Charafeddine Jama

Influence of the surface termination of boron-doped diamond electrodes on oxygen reduction in basic medium

This paper reports on the influence of the surface termination (H-, HO-, NH2-) of boron-doped diamond (BDD) electrodes on the oxygen reduction reaction (ORR) in alkaline solution. The aminated BDD surface displays a higher oxygen reduction current density and a positive shift in the oxygen reduction potential compared to H- and HO-terminated BDD surfaces. The behavior is most likely due to a preferential adsorption of oxygen species on the NH2 termination. The ORR mechanism on the H-, HO-, and NH2-terminated BDD surfaces was investigated for the first time using electrochemiluminescence (ECL) of luminol. The results indicate that the ORR proceeds via a two-electron process on H-terminated diamond, while a four-electron pathway is observed for oxidized and aminated BDD electrodes. We further show that the ECL approach can be easily extended to investigate the ORR mechanism on different electrodes and composite materials. The influence on the surface termination on the reduction of oxygen on gold-nanoparticle-modified BDD electrodes has been studied.

New routes to flame retard polyamide 6,6 for electrical applications

Polyamide 6,6 is used in many industrial fields such as housing materials, transport or electrical engineering applications. Due to its chemical composition, this polymer is easily flammable. As far as the main applications concern electrical and electronic equipments, its flame-retardant properties become an important requirement. The most discriminating tests are the limiting oxygen index, UL94 and glow wire flammability index. The aim is to obtain high limiting oxygen index values, V0 rating at UL94 test for 1.6- or 0.8-mm-thick samples and a validation at 960°C of the glow wire flammability index. The usual way to fire retard polyamide 6,6 consists of incorporating an important loading of fire-retardant additives, which often reduce the intrinsic properties of the polymer. It is also difficult to combine a thin polymer thickness (e.g. 0.8 mm) and a high amount of additives because of processing issues. In this article, we first carried out a rapid screening to determine the best fire retardant for polyamide 6,6 and its optimized amount to achieve the previously defined fire retardant properties. It was shown that an amount of 23% of aluminium diethylphosphinate Exolit OP1230 allows reaching the requirements. Then, carrying out two different surface treatments (coating of polysiloxanes by plasma-enhanced chemical vapour deposition and use of an intumescent waterborne varnish), we have tried to reach the same results. It was shown that the use of surface treatment alone does not allow reaching the objectives. As a consequence, the combination of the bulk approach at low loadings with the surface treatment was investigated. This new route allows the combination of the condensed phase mechanism of the intumescent barrier with the gas phase mechanism of the OP1230 and leads to very good results: the use of 5% of the flame-retardant additives combined with a 100-µm-thick waterborne intumescent varnish leads to better results than a 23% of additive loading.

Nisin adsorption on hydrophilic and hydrophobic surfaces: evidence of its interactions and antibacterial activity

Study of peptides adsorption on surfaces remains a current challenge in literature. A complementary approach, combining X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the antimicrobial peptide nisin adsorption on hydrophilic and hydrophobic surfaces. The native low density polyethylene was used as hydrophobic support and it was grafted with acrylic acid to render it hydrophilic. XPS permitted to confirm nisin adsorption and to determine its amount on the surfaces. ToF‐SIMS permitted to identify the adsorbed bacteriocin type and to observe its distribution and orientation behavior on both types of surfaces. Nisin was more oriented by its hydrophobic side to the hydrophobic substrate and by its hydrophilic side to the outer layers of the adsorbed peptide, in contrast to what was observed on the hydrophilic substrate. A correlation was found between XPS and ToF‐SIMS results, the types of interactions on both surfaces and the observed antibacterial activity. Such interfacial studies are crucial for better understanding the peptides interactions and adsorption on surfaces and must be considered when setting up antimicrobial surfaces. Copyright

Effect of materials mixture on the higher heating value: Case of biomass, biochar and municipal solid waste

The heating value describes the energy content of any fuel. In this study, this parameter was evaluated for different abundant materials in Morocco (two types of biochar, plastic, synthetic rubber, and cardboard as municipal solid waste (MSW), and various types of biomass). Before the evaluation of their higher heating value (HHV) by a calorimeter device, the thermal behavior of these materials was investigated using thermogravimetric (TGA) and Differential scanning calorimetry (DSC) analyses. The focus of this work is to evaluate the calorific value of each material alone in a first time, then to compare the experimental and theoretical HHV of their mixtures in a second time. The heating value of lignocellulosic materials was between 12.16 and 20.53MJ/kg, 27.39 for biochar 1, 32.60MJ/kg for biochar 2, 37.81 and 38.00MJ/kg for plastic and synthetic rubber respectively and 13.81MJ/kg for cardboard. A significant difference was observed between the measured and estimated HHVs of mixtures. Experimentally, results for a large variety of mixture between biomass/biochar and biomass/MSW have shown that the interaction between biomass and other compounds expressed a synergy of 2.37% for biochar 1 and 6.11% for biochar 2, 1.09% for cardboard, 5.09% for plastic and 5.01% for synthetic rubber.

