Have Mechanical Stresses Any Effect on the Oxidizability of Rubber?

1949 ◽  
Vol 22 (3) ◽  
pp. 690-698
Author(s):  
Jean Le Bras ◽  
André Salvetti
Keyword(s):  
Tensile Strength ◽  
Infrared Absorption ◽  
Vibration Frequency ◽  
Molecular State ◽  
Mechanical Stresses ◽  
Point Of View ◽  
Negative Evidence ◽  
Linear Extensions ◽  
Vulcanized Rubber ◽  
Appreciable Increase

Abstract Subjection of rubber to mechanical stresses, whether static or dynamic, does not change its inherent oxidizability, at least within the limits of stress which were applied in the experiments described. Perhaps changes would have been observed if the range of stresses had been reached where crystallization phenomena became pronounced, for sufficient distortion or change in molecular state might have a certain influence on the oxidizability. For example, Williams and Dale, in a study of infrared absorption by rubber, pointed out that linear extensions greater than 400 per cent are necessary to bring about any appreciable increase in the vibration frequency of the C — C groups. However, the elongations employed in the present work cover, in general, the range of deformations to which vulcanized rubber products are normally subjected in service; hence there seemed to be no advantage in attempting to carry out the tests under more severe conditions. From another point of view, it would appear of interest to record the following observation. In all the oxidation tests under dynamic conditions, the test-specimens broke either by being cut through near the points where they were fastened, at random points where rupture began, or when the tensile strength was lowered too much by oxidation; but in no case was actual flexcracking observed. Although this is only negative evidence, the view of Eccher that ozone is indispensable to the formation of cracking would appear to be confirmed.

Resilient Energy

1943 ◽  
Vol 16 (3) ◽  
pp. 591-608
Author(s):  
E. C. B. Bott
Keyword(s):  
Tensile Strength ◽  
Finite Differences ◽  
Practical Method ◽  
Cross Sectional Area ◽  
Point Of View ◽  
Sectional Area ◽  
Cross Sectional ◽  
Vulcanized Rubber ◽  
Reinforcing Agent ◽  
Strength Based

Abstract 1. The tensile strength of vulcanized rubber may be expressed in terms of its elongation by means of the calculus of finite differences. 2. This expression for tensile strength, based on the theoretical cross-sectional area, gives an expression for the tensile strength based on the original cross-sectional area when the former quantity is divided by the factor (E + 1), E being the elongation. 3. The expression for tensile strength based on the original cross-sectional area is integrated with respect to the elongation to give the resilient energy. 4. The trapezoidal rule has proved itself to be superior to the calculus of finite differences as a practical method of obtaining the resilient energy. 5. The total resilient energies are plotted on graphs against the percentage by volume of reinforcing agent or filler. Tangents drawn at any desired point corresponding to a certain percentage of filler give values for the partial resilient energies of base mix and of filler by the method of tangent intercepts. 6. The expressions for tensile strength are composed of one, two or three functions ; the number of functions is, in general, inversely proportional to the percentage of the filler in the vulcanizate. 7. The expressions for tensile strength and for resilient energies have no significance regarding the structure of vulcanized rubber; they have been evolved from the point of view of usefulness for evaluating compounds. 8. The values of the partial resilient energies of base mix and of filler obtained by the method of tangent intercepts have no physical meaning; they are a means of calculating the total resilient energy of a sample of vulcanized rubber.

X-Ray Investigation of the Crystallization of Vulcanized Rubber on Stretching

1948 ◽  
Vol 21 (3) ◽  
pp. 621-626 ◽  
Author(s):  
B. V. Lukin ◽  
V. I. Kasatochkin
Keyword(s):  
Tensile Strength ◽  
Crystalline Phase ◽  
Oxidative Degradation ◽  
Point Of View ◽  
Crystal Formation ◽  
Stress Strain ◽  
X Ray ◽  
Vulcanized Rubber ◽  
Cross Links ◽  
Ray Methods

Abstract 1. x-Ray methods have been used to investigate the amount of crystalline phase in stretched samples as a function of the vulcanization time. 2. Curves relating the percentage of crystalline phase to the vulcanization time have sharply defined maxima. 3. A comparison of the curves relating tensile strength to vulcanization time with the curves of crystal formation shows their analogous character, the position of the maxima approximately corresponding to one and the same vulcanization time. 4. The position of the maxima on the curves of crystal formation is not related to the degree of stretching. 5. The effect of accelerators is to shift the maximum on the curve of crystal formation to the region of short vulcanization times and to increase the percentage of crystalline phase. 6. The curves of crystal formation and of tensile strength, and thus the behavior of the stress-strain curves for various vulcanization times, is interpreted from the point of view of the existence of two processes—the process of forming a network of cross-links by the interaction of rubber with sulfur, and the process of oxidative degradation of the rubber.

