Elaboration d'un nouveau complexe multicouche issu d'éco-matériaux

ROUEN-BU Sciences (764512102) / SudocSudocFranceF

Influence du vieillissement sur le comportement des matériaux et des interfaces des systèmes mécatroniques

Les systèmes mécatroniques sont des systèmes électroniques intégrés directement dans les pièces mécaniques. Leur environnement est sévère (courants>200A) et des défaillances peuvent survenir. Cette thèse est consacrée à l'étude de deux matériaux mécatroniques courants : compsite résine époxy/fibres de verre PCP FR4 (Printed Circuit Board Flame Retardant 4) et alliage PbSnAg. Un vieillissement isotherme est appliqué au PCP FR4 durant 8800 h à 110C. Il affecte principalement l'époxy, qui évolue de manière complexe dès 2800 h. Celle-ci est révélée par l'apparition de courbes bimodales pour C'', le signal "out of phase" en TMDSC (Thermo-Modulated Differential Scanning Calorimetry) et pour tan ð, le rapport entre les modules de perte et de conservation en DMA 'Dynamic Mechanical Analysis). La transformation de l'époxy en deux parties causée par l'oxydation peut expliquer ce phénomène. Une estimation du module d'Young de celles-ci est proposée en associant les analyses de l'époxy aux lois de comportement mécanique du composite (loi rhéologique, modèle de Berthelot et loi mathématique). Pour l'alliage PbSnAg, le vieillissement isotherme à 200C durant 7000 h révèle l'évolution de la microstructure et des propriétés mécaniques de l'alliage coulé d'une part et brasé entre deux substrats Cu revêtus de Ni puis de Ni-P d'autre part. Coulé, l'évolution des intermétalliques (IMCs) d'Ag3Sn est observée mais elle n'affecte pas les propriétés mécaniques en traction de l'alliage. Brasé, outre l'Ag3Sn , d'autres IMCs à base de Ni, de P et de Sn sont formés aux interfaces, évoluent selon une loi de Fick entraînant une baisse des propriétés mécaniques de l'assemblage en cisaillement Arcan.Mechatronic systems resultt from the tight integration of the electronic and mechanical components. Their used condeition is stringent (currents>200A), so failures can occur. This thesis is devoted to study two common mechatronic materials: epoxy matrix/glass fiber woven PCB FR4 (Printed circuit Boiard Flam Retardant 4) composite and PbSnAg alloy. Isothermal aging at 110C is applied to PCB FR4 for over 8800 h. It mainly affects the epoxy, which has evolved in complex ways since 2800 h. This is reflected by the appearance of bimodal curves for C'', "out of phase" signal by TMDSC (Thermo-Modulated Differential Scanning Calorimetry) and for tan ð, the ratio between storage and loss modulus by DMA (Dynamic Mechanical Analysis). The oxidation of a certain volume fraction of the resin leading to the appearance of a new phase can be an explanation. The Young's modulus of thes two phases is modelised and combines the analysis of the aged epoxy with several models of the composite's behavior (rheological laws, Berthelot's model and mathematical law). Concerning the PbSnAg alloy, isothermal aging at 200C for 7000 h is applied to the cast and soldered alloys. In the cast condition, formation, coalescence and fragmentation of Ag3Sn intemetallic compounds (IMCs) are observed but the tensile properties of the alloy are not affected. When the same alloy is soldered between two copper substrates coated with Ni and Ni-P layers, in addition to Ag3Sn, other IMCs based on Ni, P and Sn are also observed and grow during aging according to Fick's law. This microstructural evolution leads to a decrease of the mechanical properties of the solder when they are measured with the Arcan shear test.ROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Étude de la microstructure et des phénomènes de relaxation dans un polyester biodégradable (le Poly (Acide Lactique) (PLA))

