Study on encapsulation of modified CaCO₃ by emulsion copolymerization of styrene and crosslinker

PS/CaCO₃ composite nanoparticles with nanometer CaCO₃ particles as the core and cross-linked PS as the shell were prepared by emulsion copolymerization of styrene and multivinyl monomer as crosslinker in the presence of stearic acid coated nanometer CaCO₃ particles. The effects of the type and amount of multivinyl monomer, the amount of CaCO ₃ on polymerization reaction and encapsulation were investigated. The results show that the introducing of multivinyl monomer and CaCO₃ can slow down polymerization rate to different extent. Using 1%-5% trimethylolpropane trimethacrylate (TMPTMA) or divinyl benzene (DVB), tight encapsulation of CaCO₃ can be realized and beyond 94% PS cannot be extracted. The amount of crosslinker or emulsifier should be accommodated when the load amount of CaCO₃ is increased. CaCO₃ content in the product increases consequently with the increase of the loaded amount of CaCO₃, which can be known from FT-IR and TGA. TEM observations reveal that when the load amount of CaCO₃ is 14.8%, most CaCO₃ particles are encapsulated and each latex particle contains one CaCO₃ particle. Composite particles have well-defined core-shell structure and the thickness of polymer shells is around 10 nm. However, the thickness of polymer shell decreases and many free CaCO₃ particles appear when the load amount of CaCO₃ reaches 29.3% and 58.7%, respectively.