Bruno Vergnes - Academia.edu (original) (raw)

Papers by Bruno Vergnes

HAL (Le Centre pour la Communication Scientifique Directe), 2017

International Polymer Processing

In the present work, a prototype was developed to observe the flow behavior of viscous fluids und... more In the present work, a prototype was developed to observe the flow behavior of viscous fluids under free surface shear and determine an adhesion energy in this flow geometry. The geometry consists of an eccentric Couette cell (outer cylinder radius of 89.5 mm, inner cylinder radius of 43.75 mm and minimal gap of 3 mm) that can be used in two modes, where both cylinders can respectively rotate in the same or opposite directions. Cylinders are horizontal and short relatively to their diameters (30 mm long). Transparent windows allow in-situ flow observations. The design, development, and testing of the prototype with a model viscous fluid (silicone fluid with a 2.2 104 Pa.s Newtonian viscosity) are reported in this paper. The flow behavior of small fluid volumes (fill factor smaller than 15%) was investigated under co- and counter-rotating configurations to determine steady-state flow conditions. Stationary conditions were identified in the counter-rotating mode. The velocity conditio...

HAL (Le Centre pour la Communication Scientifique Directe), 2014

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Un modèle de cinétique d'évolution de populations de bulles dans un fluide à seuil

SIGLECNRS AR 10547 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

The aim of this work is to assess the potential of graphene nanoplatelets (GNP) according to thei... more The aim of this work is to assess the potential of graphene nanoplatelets (GNP) according to their production method to improve properties of composites based on polypropylene and elaborated by melt mixing. The effects of GNP size on structural, thermal, rheological and mechanical properties of composites were investigated. Three grades of GNPs, obtained by a thermomechanical process and commercialized by Knano under KNG-180, KNG-150 and KNG-G5 references, were considered in this work. KNG-180 and KNG-150 GNPs were obtained from graphite through a three step process: i) graphite was intercalated by sulfuric acid under stirring and then washed and dried, ii) then, it underwent a thermal treatment and finally iii) the obtained expanded graphite was ultrasonicated in hydroalcoholic solution. From this step, particles were considered as graphene nanoplatelets [1]. An additional ball milling process in good solvent, followed by centrifugation, enabled to obtain thinner KNG-G5 from KNG-18...

Summary : Reaching nanoscale dispersion of the layered silicate within polypropylene (PP) matrix ... more Summary : Reaching nanoscale dispersion of the layered silicate within polypropylene (PP) matrix is challenging and requires both the use of a compatibilizer and optimal processing method. We showed in a previous work that the specific mechanical energy received during extrusion was the key parameter controlling this microstructure with a saturation of the dispersion state above a certain level of energy [1-2]. The present study aims at better understanding the effect of the specific mechanical energy on the dispersion process. Nanocomposites of polypropylene, maleated polypropylene and organomodified montmorillonite were prepared in a co-rotating twin-screw extruder by direct mixing. The effect of the specific mechanical energy was investigated by varying extrusion parameters such as the screw speed, the barrel temperature and changing the matrix viscosity level. A particular attention was paid to high screw speed conditions. Dead stop experiments were conducted and the nanocomposi...

Cereal Chemistry, 1995

The effect of energy input during mixing on the standard French biscuit petit beurre was observed... more The effect of energy input during mixing on the standard French biscuit petit beurre was observed by means of an experimental mixer fitted out with monitoring devices. Results showed an energy threshold of 60 kJ/kg, beyond which the biscuits retracted and grew thicker. This phenomenon was accurately studied by a rheological and physicochemical characterization of the dough. The viscoelastic properties of the biscuit dough were determined by dynamic measurements on a parallel plate rheometer The parameter tg δ (G/G) decreased proportionally to the mixing energy, indicating an increase in the elasticity of the material. Consequently, doughs characterized by tg δ values >0.48 are of poor quality, producing short and thick biscuits that are unsuitable for packaging. For low strains, G' is higher than G, whereas for high strains, the rheological behavior is modified (G > G'), indicating a change in the structure of the material. The value of the limit deformation D correspo...

The flow behaviour of a SBR compound during single screw extrusion process has been investigated.... more The flow behaviour of a SBR compound during single screw extrusion process has been investigated. Experiments were conducted on a single screw extruder equipped with various pressure and temperature sensors along the screw profile. Influences of temperature of feed section, screw and barrel were characterised. In order to modify the pressure drop, different dies were used. Three parameters were varied during the tests: the screw rotation speed (15, 40 and 70 min-1), the temperature of the feed section and barrel (30, 60 and 90 °C) and that of the screw (50 and 90 °C), and fi nally the die restriction. The characteristic curves of the extruder were deduced from the values of head pressure and flow rate. A comparison of the characteristic curves was made to determine which factor (temperature of the feed section, of the barrel or of the screw) was the most signifi cant. An increase in the temperature of feed section induced a decrease of flow rate and pressure. An opposite effect was ...

