bluuebunny/crossref_metadata_2025 huggingface dataset:
Silica and Silane Coupling Agent for in Situ Reinforcement of Acrylonitrile-Butadiene Rubber
Authors: Murakami K. , Osanai S. , Shigekuni M. , Iio S. , Tanahashi H. , Kohjiya S. , Ikeda Y.
Published: February 2011

In situ silica reinforcement for the acrylonitrile-butadiene rubber (NBR) vulcanizates, which were premixed with a conventional silica (VN-3) and γ-mercaptopropyltrimethoxysilane (γ-MPS), was achieved by the sol-gel reaction of tetraethoxysilane (TEOS) using ethylenediamine. It was observed that the reinforcement efficiency tended to increase with the increase of mechanically premixed conventional silica. From the observations of transmission electron microscopy and scanning electron microscopy, the simultaneous use of VN-3 and γ-MPS was found to promote the formation of large silica particles and clusters with a relatively good dispersion by the sol-gel reaction of TEOS in the NBR vulcanizate. The results of hysteresis measurements supported this promotion. It was considered to be due to the surface modification of VN-3 by the sol-gel reaction of TEOS and the presence of γ-MPS which worked as a dispersion agent for silica particles. The relationship between the mechanical properties and the morphology of the in situ silica filled vulcanizates is discussed.
Basic Study of Continuous Ultrasonic Devulcanization of Unfilled Silicone Rubber
Authors: Diao B. , Isayev A. I. , Levin V. Y.
Published: February 2011

The present paper describes a basic study of the devulcanization of unfilled model silicone rubber vulcanizates using a continuous ultrasonic reactor. The devulcanization was conducted under several processing conditions. Cure behavior, rheological properties, structural characteristics of the devulcanized rubber, and mechanical properties of revulcanized rubbers were studied. Gel fraction and crosslink density measurement indicate that the rubber is partially devulcanized. The gel permeation chromatography (GPC) results imply that the creation of a branched structure in the network is a possibility after devulcanization. Under the optimal devulcanization condition, the mechanical properties of revulcanized rubber are better than those of the virgin rubber. Devulcanized silicone rubber was also blended with the virgin one. The blends show the same tensile strength and modulus as the virgin rubber but higher elongation.
Homogeneous Zinc(II) Catalysis in Accelerated Vulcanization II. (Poly)Olefin Oxidation, Dehydration, and Reaction with Anti-Reversion Coagents
Authors: Nieuwenhuizen Peter J. , Haasnoot Jaap G. , Reedijk Jan
Published: February 2011

This paper establishes a new and previously unrecognized pathway for the formation of dienes and trienes from model 1,5-polyolefins. It has been found that in the presence of dioxygen and at high temperatures model 1,5-polyolefins are oxidized to yield allylic alcohols or hydroperoxides. These structures subsequently dehydrate to form dienes and trienes, a reaction which was found to be catalyzed by bis(dimethyldithiocarbamato)zinc(II) (ZDMC) and bis(mercaptobenzothiazolato)-zinc(II) (ZMBT), but not by zinc stearate. The observed dehydration reaction has been established to occur exclusively via a 1,2-dehydration pathway; whereas 1,4-dehydration was not observed. In addition, the present paper reports that NBCI, a model compound for the anti-reversion agent 1,3-bis(citraconimidomethyl)benzene (BCIMB), reacts completely within 2 h with squalene at 170 °C in the absence of vulcanization curatives, which can be attributed to this oxidation/dehydration mechanism. The combined results suggest that the occurrence of dienes and trienes in vulcanized rubber may in part be caused by oxidation of the rubber backbone and subsequent dehydration.
Reactions of 2-t-Butylbenzothiazole Sulfenamide with Sulfur and Zinc Oxide in the Absence of Rubber
Authors: Gradwell M. H. S. , van der Merwe M. J.
Published: February 2011

The interaction of sulfur, ZnO and 2-t-butylbenzothiazole sulfenamide (TBBS) was investigated by differential scanning calorimetry (DSC) in the absence of rubber. Special reference was made to the role of the amine, the distinguishing characteristic of all sulfenamides. TBBS decomposes rapidly at 211 °C, the major products being 2-bisbenzothiazole-2,2′-disulfide (MBTS) and 2-bisbenzothiazole-2,2′-monosulfide (MBTM). High mass losses occured and very little free amine was found at these high temperatures. The major degradation products of the TBBS/sulfur system were MBTS, 2-bisbenzothiazole-2,2′-polysulfides (MBTP) and 2-t-butylaminobenzothiazole polysulfides (TBBP). Little free amine and very small mass losses were found. Reaction mechanisms were proposed to account for the formation of the products.
Insights into Sulfur Vulcanization from QSPR Quantitative Structure-Property Relationships Studies
Authors: Ignatz-Hoover Fred , Katritzky Alan R. , Lobanov Victor S. , Karelson Mati
Published: February 2011

