81 research outputs found
Oxidative degradation of polylactide (PLA) and its effects on physical and mechanical properties
The thermo-oxidative degradation of polylactide (PLA) films was studied between 70 and 150 C. It was shown that the oxidative degradation of PLA leads to a random chain cission responsible for a reduction of the molar mass. These molar mass changes affect Tg and the degree of crystallinity, and it was found that Tg decreases according to the FoxâFlory theory whereas the degree of crystallinity increases due to a chemicrystallization process. A correlation between molar mass and strain at break during oxidation has been established: PLA displays a brittle behavior when Mn falls below 40 kg mol 1 in agreement with relationships linking the critical value for embrittlement with the molar mass between entanglements
Thermo-oxidative stabilization of poly(lactic acid)-based nanocomposites through the incorporation of clay with in-built antioxidant activity
In this work, an innovative approach to overcome the issue of the poor thermo-oxidative stability of polymer/clay nanocomposites is proposed. Specifically, biodegradable polylactic acid (PLA)-based nanocomposites, containing organo-modified clay with in-built antioxidant activity, were prepared. Through a two-step chemical protocol, a hindered phenol antioxidant was chemically linked to the ammonium quaternary salt which was then intercalated between the clay platelets [(AO)OM-Mt]. The nanocomposites were characterized and their thermo-oxidative stability during melt processing and under long-term thermal test conditions was investigated. PLA nanocomposites containing the (AO)OM-Mt showed higher oxidative stability, along with better clay dispersion, compared to PLA-nanocomposites containing commercial clay and a free hindered phenol antioxidant. Obtained results can be explained considering that (AO)OM-Mt may act locally, at the interface, between the silicate layers and the polymer macromolecules, thus contributing to the observed improved stability of the polymer both during processing and under long-term thermal-oxidative conditions
Physical and mechanical characterization of PLLA interference screws produced by two stage injection molding method
Study of nanocomposites based on PLA/PA11 polymer blends
Lâacide polylactique (PLA) est lâun des polymĂšres biosourcĂ©s qui suscite le plus dâintĂ©rĂȘt, mais ses propriĂ©tĂ©s thermomĂ©caniques nĂ©cessitent dâĂȘtre amĂ©liorĂ©es. Pour ce faire, les mĂ©thodes les plus utilisĂ©es et Ă©tudiĂ©es sont de le mĂ©langer avec dâautres polymĂšres ou bien dây ajouter des charges minĂ©rales nanomĂ©triques (nanoparticules), afin de constituer un nanocomposite Ă matrice PLA. Câest dans la combinaison de ces deux approches que sâinscrivent ces travaux de thĂšse, consacrĂ©s Ă lâĂ©laboration et Ă la caractĂ©risation des propriĂ©tĂ©s de nanocomposites Ă base dâun alliage de PLA et de polyamide 11 (PA11) 80/20 m/m. Lâobjectif de cette thĂšse est lâobtention dâun matĂ©riau biosourcĂ© aux propriĂ©tĂ©s thermiques, mĂ©caniques et de rĂ©action au feu amĂ©liorĂ©es par le contrĂŽle de sa morphologie et lâajout de nanoparticules et de retardateurs de flamme (RF). Pour y parvenir, deux techniques de compatibilisation, destinĂ©es Ă amĂ©liorer lâadhĂ©sion interfaciale entre le PLA et le PA11, ont Ă©tĂ© Ă©valuĂ©es. La premiĂšre consistait Ă incorporer des nanoparticules de silice. Il a Ă©tĂ© notĂ© dâimportantes modifications de la morphologie et des propriĂ©tĂ©s rhĂ©ologiques du mĂ©lange dâĂ©tude, selon leur localisation dans le mĂ©lange Ă©tudiĂ© fonction de la nature chimique de la surface de la silice. La deuxiĂšme consistait Ă introduire un copolymĂšre Ă©poxyde multifonctionnel rĂ©actif, dĂ©nommĂ© Joncryl. La rĂ©activitĂ© de ce copolymĂšre avec le PLA et le PA11 a permis de compatibiliser le mĂ©lange dâĂ©tude, conduisant Ă une morphologie plus fine et Ă lâobtention de propriĂ©tĂ©s mĂ©caniques supĂ©rieures Ă celles du mĂ©lange dâĂ©tude, en particulier avec lâajout de 3%m de Joncryl. Des Ă©chantillons basĂ©s sur les mĂ©langes compatibilisĂ©s par cette mĂ©thode ont Ă©tĂ© prĂ©parĂ©s par le procĂ©dĂ© de fabrication additive FDM. Une Ă©tude de lâimpact de