Properties of Ebonite. XXXVII. Electrical Properties of Synthetic Rubber Ebonites

1949 ◽  
Vol 22 (4) ◽  
pp. 1084-1091
Author(s):  
D. G. Fisher ◽  
L. Mullins ◽  
J. R. Scott
Keyword(s):  
Natural Rubber ◽  
Power Factor ◽  
Power Loss ◽  
Ionic Conduction ◽  
Effect Of Temperature ◽  
Plastic Yield ◽  
Styrene Copolymers ◽  
Synthetic Rubber ◽  
High Dielectric ◽  
Butadiene Styrene

Abstract Experiments were carried out to explore the possibility of making good electrical ebonites from various types of synthetic rubber. The ebonites produced were tested for permittivity and power factor over wide ranges of temperature and frequency. Thioplasts (Thiokols AZ and FA) apparently do not produce hard ebonitelike vulcanizates by the normal procedure. Neoprenes (GN and I) give ebonites, but with such high dielectric power loss as to be unsuitable for use as high-frequency dielectrics; moreover, if the mix contains zinc oxide, the ebonite has a very hygroscopic and therefore electrically unsatisfactory surface. Butadiene copolymers containing polar groups (butadiene-acrylonitrile types and Thiokol RD) give ebonites with high power loss, hence are not suitable for making high-grade electrical ebonites. Polybutadiene (Buna-85) and butadiene-styrene copolymers (GR-S, Hycar-EP, Buna-S) are much nearer to natural rubber as far as the radio-frequency (100 to 2,500 kc. per sec.) power loss of their ebonites is concerned. The GR-S ebonite examined was not so good as natural rubber at room temperature, but was superior above about 50° C. Buna-85 and Hycar-EP were superior to natural rubber over the whole temperature range; indeed, the high-styrene copolymers, as represented by Hycar-EP and Buna-SS, appear to be the best type of synthetic rubber for making ebonite with low power loss, especially at high frequencies and temperatures. The effects of changing temperature and frequency on permittivity and power factor are discussed. Attention is drawn to the big effect of temperature on power factor; this was less with polybutadiene and butadiene-styrene ebonites than with natural rubber ebonite, in keeping with the greater heat resistance of the former as judged by plastic yield tests. Comparison of the effects of rising temperature and decreasing frequency shows that these produce broadly similar effects on power factor, as would be expected on theoretical grounds, but that rising temperature superposes a second effect (an increase), presumably due to increased ionic conduction.

The Thermal Vulcanization of Synthetic Rubber

1958 ◽  
Vol 31 (1) ◽  
pp. 132-146 ◽  
Author(s):  
H. Luttropp
Keyword(s):  
Thermal Treatment ◽  
Natural Rubber ◽  
Dynamic Stress ◽  
Effect Of Temperature ◽  
Synthetic Rubber ◽  
Aging Phenomena ◽  
Lower Tensile Strength ◽  
Soft Rubber ◽  
Acrylonitrile Copolymers ◽  
Butadiene Styrene

Abstract It is shown that synthetic rubbers, in contrast to natural rubber, can be vulcanized to soft rubber by a simple thermal treatment without any previous admixture of sulfur or accelerators. This process has been designated as “Thermovulcanization” to distinguish it from the regular vulcanization procedure under heat with the addition of sulfur and accelerators. Various synthetic rubbers of Schkopau production have been investigated for their behavior in the process of thermovulcanization. Both butadiene-styrene and butadiene-acrylonitrile copolymers as well as the butadiene block polymerizate lend themselves to vulcanization by this thermal treatment. For the butadiene-styrene copolymer with higher styrene content, thermovulcanization leads to products which are not equivalent to the regular sulfur-accelerator vulcanizates. Natural rubber cannot be vulcanized to soft rubber by thermovulcanization. The investigation of the effect of temperature revealed that a temperature of 195° C, for example, was applicable for all the synthetic rubbers studied. The addition of active carbon was found to accelerate the thermovulcanization process and certain properties of the vulcanizates are improved. The results of some comparative studies are presented, and it is pointed out that thermovulcanizates and normal vulcanizates show agreement in some of their properties and vary in others. The thermovulcanizates, as compared with normal vulcanizates, show somewhat lower tensile strength and somewhat lower fatigue resistance. Also their resistance to swelling is lower. On the other hand they are better in abrasion, have somewhat improved elastic properties, and show improved resistance to aging including surface aging phenomena under static and dynamic stress.

