Impact of oxygen transport properties on the kinetic modeling of polypropylene thermal oxidation. II. Effect of oxygen diffusivity

François-Heude, Alexandre; Richaud, Emmanuel; Guinault, Alain; Desnoux, Eric; Colin, Xavier

doi:10.1002/app.41562

Cited by 8 publications

(7 citation statements)

References 66 publications

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“…The CLS is still fundamentally the BAS, but the initiation step is simplified by making the assumption that all initiation is due to the decomposition of hydroperoxide species. Subsequent improvements included parameters and relationships to account for oxygen solubility and diffusion within polymer samples. The model has also been expanded to incorporate chain scission, branching, and cross-linking in order to predict the molecular weight of the degraded polymer. , Studies have been performed for the thermal and photothermal oxidation of PP at temperatures of 45, 60, and 80 °C.…”

Section: Kinetic Modelingmentioning

confidence: 99%

“…Subsequent improvements included parameters and relationships to account for oxygen solubility and diffusion within polymer samples. The model has also been expanded to incorporate chain scission, branching, and cross-linking in order to predict the molecular weight of the degraded polymer. , Studies have been performed for the thermal and photothermal oxidation of PP at temperatures of 45, 60, and 80 °C. The degradation of molecular weight and the production of degradation species, including hydroperoxides, were fitted to the model rate parameters.…”

Section: Kinetic Modelingmentioning

confidence: 99%

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The Fate of the Peroxyl Radical in Autoxidation: How Does Polymer Degradation Really Occur?

2018

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Bolland and Gee's basic autoxidation scheme (BAS) for lipids and rubbers has long been accepted as a general scheme for the autoxidation of all polymers. This scheme describes a chain process of initiation, propagation, and termination to describe the degradation of polymers in the presence of O. Central to this scheme is the conjecture that propagation of damage to the next polymer chain occurs via hydrogen atom transfer with a peroxyl radical. However, this reaction is strongly thermodynamically disfavored for all but unsaturated polymers, where the product allylic radical is resonance-stabilized. Paradoxically, there is no denying that the autocatalytic degradation and oxidation of saturated polymers still occurs. Critical analysis of the literature, described herein, has begun to unravel this mystery. One possibility is that the BAS still holds for saturated polymers but only at unsaturated defect sites, where H transfer is thermodynamically favorable. Another is that peroxyl termination rather than H transfer is dominant. If this were the case, tertiary peroxyl radicals (formed at quaternary centers or quaternary branching defects) may terminate to form alkoxy radicals, which can much more readily undergo chain transfer. This process would lead to the creation of hydroxy groups on the degraded polymer. On the other hand, primary and secondary peroxyl radicals would terminate to form nonradical products and halt further degradation. As a result, under this scenario the degree of branching and substitution would have a major effect on polymer stability. Herein we survey studies of polymer degradation products and of the effect of polymer structure on stability and show that indeed peroxyl termination is competitive with peroxyl transfer and possibly dominant under some conditions. It is also feasible that oxygen may not be the only reactive atmospheric species involved in catalyzing polymer degradation. Herein we outline plausible mechanisms involving ozone, hydroperoxyl radical, and hydroxyl radical that have all been suggested in the literature and can account for the experimentally observed formation of hydroperoxides without invoking peroxyl transfer. We also show that oxygen itself has even been reported to slow the degradation of poly(methyl methacrylate)s, which might be expected if peroxyl radicals are unreactive toward hydrogen transfer. Discrepancies between the rate of oxidation and the rate of degradation have been observed for polyolefins and also support the counterintuitive notion that oxygen stabilizes these polymers against degradation. We show that together these studies support alternative mechanisms for polymer degradation. A thorough assessment of kinetic studies reported in the literature indicates that they are limited by their propensity to use models based on the BAS, disregarding the chemical differences intrinsic to each class of polymer. Thus, we propose that further work must be done to fully grasp the complex mechanism of polymer degradation under ambient conditions. Nonetheless, ...

