bluuebunny/crossref_metadata_2025 huggingface dataset:
Rheological Behavior of Highly Filled EPDM Compounds with Calcium Carbonate, Carbon Black, Silica and Zinc Oxide
Authors: Li Li Li , White James L.
Published: February 2011

The shear viscosity, creep and constant shear rate transients have been measured for 0.20 volume fraction compounds of an EPDM with calcium carbonate, carbon black, silica and zinc oxide of similar particle size at 100°C. Measurements have been made in a creep sandwich instrument, pressurized rotational rheometer and a capillary rheometer and cover nine decades of shear rate. All of the compounds exhibit enhanced viscosities and yield values; i.e. there are stresses below which there is no flow. The greatest yield values and increased viscosities are with the compounds with calcium carbonate and zinc oxide. More extensive studies were made with the EPDM-calcium carbonate system, where it was shown that, increasing particle size reduces shear viscosity and yield values. Further, surface treating calcium carbonate with stearic acid signifcantly reduces the shear viscosity and yield value of the corresponding EPDM compound.
Analysis of Ice- and Snow Traction of Tread Material
Authors: Futamura Shingo
Published: February 2011

The critical property of tire tread material for ice-skid resistance was analyzed. This skid resistance in the temperature range of 0 to −15°C is related to the compliance, not the hysteresis, of the tread material. Mechanistic analysis of the phenomena is presented in terms of the viscous resistance of a thin liquid-like layer on the surface of ice. The microscopic contact area and the wiping action of the tread material seem to be important factors for ice skid resistance. In a winter tire, the critical tread material property for traction on packed snow follows the same relationship.
Simulation of Flow in an Intermeshing Internal Mixer and Comparison of Rotor Designs
Authors: Kim Pan Soo , White James L.
Published: February 2011

This paper describes a simulation of flow in various intermeshing rotor internal mixer designs. The rotor designs studied were obtained from the patent literature and presentations of the major intermeshing rotor machinery mixer manufactures. The results of the simulation are compared to those for rotors of commercial separated rotor mixers. We seek to compare intermeshing and separated rotor mixers by contrasting estimated rates of mixing per unit total mixing chamber volume. Intermeshing rotors are generally predicted to perform better. This indicates they will mix more material despite smaller available internal mixer volume.
High Frequency Viscoelasticity of Carbon Black Filled Compounds
Authors: Gerspacher M. , O'Farrell C. P. , Nikiel L. , Yang H. H. , Le Méhauté F.
Published: February 2011

A high frequency viscoelasticity spectrometer, using the state-of-the-art ultrasonic technology, was constructed. The longitudinal and shear waves characteristics were measured in rubber compounds to obtain the attenuation coefficient, α, and sound velocity, v Preliminary results were obtained for a number of filled and unfilled polymers. The grade of carbon black used, filler loading, crosslinking density and filler dispersion were varied during the study. Temperature sweepS from −100°C to +60°C were also studied. It was found that the polymer type had a greater influence on α and v than did the grade of carbon black, loading or dispersion. The experimental data show that shear waves do not propagate in the rubbery state. Above the glass transition temperature, Tg, the longitudinal wave measurements could be sufficient to determine the high frequency dynamic properties of filled and unfilled polymers to characterize a tire tread compound. The temperature sweep measurements allowed the determination of the Tg of polymers at high frequency. It is proposed that the described method of measuring α and v be used as a laboratory tool for potential tire traction prediction.
Cut Growth in Vulcanizates of Natural Rubber, cis-Polybutadiene, and a 50/50 Blend during Single and Repeated Extension
Authors: Hamed G. R. , Kim H. J. , Gent A. N.
Published: February 2011

A typical passenger sidewall composition was employed using three elastomer systems NR, BR, and a 50/50 blend of NR and BR. Tensile strips with edge cuts of various depths were strained in two ways continuously increasing extension up to rupture, or repeatedly stretching them to progressively higher strains until failure occurred. For BR, the tensile strength σb decreased steadily with increasing cut depth, c, while NR and NR/BR showed an abrupt decrease in σb at a critical cut size, ccr. This is attributed to crystallization of NR throughout the specimen at high strains, when cccr. Furthermore, in samples of NR and NR/ BR the crack tip split, forming two secondary cracks which grew a considerable distance parallel to the direction of straining, and even turned backwards, before stopping. Rupture of the specimen did not occur until a new (third) crack was initiated from the smooth torn surface of the secondary crack. Under repeated straining NR specimens developed secondary cracks repeatedly in a characteristic alternating pattern. These are instances of severe “knotty” tearing. In contrast, in BR samples the initial cut always grew in a forward direction and secondary, longitudinal cracks did not develop.
The Feasibility of Using Supercritical Fluid Extraction for the Determination of Total Extractables in Styrene-Butadiene Rubber
Authors: Sekinger J. K. , Ghebremeskel Ghebrehiwet N. , Concienne L. H.
Published: February 2011

