The agglomerate of particles and voids at the polymer-particle interface and the heterogeneous structure, have been characterized by scanning acoustic microscopy for polypropylene (PP)/ethylene vinyl acetate polymer blends (EVA) filled with modified calcium carbonate (CaCO
3). The relationships between the hoterogeneous structure and mechanical properties (tensile strength, elongation at break, impact strength) of the PP/EVA/CaCO
3 series were investigated.
Using ultrasonic images, the haterogeneous structure in the PP/EVA/CaCO
3 series was evaluated based on the binarization method. Polymer blends were prepared by mixing PP and EVA using a two-roll mill, then the PP/EVA mixture and various size CaCO
3 particulates were mixed on the same mill. Stearic acid was used as a modifier for CaCO
3.
By adding 2wt% EVA to PP, the heterogeneous structure decreased to about one-seventh the value of the PP/CaCO
3 blend. Furthermore, the heterogeneous structure in the modified CaCO
3 series was about one-thirtieth that of the unmodified blends. The tensile elongation at break depends on the heterogeneous structure, irrespective of CaCO
3 size and EVA content. However, it is recognized that impact strength depends on the heterogeneous structure and particle size. The impact strength of PP/EVA filled with small CaCO
3 particulates was greater than that with larger CaCO
3 particulates for the same heterogeneous structure.
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