Oxidative Aging of Natural Rubber

1968 ◽  
Vol 41 (1) ◽  
pp. 182-208 ◽  
Author(s):  
J. I. Cunneen
Keyword(s):  
Natural Rubber ◽  
Recent Work ◽  
Structural Characteristics ◽  
Degradation Process ◽  
Antioxidant Efficiency ◽  
Oxidative Aging ◽  
Aging Studies ◽  
Different Types ◽  
Controlled Structure ◽  
Natural Rubber Vulcanizates

Abstract In the last few years several reviews and books have been published on the aging of elastomers, but the overall view which they present of the oxidation of natural rubber and its vulcanizates still contains many puzzling features. Two of these are the variation of antioxidant efficiency in different types of vulcanizate, and the extent of the involvement of crosslink scission in the overall degradation process in sulfurated vulcanizates. Sometimes apparent contradictions have arisen from a failure to appreciate that aging of natural rubber vulcanizates depends primarily on four factors; the purity and type of rubber, the presence of additives, the type and extent of vulcanization, and the purification (if any) after cure. In many cases direct comparisons have been attempted without due consideration being given to all these factors, leading inevitably to some confusion. Recent work on the structure of vulcanizates has enabled the NRPRA to embark on a program of aging studies with vulcanizates of carefully controlled structure and complexity, which has already led to a better understanding of the processes involved in vulcanizate degradation. This review will attempt to elucidate the present state of knowledge, and will therefore be largely concerned with recent work at NRPRA, and its relation to previous studies. The review is divided into two main parts, they are: the effect of vulcanizate structure on aging, and the chemistry of oxidative scission reactions. Before attempting to rationalize the effect of vulcanizate structure on aging, structural characteristics of the most important types of vulcanizate are briefly discussed.

Oxidative Aging of Natural Rubber Vulcanizates. Part III. Crosslink Scission in Monosulfidic Networks

1969 ◽  
Vol 42 (3) ◽  
pp. 924-935 ◽  
Author(s):  
T. Colclough ◽  
J. I. Cunneen ◽  
G. M. C. Hrggins
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Chemical Structure ◽  
Spectroscopic Methods ◽  
Chemical Probes ◽  
Conjugated Diene ◽  
Strain Measurements ◽  
Oxidative Aging ◽  
Tert Butyl Hydroperoxide ◽  
Natural Rubber Vulcanizates

Abstract A natural rubber vulcanizate containing almost entirely monosulfidic crosslinks was oxidized in oxygen and with tert-butyl hydroperoxide. The changes in physical properties due to oxidation were followed by stress—strain measurements, and the changes in chemical structure were investigated with chemical probes, and by spectroscopic methods. The results show that when the oxidized vulcanizates are heated at 75° C, the monosulfidic crosslinks are broken, that crosslinks containing two sulfur atoms are formed, and that conjugated diene and triene structures are introduced into the main polyisoprene chains.

Rubber Oxidation and Aging Studies Safe Limits of Sample Thickness

1951 ◽  
Vol 24 (4) ◽  
pp. 999-1016
Author(s):  
George W. Blum ◽  
J. Reid Shelton ◽  
Hugh Winn
Keyword(s):  
Natural Rubber ◽  
Accelerated Aging ◽  
Sample Thickness ◽  
Oxygen Absorption ◽  
Absorption Data ◽  
Synthetic Rubber ◽  
Constant Rate ◽  
Aging Studies ◽  
Safe Limits ◽  
Natural Rubber Vulcanizates

Abstract Safe limits of sample thickness for rubber oxidation and aging studies, such that the chemical reaction rather than the rate of diffusion will be rate-controlling have been investigated for natural-rubber vulcanizates and for four synthetic-rubber types. For studies involving the entire range of oxidation, including the autocatalytic stage of rapid oxygen absorption, the conventional 0.075-inch thickness is frequently not satisfactory for accelerated aging and oxidation studies if it is desired to avoid limitation by diffusion. Only in the GR-S black stock was this thickness found to be satisfactory up to a temperature of 100° C. The other stocks, including natural rubber, Butaprene-NXM, and Neoprene black and gum stocks all require thinner samples to ensure that the observed rate of oxygen absorption is free of limitation by diffusion. A method of calculating the probable limiting value of sample thickness, above which the rate of oxidation in the autocatalytic stage is limited by diffusion, has been developed on the basis of volumetric oxygen absorption data obtained with GR-S. The method has also been applied to natural-rubber vulcanizates and to other synthetic-rubber types to locate the approximate limiting values at various temperatures for oxidation and aging studies which extend into the autocatalytic stage of rapid reaction. The constant-rate period of oxidation is more important from a practical point of view than the autocatalytic stage, since properties are so seriously degraded as to make the rubber of little value before it reaches the final stage of rapid oxidation. Somewhat thicker samples may be used for studies that are confined to the earlier stages of oxidation. A 0.075-inch sample is free of limitation by diffusion in the constant-rate stage in the following cases: GR-S black and gum stocks at 110° C; Hevea black with added antioxidant at 100° C; and uninhibited Hevea black and gum stocks at 60° C. A 0.040-inch sample is satisfactory in this range for: uninhibited Hevea black at 100° and gum at 80° C; Butaprene-NXM black at 100° and gum at 90° C; and Neoprene black and gum stocks at 100° C.

