bluuebunny/crossref_metadata_2025 huggingface dataset:
Reproducibility of Tensile, Permanent Set, and Hardness Test Results in the Same Laboratory
Authors: Morley J. F. , Porritt B. D. , Scott J. R.
Published: February 2011

1. An investigation has been made into the accuracy with which measurements of tensile strength, breaking elongation, elongation at constant load, modulus, permanent set, and hardness can be repeated on successive days, using specimens taken from the same sample of rubber. 2. There is evidence that the gradual blunting, during normal use, of the knives used for cutting ring or dumb-bell specimens may appreciably reduce the tensile strength of the specimens. 3. After allowing for the apparent effects of blunting, aging of the rubber, and day-to-day variations in test temperature, the variability of the results has been examined by determining (1) the variability within each day's results (standard deviation of individual results); (2) the variability among the means of different days' results (observed standard error of daily means); and (3) the variability of daily means that would be expected to arise from (1) (calculated standard error of daily means). 4. In nearly every case the observed error of the daily means is greater than calculated value, showing that the results are affected by some factors (other than those already allowed for) that vary from day to day. It is not possible at present to say definitely what these factors are, although two causes of variation are suggested. In many cases, however, particularly with tensile strength and breaking elongation, a considerable part of the variation among daily means can be ascribed to the variation among individual results obtained on one day. 5. Examination of the frequency distribution of the tensile strength results shows that the majority (90–98 per cent) usually form a substantially symmetrical curve of the normal type, the remainder being abnormally low values, though not necessarily unreliable values. If the low values are excluded, the standard deviations and (in most cases) standard errors are reduced, but the conclusions deduced from them remain substantially unchanged.
Statistical Control in the Physical Testing of Rubber
Authors: Heide J. D.
Published: February 2011

In conclusion, may I repeat that the statistical methods find a useful and important application in the control of physical testing of rubber. An attempt has been made to show how the physical testing of rubber might yield more useful information if these methods were adopted. The illustrations and examples given have been of a very general nature. It is hoped, however, that they are of sufficiently fundamental nature to point the way to specific uses in any laboratory.
A Viscometer for Measurements during Thixotropic Recovery. Results with a Compounded Latex
Authors: Mooney M.
Published: February 2011

A viscometer is described for measuring the viscosity of a liquid immediately after an abrupt reduction of the shearing stress to a very low value. A hollow cylinder on a torsion suspension is immersed in the liquid contained in a narrow annular channel. The inner wall of the channel is rotatable with respect to the outer wall, and by this rotation the liquid is stirred or sheared. After the stirring is stopped, the viscosity is measured by recording photographically the rotation of the hollow cylinder, driven by a nearly constant torque applied through the torsion suspension. Measurements were made on a commercial compounded rubber latex containing 47.5 per cent of total solids. Immediately after stirring, the latex is a Newtonian liquid with a viscosity of 0.05 poise. Thereafter the viscosity increases at an initial rate and to an ultimate value, both of which decrease as the shearing stress for measuring the viscosity is increased. The steady viscosity is attained approximately in 10 seconds. The observed extremes in steady viscosity were 11 and 0.5 poise, corresponding to the shearing stresses 1.3 and 10.7 dynes per sq. cm. The experimental data are fitted approximately by theoretical curves based on these assumptions. All aggregates of solid particles are broken up by the stirring. During subsequent thixotropic recovery, loose aggregates are formed which contain considerable trapped water. The rate of aggregation follows Smoluchowski's theory of slow coagulation, but both the coagulation rate constant and the percentage volume of water in the coagulates vary with the applied shearing stress. The relative viscosity of the suspension of aggregates follows an empirical law based on Eilers' data on aqueous suspensions of bitumen spheres.
The Measurement of the Adhesion of Unvulcanized Rubber to Metal
Authors: Blow C. M.
Published: February 2011

A method is described for measuring the adhesion of metal to unvulcanized rubber and rubberlike materials, which involves the observation of the angle at which a metal ball rolls off the rubber surface when it is tilted. Experimental results are given to confirm the theoretical basis of the method and to illustrate the value of the method in studying the processing characteristics of rubber compounds.
A Method for Preparing Rubber Latex Specimens for the Electron Microscope
Authors: Kelsey R. H. , Hanson E. E.
Published: February 2011

