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The effect of Bi2O3 nanoparticles and nanowires as fillers in flexible PVC composites was investigated on the shielding properties against X-ray radiation at radiodiagnostic energies (50-129 kV). The PVC composites were gamma radiation cross-linked at 75 kGy. Materials were characterized by thermal analyses, and microstructure studied by SEM. The evaluation involved attenuation measurements and toxicity through cell viability assay. The mechanical properties and toughness were highly improved, according to DMA results, and the TGA analysis shows a small influence of the Bi2O3 nanostructures in the dehydrochlorination reaction of PVC during its thermal decomposition. Moreover, SEM images show a uniform distribution of the Bi2O3 nanostructures in the PVC matrix. Attenuation measurements showed low levels of X-ray transmission for PVC composites with 50 %wt of Bi2O3 and a mass attenuation coefficient greater than those reported for lead in the energy ranges studied, which is an improvement with the use of Bi2O3 NWs. In addition, PVC composites show low HVL and TVL values, making them feasible for the attenuation property. Density measurements show that the composites are lighter than lead. No-toxicity was observed for these composites through cell viability assay. Therefore, the investigated PVC composites are suitable for preparing new radiation-attenuating materials using Bi2O3 NWs.

The effects of ultrasound on the chemical structure of polypropylene (PP) and its composites with different MWCNT content were investigated. The PP composites with 0

This work reports a synthesis methodology for preparing a Pt catalyst supported in reduced graphene oxide (rGO), using magnetite (Fe3O4) as a strategy to decrease re-stacking layers of the rGO and improve the Pt catalytic activity during oxygen reduction reaction (ORR) and methanol tolerance effect. Pt nanoparticles supported on rGO-Fe3O4 were synthesized by chemical reduction and evaluated as cathode for the ORR. Pt nanoparticles with an average size of 4–5 nm were obtained, and XRD results give the guideline to affirm that Fe3O4 nanoparticles prevent to some extent the stacking effect in the rGO sheets that generally occur during the reduction process of GO. The catalytic evaluation demonstrates that ORR onto the Pt/rGO-Fe3O4 surface proceeds through a 4-electron transfer mechanism. The rGO-Fe3O4 support increases the specific catalytic activity of Pt at ≥ 0.84 V, which can be attributed to the electronic modification of Pt by Fe3O4 besides its high specific electrochemical surface area (27 m2 g− 1Pt). The selectivity tests of Pt/rGO-Fe3O4 show a highly methanol tolerant material in terms of oxidation current densities and a slightly Eonset displacement of 20 mV.

Nitrogen-doped mesoporous carbon (N-MC) was prepared by pyrolysis of melamine-modified resorcinol-formaldehyde (RF) resin in different melamine molar ratios under N2 atmosphere at 900 °C. The resulting N-MC materials were used as a support of Pd nanoparticles (Pd/N-MC) and evaluated as catalyst for a formic acid electro-oxidation reaction (FAOR) by cyclic voltammetry. The physical-chemical characteristics of the N-MCs were evaluated by FTIR, XRD, SAXS, Raman, and BET techniques. The N-MC obtained from resins with higher melamine concentration resulted in carbon structure with higher graphitic crystallinity and morphology with deformed pores caused by inefficient self-assembly; furthermore, the N content, determined by elemental analysis, ranged from 1.2 to 3.3

Plasticized polyvinyl chloride (PVC) composites were prepared with tantalum oxide V (Ta2O5) and/or bismuth oxide III (Bi2O3) nanoparticles (NPs) at different concentrations and further cross-linked with a dose of 75 kGy of gamma rays. The materials obtained are light, flexible and nontoxic, to be used as radiation attenuators in the medical area for replacing the traditional lead which is toxic and dense. Mechanical tests through mechanical dynamic analysis (DMA) show an enhanced tenacity for composites and lightness, according to density mea-surements. By means of scanning electron microscope images (SEM), an adequate dispersion of the nanoparticles (NPs) was observed. The X-ray attenuation property was evaluated at radiodiagnosis energies (50-129 kV) using a conventional X-ray equipment, observing values of mass attenuation coefficients greater than those of lead, when PVC composites were loaded with 50 wt percent (% wt) of a combination of Ta2O5 and Bi2O3 NPs. Half and tenth value layers of 0.77 and 2.20 mm respectively, for 129 kV X-Rays were also obtained. Non-toxicity of the composites was observed by means of a cell viability test. Therefore, the investigated materials are promising for the fabrication of medical diagnostic X-ray shielding attachments.