Tensile Tests of Vulcanized Rubber at High Speed

1931 ◽  
Vol 4 (2) ◽  
pp. 147-155 ◽  
Author(s):  
A. van Rossem ◽  
H. B. Beverdam
Keyword(s):  
Tensile Strength ◽  
High Speed ◽  
Strain Curve ◽  
Tensile Tests ◽  
Point Of View ◽  
General Tendency ◽  
Technical Literature ◽  
Rubber Ring ◽  
Vulcanized Rubber ◽  
Increase With Increase

Abstract The types of apparatus most frequently used for elongation tests of rubber have only a slow speed. Thus the maximum rate of elongation of the Schopper dynamometer is 120 cm. per minute and in ordinary practice 60 cm. per minute is the speed used. The normal rate ordinarily used in America with the Scott apparatus is 20 in. per minute. On the other hand, it has been found by experience that slightly vulcanized rubber which, on the Schopper machine, gives very good values of tensile strength and resilient energy at rupture, even excellent values, is on the contrary brittle when stretched very rapidly by hand and breaks with a very low elongation. Consequently it is of interest, chiefly from the point of view of a study of rubber, to carry out elongation tests at high speed. As is easily seen from the technical literature, this problem has been neglected. At the Bureau of Standards the influence of the rate of elongation on the results of tensile tests has already been studied, but the rate varied only between five and forty-five inches per minute. Briefly, the results of this study seem to indicate a general tendency for the elongation and resistance to extension to increase with increase in speed of elongation. Hauser and Rosbaud have also made tests on the influence of the speed of elongation, but their tests were on raw rubber and at extremely slow speeds. As for the brittleness which appears at high rates of elongation, only very casual references are to be found in the literature. By a study of gas black Park has proved that the maximum physical properties found by hand-testing do not agree with the maximum obtained with the Scott dynamometer. Recently Wright5 has also pointed out the “shortness” of vulcanized rubber and has emphasized the importance of tensile tests at high speed. Unfortunately, we did not have at our disposal any apparatus which permitted recording the stress-strain curve at high speed and reading the ultimate elongation and tensile strength. Accordingly, we used in our tests a Charpy ram pendulum, belonging to the section of metallography of the Polytechnical School of Delft. It is known that this apparatus as well as others similar to it are used in determining the energy necessary to rupture various materials. This apparatus was changed and on the two supporting surfaces were attached two pins in such a way that a rubber ring could be placed there without elongation as seen in Fig. 1. This ring was then broken with the ram pendulum. The greater the energy expended in breaking the ring, the less the pendulum rises. As is known, the energy expended in breaking the ring is calculated by the aid of a numerical table by comparison with an oscillation without rupture of the ring. For each type of vulcanizate, at least six rings were tested by this pendulum method. In addition some rings from the same vulcanizates were given the usual tensile test on the Schopper dynamometer. From the resulting curve the energy of rupture can be determined in kilograms in the usual manner by the aid of a planimeter.

Sulfur Linkage in Vulcanized Rubber. Reaction of Methyl Iodide with Sulfur Compounds

1949 ◽  
Vol 22 (1) ◽  
pp. 1-7
Author(s):  
M. L. Selker
Keyword(s):  
Methyl Iodide ◽  
Room Temperature ◽  
Sulfur Compounds ◽  
Point Of View ◽  
Secondary Reaction ◽  
Reaction Products ◽  
Sulfide Sulfur ◽  
Vulcanized Rubber ◽  
Allyl Sulfide

Abstract The work described here is an extension of the study of the reaction of methyl iodide with sulfur compounds originally begun with the purpose of using such data in determining the sulfur linkage in vulcanized rubber. A previous paper dealt with the reactions of methyl iodide with propanethiol, propyl sulfide, propyl disulfide, allyl sulfide, and thiophene. This article adds to the list, n-butyl methallyl sulfide, allyl disulfide, allyl tetrasulfide, n-propyl tetrasulfide, and trithiane. The removal of combined sulfur from vulcanized rubber as trimethylsulfonium iodide on treatment with methyl iodide at room temperature was persuasive evidence of the presence of sulfide sulfur linked to allylic type residues. The evidence offered, however, did not constitute exclusive proof because it was not known whether still other types of sulfur linkage would also yield trimethylsulfonium iodide. To shed more light on this question, the sulfur linkages most likely to occur in vulcanizates—the allyl-alkyl monosulfide, diallyl and dialkyl di- and polysulfide—were investigated. The trithiane reaction is of interest mostly from the point of view of the reaction of overcured stocks or secondary reaction products stemming from the original polysulfides. The reactions were carried out using the method described in a previous paper.