The preparation of natural and synthetic rubber latex specimens for examination with an electron microscope is difficult because the individual particles are easily deformed and, under the usual conditions of specimen preparation, the particles tend to agglomerate. Von Ardenne and Beischer and others used a method which consisted of depositing a drop of highly diluted latex on a collodion film and allowing the drop to dry completely. In some instances the drop was withdrawn again into a glass capillary. It was found that in either case the latex particles were flattened at their areas of contact with the collodion film. The collodion film method was tried in this laboratory with the same poor results observed by Hendricks, Wildman, and McMurdee. Figure 1 is an electron micrograph of a natural rubber latex particle deposited by evaporating latex diluted 200 to 1 on a collodion film. The film has broken and curled to give a profile view of the particle which is observed to be badly flattened at its area of contact with the film. Figure 2 is a typical electron micrograph of natural rubber latex particles deposited on a collodion film. The blurred outlines of the particles are explained by the effect shown in Figure 1. It was obviously impossible to make good particle-size measurements from micrographs of this type. It was found further that severe aggregation of particles usually took place when a drop of the diluted latex was dried down. The latex particles which were left behind when the drop was removed with a glass capillary usually were not badly agglomerated, but it was felt that there was some possibility that the latex particles might adhere selectively according to size to the collodion film. An attempt was made to reduce the amount of agglomeration by incorporating in the diluting water various amounts of such wetting or dispersing agents as sodium oleate, orvis paste, Aerosol-OT, and ammonium caseinate. None of these materials helped very much in reducing the agglomeration of particles. It was found also in this study that very often the latex particles appeared granular around their edges due to foreign material being swept in during the evaporation of the water and crystallizing out upon the surface of the particle. This effect may also be observed in Figure 1.
Kinetic Studies in the Chemistry of Rubber and Related Materials. II. The Kinetics of Oxidation of Unconjugated Olefins
Authors: Holland J. L. , Gee Geoffrey
Published: February 2011

A brief review is given of kinetic work on the oxidation of representative mono, 1,4 and 1,5 olefins. The essential process in each case is identified as a chain reaction in which hydrocarbon radicals are formed, absorb oxygen, and then react with another molecule of olefin to give a hydroperoxide and a new free radical. Three methods of chain initiation are considered: (1) direct attack of oxygen on the olefin, (2) thermal decomposition of the hydroperoxide, (3) thermal decomposition of added benzoyl peroxide. Chain termination results from interaction of two free radicals; except at low oxygen pressures, these are both peroxidic.
Sulfur Bond in Vulcanizates Implications of Halogen Reactions
Authors: Olsen S. R. , Hull C. M. , France Wesley G.
Published: February 2011

1. When iodine chloride is used for the determination of double bonds in sulfur-vulcanized rubber or GR-S, it undergoes side reactions induced by combined sulfur. 2. Bromine in carbon tetrachloride is believed to give a satisfactory measure of the double bonds in a rubber-sulfur vulcanizate dissolved in dichlorobenzene-chloroform mixture. 3. The relation of one double bond consumed per sulfur atom combined in the rubber-sulfur type vulcanizate was confirmed. 4. Organic accelerators (in the absence of metal activators) catalyze the combination of sulfur without altering the ratio of one double bond loss per sulfur atom combined. 5. The introduction of a metal oxide or soap, such as zinc, causes a different type of vulcanization, which results in less than one double bond consumed per sulfur atom combined. 6. The reactions of propyl sulfide, dodecyl sulfide, propyl disulfide, allyl sulfide, methallyl sulfide, and butylmethallyl sulfide with iodine chloride and with bromine, respectively, are described. 7. The behavior of rubber-sulfur vulcanizates resembles that of butylmethallyl sulfide in reactions with iodine chloride and bromine, respectively; this suggests an alkyl-allyl type sulfur bond. 8. The theory of vulcanization proposed by Armstrong, Little, and Doak, based on the α-methylenic concept of Farmer, is supported by the findings of this investigation.
Mineral Sulfide as Index of Disulfide Cross-Bonding
Authors: Hull C. M. , Olsen S. R. , France Wesley G.
Published: February 2011

1. The mechanism proposed by Armstrong, Little, and Doak to explain sulfur vulcanization in the presence of metal soap was investigated in polyprene and simpler systems from the viewpoint of the inorganic sulfide produced and, in the case of polyprenes, of the accompanying modulus. 2. Dodecanethiol was found to react with sulfur and zinc soap to produce inorganic sulfide equivalent to the oxidation of 80 to 100 per cent of the thiol to disulfide ; with excess thiol substantially quantitative conversion of sulfur or of zinc soap to inorganic sulfide can be obtained. 3. Several simple olefins were found to react readily with sulfur and zinc soap under vulcanizing conditions. The reaction is promoted by M.B.T. On the basis of the mechanism assumed, the inorganic sulfide formed is sufficient to indicate extensive conversion of the olefin to a substituted diallyl disulfide. 4. Assuming the validity of the proposed mechanism, inorganic sulfide production indicates substantial disulfide cross-linking between α-carbon atoms in conventional cures with natural rubber, and appreciable, though relatively less, cross-bonding of this type in the case of GR-S. The smaller extent of this type of cross-linking with GR-S is believed to result from greater tendency on the part of this elastomer to add the intermediate mercapto compound to double bonds, as proposed in the first paper of this series.
Chemical Derivatives of Synthetic Isoprene Rubbers
Authors: D'Ianni I. D. , Naples F. J. , Marsh J. W. , Zarney J. L.
Published: February 2011

