bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Antioxidants in Hevea Latex
Authors: Altman R. F. A.
Published: February 2011

An elaborate investigation on the identity and usefulness of the antioxidants naturally occurring in Hevea latex is of value because there is an increasing demand for special types of rubber with low nitrogen and ash contents, less water absorption, better electrical properties, and less odor than common crepe, and because these rubbers are generally unstable in comparison with the usual grades of rubber crepe and sheet. for the purpose of the investigation, fresh latex was separated into main-fractions, the most important of which have been called water-solubles and ether-solubles. These were further separated into various subfractions, which, one by one, have been tested for their antioxidant activity on raw rubber. In the following table only those fractions which show an outstanding antioxidant action are recorded. It is shown further that the amino acids are most remarkable in their antioxidant action : minute quantities exert a strong retarding action on the oxidation of raw rubber. Choline and cephaline are most probably the active components of the second water layer. The active ether-soluble fractions could not be identified due to the small quantities separated.
Latex Strainability Test
Authors: Brass P. D. , Slovin D. G.
Published: February 2011

The presence of fine eoagulum in latex affects some processes very adversely. This coagulum is often wrongly blamed on some complicated chemical or physical action in the compound when the true explanation is that all the larger particles were present in the original latex or dispersions from which the compound was made. The latex strainability test measures the amount of latex that will pass through a filter medium before clogging.
Testing Reclaimed Rubber
Authors: Kilbourne F. L.
Published: February 2011

1. A new test formula for reclaimed rubber based on the percentage of rubber hydrocarbon in the reclaim has been in use since 1942. 2. Details of the mixing and a simplified program for testing a large number of reclaims have been outlined. 3. The test formula gives consistent results in the hands of experienced technicians.
On the Degree of Crystallinity in Natural Rubber. I. An Improved Method to Determine the Degree of Crystallization in Rubber
Authors: Goppel J. M.
Published: February 2011

There are indications that the degree of crystallization in high polymeric substances is of importance in studying mechanical properties. With regard to the crystallization of rubber, few measurements have been made, mainly by Field. The results, however, are in contradiction to estimates of an earlier date, and therefore the necessity was felt to have them checked. An x-ray method, in some respecta differing from that of Field, was developed, the results of which diverged considerably from the figures reported by Field. The present article deals with a description of the method.
On the Degree of Crystallinity in Natural Rubber. II. The Orientation of Rubber Crystallites in Stretched Samples
Authors: Goppel J. M.
Published: February 2011

In the foregoing article a method for determining the proportion of crystalline rubber in stretched samples has been described. A complication due to varying crystallite orientation in different samples appeared to interfere with the application. A simple relation is given between the degree of orientation and an empirical constant which makes possible a rapid determination of the degree of crystallization, regardless of the orientation in the sample under investigation.
Comparative Studies on Photoelasticity of Elastomers and Plastomers
Authors: Heller Wilfried , Oppenheimer Hans
Published: February 2011

Transparent films of elastomers and plastomers were found to differ sufficiently in their photoelastic behavior to make stress double refraction a useful criterion of the prospective mechanical properties of a given material. The stress double refraction in such films is mostly an effect of deformation, of orientation, or of both deformation and orientation of polymer chains. In such polymers, however, which crystallize under stress, a large part of the optical effect may be due to oriented crystallization. In addition to its practical value as a testing method for polymers, the photoelastic method offers, therefore, particularly in combination with simultaneous investigations of mechanical properties, the prospect of correlating mechanical properties of a polymer film with its internal structure, and of correlating changes in both qualities on exposure of the film to different degrees of stress. Although results obtained on such films, by means of x-ray diffraction or x-ray scattering and electron-diffraction, are, in general, easier to interpret, the photoelastic method has the considerable advantage of making possible a quantitative follow-up of rapid changes in film structure, e.g., of relaxations.
The Infrared Spectrum of Vulcanized Rubber and the Chemical Reaction between Rubber and Sulfur
Authors: Sheppard N. , Sutherland G. B. M.
Published: February 2011

In an earlier paper we described an infrared spectroscopic investigation of the vulcanization of rubber, and drew attention to a band at 10.4 µ (960 cm.−1) which appeared in the spectrum of both straight and accelerated vulcanization. We have investigated further this phenomenon, and find that the intensity of this band correlates well with the proportion of sulfur chemically incorporated, but not with the degree of vulcanization as reflected in the physical properties of the finished product. We were unable to explain this band in a convincing manner in terms of C—S linkages, but more recently have found a band in the same position (10.4 µ) and another at 11.2 µ (890 cm.−1) in certain thermally degraded rubbers. Since in this case the two new bands are obviously due, respectively, to the development of new CHR:CHR′ and CRR′:CH2 groups, it seemed probable that the 10.4 µ band might also be caused by new groupings of the former type. An investigation of the spectrum of an ebonite (in which the rubber-sulfur reaction has been carried to an extreme) confirmed this idea. In this spectrum, absorptions in the region of 6 µ showed that a considerable number of bonds remained, but the characteristic absorption at 12.0 µ arising from CRR′: CHR″groups in rubber had largely disappeared. On the other hand, the band at 10.4 µ (although shifted to slightly longer wave lengths) had increased greatly in intensity.
Influence of Structure on Polymer-Liquid Interaction. II. Influence of Nitrile Groups
Authors: Salomon G.
Published: February 2011

