bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of Exposure-Cracking of Rubbers. With a Review of the Influence of Ozone
Authors: Newton R. G. 
Published: February 2011

Abstract
“Exposure-cracking” is the fissuring which occurs when stretched rubber is placed in an atmosphere containing ozone, and is frequently wrongly described as “sun-cracking”. These cracks form in the rubber at right angles to the applied stress and must be distinguished from crazing, the fissures of which occur in an oxidized surface layer and may run in any direction. It is shown that there is a “critical elongation” at which cracking is maximal, but that the relation between the severity of cracking and the surface strain can be greatly modified by changes in the compounding ingredients. Butadiene type of rubbers do not differ greatly in resistance to exposure-cracking, whereas the Neoprene types and Thiokol-FA possess marked resistance. The only factors essential for the production of exposure-cracking are ozone and strain in the sample, and sufficient ozone must be present in the atmosphere to produce the deterioration observed. Light is not only unnecessary, but actually has a retarding effect on the production of cracks. Three different phenomena must be carefully distinguished (1) the rate of ozone attack ; (2) the rate of formation of cracks ; and (3) the rate of growth of cracks. The rate of formation of cracks increases with increase of strain until a maximum is reached at about 75 per cent elongation, but the mean rate of growth of cracks is most rapid at 20 per cent elongation because the surface strain is most persistent at this elongation. The actual growth of cracks has been studied microscopically, and it is shown that large cracks are formed by the coalescence of small cracks, and the collapse of neighboring ones. The rate of ozone absorption is considered, and speculations are advanced to explain the formation of cracks and their greater incidence at high strains. The course of ozone attack indicates that there is little likelihood of producing improvement in resistance by altering compounding ingredients such as fillers and antioxidants, and confirms that the most efficient methods will be based on some type of surface protection.
Retraction and Stress Propagation in Natural and Synthetic Gum and Tread Stocks
Authors: Mrowca B. A. , Dart S. L. , Guth Eugene 
Published: February 2011

Abstract
Natural and synthetic rubbers (elastomers) are characterized by their long-range reversible elasticity. More particularly, the existence of a retractive force distinguishes rubbers from materials like beeswax, which may be extended but do not snap back. Whereas all rubbers show a snapback, the good rubbers show a fast snapback. Thus the speed of snapback is an outstanding index to the quality of the rubber. For instance, both Hevea and Butyl show snapback, but Butyl snaps back much more slowly than Hevea. This is the reason for the poor rebound in Butyl. Incidentally, the speed of snapback may be, and actually is, used as a simple “hand test” for progress of cure. One bends a cured sheet and observes how fast it straightens out again. In this example the speed of recovery after bending is observed. The speed of snapback may be studied, of course, for any deformation : bending, torsion, shear, compression, extension, etc. Since stress-strain data are used so extensively in rubber technology, snapback after extension was studied first. Snapback will be used in this restricted sense in the following text. Besides characterizing the quality of a polymer, the speed of snapback is of great direct importance for tire construction. Sluggish snapback may lead to increased flexing, i.e., increased heat generation. In addition, slow snapback means less grip of the tire on the road, assuming equal wetting conditions.
Some Physical Properties of Elastomers at Low Temperature
Authors: Greene H. E. , Loughborough D. L. 
Published: February 2011

Abstract
The design of a laboratory test to duplicate the service performance of a product is always difficult. When carried out carefully, it becomes as involved as a direct use test. To circumvent these difficulties in low temperature measurements, we have chosen to measure well defined constants over a range of independent variables. From an interpretation of these data, one can predict performance in a way not possible by service-simulating tests. The analysis does, however, demand an understanding of the physical nature of stress-strain properties, including at least a qualitative understanding of the mechanism involved. Below the second-order transition temperature an elastomer is hard and brittle. This glassy state is characterized by an elastic modulus in the neighborhood of 107 lbs. per sq. in. As the temperature increases, the modulus decreases rapidly along a sigmoidal curve until the modulus has reached a value of approximately 102 lbs. per sq. in. With further increase in temperature the modulus increases linearly with absolute temperature in a manner successfully explained by the kinetic thermodynamic approach. The modulus-temperature curve consists, then, of three parts: (1) a glassy region; (2) a transition; (3) an elastic region.
The Proöxygenic Effect. Changes Which Take Place in Vulcanized Rubber
Authors: Chovin Paul 
Published: February 2011

