bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Buffing in Preparing Dumb-Bell Tensile Specimens
Authors: Morley J. F. , Scott J. R. 
Published: February 2011

Abstract
1. Experiments are described on the influence of buffing vulcanized rubber, before or after cutting into dumb-bell specimens, on the tensile test results obtained with these specimens. The influence of the following factors is examined: fineness of abrasive used for buffing, thickness of rubber removed per passage over the abrasive wheel, total period of contact between the rubber and the wheel, and rest period between buffing and testing. 2. A machine is described for carrying out buffing under controlled variable conditions; this assures the buffed surface being flat and parallel to the under surface of the rubber, and gives more uniform thickness over the test length than buffing by hand. 3. With very soft (“pure”) rubbers tensile strength may be reduced as much as 15 per cent by using a coarse abrasive, although with stiffer rubber such as tire treads and conveyer belt covers, this effect is much smaller. 4. It appears to be immaterial whether the rubber removed by buffing is taken off in several thin layers or a few thick ones. 5. Varying the total period of time occupied by buffing within reasonable limits (two to eight minutes in the present tests) does not appreciably affect the test results. 6. With increase in the rest period between buffing and testing, the results indicate a distinct fall in tensile strength and a less marked fall in breaking elongation. 7. Tests on a rubber of the tire-tread type show that, if the dumb-bell specimens have been buffed, even with a fine abrasive that leaves a good surface and taking precautions to ensure uniformity of thickness, the tensile strength is some 5 per cent lower than that of dumb-bells cut from sheets with smooth (moulded) surfaces; the breaking elongation also is correspondingly reduced by buffing. On the other hand, the buffed dumb-bells give more closely concordant results, for both tensile strength and breaking elongation, than the smooth ones. 8. The following recommendations relating to the buffing of rubber for the preparation of tensile test specimens are put forward:—(1) A machine, such as that here described, capable of removing a layer of uniform thickness should be used in preference to holding the rubber by hand against an abrasive wheel. (2) A fairly fine abrasive, say 80 grit, should be used, at least for finishing off the surface. (3) The period during which the rubber is in contact with the abrasive wheel should be kept as short as possible. (4) The rubber should be buffed down to the required thickness before the dumb-bell specimens are cut. (5) Tensile tests should be made within definite time limits after buffing, say between twelve and forty-eight hours, and the specimens should be cut just before testing, that is, after any subpermanent deformation in the rubber has been largely eliminated.
The Mechanism of Modifier Action in GR-S Polymerization. II
Authors: Wall F. T. , Banes F. W. , Sands G. D. 
Published: February 2011

Abstract
The chain transfer theory of modifier action has been tested on commercial GR-S by means of molecular weight and sulfur content determination. The number of sulfur atoms per molecule was found to range between 0.7 and 1.1, to be compared to the theoretical value of unity. In view of the experimental difficulties involved, the results are considered to be in good agreement with the theory.
Determination of Hydroperoxides in Rubber and Synthetic Polymers
Authors: Laitinen H. A. , Nelson J. S. 
Published: February 2011

Abstract
Ferrous iron has been used as a reagent for the determination of peroxide by numerous investigators. Yule and Wilson estimated peroxide in cracked gasoline by shaking with an acid solution of ferrous thiocyanate and back-titrating the resulting ferric salt with titanous chloride. The method was criticized by Young, Vogt, and Nieuwland, who used the color of the resulting ferric thiocyanate complex as a basis for a colorimetric determination of peroxide. In this procedure methanol was used as the solvent. Bolland, Sundralingam, Sutton and Tristram modified the method to enable rubber samples to be analyzed by changing the solvent to a mixture of benzene and methanol (73 per cent benzene by volume). For determining peroxide in GR-S (butadiene-styrene copolymer) and other butadiene copolymers it would be desirable to employ a solvent rich in benzene, since these polymers tend towards insolubility upon oxidation. A solvent composed largely of benzene would also improve the sensitivity of the determination, since larger quantities of polymer could be dissolved in a given volume of solvent.
The Preparation of Positive Latex
Authors: Sarrut Jean 
Published: February 2011