Vulcanization of styrene-butadiene rubber, as accelerated by a series of sulfenamides and sulfenimides prepared from various aromatic heterocyclic thiols and various aliphatic amines, was studied using the curemeter under isothermal conditions. Further studies using MOPAC AM1 semiempirical quantum mechanical calculations and CODESSA QSAR software yielded excellent correlations of molecular descriptors of accelerators or accelerator thiolate zinc complexes to the onset of cure and maximum rate of vulcanization. The QSAR results support previously proposed mechanisms describing the origin of scorch delay for the delayed action, fast curing sulfenamide accelerators. In addition, the results support a carbanionic concerted mechanism for the sulfurization and crosslinking reactions.
Topology of Wear Particles
Authors: Padovan Joe , Prasad Neelesh , Gerrard David , Park S. W. , Lindsley Ned
Published: February 2011

This paper describes the evolution of elastomer/rubber wear debris morphology from the in situ leading to trailing edges of sliding contacted wear surfaces. Special attention is given to establishing the role of grit size, slip rate, and contact length on the formation of wear particles, as well as the subsequent in situ aggregation of such product into a hierarchy of particulate material. Of specific interest is the determination of the in situ mass/number count partitioning between true wear particles and aggregates. This population balance is achieved by establishing and monitoring the morphological signature of the various particle types as one moves along various in situ positions to the wake location. The validity/reliability of the empirical trends obtained are verified through the use of the appropriate statistical measures.
An Approach to Chemorheology of a Filled SBR Compound
Authors: Ding R. , Leonov A. I.
Published: February 2011

Three steps in complex chemorheological studies are necessary for complete rheological characterization of filled rubbers during cross-linking reaction. They include: (i) kinetic studies of cross-linking reaction, (ii) rheological studies of green rubber compounds, and (iii) correlation between the rheological parameters and the degree of cure. Basic experiments in the steps (i)–(iii) and their modeling are presented in this paper on the example of a filled SBR compound with sulfur accelerated vulcanization. The approach provides a unique possibility to trace therheological properties of rubber compounds from the green to completely cured states.
Strain-Dependent Dynamic Properties of Filled Rubber: A Non-Linear Viscoelastic Approach Based on Structural Variables
Authors: Lion Alexander
Published: February 2011

This essay deals with a general framework based on the phenomenological theory of non-linear thermoviscoelasticity to represent the characteristic strain dependence of dynamic moduli of carbon black-filled vulcanizates (Payne effect). By virtue of thermodynamical arguments we develop a one-dimensional model consisting of non-linear springs and damping elements. We introduce viscosity functions depending not only on the temperature but on other variables besides. They can be related to the current state of the material's microstructure. Under dynamic loads and stationary conditions, these variables become approximately constant so that the model can be simplified. One of the main results is that the reduced set of equations becomes comparable to linear viscoelasticity but the structural variables imply a dependence of the viscosities on the deformation amplitude. It follows from our theory that the amplitude-dependent parts of storage and dissipation modulus are not independent of each other, as frequently assumed. Both moduli depend in a characteristic manner on the strain amplitude. If we assume, for example, a decreasing power-law relation between viscosities and structural variables, the theory reduces to the widely-accepted G′(Δε) and G′″(Δε) models proposed by Kraus and substantiated by Huber and Huber et al. If we introduce an additional mechanism of exponential-type we obtain the improved G′″(Δε) model developed by Ulmer. Under transient conditions with varying strain amplitudes, as studied experimentally by Wang et al., the model describes thixotropic recovery effects of the moduli as well as more complicated memory phenomena. Under further assumptions we can apply the frequency/temperature shift principle in combination with a frequency/amplitude shift principle to determine the material parameters. Since the model is based on rheological elements, its compatibility with the second law of thermodynamics is ensured.
Stresses, Slip and Abrasion of Rubber Covered Conveyor Rollers
Authors: Metlikovič Peter , Meinecke Eberhard A.
Published: February 2011

Conveyors consist of rubber coated, fiber reinforced belts which are supported and driven by rollers. The rollers are generally coated to increase and stabilize the friction and to reduce abrasion, noise and dirt buildup. Pressures and shear stresses in the rubber layer depend on belt tension, driving forces, geometry and material properties of belt and roller. Most rollers fail due to abrasion when the shear stresses are higher than the friction forces. Slip due to pressure between the belt and the rubber layer is proportional to pressure. Additional slip arises from troughing transitions, uneven belts and rollers and from driving forces. Abrasion due to slip is proportional to the pressure of the belt to the power 1.5 to 3. Equations to predict stresses, slip and abrasion are presented. To reduce abrasion rates, conveyors should have large diameter rollers, low belt tension and a wide belt. Also, cylindrically machined pulleys, high quality belts and long troughing transitions should be employed.
Glass Transition of Elastomers Using Thermal Analysis Techniques
Authors: Sircar A. K. , Galaska M. L. , Rodrigues S. , Chartoff R. P.
Published: February 2011

The paper defines the glass transition temperature (Tg) of elastomers using various thermal analysis techniques (differential scanning calorimetry, DSC; derivative DSC; thermomechanical analysis, TMA; dynamic mechanical analysis, DMA; dielectric analysis, DEA; thermal stimulated current, TSC) and compares Tg values of eight elastomers by the first four techniques. Comparison of Tg by two TMA methods (expansion and penetration) is also included. Necessary information regarding both the specific technique and the sample used to compare published data is mentioned. Their inclusion, along with the Tg data, is emphasized. Correlation of Tg, as determined by thermal methods with that determined by an industrial low-temperature test method (ASTM D 1053-89a) is discussed. The factors that are unique to elastomer Tg determination, such as subambient operation, as compared to other polymers, are pointed out.
Ethylene—Styrene Copolymerization
Authors: Pellecchia Claudio , Oliva Leone
Published: February 2011

