bluuebunny/crossref_metadata_2025 huggingface dataset:
Oil Resistant Elastomers for Hose Applications
Authors: Dunn J. R. , Vara R. G.
Published: February 2011

Since there are so many types of hose based on oil resistant elastomers and so many specifications for each type, sometimes with conflicting requirements, it is not possible to generalize regarding current uses or future trends. NBR makes up the bulk of elastomer usage for hose tubes; CR has the highest usage in covers and is used in tubes also. NBR/PVC is used in both tubes and covers. High volume usage of these polymers is expected to continue where low cost and ease of handling are paramount. When higher heat resistance is required in covers, CSM and CM are used, and the trend towards use of these is expected to continue. XNBR/PVC blends may also be used in covers when excellent abrasion resistance is required. CSM and CM may be used in tubes requiring moderate oil resistance and good heat aging. For still better heat aging, the tendency is to use ethylene-methylacrylate or silicone. When low fuel permeability is required, ECO is used; it may also be used in the cover, since it is inherently ozone resistant. The ultimate in combined fuel, oil, and heat resistance is afforded by fluoroelastomers, the use of which is increasing, where hose service requirements are particularly severe, despite their higher cost.
Particle Size Measurement of Rubber Latices
Authors: Gorton A. D. T. , Pendle T. D.
Published: February 2011

It is obvious that there are a wide variety of experimental techniques available for the examination of the particle size in polymer latices. Some of these are well-established, such as the electron microscope, while others, such as chromato-graphic and photon correlation methods, are relatively new. Some systems are used for routine investigations of particle size distribution while others appear to be largely academic. Different methods yield diverse information with regard to the particles, and some are plainly unsuitable for latices with marked polydispersity. In order to summarize the various methods and the information they supply, Table I has been provided. This is an attempt to show, in a simplified manner, the chief features of the various techniques described above. It is hoped that this will be of value both to those established in this field and those beginning to lake an interest in the particle size of polymer latices.
Modification and Dielectric Properties of Polyisoprene
Authors: Honskus J.
Published: February 2011

The dielectric method can be used for determination of the polar groups modifying the nonpolar polymers. This method was used for the study of such complicated systems as the sulfur-accelerated vulcanizates. Results of the chemical analyses were compared with the results of dielectric measurements, and very good agreement was obtained.
Effect of Extending Oil on Viscoelastic Behavior of Elastomers
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

For a number of years, oil-extended elastomers have been in commercial use. The obvious advantage is to dilute elastomers with less expensive oil. In addition, oil improves the processability of the elastomer. This enables the use of a higher-molecular-weight polymer, which, in turn, yields mechanical properties comparable or superior to those of a lower-molecular-weight polymer without oil extension. The viscoelastic properties of the oil-elastomer mixtures at a wide range of concentration and temperature offer information useful for understanding elastomer processability. The viscoelastic properties of such systems are also most sensitive manifestations of the polymer chain structure and, therefore, they represent fundamental characteristics of a given elastomer sample. In this work, two samples of ethylene-propylene copolymer differing in chain structure were selected. The oil-elastomer mixtures were prepared for polymer concentration in the range of 2.5–100%. The viscoelastic properties have been measured in the temperature range of 30–150°C. The frequency range was 10−1–102 rad/s and in some cases −2–102 rad/ s. The superposition principles have been examined with these data for both the temperature and concentration dependence.
Fatiguing of Rubber-Rubber Interfaces
Authors: Fielding-Russell G. S. , Rongone R. L.
Published: February 2011

Mechanical fatigue results of three rubber systems, obtained by using a Painter adhesion testpiece, modified in such a way that it mates rubber-rubber surfaces (rather than metal-rubber surfaces) indicated that the testpiece is capable of fatiguing a rubber-rubber interface and therefore is useful for evaluating rubber-rubber joints. The mode of failure, correlation of the present results with static interfacial results, and the wide range of crack growth constants all indicated interfacial fatiguing. Test results, i.e., time to failure versus applied dynamic load, gave good agreement with established rubber fracture theory.
Strength of Neoprene Compounds and the Effect of Salt Solutions
Authors: Bhowmick A. K. , Gent A. N.
Published: February 2011

Soft CR vulcanizates resemble NR vulcanizates in many ways. Their tensile strength is high at low temperatures and drops sharply at a characteristic temperature to a value of about 1–1.5 MPa. Their tear resistance decreases smoothly as the temperature is raised and does not reach a lower limit, even at temperatures as high as 150°C. However, they show continuous tear propagation at room temperature under relatively large tear forces, whereas NR materials do not. This difference must reflect different strengths of the crystallites formed at the tear tip, those in CR being significantly weaker. Also, a specific environmental effect is noted: When immersed in solutions of FeCl3, the CR materials show more rapid tearing, and they tear at significantly lower forces than in water or in NaCl solutions (or in air). Although they swell continuously in water and in salt solutions, the rate of swelling seems far too low to account for the weakening observed. Moreover, the swelling is greater in water, whereas the weakening is specific to FeCl3 solution. It is attributed to a chemical reaction between FeCl3 and the CR molecule.
Improvements in the Oxidized Gasoline Resistance of NBR Elastomers
Authors: Killgoar Paul C. , Lemieux Marvin A.
Published: February 2011

