Characteristics of Ethylene−Methyl Methacrylate Copolymer and Ultrahigh Molecular Weight Polyethylene Composite Filled with Multiwall Carbon Nanotubes Prepared by Gelation/Crystallization from Solutions

Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) and ethylene-methyl methacrylate copolymer (EMMA) composites containing multiwall carbon nanotubes (MWNTs) were prepared by the gelation/crystallization method. The conductivity and Young's modulus were obtained as a function of EMMA content. When 5 wt % MWNT was admixed into neat EMMA known as an insulator, conductivity of the composite reached ca. 0.05 S/cm, which was much higher than the conductivity of UHMWPE with 5 wt % MWNT. The UHMWPE/EMMA-MWNT composite containing 14 wt % EMMA and 5 wt % MWNT could be stretched up to 50 times. The conductivity and Young's modulus reached 3.84 × 10 -3 S/cm and 37 GPa, respectively, which denoted a successful result for preparing a conductive material with high modulus. The electrical conductivity of the composite increased with increasing draw ratio, indicating that the band gap became narrower by elongation. Furthermore, the conductivity increased with elevating temperature, but it tended to decrease beyond the melting point of the composites. Such a temperature dependence of the conductivity is perfectly different from the characteristics of polymer-carbon fiber and polymer-carbon black particles reported already. Such interesting phenomena were mainly analyzed by using X-ray and scanning electron microscopy in terms of morphological aspects.

Electrical properties of segregated ultrahigh molecular weight polyethylene/multiwalled carbon nanotube composites

“…At low MWNT content (1%), the conductivity increases with frequency, following the power law sðf Þ $ f s where s is the critical exponent, which follows the inequality 0 s 1, characterizing hopping conduction. For 3-5% MWNT content, the conductivity remains nearly independent of the frequency below 10 4 Hz, and at higher frequency, the conductivity increases with frequency following the power law sðf Þ $ f s just like 1% MWNT content. When increasing the MWNT content above 7%, the conductivity becomes less dependent on the frequency and the frequency value of the step shifts to higher frequency.…”

“…As the MWNT content decreases, the intensity of PTC effect increases. Compared with that of the composites of polyethylene and CB 4 or CFs, 9 the intensity of PTC effect of UHMWPE-MWNT composites is not so large considering the higher agglomerating force and bigger aspect ratio of MWNTs. Moreover, the thermal expansion of UHMWPE beyond the melting point is not significant enough to cause the separation of the contacted MWNTs, especially when the MWNT content is high, so the conductive paths for charge transportation still exist.…”

“…When MWNT content is above 7%, the plots of dielectric loss are the straight line and the slope of these lines is about À1, which means that DC conductivity is more significant than interfacial polarization at higher MWNT content. When MWNT content is below 7% and the frequency is higher than 10 4 Hz, the plots of dielectric loss change from straight lines to sigmoidal curves. These sigmoidal curves indicate that the interfacial polarization becomes pronounced since the interfacial polarization equation of dielectric loss does not follow a linear behavior at higher frequencies.…”

“…Furthermore, the dispersion of multiwalled carbon nanotubes (MWNTs) could be improved drastically using small amount of ethylenemethyl methacrylate copolymer as one of components, when MWNTs with curved grapheme sheets with few defects were used as fillers into UHMWPE matrix. 4 In this article, using the paraffin as solvent, the segregated UHMWPE-MWNT composites were made. Compared with our previous results, 3,4 the lower percolation threshold and higher maximum conductivity are obtained because the new method using the paraf-fin as solvent can disperse MWNTs as isolated agglomerates in the matrix rather than a network of the particles.…”

“…4 In this article, using the paraffin as solvent, the segregated UHMWPE-MWNT composites were made. Compared with our previous results, 3,4 the lower percolation threshold and higher maximum conductivity are obtained because the new method using the paraf-fin as solvent can disperse MWNTs as isolated agglomerates in the matrix rather than a network of the particles. EXPERIMENTAL UHMWPE (Hizex; Mitsui Chemicals) with an average viscosity molecular weight (M n ¼ 6,300,000) and fibrous type MWNTs were used as test specimen.…”