Joong-Hee Lee

Preparing PP/clay nanocomposites using a swelling agent

Abstract Polypropylene (PP)/clay nanocomposites (PPCN) were prepared using a swollen organoclay, which had a larger interlayer spacing than pristine organoclay. The organoclay was first treated with a swelling agent (maleic anhydride, MA) and a co-swelling agent in solution. Then, it was melt blended with PP-g-MA to generate a pre-intercalated composite (PIC). Finally, the PIC was blended with PP to obtain a PPCN, which contained small amounts of PP-g-MA. The materials were characterized using X-ray diffraction (XRD), Scanning electron microscopy, Transmission electron microscopy (TEM), and TGA. The XRD graphs showed that the basal spacing of the pristine clay treated with MA was 1.6 nm, which was larger than that of the original clay, but smaller than that of the organoclay. The XRD graphs of the organoclay treated with MA showed double peaks at 3 and 5.5°. As the ratio of MA to the organoclay increased, the peak at 5.5° decreased gradually. TEM micrographs indicated that the clay layers in the pre-intercalated blends were still stacked in an orderly manner. However, partial exfoliation of the clay layers was observed in the PPCN. The nanocomposites prepared with the aid of swelling agents contained some PP-g-MA. Good dispersion of the clay layers gave the PPCN greater thermal stability and an enhanced storage modulus, which indicated a reinforcing effect of the clay in the PP matrix. The increased Tg (derived from Dynamic mechanical analysis) of PPCN implied that the PP macromolecules were intercalated between interlayers of the silicate.

Effect of Polyaniline Functionalized Carbon Nanotubes Addition on the Positive Temperature Coefficient Behavior of Carbon Black/High-Density Polyethylene Nanocomposites

The influence of addition of polyaniline functionalized multiwalled carbon nanotubes (PANI-MWNTs) on the positive temperature coefficient (PTC) characteristics of carbon black (CB) filled high-density polyethylene (HDPE) nanocomposite materials have been studied. Polymer nanocomposites were prepared by the combined solution and melt-mixing process. The experimental results showed that the PTC intensity and maximum resistivity of the hybrid nanocomposites were obviously influenced by the polyaniline functionalization of multiwalled carbon nanotubes (MWNTs). A noticeable PTC of resistivity was observed for PANI-MWNTs/CB/HDPE hybrid nanocomposites near the melting point of HDPE. This is due to the significant volume expansion near the melting point of the HDPE in presence of hybrid fillers and a sudden increase of the resistivity due to the disconnection of the conductive paths. The PTC effect of CB/HDPE composites can be effectively modified by the addition of PANI-MWNTs.

Intercalation behavior of polyimide/organoclay nanocomposites during thermal imidization

Abstract To understand the intercalation behavior of polyimide (PI)/clay nanocomposites during thermal imidization, two different types of poly(amic acid) (PAA) were synthesized, and the corresponding hybrids with organically treated clays (O-MMT) were also prepared. The changes in molecular structure of the polymer matrix, interlayer spacing, and fracture morphology with a series of thermal imidization steps were investigated. The PAA/clay nanocomposites initially showed two X-ray diffraction peaks, indicating two levels of intercalation. As the temperature at which the thermal imidization step was performed increased, the peak intensity of the higher angle peak increased, and it remained as a unique peak at 2θ=6.70 (d-spacing of 13.2xa0A) for both PI(1), based on pyromellitic dianhydride (PMDA)+4,4′-oxydianiline (ODA), and PI(2), based on PMDA+4,4′-(9-fluorenylidene)-dianiline (9FDA). However, the lower angle peak became smaller and broader, and the angle became higher. This peak finally disappeared after thermal treatment at 300 °C for PI(1), but did not disappear completely for PI(2), although the peak showed a marked decrease in intensity and became broader.

Preparation and characterization of carbon nanotube filled poly (2-hydroxyethylmethacrylate) nanocomposites

Poly(2-hydroxyethylmethacrylate) (PHEMA)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared by solvent casting using dimethyl formamide (DMF) solvent via sonication process. Effect of addition of MWNTs on the properties of nanocomposites was investigated at different nanofiller contents. Uniform dispersion and distrubution of nanotubes in PHEMA matrix is obtained within the studied composition range. The electrical resistivity, dielectric permittivity and the loss factor of dry PHEMA and PHEMA/MWNT nanocomposites were studied by varying the MWNT concentration in the frequency range of 30 Hz to 1 MHz. The obtained results indicated that the addition MWNTs to PHEMA matrix decreases the electrical resistivity and increases the dielectric constant at low dielectric loss. The thermal properties of the PHEMA/MWNT nanocomposites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal behavior of these nanocomposites was also compared with PHEMA homopolymer. The glass transition temperature (Tg) of PHEMA homopolymer was found to increase with nanotube concentration. Experimental results also demonstrated that the incorporation of the MWNTs into the PHEMA matrix not only enhanced the mechanical property but also increased and the thermal stability of the PHEMA/MWNT nanocomposites increases with increase in MWNT concentration.

