Mécanismes de dégradation des enveloppes barrières pour application panneaux isolants sous vide

Vacuum Insulation Panels (VIPs) were already developed some time ago for low-temperature applications such as refrigerators. More recently, they have been used for the building application. They consist of a fine powder or fiber core material (fumed silica, glass fiber, PU foam) enveloped by a polymer-metal. The latter is responsible for preventing gas and water molecules from breaking the vacuum. Nevertheless, the use of VIPs for this application was limited for applications in severe conditions as for example: temperature, humidity and mechanical load. At high temperature and/or humidity, the most critical component of a VIP is the envelope: both for the tightness point of view and for its degradation. Consequently in these conditions, the vacuum was degraded and durability of the panel performance was decreased sharply.This work focuses on the degradation mechanisms of the polymer-metal envelope. The effect of hygrothermal ageing (70 °C and 90 %RH) on envelope was investigated at different scales: Microscopic: High humidity is at the origin of the hydrolysis of some components such as Polyethylene terephthalate (PET) and polyurethane adhesive (PU). Hydrolysis is directly at the origin of the changes mechanical properties, leading to embrittlement of the complex. An additional microstructural modifications was evidence in PET at high humidity and also contributes to embrittlement of the complex. Macroscopic: shrinkage of polymer film seems to be the origin of debonding in polymer-metal multilayer.Le panneau isolant sous vide, PIV est principalement constitué d’un matériau de cœur nano-poreux encapsulé sous vide par une enveloppe barrière multicouche polymère-métal. Dans l’objectif d’étendre le domaine d’emploi des PIV sur le marché de l’isolation thermique du bâtiment, il est nécessaire d’améliorer les performances d’étanchéités et la résistance en température et humidité des complexes barrières métallisés, ces derniers représentant le point faible des PIV. Ce travail a pour objectif d’identifier les différentes modifications subies par ces complexes au cours de leurs fonctionnement et de déterminer les mécanismes à l’origine de leur dégradation prématurée. Des vieillissements à 70 °C et 90 %RH (conditions maximales d’utilisations identifiées pour le bâtiment français) ont été réalisés à la fois sur les composants, sur les complexes et sur les PIV pour des temps compris entre 1 et 870 jours. A l’échelle microscopique, la dégradation chimique du polyéthylène téréphtalate (PET) et de l’adhésif polyuréthane (PU) ont été étudiées par spectroscopie IR. Des marqueurs de l’hydrolyse ont ainsi pu être identifiés et ont permis de mettre en évidence la dégradation de ces deux composants au sein du complexe. L’hydrolyse ayant des répercussions directes sur les propriétés mécaniques des polymères explique la fragilisation à long terme de l’enveloppe. L’action de l’eau entraine également un gonflement et une plastification du PET, mis en évidence par mesure gravimétrique. Ces derniers peuvent entrainer des modifications de microstructure ayant des répercussions directes sur les mécanismes de transports des molécules d’eau et ainsi participer à la fragilisation du complexe. A l’échelle macroscopique, des mesures fines de retrait des films polymères ont été réalisées. Ces dernières ont été corrélées aux différentes délaminations de l’enveloppe barrière. Des analyses aux interfaces ont permis de déterminer le mode de rupture, adhésif ou cohésif

Vacuum insulation panels (VIPs) : defects identification on the multilayer in order to investigate the effect of hygrothermal ageing in severe conditions

Le panneau isolant sous vide, PIV est principalement constitué d’un matériau de cœur nano-poreux encapsulé sous vide par une enveloppe barrière multicouche polymère-métal. Dans l’objectif d’étendre le domaine d’emploi des PIV sur le marché de l’isolation thermique du bâtiment, il est nécessaire d’améliorer les performances d’étanchéités et la résistance en température et humidité des complexes barrières métallisés, ces derniers représentant le point faible des PIV. Ce travail a pour objectif d’identifier les différentes modifications subies par ces complexes au cours de leurs fonctionnement et de déterminer les mécanismes à l’origine de leur dégradation prématurée. Des vieillissements à 70 °C et 90 %RH (conditions maximales d’utilisations identifiées pour le bâtiment français) ont été réalisés à la fois sur les composants, sur les complexes et sur les PIV pour des temps compris entre 1 et 870 jours. A l’échelle microscopique, la dégradation chimique du polyéthylène téréphtalate (PET) et de l’adhésif polyuréthane (PU) ont été étudiées par spectroscopie IR. Des marqueurs de l’hydrolyse ont ainsi pu être identifiés et ont permis de mettre en évidence la dégradation de ces deux composants au sein du complexe. L’hydrolyse ayant des répercussions directes sur les propriétés mécaniques des polymères explique la fragilisation à long terme de l’enveloppe. L’action de l’eau entraine également un gonflement et une plastification du PET, mis en évidence par mesure gravimétrique. Ces derniers peuvent entrainer des modifications de microstructure ayant des répercussions directes sur les mécanismes de transports des molécules d’eau et ainsi participer à la fragilisation du complexe. A l’échelle macroscopique, des mesures fines de retrait des films polymères ont été réalisées. Ces dernières ont été corrélées aux différentes délaminations de l’enveloppe barrière. Des analyses aux interfaces ont permis de déterminer le mode de rupture, adhésif ou cohésif.Vacuum Insulation Panels (VIPs) were already developed some time ago for low-temperature applications such as refrigerators. More recently, they have been used for the building application. They consist of a fine powder or fiber core material (fumed silica, glass fiber, PU foam) enveloped by a polymer-metal. The latter is responsible for preventing gas and water molecules from breaking the vacuum. Nevertheless, the use of VIPs for this application was limited for applications in severe conditions as for example: temperature, humidity and mechanical load. At high temperature and/or humidity, the most critical component of a VIP is the envelope: both for the tightness point of view and for its degradation. Consequently in these conditions, the vacuum was degraded and durability of the panel performance was decreased sharply.This work focuses on the degradation mechanisms of the polymer-metal envelope. The effect of hygrothermal ageing (70 °C and 90 %RH) on envelope was investigated at different scales: Microscopic: High humidity is at the origin of the hydrolysis of some components such as Polyethylene terephthalate (PET) and polyurethane adhesive (PU). Hydrolysis is directly at the origin of the changes mechanical properties, leading to embrittlement of the complex. An additional microstructural modifications was evidence in PET at high humidity and also contributes to embrittlement of the complex. Macroscopic: shrinkage of polymer film seems to be the origin of debonding in polymer-metal multilayer

