Yun Kyun Lee

Effect of multi-walled carbon nanotube dispersion on the electrical, morphological and rheological properties of polycarbonate/multi-walled carbon nanotube composites

The effect of a multiwalled carbon nanotube (MWCNT) dispersion on the electrical, morphological and rheological properties of polycarbonate (PC)/MWCNT composites was investigated, with and without pretreating the MWCNTs with hydrogen peroxide oxidation and lyophilization. The resulting PC/treated MWCNT composites showed higher electrical conductivity than the PC/untreated MWCNT composites. The morphological behavior indicated the treated composites to have greater dispersion of MWCNTs in the PC matrix. In addition, the electromagnetic interference shielding efficiency (EMI SE) of the treated composites was higher than that of the untreated ones. Rheological studies of the composites showed that the complex viscosity of the treated composites was higher than the untreated ones due to increased dispersion of the MWCNTs in the PC matrix, which is consistent with the electrical conductivity, EMI SE and morphological studies of the treated composites. The latter results suggested that the increased electrical conductivity and EMI SE of the treated composites were mainly due to the increased dispersion of MWCNTs in the PC matrix.

Effect of multi-walled carbon nanotube dispersion on the electrical and rheological properties of poly(propylene carbonate)/poly(lactic acid)/multi-walled carbon nanotube composites

In this study, the morphological, electrical, and rheological properties of the poly(propylene carbonate) (PPC)/poly(lactic acid) (PLA)/multi-walled carbon nanotube (MWCNT) composites were investigated. From the results of transmission electron microscopy of the PPC/PLA/MWCNT composites, the MWCNT preferred to locate more in the PPC phase than in the PLA phase. This maybe due to the lower interfacial tension of the PPC/MWCNT composites compared to that of the PLA/MWCNT composites. The electrical conductivities of the PPC/PLA/MWCNT composites were higher than those of the PPC/MWCNT and the PLA/MWCNT composites, which was likely due to the selective localization of the MWCNT in the PPC phase (continuous phase). From the results of the complex viscosity of the composites, the ratio of increasing the complex viscosity of the PPC/MWCNT composites with the MWCNT content was higher than that of the PLA/MWCNT composites. This is maybe due to the fact that the MWCNT dispersion in the PPC phase was higher than in the PLA phase. The results from the morphology, electrical conductivity, and complex viscosity of the PPC/PLA/MWCNT composites suggest that the selective localization of the MWCNT in the PPC phase can improve the conductive path and increase the electrical conductivity of the PPC/PLA/MWCNT composites.

Effects of hybrid fillers on the electrical conductivity and EMI shielding efficiency of polypropylene/conductive filler composites

AbstractIn this study, the effects of hybrid fillers on the electrical conductivity and electromagnetic interference shielding efficiency (EMI SE) of the polypropylene (PP)/Ni-coated carbon fiber (NCCF) composites with the second fillers, such as multi-walled carbon nanotube (MWCNT), carbon black and TiO2, were investigated. The morphological behavior showed that the NCCF and the second fillers, such as MWCNT, carbon black and TiO2, seemed to disperse evenly in the PP phase. Among the PP/NCCF composites with MWCNT, carbon black and TiO2, the PP/NCCF/TiO2 composites showed the higher electrical conductivity and EMI SE compared with those of the PP/NCCF/MWCNT and PP/NCCF/carbon black composites. This was the case because TiO2 has high dielectric constant with dominant dipolar polarization. The estimated EMI SE values of the PP/NCCF composites with MWCNT, carbon black and TiO2 are in good agreement with the experimentally obtained values of the composites. Based on the electrical properties of the composites, it was suggested that TiO2 was the most effective second filler when it was hybridized with the NCCF of the PP/NCCF/TiO2 composite. Based on the analysis of the flexural modulus, the PP/NCCF/MWCNT composite had a higher flexural modulus than the PP/NCCF/TiO2 and PP/NCCF/carbon black composites because of the higher aspect ratio of the MWCNT.

Effects of PP-g-MAH on the Mechanical, Morphological and Rheological Properties of Polypropylene and Poly(Acrylonitrile-Butadiene-Styrene) Blends

The effects of maleic anhydride-grafted polypropylene (PP-g-MAH) addition on polypropylene (PP) and poly(acrylonitrile-butadiene-styrene) (ABS) blends were studied. Blends of PP/ABS (70/30, wt%) with PP-g-MAH were prepared by a twin-screw extruder. From the results of mechanical testing, the impact, tensile and flexural strengths of the blends were maximized at a PP-g-MAH content 3 phr. The increased mechanical strength of the blends with the PP-g-MAH addition was attributed to the compatibilizing effect of the PP and ABS blends. In the morphological studies, the droplet size of ABS was minimized (6.6 μm) at a PP-g-MAH content of 3 phr. From the rheological examination, the complex viscosity was maximized at a PP-g-MAH content of 3 phr. These mechanical, morphological and rheological results indicated that the compatibility of the PP/ABS (70/30) blends is increased with PP-g-MAH addition to an optimum blend at a PP-g-MAH content of 3 phr.

