bluuebunny/crossref_metadata_2025 huggingface dataset:
Reinforcement of Butyl with Carbon Black. I. Effect of Oxidized Blacks on Stress-Strain Properties and Bound Rubber
Authors: Gessler A. M.
Published: February 2011

The increased reinforcing capacity of oxidized blacks in butyl is illustrated, and the results are discussed in terms of the relationships which exist between polymer and black. Oxygen functionality on the black, it is shown, is the critical factor controlling the extent to which butyl is reinforced by the black. The lesser effects of decreased aggregate structure in the black are also demonstrated. These results are obtained using blacks which, though similar to attrited blacks, derive both their physical and chemical properties without the use of comminution. A much more unambiguous approach to the questions of black structure and oxygen content is therefore provided. In butyl, the unique sensitivity of the stress-strain curve to reinforcing effects is attributed to low unsaturation in the polymer. This sensitivity is used to qualify the nature of the reinforcement which is obtained. With oxidized blacks, true reinforcement is pictured as a stiffening effect which, starting with the gum vulcanizate, shifts the stress-strain curve without essentially changing its shape. The result is a “reinforced gum” which, it is suggested, derives its physical characteristics through the bonding of carbon black in the rubber network. With untreated black, carbon black is pictured as being enmeshed or entangled in an independently formed rubber network. Changes in the shape of the stress-strain curve are therefore attributed to steric restrictions which this arrangement imposes on the initial movement and subsequent orientation of network chains when the sample is extended.
Improvement of Asphalt by Addition of Rubber and Latex
Authors: Esser H.
Published: February 2011

Since the technical expressions and measurement methods appearing in this article are apt to be unfamiliar to many readers, they will be defined briefly. It is realized that on the one hand a certain eonfusion in concepts exists with respect to the terms bitumen, tar, and asphalt, and on the other, the test methods leave much to be desired, in the opinion of experts in the field. Bitumen differs from tar in its origin, for one thing. Whereas tar is the residue of the distillation of coal, bitumen is understood to be distillation residues derived from petroleum. Bitumens are colloidal systems, one phase of which contains organic substances, dispersed in the second phase, which consists of hydrocarbons having different molecular weights. Asphalt is understood nowadays to be a mixture of bitumen and mineral substances. Such mixtures, when found already combined in nature, are called natural asphalt, asphaltic rock, or crude asphalt. The uses of bitumen in technology and industry are very manifold; mention need be made only of applications for roofing paper and electrical insulations, in construction both below and above ground, for interior, exterior, and underwater coatings, for sealing purposes, and in the rubber industry. Of special importance is the use of bitumen in road construction. The combined use of bitumen and rubber is very old. Pertinent patent applications go back to the year 1843. Large scale experiments with rubber-modified bitumen in the road construction sector have been going on for about 30 years. Important investigations and contributions have been made by Anglo-American and, especially, Dutch scientists. In the addition of rubber to bitumen, the latter undergoes many essential and (for the road engineer) advantageous changes in its properties. Before these properties are taken up individually, a report will be given of the methods of physical investigation employed to test the characteristics of both “pure” bitumen and rubber-modified bitumen. Among the tests intended to characterize the properties of bitumen are those for penetration, softening point, breaking point, flow length, ductility, tenacity, toughness, and elasticity. It was only a few years ago that another method was developed, which provides for a very practical assessment (and one suitable for industrial applications) of the essential characteristics of rubber-modified bitumen. These basic features are useful for putting into proper perspective the unusual improvements which can be realized by the addition of rubber. This new method is known in the literature as the “tenaacity—toughness test. It will be explained later on, in more detail. The various methods can be summarized as follows:
Fibrous Structure in Stretched Crystalline Elastomers
Authors: Walters M. H.
Published: February 2011

Stree-induced crystallinity in elastomers produces a strengthening structure, and tearing the rubber along the axis of extension leaves this structure outlined in the rupture surface. By maintaining the initial elongation, and taking replicas of this torn surface, the morphology of stress crystallinity has been examined in the electron microscope. The crystallites were found to be closely spaced fibers, rounded in section, and oriented in the direction of elongation. The fibers were usually between 100 and 1000 A in diameter, and individual crystallites could be traced for distances of several microns before disappearing beneath the exposed surface. Noncrystallizing polymers showed no structure in the rupture surface. The addition of fine particle fillers had little effect on the structures observed in crystallizing polymers. In amorphous polymers traces of structure were observed, apparently consisting of groups of carbon black particles linked by rubber molecules.
Sol-Gel Analysis to Estimate Chain Scission during Cure. I. Peroxide Vulcanization of Natural Rubber
Authors: Bristow G. M.
Published: February 2011

Sol-gel analysis, that is, the measurement of the fraction of rubber remaining unconnected to the network as a function of the degree of cure, has been used to estimate the extent of chain scission in the vulcanization of natural rubber with dicumyl peroxide at 130° C. For peroxide concentrations in the range 1–5 per cent and masticated rubbers of Mn=0.84−2.67×105 there are only 1–3 sites of scission per 100 crosslinked isoprene units.
Modification of a Thermogravimetric Balance for Pyrolysis in a Controlled Atmosphere
Authors: Smith Derek A.
Published: February 2011

