The Attack of Ozone on Stretched Rubber Vulcanizates. II. Conditions for Cut Growth

1960 ◽  
Vol 33 (4) ◽  
pp. 1156-1165
Author(s):  
M. Braden ◽  
A. N. Gent
Keyword(s):  
Experimental Study ◽  
Tensile Stress ◽  
Natural Rubber ◽  
Critical Value ◽  
Rubber Sheet ◽  
Test Pieces ◽  
Rubber Vulcanizate ◽  
Present Part ◽  
Applied Tensile Stress ◽  
Made In

Abstract In Part I an experimental study was reported of the factors determining the rate of propagation of a cut through a stretched rubber sheet under the action of an atmosphere containing ozone. It was remarked that no growth took place from a small razor cut made in one edge of the test pieces unless a critical value of the applied tensile stress was exceeded. The value was quite small, of the order of 100 g/cm2 for a soft natural rubber vulcanizate. In the present part an examination is reported of the conditions necessary for a crack to form or, being present, to grow.

The Mechanics of Ozone Cracking

1962 ◽  
Vol 35 (1) ◽  
pp. 200-209 ◽  
Author(s):  
M. Braden ◽  
A. N. Gent
Keyword(s):  
Tensile Stress ◽  
Crack Growth ◽  
Energy Requirement ◽  
Critical Energy ◽  
Critical Value ◽  
Experimental Measurements ◽  
Rubber Sheet ◽  
Polymer Molecules ◽  
Two Factors ◽  
Applied Tensile Stress

Abstract Experimental measurements are described of the growth of a cut in a stretched rubber sheet under the action of an atmosphere containing ozone. A well-defined rate of crack growth is obtained, substantially independent of the applied tensile stress when this exceeds a critical value necessary for growth to occur at all. The rate of growth is found to be similar for a number of polymers and principally determined by the ozone concentration when the mobility of the polymer molecules is sufficiently high. When the molecular mobility is inadequate, crack growth is retarded. The critical condition is found to be similar for all the polymers examined, and largely independent of the conditions of exposure; it appears to reflect an energy requirement for growth of about 40 ergs/cm2 of newly-formed surface. The effect of the degree of vulcanization and the presence of additives, including antiozonants, on these two factors has also been examined. The dialkyl-p-phenylene diamines are found to confer protection by raising the critical energy required for growth to occur, in contrast to other protective agents which affect only the rate of crack propagation.

Crystallization and the Relaxation of Stress in Stretched Unvulcanized Natural Rubber

1956 ◽  
Vol 29 (4) ◽  
pp. 1195-1198
Author(s):  
A. V. Tobolsky ◽  
G. M. Brown
Keyword(s):  
Natural Rubber ◽  
Temperature Region ◽  
Effect Of Temperature ◽  
Careful Study ◽  
Rubber Vulcanizate ◽  
Crystallization Region ◽  
Different Temperatures ◽  
Made In

Abstract The first observation made in this laboratory in 1946 on the effect of crystallization on stress decay at constant extension was made on a vulcanized Neoprene GN gum stock. It was found that this rubber showed only slight stress decay after 100 hours at 35° C and 50 per cent extension. However, a complete decay of stress to zero stress was observed after only 50 hours at 0° C and 50 per cent extension. Furthermore, the sample after reaching zero stress began to increase in length (spontaneous elongation). This phenomenon was attributed to crystallization. Observations of spontaneous elongation, but no stress decay measurements, were previously reported for vulcanized and unvulcanized natural rubber and for vulcanized and unvulcanized ether polysulfide rubber. It was decided to make a careful study of the effect of temperature and elongation on the stress-decay curves of unvulcanized rubber (cast latex sheet) in the temperature region of crystallization. Some time after these studies were completed, two papers have appeared in which stress decay to zero stress in rubber vulcanizates due to crystallization were reported. In one of these a rather thorough study was made of the decay of stress and change in volume of a natural rubber vulcanizate at −26° C and maintained at four different extension ratios. Our own work on unvulcanized natural rubber was carried out at seven different temperatures in the crystallization region, and were made at five different extension ratios. Quite surprisingly, four of these are the same as were used by Gent. There are interesting differences as well as similarities between our work and the results reported for vulcanized natural rubber.

Mechanochemical devulcanization of natural rubber vulcanizate by dual function disulfide chemicals

2016 ◽  
Vol 129 ◽  
pp. 34-46 ◽  
Author(s):  
Soumyajit Ghorai ◽  
Satyaban Bhunia ◽  
Madhusudan Roy ◽  
Debapriya De
Keyword(s):  
Natural Rubber ◽  
Dual Function ◽  
Rubber Vulcanizate

scholarly journals Effect of Applied Tensile Stress on the Transformation Behavior of Medium Carbon Low Alloy Steels

1991 ◽  
Vol 77 (6) ◽  
pp. 816-823
Author(s):  
Yutaka KANETSUKI ◽  
Osamu KAIDA ◽  
Masato KAISO ◽  
Masaaki KATSUMATA
Keyword(s):  
Tensile Stress ◽  
Low Alloy Steels ◽  
Transformation Behavior ◽  
Medium Carbon ◽  
Alloy Steels ◽  
Applied Tensile Stress

Influence of shrinkage during natural rubber sheet drying: Numerical modeling of heat and mass transfer

2019 ◽  
Vol 149 ◽  
pp. 798-806 ◽  
Author(s):  
Clement Ajani ◽  
Stefano Curcio ◽  
Racha Dejchanchaiwong ◽  
Perapong Tekasakul
Keyword(s):  
Mass Transfer ◽  
Numerical Modeling ◽  
Natural Rubber ◽  
Heat And Mass Transfer ◽  
Rubber Sheet

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.

Mechanism of the Crystallization of High Polymers

1954 ◽  
Vol 27 (2) ◽  
pp. 374-384 ◽  
Author(s):  
G. Schuur
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Amorphous Material ◽  
Crystalline Polymer ◽  
Longitudinal Direction ◽  
Crystalline Material ◽  
Current View ◽  
X Ray ◽  
Made In ◽  
High Polymers

Abstract The crystallization of higher polymers is a phenomenon which is not yet fully understood, one of the main difficulties being to explain how the spherulites arise. An attempt will be made in this paper to draw a clearer picture of the mechanism of crystallization and thus to account for the origin of spherulites. It will then be seen how several other phenomena involved in the crystallization of natural rubber can be shown to be logically interrelated. The current view is that a crystalline polymer consists of a continuous amorphous phase containing small crystalline regions, the crystallites. The evidence as to the size of these crystallites, however, is at present inconclusive, because only the lower limit of their size can be measured by means of x-ray examination. The reason is that, owing to the absence of reflections of a higher order, the effect of irregularities in the crystallites and of the heat motion of the molecules cannot be measured separately. Another doubtful question is whether the small angle interference maxima are to be interpreted as a measure of mean distances between the crystallites. To do this, Wallner has to resort to the assumption that the crystallites are unstable, whereas it is presumed, on the evidence of the mechanical properties of the high polymers, that a crystallite is stable and permanent. Hoffmann found 82 ± 7 per cent of crystalline material in polychlorotrifluoroethylene and Buckley, Cross, and Ray found as much as 95 per cent in polymethylene. Such high percentages make it doubtful whether the crystalline phase can be discontinuous at all. In this article any volume of material in which the molecules lie parallel is called a crystallite. The direction in which the molecules are oriented is termed the longitudinal direction of the crystallite. It is immaterial to the argument whether a crystallite consists of several crystallites, aligned in parallel separated by a small amount of amorphous material, or of a single crystallite containing large irregularities.

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