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.

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.

Oxidation of GR-S Vulcanizates

1946 ◽  
Vol 19 (3) ◽  
pp. 696-711
Author(s):  
J. Reid Shelton ◽  
Hugh Winn
Keyword(s):  
General Nature ◽  
Oxygen Absorption ◽  
Specimen Thickness ◽  
Absorption Data ◽  
First Order ◽  
Rapid Absorption ◽  
Constant Rate ◽  
Absorption Studies ◽  
Three Stages ◽  
Useful Life

Abstract Oxygen absorption studies on a tread type GR-S vulcanizate show: 1. There are three stages involved in the oxidation: (1) an initial rapid absorption, of apparent first order at constant pressure, which is of short duration and appears to involve a limited number of especially reactive centers in the vulcanizate ; (2) a constant-rate reaction, of apparent zero order at constant oxygen pressure, which would extend over most of the useful life of the vulcanizate in service ; (3) an autocatalytic reaction, beginning after a given stock has absorbed a definite amount of oxygen that is independent of the temperature at which the absorption takes place. 2. The rate of oxygen absorption increases with temperature. The temperature coefficient for the constant rate reaction is 2.6 for a 10° C change in temperature over the range 80° to 120° C. 3. Diffusion is not rate controlling, provided the specimen thickness does not exceed 0.080 inch at 100° C or 0.040 inch at 120° C. 4. The effect of cure on the rate of oxygen absorption by GR-S vulcanizates is slight, and consequently, the technique is particularly useful for studying the effect of changes in compounding upon aging resistance. 5. Oxygen absorption data can be satisfactorily correlated with changes in physical properties during aging. While the fundamental nature of the mechanism of the oxidation of GR-S is still unknown, considerable information has been obtained with respect to some of the factors involved, and the general nature of the reaction has been established. This information, together with the work still in progress, should be of value in pointing the way toward possible methods of improving the resistance of GR-S to aging.

Polymeric Antioxidant Based on Natural Rubber Grafted with N-(4-Hydroxyphenyl)maleimide

2012 ◽  
Vol 488-489 ◽  
pp. 211-215 ◽  
Author(s):  
Pairote Klinpituksa ◽  
Sittaporn Somkieowan ◽  
Wae Asae Waehamad ◽  
Natinee Lopattananon
Keyword(s):  
Tensile Strength ◽  
Maleic Anhydride ◽  
Natural Rubber ◽  
Ftir Spectroscopy ◽  
Accelerated Aging ◽  
Elongation At Break ◽  
Optimal Amount ◽  
Melt Grafting ◽  
Natural Rubber Vulcanizates

A novel rubber bound antioxidant NR-g-HPM was prepared by melt grafting HPM (N-(4-hydroxyphenyl)maleimide) onto natural rubber in a brabender plasticorder. HPM was synthesized from p-aminophenol and maleic anhydride. The yield was found to be over 80%. The grafting products were observed with FTIR spectroscopy and TGA. The ageing resistance of natural rubber vulcanizates using NR-g-HPM was studied. It was found that an optimal amount of NR-g-HPM (6 phr) gave about 25% better tensile strength and elongation at break as compared with conventional BHT addition, for filled natural rubber after 48 h of accelerated aging.

Effect of Curing Systems on Fatigue of Natural Rubber Vulcanizates

1966 ◽  
Vol 39 (3) ◽  
pp. 785-797 ◽  
Author(s):  
W. L. Cox ◽  
C. R. Parks
Keyword(s):  
Fatigue Life ◽  
Natural Rubber ◽  
Main Chain ◽  
Accelerated Aging ◽  
Chain Scission ◽  
Rapid Loss ◽  
Effective Antioxidant ◽  
Natural Rubber Vulcanizates ◽  
Aging In Air ◽  
Oxidative Effect

Abstract The fatigue life of natural rubber-HAF black vulcanizates showed maxima when plotted as a function of crosslink concentration as did other properties related to a tearing process such as tensile strength, crack growth, and tear strength. Accelerated-sulfur vulcanizates were superior to peroxide and nonelemental-sulfur cures; this can be attributed to an exchange of polysulfide crosslinks under stress. An effective antioxidant was essential for maximum fatigue resistance. Accelerated-sulfur systems, although having a higher original fatigue life than peroxide or nonelemental-sulfur cures, showed a rapid loss on accelerated aging in air. This would indicate that an oxidative effect was involved. Sulfur group analyses of the flexed samples showed an increase in the concentration of RSSxSR linkages but a decrease in the total polysulfide sulfur, Sx, with no change in the crosslink densities. This suggests that the polysulfide linkages not only underwent exchange during the fatigue process but also homolytic cleavage to polythiyl radicals. These radicals can add to double bonds and in the presence of oxygen initiate oxidation chains which would lead to main chain scission.

