bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison between the Observed Density of Crystalline Rubber and the Density Calculated from X-Ray Data
Authors: Smith W. Harold , Hanna Nancy P.
Published: February 2011

When unvulcanized rubber is stretched quickly, an orientation of structure occurs parallel to the direction of extension. This orientation is usually regarded as a form of crystallization, because of the optical and other phenomena which accompany it. It is also accompanied by a change of volume. When unstretched rubber is subjected to suitable temperatures below about 10° C, it too becomes crystalline. The crystallization of rubber is accompanied by an increase of density, and the simultaneous production of an x-ray diffraction pattern is usually interpreted as evidence that crystallization has occurred. A diffraction pattern of this kind results from regular repetition, within the crystal structure, of groups of atoms or molecules in a definite spatial arrangement. The smallest group from which the structure can be built up in this way is called the unit cell; and the dimensions can be computed from measurements of the pattern, provided it is possible to determine the crystal form. The pattern of stretched rubber consists of interference spots, and that of frozen rubber consists of rings, but both of their measurements have been shown to indicate the same unit cell. If, in addition, the number of atoms in the unit cell is known, the density of the material can be computed. If the computed density agrees with that found by direct measurement, the fact is a valuable indication of the correctness of the assumed structure on which the calculation of density was based. Accurate knowledge of the density of completely crystallized rubber would therefore serve both as a guide in studies of structure and as a measure of the degree of crystallization of any material under consideration. In the experimental work described in this paper, the rubber was crystallized as completely as possible. Its density was determined by recognized methods, and compared with the densities calculated from x-ray measurements.
The Viscosity of Preserved and Concentrated Latex. III. Relationship of Viscosity to Temperature and Dry-Rubber Content
Authors: Smith H. Fairfield
Published: February 2011

The purpose of this paper is to deduce, from data given by Rhodes on the viscosity of latices and of latex-water mixtures at different temperatures, mathematical formulas by which the observations may be succinctly described. These will serve as a convenient means for interpolation and for the deduction of quantitative estimates of the changes in the viscosity of latex with temperature and dry rubber content (d.r.c.); and may facilitate comparison with the variations in viscosity of other substances and with theories or hypotheses.
Trilinear Compounding
Authors: Forman D. B.
Published: February 2011

Trilinear compounding enables the factory compounder to select the particular rubber or synthetic rubber composition that will have the physical properties specified. It saves time in eliminating trial-and-error methods of compounding. Briefly, charts of this type actually tell the ratio of rubber (or synthetic rubber): filler: softener, and similar charts can be made to show other systems. Every rubber chemist knows that there are two primary methods of altering the physical properties of vulcanized rubber and synthetic rubber—chemical and physical. The former is controlled by antioxidants, accelerators, activators, and other curing agents; the latter is controlled by fillers and softeners. This discussion deals with the physical methods that are applicable after factors influencing rate and state of cure have been fixed. This method of compounding has been named “trilinear compounding”. It employs charts which show the effects of varying three ingredients in a compound. In other words, it deals with a compound as a unit which is divisible into three parts. Trilinear compounding is not new; it is used regularly in the paint and plastics industry. Undoubtedly, several rubber chemists have used it in connection with compounding by chemical means and in many special applications, but its recourse to fillers and softeners is believed to be new to most rubber chemists.
Determination of Zinc in Rubber Compounds. A New Internal Indicator Method
Authors: Tyler Willard P.
Published: February 2011

Two internal indicator volumetric methods for the determination of zinc in rubber compounds have been devised and investigated. The first method is a wet-oxidation method employing nitric acid, bromine, and perchloric acid as oxidants, and p-ethoxychrysoidine, a new oxidation-reduction indicator for this use, as indicator. It is of general application to all types of rubber compounds. The second method, less generally applicable to rubber compounds, utilizes either the new indicator or the well-known indicator, diphenylbenzidine. This method depends on ashing of the sample, and cannot be used for the analysis of zinc in rubber compounds containing lead or silicates, since it has been found that no method in which the sample is ashed yields accurate results if these substances are present. Both methods use potassium ferrocyanide as the volumetric precipitant and potassium ferricyanide as an integral part of the indicator system. Both methods are applicable to other organic and inorganic zinc-containing materials. The first method appears to have a slight advantage in ease of manipulation, total time of determination, and range of applicability. There is little choice between the methods or indicators as regards precision, accuracy, or the actual time used by the analyst for a determination, providing each method and indicator is used only under the proper conditions. Both methods are superior to the external indicator method using uranyl acetate, the method now in common use in rubber laboratories.
The Economics of the use of Neoprene Reclaim
Authors: Fraser Donald F.
Published: February 2011