Nitrile compounds have been developed which have excellent sour gasoline resistance. The compounds are cured with a mixed urethane/sulfur (80/20) crosslinking system. After 6 weeks aging in sour gasoline, the physical properties of the urethane cured nitriles were still superior to the best sulfur-cured nitrile and epichlorohydrin compounds which had been tested for 3 weeks. Heat resistance of the urethane-cured compounds is not as good as the sulfur-cured compounds; however, it is anticipated that the new compounds can meet the current temperature requirements for the fuel hose tube.
Fracture Mechanics Applied to Elastomeric Composites
Authors: Gent A. N.
Published: February 2011

Griffith introduced a general fracture criterion in 1920: a crack will grow only when enough energy is available in the system to cause further fracture. This simple concept has been applied by Rivlin and Thomas to various tear processes in elastomeric materials and by Kendall to a variety of adhesive failures. Their results are reviewed, with particular reference to the fracture and debonding of elastomeric composites. Two further cases are then considered: the detachment of an elastic matrix from a rigid spherical inclusion and the pullout of inextensible cords from an elastic block in which they are embedded.
Structure-Property Relations in Amorphous and Crystallizable ABA Triblock Copolymers
Authors: Morton Maurice
Published: February 2011

The properties of the thermoplastic elastomers derived from ABA triblock copolymers depend largely on the nature of the A blocks, which form rigid, thermoplastic domains holding the elastic network together. These domains may be either amorphous or crystalline in nature, the former resulting from an inherent incompatibility between the A and B blocks, while the latter form by normal crystallization processes. It can be demonstrated convincingly that the formation of the amorphous (glassy) domains is enhanced by a higher degree of incompatibility between the A and B blocks and that the strength of the material depends on the degree of phase separation and on the integrity of the amorphous domains. However, the viscosity increases with increasing incompatibility between the two phases, presumably because the two-phase morphology persists even in the melt. On the other hand, the presence of crystallizable A blocks, which do not phase separate in the melt, leads to good flow properties. However, the strength of the material and other mechanical properties are strongly dependent on the molecular weight and crystallization of the A blocks.
Improved Particle Size Measurements on Pigments for Rubber
Authors: Hess W. M. , McDonald G. C.
Published: February 2011

High shear mixes of carbon black and many other pigments in a cellulose acetate butyrate paint chip formulation have provided superior specimens for analysis by automated electron microscope image analysis. Specimens prepared from these mixes exhibit reduced aggregation and improved dispersion. Testing accuracy, precision, and sampling are significantly improved in comparison to previous techniques. The CAB method is applicable to carbon blacks, silica, precipitated calcium carbonate, red iron oxide, titanium dioxide, and any rubber grade pigment that is composed of stable particles that are reasonably isotropic in nature. Certain ground pigments or those containing highly anisotropic particles may give erroneous results due to breakage (e.g., clay, acicular zinc oxide). An improved particle size analysis program for automated electron microscope image analysis was developed. This utilizes a self-determining factor to correct for particle aggregation. The method provided good grade classification for a broad range of carbon blacks in CAB and is also suitable for screening blacks in the dry state or extracted from rubber.
Fracto-Emission from Filled and Unfilled Elastomers
Authors: Dickinson J. T. , Jensen L. C. , Jahan-Latibari A.
Published: February 2011

We have tried to show a variety of EE and PIE results on a number of systems involving fracture of filled and unfilled elastomers and consider some of the parameters that influence this emission. The need for careful studies of the physics and chemistry of these phenomena is obvious. The usefulness of FE as a tool for investigation of failure mechanisms and fracture phenomena in elastomers requires a broad-based attack combining fracture mechanics, materials science, and fundamental fracto-emission studies on well characterized elastomer. Since the field is relatively unexplored, we will conclude by speculating on some potential areas of usefulness of FE, many of which depend critically on further understanding of FE itself.
Ionic Crosslinking of Carboxylated SBR
Authors: Sato Kyosaku
Published: February 2011

1. Ionic bonding of carboxylated SBR with zinc oxide is detectable by means of measurements of the temperature dependence of tan δ. There is an α peak in the region of 60°C at 3.5 Hz. The position and shape of the α peak are strongly dependent on the state of cure of the vulcanizates. Without permanent crosslinking, the α peak is a plateau; as the crosslink density increases, the α peak becomes sharper and shifts to lower temperatures. The presence of carbon black causes the α peak to shift to higher temperatures, regardless of the presence of permanent crosslinks. 2. Ionic bonds in carboxylated SBR reacted with zinc oxide are in the form of ion clusters which function as crosslinks at room temperature. The ionic crosslinks provide carboxylated SBR with high tensile strength in the absence of reinforcing fillers. The presence of carbon black causes the 300% modulus to increase. The ionic crosslinks are labile, and the strength is lost at moderately elevated temperatures. A mixed cure system consisting of both sulfur and zinc oxide provides higher heat resistance than either of the single cure systems.
On the Small Strain Behavior of Peroxide Crosslinked Natural Rubber
Authors: McKenna Gregory B. , Zapas Louis J.
Published: February 2011

