bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of Sulfur-Free Thiuram Vulcanization
Authors: Ducháček Vratislav
Published: February 2011

Sulfur-free thiuram vulcanization has been investigated at temperatures from 160° to 190° C over 0.5 to 600 min. Continuous measurements in a VUREMO curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. Simultaneously the values of the network chain density were calculated from swelling measurements on the vulcanizates. The cure curves show clearly an induction period (ti), then fast crosslinking, a partial degradation, a “long-time” crosslinking, and finally a slow, limited degradation. Apart from the induction period, the kinetic graphs are satisfactory represented by a rate equation assuming three independent first-order reactions: fast crosslinking, degradation, and slow crosslinking. The rate equation contains seven kinetic parameters. Over the temperature range studied, there is no difference between the values of activation energy for fast crosslinking, for degradation, for slow crosslinking, and for ti−1. Due to the presence of thiourea, the values of the induction period, the rate constant, and the extent of slow crosslinking are decreased. Simultaneously the activation energies calculated from degradation and slow crosslinking are significantly increased. On the basis of the above results, the mechanism of the sulfur-free thiuram vulcanization, in which ionic and radical reactions take place, is discussed.
Thermodynamics of Solutions of Poly(Dimethylsiloxane) in Benzene, Cyclohexane, and Chlorobenzene
Authors: Flory P. J. , Shih Hsiang
Published: February 2011

Excess volumes have been measured at 25° for mixtures of poly(dimethylsilo xane) (PDMS) of high molecular weight with each of three solvents: benzene, cyclohexane, and chlorobenzene. Chemical potentials have been determined for solutions in the first two of these solvents by high-pressure osmometry and by vapor sorption. These results, in conjunction with osmotic measurements by Kuwahara and coworkers in chlorobenzene at 20 and 60°, and the heats of mixing determined by Delmas and coworkers for each of these systems permit a comprehensive analysis of the thermodynamic properties of the PDMS mixtures. They are characterized by entropies of dilution and excess volumes that are abnormally low compared with theoretical calculations.
Characterization of Polymers under Large Deformation. I. Repeated Chemical Stress Relaxation of Vulcanized Rubbers
Authors: Kusano Takae , Murakami Kenkichi
Published: February 2011

In this investigation, repeated chemical stress relaxation measurements were carried out to observe the relaxation behavior at large deformation. It was found that the repeated chemical stress relaxation curves were affected by both measurement temperature and the extension ratio of rubber. It was suggested on the basis of the results that temperature and mechanical stimulus have a similar effect on the stress relaxation curves.
Large Deformation Isotropic Elasticity—On the Correlation of Theory and Experiment for Incompressible Rubberlike Solids
Authors: Ogden R. W.
Published: February 2011

Many attempts have been made to reproduce theoretically the stress-strain curves obtained from experiments on the isothermal deformation of highly elastic ‘rubberlike’ materials. The existence of a strain-energy function has usually been postulated, and the simplifications appropriate to the assumptions of isotropy and incompressibility have been exploited. However, the usual practice of writing the strain energy as a function of two independent strain invariants has, in general, the effect of complicating the associated mathematical analysis (this is particularly evident in relation to the calculation of instantaneous moduli of elasticity) and, consequently, the basic elegance and simplicity of isotropic elasticity is sacrificed. Furthermore, recently proposed special forms of the strain-energy function are rather complicated functions of two invariants. The purpose of this paper is, while making full use of the inherent simplicity of isotropic elasticity, to construct a strain-energy function which: (i) provides an adequate representation of the mechanical response of rubberlike solids, and (ii) is simple enough to be amenable to mathematical analysis. A strain-energy function which is a linear combination of strain invariants defined by ϕ(α)=(α1α+α2α+α3α)/α is proposed; and the principal stretches α1, α2, and α3 are used as independent variables subject to the incompressibility constraint α1α2α3=1. Principal axes techniques are used where appropriate. An excellent agreement between this theory and the experimental data from simple tension, pure shear and equibiaxial tension tests is demonstrated. It is also shown that the present theory has certain repercussions in respect of the constitutive inequality proposed by Hill.
Viscoelastic Behavior of Butadiene-Acrylonitrile Copolymers at Small and Large Deformations and Their Ultimate Properties
Authors: Nakajima N. , Bowerman H. H. , Collins E. A.
Published: February 2011

With four samples of butadiene-acrylonitrile copolymers the following viscoelastic measurements have been performed: dynamic mechanical measurements in tension at 110 Hz from −60 to 180° C, tensile stress relaxation measurements with 100 per cent elongation at 25, 54, and 97.5° C, capillary flow measurements at 70, 100, and 125° C, and high-speed tensile stress-strain measurements carried to break at 25, 54, and 97° C. All the data have been treated with the same equation for the time-temperature conversion. The complex viscosity-frequency curves calculated from the dynamic measurements were found to be in good agreement with the capillary viscosity-shear rate curves. From the stress-strain relationship at the yield point the viscosity is estimated; such viscosity as a function of the strain rate is similar to the viscosity-shear rate curve. Good agreement was found with some samples. The elongation to break may be predicted with some samples from the treatment of stress relaxation data together with steady shear flow data.
Unperturbed Polymer Chain Dimensions from Intrinsic Viscosities Determined in Good Solvents
Authors: Stacy C. J. , Arnett R. L.
Published: February 2011

