Chemical Structure of VULCANIZED RUBBER

1938 ◽  
Vol 30 (11) ◽  
pp. 1291-1295 ◽  
Author(s):  
J. R. Brown ◽  
E. A. Hauser
Keyword(s):  
Chemical Structure ◽  
Vulcanized Rubber

The Chemical Structure Responsible for the Deactivating Effect of Compounds Which Protect Rubber from Deterioration by Oxygen

1951 ◽  
Vol 24 (3) ◽  
pp. 638-639
Author(s):  
Jean Le Bras ◽  
Jacques Le Foll
Keyword(s):  
Nitrogen Atom ◽  
Systematic Study ◽  
Chemical Structure ◽  
Thiol Group ◽  
Vulcanized Rubber ◽  
Thiol Form

Abstract One of the present authors has already offered evidence which indicates the existence of a deactivating effect, whereby vulcanized rubber is protected against deterioration by oxygen. This effect is evident with such compounds as mercaptobenzimidazole (I), mercaptobenzoxazole, and ethylene-bis (N,N′-phenylthiourea) (II), and the phenomenon seems to be connected in some way with the presence in the molecule of a thiol group united to a nitrogen atom under such conditions that the possible tautomerism between the thion and thiol forms (III) is probably displaced toward the thiol form. We have completed these earlier experiments by a more systematic study, which has included an examination of the influence of cyclization, the nature of the ring, and hetero atoms.

Chemical Structure of Vulcanized Rubber

1939 ◽  
Vol 12 (1) ◽  
pp. 43-55
Author(s):  
J. R. Brown ◽  
E. A. Hauser
Keyword(s):  
Chemical Structure ◽  
Empirical Knowledge ◽  
Extensive Investigation ◽  
Practical Application ◽  
True Nature ◽  
Rubber Industry ◽  
Vulcanized Rubber ◽  
Metallic Salts ◽  
Other Substances

Abstract A CENTURY ago, Charles Goodyear in America and Th. Hancock in England found that the properties of crude rubber could be greatly improved by heating it with sulfur. The product resulting was more elastic, more resistant to tear and abrasion, less affected by solvents, and decidedly less thermoplastic. The treatment of rubber to give these desired properties is known generally as vulcanization and must be considered as the basis for the enormous growth of the rubber industry and the extensive use of rubber products in our everyday life. Broadly speaking, vulcanization involves the reaction, in some fashion, of sulfur with rubber. Extensive investigation has revealed other substances, such as benzoyl peroxide or polynitrobenzenes, which can transform rubber into a “vulcanized” condition. Experience has also shown that metallic salts of zinc or lead and especially certain organic compounds called “accelerators” greatly affect the rate of vulcanization, and these are favorably employed in practice. A vast amount of empirical knowledge has been gained which has greatly improved the practical application of vulcanization and the quality of rubber products, but which has failed as yet to reveal a complete picture of the true nature of the process.

Studies of the Vulcanization of Rubber

1952 ◽  
Vol 25 (2) ◽  
pp. 209-229 ◽  
Author(s):  
Shu Kambara ◽  
Kumakazu Ohkita
Keyword(s):  
Organic Compounds ◽  
Chemical Structure ◽  
Room Temperature ◽  
Great Influence ◽  
Cross Linking ◽  
Oxidizing Agent ◽  
Vulcanized Rubber ◽  
Cross Linkage ◽  
Bridge Type ◽  
The Difference