The quartz spring balance of Madorsky has been criticized by Jellinek. He points out the danger, in any suspended system, of condensation of volatiles on the (cooler) support and spring early in the pyrolysis, resulting in too low a measured weight loss. Later in the pyrolysis, the condensate may volatilize, giving too high a weight loss at long times of heating. To show the absence of such condensation effects, it is clearly not sufficient to weigh the support and spring before and after the pyrolysis, as has been proposed in the literature. A similar difficulty has arisen in the modification of the newer recording thermogravimetric balances for pyrolysis in a controlled atmosphere. For example, the otherwise satisfactory technique of Vassallo employs a downward flow of inert gas which may encourage condensation on the lower part of the weight transfer rod—the rod which transmits the load of the sample in its holder to the balance mechanism. A similar criticism can probably be made of the more elaborate system described by Stonhill. In an attempt to overcome this disadvantage, Soulen and Mockrin have modified the Chevenard balance by passing the weight transfer rod through a sleeve, with most of the outflow gas passing down the outside of the sleeve where condensation may occur without influencing the recorded sample weight. They claim that, in the absence of the sleeve, the thermogravimetric curves may be seriously in error.
Role of Antiozonants in Modern Tire Compounding
Authors: Thornley E. R.
Published: February 2011

The need to provide tire compounds with improved resistance to ozone has been very largely met by the use of N,N′ disubstituted-p-phenylenediamines as protective agents. These chemicals are for this reason commonly thought of as antiozonants but they also possess important antioxidant properties and in considering their role in modern compounding, it is necessary to distinguish between their antiozonant and antioxidant functions. The choice of protective system used in any particular tire component depends a good deal on the nature of the polymer. The relative behavior of natural rubber and SBR with respect to ozone cracking and flexcracking is demonstrated by data given in the paper and it is shown how a typical “antiozonant” such as isopropyl phenyl-p-phenylenediamine (IPPD) will protect SBR tread and sidewall compounds principally from static and dynamic ozone cracking and natural rubber compounds not only from ozone attack but also from various oxidative processes such as flexcracking, cut-growth and heat degradation. The effects of the partial replacement of natural rubber and SBR by polybutadiene on the antiozonant and antioxidant requirements of such tire compounds are also briefly considered.
Accelerated Ozone Test for Predicting Outdoor Effectiveness of Ozone Protective Waxes in SBR
Authors: Mueller W. J. , Palinchak S. , Stickney P. B.
Published: February 2011

Accelerated laboratory and outdoor aging studies were made to establish base lines leading to the development of an accelerated test method which could be used to predict the efficiency of ozone-protective waxes under static conditions. The effect of several variables on the rate of ozone cracking in an ozone chamber was determined, and it was found that exposure temperature was the most critical variable. The type of recipe and time between curing and stretching the samples were also found to be important in arriving at a suitable test procedure. The ozone concentration, although important, was found to be less critical than some of the other variables. An accelerated test method is proposed for determining the effectiveness of ozone-protective waxes. Two outdoor aging studies were made to determine the reliability of the accelerated test in predicting the protective effectiveness of waxes. For a limited number of waxes, it was found that a good correlation exists between the results of the two methods, provided that correct temperatures are used. The best correlation was obtained between dumbbell and bent loop specimens exposed outdoors and the accelerated test if the accelerated test was run at 60° and 120° F. The optimum conditions for correlating between the accelerated test and cable exposed outdoors involved carrying out the accelerated test at 60° and 105° or 110° F.
Diffusion in Elastomers
Authors: van Amerongen G. J.
Published: February 2011

In this paper the various aspects of diffusion of matter in rubber are reviewed. Besides diffusion itself, attention has been given to the closely related subjects of solubility in and permeation through rubber of foreign matter. First, a survey is given of the fundamental background, including the most important mathematical equations required for an experimental approach to diffusion, the interpretation of measurements, and the application of available data to specific problems. The subjects discussed include furthermore: self-diffusion; diffusion, solubility, and permeation of gases, organic liquids, water, and solids such as sulfur and other compounding ingredients in and through rubber; temperature dependence of diffusion; effect of modification of the rubber by vulcanization, aging, crystallization, and addition of fillers; various technical problems such as diffusion in composite rubber or in porous rubber and separation by diffusion. It is shown that many facts concerning diffusion in rubber can be satisfactorily explained and even predicted from the molecular properties of rubber and the diffusing substance. Knowledge of diffusion moreover offers an opportunity of gaining an insight into the intermolecular forces of rubber and this may help to understand polymer behavior when other properties are concerned.
Fatigue of Rubber
Authors: Beatty J. R.
Published: February 2011

