bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Temperature on the Stress-Strain Isotherms of Polyisobutylene Networks at High Elongation
Authors: Kato M. , Mark J. E.
Published: February 2011

Three chemically cured, unfilled polyisobutylene networks were studied in elongation to their rupture points at several temperatures in the range 15–80°C. At the lower temperatures, the stress-strain isotherms obtained were similar to those reported for unfilled networks of natural rubber and several other polymers in that they showed an anomalous, marked increase in the modulus or reduced force at high elongations. At intermediate temperatures, this upturn in the force is significantly diminished, however, and the networks rupture at lower elongations. At the higher temperatures, there is no evidence whatever for an upturn in the force, and the elongation at rupture is further reduced. These results on polyisobutylene networks implicate strain-induced crystallization rather than limited chain extensibility as the origin of the pronounced increase in the force at high elongations. The reinforcement provided by the crystallites formed in this manner would account for the increased extensibility of the networks at the lower temperatures. Since natural rubber is very similar to polyisobutylene in its crystallizability, the anomalous stress-strain isotherms widely reported for networks of this polymer are thus probably also due largely, if not entirely, to network crystallization.
Changes of State in Polymeric Networks during Orientation. II. Analysis of Elongation-Induced Crystallization by Calorimetry
Authors: Göritz D. , Müller F. H.
Published: February 2011

Studies of the elongation-induced crystallization have shown that crystallization during stretching follows a different mechanism than that in the extended state. The final degree of crystallization is found to be dependent on temperature and elongation. The dependence on elongation does not follow Flory's theory of crystallization induced by stretching polymeric networks. However, separating the crystallization into one process developing during stretching and another in the extended state shows that this theory applies to the latter one. Time analysis of the oriented crystallization on axial stress yields similar results. This crystallization cannot be described as a single uniform process by the theory of Avrami. However, by considering two separate processes, each can be described quantitatively with sufficient accuracy. The stress-induced crystallization is controlled by homogeneous formation of nuclei which grow three-dimensionally. After termination of stretching no further nuclei are formed. Further crystallization is restricted to one-dimensional growth of existing crystallites in the direction of stress. Both mechanisms of crystallization are independent of temperature, elongation, and degree of crosslinking.
Block Copolymers, Polymer-Polymer Interfaces, and the Theory of Inhomogeneous Polymers
Authors: Helfand E.
Published: February 2011

Most of the polymeric materials one encounters so widely are heterogeneous. For instance, commercial plastics may be blends of immiscible polymers; they may contain antioxidants or other modifiers which are not totally soluble; andfrequently they have added inorganic fillers. Other examples of inhomogeneity in polymer systems are composites, partially crystalline materials, surface layers, ionomers, and block and graft copolymers. In some cases the heterogeneity is the essence of the material's virtue (e.g., its mechanical properties). In other cases heterogeneity is an affliction. But, whether one's goal is to maximize or minimize the effect of nonuniformity, it is well to understand the factors which determine the features of inhomogeneous polymers. This we will attempt to do in a qualitative way by describing, from a simple molecular point of view, the entropy and energy terms which control the systems' physical features. Rather than dealing in generalities, however, let us focus on two particular cases : interfaces between immiscible polymers, and block copolymers. This should provide the reader with some insight into the myriad of recent developments in the field of polymer blends, composites, and microheterogeneities.
Coordination Complexes of 4,4′-Diaminodiphenylmethane—Chemistry and Applications
Authors: van Gulick N. M. , Verbanc J. J. , Caruso P. P. , Athey R. J.
Published: February 2011

Coordination complexes of 4,4′-diaminodiphenylmethane and alkali metal salts are effective delayed-action curatives for amine-curable polymers. In polyurethanes, particle size of the complex, the polarity of the reaction medium, and the isocyanate concentration of the polymer determine processing safety, curing temperature, and curing rate. Vulcanizate properties observed with polyether- and polyester-based cast urethane systems parallel those obtained with MOCA. Exceptions include the influence of residual salt, which increases water swell, and the presence of plasticizer, incorporated with predispersions, which lowers modulus and hardness slightly and influences solvent swell due to plasticizer extraction. The salt is bound in the vulcanizate and cannot be removed by simple water immersion. Alkali metal salt is liberated by hydrolytic destruction of the vulcanizate. Preliminary evidence suggests no increase either in corrosion of steel inserts embedded in urethane parts or in property loss during aging despite the presence of ∼1% residual salt.
The Effect of Reusing Ground Flash and Scrap Rubber in Parent Compound
Authors: Burgoyne M. D. , Leaker G. R. , Krekic Z.
Published: February 2011

We have described a method of grinding flash and scrap product to such a particle size that it may be added back into parent compound with minimal reduction in properties. At the same time, this method affords valuable cost savings.
Rheo-Optical Studies of Rubbers
Authors: Stein R. S.
Published: February 2011

It is evident that optical techniques can provide much information about the morphology, orientation, and phase transformations of homogeneous rubbers, rubber blends, copolymers, and composites. While no one method offers complete characterization, it is believed that the combination of these techniques can be of great value in the elucidation of these useful materials.
Reinforcing Silicas and Silicates
Authors: Wagner M. P.
Published: February 2011

