bluuebunny/crossref_metadata_2025 huggingface dataset:
Urethane Energy Absorbers for Automobile Bumpers
Authors: Weller P. A.
Published: February 2011

It is believed that the concepts and data presented here are not only useful for the design and application of urethane foam for bumpers, but demonstrate the inherent fitness of the material for this purpose. To review quickly the factors listed in the beginning of the paper: 1. Urethane-faced bumpers will not only prevent damage to the bumper or vehicle, but will eliminate or minimize damage to the object impacted. 2. Repeated tests at severe overloads have demonstrated the recoverability of the foam after repeated impacts. 3. High hysteresis of urethane results in minimum rebound. 4. The material is velocity responsive within the specification range. 5. A wide variety of usable arrangements plus ready moldability provide considerable styling freedom. 6. Temperature compensation features assure designable performance consistency. 7. High efficiency or form factor is achievable, resulting in minimum force and stroke. 8. No maintenance is required. 9. Urethane microcellular foam is among the lower cost plastic materials on a per pound basis. Low densities and discreet placement can result in very competitive systems. Steel stroking bumpers are designed to ward off blows with emphasis on protection of the vehicle on which they are mounted. As a result, they present a far more hostile motoring environment than ever before for anything or anyone except another similar bumper. Urethane bumpers have a great potential for creating a far less hostile environment for everyone and everything, including fronts and rears of current vehicles, sides of all vehicles, other objects, pedestrians, and occupants. The current specification severely inhibits the realization of that potential. Doing anything about it is no easy matter since it could easily lead into a specification of horrendous complexity. However, following is one suggested approach. In testing for occupant protection, a manikin or dummy is selected as a representative test device. It is by no means truly interchangeable with the real thing or all situations, but does provide a firm and representative means for reasonable evaluation and standardization. In like manner, it would be possible to select a reasonably typical front or rear current-model configuration to serve as a representative test device on the face of the pendulum, and simply specify “no damage to the test device” rather than “no contact to specified planes”. A manufacturer could be contracted with by the government to produce identical test devices for all who wished to run such tests. Such a specification could be amended to the current specification as an alternate, rather than attempting to revise what is already an excellent document for the steel stroking bumper.
An Elastomeric Impact-Absorbing Bumper System
Authors: Rusch K. C. , Slessor J. M.
Published: February 2011

An elastomeric impact absorber was selected from a variety of mechanical designs involving a mechanical strut (Torshok), a buckling-column flat spring and an involute spring, several hydraulic shock absorbers, and various concepts utilizing elastomeric polyurethane foam. Functional and economic criteria as well as manufacturing considerations dictated the choice. The following list outlines the functional attributes that favored a rubber shear spring in the elastomeric impact absorber: 1) Simple, rugged design—all parts except rubber blocks are conventional steel stampings. 2) The device is capable of accepting high angular impacts. Due to the rugged I-beam arm, comer impacts and large torsion loads are tolerated. 3) Mounting requirements are incorporated in the case of the unit. This eliminates the need for separate brackets which results in a cost savings as well as a stronger, more integrated attachment between device and structure. 4) The device has very high compliance in skewed loading. This refers to the bumper geometry resulting from an in-line impact on one unit causing it to stroke fully while the other unit remains unstroked. Since the I-beam arm is unrestricted in the lateral direction except by the rubber blocks, the arm of the unstroked unit can assume an angular position in the plan view and does not bind up the bumper system nor does it unnecessarily load absorber faceplate or bumper reinforcement. 5) A high degree of interchangeability could be achieved with this device. In 1973, four basic designs satisfy the front bumper requirements of fourteen (14) different car lines, including attachment requirements. In addition to the many functional attributes for which this unit was selected, there are also several non-functional factors that were of significance. Some of these are: 1 ) The unit, with the exception of the rubber blocks, requiring only stamping plant facilities and technologies to fabricate, can be contained within existing facilities at moderate investment costs. 2 ) Only limited training is required for the work force. The typical automotive worker can be easily trained to produce this unit. 3) The only critical part in the device, the rubber block, can be obtained from a sufficient number of rubber suppliers to ensure adequate supply protection and complete rubber technology support. In summary, high volume production of a bumper impact absorbing device makes necessary a design that is simple yet rugged and reliable.
The Effect of Carbon Black Type on the Dynamic Properties of Natural Rubber
Authors: Ulmer J. D. , Chirico V. E. , Scott C. E.
Published: February 2011

The influence of carbon black type on the dynamic properties of natural rubber is examined for nine carbon blacks, encompassing a wide range of structure and surface area. The dynamic properties are measured at 23° C and 100° C, over a 2 decade range of log frequency, and over a range of 1 to 25 per cent dynamic strain. The effect of carbon black structure and surface area on dynamic properties of a natural rubber compound are dependent on the combination of strain amplitude and frequency test conditions. The effect of carbon black surface area and structure at different temperatures varies on an absolute basis but not necessarily on a relative basis. Correlations of forced non resonant measurements of dynamic properties with dynamic measurements using other instruments confirms the strain amplitude and frequency interaction with carbon black type. Also, the Goodyear-Healy Rebound machine, the Goodrich Flexometer, and the Pirelli Hysteresimeter can be used to estimate basic dynamic properties over limited strain amplitude and frequency conditions. In addition, mixing procedure was found to have a significant effect on the dynamic properties of a natural rubber compound filled with N-327.
Some Observations on the Mechanism of Cure Retardation
Authors: Son P. N.
Published: February 2011