Ethylene—styrene copolymers are new materials developed within the last decade using the new homogeneous olefin polymerization catalysts (generally referred to as “metallocene catalysts”). By proper selection of the catalytic system and the reaction conditions, a variety of copolymers with different compositions, structures, and properties can be obtained. Thus, copolymers containing a very low amount of styrene (or p-methylstyrene) on a substantially polyethylenic backbone are crystalline thermoplastics, which could be used to produce functionalized PEs. Increasing the styrene content leads to a rapid decrease in the crystallinity, affording materials which show good thermoelastomeric properties. Copolymers containing around 20 mol % styrene are effective compatibilizers for polyethylene—polystyrene blends. The molecular structure of these copolymers has been defined being “pseudorandom,” since EEE, EES, ESE, and SES sequences are observed, and no SS sequences are present, thus the styrene content cannot exceed 50 mol %. Very recently, however, a random copolymer containing SS sequences in a stereoregular arrangement has been reported. Also, truly alternating E-S copolymers have been obtained with suitable catalysts. These poly(ethylene-alt-styrenes) can be either atactic (and thus amorphous) or stereoregular, depending on the particular catalyst used. Interestingly, isotactic poly(ethylene-alt-styrene) is a new crystalline material with a melting point of 145 °C, whose crystal structure has recently been determined. In conclusion, further research on ethylene—styrene copolymerization promises to afford a variety of new interesting materials starting from two widespread, easily available and inexpensive monomers.
Thermodynamic Interactions in Blends of Polydienes
Authors: Krishnamoorti Ramanan
Published: February 2011

Thermodynamic interactions and phase behavior in binary blends of model mixed microstructure polybutadienes with model 1,4-polyisoprene were studied using small angle neutron scattering and differential scanning calorimetry (DSC). The microstructure of the polybutadiene ranged from 8% 1,2 (92% 1,4) to 90% 1,2 (10% 1,4) units, while the polyisoprene contained 93% 1,4 and 7% 3,4 units. The blends of protonated polybutadienes (HPB) with deuterated 1,4 polyisoprene (DPI) exhibited lower critical solution temperature (LCST) behavior when the polybutadiene contained 38 mol % or more of 1,2 units. Below this 1,2 content of the polybutadiene, all HPB/DPI blends were found to be phase separated at all temperatures above 25 °C. The DSC measurements revealed that other than a blend containing 8% 1,2-polybutadiene and (protonated) 1,4 polyisoprene, all other blends were single phase at room temperature. These results are understood in the context of previous work performed by Han and coworkers on deuterated polybutadiene-protonated polyisoprene blends.
Relationship between Viscoelastic Properties and Characteristics of Filler-Gel in Filled Rubber System
Authors: Yatsuyanagi Fumito , Kaidou Hiroyuki , Ito Masayoshi
Published: February 2011

The wide-line NMR and viscoelastic measurements were carried out for the filled rubber systems. NMR results revealed that the filler-gel in the filled rubber composites had a multi-component system depending on the mobility of rubber molecules. The fraction and the spin-spin relaxation time of each component were well correlated with the viscoelastic properties such as dynamic storage modulus (E′) and loss-tangent (tan δ) of the filled rubber systems. Such findings turned out to be useful in designing new tread materials with well-balanced wet traction and rolling resistance in tires.
Modeling of Carbon Black Filled Natural Rubber Vulcanizates by the Standard Triboelastic Solid
Authors: Coveney V. A. , Johnson D. E.
Published: February 2011

Mathematical modeling of the dynamic behavior of vulcanizates is reviewed with the emphasis on carbon black filled natural rubber (NR). The 3 constant standard triboelastic solid (STS) model and its behavior are described, in general terms and with specific reference to low frequency shear data for a wide range of filled NR vulcanizates. Good general agreement is found between model and experiment for the data obtained at strain amplitudes down to 0.01; there is also acceptably good correlation between carbon black loading and values of STS constants. For previously published data down to very low strain amplitudes (1×10−4), agreement is much less satisfactory.
Elastomer-Elastomer Autohesion-Interphase Gradient of Elastic Modulus
Authors: Vallat M. F. , Giami S. , Coupard A.
Published: February 2011

The effect of migration on the vulcanizing ingredients is considered when two sheets of carbon black reinforced polyisoprene are brought into contact. Two formulations (conventional and efficient ones) are chosen. The formation of macroscopic interphases on both sides of the interface is shown by measurements of local modulus by microindentation. The local concentration of sulfur is determined by energy dispersive X-ray analysis. Near the interface, the modulus is always higher than in the bulk of the sheets although the interfacial strength may be quite low. Co-crosslinking of the chains in the interphase at the molecular level and macroscopic thick interphases are two important aspects of elastomer-elastomer joints.
Long-Chain Branching and Mechanism Controlling Molecular Weight in Hevea Rubber
Authors: Sakdapipanich Jitladda Tangpakdee , Kowitteerawut Tippawan , Suchiva Krisda , Tanaka Yasuyuki
Published: February 2011