Since the first intensive literature review on silicas and silicates was published, significant new technology for their use in rubber has developed. Usage in the rubber industry has broadened considerably, and increases in their consumption have occurred during the ensuing fifteen years. From the “soles and heels” fillers of the 1950's, the usage of precipitated silicas and silicates since has gained significantly in quality components of tires and mechanical goods. Potential applications in the immediate future are no longer limited by the “good, but second to carbon black” performance that has prevailed for the past twenty-five years. Besides the traditional unique properties of tear resistance, hardness, stiffness, flex resistance, heat resistance, low modulus, and neutral color imparted to rubber by silicas and silicates, it is now possible to add adhesion, low heat buildup, high resilience, high modulus, and high abrasion resistance. This is part of the new technology which has developed that provides an alternative type of filler to meet the demanding needs of tire components, conveyor belts, automotive mounts, gaskets and seals, and other quality rubber compounds previously inaccessible to silicas. The present review covers the period 1960–1975. Because of the volume of available literature, it became necessary to be quite selective, in a way perhaps that may seem arbitrary. Nevertheless, coverage will be confined largely to that relevant to more general rubber uses. Silicone rubber technology was not covered because of its highly specialized and generally proprietary nature. The definitions used in the previous review were expanded somewhat. Silicas and silicates (henceforth, “silicas”) germane to this review were generally restricted to those which are synthetic and amorphous. However, the size limitations were relaxed somewhat to include those having a specific surface area greater than 25 m2/g or an average particle diameter less than 100 nm. Natural products (e.g., clays, diatomaceous earth, sand, etc.), as well as their modified forms, were excluded.
Accelerated Heat-Aging Studies on Fluororubber in Various Media
Authors: Kalfayan S. H. , Silver R. H. , Liu S. S.
Published: February 2011

The nature, extent and, rate of chemical changes that take place in certain elastomers at long times is being studied. The chemical degradation of styrene-butadiene rubber (SBR) and fluorosilicone rubber (FVMQ) were reported previously. Investigations carried out with fluororubber (FKM) are discussed in this paper. Like fluorosilicone, this fluorocarbon elastomer is regarded as a high-temperature- and hydrocarbon-fuel-resistant rubber. The designation FKM is given to the copolymers of vinylidene fluoride (VF) and perfluoropropylene (PFP). The one discussed here is reported to contain also small quantities of a third component, tetrafluoroethylene. The detailed structure, assigned to the FKM polymer as a result of nuclear magnetic resonance studies, shows that it consists of blocks of VF homopolymer, 95% of which is head-to-tail, and blocks of VF-PFP copolymer, 93% of which is head-to-tail. The ratio of the copolymer to the VF homopolymer is dependent on the mole fraction of VF used. Vulcanization of FKM with derivatives of diamines is the commercially preferred method, although peroxides and high-energy radiation can be used for the same purpose. In the present study, N, N-dicinnamylidene-1,6-hexanediamine a Schiff 's base of 1,6-hexanediamine, was used with magnesium oxide as the acid acceptor. Chemical stress relaxation was the method most extensively used to determine the network changes taking place in the heat-aged fluororubber. Swelling, gel permeation chromatography (gpc), and infrared (ir) spectroscopy were also used to obtain additional information.
Effect of Carbon Black on Hysteresis of Rubber Vulcanizates: Equivalence of Surface Area and Loading
Authors: Caruthers J. M. , Cohen R. E. , Medalia A. I.
Published: February 2011

We have developed an empirical correlation between the loss tangent (tan δ) and the product of the volume fraction (ϕ) of carbon black in the composite and the total filler-polymer interfacial area per unit volume of composite (ψ). This correlation was applied to vulcanizates based on SBR-1500, SBR-1712, and NR with various compounding procedures and under different deformation conditions, including forced vibration nonresonant dynamic test machines, and the Goodyear-Healey pendulum rebound. The functional form of the correlation was qualitatively similar in all instances ; however, quantitative aspects of the correlation are dependent upon the particular experimental conditions. Tan δ is a weak function of the deformation amplitude over the region of practical interest. This is in contrast to hysteretic energy loss, which is proportional to the square of the amplitude. The validity of the correlation over wide ranges of amplitude, temperature, and frequency indicates that the viscoelastic relaxation or loss processes are similar over the range of conditions studied. Since the combined parameter, ϕψ, is proportional to ϕ2 multiplied by the specific surface area of the carbon black, this relation implies an equivalence between surface area and loading, with regard to tan 5. It has previously been shown that the elastic modulus depends on structure and loading. Thus, the dynamic properties, including hysteresis under various conditions, can be predicted from the carbon black properties, and compounds can be designed for desired dynamic properties by independent adjustment of loading, structure and surface area.
Conversion of Scrap Tires by Pyrolysis in Molten Salts
Authors: Larsen J. W. , Chang B.
Published: February 2011

