Showing papers in "Rubber Chemistry and Technology in 1997"

Investigations into the Silica/Silane Reaction System

Abstract: 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 (se...

Scanning Probe Microscopy of Polymer Surfaces

Abstract: Basic principles and recent results of scanning probe microscopy (SPM) studies of polymer surfaces are reviewed. Applicability of various SPM techniques—including contact, dynamic, force modulation, friction force, chemical force, electrostatic, adhesion, and thermal modes—to probing of polymer surfaces is illustrated. Examples of recent studies of surface morphology and properties of various polymers are presented and briefly discussed. An extensive bibliography of more than 200 references is included. Classes of polymers considered here are: crystalline and amorphous, composites and blends, fibers and deformed polymers, block polymers and latexes, rubbers and liquid crystalline polymers, thin films and ionomers. Current focuses and future trends are summarized including quantitative SPM measurements, probing of nano- and microscale mechanical properties, studying dynamical surface properties, and exploring local chemical interactions.

Structure and properties of reinforcing fractal filler networks in elastomers

Abstract: The effect of filler networking on mechanical and electrical properties of elastomers is discussed on the basis of percolation theory and a recently developed kinetical cluster-cluster agg...

Thiuram- and dithiocarbamate-accelerated sulfur vulcanization from the chemist's perspective; methods, materials and mechanisms reviewed

Abstract: This paper describes research methodologies for the investigation of the mechanism of vulcanization and discusses the reactivity of thiuram and dithiocarbamate chemicals. The combined knowledge is subsequently applied to thoroughly review the mechanism and chemistry of both thiuram- and dithiocarbamate-accelerated sulfur vulcanization. Integration of the original mechanistic ideas from the 1960s and the results obtained in the past three decades now have led to a more balanced appraisal of events during vulcanization. Questions have been answered, solutions for old problems are proposed, and remaining fields of endeavor are identified.

Characterization of sol and gel in Hevea natural rubber

Abstract: 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 reduce...

Hydrogenation of diene elastomers, their properties and applications : A critical review

Abstract: This chemistry and technology of hydrogenation of diene elastomers have substantially grown during the past decade. New applications of hydrogenated elastomers have emerged. Homogeneous hydrogenation has several advantages over heterogeneous hydrogenation because of its higher selectivity, faster rate and cleaner end products. However, separation of catalysts and recycle/reuse of expensive metals still poses problems. The preferred alternative for the hydrogenation of elastomers in solution is the use of Zeigler type catalyst which are less expensive than the noble metal catalysts like Rh, Pd etc. However, such catalysts are not effective when strongly coordinating groups are present in the elastomer. One approach would be to use transition metals, which have less tendency to coordinate with polar monomers in the elastomer. Research is also warranted in the use of less expensive metals for elastomer hydrogenation (Ni, Co, Ru). Use of large quantities of solvent (to keep the solution viscosity low) is another significant cost center in elastomer hydrogenation. Novel agitator systems/reactor configuration to handle higher concentration of rubber in solution, yet provide adequate heat and mass transfer in gas-liquid hydrogenation reaction, needs to be explored. Hydrogenation of diene elastomers in the latex form using water soluble catalyst appear to be hold great promise at the present time since many diene elastomers (like SBR, CR and NBR etc.) are commercially produced directly in the form of latex. Creative exploitation of biphasic catalysts for hydrogenation is expected to gain momentum since early results look promising. This would require greater fundamental understanding of the aqueous-organic interphase in a latex process and the mechanism of transport of catalytic reagent across this interphase. More studies are needed to achieve homogeneous chemical reaction inside of each individual latex particles.