Swelling equilibria of a number of copolymers in various organic solvents have already been discussed. The influence of polarity and polarizable groups has been derived from the gradual changes of swelling equilibria. We shall deal with the same problem in the present paper, but, by considering only nitrile groups in the polymer, the resulting picture becomes less complex. The polymers under investigation are the three series of copolymers from acrylonitrile, with butadiene, isoprene, and dimethylbutadiene, respectively. In each series, the mechanical properties change with nitrile concentration, as indicated by a gradual increase in brittleness. The combination of nitrile and methyl groups leads to a further immobilization of the flow units; the copolymers from dimethylbutadiene are, therefore, plastics at room temperature—as has been discussed in another paper.
Preparation and Properties of Rubberlike High Polymers. V. Influence of Nitrile Groups on the Properties of Copolymers
Authors: Salomon G.
Published: February 2011

The introduction of methyl groups in butadiene leads to a decrease in 1,2- and 3,4-addition as well as to a reduction of cross-linking reactions. The same regularity can be observed in a series of copolymers, which will be discussed in the present paper. Apart from these interrelations between diene structure and pattern of the chain molecule, other physical properties such as the second order transition point and the closely related brittle point depend on the presence of methyl groups. Nitrile groups enhance these differences between the three series of diene polymers, as will be seen from the following results. A striking contrast between these widely diverging physical and mechanical properties is the similarity of swelling equilibria, which are obviously determined only by the number of nitrile groups per volume unit of polymer, as will be discussed in another communication.
Measurement of Internal Double Bonds in Polymers by Perbenzoic Acid Addition
Authors: Saffer Alfred , Johnson B. L.
Published: February 2011

Internal double bonds formed by 1,4-polymerization of diene monomers add perbenzoic acid more rapidly than do vinyl double bonds which are the products of the 1,2-type of addition. The extrapolation procedure proposed for determining internal double bond contents of diene polymers is based on this difference in addition rates. Oleic acid mixtures with 10-undeeylenie acid were prepared and analyzed with an accuracy of 1 per cent. However, the method is limited to systems containing 70 per cent or more internal double bonds. Minimum interference of side-chain oxidation by perbenzoic acid was attained by using a low temperature and a small excess of perbenzoic acid. Methyl-substituted emulsion polymers are characterized by high amounts of 1,4-addition. Polymerizations with alkali-metal catalysts result in products of high vinyl double-bond content. A slight preference for the 1,4-type of polymerization is favored in media of low pH. Natural rubbers are formed almost completely by 1,4-polymerization. Heat softening, modifier concentration, and extent of conversion do not influence the degree of 1,4-polymerization.
The Determination of Unsaturation in Butadiene Synthetic Rubber
Authors: Kobeko P. P. , Moskvina E. K.
Published: February 2011

1. It has been found that synthetic rubber does not precipitate from a solution of dichloromethane by the addition of Wijs reagent, whereas natural rubber does precipitate under the same conditions. The reverse relation occurs with carbon disulfide as solvent. 2. A method has been developed for the determination of the unsaturation of butadiene rubber in solution in dichloromethane by the use of Wijs reagent. 3. It has been demonstrated that, by the use of a solution of iodine chloride in carbon tetrachloride, the reaction with rubber is complicated by the hydrolysis of iodine chloride during titration, but not by the substitution of hydrogen by halogen nor by the hydrolysis of the rubber-halogen addition product. 4. The possibility of obtaining accurate values for unsaturation by a calculation of this hydrolysis is demonstrated. 5. Two methods have been developed for the determination of the unsaturation of natural and butadiene rubbers.
Determination of Unsaturation of Synthetic and Natural Rubbers by Means of Iodine Monochloride
Authors: Lee T. S. , Kolthoff I. M. , Mairs Mary Anne
Published: February 2011

The unsaturation of GR-S at various conversions corresponds to the spectrophotometrically determined styrene content. It is concluded that GR-S at various conversions has the theoretical unsaturation. Emulsion polybutadiene was found to have 97 to 98 per cent of the theoretical unsaturation, emulsion polyisoprene 97 per cent. Sodium polybutadiene and polyisoprene had unsaturations which were considerably less than theoretical. The unsaturation of sodium polybutadiene was 92 per cent and that of sodium polyisoprene was 85 per cent. Sodium copolymer of butadiene (75) and styrene (25) also had an unsaturation considerably less than the theoretical value.
Natural Vulcanization Accelerators in Hevea Latex
Authors: Altman R. F. A.
Published: February 2011

