bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Determination of Some Inhibitors in Polymers by Light Absorption
Authors: Banes F. W. , Eby L. T.
Published: February 2011

A spectrophotometric method of analysis for inhibitors in polymers has been developed. This method corrects for background absorption and has been found to be rapid and more reliable than chemical methods of analyses which were investigated.
The Preparation of Positive Latex
Authors: Sarrut Jean
Published: February 2011

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

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

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

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

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

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

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

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

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

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

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.
Chromatographic Analysis of Rubber Compounding Ingredients and Their Identification in Vulcanizates
Authors: Bellamy L. J. , Lawrie J. H. , Press E. W. S.
Published: February 2011

The work is still in a preliminary stage, but sufficient has now been done to demonstrate the applicability of chromatographic methods to rubber analysis. The acetone extracts of vulcanizates are complex mixtures not readily amenable to analysis by normal chemical methods. By the use of this elegant technique, however, it has been possible to effect the efficient separation of wax, fat acids, accelerators, and antioxidants, not only from each other but also from naturally occurring coloring matter and from degradation products. The subsequent identification of the main fractions is then a relatively simple matter, as tests such as the cobalt oleate reaction for accelerators and the spot reactions for antioxidants can be applied without interference from any other components. The elegance of the method is further demonstrated by the fact that it can be used in the identification of components present in much smaller quantities than are detectable by other chemical methods. The accelerators and antioxidants studied so far are rather limited in number, but cover the main classes of these materials, and the method should, therefore, be applicable to the analysis of a number of technical vulcanizates, and the authors have, in fact, already made use of it with some success for this purpose. It is noteworthy that the adsorption and elution processes are quantitative, and that the whole of the material put on to a column can, therefore, be recovered from the various fractions. This, therefore, offers the possibility of quantitative work on such problems as the rate of consumption of accelerators during cure or the relationship of antioxidant content to behavior on aging. Such work would necessarily be restricted to experiments using pure accelerators and pure antioxidants which are single chemical entities. In this connection the degradation products obtained from mixes accelerated with T.M.T. or M.B.T.S. or D.P.G. are of interest both in the actual isolation of the components in question and in partial confirmation of the work of others in this field. A much more intensive study of the degradation products of each accelerator in mixes cured to varying degrees may well throw more light on the complex subject of accelerators. Although, therefore, the authors have been able to show the utility of chromatography for their own particular analytical problems, it is likely, ultimately, to be of great value in the exploration of some of the fundamental problems of rubber chemistry.
Vulcanization of Rubber with Sulfur
Authors: Williams Ira
Published: February 2011

Vulcanization is a change in rubber which results in an increased resistance to deformation at ordinary temperature. This definition disregards entirely any chemical agents or chemical actions involved. It requires only that the rubber lose its plastic properties and become more resistant to compression, stretching, or swelling. Freeze resistance may or may not be affected; this depends largely on the extent of any chemical attack which may be involved. The earliest method of vulcanization, discovered by Goodyear over a hundred years ago, still remains the basis for essentially all vulcanization of rubber today. The only refinements which have been introduced consist in the addition of accelerators and accelerating accessories, and in a manipulation of the quantity of sulfur. All of the other methods, such as the use of sulfur chloride, peroxides, quinones, nitro compounds, and selenium, remain quite unimportant from a commercial standpoint. The study of vulcanization, particularly with sulfur, has received the attention of many chemists, most of whom have differed in their final interpretation of the action. The earliest work on the nature of vulcanization was carried out by Henriques, who found that sulfur chloride combines chemically with rubber, and the natural assumption was made that molecules of rubber are joined by means of sulfur. Weber soon found that sulfur combined during hot vulcanization. Stern found that the amount of sulfur combined was directly proportional to the time of heating and depended on the original concentration of sulfur. Whereas Stern conducted his vulcanization in solution, Hübener obtained substantially the same results in a direct manner.
Crude Rubber Preparation. Sheet Production by Continuous Coagulation of Hevea Latex
Authors: Newton E. B. , Stewart W. D. , Willson E. A.
Published: February 2011

