bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Adhesion on the Equilibrium Swelling of Short Sisal Fiber Reinforced Natural Rubber Composites
Authors: Varghese Siby , Kuriakose Baby , Thomas Sabu , Joseph Kuruvilla
Published: February 2011

Solvent swelling of natural rubber composites, containing both untreated and acetylated short sisal fiber, has been investigated in a series of normal alkanes such as pentane, hexane, heptane and octane. The restriction on elastomer swelling exerted by sisal fiber as well as the anisotropy of swelling of the composite have been confirmed by this study. The results showed that increased fiber content and the addition of bonding agent reduced the swelling considerably. It has been demonstrated that with improved adhesion between short fiber and rubber, the factor, (VI−VF)/VI, decreases, where VI and VF are the volume fraction of rubber in dry and swollen samples, respectively.
Rheological Properties of Rubber-Carbon Black and Carbon Black-Oil Compounds Including Measurements at Very Low Shear Stresses
Authors: Osanaiye Gabriel J. , Leonov Arkadii I. , White James L.
Published: February 2011

The rheological properties of binary rubber-carbon black compounds at compositions 5, 20, 30, 40 and 50 volume percent carbon black have been investigated as well as ternary compounds with rubber/carbon black/oil compositions of 70/20/10, 60/20/20 and 50/20/30, respectively. The compounds were investigated using (1) a constant stress creep instrument at very low rates of deformation, (2) a rotational rheometer at intermediate shear rates and (3) a capillary extrusion instrument at higher shear rates. In experiment (1), it was found that below a critical yield stress, the strain becomes saturated and finite. Above this stress the strain becomes unbounded and the compound maintained a steady shear flow. This observation was made for all compounds investigated. The values of the yield stresses obtained using the creep instrument were found to be significantly lower than those obtained from common extrapolations from rotational and capillary rheometers. In the ternary compounds it was also observed that as the oil content increases, not only the viscosity but the yield stress is reduced significantly. This observation is important because it can throw light on the type of interactions between carbon black and the rubber matrix.
Large Deformation Micropolar Theory for Cord Rubber Composites
Authors: Padovan Joe , Parris Hua , Ma Jin
Published: February 2011

Based on a 2nd Piola Kirchhoff type formulation, a new unipolar cord rubber composite constitutive theory is developed. It has the capability to handle the local/global effects of cord twist under both small and large deformation situations. In this context, the theory handles the coupling between stress and moment stress and associated kinematics. The development also handles several new Poisson effects which involve the coupling of both axial elongation and twist, as well as axial twist and lateral elongation. The theory incorporates both experimentally and analytically based parameters to define the various response characteristics. The analytical results involve the use of several finite element simulations to define local cord rubber response. Several elasticity/strength of materials based limiting arguments were used to define asymptotic behavior, thereby providing for a more physics based curve fit of empirical data.
Fracture of Elastomers by Gas Decompression
Authors: Stevenson Andrew , Morgan Glyn
Published: February 2011

A study has been made of gas decompression failures in elastomeric seals using a fracture mechanics approach and considerations of gas permeation. An equation is proposed for the tearing energy associated with crack growth from internal gas bubbles in a finite thickness elastic media. When applied to a model experiment where an internal flaw of known size was pressurized up to failure, the equation agreed with experimental results. A series of seals were then subjected to high gas pressures (up to 69 MPa or 10,000 psi) for a range of temperatures between 20 and 230°C and the amount of crack growth was measured after decompression. The trends in crack growth were correctly accounted for when values for tearing energy and modulus were used that were appropriate for the temperature of decompression. The effect of mechanical boundary constraint was studied by varying the compression on the seal in specially designed test holders. The effect of decompression rate is also considered. The conditions under which failure will occur are created by a complex balance of the available tearing energy and the gas permeation kinetics. A fundamental problem is the unknown size of the initial flaw from which crack growth and rupture occurs. This is discussed in the light of the experimental results and it is proposed that effective surfaces of weakness form in the elastomer phase of size to provide initiation sites for crack growth.
Effect of Hydrocarbon and Amine Diluents on the Properties of Dicumyl Peroxide Cured Styrene-Butadiene Rubber, Part I: Gum Compositions
Authors: Hamed Gary R. , Hsu Jing-Ming
Published: February 2011