As numerous investigators have shown, some of the nonrubber components of Hevea latex have a decided accelerating action on the process of vulcanization. A survey of the literature on this subject points to the validity of certain general facts. 1. Among the nonrubber components of latex which have been investigated, certain nitrogenous bases appear to be most important for accelerating the rate of vulcanization. 2. These nitrogen bases apparently occur partly naturally in fresh latex, and partly as the result of putrefaction, heating, and other decomposition processes. 3. The nitrogen bases naturally present in fresh latex at later stages have been identified by Altman to be trigonelline, stachhydrine, betonicine, choline, methylamine, trimethylamine, and ammonia. These bases are markedly active in vulcanization, as will be seen in the section on experimental results. 4. The nitrogenous substances formed by the decomposition processes have only partly been identified, on the one hand as tetra- and pentamethylene diamine and some amino acids, on the other hand as alkaloids, proline, diamino acids, etc. 5. It has been generally accepted that these nitrogenous substances are derived from the proteins of the latex. 6. Decomposition appears to be connected with the formation of a considerable amount of acids. 7. The production of volatile nitrogen bases as a rule accompanies the decomposition processes. These volatile products have not been identified. 8. The active nitrogen bases, either already formed or derived from complex nitrogenous substances, seem to be soluble in water but only slightly soluble in acetone.
Effect of Prolonged Storage of Unvulcanized Stock on the Properties of the Vulcanizate
Authors: Moakes R. C. W. , Soden A. L.
Published: February 2011

The effects of prolonged storage, in both the unvulcanized and vulcanized states, on the physical properties of four samples of tire tread stock were studied. Storage of unvulcanized stock for four years did not cause any appreciable change in its rate of vulcanization or in the deterioration of any of the important properties of the vulcanizate. Comparison with the results for samples stored in the vulcanized condition shows that the unvulcanized stock was, in fact, more stable than the vulcanizate as far as changes during storage were concerned.
Effect of Storage and Temperature on Flexibility of Natural and Synthetic Rubbers
Authors: Gregory John B. , Pockel Irving , Stiff John F.
Published: February 2011

A new method for measuring the flexibility of rubber has been described. The method consists essentially in determining the stress-strain curve obtained by loading and unloading a loop formed from a one-inch by six-inch strip cut from a test slab. A coefficient of flexibility independent of the thickness of the sample and, in addition, information on per cent resilience were obtained. By the use of the method described, the behavior of various natural and synthetic rubber gas mask facepiece compounds was studied during one month to three months' exposure at various temperatures down to −20° F. Progressive stiffening probably due to crystallization was found for natural rubber, GR-I, and GR-M compounds at low temperatures. No tendency to crystallize was noted for the GR-S compound. Of the crystallizable polymers GR-I was the most resistant, and GR-M the least resistant to stiffening during low temperature storage. It is of course evident that different polymers have inherently different degrees of resistance to low temperatures. Disregarding these inherent differences the work reported indicates that the resistance of elastomer compounds to stiffening during prolonged low temperature storage is favored by the following: 1. Use of interpolymers made from monomer mixtures having a relatively large proportion of each component, thus obtaining mutual intereference with crystallization. 2. Use of a “tight” cure which probably so impedes the movement of the polymer chains as to make crystallization difficult.
Effect of Iron on Aging of GR-S
Authors: Albert H. E. , Smith G. E. P. , Gottschalk G. W.
Published: February 2011

Soluble iron decreases the resistance of the GR-S polymer to aging. The effect of iron is greater than that of copper or manganese. The aging of an aluminum sulfate—coagulated polymer can be improved by the use of low-iron aluminum sulfate instead of the commercial grade of this material. The use of commercial aluminum sulfate as a coagulant gives a polymer somewhat superior in aging to one coagulated with salt and acid. The aging of GR-S vulcanizates is accelerated slightly by polymer-soluble iron. Relatively high iron concentrations are required to produce much effect. The effect of iron on vulcanizate aging is much less than in the case of polymer aging. The presence of iron increases the rate of oxygen absorption of GR-S polymer and vulcanizates, the effect being less in the latter case. The rate of oxygen absorption of aluminum sulfate—coagulated GR-S polymer is decreased by employing low-iron aluminum sulfate instead of the commercial grade. A polymer coagulated by commercial aluminum sulfate absorbs oxygen at a slower rate than one coagulated by salt and acid.
High-Solids Synthetic Latex Directly from Reactor
Authors: Chittenden F. D. , McCleary C. D. , Smith H. S.
Published: February 2011