The long-range elastic properties of rubber suit it ideally to dynamic service applications. Vibration isolation, suspension, and force transmittal are examples of such uses of rubber compounds. Common examples illustrating these uses are isolation devices of all types, e.g., motor mounts, torsion, shear and compression springs, and tires—just to name a few. While fatigue failures may occur under static loads, they are generally accelerated by cyclic stresses. In most applications of rubber, a failure is critical in that the device depends for its functioning on the properties of the rubber and ceases to function when fatigue or other types of failure occur. Examples of fatigue failures are groove cracking in tires, tread and ply separations in tires, failures in torsion springs and motor mounts, etc. This review is concerned with fatigue of rubber under conditions of dynamic stress. Two specific areas are treated, the case where frequency of stressing is low enough and the samples are small enough that heat generation is not an important factor in failure and, to a lesser extent, the case where heat generation due to large samples and high frequency load application builds up temperatures which contribute to failure. Both of these cases of fatigue failure are encountered widely in service. For example, the first is found in vibration isolation devices such as motor mounts, and the latter in the shoulder area of heavy duty tires.
Analytical Method for Measuring SBR Tire Debris in the Environment
Authors: Brachaczek Wanda , Pierson W. R.
Published: February 2011

A procedure has been developed for assaying submilligram amounts of debris from synthetic tire tread rubber in aerosol samples collected from the atmosphere. The procedure involves separation from the bulk of the sample by Soxhlet extraction with orthodichlorobenzene in a stream of oxygen, followed by infrared spectroscopic determination of the rubber hydrocarbon SBR (styrene-butadiene copolymer) in the extract. The procedure was developed to overcome serious difficulties having to do with the small amounts of rubber normally encountered and with losses of SBR during extraction from aerosol samples. These matters are discussed in some detail and some applications of the method are illustrated.
A Dynamic Rubber-Cord Composite Adhesion and Fatigue Test
Authors: Langevin P. P. , Payne R. J. , Shephard C. S.
Published: February 2011

Dynamic adhesion and fatigue tests can be conducted on the Firestone Flexometer, where the hysteresis effect of the rubber compound can be brought to bear on the rubber-cord interface. Only minor modifications of equipment need to be made to run this test under a range of different conditions. Although the test is designed for single-station testing, several samples can be run at once, and test conditions can be adjusted to prevent cycle-life from becoming excessive. Rubber-steel cord composites have been studied under dynamic conditions, and indications are that other cord types and dips can also be evaluated with this method. Thus, the study of adhesion can be approached from a different point of view than that which is provided by current static and dynamic tests.
A New Tester for Dynamic Rubber-to-Metal Adhesion
Authors: Beatty J. R. , Dalglish Edward C.
Published: February 2011

A simple test for dynamic fatigue of a rubber to metal bond has been developed which will evaluate cements with reasonable speed and accuracy. It appears more discerning than static results. This is important since most rubber-metal bonds are used under dynamic service conditions. For example, for two cement systems the static conical pull values were 379 lbs vs 325 lbs while the dynamic fatigue lives were 1.5 × 106 vs 0.27 × 106 cycles, respectively. The values of 379 vs 325 lbs are essentially within experimental error while the dynamic test results leave no question as to which is the superior cement.
Fracture Mechanics of Adhesive Bonds
Authors: Gent A. N.
Published: February 2011

A survey is given of the mechanics of rupture of a simple adhesive joint, comprising two relatively rigid adhering members joined by a layer of a deformable adhesive. Several different modes of failure are treated in terms of a critical energy requirement for growth by unit area of a pre-existing interfacial flaw or debond. They are: (i) Tensile rupture of joints with thick or thin adhesive layers, (ii) Shear rupture, (iii) Separation by stripping apart stiff or flexible adherends, i.e. cleavage. In addition, the stresses set up in joints by shrinkage of the adhesive, for example due to differential thermal contraction, are evaluated. Attention is drawn to probable sites and conditions for failure.
Co-Curing of EPDM and Diene Rubbers by Grafting Accelerators Onto EPDM
Authors: Baranwal K. C. , Son P. N.
Published: February 2011

The object of this work was to find ways to co-cure blends of EPDM and diene rubbers for improved properties. We found that by grafting accelerators onto EPDM we obtain excellent cure compatibility between EPDM and natural rubber. The modified EPDM rubbers were obtained by reacting a benzene solution of EPDM with either 4,4′-dithiobismorpholine or 2-mereaptobenzothiazole (MBT). A method which grafts MBT onto EPDM in the presence of tert-butyl hypochlorite or other halogen donors is more versatile, and can be used for various EPDM rubbers regardless of the nature of the termonomers. We have proposed possible mechanisms by which the modified EPDM rubbers co-cure with natural rubber or other diene rubbers. In these mechanisms we point out the importance of the presence or the in situ formation of reactive sites in modified EPDM rubbers.
Tensile Stress—Strain and Stress Relaxation Behavior of Raw Elastomers Using a High Speed Tester
Authors: Bowerman H. H. , Collins E. A. , Nakajima N.
Published: February 2011

