Stress Relaxation during the Thermal Oxidation of Vulcanized Natural Rubber

1960 ◽  
Vol 33 (2) ◽  
pp. 423-432
Author(s):  
J. R. Dunn ◽  
J. Scanlan ◽  
W. F. Watson
Keyword(s):  
Free Radical ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
Thermal Aging ◽  
Elevated Temperatures ◽  
The Other ◽  
Tetramethylthiuram Disulfide ◽  
Oxidative Aging ◽  
Relaxation Measurements ◽  
Cross Links

Abstract The photoinitiated oxidative aging of peroxide vulcanized natural rubber (which contains only carbon-carbon cross-links) was found by stress relaxation measurements to be autocatalytic and to be sensitive to the presence of free radical retarders and catalysts. Similar behavior would be expected in thermal aging. However, earlier work in these laboratories indicated that the thermal aging of peroxide vulcanizates was not autocatalytic. Because of this discrepancy the stress relaxation of peroxide vulcanizates at elevated temperatures has now been reinvestigated and the study has been extended to include also the aging of the other types of networks which are produced on vulcanization by tetramethylthiuram disulfide in the absence of sulfur, by sulfenamide-sulfur, and by sulfur alone.

Investigation of Un-Vulcanized Natural Rubber by Means of Temperature Scanning Stress Relaxation Measurements

2013 ◽  
Vol 718-720 ◽  
pp. 117-123 ◽  
Author(s):  
Miao Wu ◽  
Michael Heinz ◽  
Norbert Vennemann
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
Branch Points ◽  
Relaxation Spectra ◽  
Green Strength ◽  
Testing Method ◽  
Relaxation Measurements ◽  
Different Types ◽  
Temperature Scanning

Two different types of un-vulcanized natural rubber, air dried sheets (ADS) and SVR-3L block rubber, were investigated by a new testing method and the results are compared with other mechanical properties. It was found that green strength is strongly reduced if the sample is ther­mal­ly treated before testing. Presumably, the decrease of strength is caused by a decrease of branch points, mainly composed of phospholipids, which are linked to the a - terminal groups of the rubber molecules. The existence of two different types of branch points is indicated by relaxation spectra, obtained from temperature scanning stress relaxation (TSSR) measurements.

Stress Relaxation Measurement as a High-Speed Method for Predicting the Long-Term Behavior of Vulcanized Rubber

1983 ◽  
Vol 56 (1) ◽  
pp. 31-50 ◽  
Author(s):  
R. Clamroth ◽  
L. Ruetz
Keyword(s):  
Stress Relaxation ◽  
High Speed ◽  
Elevated Temperatures ◽  
Pure Oxygen ◽  
Relaxation Measurement ◽  
Hot Air ◽  
Vulcanized Rubber ◽  
Relaxation Measurements ◽  
The Times ◽  
Speed Method

Abstract Intermittent stress relaxation is well suited for quantifying aging processes in rubber. For NR, the effects of different antioxidants can be measured by the rates at which the modulus falls. In synthetic rubbers (SBR, NBR, and CR), it can be measured through the modulus increases caused by oxygen crosslinking. Equal-value times, e.g., t0.75 for NR and t1.25 for SBR, NBR, and CR, are the times taken by the modulus to decrease or increase to a given percentage of its original level. They are better measures of aging than the modulus change after a given time. For NR, it has been shown that stress relaxation measurements at elevated temperatures and in pure oxygen correlate with the results of conventional aging methods. Thus the testing times can be drastically reduced—from up to 28 days to 1–8 hours. Discontinuous stress relaxation measurements are considerably more accurate and selective than conventional oxygen aging. For the repeatability of a single equal-value time measurement, we obtained a coefficient of variation (s/x) of 5–10% for stress relaxation measurement and about ±20% for oxygen aging. The degree of selectivity for oxygen aging and stress relaxation was found to be 3.6 and 18, respectively. The correlation between the results of stress relaxation measurements and those of the conventional oxygen and hot air aging tests was investigated for a large number of NR compounds and for some SBR, NBR, and CR compounds. The correlation is not very good, but it must be remembered that the equal-value times determined according to the two methods show relatively pronounced variability. With the conventional aging methods, the results also depend on what quantity is measured, e.g., the change in tensile strength or hardness, and on what equal-value time is chosen, e.g., the time taken by the property concerned to decrease to 90 or 75% of its original value. The conclusion of the investigations described above is that intermittent modulus measurement is an interesting high-speed method for the assessment of aging behavior. It will acquire a firm position in the arsenal of rubber testing methods, but will probably supplement, and not completely replace, the aging methods currently used.

