bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Chemical Structure on the Dynamic Properties of Sulfur-Vulcanized, Carbon Black-Reinforced Natural Rubber
Authors: Doyle G. M. , Humphreys R. E. , Russell R. M.
Published: February 2011

A comparison is made of the composition and properties of the different rubber vulcanizate networks obtained by varying the ratio of sulfur to sulfenamide accelerator and by the thermal aging of vulcanizates containing predominantly polysulfide crosslinks. It is concluded that the changes in network structure which can take place, for example, during the service life of natural rubber tires are not the direct cause of failures of the type associated with rubber fatigue at high temperatures. However, a reduction in the total number of crosslinks can accelerate failure by increasing the amount of heat generated during flexing. More stable networks giving improved resistance to fatigue at high operating temperatures are obtained by the use of higher ratios of accelerator to sulfur than are conventionally employed.
Evaluation of the Thermal Stress Relaxation Method for the Estimation of Polysulfidic Crosslinks in Natural Rubber Vulcanizates
Authors: Farmer J. H. , Stuckey J. E.
Published: February 2011

The variation of the polysulfidic crosslink content of a natural rubber vulcanizate during cure has been determined from thermal stress relaxation data obtained using a Monsanto Rheometer and the results have been compared with those obtained by chemical probe analysis. No correlation could be found. Attempts to isolate the relaxation due solely to polysulfide crosslink interchange gave no better agreement and it is concluded that competing maturing reactions prevent such a resolution. The first order rate constant for the fast relaxation attributed to polysulfide crosslink exchange reactions has been found to vary in a linear manner with the total crosslink density of the vulcanizates.
Influence of Vibrations on the Viscoelastic Behavior of Monodisperse Polybutadienes
Authors: Vinogradov G. V. , Yanovsky Yu G. , Isayev A. I. , Shatalov V. P. , Shalganova V. G.
Published: February 2011

The viscoelastic behavior of monodisperse polybutadienes is studied at different amplitudes of cyclic deformation. The concept of initial relaxation spectrum is introduced, this spectrum corresponding to small amplitudes. Under the action of high amplitudes the relaxation spectrum changed. This changed-effective spectrum can be calculated by means of the linear theory of viscoelasticity. The initial spectra of monodisperse polybutadienes have maxima. Under the action of high amplitudes the long-time parts of the spectra are truncated and the maxima shift into the short-time regions. There is an unambiguous correspondence between the amplitude of the deformation rate on cyclic deformation and the rate of shear on continuous deformation. It is shown that the length of the high-elasticity plateau, estimated on a logarithmic scale of relaxation times, and the maximum relaxation times of polybutadienes, as well as their initial Newtonian viscosities are dependent on molecular weight to a power of 3.6. The apparent viscosity is calculated, making use of the approximate initial relaxation spectrum concept, the law of change of its long-time boundary with the shear rate, and the commonly known relation of the linear theory of viscoelasticity. The results of these calculations were found to agree approximately with the data obtained under conditions of continuous deformation.
On the Linear Constitutive Equations of Transversely Isotropic Incompressible Elastic Materials
Authors: Demiray H. , Levinson M.
Published: February 2011

The linear constitutive equations of a transversely isotropic, incompressible, elastic material are derived in this paper as a limiting case of the constitutive equations for the corresponding compressible materials. These equations should be appropriate for the stress analysis of products fabricated from certain laminated, reinforced rubber composites. Some details of a problem concerned with the stress concentration around a circular hole are also given.
Stimulation of Latex Flow in Hevea Brasiliensis by 4-Amino—3,5,6-Trichloropicolinic Acid and 2-Chloroethanephosphonic Acid
Authors: Abraham P. D. , Wycherley P. R. , Pakianathan S. W.
Published: February 2011

Application of 4-amino—3,5,6-trichloropicolinic acid, alone or in mixtures with 2,4,5-T, gave larger and more persistent yield responses than application of 2,4,5-T alone in one experiment, but this was not confirmed in another. One morphactin was moderately effective but another was ineffective. N-dimethylamino-succinamic acid did not stimulate longer flow or give larger yields. Acetylene, ethylene, halogenoparaffins and 2-chloroethanephosphonic acid (which releases ethylene in plant tissues) were all effective in prolonging flow and increasing yields. All effective non-gaseous stimulants of latex flow seemed to have one common feature, namely, production of ethylene.
Properties of Poly(Alkylene Oxide) Elastomers
Authors: Hsieh H. L. , Wright R. F.
Published: February 2011

The catalyst comprised of triisobutylaluminum, zinc acetylacetonate, and water was used to prepare homopolymer of epichlorohydrin; copolymers of epichlorohydrin with propylene oxide, ethylene oxide, and allyl glycidyl ether; and terpolymers of epichlorohydrin, propylene oxide, and allyl glycidyl ether and of epichlorohydrin, ethylene oxide, and allyl glycidyl ether. The vulcanizates of these rubbers provide variations of stress-strain and dynamic properties, freeze point, hardness, and solvent resistance depending on the type and amount of comonomer. In general, these rubbers have excellent heat, ozone, and oxidation resistance as well as oil and solvent resistance.
Equation-of-State Parameters for Poly(Dimethylsiloxane)
Authors: Shih Hsiang , Flory P. J.
Published: February 2011

