Le Touquet – Paris-Plage, France
Le Touquet – Paris-Plage, France

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Collette F.M.,Laboratoire dIngenierie des Materiaux | Thominette F.,Laboratoire dIngenierie des Materiaux | Escribano S.,CEA Grenoble | Ravachol A.,CEA Grenoble | And 2 more authors.
Journal of Power Sources | Year: 2012

Nafion ® membranes stored for long periods at 80 °C under elevated relative humidity up to 95%RH exhibit large modifications of their properties attributed to the sulfonic acid end-group condensation into sulfonic anhydrides. The present study is devoted to the membrane property rejuvenation, namely the hydrolysis of the sulfonic anhydrides under different experimental conditions. Aged membranes were exposed to pure water and to acid solutions or vapors in order to check the reversibility of the condensation reaction. Indeed, the hydrolysis process is slow in pure water and limited while it is fast and complete in the presence of acid or base. The native polymer chemical structure and the main membrane properties (mechanical properties, hydrophilicity, etc.) are completely restored. No evidence of hygrothermal aging was observed after fuel cell operation and it is shown that a membrane previously aged under ex situ conditions can be completely rejuvenated when operated in fuel cell. © 2011 Elsevier B.V. All rights reserved.


Naudy S.,University Claude Bernard Lyon 1 | Collette F.,Laboratoire dingenierie des materiaux | Thominette F.,Laboratoire dingenierie des materiaux | Gebel G.,CNRS Structure and Properties of Molecular Architectures Laboratory | Espuche E.,University Claude Bernard Lyon 1
Journal of Membrane Science | Year: 2014

The membrane durability is a critical issue for proton exchange membrane fuel cell development. Nafion® is usually considered as a reference membrane due to its high chemical stability. However, a condensation mechanism of the sulfonic groups to form anhydrides was evidenced when Nafion® membranes were stored at 80°C under humid atmospheres. In the present work, Nafion® 112 membranes and chemically stabilized Nafion® NRE212CS membranes commercialized to replace Nafion® 112 were studied under hygrothermal aging performed at 80°C for two relative humidity conditions: 80% and 95%. The impact of the aging conditions was investigated on membrane water and gas transport properties over the whole range of water activity. For both membrane types, a progressive decrease of the water uptakes was observed as a function of aging time. The hygrothermal aging process was faster for Nafion® 112 membranes than for the chemically stabilized Nafion® membranes. It became slower as the relative humidity of the aging atmosphere decreased from 95% to 80%. A water transport mechanism based on sorption and permeation data was proposed for the aged membranes taking account of the water/polymer interactions and of the progressive crosslinking of the Nafion® hydrophilic phase. The gas transport properties were studied for H2, O2 and CO2 at different water activities. The decrease of the gas permeability coefficients observed for the aged membranes in comparison with the neat membranes confirmed the presence of gas diffusion pathways within the Nafion® hydrophilic phase. The role of these diffusion paths was discussed as a function of the membrane hydration state, as a function of the aging conditions and of the polarity and size of the diffusing gas molecules. © 2013 Elsevier B.V.


Liang G.G.,Monash University | Cook W.D.,Monash University | Tcharkhtchi A.,Laboratoire dIngenierie des Materiaux | Sautereau H.,INSA Lyon
European Polymer Journal | Year: 2011

An oligomer of a diepoxy (diglycidyl ether of bisphenol-A, DGEBA) and an aromatic diamine (MCDEA) have been used as reactive plasticizers for polycarbonate (PC). A small amount of PC chain scission occurred during this blending process, probably due to transesterification of the PC carbonate group by the hydroxyl group of the DGEBA oligomer. Addition of DGEBA to PC was found to greatly reduce the Tg and processing temperature. Dynamic rheology measurements showed that the added epoxy can very effectively reduce the viscosity, but that the addition of epoxy also accelerated the crystallisation rate of the PC, which was confirmed by XRD, optical transmission microscopy and DMTA. The DMTA results of cured blends also showed that this crystallization of the PC enhanced their heat resistance properties. Sol-gel studies of the cured samples showed that some of the PC was grafted to the crosslinked epoxy network. Studies of the rubbery behaviour, solvent resistance of the cured blend and SEM images suggest that PC is the main continuous phase in the matrix and that the epoxy phase is mainly dispersed as sub-micron particles in the matrix. © 2011 Published by Elsevier Ltd. All rights reserved.


