Melt‐mixed polypropylene/acrylonitrile‐butadiene‐styrene blends with multiwall carbon nanotubes: Effect of compatibilizer and modifier on morphology and electrical conductivity

Cocontinuous blends of 45/55 polypropylene (PP)/acrylonitrile‐butadiene‐styrene (ABS) with multiwall carbon nanotubes (MWNT) were prepared by melt‐mixing in a conical twin‐screw microcompounder. PP‐grafted‐maleic anhydride (PP‐g‐MA) and styrene MA were used as compatibilizers for PP/ABS blends. Scanning electron microscopic observations showed phase segregation of PP‐g‐MA in the blends. State of dispersion of MWNT in the presence or absence of the compatibilizers was assessed through AC electrical conductivity measurements and crystallization studies of the blends. An improvement in AC electrical conductivity was observed in blends in presence of either styrene MA or dual compatibilizers. The lowest electrical percolation threshold was achieved at 0.1 wt % of MWNT using sodium salt of 6‐amino hexanoic acid‐modified MWNT. Significant increase in crystallization temperature of PP phase of blends with MWNT was observed in the presence of compatibilizers as compared to blends without compatibilizers. An attempt has been made to address the complex issues of phase segregation, compatibilization, and dispersion of MWNT in cocontinuous blends of PP/ABS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Composites of Ultrahigh‐Molecular‐Weight Polyethylene with Graphene Sheets and/or MWCNTs with Segregated Network Structure: Preparation and Properties

UHMWPE/MWCNT and UHMWPE/GNS composites with a segregated network are prepared. TEM and SEM images indicate that the conducting fillers are distributed on the UHMWPE surface and form a segregated conducting network. The percolation threshold of UHMWPE/GNS composites is ≈0.25 wt% and that of UHMWPE/MWCNT composites is 0.20 wt%. The electrical conductivity of UHMWPE/GNS composites is almost four orders of magnitude lower than that of the UHMWPE/MWCNT composites. For equivalent concentrations of GNS and MWCNT, the composites with hybrid fillers exhibit a lower percolation threshold and a higher conductivity than that with GNS or MWCNT alone. Due to the high strength of the fillers and the segregated network structure, the mechanical properties of the composites first increase and then decrease with increasing filler content.

     

Synthesis and characterization of core‐shell SiO2 nanoparticles/poly(3‐aminophenylboronic acid) composites

SiO₂/Poly(3‐aminophenylboronic acid) (PAPBA) composites were synthesized under different experimental conditions, using ultrasonic irradiation method. Polymerization was carried out in the presence of sodium fluoride and D ‐fructose to anchor 3‐aminophenylboronic acid groups on to SiO₂ surface. The SiO₂/PAPBA nanocomposite prepared by NaF and D ‐fructose in the polymerization medium was found to show different morphology, electrical properties, thermal behavior and structural characterization in comparison to the nanocomposites prepared under other conditions. Ultrasonic irradiation minimizes the aggregation of nanosilica and promotes anchoring of PAPBA units over SiO₂ surface. The morphology of PAPBA/ SiO₂ nanocomposite was investigated by using transmission electron microscopy, UV‐visible spectroscopy; thermogravimetric analysis, Fourier transform infrared spectroscopy, and X‐ray diffraction analysis were used for characterization. Transmission electron microscope of the nanocomposites observation shows that SiO₂/PAPBA composite, prepared with D ‐fructose and NaF under ultrasonication has a core–shell morphology. The thermal and crystalline properties of core‐shell SiO₂/PAPBA nanocomposite was prepared via ultrasonication method is different from the SiO₂/PAPBA nanocomposite prepared via conventional stirring method, in which SiO₂ nanoparticles are submerged in PAPBA. Conductivity of the composite prepared via ultrasonication shows around 0.2 S/cm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2743–2750, 2007     

Bamboo-like N-doped carbon nanotubes encapsulating M(Co,Fe)-Ni alloy for electrochemical production of syngas with potential-independent CO/H2 ratios

The electrochemical conversion of CO₂-H₂O into CO-H₂ using renewable energy is a promising technique for clean syngas production. Low-cost electrocatalysts to produce tunable syngas with a potential-independent CO/H₂ ratio are highly desired. Herein, a series of N-doped carbon nanotubes encapsulating binary alloy nanoparticles (M_xNi-NCNT, M= Fe, Co) were successfully fabricated through the co-pyrolysis of melamine and metal precursors. The M_xNi-NCNT samples exhibited bamboo-like nanotubular structures with a large specific surface area and high degree of graphitization. Their electrocatalytic performance for syngas production can be tuned by changing the alloy compositions and modifying the electronic structure of the carbon nanotube through the encapsulated metal nanoparticles. Consequently, syngas with a wide range of CO/H₂ ratios, from 0.5:1 to 3.4:1, can be produced on M_xNi-NCNT. More importantly, stable CO/H₂ ratios of 2:1 and 1.5:1, corresponding to the ratio to produce biofuels by syngas fermentation, could be realized on Co₁Ni-NCNT and Co₂Ni-NCNT, respectively, over a potential window of –0.8 to –1.2 V versus the reversible hydrogen electrode. Our work provides an approach to develop low-cost and potential-independent electrocatalysts to effectively produce syngas with an adjustable CO/H₂ ratio from electrochemical CO₂ reduction.     