Torque and normal force measurements on a cylinder subjected to torsion at constant length were used to study the behavior of NR crosslinked with 5 phr dicumyl peroxide. The derivatives of the strain-energy density function ∂W/∂I1 and ∂W/∂I2 were calculated from the data using the scaling law of Penn and Kearsley. The new results extend the limit of small strains at which the strain-energy density function derivatives have been measured to γ<0.005 and further confirm our previous results that for peroxide-crosslinked NR, ∂W/∂I2 does not become negative at small strain, contrary to several reports in the literature. Reduced stress was determined for the rubber by using the approach of Kearsley and Zapas to calculate the derivative w′(λ) of the Valanis-Landel form of the strain energy function. The results were compared with the measured values for reduced stress in tension and compression at small strains. While the deviation between the predictions and the experimental behavior do not exceed 6%, the characters of the calculated and measured reduced stress plots are different. The measurements in torsion were not obtained at small enough strains to enable direct comparison with the extension/compression behavior at |ε|<0.002. Extrapolation of the results did not produce the anomalous cusp observed in the reduced stress for 0.998<1/λ<1.002 which was reported in our previous study. The fact that torsional data do not show the cusp offers support to the Kearsley suggestion that at these extremely small deformations, rubber compressibility may play an important role in the stress-strain behavior. This could also explain the apparent discrepancy between the predicted Valanis-Landel behavior and the observed behavior. Future work involving higher precision experiments is required to resolve the matter.
Application of Flow Behavior to Design of Rubber Extrusion Dies
Authors: Kannabiran R.
Published: February 2011

It is common in the tire industry to extrude profiles like treads using a hot-feed dual extrusion line. There is a need to extrude the profiles with zero drawdown in the extrusion line after exiting from the die. Also, the extrudate from the two extruders in a dual extrusion must knit together to form a well-defined and reproducible junction line. A contoured flow channel called a preform is customarily used to achieve a desired junction line and to roughly preshape the stream before passing it through the final die. In practice, several trials are usually required to arrive at an optimum die combination to obtain desired size and shape of extrudate after due allowance for extrudate swell, as well as uniform velocity across the width of the extrudate profile. It is helpful to eliminate some of these trials by developing calculation methods for estimating pressure profile, velocity and swell distribution. There are a number of articles on calculating pressure drop from flow rate for non-Newtonian fluids in odd shaped ducts and tapered channels. Also, many simple techniques are available for analyzing non-Newtonian flow of polymer melts in simple extrusion dies. Most of these calculations assume a one-dimensional flow. More recently, there has been much work on developing finite element and other numerical methods for computing complex die flows. This paper describes and tests the utility of a quick and easy method of estimating extrusion pressures and velocities in and at the exit of extrusion dies using material properties and geometry. This method allows for abrupt changes in geometry such as sudden contractions in the flow channel.
Empirical Equations for Tire Footprint Area
Authors: Pillai P. S. , Fielding-Russell G. S.
Published: February 2011

Two simple predictive equations for tire footprint area in terms of tire deflection and tire and wheel dimensional parameters found on the tire sidewall, have been empirically developed. Footprint areas calculated using these equations agreed with measured areas for a number of passenger, truck, and off-the-road tires, of both radial and bias belted constructions, indicating the general predictive usefulness of the equations. The form of one of the equations is similar to that of equations presented in the literature that were derived using different assumptions.
Sequence Distribution of Commercial SBR by Ozonolysis-GPC Measurement
Authors: Tanaka Yasuyuki , Sato Hisaya , Adachi Junichi
Published: February 2011

Sequence distribution of commercially obtained styrene-butadiene copolymers (SBR) was investigated by high-resolution-GPC measurement of ozonolysis products. The ozonolysis-GPC of emulsion SBR samples showed peaks corresponding to 1 to 4 styrene sequences and styrene-1,2-butadiene sequences flanked by 1,4-butadiene units. In random SBR samples with anionic polymerization, long styrene sequences of from 8 to 19% were detected in addition to the short styrene sequences. So-called tapered-block structure was clearly observed in partially block SBR samples; a broad peak derived from block styrene sequences in a relative intensity of 49 to 55% was overlapped by peaks due to styrene sequences longer than 10 styrene units. The content of pure-block styrene sequences in S-B-S type triblock SBR samples was found to be 85 to 99% or above.
Effects of Salt Corrosion on the Adhesion of Brass Plated Steel Cord to Rubber
Authors: Ishikawa Yasuhiro , Kawakami Shinji
Published: February 2011

Adhesion loss caused by salt corrosion is proposed to occur by the following process: 1) During a salt corrosion test, the NaCl solution rises in the cavity located at the steel-cord center. 2) An electrochemical oxygen concentration cell is formed. 3) OH− is produced by the reduction of oxygen. 4) An increase of the NaOH concentration causes the reverse of ion tendency between brass and steel. 5) Dezincification and dissolution of brass take place in the brass plating. The same process also occurs in the corrosion of a bare brass plated steel cord immersed in NaCl solution. Compounds containing cobalt stearate and a compound free from cobalt show adhesion deterioration by the process described above. Many other cobalt salts suppress the corrosion of brass in NaCl solution. At the same time, the underlying steel changes to become ignoble compared with brass, leading to the production of a large amount of rust. In view of the above considerations, it is desirable to remove the cavity located at the steel-cord center in order to suppress the steel-cord corrosion. Use of an open type of steel cord is useful in this respect.
Prediction of Equilibrium Swelling in Fuel and Lubricant Ingredients
Authors: Neppel A.
Published: February 2011