Two different sulfonating agents: sulfuric acid (S) and acetyl sulfate (AcS) were evaluated for chemical modification of poly (styrene-co-butyl acrylate) (StBuA) copolymer, as low-cost membranes. The reaction was carried out by direct sulfonation during 2-5 h of sul-fonation time. FTIR confirmed sulfonation through the presence and widening of the several SO3H characteristic absorption bands. The molecular weight decreased after sul-fonation, compared with pristine StBuA. TGA thermal analysis showed stability over 150 C with residues suggesting crosslinking and a glass transition (Tg) enhanced. Even with higher Tg values, sulfonated copolymers became flexible, as seen by their lower complex modulus (E*). Ion exchange capacity (IEC) ranged from 0.91 to 1.53 meq g-1 and degree of sulfonation (DS) from 7 to 40%. The proton conductivity for sulfonated membranes exhibited similar or higher to Nafion membrane, particularly for S-4h membranes. A Grotthuss mechanism is envisaged for AcS and vehicular mechanism for S membranes.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Polyelectrolytic membranes, such as the well-known commercial grade Nafion™, suffer mechanical failure and chemical decomposition after many hours of operation into a fuel cell. Mechanically due to expansion–contraction phenomena during water management and chemically due to the hydrogen peroxide and radicals produced from the H2/O2 redox electrochemical reactions. Considering that such behavior exists for the most used and reliable Nafion™ membranes, it is also expected similar properties depletion for alternative membrane copolymers. In this work, we examined the performance of sulfonated Styrene/butyl acrylate (S-St-BuA) copolymers during proton exchange activity through redox electrochemical reactions and their interactions with Fenton’s reagent (H2O2/FeCl2), compared with Nafion™. In situ, FTIR is a simultaneous analysis that evaluates the spectroscopic characteristics while the proton exchange into membranes is also measured. The in situ FTIR analysis showed chemical stability in the structure of the alternative membranes of S-St/BuA, compared with Nafion™ when both were exposed to Fenton's reagent.

In this article, we present the results of the composite development obtained from polyurethane (PU), polyvinyl chloride (PVC), and aluminum anodizing sludge (AAS). The composites were prepared in different compositions and the properties were compared with PU. The apparent density, mechanical resistance to compression, thermal stability study (UL94, DSC, calorimetric cone, SEM and DRX) and simulation of the energy use intensity (EUI) by Green Building Studio® (GBS) were analyzed. The specimens showed flame extinction in the horizontal and vertical flammability tests and less loss of mass when associated with AAS to PVC. Microscopy shows that for the flammability test of the composites a ceramic layer was formed due to the presence of AAS, which improved flame retardation and smoke suppression (UL94 and calorimetric cone). EUI for building using construction elements with composite (PVC 40 wt%) was 28% lower than EUI with ceramics, with CO 2 and cost reduction. The developed materials can contribute to the construction industry as a safe insulator, saving natural resources.

Flexible PVC composites loaded with various levels of tantalum carbide (TaC) were gamma irradiated at two different dose rates and their effect on crosslinking level, thermal stability and mechanical properties evaluated. The shielding properties of composites against X-Rays at radiodiagnosis energies were also evaluated. Gel percentage results indicate a relatively stable crosslinking level after irradiation, only some reduction was observed for highly loaded composite treated at a low dose rate, although thermal stability observed by TGA was maintained. TaC particles were properly dispersed within the PVC material, as seen by SEM and toughness increased when both E' and E" Moduli were enhanced after irradiation; even Tg, followed by Tan delta DMA curves, increased noticeably after treatment and for the higher TaC loaded composites, particularly when treated at low dose rate irradiation. Density measurements indicated lighter and manageable materials with respect to traditional shielding items. The shielding properties for composites, evaluated in a clinical X-Ray apparatus, in the 50-129 kV interval, show mass attenuation coefficients close to the ones reported for lead, even higher for 50% TaC loaded composite and a very competitive half-value layer (HVL) for all of them.