The linear character of transesterified deproteinized natural rubber (DPNR-TE) was confirmed by the analysis of terminal groups with NMR and viscometric analyses. The branch content of DPNR rubber from fresh latex was found to range from 0.3 to 1.3 and 0.7 to 3.2, based on tri- and tetra-functionalities, respectively. The plot between the number of branch-points and molecular weight (MW) can be divided into three fractions: (A) the rubber fractions in MW ranging from 2.4×105 to 1.9×106; (B) between 1.9×105 and 2.4×105; and (C) those of MW less than 1.9×105. The fraction (A) showed the number of branch-points per a branched molecule (m) higher than that of fractions (B) and (C). This plot is superimposable with the bimodal molecular-weight distribution (MWD) of Hevea rubber, showing a good coinciding of peak-tops at the high and low MW fractions. It seems likely that there is a close relationship between the number of branch-point and bimodal MWD of natural rubber.
Tensile Behavior after Oxidative Aging of Gum and Black-Filled Vulcanizates of SBR and NR
Authors: Hamed G. R. , Zhao J.
Published: February 2011

Typical sulfur-cured vulcanizates of styrene-butadiene rubber (SBR) and natural rubber (NR) were prepared, and subjected to air-oven aging at 100 °C. Gum specimens exhibited an initial aging period in which stiffness was unchanged, while tensile strength and strain-to-break were significantly reduced. In contrast, black-filled vulcanizates stiffened during early aging. After intermediate aging times, NR specimens softened, while SBR stiffened. With prolonged aging, all compositions became hard and inextensible.
Modeling Dispersive Mixing of Rubber Compounds
Authors: Clarke J. , Petera J.
Published: February 2011

With the ultimate aim of improving mixer geometry by using a mathematical model for rubber mixing, this paper concentrates on the dispersive mixing process of filler disagglomeration. Specially designed elongational flow experiments were used to achieve dispersive mixing under conditions of known stress and strain rate history. It was found that the disagglomeration process is satisfactorally described by a first order differential equation with the rate constant proportional to the power density experienced by the compound during mixing. The kinetic model was implemented in original finite element software to obtain a 2-dimensional simulation of mixing in a twin rotor internal mixer. It was concluded that the 2-dimensional simulation was not only a necessary precursor to 3-dimensional modeling, but would in itself be useful for relating cross-sectional rotor geometry to efficiency of filler disagglomeration, and hence, dispersive mixing.
Fourier Transform Raman Spectroscopy for Characterization of Natural Rubber Reversion and of Antireversion Agents
Authors: Datta R. N. , Hofstraat J. W. , Geurts F. A. J. , Talma A. G.
Published: February 2011

Fourier Transform Raman spectroscopy is employed to study the mechanism of reversion and the influence of the antireversion agent, 1,3 bis(citraconimidomethyl)benzene (BCI-MX) in squalene as well as in low molecular weight synthetic polyisoprene. The formation of non-sulfidic main chain modifications, such as conjugated diene and triene units, along the squalene and isoprene backbone is followed by using this technique. The mode of action and the efficacy of BCI-MX is studied. The decrease in concentration of conjugated diene and trienes by the addition of BCI-MX confirms the reaction of BCI-MX with polyenes to be a Diels-Alder reaction. In addition to the detection of reversion reactions also other processes which occur during rubber vulcanization are monitored via Raman spectroscopy.
Devulcanization of Guayule Rubber by Ultrasound
Authors: Gonzalez-de los Santos Eduardo A. , Soriano-Corral Florentino , Lozano-Gonzalez Ma Josefina , Cedillo-Garcia Rodrigo
Published: February 2011

The present study describes the effect of ultrasonic irradiation on vulcanized guayule rubber using 1 to 3.5 parts per hundred of rubber (phr) of sulfur as the crosslink agent. The effect on crosslink density, gel fraction, torque and glass transition temperature was measured. After exposure to different powers of ultrasonic irradiation, the devulcanization effect was evident on the guayule rubber samples.
Phase Behavior of Brominated Poly(Isobutylene-co-4-Methylstyrene)/General Purpose Rubber Blends
Authors: Rabeony M. , Garner R. T. , Elspass C. W. , Peiffer D. G. , Lin M. , McElrath K. O. , Dias J. A. , Cross J. P.
Published: February 2011

The thermodynamic interaction and phase behavior of elastomeric blends, specifically brominated poly(isobutylene-co-4-methylstyrene) and a general purpose rubber, polybutadiene, have been examined using small-angle neutron scattering (SANS) and cloud points measurements. The low molecular weight equivalent of each segment was used to produce a single phase blend from which the Flory-Huggins interaction parameter (λ) was extracted. The results were analyzed using the random copolymer formalism. The results show that the “repulsive” interaction between the isobutylene and 4-methylstyrene monomer units enhances the compatibility of brominated poly(isobutylene-co-4-methylstyrene) with polybutadiene. A maximum in compatibility occurs at approximately 50 mol % 4-methylstyrene. This fundamental information is essential for the determination of the phase behavior of these materials, and their regions of miscibility/immiscibility. In addition, this information can be used to calculate the optimum copolymer composition for this scientifically interesting and technologically important blend system.
Surface Structure of Carbon Black and Reinforcement
Authors: Göritz Dietmar , Raab Horst , Fröhlich Joachim , Maier Peter G.
Published: February 2011

