Sulfonated poly(ether ketone ketone) ionomers as proton exchange membranes

Sulfonated poly(ether ketone ketone) ionomers (SPEKK) with ion‐exchange capacities (IEC) between 0.2 and 3.4 meq/g were prepared by sulfonating PEKK with a mixture of concentrated and fuming sulfuric acids. Sulfonation occurs only on the phenyl rings attached to ether and ketone groups. The glass transition temperature of the dry SPEKK ionomers increased linearly with increasing IEC, and the ionomers were thermally stable to ～250°C, above which desulfonation occurred. Water‐swollen ionomers exhibited microphase separated morphologies, and the average correlation length determined by small angle X‐ray scattering increased with increasing IEC. The proton conductivity of hydrated SPEKK membranes measured by impedance spectroscopy ranged from ～10^–3 to 10^–1 S/cm as the IEC increased from ～1.0 to 2.4 meq/g. Single cell performance curves on membrane‐electrode assemblies (MEA) indicated that the SPEKK membranes approached the performance of Nafion? for an IEC of 2 meq/g. POLYM. ENG. SCI., 45:1081–1091, 2005. © 2005 Society of Plastics Engineers     

Enhanced surface morphologies of screen-printed carbon nanotube films by heat treatment and their field-emission properties

A heating process for obtaining free-standing carbon nanotube emitters is presented with the aim of improving field-emission properties from the screen-printed multiwalled carbon nanotube (MWCNT) films. Using an atmosphere with an optimum combination of nitrogen and air for heat treatment of CNT films, the CNT emitters can be made to protrude from the surface. This allows for a high emission current and the formation of very uniform emission sites without special surface treatment. The morphological change of the CNT film by this technique has eliminated additional processing steps, such as surface treatment which may result in secondary contamination and damage to the film. Despite its simplicity the process provides a high reproducibility in emission current density which makes the films suitable for practical applications.     

A kinetic model for polystyrene (PS) pyrolysis reaction

A mathematical model for the pyrolysis reaction of polystyrene (PS) in a semi-batch reactor has been presented. The thermal degradation of PS was flexibly modeled by a combination of random and specific chain-end scissions. Numerical simulation was used to investigate the effect of operating conditions on the PS products spectrum, the results of which were validated by the experimental data. It was found that as the reaction temperature increased (decreased), the monomer fraction in the products became lower (higher) while the trimer higher (lower). No significant variation in the product composition was, however, observed while constant temperature was maintained. These results indicate the reaction temperature is an effective manipulated variable for the control of products composition of PS pyrolysis. The calculation of the optimum temperature trajectories through the optimization study can thus be of interest for achieving productivity enhancement in plastics pyrolysis processes. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Relationship between chemical degradation and thickness loss of an amine-cured epoxy coating exposed to different UV environments

The relationship between chemical degradation and thickness loss of an unpigmented, non UV-stabilized, crosslinked amine-cured epoxy coating exposed to three UV conditions was investigated. Spin-coated samples having a thickness of approximately 7 μm on an Si substrate were prepared from a stochiometric mixture of a bisphenol A epoxy resin and a tetra-functional amine curing agent. Samples were exposed outdoors and to two accelerated laboratory UV environments. Chemical degradation and thickness loss were measured by transmission Fourier transform infrared spectroscopy (FTIRS) and laser scanning confocal microscopy (LSCM), respectively. In addition, surface roughness and morphological changes were measured by atomic forcemicrosocopy (AFM) and LSCM. Substantial chemical degradation, thickness loss, and morpholocal changes occurred in the exposed films, and the rate of chemical degradation was greater than that due to the thickness loss. This additional chemical loss was attributed to an inhomogeneous degradation process in which nanoscale localized depressions initiate at certain sites on the surface, which then enlarge and deepen with exposure time. The results of this study provide a better understanding of the degradation mechanism and should lead to the development of scientific-based models for predicting the service life of crosslinked amine-cured epoxy coatings. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL     

Preparation and electrical properties of metal sulfides–amidoximated PAN composite film

To improve the electrical conductivity of polyacrylonitrile (PAN) film, metallic sulfides and PAN composite film were prepared by the chelating method. Dense PAN film and porous PAN film were prepared by dry process and wet process, respectively. These PAN films were treated to NH₂OH solution to introduce the amidoxime group coordinated with metallic ion. Cu⁺² and Cd⁺² ions were adsorbed to amidoximated PAN films, the sulfur ion was treated with metal-adsorbed PAN films, and thus CuS—and CdS–PAN composite films were prepared. The adsorptive capacity of amidoximated PAN film for the Cu⁺² ion was independent of the morphology of the PAN film, but the adsorptive capacity of the Cd⁺² ion on amidoximated PAN film was dependent on porosity of the polymer. Adsorptive capacity of amidoximated porous PAN film for Cd⁺² was improved about four times than that of amidoximated dense PAN film. The electrical conductivities of CuS–dense and porous PAN composite film were both 10^?1 S/cm in optimum condition, but because of the difference in adsorptive capacity, the electrical conductivities of CdS–dense and CdS–porous PAN composite films were 10^?9 S/cm and 10^?4 S/cm, respectively. Additionally, because CdS was known as a photoconductive material, the photoconductive properties of CdS–porous PAN composite film were investigated.     