Low-Temperature Behavior of Butadiene-Styrene Copolymers. Effect of Compounding Variables

1950 ◽  
Vol 23 (4) ◽  
pp. 760-769
Author(s):  
R. D. Juve ◽  
J. W. Marsh
Keyword(s):  
Low Temperature ◽  
Natural Rubber ◽  
Compression Set ◽  
Similar Work ◽  
Styrene Copolymers ◽  
Synthetic Rubber ◽  
Low Temperature Flexibility ◽  
Extended Exposure ◽  
Butadiene Styrene ◽  
Elastic Characteristics

Abstract Synthetic rubbers and natural rubber increase in stiffness at low temperatures and tend to lose their elastic characteristics. This stiffening and hardening phenomenon occurs in varying degrees with various elastomers. Natural rubber and certain synthetic rubbers crystallize during extended exposure at low temperature, whereas other synthetic rubbers such as GR-S remain amorphous. In a general review of the low temperature properties of synthetic rubber, Liska has shown that decreased styrene in butadiene-styrene copolymers improves the flexibility at low temperature. The low temperature flexibility of vulcanized articles made from any particular rubber or synthetic rubber is influenced by the compounding ingredients admixed with the elastomer. This paper shows the results of some studies of the effect of these compounding ingredients on the low temperature serviceability of butadiene-styrene copolymers. Somewhat similar work on the effect of a large number of plasticizers in GR-S has been conducted at the Rubber Laboratory, Mare Island Naval Shipyard, with particular emphasis on compression set at low temperature.

Plastic Yield of Butadiene-Styrene and Isoprene-Styrene Ebonites

1951 ◽  
Vol 24 (2) ◽  
pp. 381-383 ◽  
Author(s):  
J. R. Scott
Keyword(s):  
Plastic Deformation ◽  
Natural Rubber ◽  
Elevated Temperatures ◽  
Styrene Copolymer ◽  
Heat Resistant ◽  
Plastic Yield ◽  
Styrene Copolymers ◽  
Styrene Content ◽  
Butadiene Styrene

Abstract In unloaded ebonites made from butadiene-styrene copolymers, the resistance to plastic deformation at elevated temperatures is better the higher the styrene content of the copolymer, at least up to 46 per cent. An isoprene-styrene copolymer ebonite has poorer plastic-yield resistance than a corresponding butadiene-styrene ebonite. All the styrene-containing copolymers, however give ebonites more heat-resistant than natural rubber ebonite, the best giving yield temperatures 30° C above the latter. To attain the best plastic-yield resistance in butadiene-styrene ebonites, the amount of sulfur added should correspond to more than 1 atom (e.g., 1.2 or even 1.4 atoms) per butadiene molecule.

Effect of Temperature on Ozone Cracking of Rubbers

1966 ◽  
Vol 39 (3) ◽  
pp. 643-650
Author(s):  
A. N. Gent ◽  
J. E. McGrath
Keyword(s):  
Polymer Chains ◽  
Effect Of Temperature ◽  
Ozone Molecule ◽  
Segmental Mobility ◽  
Network Chain ◽  
Styrene Copolymers ◽  
Rates Of Growth ◽  
Rate Controlling Step ◽  
Limiting Value ◽  
Butadiene Styrene

Abstract The rates of growth of single ozone cracks have been measured for vulcanizates of a series of butadiene—styrene copolymers, over a temperature range from − 5° C to 95° C. The rates appear to be determined by two mechanisms. At low temperatures, near the glass transition temperature, they are quantitatively related to the segmental mobility of the polymer. The principal rate-controlling step in this case is concluded to be movement of the polymer chains after scission to yield new surface. At high temperatures the rate approaches a limiting value of 10−3 cm/sec/mg of ozone/1. This is about 1/1000 of the maximum possible value when instantaneous reaction of one incident ozone molecule causes scission of one network chain.