Montazeri A.,Iran University of Science and Technology | Javadpour J.,Iran University of Science and Technology | Khavandi A.,Iran University of Science and Technology | Tcharkhtchi A.,Laboratoire dingenierie des materiaux | Mohajeri A.,Research Institute of Petroleum Industry RIPI
Materials and Design | Year: 2010

Untreated and acid-treated multi-walled carbon nanotubes (MWNT) were used to fabricate MWNT/epoxy composite samples by sonication technique. The effect of MWNT addition and their surface modification on the mechanical properties were investigated. Modified Halpin-Tasi equation was used to evaluate the Young's modulus and tensile strength of the MWNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. There was a good correlation between the experimentally obtained Young's modulus and tensile strength values and the modified Halpin-Tsai theory. The fracture surfaces of MWNT/epoxy composite samples were analyzed by scanning electron microscope. © 2010 Elsevier Ltd.


Montazeri A.,Iran University of Science and Technology | Khavandi A.,Iran University of Science and Technology | Javadpour J.,Iran University of Science and Technology | Tcharkhtchi A.,Laboratoire dingenierie des materiaux
Materials and Design | Year: 2010

Along with carbon nanotubes (CNT) morphology, impurity, and functionalization, polymer curing cycle is another important factor in determining the mechanical properties of the CNT/polymer composite samples. This work investigates the effect of two different curing cycles on mechanical and thermo-mechanical properties of the nanotube in the composite in order to optimize the curing condition in term of time and temperature. Nanocomposite samples were prepared by mixing multi-wall carbon nanotubes with epoxy resin using sonication method. The mechanical and viscoelastic properties of the resulting composite samples were evaluated by performing tensile and dynamic mechanical thermal analyses (DMTA) test. The results indicate that the mechanical and viscoelastic properties of pure epoxy and composite samples have been affected by the condition curing process. Concerning viscoelastic modeling, the COLE-COLE diagram has been plotted by the result of DMTA tests. These results show a good agreement between the Perez model and the viscoelastic behavior of the composite. © 2010 Elsevier Ltd.


Montazeri A.,Iran University of Science and Technology | Khavandi A.,Iran University of Science and Technology | Javadpour J.,Iran University of Science and Technology | Tcharkhtchi A.,Laboratoire Dingenierie des Materiaux
Advanced Materials Research | Year: 2011

This work studied the effect of sonication time and dispersing medium on the dispersion state of 0.1%wt multi-wall carbon nanotube (MWCNT) in the MWCNT/epoxy nanocomposite system. Epoxy, hardener, and epoxy/solvent were used as dispersing mediums in this study. Tensile strength, strain at failure, Young's modulus and fracture toughness were measured under different dispersion state of MWCNT. The results indicate that with the increase in sonication time, initially there was an increase in tensile strength and fracture toughness values which was followed by a drop in values at longer sonication times. The highest Young's modulus values were seen in epoxy dispersion and the highest tensile strength and fracture toughness values were observed when the hardener was used as dispersing medium. The results also indicated that the effect of sonication time was more pronounced in the case of epoxy dispersion. The effect of time was least when the epoxy / solvent system was used as CNT dispersing medium. It should also be pointed out that the Young's modulus for the nanocomposite sample obtained after 1h of dispersion in hardener showed good agreement with a modified Halpin-Tsai theory. The scanning electron microscope (SEM) was used to characterize the dispersion state of MWCNT. A good dispersion was obtained when either hardener or solvent were selected as the dispersing medium. © (2011) Trans Tech Publications, Switzerland.


Montazeri A.,Iran University of Science and Technology | Khavandi A.,Iran University of Science and Technology | Javadpour J.,Iran University of Science and Technology | Tcharkhtchi A.,Laboratoire dingenierie des materiaux
International Journal of Polymer Analysis and Characterization | Year: 2010

Along with carbon nanotube (CNT) morphology, impurity, and fuctionalization, polymer curing cycle is another important factor in determining the mechanical properties of CNT/polymer composite samples. Nanocomposite samples were prepared by mixing multiwall carbon nanotubes with epoxy resin. The main objective is the investigation of the effects of four curing cycles on the mechanical and thermo-mechanical properties of the conductive filler in the composite and the development of new nanocomposite materials based on epoxy resins with controlled structural and mechanical properties. The mechanical and thermo-mechanical properties of the resulting composite samples were evaluated by performing tensile and dynamic mechanical analyses (DMA) test. The results indicate that the mechanical properties of pure epoxy and composite samples have been affected by the conditions of the curing process. It seems that the effect of the reinforcement is more evident for a less cured resin. © Taylor & Francis Group, LLC.


