Laurent Lebrun

Effect of chemical treatments on water sorption and mechanical properties of flax fibres.

In this work, in order to improve the adhesion between a polyester matrix (unsaturated polyester resin) and flax fibres (Linum usitatissimum L.) and to increase their moisture resistance, chemical surface treatments have been used. These different treatments were performed with maleic anhydride (MA), acetic anhydride (Ac), silane (Si) and styrene (S). The modified flax fibres were characterized by means of infrared spectroscopy and surface energy analysis. The effect of these treatments on water sorption was investigated by using a gravimetric static equilibrium method. Water sorption isotherms were derived from kinetic data. The Park model based on the three sorption modes: Langmuir, Henrys law and clustering, was successfully used to simulate the experimental sorption data. It was found that the (Ac) and particularly (S) treatments reduced overall water uptake of flax fibres. We show that tensile modulus, breaking strength and breaking strain depend on the chemical treatment used.

Diffusion of dextran through microporous membrane filters

Abstract The production of large macromolecules such as polysaccharides by microbial cells retained behind microporous membranes is subject to mass transfer limitations within the membranes. This paper describes a quantitative investigation of these diffusional limitations in commercially available microporous membrane filters using various dextran fractions as solutes. Dextran diffusivities in membrane pores were determined using a well-stirred diffusion cell. Dextran fractions were characterized by their intrinsic viscosity and weight-average molecular weight ( M w determined by light scattering. Hydrodynamic radii (rH) were estimated from the macromolecular parameters using the Mark—Houwink and Stokes—Einstein relationships. The tested membranes involved a series of mixed ester cellulose filters with pore radii (rp) ranging from 0.11 to 0.6 μm, two track-etched polycarbonate membranes and one inorganic (alumina) membrane. All macromolecules except the smallest ( M w=10,500, rH=27 A) showed restricted diffusion in the membranes. Their effective diffusivities (Dp) were an increasing function of the membrane pore size. For any given membrane, Dp decreased as M w increased. The diffusion data did not fit the Renkin model for a hard sphere diffusing through a cylindrical pore. These results are discussed in terms of membrane and solute characteristics.

Novel Metal-Complexing Membrane Containing Poly(4-vinylpyridine) for Removal of Hg(II) from Aqueous Solution

A novel poly(vinyl alcohol)/poly(4-vinylpyridine) (PVA/P(4)VP) complexing membrane for removal of Hg(II) ions from aqueous solutions represents a significant improvement over a previously reported PVA/poly(ethylenimine) (PEI) membrane. This membrane was prepared by the semi-interpenetrating polymer network technique, and its cross-linking by three different agents was studied. The best results were obtained with gaseous 1,2-dibromoethane at 140 degrees C for 1 h that gave a membrane with a swelling ratio of 0.66. The sorption reaction of Hg(II) followed a first-order rate law, and the rate-limiting step was shown to be the association of Hg(II) ions with the complexing sites of P(4)VP. Sorption experiments at pH 2.5 showed that the retention ratio could reach 100% under optimized conditions for the initial concentration of Hg(II) and mass of membrane, c(0) = 100 mg L(-1) and m(D) = 100 mg, respectively. The retention ratio was remarkably insensitive to water hardness or the presence of NaCl, suggesting possible use for the purification of real wastewaters. The retention capacity of the membrane was 450 mg g(-1) compared to 311 mg g(-1) reported for the PVA/PEI membrane. Sorption isotherms were determined at various temperatures, according to the Langmuir model, for the determination of the thermodynamical parameters. When T increased, mercury uptake at equilibrium did not change, whereas the sorption coefficient b decreased and the change in free energy DeltaG degrees decreased. This result is probably due to a large favorable entropic effect, ascribed to the displacement of protons from the protonated sites of P(4)VP while they bind with Hg(II) ions. The membrane could be regenerated by 0.5 M nitric acid with less than 3% loss of efficiency. The membrane was used for filtration experiments. The elimination ratio was 99.9% or more for filtration of Hg(II) solutions in the c(0) = 16.6-89.1 mg L(-1) range.

Facilitated transport of α-alanine and phenylalanine through sulfonic cation-exchange membranes

Abstract Facilitated transport of amino acid zwitterion (S) through sulfonic plane and tubular cation-exchange membranes (CEM) in a reactive form H + is studied. This transport uses the ability of a non-charged species S to combine with H + in order to form a counter-ion SH + in the membrane. A theoretical model of the facilitated transport taking into account effect of the diffusion layers adjoining the membrane is developed. It is illustrated by the experimental results of α-alanine (Ala) and phenylalanine (Phe) transport through plane Nafion® 117 and Nafion® 120 membranes (Du Pont de Nemours), Ala transport through a plane CRP membrane (Rhone Poulenc®), and Ala transport through a tubular Nafion® 811X.

Pressure impact of autoclave treatment on water sorption and pectin composition of flax cellulosic-fibres.