It is possible to reclaim mould and other vulcanized Neoprene scrap by suitable reclaiming procedures. At the present time, most of the reclaim manufacturers are prepared to do this reclaiming on a custom basis. The Neoprene of the reclaim may replace as much as 50 per cent of raw Neoprene in a compound to reduce by as much as 25 per cent the volume cost, without greatly impairing the physical properties of medium-or low-grade mechanical goods vulcanizates. Use of Neoprene scrap in this manner will conserve the supply of Neoprene, and under present conditions the value of such conservation is obvious. Besides, this utilization of scrap will reduce the overall factory cost of many types of Neoprene products. Although the volume of Neoprene scrap available at the present time is small, the presence of larger amounts on the market, as a result of increased Neoprene production, must be anticipated. Because of increased interest in Neoprene reclaims, due attention should be given to the problem of classifying and standardizing types of Neoprene scrap and reclaim.
Vulcanizing of Ebonite. Controlled Curing of Natural and Synthetic Rubber Ebonites of Large Cross-Section
Authors: Quinn N. G.
Published: February 2011

The vulcanizing of ebonite, particularly of large blocks or bars of substantial cross-section, has long been a source of production difficulty. The tendency of such vulcanizates to develop porosity or even more serious gassing has always necessitated a prolonged curing period at a comparatively low temperature. Improved compounding technique has greatly accelerated the curing process, but the period is still excessive and production is impaired. The proposed method of control enables a higher curing temperature to be used, with a consequent considerable reduction in curing time; it further makes possible the use of stocks which previously could not be satisfactorily cured at all above a certain thickness.
Transparency of Rubber and Its Solutions
Authors: Stevens Henry P.
Published: February 2011

When rubber is dissolved in benzene or a mixture of coal-tar hydrocarbons, a clear bright solution is usually obtained. On the other hand, when dissolved in a petroleum solvent, the solution is opalescent. In the latter case it is necessary to postulate the presence of small particles having a different refractive index from that of the solvent. As rubber gives a substantially clear solution in benzene, it follows that the foreign particles are invisible and must, therefore, possess the same refractive index as this solvent or one very close to it.
Heat Generation in Flexed Rubber
Authors: Gehman S. D. , Jones P. J. , Woodford D. E.
Published: February 2011

The problem of heat generation in tires assumes new importance with the advent of synthetic rubber and the increased use of reclaimed rubber. Even if reduced speeds may prevent heat blowouts, higher temperatures mean that both fabric and rubber are operating under unfavorable conditions. Synthetic rubber, in particular, is then working at reduced tensile strength and tear resistance. It is more susceptible to heat embrittlement, cuts, and abrasion. A number of flexometers for rubber testing have been described, and some of these instruments have been widely used. The flexometer described here is characterized by simplicity of construction, high speed, and convenience of operation.
Rubber, Polyisoprenes and Allied Compounds. V. The Chemical Linking of Rubber and of Other Olefins with Phenol-Formaldehyde Resins
Authors: Cunneen J. I. , Farmer E. Harold , Koch H. P.
Published: February 2011

Rubber combines readily with maleic anhydride up to a limit of one molecule of the latter per isoprene unit of the former. The comparative ease of occurrence of this reaction made it seem feasible to use maleic and similar unsaturated anhydrides (or acids) as a means of linking rubber chemically with various types of hydroxylic compound, the ethylenic carbon pairs of the maleic molecules serving to form C—C links with the rubber, and the anhydro groupings to form ester links with hydroxy compounds. Although it was possible to carry out this linking process successfully in a number of examples, the combination of rubber with phenol-formaldehyde resins could be much more satisfactorily effected if the rubber-maleic anhydride compound was not preformed, but, instead, a somewhat oxidized rubber together with maleic anhydride, phenol, and formaldehyde were simply heated together until resin formation occurred. Subsequently, it was found that considerably oxidized rubber (oxygen, approximately 10–13%; M, 3000–4000) reacted more readily than slightly oxidized rubber, the product being a thermosetting resin of Bakelite type, remarkable in possessing valuable residual thermoplastic properties. Investigation of the chemical reaction by which this resin is produced has given rather unexpected results in the field of additive reactions, and has thrown new light on the process of resinification.
The Course of Autoöxidation Reactions in Polyisoprenes and Allied Compounds. VII. Rearrangement of Double Bonds during Autoöxidation
Authors: Farmer E. Harold , Koch H. P. , Sutton Donald A.
Published: February 2011

In Part V of this series, it was reported that a typical drying-oil ester, methyl docosahexaenoate, showed a marked increase in its capacity to absorb ultraviolet light as the result of exposure to atmospheric oxygen in the illumination of the laboratory. The rapid peroxidation of the polyene system which set in during this exposure promoted a structural change apparently of a conjugative nature. The nature of this change is now examined. Two types of unconjugated unsaturation are, however, taken into consideration: (1) the methylene-interrupted unsaturation, ⋅C:C⋅C⋅C:C⋅C⋅C:C⋅, characteristic of numerous unconjugated drying-oil acids such as linoleic, linolenic, and various polyene fish-oil acids, and (2) the more widely spaced unsaturation found in rubber and in other unconjugated polyisoprene hydrocarbons. The structural changes that ensue on oxidation are of particular interest in relation to the free-radical mechanism of olefinic peroxidation already formulated by Farmer, Bloomfield, Sundralingam, and Sutton, in which the olefin is regarded as passing through the stages:
Flex Life and Crystallization of Synthetic Rubber
Authors: Fielding J. H.
Published: February 2011

