Effect of Oxygen Concentration on Aging of Rubber Vulcanizates. II. Effect of Partial Pressure of Oxygen on Changes in Physical Properties Accompanying Oxidation

Abstract The over-all rate of deterioration of physical properties increases with the oxygen concentration, as would be expected from the increased rate of oxygen absorption: The nature of the deterioration resulting from a given amount of oxygen absorbed is influenced also by changes in the partial pressure of oxygen in the aging atmosphere. It appears that chain scission is favored at higher oxygen concentrations, while cross-linking becomes of greater relative importance at lower oxygen concentrations. These data suggest that R⋅ radicals are more effective than RO2⋅ radicals in reacting with double bonds to form crosslinks. Heat aging in the absence of oxygen, as observed by heating a vulcanizate in lamp-grade nitrogen, results in considerable stiffening, particularly in the case of a GR-S black stock. This effect is observed primarily in the first few hours of heating, and may account for some of the erratic behavior observed in the early stages of aging when changes in physical properties are compared on the basis of amount of oxygen absorbed. Higher oxygen concentration brings about a more rapid oxidation, and also results in a higher proportion of chain scission compared to cross-linking for a given amount of oxygen absorbed. As tensile decay is the most evident sign of deterioration of Hevea stocks, it follows that the aging behavior of natural rubber in air at normal storage temperatures will be better than that predicted by high temperature testing in oxygen. In the case of GR-S stocks, on the other hand, oxidative hardening is the most serious result of aging, and consequently, the aging behavior of GR-S stocks in air at normal storage temperatures is poorer than would be expected on the basis of comparative tests in oxygen at higher temperatures.

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Effect of Oxygen Concentration on Aging of Rubber Vulcanizates - Effect of Partial Pressure of Oxygen on Changes in Physical Properties Accompanying Oxidation

Industrial & Engineering Chemistry ◽

10.1021/ie50518a042 ◽

1953 ◽

Vol 45 (2) ◽

pp. 397-401

Author(s):

William L. Cox

Keyword(s):

Physical Properties ◽

Partial Pressure ◽

Oxygen Concentration ◽

Partial Pressure Of Oxygen ◽

Effect Of Oxygen

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Effect of Oxygen Concentration on Aging of Rubber Vulcanizates - Effect of Partial Pressure of Oxygen on Rate of Oxygen Absorption

Industrial & Engineering Chemistry ◽

10.1021/ie50518a041 ◽

1953 ◽

Vol 45 (2) ◽

pp. 392-396 ◽

Cited By ~ 3

Author(s):

J. Reid Shelton ◽

William Cox

Keyword(s):

Partial Pressure ◽

Oxygen Concentration ◽

Oxygen Absorption ◽

Partial Pressure Of Oxygen ◽

Effect Of Oxygen

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Effect of Oxygen Concentration on Aging of Rubber Vulcanizates. I. Effect of Partial Pressure of Oxygen on Rate of Oxygen Absorption

Rubber Chemistry and Technology ◽

10.5254/1.3539847 ◽

1953 ◽

Vol 26 (3) ◽

pp. 632-643 ◽

Cited By ~ 3

Author(s):

J. Reid Shelton ◽

William L. Cox

Keyword(s):

Partial Pressure ◽

Oxygen Concentration ◽

Oxygen Absorption ◽

Partial Pressure Of Oxygen ◽

Effect Of Oxygen

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A high temperature, pressure study of the comparative rates of enolization and oxidation of acetone in aqueous solution

Canadian Journal of Chemistry ◽

10.1139/v86-369 ◽

1986 ◽

Vol 64 (11) ◽

pp. 2235-2237 ◽

Cited By ~ 2

Author(s):

John W. Thomas ◽

Jay E. Taylor

Keyword(s):

Aqueous Solution ◽

High Temperature ◽

Partial Pressure ◽

Oxygen Concentration ◽

Total Pressure ◽

Room Temperature ◽

Isotopic Exchange ◽

Partial Pressure Of Oxygen

The rate of enolization and acetone has been determined as 6.6 × 10−4 s−1 at 193.5 °C under nitrogen at 136 atm total pressure via isotopic exchange. The rate of oxidation was determined to be 8.8 × 10−6 s−1 at 193.5 °C in 123 atm partial pressure of oxygen (136 atm total pressure). In a previous study it was shown that the rates of oxidation of several ketones correlated with the extents of enolization at room temperature. This prompted the suggestion that the enol is an intermediate in the oxidation. Since the rate of enolization exceeded the rate of oxidation by a factor of 75, this suggestion is further supported. A dependence of the rate of oxidation of acetone on oxygen concentration was also demonstrated.

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Oven and Bomb Aging of GR-S at Corresponding Temperatures

Rubber Chemistry and Technology ◽

10.5254/1.3546894 ◽

1948 ◽

Vol 21 (1) ◽

pp. 180-187

Author(s):

J. Reid Shelton ◽

Hugh Winn

Keyword(s):