Natural rubber was the subject of intensive investigation with respect to its chemical reactions and the preparation of commercially useful derivatives. General reviews in this field have been written by Fisher, Schidrowitz, Jones, Sibley, Memmler, Dawson and Schidrowitz, and Farmer. Before World War II several of these reaction products, such as rubber hydrochloride (Pliofilm), isomerized rubber (Pliolite), and chlorinated rubber (Parlon), had been marketed successfully. During the past five years drastic restriction of the commercial use of natural rubber for chemical derivatives prompted the study of synthetic rubbers for this purpose. Endres recently reported on chlorinated and cyclized synthetic lubbers, with special emphasis on GR-S as the starting material. This paper deals particularly with derivatives of polyisoprene and other isoprene-containing synthetic rubbers which behave chemically very much like natural rubber because of the similarity in structure. It is shown that GR-S and other butadiene-containing synthetic rubbers, under the same conditions, are either nonreactive or behave differently. Because of its similarity to the natural rubber product, isomerized synthetic polyisoprene has been designated Pliolite S-1. Chlorinated synthetic polyisoprene is referred to as Pliochlor.
Observations on the Action of Unsaturated Compounds on Rubber in Solution
Authors: Compagnon Patrice , Delalande André
Published: February 2011

At the time Le Bras and one of the present authors pointed out the possibility of combining unsaturated compounds with rubber in the form of latex or by an ordinary mixing operation, reference was made to an interesting work, published by Bacon and Farmer in 1938, in which these authors described the addition of maleic anhydride to rubber in solution. At the same time it was emphasized, and this point was taken up in more detail in a later publication of Le Bras, that there are essential differences between the products obtained by the two methods, both with respect to their appearance and their properties, according to whether the technique employed is emulsion or mixing, or is that described by Bacon and Farmer. It should be borne in mind that the most distinguishing feature is that the first type of product is always to a great extent insoluble in solvents of rubber, whereas the second type of product may still be soluble even when 10–15 per cent, for example, of maleic anhydride has become fixed by the rubber. However, in spite of the products differing in certain attributes, the reactions involved in these two different experimental techniques should be fairly similar. Accordingly, in attempting to increase the action of these reagents on rubber, both in the form of latex and in solid admixture, and to throw further light on the mechanism of the reaction, the present authors have studied the effect of the reagents under the operating conditions employed by Bacon and Farmer, i.e., in solution. In what follows, various observations are reported which may contribute to a better understanding of certain peculiarities of this last type of reaction and to its wider application.
The Variation of Composition of 40 : 60 Isoprene-Styrene Copolymers with Conversion
Authors: Dyer Elizabeth , Munroe Dorothy Levis
Published: February 2011

There is little published work dealing with the emulsion copolymerization of isoprene and styrene. In ascertaining the effect of varying conditions on the emulsion copolymerization of a 40:60 mixture of isoprene and styrene, an approximately equimolecular mixture, it was observed that the initially formed copolymer contained about 80 per cent of styrene. As the reaction was continued to maximum conversion, the styrene content decreased to approximately 60 per cent. These results show that at this monomer ratio styrene enters the copolymer faster than does isoprene. This behavior is similar to that of styrene when copolymerized with acrylonitrile and with vinylidene chloride. The evidence indicates also that the copolymer is not homogeneous with respect to composition.
Emulsion Polymerization of Diene Hydrocarbons
Authors: Starkweather H. W. , Bare P. O. , Carter A. S. , Hill F. B. , Hurka V. R. , Mighton C. J. , Sanders P. A. , Walker H. W. , Youker M. A.
Published: February 2011

In any study of polymerization, careful consideration must be given to factors such as type and concentration of emulsifying agent, concentration of monomer, temperature, catalyst, and certain added chemicals which may have a marked effect on the results obtained. It is possible to make elastomers of considerable utility from mixtures of butadiene and many other polymerizable compounds. Several of these are superior to those made from butadiene and styrene in particular respects; but considering availability and cost of raw materials, this work has not uncovered any butadiene copolymers which would have been preferred over those made with styrene or acrylonitrile in the period of national emergency. The possibility of obtaining high grade elastomers from the diene hydrocarbons alone appears to justify further investigation.
Absorption of Oxygen by Rubbers
Authors: Carpenter A. S.
Published: February 2011