Mechanochemical Devulcanization of Vulcanized Gum Natural Rubber

2005 ◽  
Vol 21 (3) ◽  
pp. 183-199
Author(s):  
G.K. Jana ◽  
C.K. Das
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Natural Rubber ◽  
Three Dimensional ◽  
Elongation At Break ◽  
Tear Strength ◽  
Vulcanized Rubber ◽  
Dimensional Network ◽  
Polymeric Chains ◽  
Cure Time

De-vulcanization of vulcanized elastomers represents a great challenge because of their three-dimensional network structure. Sulfur-cured gum natural rubbers containing three different sulfur/accelerator ratios were de-vulcanized by thio-acids. The process was carried out at 90 °C for 10 minutes in an open two-roll cracker-cum-mixing mill. Two concentrations of de-vulcanizing agent were tried in order to study the cleavage of the sulfidic bonds. The mechanical properties of the re-vulcanized rubber (like tensile strength, modulus, tear strength and elongation at break) were improved with increasing concentrations of de-vulcanizing agent, because the crosslink density increased. A decrease in scorch time and in optimum cure time and an increase in the state of cure were observed when vulcanized rubber was treated with high amounts of de-vulcanizing agent. The temperature of onset of degradation was also increased with increasing concentration of thio-acid. DMA analysis revealed that the storage modulus increased on re-vulcanization. From IR spectroscopy it was observed that oxidation of the main polymeric chains did not occur at the time of high temperature milling. Over 80% retention of the original mechanical properties (like tensile strength, modulus, tear strength and elongation at break) of the vulcanized natural rubber was achieved by this mechanochemical process.

Devulcanization of Automobile Scrap Tyres by a Mechanochemical Process

2005 ◽  
Vol 21 (4) ◽  
pp. 319-331 ◽  
Author(s):  
G.K. Jana ◽  
C.K. Das
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Chemical Process ◽  
Crosslink Density ◽  
Diallyl Disulfide ◽  
Density Data ◽  
Vulcanized Rubber ◽  
Rubber Waste ◽  
Mechanical Shearing ◽  
Vulcanization Process

The de-vulcanization of rubber waste poses a challenging economical, environmental and social problem. We propose a new de-vulcanization process to re-use the rubber waste. It is a mechano-chemical process (MCP), where the waste is de-vulcanized by a combination of mechanical shearing, heat (110 °C) and the use of a de-vulcanizing agent (diallyl disulfide). A new look at the de-vulcanization mechanism and the influence of the de-vulcanizing agent on the mechanical properties of the ultimate re-vulcanized rubber is also presented. One of the most interesting observations is that the retention of tensile strength of the re-vulcanized rubber with respect to the original tyre was 34.9% when de-vulcanized in the absence of diallyl disulfide and 72.4% in its presence. The formation of extra crosslinks in those re-vulcanized rubbers containing disulfide was confirmed from crosslink density data and from TGA results. DMA analysis revealed that the storage modulus also increased for re-vulcanized rubber containing the disulfide.

The Effect of Thermal Aging on Mechanical Properties and Morphological Properties of Thermoplastic Vulcanizates Based on Natural Rubber and Polystyrene

2020 ◽  
Vol 990 ◽  
pp. 262-266
Author(s):  
Prathumrat Nu-Yang ◽  
Atiwat Wiriya-Amornchai ◽  
Jaehoon Yoon ◽  
Chainat Saechau ◽  
Poom Rattanamusik
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Impact Strength ◽  
Natural Rubber ◽  
Thermal Aging ◽  
Morphological Properties ◽  
Vulcanized Rubber ◽  
Thermoplastic Vulcanizates ◽  
Internal Mixer ◽  
Processing Properties

Thermoplastic vulcanizates or TPVs is a type of materials exhibiting excellent properties between thermoplastic and elastomer by combining the characteristics of vulcanized rubber with the processing properties of thermoplastics. This research aims to study the effect of thermal aging on the morphology and mechanical properties of thermoplastic vulcanizates (TPVs) based on a mixture of natural rubber (NR) and polystyrene (PS). TPVs samples were prepared using the internal mixer at a mass ratio of NR/PS 70/30, 50/50, 30/70 and 0/100. Tensile properties and impact strength showed that when the amount of NR increased tends of impact strength and elongation at break increased but tends of tensile strength decreased. On the other hand, tends of tensile strength for thermal aging at 70°C for 3 days increased when the amount of PS increase. The blending ratio of NR / PS at 70/30 is the best. It gave a worthy increase from 19.94 MPa to be 25.56 MPa (28.18%).

