bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Aggregation in Amorphous Polymers
Authors: Kasatochkin V. I. , Lukin V. V. 
Published: February 2011

Abstract
We have already established the existence of two types of packing of the links of neighboring molecular chains in amorphous rubber. The association of the links whose packing is characterized by a relatively dense distribution, similar to the packing of the molecules in low-molecular liquids, constitutes the liquid phase of amorphous rubber. In an x-ray diffraction diagram, this phase of the rubber shows an outer interference maximum caused by the intermolecular interference of the x-ray radiation which is coherently scattered by the adjacent links and corresponds to the average intermolecular spacing. Another phase of amorphous rubber, formed by the association of the segments of adjacent molecular chains, of quite disordered distribution, was called the gaseous phase. The links of the molecular chains which make up this phase of the rubber, because of their irregular distribution, scatter x-rays and show no intermolecular interference effect, so the scattering is like that in molecular gases. The dense background usually observed in diffraction diagrams of rubber, the intensity of which increases in the region of small scattering angles, can be explained by the effect of the independent scattering of the disordered links of the molecular chains of the rubber. It has the nature of scattering by a gas. The presence of such a type of molecularly disordered gaseous component is a peculiarity of the aggregation of molecules in amorphous high-molecular substances. Its existence is shown by the x-ray diffraction diagrams of amorphous high-molecular substances, in which, in the absence of low-molecular liquids, a background of independent scattering is always observed, besides the outer interference maximum which corresponds to the intermolecular spacing. The intensity I of the scattered (monochromatic) x-rays at any angle is, according to the theories developed, determined by the sum of the scattering intensities of the gaseous (Ig) and liquid (Il) phases of the amorphous substance.
Determination of Intrinsic Low Stress Properties of Rubber Compounds. Use of Inclined Plane Tester
Authors: Dunlap W. B. , Glaser C. J. , Nellen A. H. 
Published: February 2011

Abstract
A hysteresis loop test made at low stress over a series of cures provides an extremely accurate measure of state of cure. The test is accurate and reproducible when made on test pieces which have been conditioned and are tested under controlled conditions of temperature and relative humidity. Furthermore, the type of test machine used and the autographic recording of the data practically eliminate the human element in testing. The accurate molding of the test pieces eliminates possibilities of error in gaging and compensating found frequently in the standard stress-strain test. The initial load data at 50, 100, and 150% elongation on the shortest cure in the series provide a scorch test which is accurate enough for practical factory control. The ratio of initial modulus at 50% elongation to modulus on recovery at 50% elongation provides a measure of hysteresis loss or heat build-up. Measurements made in the range of 50% elongation appear to be a more accurate measure of the properties of tire stocks, because the test range more closely approaches the conditions under which tire stocks operate in service. Finally, the use of this test provides a considerable saving in testing time.
Some Properties of Vulcanized Rubber under Strain. Degree of Crystallization as Calculated from Temperature Coefficient of Elastic Tension
Authors: Boonstra B. B. S. T. 
Published: February 2011

Abstract
To elucidate the crystallization phenomenon in natural rubber and to investigate the applicability of thermodynamic calculation to measurements of the elastic tension as a function of temperature, it seemed necessary to check whether crystallization determined by x-ray analysis (and combined with density) lined up reasonably with the percentage of crystallization computed from the energy change found by applying thermodynamics to stretched vulcanized rubber) on stretching. Calorimetric measurements were desirable, as no accurate figures are available for the heat of crystallization of rubber crystallites. The heat of melting of rubber crystallites was determined to about 66 joules per gram, which is of the same order as that of isoprene. The spreading in the results was large; the determination is based on the degree of crystallization found by x-ray analysis of raw rubber. The heat of crystallization on stretching, found by thermodynamic evaluation of the elastic tension and its temperature coefficient, is combined with the value of 66 joules for the heat of melting of the pure rubber crystallites. The degree of crystallization calculated in this way agrees reasonably well with the direct x-ray measurements of Goppel and Arlman. Crystallization as determined by x-ray analysis and that responsible for the energy change on stretching are much the same. This also means that thermodynamic evaluation of the change of stress with temperature is justified if pufficient relaxation of stress has taken place.
Stoichiometry of Vulcanization with Sulfur
Authors: Zapp R. L. , Decker R. H. , Dyroff Margaret S. , Rayner Harriet A. 
Published: February 2011