Thermal decomposition in molten salts shows some promise as a method for recovering useful materials from scrap tires. Obviously, much technical development and engineering work needs to be done to evaluate that process. Applications of these techniques to other polymers is possible and is under study.
Silicone Rubber—A Perspective
Authors: Warrick E. L.
Published: February 2011

Silicone rubber began as a polydimethylsiloxane elastomer vulcanized by benzoyl peroxide. Today, 33 years after its discovery, silicone rubber is a line of products of widely different compositions and vulcanized by many different systems. Our knowledge of the rubber is far better than it was but it is by no means complete. Applications are many, but in general, they are in vital areas where extreme environmental conditions will not permit the use of any other material. Service life cost is usually lower than for other rubbers, despite higher initial cost. Uses in surgery fulfill a unique role in saving lives or improving the quality of life for many. Dr. R. R. McGregor said of the field of silicones, in general, “What had been started as a search for further knowledge proved to be the groundwork for technological advances that have proved helpful to industry, and in so doing, have contributed to improving our standard of living”. What he said of silicones as a whole, certainly applies to silicone rubber, and I have been happy to have contributed to the knowledge of silicone rubber and to have been a part of these advances which, in addition, contribute to our physical wellbeing by their use in the human body. These remarks are not in any way an epitaph for silicone rubber, but rather, they are the opening words in a book of growing usefulness for silicone rubber for us all. The adventure has just begun.
Copolymerization of Isobutene and Isoprene at “High” Temperature with Syncatalyst Systems Based on Aluminum Organic Compounds
Authors: Cesca S. , Bruzzone M. , Priola A. , Ferraris G. , Giusti P.
Published: February 2011

New catalyst systems based on alkylaluminum derivatives and halogen or interhalogen compounds were found highly efficient in the synthesis of high-molecular-weight IIR at temperatures above − 50°C. The reaction mechanism was studied in detail for the system Et2AlCl + Cl2. The reactions occurring between chlorine, isobutene, Et2AlCl, and the solvent (CH3Cl) were elucidated and studied under various experimental conditions (e.g. presence or absence of light, simultaneous presence of the copolymerization system components, temperature, type of halogen, use of model compound of isobutene). It was concluded that halogenium ions, i.e. Cl+, Br+, or I+, are the initiating species. Kinetic and conductometric investigations showed that scarcely dissociated ion pairs, e.g. Cl+[Et2AlCl2]−, were formed in the absence of monomer; but in the presence of isobutene, a noticeable increase of the electrical conductivity and rapid polymerization occurred. The maximum polymerization rate was first order with respect to the concentrations of monomer, Cl2, and Et2AlCl. In the homopolymerization of isobutene, transfer to monomer and termination reactions were negligible. The MW of IIR was found to be mainly dependent on the concentrations of the catalyst components, on isoprene concentration, and on temperature. The reactivity ratio of isobutene with isoprene was found to be r1=2.5±0.5 at −35°C, while the activation energies relative to MW were −5.8 ± 0.4, kcal/mol for polyisobutene, and −5.7 ± 0.7 and − 4.3 ± 0.5 kcal/mol for IIR containing, respectively, 1.3 and 1.9 mol% of isoprene. The evaluation of some physicochemical and technological properties of typical IIR produced with the system Et2AlCl + Cl2, indicated that isoprene is randomly distributed along the chains and that the MWD is monomodal, while the glass transition temperature, tensile properties, mechanical-dynamic spectra, and kinetics of vulcanization are very similar to those of commercial IIR. Very preliminary data, referring to several classes of new catalyst systems yielding IIR having good properties, were also obtained. The syncatalyst systems here described can work in a homogeneous phase consisting of an aliphatic hydrocarbon besides methyl chloride, still giving IIR with high MW. Therefore, a completely homogeneous process can be envisioned for the synthesis of IIR at −50°C thus avoiding a great part of the fouling problems of the slurry process. The economic advantage of using “high” temperatures of polymerization is briefly discussed in terms of energy savings.
High-Molecular-Weight, High-Unsaturation Copolymers of Isobutylene and Conjugated Dienes. II. Properties and Performance
Authors: Cohen H. , Rae J. A. , Buckley D. J.
Published: February 2011

Recent advances in cationic polymerization have resulted in the experimental production of a new class of isobutylene elastomers. These elastomers are copolymers of isobutylene with isoprene, piperylene, or cyclopentadiene with unsaturation levels up to about 40 mol%. Terpolymers can be made at similar unsaturation levels. Selected examples of these materials have been used to describe the general properties and also to investigate applications. The new compositions and structures exhibit a wide range of properties not attainable to date in isobutylene type elastomers. The new properties, in a number of instances, indicate that these elastomers are useful for certain tire applications. The tire performance studies included adhesion, ozone and fatigue cracking, skid resistance, and resistance of barriers to stain migration.
Blends of Elastomers and Thermoplastics—A Review
Authors: Dunn J. R.
Published: February 2011

