Vulcanization of Synthetic Rubbers

1951 ◽  
Vol 24 (3) ◽  
pp. 569-573 ◽  
Author(s):  
A. P. Pisarenko ◽  
P. A. Rebinder
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Plastic Flow ◽  
Point Of View ◽  
Degree Of Saturation ◽  
Spatial Structures ◽  
Practical Point ◽  
Synthetic Rubber ◽  
Physico Chemical ◽  
Vulcanization Process

Abstract Although for a century since the discovery of the vulcanization of rubber by sulfur many investigators have worked in this field, the problem of vulcanization can still not be considered to be well understood, either from the theoretical or the practical point of view. The basis of the most widely accepted theory of vulcanization of rubber is the concept of bridges, according to which the vulcanizing agent, sulfur, unites the macromolecules of rubber into spatial chains by primary valences. The concept that such spatial structures are formed during the vulcanization process explains well the decrease in the degree of saturation of the rubber and the changes in its physical properties, e.g., decreases in solubility and plastic flow, and considerable increases in strength, modulus, and resilience. A number of experimentally established facts, however, can never be reconciled with the bridge theory of vulcanization, especially when the vulcanization of synthetic rubbers is investigated. As a consequence of this, a number of investigators in this country have pointed out the shortcomings of the bridge theory and the necessity of finding a better explanation of the physico-chemical and colloidal reactions which take place during the vulcanization of rubber. More recently Dogadkin and his associates have shown that even when an accelerator is added, which leads to an increase of the bridge sulfur content of the vulcanizate, the total amount remains insignificant, e.g., in the case of natural rubber it amounts to only 7–10 per cent and, in the case of synthetic rubber, to 2–6 per cent of the total bound sulfur.

Two Methods of Protection against Oxygen and the Improvement Which Results from Their Combined Use. I. Observations on the Mechanism of Protection

1947 ◽  
Vol 20 (4) ◽  
pp. 949-961 ◽  
Author(s):  
Jean Le Bras
Keyword(s):  
Physical Properties ◽  
Single Case ◽  
Protective Action ◽  
Harmful Effect ◽  
Point Of View ◽  
Theoretical Conclusion ◽  
Free Oxygen ◽  
Practical Point ◽  
Combined Use ◽  
Rate Of Absorption

Abstract The observations which are recorded in the present paper represent an extension of the single case of litharge which has already been described. They show that, when small percentages of certain substances are added to rubber with a view to protecting the rubber from deterioration by oxygen, these substances are capable of directing the combination of oxygen with the rubber in different ways. This is shown by the fact that, as a result, a given percentage of combined oxygen does not lead to the same deterioration in physical properties. This difference in behavior can be explained logically on the basis of the antioxygenic theory by assuming that some agents act, not by retarding the rate of oxidation, but by deactivating the peroxides as soon as they are formed. By what term are these agents to be designated? First of all it should be recalled how an antioxygenic substance is defined. Every substance is an antioxygenic agent when it has the power, in small percentages, of retarding the rate of absorption of free oxygen by an autoxidizable substance. This definition obviously does not apply to a perfect deactivating agent, since the latter has no effect on the rate of absorption of oxygen, in spite of it too protecting rubber against deterioration by oxygen, and therefore being equally worthy, from the practical point of view, of being called an antioxygenic agent. However, this would only lead to confusion between the phenomenon itself and its effects. Furthermore, since commercial antioxygenic substances appear to show, to a greater or less degree, a combination of the two actions, one might consider designating them by some term which would embody both mechanisms. The word “antiaging agent” is not suitable, for it is too general and applies to cases where, in addition to oxygen, other influences such as light and repeated flexing play a part. There is, then, a problem in terminology to be settled, but this will have to be left unanswered provisionally until sufficient facts which have a more direct bearing on the case are available. Finally attention should be called to the useful effect which may be pictured as a possibility when the two types of protective agents which have been described act jointly. In other words, if the two mechanisms in question were to be superimposed, it would appear to be possible to improve considerably the resistance of rubber to deterioration by oxygen, since any oxygen which escapes the protective action of the true antioxygenic agent has its harmful effect reduced by the deactivating agent. To express it figuratively, it might be said that oxygen which has succeeded in overcoming the first obstacle opposing its action finds itself confronted with a new defense which puts the oxygen partially out of action. As shown by experiments carried out on this subject, which are described in the following paper of this series, this theoretical conclusion is actually borne out by the results of the experiments.