Abstract
The autoöxidation of rubber is sensitive to the action of catalysis; anti-oxygenic compounds are antagonistic to the process and retard its progress; proöxygenic compounds on the contrary promote autoöxidation, and in their presence the effects of autoöxidation are evident sooner. In the present paper, experiments are described, the object of which was to study the action of a few typical proöxygenic compounds on rubber hydrocarbon. Among the substances which accelerate the action of oxygen, certain salts of copper, iron, cobalt, and manganese are known to be very active. Various organic derivatives of these metals were studied in the present work, including (1) copper acetylacetonate, oleate, linoleate, sulforicinoleate, elaidate, stearate, enanthate, pelargonate, hendecenate, erucate, and diethylthioneethiolcarbamate; (2) iron acetylacetonate, oleate, linoleate, sulforicinoleate, and pelargonate, and the dibenzoylmethane derivative of iron; (3) cobaltous oleate, linoleate and sulforicinoleate, and cobaltic acetylacetonate; (4) manganous oleate, linoleate, sulforicinoleate and pelargonate, and manganic acetylacetonate. A study was also made of certain more complex metal derivatives, including salts of the dithizone of cupferron, of mercaptobenzothiazole, of α-nitrose-β-naphthol, of benzyldioxime, etc. The method followed involved two steps: (1) incorporation of a predetermined percentage of a proöxygenic metal compound into samples of vulcanized rubber, (2) estimation of the acceleration of autoöxidation induced by the particular proöxygenic compound. In the first step, the rubber sample was cut into small cubical pieces 2–3 mm. on a side, and these were placed in a chloroform solution of the particular salt under investigation. The average content of proöxygenic compound which was absorbed was about 0.1 per cent. The swelling of the rubber in the solution was the determinant factor in the total amount of proöxygenic compound and solvent which were absorbed.
Plasticity Measurements in the Rubber Industry. IV
Authors: Behre J. 
Published: February 2011

Abstract
In the present work, the volume of rubber which flows in unit time from an extrusion plastometer as a function of the pressure and temperature was determined, and the socalled yield value was calculated. This latter value represents the critical shearing stress which must be overcome for true plastic flow to take place. It is shown also that the yield value depends greatly on the temperature and preliminary treatment undergone by the sample.
High-Temperature Oven Aging of Oil-Resisting Synthetic Rubber Compounds
Authors: McCarthy G. D. , Juve A. E. , Boxser H. , Sanger M. , Doner S. R. , Cunningham E. N. , McWhorter J. F. , Crossley R. H. 
Published: February 2011

Abstract
An investigation of the effect of varying conditions of high-temperature exposure has shown that, at a constant temperature, the supply of oxygen is the principal factor which causes stiffening of the vulcanizates. The loss of volatile plasticizers, when present, also contributes to the stiffening. The test-tube technique, developed in the course of this investigation, in which dumbbell samples are suspended in stoppered test-tubes (38 by 300-mm.) heated by immersion in an oil bath, appears to give results which are considerably more duplicable than those obtained by the usual aging in circulating air ovens. The test-tube technique also gives somewhat better differentiation between good-heat aging and poor-heat aging compounds. The rate of deterioration as measured by elongation change is doubled for an 18° F increase in the exposure temperature. As measured by hardness change the rate is doubled by an increase of 42° F. Tests run at 250° F by this method are no more reproducible than those run at 300° F.
Physical-Chemical Investigations of Goldenrod Rubber. IV. Increase in Viscosity and Formation of Photogels by Irradiation of Goldenrod Rubber in the Absence of Oxygen
Authors: Graff Morris M. , Skau Evald L. 
Published: February 2011