The Effect of Softeners in Rubber

1953 ◽  
Vol 26 (1) ◽  
pp. 152-155
Author(s):  
Ira Williams
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
High Modulus ◽  
Mineral Oils ◽  
Cohesive Forces ◽  
Commercial Use ◽  
Effect Of Solvents ◽  
Vulcanized Rubber ◽  
Unfavorable Effect ◽  
The Cost

Abstract The use of oils and liquid softeners to assist in the mastication and processing of rubber or to produce softer vulcanized stocks has been standard practice since the early commercial use of rubber. More recently certain synthetic rubbers, polymerized under special conditions, have been treated with rather large amounts of mineral oils, with a resulting decrease in the cost of the rubber and apparently with no unfavorable effect on the rubber in most instances. A number of investigators have reported the effect of swelling agents on the properties of vulcanized rubber. Busse discusses the effect of solvents in a general way. Tiltman and Porritt conclude that the decrease in modulus caused by swelling in benzene is caused by a “loosening of cohesive forces.” Tire treads of natural rubber containing such softeners as pine tar and mineral rubber decrease in wear resistance in proportion to the softener content. Well vulcanized rubber of high modulus is most resistant to swelling in oils. Naunton, Jones, and Smith find that unaccelerated stocks lose the most tensile strength after being swollen, that milling of the raw rubber increases swelling, and that the presence of softeners in the rubber during vulcanization reduces the oil resistance. A limited amount of swelling has been reported to have little effect on the tensile strength of vulcanized natural rubber. Bourbon points out that separating the rubber molecules with solvent decreases the rate of vulcanization.

Analysis of the Dynamic Response of a Controlled Detonation Chamber

2010 ◽  
Author(s):  
B. Simoens ◽  
M. H. Lefebvre ◽  
J. K. Asahina ◽  
F. Minami ◽  
R. E. Nickell
Keyword(s):  
Vibration Frequency ◽  
Explosive Charge ◽  
Cylindrical Vessel ◽  
Point Of View ◽  
Scale Model ◽  
Cylindrical Charge ◽  
Strain Gages ◽  
Spherical Charge ◽  
Wide Range ◽  
Predicted Values

Detonation chambers (either mobile or fixed) are used worldwide for a wide range of applications. At present, a 1/7 scale model of a 1 ton detonation chamber is available for extended testing in Belgium. The chamber is a single wall cylindrical vessel with semi-elliptical ends. Each time an explosive charge is fired in the vessel, that vessel is submitted to a number of deformation cycles. A series of strain gages measure the deformation of the vessel walls. Experimental peak strains and vibration frequency can be compared to predicted values based on simple formulas. Measured values are reasonably close to the estimated values. The influence of the shape of the charge is studied. The shape has an important influence on the chamber response. For a fixed charge mass, a spherical charge causes less deformation than a cylindrical charge and is therefore advantageous from a fatigue point of view.

Specific Heat of Strained Rubber

1939 ◽  
Vol 12 (4) ◽  
pp. 794-798 ◽  
Author(s):  
Charles G. Boissonnas
Keyword(s):  
Specific Heat ◽  
Room Temperature ◽  
Molecular State ◽  
Strong Variation ◽  
Temperature Changes ◽  
Vulcanized Rubber ◽  
Two Samples ◽  
The Subject

Abstract The specific heat of unstrained rubber as a function of temperature has been the subject of many investigations; but only one set of data has been published on the specific heat of strained rubber. (Ornstein, Wouda and Eymers, Proc. Acad. Sci. Amsterdam, 33, 273 1930). Ornstein and his coworkers heated samples of strained vulcanized rubber to 80° C and dropped them into a calorimeter at room temperature. The results they obtained are presented in Figure 1, where the specific heat of one gram of rubber is plotted against extension: As Figure 1 shows, the specific heat diminishes to about two-thirds of its original value when the extension is increased from 0 to 100 per cent (Δl=1); it increases again on further extension. According to Ornstein et al., “the form of the curve for the specific heat is most interesting, as the strong variation of this quantity with the elongation must be of utmost importance for the understanding of the molecular state of rubber.” In order to check these results by another method, the writer measured the specific heat of rubber at room temperature (19° to 21° C) by a process involving temperature changes of less than 0.1° C. Two samples of rubber were chosen. Sample I was highly vulcanized for 30 minutes under 3 atmospheres' pressure. Its composition was as follows:

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