Microcellular Foaming of Polymethylmethacrylate in a Batch Supercritical CO2 Process: Effect of Microstructure on Compression Behavior

Microcellular foaming of reinforced core/ shell Polymethylmethacrylate (PMMA) was carried out bymeans of supercritical CO2 in a single-step process. Samples were produced using a technique based on the saturation of the polymer under high pressure of CO2(300 bars,40 C), and cellular structure was controlled by varying the depressurization rate from 0.5 bar/s to 1.6 x10-2 bar/sleading to cell sizes from 1lm to 200l m, and densities from 0.8 to 1.0 g/cm3. It was found that the key parameter to control cell size was depressurization rate, and larger depressurization rates generated bigger cell sizes. On the other hand, variation of the density of the samples was not so considerable. Low rate compression tests were carried out, analyzing the dependence of mechanical parameters such as elastic modulus, yield stress and densification strain with cell size. Moreover, the calculation of the energy absorbed for each sample is presented, showing an optimum of energy absorption up to 50% of deformation in the micrometer cellular range (here at a cell size of about 5 µm). To conclude, a brief comparison between neat PMMA and the core/shell reinforced PMMA has been carried out, analyzing the effect of the core/shell particles in the foaming behavior and mechanical properties

Amorphous Polymers’ Foaming and Blends with Organic Foaming-Aid Structured Additives in Supercritical CO2, a Way to Fabricate Porous Polymers from Macro to Nano Porosities in Batch or Continuous Processes

Organic polymers can be made porous via continuous or discontinuous expansion processes in scCO2. The resulting foams properties are controlled by the interplay of three groups of parameters: (i) Chemical, (ii) physico-chemical, and (iii) technological/process that are explained in this paper. The advantages and drawbacks of continuous (extrusion, injection foaming) or discontinuous (batch foaming) foaming processes in scCO2, will be discussed in this article; especially for micro or nano cellular polymers. Indeed, a challenge is to reduce both specific mass (e.g., ρ < 100 kg·m−3) and cell size (e.g., average pore diameter ϕaveragepores < 100 nm). Then a particular system where small “objects” (coreshells CS, block copolymer MAM) are perfectly dispersed at a micrometric to nanometric scale in poly(methyl methacrylate) (PMMA) will be presented. Such “additives”, considered as foaming aids, are aimed at “regulating” the foaming and lowering the pore size and/or density of PMMA based foams. Differences between these additives will be shown. Finally, in a PMMA/20 wt% MAM blend, via a quasi one-step batch foaming, a “porous to nonporous” transition is observed in thick samples. A lower limit of pore size (around 50 nm) seems to arise

Optimisation des conditions de mise en oeuvre d'un alliage de polymères ABS-PC recyclé contenant une impureté

La faible présence sur le marché de polymères recyclés issus de produits en fin de vie peut s’expliquer en grande partie par le manque de confiance de la part des industriels envers la qualité de la matière recyclée. En effet la matière recyclée et particulièrement les polymères recyclés, lorsqu’ils proviennent d’un gisement de produits hors d’usage, comme les DEEE peuvent avoir une qualité fluctuante, notamment en raison des impuretés qu’ils peuvent contenir. Or, les conditions de mise en œuvre peuvent avoir une grande influence sur la qualité d’un alliage de polymères de 2° génération. Ce deuxième cycle de remise en forme peut dégrader la matière recyclée ou bien, si il est correctement maîtrisé, il peut permettre de lisser les propriétés de la matière en masquant la présence de certaines impuretés [1]. Dans la première partie de cette étude, nous montrons d’une part l’impact des paramètres d’injection sur la morphologie complexe d’un alliage de polymères (ici l’ABS-PC) contenant une impureté ; et d’autre part, nous expliquons les relations entre ces morphologies et la résistance au choc du matériau recyclé. Dans une seconde partie, nous montrons comment il est possible, après optimisation des paramètres de mise en œuvre de l’ABS-PC recyclé de réaliser une matière de seconde génération aux propriétés stables malgré la présence d’une impureté. Nous montrons dans cette étude que la maîtrise des conditions de recyclage permet au matériau recyclé de tolérer la présence de certaines impuretés sans modification significative de ses caractéristiques mécaniques. L’objectif à terme est d’être en mesure de produire un matériau recyclé de qualité environnementale et technique et apte à être remis en forme et à subir un nouveau cycle de vie. Références : [1] ARNOLD et al. ; Polymer testing, Vol 29, N°4, 2012 [2] VILAPLANA FJ et KARLSSON S.; Macromol Mater Eng, Vol 293, N°4, 200

