https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Sun, 12 Apr 2026 19:03:36 GMT 2026-04-12T19:03:36Z http://hdl.handle.net/10985/12457 Hysteresis in the relation between moisture uptake and electrical conductivity in neat epoxy LUBINEAU, Gilles; SULAIMANI, Anwar; EL YAGOUBI, Jalal; MULLE, Matthieu; VERDU, Jacques Monitoring changes in electrical conductivity is a simple way to assess the water uptake from environmental moisture in polymers. However, the relation between water uptake and changes in conductivity is not fully understood. We monitored changes in the electrical volume conductivity of an anhydride-cured epoxy polymer during moisture sorption-desorption experiments. Gravimetric analysis showed that the polymer exhibits a two-stage sorption behavior resulting from the competition between diffusive and reactive mechanisms. As expected, the macroscopic electrical conductivity increases with the diffusion of water. However, our most surprising observation was severe hysteresis in the relation between water uptake and electrical conductivity during the sorption and desorption experiments. This indicates that change in the electrical conductivity depends on both the water uptake and the competition between the diffusive and reactive mechanisms. We studied samples with various thicknesses to determine the relative effects of the diffusive and reactive mechanisms. This is an important observation as it means that general electrical monitoring techniques should be used cautiously when it comes to measuring the moisture content of polymer or polymer-based composite samples. Sun, 01 Jan 2017 00:00:00 GMT http://hdl.handle.net/10985/12457 2017-01-01T00:00:00Z LUBINEAU, Gilles SULAIMANI, Anwar EL YAGOUBI, Jalal MULLE, Matthieu VERDU, Jacques Monitoring changes in electrical conductivity is a simple way to assess the water uptake from environmental moisture in polymers. However, the relation between water uptake and changes in conductivity is not fully understood. We monitored changes in the electrical volume conductivity of an anhydride-cured epoxy polymer during moisture sorption-desorption experiments. Gravimetric analysis showed that the polymer exhibits a two-stage sorption behavior resulting from the competition between diffusive and reactive mechanisms. As expected, the macroscopic electrical conductivity increases with the diffusion of water. However, our most surprising observation was severe hysteresis in the relation between water uptake and electrical conductivity during the sorption and desorption experiments. This indicates that change in the electrical conductivity depends on both the water uptake and the competition between the diffusive and reactive mechanisms. We studied samples with various thicknesses to determine the relative effects of the diffusive and reactive mechanisms. This is an important observation as it means that general electrical monitoring techniques should be used cautiously when it comes to measuring the moisture content of polymer or polymer-based composite samples. http://hdl.handle.net/10985/9896 A fully coupled diffusion-reaction scheme for moisture sorptionedesorption in an anhydride-cured epoxy resin EL YAGOUBI, Jalal; LUBINEAU, Gilles; ROGER, Frederic; VERDU, Jacques Thermoset materials frequently display non-classical moisture sorption behaviors. In this paper, we investigated this issue from an experimental point of view as well as in terms of modeling the water transport. We used the gravimetric technique to monitor water uptake by epoxy samples, with several thicknesses exposed to different levels of humidity during absorption and desorption tests. Our results revealed that the polymer displays a two-stage behavior with a residual amount of water that is desorbed progressively. We proposed a phenomenological reaction-diffusion scheme to describe this behavior. The model describes water transport as a competition between diffusion and the reaction, during which the local diffusivity and solubility depend on the local advancement of the reaction. We then implemented our model using COMSOL Multiphysics and identified it using a MATLAB-COMSOL optimization tool and the experimental data. We discussed the relation between the hydrophilicity of the product of the reaction and the diffusion behavior. We examined the reaction-induced modification of the water concentration field. It is worth noting that part of the phenomenology can be explained by the presence of hydrolyzable groups. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10985/9896 2012-01-01T00:00:00Z EL YAGOUBI, Jalal LUBINEAU, Gilles ROGER, Frederic VERDU, Jacques Thermoset materials frequently display non-classical moisture sorption behaviors. In this paper, we investigated this issue from an experimental point of view as well as in terms of modeling the water transport. We used the gravimetric technique to monitor water uptake by epoxy samples, with several thicknesses exposed to different levels of humidity during absorption and desorption tests. Our results revealed that the polymer displays a two-stage behavior with a residual amount of water that is desorbed progressively. We proposed a phenomenological reaction-diffusion scheme to describe this behavior. The model describes water transport as a competition between diffusion and the reaction, during which the local diffusivity and solubility depend on the local advancement of the reaction. We then implemented our model using COMSOL Multiphysics and identified it using a MATLAB-COMSOL optimization tool and the experimental data. We discussed the relation between the hydrophilicity of the product of the reaction and the diffusion behavior. We examined the reaction-induced modification of the water concentration field. It is worth noting that part of the phenomenology can be explained by the presence of