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.

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.

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.

Effects of accelerator type on stress relaxation behavior and network structure of aged natural rubber/chloroprene rubber vulcanizates

2016 ◽  
Vol 49 (5) ◽  
pp. 381-396 ◽  
Author(s):  
Farzad A Nobari Azar ◽  
Murat Şen
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Structural Changes ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Rubber Blends ◽  
Chloroprene Rubber ◽  
Weather Changes ◽  
Behavior Network

Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

1959 ◽  
Vol 32 (3) ◽  
pp. 739-747 ◽  
Author(s):  
J. R. Dunn ◽  
J. Scanlan
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Protective Action ◽  
Dicumyl Peroxide ◽  
Vulcanized Rubber ◽  
Aging Properties ◽  
Photochemical Aging ◽  
Natural Rubber Vulcanizates

Abstract The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.

Stress relaxation of natural rubber during irradiation

1969 ◽  
Vol 7 (4) ◽  
pp. 725-733 ◽  
Author(s):  
D. Evans ◽  
J. T. Morgan ◽  
R. Sheldon ◽  
G. B. Stapleton
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber

Longitudinal Cracking in a Carbon Black Filled Natural Rubber Vulcanizate during Chemical Stress Relaxation

1998 ◽  
Vol 71 (2) ◽  
pp. 157-167 ◽  
Author(s):  
G. R. Hamed ◽  
J. Zhao
Keyword(s):  
Stress Relaxation ◽  
Carbon Black ◽  
Natural Rubber ◽  
Longitudinal Crack ◽  
Chemical Stress ◽  
Loading Direction ◽  
Rubber Vulcanizate ◽  
Edge Cracks ◽  
Forced Air ◽  
Oxidative Attack

Abstract Thin specimens of a black-filled, natural rubber vulcanizate have been held in uniaxial tension at 72°C and 200% elongation in a forced air oven. After substantial oxidative attack (inferred from stress relaxation), small edge cracks formed. Initially, these cracks grew perpendicular to the loading direction, but, upon reaching about 0.1 mm in depth, longitudinal crack growth commenced and fracture progressed by a kind of 0°-peel process with “splitting-off” of successive strands of rubber. This phenomenon is attributed to anisotropy in strength caused both by straining and by oxidative attack.

scholarly journals Cross-Linker Control of Vitrimer Flow

2020 ◽  
Author(s):  
Bassil El-Zaatari ◽  
Jacob Ishibashi ◽  
Julia Kalow
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Bulk Material ◽  
Relaxation Rates ◽  
Exchange Reactions ◽  
Activation Barriers ◽  
Flow Activation Energy ◽  
Wide Range ◽  
Cross Linker ◽  
Frequency Sweeps

<div><p>Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that cross-linker reactivity represents an additional design parameter to tune stress relaxation rates in vitrimers. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition—elimination of thiols in a PDMS vitrimer. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.</p></div>

Effect of vulcanization time on crosslink density and aging performance of natural rubber composites

2020 ◽  
Vol 62 (8) ◽  
pp. 858-862
Author(s):  
Ece Unur Yilmaz ◽  
Ahu Kor Dayioglu ◽  
Seda Balaban
Keyword(s):  
Natural Rubber ◽  
Crosslink Density ◽  
Elevated Temperatures ◽  
Mechanical Performance ◽  
Operating Conditions ◽  
Rubber Composites ◽  
Rubber Mixture ◽  
Natural Rubber Composites ◽  
Different Temperatures ◽  
Auto Parts

Abstract Natural rubber composites are widely used in the automotive industry because of their improved viscoelastic characteristics that are mostly governed by crosslink density. However, rubber parts suffer deterioration of performance over long service lives. Therefore, optimization of crosslink density and prediction of changes in physico-mechanical properties over time at elevated temperatures is extremely important for the production of safe auto parts. In this work, the effect of vulcanization time on crosslink density and thus the performance and lifetime of natural rubberbased auto parts was investigated. The natural rubber mixture prepared in this context was vulcanized for 3, 5, 10 and 15 minutes at a constant temperature of 160 °C. The crosslink density of each vulcanizite was determined by equilibrium swelling tests and the Flory-Rehner equation. The maximum crosslink density (10.75 × 10-5 mol × cm-3) and the minimum permanent compression set values (10 % at 70 °C and 25 % at 100 °C) were recorded for the sample vulcanized for 10 minutes (v10). Aging behavior of the samples were investigated by stress relaxation tests performed at 85 °C, 100 °C and 120 °C. The service lives of the vulcanizites at different temperatures were predicted by linear Arrhenius fits of degradation times. The sample vulcanized for 10 minutes (v10) was shown to exhibit a service life of 2282 hours at 70 °C in air and the optimum physico-mechanical performance under real operating conditions. The performance and lifetime prediction procedure used in this work could be employed in an early design of rubber components for specific applications.

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