Maude Jimenez

Remediation of Heavy Metals by Biomolecules: A Review

Some biomolecules are well known for the complexation of heavy metals from wastewater: cellulose, alginate, pectins, and starches for example. However, less used natural molecules could also be efficient to chelate heavy metals. Indeed, some cells contain polypeptides that can help detoxifying living organisms containing heavy metals. This natural detoxification process is of great interest, and particularly the molecules taking part in it. The amino acids composing these polypeptides, especially cysteine, tyrosine, and histidine, can be used for water purification. The efficiency of biomolecules containing aromatic rings on heavy metals complexation is also investigated. All these biomolecules are able to chelate heavy metals thanks to some chemical groups and atoms: the most well-known and efficient chemical groups are listed in the article. Finally, some potential environmental applications of biomolecules are suggested at the end of the article.

Anticoagulant and antimicrobial finishing of non-woven polypropylene textiles

The aim of this work is to prepare non-woven polypropylene (PP) textile functionalized with bioactive molecules in order to improve its anticoagulation and antibacterial properties. This paper describes the optimization of the grafting process of acrylic acid (AA) on low-pressure cold-plasma pre-activated PP, the characterization of the modified substrates and the effect of these modifications on the in vitro biological response towards cells. Then, the immobilization of gentamicin (aminoglycoside antibiotic) and heparin (anticoagulation agent) has been carried out on the grafted samples by either ionic interactions or covalent linkages. Their bioactivity has been investigated and related to the nature of their interactions with the substrate. For gentamicin-immobilized AA-grafted samples, an inhibition radius and a reduction of 99% of the adhesion of Escherichia coli have been observed when gentamicin was linked by ionic interactions, allowing the release of the antibiotic. By contrast, for heparin-immobilized AA-grafted PP samples, a strong increase of the anticoagulant effect up to 35 min has been highlighted when heparin was covalently bonded on the substrate, by contact with the blood drop.

Toward the understanding of the interfacial dairy fouling deposition and growth mechanisms at a stainless steel surface: a multiscale approach.

The microstructures of two dairy fouling deposits obtained at a stainless steel surface after different processing times in a pilot plate heat exchanger were investigated at different scales. Electron-Probe Micro Analysis, Time-of-Flight Secondary Ion Mass Spectrometry, Atomic Force Microscopy, and X-Ray Photo-electron Spectroscopy techniques were used for this purpose. The two model fouling solutions were made by rehydrating whey protein in water containing calcium or not. Results on samples collected after 2h processing show that the microstructure of the fouling layers is completely different depending on calcium content: the layer is thin, smooth, and homogeneous in absence of calcium and on the contrary very thick and rough in presence of calcium. Analyses on substrates submitted to 1 min fouling reveal that fouling mechanisms are initiated by the deposit of unfolded proteins on the substrate and start immediately till the first seconds of exposure with no lag time. In presence of calcium, amorphous calcium carbonate nuclei are detected in addition to unfolded proteins at the interface, and it is shown that the protein precedes the deposit of calcium on the substrate. Moreover, it is evidenced that amorphous calcium carbonate particles are stabilized by the unfolded protein. They are thus more easily trapped in the steel roughnesses and contribute to accelerate the deposit buildup, offering due to their larger characteristic dimension more roughness and favorable conditions for the subsequent unfolded protein to depose.

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.

Novel flame retardant flexible polyurethane foam: plasma induced graft-polymerization of phosphonates

Flame retardancy of flexible polyurethane foams has become an issue due to very severe regulations. To overcome the challenge of incorporating flame retardant (FR) additives during the foaming process without altering the foam properties, a plasma surface treatment was used for the first time in this work: a cold plasma induced graft-polymerization of phosphonate containing precursors (diethylvinylphosphonate-DEVP) with or without a crosslinking agent (1,4 butanedioldiacrylate) was applied on open cell flexible polyurethane foams (PUF). The flame retardant properties of these foams, before and after further rinsing, were evaluated using horizontal UL-94 test for 10 s and 60 s. One of the tested systems (DEVP + crosslinker), even after sonication, completely stops the melt dripping of the foams when exposed to the flame of the butane torch and charring occurs. This efficient surface treatment was characterized before and after burning by Scanning Electron Microscopy (SEM), electron probe microanalysis (EPMA), 31P solid state NMR and X-ray Photoelectron Spectroscopy (XPS). Its FR mechanism of action was then further investigated using microscale combustion calorimetry (MCC), thermogravimetric analyses coupled with infrared Fourier transform spectroscopy (TGA-FTIR), pyrolysis gas-chromatography coupled with mass spectrometry (GC-MS pyrolysis) and 31P solid state NMR. The results obtained show that it is necessary (i) to use the crosslinking agent, as DEVP mainly reacts with this crosslinker and (ii) to activate the PU foam before graft-polymerization to promote further reaction with the crosslinker. The characterizations also proved that before sonication, non-reacted DEVP precursors mainly act in the gas phase, preventing ignition, whereas after sonication the covalently grafted phosphorus containing species mainly act in the condensed phase to form phosphonic acid which will promote charring and thus will limit dripping and flame spread.

