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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 13 Jul 2024 07:31:31 GMT2024-07-13T07:31:31ZTowards a general kinetic model for the thermal oxidation of epoxy-diamine networks. Effect of the molecular mobility around the glass transition temperature
http://hdl.handle.net/10985/19198
Towards a general kinetic model for the thermal oxidation of epoxy-diamine networks. Effect of the molecular mobility around the glass transition temperature
ESSATBI, Fatima; DELOZANNE, Justine; MOREAU, Gurvan; COLIN, Xavier
The kinetic model previously established for describing the thermal oxidation of polymethylenic substrates has been successfully generalized to a series of six epoxy-diamine networks (EPO-DA) characterized by very different glass transition temperatures. This model is derived from the so-called “closed-loop” mechanistic scheme which consists in a radical chain reaction initiated by the decomposition of hydroperoxides and propagating via the C-H bonds located in α of heteroatoms (N and O). The numerous model parameters were determined by applying a “step by step” procedure combining experiment and simulation. On the one hand, oxygen transport properties (i.e. coefficients of oxygen diffusion and solubility) were estimated from a compilation of literature data. On the other hand, rate constants and formation yields were determined by inverse solving method from the measurements of oxygen consumption and carbonyl build-up performed on six different EPO-DA networks between 25 and 200 °C and between 0.16 and 20 bars of oxygen partial pressure in our laboratory or in the literature. It was found that the molecular mobility mainly affects the rate constants of the elementary reactions involving the reactive species in the lowest concentration, i.e. peroxy radicals. In fact, the rate constant k6 of the apparent termination of peroxy radicals is reduced by about five orders of magnitude when passing from rubbery to glassy state due to the freezing of large amplitude cooperative molecular movements. In contrast, the rate constant k3 of the propagation of oxidation, involving peroxy radicals but also the polymer substrate, is only changed by one order of magnitude around the glass transition temperature. The introduction of the effect of molecular mobility into the Arrhenius laws of k6 and k3 allows building master curves and finally, proposing a single kinetic model for the whole family of EPO-DA networks.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10985/191982020-01-01T00:00:00ZESSATBI, FatimaDELOZANNE, JustineMOREAU, GurvanCOLIN, XavierThe kinetic model previously established for describing the thermal oxidation of polymethylenic substrates has been successfully generalized to a series of six epoxy-diamine networks (EPO-DA) characterized by very different glass transition temperatures. This model is derived from the so-called “closed-loop” mechanistic scheme which consists in a radical chain reaction initiated by the decomposition of hydroperoxides and propagating via the C-H bonds located in α of heteroatoms (N and O). The numerous model parameters were determined by applying a “step by step” procedure combining experiment and simulation. On the one hand, oxygen transport properties (i.e. coefficients of oxygen diffusion and solubility) were estimated from a compilation of literature data. On the other hand, rate constants and formation yields were determined by inverse solving method from the measurements of oxygen consumption and carbonyl build-up performed on six different EPO-DA networks between 25 and 200 °C and between 0.16 and 20 bars of oxygen partial pressure in our laboratory or in the literature. It was found that the molecular mobility mainly affects the rate constants of the elementary reactions involving the reactive species in the lowest concentration, i.e. peroxy radicals. In fact, the rate constant k6 of the apparent termination of peroxy radicals is reduced by about five orders of magnitude when passing from rubbery to glassy state due to the freezing of large amplitude cooperative molecular movements. In contrast, the rate constant k3 of the propagation of oxidation, involving peroxy radicals but also the polymer substrate, is only changed by one order of magnitude around the glass transition temperature. The introduction of the effect of molecular mobility into the Arrhenius laws of k6 and k3 allows building master curves and finally, proposing a single kinetic model for the whole family of EPO-DA networks.A new analytical model for predicting the thermal oxidation kinetics of composite organic m atrices. Application to diamine cross-linked epoxy
http://hdl.handle.net/10985/19940
A new analytical model for predicting the thermal oxidation kinetics of composite organic m atrices. Application to diamine cross-linked epoxy
ESSATBI, Fatima; DELOZANNE, Justine; MOREAU, Gurvan; COLIN, Xavier
The system of differential equations derived from the so-called “closed-loop” mechanistic scheme was solved analytically by applying realistic proportionality assumptions between the different concentrations of reactive species during the entire course of the thermal oxidation. This new method of analytical resolution allowed obtaining a sounder kinetic model accurately describing the three first stages of the thermal oxidation kinetics: the induction period, the auto-acceleration of the oxidation kinetics at the end of the induction period, and the steady-state regime. This kinetic model was used to identify the thermal oxidation behavior at 120 and 150°C in a large range of oxygen partial pressures (typically between 0.21 and 10 bars) of two epoxy-diamine (EPO-DA) matrices. In addition, the kinetic model was used to determine the accelerated aging conditions representative of the cruising flight of a commercial airliner. It was found that the oxygen partial pressure must be increased much more than the temperature to avoid any deformation of the structural degradation state in the two EPO-DA matrices, thus leading to the definition of extreme environmental conditions very difficult to access in practice.