Constant-pressure oxidation experiments on natural rubber in the absence of antioxidant confirm that the reaction is autocatalytic and essentially similar to that for the oxidation of simple, unconjugated olefins. The results are in accord with a free-radical chain reaction mechanism. In the presence of antioxidant at constant pressure, rubbers reach a dynamic equilibrium state of oxidation at a constant rate. This rate is greater, the greater the pressure, but increases less rapidly than pressure. Several graphs are given to show the relation between equilibrium oxidation rate and oxygen pressure for several rubbers. If the pressure is reduced and again maintained constant after the attainment of the equilibrium oxidation rate at one pressure, the rate at the new pressure falls slowly over several hours from an initial high value to that consistent with the new pressure. This effect is more marked the less susceptible the rubber to oxidation. Methods of investigating the rubber-oxygen reaction in which pressure is allowed to fall spontaneously as oxidation proceeds are experimentally shown to lead to erroneous conclusions. The reasons suggested for this are the auto-catalytic nature of the reaction in the absence of antioxidants and the persistence of a high oxidation rate after a pressure reduction in the presence of anti-oxidant. An approximate relation is deduced between uniformity of oxidation, oxidizability, and specimen dimension for rubbers containing antioxidant.
Oxidation of GR-S and Other Elastomers
Authors: Cole John O. , Field James E.
Published: February 2011

The effect of heat aging on the physical properties of an elastomer is generally considered the result of oxidation, which produces both chain scission and cross-linking in the polymer. Early in the development of GR-S, a marked difference in the aging of GR-S and natural rubber vulcanizates was observed. From the effect of aging on hardness, tensile strength, modulus, and elongation it appeared that cross-linking occurred more rapidly than chain scission with GR-S, but the reverse was true with natural rubber. The work reported here was undertaken to provide a better understanding of the differences in aging of GR-S and natural rubber and to introduce new experimental methods for studying the mechanism of oxidation and antioxidant action in elastomers.
The Possibility of Transforming Rubber into an Ion Exchanger
Authors: Austerweil G.
Published: February 2011

Before taking up the actual subject of the present work, it is well to point out what is meant by an exchange of ions and to define an ion exchanger. An exchange of ions is a chemical reaction which takes place in a heterogeneous medium; when a solid heteropolar substance is immersed in a liquid, usually aqueous, ions belonging to the solid pass into the liquid in exchange for ions of the same polarity in solution in the liquid, and these dissolved ions thereby become fixed on the solid substance in place of the ions which the latter has just given up. As an example, minerals of the type of zeolite (green sand, harmatome, chabasie, etc.) can exchange their alkaline-earth metal ions, i.e., their cations, for sodium ions in an aqueous solution of sea salt which wets them or penetrates through them, and this phenomenon is reversible. Such a reaction is the basis of the detartarizing purification of industrial waters containing lime. Likewise the heteropolarity of exchangers sometimes renders their anions mobile, i.e., some substances give up their anions to liquids which wet them in exhange for the anions of these liquids, which thereby replace the anions liberated from the solids.
Alkylphenol Sulfides as Vulcanizing Agents
Authors: Wolf G. M. , Deger T. E. , Cramer H. I. , DeHilster C. C.
Published: February 2011

An approach to the problem of improving the property of tackiness of butadiene copolymers and a new class of vulcanizing agents for these polymers are discussed. The tack-producing qualities of a number of the alkylphenol sulfides were investigated with respect to their molecular structure and sulfur-content. The precise adjustment of the state of vulcanization is fundamental to the problem of improving the quality of vulcanizates of the butadiene copolymers. The principal approach to the realization of this adjustment previously has been by means of acceleration. It has since been found that the choice of the proper type of vulcanizing agent offers an equally promising approach whereby improvements in quality of the product may be achieved.
Development of a Better Processing GR-S
Authors: Schoene D. L. , Green A. J. , Burns E. R. , Vila G. R.
Published: February 2011

Poor prbcessability has long been recognized as one of the shortcomings of GR-S. Since the problem is of major importance, this deficiency has been the subject of a number of investigations. Freshly milled samples of GR-S shrink rapidly and become very rough. Samples extruded through a die swell excessively and give irregular and broken edges. These faults have, in many instances, necessitated excessive loading with compounding materials to permit satisfactory calendering and extrusion. Sacrifices in quality have often been tolerated to obtain suitable processing. The present paper describes a new type of GR-S in which vastly improved processing properties have been imparted to the polymer during the copolymerization reaction.
Thiuram Disulfides in Compounding
Authors: Morrison G. D. , Shepherd T.
Published: February 2011

Perhaps the chief drawback to the greater employment of thiuram disulfides has been the fear, often groundless, of scorching during processing, and for this reason the work detailed in this paper is devoted entirely to this aspect of their use. The scorching tendency, taken as the commencement of cure, and the rate of vulcanization were studied by means of a modified Goodrich type of plastometer, and the results are expressed as the percentage recovery against time in minutes at 120° C. This temperature (equivalent to 15 lbs. per sq. in. steam pressure) was chosen as being the highest likely to be reached in normal mixing, calendering and extrusion. The rubber compounds tested were prepared from one large batch of base stock comprising: smoked sheet rubber, 100 parts; zinc oxide, 5 parts; and stearic acid, 2 parts. After mixing, the stock was divided into the required number of portions and to these were added the various ingredients detailed later; in all cases the same milling time and temperatures were adhered to so that results would be comparable, especially plasticity. An interval of 24 hours at room temperature was allowed in each case before cutting plastometer test-pieces to dissipate strains imposed in the stock during mixing and sheeting. The test-pieces were then placed in an oven at 120° C, and percentage recovery determinations were made at 5-minute intervals over a range of 5 to 60 minutes.
Accelerated Ozone Weathering Test for Rubber
Authors: Crabtree James , Kemp A. R.
Published: February 2011