Numerical and experimental investigations of buffet on a diamond airfoil designed for space launcher applications

Purpose – The development of reusable space launchers requires a comprehensive knowledge of transonic flow effects on the launcher structure, such as buffet. Indeed, the mechanical integrity of the launcher can be compromised by shock wave/boundary layer interactions, that induce lateral forces responsible for plunging and pitching moments. Design/methodology/approach – This paper aims to report numerical and experimental investigations on the aerodynamic and aeroelastic behavior of a diamond airfoil, designed for microsatellite-dedicated launchers, with a particular interest for the fluid/structure interaction during buffeting. Experimental investigations based on Schlieren visualizations are conducted in a transonic wind tunnel and are then compared with numerical predictions based on unsteady Reynolds averaged Navier–Stokes and large eddy simulation (LES) approaches. The effect of buffeting on the structure is finally studied by solving the equation of the dynamics. Findings – Buffeting is both experimentally and numerically revealed. Experiments highlight 3D oscillations of the shock wave in the manner of a wind-flapping flag. LES computations identify a lambda- shaped shock wave foot width oscillations, which noticeably impact aerodynamic loads. At last, the experiments highlight the chaotic behavior of the shock wave as it shifts from an oscillatory periodic to an erratic 3D flapping state. Fluid structure computations show that the aerodynamic response of the airfoil tends to damp the structural vibrations and to mitigate the effect of buffeting. Originality/value – While buffeting has been extensively studied for classical supercritical profiles, this study focuses on diamond airfoils. Moreover, a fluid structure computation has been conducted to point out the effect of buffeting

Fluid-structure interaction between a composite aileron and a turbulent flow at transonic conditions

This work reports some numerical and experimental investigations about the aerodynamic and aeroelastic behavior of a diamond aileron for a launcher dedicated to microsatellites. This work focuses mainly on the flow at transonic conditions with an emphasis on the buffet phenomenon. Indeed, the mechanical integrity of the launcher is largely compromised at transonic regime due to such shock/boundary layer interaction, that induces forces responsible for plunging and pitching moment that can damage the structure. An experimental campaign has been conducted, based on Schlieren visualizations. The experimental data are then compared with numerical predictions obtained with unsteady RANS and LES. The final objective is the analysis of buffeting impact on the composite material of the aileron

Numerical and experimental investigations of buffet on a diamond airfoil designed for space launchers applications

The capability to reuse space launchers for new missions requires to better understand flow phenomena in the transonic regime, such as buffet, and its interaction with the structure. Indeed, the mechanical integrity of the launcher can be compromised by shock/boundary layer interactions, that induce lateral forces responsible for plunging and pitching moments. This work reports some numerical and experimental investigations about the aerodynamic and aeroelastic behavior of a diamond airfoil, designed for microsatellite-dedicated launchers, with a particular interest for the fluid/structure interaction during buffeting. Experiments have been conducted, based on Schlieren visualizations, and compared with numerical predictions obtained with unsteady RANS and Large-Eddy Simulation. Finally, the effect of buffeting on the composite aileron is studied by solving the equation of the dynamics, showing that the aerodynamic response of the airfoil tends to damp the structural displacement, and thus limit the effect of buffeting

Production, cellular structure and thermal conductivity of microcellular (methyl methacrylate)–(butyl acrylate)–(methyl methacrylate) triblock copolymers.

Microcellular foaming of a (methyl methacrylate)–(butyl acrylate)–(methyl methacrylate) triblock copolymer was carried out by means of supercritical CO2 in a single-step process. The experiments were performed at 40 °C using a pressure of 300 bar (30 MPa) during 24 h. The depressurization times were modified from 2 to 30 min, leading to cell sizes from 10 to 100 µm, and relative densities from 0.11 to 0.17. It was found that the key parameter to control cell size and density was depressurization time: longer depressurization times generated larger cell sizes and lower densities. The thermal conductivity of these materials was measured using the transient plane source technique, and it was found that this decreased as the density was reduced. Various models for the prediction of thermal conductivity by conduction were tested. It was found that all the models underestimated the experimental results due to a significant contribution of radiation heat flow for these material