In accord with the Porter equation, linear relationship has been found between the apparent and actual network-chain concentrations of DCP-cured NBR reference elastomers containing 18–39% ACN and 0–70 phr N550 black while Porter's k factors and, therefore, the extent of the restriction of swelling by the filler vary somewhat with the diluent. Taking this variation into account, a self-consistent relationship has been obtained between data on swelling in MEK (24 h) and those on equilibrium swelling in some fuel and lubricant ingredients (2 to 4 weeks). By using this relationship and the modified Flory-Rehner equation, the equilibrium swelling in fuel and lubricant ingredients of NBR test vulcanizates can be estimated from determining their nitrile content and from an MEK immersion test if these vulcanizates are filled with only N550 black, and if the only variables in their compositions are nitrile content, state of peroxide cure, and carbon black loading. The development of a similar technique to predict the swelling in mixed solvents of unknown NBR vulcanizates would probably involve serious difficulties which would stem from the presence of plasticizers, antioxidants, and fillers other than N550 black as well as from the assessment of the polymer-solvent interaction factor.
Diffusion of Heavy Oil in a Swelling Elastomer
Authors: Bouvier J. M. , Gelus M.
Published: February 2011

The swelling of SBR by an aromatic oil has been experimentally studied at temperatures ranging from ambient to 200°C with thermally stable networks. A model based on Fick's law was developed, and the change of geometry of the elastomer sample was taken into account. The proposed approach is global or macroscopic, and a constant diffusion coefficient has been defined. The diffusion number, ND, defined by two characteristics of a solvent-polymer system, tf the swelling time and tD the diffusion time, represents an important result for engineering applications; it allows prediction of the behavior of amorphous elastomers in contact with a diffusing organic liquid.
Differential Dynamic Shear Moduli of Carbon Black-Filled Styrene-Butadiene Rubber Subjected to Large Shear Strain Histories
Authors: Arai Koichi , Ferry John D.
Published: February 2011

Combined measurements of shear-stress relaxation and differential dynamic storage and loss shear moduli G′ and G″ following a single-step shear strain of 0.4, as well as measurements of dynamic moduli in on-off strain and stress histories, have been made on styrene-butadiene rubber (type 1502) filled with carbon black (N299) at loadings of 40, 50, 60, and 70 phr, with 10 phr Sundex 790 oil. Both cured and uncured compounds were studied at temperatures of 25.0° and −0.5°C respectively. The maximum oscillatory shear strain was 0.005, and the frequency was from 0.4 to 1.8 Hz. The storage shear modulus G′(ω, 0) measured without imposition of static strain was approximately proportional to the fourth power of the volume fraction of black. With imposition of single-step strain, the differential storage modulus G′(ω, γ; t) fell 25% to 35% but slowly recovered somewhat while the strain was maintained for 4 to 5 h. During this period, the static stress relaxed continuously. At the highest content of black, the drop in log G′ was the least, and the final recovery was closest to the initial value of G′(ω, 0). In on-off experiments on uncured compounds, when the strain was “on” for 250 s and then “off” (either stress or strain returned to zero), G′ decreased when the strain was imposed as before and decreased further when it was removed. In the “off” state, G′ recovered partially but did not attain the initial value of G′(ω, 0) even after 7 d. In on-off experiments on cured compounds, removal of stress caused G′ to either increase or decrease depending on the content of black; in any case, in the “off” state, G′ recovered completely to its initial value. Other strain histories involved on-off sequences with different “on” periods and multiple on-off sequences with different “on” periods and multiple on-off sequences. The results are interpreted in terms of a network of black particle aggregates whose contacts can slowly rearrange even in the absence of stress as shown by stress relaxation at very small strains in earlier studies. In large strains, it is postulated that some contacts are broken but can partially reform, especially in the stress-free state; the rate of reformation is similar to that of small-strain stress relaxation. Only in cured compounds is the network fully recovered, presumably because in these the particles are imbedded in a crosslinked matrix and have crosslinked bridges that facilitate reestablishment of interparticle contacts, whereas in uncured compounds the matrix has no crosslinks and the bound rubber on adjacent particles may be merely entangled.
A Quantitative Determination of the Damping Behavior of Acrylic Based Interpenetrating Polymer Networks
Authors: Fradkin D. G. , Foster J. N. , Sperling L. H. , Thomas D. A.
Published: February 2011