From scanning tunneling microscopy (STM) and atomic force microscopy (AFM) measurements, it was found that the lateral dimensions of the nanocrystallites systematically decrease with decreasing diameter of the primary particles. Furthermore these experiments suggest that these nanocrystallites, unregularly tilted, form the rough surface of carbon blacks. Hence, the activity of carbon black is the result of the size of the nanocrystallites and the degree of disorder on the surface. Temperature treatments of carbon black lead to a continuous increase of the lateral dimensions of the crystallites and a steady decrease in roughness. In order to quantify the surface roughness small-angle X-ray scattering (SAXS) measurements, that spanned a large scattering vector range, were evaluated by a fractal analysis. The surface fractal dimensions systematically increased with rising activity of the carbon black. Reinforcement is discussed within the scope of interaction of network chains with the carbon black surface. For this purpose, the dependency of the Payne effect on temperature, prestrain and swelling is interpreted using an adsorption mechanism of network chains on the surface of the filler particles. This mechanism requires the existence of stable and unstable bonded chains. Only the weakly bonded chains seem to be responsible for the Payne effect.
The Mechanism of Carbon Black Reinforcement of SBR and NR Vulcanizates
Authors: Hamed G. R. , Park B. H.
Published: February 2011

Gum and black-filled vulcanizates of styrene-butadiene rubber (SBR) and natural rubber (NR) were prepared. Strengths in uniaxial tension were determined for specimens with and without edge-cuts. Normal tensile strengths (no cut) of the gum NR, filled NR and filled SBR were similar; whereas, with pre-cuts, even as small as 0.1 mm, strengths of these were markedly different. The SBRs exhibit a steady decrease in strength with increased cut size, while the NR vulcanizates show a drop in strength at a critical cut size ccr. With small cuts, when the gum NR substantially crystallizes in bulk, its strength greatly exceeds that of the filled SBR. The opposite is true with large cuts, due to the large drop in strength of gum NR at ccr. Remarkably, above ccr, the gum NR is only about twice as strong as the gum SBR. Rupture in the gum SBR, gum NR and filled SBR all take place by simple lateral cut growth. At all cut sizes, the filled NR is the strongest material by at least a factor of two, and prior to catastrophic fracture it exhibits auxiliary cracking. It is proposed that crystallization and filler act synergistically, resulting in sufficient anisotropy to cause longitudinal cracking. This provides a super-blunting mechanism, which augments resistance to catastrophic cut growth.
Improved Tire Wet Traction through the Use of Mineral Fillers
Authors: Mouri Hiroshi , Akutagawa Keizo
Published: February 2011

Silica is widely used in passenger tire treads to improve the balance between wet traction and rolling resistance, compared to the balance achieved when the filler is strictly carbon black. Improvement in wet traction with silica is attributed to the difference in energy loss encountered at high frequencies. The energy loss difference is deduced from the difference in shift factors, determined by time temperature superposition in viscoelastic testing of silica compounds compared to carbon black compounds. Further investigation indicated that some mineral fillers other than silica showed similar behavior. Thus, some mineral fillers could improve tire wet traction without adverse effects on other tire performance traits.
Mechanism of Peroxide Vulcanization of Elastomers
Authors: Loan L. D.
Published: February 2011

As is now well known, the use of an organic peroxide as a crosslinking agent for an elastomer was first reported by Ostromislensky in 1915. In this work benzoyl peroxide was used to cure natural rubber; similar acyl peroxides together with more recently discovered, less active, and more convenient dialkyl peroxides have since this time been used to crosslink a very large number of polymers. With the common unsaturated polymers the vulcanizates produced have mechanical properties rather inferior to those obtained with accelerated sulfur cures. They do, however, have the good aging and low compression set properties which are, in general, associated with sulfurless cures. The commercial use of peroxides in unsaturated elastomers is nevertheless small, being employed only where the presence of sulfur would be deleterious. In spite of its technological disadvantages peroxide crosslinking has been extensively studied since it forms a chemically simple means of introducing crosslinks into a wide variety of rubbers and leads to vulcanizates of simple structure with physically and chemically stable, carbon-to-carbon crosslinks. Interest in the industrial use of peroxides as curing agents has increased recently with the introduction of a number of fully saturated rubbers for which the usual accelerated sulfur systems are unsuitable. Such saturated rubbers are, in general, more resistant to aging, are more thermally stable, and will probably be used to increasingly greater extents as operational conditions become more and more severe. The study of curing systems available for use with such rubbers is therefore of considerable importance and organic peroxides, forming one such system, are worthy of detailed examination. Much work has been done on the technological evaluation of peroxide vulcanizates and much of this is summarized in a recent book edited by Alliger and Sjothun which is recommended as a source of references for a more detailed study of this aspect of the subject. The basic mechanism of the peroxide crosslinking of a wide variety of rubbers has, however, been neglected until relatively recently. For this reason, and for reasons of length, it is proposed to limit the present review to this latter aspect of the subject.
Thermodynamics of Non-Dilute Polymer Solutions
Authors: Patterson D.
Published: February 2011