Experimental criteria are presented to determine the region of validity of the intrinsic viscosity-molecular weight relation proposed by Stockmayer and Fixman for use in good solvents. Use of these criteria in several good solvents yields the same value for unperturbed polymer dimensions as do measurements made at “θ” conditions. Intrinsic viscosity determinations conforming to these criteria, made in two good solvents, allow the determination of weight-average molecular weights of the polymer solute.
Network Changes in Nitrile Rubber at Elevated Temperatures
Authors: Lee T. C. P. , Morrell S. H.
Published: February 2011

The network analysis of the aged sulfur vulcanizates of nitrile rubber serves to re-emphasize the complexity of the structural changes which can occur at elevated temperatures. Three factors control the rate and degree of crosslinking in these systems. First there is the crosslink structure. An essential feature for heat resistance in sulfur compounds is that they should contain, as near as possible, 100 per cent monosulfide crosslinks. Systems which contain polysulfide crosslinks, and probably to a lesser extent disulfide crosslinks, are prone to purely thermal crosslink shortening or cleavage reactions. The physical effect of these thermal changes would be superimposed on the effects brought about by thermooxidative changes. Despite their thermal stability monosulfide crosslinks can oxidize and cleave, a process which will result in stress relaxation if the sample is held in tension or compression. Hence for truly inert systems one will have to turn to non-sulfur cure in conjunction with a suitable stabilizer. Because the results indicate that scission associated with chemistry at the monosulfide crosslink is reversible, this cleavage does not contribute to the change in modulus or hardening during aging. This brings in the second controlling factor. The degree and rate of hardening depends on the nature of the products of vulcanization, and also possibly on those species intermediate between crosslink and accelerator, the pendent accelerator groups. In acting as an antioxidant ZDMC is apparently oxidized to a new source of sulfur. The more heat resistant cadmate system contains no such products and also a minimum of pendent accelerator groups. This leads to the third factor—the added antioxidant. For its heat resistance the cadmate system relies on an antioxidant. It is this which stops crosslinking reactions through autooxidation of the polymer backbone. The efficiency with which the antioxidant (dioctyldiphenylamine) works suggests that there is a synergistic effect in operation, which in some way involves cadmium. Thus the best heat resistance will be obtained where the compound yields monosulfide crosslinks, an uncomplicated network structure, unreactive vulcanization products, and contains a highly effective antioxidant system. Many facets of the aging of nitrile rubber are still open to explanation. Not the least of these is why crosslinks formed during the aging of the TMTD/S vulcanizate, which, by reason of their reactivity to methyl iodide, are thought to be sulfidic, are not themselves oxidized in a manner similar to the original monosulfide crosslinks. Model compound studies would answer this and other questions.
The Discovery of Polychloroprene Charles Goodyear Medal Address—1973
Authors: Collins Arnold M.
Published: February 2011

I will start by giving you some background from the early twenties, a time which many of you may not remember. There was a rapidly growing automotive industry. Since all cars then ran on tires of natural rubber, there was a question as to whether enough rubber could be produced from the trees of southeast Asia for future needs. Other plant sources of rubber were being investigated. A synthetic rubber had been made from isoprene in Germany during World War I but it was expensive and of poor quality. There was also at this time a well established organic chemical industry, which had developed largely from the dyestuff manufacture established during World War I and included a substantial rubber chemicals industry. Chemistry was a popular subject, both in the universities and in the public mind. Most “fundamental research” was done in the universities. Industrial laboratories were just beginning to do research for which no immediate practical results were expected. Polymers and polymerization were little understood.
1,1,4-Derivatives of Thiosemicarbazide—New Non-Staining Antiozonants
Authors: Zolotarevskaya L. K. , Lipkin A. M. , Grinberg A. E. , Angert L. G.
Published: February 2011

In the nature of non-staining antiozonants, a new class of compounds, 1,1,4-derivatives of thiosemicarbazide, are proposed. The mechanism of reaction of thiosemicarbazide derivatives with ozone is analogous to the mechanism of this reaction with thiourea derivatives. Within this, the rate constant of the initial reaction of the thiosemicarbazide derivatives with ozone is somewhat higher than that of the thiourea derivatives. 1,1,4-Trialkyl-substituted thiosemicarbazides appear to be the most effective antiozonants, not changing the color of light vulcanizates. Of the investigated compounds, 1,1,4-tributylthiosemicarbazide, being distinguished by a large protective effect against ozone, inhibiting activity in the process of heat aging of the vulcanizates, and lesser ability for leaching out of the vulcanizates by water than tributylthiourea, presents the greatest practical interest.
The Use of Radio-Frequency Activated Gas Treatment to Improve Bondability
Authors: DeLollis N. J.
Published: February 2011