The crystalline structure of stretched natural rubber has been the subject of much experimental work in the past. A great deal of this has been devoted to the more theoretical aspects, such as x-ray patterns, thermal effects, and volume change. It is now known that neither Buna-N nor GR-S has a fiber diagram when stretched and that Butyl-B and Neoprene do have such patterns. Since the industry is now in the process of changing from natural rubber to GR-S, it is of interest to see just what this lack of crystallinity means from a compounding and performance standpoint. It is possible that many of our ideas based on rubber must change, that GR-S must be considered to be a new material, and that radical changes in formulation and construction must be made.
Temperature Coefficient of Vulcanization of Buna-S
Authors: Cheyney La Verne E. , Duncan Robert W.
Published: February 2011

Temperature coefficient of vulcanization may be defined as the increase in time of vulcanization necessary to produce a given property in the vulcanizate per unit range of temperature decrease, the latter being taken usually as either 10° F or 10° C. Coefficients of vulcanization for natural rubber stocks have been determined by several investigators. Although the data vary somewhat with the worker and with the stock investigated, the general range of temperature coefficients is close to 2.0 per 10° C. This is regarded as evidence of the chemical nature of the vulcanization reaction. The values obtained from physical test data do not always agree with those from combined sulfur analyses. This has been interpreted as an indication that the chemical reaction between the rubber and sulfur is not a simple bimolecular one, and that the rate of change of physical properties is not directly related to the rate of chemical combination of rubber and sulfur. A number of studies were published recently on the effect of variables on the vulcanization of Buna-S (now called GR-S in the United States) and on the properties of the resulting vulcanizates. In addition, compounding reports have been issued by manufacturers of rubber chemicals, as well as confidential reports submitted to the Rubber Director's office by rubber manufacturers. None of the published investigations, however, have been concerned with the determination of numerical relations among the properties of vulcanizates obtained at various temperatures. The properties of Buna-S vulcanizates differ markedly from those of rubber in certain characteristics, while possessing certain similarities in others. The only published mention of the effect of temperature on Buna-S stocks was in a release from the office of the Rubber Director, giving tables for conversion of cure to a standard temperature. These tables are based on a temperature coefficient of 1.43 per 10° F. The source of this information is not available, however.
Funtumia and Ceara Vs. Hevea
Authors: Martin G.
Published: February 2011

It has to be admitted that both Ceara and Funtumia have some advantages over Hevea. Neither is so exacting regarding climate, and Ceara will thrive on soil unsuitable for Hevea. Ceara has the advantage of quick growth, and Funtumia yields an appreciable amount of rubber per tapping per tree. On the other hand, both of them are difficult to tap, and the trees are easily damaged. The yield per acre is much less than that given by Hevea and the quality of the rubber produced under the best conditions is from 5 to 8 per cent inferior. The crux of the problem is to increase the yield per acre, with a corresponding reduction in tapping costs. Until this has been achieved it is difficult to believe that either tree will receive the serious attention of planters after the present emergency has disappeared.
Processes of Reclaiming Rubber and Their Relative Merits
Authors: Owen E. W. B.
Published: February 2011

1. A more complete reclamation is possible by the thermal and pan process than with the alkali process, and both the former effect a saving in time. 2. The thermal process calls for a higher temperature, but the after-treatment consumes less power for grinding. The pan process makes use of a lower temperature; but the expenditure of more power for grinding before and after treatment, as well as a drying period, are entailed. 3. The new products are neutral, and softer than alkali reclaim. 4. Accelerated with BA, stocks with these new types of reclaim give poor results. On the other hand, MBT offers good prospects, both for aging and acceleration. 5. Whether refined or not, the pan reclaim produced a tensile strength 95 per cent of alkali reclaim, and the thermal reclaim 80 per cent, in MBT stocks. 6. With modified acceleration, thermal reclaim stock can be made to give improved tensile properties. 7. Laboratory abrasion resistance of both new types was superior to the standard, the losses being 92 per cent and 74 per cent for thermal and pan reclaims, respectively. 8. The permanent set was lower despite the softener in the pan reclaim. 9. Despite the lack of refining, articles formed by extrusion from stocks containing thermal and pan reclaims compared favorably with those from alkali reclaim with regard to surface finish. 10. Thermal reclaim ages extremely well. Independent workers in the field of thermal reclaim have been able to exercise a finer control of the process, and a large scale plant is in course of erection as a result of the improvements effected. Further work is proceeding, and it is hoped that a product superior in all respects to alkali reclaim will be obtained.
The Retraction of Stretched Rubber
Authors: Stambaugh R. B.
Published: February 2011

