Viscoelastic properties of nanosilica‐filled polypropylene in the molten state: Effect of particle size

Composites of polypropylene (PP) with nontreated nanosilica at different particle sizes are prepared, and their viscoelastic properties are studied by dynamic strain‐ and frequency‐sweep experiments. It is clear that incorporation of nanoparticles in a polymer matrix due to the huge specific surface area enhances both moduli so that the storage modulus is intensified more than loss modulus. The specific surface area of a particles increases as a particle size decreases, leading to a stronger tendency to form reinforcing structures. In nanocomposites of smaller particles due to existence of a larger contact area between particles, more and stronger filler clusters are formed. Thus, a stronger filler‐‐filler network is formed by decreasing the particle size so that both storage and loss moduli present higher values. The slope of dynamic moduli as a function of frequency decreases with filler loading augmentation in a low‐frequency region, and this solid‐like behavior becomes more significant with particle size reduction. The PP composites in high filler loadings exhibit a yield stress, and weight fraction corresponds to the onset of this well‐defined yield stress and is lower in the case of smaller filler particles. In addition, the polymer chains adsorption on the particles and/or clusters surface and formation of filler‐‐polymer network increases with filler loading augmentation. The influence of these two reinforcing mechanisms leads to a gradual enhancement of the Payne effect and the solid‐like behavior in strain‐ and frequency‐sweep experiments, respectively.