It has been previously shown by the authors that two separate and distinct factors are responsible for the changes which rubber compounds undergo when exposed outdoors : a light-energized oxidation and attack by ozone which is normally present in the atmosphere in minute concentration. The former acts independently of stress in the rubber, the latter only when the material is stretched. Since sunlight, ozone, and temperature vary hourly, daily, seasonally, and with locality, the overall result to the exposed material depends on the balance between the causative factors and is unique, since any given combination of such factors is not duplicated. It is, therefore, essential that the susceptibilities of a given compound to damage by these two factors be determined separately. The information thus furnished will then make it possible to estimate the durability of the compound under any given set of conditions. Damage by light-energized oxidation can be mitigated to any great extent only by physical protection from light, which can be partially achieved by incorporation of carbon black or ferric oxide. It is likely to be the major factor in the case of light-colored goods. Susceptibility can be readily gauged by measurement of the oxygen absorbed when the material is irradiated in air or oxygen under controlled conditions. The present obstacle to formulation of a standard test is the lack of a constant and reproducible light source which simulates sunlight. This article is principally concerned with the ozone factor. In the case of rubber goods containing appreciable loadings of carbon black, such as insulated cable jackets and hose, by far the most important cause of deterioration is the familiar cracking at stressed locations by the ozone of the atmosphere, popularly and erroneously referred to as “light cracking”.
Hysteresis and Methods for Its Measurement in Rubberlike Materials
Authors: Dillon J. H. , Gehman S. D.
Published: February 2011

After a piece of rubber undergoes a mechanical distortion, it is never the same again. The truth of this statement depends, of course, on the degree of precision and discrimination of the observations. Superficially, and for most most practical purposes, it may appear to be unaltered. The point is that in any deformation of rubber there are always some irreversible processes which lead to the conversion of mechanical energy into heat and to a departure from the behavior of an ideal elastic material. Tests which have been used to evaluate hysteresis loss in rubberlike materials may be classified as follows : 1. Low-speed stress-strain loop. 2. Impact resilience. 3. Free vibration. 4. Forced vibration at resonance. 5. Forced vibration ; nonresonance. We shall first discuss the general principles involved in these different methods of testing and then will describe the experimental procedures and results in more detail. For relatively large, slow deformations, depending on the experimental conditions, imperfections in elasticity become evident as hysteresis, permanent set, creep, time lag for recovery or stress relaxation.
A Simple Cold Test for Vulcanized Polymers
Authors: Leeper Harold M.
Published: February 2011

The freeze resistance of vulcanized polymers has been evaluated for the past two years at this laboratory by a method which involves measurements of primary creep at successively lower temperatures. This method has been found to be particularly useful when it is desired to know, within 5° or 10° F, the temperature at which the polymer ceases to function as a rubberlike material. In a laboratory of this kind, where considerable work is done in evaluating new polymer types and where the polymerization variables studied often are of such a nature as to produce relatively large changes in the freeze resistance of the vulcanized polymer, a tolerance of 5° to 10° F has been found to be a workable value. The test is simple and can be carried out with the Shore A durometer or the A.S.T.M. hardness tester, one or both of which are generally available in a rubber laboratory. Its simplicity notwithstanding, the test is reasonably objective. Both the durometer and the A.S.T.M. tester are handled in the conventional manner, and readings are taken five and 30 seconds, respectively, after the pressure plate or presser foot contacts the specimen. The degree of creep is recorded as the difference in hardness points between these two readings. It is a matter of experience that, for most polymers, the amount of creep or flow exhibited at successively lower temperatures increases gradually, reaches a maximum, and then begins to decrease at a relatively high rate. The temperature at which this rapid drop-off occurs is considered significant because at this point the polymer begins to lose, at an accelerated rate, the fluidity which it had at higher temperatures and is being transformed into a hard, nonrubberlike material.
Moulding Anisotropy
Authors: Gurney W. A. , Gough V. E.
Published: February 2011