Supercritical fluid extraction (SFE) is gaining popularity as an extraction technique. This report details the use of SFE for the extraction of extender oil, organic acid and antioxidant from styrene—butadiene rubber ( SBR ) Extraction parameters such as density, temperature, flowrate, and extraction time were investigated. The effect of sample size and modifier was also studied. Recovery and reproducibility data was generated for various SBR types, including oil-extended and carbon black filled polymers. Complete extraction was achieved in 30 minutes with 100 mg of sample using carbon dioxide. Sample masses of up to 1 gram were successfully extracted in the same time with the addition of a modifier.
Biscitraconimides as Anti-Reversion Agents for Diene Rubbers: Spectroscopic Studies on Citraconimide-Squalene Adducts
Authors: Datta R. N. , Schotman A. H. M. , Weber A. J. M. , van Wijk F. G. H. , van Haeren P. J. C. , Hofstraat J. W. , Talma A. G. , Bovenkamp-Bouwman A. G. V. D.
Published: February 2011

The mechanism of anti-reversion activity of biscitraconimides (BCI) during rubber vulcanization has been investigated. Biscitraconimides form crosslinks by reaction with chain modifications which are formed during the reversion process. These additional crosslinks compensate for the sulfidic crosslinks that are lost during the reversion. To allow structural assignments of the adducts formed between rubber and citraconimides, squalene has been used as a simple model system in combination with the currently used additives and sulphur. The products were identified as Diels—Alder adducts of conjugated polyenes, formed during reversion, with citraconimide. The nuclear magnetic resonance (NMR) spectroscopic assignments of the products are discussed. Furthermore the quantification of squalene-BCI adducts via NMR and mass spectrometry (MS) using 13C labelled 1,3-bis (citraconimidomethyl) benzene (BCI-MX) is described. It was found that under the applied conditions (2 h, 170 °C), approximately 80% of the citraconimide groups are converted into squalene-BCI adducts. Diels—Alder adducts are the main reaction products of the reaction. Products from an ene reaction are formed as minor component (less than 20%).
Hysteresis Friction of Sliding Rubbers on Rough and Fractal Surfaces
Authors: Heinrich Gert
Published: February 2011

The friction force generated between sliding rubber and rough surfaces has two components commonly described as the adhesion and hysteretic components, respectively. Under wet conditions, the adhesion component of the total friction is drastically reduced, whereas the hysteresis loss remains largely unaffected. Such situations arise in daily life during blocked wheel braking where tire treads slide over wet road asperities. The situation becomes more complex in Anti Blocking System (ABS) braking on wet roads where both adhesion and hysteresis components of the friction force act. We present a new model of the hysteretic friction coefficient of a sliding rubber sample over a rough or even fractal surface. The model uses the basic assumption that the damping properties of the dynamically strained rubber depend on specific properties of the surface profile through its power spectral density. This assumption is based on recent findings that the fractal texture model is the only one developed to date to successfully address the complete multiscale behavior of paved road surface texture. The spectral density depends on the ‘topothesy’ k of the surface and scales with the spatial frequency f according to a power law. The corresponding power is related to the surface fractal dimension D. The quantities k and D are scale-independent parameters that characterize the multiscale self-affine topography of road surfaces in the characteristic length scale range of interest. The influence of surface roughness on the frictional properties of the rubber depends on the sliding velocity and is described through a retarded coupling between relaxational modes of the polymer network and roughness modes of the surface. The results of the theory are discussed in comparison with recent experimental results of Grosch. Finally, we demonstrate how the fractal descriptor parameters of different test road pavements are used to compare tire traction measurements performed on wet test roads.
Phase Structure Changes in a Sheared Blend of High Molecular Weight Polybutadiene and Polyisoprene Elastomers
Authors: Remediakis Nikolais G. , Weiss R. A. , Shaw Montgomery T.
Published: February 2011

The flow-induced phase behavior of polyisoprene—polybutadiene elastomer blends is of concern to the rubber industry because of the wide practical applications of these blends. We have been investigating examples of these blends using a Rheo-SALS instrument in conjunction with light microscopy. The subject of this work was a high molecular weight, near-critical blend (35/65 ratio) comprising polybutadiene (Mn=413, 000) and polyisoprene (Mn=177, 000) (Blend II). The results were contrasted with those for a previously studied blend (Blend I) comprising polybutadiene (Mn=164, 000) and polyisoprene (Mn=125, 000), also near the critical composition at a 40/60 ratio. Both featured the same microstructure. Each was examined under quiescence and flow conditions. For Blend I at a 24 °C quench depth, the scattering pattern was the expected spinodal ring; which, upon shearing, changed to an H-shaped pattern and then to a bright streak in the vorticity direction. Direct observation showed that these patterns corresponded to a fibrillar structure aligned in the flow direction. Similar light scattering patterns were obtained after a temperature jump (24 °C) under steady-state shearing. With Blend II at a 40 °C quench depth, the scattering pattern was again a spinodal ring, but this changed on shearing to an anisotropic pattern having the shape of an “8” or a “butterfly.” The shape of this pattern depended on shear rate, and its origin was hypothesized to be phase domains following helical paths with axes aligned in the vorticity direction. The corresponding micrographs are consistent with this supposition, as is an instability phenomena observed in the parallel-plate rheometer at higher shear rates. These purely hydrodynamic phenomena should be kept in mind when interpreting observations of “flow-induced mixing” at lower quench depths.
Direct Adhesion between Electroless Nickel-P Plated Metals and NBR Compounds during Curing
Authors: Mori Kunio , Hirahara Hidetoshi , Oishi Yoshiyuki
Published: February 2011