For some time we have been making measurements of the velocities acquired by rubber strips when retracting after being stretched. The rubber band is stretched in front of two photocells, cutting off two sharply focussed light beams. When the strip is released, the beams impinge successively on the photocells, the first of which starts the charging of a condenser, and the second of which stops the charging current. The resulting voltage on the condenser is thus a measure of the time required for the free end of the rubber strip to traverse the distance between the two light beams. Retraction velocities of the order of several hundred miles per hour have been observed. To explain some of our results and to secure a more detailed picture of the mechanism of retraction, we have also taken pictures of retracting rubber strips, with a high-speed stroboscopic lamp. These seemed to be of sufficient general interest to present here.
Rheological Properties of Natural and Synthetic Rubbers
Authors: Kelsey R. H. , Dillon J. H.
Published: February 2011

One of the important factors determining the processing characteristics of a rubber or unvulcanized rubber stock is the “plasticity”. This term has been used by rubber technologists to define the rate at which a material can be made to flow under a set of conditions of stress, geometry, and temperature. Strictly speaking, plasticity is not a quantitative term but, because of past usage, it seems justifiable to continue to employ it as an inverse index of resistance to flow. Three principal types of instruments have been employed for measuring plasticity of rubberlike materials: parallel plate, rotating disk or cylinder, and extrusion plastometers. The parallel-plate type, like the rotary type plastometer, is designed to operate with no slippage between rubber and confining surfaces, and both operate at rather low rates of shear. The rotating disk plastometer, however, permits attainment of thixotropic equilibrium and simple calculation of the mean shearing stress at a given average rate of shear. All extrusion plastometers described in the literature have employed rather short, large bore extrusion tubes, which permit appreciable slippage between rubber and tube walls, and have operated at a constant driving pressure and temperature, the rate of efflux serving as the plasticity index. The existence of slippage, of course, eliminates the possibility of calculating absolute consistency (inverse of plasticity), but is an advantage in that factory processing conditions, where slippage is a factor, are simulated. High rates of shear of the order of magnitude of those existing in factory extruders may be readily attained with extrusion plastometers. It has been argued that high rates of shear in a plastometer are desirable from the standpoint of predicting processability, since the shear stress vs. rate of shear relationship for rubberlike materials departs radically from linearity.
GR-S, an Elastically Inverted Polymer
Authors: Braendle H. A. , Wiegand W. B.
Published: February 2011

To the compounder faced with the necessity of making tires of GR-S, three main problems need to be faced; (1) processing and handling, including building tack; (2) hot running of the tires on test wheel or road, and (3) heat embrittlement and flex-crack growth. Ways and means have been devised to make processing of GR-S possible, even though not so easy as with natural rubber. Laboratory investigation of the hysteresis and heat build-up characteristics of GR-S has so far followed closely the lines developed for natural rubber. These fall into distinct types. Probably the oldest are rebound tests. Rubber balls are dropped onto solid steel plates or, conversely, steel balls are dropped onto firmly supported rubber test slabs. The Lüpke pendulum employs a horizontal ram with a double V filar suspension. The pendulum with a rigid arm by which the degree of penetration of the hammer may also be determined has found wide acceptance as a means of measuring impact resilience. The damping effect on free vibration of rubber members is measured on an oscillograph or a torsion pendulum as a means of evaluating hysteresis. Much ingenuity has been shown in the various forms of flexometers which have been developed to duplicate to a greater or lesser degree the amplitude and frequency of vibration and load carrying conditions of service to predict heat build-up. These tests have two things in common. They subject the specimen to relatively low deformations, and they show GR-S to have greater hysteresis than natural rubber. Useful as flexometer tests are in predicting heat build-up of rubber when used as a shock absorber, they throw no light on the mechanism of failure of GR-S due to rapid flex cut growth. This is particularly true when these tests are carried out in the laboratory under substantially isothermal conditions and at ordinary room temperatures. The obvious reason is that the deformations induced fall far short of the strains just antecedent to rupture. The problem, therefore, demanded the study of rubber stretched nearly to rupture.
Observations on the X-Ray Structure of Rubber and the Size and Shape of Rubber Crystallites
Authors: Gehman S. D. , Field J. E.
Published: February 2011