Abstract
The viscosity of goldenrod rubber can be increased until gelation takes place by irradiation of its benzene solution in the presence of catalysts and in the absence of oxygen. Benzophenone, benzaldehyde and carbon tetrachloride seem to be the best of the activators tested.
“Rubber Acid” Damage in Fire Hoses
Authors: Thaysen A. C. , Bunker H. J. , Adams M. E. 
Published: February 2011

Abstract
The conclusions to be drawn from the experiments which have been carried out would appear to be that : The production of rubber acid in hose is due to the activity of sulfur-oxidizing bacteria of the Thiobacterium thioöxidans group. Such acid will invariable be formed in rubber-lined hose which is stored with the linings wet, when the responsible bacteria are present, and when the free sulfur content of the hoses exceeds 0.1 per cent. If acid production is to be prevented, it is necessary to ensure, either that the rubber-lined hose is stored dry, or that its content of free sulfur is less than 0.1 per cent. The alternative of preventing the introduction of the causal bacteria does not appear practicable, since the water used in fire-fighting is a frequent habitat of these bacteria. In a series of additional experiments it was established that various organic sulfur compounds, commonly used in the vulcanization of rubber, failed to give rise to acid production, even in the presence of sulfur-oxidizing bacteria.
Composition of Rubber from Different Botanical Sources
Authors: Bennett H. 
Published: February 2011

Abstract
Natural rubber from botanical sources other than Hevea brasiliensis now forms an appreciable proportion of the total rubber available to manufacturers in Allied countries. The principal source of this wild rubber is the African continent, the home of Landolphia, Funtumia and other rubber-producing vines and trees. RUBBER HYDROCARBON CONTENT The information given in Table 1 summarizes the general chemical characteristics of natural rubber from different botanical sources and, in particular, shows the amount of rubber hydrocarbon normally present in each type. Column 9 shows the values obtained by difference and column 10 those obtained by direct estimation, using the chromic acid oxidation method (ASTM Bull. No. 120, Jan. 1943, p. 23; Rubbee Chem. Tech. 16, 660 (1943)). The difference method assumes that the nitrogen is present as protein with a factor of 6.25; and, in calculating the results, allowance is made for the nitrogen and ash in the material insoluble in boiling nitrobenzene (See Table II). The direct estimation calls for no special comment except that the samples required very thorough blending to obtain concordant results, and varied considerably in the time required for digestion with oxidizing mixture.
Recent Advances in the Physics and Chemistry of Rubber. III. The Solubility and Swelling of Rubbers
Authors: Gee Geoffrey 
Published: February 2011

Abstract
In Parts I and II we have built up a picture of the molecular structure of a piece of rubber, which we have envisaged as a mass of interpenetrating chains, each of considerable length, but randomly kinked and in constant thermal motion, so that its shape is continually changing. Vulcanization restricts the possible motions of the mass by introducing permanent connections between pairs of chains at a series of irregularly spaced points. The purpose of Part III is to show how the picture can be extended to account for the behavior of such a system in contact with a liquid. If we imagine a liquid as a mass of more or less spherical molecules in constant thermal motion, it is clear that, when a liquid is brought into contact with a rubber, there is a tendency for molecules of liquid to diffuse into the rubber structure. Considering first the case of an unvulcanized rubber, we should expect the liquid to enter in increasing amounts, thereby separating the rubber chains and giving them very much greater freedom of motion, until finally some of them begin to find their way out of the main body of rubber and into the liquid. The rubber would thus be observed first to swell and then slowly to disperse until a uniform mixture of rubber and liquid is produced. This is, of course, the behavior actually observed when raw rubber is brought into contact with a liquid in which it is soluble. It is important to emphasize that the driving force which causes the mixing is simply the thermal motion of the components, and is not essentially dependent on any molecular attraction between rubber and liquid. It can be given a quantitative measure in terms of the thermodynamic concept of the increase of entropy consequent on mixing, but this development will not be considered here, our purpose being only to discuss the essential physical basis of the phenomenon.
Systems Manifesting Superposed Elastic and Viscous Behavior
Authors: Tobolsky A. V. , Andrews R. D. 
Published: February 2011