An excellent new text, “Macromolecules in Solution,” by A. Morawetz emphasizes advances in polymer solution thermodynamics since publication of standard texts such as those of Tompa and Flory. Detailed development of the subject from 1950 may be followed in articles on polymers in Annual Reviews of Physical Chemistry, and particularly in the articles appearing every three years specially devoted to solution properties: Flory and Krigbaum (1951), Wall and Hiller (1954), Hermans (1957), Casassa (1960) and Hughes and von Frankenberg (1963). The articles on solutions of non-electrolytes are, of course, always of general interest and often deal directly with polymer solutions or mixtures of chain molecules. Because of this very satisfactory situation, the author has decided that the best thing is to review in more detail the single topic which is most interesting to him. This is the thermodynamics of non-dilute solutions where it is usually supposed that the quasi-lattice theories of the 40's are quite adequate at concentrations greater than about 10 per cent. For fifteen years or so, interest has centered on very dilute polymer solutions and the dimensions of isolated polymer molecules, particularly at temperatures near the θ point. Increasingly difficult mathematical problems have followed the McMillan-Mayer comparison of solutions and imperfect gases first applied to polymer solutions by Zimm and Stockmayer. Polymer solution thermodynamics seems to have moved far beyond the intuitive questions of Meyer as to why a polymer solution differs from an ideal solution or from a mixture of a monomeric solute and solvent. However, certain results, apparently not very widely known, make one feel that such qualitative questions are not out of date and that the thermodynamics of concentrated polymer solutions may be open to much further development.
Analysis, Composition and Structure of Rubber and Rubber Products
Authors: Tyler Wlllard P.
Published: February 2011

Seven years has passed since the review of methods of analysis of rubber and rubber products by Burger was published in this Journal. At that time the author covered a broad field of endeavor with special emphasis on classical methods of analysis. He also foresaw the future of instrumental techniques, many of which were only beginning to be useful in rubber chemistry. The questions that must be answered today seem to us, from the vantage point of seven years of remarkable progress, to be more complex. Which new techniques have proved to be most useful in helping the analytical chemist to solve daily problems of analysis of his own and his competitors' products? Which techniques are giving him a tool to study the relation between composition, structure, and properties of rubbers? Which techniques can help the polymer chemist to better chart his course in the search for new and better elastomers? The new techniques, and a few of the old ones, have advanced so rapidly in the last decade that it is presumptuous to think that we can answer these questions completely in a review paper. What, then, is the purpose of this review? We could prepare a complete bibliography and comment briefly on the more important papers. But this has been adequately done, with a very broad scope, in the reviews appearing in Analytical Chemistry every two years. We feel this approach would be redundant. We have chosen, instead, to attempt to cover available techniques from the standpoint of what can be done with them in several important areas, using key papers from the literature as a basis. Our added comments are the result of years of experience in the ceaseless quest for the best use of analysis and structure-determining tools in advancing research, development, and production in the field of elastomers.
Heat Transfer in Processing and Use of Rubber
Authors: Gehman S. D.
Published: February 2011

Heat transfer in rubber is likely to be significant from the first processing steps to the end use of the product. At the start, it is encountered in preparing, drying, and handling raw polymers; then in mixing and forming or molding compounds. In this stage, the thermoplastic nature of rubber is such that viscosity and other physical characteristics are especially temperature sensitive. Heat is the most important processing agent. The rate at which heat can get into and out of rubber, how expertly it can be transferred, affects the design of processing machinery and controls the speed of many mixing, extruding, and molding operations. In these processes, primary, turbulent heat transfer between rubber and steel and mass transfer in the rubber are complicated by frictional heat generation at the rubber-metal surfaces and large conversion of mechanical energy into internal heat. Convection heat transfer with air, steam, or fluids also usually occurs in processing rubber. Localized overheating at any stage can be disastrous for quality. Hence the basic heat problems in processing usually lie in rapidly and efficiently securing, and then maintaining, satisfactory temperature uniformity in a material with inherently poor heat transfer characteristics. Dispersing fillers in rubber requires large power inputs but the resulting temperature rise must not be so great as to cause prevulcanization or reduce unduly the efficiency of the mixing operation by too great reduction in plasticity and hence shearing stresses. On the other hand, Hahn has pointed out how advantageous such mechanical heating of rubber may be. A few minutes working on a mill may accomplish more in raising the temperature than hours of conduction heat flow. After rubber is mixed and formed, vulcanization ensues with flow of heat to raise the temperature throughout to the vulcanization range and thus activate the chemical reactions of vulcanization. At this stage, control of heat is exceedingly important for costs and quality. Any shortening of the vulcanizing cycle without detriment to quality provides opportunity to increase productivity of a large capital investiment. Finally, heat is one of the most destructive agents for finished rubber products. It presents a frontier for development of new rubbers and applications. External environmental heat imposes service limitations and in dynamic uses involving repeated, rapid deformations internal transformation of mechanical energy into heat may readily destroy thick rubber sections.
Displacement of Elastomers from Carbon Gel in Filled Mixes
Authors: Craig David
Published: February 2011