Effects of hybrid fillers on the electromagnetic interference shielding effectiveness of polyamide 6/conductive filler composites

The effects of hybrid conductive fillers on the electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of polyamide 6 (PA6)/conductive filler composites were investigated. Nickel-coated carbon fiber (NCCF) was used as the main filler and multi-walled carbon nanotube (MWCNT), nickel-coated graphite, carbon black, and titanium dioxide (TiO2) were used as the second fillers in this study. From the results of morphological studies of the PA6/NCCF/second filler composites, NCCF easily formed an electrical pathway since it has a high aspect ratio and random orientation, and the second fillers seemed to disperse evenly in the PA6 matrix. The electrical conductivity and EMI SE of the PA6/NCCF composites were increased with the increase of NCCF content. Among the second fillers used in this study, TiO2 appeared to be the most effective second filler with regard to increasing the EMI SE and electrical conductivity of the PA6/NCCF composite. This was probably because TiO2 has a high dielectric constant with dominant dipolar polarization, consequently leading to greater shielding effectiveness due to the absorption of electromagnetic waves. From the above results of EMI SE and electrical conductivity, it was suggested that the TiO2 produced a synergistic effect when it was hybridized with the NCCF of the PA6/NCCF/TiO2 composites.

Influence of lactic acid-grafted multi-walled carbon nanotube (LA-g-MWCNT) on the electrical and rheological properties of polycarbonate/poly(lactic acid)/ LA-g-MWCNT composites

AbstractThe effects of lactic acid-grafted multi-walled carbon nanotube (LA-g-MWCNT) on the electrical and rheological properties of the polycarbonate (PC)/poly(lactic acid) (PLA)/LA-g-MWCNT composite were studied. To increase dispersion of the conductive filler in the PC/PLA (70/30) blend, chemically-modified MWCNT, which is LA-g-MWCNT, was used as a compatibilizer between the conductive filler and polymers. For the PC/PLA/LA-g-MWCNT composite, the increased values of the electrical conductivity, electromagnetic interference shielding effectiveness, and complex viscosity were observed compared to those of PC/PLA/MWCNT composite. The results suggested that the increased dispersion of the LA-g-MWCNT in the PC/PLA (70/30) blend is caused by increased connectivity of the MWCNT-MWCNT network structure of the composite. The interfacial tension of the PLA/ MWCNT composite was lower than that of the PC/MWCNT composite. The lower value of interfacial tension of the PLA/MWCNT composite affected the dispersion of the MWCNT in the PLA phase (dispersed phase) more than in the PC phase (continuous phase). After hydrolysis, the PC/PLA/LA-g-MWCNT composite showed higher electrical conductivity than the PC/PLA/MWCNT composites. As a result, it is suggested that the increased dispersion of the LA-g-MWCNT in the PC/PLA blend has affected the increase in the electrical conductivity and lowering of the hydrolytic degradation of the PC/PLA/LA-g-MWCNT composite compared to the PC/PLA/MWCNT composite.

Effects of Fiber Characteristics on the Rheological and Mechanical Properties of Polycarbonate/Carbon Fiber Composites

Rheological and mechanical properties of the polycarbonate (PC)/carbon fiber (CF) composites with different initial fiber length, sizing effect of the fiber, fiber content and screw speed have been studied. PC/CF composites were prepared by twin screw extruder. In the studies of sizing effect of the fiber on the rheological properties of the PC/CF composites, the viscosities of the composites prepared with the sized carbon fibers gave higher values than that prepared with unsized carbon fibers because of the increase in the fiber length after extrusion for the sized fibers. From the results of the effect of screw speed on the rheological and mechanical properties of PC/CF composites, we found that the viscosity and tensile strength decreased with increasing screw speed. This is mainly due to that the fact that the fiber length after extrusion has been decreased from 163 to 148 μm with the increase of the screw speed from 100 to 200 rpm when the fiber content used in the composites is equal. From the above results, it is suggested that the fiber length after extrusion of the PC/CF composites has a strong effect on the rheological and mechanical properties of the composites. Also, a relationship among the initial fiber length, sizing effect of the fiber, fiber content and screw speed has been studied comprehensively for the PC/CF composites.