Statistical Lengths of Rubberlike Hydrocarbon Molecules

1943 ◽  
Vol 16 (3) ◽  
pp. 479-485
Author(s):  
Frederick T. Wall
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Chemical Properties ◽  
Hydrocarbon Chain ◽  
Point Of View ◽  
Double Bonds ◽  
Gutta Percha ◽  
Cis And Trans ◽  
Trans Structure ◽  
And Chemical Properties

Abstract It has been known for some time that the pure hydrocarbons of balata (or gutta-percha) and natural rubber have the same chemical composition and chemical properties. Both balata and rubber appear to be polymers of isoprene, (C5H8)n, with the same degree of unsaturation. Their physical properties are sufficiently different, however, to make it clear that their structures must differ in some important respect. Since the molecules contain numerous double bonds, it has been suggested that rubber and balata are geometric isomers. Every fourth bond in a rubber or balata molecule is a double bond, so it follows that the possibilities for geometric isomerism are considerable. It was proposed by Meyer and Mark that natural rubber hydrocarbon has a structure for which the molecular chain is cis with respect to all of the double bonds. Balata (or gutta-percha) is then supposed to have a trans-structure throughout, this view having been verified by Fuller and Bunn. It is the purpose of the present paper to consider, from the point of view of recent theories of rubber elasticity, to what extent these structures explain the differences in physical properties. The method to be employed involves calculation of the root mean square lengths of the cis- and trans-structures, which, when compared to their maximum lengths, should give an indication of their extensibilities. In 1932 Eyring treated the problem of the average square length of a hydrocarbon chain. In the present paper a different derivation of Eyring's equation is given (for illustrative purposes), after which this derivation will be extended to the rubberlike molecules with double bonds.

Reaction of Elemental Sulfur and Mercaptobenzothiazole

1956 ◽  
Vol 29 (4) ◽  
pp. 1369-1372
Author(s):  
G. A. Blokh ◽  
E. A. Golubkova ◽  
G. P. Miklukhin
Keyword(s):  
Elemental Sulfur ◽  
Active Form ◽  
Chemical Properties ◽  
Intermediate Compound ◽  
Point Of View ◽  
Experimental Fact ◽  
Acceleration Process ◽  
Physico Chemical ◽  
Lower Temperature ◽  
Vulcanization Process

Abstract One of the most important problems in the field of the physics and chemistry of rubber is that of vulcanization. Until now no single theory has been established, which elucidates the complex physico-chemical changes which occur during this process. Still more obscure has been the mechanism of the action of vulcanization accelerators, which, as is well known, not only reduce the time and the temperature of vulcanization, but also influence the physico-mechanical and chemical properties of the rubber. Most investigators have assumed that in the acceleration process a reaction with sulfur converts it to an active form which is capable of bringing about vulcanization at a lower temperature and at a greater rate, than with ordinary elemental sulfur in the absence of an accelerator. This point of view is based on the experimental fact that the vulcanization of rubber by sulfur dioxide and hydrogen sulfide, for example, which form sulfur in the nascent condition, proceeds rapidly even at room temperature. Investigators have also assumed that in the vulcanization process activation of sulfur in the presence of accelerators may occur by different mechanisms. It is possible that the accelerator, reacting with elemental sulfur, forms unstable intermediate compounds, which decompose with liberation of sulfur in an active form. The latter reacts with rubber, and the regenerated accelerator reacts again with elemental sulfur, etc. However, a different process is possible for the activation of elemental sulfur. By this second mechanism the unstable combination of accelerator and sulfur reacts directly with rubber without the formation of active sulfur. Both these mechanisms necessarily assume the formation of intermediate unstable combinations of the accelerator with sulfur. However, direct, experimentally-based demonstrations of such an interaction are lacking in the literature. There exist only theoretical hypotheses concerning the nature of the possible intermediate combination of the accelerator with sulfur. According to Ostromislensky's concepts, further developed by Bedford, such an intermediate compound has the character of a polysulfide. According to Bruni and Romani, this intermediate compound is a disulfide. As is well known, the disulfide theory was placed in doubt by Zaide and Petrov on the basis of data from the vulcanization of rubber in the presence of benzothiazolyl disulfide.