Study of Temperature Effect on the Corrosion Inhibition of C38 Carbon Steel Using Amino-tris(Methylenephosphonic) Acid in Hydrochloric Acid Solution

Tafel polarization method was used to assess the corrosion inhibitive and adsorption behaviours of amino-tris(methylenephosphonic) acid (ATMP) for C38 carbon steel in 1 M HCl solution in the temperature range from 30 to 60∘C. It was shown that the corrosion inhibition efficiency was found to increase with increase in ATMP concentration but decreased with temperature, which is suggestive of physical adsorption mechanism. The adsorption of the ATMP onto the C38 steel surface was found to follow Langmuir adsorption isotherm model. The corrosion inhibition mechanism was further corroborated by the values of kinetic and thermodynamic parameters obtained from the experimental data.

Elaboration and Grafting of Cold Plasma Organo-Phosphorus Copolymers on Polyamide 6: New Approach to Flame Retardancy

Argon plasma-induced graft polymerization of (ethylene glycol) methacrylate phosphate (EGMAP) was performed on the polyamide-6 (PA6) surface to improve the fire retardancy properties. The surface composition and morphologies of the PA6-g-poly(EGMAP) surfaces were then characterized by Attenuated total reflection-Infrared and Scanning electron microscopy. The thermal properties were investigated by using Thermogravimetry analysis. It was found that weight loss rate of the grafted substrates was lower, as compared to the virgin PA6. The results obtained showed also that the grafting allows to obtaining a residue of about 30% at 600°C, temperature at which the virgin PA-6 was totally decomposed.

Thermodynamic prediction of growth temperature dependence in the adhesion of Pseudomonas aeruginosa and Staphylococcus aureus to stainless steel and polycarbonate.

This study investigated the effect of growth temperature changes (20, 30, and 37°C) on the adhesion behavior of Pseudomonas aeruginosa and Staphylococcus aureus to stainless steel and polycarbonate. Adhesion assays were performed under static conditions at 20°C. In addition, the validity of the thermodynamic and extended Derjaguin, Landau, Verwey, and Overbeek theories as predictive tools of bacterial adhesion were studied. The surface properties of the bacterial cells and the substrates of attachment were characterized, and atomic force microscopy was used to analyze the surface topography. The results indicated that the highest adhesion rate of P. aeruginosa and S. aureus on both surfaces was observed when the cells were grown at 37°C. The bacterial adhesion to stainless steel was found to be two times higher than to polycarbonate for both bacteria, whatever the condition used. The present study underlined that the thermodynamic and the extended Derjaguin, Landau, Verwey, and Overbeek theories were able to partially predict the empirical results of P. aeruginosa adhesion. However, these theories failed to predict the adhesion behavior of S. aureus to both surfaces when the growth temperature was changed. The results of the microbial adhesion to solvent indicated that the adhesion rate to abiotic surfaces may correlate with the hydrophobicity of bacterial surfaces. The effect of surface topography on bacterial adhesion showed that surface roughness, even on the very low nanometer scale, has a significant effect on bacterial adhesion behavior.

Effects of fire retardants and nanofillers on the fire toxicity

Four polymers, polyamide 6, polypropylene, ethylene vinyl acetate and polybutylene terephthalate have been prepared with fire retardants, nanofillers, (both separately and together). The toxic product yield of each material has then been measured under different fire conditions. The influence of polymer nanocomposites and fire retardants in the formulations, on the yields of toxic products from fire, have been studied using the ISO 19700 steady state tube furnace, and it was found that under early stages of burning more carbon monoxide may be formed in the presence of nanofillers and fire retardants, but, under the more toxic under-ventilated conditions, there was a relative reduction in the toxic product yields. In general, the differences between the samples containing fire retardants and nanofillers are very small compared to the differences obtained under different fire conditions or in the presence of certain heteroelements, such as nitrogen or halogens.

Study of the Relationship Between Flammability and Melt Rheological Properties of Flame-Retarded Poly(Butylene Terephthalate) Containing Nanoclays

Recent studies on a new class of flame retardant (FR) systems that contain nanoclay and conventional FR microparticles have shown that the threshold concentration of FR required to achieve acceptable levels of flame retardancy can be significantly reduced in the presence of nanoclay. Bourbigot et al...

Surface Modification of Plasma-Treated Polyamide-6 with Fluorinated Alcohols and Azobenzene Compounds using Chlorinated Phosphazenes as Coupling Agents

A three-step procedure for surface functionalization of polyamide-6 plates is presented. The substrate was first treated with cold, low pressure Ar plasma to generate surface OH groups, which were successively reacted with chlorophosphazenes to ensure grafting of these molecules. Substitution of the residual chlorines of the phosphazenes with fluorinated alcohols and 4-hydroxyazobenzene yielded the final surface modification. Characterization was performed by contact angle, XPS and UV-Vis techniques.