ce procĂ©dĂ© sur la morphologie et les propriĂ©tĂ©s mĂ©caniques obtenues a Ă©tĂ© entreprise. Enfin, une meilleure rĂ©action au feu pour le mĂ©lange compatibilisĂ© avec 3%m de Joncryl a pu ĂȘtre obtenue par lâajout combinĂ© de nanoparticules de phyllosilicates et de RF.Polylactic acid (PLA) is one of the biobased polymers that generates the most interest, but its thermomechanical properties need to be improved. To do that, the most used and studied methods consist of blending PLA with other polymers or adding nanoscaled mineral fillers (nanoparticles) to get a PLA based nanocomposite. This PhD work is dedicated to the elaboration and properties characterization of nanocomposites based on a filled PLA and polyamide 11 80/20 wt/wt blend. The aim is to obtain a biobased material with improved thermal, mechanical and fire reaction properties by controlling its morphology through the addition of nanoparticles and flame retardants additives.To achieve that, two compatibilization techniques, aiming to improve PLA-PA11 interfacial adhesion, were evaluated. The first one consisted of adding silica nanoparticles. Important changes of the blend morphology and rheological properties were noticed, depending on the localization of the two different silica nanoparticles used into the polymer blend phases. The second one consisted of introducing a reactive multifunctional epoxy copolymer, named Joncryl. The reactivity of this copolymer with PLA and PA11 allowed to compatibilize the blend, leading to a fine morphology and higher mechanical properties compared to those of the pristine blend. Samples of compatibilized blends obtained through this method were processed using FDM additive manufacturing process. A study of the influence of this process on the morphology and mechanical properties obtained for these samples was performed. Finally, a better fire reaction of compatibilized polymer blend with 3%wt Joncryl was obtained by the combined addition of phyllosilicates nanoparticles and flame retardants
Etude de nanocomposites basés sur des alliages PLA/PA11
Polylactic acid (PLA) is one of the biobased polymers that generates the most interest, but its thermomechanical properties need to be improved. To do that, the most used and studied methods consist of blending PLA with other polymers or adding nanoscaled mineral fillers (nanoparticles) to get a PLA based nanocomposite. This PhD work is dedicated to the elaboration and properties characterization of nanocomposites based on a filled PLA and polyamide 11 80/20 wt/wt blend. The aim is to obtain a biobased material with improved thermal, mechanical and fire reaction properties by controlling its morphology through the addition of nanoparticles and flame retardants additives.To achieve that, two compatibilization techniques, aiming to improve PLA-PA11 interfacial adhesion, were evaluated. The first one consisted of adding silica nanoparticles. Important changes of the blend morphology and rheological properties were noticed, depending on the localization of the two different silica nanoparticles used into the polymer blend phases. The second one consisted of introducing a reactive multifunctional epoxy copolymer, named Joncryl. The reactivity of this copolymer with PLA and PA11 allowed to compatibilize the blend, leading to a fine morphology and higher mechanical properties compared to those of the pristine blend. Samples of compatibilized blends obtained through this method were processed using FDM additive manufacturing process. A study of the influence of this process on the morphology and mechanical properties obtained for these samples was performed. Finally, a better fire reaction of compatibilized polymer blend with 3%wt Joncryl was obtained by the combined addition of phyllosilicates nanoparticles and flame retardants.Lâacide polylactique (PLA) est lâun des polymĂšres biosourcĂ©s qui suscite le plus dâintĂ©rĂȘt, mais ses propriĂ©tĂ©s thermomĂ©caniques nĂ©cessitent dâĂȘtre amĂ©liorĂ©es. Pour ce faire, les mĂ©thodes les plus utilisĂ©es et Ă©tudiĂ©es sont de le mĂ©langer avec dâautres polymĂšres ou bien dây ajouter des charges minĂ©rales nanomĂ©triques (nanoparticules), afin de constituer un