CHANGES OF CHEMICAL STRUCTURE AND MECHANICAL PROPERTY LEVELS DURING THERMO-OXIDATIVE AGING OF NBR

2013 ◽  
Vol 86 (4) ◽  
pp. 591-603 ◽  
Author(s):  
Jiaohong Zhao ◽  
Rui Yang ◽  
Rossana Iervolino ◽  
Stellario Barbera
Keyword(s):  
Mechanical Property ◽  
Thermal Aging ◽  
Chemical Structure ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Chain Scission ◽  
Bending Test ◽  
Cross Linking ◽  
Butadiene Rubber ◽  
Oxidative Aging

ABSTRACT The accelerated thermo-oxidative aging of acrylonitrile–butadiene rubber (NBR) was studied at elevated temperatures. The chemical structure characterized by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and pyrolysis gas chromatography–mass spectroscopy (PGC-MS) showed the loss of low-molecular-weight additives, such as antioxidants and paraffin, and the formation of carbonyl groups and unsaturated double bonds. The cross-linking degree characterized by NMR and a swelling test showed that aging is a competitive process of cross-linking and chain scission. Cross-linking dominated the thermal aging of NBR most of the time, whereas chain scission began to increase after a long time at high temperatures. The changes of mechanical property magnitudes during thermal aging of NBR were studied by using the recovery from bending test (RFB) and tensile test. By comparing the physical property results and the structural changes, their relationship is discussed.

Thermomechanical Effects Associated With Crystallization of Rubber Under Stretch and During Slow Extension

1997 ◽  
Vol 119 (3) ◽  
pp. 298-304 ◽  
Author(s):  
Mehrdad Negahban
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Thermodynamic Model ◽  
The Other ◽  
Equilibrium Stress ◽  
Rubber Sample ◽  
Other Hand ◽  
The Difference ◽  
Thermomechanical Effects

A natural rubber sample which crystallizes after stretching normally shows stress relaxation associated with this crystallization and normally ends up at a stress lower than that of the fully amorphous rubber before crystallization. On the other hand, a natural rubber sample which crystallizes during stretching becomes more rigid as a result of the crystallization and the stress required to extend it to a given stretch increases substantially above the stress needed to extend the fully amorphous rubber to the same elongation. Even though the former effect has been modeled and studied by the likes of Flory (1947), the latter effect has not yet been properly modeled or studied. The difference between crystallization during or after stretching will be studied in this article based on a thermodynamic model developed by the author to capture the thermomechanical effects of crystallization in natural rubber. The two limit cases of very rapid and very slow extension to a given stretch are singled out for comparison of the equilibrium stress.

Influence of the Type of Alkylamine Organic Modifiers on Thermal Mechanical Behavior and other Related Properties of Natural Rubber/Clay Nanocomposites

2013 ◽  
Vol 844 ◽  
pp. 217-220 ◽  
Author(s):  
Uraiwan Sookyung ◽  
Woothichai Thaijaroen ◽  
Norbert Vennemann ◽  
Charoen Nakason
Keyword(s):  
Mechanical Properties ◽  
Thermal Stability ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
The Other ◽  
Clay Nanocomposites ◽  
Organic Modifier ◽  
Organic Modifiers ◽  
Different Types ◽  
Thermal Stability Of

Sodium-montmorillonite (Na-MMT) nanoclay was modified with different types of alkylamine organic modifier including primary and quaternary alkylamines. Influence types of alkylamine on properties of natural rubber/clay nanocomposites was investigated. It was found that organoclays caused improvement of mechanical properties of natural rubber, and accelerated vulcanization reaction with higher degree of crosslinking. In addition, organoclay modified with quaternary alkylamine showed significance cure reversion phenomenon which caused reduction of thermal stability. On the other hand, primary alkylamine modified nanoclay caused improvement of thermal stability of natural rubber. Moreover, stress relaxation was observed at the melting temperature of the modifying agent.

