Effect of nano-silica filler on the rheological and morphological properties of polypropylene/liquid-crystalline polymer blends

A fumed hydrophilic nano-silica-filled polypropylene (PP) composite was blended with a liquid-crystalline polymer (LCP; Rodrun LC5000). The preblended polymer blend was extruded through a capillary die; this was followed by a series of rheological and morphological characterizations. The viscosity of the PP matrix increased with the addition of the hydrophilic nano-silica. At shear rates between 50 and 200 s^-1, the composite displays marked shear-thinning characteristics. However, the incorporation of LC5000 in the PP composite eliminated the shear-thinning characteristic, which suggests that LC5000 destroyed the agglomerated nano-silica network in the PP matrix. Although the viscosity ratio of LCP/PP was reduced after the addition of nano-silica fillers, the LCP phases existed as droplets and ellipsoids. The nano-silicas were concentrated in the LC5000 phase, which hindered the formation of LCP fibers when processed at high shear deformation. We carried out surface modification of the hydrophilic nano-silica to investigate the effect of modified nano-silica (M-silica) on the morphology of the PP/LC5000 blend system. Ethanol was successfully grafted onto the nano-silica surface with a controlled grafting ratio. The viscosity was reduced for PP filled with ethanol-M-silica when compared to the system filled with untreated hydrophilic nano-silica. The LC5000 in the (PP/M-silica)/LC5000 blend existed mainly in the form of fibrils. At high shear rates (e.g., 3000 s^-1), the LC5000 fibril network was formed at the skin region of the extrudates. The exclusion of nano-silica in the LC5000 phase and the increased viscosity of the matrix were responsible for the morphological changes of the LCP phase.