It has long been an accepted fact that the properties of vulcanized rubber articles are not uniform in all directions. Vulcanized rubber is, in general, an anisotropic material, and the results obtained from tests vary, to a greater or less extent, with the direction in which the strain is applied or the measurements are made. In much experimental work elaborate precautions have been followed whereby replicate samples have been taken in the same directions from the rubber material. The cause of anisotropy has always, as far as the authors are aware, been attributed to the methods of processing or shaping the raw stock. This is the view taken by the authors of one of the most recent publications. As calendering is an operation that produces an extreme distortion of the raw stock, such processing effects are considerable, and the resulting anisotropy has been known for many years as calender grain, or in appropriate cases, as extruder grain. It has been evident, however, for some years that the theory that the method of preparation of the raw stock is the sole or even the major cause of anisotropy is not adequate to explain certain phenomena. Some products exhibit pronounced anisotropy, although their method of preparation does not involve much distortion of the raw stock, and in other cases, such variation in properties as does exist does not give any correlation with the direction of processing. Consideration of cases such as these have led to the conclusion that the movement of the stock during moulding is an important factor in the problem, and one that, as far as can be seen from the literature, has been hitherto neglected.
Proper Preservation and Storage of Latex
Authors: McGavack John
Published: February 2011

During the war years, when the maintenance of a stockpile of natural rubber latex was of critical importance, great opportunities were offered to establish new and improved techniques for its preservation and storage. Eight precautions are essential if latex is to be kept in good condition during long-term storage: (1) it should be kept free from bacteria; (2) it should have a sufficiently high pH level, which depends on the type of latex ; (3) it should be maintained at uniform total solids ; (4) its temperature should be uniform and properly regulated; (5) it should undergo minimum exposure to oxygen; (6) storage vessels should have smooth side walls and should be properly sterilized; (7) it should not be exposed to either indirect or direct light, and (8) it should have a low KOH number. Every one of these items must be considered carefully if the latex is to be maintained at highest quality. Each one will be discussed separately.
Control of pH of Neoprene Latex
Authors: Livingston H. K. , Walsh R. H.
Published: February 2011

One of the major contributions to the development of the use of rubber latex in manufacturing processes has been the introduction of methods for regulating the pH of the latex compounds. On the basis of this knowledge the coagulating dip process, the use of heat-sensitive latex mixes, and the use of gelling agents have become standardized and accepted methods of manufacturing rubber goods. Most of the techniques used in rubber latex manufacturing processes have been applied to the alkaline Neoprene latices, such as Types 571 and 60. However, in the case of the gelling agents the methods normally used to control coagulation of natural-rubber latex do not always apply to Neoprene latex. An investigation was made of the effect of pH reduction on the reaction between Neoprene latex and gelling agents, and also of methods for the control of this reaction. The effectiveness of the gelling agents as coagulants arises from the delayed formation of hydrogen ions or multivalent metallic ions in the latex which these agents produce under certain specified conditions. A good example of this phenomenon is the reaction that takes place when sodium fluosilicate is added to either natural rubber or Neoprene latex. The sodium fluosilicate hydrolyzes in the latex forming sodium fluoride, hydrofluoric acid, and silicic acid. Twiss and Amphlett state that the reaction probably proceeds according to the following equation:
Exposure Cracking of Rubber
Authors: Fielding J. H.
Published: February 2011

Exposure cracking, sometimes referred to as sun-checking or weather checking, is a term used to describe the behavior of stretched rubber when exposed to the atmosphere under conditions which cause cracking. Cracking can occur when a rubber product under slight tension is exposed to the atmosphere or to ozone. It can occur whether the product is at rest or in motion, in sunlight or in the shade ; or whether the exposure is in the daytime or at night. Susceptibility to cracking may be different under these different conditions. In a recent very excellent and comprehensive paper by Newton, many known facts about weathering and cracking were assembled, and the theory was proposed that all cracking of stretched rubber under exposure is due to ozone. A careful distinction was drawn between this and the crazing or weathering which occurs on unstretched rubber. If, as he contends, ozone is the active agent, the term “sun cracking” is obviously incorrect, and the term “exposure cracking” is to be preferred in describing the behavior of stretched rubber when exposed to atmospheric conditions or ozone. In spite of the fact that we now consider all cracking of this type to be due to ozone, the testing of compounds for resistance to cracking is not a simple matter. The more obvious laboratory test methods disagree frequently with each other and with service behavior. It is difficult offhand to explain why a stock containing wax, which is excellent under static exposure of test strips, may be very bad as a tire sidewall ; why an inflated tire stored in the shade may crack worse than a similar tire stored in the sun ; why a tire on a parked car may crack worse than a running tire ; or why a good compound in resisting sun exposure may appear to be inferior in resisting ozone. The present work adds further weight to the new well-established ozone theory. It demonstrates clearly, however, that neither outdoor nor indoor testing is a simple matter. This work also offers for consideration new testing methods and some explanation of their meaning.
The Rheology of Processing Quality of Raw Rubbers
Authors: Mooney M.
Published: February 2011