OXIDATIVE STRESS RELAXATION OF NATURAL RUBBER GUM VULCANIZATES CONTAINING VARIOUS ANTIOXIDANTS. I: EFFECT OF SAMPLE THICKNESS

2017 ◽  
Vol 90 (4) ◽  
pp. 633-641
Author(s):  
Junling Zhao ◽  
G. R. Hamed
Keyword(s):  
Oxidative Stress ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
Aging Time ◽  
Oxygen Concentration ◽  
Chain Scission ◽  
Sample Thickness ◽  
Oxygen Absorption ◽  
Square Root ◽  
Diffusion Controlled

ABSTRACT Conventional sulfur-vulcanized natural rubber gums containing various antioxidants have been subjected to oxidative stress relaxation at 72 °C and 25% strain. Oxidation is diffusion controlled, even for samples as thin as 0.15 mm. Assuming that the rate of chain scission is proportional to the rate of oxygen absorption, which previously has been shown to depend on the square root of the oxygen concentration, an equation is derived predicting that stress decay is proportional to aging time to the three-quarters power. Moreover, slopes of these plots are predicted to depend inversely on thickness. Experimental results are in reasonable accord with these predictions.

The Effect of Crosslink Structure on the Tensile Strength and Oxygen Absorption Characteristics of Natural Rubber Vulcanizates

1969 ◽  
Vol 42 (5) ◽  
pp. 1412-1419
Author(s):  
J. Lal
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Chemical Nature ◽  
Oxygen Absorption ◽  
High Tensile Strength ◽  
Modulus Curve ◽  
Natural Rubber Vulcanizates ◽  
Absorption Characteristics ◽  
Control Samples

Abstract The chemical nature of crosslinks in natural rubber—sulfur—diphenylguanidine vulcanizates was modified by reaction with triphenylphosphine under nitrogen to determine the effect of this change on tensile strength and oxygen absorption characteristics of the vulcanizates. The vulcanizates were characterized by organically combined sulfur and polysulfidic sulfur. Polysulfidic crosslinks, i.e., crosslinks containing three or more sulfur atoms in the crosslink, were found not to be essential for the attainment of high tensile strength in these vulcanizates. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted the tensile strength versus 300% modulus curve for the control samples. Vulcanizates which had been reacted with triphenylphosphine for 16 days at 80° C, had lost 95–99.6% of their polysulfidic sulfur. These triphenylphosphine-reacted vulcanizates exhibited significantly lower rates of oxygen absorption at 100° C as compared to the untreated vulcanizates. This suggests that polysulfidic structures in the original vulcanizates act as oxidation initiators.

Studies of the Heat Deterioration of Specially Prepared Natural Rubber Vulcanizates

1954 ◽  
Vol 27 (2) ◽  
pp. 459-467
Author(s):  
Donald J. Metz ◽  
Robert B. Mesrobian
Keyword(s):  
Natural Rubber ◽  
Elevated Temperatures ◽  
Experimental Methods ◽  
Oxygen Absorption ◽  
Cross Linking ◽  
Vulcanized Rubber ◽  
Chemical Agents ◽  
Complex Process ◽  
Cross Linkage ◽  
Natural Rubber Vulcanizates

Abstract In 1949, Flory, Rabjohn, and Shaffer presented an article describing the dependence of the elastic properties of vulcanized rubber on the degree of cross-linking. In order to prepare rubber vulcanizates characterized by known degrees of cross-linkage recently developed, disazodicarboxylate vulcanizing reagents were employed. These reagents react quantitatively with rubber, one cross-linkage being introduced for each molecule of the reagent. Whereas the conventional vulcanization of rubber with sulfur and accelerators is a complex process and it does not appear possible at the present time to specify the exact number of cross-linkages present in sulfur vulcanizates, the use of disazodicarboxylate vulcanizing reagents presents an opportunity to investigate the changes that occur in the physical properties of vulcanized rubber, characterized by known degrees of cross-linkage, on exposure to oxygen at elevated temperatures. Furthermore, the effect of heat deterioration of various chemical agents commonly employed in sulfur vulcanization recipes may be investigated in a unique way by incorporating such chemical agents in the free state into natural rubber previously vulcanized by disazodicarboxylate reagents. Recent studies of the deterioration of rubber vulcanizates at elevated temperatures have been reported by several workers. In this article, the experimental methods employed to study heat deterioration involve measurements of oxygen absorption, stress relaxation, and changes of 100 per cent modulus of natural rubber vulcanized to known extents of cross-linkage by decamethylene-dismethyl azodicarboxylate.

The Effect of Ozone on Neoprene Vulcanizates and the Influence of Some Protective Agents and Fillers

1956 ◽  
Vol 29 (1) ◽  
pp. 166-175 ◽  
Author(s):  
A. Hartmann ◽  
F. Glander
Keyword(s):  
Experimental Investigation ◽  
Natural Rubber ◽  
Crack Growth ◽  
Crack Formation ◽  
Protective Agents ◽  
Experimental Part ◽  
Synthetic Rubber ◽  
Starting Point ◽  
Undercooled Melt ◽  
Natural Rubber Vulcanizates

Abstract In this investigation an attempt was made to show a certain analogy between the nature of the phenomenon of the crystallization of an undercooled melt and ozone crack formation in stretched natural or synthetic rubber, in order in this way perhaps to have some starting point for a more detailed experimental investigation of these interesting problems. At the same time the observed qualitative differences in the effects of ozone on natural rubber vulcanizates and on Neoprene vulcanizates might be explained. In the experimental part it is first shown, with the help of a simplified experimental method, that the rate of crack growth can be considerably reduced by the presence of protective agents. In addition, a great change in the temperature dependence of crack growth is observed under certain conditions. It can not yet be decided whether or not the rate of nuclei formation is similarly influenced. Furthermore, vulcanizates containing different fillers and different Neoprene contents have been examined.

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.

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