A high-speed, tensile-testing device was used to determine the stress—strain behavior of uncompounded butadiene—acrylonitrile copolymers over a range of temperatures and deformation rates. The strain rates were varied from 267 to 26,700 per cent/sec and the temperature was varied from 25 to 97° C. The high-speed tester was also used for stress—relaxation measurements by applying the strain nearly instantly in conformity with theoretical requirements in order to obtain the short time behavior. The WLF equation was obtained from the stress—relaxation data and then used to reduce the ultimate properties to one temperature over four decades of the strain rates. The ultimate properties could be represented by a failure envelope similar to those obtained for vulcanizates.
Master Curve for Tensile Stress—Strain Behavior of Amorphous Elastomers at Small and Large Deformations
Authors: Nakajima N. , Collins E. A. , Bowerman H. H.
Published: February 2011

A master curve scheme for small and large deformations was developed for tensile stress-strain behavior of butadiene—acrylonitrile uncrosslinked elastomers. Measurements were carried out at strain rates of 267 to 26,700 per cent/sec at temperatures of 25 to 97° C.
Bending Hysteresis Losses in Cord—Rubber Composites
Authors: Skelton John
Published: February 2011

An experimental technique is described which permits the direct measurement of the bending hysteresis loss in cord—rubber composites under carefully controlled conditions of cyclic strain. The equipment can readily detect differences between composites made with different cords. The current version of the equipment is intended only for low-speed cycling, but the extension to high speed capability is contemplated. The robust nature of equipment should make it possible to carry out tests in a wide range of hostile environments.
The Elasticity and Related Properties of Rubbers
Authors: Treloar L. R. G.
Published: February 2011

In Section I the relation of rubbers to other classes of polymers and the molecular basis of rubber elasticity are briefly examined. In Section II the methods used in the quantitative development of the statistical-thermodynamic theory of a molecular network are outlined, and the main conclusions, in the form of stress—strain relations, etc., are presented and compared with experimental data. Section III examines the photoelastic properties of rubbers from both theoretical and experimental standpoints and discusses in detail the evidence derived from photoelastic studies on the statistical segment length in the molecular chain and its relation to intramolecular energy barriers. Section IV is concerned with the thermodynamic analysis of stress—temperature data for rubber and other polymers, with particular reference to the internal energy and entropy changes during extension under constant pressure or constant volume conditions. Methods of deriving these quantities are compared and the results related to the modified molecular network theory due to Flory. Section V deals with the phenomena of swelling in liquids and considers both the effect of swelling on the mechanical properties and the effect of different types of stress or strain on the swelling equilibrium. Sections I–V are concerned mainly with the statistical theory and its applications. The final section examines in considerable detail the formulation of more general theories of large elastic deformations on a purely empirical or phenomenological basis, so as to overcome some of the limitations of the statistical theory. The logical basis of these formulations is presented and the conclusions are discussed in relation to the available experimental evidence. Some common pitfalls to be avoided are emphasized.
Heat Generation and Rubber—Filler Coupling Bonds
Authors: Wagner M. P.
Published: February 2011

It is well known that heat generation is dependent upon the type of polymer, filler, and other components of the compound. In addition, the state of cure has a large effect on heat buildup. With any given vulcanizate system, network constraints can reduce heat generation to a minimum. These network constraints include crosslinks, as well as coupling bonds between filler particles and the polymer chains. Using peroxide crosslinking of natural rubber and organofunctional silanes with a silica filler, network crosslinks, and filler coupling bonds can be independently varied. From equilibrium swelling, it was possible to determine the quantity of each type of constraint. Network crosslinks and coupling bonds respond to equilibrium swelling in approximately the same way, although the peroxide and silane functionality interact chemically to influence the number of each type of constraint. The rate of heat buildup and the maximum temperature generated were obtained from the Goodrich Flexometer (ASTM—D623). Increasing either network bonds or coupling bonds reduced the rate of heat generation and the heat buildup monotonically to a minimum value dependent upon the elastomer system. Both types of network constraint affected these responses about equally. Comparison of silica and carbon black fillers in SBR demonstrated that the insertion of coupling bonds was an efficient method of reducing heat buildup. Other rubber properties (particularly modulus and abrasion resistance) optimized more readily since their response to the coupling bonds and network crosslinks were quite different.
The Effects of Carbon Black on Rubber Hysteresis
Authors: Ulmer J. D. , Hess W. M. , Chirico V. E.
Published: February 2011