Quantitative experiments in controlling the rate of coagulation of fresh Hevea latex are described, and the results have been applied in a process for the continuous preparation of sheet rubber on a laboratory scale. As with most continuous processes, this method is more applicable where large, rather than small, volumes of latex must be worked up. Its apparent advantages reside in a possible improvement in uniformity of product and a reduction in factory floor space for a given output of rubber.
Chemical Changes in Ammoniated Hevea Latex
Authors: Altman R. F. A.
Published: February 2011

As generally accepted, the preservative action of ammonia on latex is due to the neutralization of the acids formed from certain latex components by bacteria or enzymes and to its inhibiting action on bacterial growth. The chemical composition of latex undoubtedly changes on ammoniation as different components, probably including the rubber itself, are chemically affected by the alkaline action of ammonia. So far, only little insight has been obtained into the chemistry of these changes. In this connection reference should be made to the work of Rhodes, who systematically followed the changes in various characteristics of the latex over a period of fourteen months. The averages of the figures obtained by Rhodes are recorded in Table 1. The reader is referred to the original paper for the interesting comments made on these figures. In the present publication the changes in the nonrubber ether-soluble part of the latex have been followed analytically over a fifteen months' period. The experiments were conducted in such a way that, at certain time intervals, samples of 100 cc. were taken from the vigorously shaken bulk of latex which had been ammoniated immediately on arrival in the laboratory. Exclusively latex of clone Tjirandji 1 from the Experimental Garden Tjiomas near Buitenzorg, Java, was gathered for this purpose.
The Thermoplasticity of Thermoprene. A Study of the Adhesion of Rubber to Metal
Authors: Jarrijon André , Louïa Pierre
Published: February 2011

Among chemical derivatives of rubber, there is a type to which has been given the name of isorubbers or cyclorubbers in the technical literature. Kirchhof has described at length these products, which can be prepared by various methods, e.g., by the action of heat, as described by Harries, who isolated a white amorphous powder, having a density of 0.992, by heating rubber for several hours in ether at 250–300°, under pressure, or by the action of chemical reagents, particularly sulfuric acid and inorganic and organic halogenated compounds, with which a range of products suitable for molding powders, paints, sheets, wire, etc., can be prepared. The present work is concerned, not with a further study of these products, but rather with an investigation of a particular one of these products, viz., that which is obtained by treating rubber with phenolsulfonic acid. The B. F. Goodrich Company, and Fisher in particular, have successfully developed the manufacture and use of this product, and have given it the generic and commercial name of Thermoprene. At the beginning, a large number of applications of Thermoprene were foreseen, but only one application has survived and undergone any extensive development, viz., the use of Thermoprene as an adhesive for bonding rubber to metal, a process known as the Vulcalock process. As a result of newly observed facts, it seemed of interest to take up this problem again in an attempt to improve the process in certain ways.
Determination of Resistance to Abrasive Wear. V. Influence of Calender Grain
Authors: Parris R. W. , Scott J. R.
Published: February 2011

The standard form of test-piece used on the type of abrasion testing machine of the Akron Standard Mold Company is a disc of about 63.5 mm. diameter and 12.5 mm. thick. This can be made either (1) by vulcanizing in a mold of appropriate shape, which is filled with a blank cut from a sheet of stock about 13 mm. thick, or (2) by cutting out from a mold-vulcanized slab 12.5 mm. thick. In either case the abrasive wear takes place on a surface corresponding to the edge of a disc cut from the sheet of stock. The same is true if tests are made on discs cut from rubber articles such as soles, flooring, or other material in sheet form. In the actual use of such articles as tires, soles and heels flooring, conveyor belting, and tough rubber cable sheaths, the abrasive wear occurs on a surface representing substantially the flat surface of the sheet of stock. If the stock contains fillers that produce a calender grain effect, e.g., magnesium carbonate and clay, it cannot be assumed that the wear on the flat surface of the sheet is the same as that on the edge of a disc cut from it, which lies in a plane perpendicular to the former surface. If there is a difference between the rates of wear on these two surfaces, the type of test-piece described above must give an incorrect indication of the abrasion resistance of the rubber in actual use.
Determination of Resistance to Abrasive Wear. VII. Uniformity of Results Obtained with the Du Pont Machine
Authors: Morley J. F. , Scott J. R.
Published: February 2011