The tensile properties of flax fibres might permit them to be used in composites as reinforcement in organic resin, as long as their mechanical properties are reproducible and their water sorption are reduced. In this study, to minimise the variability of mechanical properties, several samples of flax fibres were blended as a non-woven fabric. In order to reduce the water absorption of this non-woven technical fibres, an autoclave treatment was performed which was expected to remove the pectins and then to reduce the water sorption on their negative charges. The impact of autoclave pressure (0.5, 1 and 2 bars) on water sorption was investigated by using a gravimetric static equilibrium method. The Park model based on the three sorption modes: Langmuir, Henrys law and clustering, was successfully used to simulate the experimental sorption data. The lowest pressure treatments impacted only the Langmuir contribution while the 2 bar autoclave-treatment positively impacted the water resistance in the core of fibres by reducing Henrys absorption rate. This was shown to be related to the chemical modifications at the surface and in the core of fibres. A schematic model is presented relating the water sorption and the pectic composition of the fabric.

Antiviral effects of polyphenols: Development of bio-based cleaning wipes and filters

Polyphenol molecules play multiple essential roles in plant physiology such as defences against plant-pathogens and micro-organisms. The present study reports a chemical modification of the surface of non-woven cellulosic fibre filters (Kimwipes(®)) by fixing polyphenol in order to confer them antiviral properties. The grafting of the non-woven fibres by the antiviral entity was performed using laccase. T4D bacteriophage virus of Escherichia coli B was used as virus model. Catechin polyphenol was tested as antiviral entity. Proteomic experiments were performed to quantify the potential protein target of catechin on viruses. When the modified filter was in contact with the viral suspension a large improvement in the reduction of the viral concentration was observed (5-log after 1h). Thus, we propose that this material could be used as virucidal wipes for the virus elimination from contaminated surfaces. Virus filtration experiments were performed by spraying an aerial suspension of T4D bacteriophage virus through the designed filter. The best virus capture factor f (ratio of upstream to downstream virus contents) was obtained when using 2 functionalized filters (f=2.9×10(3)). When these 2 layers were placed inside a commercial medical mask in place of its cellulose layer (Kolmi M24001 mask) (f=3.5×10(4)), the f ratio then reached 2.6×10(5) for 2h of filtration. Based on these results, this novel bio-based antiviral mask represents a significant improvement over conventional medical masks.

Characteristics of polyurethane-based sustained release membranes for drug delivery

AbstractThis paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications.

Design and Sustained Release Evaluation of Rifampicin from Polyurethane Membranes

Drug delivery membranes based on polyurethanes have been used for prolonged release of rifampicin. Therefore, two polyurethane structures with concentrations in urethane groups of 1.5 mmol/g and 2.5 mmol/g, respectively were tested for delivery of rifampicin. The influence of the surface morphology in drug release was evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. The kinetics, drug release mechanisms and dynamic vapour sorption (DVS) were studied. Prolonged nature of the release of rifampicin is assured by the urethane concentration 2.5 mmol/g but also to the surface of the membrane systems. It was found that the rifampicin release is function of polymer-drug membranes composition and the surface properties. One can assume that the mechanism of diffusion is Fickian, and the experimental data verify this law. Finally, the possibility of applications of the polyurethane matrix with rifampicin was shown by biological test.

Process of Facilitated Extraction of Vanadium Ions through Supported Liquid Membranes: Parameters and Mechanism

To conduct experiments related to the facilitated extraction phenomenon of vanadium ions (), three supported liquid membranes (SLMs) were prepared, each containing 0.01 M of methyl cholate (MC), resorcinarene (RESO), or trioctylamine (TOA) as extractive agents. Kinetic and thermodynamic models were developed, based on the interaction of the substrate () with the extractive agent T and the diffusion of the formed entity (TS) through the membrane. The experimental results verify the models, and to determine, macroscopic parameters, permeabilities (P) and initial fluxes (), and microscopic parameters, association constants () and apparent diffusion coefficients () related to formed entities (TS) and their diffusion through the membrane organic phase. The experimental results indicate that the mechanism on the migration of the ions through the membrane organic phase is based on the successive jumps of substrate, from one site to another of the extractive agent. To explain these results and understand the mechanism, we studied influence of temperature factor, and we determined activation parameters (, , and ). The results show that this extraction phenomenon is governed by a structural term. Therefore, the membrane performance changes according to nature and structure of the association site presented by each of extractive agents.

Water Diffusion Mechanisms in New Bio-Nanocomposites Based on Polyhydroxyalkanoates/Nanoclays

Nanocomposites based on bacterial semi-crystalline polyhydroxyalkanoates, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) or poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)), and organo-modified montmorillonite nanoclay are prepared by melt processing. All nanocomposites are characterized by X-Ray Diffraction (XRD) and Transmission Electronic Microscopy (TEM) and exhibit a mainly intercalated structure. Concerning water transport properties, a decrease of barrier properties for PHBV/nanoclay films is measured due to the affinity of nanoclay to water; whereas for P(3HB-co-4HB)/nanoclay nanocomposites, a decrease of the water permeability is observed relative to the tortuosity effect. Eventually, as a function of nanoclay content, a competition is evidenced between the tortuosity effect and the water sorption induced by nanoclay.