In the ten-year period preceding the outbreak of hostilities with Japan, imports of natural latex into the United States assumed a sharply rising trend. (Figure 1 shows that the 1940 figure is somewhat high owing to the inception of stockpiling.) Roughly 80 per cent of this latex was shipped in as a concentrate of 60–65 per cent solids, since this eliminated shipping excess water originally present in the latex, and constituted a material suitable for various applications in which the normal latex could not be used. Although small quantities of special-purpose synthetic latices had been produced domestically before 1941, it was not until 1944 that substantial production of a general-purpose synthetic latex got under way (Figure 1). With this production, there arose the problem of producing a concentrate for use in applications where a high-solids latex is essential. Natural rubber latex can be concentrated readily, either by centrifuge or a creaming process, since it has a large particle size. Synthetic rubber latex, on the contrary, has a very small particle size, which makes concentration a more difficult and costly operation. In practical creaming operations a significant amount of polymer is usually lost in the serum. This article presents a description of two new synthetic latices made to 55–60 per cent solids directly in the reactor and a short description of the methods of preparation. Since the production of these high-solids latices is only slightly more expensive than the production of low-solids types, they can be sold at only a small increase in cost over the latter.
Quantitative Estimation of GR-S in Rubber Reclaim
Authors: Le Beau D. S.
Published: February 2011

The method is none too accurate above 90 per cent of either natural or synthetic rubber present, unless the reclaim analyzed is well known. If the degree of deviation for a given reclaim is well established, it is possible to determine the mixtures up to 95 per cent of either component. However, if the degree of deviation is only an average figure, derived by such critical scrutinization of a number of reclaims as shown in Table I, greater accuracy cannot be expected in the estimation of the components of mixtures containing more than 90 per cent of either natural or synthetic rubber. The GR-S or natural rubber content of reclaims containing a great variety of scraps, such as some of the so-called victory reclaims, can be estimated only with a lesser degree of accuracy than ±2.5 parts. Difficulties in the estimation of the polymer components may also be encountered in light colored reclaims. However, such estimations are seldom necessary because of the peculiar compounding technique required by GR-S for proper physical performance.
Hardness Testing of Vulcanized Rubber. VIII. Hardness Tests with a Conical Indentor
Authors: Scott J. R.
Published: February 2011

The relation between load and depth of indentation for a conical indentor has been investigated. The theoretical relationship applicable to perfectly elastic materials (indentation proportional to square root of load) is found to hold for all the rubbers examined except one very hard sample, whose comparative inelasticity causes some deviation from this relationship. This result further confirms the correctness of the theoretical investigation on indentation hardness testing of rubber by indicating that the forces required to produce indentations of similar shape, but different sizes, are proportional to the squares of corresponding linear dimensions of the indentations. With a conical indentor under a constant load, the depth of indentation is approximately inversely proportional to the square root of the elastic modulus of the rubber at small elongations. A conical indentor is preferable to a ball indentor in that it shows more nearly uniform sensitivity to small differences in modulus (i.e., true hardness) at all parts of the hardness scale. It has previously been shown that the ball is superior to a flat-ended plunger in this respect. To approach still nearer to uniform sensitivity would presumably require a pointed indentor having a profile with concave sides. This would be difficult to make accurately, and very likely to damage on account of its sharp point; this might, indeed, be a disadvantage of the conical form also.
Hardness Testing of Vulcanized Rubber. XI. Influence of Gauge-Spring Pressure and Friction in the Indentation Hardness Test
Authors: Scott J. R.
Published: February 2011

A discussion is given of the effects of the spring which, in many dial micrometer gauges, applies a small upward or downward force to the gauge stem, and of the effects of friction in the gauge. When hardness tests are made by the differential method, the reading being taken as the difference between the indentations produced by a small zero load and a much larger total load, the errors introduced by unbalanced gauge spring pressure and by friction may be much more serious than when a direct hardness reading, i.e., without an initial zero load, is taken. Other things being equal, the resulting percentage error in the hardness reading is greater the smaller indenting load. This is a further reason, additional to that already advanced3, for limiting the reduction of ball size and load which has been advocated to reduce the influence of the thickness of the rubber. If the gauge contains a spring, or if friction is present, it is not possible to adjust conditions so as to eliminate the resulting errors in the differential readings on all rubbers. The errors can, however, be minimized in the following ways. (1) By increasing the ratio (z) of zero load to total load. An excessive zero load, however, is undesirable for other reasons; a value of 0.05 for z is a suitable compromise. (2) By adjusting the unbalanced spring pressure to zero when the gauge stem is in a certain position which depends on the value of z and the hardness of the rubber under test. Taking z as 0.05 and the average B.S. hardness number of normal rubbers as 75 (i.e., an indentation of about 0.75 mm.), this position is that in which the tip of the indenting ball is 0.5 mm. above the surface of the rubber.
Some Problems Involved in the Grading and Testing of Natural Rubber. A Progress Report
Authors: Fletcher W. P.
Published: February 2011