In blends of elastomers and thermoplastics one component may be regarded as reinforcing the other. Examples are enhancement of tensile strength, tear strength, abrasion resistance, and modulus of elastomers by thermoplastics and improvement of impact resistance and environmental stress-cracking resistance of thermoplastics by elastomers. Certain elastomer-thermoplastic blends are rapidly growing in importance as thermoplastic rubbers because they combine the processing characteristics of plastics with physical properties similar to those of vulcanized elastomers.
In-Place Cleaning of Rubber Curing Molds
Authors: Sommer J. G. , Grover H. N. , Suman P. T.
Published: February 2011

Causes of mold fouling and conventional methods for cleaning fouled curing molds are reviewed. These methods generally require removal of the mold from the press for cleaning, and can abrade the mold surface. This paper describes the nature of some of the deposits that build up in the mold, and a new technique for cleaning in the curing press. Undesirable deposits are removed by vulcanizing a mold cleaning compound in the dirty mold. The aminohydroxy additive in the compound releases the deposit, which is then removed with the vulcanizate. Infrared analysis established both the presence of deposits on a metal surface by several different rubber compounds and their removal after treatment with the mold cleaning compound. In-place cleaning of rubber curing molds offers distinct advantages over conventional cleaning methods.
Reactions in Crosslinked Polymers. 3. A Metal Mold for Collecting Volatile Products during the Crosslinking Reactions
Authors: Wewerka D. , Hummel K. , Inselsbacher W.
Published: February 2011

Most methods of chemical and physicochemical analysis require the materials to be in homogeneous solution. The examination of crosslinking reactions, therefore, is subject to experimental difficulties since covalently crosslinked products are necessarily insoluble, and at best, swellable. Frequently it is simpler to analyze the low-molecular-weight byproducts of the crosslinking reactions and, in this way, to obtain information about their course. The separation of low-MW products by extraction has been valuable in investigations of reaction kinetics. Volatile compounds can also be collected by evaporation. We have previously described apparatus for investigating polymer reactions in solvents (e.g. bromobenzene) from which the volatile products can be distilled off. The present paper shows how the byproducts of crosslinking that are volatile at practical vulcanization temperatures (100–200°C) can be isolated. Several possibilities can be considered: The reaction mixture in powder form might be reacted in a glass vessel, or the mixture in film form might be reacted in an appropriate apparatus (e.g. that described by Voigt and Krüger for oxidative degradation). Both of these methods fail to give test specimens suitable for the customary crosslink measurement methods (e.g. equilibrium swelling). Hence we choose to conduct the reaction in a specially designed metal mold.
The Mechanical Behavior of Short-Fiber-Elastomer Composites
Authors: Coran A. Y. , Hamed P. , Goettler L. A.
Published: February 2011

The measured elastic and strength properties of angle-ply composites of short fibers and rubber depend on test-piece geometry. In general, higher tensile moduli and strengths are obtained when plies are both thin and wide. Once the effects of test-piece geometry are taken into account, elastic properties can be calculated as functions of the properties of a single ply. Classical compliance transformation equations can be used. However, because of the invariance of shear modulus in aligned composites, the tensor transformation equations are somewhat simplified. Tensile strengths of off-axis unidirectional composite plates and balanced-angle plies can be fitted by Hill's criterion. Unidirectional composites tend to fail in the weakest mode, depending on the angle of stress, but laminating causes all principal stresses in a ply to be near their ultimate limit at the time of failure.
Effect of Temperature on the Course of Thiuram-Accelerated Sulfur Vulcanization
Authors: Ducháček V.
Published: February 2011

These results confirm the validity of our theory of thiuram-accelerated sulfur vulcanization supposing that ZnDMDC arising from TMTD and zinc oxide is the actual accelerator in this type of curing system. The formation of ZnDMDC from TMTD during the curing process affects particularly the slow crosslinking reaction. Therefore, the activation energy of slow crosslinking is in very good accordance with the activation energy of TMTD decrease, and its value differs significantly from the activation energies of fast crosslinking and degradation. Simultaneously, these facts answer the question why the shape of the cure curves depends strongly on the temperature of cure.
Functionality Distribution of Hydroxyl-Terminated Polybutadienes by Gel Permeation Chromatography. II. Measurements for Commercial Polymers
Authors: Baczek S. K. , Anderson J. N. , Adams H. E.
Published: February 2011

The study of molecular weight and functionality parameters of telechelic hydrocarbon-based prepolymers has received much attention in recent years owing to the influence that these parameters exert on the vulcanization and product properties. An excellent review of these systems has been presented by French. Previous work has been limited to the determination of the average functionality of the whole polymer or of fractions obtained by some appropriate fractionation procedure. Muenker and Law, for instance, used extensive column elution techniques for separating the various species and then determined the average functionality of the fractions. In the previous paper, we described a dual-detector gel permeation chromatography (GPC) method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distributions of hydroxyl-terminated polybutadienes. The method is based on the simultaneous use of a differential refractive index and ultraviolet GPC detectors to analyze the polymers before and after derivatization of the hydroxyl groups with phenyl isocyanate. In this paper, the method will be utilized to determine these parameters for several commercial hydroxyl-terminated polybutadiene prepolymers and to compare the data with existing literature values.
Sequence Distribution of Polyisoprenes
Authors: Tanaka Y. , Sato H.
Published: February 2011