The thermal expansivity α=V−1(∂V/∂T)p and thermal pressure coefficient γ=(∂p/∂T)v for poly(dimethylsiloxane) (PDMS), mol wt ≈ 105, have been determined accurately over the temperature ranges 20–207 and 24–161°, respectively. Characteristic parameters ν*, T*, and p* calculated from these results are compared with those for other polymers and for low molecular weight liquids. For PDMS, α is much larger and γ much smaller than for any other polymer. The characteristic pressure p* appears to be a more reliable index of the intermolecular energy than the cohesive energy density for this purpose. It is approximately the same for a polymer as for corresponding low molecular weight liquids. For PDMS and HMDS (hexamethyldisiloxane) p* assumes exceptionally low values of 341 and 358 J cm−3, respectively, which are duplicated only by the fluorocarbons (p* ≈ 360 J cm−3).
Study of Configurational Sequence Structures of Poly(Butadiene)s by Carbon-13 Proton Decoupled Fourier Transform Nuclear Magnetic Resonance Spectroscopy
Authors: Alaki Yasuhide , Yoshimoto Toshio , Imanari Mamoru , Takeuchi Makoto
Published: February 2011

Carbon-13 proton nuclear magnetic resonance (NMR) of poly(butadiene) s consisting of various ratios of cis-1,4-, trans-1,4- and 1,2-structures were measured by the pulsed Fourier transform NMR method. The spectra of poly(butadiene)s with two or three kinds of butadiene configurations show several new signals which were not observed for homopolymers comprising merely one kind of butadiene configuration. All of these peaks are ascribed to the carbons linked by different kinds of configurations. From these results, the configurational sequence structure of butadiene units in polymer chains has been revealed.
Comparisons of the Carbon-13 Nuclear Magnetic Resonance Spectra of Some Solid Cis- and Trans-Poly(Isoprene)S
Authors: Schaefer Jacob
Published: February 2011

Fourier transforms have been obtained of the 1H and 2H simultaneously noise-decoupled, natural-abundance, 22.6-MHz 13C free-induction decays of solid cis- and trans-poly (isoprene), cis-poly(isoprene-з-d1), and carbon-black-filled cis-poly (isoprene). Carbon-13 line widths and Overhauser enhancements have been measured from the phase-corrected normal and selectively saturated absorption spectra, and spin-lattice relaxation times measured from partially relaxed Fourier transform absorption spectra. The spin-lattice relaxation times and Overhauser enhancements of the individual carbons of the amorphous part of trans-poly (isoprene) are all greater than those of the corresponding carbons of cis-poly (isoprene), and, excluding the deuterated carbon, of cis-poly (isoprene-з-d1). These spin-lattice relaxation times are interpreted in terms of a dipolar relaxation mechanism modulated by the segmental motion of the chain. The greater relative segmental flexibility of the trans-poly (isoprene) chain leads to longer spin-lattice relaxation times. The flexibility of the trans chain also permits more of its segmental motions to satisfy the extreme narrowing conditions, and this leads to the larger observed Overhauser enhancement. The various spin-lattice relaxation times of the individual carbons of cis-poly (isoprene) are not noticeably affected by the addition of carbon black. However, the 13C line widths are affected by the filler. The line widths of individual carbons of the carbon-black-filled cis-poly (isoprene) are greater than those of ordinary cis-poly (isoprene) by factors of 5–10. The broadening is different for different carbons. These results are interpreted in terms of the exclusion by the filler of the polymer from some spatial orientations leading to only partial motional narrowing of the NMR lines. Even in the absence of a filler, factors such as chain entanglements can prevent total isotropic motional narrowing of the lines. This effect can be used to explain the absence of any pronounced line narrowing upon selective deuteration of cis-poly (isoprene), even though large differences in spin-lattice relaxation times result. The 13C line widths of all of these solid, rubbery polymers are as much as a factor of 20 less than the 1H NMR line widths of the same polymers. The narrow lines are attributed to the isolation of the 13C spins from dipolar interactions with each other and with most protons.
Rubber Stocks for Improved Performance of Polyester Cord Tires
Authors: Iyengae Y. , Ryder D. F.
Published: February 2011