1. A good retarder reacts fast with MBT and forms a non-scorchy accelerator. 2. The decrease in cure rate (k2.) is attributable to the slow cure rate of 2-cyclohexyldithiobenzothiazole (CDB). 3. Cyclohexyl polysulfides (CPS) and cyclohexylthioamine are believed to be also involved in the cure retardation. 4. The new retarder can stop crosslinking by intercepting the crosslink precursors. 5. Formation of cyclohexyl polysulfides (CTP) and their lack of curing property may be responsible for the low state of cure when the new retarder is used. These results are schematically summarized in Figure 7.
Electron Spin Resonance Study of Phenolic Antioxidants. II. Free Radical Structures Arising from Antioxidants Containing the 3,5-DI-Tert.-Butyl-4-Hydroxy-Benzyl Group
Authors: Westfahl J. C.
Published: February 2011

Oxidation of a series of phenolic antioxidants, or compounds related to antioxidants, was carried out using ferricyanide ion in dimethylsulfoxide solution. The free radicals produced were studied by ESR spectroscopy. Most of the antioxidants examined contained one or more 3,5-di-tert-butyl-4-hy-droxybenzyl groups. Based on their behavior on oxidation, the compounds can be divided into two classes. One class forms a relatively unstable primary radical which decomposes to give 2,6-di-tert-butyl quinone methide.
Analysis of Chain Unit Structure of Poly(Butadiene) by Means of the HR-300 NMR Spectrometer
Authors: Santee E. R. , Malotky L. O. , Morton M.
Published: February 2011

The data presented in this paper can best be summarized as follows: 1. With present equipment 13C-NMR cannot distinguish cis—trans junctures in BuLi catalyzed poly(butadiene). 2. Cis—trans content in poly(butadiene) can now be determined by 1HNMR at 300 MHz. 3. The cis—trans content in low vinyl n-BuLi catalyzed polymers is best determined in the olefinic region. 4. The cis—trans content in high vinyl is best determined in the aliphatic region, although contents above 60 per cent become difficult to determine because of overlap with the methine proton of the vinyl unit. 5. Cis—trans ratios are constant over the measurable range of vinyl content. 6. The cis—trans triad sequence distribution and hence the mole fraction of triads can be determined by 1HNMR at 300 MHz. 7. The triad sequences best fit a random distribution. 8. The 1,2 unit is inserted in a random manner, i.e., the unit enters the chain with no preference for any triad sequence.
The Dependence of Processability on Molecular Weight Distribution of Elastomers
Authors: Tokita N. , Pliskin I.
Published: February 2011

After examining the mechanism of mixing of elastomer with filler by both internal mixers and open mills, the failure characteristics of an elastomer (extension to break and ratio of elasticity to plasticity) were found to be important properties affecting the filler wetting and dispersion rates. The failure characteristics have also been shown to depend on the polymer MWD, branching, and microstructure. A quantitative characterization of deformational behavior and failure of uncured material has been presented. Also, an attempt has been made to establish a link between the more basic properties of elastomers and processability, particularly the rate of filler dispersion in mixing. The variation of compound Mooney torque and die swell with mixing time can be explained theoretically by taking account of the occluded rubber trapped by the carbon black agglomerates. As filler dispersion increases, the amount of such occluded rubber decreases, Mooney torque decreases, and die swell increases as expected from the theory of rheology of composites.
Effect of the Compatibility of Rubbers on the Viscous Flow Properties of Their Binary Mixtures
Authors: Kongarov G. S. , Bartenev G. M.
Published: February 2011

The viscosity of binary systems of incompatible polymers is lower than that of the individual rubbers. In the case of compatible polymers, the viscosity of the systems changes additively with its composition or may increase somewhat. The degree of compatibility of the polymers affects the size of the entrance effect and the character of its dependence on strain rate.
Rheology of Elastomer Blends
Authors: Folt V. L. , Smith R. W.
Published: February 2011