Isoprene can be polymerized into four types of isomeric structures; cis-1,4, trans-1,4, 3,4, and 1,2, depending on catalysts and polymerization conditions. So far, the difference of mechanical and thermal properties among polyisoprenes has been discussed chiefly on the basis of amounts of these isomeric structures. However, it is quite reasonable to expect that the polymer properties are affected not only by the composition of isomeric structures but also by the distribution of isomeric structures, the arrangement of head and tail linkages, and the degree of branching. This idea was adopted by Hackathorn and Brock as an explanation of the poor crystallizability of lithium polyisoprene; i.e. head-to-head and/or tail-to-tail linkages of 1,4- and 3,4-units prevented the crystallization of the polymer. Pyrolysis-gas chromatography has been applied to the investigation of the sequence distribution of 1,4- and 3,4-units in polyisoprenes. This method is based on the structural relationship between the isoprene dimers and the diad sequences of 1,4- and 3,4-units. However, it is difficult to discuss the slight differences in the yield of each dimer because the absolute amount of the dimers is small (∼30%) compared to the isoprene monomer (∼65%). Ozonolysis has been used to measure the amount of head-to-head, head-to-tail, and tail-to-tail linkages of the 1,4-unit in polyisoprenes. This method, however, is limited to the detection of these linkages of 1,4-units. In a previous paper, we have investigated 13C NMR spectra of chicle and cis-trans isomerized polyisoprenes and determined the sequence distribution of cis-1,4- and trans- 1,4-units in these polymers. We have also studied 13C NMR spectra of hydrogenated polyisoprenes prepared with n-BuLi-Et2O catalysts and found that 1,4- and 3,4-units were distributed randomly along the polymer chains regardless of the amounts of 3,4-units. In the present investigation we prepared various types of polyisoprenes and discussed the distribution of 1,4-and 3,4-units, arrangements of head and tail linkages, the branches of polymer chains, and the tacticity of polyads of 3,4-unit by the use of 13C NMR spectra of hydrogenated polyisoprenes.
Randomly Branched Polymers. II. Computer Analysis of Gel-Permeation Chromatograms
Authors: Kurata M. , Okamoto H. , Iwama M. , Abe M. , Homma T.
Published: February 2011

An iterative computer method was proposed for estimating the degree of branching and molecular weight distribution simultaneously from a pair of measurements on intrinsic viscosity and gel-permeation chromatography. The validity of the method as applied to randomly branched polymers was tested by using both fractionated and unfractionated samples of branched polystyrenes. It was experimentally concluded that the average number of branch points per unit molecular weight, λ, can be determined by this method with an accuracy of about 15%, and the weight-average molecular weight with accuracy of about 10%.
Effect of Curing Temperature on the Technical Properties of Nitrile Rubber and Carboxylated Nitrile Rubber
Authors: Bhowmick A. K. , De S. K.
Published: February 2011

In a mixed crosslink system (sulfur and metal carboxylate) of XNBR vulcanizate, the variations of the proportions of curatives (low sulfur/high accelerator or high sulfur/low accelerator) have little effect on the vulcanizate properties. But aging studies indicate that the metal ion crosslinks are modified in the presence of a sulfur vulcanizing system. NBR vulcanizates with a comparable recipe have less crosslink density than the corresponding XNBR ones. In general, the technical properties and aging resistance of mixed crosslink systems using ZnO2 and sulfur donor-sulfur are better than the NBR vulcanizates. Increase of curing temperature does not always lower the technical properties of XNBR and NBR vulcanizates. Addition of XNBR to NBR in XNBR-NBR blends lowers most of the technical properties, possibly due to different vulcanization characteristics.
Molecular Interpretations of Modulus and Swelling Relations in Natural Rubber Cross-Linked by Dicumyl Peroxide
Authors: Wood Lawrence A.
Published: February 2011

A survey of published experimental work on the modulus of natural rubber crosslinked by dicumyl peroxide permits a comparison with the results and molecular interpretations obtained in recent NBS work. Excellent agreement was found among values of the shear modulus G at the same crosslinking when the crosslinking is calculated from the amount of decomposed dicumyl peroxide. The types of deformation included torsion as well as uniaxial extension and compression. G increases linearly with crosslinking (except at the lowest degrees) with a slope from 5 to 15 percent greater than that predicted by the simple statistical theory. Data of Mullins demonstrated that at each degree of crosslinking the value of G is intermediate between 2C1 and 2(C1+C2) where C1 and C2 are the Mooney-Rivlin constants. Measurements of equilibrium swelling at a given degree of crosslinking are in reasonable agreement with each other. However, the entropy components of the modulus and the sub-chain density calculated from swelling measurements are appreciably greater than those calculated from crosslinking or from direct mechanical measurements. They increase linearly with crosslinking. It is concluded that the number of sub-chains effective in limiting swelling is greater than that effective in direct mechanical measurements.
Natural Rubber Foundation Bearings for Earthquake Protection—Experimental Results
Authors: Derham C. J. , Thomas A. G. , Eidinger J. M. , Kelly J. M.
Published: February 2011