(1) Tests have been made to investigate the variability of the abrasive papers used on the du Pont abrasion machine; the data obtained have also been examined to detect any variation in rate of abrasion during one test, and differences between the right- and left-hand specimens. (2) Differences in abrasiveness of 13 per cent were found between the different sheets of emery paper, even when compared with the differences between the rubber specimens, and it is considered that a solid disc of bonded abrasive, as used on the Akron machine, would be preferable to emery papers. (3) As there is no evidence of variation in rate of abrasion during a 20-minute run, there seems to be no objection to using different test-periods for different rubbers if circumstances render this desirable. (4) There are small, but not consistent, differences between the abrasion losses on the right- and left-hand specimens, which may arise from the 8-lb. load not being equally distributed between them. It is considered that the machine could be improved by making the arm that carries the specimens free to oscillate in a plane perpendicular to the abrasive, so that the loads on the specimens would be automatically equalized. The practice of rigidly fixing the arm parallel to the plane of the abrasive seems unsound because, if the parallelism were really rigid, the rates of wear on the two specimens would of necessity be equal, even if the rubbers had different abrasion resistances. Moreover, any suggestion to test the sample under examination and a standard rubber simultaneously is clearly unsound unless a freely oscillating arm is provided.
The Effect of Air Circulation by Convection in the Test-Tube Method of High-Temperature Aging of Synthetic Rubbers
Authors: Juve A. E. , Boxser H. , Reahard D. H. , Doner S. R. , McWhorter J. F. , Cashion C. G. , McCarthy G. D. , Howlett R. M.
Published: February 2011

By modifying the present test-tube method of high-temperature aging to permit air circulation by convection, the test is made appreciably more severe, but at the same time more reproducible. The velocity of air circulation under the conditions used here, which varied over a three-fold range from 1.1 to 3.4 changes of air per hour, did not affect the results obtained. The loss in weight during aging was somewhat greater in the circulating-air tests than in the stoppered-tube tests. The poorer reproducibility of the stoppered test-tube method over the circulating-air method is thought to be due to variations in the permeability of the stoppers used. The more impermeable the stopper, the less severe is the test. It is recommended that the present test-tube aging method D-865 be amended to require the use of a pair of glass tubes extending through the stopper using the dimensions and arrangement illustrated in Figure 1.
Effect of Fungicides on Natural and Synthetic Rubber
Authors: Stief J. L. , Boyle J. J.
Published: February 2011

During the recent war a great part of the military operations were conducted in warm, humid, tropical regions, ideal for the growth of fungi. The protection of the cotton cloth used in rubber-coated fabrics thus became a major problem of the armed forces. Because the area was of minor importance in the world consumer market, comparatively little work had been done on this problem by the research laboratories of private industry. A tropical testing chamber which simulated tropical conditions was built at Fort Belvoir to study the problems of fungus growth and effective countermeasures. The problem was complicated by the possibility that the fungicide which had a protective effect on the cloth might have had a destructive effect on the rubber coating. Tests on pentachlorophenol and 2,2′-methylene-bis (4-chlorophenol) by two industrial concerns had indicated that these two fungicides had no adverse effect on either natural rubber or GR-S when used in small concentrations. Tests by another industrial concern had indicated that salicylanilide was satisfactory for use with natural rubber and Neoprene. However, because of the meager amount of information available, a study was conducted to determine what fungicides, and in what concentrations, might abnormally deteriorate rubber coatings.
Certain Fundamental Concepts Relating to Nonpolar Mechanisms in Olefinic Systems
Authors: Farmer E. H.
Published: February 2011