Two apparent contradictions are indicated in comparing recent work with previous work in the field of adhesion. The first contradiction concerns the significance of a weak boundary layer in adhesion failure. Bikerman and Hansen infer the presence of a weak boundary layer and imply that its removal is necessary to improve adhesion. Yet, neither its presence nor its removal are confirmed experimentally. Recent work with RTV silicone confirms experimentally the presence of a material meeting the definition of a weak boundary layer before and after the radio—frequency activated oxygen treatment, which improves adhesion. These results indicate that a possible bonding mechanism involves desorption or displacement of the weak bondary layer and preferential adsorption of the adhesive to form the bond. The other contradiction involves the report by Hansen and Schonhorn that the “CASING” treatment improves adhesion to poly (ethylene) without changing surface energy characteristics. Three laboratories report relatively large changes in contact angle on poly (ethylene) even after exposure to an activated gas for as little as 5 sec. Malpass and Bright report that, while there may be no change in contact angle immediately after removal from the activated inert gas environment, the contact angle rapidly decreases to very low values. This indicates that the low energy state is rather transitory in nature. These results along with those of Sowell and Westerdahl indicate that there may be no serious contradiction to the rule of energetics in bonding, i.e., the adhesive in the liquid state shall have a lower surface tension or surface free energy in order to wet, spread, and adhere to the higher surface energy adherend. Recent findings by Hudis, confirmed by Sowell, indicate that the ultraviolet emission from the radio—frequency gas plasma is the basic factor in the cross-linking of poly(ethylene). Sowell has shown that exposure to ultraviolet radiation also causes increase in critical surface energy and improvement in bondability of poly (ethylene).
Infrared Studies of Oxygen-Containing Groups on the Surface of Carbon Black
Authors: Studebaker M. L. , Rinehart R. W.
Published: February 2011

Results of this infrared study give strong qualitative support for the presence of quinones and support the presence of lactones. Considerable chemical reactivity is associated with the presence of these two groups. Absorption typical of phenols and ethers was obtained in the 1205–1195 cm−1 and 1275-1265 cm−1 regions; and it is suggested by this study that the oxygen not present in quinone, lactone, or phenolic form is present as aromatic ring-type ether groups.
Large Particle Oil Furnace Black. A New Type of Carbon Black
Authors: Johnson P. H. , Cooper W. T. , Forseth G. J.
Published: February 2011

Continuous-oil-furnace blacks have dominated the tire-black portion of the carbon black spectrum while the large particle blacks have been produced by the older gas-furnace and thermal processes. New technology has led to the extension of the oil-furnace-black process to include the Thermal black portion of the spectrum. Amenability to control of structure, particle size, and extractables are important features of the process which produces new carbon blacks called LPF for Large Particle Furnace blacks. These new blacks are in the 100–350 nanometer particle size span and can be produced in a range of Dibutyl Phthalate Absorption numbers (ASTM) from about 25 to 120. LPF blacks appear to be similar to existing large particle types, based on general physical properties. However, detailed examination of LPF black morphology with the electron microscope shows unique differences in microstructure. Compared directly in compounds, the new blacks are often more reinforcing than existing counterparts, yielding higher modulus and tensile strength. Substitution of some LPF blacks for Thermal types in mechanical rubber goods can result in substantial savings in terms of plasticizer oil and curative use. Often LPF types can be used to an advantage by replacing blends comprising Thermal types and more reinforcing blacks.
Wire Adhesion Testing
Authors: Coates L. C. , Lauer C.
Published: February 2011

The results of this study are conclusive. The ASTM D-2229 Test Method is not a reliable test for measuring adhesion of wire cords to rubber compounds. However, by using the basic design and modifying it, an accurate measurement of bond strength on a macroscopic level can be obtained. This test is insensitive for all practical purposes to compound physical properties and changes in cord diameter and embedded length—for both stranded and rod-like cords. It is also possible with this test to calculate the amount of stress that is exerted on the surface of the wire cord to determine the relationship between failing stress and the material strength of the rubber compound. Properly used, this new test should give the compounder a better tool to study the adhesion of compounds to metal.
The Chemistry and Technology of Rubber-Bound and Related Novel Antioxidants
Authors: Cain M. E. , Gazeley K. F. , Gelling I. R. , Lewis P. M.
Published: February 2011

The discovery that C-nitrosoanilines react with olefins to give p-phenylenediamines has made possible the synthesis of powerful antioxidants from a wide range of naturally occurring and synthetic unsaturated compounds. Simple alkenes, vegetable oils, and factices may be converted to antidegradants whose behavior parallels that of commercially available materials. The reaction of 4-nitrosoanilines or 4-nitrosophenols with natural and synthetic rubber or latices gives rubber-bound antioxidants which are completely resistant to extraction by water or organic solvents. No major modification of technological processing or fabrication techniques is necessary, and the reaction takes place conveniently during vulcanization. Attachment of the protective group to the rubber molecule does not affect its antioxidant activity, but reduces its effectiveness when migration to the surface is required, e.g., in protection against ozone. Although faster at elevated temperatures, the nitroso-olefin reaction will occur at room temperature, and this allows the preparation of chemically modified raw rubbers by carrying out the reaction in latex before coagulation and drying.
Phase Stability in Heterogeneous Compositions of Butadiene-Acrylonitrile Copolymer
Authors: Landi V. R.
Published: February 2011