The melt flow properties of certain elastomer blends are shown to be a function of the mixing history and the morphology of the blends. And, more significantly, the melt flow properties are found to be non-additive functions of the melt flow properties of the homopolymers comprising the blends. Mixing studies using a Brabender Plastograph show that blends of certain elastomers generate much higher temperatures while, simultaneously, generating much higher torques than either of the homopolymers over time cycles of practical interest in elastomer processing operations. A sharp minimum in the early stages of the torque/time relationship in the mixing operation, followed by an abrupt maximum, is correlated with abrupt changes in the morphology of the blends as determined by electron microscopy. The morphological structure of certain well mixed elastomer blends consists of domains of the lesser component dispersed into a matrix of the major component. For well mixed blends near 50/50 weight per cent composition the morphological structure appears to consist of two continuous interpenetrating phases. Mooney values as well as Plastograph torque values are observed to be non-additive functions of the corresponding properties of the homopolymers. A minimum in the Mooney/blend ratio relationship over a rather narrow range of blend compositions is observed for certain systems. In contrast, the Plastograph torque values for the identical compositions are observed to be higher in all instances than those for the homopolymers. A phenomenological description of these apparent contradictions is obtained from a simple analysis of capillary melt viscosity measurements carried out on the same blends. These melt viscosities are also a non-additive function of the viscosities of the homopolymers. Minimum and/or maximum viscosities for specific blend ratios are observed for a given rate of shear. The minimum or maximum shift (s) to different blend ratios with changes in the rate of shear. Viscosity/composition plots similar to the Mooney/composition plot are observed at low rates of shear and plots similar to the torque/composition plot are observed at high rates of shear. These behavior patterns remain unexplained at this time.
Dependence of the Glass Transition Temperature on the Composition of Elastomer Mixtures
Authors: Zlatkevich L. Yu , Nikolskii V. G.
Published: February 2011

The dependence of the glass transition temperature on the composition of some compatible, partially compatible, and incompatible elastomer mixtures have been investigated by means of the radiothermoluminescence method. It has been established that the glass temperature of a homogeneous mixture of two elastomers, Tgm, is related to the glass temperature of these elastomers, Tg1 and Tg2, by Tgm=Tg2−(Tg2−Tg1)⋅W1c, where C is lower than unity for each investigated mixture. Incompatible mixtures are characterized by two glass temperatures practically equal (to within 0.5° C) to that of initial components in a rather wide range of concentrations. Two Tg's are also characteristic of partially compatible systems though their values are different from those of the individual components.
Observations of Die Swell Behavior of Filled Elastomers Measured Automatically with a New “Die Swell Tester”
Authors: Pliskin Irwin
Published: February 2011

A new instrument has been developed to measure the elastic memory of rubber or plastic compounds by automatically indicating the die swell of the material when a small amount is extruded. It has the potential to be used as a quality control instrument in a manufacturing plant. The new Die Swell Tester measures the time (in sec.) necessary to extrude a fixed length of extrudate at a constant volumetric flow rate. The time measurement is directly proportional to the die swell when expressed as an area ratio, and it can be made equal to the die swell by choosing the extrudate length judiciously. Furthermore, it is measured electronically and has a digital readout in hundredths of a second. Measurements made on tire tread compounds using the Die Swell Tester correlate well with die swell measurements made using a more conventional gravimetric method. The die swell of filled elastomers generally decreases with increase in filler loading and structure. When a composite of fixed filler loading is mixed, its die swell first increases due to the dispersing of filler, but it eventually reaches a maximum and begins to decrease. The composite viscosity, on the other hand, decreases monotonically as it is mixed. These variations can be explained by taking into account changes in the amount of rubber occluded by filler agglomerates and simultaneous degradation of free rubber during the mixing process. The time to reach the peak in die swell is a simple macroscopic measure of the filler dispersion rate for a given elastomer-carbon black composition.
Investigation of the Molecular Structure of Synthetic Cis-Polyisoprene
Authors: Grechanovskii V. A. , Ivanova L. S. , Poddubnyi I. Ya
Published: February 2011

Some thermodynamic and hydrodynamic properties of solutions of a series of commercial samples of cis-poly(isoprene) (SKI-3 rubber) were studied. Data on solubility, gel content, and its swelling in different solvents was obtained. It was shown that the intrinsic viscosity of the whole rubbers, as a rule, diminishes with transfer of the gel into solution. The obtained experimental data confirm the supposition made earlier about an aggregate and not a network structure of synthetic cis-poly (isoprene) gel.An approximate equation for finding the average number of macromolecules entering into the gel aggregates was obtained. It was shown that the average content of macromolecules in one aggregate varies from several tens to several hundreds for the investigated samples and that the aggregates are characterized by an extremely broad distribution with respect to the number of macromolecules entering into them.
A Study of Mechanical and Optical Properties of an Alternating NBR and an Emulsion NBR
Authors: Mukherjee U. P. , Goldstein C.
Published: February 2011

At low elongation, over the range of temperatures and frequencies studied, the dynamic properties (elastic modulus and loss factor) and activation energy for the glass-rubber transition are the same for highly alternating and emulsion copolymers of acrylonitrile and butadiene. At higher elongation the stress-birefringence and x-ray data on cured (1.7 phr dicumyl peroxide) highly alternating copolymer show the occurrence of strain-induced crystallization, whereas the emulsion copolymer does not crystallize under strain. The stress-strain data for the highly alternating copolymer cured at 1.7 phr dicumyl peroxide and for the emulsion copolymer cured at 1.7 phr and 0.8 phr show that at 1.7 phr dicumyl peroxide the highly alternating copolymer has higher ultimate strength. However, the emulsion copolymer cured by 0.8 phr dicumyl peroxide shows tensile properties similar to those of the highly alternating copolymer cured by 1.7 phr dicumyl peroxide. Therefore, it may be concluded that the increased strength and ultimate elongation of highly alternating copolymer, as reported by Furukawa, are due to the fact that at the same curative level the emulsion copolymer gets over-cured resulting in lower ultimate strength and elongation. This present study indicates that it is not appropriate to compare the ultimate properties of the emulsion and highly alternating copolymers cured at the same level of dicumyl peroxide. Slight adjustment in curing condition brings highly alternating and emulsion copolymers closer in tensile strength and ultimate elongation. In conclusion, it may be said that this study indicates that highly alternating NBR shows tensile properties similar to those obtained for emulsion NBR already produced commercially.
Stress-Strain Isotherms and Stress-Temperature Coefficients of Poly(Dimethylsiloxane) Networks in Compression
Authors: Chen R. Y. S. , Yu C. U. , Mark J. E.
Published: February 2011