Synthesis of sulfated β‐cyclodextrin/cotton/ZnO nano composite for improve the antibacterial activity and dyeability with Azadirachta indica

The sulfated β‐cyclodextrin (sb‐cd) was prepared from β‐cyclodextrin and the sb‐cd was crosslinked with cotton fabric using ethylenediaminetetraacetic acid (EDTA) as crosslinker. After crosslinking, the synthesized ZnO nanoparticles were padded on this fabric surface. Then, the treated fabrics were dyed with neem extract. The synthesized polymer, crosslinked and nanoparticle‐treated cotton fabrics were characterized using fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), particle sized analyzer, and transmission electron microscopy (TEM) studies. The antibacterial test was done against Staphylococcus aureus and Escherichia coli bacterium. The composite coated with neem dyed cotton fabric has exhibited 71% of dye uptake with 2–3 fastness grade and it has 99% of antibacterial efficiency for S. aureus and 97% for E. coli bacterium. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of nitrogen–phosphorus fire retardant blended with Mg(OH)2/Al(OH)3 and nano‐SiO2 on fire‐retardant behavior and hygroscopicity of poplar

The aim of the study was to screen any possible synergistic effects related to the combination of nitrogen–phosphorus fire retardant and Mg(OH)₂/Al(OH)_3. This combination is used to improve fire performance, especially smoke suppression of poplar through ultrasonic wave impregnation after microwave treatment. In this study, nano‐SiO₂ was used to impregnate poplar treated with nitrogen–phosphorus fire retardant and form a hydrophobic layer on wood cells in order to improve hygroscopicity and reduce water uptake. Cone tests and thermal analysis showed that poplar treated with blended fire retardant had improved behavior. Results show that a 20% and 25% nitrogen–phosphorus fire‐retardant solution (blended by adding 10% Mg(OH)₂/Al(OH)₃ based on the dry weight of nitrogen–phosphorus fire retardant) was more effective for smoke suppression. The heat release rate, total heat release, and total smoke production of a 25% nitrogen–phosphorus fire‐retardant solution blended by adding 10% Mg(OH)₂/Al(OH)₃ showed significant reduction. The char residual yield showed a marked increase to 35.5%. Fourier transform infrared analysis suggested a –CH₂–Si–CH₂– and Si–O–C stretching vibration in nano‐SiO₂ treated poplar, which greatly decreased the hygroscopicity of fire‐retardant‐treated poplar. Copyright © 2014 John Wiley & Sons, Ltd.     

Cornet‐Like Phosphotriazine/Diamine Polymers as Reductant and Matrix for the Synthesis of Silver Nanocomposites with Antimicrobial Activity

The synthesis of silver nanoparticles attached on the surface of a hollow cornet‐like polymer matrix which served as a reductant and host matrix is described. This hybrid organic/inorganic macromolecular matrix is exhibiting anion‐exchange properties, porous structure and hollow morphologies, and absorptions in the visible light region. Due to the anion‐exchange property and the 3D orientation of the macromolecular chains the material is defining a new functional organic/inorganic hybrid. For the synthesis of nanoparticles, no other reducing agents were used and silver nanoparticles with a mean diameter of less than 20 nm were attached on the surface of the polymer, thus inheriting the composite with high antibacterial activity tested in bacterial strains and yeasts.

     

Conductive Materials for Proton Exchange Membrane Fuel Cell Bipolar Plates Made from PVDF,PET and Co‐continuous PVDF/PET Filled with Carbon Additives

The aim of this work was to develop and characterise electrically conductive materials for proton exchange membrane fuel cells and bipolar plates (BPPs). These BPPs were made from highly conductive blends of polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF), as matrix phase. The conductive materials were developed from carefully formulated blends composed of conductive carbon black (CB) powder and, in some cases, graphite synthetic flakes mixed with pure PET, PVDF or with PVDF/PET systems. They were first developed by twin‐screw extrusion process then compression‐molded to give BPP final shape. As the developed blends have to meet properties suitable for BPP applications, they were characterised for their rheological properties, electrical through‐plane resistivity (the inverse of conductivity), oxygen permeability, flexural and impact properties. Results showed that lower resistivity was obtained with PVDF/CB blends due to the higher interfacial energy between the PVDF matrix and CB and also the higher density and crystallinity of PVDF, compared to those of PET. It was also observed that the lowest resistivity values were obtained with mixing PVDF and PET at controlled compositions to ensure PVDF/PET co‐continuous morphology. Also, slow cooling rates helped to attain the lowest values of through‐plane resistivity for all studied blends. This behaviour was related to the higher crystallinity obtained with low cooling rates leading to smaller amorphous regions in which carbon particles are much more concentrated.     