Viscoelastic Properties of Elastomers and Tire Wet Skid Resistance

Abstract: Many studies concerning tire wet skid resistance have been published in the past, but they have in general involved the use of only a few grades of SBR and BR. We have evaluated the British Portable Skid Tester (BPST) wet skid resistance of eighteen sulfur curable polymers which might be used for automobile tires. These results have been analyzed in relation to the viscoelastic properties of the polymer systems. Analysis of wet skid resistance in terms of the peak value of tan δ over a prescribed temperature range, designated as Tα, and abrasion loss—derived from the theory of rubber friction—was concluded to give a better general relationship for a wide range of polymers.

Thermoplastic Elastomeric Blends of Nylon-6/Acrylate Rubber: Influence of Interaction on Mechanical and Dynamic Mechanical Thermal Properties

Abstract: Nylon-6 and acrylate rubber (ACM) were melt blended in a Brabender Plasticorder at 220 °C and 40 rpm rotor speed. The reactive nature of the blend is reflected in the mixing torque behavior of the blends at different compositions. The solubility characteristics of the blends in formic acid solution gives an approximate idea of the amount of nylon-6 grafted onto ACM and vice-versa. A reaction mechanism is proposed based on the well known epoxy—amine and epoxy—acid reactions and is confirmed by infrared spectroscopic studies of the blends. The influence of interaction between the two polymers on the mechanical and the dynamic mechanical properties of the blends is analyzed in detail, and the results are interpreted on the basis of the formation of nylon—ACM graft copolymer at the interfaces. The dynamic mechanical thermal analysis (DMTA) reveals a two phase morphological structure, indicating incompatibility of the blend components. The grafting reaction results in dramatic increase in both the sto...

Hysteresis Friction of Sliding Rubbers on Rough and Fractal Surfaces

Abstract: 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 ...

NMR Imaging of Elastomers: A Review

Abstract: From curiosity driven investigations about 10 years ago NMR imaging of materials has developed into a useful tool for characterization of polymers, in particular of elastomer products. A clear indicator of this development is the increasing number of imaging spectrometers in use at industrial research and quality-control laboratories. Typical applications of NMR imaging to elastomers are investigations of the homogeneity of a compound or product components like gaskets or tire profiles, studies of the aging behavior under different loading conditions, the mapping of stress, strain and temperature distributions, and the analysis of material change after application of an overload. Elastomers constitute a class of materials particularly suitable to NMR imaging, because they are rich in protons, the most sensitive, stable NMR nucleus, and the material is soft, giving rise to small dipole-dipole couplings and thus to comparatively narrow lines and favorable imaging conditions. Yet the residual dipole...

Vulcanization of Ultrasonically Devulcanized SBR Elastomers

Abstract: Sulfur cured SBR elastomers, devulcanized by high power ultrasonic irradiation, were revulcanized by using the same curing conditions as for virgin SBR. Crosslink density and gel fraction of virgin, devulcanized, and revulcanized elastomers were measured. Curing behavior of some model compounds based on virgin and devulcanized SBR was investigated. Strongly pronounced differences between the curing behavior of virgin and devulcanized elastomers were observed. Torque and DSC studies indicate that two different processes during the crosslinking of devulcanized rubber take place. The existence of these two processes is explained by crosslinking of sulfidized polymer chains followed by crosslinking due to the presence of sulfur and accelerator. Chemical differences between virgin and devulcanized elastomers, explaining the observed phenomena, are discussed.

Superior Mechanical Properties of Reclaimed SBR with Bimodal Network

Abstract: The correlation between the mechanical properties of revulcanized SBR, total and polysulfidic crosslink density, gel fraction of original vulcanizate, ultrasonically devulcanized, and revulcanized rubber is described. Under some processing conditions the tensile strength of revulcanized SBR is found to be much higher than that of the original vulcanizate with elongation at break being practically intact. A model explaining the increase in mechanical properties of revulcanized rubber is proposed.

The Morphology of Rubber/Plastic Blends

Abstract: 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 ...