Stress-strain isotherms at 30, 45, 60, 75, and 90°C have been determined for compressed, unswollen poly(dimethylsiloxane) networks which had been prepared either in the undiluted state or in solution. For these networks in compression, deviations of the dependence of stress on strain from that predicted by the statistical theory of rubberlike elasticity are much less than is the case for polymer networks in elongation. The present data nonetheless give a value for the temperature coefficient of the unperturbed dimensions of the network chains which is in good agreement with published results on networks of poly(dimethylsiloxane) in elongation. This agreement thus seems to validate the intentional disregard of such deviations in analyses of stress-temperature measurements.
Evaluation of the Theories of Rubberlike Elasticity Using Swollen Networks Crosslinked at Different Degrees of Dilution
Authors: Yu C. U. , Mark J. E.
Published: February 2011

A recently reported study described the preparation of elastomeric networks by crosslinking poly(dimethylsiloxane) chains in both the undiluted state and in solution. Measurements of the moduli of these networks in the unswollen state gave results supporting the theory of rubberlike elasticity developed by Flory and coworkers, rather than the corresponding theory due to James and Guth. These results were not entirely unambiguous, however, because of complications due to departures (“2C2 corrections”) from the expected elastic equation of state. Much of this uncertainty has now been removed by measurements of the moduli of such networks in the swollen state, a condition under which the effects of the 2C2 contributions are known to be minimized. These new results strongly support the earlier conclusion that the Flory theory is the more nearly correct. Nonequilibrium effects, as well as the 2C2 corrections, diminish upon incorporation of a diluent into the crosslinked network; similar decreases occur if diluent had been present during the crosslinking process, even if such diluent is removed prior to the stress-strain measurements. Analysis of these additional results suggests that the 2C2 correction cannot be entirely due to nonequilibrium effects.
Model Polystyrene Networks
Authors: Allen G. , Holmes P. A. , Walsh D. J.
Published: February 2011

Model polystyrene networks have been prepared, at different concentrations in an inert solvent, in such a way that the number of crosslinks is accurately known, and the topology of the network can be varied in a controlled way. The contribution of various network defects to the modulus of the network has been examined. A theoretical estimate of their effect has been made and compared to the experimental result. Two tentative conclusions have been made; first, that the front factor A in the equation for the free energy of deformation of the network has a value of 1/2 and not the alternative value 1; and secondly that the contribution of entanglements to the modulus of the network varies as the concentration squared rather than as the concentration to the first power.
A Study of Compatible Polymer Mixtures
Authors: Kwei T. K. , Nishi T. , Roberts R. F.
Published: February 2011

The compatibility of various compositions of polystyrene (PS)-poly (vinyl methyl ether) (PVME) films and the thermally induced phase separation of such mixtures have been studied using several methods. Density measurements indicate extensive mixing of the PS and PVME chains in compatible PS-PVME films. Vapor sorption measurements have enabled calculation of the PS-PVME interaction parameter X′23 as a function of composition and temperature. The parameter X′23 is negative for compatible PS-PVME films in the composition range 35-65 wt % PVME satisfying the thermodynamic criterion for stability in a binary mixture. The temperature dependence of X′23 for the PS-PVME system suggests the existence of a lower critical solution temperature and an upper critical solution temperature. Vapor sorption measurements also indicate that the diffusion of benzene into a 45.3:54.7 PVME-PS film is Fickian, supporting the notion of extensive mixing of PS and PVME chains in the compatible mixture. Temperature-dependent measurements of spin-lattice relaxation time T1 component, spin-spin relaxation time T2, and fraction of long T2 component by pulsed NMR indicate that compatible PS-PVME films can be described as microheterogeneous, in which PVME and PS chains, although being extensively mixed, are not completely mixed on the segmental scale. This is to be expected based on excluded volume and geometrical considerations.
Effect of Carbon Black on Poisson's Ratio of Elastomers
Authors: Holownia B. P.
Published: February 2011

The experimental method developed is mostly suitable for measuring K of relatively incompressible materials such as members of the elastomer family. The accuracy of K values are estimated to be within ±3% for all rubber specimens. Its use can be extended to plastics with somewhat reduced accuracy. The results show that bulk modulus K for the four different rubbers tested increases almost linearly with carbon black content while the Young's modulus E increases much more rapidly as shown in Figure 3. It is interesting to note that Poisson's ratio v calculated using K and E does not fall below 0.4940 (Figure 5), and the value of v=0.4997 as quoted in engineering handbooks would be reasonable to use for most practical applications where the carbon black content is not excessive.
Degradation of Vulcanizates and Their Identification by IR Spectrometry
Authors: Gross D.
Published: February 2011

