Etude rhéocinétique d'un système polyuréthane

International audienceL'étude cinétique et rhéocinétique d'un système polyuréthane est réalisée pour déterminer les modèles théoriques les mieux adaptés, l'objectif final étant la simulation du remplissage d'un moule par injection. Le paramètre le plus important est la viscosité et son évolution avec le temps et la température. Pour un système réactif, l'évolution de la réaction entraîne la formation de liaisons covalentes et par conséquent un dégagement de chaleur. Une étude de la cinétique de réaction s'avère donc nécessaire pour prédire les profils de température à l'intérieur du moule. Les méthodes isoconversionnelles sont appliquées pour mieux comprendre le mécanisme mis en jeu. Elles permettent de mettre en évidence une dépendance de l'énergie d'activation avec le taux d'avancement. Trois réactions distinctes ont lieu et ne peuvent être prises en compte par un modèle global. Il est donc nécessaire d'utiliser un modèle multi - réactions. L'évolution de la viscosité en condition isotherme est reliée au taux d'avancement de la réaction à l'aide d'un modèle phénoménologique. Le temps de gel est déterminé par le croisement de la tangente de l'angle de perte en fonction du temps à différentes fréquences = The crosslinking kinetics and rheological behavior of a polyurethane system during curing were investigated for mold filling modeling. The important parameters required in modeling with reactive systems are the viscosity and its evolution with time. Hence, cure kinetics study is necessary to quantify the extent of chemical reaction and to predict the temperature distribution inside the mold. In this study, isoconversional method is applied to understand the reaction complexity. The activation energy depends on the extent of conversion. It can be shown that three parallel reactions occur during the evolution of global reaction in nonisothermal conditions. A simple multi-step model can therefore involve the three parallel independent reactions. Viscosity was measured as a function of time and was found independent of shear rate. Isothermal viscosity rise was related to extent of reaction by a phenomenological model. The gelation time is determinated by the δtan crossover at different frequencies

A Perspective on PEF Synthesis, Properties, and End-Life

This critical review considers the extensive research and development dedicated, in the last years, to a single polymer, the poly(ethylene 2,5-furandicarboxylate), usually simply referred to as PEF. PEF importance stems from the fact that it is based on renewable resources, typically prepared from C6 sugars present in biomass feedstocks, for its resemblance to the high-performance poly(ethylene terephthalate) (PET) and in terms of barrier properties even outperforming PET. For the first time synthesis, properties, and end-life targeting-a more sustainable PEF-are critically reviewed. The emphasis is placed on how synthetic roots to PEF evolved toward the development of greener processes based on ring open polymerization, enzymatic synthesis, or the use of ionic liquids; together with a broader perspective on PEF end-life, highlighting recycling and (bio)degradation solutions

Thermal degradation kinetics of a commercial epoxy resin-Comparative analysis of parameter estimation methods

The thermal degradation behavior of a commercial epoxy resin, EpoFix® (Struers), has been investigated by thermogravimetry (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) under nonisothermal conditions in an argon atmosphere. Different methods (Kissinger, Flynn-Wall–Ozawa (FWO), Friedman isoconversion methods, and nonlinear least‐squares (NLSQ) estimation method) have been used to analyze the thermal degradation process and determine the apparent kinetic parameters. The methods produce similar results in terms of activation energy estimations. Nevertheless, the NLSQ method has several advantages over the other methods in terms of both characterizing the activation energy and modeling the thermal degradation—i.e., including this model in a resin degradation process simulation. However, it is interesting to combine the NLSQ method with other isoconversion methods: they can reflect the dependence and variability of the activation energies during pyrolysis processes, while providing a good starting point for a nonlinear procedure, especially with respect to the activation energy E. This work is the first step (apparent kinetic reaction) of complete simulation of experimental oven of degradation of epoxy resin coating of impregnate nuclear fuel sample

Simple approximate analytical solution for non-isothermal single-step transformations: kinetic analysis

In this paper, we develop a method for obtaining the approximate solution for the evolution of single-step transformations under non-isothermal conditions. We have applied it to many reaction models and obtained very simple analytical expressions for the shape of the corresponding transformation rate peaks. These analytical solutions represent a significant simplification of the system's description allowing easy curve fitting to experiment. A remarkable property is that the evolutions of the transformed fraction obtained at different heating rates are identical when time is scaled by a time constant. The accuracy achieved with our method is checked against several reaction models and different temperature dependencies of the transformation rate constant. It is shown that its accuracy is closely related with that of the Kissinger method