Multiple glass transitions in emulsion polymerized butadiene—acrylonitrile copolymer at leass than 36% acrylonitrile by weight were studied using the Differential Scanning Calorimeter. The appearance of two rather than one transition was shown to be related to the drift in composition with degree of monomer conversion, when all monomer was introduced initially. Material responsible for either glass transition in 29% ACN copolymer was concentrated by phase separation in solution. Phase separation in the butadiene—acrylonitrile copolymer system when the width of the distribution of compositions is above a critical value is shown to be predicted by Scott's thermodynamic treatment of multi-component copolymer mixtures. The partitioning of species of different compositions between phases was calculated for a model distribution of polymeric compositions.
Mechanical Fatigue of Rubber
Authors: Lake G. J.
Published: February 2011

Fatigue failure of rubber under repeated loading is reviewed. The process considered is that occurring in the absence of appreciable temperature rise as a result of the development of one or more cracks. A fracture mechanics approach, based on the elastic energy available for crack propagation, enables the crack growth and fatigue behavior to be interrelated quantitatively and is helpful from both basic and applied viewpoints. Initiation of mechanical crack growth is governed by a critical value of the available energy, which is of similar magnitude for various elastomers and can be related approximately to the primary bond strength and molecular structure. Once this value is exceeded, the characteristics of growth vary markedly for different elastomers and appear to be influenced primarily by the elastic hysteresis of the rubber at high strains. Although the mechanical deformations are the basic driving force, the crack growth and fatigue behavior can also be strongly affected by atmospheric oxygen and ozone and the mechanisms of action of these gases are described. Implications of the work from the testing and service viewpoints are considered. A major problem in applying the fracture mechanics approach is to determine the energy available for crack growth in a component of complex shape. Recently-developed methods of doing this are discussed and the quantitative application of the approach to predict service performance is illustrated.
Constitutive Equations for Elastomers
Authors: Tschoegl N. W.
Published: February 2011

General relations were derived by expanding the strain-energy density function in terms of the invariants of the deformation tensor. Some constitutive equations obtained by keeping a third term in the expanson in addition to the two terms retained in the Mooney-Rivlin equation were tested in the light of currently available experimental data. It is shown that by the retention of the third term the upswing in the Mooney stress at low values of γ−1 is successfully predicted, and the stress—strain behavior can be described with excellent accuracy up to break, even in carbon black-filled rubber which is difficult to describe by the Mooney-Rivlin equation.
Low Temperature Relaxation Phenomena in Rubber-Like Polymers Subjected to Low Deformation
Authors: Bartenev G. M. , Kucherskii A. M.
Published: February 2011

1. A new relaxation process was discovered which explains the change, at critical tensile stresses (0.1–0.5 kg/cm2), in the elasticity of rubber-like polymers subjected to small deformations. This new process is characterized by relatively low activation energies (weak dependence of temperature on relaxation time) and kinetic units that are large (strong dependence of relaxation time on stress). The kinetic stress is a function of the temperature and for rubbery polymers it is reduced to zero, at 40° –60° C. 2. The mechanism of this phenomenon is elucidated by the existence of ordered, supermolecular microregions forming, with the free chains of 3-dimensional networks, supplementary bundles of non-chemical origin which disintegrate under, critical stresses. The activities observed are analogous to the processes of forced-elastic deformation in the same polymers in the glassy state. The critical stress is analogous to the limit of forced elasticity at low second order (glass) transition temperatures.
Electron Spin Resonance Study of Phenolic Antioxidants. Correlations of Organic Free Radical Stability with Antioxidant Activity
Authors: Westfahl J. C. , Carman C. J. , Layer R. W.
Published: February 2011

Electron spin resonance (ESR) is a well established, sensitive spectroscopic technique for determining the molecular structure, as well as the lifetime or stability of organic free radicals. Consequently, ESR spectroscopy provides a logical method for gaining insight into the role that free radicals play in the stabilization of rubber by organic antioxidants. We used ESR spectroscopy to determine the molecular structure of the phenoxyl free radicals derived from a series of twelve phenolic antioxidants. We also used ESR to measure relative radical concentrations of the free radicals and evaluated the twelve phenolic antioxidants relative to each other. We have found that the ESR measurement of relative radical concentration is a measure of relative radical stability, and that the relative radical stability is temperature dependent. By plotting relative radical concentration (or stability) as a function of temperature, we can rank these twelve antioxidants relative to each other. This ranking is in good agreement with the activity of these antioxidants in EPDM. These data were discussed in relation to antioxidant mechanism.
Polydiene Oxidations with Singlet Oxygen
Authors: Kaplan M. L. , Kelleher P. G.
Published: February 2011

