Bernard Yrieix

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

The dynamic and equilibrium water vapor sorption properties of amorphous polyethylene terephthalate were determined via gravimetric analysis over a wide range of temperatures (23-70 °C) and humidities (0-90% RH). At low temperature and relative humidity, the dynamics of the sorption process was Fickian. Increasing the temperature or relative humidity induced a distinct up-swing effect, which was associated with a plasticization/clustering phenomenon. For high temperatures and relative humidity, a densification of the polymer was evidenced. In addition to the classical Fickian diffusion, a new parameter was introduced to express the structural modifications of PET. Finally, two partial pressures were defined as thresholds that control the transition between these three phases. A simplified state diagram was finally proposed. In addition, the thermal dependence of these sorption modes was also determined and reported. The enthalpy of Henrys water sorption and the activation energy of diffusion were independent of vapor pressure and followed an Arrhenius law.

Water vapour permeation through high barrier materials: numerical simulation and comparison with experiments

The long-term thermal performance of vacuum insulation panels (VIP) is brought by the capacity of their barrier envelope to maintain the core material under vacuum. This study is focused on the detailed modelling of gas transfer through the defects of aluminium-coated polymer films used for VIPs’ envelopes. The 3D simulations were performed with monolayer and multilayer metal-coated polymer films. They have been carried out in dynamic conditions with the SYRTHES® software developed by EDF R&D. The results show that the water vapour and air permeations through a monolayer film slightly depend on the polymer substrate thickness, diffusivity and solubility, but primarily, on the defects geometry and arrangement. Regarding multilayer films, the permeation can be deduced from the ideal laminate theory. We are now able to provide and operate a numerical model, which can calculate the permeance of monolayer or multilayer metallized polymer films as a function of the coating quality and the geometry of the layers. Even if calculated permeances are ten times higher than measurements, this study improves our understanding of gas transports through VIPs’ barrier envelope and allows to manage more efficiently the relations between the films microstructures and their overall permeability. This paper is split into 6 parts: physical phenomena, methodology and modelling tools, simulation results, experiments and model validation and then, discussion and conclusion.

3D Multiscale Characterization of Silica Aerogels Composites

New composites based on a matrix of silica aerogel grains are currently being developed to answer the expectations of thermal renovation. One of the key parameters for their commercial use is the control of their porous network. In this study, we aim to propose a three-dimensional characterization from the nanometer to the millimeter scale of the silica aerogel particles themselves. Transmission electron microscopy (TEM) is used to characterize the mesoporous network within the aerogel grain. The arrangement in three dimensions of the grains and the voids within the aerogel grain pileup is investigated at the micron scale by X-ray tomography.