The concept of earthquake protection of civil engineering structures by the use of rubber mountings of low shear stiffness has been discussed by Derham, Wootton, and Learoyd. Figure 1, taken from these references, shows the predicted response of a five-story shear-wall structure to an earthquake having a peak ground acceleration of 0.3 g. The accelerations shown at the various mass levels have been computed both for the building with its foundation fixed conventionally, and for the building “floating” on natural rubber bearings. The bearing stiffness was such as to make the horizontal natural frequency of the mounted structure 0.5 Hz. The basis of computation was the response spectrum of Housner. The results were later confirmed further by using a time-history analysis. The basic conclusion from these computer studies was that the use of rubber mountings leads the building to behave in an earthquake essentially as a rigid body. The rigid body accelerations, and hence the forces, are very much smaller than the accelerations experienced by a fixed-foundation structure, particularly in upper storys. For the case studied the overall maximum acceleration of the rubber-mounted structure was calculated to be one-tenth the maximum acceleration experienced by the fixed-foundation structure.
New Methods for Estimating Dispersibility of Carbon Blacks in Rubber
Authors: Jansen Jay , Kraus Gerard
Published: February 2011

Two convenient experimental methods are described for ascertaining dispersibility characteristics of carbon black. Both are based on the rate of development of optical density with dispersion or mixing time in a dilute suspension. One procedure uses polybutadiene medium and a roll mill to effect dispersion, the other chloroform and ultrasonic agitation. Correlations with conventional dispersion test results based on photomicrography are good. Advantages are precision and objectivity, not available to the same degree in photomicrograph evaluations.
A New Concept of Tire Load Inflation Formulae
Authors: Zheng-ren Z.
Published: February 2011

Since World War II the size and number of vehicles has increased greatly. Passenger cars have greater power and acceleration, whereas truck tires carry heavier loads at greater speeds. Earthmover vehicles now have heavier loads as well as greater traction. To keep up with the demands of the automotive industry, tire technologists have had to change from cotton and rayon cord to nylon, polyester, steel and aramid. Tire construction has changed from the conventional high aspect ratio to a lower one and from bias to radial design. A difference in thinking between European and American tire technologists appears based on different concepts of single and dual load capacities. The Americans (TRA) base their calculations on the dual load while the Europeans (ETRTO) base theirs on single load. This is not the principal argument, since both can use dual or single as the basis of calculating the tire load. Some do not believe in load calculation formulas; instead, they rely on their experience and estimation. It is not scientific to “estimate” the load of a tire by experience.
The Synthesis of Isocyanate-Modified Novolak Resins for Use in Natural and Synthetic Rubber
Authors: Ghatge N. D. , Shinde B. M.
Published: February 2011

Resin-C and Resin-B give higher values for tensile strength, modulus, and hardness than all other resins.
Molecular Fracture in Polychloroprene
Authors: Mead W. T.
Published: February 2011

The ESR spectra from polychloroprene uniaxially deformed at 77 K in an oxygen environment are composite spectra arising from two radical species. An allyl radical species results from main-chain rupture midway between the α-methylene groups, and a peroxy radical species is formed by reaction of the oxygen in the environment with the allyl radical species. The stability of these allyl radicals with respect to oxygen and temperature is apparently similar to the allyl radicals formed in polybutadiene and polyisopropene. At liquid nitrogen temperature all the radicals were stable. The peroxy radical species is unstable as Tg is approached and decays to give a resonance-stabilized allylic species, which is stable until the temperature of the sample is slightly above Tg. Above Tg a broad singlet is observed, and it is attributed to a polyenyl radical species.
Contribution of Power Profiles to Mixing Efficiency
Authors: Dolezal P. T. , Johnson P. S.
Published: February 2011

Our studies have shown that, on a laboratory scale, power curves can be used to elucidate the processes involved in mixing butyl rubber compounds. Through an understanding of the process and the construction of mixing profiles, it is possible to optimize mixing efficiency. In a production environment, power curves can obviously be of great value in monitoring quality control.
Scanning Electron Microscopy Studies of Fractured Natural Rubber Surfaces
Authors: Bhowmick A. K. , Nando G. B. , Basu S. , De S. K.
Published: February 2011

A tensile ruptured gum specimen shows formation of crystalline regions at an angle of 45° to the flow lines, whereas a tensile ruptured filled specimen shows formation of depression. A tear fractured gum specimen shows again the formation of crystallites at an angle of 45° to the flow lines. Tear fractured filled specimens show the enhancement of crystallinity throughout the matrix, but the surface is rough. Flex fractured gum specimen show a large number of cracks on the surface while the filled vulcanizate shows formation of balls presumably due to coiling of polymer chains on the filler surface. An abraded gum surface shows dimple structure, while a filled vulcanizate indicates coarse ribbed structure. Addition of lignin, in general, reduces the crystallinity of tensile and tear fractured samples and increases the fibrosity of flex cracked and abraded samples.
New Factors Affecting the Performance of Automotive Fuel Hose
Authors: Pfisterer H. A. , Dunn J. R.
Published: February 2011