The damping function, D.F., as derived from the area under the linearE″— temperature curve, expresses the amount of mechanical energy converted to heat per unit volume of material. Sometimes characteristics of the damping behavior of homopolymers and IPN's are more apparent in the linear E″—temperature plot, such as glass transitions and secondary transitions. Decrosslinking and/or annealing the IPN's have no effect on the D.F.'s, although these treatments significantly modify the shape of the E″—temperature curves as a result of molecular and phase rearrangements. Thus, to a first approximation, the area expressed by D.F. is a polymer chain characteristic, depending on the chain structure itself but not on crosslinking and/or annealing.
Curing SBR with Thiocarbamyl Sulfenamide Accelerators
Authors: Layer Robert W.
Published: February 2011

We have found that the physical properties of conventional SBR/BR tire tread vulcanizates obtained with benzothiazole sulfenamide accelerators can more efficiently be obtained using a thiocarbamyl sulfenamide accelerator. Since thiocarbamyl sulfenamides utilize sulfur more efficiently than benzothiazole sulfenamide accelerators, they should be used at 15 to 20% higher sulfur levels compared to those used with the benzothiazole sulfenamides. The combination of greater efficiency and higher sulfur level used with the thiocarbamyl sulfenamides allows the accelerator level to be reduced by about 40%. Vulcanizate properties as well as the crosslink networks of these two systems are the same when used in this manner.
Recent Developments in the Flammability of Elastomeric Materials
Authors: Lawson David F.
Published: February 2011

Most of the flame-retardant technology now used with elastomers has been known for some time. Advances have been made in recent years in the understanding of elastomer combustion and inhibition mechanisms, in the measurement and control of visible smoke generation from elastomers, and the toxic effects of combustion atmospheres. By integrating existing technology with recent developments and the likely advances of the future, elastomeric materials will continue to receive acceptance for a wide variety of applications. Author's note: A review stressing quantitative aspects of polymer combustion has recently appeared.
Engineering with Rubber
Authors: Mullins Leonard
Published: February 2011

First I must thank you Mr. Chairman for your most generous introduction. I understand that there will be another opportunity later today to thank the Executive Committee of the Rubber Division of the American Chemical Society for nominating me as the Charles Goodyear Medalist for 1986, for the pleasure of being here today, and for the privilege of addressing you. But I would wish to say, at this stage, how deeply honored I am to receive this most distinguished award. It is a tradition that this address should reflect the author's special interests and his own contribution to rubber science and technology, and they have tended to be autobiographical in nature. However the title which I have chosen, “Engineering with Rubber,” covers a broad field of activity, but in the relatively short time at my disposal I will perforce have to restrict myself to those areas in which I have been personally involved. Like so many recent Charles Goodyear Medalists it was my good fortune to be active during the period of almost explosive growth of polymer science and technology which occurred during the 1940's and 1950's and which provided a proper scientific basis for the polymer industries created during this period. The rubber industry is, of course, much older, but hitherto it had relied upon an essentially empirical approach to provide practical answers to most of its problems. It was also my good fortune to work with and alongside many outstanding individuals both at the Research Association of British Rubber Manufacturers (now the Rubber and Plastics Research Association) and at the Malaysian Rubber Producers' Research Association (formerly the British Rubber Producers' Research Association). To these I owe much and I would wish to share this recognition with my colleagues.
Effect of Cyclohexyl Thiophthalimide on NR Vulcanization Accelerated by Thiocarbamyl Sulfenamide-Dibenzothiazyl Disulfide System
Authors: Datta Rabindra Nath , Das Prasanta Kumar , Basu Dipak Kumar
Published: February 2011

Investigations have been carried out on the effect of CTP on thiocarbamyl sulfenamides, either alone or in combination with MBTS, in the vulcanization of NR. It has been observed that CM, CP, CPTCD, OTCD, and CDB formed from various thiocarbamyl sulfenamides like OTOS, OTCS, and CTOS in the presence of CTP play a vital role in cure retardation. CM and CDB under the experimental conditions have been found to prolong the onset of cure, while CP, CPTCD, and OTCD reduce scorch time. The presence of a substituent on the carbamate N-atom of thiocarbamyl sulfenamides greatly influences cure retardation. OTOS and CTOS give rise to CM and CP respectively in the presence of CTP. OTCS, however, generates both CM and CP under the identical conditions and thus differs from OTOS and CTOS. CPTCD and OTCD formed from thiuramdisulfides have been shown to be poor and scorchy accelerators, and these, like CM and CP, play a significant role in cure retardation.
Characterization of Polymers by GPC-Lalls. II. Concentration Effect of Polydisperse Polymers in GPC
Authors: Shiga S. , Sato Y.
Published: February 2011

The concentration effect in a GPC is studied on the following polydisperse polymers: HDPE, EVA, EPM, and EPDM. The GPC is equipped with a dual detector system consisting of a LALLS and a differential refractometer. A proportional relationship is widely observed between the degree of the concentration effect and the elution concentration, and classified in two groups according to the molecular weight: in the first where the molecular weight is larger than 100–200 thousand, the effect becomes more severe as the molecular weight increases; and in the second where the molecular weight is smaller, the effect is less apparent with the molecular weight. The branched molecule is more gently influenced than the linear one. Hypothetical equations are proposed for the molecular coil-size-reduction effect and the viscosity effect under the experimental conditions. In combination they would constitute most of the concentration effect, though the estimation of the latter effect would remain uncertain because of the optional character of the equation constant. It is indicated that the correction of the concentration effect is necessary to measure long chain branches exactly by GPC.
Analysis of EPM Elastomers by Infrared and NMR Methods
Authors: Johnson-Plaumann M. E. , Plaumann H. P. , Keeler S. E.
Published: February 2011