Properties of Ebonite. XXX. Influence on Properties of Ebonite of the Type of Raw Rubber Used, with Special Reference to Purified Rubbers

1949 ◽  
Vol 22 (1) ◽  
pp. 232-244
Author(s):  
D. G. Fisher ◽  
J. R. Scott ◽  
W. H. Willott
Keyword(s):  
Dielectric Properties ◽  
Electrical Properties ◽  
Dielectric Loss ◽  
Natural Rubber ◽  
Power Factor ◽  
Breakdown Strength ◽  
Practical Importance ◽  
Water Soluble ◽  
Plastic Yield ◽  
Latex Rubber

Abstract Tests have been made on unloaded ebonites prepared from ordinary commercial types of natural rubber, special (deproteinized) rubbers having reduced contents of protein and(or) other water-absorbent substances, and a whole-latex rubber containing relatively large percentages of these substances, to determine to what extent these substances influence the electrical properties of the ebonite and, hence, whether any technically useful improvement can be effected by using specially prepared rubbers. Permittivity and power factor at 106 cycles per second, but particularly power factor, are somewhat improved by using the special rubbers, so that the dielectric loss can be reduced by about 30 per cent. In addition, the increase in dielectric loss caused by exposure to high humidity or by a rise of temperature is in general lessened by the use of these rubbers. Similar, though smaller, improvements in the properties of the ebonite are obtained by washing ordinary commercial rubber (smoked sheet). Although a definite improvement in dielectric loss is obtained, it does not seem probable that purification of natural rubber would lead to ebonites with dielectric properties approaching those of polystyrene, for instance. It seems unlikely that even complete elimination of the water-absorbent impurities would reduce the dielectric loss by more than 50 per cent; the rubber-sulfur compound itself thus appears to be responsible for a fair proportion of the loss normally observed. The large percentages of water-soluble substances present in whole-latex rubber increase the permittivity and especially the power factor of the ebonite made from it. The dielectric properties of ebonite are related, though not closely, to its water-absorbing capacity and that of the raw rubber used, low absorption being in general accompanied by low dielectric loss and reduced sensitiveness to humidity variations. There is only a rough parallelism between the water absorptions of raw rubbers and the corresponding ebonites. Probable reasons for this are indicated. It is concluded that water absorption tests on raw rubber form a useful, though only approximate, guide to its value for making electrical ebonite; electrical tests on the ebonite must be the final criterion. Apart from very impure whole-latex rubber, no correlation can be traced between the inorganic content (ash) of ebonite and its electrical properties. The probable reason for this is indicated. There is evidence that the dielectric loss of ebonite may increase with the passage of time. In view of its obvious theoretical and practical importance, this phenomenon requires further study. No technically useful advantage as regards breakdown strength, volume resistivity, surface resistivity, or stability to light, by the use of the special rubbers, is evident in the present work. The plastic yield characteristics of ebonite are not appreciably altered by using special rubbers. Estimations of uncombined sulfur and also plastic yield tests show that one of the deproteinized rubbers vulcanizes more rapidly than the rest, which differ little among themselves.

