Stress Relaxation of Peroxide and Sulfur Vulcanizates of Natural Rubber

1956 ◽  
Vol 29 (2) ◽  
pp. 398-408
Author(s):  
J. P. Berry ◽  
W. F. Watson
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Chemical Reactions ◽  
Network Structure ◽  
Small Proportion ◽  
Polymeric Networks ◽  
Relaxation Curves ◽  
Physical Changes ◽  
Direct Proportionality ◽  
Experimental Difficulty

Abstract Direct chemical investigation of the degradation of polymeric networks is usually impracticable owing to the experimental difficulty of insolubility and to the fact that reaction at only a small proportion of network units is sufficient to cause marked alteration of network structure. Resort has, therefore, to be made to the measurement of physical changes brought about by the chemical reactions. Change of tension at constant extension is a useful measure for this purpose, since statistical elasticity theory predicts a direct proportionality between the tension and the number of chains supporting the stress. The present purpose is: (1) to describe a stress relaxometer possessing certain advantages over previous models; (2) to report on the stress relaxation of peroxide-crosslinked rubber, which can be considered from a chemical viewpoint to be the simplest possible rubber network; (3) to point out some complications in the relaxation behavior of sulfur vulcanizates, and (4) to interpret the shapes of stress relaxation curves.

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.

Estimation, from Swelling, of the Structural Contribution of Chemical Reactions to the Vulcanization of Natural Rubber. Part I. General Method

1964 ◽  
Vol 37 (2) ◽  
pp. 563-570 ◽  
Author(s):  
Bryan Ellis ◽  
G. N. Welding
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Chemical Reactions ◽  
Network Structure ◽  
Reference Data ◽  
Direct Method ◽  
High Elasticity ◽  
Rubber Part ◽  
Structural Contribution ◽  
General Method

Abstract A procedure is described for estimating indirectly the contribution of vulcanization reactions to the build-up of network structure. This method is useful with technically important vulcanizing systems for which no direct method of estimation has been found. Errors of the theory of high elasticity are avoided by using published results, such as those of Moore and Watson of direct chemical estimates obtained with a special vulcanizing system that is chemically well understood. Reliance on the theories of end correction and swelling is also avoided by using published experimental relations. The method is applicable to any linear primary polymer of arbitrary molecular weight and any suitable swelling liquid, for which the required reference data have been obtained.

Stress Relaxation during the Photoxidation of Peroxide Crosslinked Rubber

1960 ◽  
Vol 33 (2) ◽  
pp. 433-444
Author(s):  
J. R. Dunn ◽  
J. Scanlan ◽  
W. F. Watson
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Physical Properties ◽  
Chemical Reactions ◽  
Small Extent ◽  
Organic Peroxides ◽  
Physical Measurement ◽  
Crosslinked Networks ◽  
Photochemical Aging ◽  
Natural Rubber Vulcanizates

Abstract The chemical reactions involved in the thermal and photochemical aging of natural rubber vulcanizates are largely unknown. Experimental difficulties have precluded direct chemical investigation owing to the insolubility of the crosslinked networks and the small extent of reaction required for a great deterioration in physical properties. Accordingly recourse has been made to physical measurement. Tobolsky et al. (e.g. Ref. (1)) have shown that the relaxation in stress on holding a rubber strip at constant extension during aging is a convenient experimental measure capable of interpretation in terms of network breakdown. In photochemical studies the opacity of conventional sulfur vulcanizates provides a further complication. In the present work, the stress relaxation technique has been used in a study of the degradation by 365 mµ radiation of the comparatively transparent and chemically simple rubber networks obtained after crosslinking by organic peroxides.

Determination of Crosslink Density and Network Structure of NR Vulcanizates by Means of TSSR

2013 ◽  
Vol 844 ◽  
pp. 482-485 ◽  
Author(s):  
Norbert Vennemann ◽  
Christina Schwarze ◽  
Claudia Kummerlöwe
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Crosslink Density ◽  
Relaxation Spectrum ◽  
Strong Impact ◽  
Relaxation Spectra ◽  
Peak Separation ◽  
Temperature Scanning

Unfilled vulcanizates based on natural rubber (NR) were investigated by temperature scanning stress relaxation (TSSR) measurements. Different sulfur based cure systems, i.e. conventional (CV), semi-efficient (SEV) and efficient (EV) vulcanization system, were used to prepare the vulcanizates. It was found that sulfur/accelerator - ratio has a strong impact on the shape of the relaxation spectrum, deduced from TSSR measurements. By deconvolution of the relaxation spectra, peak separation was performed and 3 different peaks were found in case of CV - cured samples. In contrast, only a single peak was found, in case of the EV-cured sample. After thiolamine treatment the shape of the relaxation spectra altered significantly in case of the CV-cured sample whereas the spectra of the SEV-and EV-cured sample exhibited only slight differences. Additionally, the crosslink density of the samples decreased after thiolamine treatment. This is due to selective cleavage of polysulfidic crosslinks. It has been concluded, that the significant peak in the relaxation spectrum at about 120 °C can be attributed to the cleavage of polysulfidic crosslinks. Furthermore, a linear relationship between the percentage of polysulfidic crosslinks and the sulfur/accelerator - ratio is assumed.

Degradation of Highly Elastic Polymers. VI. The Intermittent Chemo-Stress Relaxation of Crosslinked 1,5-Polyenes

1970 ◽  
Vol 43 (4) ◽  
pp. 788-798
Author(s):  
K.-H. Hillmer ◽  
W. Scheele
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Chemical Reactions ◽  
Oxidative Degradation ◽  
Sample Pretreatment ◽  
Relaxation Method ◽  
Relaxation Curve ◽  
Made In

Abstract Measurements of the continuous stress relaxation of thiuram vulcanizates and intermittent stress relaxation of both sulfur and C—C crosslinked vulcanizates of natural rubber were discussed. These measurements were made in the presence of either oxygen or nitrogen at various temperatures both with and without sample pretreatment. The following conclusions were drawn: 1. Determination of the rate of continuous tension loss is not suitable for measuring the oxidative degradation of vulcanizates from 1,5 polyenes according to a stress relaxation method. The reason for this is that rheological processes superimpose themselves on the chemical reactions initiated by oxygen, cause a reduction in tension, and affect both the form of the relaxation curve and also the rate of tension loss. This is particularly noticeable in the case of vulcanizates containing polysulfide bonds. 2. It was possible, using intermittent stress relaxation and by choosing suitable temperatures and frequencies, to eliminate the influence of rheological processes and thus to measure only the rate of tension loss due to oxidative degradation.

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
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