In former times, we used to be painfully aware of the shortcomings and elastic imperfections of Hevea rubber. With its disappearance, we have come to think of it as having an ideal balance in physical properties for a rubberlike material which it has been difficult to approach with synthetic polymers. for this reason, it is still important to investigate the molecular structure of Hevea rubber and to try to understand the characteristics of this structure which are responsible for its physical properties. X-Ray diffraction methods can be applied to the problem of the molecular structure of Hevea rubber and a few synthetic rubbers, such as Butyl rubber and Neoprene, because crystallization occurs upon stretching. A detailed description of the x-ray diffraction results with rubber is available in a review article and need not be repeated here. It should be pointed out that the story obtained from the x-ray structure is not complete because there are important aspects of the structure which are not revealed by this means. It is not possible to measure directly the length of the chain molecules. The nature of the amorphous phase, such as the system of cross-linking of the long chain molecules on vulcanization, does not become evident in x-ray patterns. The physical properties of Hevea rubber must depend on a delicate balance of primary and secondary valence forces. The x-ray method does not permit any direct measurement of these forces but merely shows the geometrical arrangement which results from the molecular forces. Even with these limitations, much valuable information can be secured on the nature of the molecular rearrangements which occur upon stretching. Deductions can be drawn from the x-ray diffraction results regarding the form and spatial relationships of the long chain polymeric molecules and the manner in which they interact under stress. Correlations can then be looked for between the crystallization and the physical properties.
The Physical Chemistry of Rubber Solutions
Authors: Gee G.
Published: February 2011

The physicochemical behavior of rubber may conveniently be described in terms of two main factors, (1) its long-chain character, and (2) its chemical nature. It is frequently possible to neglect one of these; e.g., Farmer and his coworkers have shown that much light can be thrown on the organic chemistry of rubber from a study of structurally related, low-molecular hydrocarbons. In the following we shall, in the main, consider rubber as a typical member of the class of long-chain compounds, and much of this section is therefore of general application to linear high polymers.
Determination of Total and Combined Sulfur in Butyl Rubber
Authors: Rehner John , Holowchak Joseph
Published: February 2011

Methylethyl ketone has been shown to be a much more effective solvent than acetone for the removal of extractable sulfur and certain accelerators from Butyl rubber vulcanizates in a standard Soxhlet extraction. The use of this extraction agent, together with combustion of the original and extracted samples in the Braun-Shell sulfur apparatus, provides a satisfactory procedure for determining the amounts of total and combined sulfur in Butyl compositions.
The Testing of Rubber in Compression
Authors: Blow C. M. , Fletcher W. P.
Published: February 2011

With the increased use of rubber as an engineering material, considerable attention has to be paid to the characteristics of natural and synthetic rubbers in compression. For oil seals, in particular, what is loosely termed permanent set of the rubber must not be so great as to lead to breakdown of efficiency. Up to the present the need for laboratory evaluation of different rubbers for this property has been met by tests which involve measuring the dimensional changes in a test-piece subjected to a constant strain or stress for a certain time and then allowed to recover for a certain time. Although it gives some indication of behavior, this method of test suffers from the great disadvantages that the time factor is arbitrary and the change of dimension is measured, whereas in service the dimension of the rubber is maintained virtually constant by the rigid members of the system. In other words, in the case of a sealing ring on a piston working in a cylinder, the effectiveness of the seal depends, in large measure, on the pressure exerted by the rubber on the cylinder wall. As this pressure decays, so, it is believed, the sealing efficiency decreases.
Rubber, Polyisoprenes, and Allied Compounds. VII. Action of Nitric Oxide
Authors: Bloomfield George F. , Jeffrey G. A.
Published: February 2011

The reaction of nitric oxide with the olefins cyclohexene, 1-methylcyclohexene, dihydromyrcene, and rubber presents characteristics of a free-radical, chain reaction. In the products, the molecular ratio of combined oxygen to nitrogen is considerably in excess of 1:1, the nitrogen atom being generally directly linked to carbon. In many instances definite nitro compounds have been isolated, and a considerable part of the attack appears to proceed at the ethylenic carbon atoms, either by substitution or addition of NO2 and N2O3 groups. The precise reaction mechanism is obscure.
Properties of Hard Rubber. XIII. Experiments on Thermal Effects during Vulcanization
Authors: Church H. F. , Daynes H. A.
Published: February 2011

The characteristics and technical importance of the internal heating effect during the vulcanization of hard rubber, due to the exothermic reaction between rubber and sulfur, are recalled, and the conditions under which thermal instability may occur are outlined. The necessity of avoiding even slight increases in internal temperature when vulcanizing material for research purposes is emphasized. Experiments are described in which sheets of rubber-sulfur mixings of various thicknesses were vulcanized in a platen press at various temperatures, and the internal and surface temperatures were measured throughout the vulcanization period by means of thermocouples. The time-temperature curves are reproduced. The relations between internal temperature rise, platen temperature, and thickness of sheet are indicated. The choice of maximum safe thickness for a given platen temperature or of maximum safe platen temperature for a given thickness is shown to be very critical. The rise of temperature is greater in open steam vulcanization than in press-vulcanization, for a reason which is pointed out. It is important that these limiting factors in the use of high-grade rubber-sulfur materials should be taken into account in designing hard rubber articles.
Applications of Ultraviolet Spectrography a Study of the Transformations of Tetramethylthiuram Disulfide When It Functions as a Direct Vulcanizing Agent
Authors: Dufraisse Charles , Jarrijon André
Published: February 2011

