Contribution à l'étude des propriétés d'un composite PP/lin mis en oeuvre par extrusion

International audienceLe comportement mécanique d'un composite polypropylène (PP) renforcé avec des fibres de lin extrudé sous forme de bande plate a été étudié et comparé à celui du PP/talc. Ces mêmes matériaux ont aussi été injectés et leur propriétés comparées à celles des pièces extrudées. Les propriétés mécaniques et leur microstructure ont été étudiées après transformation. L'utilisation des fibres de lin comme renfort permet de dépasser les propriétés mécaniques du PP/talc tout en permettant une diminution du retrait et de la masse volumique. L'ajout d'anhydride maléique a permis une nette amélioration des performances grâce à l'amélioration de l'interface fibres/matrice. Les matériaux injectés présentent de meilleures caractéristiques mécaniques que ceux extrudés grâce à une meilleure orientation des fibres et une plus faible porosité

Unravelling the consequences of ultra-fine milling on physical and chemical characteristics of flax fibres

In recent years, lignocellulosic biomass has been increasingly used in various applications, often replacing petro-sourced materials. While for many of these applications the plant materials require coarse milling, some new applications for green chemistry, bio-energy and bio-packaging necessitate comminution to obtain very finely calibrated particles (below 200 m in size). This milling step is not inconsequential for lignocellulosic materials and can influence the physical (size, shape) and chemical characteristics (cellulose crystallinity, composition) of the powder. However, these different effects are still poorly understood. In this work, we study and elucidate the impact of intense and ultra-fine milling on the physico-chemical properties of plant fibres. Flax was chosen for this study because of its well-described hierarchical structure and biochemical composition in literature, making it a model material. Our main results evidence a strong impact of 0 to 23hrs ball milling on flax fibre morphology, especially on fibre aspect ratio falling from 20 to 5 but also on cell wall ultrastructure and composition. Cellulose content and crystallinity significantly decrease with milling time, leading to higher water sorption and lower thermal stability.The authors also thank the French national research Network ‘GDR 3710 INRA/ CNRS SYMBIOSE – Synthons et matériaux biosourcés’, for its financial suppor

Etude en rupture d'un composite à fibres végétales d'Alfa

National audienceThe behavior under monotonic loading of reinforced natural fibre composites begins to be fairly well known today. However, the fracture behavior is still poorly controlled. This work describes a numerical approach developed to simulate the propagation mechanism of a matrix crack in natural fibre reinforced composites.To this end, the fracture behavior of a REV; constituted of alfa fibre, with linear anisotropic behavior, surrounded by a matrix with non-linear viscoelastic behavior, was investigated using a finite element model. The analysis of the fracture behavior of the composite alfa fibre / epoxy resin shows that under uniaxial longitudinal or transverse load to the fibre, a crack initiated in the matrix is propagated perpendicularly to the direction of the load. Near the interface, the energy release rate decreases and this energy is higher in the presence of interfacial debonding areas generated by problems of fibre wettability. Reaching the interface, the crack is either blocked or deflected. Once deflected, the crack propagates along the interface and causes the complete debonding of the fibre.Le comportement sous chargement monotone des composites renforcés par des fibres naturelles commence à être assez bien connu aujourd'hui. Cependant, le comportement à la rupture est encore mal maîtrisé. Le présent travail décrit une approche numérique développée pour simuler le mécanisme de propagation d'une fissure matricielle à l'interface fibre végétale alfa / résine époxy dans les composites à matrice polymère. A cette fin, le comportement à la rupture d'un VER constitué d'une fibre unitaire d'alfa, de comportement linéaire anisotrope, entourée d'une matrice de comportement non linéaire viscoélastique, a été étudié à l'aide d'un modèle éléments finis. L'analyse du comportement à la rupture du composite fibre alfa/résine époxy montre que sous l'action d'un chargement uniaxial, longitudinal ou transversal par rapport à la fibre, une fissure initiée dans la matrice se propage perpendiculairement au sens de la sollicitation. Au voisinage de l'interface, le taux de restitution d'énergie diminue et ce taux est plus élevé en présence de zones de non adhésion générées par des problèmes de mouillages. Arrivée à l'interface, la fissure est soit bloquée soit déviée. Une fois déviée, la fissure se propage le long de l'interface et entraîne la décohésion de la fibre

Beating of hemp bast fibres: an examination of a hydro-mechanical treatment on chemical, structural, and nanomechanical property evolutions