Abstract In this study much information about the method of distinguishing the state in which sulfur is combined in simple organic compounds consisting of carbon, hydrogen, and sulfur was obtained, and a new theory of vulcanization was postulated as a result of its application to vulcanized rubber. When activated sulfur reacts with rubber, it first adds to the double bonds, forming thioketones, which in turn, as a characteristic of these radicals, combine with each other, with the formation of a thioether structure. This transformation of thioketone into thioether takes place, not only during vulcanization, but also gradually after vulcanization. Because of the presence of thioketone, treatment of vulcanized rubber with hydrazine, forms a new network, that is, a ketoazine cross-linkage. Combined sulfur of the thioketone type was determined by an oxidizing agent, and as the difference of this value and total combined sulfur a method of determining bridge type of combined sulfur has been proposed. By this method, it was found that, even in ebonite, about one-third of the combined sulfur is the thioketone type, and that the bridge type is only about two-thirds of the total. The thioketone type of combined sulfur in soft vulcanized rubber is transformed gradually into the thioether type of cross-linkage when allowed to stand at room temperature, and this transformation is accelerated when the temperature is raised. In the case of hard rubber, this phenomenon is also observable, but the rate of this transformation is much slower compared to the former. This tendency is the same in the case of ketoazine cross-linking when rubber vulcanizates are treated with hydrazine. From these facts, it seems that the distribution of the thioketone radicals is not uniform, and the magnitude of the probability for collision of these radicals to form cross-linkages has a great influence on the properties of rubber after vulcanization. That is, the property of the vulcanizate is greatly affected by the fact whether the thioketone radicals in the vulcanizates are comparatively uniformly distributed or whether they exist in sectional groups or in colonies. The authors are the first to advance this postulate concerning the chemical structure of vulcanized rubber and its transformation. We believe that when the study is extended, using this postulation, problems such as aging and the differences in the properties of vulcanized rubber accelerated with various accelerators will become clear. Moreover, we believe that it will be of interest to physicists studying rubber elasticity to suggest this idea of colony of cross-linkages. We are now carrying on researches on these problems, and we shall report on them later.

Heat Treatment of Vulcanized Rubber

1933 ◽  
Vol 6 (2) ◽  
pp. 225-231
Author(s):  
Takeo Fujiwara ◽  
Toshio Namiki
Keyword(s):  
Chemical Structure ◽  
Chloroform Extract ◽  
Rapid Decrease ◽  
Acetone Extract ◽  
Maximum Point ◽  
Total Sulfur ◽  
Vulcanized Rubber ◽  
Experimental Findings ◽  
Maximum Content ◽  
Control Samples

Abstract By heating samples of a rubber—sulfur system at 160° C., the following results in relation to the time of heating were obtained: 1. The maximum acetone extract was obtained after 0.5–1 hour of heating, and the amount decreased rapidly thereafter with increase in the time of heating until it became equal to or less than that of the control samples. 2. The maximum chloroform extract was obtained after 0.5 hour of heating, beyond which the amount decreased rapidly until it was less than that of the control samples. 3. The amount of total sulfur decreased, and this tendency to decrease is to be attributed to three factors. 4. There was also a rapid decrease in free sulfur. 5. The maximum combined sulfur content was reached after a certain time of heating, beyond which it decreased. The maximum point was reached after the acetone and chloroform extracts had reached their maximum values. 6. The maximum content of resinous substance was also obtained after a certain time. 7. The weights of the samples increased during the heating, and this increase was greater in over-vulcanized samples. A general discussion of these experimental findings leads to the conclusion that the processes of aging and reclaiming of rubber may both be attributed to a change in the chemical structure of the rubber molecules produced by heat in the presence of sulfur and oxygen. This investigation is an outcome of our work on reclaimed rubber. Thanks are due to Prof. Y. Tanaka for his kindly advice.