Graphene produced by electrochemical exfoliation

Abstract: The production of graphene by electrochemical exfoliation is described and methods of synthesis of high-quality graphene nanosheets on a large scale via the electrochemical exfoliation of graphite and/or electrochemical reduction of exfoliated graphite oxide in a selected electrolyte solution are discussed in depth. The potential of the process is explored and applications of electrochemically exfoliated graphene are examined.

Positive Temperature Coefficient Characteristics of Multi-walled Carbon Nanotube Filled Polyvinylidene Fluoride Nanocomposites

Composites of polyvinylidene fluoride (PVDF) and multi-wall carbon nanotubes (MWNT) were prepared by a melt mixing process. Temperature dependence of electrical properties of the nanocomposites was investigated for composites containing different amounts of MWNT. An obvious positive temperature coefficient was observed. It was found that resistivity of the composites was decreased with increasing MWNT content and the electrical percolation threshold was formed at 3 wt% MWNT, which were caused by the formation of conductive chains in the composites. The mechanism of the positive temperature coefficient behavior of the nanocomposites is discussed. The rheological results showed that the materials experience a fluid–solid transition at the composition of 2 wt%, beyond which a continuous MWNT network forms throughout the matrix leading to a percolated network structure, which further indictes the nanotubes were dispersed uniformaly, in the PVDF matrix.

Sharkskin Mechanism of LDPE and the Dispersion of Inorganic Fillers in Flow

The correlation between the sharkskin formation of polymers and the flow‐induced dispersion of fillers is discussed. The rheological behaviors of low‐density polyethylene (LDPE) and LDPE/TiO2 composites were investigated and analyzed based on the temperature dependence of critical points of the sharkskin formation. This examination revealed the influence of shear thinning on sharkskin behavior. The analysis indicated that the sharkskin formation of LDPE was governed by the mechanism of molecular absorption and de‐absorption at the flow boundary, or by wall‐slip at the polymeric layer with low viscosity. Sharkskin formation of LDPE occurs at different ranges of shear rates, depending on the mechanism in effect. In a further study, the shear‐induced de‐aggregation and dispersion of the TiO2 in LDPE was found to occur at a shear‐rate range that was close to the range for sharkskin formations that are controlled by the adsorption mechanism.

Synergistic Enhancement on the Conductivity of Polyaniline via Copolymerization and Carbon Nanotubes

Polyaniline and aniline/5‐aminoisophthalic acid (AIA) copolymer have been successfully synthesized via oxidation polymerization, as well as their composites containing carbon nanotubes. AIA can benefit the formation of quinoid rings in the aniline polymerization and promote the conductivity of the copolymer. IR and Raman spectra reveal AIA/aniline copolymers have both benzonoid and quinoid rings, as well as their doped structures. Good conductivity of the copolymer could be achieved at high AIA content. Carbon nanotubes can also simultaneously promote the formation of quinoid rings in the copolymer, enhance conductivity and improve thermal stability. The copolymerization of AIA with aniline and the introduction of carbon nanotubes show a synergistic enhancement of conductivity.

Synthesis of graphene-based polymeric nanocomposites

Graphene, a single atom thick two-dimensional sheet of sp2 – bonded carbon atoms, is one of the allotropes of carbon. It is a monolayer of carbon atoms arranged into a two-dimensional planar honeycomb lattice. It is a unique material due to its superior mechanical property, exceptional thermal and electrical properties, along with high specific area. Due to these excellent properties, graphene has been used as filler in advanced nanocomposites for various applications such as electronics, electrode for supercapacitors, sensors, and structural composites. However, the fabrication of graphene and graphene oxide based nanocomposites faces significant challenges including the surface modification for better interfacial interactions and uniform dispersion of graphene sheets in polymer matrices. This work will provide the recent research progress in graphene based polymeric nanocomposites including the synthesis method of graphene, its surface modification method, fabrication techniques and the applications of graphene nanocomposites.

Study of the Characteristics of Hydrogen-Gas Filling Process of Ultra-Light Composite Tanks for Fuel-Cell Vehicles

났다. Abstract: In this research, we investigated the hydrogen-gas filling characteristics of ultra-light composite tanks that have a plastic or aluminum liner inside the composite shell. The study was performed for different gas and tank temperatures. The temperature changes at various positions in the Type-4 tank during hydrogen-gas filling were monitored in order to understand the effects of the filling conditions. The results were compared with those obtained for a Type-3 tank. As the filling speed was increased, a quicker temperature rise was observed, and the temperature distribution over the entire region showed significant discrepancies.