Abstract
In the study of vulcanization with natural rubber and other polymers of relatively high chemical unsaturation, it has always been difficult to represent the vulcanization process molecularly because of the complexity of the sulfur-polymer reactions. To circumvent this difficulty, reactions of small olefin molecules with sulfur have often been studied to obtain this molecular insight. Some investigators have resorted to cross-linking the polymer with agents other than sulfur to characterize the network for comparisons with physical properties. By cross-linking rubber molecules with diazo compounds, which add quantitatively to the olefin bond, Flory has characterized the network so formed in a molecular manner and correlated the degree of cross-linking with physical properties. When correlating physical properties with degree of cross-linking in butadiene-styrene polymers, others have cross-linked the polymer as a final step in the polymerization process. When a polymer of low unsaturation is used, many of the experimental difficulties are eliminated or reduced, and a more reliable stoichiometric picture of the phenomenon can be obtained. The emphasis in this work is placed on the chemical combination of sulfur with polymer rather than on any correlation with physical properties, and rests upon the “dimensions” of swollen polymer networks as related to total combined and organically combined sulfur. The low unsaturation of Butyl rubber makes it possible to satisfy all the potential points of cross-linkage while still possessing a network that is soft and elastic. In actual practice, there probably is a small percentage of the reactive sites or points of unsaturation disposed in such a way that they cannot approach an active site in another molecule. Experimentally, however, one can obtain a “maximum” state of vulcanization where further vulcanization time or additional sulfur and accelerator do not contribute further to additional cross-linkage. This feature is utilized in the present investigations.
The Transformation of Thiols Compounded in Raw Rubber
Authors: Bras Jeanle , Montu Michel 
Published: February 2011

Abstract
During the last few years the rubber industry has made use of certain thiols, under the technical name of peptizing agents, which have the property of accelerating the plasticization of raw rubber during mastication. It is now known that this process of plasticization involves oxidation of the rubber, and that it does not take place in an atmosphere of an inert gas. Accordingly the present authors were induced, on the one hand, to follow the transformation of thiols during their participation in the mastication of rubber and, on the other hand, to observe their influence on the tendency of rubber to oxidize. In the first of these objectives, the analytical method utilized was ultra- violet absorption spectrography. To avoid pertubations in the spectra caused by the resins present in rubber, crepe rubber purified by acetone extraction was used in the experiments. The rubber was masticated at 100° C, and the thiol was added soon after the beginning of this mastication in the proportion of 5 per cent of the rubber. Samples were withdrawn at successive intervals of time, and the transformation products of the thiol, which were isolated by acetone extraction, were identified by their ultraviolet absorption spectra. In these experiments, chloroform solutions containing 0.5 gram per liter were employed.
Belt-Flexing Test of the Du Pont Type
Authors: Buist J. M. , Williams G. E. 
Published: February 2011

Abstract
In general, flexing tests are subject to large errors, some of which have been studied using a test of the du Pont belt type. An improvement in the standardization of the test conditions can be effected by using a suitably designed belt balance arm and regularly adjusting the length of the belt. The rate of cracking and also the reproducibility of the results is affected by the design of the test-piece and also by the type of fastener used. Although the error between the results on replicate test-pieces is extremely large, more important are the large errors due to lack of reproducibility of replicate molded slabs, and this variability probably arises during vulcanization. Extremely large differences can also occur between nominally identical repeat experiments. This may be due to differences in the judgment of the stages of cracking in different experiments. Graded photographs were found not to be of any value in improving the reproducibility of results between two different operators. Attention is drawn to the differences in types of cracking obtained with the du Pont and De Mattia test-pieces. It is pointed out that with the du Pont test-piece the cracking tends to develop in depth more than is the case with the De Mattia, and therefore it is more difficult to construct or use graded photographs with the du Pont test. Accepting the fact that variations in the disposition of the stages of cracking do occur between two different experiments, a method of treating flex-cracking results graphically is suggested. By this method random variations in results are ignored and the average flex-cracking results obtained. It is suggested that flexing properties may be defined by two characteristics, viz., (1) Crack initiation time, and (2) Crack propagation time, and an example of the method of determining these characteristics is given.
The Molecular Structure and Properties of Rubber
Authors: Kasatochkin V. I. , Lukin B. V. 
Published: February 2011

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.