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.

Cis-Trans Isomerization of Natural Rubber under the Influence of Hydrogen Chloride or Ethylaluminum Dichloride

1960 ◽  
Vol 33 (4) ◽  
pp. 985-987 ◽  
Author(s):  
I. I. Boldyreva ◽  
B. A. Dolgoplosk ◽  
E. N. Kropacjeva ◽  
K. V. Nel'son
Keyword(s):  
Natural Rubber ◽  
Hydrogen Chloride ◽  
Benzene Solution ◽  
Polymer Chains ◽  
Trans Content ◽  
Aluminum Compounds ◽  
Cis And Trans ◽  
Chloride Activity ◽  
Made In

Abstract We have established earlier that organo-aluminum compounds, and titanium tetrachloride, bring about the isomerization of the cis-isoprene units in natural rubber into the trans. The isomerization process, as influenced by the above materials, proceeds at appreciable velocity even at room temperature. The present communication reports the results of investigating the cis-trans isomerism of natural rubber as influenced by hydrogen chloride and ethylaluminum dichloride. The isomerizing action of hydrogen chloride upon unsaturated acids and stilbene was dislosed earlier in a series of papers. We investigated the action of dry hydrogen chloride and ethylaluminum dichloride on benzene solutions of natural rubber under the conditions described earlier. Hydrogen chloride was introduced in the form of a saturated benzene solution. In investigating the hydrogen chloride activity, each polymer sample was examined for unsaturation, chlorine content of the polymer chains and microstructure. The latter was characterized with the aid of infrared absorption spectra. As in the previous report, quantitative determination of the cis and trans content was made in the 840 cm−1 region, where the intensity and contour are substantially dissimilar for natural rubber and guttapercha. Furthermore, an additional inspection was made qualitatively in other regions of the IR spectrum (1100–1150 cm−1 and 1300–1330 cm−1), the feasibility of utilizing the 1300–1330 cm−1 region having been reported in a recent publication by Golub, who investigated the isomerization of natural rubber and guttapercha under the influence of selenium at temperatures of 180–220°.

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.

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.

scholarly journals Analytical applications of oscillatory chemical reactions: Determination of some pharmaceuticaly and biologically important compounds

2012 ◽  
Vol 66 (2) ◽  
pp. 153-164 ◽  
Author(s):  
Natasa Pejic ◽  
Slobodan Anic ◽  
Ljiljana Kolar-Anic
Keyword(s):  
Chemical Reactions ◽  
Stirred Tank ◽  
Analyte Concentration ◽  
Tank Reactor ◽  
The Past ◽  
Quantitative Characteristics ◽  
Oscillatory Chemical ◽  
Kinetics Of ◽  
Made In

Novel analytical methods for quantitive determination of analytes based on perturbations of oscillatory chemical reactions realized under open reactor conditions (continuosly fed well stirred tank reactor, CSTR), have been developed in the past twenty years. The proposed kinetic methods are generally based on the ability of the analyzed substances to change the kinetics of the chemical reactions matrix. The unambiguous correlation of quantitative characteristics of perturbations, and the amount (concentration) of analyte expressed as a regression equation, or its graphics (calibration curve), enable the determination of the unknown analyte concentration. Attention is given to the development of these methods because of their simple experimental procedures, broad range of linear regression ( 10-7 10-4 mol L-1) and low limits of detection of analytes ( 10-6 10-8 mol L1, in some cases even lower than 10-12 mol L-1). Therefore, their application is very convenient for routine analysis of various inorganic and organic compounds as well as gases. This review summarizes progress made in the past 5 years on quantitative determination of pharmaceutically and biologically important compounds.

scholarly journals Study on Crystallization of Masticated Natural Rubber by Stress Relaxation Method

1964 ◽  
Vol 13 (128) ◽  
pp. 390-393
Author(s):  
Hiroshi SOBUE ◽  
Tetsuhiko MIGITA ◽  
Kenichi MURAKAMI
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Relaxation Method

Oxidative Stress Relaxation of Natural Rubber Vulcanizates at High Strains

1966 ◽  
Vol 39 (5) ◽  
pp. 1577-1583
Author(s):  
C. L. M. Bell
Keyword(s):  
Oxidative Stress ◽  
Tensile Strength ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
High Strain ◽  
Oxidative Degradation ◽  
Relaxation Measurement ◽  
Premature Failure ◽  
Surface Flaws ◽  
Natural Rubber Vulcanizates

Abstract The effect of high strain on the oxidative stress relaxation of several natural rubber vulcanizates has been investigated. In peroxide and CBS accelerated vulcanizates, the rate of stress relaxation increases with increasing strain, and this increase appears to be due to an increase in the rate of oxidation of the network. TMTD and MBT vulcanizates showed marked premature failure at high strains and no oxidative stress relaxation measurement could be made. The tensile strength of a TMTD vulcanizate was at least 20 per cent higher in vacuum than in oxygen, due, it is believed, to stress-induced oxidative degradation at the tip of surface flaws in the rubber.

Evaluation of the Thermal Stress Relaxation Method for the Estimation of Polysulfidic Crosslinks in Natural Rubber Vulcanizates

1972 ◽  
Vol 45 (4) ◽  
pp. 1064-1073 ◽  
Author(s):  
J. H. Farmer ◽  
J. E. Stuckey
Keyword(s):  
Thermal Stress ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
Relaxation Method ◽  
Order Rate Constant ◽  
Exchange Reactions ◽  
Fast Relaxation ◽  
Thermal Stress Relaxation ◽  
Natural Rubber Vulcanizates ◽  
Linear Manner

Abstract The variation of the polysulfidic crosslink content of a natural rubber vulcanizate during cure has been determined from thermal stress relaxation data obtained using a Monsanto Rheometer and the results have been compared with those obtained by chemical probe analysis. No correlation could be found. Attempts to isolate the relaxation due solely to polysulfide crosslink interchange gave no better agreement and it is concluded that competing maturing reactions prevent such a resolution. The first order rate constant for the fast relaxation attributed to polysulfide crosslink exchange reactions has been found to vary in a linear manner with the total crosslink density of the vulcanizates.

The quantitative comparison of experimental and simulated diffraction contrast images

1995 ◽  
Vol 53 ◽  
pp. 102-103
Author(s):  
Stuart McKernan
Keyword(s):  
Image Processing ◽  
Personal Computer ◽  
Close Agreement ◽  
Quantitative Comparison ◽  
Image Simulation ◽  
Computing Power ◽  
Diffraction Contrast ◽  
Simulated Images ◽  
Made In

For many years the concept of quantitative diffraction contrast experiments might have consisted of the determination of dislocation Burgers vectors using a g.b = 0 criterion from several different 2-beam images. Since the advent of the personal computer revolution, the available computing power for performing image-processing and image-simulation calculations is enormous and ubiquitous. Several programs now exist to perform simulations of diffraction contrast images using various approximations. The most common approximations are the use of only 2-beams or a single systematic row to calculate the image contrast, or calculating the image using a column approximation. The increasing amount of literature showing comparisons of experimental and simulated images shows that it is possible to obtain very close agreement between the two images; although the choice of parameters used, and the assumptions made, in performing the calculation must be properly dealt with. The simulation of the images of defects in materials has, in many cases, therefore become a tractable problem.

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