Gum SBR compositions containing dicumyl peroxide and either alkane (nonadecane) or amine (octadecylamine or oleylamine) diluent were prepared. Dilution caused a reduction in rheometer torque upon curing and in the resulting crosslink density based on solvent swelling. Results for each diluent were indistinguishable. However, tensile strengths and especially storage moduli were different for nonadecane- and octadecylamine-diluted vulcanizates. Added octadecylamine mildly reinforced the gum, while nonadecane lowered strength and stiffness. Furthermore, quite strikingly, octadecylamine-diluted samples had a large, low-strain storage modulus, which decreased markedly with strain amplitude (Payne effect), while vulcanizates diluted with nonadecane showed no Payne effect.
Relationship between the Cohesive Strength and Tack of Elastomers: Part IV, Carbon Black Filled Styrene-Butadiene Rubber
Authors: Hamed G. R. , Wu P. S.
Published: February 2011

The autohesion and cohesion of uncrosslinked SBR (gum and black-filled) have been determined over a broad range of test temperatures and rates using a T-peel geometry. Peeling energies can be time-temperature superposed to form mastercurves using shift factors in accord with the WLF form. Universal constants are appropriate for the gum. While experimental constants were obtained for the black composition. Cohesion for the gum and filled SBR increase continuously with increasing test speed or reduced temperature. On the other hand, autohesion for the gum shows an abrupt transition by decreasing at a critical reduced rate, while autohesion of the filled SBR does not exhibit the transition. The transition is associated with a viscous-to-elastic response change with increasing RaT; filled SBR has reduced elasticity relative to the gum and hence the transition is not present. By examining relative autohesion, it is seen that the gum undergoes an interfacial-cohesive-interfacial transition response with increasing RaT. This is quite different than the behavior found when peeling apart elastomer/hard substrate bonds, such as the SBR/polyester bonds of Gent and Petrich; here, there is simply a cohesive-interfacial transition with increasing RaT. For elastomer-elastomer junctions there is interpenetration and chain mobility in the interphase formed. At sufficiently low RaT, interdiffused chains simply slide by one another giving interfacial failure. With increasing RaT entanglement couplings in the interphase become effective in preventing facile flow, and, at this point, failure becomes cohesive; finally, at even higher RaT, with a sufficiently elastic response, stresses apparently become concentrated at the interface and failure proceeds there. When an elastomer is bonded to a hard, immobile material, the mechanism of bonding is restricted to surface site adsorption. This reduces elastomeric chain mobility and produces more “glassy” dispersive interactions which resist separation relative to the chains which are held together by “rubbery” dispersive forces. Again at sufficiently high RaT, with increased elasticity, failure becomes interfacial.
Vulcanization: Conventional and Dynamic
Authors: Coran Aubert Y.
Published: February 2011

Conventional vulcanization, has a history of over 150 years, during which there have been increasing needs for technology to permit more and more rapid processing before the vulcanization of a rubber article in its final shape. But, at the same time, one desired increased rates of crosslinking after the part was in its final shape, e.g., in a mold. These two objectives are opposed to one another. For fast processing, we would like to increase temperatures to reduce the resistance to flow; but we do not want vulcanization to occur before processing flow is complete. On the other hand, after a rubber article is in its final shape or form, we would like for vulcanization to occur as rapidly as possible. The reasons for these objectives, are to increase capital utilization and to reduce the cost of money. The use of the premature vulcanization inhibitor, CTP, can give improved processing safety without loss of vulcanization throughput. In the case of thermoplastic elastomers prepared by dynamic vulcanization, all of the vulcanization is done rapidly during mixing, before the rubber compound flows into its final shape, e.g., during rapid thermoplastic injection molding (in seconds, not minutes). The dynamic vulcanization process does add cost to the material; however, this is more than offset by the gains in capital utilization. I would be remiss if I did not mention some potential disadvantages associated with the thermoplastic elastomers. One of these is that, at temperatures above the temperatures of flow, there is a great reduction in the usefulness of the properties (the materials can melt). A related disadvantage is that resistance to permanent set at high temperatures may be inadequate. However, the elevated-temperature set resistance of thermoplastic elastomers prepared by dynamic vulcanization is generally better than that of those prepared by other means. Both kinds of vulcanization are important and may continue to be so for another 150, or so, years.
Identification of Different Modes of Molecular Motion in Polymers That Cause Thermorheological Complexity
Authors: Ngai K. L. , Plazek D. J.
Published: February 2011

