Linear and non-linear rheological behavior of polypropylene/polyamide blends modified with a compatibilizer agent and nanosilica and its relationship with the morphology

• Nanosilica particles locate either on the interface or on the dispersed phase of the 80/20 PP/PA blends depending on their surface treatment.
• A clear relation between Small Amplitude Oscillatory Shear (SAOS) experiments results and morphology and interfacial tension between PP and PA is found.
• The coalescence of PA droplets promoted by an applied continuous flow has been studied.
• An unique equation that links a non-linear viscoelastic parameter obtained by Large Amplitude Oscillatory Shear (LAOS) and the radius of PA droplets has been obtained.

The morphology of immiscible 80/20 polypropylene/polyamide 6 (PP/PA) blends that contain different types of nanosilica and a compatibilizer agent was correlated with their linear and non-linear rheological behavior. Polypropylene grafted with maleic anhydride (PPgMA) was used as compatibilizer agent. Two types of modified silica nanoparticles were added to the blends, one hydrophilic (NSE) and the other hydrophobic (NSH). SEM and TEM microscopy were employed to observe the sea-island morphology of the 80/20 blends. The size of the PA droplets was reduced 12 times when the compatibilizer agent was added; and 25 times when hydrophobic nanosilica (NSH) was additionally included in the formulation. TEM results revealed that NSH particles are preferentially located at the PP-PA interface, whereas NSE particles remain inside the PA droplets. A good agreement between morphology and Small Amplitude Oscillatory Shear tests (SAOS) was observed. At low frequencies a suspension-like rheological behavior was identified for the blends containing nanosilica. The results at intermediate frequencies allowed the evaluation of the shape relaxation time of the droplets. Large Amplitude Oscillatory Shear tests (LAOS) results correlate well with droplets size. The coalescence promoted by flow was investigated, and in the case of the neat binary blend, coalesced blends were obtained. Employing LAOS results determined by measuring blends with a wide range of droplet sizes, an inversely proportional function of a characteristic LAOS parameter with the diameter of the droplets was obtained.

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