In this study, an examination was made of the various causative factors for the direct adhesion between nickel-P alloy (nickel alloy) and acrylonitrile-butadiene rubber (NBR) compounds during curing. In a high sulfur curing system (SV), direct adhesion was found to depend on time of exposure to air and not to occur after more than 48 h of exposure. In the peroxide curing system (PV), there was no adhesion at all regardless of the exposure time. The addition of triazine thiols to NBR compounds resulted in adhesion between NBR compounds and nickel alloy for exposures exceeding 48 h. Typical curing systems such as SV, low sulfur curing (LSV), sulfurless curing (SLV), and PV gave good NBR-nickel adherends when the NBR compounds contained the monosodium salt of triazine trithiol (TTN). In these system, peel strength in the adherends increased with triazine thiols, to a maximum, and then decreased. This parameter was influenced by the chemical structures of triazine thiols, such as those containing thiol(-SH) and the sodium salt of thiol (-SNa) groups, and by the exposure of nickel alloy to air. Peel strength decreased with the formation of nickel oxides on the surface. When the nickel oxides were removed from the nickel alloy surface, peel strength was recovered. High peel-strength adhesion between NBR compounds with TTN and nickel alloy is due to the formation of interfacial bonds and reinforcement layers at the adhesive interface during curing.

Adherends consisting of NBR compounds with TTN and nickel alloy generally showed high heat resistance, oil resistance, and water resistance. The values for these parameters differed accordingly to the curing system and were optimal in the following order: SV < SV with TTN < PV with TTN.
The Effect of Network Formation on the Rheological Properties of SBR Modified Asphalt Binders
Authors: Lee Yong-Joon , France Lawrence M. , Hawley Martin C.
Published: February 2011

Styrene-butadiene rubber (SBR) was used to modify asphalt binders. The rheological and thermo-mechanical properties of the binders were investigated using rotational viscometry, dynamic shear rheometry, and thermal mechanical analysis. The optimum SBR content and mixing procedure were determined based on the rheological properties of the asphalt/SBR blends. The addition of 3–5% (w/w) SBR resulted in enhanced high temperature performance of the binders. The SBR progresses from a dispersed polymer to local networks to a global network with increasing SBR content. This phenomenon is exhibited in rheological properties such as complex modulus and melt viscosity. It is also verified visually by using a Laser Scanning Confocal Microscope. Because of this network formation, the binders showed a large increase in the complex modulus which indicates resistance to rutting.
The Microscopy of Catastrophic Tire Failures
Authors: Smith Ronald W.
Published: February 2011

Tires sometimes suffer catastrophic failure during travel on highways, resulting in a scatter of tire fragments along the pavement and berms. A large number of these fragments, including partial and whole tires, were collected and examined microscopically. The goal was to determine what sort of evidence might be “read” from these fragments via the optical stereo microscope using examinations of 7× to 60×. It was found that these fragments contain a wealth of well preserved information. Rubber tear lines and other fracture topographies are readable, allowing the failure analyst to determine directions of fracture/tear propagation which make it possible to postulate modes of separation. The features of torn surfaces that are normally encountered in laboratory testing are modified in tire failures due to the presence of adjoining compounds, complex shapes, and nonrubber components. Guidelines have been established to account for these complicating variables. A concept of “directional anisotropy” aids the analyst in understanding product failure surfaces. Additional items surveyed in this post mortem study were the condition at wire belt ends and indications of wire corrosion.
Metathetical Degradation and Depolymerization of Unsaturated Polymers
Authors: Marmo J. C. , Wagener K. B.
Published: February 2011

The employment of transition metal catalysts has been a viable route in the degradation and depolymerization of unsaturated polymers. Initially, unsaturated polymers were degraded with a catalytic system containing a transition metal and a Lewis acid cocatalyst (WCl6/SnBu4). Degradation chemistry was effective in reducing the molecular weight of the polymer, however, the classical catalyst system induces side reactions which generates ill-defined products. These side reactions were obviated by using a preformed alkylidene without a Lewis acid cocatalyst, and perfectly difunctional telechelics were synthesized.
Investigations into the Silica/Silane Reaction System
Authors: Goerl Udo , Hunsche Andrea , Mueller Arndt , Koban H. G.
Published: February 2011

Silica in combination with organosilanes (e.g. [bis(3-triethoxysilylpropyl)tetrasulfane] = TESPT) has recently become more important in tire applications. Their use in tire treads leads to an improvement in rolling resistance and wet traction. The requirements for the attainment of these properties are, that the triethoxysilyl groups of TESPT react with the silanol groups on the silica surface during compounding, and the polymer active groups react with the polymer during cure. The reaction of precipitated silica with this silane was investigated. The influence of various parameters on the reaction type and the reaction kinetics was considered. The results of the investigation obtained using 29Si-CP/MAS solid state NMR spectroscopy agree well with a horizontal reaction model in which a single siloxane bond is first formed with the silica surface (primary reaction). It is followed by condensation reactions between silanol groups of silane molecules which are already bound to the silica surface (secondary reaction). The kinetic studies data show a clear difference between the fast primary reaction and the slow secondary reaction. Both reactions become more rapid in acidic and alkaline pH ranges. The primary reaction accelerates up to a particular H2O content after which the rate remains constant. The secondary reaction keeps on accelerating with rising H2O content. Modification with different silane concentrations showed a higher rate constant at low concentrations.
Characterization of Sol and Gel in Hevea Natural Rubber
Authors: Tangpakdee Jitladda , Tanaka Yasukuki
Published: February 2011