Carcass stocks were developed with acceptable properties and good adhesion to polyester tire cords after severe heat aging in laboratory tests. These stocks contained vulcanization accelerators that did not liberate amines and were based either on synthetic poly (isoprene) (IR)/butadiene/styrene (SBR) elastomer blends, as recommended in previous work, or natural rubber/SBR compounds containing an additive to inhibit the deleterious effects of amines present as impurities in NR. Standard SBR/poly (butadiene) (BR) tread stocks containing amine-free accelerators were developed to match the exceptionally long scorch time and good physical properties attained with sulfenamide accelerators normally used in such stocks. Large batches (˜400 pounds) of amine-free tread stock were processed without any scorch problems on a commercial Banbury mixer and tread extruder. With these tread stocks, containing amine-free accelerators, it is possible to build completely amine-free polyester cord tires. In a variety of wheel tests designed to assess durability under extreme conditions, 2-ply tires with cords of Dacron polyester containing amine-free tread and carcass stocks showed highly improved durability (180-440 per cent) compared to control tires made with stocks containing amines. In a wheel test simulating the running of a tire underinflated for an extended period (low pressure endurance test), tire durability increased with decreasing amine content of the rubber stocks used. In a special high temperature tire fatigue test to produce break-above-bead failures, tires combining an experimental Dacron polyester with low carboxyl content and in amine-free stocks ran 350 per cent longer than tires of standard T-68 Dacron in amine containing stocks. These tests clearly illustrated the additive benefits of combining an improved polyester with stocks having reduced amine content.
Multidetectors for Analysis of the Composition of Copolymers as a Function of Molecular Size Distribution by Steric Exclusion Chromatography
Authors: Harmon D. J. , Folt V. L.
Published: February 2011

Analysis of molecular size distribution of polymers by steric exclusion liquid chromatography (GPC) is well known. Problems exist, however. These problems involve copolymers and polymer blends. The objectives of the research were to develop methods of analyzing comonomer distribution in copolymers, to study the breakdown of one polymer independent of another in a polymer blend, and to obtain any additional information as might be available. The separations were performed on a Waters Model 200 Gel Permeation Chromatograph. Detectors employed were a Waters R-4 differential refractometer, a Wilks Miran-1 infrared analyzer, and a Beckman Model 144 UV photometer. Examples are given of analysis of average styrene, styrene distribution, and oil content of oil extended SBR. The data is compared with that obtained by other methods. In general the agreement is good. The ability to examine one polymer of a blend independent of the other is also demonstrated. Since elastomers are frequently used as blends, this becomes very important to such studies as milling and extrusion behavior.
Latex Maturation Studies by Low Angle Light Scattering Photometry
Authors: Myers M. E. , Wims A. M. , Lee W. R.
Published: February 2011

Basic information on the relationship between processing variables and the physical chemical changes occurring during the “precure” of latex blends is required for optimum process control. To obtain this type of information, the particle size and particle size distribution of a latex blend undergoing a maturation or precure treatment were monitored by low angle light scattering techniques. The absence of any measurable particle size change during precure indicates that the process is simply an initiation of crosslinking within the individual latex particles which is caused by penetration of molecular sulfur and other activators and accelerators. Volume swelling measurements were performed at intervals to determine the degree of precure attained by the blend.
The Thermal Decomposition of Amine Complexes of Zinc Bis(Dimethyl-Dithiocarbamate)
Authors: Gelling I. R.
Published: February 2011

It has been shown that primary alkylamine complexes of zinc bis(dimethyl-dithiocarbamate) (ZDMC) are thermally unstable. The reaction proceeds via an amine exchange reaction to yield an intermediate zinc alkyldithio-carbamate dimethyldithiocarbamate which then decomposes to give N-alkyl-N′, N′-dimethylthiourea, the dimethylammonium salt of dimethyldithio-carbamic acid, and zinc sulfide as the major products. Secondary amine complexes undergo similar initial amine exchange reactions but the new dithiocarbamates produced are stable. Tertiary amine complexes undergo neither of these reactions. These reactions can occur when zinc dithiocarbamates are used as accelerators for the vulcanization of rubber.
Bond Rupture during Ozone Cracking of Torsional Loaded Styrene-Butadiene Rubber
Authors: Devries K. L. , Moore N. B. , Williams M. L.
Published: February 2011

The molecular bond rupture rate during ozone attack of torsionally loaded rubber was determined from electron paramagnetic resonance (EPR) measurements. The rupture rate was successfully correlated by a Griffith-type energy balance to the strain-energy release rate in the samples. These observations substantiate the results from a similar study on tensile loading previously reported. In both cases there is a one-to-one correspondence between the rate of bond rupture (or crack growth) and the rate of energy release from the strain field and external work. A fracture energy, γn, of approximately 5×10−12 (α20 per cent) ergs per free radical formed during the cracking was experimentally determined.
Performance of Tread Compounds in Various Tire Constructions
Authors: Wilder C. R. , Haws J. R.
Published: February 2011

There are now three major types of construction used in passenger car tires—cross-ply (or bias), belted cross-ply, and radial. The same rubber compounds and tread designs may not always provide optimum performance in these but it was considered of interest and importance to compare the relative performance of several typical tread compounds on each type of tire. Four tread compounds were applied as retreads to four tires of each type. These were road tested over a highway route which included some rapid cornering. Two polymer systems were employed: 1. a low vinyl, 85/15 butadiene/styrene, oil-extended, solution copolymer and 2. a 40/60 blend of high-cis polybutadiene/SBR 1712. These were reinforced with N330 (HAF) and N339 type carbon blacks. Some other tire tests were also available for supporting evidence. The solution copolymer gave 8 to 12% better resistance to abrasion than the polybutadiene/SBR blend. The N339 carbon black was 10 to 15% better in wear resistance than N330 black and the best combination was 23% improved over the poorest. These relationships were affected very little by the type of tire construction and indicate that treadwear data on compounds in one type of tire may be useful to predict performance in another. Results also indicate that treads of equal composition will provide a mileage ratio of approximately 1 to 1.5 to 2 or 2.5 on cross-ply, belted cross-ply, and radial tires, respectively.
Adsorption and Calorimetric Investigations on Carbon Black Surfaces. III. Immersion Heats in Model Elastomers and Isosteric Heats of Adsorption of C-4 Hydrocarbons
Authors: Wade W. H. , Deviney M. L. , Brown W. A. , Hnoosh M. H. , Wallace D. R.
Published: February 2011

