Dynamic mechanical properties of polypropylene composites filled with ultrafine particles

The dynamic moduli of isotactic polypropylene (PP) filled with ultrafine SiO2 and micron sized glass particles are measured in the temperature range 30–130°C at frequency 10 Hz. The storage moduli of PP composites, E′c, increase with filler content and decreasing filler size in the whole range of temperature. The loss moduli of PP composites, E″c, increase with filler content and decreasing filler size above 40°C. The intensity of the broad despersion which appears at ca. 60°C increases with filler content and decreasing filler size. By assuming that the energy is not dissipated in the effective volume, namely, filler volume plus that of immobilized interfacial region, the effective volume fraction is evaluated from the relative loss modulus, E″cE″0 at 60°C. The effective volume fraction increases with filler content and decreasing filler size. The effect of addition of ultrafine particles on the broad dispersion at ca. 60°C resembles the effect of increasing crystallinity of pure PP. It is concluded that the broad dispersion which appeared at ca. 60°C seemed to be assigned to the grain boundary of PP composities or crystalline boundary of pure PP.