The gel content of rubber from high-ammonia latex (HA-latex) decreased significantly after deproteinization with proteolytic enzyme. The addition of 1–2% ethanol in toluene solution reduced the gel content of rubbers from HA-latex, deproteinized HA-latex (HA-DP) and pale crepe. Transesterification of the rubber in toluene solution with sodium methoxide dissolved the gel fraction. The gel fractions solubilized after transesterification showed molecular weight distribution rich in low molecular-weight fraction. The Huggins k′ constant of the fractionated rubbers from solubilized-gels was in the range of 0.42–0.45, lower than that of the fractionated HA-DP of 0.5–0.8. This indicates that all the branch-points were decomposed by transesterification to form linear molecules. The Mn values of rubber chains assembling the gel was 5.5−8.3×105 by 13C-NMR measurements of the ratio between cis- and trans-isoprene units, which were comparable to the molecular weight between crosslinks, Mc, of 7−11×105 by swelling measurements. These findings suggest that the branching and crosslinks are composed of two types of branch-points, i. e. one by association or aggregation of proteins or oligopeptides at the initiating end and the other by ester linkages including phosphoric ester at the terminal end.
New Polybutadiene-Based Thermoplastic Elastomers: Synthesis, Morphology and Mechanical Properties
Authors: Dubois Ph , Yu Y. S. , Teyssié Ph , Jérôme R.
Published: February 2011

Well defined poly[styrene-b-butadiene-b-styrene] block copolymers (SBS) end-capped with poly(t-butyl methacrylate) (PtBMA) and poly (meth acrylic acid) (PMA) outer blocks, respectively, have been synthesized by the sequential anionic polymerization of butadiene, styrene and tBMA, followed by the selective hydrolysis of the PtBMA blocks into the corresponding PMA blocks. The structure-property relationships of these new thermoplastic elastomers have been investigated, with a special emphasis on the effect of the ester or acid outer blocks on the bulk properties.

As a rule, tensile strength is improved by increasing the length of the ester or acid outer blocks from 0 to 140 methacrylic units. Dipole—dipole intermolecular interaction of the PtBMA blocks and hydrogen bonding of the PMA blocks may account for enhanced mechanical properties. However, too high a degree of strong intermolecular interactions can constitute a deterrent to good phase separation. This is supported by morphological observations and loss in tensile properties when the relative content of the ester or acid outer blocks exceeds some critical value. In the case of a high acid content, DSC analysis shows two thermal transitions at −70 °C and 230°C for PBD and PMA blocks, respectively.
Anisometry Measurements in Carbon Black Aggregate Populations
Authors: Gruber Tyler C. , Herd Charles R.
Published: February 2011

Transmission electron microscopy with automated image analysis (TEM/AIA) was used to characterize the three-dimensional morphology and anisometry of carbon black aggregates. Individual carbon black aggregates were imaged at multiple goniometer angles, and their three-dimensional aggregate structure was modeled, yielding greatly enhanced morphological information. Aggregate size distributional properties were determined at multiple goniometer orientations for N300 and N600 series grades of varying aggregate structure levels. Aggregate projections were found to exhibit statistical decreases of 10 to 25% in area and perimeter with rotation. Decreases in other morphological parameters, including non-dimensional shape parameters, were also observed. In general, higher structure grades (aggregates) were found to display larger relative changes in morphological parameters with rotation than lower structure grades. Ramifications for conventional TEM/AIA and void-volume/polymer occlusion capacity measurements are addressed. Further analysis includes an assessment of aggregate anisometry on the TEM sample grid and new insights into the three dimensional nature of carbon black aggregate structure.
Surface Energy of Commercial and Pyrolytic Carbon Blacks by Inverse Gas Chromatography
Authors: Darmstadt Hans , Roy Christian , Kaliaguine Serge , Cormier Helga
Published: February 2011

The surface properties of carbon blacks obtained by vacuum pyrolysis of different used rubbers (CBp) and of commercial carbon blacks were measured by inverse gas chromatography (IGC). The dispersive component of the surface energy (γsd) and the specific interaction (Isp) of the recovered CBp were lower than γsd and Isp of the virgin carbon black initially present in the rubber. However, γsd and Isp of recovered medium surface area carbon black and of virgin low-surface-area carbon black were comparable. During the pyrolysis, carbonaceous deposits are formed on the CBp surface. A correlation between γsd and Isp and the amount of the carbonaceous deposits, measured by ESCA, was found, suggesting that the formation of these deposits is responsible for the decrease of γsd and Isp.
The Morphology of Rubber/Plastic Blends
Authors: Chung O. , Coran A. Y.
Published: February 2011