The application of polar concepts to the interpretation and systematization of experimental observations in the field of organic chemistry has had such striking success and usefulness during the past twenty-five years that the concepts have become an integral part of organized chemical knowledge. Recent years, however, have seen the steady accumulation of experimental results which do not fit in the polar scheme, and these may be rationally and consistently interpreted as resulting from the occurrence of apolar types of reaction in which the participants are short-lived neutral entities (molecules or atoms) displaying free-radical characteristics. On the apolar basis, the author outlines a hypothetic correlation of a considerable array of experimental results with which he has been concerned—both as an immediate aid to making sense of what would otherwise seem to be unusually complicated and unintelligible, and with the hope that the views tentatively advanced will furnish suggestive starting points for future kinetic experimentation. The foregoing account relates to subjects forming part of a program of fundamental research undertaken by the British Rubber Producers' Research Association.
The Addition of Thiocompounds to Olefins. I. Reactions of Thioglycolic Acid, Thiophenol, and Isopentanethiol
Authors: Cunneen J. I.
Published: February 2011

The interaction of thiols with unsaturated hydrocarbons was first reported by Posner, who treated thiophenol and benzylthiol with a variety of olefins at room temperature in the presence of acetic and sulfuric acids. With simple olefins, conjugated and nonconjugated, addition of fragments of the thiol produced by scission of the S-H link proceeded readily and, at asymmetrically substituted double bonds, in opposition to Markovnikov's rule: CR′R″:CHR‴+SHPh→CHR′R″⋅CH(SPh)R‴. More complex nonconjugated olefins (terpinolene and sylvestrene) showed depressed reactivity in that addition occurred at only one double bond, and the highly conjugated systems, stilbene and diphenylbutadiene, failed to react at all. Ashworth and Burkhardt confirmed Posner's formulation of the styrene-thiophenol reaction, and pointed out the catalytic activity of sunlight and the inhibition induced by small amounts of piperidine. Ipatieff and others investigated the reaction of thiophenol and ethanethiol and propylene, isobutylene, trimethylethylene, and isopropylethylene at 100–150°, and found that, although addition products abnormal with respect to Markovnikov's rule were formed in the absence of catalysts, yet the presence of sulfuric acid, contrary to Posner's findings, reversed the orientation of the addition and led to normal products. Contemporaneously, Jones and Reid and Kharasch, Reid, and Mayo showed that traces of peroxides, either as present normally in unsaturated hydrocarbons or as added ascaridole, strongly catalyze the abnormal addition, and that quinol effectively impedes the reaction. Mayo and Walling have proposed a free-radical chain-reaction mechanism, but kinetic evidence on which to found a detailed reaction scheme is so far lacking.
Structural Changes in Rubbers Brought about by Molecular Oxygen
Authors: Dogadkin B.
Published: February 2011

The nature of the changes of physical properties of rubber resulting from oxidation processes is determined by its initial structure and also by the conditions of the process (temperature, concentration of reagents, extent of their interaction, type of reaction, etc.). In the interaction of molecular oxygen with linear polymers containing double bonds in the main chains, e.g., with natural rubber, a disintegration of the chains takes place in the initial stages, as a result of which an increase of solubility, a decrease of strength, an increase of plasticity and a decrease in the viscosity of solutions of the rubber are observed. The decrease in solubility and the increase of strength and elasticity set in at that stage of oxidation at which local links of ether type are formed between individual chains, or at which the accumulation of polar groups containing oxygen increases to a noticeable extent the intensity of intermolecular attractive forces. In the interaction of molecular oxygen with spatial (network) polymers, e.g., with the insoluble fraction of butadiene and butadiene-styrene polymers, with a solvent medium, there occurs a disintegration of structure and passage (dispersion) into the solvent medium. The solutions obtained contain massive particles of spherical form and display over a wide range of concentrations a Rayleigh type of light scattering and obedience to the law of Einstein and Poiseuille. The chemical nature of the dissolution of spatial polymers is confirmed by the magnitude of the activation energy of the process (27,000 calories per mole). A similar breakdown of spatial structures occurs in the milling of rubbers of this type, in which, in contrast to cases of mastication of linear polymers, the viscosity of solutions of spatial polymers does not change during the time of mastication. In the interaction of molecular oxygen with linear polymers containing double bonds in side chains, e.g., with sodium-butadiene rubber, the principal effect which takes place is the secondary process of combination of chains to spatial structures, resulting in the observation of a decrease of solubility, and an increase of strength and elastic properties of the polymer. This formation of spatial structures in the second stage of oxidation is facilitated by the polyfunctionality of the products of the initial stage of oxidation of the original polymer. The structural changes described, proceeding under the action of oxygen, constitute one of the causes of the appearance of the vulcanization optimum.
The Action ox Benzoyl Peroxide on Natural Rubber in Solution
Authors: Compagnon Patrice , Delalande André
Published: February 2011