In the establishment of grading and testing procedures for natural rubber based on the properties of vulcanizates, four main questions arise. First it is necessary to decide on the property to be measured, and reasons are given for the choice of elongation at a fixed load for the purpose, elongations being below 250 per cent. Secondly the method of test had to be decided, and a simple version of the National Bureau of Standards' strain tester has been developed and is in use. Thirdly a standard test mix, into which the raw rubber samples are compounded, must be selected; the well known No. 1 compound of the Crude Rubber Committee of the American Chemical Society has been found to be defective because of its great sensitivity to moisture, whereas a mixed mercaptobenzothiazole-diphenylguanidine stock and a stock accelerated with N-cyclohexyl-2-benzothiazole sulfenamide appear suitable. Finally the interpretation of results is discussed. The use of a single cure for classification of rubbers is felt to be inadequate, and to determine both the maximum modulus of which the rubber is capable in the compound and also the cure time to obtain this condition, it is proposed to define the property with tolerance limits at three cures. Incidental problems arising include mixing error, and some investigation of this is described.
Effect of Soil Microörganisms on Rubber Insulation
Authors: Blake John T. , Kitchin Donald W.
Published: February 2011

Evidence is presented that some of the rare failures of nonleaded rubber-insulated underground cables were caused by soil microörganisms. Laboratory conditions deliberately chosen to favor microbial attack made possible greatly accelerated tests in which failures like those found after ten years or more in service have been produced in a few weeks or months. These failures are characterized by discrete, minute low resistance spots. Drastic decrease of insulation resistance was used as the criterion of failure. The exact distribution of low-resistance spots has been shown by an electrolytic test. Parallel tests in sterile and in active soil proved that the failures in soil were caused by living microorganisms. Soil exposure tests have been made on natural and synthetic rubbers and several other plastic insulations. Natural rubber compounds were found to be the most susceptible. In some soils GR-S compounds proved stable up to two years, but failed in a more active soil. The exact mechanism of attack is not known. In some cases there is drastic electrical failure without visible surface effect. In actual operation of underground cables the exact combination of conditions necessary for producing failure by microbial attack can occur only rarely. The purpose of the severe laboratory tests is to make possible the development of insulations stable under all soil conditions.
Tear Initiation and Tear Propagation
Authors: Buist J. M.
Published: February 2011

(1) Both the crescent and angle tests are group (2) tests; therefore the width of the sample must fee taken into account when the tear resistance is being calculated. (2) There is one exception to the above, and that is the case of knotty tears in group (2) tests. When knotty tears occur, the test becomes a direct tear test [group (1)], and the width is no longer important. (3) When knotty tears occur with group (1) tests, the width must be considered for, in reality, the test has become a group (2) test. (4) Some rubbers exhibit fibering during tearing, and this is explained by the cohesive forces between fibers reaching a limiting value before the limiting value of the breaking strength of a fiber is reached. (5) Differences in the mechanism of tearing with different fillers have been noted. (6) Practical evidence of the existence of maximum shear stress in subsurface planes of the material has been obtained, and a mathematical solution for a simple case has been given. (7) The angle tear method is a combination of tear initiation and tear propagation, and can be regarded as complementary to the crescent test. It cannot be regarded as a replacement for the crescent test. (8) With certain rubber compounds the component of stress in the direction of pull is too high in the case of the angle test-piece. (9) It is suggested that the unnicked crescent be used in preference to the angle test-piece for tear initiation measurements, as the unnicked crescent test-piece has more discriminating power. (10) The same proportion of straight and knotty tears occurs with both the crescent and angle methods. (11) A preliminary evaluation of the I.G. tear cutter indicates that the fairest comparison with other methods requires a single slit to be inserted in the outside circumference of the ring.
The Velocity of Propagation of Ultrasonic Waves and the Form of the Molecules of High Polymers
Authors: Natta Giulio , Baccaredda Mario
Published: February 2011

The velocity of propagation of ultrasonic waves in numerous substances of high molecular weight was determined. For substances not fusible at temperatures below 100° C, this velocity was determined by extrapolation from solutions considered ideal. For linear macromolecules without side chains, the ultrasonic velocity appears to be practically equal, within the limits of experimental error, to that calculated by the formula of Rao and on a basis of the additive values of the bond velocity of Lagemann and Corry. For molecules which have many side chains, the velocity is lower than the calculated value, whereas for compounds of low molecular weight this deviation is relatively small, viz., less than 10 per cent; it becomes much higher, viz., almost up to 40 per cent, for macromolecules. The form factor is defined as the ratio of the velocity determined experimentally to the velocity calculated by the formula of Rao. This form factor is equal to 1 for polymers without side chains or with very few side chains, such as paraffins, polyethylenes, Nylon, polyethylene oxides, and polyoxymethylenes; is only 0.89–0.90 for natural rubber; only 0.82–0.84 for Buna and for hydrogenated Buna, poly-α-butylenes, and polystyrenes; only 0.79–0.80 for polyisobutylenes; only 0.89 for polymethacrylates; only 0.78 for polyvinylisobutyl ethers; only 0.65 for Butyl rubber; and only 0.63 for polymethyl methacrylates. The form factor is thus affected by the frequency and length of the side chains, and by any secondary side chains which may be present.
Propagation of Audiofrequency Sound in High Polymers
Authors: Witte R. S. , Mrowca B. A. , Guth E.
Published: February 2011