This study considers the rheological and interfacial effects on the phase morphology of the rubber/plastic blends during molten-state mixing, cold pressing, and compression molding. We utilized a specially designed tool to take a sample from the mixer and quickly cool it with little chance for coalescence. The work of this report is mainly concerned with soft rubbery compositions, which contain large concentrations of elastomeric phases. The morphologies of rubber/plastic blends having low concentrations of plastic or rubber can be explained by the understanding gained from work previously reported by others. The viscosity-matched and polarity-matched rubber/plastic blend systems give the finer states of dispersion, especially during the early stages of mixing. At intermediate concentrations of rubber, (e.g., 60 vol. %) co-continuous and laminar structures are frequently formed. The determinants of the concentration where the phase inversion occurs and the determinants of phase-domain dimensions near this phase-inversion concentration (e.g., a thickness of a highly shaped structure) are complex and can only be rationalized qualitatively. However, we were able to quantitatively relate phase-morphological dimensions to interfacial tension, rheology, and the observed type of morphology. When the hot batch is cold pressed, then a striated or laminar phase morphology is formed. Even very small particles deform greatly if the interfacial tension is low. Higher viscosities in the dispersed phase give rise to lesser deformations during cold pressing. During compression molding, the laminar structure transforms itself into a random co-continuous structure of vastly increased textural dimensions. This coarsening is greatest when polarities are most divergent and when the viscosities of the polymers are lowest.
Composites of Waste, Ground Rubber Particles and Poly(Vinyl Chloride)
Authors: Tipanna M. , Kale D. D.
Published: February 2011

Composites of poly(vinyl chloride) (PVC) were prepared with waste, finely ground printing rollers of nitrile rubber over a wide range of composition (up to 90% by weight of rubber component), through melt blending. The effect of different amounts of waste rubber on the tensile strength, % elongation, hardness, and flex crack resistance was studied. There was a considerable increase in the impact properties of PVC. Flex crack resistance was also significantly improved as the specimen did not crack even after 150,000 cycles for all composition containing more than 40% waste rubber. The waste rubber also imparted a plasticizing effect to PVC. The improvement in these properties could be due to interaction between PVC and the acrylonitrile part of nitrile rubber.
Degradation of Hydrogenated Styrene—Butadiene Rubber at High Temperature
Authors: Sarkar Mousumi De , Mukunda P. G. , De Prajna P. , Bhowmick Anil K.
Published: February 2011

Degradation of hydrogenated styrene—butadiene rubber (HSBR) having different levels of unsaturation has been studied over a wide range of temperatures under anaerobic and aerobic conditions using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), IR and NMR spectroscopy. TGA data indicate higher thermal stability of hydrogenated rubber as compared to SBR in nitrogen, although an anomalous behavior is observed in air due to crosslinking and oxidation of styrene—butadiene rubber (SBR). Isothermal data confirm the above observations. IR and NMR results reveal thermal isomerization, cyclization, oxidation, depolymerization, and chain scission processes. The nature and amount of products formed depend on the time and temperature of degradation and also on the level of hydrogenation of SBR.
The Density of Chemical Crosslinks and Chain Entanglements in Unfilled EPDM Vulcanizates as Studied with Low Resolution, Solid State 1H NMR
Authors: Litvinov V. M. , Barendswaard W. , van Duin M.
Published: February 2011

The network density in unfilled EPDM vulcanizates was studied by the following methods: low resolution, proton T2 NMR relaxation, Mooney—Rivlin analysis of stress—strain curves, and equilibrium swelling experiments. For the vulcanizates as such, the NMR method measures the total network density, which is composed of chemical crosslinks (CC) and of temporary (EN/TE) and trapped chain entanglements (EN/TR). The estimated molar mass of EPDM chains between apparent chain entanglements (EN) is 1900 ± 200 g/mol. For partially swollen samples, the NMR method determines the network density composed of CC and EN/TR. The CC density is obtained from the total density of network junctions and the measured entanglement density assuming that CC and chain entanglements are decoupled and additive. The contribution of CC, EN/TE and EN/TR to the total network density is estimated.
The Effects of Heating and Cooling Rates on the Structure of Carbon Black Particles
Authors: Zerda T. W. , Xu W. , Yang H. , Gerspacher M.
Published: February 2011

The effects of heating and cooling rates on the structure of N660 and N299 carbon black particles have been investigated using Raman spectroscopy, X-ray scattering, and the BET technique. Carbon blacks were kept at 2700 K for various lengths of time and next cooled down at different rates. The size of crystallites and the surface roughness of the particles have been determined for these different treatment schedules. The fractal dimension decreases from 2.2 for untreated samples to 2.0 for samples heat treated to 1300 K. Cooling rates do not affect the surface roughness. However, rapid cooling reduces crystallite sizes. We postulate that the surface of carbon particles is composed of crystallites and amorphous carbon. The amount of amorphous carbon depends on the thermal treatment. The role of amorphous carbon in determining reinforcing properties of carbon blacks in tires is discussed.
Origin of Characteristic Properties of Natural Rubber—Effect of Fatty Acids on Crystallization of cis-1,4-Polyisoprene
Authors: Kakubo Takashi , Matsuura Ai , Kawahara Seiichi , Tanaka Yasuyuki
Published: February 2011