hydrolyzable groups. http://hdl.handle.net/10985/8969 Monitoring and simulations of hydrolysis in epoxy matrix composites during hygrothermal aging EL YAGOUBI, Jalal; LUBINEAU, Gilles; TRAIDIA, Abderrazak; VERDU, Jacques In this paper, we studied the water transport in thermoset matrices. We used Fourier Transform Infrared analysis (FTIR) during sorption/desorption experiments to investigate the interaction between sorbed water and the epoxy network. Our results demonstrated that the polymer matrix undergoes hydrolysis. We found that the chemical species involved in the reaction process was the residual anhydride groups. These results support the physical basis of the three-dimensional (3D) diffusion/reaction model. We finally showed that this model is able to reproduce multi-cycle sorption/desorption experiment, as well as water uptake in hybrid metal/epoxy samples. We simulated the 3D distributions of the diffusing water and the reacted water. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/8969 2014-01-01T00:00:00Z EL YAGOUBI, Jalal LUBINEAU, Gilles TRAIDIA, Abderrazak VERDU, Jacques In this paper, we studied the water transport in thermoset matrices. We used Fourier Transform Infrared analysis (FTIR) during sorption/desorption experiments to investigate the interaction between sorbed water and the epoxy network. Our results demonstrated that the polymer matrix undergoes hydrolysis. We found that the chemical species involved in the reaction process was the residual anhydride groups. These results support the physical basis of the three-dimensional (3D) diffusion/reaction model. We finally showed that this model is able to reproduce multi-cycle sorption/desorption experiment, as well as water uptake in hybrid metal/epoxy samples. We simulated the 3D distributions of the diffusing water and the reacted water. http://hdl.handle.net/10985/7976 Thermomechanical and hygroelastic properties of an epoxy system under humid and cold-warm cycling conditions EL YAGOUBI, Jalal; LUBINEAU, Gilles; SAGHIR, Shahid; VERDU, Jacques; ASKARI, Abe In this paper, we study the hygrothermal aging of an anhydride-cured epoxy under temperature and hygrometry conditions simulating those experienced by an aircraft in wet tropical or subtropical regions. Gravimetric and dimensional measurements were performed and they indicate that there are three stages in this aging process: the first one, corresponding to the early cycles can be called the “induction stage”. The second stage of about 1000 cycles duration, could be named the “swelling stage”, during which the volume increase is almost equal to the volume of the (liquid) water absorbed. Both the first and second stages are accompanied by modifications of the mechanical properties and the glass transition temperature. During the third (“equilibrium”) stage, up to 3000 cycles, there is no significant change in the physical properties despite the continuous increase of water uptake. This can be explained by the fact that only physically sorbed water can influence physical properties. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/7976 2014-01-01T00:00:00Z EL YAGOUBI, Jalal LUBINEAU, Gilles SAGHIR, Shahid VERDU, Jacques ASKARI, Abe In this paper, we study the hygrothermal aging of an anhydride-cured epoxy under temperature and hygrometry conditions simulating those experienced by an aircraft in wet tropical or subtropical regions. Gravimetric and dimensional measurements were performed and they indicate that there are three stages in this aging process: the first one, corresponding to the early cycles can be called the “induction stage”. The second stage of about 1000 cycles duration, could be named the “swelling stage”, during which the volume increase is almost equal to the volume of the (liquid) water absorbed. Both the first and second stages are accompanied by modifications of the mechanical properties and the glass transition temperature. During the third (“equilibrium”) stage, up to 3000 cycles, there is no significant change in the physical properties despite the continuous increase of water uptake. This can be explained by the fact that only physically sorbed water can influence physical properties. http://hdl.handle.net/10985/6613 Estimation de la diffusivité thermique de composites C/SiC sous chargement mécanique LORRETTE, Christophe; EL YAGOUBI, Jalal; COUPE, Aurélie; CATY, Olivier; SAUDER, Cédric; BATSALE, Jean-Christophe L'accès aux propriétés thermiques des matériaux composites thermostructuraux destinés aux applications nucléaires est un enjeu important pour prévoir leur comportement en condition d'utilisation. Dans un objectif prévisionnel mais également de compréhension des transferts de chaleur, ce travail s'intéresse à l'évaluation des diffusivités thermiques transverses de composites Cf/SiC soumis à un chargement mécanique de type traction. La démarche mise en place s'appuie sur l'utilisation de la méthode flash associée à une analyse du signal par thermographie IR permettant de générer des cartographies de propriétés. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10985/6613 2012-01-01T00:00:00Z LORRETTE, Christophe EL YAGOUBI, Jalal COUPE, Aurélie CATY, Olivier SAUDER, Cédric BATSALE, Jean-Christophe L'accès aux propriétés thermiques des matériaux composites thermostructuraux destinés aux applications nucléaires est un enjeu important pour prévoir leur comportement en condition d'utilisation. Dans un objectif prévisionnel mais également de compréhension des transferts de chaleur, ce travail s'intéresse à l'évaluation des diffusivités thermiques transverses de composites Cf/SiC soumis à un chargement mécanique de type traction. La démarche mise en place s'appuie sur l'utilisation de la méthode flash associée à une analyse du signal par thermographie IR permettant de générer des cartographies de propriétés.