The viscous modulus of oil-extended SBR loaded with carbon black relative to the gum stock increases with volume fraction of carbon black. This increase is much larger than predicted by the Guth-Gold equation and also greater than the increase in the elastic modulus. This behavior reflects the sum of at least three effects: geometrical (strain amplification), changes in the viscoelastic properties of the rubber, and formation of a three-dimensional network of carbon black and rubber. The geometrical effect increases with volume fraction of carbon black. Its per cent contribution to the viscous modulus decreases as the carbon black loading increases because of increased contribution of the viscoelastic effect at low loadings and of the network effect at high loading. The geometrical effect can be described reasonably well by the Guth equation with a shape factor and with the volume fraction increased by the additional immobilized rubber (bonded elastomer). The viscoelastic effect due to 60 phr black contributes at least 20 per cent to the viscous modulus and is related to structure, surface area, and volume fraction of the carbon black. It can be at least partially accounted for by rubber breakdown during mixing. At high volume fractions of carbon black (60 phr), network formation contributes about 25 to 45 per cent to the viscous modulus. It increases with decreasing interunit spacing which depends on the average volume of the carbon-black units and the amount of bonded elastomer. For a thermal black, N—990, the interpretation of the results is complicated by the distinct possibility that slippage contributes to hysteresis. We conclude, however, that at low loadings the increase of the viscous modulus is much greater than that of the elastic modulus and that network effects contribute to the viscous modulus at high loadings.
Dynamic Viscoelastic Properties of Raw Butadiene—Acrylonitrile Elastomers
Authors: Nakajima N. , Collins E. A. , Kumler P. R.
Published: February 2011

The dynamic viscoelastic properties of four samples of butadiene—acrylonitrile raw elastomers, were obtained with a Rheovibron at 110 Hz and temperature range of −80 to 160°C. The complex properties were in agreement with the master curves obtained previously from stress-strain measurements. A master curve encompassing 13 decades of time was constructed using data from Mooney rheometer shear stress-strain, MTS high speed tensile stress-strain, and the Rheovibron. The master curve represents the rubbery region of viscoelastic behavior in terms of time, temperature, and the magnitude of deformation up to the breaking point. This study demonstrates that corresponding states can be found between small (ca. 1 per cent) and large deformation up to break (e.g., 1400 per cent).
Effects of Compounding on Dynamic Mechanical Properties of Rubber
Authors: Studebaker M. L. , Beatty J. R.
Published: February 2011

Stiffness—hysteresis charts show differences in dynamic mechanical properties resulting from compounding changes, such as elastomer, crosslink density (and, under certain test conditions, crosslink type), filler type(s) and loading (s), and softeners and their level. Processing, including vulcanization, aging, and any network changes during testing or service can be depicted by these charts.
Petroleum Pitch as a Plasticizer for SBR and SBR Blends
Authors: Deviney M. L. , Weaver E. J. , Wade W. H. , Gardner J. E.
Published: February 2011

Two petroleum pitch products have been shown to impart greater stiffness and hardness, and lower rebound properties to SBR and SBR/BR vulcanizate systems, through unusual molecular interaction effects. These solid pitch materials can be used alone as plasticizers or in combination with conventional aromatic extender oils. Vulcanizates containing these materials at 10–25 per cent concentrations maintain enhanced stiffness and hardness at temperatures to 150° C. Plasticizer evaporative loss and migration from higher to lower concentration areas is much less in pitch-containing vulcanizates than in stocks containing usual aromatic extender oils. Vulcanizate physical properties are presented. An immersional microcalorimetry study was conducted to investigate the energetics of interaction of carbon black with pitch in comparison with other major components of the elastomeric matrix. The thermodynamic measurements, which indicate specific pitch—carbon black interactions, provide much insight into the mechanisms responsible for the unusual properties which pitch imparts to rubber systems.
Thermal Diffusivity Measurements on Elastomers
Authors: Frensdorff H. K.
Published: February 2011

Thermal diffusivity, rather than thermal conductivity, is the property which governs rates of heating up and cooling down of a rubber article in the mold. It is preferable to measure it directly, rather than to derive it from separate measurements of thermal conductivity and volumetric heat capacity. A straightforward measurement method is described together with procedures for deriving the required results from the raw data. The sources of error are discussed, and ways for minimizing them are suggested. Thermal diffusivities for gum and black EPDM and fluoroelastomer are reported for temperatures from 0° to 100° C.
New Studies of Carbon—Rubber Gel
Authors: Ban L. L. , Hess W. M. , Papazian L. A.
Published: February 2011

High resolution electron micrographs of undistorted carbon—rubber gel were obtained by ultramicrotomy of frozen unvulcanized SBR compounds which were subsequently extracted with benzene to remove any soluble rubber. The remaining black and rubber form a 3-dimensional, meshlike network which is larger than the size of primary units of the black itself. The networks for different blacks indicate considerable compaction which increases in the direction of lower structure and surface activity (e.g., normal vs. graphitized carbon black). Removal of the soluble rubber from the carbon—rubber gel network produces visible gaps between the black units which diminish in size as the black loading increases. Soluble rubber is also removed from many regions of the black surface indicating that there is no uniform layer of surface-bonded rubber. The swollen carbon—rubber gel networks are readily dispersible in good solvents using ultrasonic energy. In the process, a high percentage of the rubber is solubilized and removed from the black surface. GPC analyses of this soluble rubber from the gel indicate higher molecular weight in comparison to the soluble portion removed by benzene extraction.
A Quantitative Test for Ozone Resistance of Rubber Vulcanizates
Authors: Wilchinsky Z. W. , Kresge E. N.
Published: February 2011