Abstract
Actual substances exhibit a very complicated behavior under mechanical stresses which cannot be described by classical elasticity theory nor by the classical theory of the hydrodynamics of viscous fluids. A general molecular theory describing the behavior of matter under stress is discussed and related to previous investigations and to experimental observations. Particular attention is devoted to rubberlike substances for which the classical theories are definitely inadequate. Experimental results on relaxation and creep of rubbers are interpreted in terms of modern structural concepts. It is found that these substances exhibit three regions of stress-temperature-time dependence. At intermediate temperatures there is a region of relative stability in which the statistical-thermodynamic theory of rubber elasticity is valid. At elevated temperatures, relaxation and creep are caused by chemical changes involving the rupture and formation of primary valence bonds. These chemical changes, which are responsible for the aging of rubber, can be isolated and studied by appropriate experimental techniques. At low temperatures relaxation and creep are caused by the slipping of secondary interchain bonds which are breaking and reforming in times comparable to experimental times of measurement. Theories are advanced to explain the observed stress-temperature-time behavior of rubbers over the entire temperature range studied.
Objective Laboratory Testing of the Processability of Elastomers
Authors: White L. M. , Ebers E. S. , Shriver G. E. 
Published: February 2011

Abstract
Ananalysis is made of the types of adverse behavior encountered in compounding and fabricating dry-mixed elastomers on a factory scale, with an attempt to ascribe the different modes of behavior to semifundamental properties of the elastomer and its compounds. On the basis of this analysis, four simple tests—filler stiffening, compound viscosity, length shrinkage, and rugosity—are proposed for determining the processing properties of elastomers on a laboratory scale. Extended correlations of predictions made from these tests with factory data demonstrate their reliability and usefulness in laboratory evaluation of new rubberlike materials. Much of the background information referred to in this and the following paper (page 833) was accumulated by the rubber industry at large working on the government-sponsored rubber program through the Research and Development Section, Rubber Reserve Company, and therefore has been subject to the usual secrecy orders. For this reason much of the earlier literature has not been published in the usual channels. However, every effort has been made to recognize contributions, made but not released, by other investigators by reference to their names and organizations.
The Vulcanization of Rubber with Phenol Formaldehyde Derivatives. I
Authors: van der Meer S. 
Published: February 2011

Abstract
Referring to Part I, describing the methylene quinone theory of the vulcanization of rubber with phenol-formaldehyde derivatives, in this paper the arguments in favor of that theory are considered in detail. The results of the investigations in question can be summarized as follows. 1. The vulcanizing properties of the pseudophenol halides are based on the easy transformation of these compounds into methylene quinones, with liberation of gaseous hydrogen halide. 2. The vulcanizing properties of the phenol-dialcohols are also based on the formation of methylene quinones as intermediates, but only at higher temperatures. 3. Phenol-dialcohols vulcanize slowly at temperatures only slightly below their decomposition temperatures, and yield comparatively good vulcanizates. Pseudophenol halides vulcanize rapidly at temperatures considerably below their decomposition temperatures, and yield comparatively poor vulcanizates. 4. The vulcanization temperature of 4,6-dihydroxymethyl-2-methylphenol (about 200° C) is higher than that of 2,6-dihydroxymethyl-4-methylphenol (about 155° C), as in the first case the vulcanization is based on the formation of an o-methylene quinone as well as a p-methylene quinone, and in the second case on the formation of o-methylene quinones exclusively. Generally these last compounds are formed more easily than the p-isomers. 5. The vulcanizing properties of 2,6-dihydroxymethyl-4-methylphenol at 155° C are reduced by the addition of 4,6-dihydroxymethyl-2-methylphenol, in consequence of the formation of molecular complexes which are unable to form o-, but only p-methylene quinones. 6. The vulcanizing properties of phenol-formaldehyde derivatives are entirely destroyed by hexamethylenetetramine, as that substance combines with the methylene quinones first formed. 7. The vulcanization reactions of the phenol-formaldehyde derivatives are not based on the formation of an irregular knot of entangled rubber and resin molecules, but on primary chemical bonds between these two. 8. The vulcanizing properties of the esters of the phenol-dialcohols, as well as those of the pseudophenol halides, are based on the formation of methylene quinones as intermediates, with liberation of acids. The higher fatty acid esters of 2,6-dihydroxymethyl-4-methylphenol are unstable, with the liberation of acids already at room temperature. 9. Compounds which may be supposed to be derived from phenol-dialcohols by a change in their configuration do not show vulcanizing properties if the formation of methylene quinones is impossible. If a repeated formation of these intermediates is only possible to a very limited extent, as is the case with phenol-monoalcohols, vulcanizing properties are also present on a minor scale.
Compression-Tear Test for Susceptibility to Road-Cracking of Synthetics
Authors: Trepp S. G. , Ward A. L. , Chaney N. K. 
Published: February 2011

