Thermo‐oxidative degradation of additive free polyethylene. Part I. Analysis of chemical modifications at molecular and macromolecular scales

Abstract

The effects of thermal oxidation on the molecular and macromolecular structures of additive free PE were investigated between 100 °C and 140 °C in air in order to tentatively establish non‐empirical structure/property relationships. In the first part, the changes in POOH concentration were assessed by three different analytical methods: iodometry, modulated differential scanning calorimetry, and Fourier transform infrared (FTIR) spectrophotometry after SO2 treatment. All these methods provided very similar results until the end of the induction period, after which iodometry overestimated strongly POOH concentration because it titrates also other chemical species formed at high conversion ratios, namely double bonds. In parallel, the changes in carbonyl group concentration were determined by FTIR spectrophotometry after NH3 treatment. As the accumulation kinetics of ketones, aldehydes, and carboxylic acids were closely interrelated, the question of their actual formation mechanisms in the current thermal oxidation mechanistic scheme was raised. An alternative reaction pathway was proposed for the bimolecular decomposition of POOH. In the second part, the corresponding changes in weight and number average molecular masses were monitored by high temperature gel permeation chromatography equipped with a triple detection technology. As both quantities decreased dramatically from the beginning of exposure and their ratio Mw/Mn tends toward the asymptotic value of 2 and it was concluded that a “pure” chain scission process operated. Finally, as the number of chain scissions perfectly correlates, the concentration sum of aldehydes and their oxidation products (i.e., carboxylic acids), it was also concluded that these carbonyl groups result exclusively from the β scission of alkoxy radicals. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43287.

Ageing Assessment of XLPE LV Cables for Nuclear Applications Through Physico-Chemical and Electrical Measurements

“…When the polymer matrix is no longer sufficiently protected, oxidation accelerates suddenly leading to the formation of a large variety of carbonyl and hydroxyl products [8], but also to consequential changes in the macromolecular and morphological structures that are responsible for a catastrophic decay in fracture properties [9]. As an example, the following causal chain was established for linear PE [10]:…”

Polyisobutylene containing covalently bound antioxidant moieties

“…Polyolefins generally display high resistance to thermal degradation in an inert atmosphere, but are more susceptible to thermo‐oxidative degradation in the presence of pure oxygen or air . TGA results from the experiments performed in air (Fig.…”

“…Polyolefins generally display high resistance to thermal degradation in an inert atmosphere, 38 but are more susceptible to thermo-oxidative degradation in the presence of pure oxygen or air. [39][40][41] TGA results from the experiments performed in air ( Fig. 7 and Table 3) showed that all PIB samples displayed reduced T 10 , T 50 , and T 90 values in air compared to N 2 ; the differences were greatest for the samples synthesized by living polymerization and least for the DTP-functionalized samples.…”

A kinetic model for predicting the oxidative degradation of additive free polyethylene in bleach desinfected water

“…, it was concluded that carbonyls are mainly composed of ketones and carboxylic acids [40]. The carbonyl concentration across the entire PE film thickness [CO] global was then calculated from the absorbance Abs at 1715 cm −1 by using the classical Beer-Lambert's law and taking a coefficient of molar extinction of ε = 300 L mol…”

“…methylene groups) c) Cl%HO%, P%, PO 2 % and PO% account respectively for chlorine, hydroxyl, alkyl, peroxy and alkoxy radicals; d) POOH, POOP, P=O and P-OH account respectively for hydroperoxides, dialkyl peroxides, carbonyls and alcohols as macromolecular oxidation products; e) P-Cl is an attempt at representing the grafting of chlorine onto the polymer chain as organic chlorides f) F, S and X account for double bonds, chain scissions and crosslinking nodes (i.e. covalent bridges) respectively; g) γ S is the yield of β-scission of PO% radicals (leading to aldehydes) in competition with hydrogen abstraction (leading to alcohols), irrespectively of the molecularity of the initiation reaction; h) From a practical point of view, it is more convenient to use an apparent yield γ CO for the carbonyl production owing to the high uncertainty on the nature of these species and the value of their corresponding molar extinction coefficients [40]; i) γ 4 and γ 5 are the respective yields for the coupling of alkyl-alkyl and alkyl-peroxy radicals in competition with disproportionation j) k i are the elementary rate constants of the different chemical reactions under consideration.…”