nanocomposite Ă matrice PLA. Câest dans la combinaison de ces deux approches que sâinscrivent ces travaux de thĂšse, consacrĂ©s Ă lâĂ©laboration et Ă la caractĂ©risation des propriĂ©tĂ©s de nanocomposites Ă base dâun alliage de PLA et de polyamide 11 (PA11) 80/20 m/m. Lâobjectif de cette thĂšse est lâobtention dâun matĂ©riau biosourcĂ© aux propriĂ©tĂ©s thermiques, mĂ©caniques et de rĂ©action au feu amĂ©liorĂ©es par le contrĂŽle de sa morphologie et lâajout de nanoparticules et de retardateurs de flamme (RF). Pour y parvenir, deux techniques de compatibilisation, destinĂ©es Ă amĂ©liorer lâadhĂ©sion interfaciale entre le PLA et le PA11, ont Ă©tĂ© Ă©valuĂ©es. La premiĂšre consistait Ă incorporer des nanoparticules de silice. Il a Ă©tĂ© notĂ© dâimportantes modifications de la morphologie et des propriĂ©tĂ©s rhĂ©ologiques du mĂ©lange dâĂ©tude, selon leur localisation dans le mĂ©lange Ă©tudiĂ© fonction de la nature chimique de la surface de la silice. La deuxiĂšme consistait Ă introduire un copolymĂšre Ă©poxyde multifonctionnel rĂ©actif, dĂ©nommĂ© Joncryl. La rĂ©activitĂ© de ce copolymĂšre avec le PLA et le PA11 a permis de compatibiliser le mĂ©lange dâĂ©tude, conduisant Ă une morphologie plus fine et Ă lâobtention de propriĂ©tĂ©s mĂ©caniques supĂ©rieures Ă celles du mĂ©lange dâĂ©tude, en particulier avec lâajout de 3%m de Joncryl. Des Ă©chantillons basĂ©s sur les mĂ©langes compatibilisĂ©s par cette mĂ©thode ont Ă©tĂ© prĂ©parĂ©s par le procĂ©dĂ© de fabrication additive FDM. Une Ă©tude de lâimpact de ce procĂ©dĂ© sur la morphologie et les propriĂ©tĂ©s mĂ©caniques obtenues a Ă©tĂ© entreprise. Enfin, une meilleure rĂ©action au feu pour le mĂ©lange compatibilisĂ© avec 3%m de Joncryl a pu ĂȘtre obtenue par lâajout combinĂ© de nanoparticules de phyllosilicates et de RF
Peculiar Morphologies Obtained for 80/20 PLA/PA11 Blend with Small Amounts of Fumed Silica
This work highlights the possibility of obtaining peculiar morphologies by adding fumed silica into 80/20 polylactic acid/polyamide11 (PLA/PA11) blends. Two kinds of fumed silica (A200 and trimethoxyoctylsilane modified R805 fumed silica) were dispersed (by twin-screw extrusion, TSE) at a weight amount of 5% in neat PLA, neat PA11 and a 80/20 PLA/PA11 blend. Thermal Gravimetric Analysis (TGA) was used to verify this 5 wt % amount. Oscillatory shear rheology tests were conducted on all the formulations: (1) on neat polymer nanocomposites (PLASi5, PLASiR5, PA11Si5, PA11SiR5); and (2) on polymer blend nanocomposites (PLA80Si5 and PLA80SiR5). Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscope (STEM), Atomic Force Microscopy (AFM) characterizations and laser granulometry were conducted. Microscopic analysis performed on polymer blend nanocomposites evidenced a localization of A200 silica in the PA11 dispersed phase and R805 silica at the PLA/PA11 interface. Frequency sweep tests on neat polymer nanocomposites revealed a pronounced gel-like behavior for PLASi5 and PA11SiR5, evidencing a high dispersion of A200 in PLA and R805 in PA11. A yield behavior was also evidenced for both PLA80Si5 and PLA80SiR5 blends. For the blend nanocomposites, PA11 dispersed phases were elongated in the presence of A200 silica and a quasi-co-continuous morphology was observed for PLA80Si5, whereas PLA80SiR5 exhibits bridges of silica nanoparticles between the PA11 dispersed phases
Analyse et modélisation du comportement mécanique d'un composite renforcé de fibres de carbone, soumis à des chargements complexes
Today, the aeronautic structure lightening is subjected to costs considerations: the materials must all at once be lightweight, have good mechanical properties and their cost must remain low. Short carbon fiber reinforced organic matrix composites are good candidates in order to handle that issues. However, the injection molding process uses to make that kind of materials induces a complex microstructure which influences the composite behavior. The presented thesis work aim to identify, study, characterize and model the specific scales of the material: the components, the microstructure and the global material in order to propose a modelling approach based on the local enrichment of the composite behavior under