The permeation of fuels through fuel hose compounds based on medium acrylonitrile NBR increases with aromatic content. Addition of low molecular weight alcohols as fuel extenders has an adverse effect on swelling and permeability, which is most marked at levels of 10–20%. NBR is resistant to unblended alcohols. Addition of tertiary butyl alcohol at levels up to 7% for improved octane rating does not adversely affect NBR. High acrylonitrile NBR and NBR-PVC blends have lower permeability to and greater resistance to swelling by aromatic fuel. They also exhibit improved resistance to swelling by alcohol modified fuel. XNBR has somewhat lower fuel permeability than regular NBR. A two-component fuel hose composed of a veneer of high acrylonitrile NBR, NBR-PVC or XNBR-PVC with the highest practical acrylonitrile level inside a medium acrylonitrile NBR is suggested as a route to satisfactory permeability and low temperature performance.
Polymerization of Diene Monomers by Ziegler Type Catalysis
Authors: Horne S. E.
Published: February 2011

I have not gone into compounding and testing results on polyisoprene and polybutadiene. As you well know, they are widely used in the rubber industry. From a technical standpoint, we know we can replace natural rubber with cis-polyisoprene. However, the profitability of the process is closely tied to the availability of isoprene monomer and the price ratio of cis-polyisoprene and natural rubber. Sometimes the economics is favorable and sometimes unfavorable. Consequently, polyisoprene expansion is slow in the Free World. In the Communist countries, however, the planned economy is pushing ahead with polyisoprene—projections for 1985 are for 817 000 metric tons versus 227 000 metric tons in the Free World. Is there a possibility of an entirely new synthetic rubber that will be the equal of polyisoprene, but more economical? Is there a blend of elastomers that will replace natural? Is there a chance the economics of polyisoprene might become more favorable? Certainly the answers pose a challenge to those of us in research. We cannot sit back and say we have reached the ultimate, for the world of the tire is constantly changing, and we must be able to meet the change. The work reported here could not have been carried out without the invaluable contributions of my colleagues at BFGoodrich. I wish to especially mention: Jim Shipman and Jack Kiehl for the early infrared work and claiming that I was trying to fool them with my first copolymer; Vern Folt, the enthusiastic section leader for the early project ; Earl Carlson, who elucidated the conditions for making trans-polyisoprene and trans-polybutadiene ; Dave Craig for supplying the pure isoprene for the early work; Bob Minchak and Harold Tucker for some of the cobalt studies and titanium studies; Harvey Scott for the cobalt chloridealuminum chloridethiophene catalyst; Ed Wilson and M. Reinhart for compounding studies; Waldo Semon and Carlin Gibbs for directing it all and allowing us such a free hand; Floyd Miller, who did such an outstanding job of scaling the process directly from a 50 g lab recipe to production size runs; and the numerous, capable technicians who have worked for me— they are the unsung heroes of the laboratory work. Let me say again how highly honored I feel to receive this award. I am accepting it for all at BFGoodrich, for it was truly a team effort.
Experimental Studies of the Influence of Particle and Fiber Reinforcement on the Rheological Properties of Polymer Melts
Authors: White James L. , Czarnecki Lech , Tanaka Hideho
Published: February 2011

An experimental study is reported on the rheological properties of compounds of a polystyrene melt with calcium carbonate, carbon black, titanium dioxide, calcium sulfate anhydride fiber, mica, glass beads and aramid, cellulose and glass fibers. Comparison is made of the shear viscosity, elongational viscosity and principal normal stress difference of these compounds at 20 volume per cent loadings. The polymer matrix and compounds with the smallest particle dimension greater than 10µ exhibit low shear rate Newtonian viscosities. Suspensions with particle sizes 0.5µ and smaller exhibit yield values. Yield values are also observed in elongational flow for systems exhibiting yielding in shear flow. The experimental data are contrasted to both mechanistic theories of suspensions with interaction between particles and a phenomenological plastic-viscoelastic tensor constitutive equation.
A Simple Method for Estimating Viscosity of Highly Viscous Liquids
Authors: Graessley W. W. , Ver Strate G.
Published: February 2011

The results indicate that the hanging-strip method provides good values of η0 under favorable circumstances. The value of the method lies in the convenience and simplicity of the experiment. With little more than a meter stick and a clock, one can estimate zero-shear viscosities which are above 0.1 MPa·s. Careful testing is very important to avoid the effects of molding history and clamping, and to assure that the time-dependence of specimen elongation conforms to the Newtonian liquid model.
Environmental Degradation of Tire-Wear Particles
Authors: Cadle S. H. , Williams R. L.
Published: February 2011

