Influence of temperature, UV-light wavelength and intensity on polypropylene photothermal oxidation

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 criterion based on the energy absorbed by photosensitive species was proposed to describe the contribution of UV-light to the initiation of the polypropylene photothermal oxidation whatever the light source. The calculation of this energy was performed using the widely accepted quantum theory. The criterion was then introduced in two different types of analytical models commonly used to describe the combined effects of UV light and temperature on induction time, namely: the reciprocity law and kinetic model. The limitations of both types of analytical models were then investigated: the latter, derived from a realistic mechanistic scheme, was found to be much more relevant than the former, which is presumably valid in a restricted range of light intensities, essentially due to its empirical origin. Ó

A general kinetic model for the photothermal oxidation of polypropylene

“…It is also noteworthy that this value of f POOH is twice lower than the value found by using the analytical kinetic model (f POOH = 8) in a previous publication [21]. Since ketones and peroxide bridges photolysis have been found to have negligible contribution to the photothermal oxidation kinetics, most of the modeling improvement comes from a better description of the coupling between temperature and UV-light effects in the numerical kinetic model.…”

“…However, it is relevant to be precise that these latter conditions cover a domain where photochemical initiation largely predominates (above 90%) over thermal initiation, even in WOM device. This is the reason why the validity of the kinetic model was also tested in intermediary exposure conditions where both thermolysis and photolysis contribute to initiation with a similar order of magnitude (as evidenced in previous work [21]). As an example, the simulation of the kinetic curves of carbonyl products reported by Audouin et al [55] for iPP exposed to fluorescent lamp between 40 and 70 C is presented in Fig.…”

“…In a previous paper [21], it was shown that alkyl-peroxides are more photosensitive than hydroperoxides while their O-O bond is almost as cleavable. Then, their photolysis must also occur.…”

“…The introduction of a term of photo-induced initiation in a numerical model has been performed by Kiil in the case of the photooxidation of epoxy coatings, but the corresponding initiation rate has been described through an empirical law [20], whereas it would be possible to use the quantum theory. A criterion, based on the absorbed energy by photosensitive species, was recently proposed in this purpose and tested through an analytical model [21]. This theory allowed describing the competition between thermal and photochemical initiations during polypropylene oxidation.…”

Degradation of Plastics in the Environment

“…if the mechanism of degradation changes with temperature, Equation 6.2 cannot be used to estimate the value of ΔE. Typical values for ΔE for unstabilized PP was reported to be 27 kJ/mol (François-Heude et al, 2014). Temperature effect is especially pertinent to outdoor exposure of plastics.…”