Three methods have been discussed which have been successfully used for the degradation of vulcanizates for infrared analysis: pyrolysis between 450 and 600°C, degradation in 1,2-dichlorobenzene, and incomplete degradation at 200°C. Because of the relatively low cost, pyrolysis is generally used for the identification of single elastomers, but this method is less suited to blends where it may lead to the loss of ir bands characteristic of a certain component, e.g. polybutadiene. It is similarly unsuited when polymers which form mostly gaseous components are present in small amounts. Since it cannot be excluded in the analysis of vulcanizates of unknown composition, it is recommended to confirm the identification by partial decomposition at 200°C. Because of its greater cost, degradation in 1,2-dichlorobenzene is preferred only for vulcanizates containing small proportions of thermally stable rubbers. When one operates in this way, it is safe to assume that no polymer components will be missed which constitute more than 20 wt % of a rubber blend. Below this limit, identification depends greatly on the components of the blend.
Free Radicals Generated in Rubber during Fracture
Authors: DeVries K. L.
Published: February 2011

EPR has been used to measure molecular phenomena during fracture of elastomers. To date, because of various technical limitations, the studies have been largely confined to identification of the polymer chain scission site during fracture at low temperature in rubbers, to studying ozone-stress-induced cracking of rubber, to development of a micro-macro Griffith-type failure criteria for this type of failure, and lastly to systematic investigation of the role of filler-matrix interaction in fracture of filled elastomers. It is hoped that the brief outline presented here will give the reader some insight into the uses and potential of the EPR methods for the study of fracture. As a final note, while we have concentrated almost totally on EPR fracture studies in rubbers, there has been fairly extensive EPR work on fracture in oriented plastic, fibers, and films. Even though some of this knowledge may be transferable, directly or indirectly, to elastomers, it has not been reviewed here, but important aspects of these studies have been reviewed elsewhere.
Processing Conditions in the Batch-Operated Internal Mixer
Authors: Palmgren H.
Published: February 2011

This review represents an attempt to summarize and discuss some of the literature on the batch operated internal rubber mixer, with the primary view of studying processing conditions and how they influence efficiency and productivity of the process. The scope does not include materials to be mixed, their physical state, order of loading the mixer, compounding principles, systems layout, machine design, automation, mechanization, labor utilization, or other aspects of the mixing process. The discussion is limited to mixing and processing conditions connected with typical compounds, normally based on general-purpose rubbers, which today comprise by far the largest share of rubber batches mixed. It is assumed that the reader is acquainted with the mixing process and with rubber technology in general. The principal elements of the internal rubber mixer are sketched in Figure 1. Some scattered and not very coherent data on important makes of rubber mixers are collected in Tables II, III and IV and referred to in the following discussions. Since the different machines may have different applications, caution should be used in making intercomparisons. It is hoped that this review will contribute to the understanding of the mixing process, and its efficient utilization. A list of problem areas is presented at the end with the hope of stimulating future research.
Study on Bound Rubber in Silicone Rubber Filled with Modified Ultrafine Mineral Powder
Authors: Wu Jihuai , Shen Zhen , Hu Donghong , Huang Jinling , Chen Naisheng
Published: February 2011

The bound rubber measurement method was improved by ethylenediamine (NH2-CH2-CH2-NH2) replacing ammonia (NH3) as the basic agent. Using the new method, the influence of organic base on bound rubber content was investigated, the relation between bound rubber content and the mechanical properties of the silicone rubber filled with modified ultrafine mineral powder was studied, and the interaction between silicone rubber matrix and mineral filler was discussed. As a result, it is suggested that chemical interaction plays the main role in the bound rubber of silicone filled with modified ultrafine mineral powder.
Carbon—Silica Dual Phase Filler: Part V. Nano-Morphology
Authors: Murphy Lawrence J. , Wang Meng-Jiao , Mahmud Khaled
Published: February 2011

This paper demonstrates that the carbon—silica dual phase fillers are comprised of aggregates containing both carbon and silica phases. The silica is shown to be finely distributed among the carbon phases within the aggregates and within the particles of the dual phase aggregates. Analysis of the silicon content and pore volumes before and after treatment with hydrofluoric acid indicates that the silica is incorporated into the particle matrix, rather than exclusively at the surface. The silica domains are estimated to have dimensions similar to the dimensions of the carbon crystallites.
Crystallization Behavior and Strength of Natural Rubber Isolated from Different Hevea Clone
Authors: Kawahara Seiichi , Isono Yoshinobu , Kakubo Takashi , Tanaka Yasuyuki , Aik-Hwee Eng
Published: February 2011