The IR absorbances at 1465 and 1378 cm−1 formed the basis of an infrared method for estimating the ethylene/propylene ratio in EPM polymers. Calibration curves were set up for both self-supporting and silver chloride supported films of ASTM EPM polymers. The adequacy of the calibration curves was verified by 1H and 13C NMR data and by testing the methods on several commercial polymers. The self-supporting film method provided more reproducible data than the silver chloride film method. Even so, the confidence intervals for predicting the composition of new polymers were rather broad. They could be reduced to about ±2 wt.% ethylene on polymers of 40 to 70 wt.% ethylene by running five analyses. We have illustrated some of the problems which face the analytical chemist in setting up calibration curves with particular focus on the quality of new data arising from the calibration.
Dynamic Mechanical Thermal Analysis and Transmission Electron Microscopy of Elastomer Blends
Authors: Mazich K. A. , Samus M. A. , Killgoar P. C. , Plummer H. K.
Published: February 2011

Dynamic mechanical thermal analysis and transmission electron microscopy have been used to elucidate the structure of binary and ternary blends of NR, BIIR, and IM. Dynamic measurements at 10 Hz were able to resolve loss-tangent peaks into a major peak due to NR and a broad shoulder associated with BIIR and IM. Interpretation of these data in conjunction with electron micrographs indicate that the butyl polymers (BIIR and IM) form a second phase in a matrix of NR for compositions containing at least 67% NR. Dynamic mechanical properties and TEM micrographs of binary blends of NR with BIIR or IM show that the structure of these binary blends differ; IM forms larger, more distinct domains in the NR matrix. This difference in structure may result from the different molecular weights of the butyl polymers and the ability of BIIR to crosslink with NR. TEM micrographs of both binary blends indicate that carbon black is dispersed in the matrix material and is excluded from the isobutylene-rich domains, The two-phase structure of these blends and the partitioning of carbon black between the phases may enhance the fatigue lives of these composites. Cure temperatures in the range from 130°C to 170°C affected the properties and structure of only one blend studied in this work. This blend, an 80:20:20 mixture of NR, BIIR, and IM, respectively, was able to alter its morphology when the cure temperature was elevated. Material cured at 130°C contained domains with a wide variety of shapes and sizes; material cured at 170°C contained uniform, well-defined inclusions. This ternary blend was the only material that also exhibited a higher fatigue life when the cure temperature was raised. Achieving a well-defined dispersion in a two-phase elastomer blend apparently maximizes the fatigue life of the composite material.
Stress—Strain Fields in Compressed Elastomeric Seals and Their Extension to Fracture Mechanics
Authors: Medri Gianluca , Strozzi Antonio
Published: February 2011

The modeling of an elastomer in terms of hyperelastic material has been discussed. The peculiarities of the finite element method when applied to nearly incompressible materials have been underlined. The mechanical analysis of various uncracked elastomeric seals has been treated with particular regard to possible crack initiation. The theoretical aspects of fracture mechanics applied to elastomers have been discussed, and the validity of the J-integral approach has been checked against experiments. The J-integral has been computed numerically in cracked O-ring seals for various fractional compressions and crack lengths. The numerical stress field has been compared to the experimental findings. The influence of the crack length on the contact pressure profile has been considered. Various difficulties still exist in modeling efficiently the elastomeric materials and in developing suitable numerical tools. Nevertheless, it is believed that statistical predictions on the debasement in the sealing characteristics due to viscoelastic effects and to crack propagation will become shortly feasible.
Water Permeation through Elastomer Laminates, II. SBR/EPDM
Authors: Cassidy Patrick E. , Aminabhavi Tejraj M.
Published: February 2011

In summary, the measurements described here suggest that the temperature dependence of permeation rate had an Arrhenius behavior. Activation energies fall within the range expected for those membranes that follow activated transport mechanism. For all single elastomers, salt water exhibited higher permeation rates than did distilled water. The laminates show a directional behavior but more distinctly for distilled water than for salt water. Solubility data alone cannot, however, always account for this phenomenon.
J-Integral and Crack Opening Displacement as Crack Initiation Criteria in Rubber
Authors: Lee R. F. , Donovan J. A.
Published: February 2011

1. Evaluation of ∫σdδ where σ is the net section stress and δ is the deformed crack tip diameter requires only one specimen to characterize the initiation of crack growth in unfilled and carbon-black-filled NR. 2. ∫σdδ is equal to one half of the J-integral for crack growth initiation, which is identical to the Thomas tearing energy for a blunt notch. 3. The critical J-integral for crack initiation increases linearly with carbon black content. 4. The critical crack tip radius for crack initiation is independent of carbon black content, and the required crack tip region stress increases linearly with carbon black content.
Effect of Resin Components on the Reversion Process of Sulfur-Vulcanized Guayule Rubber
Authors: Sloan James M. , Maghochetti Michael J. , Zukas Walter X.
Published: February 2011

