Induction period in the low‐temperature thermal oxidation of saturated hydrocarbons: Example of polyethylene

Abstract

Thermal oxidation of hydrocarbon substrates at low-to-moderate temperature, typically T ≤ 150 • C, results from a radical chain process initiated by hydroperoxide decomposition and displays an induction period. A reliable model exists to simulate oxidation kinetics, but an incertitude remains on initial steps because they are out of reach of all available analytical methods. This work is aimed to have a kinetic approach of the problem, by comparing various mechanisms, i.e., (A) bimolecular decomposition of initially present hydroperoxides; (B) combined uni-and bimolecular decomposition of hydroperoxides; (C) the presence of radicals at the beginning of the exposure; and (D) radicals generation at (low) constant rate from irradiation, for instance by ionizing radiation linked to natural radioactivity or from a direct oxygen-substrate reaction. Scheme A is not realistic at low initial hydroperoxide concentrations. All the other mechanisms generate similar behaviors: the induction time tends toward a constant value almost independent of the nature of initial steps, when the concentration of precursors (initially present hydroperoxides or radicals) or the rate of their initial production (from species other than hydroperoxides) tends toward zero. C 2008 Wiley Periodicals, Inc. Int

Co-oxidation kinetic model for the thermal oxidation of polyethylene-unsaturated substrate systems

“…It is warranted to consider that initial PE contains only hydroperoxides in an initial concentration [POOH] 0 , the decomposition of [POOH] 0 yielding to the same quantity of radicals than the overall unstable species initially present. Since POOH groups accumulate during oxidation while other eventually unstable species are consumed, the POOH decomposition rapidly becomes the largely predominant initiation process and this in fact justifies the mechanistic scheme chosen [22]. It was assumed that [PEOOH] 0 is equal to 10 À4 mol l À1 which is consistent with our other papers dealing with PE oxidation modeling.…”

“…All the kinetic parameters for polyethylene (k u2 , k b22 , k 22 , k 322 , k 622 and associated activation energies have been determined previously [5] hence will be used without change. They are shown in Table 2.…”

Influence of silica fillers on the ageing by gamma radiation of EDPM nanocomposites

“…For instance, the elastomers used as cable insulation in nuclear power plants are submitted to irradiation during their lifetime. Several studies have been devoted to the understanding of the consequences of ageing by gamma radiation on the mechanical properties of unfilled elastomers such as Ethylene-Propylene Diene Monomer (EPDM) or Poly DiMethyl Siloxane (PDMS) [1,2,3,4,5,6]. Thus, a scheme of the chemical reactions involved in the degradation process of EPDM under gamma radiation has been established from a fine analysis of the degradation products [3,4].…”

“…Thus, a scheme of the chemical reactions involved in the degradation process of EPDM under gamma radiation has been established from a fine analysis of the degradation products [3,4]. From a microstructural point of view, these reactions can be, within more or less important simplification, related to scissions and/or crosslinkings of the polymer chains [5,6] However in most applications, elastomers are formulated with fillers, which are in many cases nanoscopic. For instance, incorporation of nanoscopic silica fillers in elastomers is well known to improve their mechanical properties [7].…”

Review: Auto-oxidation of aliphatic polyamides

“…It was shown that the following initial condition can be used [36]: The oxygen consumption rate is given, in non-diffusion controlled conditions by:…”