Excited molecular oxygen in its singlet delta (1Δg) state can be made chemically in homogeneous solution and in the gas-phase by the electrodeless discharge of ground state oxygen. Both techniques have been used to perform oxidations of polydiene systems. Solutions of high cis, trans, and vinyl polybutadienes have been treated with singlet oxygen produced in situ. Only the high cis and high trans were oxidized, apparently by different mechanisms. Squalene, a model for polyisoprene, has been oxidized in solution and the initially formed hydroperoxides reduced and analyzed and found identical to the product from a photosensitized oxidation. Cis-polybutadiene films were treated with gas-phase singlet oxygen and the extent of surface oxidation was monitored spectroscopically and chemically.
The Oxidative Hardening of SBR
Authors: Studebaker M. L. , Beatty J. R.
Published: February 2011

During aging, SBR hardens. This hardening can be followed by swelling volume, hardness, and modulus measurements. Crosslink properties are important in determining the amount of oxidative hardening. The quantity of Sx-type sulfur in the R−S−Sx−S−R polysulfide crosslinks correlates well with the extent of hardening. A drastic reduction in ultimate elongation accompanies hardening, and this is believed to be intimately related to the severe reduction in resistance to cut growth and flexing.
Pendent Accelerator Groups in the Aging of Rubber
Authors: Parks C. R. , Parker D. K. , Chapman D. A.
Published: February 2011

As pendent accelerator groups are believed to be precursors to the formation of crosslinks in accelerated sulfur vulcanization, their original composition and concentration are largely responsible for the characteristics and properties of the final vulcanizate, including aging. This means that aging of rubber vulcanizates is inherently tied into the curing system. Dual labeled experiments using tritium-labeled accelerator and sulfur-35 were carried out to determine the number of sulfur atoms in the original pendent groups. As attached pendent accelerator groups are built up in the initial part of the vulcanization reaction before a network is formed, a dual vulcanization system was used, first curing with dicumyl peroxide followed by the addition of labeled sulfur and accelerator by infusion from benzene solution. Analyses were made by liquid scintillation counting after degrading the vulcanizates in p-xylene solution with t-butyl hydroperoxide using osmium tetroxide as a catalyst. The initial number of sulfur atoms in the pendent groups was found to be 3 for an efficient low sulfur system and 16–17 for a conventional high sulfur system. Oxygen absorption measurements have shown that vulcanizates having a low amount of sulfur in the original pendent groups resulted in superior aging. The presently proposed scheme of vulcanization requires the formation of a zinc perthiomercaptide as the actual sulfurating agent. Reaction with rubber gives rise to attached pendent groups which are the precursors to the formation of crosslinks. Results have shown, however, that pendent accelerator groups were formed not only in the presence of zinc but also in its absence where no zinc complex is possible. This would mean that the mechanism for the formation of pendent groups, at least in the absence of zinc, may be different from that presently accepted.
Fractionation of Polymers
Authors: Smith W. V.
Published: February 2011

Fractionation is an important tool for obtaining structural information on polymers. It is also important for isolating relatively homogeneous samples of polymer to use in determining relationships between structure and properties. The most common structural information obtained from fractionation is molecular weight distribution (MWD). This is a very important factor in determining processing behavior. To a lesser extent MWD affects the properties of finished polymer products. It is quite important in helping to elucidate mechanisms of polymer formation. Development of gel permeation chromatography (GPC) over the past few years has provided a fast convenient tool for comparing molecular weight distributions. GPC is fast enough that it may even be considered as a potential means of controlling polymerization processes. The chemical composition of copolymers can be determined using fractionation techniques. For this the fractionations based on polymer solubility are particularly suitable. Thin layer chromatography also shows promise in this area. This information is of importance in respect to some physical properties such as solvent and oil resistance and crystallinity. It is also useful in elucidating mechanisms of polymerization. While the ultracentrifuge has not been used extensively in the investigation of industrial polymers, it does have the advantage of being capable of providing absolute moleclar weight information. When it is desired to establish relationships between the structure of polymers and their physical properties it is always desirable to work with polymers having a narrow molecular weight distribution and a homogeneous composition. This can frequently best be accomplished by using fractionated polymer samples. At the present time fractionations based on solubility are the principal ones used through preparative fractionations based on GPC are now possible and a limited amount of literature in this area is now appearing.
Influence of Lubricating Oil Additives on Swell-Resistant Elastomers
Authors: Bertram H. H. , Brandt D.
Published: February 2011