Flow Patterns in Elastomers and Their Carbon Black Compounds during Extrusion through Dies

1985 ◽  
Vol 58 (4) ◽  
pp. 815-829 ◽  
Author(s):  
Chin-Yuan Ma ◽  
James L. White ◽  
Frederick C. Weissert ◽  
Avraam I. Isayev ◽  
Nobuyuki Nakajima ◽  
...  
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Flow Patterns ◽  
Entrance Region ◽  
Evidence Based ◽  
Streamline Flow ◽  
Basic Study ◽  
Entrance Angle ◽  
Styrene Copolymers ◽  
Butadiene Styrene

Abstract A basic study of flow patterns in elastomers in the entrance region of a die has been carried out for various gum elastomers including emulsion and solution butadiene—styrene copolymers, polybutadiene, and natural rubber. All exhibit streamline flow into the entrance with the exception of a cold mastication degraded natural rubber which gave evidence of vortices in corners. A study of a die with a sharp diverging region showed dead spaces for all the elastomers. Carbon black compounds all exhibited converging streamline flow in a 180° entrance angle die and stagnant regions in the sharply diverging die. Evidence based on marker motions has been presented for slip in elastomer compounds in the entrance region.

Effect of Temperature on Ozone Cracking of Butyl Rubbers

1968 ◽  
Vol 41 (5) ◽  
pp. 1294-1299 ◽  
Author(s):  
A. N. Gent ◽  
H. Hirakawa
Keyword(s):  
Crack Growth ◽  
Ozone Concentration ◽  
Effect Of Temperature ◽  
Segmental Mobility ◽  
Temperature Range ◽  
Styrene Copolymers ◽  
The Difference ◽  
Rates Of Growth ◽  
Rate Controlling Step ◽  
Butadiene Styrene

Abstract Rates of growth of single ozone cracks have been measured for vulcanizates of two butyl rubbers over the temperature range of 20-160° C. Over most of this range the rates are quantitatively related to the segmental mobility of the polymer and depend upon temperature in accord with the appropriate form of the WLF relation. The rates are also proportional to the concentration of ozone. It is therefore concluded that diffusion of ozone into the polymer before reaction is the rate-controlling step. This is contrasted with the behavior of butadiene styrene copolymers, for which rates of crack growth are also quantitatively related to the segmental mobility, but the rates are somewhat larger at equivalent mobilities and the dependence upon ozone concentration is smaller. The difference is attributed to different penetration distances before reaction in polymers containing low and high densities of reactive sites.

Monolayer Studies of Some Hydroxylated Polyolefin Rubbers

1958 ◽  
Vol 31 (3) ◽  
pp. 446-458
Author(s):  
W. R. Dean ◽  
V. Perera ◽  
J. Glazer
Keyword(s):  
Natural Rubber ◽  
Surface Reaction ◽  
Varying Thickness ◽  
Polar Groups ◽  
Gutta Percha ◽  
Styrene Copolymers ◽  
End Products ◽  
Balance Technique ◽  
Butadiene Styrene ◽  
Kinetic Features

Abstract The study of high polymer monolayers by the Langmuir balance technique has been almost wholly restricted to those polymers which contain polar groups, e.g., cellulose, proteins, polyacrylates, etc. Nonpolar polymers do not spread and so little attention has been paid to the hydrocarbon rubbers. Wall and Zelikoff have reported that natural rubber, gutta-percha, and butadienestyrene copolymers do not form stable monolayers on water, but that when these materials are modified chemically by thiocyanogen they form relatively thin films of varying thickness. Sivaramakrishnan and Rao have recently confirmed that natural rubber does not form a monolayer on water. However, they find that it spreads spontaneously on a subsolution of aqueous acidic potassium permanganate. We have investigated the surface reaction between certain polyolefins and aqueous permanganate ; the kinetic features of these reactions, discussed elsewhere, suggest that definite chemical end-products are formed on the surface. The purpose of this communication is to characterize the end-products obtained from natural rubber (cis-1,4-polyisoprene), gutta-percha (trans-1,4-polyisoprene), polybutadiene, and two butadiene-styrene copolymers of differing styrene content, when these react under controlled conditions at the surface of an acidic aqueous permanganate subsolution.

