Hybridizing graphitic nanoplatelets (GNP) with commercially functionalized multi-walled carbon nanotubes (MWCNTs) in a polyetherimide (PEI) composite at a total loading of 0.5 wt% resulted in considerable improvements in electrical conductivity, thermal conductivity and dynamic mechanical properties, compared to solely GNP or solely MWCNT composites at the same total loading. The results reveal a synergistic interaction between the GNPs and MWCNTs based on GNP protection against fragmentation of the MWCNTs during high power sonication, while still allowing full dispersion of both fillers, by providing a shielding mechanism against MWCNT damage during dispersion processing. A new process for molecular level dispersion of exfoliated GNPs in PEI is also reported. Field emission scanning electron microscopy revealed strong interactions between PEI and the flat surfaces of GNPs and effectively intercalated GNP morphology within the matrix. GNPs alone can also produce excellent electrical conductivity improvements: at 1.0 wt% of GNP, electrical conductivity of the composite increased by 11 orders of magnitude and the percolation threshold was determined to be between 0.5 and 1.0 wt% of GNP.

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Silane coatings with different thicknesses were synthesized on CNFs for reinforcement of polyethylene composites. The thickness of the silane coating was adjusted by using a basic catalyst to increase the overall reactivity of the silane groups, resulting in a thick coating of ≈46 nm (ca. 90% increase in fiber diameter). DMA performed on the polyethylene composites showed a substantial increase in storage modulus from 1.68 to 2.34 GPa (40%) at low temperatures in the composite with the thick silane coating (≈46 nm) at a low loading of 0.4 wt.‐%. We believe that the silane‐treated nanofillers with thick coatings are very promising for high‐performance nanocomposites with non‐polar polymer matrices. magnified image

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In this work, phase separation in carbon nanofiber (CNF) composites with a blend of ultrahigh molecular weight polyethylene (UHMWPE)/high‐density polyethylene (HDPE) was revealed, and its effects on tribological properties were investigated. Results from morphological analysis by optical and scanning electron microscopy indicated two distinct microstructures: a dispersed UHMWPE phase and a continuous microstructure containing HDPE and CNFs. The addition of CNFs into the UHMWPE/HDPE blend induced a decreased steady‐state torque indicative of a decreased dissolution and improved processability. Because CNFs predominantly resided into the HDPE phase, neat HDPE, a HDPE/CNF composite, and neat UHMWPE samples were also prepared for comparison. Wear results, determined by a pin‐on‐disk apparatus, showed that both initial run‐in and steady‐state wear rates of the UHMWPE/HDPE/CNF nanocomposites were reduced with an increasing concentration of CNFs. The wear resistance of the UHMWPE/HDPE blend was more strongly influenced than neat HDPE by the addition of CNFs, which may have been affected by a reduced dissolution and improved interfacial interaction between the two phases. Results from this study suggested that HDPE may not be appropriate for processing UHMWPE composites, as CNFs reside in the HDPE phase, and HDPE diminishes the wear resistance of the material. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers