bluuebunny/crossref_metadata_2025 huggingface dataset:
The Molecular Structure and Properties of Rubber
Authors: Kasatochkin V. I. , Lukin B. V.
Published: February 2011

The molecular structure of rubber resembles that of liquids, which have a characteristic distribution of linear-chain molecules, united by transverse van der Waals forces. The x-ray diffraction diagram of undeformed rubber shows a diffuse ring, the characteristic diffraction spectrum of liquids, and this is accepted as experimental proof of the similarity between rubber and liquids. The theory that the structure of rubber involves reactive bonds in the adjacent molecular chains at short distances apart is not in accord with the relatively free rotation of these chains, which is manifest by the elastic properties of rubber, and the theory in no way distinguishes unvulcanized rubber from straight-chain paraffins. A straight-chain molecular system in which most of the links of adjacent chains are cross-bridged by van der Waals forces is a fairly rigid system, with relatively little molecular motion. The rotation of the links is equivalent to rupture of the van der Waals bonds, and in no way corresponds to the observed high degree of motion of the molecular chains in rubber, as reflected in the high elasticity of the latter. The results of the experimental study which is described in the present paper and which is concerned with the x-ray diffraction spectra of amorphous rubber and of rubber which has become crystalline by stretching, lead to the conclusion that amorphous rubber contains fragments of molecular chains, the links of which do not scatter x-rays in the form of an amorphous ring. Futhermore, the experiments offer proof of the absolutely essential role of the above-mentioned molecular structure of rubber in determining a number of properties of the rubber.
Contribution to the Physical Chemistry of Hevea Latex. II. Adsorption of Metallic Cations on the Surface of Latex Particles. Distribution of Alkali Metals, Alkaline Earth Metals, and Iron between the Two Phases of Latex Preserved with Ammonia
Authors: Belmas Robert
Published: February 2011

The study of latex is characterized by the fact that it is always difficult to draw any definite conclusions. One is confronted with a substance which has been synthesized by a living organism, and whose extremely complex structure is very different from that of the sols currently studied by colloid chemistry. However, ultracentrifugation makes it possible to obtain reliable results as far as partition of the natural metallic components between the dispersing and dispersed phases is concerned. The existence of equilibria of adsorption as a function of the dilution of latex and comparison of the experimental curves with the isotherms of Freundlich and of Langmuir shows that, in the case of latex, adsorption is not a simple phenomenon. At least two different processes seem to be involved: (1) electrosorption of the metallic cations by the negative surface of the rubber particles, and (2) indirect adsorption, whereby the metal is bound in a slightly dissociable form to an organic anion which is itself strongly adsorbed. This would explain the much weaker adsorption of the alkali metals, which possess only a positive charge, and whose salts are in general more easily dissociated than those of the alkaline earth metals. The results obtained for metals added to latex in the form of soluble salts lead to the same conclusions. Measurement of the adsorption equilibria for samples of latex containing different concentrations of rubber show that, the smaller the proportion of dispersing phase to dispersed phase, the higher is the adsoprtion. This phenomenon, which is evident with alkali metals as well as with alkaline earth metals, can be explained by the increase of the charge on the particles when the latex is diluted. An examination of the critical adsorption values for the different metals studied confirms the fact that the behavior of latex with salts is that of a mixed sol with both lyophilic and lyophobic properties. These results would be more valuable if confirmed and determined more precisely by an electrokinetic study. The determination of the potential of the particles by measuring the cataphoretic velocity with respect to the adsorption of metal ions would surely permit a more accurate interpretation of the mechanism of this adsorption.
Relation between Stress Relaxation and Aging Resistance of Rubber Vulcanizates. Some Preliminary Investigations
Authors: Pedersen Holger Leth , Nielsen Bent
Published: February 2011

In this paper some details are given for the construction of a simple balance for the measurement of stress relaxation at constant elongation. A simple means of obtaining equal strain in two parts of the strained specimen is provided. By means of four typical stocks, covering the widest possible range of aging resistance, it is shown that the stress relaxations give approximately the same estimate of stability as does the normal Geer test using 2-mm. Dumbbell specimens. As a measure for stress relaxation, the time is used that is required to obtain 50 per cent of the value of the interpolated modulus at 200 per cent elongation 6 seconds after the straining zero time at 110° C. The parameter for the aging test is the time in days at 70° C for the 50 per cent value of tensile strengths. The range for the stress relaxation parameter may be estimated to 8–1200 minutes and the aging parameter from 10–600 days. Finally the concordance of temperature coefficient for relaxation and oxidation rates is shown.
Dilatometric Measurement of the Rate of Vulcanization of Crepe Rubber by Sulfur Monochloride
Authors: Glazer J.
Published: February 2011

The cold vulcanization of rubber by sulfur monochloride is believed to consist essentially of the cross-linking of adjacent polyisoprene units by a series of sulfide bonds. Chemical analysis of the product suggests that the cross-linking process is analogous to the mustard gas reaction of ethylene with sulfur monochloride, thus: (see PDF for diagram) Nothing is known, however, about the kinetics of this vulcanization process. General considerations lead one to expect that such a reaction, involving polymer aggregation, should be accompanied by an increase in the density of the rubber; moreover, by choosing a suitably delicate technique, it should be possible to utilize such density changes for rate determinations. A dilatometric method seemed most suitable, and the experiments described here show that the vulcanization process is, indeed, accompanied by a decrease in volume of the reaction mixture, and that the reaction may be followed quantitatively using a tap dilatometer.
Elasticity of Soft Polymers. Constant-Stress Elongation Tests
Authors: Dahlquist C. A. , Hendricks J. O. , Taylor N. W.
Published: February 2011

The elastic properties of polymeric materials which are too soft to test on conventional stress-strain machines can be obtained by elongation at constant stress. A simple apparatus has been developed for maintaining constant stress during elongation. Data illustrate the time dependence of the elastic behavior of polymeric materials and demonstrate the usefulness of the constant-stress method in the evaluation of this time dependence. The constant-stress method is useful in the evaluation of plasticizers for gum rubbers. Because of the difficulty of separating highly delayed elastic elongation from viscous flow, the method has not been found practical as a tool for measurement of viscosity in the solid state. However, under most test conditions, viscous flow has been a negligible fraction of the total deformation. Several terms for delayed elasticity are required to fit an empirical equation to the elongation-time curves, and it seems probable that these terms are only an approximation of a very large number of delayed elastic processes having different relaxation times.
The Action of Unsaturated Compounds on Natural Rubber in Solution. I. The Reaction Catalyzed by a Peroxide
Authors: Delalande André
Published: February 2011

It has been shown that, by the simultaneous use of maleic N-methylimide and p-bromobenzoyl peroxide, it is possible to gain an insight into the fixation of ethylene compounds to rubber in solution. The investigation has made it clear that the presence of a peroxide is not indispensable, since the reaction continues even after the peroxide is completely decomposed, although at a much slower rate. Furthermore, by raising the temperature, it is possible to fix maleic N-methylimide in a relatively short time. The results of an experimental study of this thermal reaction in the absence of a catalyst are to be published later.
Abrasion Resistance of GR-S Vulcanizates
Authors: Adams J. W. , Reynolds J. A. , Messer W. E. , Howland L. H.
Published: February 2011

A method for determining the abrasion resistance properties of reinforced vulcanizates was required for evaluating new GR-S type elastomers and carbon blacks developed for use in automobile tire treads. In spite of the fact that past experiences revealed that most laboratory machines are unsatisfactory for testing GR-S vulcanizates, a program for evaluating several machines was undertaken. A Lambourn abrader similar to the one recently adopted by the British Standards Institution for testing elastomer vulcanizates appeared to be most promising, for which reason efforts were expended on constructing a similar machine. The abrader that was constructed and operated to simulate wear brought about by a tire slipping on road surfaces embodied the following four modifications of the British machine: 1. All parts and accessories were either obtained or fabricated in the United States. 2. The electrical eddy current type of brake used in the original Lambourn machine was replaced with a hydraulic, gear pump braking system. 3. Intermittent talcing of the test wheel during operation was specified. 4. A revolution counter equipped with a friction drive wheel, one foot in circumference, was installed to ride on the test wheel for the purpose of conveniently determining test run distances. The conditions for testing vulcanizates were standardized to obtain abrasion loss values that could be expressed in terms of loss in cubic centimeters per 3000 feet of running at 24 per cent slip. Adjustments were made in calculating abrasion ratings from volume loss values to bring them more in line with reported service test ratings.
An Infrared Spectrometric Study of the Oxidation of Natural Rubber
Authors: D'Or L. , Kössler I.
Published: February 2011

The kinetics of the oxidation of natural rubber by atmospheric oxygen has been studied by various methods, for example, by volumetric and manometric measurements of the absorption of oxygen, by measurements of the increase of weight of the rubber, and by changes in the mechanical properties as a function of time. However, the oxidation of rubber is a complex phenomenon, and none of these techniques offers a means of following the oxidation in detail. In principle, it is possible, by infrared absorption spectrometry, to detect the presence of different groups which are present in a given sample of rubber and to determine their concentrations. Hence, it was hoped that this technique would offer a means of studying the various phenomena involved in the oxidation of rubber. In fact, this technique has already been employed in studies of the structure of rubber as well as in the qualitative and quantitative analysis of synthetic products. In addition to these already published studies, various authors have reported that the oxidation of natural rubber results in changes in its infrared spectrum, but none of the investigators has followed these changes quantitatively. Nevertheless, the possible interest of such a quantitative study, when carried out in parallel with a study of the changes in mechanical properties, has been pointed out by different authors. The authors of the present work decided, as a first approach to the problem, to prepare samples of rubber which could be studied by infrared absorption. The progress of oxidation could then be followed quantitatively by the disappearance of the principal groups present in rubber which had not undergone oxidation and the formation of characteristic groups in the oxidation products. Finally, from the data obtained, it was hoped, if not to draw conclusions as to the mechanism or mechanisms of oxidation, at least to obtain some indications of the precise kinetics of this oxidation.
Autoradiographic Technique with Carbon14 in Rubber
Authors: Kirshenbaum A. D. , Hoffman C. W. , Grosse A. V.
Published: February 2011

The autoradiograph technique making use of carbon14 is useful in studying the carbon black distribution in rubber. It is superior to the photomicrographic technique in studying carbon black dispersion in rubber. Autoradiographs of different carbon black-rubber mixes (tensile strengths varying from 300 to 3300 pounds per square inch) showed visible variations in the carbon black distribution which closely agree with the tensile strength data, whereas photomicrographs of the same mixes showed no differences among the various mixes. The autoradiographic technique is also useful in tracking down carbon black agglomeration in rubber.
Nondestructive Aging Tests for Rubber
Authors: Shaw R. F. , Adams S. R.
Published: February 2011

An improved laboratory method has been developed for evaluating the effects of aging. The test-specimens are subjected to definite loads or extensions at repeated intervals during exposure to the deteriorating influence of heat, light, air, and ozone. The degree of deterioration is evidenced by an elongation increase for specimens that become cracked and for a decrease in elongation for those that become heat-hardened. The test data are obtained on the same specimen at varying time intervals, are reproducible, and are measured in the low elongation range in which most rubber is used in service.
Improvements in Accuracy of Hardness Testing
Authors: Scott J. R.
Published: February 2011

Most hardness tests depend on penetration by an indentor under load, the penetration being measured by the movement of the plunger carrying the indentor. This movement must be measured from a zero position, and the fixing of this position has been the cause of most of the difficulties in obtaining accurate hardness measurements. In most instruments one of the following devices has been adopted : (1) Zero Load—a known small load is applied to the indentor, and its position under this load is taken as the zero; or (2) presser foot—an annular foot, surrounding the indentor, rests on the rubber test-piece, and the depth of indentation is measured relative to the plane of this foot. Rubber test-pieces generally are not perfectly flat and parallel-sided, even though nominally so. This fact leads to errors in hardness measurements by instruments using either of the devices (1) or (2) mentioned above. Moreover, if plied-up test-pieces are used to obtain the required thickness, or in testing articles that are very thick compared with their lateral dimensions, large errors can arise if no foot is used. The best general procedure is, therefore, to use both a zero load and a presser foot. Experimental data support this conclusion, which has been embodied in the revised British Standard Method (B.S. 903-1950) and in the recommendations of Committee ISO/TC/45—Rubber. Most published standard hardness tests make no provision for avoiding errors due to friction in the measuring device (usually a dial micrometer gauge). Results of tests show that by applying gentle vibration during the test, much more consistent readings are obtained, and it is possible to get better agreement between different laboratories and instruments. Lubrication of the surface of the test-piece with talc produces a definite though small further improvement in uniformity of results. It is, therefore, a useful additional precaution.
The Crystallization of Vulcanized Natural Rubber at Low Temperatures
Authors: Russell E. W.
Published: February 2011

A series of natural rubber vulcanizates have been crystallized at −36° − 26° −17.5° and −2° C and the changes followed dilatometrically. As for raw rubber there is a maximum rate of crystallization at about −26° C; vulcanization decreases the rate and alters the shape of the temperature-rate curve. The amount of combined sulfur is the chief factor in determining the rate and extent of crystallization of pure-gum vulcanizates. Cross-linking, where it is efficient so that the chains between the cross-links are chemically unaffected, also depresses the rate and extent of crystallization. The use of vulcanizates which crystallize slowly permits melting to be accomplished at much lower rates of heating than was previously possible with raw rubber. Two stages of melting are distinguished the first occurring under the influence of forces between the crystalline and amorphous regions and the second analogous to the melting of low molecular weight crystalline substances.
Stress—Temperature Studies of Transitions in Rubbers
Authors: Witte Robert S. , Anthony Robert L.
Published: February 2011

The stress-temperature method was employed as a means of studying the apparent second-order transition occurring in rubbers. The rubbers studied were a natural rubber gum, a Butyl gum, a loaded GR-S, and a loaded Hycar OS-10. Pronounced stress relaxation was observed for all rubbers at temperatures not too far below the transition region, but not at temperatures a few degrees above the transition. For both the Butyl and the Hycar OS-10 rubbers, the transition temperature was observed to depend strongly on extension, the transition temperature decreasing with increasing sample extension. No such dependence on extension was observed for the natural rubber stock. Comparison data were also obtained from volume dilatometric studies. With the exception of the data for natural rubber, the transition temperatures determined by the volume dilatometric method were somewhat lower than the lowest values obtained in the stress-temperature studies.
The Application of Polarized Infrared Radiation to Problems in Molecular Structure
Authors: Sutherland G. B. B. M. , Jones A. Vallance
Published: February 2011

The infrared spectra of rubber and of both forms of gutta-percha have been investigated between 5 and 15 µ under various conditions. When rubber and gutta-percha are each in the amorphous state, their infrared spectra are closely similar, although not identical; in the crystalline state, marked differences occur between the spectra of these three forms of polyisoprene. Using polarized radiation, the dichroic ratios of bands which can be assigned with certainty are in general qualitative agreement with the crystalline structures proposed by Bunn. The spectrum of rubber crystallized by freezing has been examined at low temperatures, and it is shown that apparent intensity changes occur in certain absorption bands on crystallization. The importance of this effect in using infrared methods to estimate the degree of crystallinity produced in rubber by stretching is emphasized. Assignments of a few of the main bands are discussed, but no attempt is made to give a complete interpretation of the spectra.
Oxidation of Unvulcanized Cold Rubber Influence of Adsorption by Carbon Black
Authors: Sweitzer C. W. , Lyon Francis
Published: February 2011

Previous investigations have shown a large difference between the amount of rubber insolubilized by carbon black in dilute solvent systems and in standard mill mixes. The purpose of this study, after reconciling these extremes, was to evaluate the role of adsorption in the insolubilization of rubber in mill-mixed compounds. An adsorption test was employed which eliminated the solvent effect of the dilute system and the mastication effect in mill mixing. Results showed that carbon black, depending on the temperature and atmosphere conditions imposed on the rubber carbon films, represses the scission, cross-linking, and gelation reactions of GR-S X-478. This repressive effect is ascribed to the adsorption and inactivation by the carbon black of the oxidized intermediates through which these various reactions proceed. The magnitude of this effect was found to vary with the type, loading, and surface chemistry of the carbon. This approach not only offers promise as a means for predicting the behavior of carbon black in rubber compounds, but also, because of its applicability to the study of all rubber-carbon systems, offers possibilities of providing additional information on the mechanism of the carbon-rubber bond.
Kinetic Analysis of Organic Halides. IV. Analysis of Macromolecular Polyhalides
Authors: Salomon G. , Koningsberger C.
Published: February 2011

Chlorination products derived from natural rubber and some synthetic polymers have been subjected to kinetic analysis with aniline at 100° C and piperidine at 20° C. The influence of the chlorinating agent on the structure of the reaction products has been elucidated. It is shown that allylic chloride groups, the rubber dichloride, (see PDF for diagram) and rubber polychlorides can be identified and separated kinetically. By a combination of kinetic and infrared analysis the structure (see PDF for diagram) can be proved as the primary reaction product of direct chlorination.
Studies of the Vulcanization and Structure of Polyacrylic Rubber
Authors: Semegen S. T. , Wakelin J. H.
Published: February 2011

Several characteristic features of the vulcanization of polyacrylates have been demonstrated. The fact that alcohol is formed and liberated during cure has been demonstrated; this finding might favor a Claisen type condensation. On the other hand, the fact that a copolymer of methyl acrylate and acrylic acid can be plasticized with alcohol and assumes a chain spacing comparable with that of cured polymethyl acrylate, whereas the uncured PMA and unplasticized copolymer are appreciably different in chain spacing, might favor a controlled hydrolysis and hydrogen association as the mechanism. The latter mechanism would be more compelling if the methyl acrylate/acrylic acid copolymer when alcohol plasticized showed other evidences of vulcanization, in situ, such as increased resistance to methylethyl ketone or reduced thermoplasticity in addition to increased rubberiness. Several different x-ray diffraction patterns are shown in Figures 6 to 15. Note the progression in spacing for the inner halo as the number of terminal carbons in the side chain increases. In comparing the pattern of α-carboxypimelic acid, a highly crystalline compound, with the patterns of the esters of the acid, we note the influence of hydrogen binding on the side chain association to produce a regular 3 dimensional structure, while esterification with relatively unreacting alkyl groups decreases cross-bonding between chains so much that the structure assumes a liquid configuration similar to that of the various polyacrylates.
Chlorinated Rubber from Latex
Authors: van Amerongen G. J.
Published: February 2011

This work was undertaken to find new ways for producing chlorinated rubber from rubber latex. Methods have been applied during which coagulation of the latex and hyprochlorination of the rubber are avoided. Passing gaseous chlorine through stabilized and strongly acidified Hevea latex proves to be a satisfactory method for the chlorination of rubber. To avoid coagulation of the latex, certain nonionogenic or cationogenic emulsifiers have to be added. A high acidity of latex prevents the formation of hypochlorous acid and improves the mechanical stability of the latex. A chlorinated rubber latex is produced, the chlorinated rubber of which contains virtually no oxygen and up to 61 per cent of chlorine. By subjecting this chlorinated rubber latex or the dry isolated chlorinated rubber to an aftertreatment, products of a satisfactory solubility and with a chlorine content up to 72 per cent have been obtained. Judging from the reactivity with aniline, maximum chemical stability is at 65 per cent chlorine content. As a similar chlorination technique is applicable to rubber hydrochloride and synthetic rubber latexes, it is seen that latexes in general are good starting materials for the production of chlorinated derivatives. Moreover, stable chlorinated rubber latexes are obtained which can be used as such, making new applications possible. Technical advantages of chlorinating rubber in latex above rubber in solution are the much higher rubber concentration which can be used, and the ease of cooling the less viscous latex during the reaction. For some applications it is advantageous that the original high molecular weight of the polymer can be conserved.
Heat Sensitization of Latex by the Zinc Salt of Mercaptobenzimidazole
Authors: Delattre Robert
Published: February 2011

The process of heat sensitization of latex by means of the zinc salt of mercaptobenzimidazole offers the following advantages. (1) Satisfactory heat sensitivity, even when the stability of the latex to cold has been increased by the addition of ammonia, soap, or other suitable protective agent. (2) Satisfactory heat sensitivity when the ammonia in the latex has been converted to the combined state by the addition of formaldehyde. (3) Permanence of heat sensitivity. (4) Remarkable stability to cold when the latex has been heat-sensitized. (5) Negligible dilution of latex when the heat-sensitizing agent is added. (6) Regularity of the conditions of gelation. (7) Elimination of the washing operation after gelation. (8) Effective heat sensitization, even in the absence of zinc oxide. (9) Compatibility of the zinc salt of mercaptobenzimidazole with all compounding ingredients ordinarily employed in latex processes and in the rubber industry in general. (10) Compatibility of the heat-sensitization process with the reinforcement of latex by means of precondensed resins. (11) Absence of any influence on vulcanizing conditions. (12) Improvement of the aging of rubber products, because the zinc salt of mercaptobenzimidazole is an antioxygenic agent of the deactivating type and an inhibitor of the degradation of rubber by copper and other harmful metals. (13) No influence on the color of rubber products, since the zinc salt of mercaptobenzimidazole has no discoloring effect, even after a product containing it has been exposed for a long time to light. (14) No influence on water absorption, since the zinc salt of mercaptobenzimidazole is not hygroscopic. (15) Invariable properties and good stability of the heat-sensitizing agent during storage. (16) Possible use of the zinc salt of mercaptobenzimidazole in latex which has been degraded biochemically. (17) Extensive applications which are possible. This list of advantages may or may not be complete, and only the future will tell, but it may even now be regarded as certain that the new process will find a notable place among the various techniques for processing latex.
Mechanical Stability Testing of Hevea Latex
Authors: Madge E. W. , Collier H. M. , Duckworth I. H.
Published: February 2011

In recent years the mechanical stability testing of latex has received increased attention, and an apparatus has been developed in the United Kingdom which has certain advantages over those previously described in the literature. Various factors relating both to the instrument and to the method of testing are discussed and the influence of these factors on the accuracy of the results is considered. Some indication is given of the way in which the mechanical stability test can be used to evaluate changes brought about by various additions and treatments of the latex.
The Zinc Oxide Stability of Latex
Authors: van Gils G. E.
Published: February 2011

A review of the factors which determine the zinc oxide stability of latex has been given. The work of Lepetit and our own experiments lead to the conclusion that the zinc oxide stability of latex is determined in the first place by substances which promote the solubilization of zinc oxide (minus factors); in the second place by substances which stabilize the colloid against the activity of the complex zinc cations or reduce the activity of these ions (plus factors). It has been generally accepted that the higher the KOH number of a latex, the lower is the zinc oxide stability. Since the KOH number is based primarily on neutralization of the acidic components of the serum only, a general correlation with zinc oxide stability could not be found when latexes of different origin were examined. Intrinsic factors or factors depending on the properties of the latex itself that influence zinc oxide stability are: (1) the dry rubber content of the latex, where high values are accompanied by low zinc oxide stability values and vice versa; (2) the yellow content fraction of latex, which in increasing amounts adds to the stability of the latex; (3) the protein content of the latex which, when degraded either artificially or naturally, reduces the zinc oxide stability. The effect of materials added to latex on zinc oxide stability includes: (1) fatty acid and sulfonic acid soaps, which have only slight influence; (2) Emulphor-O, sequestering agents, and sodium phosphates and silicates, which have a stabilizing effect; (3) ammonium salts and amines, which have a marked destabilizing effect, although triethanolamine hydrochloride is not active. Quebrachitol has a slight destabilizing effect.
Evaluating Dynamic Fatigue of Adhesion of Tire Cords to Rubber Stocks
Authors: Lyons W. James
Published: February 2011

A practical reasonably quick method for evaluating the resistance of the adhesive bond between tire cord and rubber stock to flexural (dynamic) fatigue has been developed. The method employs the Roller-Flex machine, on which the test cords, cured in rubber and under tension, are subjected to rapid cyclic flexure by being passed back and forth around small steel rollers. The resistance of the adhesive bond to dynamic fatigue is evaluated by a measurement of the cord adhesion by the familiar H pull-out test, after the sample has been flexed on the machine for a 10-hour period. There is a continual decline in cord adhesion as the flexing period is prolonged. Ten hours were selected as the flexing period in the standard test. A difference of 6 pounds per inch between samples was found necessary for significance at the 5 per cent level. Dynamic adhesion measurements by this method have been found to correlate reasonably well with adhesion performance in road tire tests.
Ozone Deterioration of Elastomeric Materials. Preliminary Results of a Study by Infrared Spectroscopy
Authors: Allison A. R. , Stanley I. J.
Published: February 2011

The work described consists of explorative studies with the ultimate objective of developing an accelerated ozone aging test for elastomers based primarily on compositional changes rather than on the conventional variation in physical characteristics. Infrared spectrographic techniques were found to be admirably suited for the reflection of accumulation or depletion of specific structural linkages in polymer molecules undergoing ozonization. Purified gum specimens of Hevea, GR-S, nitrile rubber, Neoprene, and GR-I were dissolved in chlorinated hydrocarbon solvents such as ethylene dichloride or o-dichlorobenzene, and subjected to a stream of ozonized oxygen containing approximately 50 p.p.m. of ozone. Infrared spectrograms of films cast from the treated solutions show progressive intensification of clearly defined absorption bands at 2.9 and 5.8 mµ, reflecting the functional groups hydroxyl and carbonyl, respectively. Methods for quantitating these changes by calibration against reference compounds are described. A means is available for following ozone degradation of polymers in terms of specific variations in molecular structure. Basic information of this nature is potentially useful in the development of an accelerated ozone aging test correctable with aging under conditions of actual service.
Ozone Crack Depth Analysis for Rubber
Authors: Rugg John S.
Published: February 2011

The factors that control weathering and ozone resistance are not fully understood. A major deterrent to a better understanding of these factors is the lack of a satisfactory quantitative method of analyzing the results of ozone and weathering tests. A method has been developed which follows the change in crack depth as the criterion of the extent of damage that has taken place. It has been shown that, when crack growth takes place, the depth increases proportionally. The depth of the crack is measured with the 20 × microscope in a cross-section made normal to the length of the cracks. The major cracks, which have the directing influence on the extent of cracking, are the deepest ones, and are all nearly the same length. This method has been used to analyze results of ozone cracking in which commonly recognized variables were employed. The results confirm some previously reported trends with quantitative data. This method can be used in measuring the effect of compounding variables, where results are desired in terms of a dimension of actual ozone cracking. This method is performed with moderate ease, does not require specialized equipment, is independent of human judgment, and is directly related to the growth of ozone cracks. It should contribute to a better understanding of the factors that control weathering and ozone resistance of natural rubber and other elastomers.
Yield Stress in Frozen Rubbers
Authors: Buist J. M. , Stafford R. L.
Published: February 2011

The work reported on the low temperature shear deformation properties of natural rubber and Neoprene-GN gum compounds shows that, under the conditions of storage and applied stress investigated, there is little evidence of a yield effect with Neoprene-GN. It is suggested that the very large temperature-stiffening of this polymer is too great to give the yield effect under the low shear stresses studied. In tension, however, the yield effect is very marked with Neoprene-GN. On the other hand, a definite yield effect is shown as a result of shear deformation measurements on natural rubber stored at −40° C, whereas previous tension tests failed to detect this. It is shown that, under suitable conditions of storage time and at high shearing stresses, a natural rubber unit might fail in service by yielding and giving too much deflection. The more usual type of failure of a shear unit in service arises from loss of flexibility and hence deflection properties; the oil-resisting rubbers are particularly likely to suffer from this defect. The x-ray data on natural rubber and Neoprene-GN gum compounds failed to reveal any evidence of random crystallite formation in the unstretched frozen rubbers. If the yield effect is due to crystallite formation in the unstretched state at low temperatures, then the crystallites are too small to be detected under the conditions of this investigation. In this connection, it is emphasized that a temperature of −40° C is below the temperature for maximum rate of development of crystallization for both rubbers. With both natural rubber and Neoprene-GN, crystallization resulting from stretching occurs more readily and at lower elongations at −40° C than at room temperature. In the case of Neoprene-GN stored at −40° C and then stretched, crystallization does not increase with elongation as it does at room temperature. It is suggested that this is due to the cold-drawn state of Neoprene-GN on stretching after storage at −40° C. These investigations have important practical and theoretical implications. Suggestions have often been made to include a test for crystallization in any characterization of compounds for low-temperature resistance. The results of the present work emphasize that the important factor is the time of storage at low temperature and the effects that this produces on crystallization and yield stress. The presence of crystallization is not so important as its continued development under long period exposure or its reorientation under applied stress.
Vitrification of High Polymers in Periodic Deformation
Authors: Bartenev G. M.
Published: February 2011

As is known, high polymers are readily supercooled and retain their amorphous structure below their crystallization points. Changes of the physical properties in the temperature range of crystallization are a linear function of temperature. When the temperature is lowered further, high polymers remain in their amorphous liquid state; this is indicated in particular by their retaining their high elastic properties below the crystallization temperature. However, with further decrease of temperature, the linear character of the changes of physical properties is no longer evident, and the latter undergo more or less abrupt anomalous changes. In particular, there is a change of the polymer from the amorphous-liquid state with high elasticity into a hard vitreous form, which, as is known, is not related to changes of the structure of high polymeric substances. Vitrified polymers, like amorphous liquids, possess amorphous structures. A number of investigators have found similar anomalies in the heat capacity, heat expansion, dielectric properties, and high elastic properties of various polymers during transition to the vitreous state.
A Study of the Mechanism of the Deactivation Effect
Authors: Foll Jacques Le
Published: February 2011

The only method by which significant differences between the effects of antioxygenic agents and deactivating agents can be detected has been found to be a study of relaxation phenomena. An investigation by this method has also furnished further support to the theories of Tobolsky and his coworkers. The changes which take place during aging in the physical properties of vulcanized rubber are the result of two independent phenomena which occur simultaneously: (1) chain scission, and (2) formation of intermolecular bonds. As far as the aging of vulcanizates of natural rubber under normal conditions, e.g., socalled natural aging, is concerned, the chief phenomenon involved is scission of the chain molecules. In principle, therefore, there are two methods for combatting the deterioration of rubber on aging: (1) to impede chain scission by obstructing the fixation of oxygen, and (2) to promote the progressive formation of intermolecular bonds which compensate for the effects of the scission process. The first of these processes is that in which antioxygenic agents play the active part; in the second process, deactivating agents play the active part. From this viewpoint, deactivating agents play a part analogous to that of accelerators, and they may be regarded as representing a special type of acceleration. This theory makes possible a better understanding of a number of facts which, a priori, seem surprising: (1) the relationships of both chemical structure and mode of action of accelerators and deactivating agents, and (2) the protective effect of litharge, peroxides, and nitro compounds, all of which are vulcanizing agents. With respect to the intimate mechanism of the deactivating effect, one question remains unanswered, viz., how are intermolecular bonds formed under the influence of deactivating agents? This question recalls the question of the function of vulcanization accelerators, which has been the subject of many investigations, but which still remains a mystery.
Comparison of Rotation, Extrusion, and Compression Plastometers
Authors: Whorlow R. W.
Published: February 2011

Instruments expected to give results characteristic of the various classes of plastometer have been compared in a number of respects. The Dillon extrusion plastometer, shearing cone rotation plastometer, and Williams compression plastometer, were compared for their power of discriminating between samples of smoked sheet masticated for different periods, or between samples of MPC carbon black masterbatch remilled for various periods. In the first case, the Dillon instrument was found to be inferior to the other instruments, while for the black masterbatches the Williams instrument was inferior to the other two. The Williams instrument was the most, and the shearing cone the least, influenced by carbon black structure, a result in agreement with the use of the energy expended on the rubber as a measure of structure breakdown. Consideration of the correlation between shearing cone and Dillon plasticity values gives no evidence of marked slippage effects with the extrusion instrument, although it cannot be shown conclusively whether or not slippage occurs with the present form of instrument. It is concluded that a Mooney or shearing cone instrument is probably the best for general use, but that the Dillon instrument may have advantages for tests on carbon black loaded stocks.
Tensile Properties of Films from Low-Temperature GR-S Latex
Authors: Brown R. W. , Messer W. E. , Howland L. H.
Published: February 2011