L objectif de ce travail de thèse est dans un premier temps d associer une étude microstructurale classique du Poly (acide lactique) (PLA), à une étude de la coopérativité dans la phase amorphe mobile au passage de la transition vitreuse. Pour cela, différentes microstructures ont été obtenues après divers traitements thermomécaniques sur deux PLA : le PLLA et le PLA 4042D présentant des masses molaires et des rapports L/D différents. L influence de la température de cristallisation sur l évolution des proportions des phases du PLA, en particulier la fraction amorphe rigide, est notamment décrite. Le calcul de la taille des Régions de Réarrangements Coopératifs (CRR) dans la phase amorphe mobile montre qu indépendamment du PLA et du mode de cristallisation considérés, il existe un effet analogue à un effet de confinement dans la phase amorphe intra-sphérolitique. Cet effet n est pas purement géométrique mais résulte aussi de l existence d interactions chimiques liant la phase amorphe mobile et la fraction amorphe rigide. Dans un deuxième temps, une étude de l influence de l étirage sur la coopérativité et les propriétés barrières à l eau est menée. La taille des CRR diminue avec l orientation des macromolécules. L étude des mécanismes de diffusion de l eau dans le PLA a mis en évidence un phénomène de plastification du PLA par les molécules d eau. L orientation des macromolécules est défavorable à la plastification et augmente les propriétés barrières.The aim of this work is in a first time to combine a standard microstructural study of PLA with a study of the cooperativity in the mobile amorphous phase during the glass transition. To reach this goal, different microstructures have been obtained by several thermomechanical treatments on two PLA: PLLA and PLA 4042D, presenting different molecular weight and different ratio L/D. The influence of crystallization temperature on the phase quantity evolution, particularly on the rigid amorphous fraction, is commented. It is shown by calculating the Cooperative Rearranging Region (CRR) sizes in the mobile amorphous phase, that whatever the PLA or the crystallization way, there is an effect, similar to a confinement effect, in the intra-spherulitic amorphous phase. It is not considered as a pure geometric effect but as the result of chemical interactions, linking the mobile amorphous phase and the rigid amorphous fraction. In a second time, a study of the drawing influence on the cooperativity and the water barrier properties is carried. The CRR size decreases with the macromolecule orientation. The study of the water diffusion mechanism in the PLA has shown a PLA plasticization phenomenon by the water molecules. The plasticization is decreased by the macromolecule orientation and the barrier properties are increased.ROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Élaboration et caractérisation de nouvelles membranes composites thermostables pour piles à combustible

Ces travaux sont une contribution aux efforts aujourd'hui menés pour tenter de trouver de nouveaux polyélectrolytes alternatifs à l'utilisation de la membrane référence des piles à combustible, la membrane Nafion® de Dupont de Nemours. L'ensemble de ce travail porte sur l'étude de l'effet de la sulfonation sur les mouvements moléculaires du polysulfone sulfoné et sur l'effet de l'introduction de particules de laponite modifiée sur les processus de transport des molécules d'eau et sur la conductivité ionique de ces nouvelles membranes hybrides. La diminution de la taille moyenne des mouvements coopératifs après sulfonation a permis de mettre en avant le confinement de la phase amorphe du polysulfone attribué, par analogie au modèle de structure de la membrane Nafion®, à la réorganisation des segments de chaînes du polysulfone sulfoné en clusters de groupements ioniques. De plus, l'introduction de laponite-SO3H, par une augmentation de la concentration en sites ioniques et par l'affinité que possèdent ces particules pour l'eau, a montré l'accélération de la diffusion des molécules d'eau et l'amélioration de la conductivité ionique de ces membranes composites.The present work aims at finding alternative materials for the reference membrane for fuel cells, the Nafion® membrane from Dupont de Nemours. It concerns the effect of the sulfonation of polysulfone on the polymer segment motions, and that of modified laponite particles dispersed in sulfonated polysulfone on the water transport and the proton conductivity of these new hybrid membranes. The decrease, after sulfonation, in the cooperative motion average sizes allowed us to suggest a confinement of the glassy polymer chains in ionic clusters formed by interactions between sulfonic groups, in much a similar way as those formed in the Nafion® membrane. Moreover, the incorporated laponite-SO3H particles favor water diffusion and enhance the ionic conductivity of the composite membranes, by increasing the total content in ionic groups and the overall water affinity.ROUEN-BU Sciences (764512102) / SudocSudocFranceF

Thermal decomposition study of carbon fiber-reinforced polyphenylene sulfide at high heating rates met under fire exposure

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Characteristics, management, and prognosis of elderly patients with COVID-19 admitted in the ICU during the first wave: insights from the COVID-ICU study

