A critical molar mass separating the ductile and brittle regimes as revealed by thermal oxidation in polypropylene

Outdoor and accelerated weathering tests for polypropylene and polypropylene/talc composites: A comparative study of their weathering behavior

Antioxidant consumption in squalane and polyethylene exposed to chlorinated aqueous media

In this paper, a thermodynamically consistent continuum level model is developed for high temperature oxidation in polymers, that incorporates the coupling between diffusion, chemical reaction and large deformation of polymers. The kinetics of the oxidative reactions have been incorporated in the continuum model in a consistent way. The specific constitutive forms for all the physical-chemical processes are derived based on the thermodynamic inequality conditions. Deformation due to the oxidative shrinkage has been incorporated in the kinematics as an irreversible effect. Subsequently, the model is implemented in a finite element framework to analyze numerically the coupled diffusion-reaction and mechanical behavior of polymers undergoing oxidation. Several numerical simulations are performed to understand the effect of various ambient conditions and the general stress-coupled effect on the oxidative response. The model is shown to be capable of predicting the heterogeneous oxidation profile for the diffusion-limited, reaction-limited cases within a polymer material. The model has been used to track the growth of oxide layer in the case of a long-term thermo-oxidative aging process.

A thermodynamically consistent chemo-mechanically coupled large deformation model for polymer oxidation

https://hal.archives-ouvertes.fr/hal-02545803/document

Physico-chemical characterization of the blooming of Irganox 1076® antioxidant onto the surface of a silane-crosslinked polyethylene

A kinetic model has been elaborated to predict the lifetime of polyethylene pipes transporting slightly pressurized (3―12 bars) drinking water disinfected by free radical reagents. This model is composed of three levels: i) A system of differential equations, derived from a mechanistic scheme for radical chain oxidation in the presence of free radical reagents, giving access to the spatial distribution (in the pipe wall) of oxidation products and stabilizer concentration; ii) Equations allowing to predict the profiles of average molar masses from the spatial distribution of chain scissions and crosslinking events; iii) An empirical creep equation and a failure criterion derived from regression curves obtained in pure water (without disinfectant). It is assumed that the chemical degradation modifies only the time to transition between ductile and brittle regimes of failure, and that this time is linked to the weight average molar mass according to the classical power law. By superimposing these three levels, it is possible to predict the time to failure under the coupled effects of pressure and chemical degradation. This model is successfully applied to the case of chlorine dioxide.

Towards a Non Empirical Kinetic Model for the Lifetime Prediction of Polyethylene Pipes Transporting Drinking Water

Kinetic Modeling of Low-Temperature Oxidation of Hydrocarbon Polymers

L'emploi des geotextiles en polypropylene necessite une maitrise suffisante de leur durabilite, qui est actuellement mal connue du fait de l'emploi relativement recent de ce materiau. Il n'est actuellement pas possible de predire la duree de vie de ce materiau et il n'existe pas d'essai accelere representatif susceptible d'en simuler le vieillissement a long terme. Une methodologie predictive non empirique, qui consiste a construire un modele cinetique derive de l'analyse des mecanismes de veillissement, a ete developpee. Ce modele realise des predictions a l'echelle microscopique, utiles aux chimistes concevant des materiaux adaptes aux exigences du genie civil, et a l'echelle macroscopique, pour les praticiens en charge de la bonne tenue des ouvrages en se fondant uniquement sur des donnees physico-chimiques applicables a toutes les matrices en polypropylene. Il permet de simuler l'influence des facteurs causant la ruine du polymere (temperature, teneur en oxygene, etc.), de realiser une prediction de son comportement en fonction de ses caracteristiques propres (formulation, etat apres la mise en oeuvre, etc.), et de correler l'impact de ces facteurs a la chute des proprietes mecaniques. (A). (Durability of geotextiles made of polypropylene : Kinetic modeling development).

Ludmila Audouin

Papers

Towards a Non Empirical Kinetic Model for the Lifetime Prediction of Polyethylene Pipes Transporting Drinking Water

Kinetic Modeling of Low-Temperature Oxidation of Hydrocarbon Polymers

Durabilite des geotextiles en polypropylene : Developpement de la modelisation cinetique