Crystallization behavior of natural rubbers of different clonal origins, i.e., RRIM 600, 60/2, 2025, 2026, and skim rubbers, was investigated by dilatometry at −25 °C. The latex samples were deproteinized with a proteolytic enzyme in the presence of surfactant. Skim rubbers were purified by centrifugation followed by acetone-extraction. The over-all crystallization rate of acetone-extracted rubbers could be divided into two categories: one includes RRIM 600, 60/2 and 2025, and the other RRIM 2026 and skim rubbers. This is attributed to the differences in the level of linked fatty acid groups and gel contents. The minimum level of linked fatty acid ester groups required to promote crystallization of natural rubber is about 2.8 mmol/kg. The green strength of the rubbers is dependent on the level of linked fatty acid ester groups.
High Strain Hysteresis Loss of Rubber Vulcanizates under Pure Shear and Constrained Extension and Influence of Filler
Authors: Kar Kamal K. , Bhowmick Anil K.
Published: February 2011

An experimental analysis of hysteresis loss, hysteresis loss ratio and input energy of natural rubber (NR) and styrene-butadiene rubber (SBR) vulcanizates having variations of loading of carbon black, precipitated silica and clay has been carried out under uniaxial, pure shear and constrained extension modes over a range of extension ratios (1.0 to 2.2 and 1.2 to 4.0 in X and Y directions, respectively), number of cycles (1 to 8) and temperatures (25 to 125 °C). Hysteresis loss, hysteresis loss ratio and input energy increase with an increase in filler loading, extension ratio (in both directions) and reinforcement. These parameters decrease with an increase of temperature and number of stretch cycle. Hysteresis loss, loss ratio and input energy under constrained extension are higher than those under pure shear and uniaxial modes. NR and SBR vulcanizates show similar behavior. Universal expressions relating energy input at any extension ratio, W1, to the hysteresis loss (Hy) as well as hysteresis loss ratio (Hy)r under uniaxial, pure shear and constrained extensions have been developed.
Studies of Peroxide Curing of Polybutadiene/Zinc Diacrylate Blends by Fast FT-IR Imaging
Authors: Oh Sung Joon , Koenig Jack L.
Published: February 2011

Fast Fourier transform infrared (FT-IR) imaging measurements of cured polybutadiene(PBD)/zinc diacrylate(ZDA) showed a heterogeneous distribution of zinc diacrylate. The phase structures were classified as PBD-rich and ZDA-rich domains. Upon curing, the increase in the infrared aliphatic CH stretching mode at 2916 cm−1 and the decrease in unsaturated CH stretching mode at 3075 cm−1 were observed as the single bond crosslinks were formed at the expense of double bonds. In a solvent diffusion experiment with toluene of these cured blends, it was observed that more solvent is imbibed into the PBD-rich matrix than the ZDA-rich domains. The difference is due to the lower swelling ratio of ZDA-rich domains than that of PBD-rich matrix.
Production of Soluble Protein Free Latex by Radiation Process
Authors: Varghese Siby , Katsumura Yosuke , Makuuchi Keizo , Yoshii Fumio
Published: February 2011

During irradiation of natural rubber (NR) latex for vulcanization, the latex proteins undergo disintegration which leaves a high soluble protein content in latex products. In order to follow up the effects of radiation on NR proteins, field latex was irradiated with γ-rays and the soluble protein concentration in the rubber phase and serum phase were analyzed. It was found that the water solubility of proteins in the latex increases with increasing dose. The soluble protein content in the cream phase (rubber) decreased where as that in the serum phase increased with radiation dose. SDS-PAGE analysis revealed that the 27 kD protein together with 14 kD appear in the radiation vulcanized latex up to a radiation dose of 160 kGy and at 320 kGy they disappear due to the disintegration by radiation. A new process for the preparation of protein free latex has been developed. In the new process the radiation-prevulcanized, centrifuged latex is subjected to dilution and then centrifuged. In the case of field latex, it is irradiated first and then centrifuged after dilution. The new process results in prevulcanized latex almost free from soluble proteins. Tensile strength of samples produced by the new process is comparable to that from the conventional radiation process.
Frictional Sliding on a Constrained Rubber Layer: A Simple Model for a Class of Damping Devices
Authors: Li C. G. , Steif P. S.
Published: February 2011

Resistance to the steady sliding of a cylinder over a thin rubber layer is studied theoretically. This problem underlies a model being developed for a new class of damping devices. A quantitatively accurate model requires an accounting for the amplitude-dependent dynamic moduli of industrial-grade rubbers filled with carbon black. This accounting is hindered, however, by the lack of a full multiaxial constitutive law reflecting the nonlinear, amplitude-dependent behavior of filled rubbers. Accordingly, this paper sets forth approximate methods of analysis which indirectly account for the nonlinear behavior; these ultimately lead to compact solutions which can be used in the design of new devices.
Surface Activity and Chemistry of Thermal Carbon Blacks
Authors: Darmstadt H. , Cao N-Z. , Pantea D. M. , Roy C. , Sümmchen L. , Roland U. , Donnet J-B. , Wang T. K. , Peng C. H. , Donnelly P. J.
Published: February 2011