International Polymer Processing, 2017

Polypropylene/organoclay nanocomposites were prepared by melt-mixing in a twin-screw extruder. Po... more Polypropylene/organoclay nanocomposites were prepared by melt-mixing in a twin-screw extruder. Polypropylene grafted with maleic anhydride was used as compatibilizer. The evolution of the microstructure along the screw profile was characterized through dead-stop experiments. In order to quantify the multi-scale dispersion state of the nanocomposites, different techniques have been used: scanning electronic microscopy (SEM) to observe the large remaining aggregates, X-Ray diffraction measurements to characterize the intercalation state by measuring the interlamellar distance, and finally rheological characterizations in the molten state to assess the dispersion state at the nanoscale. The effects of low barrel temperatures and high matrix viscosity were tested, in order to improve exfoliation by an increase in shear stresses.

Advanced Methods in Materials Processing Defects, 1997

Publisher Summary This chapter quantifies the sharkskin defect of a linear polyethylene resin. Us... more Publisher Summary This chapter quantifies the sharkskin defect of a linear polyethylene resin. Using profilometry, optical microscopy and observations of cross sections of extrudates, the chapter measures the evolution of amplitude and period (or frequency) of sharkskin defects over a wide range of shear rates and in different flow conditions. The chapter shows the specific behavior of the orifice die, in comparison to other flow situations. The numerical study of the flow patterns near the die exit points out the existence of a small traction zone at the periphery of the extrudate, where could be initiated the rupture of the skin, subjected to excessive elongational stresses. However, the stress is not sufficient to explain all the experimental observations and other parameters, such as elongational deformations, are also probably concerned in the mechanism of sharkskin formation.

AIP Conference Proceedings, 2016

During extrusion of starchy products, the molten material is forced through a die so that the sud... more During extrusion of starchy products, the molten material is forced through a die so that the sudden abrupt pressure drop causes part of the water to vaporize giving an expanded, cellular structure. The objective of this work was to elaborate a phenomenological model of expansion and couple it with Ludovic® mechanistic model of twin screw extrusion process. From experimental results that cover a wide range of thermomechanical conditions, a concept map of influence relationships between input and output variables was built. It took into account the phenomena of bubbles nucleation, growth, coalescence, shrinkage and setting, in a viscoelastic medium. The input variables were the moisture content MC , melt temperature T, specific mechanical energy SME , shear viscosity η at the die exit, computed by Ludovic®, and the melt storage moduli E’(at T > T g ). The outputs of the model were the macrostructure (volumetric expansion index VEI, anisotropy) and cellular structure (fineness F) of solid foams. Then a general model was established: VEI = α (η/η 0) n in which α and n depend on T, MC , SME and E’ and the link between anisotropy and fineness was established.

Rheology of Non-Spherical Particle Suspensions, 2015

In this chapter, we review the rheological behavior of multiphase systems (suspensions in Newtoni... more In this chapter, we review the rheological behavior of multiphase systems (suspensions in Newtonian fluids and polymers filled with fibers or microfibers and nanoparticles). First, we present some basic definitions and concepts useful for the understanding of the rheological properties of concentrated suspensions. We summarize key problems encountered in rheometry, and then we review the rheological behavior of suspensions of rigid and flexible fibers in polymer matrices and that of nanocomposites, based on nanoclays and carbon nanotubes (CNTs). Finally, we conclude with challenges and trends for future research.

Special Publications

International audienc

Theoretical and Applied Rheology, 1992

Journal of Food Engineering, 1992

The isothermal f7ow of a Newtonian material through the reverse screw element (RSE) of a twin-scr... more The isothermal f7ow of a Newtonian material through the reverse screw element (RSE) of a twin-screw extrusion-cooker was computed. The distribution of a tracer, whose units were incremented in time and energy along their trajectories, was simulated. This resulted in residence time and energy distributions. Both distributions are important in order to quantify the treatment received by the food material during the flow through the RSE and therefore the corresponding level of transformation. The influence of several variables (screw speed, feed rate, geometry) was evaluated. The width of the axial slots was shown to be very eficient in regulating the mechanical treatment of the material.

HAL (Le Centre pour la Communication Scientifique Directe), Feb 10, 2021

In the present work, a prototype was developed to observe the flow behavior of viscous fluids (10... more In the present work, a prototype was developed to observe the flow behavior of viscous fluids (10 3 to 10 5 Pa.s) under free surface shear. The geometry of the prototype is an eccentric Couette cell where both cylinders can rotate in the same or opposite directions. Transparent windows permit in-situ observations during flow. The design, development and testing of the prototype with a viscous model fluid are reported in this paper. In order to obtain information on contact lines and free surfaces under shear, the flow behaviour of a small fluid volume was investigated in co-and counter-rotating conditions. The different flow conditions and information that can be obtained are described. A particular attention is paid to determine steady state flow conditions.