Studies were made of the influence of a number of polymerization variables on the tensile strength of vulcanized evaporated films from low-temperature high-solids GR-S latexes. Previous reports of film tensiles on the order of 3000 pounds per square inch for latexes of 70/30 butadiene-styrene charge ratio were confirmed. The levels of accelerator necessary for optimum vulcanized properties were found to be considerably lower than those normally used, particularly for latexes shortstopped with dithiocarbamate salts. Microscopic coagulum found in some latex samples had a pronounced effect in decreasing film tensile of vulcanizates. Cured films from latexes emulsified with mixtures of fatty acid and rosin soap possessed considerably better tensile strengths than those from latexes using all fatty acid soap emulsification. Wide variations on Mooney viscosity had relatively little effect on ultimate film tensiles. Incorporation of small amounts of lignin into the latex as the ammonium or sodium salt decreased cure rates of films and aided in giving more reproducible tensile results. Both lignin and the sodium salt of cresyl monosulfide improved the aging characteristics of films.
The Polymeric Structure of Natural Rubber
Authors: Bateman L. , Watson W. F.
Published: February 2011

From the tree to the vulcanized article, the changes in the elastic properties of natural rubber are dependent on essentially second-order modifications of the parent polymer. Successfully in some ways, less so in others, rubber technologists have learned empirically how to develop advantageous qualities and to prevent or minimize the undesirable ones. This empiricism is inevitable because the chemical reactions which produce the physical changes are so little understood. For example, vulcanization represents the conversion of the chainlike polymer into a cross-linked network, but the nature, number, and distribution along the chain of the cross-links, and their variation with curing conditions and on subsequent aging are largely matters of speculation. In fact, one of the major impediments to scientific rationalization of rubber technology is the inability to interpret common physical observations, e.g., on plasticity, state of cure, deterioration on aging, cracking, in terms of molecular structure. The main chemical attack on the problem in these laboratories has been based on the rigorous, but necessarily long-term, course of first resolving the chemistry of a particular process with the aid of model systems, whereby product analysis and identification can be firmly established, and then determining how rubber behaves when caused to undergo similar reactions in a controlled manner. In other words, attention has been directed to the atomic details of aging, vulcanization, etc., rather than to their significance in modifying polymer structure. Our purpose here is to lay emphasis on the latter approach, first by surveying briefly the main physical changes encountered in rubber technology, and then, stimulated by some very recent work on the nature and degradation of raw rubber, by tracing certain fundamental factors underlying these phenomena.
Investigation of the Role of Intermolecular Forces in the Mechanism of High-Elastic Deformation. VII. The Effect of Molecular Interaction on the Fatigue Resistance of High Polymers Having Highly Developed Spatial Structures
Authors: Gul V. E. , Fedyukin D. L. , Dogadkin B. A.
Published: February 2011

It is shown experimentally that an irregular change of the fatigue resistance of loaded natural-rubber vulcanizates with increase of the degree of swelling in paraffin oil and in dibutyl phthalate is caused by the superposition of two processes: the increase of fatigue resistance, as a result of the reduction of mechanical losses, and the decrease of fatigue resistance due to the decrease of tensile strength proportional to the higher degree of swelling.
An Interesting Property of Certain Conductive Rubbers
Authors: Kersta L. G.
Published: February 2011

During the course of electrical measurements of conductive rubbers, an interesting characteristic of some such materials was discovered. As far as we know, this characteristic has not been previously reported. It was found that, under certain conditions, a polysulfide rubber (Thiokol LP2) shows a decrease of electrical resistance as the material is stretched. The resistance declines up to elongations of perhaps 20 per cent. Beyond this it becomes fairly flat for an interval, and then increases from there on to the elastic limit. An example of elongation vs. resistance is shown by the full line of the accompanying figure.
Electrophoretic Mobility Study of Fresh Hevea Latex
Authors: Bowler William W.
Published: February 2011

To both the producer of natural rubber latex and the manufacturer of latex goods, the stability of Hevea latex is one of its most important properties. Two aspects of this important property are the mechanical stability and the chemical stability. The former is measured by the sensitivity of latex to mechanical agitation, the latter by the sensitivity to addition of ionic material. Although there is no clear relation known to exist between these two stabilities, the electrical charge on the rubber particles is considered to be important in either case. Since electrophoretic mobility determinations furnish one of the most direct methods for studying the charge on colloidal particles such as those in rubber latex, the effect of seasonal and clonal variations, latex aging, ionic strength, pH, and the presence of added materials on the electrical mobility of fresh Hevea latex was studied. At the same time the mechanical stability of many latexes was measured in order to determine what correlation exists between mobility and mechanical stability.