Bound rubber may be displaced by milling filled hydrocarbon elastomers with polar rubbers such as NBR. The displacement is not complete in a single stage. Crosslinking can be detected in filled natural rubber by moderate swelling and then measuring the freezing point depression caused by the rubber in the filled and unfilled state, a greater depression being observed for the filled state. Filled and unfilled CB at the same concentration in benzene seems to cause the same freezing point depression and so crosslinking during the reinforcement of this rubber, though known to exist from other behavior, seems not to be indicated by the freezing point method.
Rates of Crystallization of cis-1,4-Polybutadiene in Elastomer Blends
Authors: Morris M. C.
Published: February 2011

Blends of polybutadiene with SBR show different crystallization behavior than blends with polyisoprene. One might suppose that the similarities in SBR and polybutadiene are sufficient to allow more intimate mixing than can be obtained by using entirely different polymers such as the polyisoprene polybutadiene pair. Possibly, bulk viscosities are important here, but no matter what the cause, crystallization properties have shown differences in the way the polybutadiene was situated. Also, large changes in the glass transition occurred for those materials which showed sizeable retardation in crystallization rate. An interpretation of the crystallization rate data based on particle size was given in this discussion because a precedent exists for this effect. However, molecular compatibility has not been ruled out. Further investigation of thermal properties should help clarify this point. It will be interesting to learn to what extent particle size alone affects the thermal behavior of blends. Perhaps more work along these lines coupled with improved optical and electron microscope techniques will provide some answers to our questions on how phase structure affects thermal and mechanical properties.
Thermographic Study of Elastomers III. Peculiarities of Crystallization of Natural Rubber
Authors: Teitel'baum B. Ya , Anoshina N. P.
Published: February 2011

Thermographic (DTA) study reveals two independent melting regions of natural rubber crystallites and a gap between them which is determined by a sharp difference in the rates of the crystallization process. Crystallites formed at a low temperature (− 25° C) and at room temperatures are distinguished by the degree of development, but pertain to the same crystallographic form. High temperature crystals play the role of seed in low temperature crystallization. During the melting of low temperature crystallites of natural rubber, they recrystallize with a rise in the melting point (without reaching, however, room temperatures). The appearance of this phenomenon on the thermograms is determined by the relation between rates of crystallization and of heating in the course of the experiment. The rate of crystallization of natural rubber and the relative amount of crystallites formed at − 25° C were studied by DTA; the effect of rubber plasticization on these magnitudes was noted.
Effect of Oil and Black on SBR Rheological Properties
Authors: Hopper J. R.
Published: February 2011

Effects of a naphthenic oil and of HAF carbon black on SBR processability were evaluated. Three rheological parameters related to processability are apparent viscosity, extrudate swell and extrudate surface roughness; they were studied with a capillary rheometer over a shear rate range of 10 to 3000 sec−1. This instrument is particularly useful because processability can be evaluated at industrial processing conditions. At constant shear rate an increase in oil level in the compound decreases viscosity, decreases swell, and reduces the shear stress range over which a smooth extrudate can be obtained. An increase in black level increases viscosity, decreases swell, and extends the range over which a smooth extrudate can be obtained. The opposing effects which oil and black have on processability demonstrate that an optimum combination of these two components exist. To best utilize the rubber process oil and carbon black the optimum processable compound must be selected. Such a selection is illustrated by the use of contour graph analysis of the data.
Correlation of Large Longitudinal Deformations with Different Strain Histories
Authors: Zapas L. J. , Craft T.
Published: February 2011

In 1963 Bernstein, Kearsley, and Zapas1 presented a theory of an elastic fluid which gave the correct stress-relaxation response for a large variety of elastomeric materials, including vulcanized rubbers. A principle attractiveness of this theory is its relative simplicity; with a single integral in time, it describes the stress-strain behavior for all types of deformation histories. In the case of simple extension, it predicts the behavior in any uniaxial strain history from the results of single step stress-relaxation experiments which cover the same range of extension and time. We designed a series of experiments to check the validity of this theory and found, as is shown in this paper, excellent agreement with experiment in all cases. We are aware that experiments cannot prove a theory. From our results, however, we feel strongly that a single integral expression with a nonlinear integrand such as the BKZ elastic fluid equation is sufficient to describe the stress-strain behavior of elastomeric materials.
Shear Dependence of Viscosity and Molecular Weight Transitions. A Study of Entanglement Effects
Authors: Chinai Suresh N. , Schneider William C.
Published: February 2011

Flow of concentrated polymer solutions covering molecular weights up to 150,000 was examined at shear rates up to 200,000 sec−1. The viscosity, molecular weight, and shear rate results of previous workers recognizing only single critical molecular weight M*, above which ordinary Bueche entanglements dominated the flow, were compared with our findings in which two distinct critical molecular weights, upper M* and lower M** exist. These results are compared with the theory, and new interpretations are presented.
Molecular Weight Distribution of Network Chains and Swelling Pressure of Vulcanizates
Authors: Gehman S. D.
Published: February 2011