After a crude rubber, such as Hevea or GR-S, has been compounded with the ingredients necessary for vulcanizing, or curing, the raw mix must be formed in some way before it is cured. This forming operation is nearly always either calendering or extruding. Naturally, it is important that the stock should take the desired form as closely as possible; but in practice it is found that elastomers are in general difficult to form. It seems to be inevitable that those materials which exhibit long-range elasticity after curing also exhibit considerable elasticity before curing and refuse, therefore, to hold their shape after a forming operation. This and other processing troubles were handled in the early history of the rubber industry simply by trial-and-error methods in the factories. Later, particularly during the last ten years, further progress in processing problems was made by introducing various plastometers and other devices for testing specific properties of the raw stock. These test methods replaced simple tests by hand and by visual inspection, and made it possible to set up specifications for some of the stock properties empirically found necessary for acceptable processing. As a final step in processing control, there are now being developed, in the industry, methods for making quantitative measurements of particular processing defects. Such methods involve a small or full-scale processing operation under standardized conditions, and a standardized procedure for quantitative evaluation of the results in terms of departures from perfection. In the present discussion of processing quality of raw stocks in the rubber industry, various specific processing defects are described, various rheological methods used for testing raw stocks are mentioned, and finally, a few experimental results are reported which show correlations between some of the rheological tests and quantitative measurements of certain processing properties.
Properties of Hard Rubber. XXI. Influence of Vulcanization Temperature
Authors: Church H. F. , Daynes H. A.
Published: February 2011

In previous reports the properties of hard rubber made from rubber and sulfur were studied with particular reference to the effects of varying the rubber-sulfur ratio and vulcanization time. In the present report, a continuation of this investigation, the influence of temperature of vulcanization of similar materials is studied. Materials having rubber-sulfur ratios of 65/35 and 70/30 were vulcanized in a press at three different temperatures, namely, 165°, 155°, and 135° C, the times of vulcanization employed being estimated to be equivalent to 5 hours at 155° C. As a check on the estimate of the equivalent times, small samples of the same materials were vulcanized for various shorter and longer periods and were tested for plastic yield temperature and percentage of free sulfur. The main materials were tested for the following properties by the methods described in the previous report : Combination of sulfur, density, cross-breaking strength and elongation, impact strength, plastic-yield temperature, permittivity and power factor at audio and radio frequencies, and surface discoloration in sunlight. Certain anomalous figures were obtained in the impact test results which were thought to be due to the necessity of carrying out the longer vulcanization processes in stages. Arrangements were made accordingly to conduct the vulcanization continuously in such cases. This procedure brought about a considerable improvement in the results. These results confirmed the conclusion reached in the previous report that impact strength is very sensitive to untraced variables in manufacture. The results of the permittivity and power factor tests are discussed at some length, since they afford useful information on a number of other variables, principally rubber-sulfur ratio, frequency, and temperature of test. In a general discussion of the results, the choice of the best vulcanization temperature is examined. It is concluded that the selection of the best temperature involves compromise between opposing tendencies in the different properties.
Properties of Hard Rubber. XXII. Development of Proof Impact Test for Insulating Materials. Comparison of Pendulum and Falling-Weight Machines
Authors: Dock E. H. , Scott J. R.
Published: February 2011

A comparison has been made of impact tests by the pendulum machine (Izod) and by the falling-weight machine (Izod and Charpy), using fabric board, paper board, molded resin (Bakelite), and ebonite, each in four types of test-pieces; unnotched, saw-cut notch, V-notch with 1 mm. root radius, and V-notch with 0.5 mm. root radius. The effect of notching on impact strength varies from one material to another, and may alter their order of merit. Saw-cut and V-notches with the same root radius nearly always give about the same results, and reducing the root radius usually (but not always) reduces the impact strength. The pendulum machine always gives higher results than the falling weight-machine in Izod tests, and the ratio varies with the material, though not sufficiently to alter the order of merit. Under the conditions used in the present tests with the falling-weight machine, Charpy tests (70 mm. between supports) nearly always give higher values than Izod tests (22 mm. striking distance), but both arrange the materials in the same order of merit. Standard errors are worked out for the pendulum test results; V-notched specimens appear to give, if anything, the best accuracy. The sources of variability in test results, and hence of errors in the final value, are discussed in an attempt to compare the accuracies of the two machines. Although an exact comparison could not be made, there appears to be no great difference between the two machines as regards the accuracy of the result obtained with a given number of test-pieces. The four types of test-piece differ very little, on the whole, in this respect. With the falling-weight machine, the Charpy test appears to give rather better accuracy than the Izod test. There is no definite evidence that the amount of excess energy in the pendulum test influences the result, except perhaps with Bakelite. The variability of all four materials tested is such that a maximum excess energy limit of 25 per cent cannot be adhered to without excluding either the weakest or the strongest specimens and so obtaining a false mean. In Izod tests on the pendulum machine a 20 mm. striking distance gives higher values for fabric board than a 35 mm. striking distance; the former has the advantage that no incomplete breaks occur, as happens with the longer striking distance. Attention is drawn to certain advantages and disadvantages of the two types of machine, and to the necessity for defining a “break” in the case of laminated materials, where cracks or incomplete breaks are frequent.
Elasticity Measurements on Polychloroprenes
Authors: Kinell Per-Olof
Published: February 2011