Abstract
In the reversion of the electric charge of latex particles, certain difficulties are encountered which have not been pointed out by various other investigators who have published work on the subject. With preserved latex in the form that it is received in consumer countries, it can hardly be hoped to obtain stable dispersions of even fairly high concentrations, unless the latex is shipped and delivered within a very short time. An interesting solution of this problem would be the preparation of positive latex directly on the plantations. Here the use of cationic soaps would make it possible to obtain still better results than have already been attained. Finally, attention should be called to the fact that certain types of latex other than that of Hevea, in particular Funtumia elastica latex, seem to show considerably greater stability with change in their pH values. These latices are, of course, not yet used industrially, but present developments in African rubbers might change this situation. The use of such latices would then be advisable in certain cases, particularly in problems such as the one just discussed, the preparation of positive latex.
Molecular Fractionation by Diffusion of Guayule and Cryptostegia Rubber
Authors: Hauser Ernst A. , Le Beau D. S. 
Published: February 2011

Abstract
In general it can be said that the molecular-size distribution of Cryptostegia as well as guayule rubber is very much different from that of Hevea. The length of the Cryptostegia chains are within the range of the Hevea chains, but their distribution is not as even as those of the latter. Guayule must be considered as a rubber of much lower molecular weight.
Effect of Polymolecularity on Deformation of Butyl Polymers
Authors: Zapp R. L. , Baldwin F. P. 
Published: February 2011

Abstract
A large quantity of a Butyl polymer was fractionated in 100-gram portions into nine relatively narrow molecular weight fractions. The respective fractions from each batch fractionation were combined in solution to obtain sufficient working samples for two types of deformation tests. The fractionation was so designed that the middle fraction of the nine was used as a building block for a series of polymer fractional blends representing equal average molecular weight with gradually increasing molecular weight distribution. The separate fractions and blends of varying distribution were studied in deformation tests involving conditions of both constant rate of deformation and constant load. Under a constant deformation, at a given rate of compression, and over a temperature range of 40° to 130° C, it was shown that species of very high molecular weight (500,000 viscosity-average molecular weight) require temperatures in excess of 130° C for a transformation to a highly plastic state from one highly elastic. Species of intermediate and low molecular weight (300,000 to 100,000 viscosity-average molecular weight) require progressively lower temperatures for this transformation. Deformations at constant rate, with polymers of constant viscosity-average molecular weight, show the material of narrower molecular weight spread to be the more thermoplastic. A corollary also exists with elasticity; the narrower distribution yields a greater decrease in elasticity when the temperature is increased. Therefore, it can be postulated from the standpoint of equal processing qualities that a narrower distribution of molecular weight can tolerate a higher average molecular weight. A method has been developed for isolating the elastic and plastic or viscous components of deformation under constant load. Under specific conditions of constant load at 40° C, variations in molecular-weight distribution for a given average molecular weight result in variations in high elastic deformation, while the viscous component remains constant. Thus, increasing the molecular-weight distribution for a given viscosity-average molecular weight tends to yield a softer, more elastic polymer. Since the viscous component of deformation is independent of molecular weight distribution and depends only on average molecular weight, the constant load deformation test described yields a rapid method of estimating average molecular weight. Rate of viscous flow, which is independent of time if precautions and limitations are observed in the testing procedures, has been determined for individual fractions as well as for blends of varying molecular weight distribution. The logarithm of flow rate is linearly related to the square root of the viscosity-average molecular weight, as suggested by Flory's viscosity equation.
Comparison of Natural and Synthetic Hard Rubbers
Authors: Winspear G. G. , Hermann D. B. , Malm F. S. , Kemp A. R. 
Published: February 2011

Abstract
The wartime replacement of natural rubber by synthetics required an unusual expenditure of effort by the hard rubber industry in a short time. At first, curtailment of normal production, coupled with War Production Board restrictions of formulations, mitigated the urgency for synthetic hard rubber research. It soon became evident, however, that a complete line of synthetic hard rubbers would be desirable. These materials could be fabricated with standard rubber processing equipment, and would offer physical and electrical equivalents for the various grades of natural hard rubber developed during nearly a century. A program was started in these laboratories with the realization that rapid progress might be difficult; research on the compounding of natural hard rubber over the years had failed to produce improvements in overall properties compared with the original “ebonites”. The latter, according to the accepted nomenclature, are simple mixtures of rubber with large proportions of sulfur vulcanized by heating until chemical saturation of the rubber is almost complete. The first approach to the problem was through a study of vulcanizing characteristics and through examination of the hard products resulting from the reaction of sulfur with butadiene-styrene copolymers. As the program progressed, the work was extended to cover the processing of GR-S for ebonite fabrication and the compounding of GR-S hard rubbers for specific applications. Studies also were conducted relating to the compounding and processing of hard nitrile rubbers, and new tests were developed to suplement standard procedures used in the physical evaluation of hard rubbers.
Rubberlike Products from Linear Polyesters
Authors: Biggs B. S. , Erickson R. H. , Fuller C. S. 
Published: February 2011