Natural rubber (NR) contains linked fatty acids, composed of mainly saturated fatty acids, in conjunction with a mixture of free saturated and unsaturated fatty acids. The crystallization of synthetic cis-1,4-polyisoprene (IR) is accelerated by the addition of 1 wt % mixture of saturated fatty acid as a nucleating agent and unsaturated fatty acid as a plasticizer. As an NR model, IR was esterified with stearic acid selectively at the 3,4-isoprene units after introduction of hydroxyl group by hydroboration. The linked stearoyl group stimulated the crystallization of IR at −25 °C, while linked fatty acids other than stearoyl group showed no stimulating effect on the crystallization. The addition of methyl linoleate to the stearoyl-esterified IR gave the highest rate of crystallization at −25°C. A rapid crystallization of NR is presumed to originate from the mixed saturated and unsaturated fatty acids composition present and the presence of saturated fatty acids linked to NR.
Crack Growth in Twisted Rubber Disks. Part II: Experimental Results
Authors: De D. K. , Gent A. N.
Published: February 2011

A simple torsion test is described in which a thin bonded rubber disk is subjected to repeated torsional strains by rotating one end-piece with respect to the other through a fixed angle. An initial circumferential cut then grows inwards as a fatigue crack. From measurements of crack depth as a function of number of strain cycles, relations are obtained for the rate of crack growth dc/dn vs. fracture energy G for three representative rubber compounds: unfilled natural rubber, unfilled SBR and a carbon-black-filled SBR. The results are closely similar in all cases to previously-published values, obtained from tensile fatigue experiments. This is an important finding, because the present specimen is subjected to simple shear strains and the agreement obtained validates the use of a fracture energy criterion for crack growth under complex states of strain. Moreover, the test method itself has marked advantages. The strain cycle is well-defined, even for relaxing materials. The crack slows as the test proceeds allowing a considerable range of G values, of the order of 10 to 1, to be examined in a single experiment. The effect of complex strain cycles, passing through zero or reversing, and the effect of superimposed tensile or compressive strains, can also be explored.
NMR of Tissues Exposed to Polysiloxane Gels
Authors: Garrido Leoncio
Published: February 2011

Silicone (polysiloxanes) gel-filled implants have been widely used for biomedical applications, mainly because they were considered to be nonbiodegradable. However, increasing concern about the health implications of polysiloxane exposure for women with silicone gel-filled breast implants has prompted interest to study the biochemistry of implanted polysiloxanes. The purpose of this work is to investigate the migration of polysiloxanes from the implant to local and distant sites and their chemical modification in living systems. Tissues from animals and humans exposed to polysiloxane gel implants are studied in vivo using proton NMR localized spectroscopy, and in vitro with proton and 29Si magic angle spinning (MAS) NMR spectroscopy. This work demonstrates that free polysiloxanes present in the gel-filled implants migrate to surrounding tissues and distant organs, such as the liver. In addition, 29Si NMR spectra of metabolically active tissues (liver) show the presence of chemically unchanged polysiloxanes and other silicon-containing compounds (silica) which suggest that these polymers are biodegradable.
Plasticization of Polyolefin Elastomers, Semicrystalline Plastics and Blends Crosslinked in situ during Melt Mixing
Authors: Ellul Maria D.
Published: February 2011

Semi-crystalline polyolefins, e.g., polypropylene in its isotactic and syndiotactic forms, become brittle at low temperature due to their inherent crystallinity and relatively high Tg. It has been discovered that certain “non-polar” aliphatic esters, in particular monomeric tallates and sebacates can effect a large depression in Tg of the polypropylene amorphous component which is in line with free volume considerations. The melting point of the crystalline fraction was also depressed albeit to a much smaller extent. This successful plasticization of polypropylene was applied to heterophase systems with the elastomer crosslinked in situ during melt blending with polypropylene and in the presence of a plasticizer. The plasticizer was distributed in both polymer components of the blend. Therefore the glass transition temperatures of both the polypropylene and the elastomer phases could be greatly depressed through simultaneous plasticization of both polymer phases resulting in a supertough material at −40°C and below. Since only the amorphous component of polypropylene is plasticized, the crystalline fraction is not much affected and the upper service temperature range is maintained. The resulting TPEs have an excellent balance of engineering properties to −125°C and are much more elastic than unplasticized TPEs due to the suppression of yielding behavior.
Mathematical Model of Diffusion of Solvents in Rubbers
Authors: Fong C. F. Chan Man , Li Y. , De Kee D. , Bovenkamp J.
Published: February 2011

The chemical potential associated with the diffusion through polymeric systems is assumed to be a function of the concentration and the stress induced by the swelling. The flux for such a model is calculated and is found to be in agreement with the experimental data involving acetone, dichloromethane, and toluene through natural rubber, bromobutyl rubber, and nitrile rubber.
Tire Black Sidewall Surface Discoloration and Non-Staining Technology: A Review
Authors: Waddell Walter H.
Published: February 2011

The tire black sidewall is the outer surface that protects the casing against weathering. It is formulated for resistance to weathering, ozone aging, abrasion, tearing and cracking, and for good fatigue life by using blends of natural rubber and cis-butadiene rubber. Protection against ozone aging is of particular interest since reaction with these olefinically unsaturated elastomers results in polymer decomposition via chain scission. Use of N-alkyl, N′-aryl-para-phenylenediamine antiozonants has proved most effective. However, their use also results in a surface discoloration, and thus they can be used in only limited amounts when tire appearance is also an important factor. A review is made of the literature describing this surface discoloration problem and approaches to formulate a black sidewall compound to eliminate this surface discoloration upon exposure to ozone. Methods include use of non-staining antiozonants, and uses of elastomers with saturated backbones such as ethylene-propylene-diene terpolymers, halobutyl rubbers and brominated-isobutylene- co-para-methylstyrene.
The Calculation of the Tear Energy of Elastomers from Their Viscoelastic Behavior
Authors: Plazek Donald J. , Rosner Mark
Published: February 2011

