Chemical treatment for the degradation of the mechanical properties of miscanthus stems to facilitate fragmentation

Chemical treatment for the degradation of the mechanical properties of miscanthus stems to facilitate fragmentation. 8. Plant Biomechanics International Conference PBM

Aliments et produits végétaux : des solides cellulaires ?

National audienc

Morphological characterization of wheat powders, how to characterize the shape of particles?

Axe 2 Structuration sous contraintes des agropolymères et réactivité des poudres. Contact: fax: (+33)4 9961 3076. E-mail address: [email protected] quantitative method was developed to evaluate the shape of wheat powder particles. The method relies on a dispersion system designed to scatter particles on a transparent glass slide. A digital image acquisition system based on specialized software was then used to analyze the acquired images. Particles (1000) were analyzed with respect to four shape factors (circularity, elongation, convexity, and compactness). Dispersion of experimental values characterizes the large heterogeneity in wheat flour particles' shapes. The results demonstrate that small particles of wheat powders have more regular shape than big ones, due to possible erosion mechanisms occurred during millin

Role of Laplace pressure in the equilibrium of a hanging drop by a mechanical loading

International audienceFor a very low feed rate, it can be assumedthat a hanging drop at the end of a capillary remains in near equilibrium just before breaking.The equilibrium condition indicates that the action of the capillary force must oppose the weight of the drop, to which should be added the force due to Laplace pressure.Thus, for a given fluid and a fixed wet perimeter, the maximum mass of a hanging drop should be constant if Laplace pressure is also constant.We modulated this pressure by modifying the main curvatures of the dropandwe observed that the mass of the drop is not constant.For three contrasting surface tension liquids, drops were made with five different needle diameters.They were loaded with glass beads of increasing mass respecting the axi-symmetry of the system.This loading induces a stretchingof the drop that modulates the main curvatures.The measurements of the volumesand curvature radii for different loadingratesare performedby image analysis.These loading experimentshighlight the increase of Laplace pressure with theloading and the non-linear decrease of the drop mass.However, we observethat the liquid mass in the loaded drop decreases linearly with the increase of the beadmasswithout verifyingthe mass balance.Such aresult isincluded ina master curve which highlights the role of the Laplace pressure in the equilibrium of a hanging drop just before its rupture.It challenges the validity of Tate's law and allows the setting of functional ranges for capillary micromanipulators

Adherence within biological multilayered systems: development and application of peel test to analyse wheat grain peripheral layers

Correspondance: fax: +33 499613076. E-mail address: [email protected] audienceThe wheat grain is surrounded by a multilayered system composed of different tissues differing in their composition and mechanical properties. Up to now, these properties have been determined using classical tensile tests. However no methodology exists to evaluate the inter-tissular adherence. With this purpose, a micromechanical device adapted to wheat tissue (5 tissues with thickness varying from 2 to 55 μm) was built in order to investigate an interface of industrial interest for wheat processing (between the aleurone layer and the nucellar epidermis). Taking into account the complexity of the peel force measured, the stored elastic energy on the peel arms was estimated using tensile tests of peel arms and was found to approximate 0.15% of the total peel force at low peel rates. The energy dissipated was investigated as a function of peel test parameters (angle, curvature radius and rate), and seems to have a minimal influence when low peel rates were applied (20 μm s−1). The peel test was finally used to investigate the adherence distribution around the wheat grain using samples dissected in different directions. The bottom of the grain was the least adherent region, whereas the top of the grain towards the brush was the most adherent region. Even though the interpretation of the peel force was complex, this technique could be appropriate to evaluate the adherence within natural biological tissues

Détermination du volume de gouttes pendantes et décrochées considérées comme des milliréacteurs capillaires

International audienc

Détermination du volume de gouttes pendantes et décrochées considérées comme des milliréacteurs capillaires

International audienc

Modélisation Mécanique de la friabilité du blé

Nous introduisons dans cet article un modèle granulaire cohésif de l'albumen de blé prenant en compte à la fois les granules d'amidon et une phase continue correspondant à la matrice protéique. La cohésion de la texture est gouvernée par l'adhérence entre l'amidon et la protéine, reflétant la nature biochimique de l'interface, et par la teneur en protéine qui assure la connectivité entre les granules. Nous présentons ici une étude paramétrique de la rigidité, de la résistance à la rupture et des régimes de fissuration en traction simple. Nous montrons que les données relatives à l'endommagement des granules d'amidon, en tant que descripteur de la friabilité, peuvent etre mises à l'échelle avec une ténacité relative tenant compte à la fois de l'adhérence entre amidon et protéine et de la quantité de protéine. Cette ténacité apparait alors comme un paramètre de controle gouvernant la transition des comportements de type "soft" à "hard". Ce paramètre combine la quantité de protéine et l'adhérence entre la protéine et les granules d'amidon, deux propriétées majeures généralement avancées pour expliquer la friabilité du blé

Wheat endosperm as a cohesive granular material

International audienceWe introduce a cohesive granular model of the wheat endosperm involving a discrete phase composed of starch granules, a continuous phase representing the protein matrix and pores. The cohesion of the texture is governed by adherence between starch and protein, reflecting the biochemical nature of the interface, and the protein content that controls the connectivity between starch granules. We present a detailed parametric study of the stiffness, yield strength and regimes of crack propagation under tensile loading. We then show that starch damage, as a descriptor of wheat hardness, scales with the relative toughness between the starch and the starch-protein interface. The toughness appears therefore to be the control parameter governing transition from 'soft' to 'hard' behavior. Interestingly, this parameter combines the starch-protein adherence with protein content, two major quantities often assumed to underly wheat hardness

Laser-induced breakdown spectroscopy and chemometrics: a novel potential method to analyze wheat grains

Correspondance: [email protected] audienceLaser-induced breakdown spectroscopy (LIBS) has been widely used to evaluate the elemental composition (e.g., minerals or metal accumulation) on vegetal tissues. The main objective of this work was to differentiate wheat outer tissues during the grain ablation using LIBS and univariate/multivariate analysis. A high resolution spectrometer and a Nd:YAG laser (532 nm, 5 ns) was first used in order to easily identify atomic wheat emission lines. Then a pulsed excimer laser ArF (193 nm, 15 ns) and a compact fiber optic spectrometer was used to acquire LIBS spectral data from each pulse. Univariate and multivariate analyses (MW2D, PLS-DA) were carried out to provide more in depth information from the LIBS experiment. The number of pulses needed to ablate wheat tissues was successfully predicted by the supervised pattern recognition procedure. LIBS used in conjunction with multivariate analysis could be an interesting technique for rapid structural analysis of vegetal materia