In the last few decades the demands made on lubricating oils have become increasingly severe; corresponding improvements in the quality of oils have been achieved primarily by adding additives of widely different composition and function. These substances, however, may severely attack elastomers which come into contact with lubricating oils, possibly making the elastomers useless within a short time. The influences of chemically defined lubricating oil additives on nitrile-butadiene, chloroprene, silicone, and acrylic rubbers are investigated at 140° C, ASTM Oil No. 1 being used as the medium. The various substances are found to have strong influences on the condition of the elastomers, depending on the structure of the polymer. See Figure 16. Sulfonated and chlorosulfonated fatty oils and hydrocarbons cause surface hardening in nitrile rubber, which results in crack formation under flexure or elongation. However, after pronounced initial deterioration of the mechanical properties, further penetration of the additive is prevented by the protective layer thus formed. Chloroprene rubber also takes part in a crosslinking reaction with these additives, though without undergoing surface hardening. Silicone and acrylic rubber, which have no double bonds in the polymer chain, are not attacked by these additives. Owing to a crosslinking reaction compounds which release hydrogen chloride, e.g., chlorinated paraffin, cause severe surface hardening in nitrile and chloroprene rubber vulcanizates, which is not restricted to the surfaces. In the case of nitrile rubber, hydrogen chloride combines with the vulcanizate. In the presence of chlorinated paraffin, acrylic rubber first softens but this is afterwards obscured by hardening. Chlorinated paraffin does not attack silicone rubber. Lead naphthenate damages acrylic and silicone rubber but stabilizes nitrile and chloroprene rubber. With reference to nitrile rubber, as an example, it is shown that the resistance of the elastomers greatly depends on the temperature and concentration of the additive and that both synergistic and antagonistic effects are possible when additives are used in conjunction with one another. The purposes of this study have been, firstly, to show that the differences in the behavior of elastomers in technical lubricating oils are usually due to the influence exerted by additives, and, secondly, to encourage the lubricating oils industry to consider and make allowances for the problems of the rubber industry.
Elastomer Abrasion at high Velocity
Authors: Staklis A. A.
Published: February 2011

The series of abrasion runs conducted indicated several trends in rubber abrasion or wear in tests conducted under conditions representative of ACLS braking. Major effects were found for variations in filler level and experimental or abrasion conditions. Optimum filler (SAF) level was found to be between 55 and 65 phr in Butyl-HT. Beneficial effects in terms of reducing rubber adhesion to the braking surface were provided by steel fibers and by talc at 2-8 phr. Rubber abrasion mechanism was found to be predominantly mechanical. The rate of wear, however, was strongly affected by heating at the abrasion interface.
Kinetics and Mechanism of the Reaction of 2-Mercaptobenzothiazole with N-(Cyclohexylthio)Phthalimide and Related Compounds
Authors: Son P. N. , Andrews K. E. , Schooley A. T.
Published: February 2011

Kinetic studies show that 2-mercaptobenzothiazole (MBT) reacts faster with N-(cyclohexylthio)phthalimide (CPT) than with such accelerators as N-t-butyl-2-benzothiozolesulfenamide (BBTS) or 2-(4-morpholinothio)benzothiazole (OBTS). Furthermore, the reaction between N-(cyclohexylthio)-o-benzoic sulfimide (CTBS) and MBT is so fast that it reacts almost instantaneously even at room temperature. However, CTBS is not a good retarder due to its thermal instability.
Acrylonitrile Copolymerizations. IV. Butadiene Copolymerization
Authors: Vialle J. , Guillot J. , Guyot A.
Published: February 2011

The kinetics of the acrylonitrile-butadiene radical copolymerization, carried out in solution at 60° C, have been followed using gas chromatographic analysis. Remote unit effects are observed only on the butadiene-ended radicals, but they seem to involve a quite long sequence of butadiene units. The following values of the reactivity ratios are proposed: rA=0.067, rAB=0.70, rABB=0.66, rABBB=0.17, rBi→0.01 to 0.06 for large values of i. The results are discussed in terms of either polarity effects, or differences in reactivities between 1,4- or 1,2-butadiene radicals, or finally of charge transfer complexes between the monomers.
New Polymer Systems: Chain Extension by Dianhydrides
Authors: Rhein R. A. , Ingham J. D.
Published: February 2011

New highly stable polymers are required for materials applications on future long-term planetary missions. This article presents the results of a systematic investigation on the use of anhydrides to prepare stable elastomeric materials using mild reaction conditions. The three anhydrides investigated were found to provide effective chain extension of hydroxy-terminated poly(alkylene oxide)s and poly(butadiene)s. These were tetrahydrofuran tetracarboxylic dianhydride, pyromellitic dianhydride, and benzophenone tetracarboxylic dianhydride. The most effective catalyst investigated was ferric acetylacetonate, which resulted in chain extension at 333 K (60° C). A novel feature of these anhydride reactants is that they are difunctional as anhydrides, but tetrafunctional if conditions are selected that lead to reaction of all carboxyl groups. Therefore, chain extension can be effected and then followed by crosslinking via the residual carboxyl groups.
Rheology of Adhesion
Authors: Kaelble D. H.
Published: February 2011