An effort to characterize the reversion process of guayule rubber when naturally-occurring guayule resin components are present has shown that these components act as a reversion-retarding material. The amount of reversion resistance varies as a function of temperature, concentration, and type of fatty acid. Of the three fatty acids used, linoleic acid, stearic acid, and oleic acid, linoleic acid performed the best for reversion resistance, followed by stearic acid, then oleic acid. When the temperature was increased 10°C, an increase of 15% reversion was observed. This held true for the three temperatures studied. In addition, the amount of reversion improvement upon addition was 20% reversion. In the case of curing at 150°C, this resulted in 0% reversion. The 20% resistance improvment was consistent for the 3 temperatures studied.
Theoretical Equilibrium Moduli and Swelling Extents for Elastomers Crosslinked in Solution
Authors: Queslel J. P. , Mark J. E.
Published: February 2011

Equilibrium elongation moduli and swelling properties have been calculated for amorphous polymer networks prepared in a diluted reference state of polymer volume fraction υ2C. The three molecular elasticity theories employed are based on (i) an idealized affine deformation model (in which the constraints on junction fluctuations are infinite), (ii) an idealized phantom chain model (in which the constraints are absent), and (iii) the more realistic Flory-Erman theory (in which the constraints vary with crosslinking conditions, degree of swelling, and extent of elongation). A discussion of the dependence of the constraint parameter κ on υ2C is given, and is applied to the calculation of stress-strain isotherms in elongation specifically for cis-polyisoprene cured with dicumyl peroxide. The experimental dependence of κ on υ2C investigated by Erman and Mark was found to be similar to the dependence of the plateau modulus on dilution, and this is consistent with the constrained contour model proposed by Erman and Monnerie.
Equilibrium Swelling of Polyurethane Elastomers
Authors: Oberth Adolf E.
Published: February 2011

Equilibrium swelling of randomly crosslinked elastomers is in satisfactory agreement with a model that considers them to be aggregates of equivalent spheres whose diameter is proportional to Mc1/2. Solvation expands these spheres, the extent of expansion being proportional to the diameter and the strength of the solvent-polymer interaction, but is independent of the number of effective chains per volume unit of the elastomer. A potential mechanistic explanation assumes that the solvent molecules form a weak complex with the elements of the polymeric chain, which forces the segments out of their equilibrium position, thus creating a force that opposes further solvation. Both forces have a very short range and are effective only in the individual segment that has formed the polymer-solvent complex. The magnitude of the extension of the whole chain will be proportional to the number of chain segments undergoing solvation, which leads to the mathematical relationship that forms the basis of Equation (6). Since the swollen volume is many times the volume of the network rubber, it is clear that only a (comparatively) small fraction of the solvent molecules will interact directly with the polymer, many of which will just fill the space created by the expanding network. In weak solvents, or at very high levels of crosslinking, where the swelling volumes are small, the extent of swelling is likely to depend on the polymer content, and the presented mechanism does not apply.
A Study of Permeation and Diffusion of Aqueous Salt Solutions through Polyurethane and Polysiloxane and Their Laminates
Authors: Wells Lisa A. , Cassidy P. E. , Aminabhavi T. M. , Perry R. B.
Published: February 2011

Effect of ion size on water permeation through polyurethane, polysiloxane, and their laminates has been studied. The results of these studies for the polyurethane membranes correlated well with the reported values of water permeation through a variety of other polyurethane elastomers. Permeation rates and the Arrhenius relationship of polyurethane and polysiloxane membranes were found to be similar. Solute size showed no observable effect on water permeation through polyurethane, polysiloxane, or their bilayer laminates, within experimental error. A small effect of solute size was observed for diffusion of water into polyurethane. Permeation rates of the bilayer laminates demonstrated a small directional dependence or “valving” effect. In the light of this evidence, it may be suggested that highly permeable systems, such as polyurethane and polysiloxane, are relatively insensitive to permeant composition.
Structure and Dynamic Properties of Solution SBR Coupled with Tin Compounds
Authors: Tsutsumi F. , Sakakibara M. , Oshima N.
Published: February 2011

The relation between the structure of the Solution SBR and the dynamic properties of carbon-black-filled SBR vulcanizates have been studied. The results obtained were as follows: 1. The hysteresis of the Solution-SBR vulcanizates was reduced markedly by the introduction of tin—carbon bonds at the polymer chain end. 2. Among the structures of tin—carbon bonds, tin-butadienyl bonds were much more effective for the reduction of hysteresis than were tin—styryl bonds. 3. Solution SBR coupled with tin compounds with molecular weight of less than 105 was not so effective for the reduction of hysteresis. Furthermore, the mechanism of the improvement of dynamic properties was investigated. It was found that polymer—carbon-black bonds were formed through the reaction of tin—carbon bonds with the functional groups of carbon black. From model reactions, it is suggested that quinone groups on carbon black are involved.
Products and Mechanism of the Thermal Reaction between 2,4-Dichlorobenzoyl Peroxide and n-Pentadecane, an Approximation of the Crosslinking of Silicone Rubbers
Authors: van Drumpt J. D.
Published: February 2011