Oxygen Concentration ◽

Lower Energy ◽

Chain Scission ◽

Activation Energies ◽

Cross Linking ◽

Oxygen Bomb ◽

Temperature Coefficients ◽

Rectangular Strips ◽

Comparison Of The Results ◽

Energy Reaction

Abstract The relations observed in this comparison of air oven and oxygen-bomb aging of GR-S at corresponding temperatures and the interpretations suggested by these relations may be summarized as follows: 1. Comparison of the results of tests in which some samples were aged in the form of tensile test strips while others were cut from rectangular strips after aging indicates that edge effects during aging are negligible and that the former practice is satisfactory. 2. Increased temperature increases the severity of both types of aging, but the effect is greater at the higher oxygen concentration of the bomb. 3. The hardening reaction, as measured by the increase in modulus, appears to be little affected by increased oxygen concentration above that in air and is the predominant reaction in the air oven. 4. Chain scission, as measured by decrease in tensile strength, increases with oxygen concentration and is the predominant reaction in the oxygen bomb. 5. Chain scission is also reflected in the smaller modulus increase observed with oxygen bomb aging compared to the air oven, and is responsible for the reversion of the modulus observed at 100° C and 300 pounds per square inch oxygen pressure. 6. Changes in temperature and in oxygen concentration, therefore, alter the ratio of the fundamental aging reactions of chain scission and cross-linking. Since the effect of these two reactions on physical properties is different, no direct correlation can be expected between methods of aging which differ in both temperature and oxygen concentration. 7. Activation energies calculated from the temperature coefficients observed for tensile breakdown in the oxygen bomb (29.7 kg.-cal.) and for modulus increase in the air oven (18.2 kg.-cal.) may be regarded as approximations of the activation energies required for chain scission and cross-linking, respectively. The observation has been made that the latter reaction is virtually independent of oxygen concentration above that in air, whereas the former increases with oxygen concentration. This may be interpreted as indicating that, at the temperatures involved, a relatively large number of oxygen molecules are sufficiently activated to maintain the lower energy reaction, even in air, while a much smaller number have the energy required for the scission reaction; consequently, increased oxygen concentration will be more effective in making a larger number of active molecules available for reaction in this case. 8. The greater dependence of chain scission on oxygen concentration may also be regarded as an indication that, although both reactions are apparently initiated by oxygen, the subsequent reactions leading to chain scission may require additional oxygen while the reactions resulting in cross-linking may not.

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Oxidation of GR-S and Other Elastomers

Rubber Chemistry and Technology ◽

10.5254/1.3543302 ◽

1947 ◽

Vol 20 (3) ◽

pp. 747-759

Author(s):

John O. Cole ◽

James E. Field

Keyword(s):

Tensile Strength ◽

Natural Rubber ◽

Physical Properties ◽

Experimental Methods ◽

Chain Scission ◽

Cross Linking ◽

Antioxidant Action ◽

Mechanism Of Oxidation ◽

Natural Rubber Vulcanizates

Abstract The effect of heat aging on the physical properties of an elastomer is generally considered the result of oxidation, which produces both chain scission and cross-linking in the polymer. Early in the development of GR-S, a marked difference in the aging of GR-S and natural rubber vulcanizates was observed. From the effect of aging on hardness, tensile strength, modulus, and elongation it appeared that cross-linking occurred more rapidly than chain scission with GR-S, but the reverse was true with natural rubber. The work reported here was undertaken to provide a better understanding of the differences in aging of GR-S and natural rubber and to introduce new experimental methods for studying the mechanism of oxidation and antioxidant action in elastomers.

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Interaction of H2O, O2 and H2 with Proton Conducting Oxides Based on Lanthanum Scandates

Alternative Energy and Ecology (ISJAEE) ◽

10.15518/isjaee.2019.13-15.88-100 ◽

2019 ◽

pp. 88-100

Author(s):

A. S. Farlenkov ◽

N. A. Zhuravlev ◽

Т. A. Denisova ◽

М. V. Ananyev

Keyword(s):

Water Vapor ◽

Partial Pressure ◽

Gas Phase ◽

Molecular Hydrogen ◽

Proton Magnetic Resonance ◽

Partial Pressure Of Oxygen ◽

Proton Conducting ◽

Conducting Oxides ◽

Temperature Range ◽

Apparent Level

The research uses the method of high-temperature thermogravimetric analysis to study the processes of interaction of the gas phase in the temperature range 300–950 °C in the partial pressure ranges of oxygen 8.1–50.7 kPa, water 6.1–24.3 kPa and hydrogen 4.1 kPa with La1–xSrxScO3–α oxides (x = 0; 0.04; 0.09). In the case of an increase in the partial pressure of water vapor at a constant partial pressure of oxygen (or hydrogen) in the gas phase, the apparent level of saturation of protons is shown to increase. An increase in the apparent level of saturation of protons of the sample also occurs with an increase in the partial pressure of oxygen at a constant partial pressure of water vapor in the gas phase. The paper discusses the causes of the observed processes. The research uses the hydrogen isotope exchange method with the equilibration of the isotope composition of the gas phase to study the incorporation of hydrogen into the structure of proton-conducting oxides based on strontium-doped lanthanum scandates. The concentrations of protons and deuterons were determined in the temperature range of 300–800 °C and a hydrogen pressure of 0.2 kPa for La0.91Sr0.09ScO3–α oxide. The paper discusses the role of oxygen vacancies in the process of incorporation of protons and deuterons from the atmosphere of molecular hydrogen into the structure of the proton conducting oxides La1–xSrxScO3–α (x = 0; 0.04; 0.09). The proton magnetic resonance method was used to study the local structure in the temperature range 23–110 °C at a rotation speed of 10 kHz (MAS) for La0.96Sr0.04ScO3–α oxide after thermogravimetric measurements in an atmosphere containing water vapor, and after exposures in molecular hydrogen atmosphere. The existence of proton defects incorporated into the volume of the investigated proton oxide from both the atmosphere containing water and the atmosphere containing molecular hydrogen is unambiguously shown. The paper considers the effect of the contributions of the volume and surface of La0.96Sr0.04ScO3–α oxide on the shape of the proton magnetic resonance spectra.

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