In this study, a gradually increased hydro-mechanical treatments duration were applied to native hemp bast fibres with a traditional pulp and paper beating device (laboratory Valley beater). There is often a trade-off between the treatment applied to the fibres and the effect on their integrity. The multimodal analysis provided an understanding of the beating impact on the fibres at multiple scales and the experimental design made it possible to distinguish the effects of hydro- and hydro-mechanical treatment. Porosity analyses showed that beating treatment doubled the macroporosity and possibly reduced nanoporosity between the cellulose microfibrils. The beating irregularly extracted the amorphous components known to be preferentially located in the middle lamellae and the primary cell walls rather than in the secondary walls, the overall increasing the crystallinity of cellulose from 49.3 % to 59.1 %, but a non-significant change in the indentation moduli of the cell wall was observed. In addition, beating treatments with two distinct mechanical severities showed a disorganization of the cellulose conformation, which significant dropped the indention moduli by 11.2 GPa and 8.4 GPa for 10 and 20 minutes of Valley beater hydro-mechanical treatment, respectively, compared to hydro-treated hemp fibres (16.6 GPa). Pearson’s correlation coefficients between physicochemical features and the final indentation moduli were calculated. Strong positive correlations were highlighted between the cellulose crystallinity and rhamnose, galactose and mannose as non-cellulosic polysaccharide components of the cell wall

Purification and characterisation of the yeast plasma membrane ATP binding cassette transporter Pdr11p.

The ATP binding cassette (ABC) transporters Pdr11p and its paralog Aus1p are expressed under anaerobic growth conditions at the plasma membrane of the yeast Saccharomyces cerevisiae and are required for sterol uptake. However, the precise mechanism by which these ABC transporters facilitate sterol movement is unknown. In this study, an overexpression and purification procedure was developed with the aim to characterise the Pdr11p transporter. Engineering of Pdr11p variants fused at the C terminus with green fluorescent protein (Pdr11p-GFP) and containing a FLAG tag at the N terminus facilitated expression analysis and one-step purification, respectively. The detergent-solubilised and purified protein displayed a stable ATPase activity with a broad pH optimum near 7.4. Mutagenesis of the conserved lysine to methionine (K788M) in the Walker A motif abolished ATP hydrolysis. Remarkably, and in contrast to Aus1p, ATPase activity of Pdr11p was insensitive to orthovanadate and not specifically stimulated by phosphatidylserine upon reconstitution into liposomes. Our results highlight distinct differences between Pdr11p and Aus1p and create an experimental basis for further biochemical studies of both ABC transporters to elucidate their function

Influence of neutropenia on mortality of critically ill cancer patients : results of a meta-analysis on individual data

Background: The study objective was to assess the influence of neutropenia on outcome of critically ill cancer patients by meta-analysis of individual data. Secondary objectives were to assess the influence of neutropenia on outcome of critically ill patients in prespecified subgroups (according to underlying tumor, period of admission, need for mechanical ventilation and use of granulocyte colony stimulating factor (G-CSF)). Methods: Data sources were PubMed and the Cochrane database. Study selection included articles focusing on critically ill cancer patients published in English and studies in humans from May 2005 to May 2015. For study selection, the study eligibility was assessed by two investigators. Individual data from selected studies were obtained from corresponding authors. Results: Overall, 114 studies were identified and authors of 30 studies (26.3% of selected studies) agreed to participate in this study. Of the 7515 included patients, three were excluded due to a missing major variable (neutropenia or mortality) leading to analysis of 7512 patients, including 1702 neutropenic patients (22.6%). After adjustment for confounders, and taking study effect into account, neutropenia was independently associated with mortality (OR 1.41; 95% CI 1.23-1.62; P = 0.03). When analyzed separately, neither admission period, underlying malignancy nor need for mechanical ventilation modified the prognostic influence of neutropenia on outcome. However, among patients for whom data on G-CSF administration were available (n = 1949; 25.9%), neutropenia was no longer associated with outcome in patients receiving G-CSF (OR 1.03; 95% CI 0.70-1.51; P = 0.90). Conclusion: Among 7512 critically ill cancer patients included in this systematic review, neutropenia was independently associated with poor outcome despite a meaningful survival. Neutropenia was no longer significantly associated with outcome in patients treated by G-CSF, which may suggest a beneficial effect of G-CSF in neutropenic critically ill cancer patients

Estimation of the interfacial shears strength, orientation factor and mean equivalent intrinsic tensile strength in old newspaper fiber/polypropylene composites

The present paper investigates the suitability of old newspapers (ONPs) as a source of reinforcing fibers for composite materials. Different percentages of ONP fibers were compounded with polypropylene (PP). A coupling agent was added to the compound to improve the interface between matrix and reinforcing fibers. Tensile test were performed to obtain the mechanical properties of the composite materials. Micromechanics of the fibers were obtained using Hirsch model, Bowyer Bader methodology and Kelly-Tyson equations. Due to the presence of a percentage of calcium carbonate in the obtained fibers (10%), the computed intrinsic characteristics were addressed as equivalent. The most important results were the mean equivalent intrinsic tensile strength of the ONP fibers, the mean orientation angle and the mean interfacial shear strength. The contributions of the matrix, the subcritical and the supercritical fibers to the tensile strength of the composite material were also computed. (C) 2013 Elsevier Ltd. All rights reserved.Serrano, A.; Espinach, FX.; Julian, F.; Rey Tormos, RMD.; Mendez, JA.; Mutje, P. (2013). Estimation of the interfacial shears strength, orientation factor and mean equivalent intrinsic tensile strength in old newspaper fiber/polypropylene composites. Composites Part B: Engineering. 50:232-238. doi:10.1016/j.compositesb.2013.02.018S2322385