The heats of immersion of U-1 channel and SAF, SPF, HAF-HS, and HAF furnace blacks have been measured at 25° C in three isoprenoid olefins and four liquid elastomers of the polybutadiene, polyisoprene, and SBR types. An extensive microcalorimeter redesign was necessary because of the high viscosity of these latter fluids. The immersion heats observed with the liquid elastomers were similar to n-decane immersion heats and there was little evidence for specific interactions between these liquids and any of the blacks. The possibility that the very high structure SPF black gives slightly enhanced immersion heats should be further investigated. Since only integral immersion heats could be measured with the non-volatile liquid elastomers, the possibility is not ruled out that specific, relatively high-energy interactions may occur between the adsorbate and a very small fraction of the black surface. The similarities between the immersion heats with n-decane and the liquid elastomers indicate that almost all of the carbon black surface is accessible to the polymer segments. It appears that the rate of heat evolution may be considered a measure of the rate of attainment of intimate molecular contact between the liquid and carbon substrate. The enhancement in heat of wetting with increasing chain length over the C6 to C16 n-alkane series reported by others with a highly uniform, graphitized black was not observed with HAF. Isosteric heats of adsorption of n-butane and butene-1 at low surface coverages on several carbon blacks were calculated from adsorption isotherms obtained with a precision microgravimetric system. The isosteric heats as a function of coverage curves were typical of those expected for heterogeneous surfaces and reflected the presence of high energy physical adsorption sites at low coverages (θ<0.1).
The Effect of Carbon Black Surface Properties and Structure on Rheometer Cure Behavior
Authors: Cotten G. R.
Published: February 2011

The cure behavior of SBR and NR compounds was examined using the Monsanto Rheometer. The three cure parameters—induction period (td), rate of crosslinking reaction (k2) and maximum increase in torque (ΔL)—were derived from the Rheometer torque curves. The data so obtained were used to calculate Westlinning's αF-values. It was shown that (1) k2 decreases with increasing total acid concentration at the carbon black surface and (2) the value of αF is related to the filler structure and the crosslink density of the rubber matrix. It was also demonstrated that the crosslink density, as measured by ΔL, is influenced by the surface chemistry of carbon black. In SBR stocks the crosslink density increases with increasing total acid concentration, while in NR compounds the reverse is true. These findings were confirmed by examining the tensile properties of regular and oxidized HAF-LS black in SBR and NR compositions. Thus the effect of carbon black surface chemistry on crosslink density can be estimated, for a given recipe, from the value of k2. An empirical relationship between the cure parameters (αF and k2) and filler structure (as measured by extrusion shrinkage) was derived and tested on a wide range of carbon blacks. This relation gives a much better correlation coefficient than the simple relation between extrusion shrinkage and αF alone. Thus by full use of the Rheometer data, the extrusion shrinkage or other structure-related properties of carbon black filled stocks can be predicted.
Electron Impact-Induced Fragmentations of 2-Benzothiazole Sulfenamides and Related Compounds. Correlation with Rubber Vulcanization Activity
Authors: Potts K. T. , Brugel E. G. , D'Amico J. J. , Morita E.
Published: February 2011

A correlation has been made between the activity of commercial rubber accelerators and vulcanizing agents and their mass spectral fragmentation patterns.
Raman Spectroscopic Studies of the Vulcanization of Rubbers. III. Studies of Vulcanization Systems Based on 2-Mercaptobenzothiazole
Authors: Coleman M. M. , Shelton J. R. , Koenig J. L.
Published: February 2011

The shoulder observed at approximately 440 cm−1 in Raman spectra of CB vulcanizates prepared from MBT based vulcanizing systems has been shown to consist of two components. There are Raman lines contributing at 440 cm−1 and 424 cm−1. The former is due to ZnO present as an extra-network material while the latter appears to be associated with polysulfidic structures. The Raman line at 505 cm−1 seen in extracted vulcanizates prepared from CB-MBT-Sulfur-ZnO-Lauric acid recipes does not appear to be solely due to disulfidic structures. The major contribution appears to be associated with an unsaturated cyclic sulfide and is most probably due to a structure of the type (I). If the assignment to cyclic sulfidic structures such as (I) is confirmed, it will have major significance with regard to the mechanism of accelerated sulfur vulcanization.
The Radiation Curing of Elastomers. I. Physical Strength
Authors: Pearson D. S. , Böhm G. G. A.
Published: February 2011

