometer CaCO₃ was encapsulated by polystyrene (PS) network via emulsion polymerization, where a polyfunctional monomer trimethyol propane trimethacrylate (TMPTMA) or divinyl benzene (DVB) was used as crosslinker. The feed modes of monomer and initiator are investigated. Batch mode is shown to be more convenient than semi-continuous mode in view of network perfection. With the amount of crosslinkers increased from 1 wt% to 7 wt%, the percentage of unextractable PS is high (not lower than 95%) for all samples in the system of TMPTMA, while this value decreases sharply from 74% to 3% in the system of DVB. The yield in the system of DVB is higher than that of TMPTMA. With increased amount of CaCO₃, encapsulation ratio can be varied from 5.2 to 2.6, while the yield and unextractable PS decrease. FT-IR spectra of the products after extraction indicate tight encapsulation between PS and CaCO₃, and TEM photographs of composite particles give direct evidence of encapsulation.