Styrene-Diene Resins in Rubber Compounding

1947 ◽  
Vol 20 (1) ◽  
pp. 241-248
Author(s):  
A. M. Borders ◽  
R. D. Juve ◽  
L. D. Hess
Keyword(s):  
Tensile Elongation ◽  
Chemical Properties ◽  
Aryl Hydrocarbon ◽  
Styrene Copolymers ◽  
Synthetic Rubber ◽  
Brittle Point ◽  
Styrene Content ◽  
Physical And Chemical ◽  
Preparation And Evaluation ◽  
Butadiene Styrene

Abstract Early in the investigation of butadiene-styrene copolymers as synthetic rubbers, this laboratory became interested in copolymers containing much more styrene than any of the American or German synthetics. This interest was soon directed to the resinous copolymers obtained when the styrene content is increased beyond the range in which rubberlike properties are observed at room temperature. The exploratory work, therefore, involved preparation and evaluation of butadiene-styrene copolymers containing from 65 to 98 per cent styrene. No description of similar polymers has been found. Konrad and Ludwig claimed the improvement of rubberlike properties of butadiene-styrene copolymers by increasing the styrene content from the normal range to “between about 47.5 and about 70 per cent”. The claims and examples of this patent emphasize the improvement of rubberlike properties, such as tensile, elongation, and rebound, at high temperatures. It is well known in this country, however, that increase in styrene content beyond a certain point, perhaps 50–55 per cent, is accompanied by a loss of overall balance of rubber characteristics. Therefore, the copolymers at the upper end of the range described by Konrad and Ludwig have definite limitations for rubber uses—for example, low rebound, high brittle point, shortness, etc. In the writers' laboratory useful resins have been prepared from dienes and vinyl aryl hydrocarbons in the range 5 to 20 per cent diene and 80 to 95 per cent vinyl aryl hydrocarbon. This paper describes the properties and certain uses of one of these copolymers containing approximately 15 parts of butadiene and 85 parts of styrene. This material possesses a combination of physical and chemical properties which permit its use in several applications where cyclized natural or synthetic rubbers are commonly employed. Cyclized natural rubber has been described by Bruson, Endres, and Thies and Clifford. Cyclized synthetic rubbers were described recently by Endres. One product of this type is made from a special synthetic rubber. The new 15 butadiene—85 styrene copolymer is now identified as Pliolite S-3, since it may be used in many Pliolite applications, often with distinct advantages over either the natural or synthetic rubber derivatives.

Comparison of Natural and Synthetic Hard Rubbers

1947 ◽  
Vol 20 (1) ◽  
pp. 99-115
Author(s):  
G. G. Winspear ◽  
D. B. Hermann ◽  
F. S. Malm ◽  
A. R. Kemp
Keyword(s):  
Natural Rubber ◽  
Rapid Progress ◽  
Rubber Industry ◽  
Styrene Copolymers ◽  
Standard Procedures ◽  
Nitrile Rubbers ◽  
Normal Production ◽  
War Production ◽  
Short Time ◽  
Butadiene Styrene

Abstract The wartime replacement of natural rubber by synthetics required an unusual expenditure of effort by the hard rubber industry in a short time. At first, curtailment of normal production, coupled with War Production Board restrictions of formulations, mitigated the urgency for synthetic hard rubber research. It soon became evident, however, that a complete line of synthetic hard rubbers would be desirable. These materials could be fabricated with standard rubber processing equipment, and would offer physical and electrical equivalents for the various grades of natural hard rubber developed during nearly a century. A program was started in these laboratories with the realization that rapid progress might be difficult; research on the compounding of natural hard rubber over the years had failed to produce improvements in overall properties compared with the original “ebonites”. The latter, according to the accepted nomenclature, are simple mixtures of rubber with large proportions of sulfur vulcanized by heating until chemical saturation of the rubber is almost complete. The first approach to the problem was through a study of vulcanizing characteristics and through examination of the hard products resulting from the reaction of sulfur with butadiene-styrene copolymers. As the program progressed, the work was extended to cover the processing of GR-S for ebonite fabrication and the compounding of GR-S hard rubbers for specific applications. Studies also were conducted relating to the compounding and processing of hard nitrile rubbers, and new tests were developed to suplement standard procedures used in the physical evaluation of hard rubbers.

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