Data has been presented which shows that sulfur crosslinks have very little importance in producing maximum tensile strength in amorphous polymers. The results suggest that the distribution of crosslinks, especially in the case of crystalline polymers, is. a factor to be considered. In general, radiation cured elastomer compounds have physical strength properties very similar to sulfur or peroxide cured compounds. This similarity has been noted for a wide number of other elastomers not reported here. The observed strength deficiency is minor in degree and of little industrial importance provided the other properties are not too different. These properties such as fatigue life, abrasion resistance, and hysteresis will be discussed in a later publication.
Solvent Effects in Styrene—Butadiene—Styrene Block Copolymer Cast Films and Evidence for Supermolecular Ordering by X-Ray and Light Scattering
Authors: Pillai P. S. , Livingston D. I. , Strang J. D.
Published: February 2011

It has been found that solution-cast films of an SBS block copolymer (Kraton 1101) have two orders of phase structure. The first is of molecular dimension and consists of elongated polystyrene domains (≈ 200 A˚) dispersed in a polybutadiene matrix. There is also a supermolecular heterogeneous structure of spherical domains of fractional micron size. A somewhat larger nearest neighbor distance is also seen. The domain size and separation are larger for the polymers cast from solvents for polystyrene than those cast from a solvent for polybutadiene alone. Furthermore, SBS films cast from good solvents for polystyrene exhibit additional supermolecular ordering in contrast to the more random arrangement of the others.
The Migration of Extender Oil in Natural and Synthetic Rubber. VI. The Use of Oil Type Molecules as Penetrants to Elucidate Elastomeric Molecular Structure
Authors: Corman B. G. , Deviney M. L. , Whittington L. E.
Published: February 2011

Previous work in diffusion of whole extender oil and extender oil fractions in practical rubber compounds has shown the nature of the rubber matrix to be the major controlling factor. Therefore, a sensitive diffusivity approach, using radiotracer labeled hydrocarbon penetrants of sizes comparable to the size of a rotating segment, was used to study various aspects of the matrix structure on penetrant diffusion for polybutadiene, styrene—butadiene, and Butyl rubbers. These results were compared with fractional free volume measurements made by a thermal expansion technique. Neither fractional free volume nor diffusivity of phenyldodecane, benz-a-anthracene, or n-octadecane was affected by 5-fold variations of crosslink density or by variations in loading of 10 to 80 parts of carbon black (HAF-LS); nor were they affected by changes from FEF to SAF black at a 50 phr level. Glass transition temperature and fractional free volume are both affected by increasing percentages of benzene or phenyldodecane, While diffusivity rises with increasing dilution, states of equal free volume in different elastomers are not states of equal diffusivity; for example, at a fractional free volume of 0.10, corresponding to 20% benzene in both polybutadiene and Butyl at 70° C, the diffusivity of benzene in Butyl is lower by a factor of 15. Comparison of diffusivity of large penetrants with their cross-sectional area gives two basic curves, one for flexible penetrants and another for molecularly rigid species. These results are explained in terms of a distribution of free volumes, wherein only holes above a critical size are effective in diffusion. Swelling the system with aromatic diluent greatly increases the total fractional free volume, but only slightly the number of holes above this critical size. To understand the diffusivity of rigid molecules in elastomers, a probability factor must be applied in estimating their effective cross-sectional area.
Identification of Elastomers by Thermal Analysis
Authors: Sircar A. K. , Lamond T. G.
Published: February 2011

Degradation of polymers by thermal and thermooxidative reactions is associated with either evolution or absorption of heat which can be followed by differential scanning calorimetry. In the present investigation, DSC thermographs of elastomers between 0° C and 500° C in nitrogen (thermal degradation) and oxygen (thermooxidative degradation) were used for identification of the elastomers from their degradation patterns. Based on the nature of the thermographs of the raw polymers in nitrogen, the elastomers studied may be divided into the following three main groups: (a) those which show an exotherm, (b) those which show an endotherm, and (c) those which show multiple peaks of endo- or exotherms. Identification is aided in some cases by the thermographs in oxygen as well as by the physical transitions. The nature (exo- or endo-) and shape of the thermal patterns and the temperature domain at which the reactions take place depend on the molecular structure, configuration, chemical composition, and nature of the substituents as well as on the environment. Consequently, thermal and thermooxidative degradation curves may be used as a “fingerprinting” device which can identify many polymers, difficult to identify by other methods.
Gel Permeation Chromatography of Natural Rubber
Authors: Subramaniam A.
Published: February 2011

The Waters Model 200 Gel Permeation Chromatograph has been used to study the molecular weight distribution of natural rubber. The cumulative weight distribution curve of synthetic cis-polyisoprene from the GPC method showed fair agreement with the distribution obtained by fractional precipitation. For natural rubber the agreement was not so good. Natural rubber samples from six clones of Hevea Brasiliensis were examined with the GPC. Differences were observed in their distributions. Five clones showed a distinct bimodal distribution. The weight and number average molecular weights from the GPC were found to be too low. Some possible reasons for this have been suggested.
Stress Relaxation Mechanisms in Rubbers Reinforced with Carbon Blacks
Authors: Bartenev G. M. , Lyalina N. M.
Published: February 2011