A simplified procedure was developed for evaluating ozone resistance of rubber vulcanizates in terms of critical stress—strain and stored energy density parameters. A selected tensile force of appropriate magnitude is applied to a tapered specimen to produce a continuous range of stress. While thus stretched, the specimen is conditioned for 16 h, then exposed to ozone for 24 h. In the portion of the specimen where the stress is greater than a critical value σc, ozone cracking occurs, whereas in the portion of the specimen where the stress is less than σc there are no cracks. Values of σc the critical strain εc, the critical elastic stored energy Wc, and the elastic modulus E are determined from the position of the boundary between the cracked and uncracked zones, the average elongation of the stressed specimen, and the specimen geometry. The quantity Wc was found suitable for quantitatively characterizing ozone resistance by a single parameter.
Effect of Alkyl Group Structure on Cure Characteristics of N,N-Dialkylthio-Carbamyl-N′,N′-Dialkylsulfenamide Vulcanization Accelerators
Authors: Taylor R. D.
Published: February 2011

Wide variations in scorch times and cure rates can be attained with tetraalkylthiocabamylsulfenamides through variation in alkyl groups. Substituent effects are substantial on either the carbamate nitrogen or on the sulfenamide nitrogen. Both inductive effects and steric effects influence the scorch times and cure rates. Positive inductive effects shorten scorch times and increase cure rates. Steric hindrance at the sulfenamide nitrogen increases the scorch time. Branching at the carbon atom beta to the nitrogen has a larger effect on scorch time than branching at the alpha carbon. Thiocarbamylsulfenamides can give appreciably higher cure rates and cure efficiencies than their benzothiazole sulfenamide analogs.
Review of Unsolved Problems in the Protection of Rubber against Oxidative Degradation
Authors: Dunn J. R.
Published: February 2011

This review has outlined some of the problems involved in the protection of rubber against oxidative degradation. There are others which are related to health, such as the choice of additives which are safe in contact with foodstuffs and approved by FDA or equivalent bodies in other countries. The matter of toxicity of antioxidants has been reviewed by McCormick and by Leyland. With so many problems it is easy to understand why the literature and patent files on antioxidants continue to grow and why it is unlikely that a single ideal material will ever be developed to protect rubber against oxidative degradation.
Autoxidation and Antioxidants. Basic Principles and New Developments
Authors: Howard J. A.
Published: February 2011

There is no doubt that liquid-phase hydrocarbon autoxidation is one of the most thoroughly understood reactions in organic chemistry. Our knowledge of the elementary reactions involved in this process is so complete that it should be possible to calculate, with a reasonable degree of precision, the overall rate of autoxidation of a hydrocarbon or mixture of hydrocarbons, provided, of course, that the rate of chain initiation can be estimated. It should also be possible to make a reasonable intelligent guess at the stability of a solid system, with the reservations appropriate to the change of phase. With regard to inhibition, there is probably not a great deal of room for further improvement in the inherent efficiency of H-atom donating antioxidants. This is because a decrease in the strength of the X—H bond makes the hydrogen more susceptible to abstraction by molecular oxygen. Radical scavenging transition metal complexes also suffer from the limitation that the more reactive the complex is to ROO the more reactive it will be to O2. There may, of course, be further improvements in the efficiency of preventative antioxidants, particularly multi-functional antioxidants with the ability to decompose hydroperoxides and peroxides by several non-radical mechanisms and also scavenge free-radicals.
Elastomeric Springs for Seismic Shock Isolation
Authors: Vickers R. A.
Published: February 2011

We have described the development of seismic isolators to meet a specific requirement. The use of ventilated blocks serves to aid in obtaining a thorough cure, and the configuration and direction of the holes control the shape of the force—deflection curves. Figure 21 shows a completed spring installed on a Minuteman support structure.
A Technique for Evaluating the Hysteresis Properties of Tire Cords
Authors: Powers E. J.
Published: February 2011

A slow speed cyclic test has been developed to evaluate tire cord hysteresis properties. Programmed stress variations on an Instron were used to simulate the magnitude and sequence of cord stresses in a running step-loaded tire and relationships were formulated to approximate the dependence of cord heat generation on tire loads, air pressures, and temperatures. The test assumes that tire air pressure imposes a peak stress on cords and that increasing loads on a running tire cause increasing intermittent cord stress relief. Nearly linear relationships result between the log of work loss and the extent of stress relief, which affords a means of comparing cord hysteresis properties over a range of simulated tire loads. The validity of the slow speed results was verified at laboratory test speeds comparable to those encountered in normal tire use. Results generally agreed with long standing qualitative observations of tire cord performance. Commercial PET and nylon greige cords were used for test development and other cord materials, both greige and dipped, have been evaluated. A range of hysteresis properties was obtained on variations in polyester cords.
Environmental Effects on RFL Adhesion
Authors: Wenghoefer H. M.
Published: February 2011