Electrical Conductivity of Polystyrene-Rubber Blends Loaded with Carbon Black

Abstract: Polystyrene/rubber blends have been loaded with carbon black (CB) and the filler localization in the two-phase polyblends has been studied in relation to the chemical structure of the rubber. The CB localization and the electrical conductivity are greatly influenced by the substitution of the rubber chains. In polystyrene/polybutadiene blends, the filler is localized within the polybutadiene phase. In contrast, in polystyrene/polyisoprene and polystyrene/ethylene—propylene rubber (EPM) blends, CB is mainly localized at the interface, so that the CB percolation threshold in cocontinuous two-phase polyblends is dramatically decreased.

On the Ogden Strain-Energy Function

Abstract: The Ogden strain-energy function for rubber appears to be gaining popularity among users of finite element analysis. This paper discusses some of the special features of this material mode...

Strain-Crystallization of Guayule and Hevea Rubbers

Abstract: A comparison was made of the room temperature strain-crystallization of naturally-occurring cis-1,4-polyisoprenes having varying non-rubber content. A variety of measurements were employed to assess crystallization, including stress relaxation, optical birefringence, and the infrared absorption spectrum. All methods yielded the same result: The strain required to induce crystallization is less for polyisoprenes having larger concentrations of impurities. The ability to crystallize at lower orientation presumably underlies the superior failure properties of guayule rubber and the poorer grades of natural rubber (NR) in comparison to deproteinized NR.

Degradation of Hydrogenated Styrene—Butadiene Rubber at High Temperature

Abstract: 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.

Preparation and Characterization of Solution SIBR via Anionic Polymerization

Abstract: Harnessing anionic terpolymerization of styrene, isoprene and butadiene to a degree where one can achieve simultaneous control of composition, microstructure and sequence distribution resu...

An evaluation of strain amplification concepts via Monte Carlo simulations of an ideal composite

Abstract: In the modeling of carbon-black filled elastomers it is important to have a good estimate of the state of the elastomer itself, since many nonlinear effects originate in the matrix material. A common notion in such estimates is the idea of a “strain amplification” factor that relates a macroscopically imposed strain state to the average strain state in the elastomer matrix material. In this paper Mullins and Tobin's interpretation of the Guth—Gold and Smallwood's amplification factor, and a more recent proposal by Govindjee and Simo will be examined. All three theories are compared to the results of a series of Monte Carlo simulations on an ideal composite with a Neo-Hookean matrix and semi-rigid inclusions. It is shown that for the idealized material, one can not interpret the Guth—Gold and Smallwood amplification factors as an estimate of the strain state of the matrix material. The theory of Govindjee and Simo, on the other hand, is shown to accurately predict the strain state of the matrix.

Anisometry Measurements in Carbon Black Aggregate Populations

Abstract: 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 measurem...

Characterization of Polymer Adsorption on Disordered Filler Surfaces by Transversal 1H NMR Relaxation

Abstract: The transversal 1H NMR relaxation of the bound rubber shell of carbon black loaded elastomers can be decomposed into three relaxation regimes corresponding to the loosely bound rubber, the rubber that is immobilized on the carbon black surface and a third component of intermediate mobility. The relaxation time T2 of the intermediate component is related to the end-to-end distance of polymer segments between adsorption sites on the carbon black surface, by converting the relaxation times to length scales on the basis of recent work on NMR relaxation of elastomeric networks. From measurements on SBR loaded with carbon black N 220, a distance of 2.3 nm was obtained in agreement with characteristic dimensions of crystallite sizes and surface roughness as determined by atomic force and scanning tunneling microscopy. The analysis was applied to novel inversion blacks which give lower tan δ/60°C, and rolling resistance without affecting tan δ/0°C and wet skid behavior. These blacks were found to possess...

Surface Energy of Commercial and Pyrolytic Carbon Blacks by Inverse Gas Chromatography

Abstract: 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.