In addition to sulfur, which is the most common vulcanizing agent, rubber mixtures usually contain various kinds of accessory ingredients, both inorganic and organic. Among the organic ingredients, some, notably accelerators and antioxidants, are present in relatively small proportions, and these are susceptible to transformation during vulcanization. However, only in rare cases has it been possible to isolate in definite form the products of these transformations, and consequently it is difficult to interpret the part played by these substances during vulcanization. Since, with few exceptions, each accelerator and each antioxidant has its own characteristic absorption spectrum in the ultraviolet region, spectrography constitutes in general an important method for following the behavior of accelerators and antioxidants. This method has been demonstrated by Dufraisse and Houpillart, who have developed a special technique for obtaining ultraviolet absorption spectra and examining them, frequently with interesting conclusions to be drawn from such analyses.
A Solution Method for the Compounding of Goldenrod Rubber
Authors: McKennon Forrest L. , Lindquist J. Raymond
Published: February 2011

A solution method of compounding rubber has been devised. It is particularly suitable for compounding a soft natural rubber such as that recovered from goldenrod, but it does not appear to be restricted to goldenrod rubber. No particular inherent disadvantage of solution compounding is indicated with hevea rubber. By proper choice of solvent and compounding chemicals, the interesting possibility is presented of improving the quality of those rubbers in which proper dispersion of chemicals is difficult. This method also shows possibilities of being a valuable research tool in the pretreatment of soft synthetic elastomers as a preliminary step to evaluation of their rubber-like qualities.
Comparison of the Structures of Stretched Linear Polymers
Authors: Huggins Maurice L.
Published: February 2011

Published x-ray data from crystalline selenium and tellurium and from stretched sulfur (amorphous), polyethylene, polyisobutylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polyoxymethylene, polyoxyethylene, polyethylene disulfide, polyethylene tetrasulfide, and polyphosphonitrile chloride are compared. In most cases the experimental identity-distance in the direction of the chain axes and the expected interatomic distances and interbond angles are found to be in agreement with the assumption that the chain atoms form a regular spiral, unidirectional in each chain and of uniform pitch. Apparent exceptions are briefly discussed.
Preparation of 2,3-Dimethylbutadiene and Its Polymerization to “Methyl Rubber”
Authors: McHenry John J. , Drumm Peter J. , O'Connor William F.
Published: February 2011

Between 1915 and 1918 the Bayer Company in Germany produced over 2,500 tons of rubber from 2,3-dimethylbutadiene. The product, called “methyl rubber”, was not a commercial success. Its tensile strength was low and it suffered from the further drawback of being very susceptible to oxidation, as a result of which it was converted into a sticky resinous material. It is of interest to note that at this period the beneficial effect of carbon black on the tensile strength of rubbers was not known, nor had the antioxidative properties of such chemicals as β-naphthol, nitronaphthalene and bipiperidyl been discovered. In the light of this knowledge the authors considered that a reinvestigation of the properties of “methyl rubber” might be of interest. The preparation of the methyl rubber from acetone is described in the following account.
Rise of Temperature on Fast Stretching of Butyl Rubber
Authors: Dart S. L. , Guth Eugene
Published: February 2011

Study of the rise in temperature by fast stretching of Butyl gum and tread stocks throws considerable light on crystallization, internal friction, and carbon black reënforcement as functions of elongation and other possible variables. For low elongations, the low-heat curves show the occurrence of thermoelastic inversion. They show also that internal friction is much larger in Butyl than in Hevea. For high elongations the high-heat curves enable one to follow the late and abrupt crystallization so characteristic for Butyl stocks. The carbon black reënforcement of Butyl is followed for the whole range of elongations up to the breaking point. Specific carbon-black reënforcement takes place in the range of elongations before crystallization of the gum stock, but the shortening of the breaking elongation by the black excludes to a large extent the added reënforcement through crystallization. Physical measurements of the type reported in this paper serve a manifold purpose. They enable one to establish a correlation between physical properties and chemical structure. Such a correlation is simpler for fundamental physical properties, as the ΔT vs. ε curve, than for more complicated physical tests, as data from flexometer, which were designed to approach service conditions. Comparing different gum stocks with Butyl polymers among themselves and with Hevea or other synthetics, these measurements may guide the development of better Butyl polymers. Finally, comparing tread with gum stocks, they may help to recognize the nature of reënforcing by carbon blacks and the action of other compounding ingredients.
The Role of Oxygen in the Plasticization of Rubber
Authors: Twiss D. F.
Published: February 2011