An earlier publication described experiments on the combination of active ethylene compounds, such as maleic anhydride and acrylonitrile, with rubber in solution under the influence of benzoyl peroxide. Control experiments on the action of benzoyl peroxide alone under the same conditions were carried out also, and from the results it was possible to come to certain conclusions. Since then, the reactions of unsaturated compounds with rubber have been investigated more extensively, and further experiments have been carried out on the action of benzoyl peroxide alone. The authors believe that it is of interest to discuss these observations at the present time, for it is not intended to continue with any systematic study of this problem, which actually is only of secondary importance as far as the main purpose of the investigation under way is concerned. Furthermore, it is felt that some of the experimental results may be of importance to other investigators who have studied, in the past few years, the photogelation and oxidation of rubber from the theoretical viewpoint. Finally, in the work already cited, no mention was made of the important part played by oxygen, even when in very low percentages, and this led to an incorrect interpretation of the phenomena, for which it is well to make amends at this time.
Influence of Structure on Polymer Liquid Interaction. I. Relative and Absolute Values of Swelling Equilibria
Authors: Salomon G. , Van Amerongen G. J.
Published: February 2011

To reach a better understanding of the correlation between molecular structure and intermolecular attraction, a comparison was made of swelling equilibria. With this aim we studied the absolute value of the swelling equilibrium under the influence of polar and polarizable groups, which were introduced in solvents and polymers with different molecular structures. The influence of temperature, cross-linking, external pressure, and mechanical strain on the position of the equilibrium was also studied. Any general treatment of swelling is obviously limited by our present knowledge of the properties of liquid mixtures. Experimentally, however, the study of high polymeric solutions and gels offers several advantages over that of ordinary liquids. Our experiments, designed to elucidate the structure of polymers, also reveal properties of some organic liquids which could not be observed easily by other means. Results obtained with commercial rubbers will be given in this paper, while analogous measurements on a series of copolymers with increasing numbers of nitrile groups will be dealt with in a second paper.
Heat Conduction and Molecular Structure in Rubberlike Polymers
Authors: Rehner John
Published: February 2011

In this paper experimentally determined values are reported for the thermal diffusivity (k) of various rubberlike polymers. Corresponding values of the thermal conductivity (W) can be computed from the well-known relationship, W=kρcP, where ρ and cP denote the density and specific heat at constant pressure of the composition. Measurements were made on (1) pure-gum stocks prepared with natural rubber, Butyl (GR-I), Perbunan-18, Perbunan-26, Perbunan-35, Buna-S (GR-S), polybutadiene, Neoprene-GN, polyisoprene, Silastic-160, and Silastic-180; (2) pure-gum stocks of the first five rubbers listed under (1) containing in addition 20 parts of a hydrocarbon softener (Bardol), based on 100 parts by weight of the polymer; and (3) the Bardol stocks containing in addition 54 parts of carbon black (Kosmobile-66). From measurements of the rate of change of temperature within a rubber sphere suddenly subjected to a change in its surface temperature, it was found possible to determine the dependence of k on temperature. A satisfactory definition of the “mean” temperature of a sphere under these conditions is described. In a discussion of the effect of chemical composition and structure on heat conduction, the bearing of hindered rotation, cross-linking and branching and interatomic bond strength on the results is pointed out. Values are derived for certain other properties of some of the polymers, including their characteristic Debye temperatures, specific heats at constant volume, flexibility of the main valence chains, compressibilities, and sound velocities.
Low Temperature Characteristics of Elastomers
Authors: Gehman S. D. , Woodford D. E. , Wilkinson C. S.
Published: February 2011

