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An ultrasound-assisted extrusion system was added to melt extrusion process to prepare polypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs). The relationships among the ultrasound vibration, exfoliation, and dispersion morphology of GNPs in PP matrix, the crystallinity, and the macroscopic properties of nanocomposites were investigated. The properties measurement results showed that the present of ultrasound vibrations increased the conductive properties, decreased the apparent viscosity and crystallinity of PP/ GNPs nanocomposites. FESEM results revealed that the ultrasound vibration increased the exfoliation and dispersion of GNPs in PP matrix. This morphology was benefit for forming electrical and thermal network, therefore the electrical conductivity and thermal conductivity of PP/ GNP nanocomposites were increased. But the powerful vibration that provided by 300 W ultrasound power would reduce the diameter of GNPs, then reduce its conductive properties. FTIR and TGA results showed that ultrasound vibration had less effect on the chemical bond and the degradation of PP/GNPs nanocomposites. POLYM. ENG.

Metallic effect in injection molded parts is created using composites of high-density polyethylene (HDPE) filled with high-sparkle aluminum (Al) pigments (HDPE/Al). The mechanism of micro shrinkage induced by the leafing phenomenon influences the surface topography and roughness, and has been studied with SEM and AFM. Reflectance, whiteness index (WI), and luminance (L*) of the surface were assessed in relation to the surface roughness, the particle sizes, the crystallinity and thermal conductivity of composites. The results show that the leafing induces the micro shrinkage and causes micro caverns, which increased surface roughness. Besides, the length of micro caverns and surface roughness increased as the particle size increased. These morphologies were not benefit for improving reflectance, WI, and L* values, therefore the reflectance, WI, and L* values decreased proportionally with the surface roughness and particle sizes increased. High-sparkle Al pigments improved the crystallinity and thermal conductivity of the composites. A higher reflectance, WI, and L* were associated with a higher crystallinity and a higher thermal conductivity. POLYM. ENG. SCI., 58:642-651, 2018. V C 2017 Society of Plastics Engineers

The metallic effect of polymer composites was produced through the loading of flash aluminum flake pigments (FAFPs) into polymers. This production method could eliminate postprocessing techniques, such as spray coating, painting, or metallization. We used a self-improved, ultrasound-assisted capillary rheometer to explore the rheological behavior of high-density polyethylene composites filled with FAFPs in the absence and presence of ultrasound treatment. The effects of the ultrasound intensity, experimental temperature, filler content, and particle size on the composite viscosity were studied. The results show that the composite viscosity not only decreased as the ultrasound intensity, experimental temperature, and particle size increased but also decreased as the filler content decreased. A viscosity model of the polymer melts was proposed to illustrate the relationship between the viscosity and ultrasonic intensity. The viscosity obeyed the equations under ultrasonic vibration. The predicted results for the composite viscosity complied greatly with the experimental values.