Rheological and electrical properties of polycarbonate/multi-walled carbon nanotube composites

Rheological and electrical properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) were studied. The MWNT was funtoinalized by treating with the hydrogen peroxide (H₂O₂). The H₂O₂ treated MWNT was dried by thermal and freeze drying methods. From the morphological studies, the degree of entanglement of the MWNT was decreased after treating with the H₂O₂. For the H₂O₂ treated MWNT (thermal drying), the length of the MWNT was shortened compared that of the H₂O₂ treated MWNT (freeze drying). The rheological and electrical properties of the PC/MWNT (H₂O₂ treated) composites increased compared that of the PC/MWNT (untreated) composites. Also, the electrical conductivity showed higher value for the PC/MWNT (H₂O₂ treated, freeze drying) composites compared that of the PC/MWNT (H₂O₂ treated, thermal drying) composites. From the results of the morphological, rheological, and electrical properties of the PC/MWNT composites, it is suggested that the electrical and rheological properties of the PC/MWNT composites are affected by the MWNT-MWNT network structure, which is related with the MWNT morphologies such as the degree of aggregation and aspect ratio of the MWNT.     

Mechanical and thermal properties of ceramic‐modified poly(amide imide)

Poly(amide imide)–epoxysilane (coupling agent) composites were reacted with silica, a condensation product of tetraethylorthosilicate (TEOS), by a sol–gel process and were then cast into films. After this procedure, the chemical characteristics and mechanical and thermal properties were measured. Fourier transform infrared showed that silica existed in the poly(amide imide) matrix. When a proper amount of silica was added to the poly(amide imide) matrix, the tensile strength, elongation, and toughness increased greatly. A poly(amide imide)/30 wt % epoxysilane composite with 20 wt % TEOS had the best mechanical properties. Thermogravimetric analysis under nitrogen and oxygen atmospheres indicated that the char contents increased with the amount of silica. The glass‐transition temperatures of the poly(amide imide)–silica nanocomposites were observed around 170–180°C with differential scanning calorimetry. This approach may be a new method for the low‐temperature thermal curing of poly(amide imide). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1780–1788, 2004     

Influences of metallic polymeric materials on the properties of fresh polyester and acrylic polymer concrete

To investigate the influences of three metallic polymeric materials in polyester and acrylic fresh polymer concretes (PCs), PC‐incorporated different levels of these materials have been investigated for their properties of fresh PC. The mix design was made and optimized for workability, strength, and economy, depending on the resin viscosity, the intended use, and the additional quantities of these polymeric materials. The properties investigated include workability, working time, and curing time of fresh PC. It is concluded that these polymeric materials offer the possibility of improving properties of polyester and acrylic fresh polymer concretes. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Fabrication of SiO2-ZrO2 composite fiber mats via electrospinning

(1 − x)SiO₂-(x)ZrO₂ (x = 0.1, 0.2) composite fiber mats were prepared by electrospinning their sol-gel precursors of zirconium acetate and tetraethyl orthosilicate (TEOS) without using a polymer binder. The electrospun composite fibers were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and mercury porosimetry. The composite fibers having a tetragonal crystalline ZrO₂ were obtained by calcining the electrospun composite fibers at high temperatures. The results show that the structure and crystallization of ZrO₂ in the composite fibers can be controlled by sintering temperature, while the porosity and morphology of the fiber mats did not depend on the sintering temperature.     

Effects of diacrylate monomers on the mechanical properties of polymer concrete made with wet aggregates

Because normal polymer concrete does not work well with wet aggregates, diacrylate (DA) monomers were evaluated for improving the mechanical properties of polymer concrete made with wet aggregates. Zinc diacrylate (ZDA) and calcium diacrylate (CDA) were each used as an additive to resins (two epoxies). The variables were the amount of diacrylate monomers and the aggregate conditions (wet or dry). Compressive strength, flexural strength, workability, working time, and curing time were measured. ZDA was found to improve the workability and the working time, and CDA was found to improve the compressive and the flexural strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1077–1085, 2004