The close relation between the degree of mastication of raw rubber and the plasticity of the milled rubber (or the viscosity of its solutions) has been practical knowledge since the earliest days of rubber manufacture. The first definite evidence of the possible importance of atmospheric oxygen in the plasticization of rubber dates apparently to the early days of the Research Association of British Rubber and Tyre Manufacturers1. The final Summary in its second Research Report in 1921 contained the following statements: “Raw rubber may be heated in an atmosphere of steam, hydrogen or nitrogen to a temperature of 150° C without any very great change being brought about in its solution viscosity.” “The effect produced by milling can be imitated by heating rubber in the presence of oxygen or air.” “The marked changes in solution viscosity which are produced in rubber by heating in air are due to some chemical action between the rubber and the oxygen present.” The report ended: “It is scarcely necessary to point out the importance of the above observations in connection with the changes which occur during washing, drying (both in air and in vacuo) in the milling of raw rubber and in connection with the storage of unvulcanized compounded stock.”
Determination of Peroxides in Synthetic Rubbers
Authors: Robey Richard F. , Wiese Herbert K.
Published: February 2011

Peroxides are found in synthetic rubbers either as the result of attack by oxygen, usually from the air, or as a residue from polymerization operations employing peroxide catalysts. Because of possible detrimental effects of active oxygen on the properties of the rubber, a method of quantitative determination is needed. The concentration of peroxides in substances of lower molecular weight may be determined with ferrous thiocyanate reagent, either titrimetrically as recommended by Yule and Wilson or colorimetrically as by Young, Vogt, and Nieuwland. Unfortunately, many highly polymeric substances are not soluble in the acetone and methanol solutions employed in these procedures. This is also the case with hydrocarbon monomers, such as butadiene, containing appreciable concentrations of soluble high molecular weight polymers. Bolland, Sundralingam, Sutton and Tristram recommended benzene as a solvent for natural rubber samples and the reagent made up in methanol. However, most synthetic rubbers are not readily soluble even in this combination. The following procedure employs the ferrous thiocyanate reagent in combination with a solvent capable of maintaining considerable concentrations of synthetic rubber in solution. The solvent comprises essentially 20 per cent ethanol in chloroform.
Determination of Unsaturation in Butyl Rubber
Authors: Rehner John , Gray Priscilla
Published: February 2011

In a recent publication on unsaturation in Butyl rubber it was pointed out that, of the various methods that had been examined, ozone degradation at the double bonds appears to give the most reliable unsaturation data, the values based on the limiting viscosity of the degraded polymer being in reasonably good agreement with those determined by end-group analyses. This paper describes in some detail the analytical method, together with certain modifications that have been introduced with the aim of facilitating routine work. It was recognized that the earlier procedure had the disadvantage of being too time-consuming, owing mainly to the steps in which the degraded polymer solution is evaporated to dryness, and the residue redissolved in diisobutylene before the viscosity measurement. An obvious possible improvement was to develop a procedure whereby the polymer solution could be ozonized and the viscosity of the degraded solution determined directly, thus eliminating evaporation and transfer to a second solvent. It was first necessary, however, to perform the experiments described below; their significance will be explained in the sequel. A further simplification was introduced through the use of carbon tetrachloride of ordinary reagent grade instead of the highly purified solvent. While this substitution usually leads to viscosity-time curves displaying a small negative slope in the region where the purified solvent gives unchanged viscosity values, a simple extrapolation to zero time gives viscosity data that are satisfactory within the limits inherent in the method. In view of the practical requirements of the method and the magnitude of the experimental error, the extra time and effort involved in further purification of the solvent appear to be unwarranted.
Identification of Raw and Vulcanized Rubberlike Polymers. II. Determination of Swelling Ratios
Authors: Parker L. F. C.
Published: February 2011

The ratios of the swellings of vulcanized rubberlike polymers in benzene, light petroleum (b.p. 40–60°), and aniline, at 25° C, have been found to be different for different polymers, but to be within a well-defined narrow range for each polymer, and the ratios substantially independent of the state of vulcanization and nature and proportion of the fillers. Hence the ratios for an unknown sample may be utilized in its identification, preferably by plotting the values on a graph showing the ratios for the common types of rubberlike polymers.
Adhesion of Rubber to Brass Plate
Authors: Gurney W. A.
Published: February 2011

The brass-plating process is one of the most important methods of bonding rubber to metal. It consists of depositing a thin layer of copper zinc alloy on the surface of the metal. The rubber is then moulded in contact with the brass deposit, and in most cases, a strong bond is established during vulcanization. Even, however, when all precautions are taken, bond failures occur, often with no obvious cause, so the process is still somewhat suspect. It is only fair to say, however, that this variability appears to be common to most methods of bonding rubber to metal, and that in general production a high level of adhesion is maintained.
The Structure of Polyisoprenes. V. Ultraviolet Absorption Spectra of Certain Carbalkoxy-Substituted 1,5-Dienes, and the Charge-Resonance Spectra of Glutaconic Ester Enolate Ions
Authors: Bateman L. , Koch H. P.
Published: February 2011