Determination of the fracture energy in polymeric films by in situ photoelasticimetry on double edge notch specimen

International audienc

The hygrothermal degradation of PET in laminated multilayer

International audienc

Water Vapor Sorption Properties of Polyethylene Terephthalate over a Wide Range of Humidity and Temperature

International audienc

Dimensional instabilities of polyester and polyolefin films as origin of delamination in laminated multilayer

International audienc

Anode Defects’ Propagation in Polymer Electrolyte Membrane Fuel Cells Stack

International audienceReliability and durability are key considerations to successfully deploy Proton Exchange Membrane Fuel Cells (PEMFCs). Defects induced by manufacturing processes and fuel cell operating conditions may shorten the lifetime of PEMFC due to membrane electrode assembly (MEA) components degradations. If the degradation mechanisms occurring along ageing are now well-known, the propagation of these defects to other materials or to other locations in the stack was poorly investigated in the literature. Recently, we investigated a defect-propagation in MEA via accelerated stress tests combining load and load-driven humidity cycling, and open-circuit voltage. Results highlighted a defect propagation in term of anode and cathode ECSA losses. Significant membrane thinning is also observed for the defective segments. If, the defect propagation was investigated at the cell scale, it has been barely studied in the literature at the stack level.The objective of this work is to quantify the impact of MEA manufacturing defects on the performance and durability in stack and to analyze how these defects can propagate within healthy areas of the same MEA or to healthies MEAs within a stack.Tests were carried out on two stacks with metallic bipolar plates. The stacks were assembled using 35 defect-free MEAs for the healthy stack and using 30 homogeneous MEAs and 5 MEAs with controlled anode defects over 25% of the active area (absence of anode catalyst layer) for the faulty one. The two stacks were operated on a test bench able to control operating conditions and electrochemical characterizations were regularly made in order to evaluate the impact of the defects on the stack behavior.The initial characterization of the stack contained faulty MEAs showed, as expected, that the defects in the anode active layers have a significant effect on the performance of the cells from the conditioning stage. The analysis of the degradation rate showed that the cells directly in contact with the defected MEAs were the ones whose performance degraded the fastest, which implies that the presence of defects within the stack induces a propagation of the performance decrease. This phenomenon could be linked to a significant increase in hydrogen leakage through the membrane identified both by off-line electrochemical characterization and by thermal camera measurements in post-mortem analysis. The mechanism of degradation is still difficult to understand but the presence of defects within the stack could lead to constriction of the current lines around the defect and to localized heating which could degrade the membrane relatively rapidly

Real-time analysis of polymer flow under real processing conditions applied to microinjection molding

International audienc

Predictive durability of polyethylene terephthalate toward hydrolysis over large temperature and relative humidity ranges

International audienc

Anode Defects’ Propagation in Polymer Electrolyte Membrane Fuel Cells Stack

International audienceReliability and durability are key considerations to successfully deploy Proton Exchange Membrane Fuel Cells (PEMFCs). Defects induced by manufacturing processes and fuel cell operating conditions may shorten the lifetime of PEMFC due to membrane electrode assembly (MEA) components degradations. If the degradation mechanisms occurring along ageing are now well-known, the propagation of these defects to other materials or to other locations in the stack was poorly investigated in the literature. Recently, we investigated a defect-propagation in MEA via accelerated stress tests combining load and load-driven humidity cycling, and open-circuit voltage. Results highlighted a defect propagation in term of anode and cathode ECSA losses. Significant membrane thinning is also observed for the defective segments. If, the defect propagation was investigated at the cell scale, it has been barely studied in the literature at the stack level.The objective of this work is to quantify the impact of MEA manufacturing defects on the performance and durability in stack and to analyze how these defects can propagate within healthy areas of the same MEA or to healthies MEAs within a stack.Tests were carried out on two stacks with metallic bipolar plates. The stacks were assembled using 35 defect-free MEAs for the healthy stack and using 30 homogeneous MEAs and 5 MEAs with controlled anode defects over 25% of the active area (absence of anode catalyst layer) for the faulty one. The two stacks were operated on a test bench able to control operating conditions and electrochemical characterizations were regularly made in order to evaluate the impact of the defects on the stack behavior.The initial characterization of the stack contained faulty MEAs showed, as expected, that the defects in the anode active layers have a significant effect on the performance of the cells from the conditioning stage. The analysis of the degradation rate showed that the cells directly in contact with the defected MEAs were the ones whose performance degraded the fastest, which implies that the presence of defects within the stack induces a propagation of the performance decrease. This phenomenon could be linked to a significant increase in hydrogen leakage through the membrane identified both by off-line electrochemical characterization and by thermal camera measurements in post-mortem analysis. The mechanism of degradation is still difficult to understand but the presence of defects within the stack could lead to constriction of the current lines around the defect and to localized heating which could degrade the membrane relatively rapidly