To improve the physical and chemical properties of styrene-derived polymers, new polystyrene-co-acrylonitrile-co-butyl acrylate terpolymers were synthesized and subsequently sulfonated. Six terpolymer compositions were prepared under mass radical polymerization conditions and further sulfonated to promote proton conductivity. The terpolymers were characterized by Fourier Transformed Infrared Spectroscopy (FTIR), proton and carbon nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR), Gel Permeation Chromatography (GPC), Thermomechanical Analysis (TMA), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Electrochemical Impedance Spectroscopy (EIS). All synthesized terpolymers have molecular weights over 160,000 g/mol and solubility on several organic solvents. Terpolymers also showed high thermal stability by TGA and comonomers reduced Tg transitions and complex moduli along BuA content; the complex moduli clearly increased with ACN content. Intermediate aliquots taken during the sulfonation reaction were charac-terized indicate that incorporation of the sulfonic group decreases the thermal stability from over 350 degrees C in terpolymers down to 150 degrees C after sulfonation. The degree of sulfonation analyzed by TGA ranged between 11.2 and 15.9% leading to a proton conductivity interval from 2.9 to 4.0 mS/cm. The results suggest a lateral crosslinking reaction through sulfone groups. The proton ion conductivity values obtained are similar to those of commercially available membranes described in the literature.

ABSTRACT Polypropylene composites and multi-walled carbon nanotubes (MWCNTs) modified with maleic anhydride (MA) and itaconic anhydride (IA) were prepared and their effect on the performance of nanocomposite properties was studied. Modification of the MWCNT was carried out in the presence of ultrasound varying the molar ratio of anhydride and dicumyl peroxide (BPO). PP nanocomposite with anhydride grafted MWCNT showed an increase, higher than 15%, in tensile strength and elastic modulus and a displacement of crystallization temperature (Tc) to higher temperatures, 1.5°C and loss weight temperature to higher temperatures, 30°C. This behavior was attributed to the better anhydride grafting in the MWCNTs induced by ultrasound.

Reduced Graphene Oxide (rGO) doped with different nitrogen (N) concentrations (5, 10, and 15 parts in weight) were successfully synthesized via hydrothermal conditions, from graphene oxide (GO) and 3-amino-1,2,4-triazole (amitrole) to obtain N-5-rGO, N-10-rGO, and N-15-rGO. These N-doped materials were characterized and evaluated for the first time as catalysts for the oxygen reduction reaction (ORR). The physicochemical characteristics confirmed the simultaneous N-doping and reduction processes with a turbostratic re-stacking of graphene layers. Nitrogen was successfully introduced as a mix of pyridine-N, amine like-N, pyrrolic-N, and quaternary bonding species into the carbon lattice. The N content were 8.1, 9.9, and 10.5 at.% for N-5-rGO, N-10-rGO, and N-15-rGO. High catalytic activity was demonstrated in alkaline media with an onset potential of similar to 0.88 V and high current density (3.9 mA cm(-2)) for N-15-rGO, leading the ORR via the 4-electron transfer pathway. The results demonstrated that the amine like-N species enhance the ORR catalytic activity in addition to pyridinic and quaternary. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The synthesis and characterization method of a styrene-vinyl tetrazole copolymer (StVTz) at different molar ratios (50:50, 60:40, 70:30, 80:20, and 90:10) is reported. The new copolymers were prepared from a previously synthesized styrene-co-acrylonitrile copolymer, followed by a Huisgen 1,3-dipolar cycloaddition reaction to obtain the styrene-tetrazole copolymers. Copolymers were characterized by Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance spectroscopy (1H NMR) analysis, and molecular weight. Membranes were further prepared by casting method and the morphology revealed by atomic force microscopy (AFM). The thermal properties were evaluated by differential scanning calorimetry (DSC) and by thermogravimetric analysis (TGA), and ionic properties by means of ion-exchange capacity (IEC) value obtained from titration measurements and by water uptake (WU). Water content (WC) present was also determined by TGA. The electrochemical behavior was followed by Electrochemical impedance spectroscopy (EIS). Morphological analysis by atomic force microscopy demonstrates the presence of a single phase with roughness proportional to hydration. No relationship between WU, IEC, and WC with the composition of the copolymer was observed; however, a correlation between ionic conductivity and the percentage of bound water in the membrane was found. The results of ionic conductivity for copolymers envisage a potential application of this class of compounds as membranes in fuel cells.