This discussion has outlined a series of considerations which begin with engineering definitions of system response of adhesive joints and end with propositions involving molecular interactions at interfaces. Connecting these extreme aspects of the argument is the central subject of the micromechanics of bonding and fracture. Cavitation theory, as simply described by Equations (6a) and (7), illustrates the scale of microresponse in which both the thermodynamic and rheological aspects of adhesion phenomena achieve a parity when applied to cavities of radius r=0.1 to 10 μ. The discussion of the micromechanics of polymer fracture provides ample evidence that pure materials, polymer composites, and adhesive joints, need to be described in terms of their microdefects. The several mathematical models for crack propagation which are imposed upon fracture mechanics data tend to oversimplify the visualization of the true micromechanisms of fracture. The fuller development of micromechanics theory and experimental analysis promises to be an important area of current developments in the better understanding of macroscopic response of filled systems, fiber reinforced composites, and adhesively bonded structures. Recent developments in the several theories of intermolecular forces and the physical chemistry of bonding provide new impetus to the chemist to design optimized polymeric materials with finely adjusted balances of surface and bulk properties. The fuller visualization of adsorption-interdiffusion bonding as a process involving both the two-dimensional interface and the three-dimensional interphase defines bonding as both a thermodynamical and a rheological process. The microstages of bond formation are somewhat the reverse of the stages of microfracture listed earlier. The microdefects that commonly exist in polymeric materials and polymer composites tend to indicate that the viscoelastic constraints typical of polymer chains and networks play an important role in preventing equilibrium bonding in the simple thermodynamic sense as expressed by idealized liquid—liquid or liquid—solid interactions. The current development and application of a refined thermodynamical and rheological argument to both bonding and fracture processes stands as a central issue in directly correlating the molecular criteria of adhesion and performance of bonded systems. Any of the simple mathematical relations introduced in this discussion may be expressed with greater detail and precision by incorporating detailed statements concerning chemical composition, macromolecular structure, and free volume state of the polymeric adhesive.
A Method of Analysis for Compressible Viscoelastic Solids
Authors: Ting E. C.
Published: February 2011

Most of the solutions in the development of methods of viscoelastic stress analysis have dealt with incompressible materials or materials with restrictions in dilatation. It is influenced in part by the increasing complexity due to the additional operator which represents the viscoelastic characteristics in dilatation. A simple procedure of solution is suggested in this paper which shows that a certain class of problems for compressible materials can be solved with the similar simplicity as the analysis of corresponding incompressible solids. Examples are given for problems with spherical boundaries.
Finite Axisymmetric Deformations of Initially Cylindrical Reinforced Membranes
Authors: Kydoniefs A. D.
Published: February 2011

We consider the axisymmetrie deformations of an initially cylindrical membrane composed of an elastic, homogeneous, isotropic and incompressible material reinforced with a two-parameter system of perfectly flexible and inextensible helicoidal cords of variable pitch. The undeformed configuration is determined so that the deformed membrane has a given axial section under specified internal pressure. The corresponding stress field and cord tensions are obtained. The solution given is exact and valid for the general form of the strain—energy function.
Dynamic Properties of a Model Reinforced Elastomer. Styrene-Butadiene Reinforced with Polystyrene
Authors: Kraus Gerard , Rollmann K. W. , Gruver J. T.
Published: February 2011

The dynamic storage and loss moduli of SBR 1503 reinforced with 400 A˚ polystyrene particles were measured at 110 cps over a 200° temperature range. The effect of the polystyrene filler on the rubber was to raise the storage modulus dramatically in the rubbery zone, but only slightly in the glassy region of viscoelastic response. As a result the transition zone appeared broadened and shifted toward higher temperature. Corresponding changes were observed in the loss maximum with a shift of 4° at the highest filler content (46%) investigated. The height of the loss maximum was nearly unaffected. The loss tangent of the filled and unfilled polymers showed no systematic shift with temperature and the dilatometric glass transition was raised only 2° C at the highest filler content. All the essential features of the dynamic behavior could be described in terms of the properties of the component polymers by the phenomenological equivalent mechanical model treatment of Takayanagi. It is concluded that the effects of the polystyrene filler, which resemble those of other fillers as well, need not be caused by restriction of segmental motion in the rubber resulting from elastomer-filler interactions.
Injection Molding with Natural Rubber
Authors: Wheelans M. A.
Published: February 2011

Injection moldings with natural rubber compounds having sections varying between 0.16 and 10 cm thick have been prepared. Almost any natural rubber compound can be satisfactorily injection molded. Cure time, and hence cycle time, is highly dependent on injection temperature and the art of injection molding is to inject at the highest possible temperature consistent with freedom from scorch. The injection temperature of natural rubber depends on the injection molding machine variables such as screw speed, screw back pressure and barrel temperature. Injection and mold filling time are dependent on injection pressure and nozzle orifice diameter. Rubber compounding variables influence injection molding behavior. A curing system with a relatively long, safe Mooney scorch time permits a reduction in the cure time of rubber by allowing a high injection temperature. Conventional curing systems are suitable for a wide range of injection moldings but “Efficient Vulcanization ” systems have special advantages in curing thin sections adjacent to thick ones because of their superior reversion resistance. The effects of compound viscosity are described. Extenders are shown to reduce injection temperatures and thus increase cure times. Black and white fillers are examined in their effect on injection temperature, injection time and cure time. Injection molded vulcanizates are similar in mechanical properties and oven aging resistance to vulcanizates prepared by conventional press methods.
Photo-Oxidation of Polymers without Light: Oxidation of Polybutadiene and an ABS Polyblend with Singlet Oxygen
Authors: Kaplan M. L. , Kelleher P. G.
Published: February 2011