1. In vulcanized rubbers containing blacks a multi-stage mechanism for stress relaxation was observed. It was discovered that the stress relaxation process consists of five fundamental processes: the first three relaxation processes, related to the slow stages of physical relaxation within the bulk of the rubber, have no connection with the fillers (“soft” domains); the fourth process has to do with the relaxation in the black-rubber domain; the fifth process involves the chemical relaxation of vulcanizates. 2. The fundamental mechanisms of the first 3 relaxation processes in the soft domains have the same activation energy values and the same segmental mechanism as the rearranged domains found in supermolecular weight structures, which are also present in unfilled vulcanizates. 3. In the investigated stress range of up to 200% elongation, the activation energy for the first 3 relaxation processes in the soft domains of filled vulcanizates is not a function of the deformation strain, whereas the activation energy of the fourth relaxation process in the black-rubber domains of filled rubbers is a function of the deformation and of the filler content. For these reasons, rubber loaded with carbon blacks, in contrast to unfilled rubbers, possess the typical nonlinearity of viscoelastic materials. 4. The activation energies of the relaxation processes in the black-rubber domains decrease in a linear fashion with the value for the initial tensile stress in filled vulcanizates, and decrease in like manner for vulcanizates containing different proportions of fillers. The kinetic units, determined from the activation energies of these processes, appeared to be segments of chains with activation energies of up to 40% more than the activation energies of the physical relaxation processes in the soft domains. The other kinetic units of the processes proved to be black particles, the dimensions of which were calculated from the values for the coefficients in the formula for relaxation time.
Oxidation of Vulcanized Natural Rubber
Authors: Barnard D. , Cain M. E. , Cunneen J. I. , Houseman T. H.
Published: February 2011

The chemistry of oxidative main chain scission in NR and its vulcanizates has been investigated using radiolabelled 2,4-dinitrophenyl hydrazine and dimedone. In this way the number of scission events has been measured and the initial products of oxidation identified and estimated. Product studies have also been carried out with 2-methylpent-2-ene, 2-methyloct-2-ene, and 2,6-dimethylocta-2,6-diene. From these results a more simple and rational mechanism has been suggested for scission in natural rubber. Studies have also been made using radiochemical techniques, of the effect of sulfur compounds structurally related to the crosslinks in vulcanized NR and of conventional antioxidants, on the efficiency of scission. In general both types of compounds increase scission. The effect of mixtures of conventional antioxidants and sulfur compounds on the rate of oxidation of polyisoprenes has been followed. Usually the sulfur compounds reduce the potency of the other antioxidants and reasons are given for this antagonistic action.
Branching in Polymer Chains
Authors: Grechanovskii V. A.
Published: February 2011

The branching that occurs in molecular chains leads to extensive changes of the physico-mechanical and technological properties of various polymers, as compared with the corresponding linear polymers. For example, branched divinylstyrene rubbers, polybutadienes, and other branched elastomers possess a low elasticity, breaking strength, etc. The decrease of strength properties and the change of the dynamic and mechanical properties with the increase of the degree of branching is characteristic for such thermoplastic polymers as polystyrene, polyethylene, polyvinyl chloride, etc. There also exist considerable differences in the rheological properties of linear and branched polymers. For example, at low loads (shear stresses) linear polymers and their melts flow like newtonian fluids and possess a lower viscosity as compared with branched polymers, whereas at high loads the character of flow deviates from that of a newtonian flow, so that the viscosity of a branched polymer is lower than that of a linear polymer or almost equal. Similar regularities have also been observed for concentrated solutions. Hence, the branching, together with the regularity of the structure of polymer chains, the molecular weight, and the molecular weight distribution, represents one of the most important molecular parameters of polymers. The branching occurs during polymerization and is caused essentially by a transfer of active centers to the polymer chain.
Environmental Health Control for the Rubber Industry, Part II
Authors: McCormick W. E.
Published: February 2011

This is the last of a two-part presentation, the first having appeared a year ago. Part I dealt with the health control relating to polymer manufacturing, processing chemicals, and accelerators. Part II is confined to a discussion of antioxidants and antiozonants. While an attempt has been made to review the known toxicology and handling experience of the commercially-used antioxidants and antiozonants, there undoubtedly have been inadvertent omissions from the list.
Polyolefin Elastomers Based on Ethylene and Propylene
Authors: Baldwin F. P. , Strate G. Ver
Published: February 2011