Velocity and attenuation measurements were made in thin strips of rubber from 0.5 to 5 kc and from −5° to 90° C to obtain the dynamic viscoelastic constants of Butyl and GR-S gum stocks. Above room temperature velocity and attenuation are higher in Butyl gum than in GR-S. In all cases, the velocity increases with decreasing temperature and increasing frequency. The attenuation shows a peak with temperature. For Butyl, the peaks are broad and occur at higher temperatures than for GR-S. For both stocks an increase in frequency gives peaks which are higher, sharper, and shifted to higher temperatures. In some instances, there are indications of peaks in the attenuation versus frequency at frequencies beyond our range of measurement. The behavior of the dynamic modulus in the temperature and frequency range studied is similar to that of the velocity. These results, combined with low temperature static measurements and very low frequency dynamic measurements, indicate a U-shaped modulus-temperature curve whose minimum broadens and shifts to higher temperatures with increasing frequency. This may be explained by a generalization of the kinetic theory of rubber elasticity, taking into account intra- and intermolecular forces, and considering time effects.
Propagation of Ultrasonic Bulk Waves in High Polymers
Authors: Ivey Donald G. , Mrowca B. A. , Guth Eugene
Published: February 2011

The propagation of supersonic waves in bulk rubbers has been studied from 40 kc per second to 10 Mc per second and from −60° to 60° C. The wave velocity was found to increase with decreasing temperature, level off both at high and low temperatures, and increase slightly with frequency. Peaks in attenuation as a function of either temperature of frequency were observed; these occurred at lower temperatures for lower frequencies. The peaks of Butyl, a high-loss rubber, are broader and higher than those of GR-S and Hevea, which are lower-loss rubbers. The results are in qualitative agreement with data obtained by strip methods at audiofrequencies. However, for bulk waves the real and imaginary parts of two elastic constants, the bulk and shear moduli, determine wave velocity and attenuation; hence, independent measurements of shear wave properties are necessary to evaluate these constants. A three constant theory is discussed, assuming a shear viscosity only, so an effective modulus K+4μ/3 is obtained, where K and μ are the bulk and shear moduli. Relaxation times of the order 10™6–10™8 second are indicated. Approximate values of the dynamic Young's modulus are obtained from the effective modulus by assuming that the high frequency dispersion is due to the appearance of a “crystalline” shear elasticity. These results are correlated with low frequency data, and the dynamic Young's modulus and the loss factor are plotted. The loss factor exhibits a maximum in the dispersion region. Results are plotted in the range from 1 to 107 c.p.s., which covers a wider range of frequency than earlier investigations. The necessary distribution of relaxation times is discussed.
Mastication of Rubber. I
Authors: van Rossem A. , Hoekstra J.
Published: February 2011

Plasticity measurements with the Williams-type (parallel-plate) balance and steam plastometers confirmed the well known influence of time, temperature, and energy consumed on mastication of raw rubber on rolls. Reproducibility of results proved fairly high. The effect of storing plasticized rubber was a slow and unimportant hardening. On hot storing, hardening during the first days took place, followed by slow softening. With the steam plastometer, a stiffening value was determined for several fillers when mixed into masticated rubber. Some experiments were done on the influence of the concentration of such fillers and on the influence of softeners, accelerators and sulfur on plasticity. The influence of the degree of mastication of the mixes on the vulcanized stocks was investigated in a few cases. Apart from the well known influence of extreme mastication on breaking strength, a remarkable influence of the temperature of mastication on modulus was found.
Mastication of Rubber. II
Authors: Hoekstra J. , van Rossem A.
Published: February 2011

Recovery of masticated rubber was measured at different temperatures. Recovery was found to be influenced, but not governed, by plasticity. A quick method, working at 100°, gave information on the influence of fillers and of storage at room temperature and at 70° C. The influence of recovery and plasticity on set up after calendering was determined.
Investigations in the Field of Rubber Vulcanization. IV. Phenomenon of Vulcanization Optimum in Mixtures with a Large Proportion of Constructive Agent
Authors: Dogadkin B. , Karmin B.
Published: February 2011