Polypropylene Oxide. IV. Preparation and Properties of Polyether Networks

1967 ◽  
Vol 40 (5) ◽  
pp. 1421-1425
Author(s):  
G. Allen ◽  
H. G. Crossley
Keyword(s):  
Energy Density ◽  
Natural Rubber ◽  
Physical Properties ◽  
Propylene Oxide ◽  
Cohesive Energy ◽  
Dynamic Properties ◽  
Point Of View ◽  
Polypropylene Oxide ◽  
Cohesive Energy Density

Abstract Stable vulcanizates of copolymers of propylene oxide and butadiene monoxide have been prepared and some physical properties studied. The cohesive energy density of a copolymer containing 84 per cent propylene oxide is determined from swelling measurements to be 83 cal cm−. The dynamic properties of the copolymer are similar to those of natural rubber. From a thermodynamic point of view the copolymer is more ideal in its rubbery behavior than natural rubber.

Tack in Rubber

1964 ◽  
Vol 37 (5) ◽  
pp. 1178-1189 ◽  
Author(s):  
O. K. F. Bussemaker
Keyword(s):  
Natural Rubber ◽  
Theoretical Approach ◽  
Point Of View ◽  
Rubber Industry ◽  
Highly Active ◽  
Synthetic Rubber ◽  
The Usa ◽  
The Subject ◽  
The Difference ◽  
Definition Of

Abstract The expressions tack, tackiness, and stickiness have been in use since the beginning of the rubber industry. During the years their meaning has changed considerably. The first occasion where tackiness was mentioned was in the case of crude natural rubber. The surface of the rubber became tacky or sticky during storage. This phenomenon has been thoroughly discussed in the literature. As a general conclusion it was accepted that both oxidation and depolymerisation occurred. Three factors were reported to be the cause of these processes: light, traces of copper, and manganese. From our point of view we would call this effect stickiness, as we are only interested in the building tack of rubber. In the period when the only rubber was natural rubber and high loadings of highly active fillers were not generally used in compounds, building tack was no problem. Building tack was first mentioned in a publication by Griffith and Jones in 1928. They started their experiments by measuring tack in their search for methods to prevent cotton liners from sticking to unvulcanized rubber. One would have expected much work on the measurement and improvement of tack in Germany and Russia during the development of synthetic rubbers. However, this only proved to be the case in Russia. The first publication available was the translation of an article by Voyutskii and Margolina in 1957. From Voyutskii's work we were able to trace the first article in 1935 by Zhukov and Talmud, who studied the adhesive power of synthetic rubber. In the USA the first theoretical approach to the subject was by Josefowitz and Mark in 1942, who at that time did not realize the difference between stickiness and tack. This difference became clear when lack of tack became the big problem in the use of synthetic rubber. In many cases it was found that addition of resins and softeners gave a very sticky compound which had no building tack at all. The tack problem was first discussed at the ASTM symposium on the application of synthetic rubbers in 1944 by Juve who gave a definition of building tack. From that time, the problem has been studied regularly, especially from the practical side, to find ways and means to improve the building tack of synthetic rubbers.

scholarly journals Pengaruh Konsentrasi Asam Sulfat (H2SO4) pada Hidrolisa Tongkol Jagung (Zea mays) Menjadi Nanokristal Selulosa sebagai Filler Penguat pada Produk Lateks Karet Alam

2019 ◽  
Vol 8 (2) ◽  
pp. 48-53
Author(s):  
Hamidah Harahap ◽  
Azwin Harfansah Nst ◽  
Ilhamdi Fujian Junaidi
Keyword(s):  
Sulfuric Acid ◽  
Natural Rubber ◽  
Physical Properties ◽  
Mechanical Test ◽  
Natural Rubber Latex ◽  
Spherical Shape ◽  
Rubber Latex ◽  
Hydrolysis Process ◽  
Cross Connect ◽  
Vulcanization Process

