Study On Surface Modification Of CaCO₃ With Core-shell Structure And Its Application In PP Composites

Polypropylene toughened by inorganic calcium carbonate (CaCO₃) particles and elastomer simultaneously is one of the promising research fields in material science. Focusing on optimizing the interfacial design to get well dispersion of inorganic particles in the matrix and the reasonable compatibility between particles and resin matrix to improve the interface adhesive strength, the present dissertation researches a new method to modify the surface of CaCO₃ with modifier of polypropylene wax (PPW) or EPDM to form chemical bonds between them. And the filling effects of modified CaCO₃ on toughening PP binary and ternary composites were studied in detail.Chapter 2 researches the preparation and characterization of modified CaCO₃ (PPW-CaCO₃). Based on our group's patent, the CaCO₃ surface modification with PPW was carried out by a reformative solid-phase grafting reaction. The technology parameters of this reaction were investigated and the probable preparation course was also suggested. The experimental results of anti-solvent test, FTIR and TGA prove that PPW can coat on the surface of CaCO₃ chemically.The microstructures, mechanical properties, crystal properties and rheological properties of PPW-CaCO₃ filled PP binary composite and PPW-CaCO₃ filled PP/EPDM ternary composite were studied in Chapter 3 and 4 respectively. The results show that in PP/PPW-CaCO₃ composite, PPW-CaCO₃ can well disperse in PP matrix and the phase interface between PP and PPW-CaCO₃ is blurry. So PPW-CaCO₃ can act as more nucleators than poorly dispersed uncoated CaCO₃ to increase the spherulite number and decrease the spherulite size in the filled PP composite, therefore the mechanical properties and process flowabilities of PP/PPW-CaCO₃ composite are better than that of PP/uncoated CaCO₃ composite. As for PP/EPDM/uncoated CaCO₃ composite and PP/EPDM/PPW-CaCO₃ composite with physical interface entanglement between PP, EPDM and PPW-CaCO₃, it's found that although a two-step processing procedure is adopted, the final phase structures of this two composites exist two kinds of morphologies regardless of CaCO₃ modification or not, one is the core-shell structure with CaCO₃ particle as core and EPDM as shell, another is CaCO₃ and EPDM dispersing separately in the PP matrix respectively. Although thermodynamic factors have the equal effects on the formation of two morphologies, the surface modification of CaCO₃ is favorable to form more core-shell structures in PP/EPDM/CaCO₃ composites in this processing procedure. The two-step processing procedure cannot control completely to form core-shell structure. When the content of EPDM is 8 phr and PPW-CaCO₃ is 15 phr, the mechanical properties of PP/EPDM/PPW-CaCO₃ composite are the best.A new interfacial structure with direct chemical bonds between CaCO₃ and EPDM was designed and achieved by compounding of EPDM and CaCO₃ modified with acrylic acid in the presence of AIBN in Chapter 5. It was found from FTIR and TGA that in the compound (named as EPDM-CaCO₃), CaCO₃ is successfully and chemically coated by EPDM. The results show that there are plenty of core-shell structures in the EPDM-CaCO₃ filled PP composite, and the interface between CaCO₃ and EPDM is obscure as well. When the content of EPDM is 8 phr and CaCO₃ is 15 phr, the mechanical properties of this material are getting the peak.