Calculations and experimental results both indicated that effects of a molecular weight distribution of network chains may become evident in swelling pressure curves under favorable circumstances. More precise experiments are required to establish this definitely. The calculations assume that a simple integration such as is used for a continuous medium may be applied to molecular units of structure deduced from the kinetic theory of rubber elasticity. The validity of this can only be determined by further comparisons with experience. Refinement of the theory might take into account interactions of the units.
Ultimate Tensile Properties of Elastomers. III. Dependence of the Failure Envelope on Crosslink Density
Authors: Smith Thor L.
Published: February 2011

Ultimate tensile properties of amorphous unfilled elastomers can be characterized by a failure envelope which results from a plot of log log  σbT0vs.log  (λb− 1) where  σb is the stress at break based on the cross section area of an unstressed specimen,   λb is the corresponding ultimate extension ratio, and T0 and T are, respectively, an arbitrarily selected reference temperature and the test temperature expressed in °K. Values of  σb and   λb are normally obtained from tests made at different extension rates at a series of temperatures. To determine the effect of crosslink density on the failure envelope, a study was made of eight vulcanizates of a hydrofluorocarbon elastomer, Viton A-HV. The number of effective network chains, νe, in these vulcanizates varied from 0.38× 10−4to 9.46× 10−4mole/cm.3 Ultimate tensile properties were determined at temperatures between −5 and 230° C and at seven to ten extension rates at each temperature. The data gave a master failure envelope on a plot of λbσb273/Tvs.log  Ee(λb−1) 273/T, where Ee is the equilibrium tensile modulus. This behavior shows that λbσbT0/T is a function of Ee(λb−1); thus the maximum value of (λb−1) is inversely proportional to νe. Ultimate tensile properties of one vulcanizate were also determined under constant loads at four temperatures and the data were found to yield the same envelope as those from tests made at constant rates of extension.
Structure and Content of Dicyclopentadiene in Ethylene Propylene Dicyclopentadiene Terpolymers
Authors: de Kock R. J. , Veermans A.
Published: February 2011

With the aid of model compounds—derivatives of endo- and exo-dicyclopentadiene—it has been established that a) the 9, 10-double bond (the double bond in the norbornane ring) is involved in the polymerization of dicyclopentadiene with ethylene and propylene, b) dicyclopentadiene, present in the polymerization mixture in the endo-configuration, occurs in the exo-configuration in the polymer chain. The same model compounds enable the dicyclopentadiene content of ethylene propylene dicyclopentadiene terpolymers to be determined by infrared spectroscopic methods. Use is made of the 3045 cm−1 band, which is characteristic of endo-cyclic double bonds in five-membered rings.
Ethylene Propylene Terpolymers
Authors: German R. , Vaughan G. , Hank R.
Published: February 2011

The general technological properties of a polymer are closely related to its molecular structure. It is, therefore, important to know polymerization methods by which to produce reproducible polymers with controlled structures. Use of several monomers in copolymerization significantly increases the difficulty of this problem, but in the end it leads to a much wider spectrum of raw materials. In addition to variations caused by changes in molecular weight and in molecular weight distribution the nature of copolymers may be altered by changing the composition of the monomer mixture and the way monomers are distributed in the polymer chain. Use of Ziegler-Natta catalysts has already given a multiplicity of materials composed of ethylene and propylene: random copolymers are particularly interesting as rubbers. Introduction of a third component to give unsaturation in the terpolymer, so that this may be vulcanized with sulfur and accelerators, has greatly increased the possible areas of application for these polymers. Utility of a diene as the third component to give EPT's which can be used as general purpose rubbers depends on its price, the ease with which it copolymerizes through one double bond, its influence on the velocity or steric course of the ethylene-propylene copolymerization, vulcanization characteristics of the resulting terpolymers, and finally on the technological properties of the vulcanizates. The amount of copolymerized termonomer should be limited to retain the advantageous chemical and physical properties of the original ethylene-propylene copolymers. However very low degrees of unsaturation limit the sulfur and accelerator system, the characteristics of which depend strongly on the structure of the terpolymer as well as on the nature and form of the vulcanization agent. It is therefore essential to have a thorough understanding of this multiple interdependency for optimal application of the materials. We describe here reproducible procedures for production of terpolymers with controlled structures, and the course of vulcanization of the products in relation to terpolymer structure. We shall describe methods, based on these investigations, which may be applied for control of the vulcanization characteristics of the polymers.
Homogeneous Polymerization of Butadiene Catalyzed by Rhodium Salts
Authors: Bawn C. E. H. , Cooper D. G. T. , North A. M.
Published: February 2011

A study has been made of the solution polymerization of butadiene, to predominantly trans 1, 4 polymer, catalysed by rhodium salts. The reaction is accelerated by protonic acids (including water) and by those reducing agents which in aqueous systems would be capable of reducing RhIII to RhI. Ligands such as organic amines, and also bromide and iodide anions, tend to retard or even inhibit the reaction. The overall process appears to be a chain reaction, but is not free radical in character. The mechanism which best fits all the observations is one in which the active species is a π-allylic rhodium hydride, initiation occurring by hydride shift and propagation occurring by a ligand displacement process.