Effect Of Oxygen Diffusion Research Articles

The kinetics and mechanism of radiation induced oxidation of polyethylene, complicated by the diffusion of oxygen

The mechanism of oxidation of low density polyethylene (LDPE) at room temperature, and the effect of oxygen diffusion on the process, have been studied. Ionizing radiation was used to initiate oxidation. The use of a model of a semi-infinite medium enabled the kinetics of oxidation of PE films to be studied directly from IR spectro-photometric measurements. An equation was obtained, which relates the optical density of the oxidation products to the kinetic and diffusional parameters of the reaction. Analysis of this equation has enabled the kinetically controlled and diffusion controlled regions of oxidation to be distinguished. The oxidation rate constant and its dependence on the rate of initiation were determined. The possibility of degenerate branching of the oxidation reaction chain is examined. It is shown that in the mechanism of oxidation of LDPE irradiated with a dosage of 5 Mrad, no stage of degenerate chain branching occurs.

The effect of oxygen diffusion on oxide-scale adhesion

The effect of oxygen diffusion on oxide-scale adhesion

Effects of oxygen diffusion on oxidation of some dry foods

SummaryThe rate of oxygen uptake and the effective diffusivity of oxygen in some porous food products were determined. The effect of oxygen diffusion on the overall rate of oxygen uptake was investigated in these foods and in other food products for which approximate values of oxidation rate constants and of oxygen diffusivity existed in the literature. The results show that diffusion can be a rate‐limiting factor under certain conditions of commercial processing and handling.

Fat oxidation at low oxygen pressure. I. Kinetic studies on the rate of fat oxidation in emulsions.

AbstractOxidation was measured by oxygen consump‐tion in a Warburg apparatus, modified to main‐tain constant partial oxygen pressure by auto‐matic electrolytic generation of oxygen with automatic recording of the oxygen consumed.The decrease in rate of oxygen consumption on the lowering of partial oxygen pressure at at‐mospheric pressure was found to depend on a) the varying influence of the nonoxygen‐dependent and the oxygen‐dependent reactions of the prop‐agation which may vary with the conditions such as the reactivity of the substrate, the tem‐perature, and the pH value but which is not affected by light irradiation; b) the varying rate‐limiting effect of slow oxygen diffusion, depending on the ratio between the rate of oxidation and the rate of oxygen diffusion.

Photolysis of Low-Temperature Glasses. II. Temperature and Oxygen Effects in Ethanol and Ether

The effect of temperature and oxygen on the processes occurring in the aromatic solute-sensitized photodecomposition of ethanol and ether glasses is described. The results are discussed in terms of the proposed sensitization mechanism, and they are shown to be in excellent agreement with predictions. The effect of oxygen diffusion (at ∼100°K) is to remove the aromatic solute triplet-state population, the latter being an intermediate in the sensitization mechanism, and thus decrease the rate of radical formation. Oxygen also reacts with any radicals present to form peroxy radicals which are stable to light with wavelengths greater than ∼2500 Å. In the absence of oxygen, the triplet-state population and rate of total radical production are virtually independent of temperature over the range 77° to 125°K. However, the composition of the radical concentration exhibits a strong temperature dependence. It is shown that the latter observation results from a competition between secondary photoreactions (temperature independent) involving the radicals produced by the sensitization process and abstraction reactions (temperature dependent) involving the products of the secondary photoreactions.

Degradation and crosslinking in irradiated polyamides and the effect of oxygen diffusion

AbstractThe changes in relative viscosity which occur when nylon 66 is irradiated with 2 m.e.v. electrons under an oxygen‐free atmosphere under various conditions have been observed. A mechanism is proposed which reconciles all of these observations, and on the basis of this postulated mechanism yields of chain breaks and crosslinks are calculated. The effect of the presence of a small concentration of a vinyl monomer (acrylic acid) in the polymer during irradiation on degradation and crosslinking is also considered. The rate of penetration of oxygen into irradiated polyamides has been measured. There is a marked reduction in penetration rate which results from the presence of free radicals in the fiber and the irreversible reaction which results. The data are treated by an approximate diffusion equation and estimates of true diffusion coefficients are given. The effect of filament diameter on the extent of degradation which occurs when fibers of nylon 66 are irradiated and then exposed to air has been investigated. The marked dependence of degradation on fiber thickness is related qualitatively to the data on rate of oxygen penetration.

Stress Relaxation Studies of Scission in Rubber Vulcanizates

Abstract Deterioration of many vulcanized hydrocarbon rubbers is known to be due to reaction with molecular oxygen. Such a process is independent of oxygen concentration down to several mm of oxygen pressure and hence proceeds quite readily in an air atmosphere provided that experiments are conducted with thin enough samples to eliminate oxygen diffusion effects. Two chemically distinct loci for attack by oxygen are available. These are the crosslinked sites which are added during the vulcanization process and the network chains which are essentially the same as in the unvulcanized material. The prime objective of this study is to show clearly that vulcanized natural rubber suffers oxidative scission predominantly along the polyisoprene chains and not at the crosslinked sites as proposed by Berry and Watson. Other literature has appeared which indicates that this important point needs further clarification. Stress relaxation experiments, which measure the rate of breaking of the weakest chemical bonds recurring throughout the structure, have been utilized. If the crosslinks are oxidized, then similar rates of scission should be obtained for different chain structures so long as the common crosslink is present in all of them. On the other hand, if chains are oxidized, then rates of scission should be essentially independent of the crosslinking agent used but rather depend markedly on each chain structure. The five chain structures used in this study are depicted in Table I. In each case at least a few per cent of double bond-containing segments are present in the main chain to allow for ordinary chemical vulcanization methods. All of these have been crosslinked by sulfur and by a nonsulfur containing agent.