Plasticized and gamma crosslinked PVC composites were prepared by adding different amounts of Bi2O3 particles to evaluate their low energy X-ray radiation shielding properties. Composites were gamma-irradiated in an industrial irradiator (Co-60 source) at the corresponding times to obtain a dose of 75 kGy to enhance mechanical properties through crosslinking. The shielding properties of composites were obtained by X-ray transmission measurements at low energies (X-ray tube voltages range 20-61 kV) by using a mammography unit and an X-ray hospital equipment. A small influence in the dehydroclorination reaction of PVC was observed during decomposition in TGA experiments due to Bi2O3 nanoparticle content, but DMA results show improved viscoelastic properties for the crosslinked composites. The X-ray transmission values decrease as a function of nanoparticle content, observing an increase in the transmission values (low attenuation) at higher energies. The composite with 50 %wt of Bi2O3 showed the lowest transmission values, at X-ray tube voltages 20-30 kV, the transmittance was almost nil, and then it increases similar to 7% at 61 kV.

Graphene oxide (GO) was synthetized, reduced and further sulfonated for the preparation of electrodes. GO was obtained using modified Hummer's method from graphite flakes. The partial reduction of graphene oxide (rGO) was performed by chemical and thermal process and subsequently functionalized using sulfuric acid or aryl diazonium salt of sulfanilic acid as sulfonating agents to afford rGO-SO3H. The influence of the reduction processes on the sulfonation reactions of rGO was evaluated through XRD, TGA, FT-IR and Raman techniques. Electrochemical properties of both rGO and sulfonated rGO materials as modified glassy carbon electrode were evaluated using a K3FeCN6 solution as a reference redox system. XRD confirmed the partial reduction of GO by two methods and FT-IR demonstrated that SO3H groups were successfully grafted on GO. VC results confirmed that both reduction and sulfonated methods leads to a better material with superior electrochemical properties compared to GO and rGO. Thermally reduced GO and functionalized with sulfuric acid [rGOT-SO3H(1)] showed the best electron transfer activity compared to those chemically reduced or sulfonated with sulfanilic acid. The electrochemical properties observed for rGOT-SO3H(1) suggest than can be a suitable support material of nanoparticles for the preparation of electrodes for fuel cells applications.

Copolymers of styrene-co-acrylic acid were synthesized by radical bulk copolymerization and sulfonated during 3 different periods of time (1, 2 or 3 h). Sulfonation reactions were carried out with sulfuric acid catalyzed with silver sulfate, at a level of 170% of benzene rings theoretically present in the copolymer. Membranes of the sulfonated copolymers were prepared by casting from their THF solutions and then subjected to gamma irradiation treatment at several doses (50, 75 and 100 kGy) in an industrial irradiator. Tg by DSC, thermal stability by TGA, water retention capacity by WU and ionic properties by IEC measurements evaluated irradiation effect on sulfonated membranes. Sulfonation reduce Tg transition and thermal stability of the copolymer (already reported), but irradiation partially recover such values; particularly for the less sulfonated material (1 h) for both, Tg and stability in the region of 200–300 °C, where sulfonated groups start to decompose. Water uptake (WU) and IEC values, as expected, are higher for more sulfonated membranes; but such values are reduced along radiation dose, ending in almost half their values at 100 kGy, after their corresponding values on non-irradiated sulfonated membranes. The general view is that gamma radiation induced crosslinking to give benefits for mechanical and thermal stability, but ion exchange properties are affected when sulfonic groups are used to crosslink the copolymer matrix.