The creep behavior and the rate dependence of the tear energy have been determined on nine elastomers with widely varying structures. When compared at their glass temperatures the short-time creep compliances, J(t), were located at the same positions on the time scale. Therefore, the terminal zones of response were widely spaced depending on the breadth of the viscoelastic spectra. The positions of the tear energy curves were similarly positioned on the reciprocal rate scale. An equation is proposed for the calculation of tear energy curves from the viscoelastic retardation spectrum.
Protection Mechanisms of p-Phenylenediamine-Type Antiozonants
Authors: Qi Chen-Ze , Wang Tian-Min , Zhang Xian-Man
Published: February 2011

The relative ozonation rate constants for p-phenylenediamines have been estimated from the linear correlation of the ozonation rate constants with the ionization potentials (Figure 1). The efficient antiozonants were found to have relatively lower ionization potentials, but not too low to react with the atmospheric molecular oxygen. The bond dissociation enthalpies (BDEs) of the N—H bonds of p-aminodiphenylamine and related derivatives were found to be about 80 kcal/mol, suggesting that the p-aminodiphenylamines are not only efficient antiozonants, but are also efficient antioxidants. Efficient antiozonants should also be efficient antioxidants to quench the reactive radical intermediates formed during the degradation.
Nitrosamine Formation in Rubber: II. Influence of Cure
Authors: Willoughby Bryan G. , Scott Keith W.
Published: February 2011

Part I of this series identified a key difference in behavior with respect to nitrosamine formation in rubber for EPDM vulcanizates compared with those from SBR, NR or NBR. This paper provides further analysis of some twenty-nine different EPDM cures to investigate both ingredient- and process-related effects. Two different levels of TMTD and carbon black were variables in this study, as was the type of carbon black used (N330 and N550). Batch effects with respect to both polymer and black were also studied, as was the presence or absence of MBT. The use of experimental design has shown how reliable data on nitrosamine formation in vulcanizates can be obtained by paying strict attention to process history, and has revealed for these EPDM cures a correlation between cure time (T90) and the level of nitrosamine formed. Moreover the presence or absence of MBT was also shown to be influential; showing the importance of vulcanization by-products in the generation of nitrosamine. The formation of the thermally unstable dimethyldithiocarbamic acid, and how fast it is produced, are seen as important in a process in which the opportunities for nitrosation are limited by the thermal decay of N2O4.
Carbon—Silica Dual Phase Filler: Part IV. Surface Chemistry
Authors: Murphy Lawrence J. , Khmelnitskaia Elena , Wang Meng-Jiao , Mahmud Khaled
Published: February 2011

A method for estimating the amount of functional groups on the carbon—silica dual phase fillers (CSDPF) available to react with organosilane coupling agents is reported. The method employs trimethylchlorosilane (TMCS) as an analytical probe, and involves equilibrating the samples with TMCS in toluene. The amount of TMCS that reacts with the surface functional groups is obtained by monitoring the concentration of reactants and products of the reaction by Gas Chromatography Mass Spectrometry. The amount of TMCS reacted with the fillers' surface functional groups is compared to the pH, and the active hydrogen content as measured by LiAlH4. Comparison of these measures with the CSDPF, carbon blacks and a fumed silica sample is provided. The dual phase fillers have a heterogeneous surface, containing both carbon and silica phases. Multipoint BET nitrogen surface area is used in combination with iodine number to estimate the individual carbon and silica phase surface areas. From this, the packing density of the trimethylsilyl group attached to the silica phase of the CSDPF surface was estimated and compared to silica. Silanols on these dual phase fillers were detected by infrared spectroscopy. The infrared band for silanols is located at 975 cm−1. The absorbance of this band is shown to correlate with TMCS uptake and diminish after reaction with TMCS, suggesting that silanols indeed are participating in the uptake of TMCS.
Study on Powder Utilization of Waste Tires as a Filler in Rubber Compounding
Authors: Kim Jin Kuk , Burford R. P.
Published: February 2011

The recycling of rubber from waste tires and other products has been of commercial and environmental interest for several decades. For recycling, bulk properties are most relevant; whereas, for crumb incorporation both bulk and matrix-crumb interface phenomena are important, which are dealt with in this study. We have taken a crumb rubber of high surface area and a diameter between 100 and 200 µm and incorporated it into uncured natural rubber (NR) or acrylonitrile—butadiene (NBR) containing silica. This non-black reinforcing filler was used to allow a better modulus match between crumb and matrix than would exist for a non-filled system, while allowing visual contrast between the two phases for microscopic examination. The micromechanics of deformation can be investigated using scanning electron microscopy. The crumb rubber was either added as received or used after a surface chlorination step. The matrix was also used unmodified or with a compatibilizer used to facilitate homogenization of polar and nonpolar elastomers. Differences in matrix/crumb polarity and interfaces were therefore able to be investigated. Chlorination of crumb has a beneficial effect in NBR matrix compounds, but causes embrittlement in NR-based compounds. In the former case, some enhanced compatibility is expected, as analogous poly(vinyl chloride) (PVC)/NBR blends are already used. The compatibilizer also imparts improved performance to the NBR/crumb compound, overcoming differences in polarity between the matrix and the nonpolar crumb. However for the NR matrix compound, similar chemical compositions already exist and so the aliphatic-hydrocarbon resin compatibilizer (STRUKTOL) provides no benefit.
Viscoelastic Characterization of High Fiber Content Filament Wound Polyurethane Matrix Composites
Authors: Orlet M. W. , Bakis C. E.
Published: February 2011