1. In mixtures with a large content of constructive (vulcanizing) agent, the vulcanization-optimum phenomenon is connected with the formation of dense space-lattices in the structure of the vulcanizate, which inhibit the formation of crystalline or highly oriented segments during elongation. 2. In contrast to mixtures with a small content of vulcanization agent, the vulcanization optimum of which is explained by superimposition of oppositely directed constructive and destructive processes, the case noted in the preceding paragraph shows a maximum only on the kinetic curve representing the change in strength. The kinetic curves representing relative elongation, swelling, and solubility are monotonic in character. 3. The maximum on the kinetic curve representing the change in strength in mixtures with a large content of constructive agent occurs before complete combination of the latter with the rubber. 4. In consequence of the absence of oppositely directed actions on the part of sulfur and oxygen, the vulcanization of sodium-butadiene rubber mixtures shows a maximum only on the kinetic curves representing the change in strength. 5. The position of the strength maximum in mixtures with a large content of constructive agent depends on the rate of deformation. As the rate of deformation is decreased, the maximum appears after more prolonged vulcanization periods of the mixtures. 6. The strength of natural rubber vulcanizates at the vulcanization optimum is a linear function of the quantity of crystalline phase formed during elongation.
Effect of Chemical Agents on Heat Deterioration of GR-S
Authors: Mesrobian Robert B. , Tobolsky Arthur V.
Published: February 2011

A detailed study of Tables III and IV, in which the effect of chemical agents on high temperature aging are evaluated by relaxation and oxygen absorption indexes and conventional test indexes, shows a much higher evaluation consistency for the Table III indexes and presents some doubt regarding the significance of the data given in Table IV and Figure 8. Although the conventional tests have the advantage of speed and convenience, the difficulties of obtaining truly significant correlation between laboratory aging tests and practical performance are considerable. The methods reported in this paper may, therefore, be of value in supplementing the numerous aging tests already in use in various laboratories.
Plasticizers for Polar Synthetic Rubbers
Authors: Cheyney La Verne E.
Published: February 2011

Natural and synthetic rubbers may be grouped in two broad classes—polar and nonpolar. Dipole linkages are involved in the plasticization of the polar group; hence they possess certain resemblances to the polar thermoplastics in this respect. Plasticizers are employed with such polymers for two general purposes: increasing plasticity of the uncured rubber; and increasing flexibility or corresponding effects in the cured material. Plasticization of the polar rubbers is a complex problem because of structural variations inherent in diene polymers and copolymers; the vulcanization process; and effects of other additives—for example, carbon black. Available data are extremely confusing because of these factors and the fact that much of the information reported is meager. Many of the materials which have been employed may be grouped into a few broad chemical classes. The effects of these vary widely among a given class because of structural variations and differences in physical properties. It is possible to generalize concerning a few types of effects, but more and better data are required before an adequate picture of the plasticization of the polar synthetic rubbers will be available.
Role of Adsorption in Reinforcement of GR-S
Authors: Barnett C. E. , Jones H. C.
Published: February 2011

1. The reinforcement of GR-S is influenced to an appreciable extent by the adsorption characteristics of pigments compounded in this polymer. 2. The relation between surface activity and reinforcing properties of a pigment in GR-S is demonstrated in the case of a basic zinc carbonate calcined through a range of temperatures. 3. Twelve pigments were immersed in GR-S cement, and the recovered polymer was evaluated. The mineral pigments, ELC magnesia and calcium silicate, selectively remove fatty acids and soaps from GR-S cements. The adsorption by EPC black is not selective with respect to fatty acids and soaps. The effects obtained on testing the recovered polymer vary in line with the amount and nature of the adsorption. 4. With ELC magnesia and calcium silicate, the effect of adsorption is predominantly due to the removal of fatty acids and soaps, and this affects the vulcanization chemistry. The process is different with EPC black, but a clear interpretation is not possible on the basis of present experimental data.
Improved-Processing GR-S by Variations in Compounding
Authors: Crawford R. A. , Tiger G. J.
Published: February 2011

The data indicate that treating GR-S for 5 minutes in the Banbury at 380° F in the presence of the combinations of cross-linking agents listed brings about improvement in processing and stress-strain properties, equal or superior to those produced by sulfur and Captax together. In turn, this GR-S polymer, treated with sulfur and Captax, was shown to be superior to GR-S-60 and to GR-S-60/GR-S blends in ratios higher than 30/70, after mastication and compounding of the polymers in a hot Banbury at about 380° F. The properties of the sulfur-Captax cross-linked GR-S closely approached the excellent processibility and excelled the poor stress-strain characteristics of GR-S-60 compounded by milling at normal temperatures.
Characteristics of Reinforcing Furnace Blacks Processing Shrinkage
Authors: Dannenberg E. M. , Stokes C. A.
Published: February 2011

A major technical development in the rubber industry has been the recent introduction of furnace blacks possessing rubber reinforcing properties in the range of channel blacks. The literature on the subject of reinforcing furnace blacks is rapidly expanding to satisfy the need for information on the compounding and rubber properties of these new products. Types of reinforcing furnace blacks are available which duplicate closely the usual rubber properties observed with channel blacks in vulcanized stocks. However, because of the flexibility of operation and the different types of raw material adaptable to the continuous furnace process, it is also possible to produce grades of reinforcing furnace blacks which differ markedly from channel blacks in rubber properties. The range of rubber stiffness and hardness obtainable with reinforcing grades of furnace blacks is much greater than with channel blacks, and although final approval of a grade of black for a particular application is based on service testing, the useful range of rubber product quality has been broadened by the introduction of new varieties of furnace blacks. Processing characteristics of carbon blacks may be described as the relative workability factors of rubber stocks in the sequence of operations preceding the completed manufacture of cured rubber articles. In those compounds where carbon black is a substantial component of the stock, the properties of the black would be expected to exert a major influence on processing. The work reported here is concerned with the effect of carbon black properties on the forming step of semifinished stocks, and includes a study of the processing shrinkage properties of carbon black loaded stocks.
The Compounding of Hard Rubber (Natural and Synthetic)
Authors: Gall W. Murray
Published: February 2011