A brief survey of modern opinion as to the nature of the rubberlike state in certain high polymers is given. The behavior of unvulcanized and vulcanized rubber samples has been investigated with a Polanyi dynamometer. By means of Wall's formula for entropy changes on stretching, certain constants characterizing the samples have been calculated. The use of these constants for comparison purposes has been discussed.
Performance of Butyl Inner Tubes. Influence on Tire Life
Authors: Lightbown I. E. , Verde L. S. , Brown J. R.
Published: February 2011

Since the first scientific paper on Butyl rubber was presented, numerous publications have described the properties and compounding technique of this polymer. Although Butyl has been referred to as a specialty rubber, it can also be used to replace natural rubber in many applications. Butyl was found to be a remarkable barrier to the passage of gases, including air. The polymer also deteriorated very little on aging and had excellent tear resistance. Because of these properties Butyl was first considered for inner tubes, and in this application Butyl has found its largest commercial acceptance. Automobile inner tubes were first made experimentally in September, 1940. With Butyl made in the Standard Oil pilot plant this experimental work continued until April, 1943, when the first government plant began producing Butyl commercially. From that time until the present Butyl has been used successfully to manufacture all types and sizes of inner tubes ranging from bicycle tubes of 1¼-inch cross-section to earth-mover tubes of 24-inch cross-section. Butyl tubes were first used by the United States Army for service in the European war theater in May, 1944. The following month Butyl was used in essential civilian trucks; but not until September, 1945, was sufficient Butyl available for civilian automobile tubes.
Lignin for Reinforcing Rubber
Authors: Keilen J. J. , Pollak Arthur
Published: February 2011

Lignin, as made from the waste black liquor of the sulfate wood pulp process, is an effective reinforcing agent for synthetic or natural rubbers when incorporated into latex by the coprecipitation or master-batching procedure. GR-S, reinforced in this manner with 38.5 volumes of lignin, yields vulcanizates having a tensile strength of 2900 pounds per square inch and a tear resistance of 380 pounds per inch, values exceeded only with channel black. With 77 volumes loading the tensile strength of 2800 pounds per square inch and tear resistance of 550 pounds per inch are higher than those for any other pigment tested. In abrasion resistance lignin vulcanizates are between carbon blacks and the common inorganic fillers. Shore hardness values are close to those for channel black. Lignin-reinforced rubbers weigh appreciably less per unit volume, owing to the low specific gravity, 1.3, of lignin. The brown color of lignin permits a wide color range, without sacrifice of mechanical properties, by blending with white pigments. Lignin coprecipitates require only a brief milling time for complete mastication. Details are given on the preferred procedure for preparing master batches of lignin and GR-S. Other suggested incorporation procedures made possible by the colloidal properties of lignin are reviewed.
Dispersoidal Analyses of Hevea Latex
Authors: Hessels J. H. E.
Published: February 2011

For the purpose of determining the weight-distribution curve of the rubber particles in Hevea latex according to their diameter, two methods were employed, namely, photomicrographic dispersoidal analysis and sedimentation analysis. In addition to the fact, that the first method is very laborious, its precision does not prove to be high, mainly because a significant percentage of the particles is too small to be determined microscopically in the visible spectrum. Sedimentation analysis with the help of a modified pipette method according to Andreasen was found, however, to be very suitable for the purpose. By an accurate regulation of the viscosity, specific gravity and temperature of the suspension it became possible to determine the weight-distribution curve of latex to a diameter of about 0.4µ within a creaming time of 10 to 14 days, while the total percentage of still smaller particles was also determined at the same time. This method is accurate, not too laborious, and lends itself very well to a series of investigations.
Natural Coagulation of Hevea Latex
Authors: Altman R. F. A.
Published: February 2011

Natural coagulation has been of interest during the last forty years. As no satisfactory explanation could be given for this phenomenon, it still continues to attract attention. It is now accepted that the instability of latex is caused by certain changes in the chemical composition of the latex components, but it is still an open question what those chemical changes are, and by what agents they are caused. The explanations of the changes have given rise to two rival theories, the so-called enzyme theory, and the bacteria theory. The first, supported by Whitby, Campbell, Barrowcliff, Stamberger, Stevens, and Paton, imputes the direct cause of the natural coagulation to the activity of an (unidentified) enzyme. They admit that, under the influence of bacteria, acids are formed in the latex during the process of natural coagulation, but they consider these acids to have only an activating influence on the enzyme. Gorter and Swart, Eaton, Denier and Vernet, Spoon, Belgrave, De Vries and Beumée-Nieuwland, Bobilioff, Corbet, Van Dillen and Heubel, and most of the modern investigators support the bacteria theory, postulated by Eaton and Grantham. According to this theory the acids produced by bacterial action are the direct cause of the natural coagulation.