Ru catalysts for levulinic acid hydrogenation with formic acid as a hydrogen source

International audienceThe catalytic hydrogenation of levulinic acid (LA) with formic acid (FA) as a hydrogen source into [gamma]-valerolactone (GVL) is considered as one of the crucial sustainable processes in today's biorefinery schemes. In the current work, we investigated the modification of Ru/C as efficient catalysts for both formic acid decomposition and levulinic acid hydrogenation in comparison with Pd and Pt catalysts. In order to better understand what features are responsible for high catalytic performance, we combined experimental tests, DFT calculations together with extensive material characterization. In LA hydrogenation with FA as a hydrogen source, the intermediate surface formate inhibits at least partially the LA hydrogenation. In addition, the FA decomposition is highly sensitive to the kind of the preparation method of the Ru/C catalyst: (i) the process looks structure sensitive favored on larger particles and (ii) residual chlorine decreases significantly the FA decomposition rate

High-pressure drop rates in solid-state batch one-step scCO2 foaming of acrylic polymers: A way to stabilize the structure of micro-nano foams

One-step solid-state batch scCO2 foaming is used with the target of achieving acrylic polymer micro-nano foams. Foaming is triggered by an average pressure drop (APDR), covering two decades, from 0.3 to 30 MPa.s−1. This study principally addresses the combined beneficial effects of block copolymer addition (BCP, here denoted as MAM) and high APDR. Numerous subtle kinetic parameters actually interplay and compete in the production of the final foams. In particular, the material effective temperature, the effective glass transition temperature of the plasticized system and the instantaneous PDR are physical quantities each having their own kinetics during foaming. The resulting foam morphologies are quantified by SEM microscopy and image analysis. A high APDR and the presence of BCP are shown to play a key role in the final structure of the foams. Over the scrutinized range of saturation temperature (40 °C to 60 °C i.e. rather ‘low’ temperatures in the CO2 supercritical state), the APDR is the main factor for significantly reducing cell size and increasing nuclei density in foams from neat PMMA. In the block copolymer approach, increasing the APDR is of secondary importance as the targeted reduction of the porosity dimensions and augmentation of nuclei density are mostly the consequence of MAM presence. In this latter case, increasing the APDR still promotes the ‘efficiency’ of the BCP nucleants. A real efficient nucleation activity of MAM additive is observed at a very high APDR (30 MPa.s−1), leading to monomodal homogeneous distribution of tiny pores in nearly nanosized foams. At lower APDR, an interesting reproducible double porosity (foams containing intra-wall and inter-wall pores) is detected in PMMA/MAM systems. In such double porosity foams, benefits from the Knudsen effect achieved within well expanded local domains (showing micron-sized pores) may remain meaningful thanks to a locally poorly expanded nanoporous thick solid skeleton encapsulating these local domains. Thereby, the radiative thermal conduction can be minimized and does not override the conductive component at the sample scale. This work provides further insight on acrylic polymer BCP foams influenced by different kinetics

Supercritical CO2‐assisted extrusion foaming: A suitable process to produce very lightweight acrylic polymer micro foams

A strategy of CO2-assisted extrusion foaming of PMMA-based materials was established to minimize both foam density and porosities dimension. First a highly CO2-philic block copolymer (MAM: PMMA-PBA-PMMA) was added in PMMA in order to improve CO2 saturation before foaming. Then the extruding conditions were optimized to maximize CO2 uptake and prevent coalescence. The extruding temperature reduction led to an increase of pressure in the barrel, favorable to cell size reduction. With the combination of material formulation and extruding strategy, very lightweight homogeneous foams with small porosities have been produced. Lightest PMMA micro foams (ρ = 0.06 g cm−3) are demonstrated with 7 wt% CO2 at 130°C and lightest blend micro foams (ρ = 0.04 g cm−3) are obtained at lower temperature (110°C, 7.7 wt% CO2). If MAM allows a reduction of Tfoaming, it also allows a much better cell homogeneity, an increase in cell density (e.g., from 3.6 107 cells cm−3 to 2 to 6 108 cells cm−3) and an overall decrease in cell size (from 100 to 40 μm). These acrylic foams produced through scCO2-assisted extrusion has a much lower density than those ever produced in batch (ρ ≥ 0.2 g cm−3).ANR : AAPG PRCE 2018CE06 0030,201