Unlike most organic rubbers, viscoelastic silicone rubbers can be either very difficult or impossible to crosslink with sulfur cure systems. Although Pt-catalyzed addition reactions and high-energy radiation curing techniques are available, most heat curing of silicone rubbers is done by means of organic peroxides. Of those, 2,4-dichlorobenzoyl peroxide is the most widely used, due to its versatility, its speed, and the low amount of gaseous decomposition products which it produces. The latter fact allows it to be used for pressureless vulcanization. In fact, 2,4-dichlorobenzoyl peroxide is the only peroxide available on the market that is successfully employed for hot air vulcanization (HAV) of extruded profiles and tubing. In addition, it is widely used in injection, compression, and transfer molding of both vinyl and nonvinyl containing gums. In spite of its widespread use, little factual knowledge is available about the reaction mechanism and products of this peroxide. This is mainly due to the analytical inaccessibility of the crosslinked silicone rubber end product and the evaporation losses caused by processing and curing in (partly) open systems. The present study addresses these issues by using a closed model system. Although many low-molecular-weight polydimethylsiloxanes are available, n-pentadecane was preferred as the substrate because it allowed a direct comparison to be made with similar studies done with other crosslinking peroxides (see e.g., References 2 and 3). The C—H bond strengths in this saturated alkane (410 kJ/mol for primary and 385 kJ/mol for secondary H atoms) were felt, to be close enough to that in polydimethylsiloxanes (approximately 412 kJ/mol) to make it an acceptable model substance for the latter. The system also allowed an estimate to be made of the amount of polychlorobiphenyls (PCBs) that might be formed under normal cure conditions.
Phase Behavior of Polymer Blends
Authors: Han Charles C.
Published: February 2011

We have demonstrated in two separate cases that SANS experiments can be used to obtain binary interaction parameters effectively and accurately. With measured χ as a function of composition and temperature, the free energy of mixing can be obtained at least numerically. The phase diagram including spinodal curves and cloud-point curves can be predicted. The second derivative of free energy of mixing w.r.t. composition, ∂2ƒ/∂ϕ2, can be used directly in the kinetics studies of spinodal decomposition. In the polybutadiene/polybutadiene case, individual pair interaction parameters can be separated out. Microstructure effect is the main contribution to the incompatibility of the blends. Nevertheless, with the use of the random copolymer theory, phase behavior can be predicted.
Composition Distribution of Acrylonitrile-Butadiene Copolymers as Analyzed by High-Performance Liquid Chromatography
Authors: Asada N. , Hosozawa H. , Toyoda A. , Sato H.
Published: February 2011

The separation of acrylonitrile-butadiene copolymer (NBR) was investigated by high-performance liquid chromatography (HPLC). The copolymer was most successfully separated on the basis of chemical composition by using crosslinked 2-chloroacrylonitrile gel as the stationary phase and with a gradient elution of chloroform/n-hexane. The separation was found to be carried out by an adsorption mechanism and essentially independent of the molecular weight of the sample. The observed chemical composition distributions (CCD) agreed with those calculated from the copolymerization theory.
Origin of the Self-Reinforcement in PDMS Bimodal Networks
Authors: Smith T. L. , Haidar B. , Hedrick J. L.
Published: February 2011

For three series of bimodal networks, the stress-relaxation rates and the tearing energies were shown to exhibit maxima at about the same concentrations of short chains as those at which the tensile strengths, reported earlier, also exhibit maxima. These findings clearly show that the reinforcement produced by the addition of short chains results because chain mobility is reduced substantially, especially when the concentration of short chains is 30 to 40% by weight (Figures 1 and 5). For each series of bimodal networks prepared in our laboratory, the maximum tensile strength also occurs when the concentration of short chains is about 30% by weight. When a bimodal network is deformed progressively, deformation occurs in the long chains moving through the matrix of short chains. Also, the network junctions and the attached short chains must be dragged along with the deforming long chains. It is probable that the low mobility of the chains (high dissipation of energy), which accounts for the high tensile strengths, especially in networks having 30% or so by weight of short chains, results primarily from the energy dissipation associated with such complex molecular rearrangements. It was also shown that the maximum tensile strength in a series of networks increases with an increase in the difference between the molecular weights of the long and short chains, or as shown in Figure 7, with a decrease in MS/ML.
Biaxial Extension Studies Using Inflation of Sheets of Unimodal Model Networks
Authors: Xu P. , Mark J. E.
Published: February 2011

Measurements of uniaxial extension and compression were made on model poly(dimethylsiloxane) (PDMS) [−Si(CH3)2−O−]x networks to examine the molecular theories of rubber elasticity. The stress-strain isotherms showed that the Flory-Erman theory of rubber elasticity is in good agreement with experimental data from extension to compression (α−1: 0.3–13), while the Mooney-Rivlin relation is useful only in a specific region of extension ratio (α−1: 0.3–0.8). The experimental results strongly support the theory of Flory-Erman, rather than those of phantom and affine networks. It is thus evident that the Flory-Erman theory of rubber elasticity is the more nearly correct.