The surface energy of thermal and furnace carbon blacks was determined by inverse gas chromatography (IGC) at infinite dilution. In general, the specific surface energy decreases with decreasing carbon black specific surface area. However, there is also an influence of the concentration of impurities during the carbon black production. The surface energy decreases with decreasing concentration of impurities. The carbon black surface and bulk chemistry was studied by electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectroscopy (SIMS) and Raman spectroscopy. Scanning tunnelling microscopy (STM) was used for characterization of the surface morphology. Thermal grades of carbon black produced from high purity natural gas feedstock do not contain fewer surface functional groups than the other grades. No correlation between the concentration and nature of the oxygen and sulphur surface groups and the carbon black surface energy was found. Instead, a correlation between the surface energy and the polyaromatic character of the carbon black surface exists. Both increased in the order: thermal blacks from high purity natural gas feedstock < thermal black from oil feedstock < furnace blacks. The increase of the surface energy might be related to the formation of active sites which are formed upon removal of non-carbon elements during the carbon black formation. There was no principal difference in the surface morphology of thermal blacks from high purity gas feedstock and other blacks.
Direct Comparison of Some Recent Rubber Elasticity Models
Authors: Seibert D. J. , Schöche N.
Published: February 2011

The paper compares the Arruda—Boyce model, the van der Waals model and the Reduced Polynomial model—a generic class of polynomial models of which Yeoh's cubic model is a special case—in their ability to predict multiaxial deformation states on the basis of uniaxial measurements. These models are reviewed in the light of novel experimental data, giving ample space to the derivation of the equations needed for optimization of the material parameters. The technological relevance of these findings is exemplified in the finite element analysis (FEA) of a complex membrane.
Constitutive Models of Rubber Elasticity: A Review
Authors: Boyce Mary C. , Arruda Ellen M.
Published: February 2011

A review of constitutive models for the finite deformation response of rubbery materials is given. Several recent and classic statistical mechanics and continuum mechanics models of incompressible rubber elasticity are discussed and compared to experimental data. A hybrid of the Flory—Erman model for low stretch deformation and the Arruda—Boyce model for large stretch deformation is shown to give an accurate, predictive description of Treloar's classical data over the entire stretch range for all deformation states. The modeling of compressibility is also addressed.
Reinforcement of Rubber
Authors: Hamed Gary R.
Published: February 2011

One of the most important phenomenon in material science is the reinforcement of rubber by rigid entities, such as dispersed particulate filler or phase-separated organic domains. In order to impart significant reinforcement, the size of the hard phase must be small, much less than a micron. The basis of this requirement is a major focus of this short review. Furthermore, the roles of energy dissipation and crack deflection in rubber reinforcement are considered. The final part of the review deals with nano-composite rubbers, in which rigid domain size is in the range of 1–10 nm.
Characterization of Silica Xerogels Surfaces by Inverse Gas Chromatography (IGC)
Authors: Donnet J. B. , Wang T. K. , Li Y. J. , Balard H. , Burns G. T.
Published: February 2011

Silylated silica xerogels, with controlled specific surface area and porosity, were prepared by a two-step procedure. In the first step, hydrogels were treated “in-situ” with hexamethyldisiloxane (HMDS) in the presence of 2-propanol and acid. In the second step, the hydrophobic gel was transferred into an organic solvent, the residual water removed by azeotropic distillation and the dried xerogel isolated by evaporating the solvent. Using this procedure, structure collapse of the hydrogels was minimized and it was possible to make xerogels with controlled specific surface area and porosity by varying the aging conditions of the hydrogels. The surface properties of both the untreated and the “in-situ” treated silica xerogels were examined by inverse gas chromatography (IGC) at either infinite dilution conditions (IGC-ID) or finite concentration conditions (IGC-FD). The former method was used to monitor the thermodynamic parameters of adsorption of molecular probes in interaction with the sites having the highest energies, while the latter method was used to provide information about the surface energy heterogeneity of the whole surface. The results for the xerogels are also compared to those obtained on untreated and silylated fumed silicas. After silylation, a systematical surface energy decrease has been observed at both ID and FD conditions of IGC for the two types of silica. However, the modified xerogels with higher surface coverage than silylated fumed silica show some different behaviors.
Carbon—Silica Dual Phase Filler, A New Generation Reinforcing Agent for Rubber: Part VIII. Surface Characterization by IGC
Authors: Wang Meng-Jiao , Tu Hairuo , Murphy Lawrence J. , Mahmud Khaled
Published: February 2011

The surface characteristics of carbon—silica dual phase filler (CSDPF) were investigated by inverse gas chromatography (IGC) at infinite dilution. It was found that due to its unique surface microstructure, the dispersive component of the surface energy γsd of CSDPF is considerably higher than those of carbon black and silica. Among CSDPFs, the surface energies increase with increasing surface area. The adsorption energies of a series of hydrocarbon probes and polar compounds were also measured with IGC. Relative to conventional fillers, the higher adsorption energies of hydrocarbon probes on dual phase fillers as well as their higher γsd, suggest a stronger interaction with hydrocarbon polymers. This is consistent with observations on bound rubber measurement. The overall polarity of CSDPF and the specific or polar component of the surface energy of CSDPF were estimated from specific free energies of adsorption of polar compounds. The polarity of this new filler, while being similar to that of its carbon black counterpart, is substantially lower than the polarity of precipitated silica. This would result in a high compatibility of this dual phase filler with hydrocarbon rubber, leading to lower filler—filler interaction and better microdispersion.
Kinetic Analysis of the Thermal Degradation of PP—EPDM Blends
Authors: López-Manchado Miguel , Torre Luigi , Kenny JoséM.
Published: February 2011