Viscoelastic Behavior of NBR/EVA Polymer Blends: Application of Models

Abstract: The viscoelastic properties of blends based on nitrile rubber (NBR) and ethylene-vinyl acetate copolymer (EVA), a thermoplastic elastomer, are investigated in terms of storage modulus and loss tangent for different compositions. These small-strain dynamic mechanical properties have been evaluated using a Rheovibron Viscoelastometer covering a wide temperature range. Attempts have been made to fit the experimental results with computations based on mean field theories developed by Kerner. Predictions based on the discrete particle model (which assumes one of the components of the blend to be the matrix and the other dispersed as inclusions) are found to be satisfactory in the case of 30/70 NBR/EVA blend but not 70/30 and 50/50 blends. The packed grain model (which assumes neither of the components to be the matrix but approximates a co-continuous structure of the two) predictions do not agree with the experimental data on 50/50 blend for which a co-continuous morphology was revealed by SEM observa...

The Effect of Network Formation on the Rheological Properties of SBR Modified Asphalt Binders

Abstract: 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.

Ultrasound devulcanization of SBR : Molecular mobility of gel and sol

Abstract: In an effort to support the recycling of rubbery polymers and composites, 1H NMR relaxation and pulsedgradient spin echo diffusion measurements have been performed on virgin and unfilled vulcanized strene-butadiene rubber (SBR), and networks after various extents of devulcanization using an ultrasound technique. The NMR methods recognize unentangled light molecules (e.g. sol), but do not distinguish between unattached entangled large molecules and chemical network segments. Devulcanization generates additional sol with a wide mass distribution, thus increasing both sol and gel mobility, but decreasing sol mean diffusivity. The latter effect is accounted for by the increasing mean sol molecular mass but also by the increasing glass transition temperature, which is related to main-chain stiffening seen in our earlier 13C NMR experiments. In addition to improving the molecular-level understanding of devulcanization, this study provides guidance for the optimization of the devulcanization parameters.

Composites of Waste, Ground Rubber Particles and Poly(Vinyl Chloride)

Abstract: 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.

Chemical Interaction between Surface Oxidized Carbon Black and Epoxidized Natural Rubber

Abstract: This study—based on Monsanto Rheometer measurements, determination of bound rubber, enthalpy of reaction, solvent swelling studies, and measurement of physical properties— revealed that the functional groups of intermediate super abrasion furnace (ISAF) carbon black chemically interact with the epoxidized natural rubber. The extent of interaction is greater in the case of an oxidized grade of ISAF black than the nonoxidized grade. Infrared spectral studies show that the interaction between the rubber and carbon black leads to chemical bond formation. It is believed that the oxidized grade of carbon black forms ester-type as well as phenolic ether-type bonds, while the nonoxidized grade forms primarily the phenolic ether-type of linkages.

The microstructure of natural rubber latex films

Abstract: An electron microscopy technique which has been used to visualize the crosslinked regions in vulcanized blends of dry rubber has now been applied to films made from natural rubber (NR) latex. The method involves swelling the latex film with styrene, polymerizing the styrene, sectioning the sample and then staining with osmium tetroxide to reveal the rubber network when observed by transmission electron microscopy (TEM). The micrographs show the higher ratio of interparticle to intraparticle crosslinks in a sulphur post-vulcanized film as compared with a sulphur prevulcanized film. They also show that, as in dry rubber films, the mesh size of the visible rubber network correlates with the crosslink density of the rubber. The technique also reveals that the crosslink distribution in peroxide prevulcanized latex (PPVL) is significantly different from that in latices prevulcanized using sulphur or radiation.

Effect of Crosslink Type on the Ultrasound Devulcanization of SBR Vulcanizates

Abstract: Sulfur-cured non-reinforced SBR with different amounts of poly-, di- and monosulfidic crosslinks is devulcanized by high power ultrasound irradiation in a continuous process under various ...

Effect of Processing Additives on Carbon Black Dispersion and Grip Property of High-Performance Tire Tread Compound

Abstract: Rubber and carbon black compounds show complex behaviors in their mixing process due to their complicated microcomposite structure. Therefore, establishing a clear relationship between the...