complex loadings.The hydrostatic pressure matrix sensitivity is identified and modeled with a Generalized Drucker-Prager plastic criterion. The composite elastic behavior is used to identify one carbon fiber behavior through a reverse engineering method. Thanks to X-ray phase contrast tomography, both the orientation and the length of each fiber are measured. The matrix confinement, responsible for the local and the global composite behavior is investigated by mean of the study of the local fiber volume fraction distribution in the microsctructure. A generation and identification approach of a representative volume element of both the unidirectional composite behavior and the microstructure morphology is developed by finite element modeling. At the same scale, a mean field model, based on morphological representative patterns is implemented and allows determining the unidirectional composite behavior. An original mean field procedure with the integration of the real orientations and fiber lengths is proposed and allows simulating the effective composite behavior. This original two-step homogenization procedure is globally and locally calibrated thanks to virtual testing. Finally, this approach is experimentally verified on a structural test, putting a strain on the composite in a complex way.LâallĂšgement des structures aĂ©ronautiques est aujourdâhui soumis Ă des contraintes Ă©conomiques : les matĂ©riaux doivent Ă la fois ĂȘtre plus lĂ©gers, avoir de bonnes propriĂ©tĂ©s mĂ©caniques et leurs coĂ»ts doivent ĂȘtre rĂ©duits. Les matĂ©riaux composites Ă matrice organique renforcĂ©e par des fibres courtes de carbone sont de bons candidats pour rĂ©pondre Ă ces enjeux. Cependant, le moulage par injection utilisĂ© pour les transformer, gĂ©nĂšre une microstructure complexe qui influence leur comportement. Les travaux prĂ©sentĂ©s dans ce manuscrit proposent une dĂ©marche visant Ă identifier, Ă©tudier, caractĂ©riser et modĂ©liser les diffĂ©rentes Ă©chelles du matĂ©riau : les constituants, la microstructure et le matĂ©riau global, afin de proposer une dĂ©marche de modĂ©lisation basĂ©e sur lâenrichissement local du comportement dans le cas de chargements complexes. La sensibilitĂ© de la matrice Ă la pression hydrostatique est identifiĂ©e et modĂ©lisĂ©e Ă lâaide dâun critĂšre de Drucker-Prager gĂ©nĂ©ralisĂ©. A lâaide de celui du composite, un comportement rĂ©versible des fibres est identifiĂ©. GrĂące Ă des observations en tomographie RX en contraste de phase, lâorientation et la longueur de chaque fibre sont mesurĂ©es. Le confinement matriciel, responsable du comportement local et macroscopique du matĂ©riau, est Ă©tudiĂ© par le biais dâune mĂ©thode de mesure de la distribution de la fraction volumique locale de fibres dans la microstructure. Une dĂ©marche de gĂ©nĂ©ration et dâidentification dâune cellule Ă©lĂ©mentaire reprĂ©sentative du comportement unidirectionnel et de la morphologie de la microstructure est dĂ©veloppĂ©e en champs complets. A la mĂȘme Ă©chelle, un modĂšle dâhomogĂ©nĂ©isation utilisant un systĂšme de motifs morphologiques reprĂ©sentatif est implĂ©mentĂ©e et permet de constituer la brique unidirectionnelle du comportement du composite en champs moyens. Une procĂ©dure dâintĂ©gration de lâorientation et des longueurs rĂ©elles de fibres est mise en place afin de simuler le comportement homogĂšne Ă©quivalent du composite de lâĂ©tude. Cette procĂ©dure dâhomogĂ©nĂ©isation originale en deux Ă©tapes est calibrĂ©e Ă de maniĂšre globale et locale lâaide dâessais virtuels. Enfin, la dĂ©marche est vĂ©rifiĂ©e sur un essai de structure, sollicitant le composite de maniĂšre complexes
Une histoire de la pensée économique pour comprendre les crises
Alors que la nouvelle crise ouverte en 2007 a relancĂ© le dĂ©bat thĂ©orique sur les crises avec la vigueur que lâon sait, lâouvrage de P. Boccara arrive Ă point nommĂ© pour apporter aux dĂ©bats en cours lâĂ©clairage bienvenu dâun retour sur lâhistoire de la pensĂ©e Ă©conomique des crises. Lâobjectif poursuivi dans cet ouvrage est ambitieux : dresser « un bilan des diverses thĂ©ories avancĂ©es [...] dans lâhistoire de la pensĂ©e Ă©conomique sur les fondements des crises et de leurs issues » (p. 8) et « e..