Transparent conductive oxide films mixed with gallium oxide nanoparticle/single-walled carbon nanotube layer for deep ultraviolet light-emitting diodes

We propose a transparent conductive oxide electrode scheme of gallium oxide nanoparticle mixed with a single-walled carbon nanotube (Ga₂O₃ NP/SWNT) layer for deep ultraviolet light-emitting diodes using spin and dipping methods. We investigated the electrical, optical and morphological properties of the Ga₂O₃ NP/SWNT layers by increasing the thickness of SWNTs via multiple dipping processes. Compared with the undoped Ga₂O₃ films (current level 9.9 × 10^-9 A @ 1 V, transmittance 68% @ 280 nm), the current level flowing in the Ga₂O₃ NP/SWNT increased by approximately 4 × 10⁵ times and the transmittance improved by 9% after 15 times dip-coating (current level 4 × 10^-4 A at 1 V; transmittance 77.0% at 280 nm). These improvements result from both native high transparency of Ga₂O₃ NPs and high conductivity and effective current spreading of SWNTs.     

Crystallization of vulcanizates. I. Low‐temperature crystallization as a function of extent of cure for polyisoprene vulcanized with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide/sulfur

The crystallization of polyisoprene, vulcanized to various degrees of cure with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur formulations, was studied in a density column at ?25°C. The densities of vulcanizates before crystallization decrease progressively with cure time, which is ascribed to an increase in free volume occasioned by the formation of accelerator‐terminated pendent groups on the polymer chain. The induction period before the onset of crystallization increases and both the rate of and the degree of crystallization decrease with extent of cure. This is attributed primarily to the presence of residual pendent groups on the polymer chain and secondly to crosslink formation. The changes are more marked with MBTS formulations where pendent groups are more bulky. MBTS compounds fail to crystallize once vulcanized to the point where a gel has formed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2565–2572, 2001     

Effects of substrates on the capacitive performance of RuOx·nH2O and activated carbon-RuOx electrodes for supercapacitors

The electrochemical energy storage and delivery on the electrodes composed of hydrous ruthenium oxide (RuO_x·nH₂O) or activated carbon-hydrous ruthenium oxide (AC-RuO_x) composites are found to strongly depend on the substrate employed. The contact resistance at the active material-graphite interface is much lower than that at the active material-stainless steel (SS) mesh interface. Thin films of gold plus RuO_x·nH₂O deposited on SS meshes (RuO_x/Au/SS) are found to greatly improve the poor contact between SS meshes and electrode materials. The maximum specific capacitance (C_S,RuOx) of RuO_x·nH₂O, 1580 F g⁻¹ (measured at 1 mV s⁻¹), very close to the theoretic value, was obtained from an AC-RuO_x/RuO_x/Au/SS electrode with 10 wt.% sol-gel-derived RuO_x·nH₂O annealed in air at 200 °C for 2 h. The highly electrochemical reversibility, high-power characteristics, good stability, and improved frequency response of this AC-RuO_x/RuO_x/Au/SS electrode demonstrate its promising application potential in supercapacitors. The ultrahigh specific capacitance of RuO_x·nH₂O probably results from the uniform size distribution of RuO_x·nH₂O nanoparticles, ranged from 1.5 to 3 nm which is clearly observed from the high-resolution transmission electron microscopy (HRTEM).     

Studies on the preparation of stable and high solid content emulsifier‐free latexes and characterization of the obtained copolymers for MMA/BA system with the addition of AHPS

3‐Allyloxy‐2‐hydroxyl‐propanesulfonic (AHPS) salt was synthesized and used as a hydrophilic comonomer for the methyl methacrylate (MMA) and n‐butyl acrylate (BA) emulsifier‐free emulsion copolymerization system to obtain latices of stable and high‐solid content. Properties of the latices, such as flow behavior, stability, and final diameter of the latex particles were studied. In addition, physical properties of the obtained copolymers, such as glass transition temperature (T_g), stress–strain behavior, and water resistance were investigated. With the addition of AHPS, the latices of stable and high‐solid content (as high as 60%) were prepared. Flow of the latices follows the law of the Bingham body. The final diameter of the latex particles is 0.3–0.5 μm in diameter, which is larger than that of the conventional latex particles and decreases with the increase of AHPS and potassium persulfate (KPS) concentration. All the copolymers are atactic polymers, showed as single T_g on dynamic mechanical analysis spectrum. Compared with the copolymers that were prepared by surfactant emulsion polymerization, tensile strength, as well as water resistance is greatly improved. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 21–28, 2001