Structure Formation and Macrorheology of Nanofilled Composites of Polypropylene/Co-polyamide/Mixed Oxide

Abstract

The influence of the content of additive of the nanosize combined sub-stance aluminium oxide/silica on the formation of microfibrillar structure within the thermodynamically incompatible blend of polypropylene/co-polyamide (PP/CPA) is studied. As established, nanoparticles (NPs) of Al2O3/SiO2 are an effective modifier in the entire studied range of their concentrations (0.1–3.0 wt.%). The mixed oxide exhibits a synergistic result: the average diameter of PP microfibrils (đ) decreases by 2 times. At the same time, the content of nanofiller is only of 0.1 wt.% that is an order of magnitude less than when using NPs of its individual compo-nents. The most subtle and homogeneous morphology is formed in the composition containing 1.0 wt.% of the modifier: the value of đ has a minimum value (1.2 μm versus 4.0 μm for the original blend), the share of microfibrils is the maximum (97.0%), and the value of the index of variability (dispersion) decreases by 5 times. As shown, the change in microrheological processes in the presence of a nanoadditive affects sig-nificantly the macrorheological characteristics of melts of filled polymer dispersions. Mixed oxide nanoparticles increase the degree of deviation from the Newtonian flow regime of three-component systems. The for-mation of anisotropic structures (PP microfibrils) in mixtures of PP/CPA/mixed oxide causes a drop in the effective viscosity compared to the melts of the original components. At the same time, the elasticity of the melts of the modified compositions increases and the values of the ex-trudate expansion coefficient (B) reach values higher than the additive ones. The indicators of the maximum deformation of the melt jet of nano-filled systems in the longitudinal tensile field (Fmax) also increase. The de-pendences of B and Fmax on the composition of the mixture have an ex-tremum at a mixed oxide content of 1.0 wt.% due to the formation of PP microfibrils with the highest degree of anisotropy.