Each of the three analysis methods contributes to an understanding of the degradation processes which occur in environmentally exposed tire-wear particles. Extraction-pyrolysis-GC is the most reliable method since it treats the whole sample rather than a few particles. In 16 months, 52% of the polymer in tread-wear particulate was degraded in soil samples. In glass beads, only 36% of the polymer in tread-wear particulate degraded, perhaps because soil microorganisms were not available to degrade sulfur linkages in the vulcanized portion of the polymer. Fresh tread particles of the same size showed no degradation. The pyrolysis-GC results showed wider scatter, presumably because only a few rubber particles could be analyzed and all the particles did not degrade at the same rate. However, this method showed that the unsaturated bonds of polybutadiene undergo oxidative degradation more rapidly than do the aromatic bonds of styrene units. These results strongly suggest that one important mode of degradation of tread-wear paniculate is atmospheric oxidation. The TGA results showed that biodegradation did not reduce the total carbon content of the tread-wear particulate in this 16-month study. However, more than half of the extender oil was oxidized sufficiently to increase its vaporization temperature to the polymer temperature range. Biooxidation may have detoxified some of the polynuclear aromatic hydrocarbon portion of the oil. Overall, these results suggest that microbial attack of tread-wear particulate is less significant than attack by-atmospheric oxygen. To match the amount of rubber observed at the California freeway site, the removal rate by all mechanisms must be 0.67% per day. For this high removal rate, the amount of rubber at the roadside would reach a steady-state value within the first two years of a freeway's use at a level equivalent to five months of tire-wear. The rate of environmental degradation found in this study is 0.15 per day, or 22% of the total removal rate found in the California study. Wind erosion and water runoff probably also contribute to the total removal rate. Most importantly, we have shown that tread-wear particles degrade at a faster rate than tread-rubber itself, and that environmental degradation plays an important role in the fate of tire-wear particulate.
Effect of Cure Temperature on Urethane Networks
Authors: Kimball M. E. , Fielding-Russell G. S.
Published: February 2011

The effect of cure temperature on the physical properties of two diamine-cured thermosetting polyurethanes was explained by differences in structure. The polymer cured at the higher temperature (140°C) exhibited properties more typical of a stable crosslinkedelastomer, whereas the behavior of the polymer cured at the lower temperature (80°C) was more typical of a domain-separated system.
N-Sulfonyl-Sulfilimines as Premature Vulcanization Inhibitors
Authors: Hopper R. J.
Published: February 2011

N-Sulfonyl-sulfilimines which undergo a thermal elimination to form N-alkyl (or aryl)thiosulfonamides act as premature vulcanization inhibitors, apparently by the same mechanism as the thiosulfonamides. S,S-di(isopropyl)-N-(p-toluenesulfonyl) sulfilimine was of particular interest due to its good inhibitory activity, ease of preparation, excellent stability, and resistance to bloom.
Comparing the Time and Rate Dependent Mechanical Properties of Elastomers
Authors: Meinecke E. A.
Published: February 2011

At attempt was made to show that the normally performed tests to evaluate the properties of elastomers (and compare different ones) are not necessarily the ones which govern failure due to small strain viscoelasticity. The easiest way to compare different rubber compounds as to their ability to keep their elastic properties is with the help of stress relaxation data. However, one has to perform loading-unloading creep experiments in order to be able to separate the permanent from the transient viscoelastic response.
Block and Graft Copolymers of Polypivalolactone : Poly(Acrylate-g-Pivalolactone)
Authors: Caywood S. W.
Published: February 2011

Thermoplastic poly(acrylate-g-pivalolactone) elastomers depend upon the crystallization of polypivalolactone side chains into discrete domains for the reversible formation of elastomeric networks. The high crystallinity of the grafted polyPVL chains and their chemical inertness leads to a highly reinforced, effectively crosslinked copolymer of unusual stability. The physical properties of the graft copolymer are similar to those of elastomeric polyacrylates compounded with carbon black and chemically crosslinked. At high deformation, as on a two-roll mill, the crystalline domains are sufficiently disrupted to allow the polymer to flow easily. At low deformation, for example in the compression-set test, there is very little flow, as shown by resistance to compression set fully equivalent to that of covalently crosslinked elastomers. The synthesis of polyacrylate-g-PVL copolymers is remarkably simple and subject to few limitations. Grafting efficiency is high and should approach 100% under slightly more rigorous conditions than employed in this work. These copolymers are unique in the ease and precision with which both hard and soft segment length can be varied to control the physical properties of the product.
Design and Engineering with Natural Rubber
Authors: Meyer D. A. , Welch J. A.
Published: February 2011

NR continues to be the preferred general-purpose elastomer for many important engineering applications. Although its stress-strain behavior is similar to most other rubbers, it possesses several unique characteristics which makes it a good or preferred candidate for a large number of applications. These include outstanding fatigue life, high rupture strength, excellent relaxation properties, and stable characteristics over a wide temperature range along with a greater flexibility for manipulating dynamic properties. Many of its apparent limitations can be overcome with proper design and sufficient consideration to end-use conditions. A few well-established engineering applications as well as the design principles involved are presented along with reasons for the use of NR.
The Poisson Ratio for Rubber—Cord Composites
Authors: Pósfalvi Ö
Published: February 2011

Elasticity equations have been devised for an orthotropic rubber-cord system based on nonlinearly elastic rubber and linearly elastic cord. The problem involves the mechanics of nonlinear, elastic, composite materials under large deformations. The Poisson ratios and Young's moduli characteristic of such a composite system under uniaxial stress can be derived. For this computation it is necessary to establish the moduli of elasticity of the cord imbedded in the rubber and the critical cord angle.