Adhesion deterioration of RFL-dipped tire cord resulting from environmental factors such as ozone, nitrogen dioxide, humidity, ultraviolet light, and heat was investigated to quantify the amount of adhesion loss and to establish the mode of adhesion failure. It was found that ozone, humidity, and ultraviolet light cause substantial adhesion deterioration, especially during the initial hours of exposure. Synergistic effects of ozone/humidity were noted. Less pronounced was the detrimental effect of heat. Adhesion loss because of nitrogen dioxide or synergistic effects of nitrogen dioxide/humidity was not seen. Adhesion loss occurred most rapidly during the first six hours of ozone/humidity exposure, regardless of fiber or adhesive system used. Adhesive treated cords of nylon, polyester, and “Kevlar” aramid showed loss in adhesion; however, no correlation between type of fiber and extent of adhesion deterioration was found. The extent of adhesion deterioration was primarily dependent upon the specific adhesive dip used. Sensitivity of the RFL adhesives to ozone/humidity varied with one- and two-step adhesive systems; with polyester, one-step adhesive systems tested were generally less sensitive to environmental conditions than two-step adhesive systems. The latter, however, had better initial adhesion. Adhesion loss because of ultraviolet light exposure was severe for all RFL adhesives, regardless of fiber. Emission of ultraviolet light from fluorescent lighting was shown to be sufficiently intense to affect adhesion. The physical properties of RFL-dip films were unaffected by ozone or ultraviolet exposure, ruling out cohesive failure of the RFL adhesive as a cause of adhesion breakdown. Adhesion failure for samples tested after environmental exposure occurred at the RFL adhesive-rubber stock interface, indicating the adhesion deterioration to be a RFL surface phenomenon.
Short Fiber Reinforcement of Elastomers
Authors: Moghe S. R.
Published: February 2011

Based upon a simple mathematical model, the directional properties of elastomers mixed with uniaxially oriented short fibers are predicted. The model takes into account a probability distribution function for a number of fibers in any direction during fiber orientation. Theory is compared with experimental data on tensile modulus for a number of rubber compounds and fibers with good success. A possibility of characterizing calendering and extrusion processes in view of orientation and mechanical properties is discussed.
Elastically Ineffective Crosslinks in Rubbers
Authors: Tonelli A. E. , Helfand E.
Published: February 2011

A significant fraction of the crosslinks formed in the process of producing a rubbery network are elastically ineffective. The reason is that they close intramolecular loops which are not otherwise attached to the rest of the network. Calculations of this fraction are performed for cis-1,4-poly(isoprene) (natural rubber) as a function of the degree of crosslinking, the length of the chemical bridge which forms the crosslink, the initial molecular weight, and the degree of dilution when crosslinking in solution. For typical rubber networks, crosslinked in the dry state with from 0 to 2 per cent of the monomer units involved in crosslinks, the fraction of crosslinks wasted in the formation of elastically ineffective intramolecular loops is ca. 0.1–0.2. This fraction is approximately doubled and quadrupled for networks formed in solution with volume fractions of rubber equal to 0.5 and 0.1, respectively. Since a sizeable percentage of the intramolecular loops formed consist of a small number of polymer units, it is believed that entanglement between the loops and other chains of the active network does not serve to reduce greatly the fraction of elastically ineffective crosslinks.
Specific Solvent Effects in Swollen Polymer Networks
Authors: Yu C. U. , Mark J. E.
Published: February 2011

Stress—strain isotherms at 25° have been determined for uniaxially elongated poly(dimethylsiloxane) networks in the unswollen state and swollen consecutively with each of the following very dissimilar diluents : low molecular weight dimethylsiloxane fluid, n-hexadecane, 2,4-dichlorotoluene, and n-octyl acetate Five constant composition experiments were carried out, at values of the volume fraction ν2 of polymer of 1.00, 0.80, 0.60, 0.50, and 0.35. At ν2=0.80, the stress—strain isotherms were found to be independent of the nature of the diluent; at lower values of ν2, however, these isotherms were significantly different, thus demonstrating the existence of a “specific solvent effect” in swollen polymer networks. Interpretation of these data in terms of the statistical theory of rubberlike elasticity gave results in good agreement with previously reported specific solvent effects on the unperturbed dimensions of uncrosslinked poly (dimethylsiloxane) chains in solution. In neither case, however, do these effects correlate well with the cohesive energy density or dielectric of the diluent or solvent medium.
Applications of Integral and Derivative Thermogravimetry to the Analysis of Rubber Formulations
Authors: Swarin S. J. , Wims A. M.
Published: February 2011