Abstract
The polymers which result from the condensation of dibasic acids with propylene glycol are viscous gums which can be vulcanized to rubberlike products. In the unpigmented condition these rubbers are quite weak, but when reinforced with suitable pigments their strength and elongation compare favorably with other synthetic rubbers. Because polyesters of known structure and molecular weight can be easily synthesized, these polymers are useful for the study of the relations between structure and properties in rubberlike materials in general. Factors affecting tensile strength, oil resistance, brittle temperature, and stability are discussed. The development of rubberlike products from linear polyesters was announced in a short news article more than three years ago, but a detailed description of their preparation and physical properties has not been published. The object of this paper is to review these properties. However, the paper is written not so much from the viewpoint of offering a synthetic rubber for practical use as from that of applying linear polyesters to the study of the relations between structure and properties of rubberlike substances in general. As has been pointed out in other articles, the linear polyesters are well suited to serve as models in such a study, since molecules of definitely known constitution and molecular-weight distribution can be synthesized by relatively simple methods. Furthermore, the chemical structure of the polyester chain molecules can be varied in a definite and controlled manner by the choice of suitable glycol and dibasic acid or hydroxy acid reactants. The structure of the chains in the case of the former, assuming equal molar proportions, may be represented by the general formula:
A Radiographic Study of Rubber-Sulfur Mixtures
Authors: Trillat J. J. 
Published: February 2011

Abstract
The method described in the present paper suggests certain interesting applications in the rubber industry, important among which are: (1) the study of the mixing of sulfur and of fillers into rubber as a function of the time of milling, temperature, etc.; (2) the study of the uniformity of distribution of sulfur grains and of fillers; (3) the statistical determination of the size of grains; (4) the study of vulcanization, particularly the proportions of free sulfur and combined sulfur after vulcanization, the influence of accelerators, and the size of sulfur grains as affected by vulcanization. It should be realized that in the present paper only the principles of the radiographic method have been outlined, and it remains for those in the industry who have problems of the kind to apply the method to the particular problems which arise and may be solved by this method. Excellent results have been obtained by the present author in an investigation of a similar kind, involving the grinding and dispersion of pigments in paints and varnishes.
Plasticization of Natural and Synthetic Rubbers. I
Authors: Piper G. H. , Scott J. R. 
Published: February 2011

Abstract
This report describes the first part of an investigation on the factors operative in the plasticization of natural and synthetic rubbers, with special reference to determining the exact part which each one plays and to elucidating the changes in molecular structure which are the fundamental causes of the effects produced. The main conclusions from the work so far completed are as follows.
Sulfur Linkage in Vulcanized Rubber. Reaction of Sulfur with 2-Methyl-2-Butene
Authors: Selker Milton L. , Kemp A. R. 
Published: February 2011

Abstract
Year by year the complete definition of vulcanized rubber in terms of organic chemistry has become more desirable. The severity of the demands on rubber products makes it imperative to extend basic knowledge of vulcanization if we are to overcome the traditional defects or use limitations in this field. Chemical investigations of the vulcanization problem can be arranged into three lines of attack. In the first method the vulcanizate network is severed at various points by chemical or thermal means to liberate small portions of the material which can be studied as are small molecules. Ideally there should be no alteration of the linkages except where cutting of the chains takes place. Unfortunately no such “scissors” are known. Midgley, Henne, and Sheppard applied the thermal decomposition method to ebonite. Their study of the fragments, based on 1 per cent of the total material involved, was inclusive. Secondly, a small molecule reagent which swells the rubber may be used to penetrate the three-dimensional network and react with the various linkages in it. This method was used by Meyer and Hohenemser, who diffused methyl iodide into vulcanized rubber. This complicated reaction and its background with pure sulfur compounds were reported in the first two articles in the present series. The conclusions of this study were that the part of the combined sulfur which could be removed as trimethylsulfonium iodide was sulfide sulfur linked to a carbon atom alpha to a double bond. In most cases the less of this type of sulfur present, the higher the tensile strength of the vulcanizate. Methyl iodide was successful to a hitherto unattained degree because both its rate of reaction and products vary with the type of sulfur bond. This work left unanswered the question of the sulfur linkages which were not attacked by methyl iodide—in some cases the greater part of the combined sulfur. The third chemical line of attack is the study of model systems. A small molecule, such as an olefin, is reacted with sulfur and rubber-compounding ingredients; then, from identification of the products and study of the reaction, conclusions concerning vulcanizates are reached by analogy. The use of this method is old in chemical problems.
Statistical Analysis of Plasticity Measurements of Natural and Synthetic Rubber
Authors: Throdahl M. C. 
Published: February 2011