Hard rubber, frequently called ebonite, is a material which has many desirable physical and chemical properties. The relatively new plastics industry has offered stiff competition, yet it is reasonably safe to say that, for certain applications, nothing else can be substituted for hard rubber and still maintain its unique properties. One of the principal qualities of this material is its finished appearance. When a high-grade ebonite compound is properly processed, it can be given a high lustrous finish which sets it apart from similar materials for beauty and richness. The highest grade of hard rubber is a compound containing only rubber and sulfur. It is in this type of compound that maximum physical properties and highest luster are found.
Dependence of Tensile Strength of Vulcanized Rubber on the Degree of Cross-Linking
Authors: Flory Paul J. , Rabjohn Norman , Shaffer Marcia C.
Published: February 2011

The suitability of disazodicarboxylates as quantitative cross-linking agents for the preparation of rubber vulcanizates of known degrees of cross-linking has been emphasized previously. In a recent paper we have presented the results of an investigation on the dependence of the equilibrium force of retraction on the elongation and degree of cross-linking of rubber and GR-S vulcanized with these compounds. The present paper reports an extension of these investigations of the relationship of physical properties of rubberlike materials to their network structure. Specifically, the tensile strength of azo vulcanized natural rubber has been explored as a function of the degree of cross-linking and of the extent of modification of the chain units. The tensile strengths of natural rubber specimens vulcanized to various extents using sulfur alone or sulfur in conjunction with various accelerators have been investigated in considerable detail recently by Gee, who has emphasized the critical dependence of the tensile strength on the degree of cross-linking. Values for the latter quantity, however, were deduced indirectly from the equilibrium force of retraction using the simple proportionality relationship between force of retraction and degree of cross-linking afforded by the theory of rubber elasticity. This relationship is known to be only approximately valid. Furthermore, the effects on the force of retraction of chain scission, which doubtless accompanied some of the vulcanizations to a considerable degree, were disregarded. For these reasons, Gee's values for the degrees of cross-linking occurring in his vulcanizates are only approximate estimates, and in a few cases they may be seriously in error. Nevertheless, the general character of the relationship between tensile strength and degree of cross-linking which he obtained is confirmed by our results on rubber samples quantitatively cross-linked with measured proportions of decamethylene-dismethyl azodicarboxylate.
Bonding of Rubber to Metal by Means of New Chemical Derivatives of Rubber
Authors: Gossot Jacques
Published: February 2011

The bonding process which has been described is of general application to all types of rubber mixtures, to metals, and to various other materials, without any change in composition of the bonding agent for the different materials. Although the problem of adhesion has been approached in this work only from the purely practical standpoint, it should be realized how little progress has been made in the theoretical knowledge of the problem. As a matter of fact, only a few authors have attempted to explain, on a basis of general concepts, certain special cases of adhesion, and there is still no real insight into the problem as a whole which might open the way to material progress. If one turns to the works of MacBain, Delmonte, and Buchan among the most important contributions to the phenomena of adhesion, the ultimate conclusion must be drawn that little has been accomplished in orienting investigations in this field toward more productive ends. From the physical point of view, particular attention must be paid to the condition of the state of the surface of the material to be bonded, to the surface tension, to the viscosity, and to the pH value of the adhesive. The chemical structure of the latter is that of a long-chain compound and, as has been proved conclusively in the present investigation, certain groups play a fundamental role, both in virtue of their chemical reactivity, and in virtue of the polar moment which they confer upon the molecule.
Color Reactions of Some Accelerators in Current Use
Authors: Schaefer W.
Published: February 2011

In taking an inventory, it was found that the labels on some accelerators had become lost, and the laboratory was called upon to identify the accelerators. However, little knowledge was available on this subject, so new analytical methods had to be developed. It was known that traces of copper can be detected by means of sodium diethyldithiocarbamate, the chemical nature of which bears a great resemblance to the compositions of Vulkazit-P, Vulkazit-P Extra-N, Vulkazit-774 and Thiuram. Hence it was to be expected that these accelerators would likewise react with copper salts. This was actually found to be the case. Encouraged by this success, a series of other accelerators were tested with the copper reagent, and it was found that every accelerator tested differed from all other accelerators in this reaction. This immediately offered a means of distinguishing some of the accelerators most widely used in the rubber industry.