Spectral evidence supports the conclusion reached in Part IV that ring-chain mesomerism in methyl and ethyl Δ1,5-hexadiene-l,1,3,3,4,4,6,6-octacarboxylates is nonexistent in solution, just as in the crystalline state. The data are not inconsistent with chain hyperconjugation in these molecules. The marked change in structural type that follows the addition of one molecule of hydrogen or hydrolytic reagent has been verified spectrographically. The spectra of methyl and ethyl α,γ-dicarboxyglutaconic esters and their sodium and cupric derivatives have been measured in various solvents, and their tautomeric behavior compared with that of other keto-enols. Of special interest is the intense long-wave absorption band of the enolate ions, which are recognized as simple structural analogs of the cyanine dyes giving rise to similar charge-resonance spectra. A preliminary comment is made on the present accepted structure of ethyl 6-ethoxy-α-pyrone-3:5-dicarboxylate.
Strength of Amorphous and of Crystallizing Rubberlike Polymers
Authors: Aleksandrov A. P. , Lazurkin J. S.
Published: February 2011

The strengths of unloaded vulcanizates and the action of active fillers differ greatly according to the types of elastomers from which they are derived. These differences are not connected directly with the chemical compositions of the elastomers. Thus, for example, vulcanizates of natural rubber and synthetic isoprene rubber differ in strength in the ratio 10–15 to 1, whereas vulcanizates of Butyl rubber and of polychloroprene are very similar to natural rubber vulcanizates with respect to tensile strength. These differences in tensile strength cannot be ascribed directly to differences in structure of the chains, linear or branched; linear polymers of styrene and of methyl methacrylate “vulcanized” by small admixtures of butadiene-benzene or dimethacrylate-ethyleneglycol have, in the elastic state, tensile strengths which are just as low as those of unloaded vulcanizates of sodium-butadiene rubber or of isoprene rubber. The differences in tensile strength must, accordingly, be looked for in the different macroscopic properties of these polymers.
The Behavior of Ketene towards Olefins and Olefinic Peroxides
Authors: Naylor Ralph F.
Published: February 2011

Ketene will not react additively with unconjugated olefins such as 1-methylcyclohexene, dihydromyrcene, and rubber. Zinc chloride or sulfuric acid promotes reaction of ketene with acetone (carried over from the ketene generator), with the formation of a compound, C7H10O3, probably β-propenyl acetoacetate. Ketene acetylates olefinic hydroperoxides, but the resultant peracetates are very unstable.
Thermal Breakdown of Rubber
Authors: Bolland J. L. , Orr W. J. C.
Published: February 2011

The degradation of rubber observed during various technological processes may arise from several different causes. Since one such contributory factor is possibly degradation by a purely thermal mechanism, it is of interest to estimate experimentally the importance of this type of degradation under the temperature conditions normally used in the processing of rubber. It may be stated immediately that the authors' experiments confirm that thermal breakdown of rubber is of negligible importance under such circumstances and is always overshadowed by more efficient alternative modes of degradation. The thermal degradation of rubber, constituting as it does its formally simplest chemical reaction, has real possibilities of giving insight into the chemical stability and reactivity of the rubber molecule. Moreover, the theoretical treatment of the degradation of long-chain molecules has apparently far outstripped the experimental investigation of the problem. To date, attention has been confined to long polymeric chains which are assumed to break in quite random fashion at the regularly recurring bonds joining the monomeric units, and it is of importance to see how far this simplifying suggestion regarding the manner of chain scission does in fact correspond to reality. With these two ends in view the writers have investigated the thermal breakdown of rubber in some detail. A preliminary report is now presented on certain complexities of the reaction which may, however, be resolved by consideration of the resonance stabilization of the intermediate degradation products.
Rubber, Polyisoprenes and Allied Compounds. VIII. The Formation of Dialkyl Sulfide Dihalides, and Its Bearing on the Problem of Determining the Unsaturation of Vulcanized Rubber
Authors: Bloomfield George F.
Published: February 2011

In determining the unsaturation of olefinic sulfides and disulfides by halogenation methods, the addition of halogen to the sulfur atom must be taken into account. The dihalides of dialkyl or dialkenyl sulfides react with aqueous potassium iodide partly to liberate iodine with regeneration of the sulfide, and partly to form halogen acid and dialkyl or dialkenyl sulfoxides. Correction for the latter reaction, which occurs extensively in the presence of alcohol or acetic acid, must be applied before reliable unsaturation values for dialkenyl sulfides can be obtained. With vulcanized rubber and iodine monochloride, the precise magnitude of the correction to be applied is uncertain, but this uncertainty can be removed by using bromine as the additive reagent. Simple rubber-sulfur vulcanizates show a loss of unsaturation corresponding to one double bond per sulfur atom combined up to at least 8 per cent of combined sulfur; vulcanizates accelerated with mercaptobenzothiazole in the presence of zinc oxide exhibit a substantially smaller loss of unsaturation. The dibromides of dialkyl sulfides readily yield a molecule of bromine to olefins, the reaction being practically exclusively additive.