Abstract
The reliability of plasticity data on rubber is affected by (1) variance in precision of measurement by the instrument used and (2) heterogeneity of the rubber. While the relative precision of the instrument and observer error must be considered, the problem is somewhat complicated by the fact that each sample is used only once. Thus a single measurement is made on n like things rather than n like measurements on a single thing. Methods commonly used are the Williams parallel-plate, Dillon and Johnston extrusion, and Mooney shear. Rather meager data have been published on plasticity measurements of large numbers of samples (200–300) of elastomers. Riebl and Martin, Davey and Baker have reported no dispersion values, only averages of D30 plasticity values of smoked sheet and crepe being shown, using a parallel-plate plastometer. Aside from Mooney plasticity values of GR-S on 45–50 samples given in recent papers by Heide and Vila and Gross no statistical data for GR-S plasticity are available in the literature. It is the purpose of this paper to present a simple statistical analysis of the three types of plasticity measurements for GR-S and natural rubber (Hevea smoked sheet) based on 256 specimens.
Method of Testing the Mechanical Properties of Vulcanizates Prepared from Latex as a Starting Material
Authors: Pirot Marcel 
Published: February 2011

Abstract
With the method which has been described, it is possible to obtain reproducible results easily. It is hoped that the method will make it easier to study the properties of rubber mixtures prepared from latex. Furthermore the quantity of a latex mixture needed for such a test is small, i.e., of the order of 400 cc., so the method is particularly well adapted to the selection of Hevea trees on a basis of the quality of their latex. As a matter of fact, it will be easy in many cases to follow the collection of latex from a limited number of trees. It should even be possible, by using a single dipping form and reducing the size of the dipping tank, to follow the quality of the latex from the daily production of one tree, a procedure which is impossible with coagulated rubber.
Oven and Bomb Aging of GR-S at Corresponding Temperatures
Authors: Shelton J. Reid , Winn Hugh 
Published: February 2011

Abstract
The relations observed in this comparison of air oven and oxygen-bomb aging of GR-S at corresponding temperatures and the interpretations suggested by these relations may be summarized as follows: 1. Comparison of the results of tests in which some samples were aged in the form of tensile test strips while others were cut from rectangular strips after aging indicates that edge effects during aging are negligible and that the former practice is satisfactory. 2. Increased temperature increases the severity of both types of aging, but the effect is greater at the higher oxygen concentration of the bomb. 3. The hardening reaction, as measured by the increase in modulus, appears to be little affected by increased oxygen concentration above that in air and is the predominant reaction in the air oven. 4. Chain scission, as measured by decrease in tensile strength, increases with oxygen concentration and is the predominant reaction in the oxygen bomb. 5. Chain scission is also reflected in the smaller modulus increase observed with oxygen bomb aging compared to the air oven, and is responsible for the reversion of the modulus observed at 100° C and 300 pounds per square inch oxygen pressure. 6. Changes in temperature and in oxygen concentration, therefore, alter the ratio of the fundamental aging reactions of chain scission and cross-linking. Since the effect of these two reactions on physical properties is different, no direct correlation can be expected between methods of aging which differ in both temperature and oxygen concentration. 7. Activation energies calculated from the temperature coefficients observed for tensile breakdown in the oxygen bomb (29.7 kg.-cal.) and for modulus increase in the air oven (18.2 kg.-cal.) may be regarded as approximations of the activation energies required for chain scission and cross-linking, respectively. The observation has been made that the latter reaction is virtually independent of oxygen concentration above that in air, whereas the former increases with oxygen concentration. This may be interpreted as indicating that, at the temperatures involved, a relatively large number of oxygen molecules are sufficiently activated to maintain the lower energy reaction, even in air, while a much smaller number have the energy required for the scission reaction; consequently, increased oxygen concentration will be more effective in making a larger number of active molecules available for reaction in this case. 8. The greater dependence of chain scission on oxygen concentration may also be regarded as an indication that, although both reactions are apparently initiated by oxygen, the subsequent reactions leading to chain scission may require additional oxygen while the reactions resulting in cross-linking may not.