Chain Scission Efficiency in the Oxidation of Natural Rubber Vulcanizates

1957 ◽  
Vol 30 (4) ◽  
pp. 1146-1161
Author(s):  
A. G. Veith
Keyword(s):  
Natural Rubber ◽  
Elevated Temperatures ◽  
Density Ratio ◽  
Direct Consequence ◽  
Chain Scission ◽  
Polymer Chains ◽  
Published Report ◽  
Relaxation Measurements ◽  
A Chain ◽  
Chain Scission Reaction

Abstract Natural rubber when it degrades under the action of oxygen does so primarily by a chain scission reaction. A technique has been developed by Tobolsky and coworkers for assessing the magnitude of this chain scission reaction in vulcanizates by means of continuous stress relaxation measurements. Since the result of the oxygen attack on the rubber is a chain scission reaction, the question of the efficiency of the reaction comes to mind. The influence of antioxidants is of importance in this regard as is the type of vulcanizate or network structure. This paper describes some measurements of the chain scission efficiency of a simple benzothiazolyl disulfide (MBTS) vulcanizate and the effect of several antioxidants on this chain scission reaction. Some of the complications inherent in this type of measurement are discussed. The first published report on the efficiency of the chain scission reaction in vulcanizates was given by Tobolsky, Metz, and Mesrobian in 1950. A more recent publication is that of Baxter, Potts, and Vodden in 1955. Tobolsky has interpreted the stress decay of gum vulcanizates at elevated temperatures as a direct consequence of the cutting of polymer chains of the network. The reduced stress is postulated as being equal to the chain density ratio:

Recent Studies in the Aging of Natural Rubber

1966 ◽  
Vol 39 (5) ◽  
pp. 1565-1576
Author(s):  
C. L. M. Bell ◽  
M. E. Cain ◽  
D. J. Elliott ◽  
B. Saville
Keyword(s):  
Natural Rubber ◽  
Elevated Temperatures ◽  
Research Effort ◽  
The Other ◽  
Detailed Knowledge ◽  
Antioxidant Action ◽  
Aging Resistance ◽  
Increasing Demand ◽  
The One ◽  
Protective Systems

Abstract Natural rubber, when properly compounded, produces articles having an unrivalled combination of properties such as strength, elastic modulus, and resilience. However, in common with the properties of all other polymers, these excellent qualities progressively deteriorate on contact with oxygen, especially at elevated temperatures. The increasing demand for elastomers capable of service at even higher temperatures requires more stringent efforts by research workers for the production of aging-resistant natural rubber, and, in general, two approaches are possible. On the one hand further developments may be sought in the efficiency of the protective systems used. This will necessitate a reasonable understanding of the mechanisms of antioxidant action, and recent reviews have shown the large amount of research effort being applied to this end. On the other hand, modification of the present vulcanization methods to give vulcanizates with inherently greater resistance to aging is a possibility, although progress in this direction requires a detailed knowledge of vulcanization mechanism and vulcanizate structure. The recent work of the Vulcanization Group at NRPRA has shed considerable light on both these aspects of natural rubber chemistry and improved the prospects of success in this direction. In this paper we report results of studies carried out in both the fields described above which have led to the development of technologically acceptable vulcanizates having improved aging resistance.

Vulcanization of Elastomers. 12. Perbunan with Thiuram Monosulfide and Sulfur. I

1959 ◽  
Vol 32 (1) ◽  
pp. 128-138 ◽  
Author(s):  
Walter Scheele ◽  
Horst-Eckart Toussaint
Keyword(s):  
Activation Energy ◽  
Natural Rubber ◽  
Temperature Dependence ◽  
Induction Period ◽  
Rate Constants ◽  
The Other ◽  
Tetramethylthiuram Disulfide ◽  
First Order ◽  
The One ◽  
Limiting Value