Thermogravimetry, in the integral and derivative modes, can be used to determine the percentage composition of oil-extended EPDM and plasticized NBR formulations, even when the weight loss steps due to the various components overlap slightly. The percentages of extender oil or plasticizer, rubber, carbon black, graphite, and mineral filler can be determined in 2 hours or less from a single experiment. Derivative thermogravimetry also provides information on the volatility and identity of the extender oil in EPDM formulations, as well as the volatility and identity of the monomeric plasticizers in NBR formulations. Information about the type of carbon black in a formulation can also be obtained. Thermogravimetry appears to be an excellent method for the quality control and receiving inspection of EPDM and NBR formulations.
The Analysis of Rubber Vulcanizates—Identification of Amine Residues from Sulfenamide Accelerators by Thin Layer Chromatography
Authors: Higgins G. M. C. , McSweeney G. P.
Published: February 2011

The amine residues from sulfenamide accelerators can be identified in rubber vulcanizates by treatment of the latter with 4-chloro-7-nitrobenzo-2,1,3-oxadiazole (NBD-Cl) and examination of the products by thin-layer chromatography.
Chemical Stress-Relaxation and Other Studies on Styrene-Butadiene Rubber
Authors: Kalfayan S. H. , Rakutis R. , Silver R. H.
Published: February 2011

The aging of styrene—butadiene rubber (SBR) was studied by three methods: stress relaxation, infrared spectroscopy, and swelling measurements, with the purpose of supplying information pertinent to understanding the basic mechanism of its aging. Stress-relaxation measurements in air and nitrogen at elevated temperatures indicated that atmospheric oxygen is the principal cause of chemical stress relaxation of SBR, rather than heat. Intermittent stress-relaxation measurements showed scission and crosslinking occurring simultaneously during network breakdown, and it was concluded that random scission in the backbone is indicated to take place in preference to scission in the crosslinks. Activation energies obtained from relaxation rates at several temperatures was 28 ± 0.5 kcal, comparable to literature values of 30 ± 2 kcals. The rates of carbonyl and hydroxyl group formation in SBR in air at various temperatures were determined by ir spectroscopy, both induction and maximum rates, νm, being measured. Activation energies calculated from these rates showed lower values compared to those obtained from stress-relaxation measurements. This may be due to the possibility that the processes being measured are not the same in each case. The three peaks appearing in the carbonyl region were ascribed to carboxyl, ketone, or aldehyde, and perester. The presence of these groups was confirmed by microanalytical methods. The absorption centered at 3450 cm−1 was attributed to hydrogen-bonded OH groups, i.e., alcohols and hydroperoxides. Positive chemical tests were obtained for hydroperoxide. The number of new network chains formed, νe, obtained from swelling measurements agreed well with those obtained from stress-relaxation measurements. It was found that the rate of the number of new network chains formed increased rapidly during the latter states of oxidation.
The Chemistry of Vulcanization. VI. Action of the Zinc Salt of 2-Mercaptobenzothiazole on the Reaction of Diphenylmethane with Sulfur
Authors: Tsurugi Jitsuo , Fukuda Haruko
Published: February 2011

Literature on rubber vulcanization with thiazole type accelerators in the presence of zinc oxide indicates that the zinc salt of 2-mercaptobenzothiazole (ZMBT) is a transformation product of the benzothiazole accelerators. Therefore, it is important to investigate the behavior of this salt in the reacting mixture of sulfur and diphenylmethane (DPM), the latter having been utilized as a molecular model of rubber hydrocarbon in previous parts of this series. The reaction of DPM, sulfur and ZMBT in the absence of zinc oxide or zinc soap will now be reported. This is preliminary to the study of the mechanism of thiazole type accelerator action in the presence of zinc soap.
Electrical and Diffusion Processes in the Adhesion of Two Polymers
Authors: Morozova L. P. , Krotova B. A.
Published: February 2011

In previous publications one of us developed the concept of the electrical theory of adhesion. On the other hand, many authors have repeatedly expressed opinions concerning the role of diffusion processes during the formation of adhesive and auto-adhesive bonds. Owing to the discussion of this problem an experimental investigation of the formation of adhesive bonds acquired special significance, in particular during the addition of two high molecular materials for the purpose of clarifying the correlation of electrical and diffusion processes in the phenomena of adhesion. The shape of the adhesiogram is very significant in solving the question of the type of adhesive bond. The effect of the velocity of rupture is comparatively small if the adhesive bond depended on the phenomenon of diffusion. If the adhesive bond is of electrical nature the adhesiogram has generally three clearly expressed sections. With the aid of a roller adhesiometer we have taken the adhesiograms of a series of polymers (gum type BF, polyurethans, polyamides, a series of vinyl polymers, rubbers, guttapercha, cellulose esters, and on.). The adhesiograms of different combinations of these polymers with glass, metal and with rubbers of a Na butadiene and acrylo nitrile rubber base usually gave three clearly expressed regions. However, in some cases there were only two sections and the third was absent. Three probably exist in all but some may be located in an area of significant velocity and experimental determination becomes difficult. Under our experimental conditions of a time interval <0.01 sec some could not be measured.