Dielectric Relaxation of Natural Rubber Vulcanizates

1951 ◽  
Vol 24 (2) ◽  
pp. 320-327 ◽  
Author(s):  
A. Schallamach
Keyword(s):  
Relaxation Time ◽  
Dielectric Loss ◽  
Natural Rubber ◽  
Dielectric Relaxation ◽  
Loss Tangent ◽  
Dielectric Loss Tangent ◽  
Dielectric Relaxation Time ◽  
Different Types ◽  
Cross Links ◽  
Natural Rubber Vulcanizates

Abstract The dielectric loss tangent of different types of vulcanizates of natural rubber has been measured as function of the frequency. Comparisons of the losses in different vulcanizates containing the same amount of combined sulfur show that they decrease with increasing modulus, and it is suggested that the dielectric loss is mostly due to sulfur which has been combined in forms other than cross-links. The dielectric relaxation time is approximately an exponential function of the percentage of combined sulfur. It has been found that moisture increases the audiofrequency losses in rubber more than the radiofrequency losses.

Antioxidant Efficiency of p-Phenylenediamines in Natural Rubber Vulcanizates

1961 ◽  
Vol 34 (3) ◽  
pp. 816-833 ◽  
Author(s):  
O. Lorenz ◽  
C. R. Parks
Keyword(s):  
Antioxidant Activity ◽  
Natural Rubber ◽  
Oxidation Products ◽  
Oxygen Absorption ◽  
Fast Reaction ◽  
Alkyl Aryl ◽  
Antioxidant Efficiency ◽  
Rate Region ◽  
Constant Rate ◽  
Natural Rubber Vulcanizates

Abstract The consumption of various p-phenylenediamines during the oxidation of natural rubber vulcanizates has been investigated in the temperature range of 80–120° C. Oxygen absorption was used to follow the oxidation. Diaryl-p-phenylenediamines were consumed mainly in a termination reaction during the constant rate region of the oxygen absorption, where five to six molecules of oxygen were absorbed per molecule of diamine consumed. The constant rate stage of the oxygen uptake was found to be about twice as long as the time of the constant rate consumption of the diamine, indicating that the reaction product also possessed antioxidant activity. The effect of the nature of the curing system, carbon black, structure of the diamine, initial concentration of the diamine, and temperature of oxidation were studied. Dialkyl- and alkyl-aryl-p-phenylenediamines were consumed predominantly by a direct, relatively fast reaction with oxygen, the rate being dependent on the structure of the diamine and also on the nature of the curing system. The oxidation products formed exhibited antioxidant activity, those of N-isopropyl-N′-phenyl-p-phenylenediamine being particularly effective.

Model Compound Vulcanization—Part II. Comparison of Accelerators

1979 ◽  
Vol 52 (5) ◽  
pp. 1030-1043 ◽  
Author(s):  
F. K. Lautenschlaeger ◽  
P. Zeeman
Keyword(s):  
Liquid Chromatography ◽  
Natural Rubber ◽  
Model Compound ◽  
Gas Liquid Chromatography ◽  
Product Yields ◽  
Isomer Distribution ◽  
Different Types ◽  
Natural Rubber Vulcanizates

Abstract The efficiency of each of 20 accelerators to convert sulfur into sulfidic products has been evaluated by Model Compound Vulcanization. The sulfidic products can be isolated and identified by gas-liquid chromatography. The sulfidic products can be separated into groups of mono-, di- and trisulfides, with several isomeric products within each group. This paper has reported on the analysis of such isomeric products which correspond to different types of sulfur crosslinks in natural rubber vulcanizates. The analysis of monosulfidic product yields and of the isomer distribution within the monosulfide group is sufficient to characterize an accelerator.

Effect of different types of vulcanization systems on the mechanical properties of natural rubber vulcanizates in the presence of oil palm leaves-based antioxidant

2013 ◽  
Vol 46 (8) ◽  
pp. 747-764 ◽  
Author(s):  
Nor Hasmaniza Husna Shuhaimi ◽  
Nur Syuleha Ishak ◽  
Nadras Othman ◽  
Hanafi Ismail ◽  
Sreenivasan Sasidharan
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Oil Palm ◽  
Different Types ◽  
Natural Rubber Vulcanizates
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