Elastomeric matrix composites (EMCs) consisting of a polyurethane matrix unidirectionally reinforced with high volume fractions of high strength fibers have interesting and unique mechanical properties such as high strength and stiffness in the fiber direction and high ductility perpendicular to the fibers. The aim of this investigation is to explore the quasi-static mechanical properties of glass and carbon fiber EMCs in the direction transverse to the fibers and to measure and model the creep of the monolithic matrix material and the transverse creep of the glass EMC. In the quasi-static tests, glass and carbon EMCs followed a monotonic stress—strain curve that was essentially flat from approximately 1–2% to over 10% strain. The maximum stresses obtained in the quasi-static tests were approximately 3.5 and 7 MPa in the carbon and glass EMCs, respectively. The monolithic matrix and the glass EMC loaded transversely to the fibers both showed highly nonlinear creep behaviors. The former creep behavior was modeled successfully with a standard power law expression. The nonlinear creep behavior of the glass EMC cannot be modeled with a standard power law expression, possibly due to creep damage.
Comparative Studies on the Crosslinking Reaction of Bis-Maleimides and Bis-Citraconimides in Squalene and Natural Rubber
Authors: Datta R. N. , Talma A. G. , Schotman A. H. M.
Published: February 2011

A study has been made to differentiate between the crosslinking reaction of bis-maleimides and bis-citraconimides in squalene as well as in natural rubber. Bis-maleimides are found to participate in the crosslinking reaction in the absence of curatives such as accelerators and sulfur. Bis-citraconimides take part in the crosslinking reaction when polysulfidic crosslinks are under the process of degradation. Sulfur and accelerator are required for the formation of polysulfidic crosslinks and hence the presence of sulfur and accelerator are essential for bis-citraconimide crosslinking. The differences in the reactivity and the chemistry of crosslinking are studied and discussed. Some application data are provided in order to elaborate the differences.
Crystallization of cis- and trans-1,4-Polyisoprene Dispersed in SBR
Authors: Gent A. N. , Kawahara S.
Published: February 2011

Crystallization of natural rubber (NR) and trans-1,4-polyisoprene (TPI) in blends with styrene—butadiene rubber (SBR) has been studied dilatometrically. For TPI, the melting temperature and Avrami index of crystallization kinetics were unchanged by blending with SBR. However, the rate of crystallization was decreased significantly when only 1 wt % of SBR was added, and much more so for amounts large enough to constitute the continuous phase. These reductions in rate are attributed to two effects: chemical changes in TPI during mechanical mixing, and restricted nucleation in small TPI particles. Similar effects were noted for NR blended with SBR. When solution-blended as a 30/70 mixture with SBR, crystallization of the NR fraction was about 9 times slower than for NR itself, and the rate was reduced still further when mixing was more thorough. However, when NR and SBR were mixed mechanically, the rate of crystallization of the NR fraction was not reduced much although the Avrami index and final degree of crystallinity were significantly lower. These effects suggest that the NR particles are strained during mechanical mixing and do not recover afterwards.
Fatigue of Cord—Rubber Composites: III. Minimum Stress Effect
Authors: Ku B. H. , Liu D. S. , Lee B. L.
Published: February 2011

The dependence of fatigue lifetime on the minimum cyclic stress was assessed for the rubber matrix composite of bias aircraft tire carcass reinforced by nylon cords as well as two model rubber composites reinforced by steel wire cables. At a given stress range, the use of higher minimum stress up to a certain level led to longer fatigue life of the composite laminate. When the minimum stress exceeded this critical level, an opposite trend of shorter fatigue life occurred with a higher level of minimum stress. The initial trend of longer fatigue life of angle-plied, cord—rubber composite laminates with a higher level of minimum stress stems from a nonlinear stress—strain relationship with a tendency of strain stiffening. Under stress-controlled fatigue loading, a shorter strain range was experienced for the same stress range when the level of minimum stress was raised. However, the increase of minimum stress raises the potential for damage initiation and accumulation. This effect of increased damage potential became dominant above the critical level of minimum stress. When the fatigue life data were plotted against the values of strain range to clarify the role of damage potential, a general trend of shorter fatigue life with a higher level of minimum stress was observed at a given strain range, in striking contrast to the trend of the stress range vs the number of cycles to failure (S-N) curve in a conventional form. The result again confirms that the damage initiation and eventual fatigue failure of angle-plied, cord—rubber composite laminates are “strain-controlled” processes, as demonstrated in our preceding paper. A modified form of the Goodman equation appears to be valid in predicting the relationship between the strain range (instead of stress amplitude) and minimum strain (instead of mean stress) for a given lifetime of a cord—rubber composite laminate.