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Grenoble, France

Boufi S.,University of Sfax | Gandini A.,CNRS Structural Engineering
RSC Advances | Year: 2015

Nanofibrillated cellulose (NFC) from biomass has become a subject of intense research activity owing to its attributes of nanosized cellulose and sustainable character. However, efficient production of nanofibrillated cellulose is still challenging with respect to the energy required for the disintegration process. In this study, a triticale crop residue was used as a source for the production of nanofibrillated cellulose, with lateral size of 20-30 nm, using a high pressure homogenizer and a conventional high speed blender. The effects of the delignification mode, fiber pretreatment and disintegration mode on the yield of NFC, the morphology of the ensuing nanofibrils and the energy consumption were investigated. The evolution of the reinforcing potential of the NFC according to the production mode was also studied. By controlling the lignin extraction mode and the carboxyl content of the fibers through TEMPO-mediated oxidation, it was possible to convert triticale pulps into nanofibrillar cellulose with an energy demand as low as 11 kW h kg-1 using a conventional high speed blender. This approach is expected to open the way toward easier and energetically cost-effective production of nanofibrillar cellulose from crop residues. © 2014 The Royal Society of Chemistry.

Isaksson P.,Uppsala University | Dumont P.J.J.,CNRS Structural Engineering
Engineering Fracture Mechanics | Year: 2014

Gradient theories are capable of describing deformation of heterogeneous elastic materials better than classical elasticity theory since they are able to capture internal length effects. Here, crack-tip displacement fields at the tip of a mode I crack in gradient enhanced elastic materials are derived in closed form and contrasted with experiments. Heterogeneous materials, represented by discrete fiber networks, are analyzed in finite element models to judge the theory. It is shown that using a classical continuum approach to describe macroscopic singular-dominated deformation fields in heterogeneous materials lead to erroneous results because a structural effect that alters the displacement field becomes pronounced and results in severe blunting of crack-tips. A key conclusion is that the average segment length in the material gives the internal length scale parameter, used in the gradient enhanced continuum theory, hence allows for bridging between scales. © 2014 Elsevier Ltd.

Viguie J.,CNRS Grenoble Laboratory for Soils, Solids, Structures, and Risks | Dumont P.J.J.,CNRS Structural Engineering
Composite Structures | Year: 2013

The optimisation of board packages often rely on their load bearing capacity. Then it seems attractive to measure how such thin-walled structures deform using for instance kinematic field measurement techniques, and to incorporate, at least partially, the gained kinematic information within mechanical models. Digital Image Correlation (DIC) can provide a vivid description of the buckling of box panels, e.g. during box compression tests. Therefore, we propose an analytical plate model to predict the elastic post-buckling behaviour of corrugated board box panels where the kinematic boundary conditions emanate from DIC measurements. Comparing experimental and calculated strain fields on the outer liner of board panels as well as box compression force lend some confidence to the model. Further results reveal the heterogeneity of in-plane forces, bending and twisting moments the box panels have to withstand as well as strain fields in usually inaccessible regions of the panels such as the inner liner. Thereby an improvement of the structure of box panels can be envisaged. © 2013 Elsevier Ltd.

Paquet O.,CNRS Structural Engineering | Krouit M.,CNRS Structural Engineering | Bras J.,CNRS Structural Engineering | Thielemans W.,University of Nottingham | Belgacem M.N.,CNRS Structural Engineering
Acta Materialia | Year: 2010

Two cellulosic substrates (microcrystalline cellulose, MCC, and bleached kraft softwood pulps, BSK) were grafted by polycaprolactone (PCL) chains with different molecular weights, following a three-step procedure using non-swelling conditions in order to limit the reaction to their surface. First, one of the two OH PCL ends was blocked by phenyl isocyanate and the reaction product (adduct 1) was subsequently reacted with 2,4-toluene diisocyanate (adduct 2) to provide it with an NCO function, capable of reacting with cellulose. The ensuing PCL-grafted cellulosic materials were characterized by weight gain, elemental analysis, contact angle measurements, attenuated total reflexion-Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and biodegradation tests. The modification was proven to occur by the presence of nitrogen atoms in the elemental analysis tests and XPS spectra of modified and soxhlet-extracted cellulose. The contact angle measurements have also shown that the surface became as hydrophobic as PCL itself. The polar component of the surface energy of cellulosic substrates before treatment was found to be about 32 and 10 mJ m-2, for MCC and BSK, respectively. This value vanished to practically zero after grafting with different PCLs. The strategy proposed in the present work is original since, to the best of our knowledge, this paper reports for the first time the chemical "grafting onto" of the cellulose surface by PCL macromolecular structures, with the aim of obtaining fibre-matrix co-continuous fully sustainable and biodegradable composite materials. © 2009 Acta Materialia Inc.

Krouit M.,CNRS Structural Engineering | Naceur Belgacem M.,CNRS Structural Engineering | Bras J.,CNRS Structural Engineering
Composites Part A: Applied Science and Manufacturing | Year: 2010

The influence of chemical and solvent extraction compatibilising techniques on the mechanical properties of poly-lactic acid (PLA) and MaterBi®-polyester (PEM) based bio-composites are compared. First, fibres were chemically grafted with two fatty chains: stearic anhydride and octadecylisocyanate. Grafted fibres were characterised by FTIR and elemental analyses. Contact angle measurements show the hydrophobisation of the fibres in spite of very low surface grafting. Extracted and non-grafted fibres were prepared to be used as references. PEM and PLA-based composites with 30% w/w were prepared by compression moulding. Their mechanical properties were studied. It was found that chemical and solvent treatment of the fibres improved the reinforcement effect in the case of a PEM matrix and the Young modulus increased by 96%. An important conclusion is that solvent extraction is as efficient as chemical grafting for compatibilisation treatment. These results open new perspectives to prepare industrially efficient bio-composite. © 2010 Elsevier Ltd. All rights reserved.

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