In 1940, the first all-hydrocarbon elastomer containing limited olefinic functionality, butyl rubber, was announced. Because of its resistance to em-brittlement on aging, cracking on exposure to ozone, its impermeability to gases, and high damping capacity, this elastomer found use in inner tubes, cable insulation and miscellaneous hose, grommet, and gasket applications, generally lumped together as mechanical goods. It was the chemist's desire to prepare elastomers from other simple, inexpensive olefins, varying the structure to meet property requirements and using limited functionality to accommodate vulcanization. But no such preparative scheme was found, and, instead, attention was turned to modifications of known, substantially saturated hydrocarbon polymers to effect elastomeric properties and vulcanizability or to prepare elastomers from other raw materials, typical examples being Hypalon (chlorosulfonated, low density polyethylene) and polymers derived from epoxides and acrylates. However, K. Ziegler and coworkers pursued the matter of dimerization or oligomerization of olefins with metal alkyls until a breakthrough was made, and the catalyst system now known as Ziegler or Mulheim catalysts was discovered. This basic discovery, initially applied to the polymerization of ethylene, was expanded by Natta and his group and others to preparation of entirely new polymer structures. And, while attention was initially devoted to the preparation of miscellaneous stereoregular, crystalline homopolymers from simple olefins, it was virtually axiomatic that it would inevitably turn to the preparation of elastomeric copolymers. So, like the development of butyl rubber from polyisobutylene, ethylene/propylene elastomers (EPM) were followed by their olefin-containing terpolymers (EPDM), all of which are commercially prepared today. The Nobel Prize Award addresses by each of these aforementioned men trace the history of this important step forward in organometallic catalysis and polymer science.
Digital Method of Calculating the flow of Heat through a Tire during Vulcanization
Authors: Ambelang J. C. , Prentice G. A.
Published: February 2011

Calculation of the complete temperature cycle in a tire cure has not been published although the digital method here presented was suggested by Gehman. This general method, attributed to Schmidt, consists in dividing the article into cubical volume elements and calculating the heat flow from contiguous surrounding cubes to obtain the temperature for a given element in the next time interval. Vostroknutov reviewed the classical differential equations in a study of retreading cures but his solutions were specific rather than general and utilized the usual graphical methods.
The Determination of “Head-Head” and “Tail-Tail” Structures in Poly(Isoprene)S
Authors: Hackathorn Marjorie J. , Brock M. J.
Published: February 2011

Pyrolysis-gas chromatography has indicated the presence of head-head structures in free radical initiated poly(isoprene)s. Microozonolysis has confirmed the presence of both head-head (15-20 per cent) and tail-tail (4-7 per cent) structures in these polymers. These structures (which are absent in natural rubber) are present in lesser amounts in Lithium and Ziegler poly(isoprene)s (1-3 per cent). Non-equivalent amounts of head-head and tail-tail structures in particular samples indicate a chain reversal in which neither head nor tail units are involved. It has been postulated that chain reversal may occur at points of 3,4 addition.
Microkinetics of Lamellar Crystallization in a Long Chain Polymer
Authors: Andrews E. H. , Owen P. J. , Singh A.
Published: February 2011

The growth kinetics of single crystal lamellae grown from poly(isoprene) melts have been determined by thin film electron microscopy which also reveals the relevant microstructure. The growth rate of a continuous lamellar crystal is independent of the length of the crystal and (in the absence of crosslinks) depends only upon temperature and the chemical composition of the polymer. The temperature dependence is closely similar to that observed for bulk crystallization and spherulite growth, with a maximum crystallization rate around —24° C. The growth rate at a given temperature is extremely sensitive to the chemical composition of the poly(isoprene), being for a polymer containing 10 per cent trans-poly(isoprene) one thousandth of that for pure cis-poly(isoprene). Between these extremes the logarithm of the growth rate decreases linearly with increasing trans content. A similar effect is produced by the introduction of chemical crosslinks instead of trans units. These effects are attributed to a reduction in the probability of formation of the ‘secondary nucleus’, whose size can be calculated from the experimental data. The secondary nucleus is found to correspond to three molecular folds and this agrees well with an independent estimate obtained, by using thermodynamical theory, from the dependence of lamellar thickness on temperature.
Structural Characterization of Vulcan-Izates. XII. Efficient Vulcanization Using a Sulfenamide-Thiuram Disulfide Accelerator System
Authors: Campbell D. S.
Published: February 2011

Vulcanizates obtained from the sulfur vulcanization of natural rubber using a combination of the accelerators N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and tetramethylthiuram disulfide (TMTD) have been analyzed in terms of the numbers of poly-, di-, and monosulfide crosslinks, network-bound accelerator residues, and cyclic sulfide chain modifications as a function of cure time. The vulcanization system produced mainly monosulfide crosslinks at optimum cure, although there were differences in detail between this mixed system and a previously reported efficient sulfur vulcanization (EV) system using a high ratio of CBS to sulfur.
Low Sulfur-Sulfenamide Accelerator Combinations for Injection Molding of Cis-1,4-Poly(Isoprene)
Authors: O'Mahoney J. F.
Published: February 2011