The thermal degradation of polypropylene (PP)/ethylene—propylene—diene rubber (EPDM) and their blends is presented. In order to evaluate the effect of the components on the thermal stability, the degradation kinetics of blends of different composition is analyzed by thermogravimetry in isothermal and constant heating rate conditions in pure nitrogen. The Flynn and Wall method is used to obtain the activation energies from the dynamic tests, while isothermal test results are used to determine the pseudo order of reaction and the shape of the ƒ(α) function which is similar to an autocatalytic type equation. Model parameters such as activation energies and pseudo order of reaction are calculated using a non-linear regression analysis. Although PP—EPDM blends are not compatible, the degradation process was not clearly characterized by two independent reactions, suggesting that both components are interacting during degradation. Moreover, the kinetic study showed that the activation energy of the whole degradation process changes linearly with the relative amount of the components; on the other hand, small differences were observed in the reaction orders.
The Chemistry of Phenol-Formaldehyde Resin Crosslinking of EPDM as Studied with Low-Molecular-Weight Models: Part II. Formation of Inert Species, Crosslink Precursors and Crosslinks
Authors: van Duin Martin
Published: February 2011

Phenol-formaldehyde resins (resols) are the preferred crosslinking agents for the dynamic vulcanization of blends of polypropylene and ethylene—propylene—diene rubber (PP/EPDM) for the production of thermoplastic vulcanizates (TPVs). The goals of this study were to elucidate in detail the chemical structures formed using low-molecular-weight model compounds and to elaborate on the chemical mechanism of resol cure of EPDM as presented in our previous study. The use of model compounds for EPDM (2-ethylidenenorbornane [ENBH] and 4-methylheptane), but also for resol (2-hydroxymethylphenol [HMP] and 2,6-di(hydroxymethyl)-p-cresol) allowed the characterization of the chemical structures formed with the aid of gas chromatography/mass spectrometry (GC/MS). In combination with derivatization of unreacted hydroxyls a large variety of species could be distinguished with the general structure of R−phenol-[-CH2−phenol-]n−R′ (n=0, 1 or 2). R and R′ can be inert end groups resulting from degradation or disproportionation, viz. —H, —CH3 or —CHO, reactive end groups, viz. —CH2OH, and products of addition to ENBH (C9H14), viz. —CH2—C9H13. When either R or R′ is —CH2—C9H13 a model crosslink precursor is formed, when both are —CH2—C9H13 a model crosslink is formed. It has been demonstrated beyond doubt that both chroman and methylene bridged species are produced. It is still unclear what parameters determine the selectivity for chroman versus methylene bridged structures (presence of activators, structure of olefin etc.). The two major model crosslink products of HMP and ENBH have also been characterized with nuclear magnetic resonance, which confirmed the chroman and methylene bridged structures and showed that the addition of the phenol predominantly occurs at the least sterically hindered C-8 of ENBH. The yield of the reaction of resol with ENBH is enhanced by temperature increase and/or the addition of SnCl2·2H2O. 4-Methylheptane does not react with HMP. This indicates that in a PP/EPDM based TPV only crosslinking of EPDM via the residual diene unsaturation occurs and that tertiary C-atoms of PP or of the ethylene—propylene rubber (EPM) chain of EPDM are not involved. The high reactivity of ENBH compared with 1-decene or hydrogenated dicyclopentadiene supports a cationic mechanism.
New Emulsion SBR Technology: Part I. Raw Polymer Study
Authors: Lewandowski Laurand , Sibbald Morgan S. , Johnson Ed , Mallamaci Michael P.
Published: February 2011

Emulsion styrene—butadiene rubber (ESBR) has been the workhorse of the tire industry since World War II. With the development of solution polymers, ESBR has seen a steady decrease in its use in tire applications. A novel ESBR has been developed which imparts some of the rheological behavior previously only observed in solution polymers. This new ESBR was prepared by blending a high molecular weight elastomer with a low molecular weight elastomer, each having a unique styrene-butadiene composition. A two-phase co-continuous morphology was observed by scanning probe microscopy when the bound styrene difference between the two components was greater than 18%, consistent with the two glass transition temperatures measured by thermal analysis. Blending also served to reduce the amount of very high molecular weight material (> 107 g/mol) readily observed in 1502- and 1712-type polymers by thermal field flow fractionation (ThFFF). ThFFF was found to be superior to size exclusion chromatography for fully characterizing the molecular weight and molecular weight distribution of the polymers. Time—temperature superposition was performed to characterize the viscoelastic behavior in the rubbery plateau and terminal zones. The ESBR blends showed a cross-over in the terminal flow region that was not observed in 1502- and 1712-type polymers.