Impact of Oxygen Transport Properties on Polypropylene Thermal Oxidation, Part 1: Effect of Oxygen Solubility

A general kinetic model is proposed to describe the polypropylene thermal oxidation of thin polypropylene films in a wide range of temperatures (from 60 to 200°C) and oxygen partial pressures (from 0.02 to 5 MPa) using a single set of parameters. This model was calibrated with several series of experimental data including analyses of primary (hydroperoxides) and secondary oxidation products (carbonyl species), and subsequent changes in macromolecular properties (average molecular masses). It predicts the experimental data previously published in the literature in terms of induction times and maximal oxidation rates. The variability of the oxygen solubility coefficient allows to explain the scattering of induction times and oxidation rates among the whole iPP family, but also the dependence of this latter quantity with oxygen partial pressure. This variability is presumably due to iPP polymorphism in the temperature range where oxygen permeability is commonly measured. It is concluded that the kinetic model can be used to study the direct effect of iPP morphology on its thermal oxidation kinetics (chemistry of oxidation)

Chemiluminescence from alkyl hyponitrites in viscous liquid media

We have studied the effect of dissolved polymers and mineral oil on the chemiluminescence from tert-butylbenzene solutions of trans-di-2-propylhyponitrite (IPHN), trans-di-1-phenylethyl hyponitrite (PEHN) and 3,3,4,4-tetramethyl-1,2-dioxetane (TMD) in the presence of a fluorescent species (2-tert-butyl-9,10-dibromoanthracene). It was found that the addition of polymers (poly(αmethylstyrene) and others) to solutions of the hyponitrites or TMD decreased their chemiluminescence. In contrast, addition of mineral oil decreased the luminescence from TMD but increased the luminescence from the hyponitrites. The decrease in luminescence was ascribed to the expected reduced rates of energy transfer to the fluorescent species in competition with decay of the carbonyl triplets. The increase in luminescence on addition of mineral oil was too be larger cage effects in the case of PEHN. The increase was tentatively ascribed to higher excited state formation efficiencies from alkoxyl radical dismutation in more viscous media. © 1994

Chemiluminescence from oxidation of polyamide 6,6 II. The effect of metals salts

Chemiluminescence (CL) emission from isothermal and non-isothermal oxidation of polyamide 6,6 in the presence of Co, Ni, Cu and Zn chlorides, alone or combined with KI, demonstrates that copper salts, irrespective of the oxidation number, are the most efficient stabilizing species. They reduce CL emission of the third stage of observed kinetic runs, ascribed to the chain oxidation of polyamide, most efficiently. Cobalt chloride has pro-oxidative rather than a stabilizing action. Synergism has been observed for chlorides of Ni, Zn and Co and for KI. The kinetic analysis of chemiluminescence against temperature was based on two different pathways of initiation: 1. A fast process via either free radicals entrapped in the polymer or terminal amino groups. 2. A slower process involving the free radical chain oxidation of the polyamide. The presence of metal salts combined with KI leads to a reduction of the rate constants of the slower stage by more than two orders of magnitude whilst the rate constants of the faster stage are increased by the presence of metal salts