Mechanistic investigation of a flame retardant coating made by layer-by-layer assembly

The efficiency of a flame retardant coating based on poly(allylamine) (PAH) and montmorillonite (MMT), deposited on polyamide 6 (PA6) bulk polymer was demonstrated in our previous work. In this paper we aim to investigate the mechanism of action of this flame retardant coating. To reach this objective, PA6-(PAH-MMT) at 40 bilayers was tested in a cone calorimeter and interrupted at different characteristic times: 25 s (after the fire test start), time to ignition, time of peak heat release rate and time of flameout. The condensed phases of the specimen residues obtained were characterized by scanning electron microscopy, X-ray diffraction, laser desorption ionization and solid state 13C nuclear magnetic resonance while the gas phase was evaluated by thermogravimetric analysis coupled with infrared spectroscopy and mass spectrometry. Finally the pyrolysis combustion flow calorimeter was used to evidence the effect of this layer-by-layer assembly in the gas phase. A possible mechanism explaining the improvement of the flame retardancy of a PA6 substrate in the presence of LbL coating made of PAH and clay is proposed.

Selective biological response of human pulmonary microvascular endothelial cells and human pulmonary artery smooth muscle cells on cold-plasma-modified polyester vascular prostheses.

The aim of this work was to improve the hemocompatibility and the selectivity according to cells of non-woven poly(ethylene terephthalate) (PET) membranes. Non-woven PET membranes were modified by a combined plasma-chemical process. The surface of these materials was pre-activated by cold-plasma treatment and poly(acrylic acid) (PAA) was grafted by the in situ free radical polymerization of acrylic acid (AA). The extent of this reaction and the number of carboxylic groups incorporated were evaluated by colorimetric titration using toluidine blue O. All samples were characterized by SEM, AFM and thermogravimetric analysis, and the mechanical properties of the PAA grafted sample were determined. A selective cell response was observed when human pulmonary artery smooth muscle cells (HPASMC) or human pulmonary micro vascular endothelial cells (HPMEC) were seeded on the modified surfaces. HPASMC proliferation decreased about 60%, while HPMEC proliferation was just reduced about 10%. PAA grafted samples did not present hemolytic activity and the platelet adhesion decreased about 28% on PAA grafted surfaces.

Antifouling Stainless Steel Surface: Competition between Roughness and Surface Energy

To increase the shelf-life qualities of dairy products, a heat treatment is usually done. However, heat treatments induce physico-chemical modifications of the products. Some of them lead to the expected product but an unwanted consequence of this process is the formation of a fouling deposit on the surfaces in contact with the processed fluid. To eliminate fouling, cleaning processes have to be done once a day. It increases the processing and maintenance costs. To control and to decrease the fouling are the main problems in food industries and an active research is carried out on efficient antifouling surface treatments. In the present study, a 316L 2B stainless steel was submitted to different surface treatments (Flame and plasma pre-treatments, Plasma Enhanced Chemical Vapour Deposition, hydrophobic coatings, mechanical polishing ...) to try to establish correlations between different surface parameters (roughness, hydrophobicity, nanostructuration, surface energy, ...) onto the fouling in heat exchangers. All the treated plates were then submitted to a fouling test using an aqueous solution of β-lactoglobulin at 1% (p/p) with a final calcium concentration of 910 mg/L and compared to a bare steel plate. The results obtained imply different influences of each parameter depending on the surface roughness: the effect of a non organized micrometric roughness is preponderant compared to the surface energy: the fouling comes from a mechanical effect mainly due to rubbing. However, when the surface is nanostructured, fouling decreases. When the roughness reaches the nanometer scale (between 100 and 400 nm), it is the surface energy and the polar/apolar components which become preponderant compared to the roughness. Fouling is this time mainly due to the hydrophilicity of the surface and to the adsorption of the β-lactoglobulin on acido-basic sites. Finally, when the roughness reaches less than 50 nm, polar/apolar components show no effect anymore, the preponderant parameter is the hydrophobicity of the surface.

Antifouling Biomimetic Liquid-infused Stainless Steel: Application to Dairy Industrial Processing.

Fouling is a widespread and costly issue, faced by all food-processing industries. Particularly, in the dairy sector, where thermal treatments are mandatory to ensure product safety, heat-induced fouling represents up to 80% of the total production costs. Significant environmental impacts, due the massive consumption of water and energy, are also to deplore. Fouling control solutions are thus desperately needed, as they would lead to substantial financial gains as well as tremendous progress toward eco-responsible processes. This work aims at presenting a novel and very promising dairy fouling-mitigation strategy, inspired by nature, and to test its antifouling performances in real industrial conditions. Slippery liquid-infused surfaces were successfully designed directly on food grade stainless steel, via femtosecond laser ablation, followed by fluorosilanization and impregnation with an inert perfluorinated oil. Resulting hydrophobic surfaces (water contact angle of 112°) exhibited an extremely slippery nature (contact angle hysteresis of 0.6°). Outstanding fouling-release performances were obtained for these liquid-infused surfaces as absolutely no trace of dairy deposit was found after 90 min of pasteurization test in pilot-scale equipment followed by a short water rinse.

Intumescence as method for providing fire resistance to structural composites: application to poly(ethylene terephtalate) foam sandwich–structured composite

Intumescence is a method for providing fire resistance to composite materials. In this paper, the fire resistance of intumescent coatings protecting structural composites (polyethylene terephthalate (PET) foam sandwich–structured composite) is evaluated at both the small and large scales according to the fire scenario described by the Steiner tunnel (ASTM E84). Results show acceptable correlations between the two scales and the approach developed at the small scale permits the fast screening of intumescent paints to predict their fire behavior at the large scale. It has been shown that intumescent paints protect efficiently the PET foam structured sandwich–structured composite used in the ceiling of railway station against fire.