International audienceBackground: The COVID-19 pandemic is a heavy burden in terms of health care resources. Future decision-making policies require consistent data on the management and prognosis of the older patients (> 70 years old) with COVID-19 admitted in the intensive care unit (ICU). Methods: Characteristics, management, and prognosis of critically ill old patients (> 70 years) were extracted from the international prospective COVID-ICU database. A propensity score weighted-comparison evaluated the impact of intubation upon admission on Day-90 mortality. Results: The analysis included 1199 (28% of the COVID-ICU cohort) patients (median [interquartile] age 74 [72–78] years). Fifty-three percent, 31%, and 16% were 70–74, 75–79, and over 80 years old, respectively. The most frequent comorbidities were chronic hypertension (62%), diabetes (30%), and chronic respiratory disease (25%). Median Clinical Frailty Scale was 3 (2–3). Upon admission, the PaO2/FiO2 ratio was 154 (105–222). 740 (62%) patients were intubated on Day-1 and eventually 938 (78%) during their ICU stay. Overall Day-90 mortality was 46% and reached 67% among the 193 patients over 80 years old. Mortality was higher in older patients, diabetics, and those with a lower PaO2/FiO2 ratio upon admission, cardiovascular dysfunction, and a shorter time between first symptoms and ICU admission. In propensity analysis, early intubation at ICU admission was associated with a significantly higher Day-90 mortality (42% vs 28%; hazard ratio 1.68; 95% CI 1.24–2.27; p < 0·001). Conclusion: Patients over 70 years old represented more than a quarter of the COVID-19 population admitted in the participating ICUs during the first wave. Day-90 mortality was 46%, with dismal outcomes reported for patients older than 80 years or those intubated upon ICU admission

A Bayesian reanalysis of the Standard versus Accelerated Initiation of Renal-Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial

Background Timing of initiation of kidney-replacement therapy (KRT) in critically ill patients remains controversial. The Standard versus Accelerated Initiation of Renal-Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial compared two strategies of KRT initiation (accelerated versus standard) in critically ill patients with acute kidney injury and found neutral results for 90-day all-cause mortality. Probabilistic exploration of the trial endpoints may enable greater understanding of the trial findings. We aimed to perform a reanalysis using a Bayesian framework. Methods We performed a secondary analysis of all 2927 patients randomized in multi-national STARRT-AKI trial, performed at 168 centers in 15 countries. The primary endpoint, 90-day all-cause mortality, was evaluated using hierarchical Bayesian logistic regression. A spectrum of priors includes optimistic, neutral, and pessimistic priors, along with priors informed from earlier clinical trials. Secondary endpoints (KRT-free days and hospital-free days) were assessed using zero–one inflated beta regression. Results The posterior probability of benefit comparing an accelerated versus a standard KRT initiation strategy for the primary endpoint suggested no important difference, regardless of the prior used (absolute difference of 0.13% [95% credible interval [CrI] − 3.30%; 3.40%], − 0.39% [95% CrI − 3.46%; 3.00%], and 0.64% [95% CrI − 2.53%; 3.88%] for neutral, optimistic, and pessimistic priors, respectively). There was a very low probability that the effect size was equal or larger than a consensus-defined minimal clinically important difference. Patients allocated to the accelerated strategy had a lower number of KRT-free days (median absolute difference of − 3.55 days [95% CrI − 6.38; − 0.48]), with a probability that the accelerated strategy was associated with more KRT-free days of 0.008. Hospital-free days were similar between strategies, with the accelerated strategy having a median absolute difference of 0.48 more hospital-free days (95% CrI − 1.87; 2.72) compared with the standard strategy and the probability that the accelerated strategy had more hospital-free days was 0.66. Conclusions In a Bayesian reanalysis of the STARRT-AKI trial, we found very low probability that an accelerated strategy has clinically important benefits compared with the standard strategy. Patients receiving the accelerated strategy probably have fewer days alive and KRT-free. These findings do not support the adoption of an accelerated strategy of KRT initiation

Regional Practice Variation and Outcomes in the Standard Versus Accelerated Initiation of Renal Replacement Therapy in Acute Kidney Injury (STARRT-AKI) Trial: A Post Hoc Secondary Analysis.

ObjectivesAmong patients with severe acute kidney injury (AKI) admitted to the ICU in high-income countries, regional practice variations for fluid balance (FB) management, timing, and choice of renal replacement therapy (RRT) modality may be significant.DesignSecondary post hoc analysis of the STandard vs. Accelerated initiation of Renal Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial (ClinicalTrials.gov number NCT02568722).SettingOne hundred-fifty-three ICUs in 13 countries.PatientsAltogether 2693 critically ill patients with AKI, of whom 994 were North American, 1143 European, and 556 from Australia and New Zealand (ANZ).InterventionsNone.Measurements and main resultsTotal mean FB to a maximum of 14 days was +7199 mL in North America, +5641 mL in Europe, and +2211 mL in ANZ (p p p p p p p p = 0.007).ConclusionsAmong STARRT-AKI trial centers, significant regional practice variation exists regarding FB, timing of initiation of RRT, and initial use of continuous RRT. After adjustment, such practice variation was associated with lower ICU and hospital stay and 90-day mortality among ANZ patients compared with other regions