Abstract The vulcanization of Perbunan 2818 by tetramethylthiuram monsulfide plus sulfur (1 mole monosulfide per gram-atom S) was thoroughly studied. The following results were shown: The limiting value for dithiocarbamate formation is 66 mole per cent of the initial thiuram monosulfide, indicating a two-thirds transformation. The limiting value is practically independent of temperature. The formation of dithiocarbamate can be described as a reaction of the first order. The formation of dithiocarbamate is characterized by an induction period which grows longer with lowering of the temperature, and at 100° C it amounts to about 100 minutes. The rate constants for dithiocarbamate formation were calculated, and it was shown that they were practically the same as those for the vulcanization of Perbunan with tetramethylthiuram disulfide. The activation energies as derived from the temperature dependence of the rate constants for dithiocarbamate formation in the vulcanization of Perbunan by thiuram monosulfide plus sulfur on the one hand and with thiuram disulfide on the other, are only very slightly different and are practically the same as the activation energy for dithiocarbamate formation during the vulcanization of natural rubber with thiuram monosulfide plus sulfur. The results were thoroughly discussed in light of the present conceptions of the course of thiuram vulcanizations.

Stress Relaxation in Rubber I. Evaluation of Antioxidants

1956 ◽  
Vol 29 (1) ◽  
pp. 240-250 ◽  
Author(s):  
H. W. H. Robinson ◽  
H. A. Vodden
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Half Life ◽  
Elevated Temperatures ◽  
Antioxidant Efficiency ◽  
Recording Potentiometer ◽  
Method Of Evaluation ◽  
Rubber Good ◽  
Evaluation Techniques ◽  
Chart Recording

Abstract Conventional evaluation techniques for rubber antioxidants are very time consuming. A method of evaluation based on stress relaxation due to oxidation at elevated temperatures, and an apparatus developed for the study of this phenomenon in a large number of natural rubber stocks, are described in this article. Results are compared with those obtained using conventional air- oven and oxygen bomb aging tests. The apparatus is suitable for testing six rubber samples simultaneously, and uses unbonded resistance wire strain gauges for the measurement of stresses in the samples. The stress vs. time curves are recorded automatically on a roll chart recording potentiometer. It has been found that the curves approximate to exponential decay curves, and, as such, can be characterized by a single parameter—the half life. This parameter, used as a measure of antioxidant efficiency, can be correlated with the loss of tensile strength for samples aged in a conventional air oven. The use of the half-life period as a measure of antioxidant efficiency leads to a rapid and easily interpreted method of evaluation for antioxidants in natural rubber. Good reproducibility and discrimination are features of the method.

The Thermal and Oxidative Stability of Chlorosulfonated Polyethylene Vulcanizates as Measured by Stress Relaxation

1971 ◽  
Vol 44 (5) ◽  
pp. 1410-1420
Author(s):  
F. Haaf ◽  
P. R. Johnson
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Oxidative Degradation ◽  
Activation Energies ◽  
Polymer Chains ◽  
Chlorosulfonated Polyethylene ◽  
Thermal And Oxidative Stability ◽  
Relaxation Measurements ◽  
Accelerator System ◽  
Interchange Reactions

Abstract Stress relaxation measurements of chlorosulfonated polyethylene vulcanizates show that curing with m-phenylene-bis-maleimide gives thermally more stable crosslinks than the conventional metal oxide/sulfur accelerator system. The superior thermal stability of the bis-maleimide cure is based on the covalent nature of the crosslinks. In conventionally cured vulcanizates interchange reactions of the metal sulfonate and polysulfide crosslinks occur at elevated temperatures. The interchange reactions of the crosslinks cause a rapid stress decline at the beginning of the stress relaxation process. Over longer aging periods stress relaxation due to oxidative degradation becomes apparent in vulcanizates of both types. The activation energies of oxidative stress relaxations are very similar for the bis-maleimide and the conventional cure. The similarity of the activation energies indicates that oxidative degradation follows the same path. The site of the oxidative attack is established for bis-maleimide cured vulcanizates. Oxidative degradation is found to occur in the polymer chains rather than in the crosslinks. The effects of fillers and stabilizers are investigated and their mode of action is explained on the basis of the stress relaxation results.

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