Hafsaoui S.L.,Polytechnic School of Algiers | Hafsaoui S.L.,Laboratoire dIngenierie des Materiaux | Mahmoud R.,Polytechnic School of Algiers | Farzaneh S.,Laboratoire dIngenierie des Materiaux | Tcharkhtchi A.,Laboratoire dIngenierie des Materiaux
6th International Conference on Thermal Engineering Theory and Applications | Year: 2012

The main drawback of rotational moulding is a long stay (several dozens of minutes) of polymer in its molten state at high temperature. To prevent any significant polymer thermal degradation, it is necessary to define, preliminary, the processing window. The aim of this present article is to check the validity of the first level of a thermal degradation kinetic model. This first level is the thermal model which hold in account of temperature change (thermal transfer mechanism) and of fusion and crystallization pseudo- stages (enthalpy method). For this, a series of tests for polyamide 6 was carried out using the rotational moulding STP LAB. Non-isothermal crystallization kinetics during cooling stage of rotational moulding PA6 grade are measured and analyzed by Differential scanning calorimetry DSC 204 F1 Phoenix (Netzsch). All results of non-isothermal crystallization of the studied material were confronted with Ozawa model in order to test the validity of enthalpic method (layer by layer).


Montazeri A.,Islamic Azad University at Tonekabon | Montazeri N.,Islamic Azad University at Tonekabon | Pourshamsian K.,Islamic Azad University at Tonekabon | Tcharkhtchi A.,Laboratoire dingenierie des materiaux
International Journal of Polymer Analysis and Characterization | Year: 2011

This work describes the effect of sonication time and dispersing medium on the dispersion state of 0.1 wt.% MWCNT in a MWCNT/epoxy composite system. Epoxy, hardener, and epoxy/solvent were used as dispersing media in this study. Tensile strength, Young's modulus, and strain at failure were measured under different dispersion states of MWCNT. The results indicate that with increase in sonication time, initially there is an increase in tensile strength values, followed by a drop in values at longer sonication times. The highest Young's modulus values were seen in epoxy dispersion and the highest tensile strength value was observed when the hardener was used as dispersing medium. The results also indicated that the effect of sonication time was more pronounced for the case of epoxy dispersion. The effect of time was the shortest when the epoxy/solvent system was used as MWCNT dispersing medium. It should also be pointed out that Young's modulus for the nanocomposite sample obtained after 1 h of dispersion in hardener showed good agreement with a modified Halpin-Tsai theory. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the dispersion state of MWCNT. A good dispersion was obtained when either hardener or solvent was selected as the dispersing medium. © Taylor & Francis Group, LLC.


Collette F.M.,Laboratoire dIngenierie des materiaux | Thominette F.,Laboratoire dIngenierie des materiaux | Mendil-Jakani H.,CNRS Structure and Properties of Molecular Architectures Laboratory | Gebel G.,CNRS Structure and Properties of Molecular Architectures Laboratory
Journal of Membrane Science | Year: 2013

Nafion®, a perfluorosulfonated ionomer used as a proton conducting membrane in fuel cells, is usually considered as highly chemically stable. However, the extruded Nafion® 112 membrane was shown to be sensitive to hygrothermal aging when stored for very long periods at 80°C under humid atmospheres. The aging process was interpreted as a condensation of the sulfonic groups to form anhydrides. The hygrothermal stability of solution-cast and chemically stabilized Nafion® (NRE212CS) commercialized to replace Nafion® 112 is investigated through the determination of water sorption, conductivity, ion-exchange capacity and mechanical properties. The evolution of the chemical and physical structure was analyzed by IR, NMR, SAXS and WAXS. The lower rate of degradation for solution cast membranes compared to extruded membranes is attributed to a lower concentration of divalent cation contaminants such as Cu2+. The hygrothermal aging process is faster at high water content but it does not occur in liquid water. It is shown to progress from the surface to the bulk without major modifications of the local microstructure and crystallinity. The results are analyzed in the framework of the polymer ribbon model and it is suggested that the aging mainly acts within the bundles while the interbundle areas appear as the main conductive pathways. © 2013 Elsevier B.V.

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