A general kinetic model for the photothermal oxidation of polypropylene

Abstract

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.

Marine Anthropogenic Litter

“…As peroxide products can themselves Andrady et al (1998) dissociate readily into radicals, the reaction sequence is autocatalytic. The main reactions involved in the sequence are as follows (François-Heude et al 2015 From a practical standpoint, it is the chain scission that accompanies this cyclic reaction sequence, which is of greater interest. The chain scission event is believed to be associated with one of the propagation reactions and is responsible for the loss in mechanical properties of the plastic material after exposure.…”

Polyolefins and the environment

“…A mathematical expression for the oxidation rate was obtained through the conventional concepts of chemical kinetics by making four simplifying assumptions: (1) unicity of reactive site, i.e., oxidation occurs exclusively on the most labile CH bond; (2) low conversion ratios of oxidation process, i.e., concentration of reactive sites remains virtually constant; (3) constancy of initiation rate in the case of oxidation induced by an extrinsic factor; (4) steady-state for radicals concentrations in all oxidation cases, but also for hydroperoxides concentration in the case of pure thermal oxidation [66]. Cunliffe and Davis [67], Furneaux et al [68], and Audouin et al [69] developed kinetics model with the aim of describing other oxidation regimes of lower oxygen concentration than oxygen excess.…”

Stability of Uv Stabilizers

“…37 Thermolysis is a uni-or bi-molecular reaction whose rate constant obeys an Arrhenius law. 38 In contrast, photolysis is exclusively a unimolecular reaction and its rate constant is independent of temperature. 38 Using these premisses kinetic model of photothermal oxidation of polypropylene was developed.…”

“…38 In contrast, photolysis is exclusively a unimolecular reaction and its rate constant is independent of temperature. 38 Using these premisses kinetic model of photothermal oxidation of polypropylene was developed. 38 It was found that the model was only valid up to energy of 10 suns, most likely because of multiphotonic excitations or chromophores photosensitization.…”

“…38 It was found that the model was only valid up to energy of 10 suns, most likely because of multiphotonic excitations or chromophores photosensitization. 38 …”