In recent years much evidence has been accumulated to implicate electronically excited oxygen ((1Δg)) molecules as the agent responsible in photo-sensitized oxidations for the formation of allylic hydroperoxides from olefins and of endoperoxides from 1 ,3-dienes. Little regarding the mechanistic aspects of the photo-oxidative degradation of polybutadiene is known, however. To determine if electronically excited oxygen ((1Δg)) molecules can oxidize PBD, the ABS polyblend and standard samples of PBD's containing high trans, high cis, and high vinyl content were treated in homogeneous solution at low temperature with chemically produced singlet oxygen in situ. The source of the singlet oxygen was the triphenylphosphite-ozone adduct. Studies by spectroscopy, elemental analysis, viscosity determinations, and gel measurements showed only the cis- and the trans-PBD were susceptible to oxidation; no chain scission was involved in the attack of cis- and trans-PBD by singlet oxygen; the oxidation of the cis-PBD involved the initial formation of hydroperoxides which on thermal decomposition yielded gel. The trans-PBD was found to oxidize but apparently by a mechanism different from that of cis-PBD. Initial singlet oxygen attack of ABS proceeds by oxidation of the PBD portion of the polyblend. It was also observed that when only a small amount of the double bonds in the cis-PBD polymer had been oxidized to hydroperoxides, subsequent thermal treatment of this sample resulted in gross structural changes in the whole polymer.
Reaction of Radical Acceptors with Polymer Radicals formed by Mechanical Degradation of Vulcanizates
Authors: Razgon D. R. , Drozdovskii V. F.
Published: February 2011

The authors investigated, by the EPR method, the kinetics of the accumulation and subsequent deterioration of polymer radicals, resulting from the mechanical degradation of sulfur and peroxide vulcanizates of SKMS-3 ARKM-15 rubbers at 80 ° K. The reaction of these radicals with a number of acceptors were also studied. The polymer radicals, independently of their nature, will deteriorate at temperatures near the Tg. Polysulfide radicals are completely destroyed at 240–250° K, the hydrocarbon radicals at 220–235° K, and the peroxide ones at 200–210° K. The peroxide radicals will react, at 80° K, with Ionol and alkylphenol disulfides to form phenoxy radicals, and with trichlorothiophenol to produce thiol radicals, but will not react with the stable nitroxide radicals or with di-(trichlorophenyl) disulfides. The carbon free radicals will react, at 150–200 ° K, with trichlorothiophenol and with alkylphenol disulfides, resulting in formation of polysulfide radicals, and, at 80° K, they will react with stable nitroxide radicals to form 2,2,6,6-tetramethyl-4-hydroxypiperidyl. The polysulfide radicals, within a temperature range of 80 to 250° K, do not react to any appreciable degree with any of the radical acceptors investigated.
The Use of a Mechano-Lattice Analogy for Determining the Abrading Stresses in Sliding Rubber
Authors: Yandell W. O.
Published: February 2011

A rigorous mechano-lattice analogy analysis for calculating the hysteretic sliding friction of and stresses in rubber sliding on variously shaped asperities is presented. The analysis allows large strains and any Poisson's Ratio, rigidity or damping factor of the rubber. The analysis was used to calculate the distributions of minor principal stress in rubber sliding over smooth and frictional prisms with different sharpnesses and over a cylinder. The potentially disruptive stress regions were thus revealed and compared. The effect of changes in the Poisson's Ratio and of the damping factor of the rubber were also examined. It was postulated that the fine texture generates more stress-strain hysteretic heat which may lead to the more rapid abrasion observed by some workers.
Monomer Sequence Distribution in Ethylene Propylene Elastomers. I. Measurement by Carbon-13 Nuclear Magnetic Resonance Spectroscopy
Authors: Carman C. J. , Wilkes C. E.
Published: February 2011

The carbon-13 chemical shifts of ethylene propylene copolymers were found to be very sensitive to monomer sequence distribution. Methylene resonances were interpreted in terms of methylene sequence length and tertiary carbon resonances were interpreted in terms of propylene centered pentad sequences. Propylene inversion was detected and measured quantitatively in the spectra. A formula was derived for calculating r1·r2, which is independent of monomer feed, and which is based on measuring contiguous and isolated propylene sequences in the copolymer. The interpretations are shown to be consistent for copolymers containing 26, 34, and 62 mole% propylene. The r1·r2 products were determined for each of these polymers. Calculation of copolymer composition based on the 13C chemical shift assignments gave excellent agreement with the compositions as determined by infrared and 1H NMR. A formula was derived, based on copolymerization theory, for calculating the reactivity ratio product, r1·r2, directly from the copolymer composition (% ethylene) and the ratio of contiguous to isolated propylene sequences. Using this formula an average value for r1·r2=0.42±0.02 was determined for the copolymers made with vanadium acetylacetonate-diethylaluminum chloride catalyst system.
Characterization of Carbon Black Structure by Mercury Penetration
Authors: Moscou L. , Lub S. , Bussemaker O. K. F.
Published: February 2011

The determination of the chain-structure of carbon black by mercury porosimetry is described. It is shown that each type of black has its own porosity curve, depending on specific surface area and degree of structure. An absolute measure for the degree of structure is proposed: The “Structure Index”, calculated from the break point in the porosity curve, the specific surface area and the density of the black. Structure Index for structureless blacks is 1.0 – 1.1, for low structure blacks 1.7 – 1.9, for normal structure blacks 2.3 – 2.4 and for high structure blacks 2.7 – 2.8.