Abstract
One of the outstanding weaknesses of GR-S rubber in tire-tread formulations is a pronounced tendency to crack in road service. In general cracks originate at the bottom of cuts or of moulded grooves in the tread, but spontaneous cracking may originate from local weak spots in the interior of the tread. Properly formulated natural rubber stocks are not susceptible to this type of failure, and usual laboratory and plant criteria and test methods developed by long experience for natural rubber formulations have been proved inadequate and misleading with respect to the evaluation of the susceptibility of GR-S rubber to this type of failure. These considerations have led to the development of the compression-tear test for susceptibility to cut growth which is the subject of this paper. The underlying principle of the test is to develop, under static easily controlled laboratory conditions, the type of strain which is the normal resultant of impact shocks of indeterminate severity under road service conditions. When pressure is applied at the surface of a cut or groove in a tire tread, the usual result is to pinch the walls of the cut together at the surface and to force them apart midway of the cut, thus producing a shearing force on the rubber under compression at the bottom of the cut. The U. G. I. compression-tear test is designed to set up a shearing force under conditions of high compression at elevated temperatures at the bottom of a standardized cut, and to measure the rate of cut growth with time.
The Weber Color Test for the Identification of Natural Rubber
Authors: Parker I. F. C. , Wake W. C. 
Published: February 2011

Abstract
The Weber color reaction, mentioned in a recent note, has become of importance in detecting natural rubber in mixtures in which it may be considerably diluted with synthetic rubber or nonrubber materials. The detailed instructions for carrying out the test are given elsewhere, and Stern has published a table which shows also the colors obtained when the test is applied to rubbers other than the natural product. It is clear from this table, and is confirmed by our experience, that the strong violet color developed is distinctive for natural rubber and gutta-percha, provided that the material has been extracted with acetone. However, color reactions in organic chemistry are rarely found to be as specific as earlier workers have claimed, and work is being carried out in these laboratories to establish the limitations of the reaction when applied to rubberlike materials. With very few exceptions, synthetic rubbers and rubberlike materials available at present do not give a positive result with this test, although very faint violet colors, which cannot be confused with a positive result, are sometimes obtained. Those giving any violet color are listed in Table I.
II. Effect of Coagulants on the Quality of Rubber
Authors: Siddiqui Rafat Husain , Mathur M. L. 
Published: February 2011

Abstract
1. Whatever coagulant is used for coagulation, a certain proportion of inorganic components, proteins and resins (1/9, 1/7, 1/5, respectively) of those originally present in latex remains adsorbed on rubber. 2. One-half of the total solids are eliminated with serum during coagulation. 3. The quality of rubber does not vary with a coagulant. 4. The molecules of latex are saclike bodies consisting of an inner core of rubber surrounded by protective films of resins and proteins, and the intervening spaces are filled with serum components. A puncture in the latex sac expels the serum components and brings about a collapse of the protective films which get adsorbed on rubber and these fused sacs float in serum as cream. By further fusion of cream particles a spongy coagulum of rubber is formed. 5. Coagulation is brought about because of profound changes in latex produced by physical and chemical agencies which destroy the stability of the system by elimination of resins, proteins and serum components, by neutralization of the charge on the rubber, and by the disruption of electrical, molecular and cohesive forces that pervade latex.