Analyse et modélisation du comportement mécanique d'un composite renforcé de fibres de carbone, soumis à des chargements complexes
Today, the aeronautic structure lightening is subjected to costs considerations: the materials must all at once be lightweight, have good mechanical properties and their cost must remain low. Short carbon fiber reinforced organic matrix composites are good candidates in order to handle that issues. However, the injection molding process uses to make that kind of materials induces a complex microstructure which influences the composite behavior. The presented thesis work aim to identify, study, characterize and model the specific scales of the material: the components, the microstructure and the global material in order to propose a modelling approach based on the local enrichment of the composite behavior under complex loadings.The hydrostatic pressure matrix sensitivity is identified and modeled with a Generalized Drucker-Prager plastic criterion. The composite elastic behavior is used to identify one carbon fiber behavior through a reverse engineering method. Thanks to X-ray phase contrast tomography, both the orientation and the length of each fiber are measured. The matrix confinement, responsible for the local and the global composite behavior is investigated by mean of the study of the local fiber volume fraction distribution in the microsctructure. A generation and identification approach of a representative volume element of both the unidirectional composite behavior and the microstructure morphology is developed by finite element modeling. At the same scale, a mean field model, based on morphological representative patterns is implemented and allows determining the unidirectional composite behavior. An original mean field procedure with the integration of the real orientations and fiber lengths is proposed and allows simulating the effective composite behavior. This original two-step homogenization procedure is globally and locally calibrated thanks to virtual testing. Finally, this approach is experimentally verified on a structural test, putting a strain on the composite in a complex way.LâallĂšgement des structures aĂ©ronautiques est aujourdâhui soumis Ă des contraintes Ă©conomiques : les matĂ©riaux doivent Ă la fois ĂȘtre plus lĂ©gers, avoir de bonnes propriĂ©tĂ©s mĂ©caniques et leurs coĂ»ts doivent ĂȘtre rĂ©duits. Les matĂ©riaux composites Ă matrice organique renforcĂ©e par des fibres courtes de carbone sont de bons candidats pour rĂ©pondre Ă ces enjeux. Cependant, le moulage par injection utilisĂ© pour les transformer, gĂ©nĂšre une microstructure complexe qui influence leur comportement. Les travaux prĂ©sentĂ©s dans ce manuscrit proposent une dĂ©marche visant Ă identifier, Ă©tudier, caractĂ©riser et modĂ©liser les diffĂ©rentes Ă©chelles du matĂ©riau : les constituants, la microstructure et le matĂ©riau global, afin de proposer une dĂ©marche de modĂ©lisation basĂ©e sur lâenrichissement local du comportement dans le cas de chargements complexes. La sensibilitĂ© de la matrice Ă la pression hydrostatique est identifiĂ©e et modĂ©lisĂ©e Ă lâaide dâun critĂšre de Drucker-Prager gĂ©nĂ©ralisĂ©. A lâaide de celui du composite, un comportement rĂ©versible des fibres est identifiĂ©. GrĂące Ă des observations en tomographie RX en contraste de phase, lâorientation et la longueur de chaque fibre sont mesurĂ©es. Le confinement matriciel, responsable du comportement local et macroscopique du matĂ©riau, est Ă©tudiĂ© par le biais dâune mĂ©thode de mesure de la distribution de la fraction volumique locale de fibres dans la microstructure. Une dĂ©marche de gĂ©nĂ©ration et dâidentification dâune cellule Ă©lĂ©mentaire reprĂ©sentative du comportement unidirectionnel et de la morphologie de la microstructure est dĂ©veloppĂ©e en champs complets. A la mĂȘme Ă©chelle, un modĂšle dâhomogĂ©nĂ©isation utilisant un systĂšme de motifs morphologiques reprĂ©sentatif est implĂ©mentĂ©e et permet de constituer la brique unidirectionnelle du comportement du composite en champs moyens. Une procĂ©dure dâintĂ©gration de lâorientation et des longueurs rĂ©elles de fibres est mise en place afin de simuler le comportement homogĂšne Ă©quivalent du composite de lâĂ©tude. Cette procĂ©dure dâhomogĂ©nĂ©isation originale en deux Ă©tapes est calibrĂ©e Ă de maniĂšre globale et locale lâaide dâessais virtuels. Enfin, la dĂ©marche est vĂ©rifiĂ©e sur un essai de structure, sollicitant le composite de maniĂšre complexes
Etude de la dynamique des prix sur séries longues : France, Angleterre et Etats-Unis au 19Úme siÚcle
International audienc
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