A Study of the Mechanism of the Deactivation Effect

1954 ◽  
Vol 27 (1) ◽  
pp. 157-164 ◽  
Author(s):  
Jacques Le Foll
Keyword(s):  
Chemical Structure ◽  
A Priori ◽  
Natural Aging ◽  
Chain Scission ◽  
Nitro Compounds ◽  
Active Part ◽  
Relaxation Phenomena ◽  
Chain Molecules ◽  
Vulcanized Rubber ◽  
The Subject

Abstract The only method by which significant differences between the effects of antioxygenic agents and deactivating agents can be detected has been found to be a study of relaxation phenomena. An investigation by this method has also furnished further support to the theories of Tobolsky and his coworkers. The changes which take place during aging in the physical properties of vulcanized rubber are the result of two independent phenomena which occur simultaneously: (1) chain scission, and (2) formation of intermolecular bonds. As far as the aging of vulcanizates of natural rubber under normal conditions, e.g., socalled natural aging, is concerned, the chief phenomenon involved is scission of the chain molecules. In principle, therefore, there are two methods for combatting the deterioration of rubber on aging: (1) to impede chain scission by obstructing the fixation of oxygen, and (2) to promote the progressive formation of intermolecular bonds which compensate for the effects of the scission process. The first of these processes is that in which antioxygenic agents play the active part; in the second process, deactivating agents play the active part. From this viewpoint, deactivating agents play a part analogous to that of accelerators, and they may be regarded as representing a special type of acceleration. This theory makes possible a better understanding of a number of facts which, a priori, seem surprising: (1) the relationships of both chemical structure and mode of action of accelerators and deactivating agents, and (2) the protective effect of litharge, peroxides, and nitro compounds, all of which are vulcanizing agents. With respect to the intimate mechanism of the deactivating effect, one question remains unanswered, viz., how are intermolecular bonds formed under the influence of deactivating agents? This question recalls the question of the function of vulcanization accelerators, which has been the subject of many investigations, but which still remains a mystery.

The strength of highly elastic materials

1967 ◽  
Vol 300 (1460) ◽  
pp. 108-119 ◽  
Keyword(s):  
Chemical Structure ◽  
Unit Area ◽  
Strength Properties ◽  
Polymer Chains ◽  
Chemical Bonds ◽  
Elastic Materials ◽  
Chemical Corrosion ◽  
Vulcanized Rubber ◽  
Theory And Experiment ◽  
Highly Elastic Materials

Under repeated stressing, cracks in a specimen of vulcanized rubber may propagate and lead to failure. It has been found, however, that below a critical severity of strain no propagation occurs in the absence of chemical corrosion. This severity defines a fatigue limit for repeated stressing below which the life can be virtually indefinite. It can be expressed as the energy per unit area required to produce new surface ( T 0 ), and is about 5 x 10 4 erg/cm 2 . In contrast with gross strength properties such as tear and tensile strength, T 0 does not correlate with the viscoelastic behaviour of the material and varies only relatively slightly with chemical structure. It is shown that T 0 can be calculated approximately by considering the energy required to rupture the polymer chains lying across the path of the crack. This energy is calculated from the strengths of the chemical bonds, secondary forces being ignored. Theory and experiment agree within a factor of 2. Reasons why T 0 and the gross strength properties are influenced by different aspects of the structure of the material are discussed.

The Mechanism of the Deactivating Effect

1957 ◽  
Vol 30 (4) ◽  
pp. 1166-1167
Author(s):  
Jeanle Bras ◽  
Jean Claude Danjard
Keyword(s):  
Test Piece ◽  
Chemical Structure ◽  
Relaxation Method ◽  
Chain Scission ◽  
Initial Structure ◽  
Vulcanized Rubber ◽  
Rubber Compounds ◽  
Relaxation Measurements ◽  
Aging Properties ◽  
Continuous Relaxation