This research studied about the effect of concentrations sulfuric acid (H2SO4) on the hydrolysis process of corn cobs waste to manufacture of cellulose nanocrystal (NCC) which will be applied as fillers in natural rubber latex. This study began with a pre-vulcanization process of natural rubber latex at a temperature of 70 oC and followed by a vulcanization process at 110 oC for 10 minutes. The results of the testing of physical properties indicate that the higher amount of NCC loading will result in higher crosslinked denotes, while the results of testing the mechanical properties indicate that the maximum value is achieved at the loading of NCCs as much as 6 phr. The mechanical test results supported by the analysis of Scanning Electron Microscopy (SEM) showing the NCC have spread well. Characterization of the Transform Electron Microscope (TEM) shown  the resulting of NCC was spherical shape with the size of NCC produced for each concentration of sulfuric acid (H2SO4) 45%, 55%, and 65% respectively 57.65 nm; 28.43 nm; and 82.61 nm with an amount of each 0.849 g; 1,824 g; and 0.681 g. The mechanical and physical properties of the optimum natural rubber latex products occurred in the loading of nanocrystal cellulose with a number of 6 bsk, where the values ​​of cross-connect density, tensile strength, elongation at break, M200 and M300 were respectively 10.6234 2Mc-1x10- 5; 18.2 MPa; 780%; 2.23 MPa and 2.7 MPa.

Properties of Some Synthetic Rubbers

1943 ◽  
Vol 16 (4) ◽  
pp. 857-862
Author(s):  
L. B. Sebrell ◽  
R. P. Dinsmore
Keyword(s):  
Molecular Structure ◽  
Natural Rubber ◽  
Point Of View ◽  
General Point ◽  
Chain Molecules ◽  
X Ray ◽  
Synthetic Rubber ◽  
The Difference ◽  
Diffraction Patterns ◽  
Long Chain

Abstract X-RAY STRUCTURE OF SYNTHETIC RUBBER In presenting a series of x-ray diagrams of various types of synthetic rubber in comparison with natural rubber, in both the stretched and the unstretched condition, it is our purpose to bring out the fact that the molecular structure of synthetic rubbers is entirely different from that of natural rubber. It is proposed also to review briefly the theories which have been advanced, based on the x-ray analysis of rubber, to account for the elasticity of natural rubber, and to advance the possible reason for the difference shown by the x-ray diagrams of synthetic rubber. At the present time, from the most general point of view, the molecular structure of a rubberlike material is envisaged as a sort of brush-heap structure of entangled long chain molecules. x-Ray diffraction patterns show that, for some rubberlike materials, notable regularities of structure sometimes occur in the tangle of long-chain molecules. It is now realized that these regularities are not essential for rubberlike behavior. Nevertheless their observation and study is important because they afford a unique opportunity for studying the molecular structure of the chains and the molecular rearrangements which occur with the application of stress.

Film from Mixtures of Natural and Synthetic Rubber Latex. Physical Properties

1952 ◽  
Vol 25 (4) ◽  
pp. 983-994
Author(s):  
R. M. Pierson ◽  
R. J. Coleman ◽  
T. H. Rogers ◽  
D. W. Peabody ◽  
J. D. D'Ianni
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Natural Rubber Latex ◽  
Synthetic Polymers ◽  
Rubber Latex ◽  
Stress Strain ◽  
Synthetic Rubber ◽  
Mooney Viscosity ◽  
The One ◽  
Rubber Stock

Abstract When tested in a single standardized procedure for cast latex films, the type of synthetic-rubber latex employed in latex blends containing 70 per cent or more natural-rubber latex had little effect on the stress-strain properties of the mixture. Cold-rubber latexes imparted higher stress-strain values to blends with natural rubber than did the corresponding hot-rubber latexes. The improvement was particularly noted on comparison of tensile product values. Low-conversion synthetic polymers produced higher stress-strain properties than high-conversion polymers in blends with natural rubber, even though their tensile strengths in 100 per cent synthetic stocks were approximately equal. Optimum physical properties were obtained by use of blends with synthetic polymers of medium Mooney viscosity. It is believed that the appearance of an optimum Mooney viscosity is tied in with the necessity of having quite high molecular weight on the one hand, and, on the other, the ability of the particles to knit well, the latter in turn requiring a comparative freedom from tight gel. Tensile product values increased with increasing styrene content in the synthetic polymer, but, correspondingly, the low-temperature stiffening increased. The physical properties of a natural rubber stock are far superior to those of any of the synthetic-rubber latexes tested to date. Cold-rubber latexes now in production are an improvement over high-temperature latexes, for example, in wet gel strength but do not approach natural rubber latex in stress-strain properties.

