Phase structure is one of the important influence factors to the properties of the polymer/elastomer/rigid filler ternary composite.In this paper

aiming to obtain the core/shell microstructure with calcium carbonate (CaCO3) particle as the core and ethylene-propylenediene monomer copolymer (EPDM) as the shell in the ternary composite

the polypropylene (PP)/EPDM/CaCO3 composites were prepared using two techniques:surface modification of rigid filler and processing control.The modified CaCO3 (PPW CaCO3) was prepared by using a patent method

and the modified layer of lower molecular weight polypropylene (PPW) on the CaCO3 surface has the characteristics of chemical bonding.The processing control has a two-step procedure. First

EPDM was compounding in a twinroll mill with raw CaCO3 or PPW CaCO3 followed by pulverization.Secondly

the pulverized EPDM/CaCO3 or EPDM/PPW CaCO3 powder was compounding with PP in a twinscrew extruder.The possible phase structures in the ternary composites were analyzed from the views of thermodynamics by measuring the surface tension of each constitute and calculating the interfacial tension and work of adhesion for all possible PP/EPDM

PP/CaCO3

EPDM/CaCO3 pairs in the ternary composites.The calculation results indicate that there are two kinds of possible phase structures existing in the ternary composites

one is the core/shell structure with CaCO3 particles as the rigid core and EPDM as the soft shell

another is CaCO3 particles and EPDM dispersing separately in PP matrix.However

SEM photos show that the proportions of the two structures in PP/EPDM/CaCO3 and PP/EPDM/PPW CaCO3 composites are different

the core/shell structure mainly exists in PP/EPDM/PPW CaCO3

resulting from the different surface properties of CaCO3.Because of the core/shell structure

the mechanical properties of PP/EPDM/PPW CaCO3 ternary composites are better than those of PP/EPDM/CaCO3 ternary composites.When the content of EPDM is 8 phr and PPW CaCO3 is 15 phr

the mechanical properties of composites are the best.The notched impact strength can reach 14.25 kJ/m2

which is 3.17 times higher than that of the PP matrix.