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Section: Kinetic Modelingmentioning

confidence: 99%

Section: Kinetic Modelingmentioning

confidence: 99%

The Fate of the Peroxyl Radical in Autoxidation: How Does Polymer Degradation Really Occur?

2018

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“…The first stages of the thermo-oxidation process are controlled by the kinetics of oxygen dissolution and intermediary products' transport through the oil bath [10,11]. Similar effects have been shown in thermoplastics, where oxidation and polymer damages start from the external surfaces and the most exposed to atmospheric oxygen [12]. In simple words, mineral oxygen from the atmosphere is converted at the oil-air interface into chemically bounded oxygen (hydroperoxides).…”

Section: Introductionmentioning

confidence: 71%

Coupling between oxidation kinetics and anisothermal oil flow during deep-fat frying

Touffet

Allouche²,

Ariane³

et al. 2021

Physics of Fluids

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Highlights  description of oil flow and temperature distribution in kitchen appliances during heating and holding times;  simplified descriptions of the generation and decomposition of hydroperoxides from triacylglycerols as a mixture of fatty esters in frying conditions;  coupling between Eulerian and Lagrangian descriptions to analyze the effects of residence times at different temperatures;  validation experiments with a modified and instrumented deep-fryer and reference decomposition kinetics in anoxia.

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“…thermo-, radio-and photo-oxidation) differ exclusively by the nature of their initiation step. Thus, the mechanistic scheme of photothermal oxidation can be obtained by introducing, into the now common "closed-loop mechanistic scheme" (CLMS) previously established for pure iPP thermal oxidation [30,31], additional initiation steps due to the effect of UV-light, in particular the photolysis of cleavable photosensitive species (i.e. chromophores).…”

Section: Multi-closed-loop Mechanistic Scheme (Mclms)mentioning

confidence: 99%

“…chromophores). The CLMS has been recently updated for iPP [30,31]. It is briefly reminded in the next section.…”

Section: Multi-closed-loop Mechanistic Scheme (Mclms)mentioning

confidence: 99%

A general kinetic model for the photothermal oxidation of polypropylene

François-Heude

Richaud

Desnoux

et al. 2015

Journal of Photochemistry and Photobiology A: Chemistry

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. A B S T R A C TA general kinetic model for the photothermal oxidation of polypropylene has been derived from the basic auto-oxidation mechanistic scheme in which the main sources of radicals are the thermolysis and photolysis of the most unstable species, i.e hydroperoxides. Thermolysis is a uni-or bi-molecular reaction whose rate constant obeys an Arrhenius law. In contrast, photolysis is exclusively a unimolecular reaction and its rate constant is independent of temperature. According to the quantum theory, this latter is proportional to the energy absorbed by photosensitive species and thus, accounts for the impact of UVlight intensity and wavelength on the global oxidation kinetics.The validity of this model has been checked on iPP films homogeneously oxidized in air over a wide range of temperatures and UV-light sources. It gives access to the concentration changes of: (i) primary (hydroperoxides) and secondary (carbonyls) oxidation products, (ii) double bonds, (iii) chain scissions and crosslinking nodes, but also to the subsequent changes in molecular masses. These calculations are in full agreement with the photolysis results reported by Carlsson and Wiles in the 70s [1][2][3]. However, the model seems to be only valid for UV-light energies equivalent to about 10 suns as upper boundary, presumably because of multiphotonic excitations or chromophores photosensitization (i.e. termolecular photo-physical reactions), both enhanced at high irradiances.

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Impact of oxygen transport properties on the kinetic modeling of polypropylene thermal oxidation. II. Effect of oxygen diffusivity

Cited by 8 publications

References 66 publications

The Fate of the Peroxyl Radical in Autoxidation: How Does Polymer Degradation Really Occur?

The Fate of the Peroxyl Radical in Autoxidation: How Does Polymer Degradation Really Occur?

Coupling between oxidation kinetics and anisothermal oil flow during deep-fat frying

A general kinetic model for the photothermal oxidation of polypropylene

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