Earlier work with cis-l,4-poly(isoprene) suggested that low levels of sulfur and high levels of sulfenamide accelerator with high levels of secondary accelerator was an excellent method for curing injection molded stocks. However, subsequent experience showed that despite the benefits of reduced sulfur concentrations on reversion, increased sulfur, increased sulfenamide, and reduced secondary accelerator concentrations were necessary for adequate cure and safety. From that experience we explored further and found that, if the sulfenamide concentration is held constant at a higher level and the secondary accelerator concentration is increased as sulfur concentration is decreased, nearly equivalent hardness and modulus can be maintained throughout most cure conditions with no loss in safety and cure rate and much improvement in reversion resistance. Studies were made in a carbon black filled stock with N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N-oxodiethylene-2-benzothiazole sulfenamide (DBS), and N-morpholinyl-2-benzothiazolyl disulfide (MBD) as primary accelerators and tetramethylthiuram monosulfide (TMTM) and tetramethylthiuram disulfide (TMTD) as secondary accelerators.
Mill Processing Behavior of Ethylene-Propylene-Hexadiene Terpolymers
Authors: Shih Chi-Kai
Published: February 2011

The mill processing behavior of ethylene/propylene/hexadiene terpolymers, one type of EPDM, has been described. In agreement with the general observations of Tokita and White, the milling characteristics of the polymers change from an elastic band (region 2) to a crumbling bag (region 3) and then to a viscoelastic fluid (region 4) as the temperature is increased from 5° C to 175° C. The 2-3 transition can be treated as a failure process which is time and temperature dependent. Hence, a continuous curve relating the transition nip setting; and the temperature exists for each polymer sample. The transition nip setting at a given temperature (or the transition temperature at a given nip width) was found to be wider (or higher) for samples of broader molecular weight distribution.
Poly(Styrene CO Acrylonitrile) Polyols. Modulus Enhancing Polyols for Urethane Polymers
Authors: Critchfield F. E. , Koleske J. V. , Priest D. C.
Published: February 2011

A novel class of polyols for polyurethane production was described in 19661. Their unique feature was the presence of an in situ polymerized vinyl polymer which markedly enchanes the modulus of the resultant polyurethane. The final product is a conventional polyol that contains a dispersion of the vinyl polymer. From among the numerous products investigated, a poly-(acrylonitrile) polyol was selected because of the excellent stability of the dispersion. Poly (acrylonitrile) polyols are opaque, cream-colored liquids with viscosities ranging from 1500 to 4500 cps, depending upon the nature of the polyol precursor. Particle size of the dispersed phase was reported to be between 0.25 and 0.5 micron as determined by electron microscopy. Poly (acrylonitrile) polyols have been used in slab-stock flexible foams as additives to conventional polyether polyols to improve load-bearing properties. More extensive utility has been identified in molding applications. Whitman described their use in producing integral skin urethane foams for uses such as automotive arm rests, horn buttons, mirror covers, etc.. Dunleavy discussed the use of polymer polyols in molded, microcellular urethane elastomers for automotive trim parts, particularly for "cosmetic" bumpers. More recently, Patten and Priest showed their utility in highly resilient automotive seating foam. In all of these applications the modulus enhancing characteristics of these polyols are particularly important.
Alternating Copolymerization of Butadiene and Propylene
Authors: Furukawa Junji
Published: February 2011

An alternating copolymer of propylene and butadiene is prepared with vanadium or titanium compounds and alkylaluminum compounds as the polymerization catalyst. The catalyst should be prepared at extremely low temperature as −70° C and halogen atom is essential to the catalyst activity. Carbonyl compounds such as ketone, acid, ester, acid anhydride, and acid peroxide are very effective additives to the catalyst for enhancement of the molecular weight of the polymer. Potentiometric titration and the ESR studies suggest that a divalent vanadium compound associated to form the dimer through a chloride bridge is a precursor of the active species. An anionic copolymerization mechanism involving the alternating coordination of monomers is proposed. The copolymer is always of a 1:1 composition irrespective of the composition of monomer feed and the alternating structure of trans-1,4-poly (butadiene co propylene) is estimated from IR and NMR data. The copolymer seems to be a new versatile synthetic rubber having excellent low temperature properties, high rebound, good compatibility with conventional rubbers, and high resistance toward aging.
The Determination of Chlorine in Polymeric Materials by Instrumental Neutron Activation Analysis
Authors: Butler J. W. , Marsh R. H.
Published: February 2011

A rapid non-destructive method for the determination of chlorine in polymeric materials by instrumental neutron activation analysis is presented. The analysis portion of the determination requires only twenty minutes for three samples and standards. Precision is better than five per cent relative standard deviation at levels above one per cent and sensitivity is obtainable to 0.01 per cent.
Long-Range Order of Supramolecular Structures in Amorphous Butadiene-Styrene Block Copolymers
Authors: Kämpf G. , Krömer H. , Hoffmann M.
Published: February 2011

The various methods for determining quantitatively the dimensions of morphological structures from electron micrographs as well as evaluation of small-angle electron and x-ray diffraction are reviewed briefly. In continuation of previous work, the types of long-range order of supramolecular structures observed in two-block butadiene-styrene (BS) copolymers of very uniform molecular structure are discussed. By phase separation, aggregates of the one type of block with uniform shapes and sizes are formed which are arranged strictly periodically in the matrix consisting of the other type of block. Apart from “lattice imperfections”, special regard is given to the formation of boundaries between regions with long-range order of domains. The macroscopic lattices observed in BS block copolymers are compared with the latticelike arrays of colloidal particles found in other systems of a completely different chemical nature.