Abstract It was shown by one of us that certain substances, called deactivates, can protect vulcanized rubber against aging by a process which is different from that of antioxidants. The proposed mechanism involved a deactivation of the primary peroxides by transforming them into oxides of rubber without causing any chain scission. This hypothesis, however, did not appear to be completely satisfactory. In fact, deactivators do not protect raw rubber against oxidation, but actually accelerate its degradation in solution, especially in the presence of a peroxide which enhances this deterioration. Moreover, if was shown that the deactivators possess a chemical structure which is very similar to that of certain vulcanization accelerators, and also that they have an effect on the vulcanization. This had led to the suggestion that their effect could be attributed to the initial structure of the vulcanized rubber. We have considered the possibility of obtaining some useful information on this subject by means of stress relaxation measurements which involve the decrease in tensile strength with time of a stretched test piece. The measurements were carried out either by maintaining the test piece at constant elongation (continuous relaxation), or by stretching the relaxed sample to a constant elongation from time to time (discontinuous relaxation). It has been established that the continuous relaxation method accounts solely for the chain scissions which are produced in the vulcanized rubber network, whereas the intermolecular linkages formed during the tests contribute to the discontinuous relaxation picture. The results of some preliminary experiments we have carried out are given in Figure 1. Two rubber compounds, accelerated with diphenylguanidine and mercaptobenzothiazole, respectively, and known to have quite different aging properties, were employed. Vulcanizates containing either an antioxidant A (phenyl-2-naphthylamine) or a deactivator D (zinc mercaptobenzimidazolate) were compared with the control vulcanizates T.

Inelastic Electron-Matter Interactions

1978 ◽  
Vol 36 (3) ◽  
pp. 259-267
Author(s):  
J. Silcox
Keyword(s):  
Electron Microscope ◽  
Energy Loss ◽  
Chemical Structure ◽  
Inelastic Electron ◽  
Primary Concern ◽  
Unique Probe ◽  
Introductory Paper ◽  
Elastic Processes ◽  
Experimental Level ◽  
Inelastic Processes

In this introductory paper, my primary concern will be in identifying and outlining the various types of inelastic processes resulting from the interaction of electrons with matter. Elastic processes are understood reasonably well at the present experimental level and can be regarded as giving information on spatial arrangements. We need not consider them here. Inelastic processes do contain information of considerable value which reflect the electronic and chemical structure of the sample. In combination with the spatial resolution of the electron microscope, a unique probe of materials is finally emerging (Hillier 1943, Watanabe 1955, Castaing and Henri 1962, Crewe 1966, Wittry, Ferrier and Cosslett 1969, Isaacson and Johnson 1975, Egerton, Rossouw and Whelan 1976, Kokubo and Iwatsuki 1976, Colliex, Cosslett, Leapman and Trebbia 1977). We first review some scattering terminology by way of background and to identify some of the more interesting and significant features of energy loss electrons and then go on to discuss examples of studies of the type of phenomena encountered. Finally we will comment on some of the experimental factors encountered.

Chemical structure of diamond-like carbon thin films

1990 ◽  
Vol 48 (4) ◽  
pp. 710-711
Author(s):  
N.-H. Cho ◽  
K.M. Krishnan ◽  
D.B. Bogy
Keyword(s):  
Electrical Resistivity ◽  
Chemical Structure ◽  
Diamond Like Carbon ◽  
Chemical Structures ◽  
Sputtering Power ◽  
Data Aquisition ◽  
Equilibrium Phases ◽  
Electron Energy Loss ◽  
Power Densities ◽  
Preparation Techniques

Diamond-like carbon (DLC) films have attracted much attention due to their useful properties and applications. These properties are quite variable depending on film preparation techniques and conditions, DLC is a metastable state formed from highly non-equilibrium phases during the condensation of ionized particles. The nature of the films is therefore strongly dependent on their particular chemical structures. In this study, electron energy loss spectroscopy (EELS) was used to investigate how the chemical bonding configurations of DLC films vary as a function of sputtering power densities. The electrical resistivity of the films was determined, and related to their chemical structure.DLC films with a thickness of about 300Å were prepared at 0.1, 1.1, 2.1, and 10.0 watts/cm2, respectively, on NaCl substrates by d.c. magnetron sputtering. EEL spectra were obtained from diamond, graphite, and the films using a JEOL 200 CX electron microscope operating at 200 kV. A Gatan parallel EEL spectrometer and a Kevex data aquisition system were used to analyze the energy distribution of transmitted electrons. The electrical resistivity of the films was measured by the four point probe method.

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