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.

Chemical Stress-Relaxation and Other Studies on Styrene-Butadiene Rubber

1974 ◽  
Vol 47 (5) ◽  
pp. 1265-1274 ◽  
Author(s):  
S. H. Kalfayan ◽  
R. Rakutis ◽  
R. H. Silver
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Activation Energies ◽  
Hydroxyl Group ◽  
Styrene Butadiene Rubber ◽  
Chemical Stress ◽  
Butadiene Rubber ◽  
Relaxation Rates ◽  
Relaxation Measurements ◽  
Styrene Butadiene

Abstract The aging of styrene—butadiene rubber (SBR) was studied by three methods: stress relaxation, infrared spectroscopy, and swelling measurements, with the purpose of supplying information pertinent to understanding the basic mechanism of its aging. Stress-relaxation measurements in air and nitrogen at elevated temperatures indicated that atmospheric oxygen is the principal cause of chemical stress relaxation of SBR, rather than heat. Intermittent stress-relaxation measurements showed scission and crosslinking occurring simultaneously during network breakdown, and it was concluded that random scission in the backbone is indicated to take place in preference to scission in the crosslinks. Activation energies obtained from relaxation rates at several temperatures was 28 ± 0.5 kcal, comparable to literature values of 30 ± 2 kcals. The rates of carbonyl and hydroxyl group formation in SBR in air at various temperatures were determined by ir spectroscopy, both induction and maximum rates, νm, being measured. Activation energies calculated from these rates showed lower values compared to those obtained from stress-relaxation measurements. This may be due to the possibility that the processes being measured are not the same in each case. The three peaks appearing in the carbonyl region were ascribed to carboxyl, ketone, or aldehyde, and perester. The presence of these groups was confirmed by microanalytical methods. The absorption centered at 3450 cm−1 was attributed to hydrogen-bonded OH groups, i.e., alcohols and hydroperoxides. Positive chemical tests were obtained for hydroperoxide. The number of new network chains formed, νe, obtained from swelling measurements agreed well with those obtained from stress-relaxation measurements. It was found that the rate of the number of new network chains formed increased rapidly during the latter states of oxidation.

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.

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.

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:

WIELAND-K88

Alloy Digest ◽  
2005 ◽  
Vol 54 (12) ◽  
Keyword(s):  
Thermal Conductivity ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Stress Relaxation ◽  
Copper Alloy ◽  
Elevated Temperatures ◽  
Heat Treating ◽  
Relaxation Resistance ◽  
Temperature Performance ◽  
Very High

Abstract Wieland K-88 is a copper alloy with very high electrical and thermal conductivity, good strength, and excellent stress relaxation resistance at elevated temperatures. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: CU-738. Producer or source: Wieland Metals Inc.

scholarly journals Appraisal of the current standards for stress relaxation measurements in compression for rubbers

1986 ◽  
Vol 6 (2) ◽  
pp. 85-105 ◽  
Author(s):  
Arthur W. Birley ◽  
Kamal P. Fernando ◽  
Mohammed Tahir
Keyword(s):  
Stress Relaxation ◽  
Relaxation Measurements ◽  
Current Standards

Structural Performance of Pultruded Composites under Elevated Temperatures

2009 ◽  
Vol 79-82 ◽  
pp. 2223-2226
Author(s):  
Ayman S. Mosallam
Keyword(s):  
Elevated Temperature ◽  
High Temperatures ◽  
Elevated Temperatures ◽  
Oxidative Degradation ◽  
Viscoelastic Behavior ◽  
Structural Performance ◽  
Crystalline Polymers ◽  
Damage To The Material ◽  
Continuous Working ◽  
Pultruded Composites

One of the major limitations for wider use of pultruded fiber reinforced polymeric (PFRP) composites in the civil engineering sector has been their behavior under elevated temperature and ultimately fire. This limitation arises not only due to the reduction in mechanical properties at high temperatures, including increased propensity to creep, but also due to limitations on the continuous working temperature causing permanent damage to the material as a result of thermal and oxidative degradation. Significant gains in property retention at high temperatures with crystalline polymers have been derived from the incorporation of fibrous reinforcement, but the development of new polymer matrices is the key for further elevation of the useful temperature range. This paper presents summary results of a research project focused on characterizing the viscoelastic behavior of commercially-produced, off-the-shelf unidirectional PFRP materials subjected to elevated temperature environments.

Chemical Stress Relaxation of NR Networks Prepared in the Swollen State

1986 ◽  
Vol 59 (4) ◽  
pp. 541-550 ◽  
Author(s):  
Kyung-Do Suh ◽  
Hidetoshi Oikawa ◽  
Kenkichi Murakami
Keyword(s):  
Stress Relaxation ◽  
Network Structure ◽  
Three Dimensional ◽  
Polymer Chains ◽  
Chemical Stress ◽  
Network Chain ◽  
Crosslinking Process ◽  
Dimensional Network ◽  
Chemical Relaxation ◽  
The Difference

Abstract From the experimental results of the present investigation, it is apparent that two kinds of networks which have a different three-dimensional network structure give quite different behavior of chemical stress relaxation, even if both networks have the same network chain density. The difference in three-dimensional network structure for the two kinds of rubber arises from the degree of entanglement, which changes with the concentration of the polymer chains prior to the crosslinking process. The direct cause of chemical relaxation is due to the scission of network chains by degradation, whereas the total relaxation is caused by the change of geometrical conformation of network chains. This then casts doubt on the basic concept of chemorheology which is represented by Equation 2.

Thermooxidative Aging Studies on Silicone Rubber and Lifetime Prediction

2013 ◽  
Vol 777 ◽  
pp. 11-14
Author(s):  
You Shan Wang ◽  
Sha Sha Jiang ◽  
Yu Peng Liu
Keyword(s):  
Silicone Rubber ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Activation Energies ◽  
Lifetime Prediction ◽  
Arrhenius Behavior ◽  
Compression Set ◽  
Degradation Processes ◽  
Aging Studies ◽  
Significant Compression

Silicone rubber have been aged in air while under 25% compression at temperature up to 250°C. These studies examined the compression set of silicone rubber at accelerated (elevated) temperatures and were then used to make predictions about compression set at room temperature. The data obtained could be amenable to timetemperature superposition and Arrhenius treatment. The results suggest the presence of two degradation processes with activation energies of 71.6 kJ mol-1 (for temperatures above 165 °C) and 26.08 kJ mol-1 (for temperatures below 165 °C). Based on the extrapolation of the non-Arrhenius behavior, it was estimated that significant compression set loss would occur after around 67 years at 25 °C.

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