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/199402021-01-01T00:00:00ZESSATBI, FatimaDELOZANNE, JustineMOREAU, GurvanCOLIN, XavierThe system of differential equations derived from the so-called “closed-loop” mechanistic scheme was solved analytically by applying realistic proportionality assumptions between the different concentrations of reactive species during the entire course of the thermal oxidation. This new method of analytical resolution allowed obtaining a sounder kinetic model accurately describing the three first stages of the thermal oxidation kinetics: the induction period, the auto-acceleration of the oxidation kinetics at the end of the induction period, and the steady-state regime. This kinetic model was used to identify the thermal oxidation behavior at 120 and 150°C in a large range of oxygen partial pressures (typically between 0.21 and 10 bars) of two epoxy-diamine (EPO-DA) matrices. In addition, the kinetic model was used to determine the accelerated aging conditions representative of the cruising flight of a commercial airliner. It was found that the oxygen partial pressure must be increased much more than the temperature to avoid any deformation of the structural degradation state in the two EPO-DA matrices, thus leading to the definition of extreme environmental conditions very difficult to access in practice.New Advances in the Kinetic Modeling of Thermal Oxidation of Epoxy-Diamine Networks
http://hdl.handle.net/10985/20818
New Advances in the Kinetic Modeling of Thermal Oxidation of Epoxy-Diamine Networks
DELOZANNE, Justine; MOREAU, Gurvan; COLIN, Xavier
This article deals with the thermal oxidation mechanisms and kinetics of epoxy-diamine (EPO-DA) networks used as composite matrices reinforced with carbon fibers in the aeronautical field. The first part of this article is devoted to a detailed presentation of the new analytical kinetic model. The so-called “closed-loop” mechanistic scheme, developed in the last 3 decades in our laboratory in order to accurately describe the thermal oxidation kinetics of saturated hydrocarbon polymers, is recalled. Its main characteristics are also briefly recalled. Then, the system of differential equations derived from this oxidation mechanism is analytically solved without resorting to the usual simplifying assumptions that seriously degrade the reliability of all kinetic models. On the contrary, the generalization of the proportionalities observed between the steady concentrations of the different reactive species (i.e., hydroperoxides and alkyl and peroxy radicals) to the entire course of thermal oxidation gives a series of much sounder equations. From this basis, the kinetic model is completed by considering new structure/property relationships in order to predict the consequences of thermal oxidation on the thermomechanical properties, in particular on the glass transition temperature (Tg). To reach this second objective, the two main mechanisms responsible for the alteration of the macromolecular network structure are recalled: chain scissions and crosslinking. Like any other chemical species, their kinetics are directly expressed from the oxidation mechanistic scheme using the classical concepts of chemical kinetics. The second part of this article is devoted to the checking of the kinetic model reliability. It is shown that this latter accurately simulates the experimental curves of carbonyl build-up and Tg decrease versus time of exposure determined in our laboratory for three EPO-DA networks under study, exposed in a wide variety of thermal oxidative environments. The values determined by inverse solving method for the different model parameters are discussed and their temperature dependence are elucidated. Finally, an end-of-life criterion is proposed for predicting the lifetime of EPO-DA networks involving a predominant chain scission process.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/208182021-01-01T00:00:00ZDELOZANNE, JustineMOREAU, GurvanCOLIN, XavierThis article deals with the thermal oxidation mechanisms and kinetics of epoxy-diamine (EPO-DA) networks used as composite matrices reinforced with carbon fibers in the aeronautical field. The first part of this article is devoted to a detailed presentation of the new analytical kinetic model. The so-called “closed-loop” mechanistic scheme, developed in the last 3 decades in our laboratory in order to accurately describe the thermal oxidation kinetics of saturated hydrocarbon polymers, is recalled. Its main characteristics are also briefly recalled. Then, the system of differential equations derived from this oxidation mechanism is analytically solved without resorting to the usual simplifying assumptions that seriously degrade the reliability of all kinetic models. On the contrary, the generalization of the proportionalities observed between the steady concentrations of the different reactive species (i.e., hydroperoxides and alkyl and peroxy radicals) to the entire course of thermal oxidation gives a series of much sounder equations. From this basis, the kinetic model is completed by considering new structure/property relationships in order to predict the consequences of thermal oxidation on the thermomechanical properties, in particular on the glass transition temperature (Tg). To reach this second objective, the two main mechanisms responsible for the alteration of the macromolecular network structure are recalled: chain scissions and crosslinking. Like any other chemical species, their kinetics are directly expressed from the oxidation mechanistic scheme using the classical concepts of chemical kinetics. The second part of this article is devoted to the checking of the kinetic model reliability. It is shown that this latter accurately simulates the experimental curves of carbonyl build-up and Tg decrease versus time of exposure determined in our laboratory for three EPO-DA networks under study, exposed in a wide variety of thermal oxidative environments. The values determined by inverse solving method for the different model parameters are discussed and their temperature dependence are elucidated. Finally, an end-of-life criterion is proposed for predicting the lifetime of EPO-DA networks involving a predominant chain scission process.