The low temperature stiffening of elastomers frequently limits their usefulness. A new laboratory test for measuring their stiffness at low temperatures is described. Strips of the stocks to be tested are mounted around a cylindrical rack in a vertical, cylindrical insulated chamber. The temperature in the chamber is controlled by cooling the base externally with dry ice and by a moderate regulated flow of precooled air through dry ice in the bottom of the chamber. This system gives stable temperatures which are easily controlled. The chamber can be rotated to attach the samples in succession, by means of projecting top grips, to a suitably mounted torsion wire. The stiffness is measured by the angle of twist of the sample when the torsion head is rotated 180°. The relative modulus for any temperature is calculated as the ratio of the modulus at this temperature to that at 25° C. Plots of angle of twist against temperature show a rather sharp break at the low temperature end of the curve. This determines a somewhat subjective “freezing point”. Curves are given to illustrate the wide variety of low temperature stiffening characteristics for elastomers. In unplasticized stocks the chemical composition of the monomers is the dominating factor for these properties for various synthetic rubbers. The stiffness of elastomers which are capable of crystallization on stretching, such as Hevea, Neoprene, and Butyl rubber, depends not only on temperature but also on time of exposure. To study these effects, the foregoing apparatus was used in a cold room. A rather long induction period occurs, during which the stiffness is essentially constant. It then increases and eventually reaches a larger constant value. Several months may be required to complete these changes. x-Ray examination of Hevea and Butyl proved that the increased stiffness on long exposure is due to crystallization. No change was observed in the stiffness of GR-S in the period of 2.5 months at − 30° C. Reduction in the speed of retraction is a critical measure of the deterioration of high elasticity at low temperatures. It gives a wide differeniation at moderately low temperatures between Butyl rubber and Hevea or GR-S, whereas a slow modulus test does not.
Effect of Stretching on the Properties of Rubber
Authors: Mullins L.
Published: February 2011

The results of tensile stress-strain, stress relaxation, swelling, electric conductivity, and power factor tests show that the properties of pure vulcanizates are only slightly affected by previous stretching or flexing; on the other hand, the properties of vulcanizates containing reinforcing agents, or fillers which stiffen the rubber, may be considerably changed by previous stretching. The increases of stiffness, electric conductivity, and power factor produced by the incorporation of the fillers are destroyed by flexing or stretching. From most practical points of view these changes are of a permanent nature, as at normal temperatures the recovery towards the initial properties is slow. These effects are attributed to the breakdown of both agglomerates and chains of filler particles, and the adsorption of the filler particles on the rubber.
Tensile Strengths of Pure Gum Natural Rubber Compounds
Authors: Gee Geoffrey
Published: February 2011

The tensile properties of a range of pure-gum natural rubbers have been reviewed, and it has been shown that their principal features can be understood on the assumption that the tensile strength measured in a given test depends directly on the amount of crystallization at break. The most important single factor in determining tensile strength is the degree of cross-linking. Cross-linking is only needed in order to prevent plastic flow, thus making it possible for the molecules to align themselves by stretching, and hence to crystallize. A very highly cross-linked rubber is weak because the load required to stretch it is so high that the rubber is broken before the elongation becomes large enough to produce crystallization. In general, vulcanization also involves reactions, e.g., the combination of sulfur with the rubber, which inhibit crystallization by producing structural modifications of the rubber. These reduce the tensile strength, especially when the degree of cross-linking is large. These ideas readily explain the effects of swelling and of the temperature of test. They are also used in a brief discussion of the phenomena of overcure, reversion, and aging.