The Effect of Silent Electric Discharges on Rubber Solutions

1940 ◽  
Vol 13 (4) ◽  
pp. 831-848 ◽  
Author(s):  
Lothar Hock ◽  
Heinrich Leber
Keyword(s):  
Natural Rubber ◽  
Softening Temperature ◽  
Point Of View ◽  
Electric Discharges ◽  
Technical Point ◽  
Soluble Polymers ◽  
Synthetic Rubber ◽  
Molecular Sizes ◽  
Technical Sense ◽  
Insoluble Polymers

Abstract The object of the investigation was to synthesize higher molecular compounds from natural rubber and from synthetic rubber by means of a process involving exposure to silent electric discharges. With both natural rubber and synthetic rubber, it was found possible to bring about polymerization by this method and to obtain polymers of various molecular sizes, which could be separated into two principal types: (1) polymers which remained soluble in benzene, and (2) polymers with a highly developed network structure, which were insoluble in benzene and therefore could be separated from the soluble polymers. After purification and drying, the insoluble polymers were obtained as inelastic, nonplastic products, in the form of soft, crumbly flakes. On the contrary, the soluble polymers retained the plasticity and elasticity of the original rubber, and behaved like raw rubber in the technical sense as well. This latter fact was proved by preparing a few mixtures and vulcanizates from these polymers, and it is noteworthy that a vulcanizate prepared from polymerized Buna-85 more nearly resembled a corresponding vulcanizate from untreated natural rubber than it did a vulcanizate prepared from the original, untreated Buna-85. Of course more extensive development work would be necessary to obtain polymers with particularly desirable properties from a technical point of view, and to find out how to compound these new polymers, e. g., what types and percentages of fillers, accelerators, and percentages of sulfur to use. Only in this way can the technical importance of these products be judged, and can any uses to which they may be applied to advantage be determined. But whatever may be their importance, the increased molecular sizes of these polymers of natural rubber and of Buna-85 are accompanied by marked increases in softening temperature without sacrifice of their technically important advantages of plasticity, tackiness and solubility. To this extent a not unimportant goal from the technical point of view may be regarded as having already been attained.

Specific Influences in the Polymerization of Dienes. Chemical Factors Influencing the Homogeneity of Synthetic Rubbers during Production

1945 ◽  
Vol 18 (2) ◽  
pp. 213-222
Author(s):  
William S. Penn
Keyword(s):  
Natural Rubber ◽  
Polymerization Process ◽  
Direct Result ◽  
Hydrogen Atoms ◽  
The Troubles ◽  
Synthetic Rubber ◽  
Factors Influencing ◽  
Fresh Material ◽  
Physico Chemical ◽  
Chemical Factors

Abstract At the present time, when so much synthetic rubber is being produced, the question of the polymerization of dienes is most important. Many thousands of tons of GR-S and related rubbers are being made by this means, and yet the process is only very imperfectly understood. Polymerization is still an uncontrolled reaction, although much work has been done in an attempt to overcome the deficiencies. The troubles are caused by the fact that the dienes do not polymerize in a regular way, because of the formation of branch chains and cross-linkages, which are a direct result of these branch chains. These irregularities must be controlled before satisfactory products can be obtained, and the present paper is written to correlate isolated evidence and present fresh material so that the processes involved during polymerization may be more perfectly understood and possibly controlled. It is natural in the first instance to examine natural rubber to see if any indication of the lines to follow can be obtained. Unfortunately, however, even natural rubber is not perfect, and from various sources of evidence it has been shown that branching does occur in the isoprene chains. This branching is, however, different from that in synthetics, and is quite regular. As will be seen shortly, it is difficult on chemical or physico-chemical grounds to see why this should be so, as the only directive group in the isoprene unit is the methyl side-group. It seems logical to conclude that natural rubber is not formed by a polymerization process, but that carbon and hydrogen atoms combine in such a way that they form directly a natural rubber-molecule.

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