Polypropylene (PP) nanocomposites reinforced with different types of graphene nanoplatelets (GNPs) and their hybrid systems are prepared via melt extrusion. On the basis of experimental analysis and simulation, the factors of thermal property of the PP/GNPs nanocomposites, including GNPs size, weight filling ratio and proportion of various sizes, are systematically investigated. At high GNPs content (9,12 wt %), GNPs are widely distributed in PP matrix and the thermal paths are basically formed. The thermal conductivity of composites is determined by the size and thermal properties of GNPs. At low GNPs content (6 wt %), for single system, the larger diameter with moderate distribution would be more conducive to achieve the higher thermal conductivity, indicating the formation of thermal paths dramatically affects the thermal conductivity. For hybrid system, the PP filled with medium and small diameter GNPs obtains the highest thermal conductivity at the ratio of medium diameter GNPs to small diameter GNPs is 8:2, and is 23.8% higher than the single system of PP filled with small diameter GNPs. More precisely, the small diameter GNPs plays a role in connecting the scattered medium diameter GNPs, as mass thermal paths are formed. This shows that the distribution state by combining the synergistic effect of various GNPs significantly affects the thermal conductivity of PP/GNPs nanocomposites. Moreover, a numerical simulation dealing with the synergistic effect of different GNPs, is developed on the thermal conductivity of GNPs-reinforced PP matrix. The heat flux images demonstrate the existence of synergistic effect between different type of GNPs.
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.
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