The viscoelastic properties of amorphous polymers are reviewed with emphasis on the glass to rubber dispersion (often referred to as the transition zone). Deviations from thermorheologieal simplicity (where molecular retardation and relaxation mechanisms have the same temperature dependence) are identified. Most theories and models of polymer chain dynamics do not address or acknowledge thermorheological complexities and correlations, such as that between the temperature dependence and the breadth of viscoelastic and dielectric dispersions of the local segmental motion. Without successful theories of these phenomena the understanding of polymer chain dynamics must be considered incomplete. In this review, old and new experimental data are used to identify the different modes of molecular motions and the domains of their contributions to the time and frequency dependence of the mechanical response of amorphous polymers. The different modes are then shown generally to have their own dependence on temperature. Thus the viscoelastic spectrum, including local segmental motions which dominate the onset of glassy behavior and largely determine the glass temperature, Tg, the glass to rubber softening dispersion, the rubbery plateau and the terminal zone, is thermorheologically complex. A coupling theory, with the physics of intermolecular interactions and cooperativity built into it, describes well the many-body dynamics of densely packed molecular systems such as polymers. The many predictions of the coupling theory are applied to the different viscoeleatic modes to explain the observed anomalous experimental facts and established correlations. The theoretical understanding has been improved to the extent that now a connection can be made between the chemical structure of the monomer and the viscoelastic properties of the polymer.
Distribution of Crosslinks in Vulcanized Blends
Authors: Tinker A. J.
Published: February 2011

All of the blend systems studied to date show a tendency to have an uneven distribution of crosslinks between the phases; this must be taken to be the norm, with instances of near-even crosslinking being the exception. When the crosslink distribution has been made to be near even, the properties investigated are generally improved. In blends of polar and nonpolar elastomers, there is a tendency for the polar elastomer to be more highly crosslinked than the less polar elastomer, because both the sulfur and accelerators partition in favor of the former. However, if one elastomer has a very high solubility parameter, the accelerator may partition in favor of the less polar elastomer. Provided this differential partition of the curatives is not extreme, the results can be beneficial. There is one recorded instance of a drastic reduction in overall crosslink density through very low crosslinking of one phase, and this may be ascribed to strong differential partition. Since crosslink distribution in blends of elastomers differing in solubility parameter appears to be controlled largely by partition of curatives and vulcanization intermediates, influence may be exerted by appropriate choice of accelerator(s). The crosslink distribution in blends of low and high unsaturation elastomers is extreme; at normal levels of curatives, the low unsaturation elastomer may be virtually uncrosslinked whilst the high unsaturation elastomer can have a higher crosslink density than is desirable. Modification of EPDM to either form an independent network in the EPDM phase or enforce the formation of sulfur crosslinks during vulcanization is effective. The level of crosslinking required in the EPDM phase in order to provide substantial improvements in properties of blends is modest, much lower than would be required to give acceptable properties in a single polymer vulcanizate. Blends of general purpose elastomers, such as NR and BR, do not differ significantly in either solubility parameter or degree of unsaturation and are generally considered not to be problematic. However, these often show an uneven distribution of crosslinks. Studies of the progress of crosslinking during vulcanization suggest that partition of curatives could play a role even here. The detailed view of crosslink distribution presented here is largely due to the success of a swollen-state NMR spectroscopy technique, and there is considerable scope for further advances in view of the list of combinations of elastomers which may be investigated in this way. The list is reproduced in Table IX, suitably updated to take account of recent developments. Further advances are expected; not just in respect of the investigation of new blend and curative systems, but also in the combination of the swollen-state NMR technique with other established procedures such as the use of chemical probe reagents to provide information on the type of sulfur crosslinks present in each phase of a blend.
Crystallization and Morphology of Rubber
Authors: Magill J. H.
Published: February 2011

Naturally occurring materials like rubber predate the development of science and engineering as we know it today. Historically, rubber and more generally elastomers, known as a class of high polymers, are versatile and useful materials. Rubber is still an elastomer of choice for many engineering applications. After decades of R&D, scientists and engineers realized that technology needs good science. This position is nicely summarized in Figure 1. This scenario brings together four main items that are essential to create and to maintain quality industry(ies). In the case of rubber, particularly natural rubber, it is not only essential to understand these individual properties, but also to comprehend the important interrelationships that contribute to material behavior. In this respect, rubber has been an enabling resource material that has served as a paradigm amongst synthetic polymers in their developmental stages. In this article crystallization of natural rubber especially, is addressed in order to provide some perspective on items that relate to the relevant areas of the pyramid. This overview is far from exhaustive on the crystallization aspects of rubber, but hopefully it strikes a balance between thermodynamics and kinetics, since each discipline has contributed significantly to improve our understanding of polyisoprenes, and in a wider sense to crystallization and morphology that helps determine properties relevant to rubber and to polymers in general.
Dynamic Mechanical Losses in Filled Poly(Dimethylsiloxane) Networks
Authors: Sharaf M. A. , Kloczkowski A. , Mark J. E.
Published: February 2011

This investigation focused on the study of dynamic mechanical losses in silica-filled networks of poly(dimethylsiloxane) (PDMS). Some of the samples were filled using a novel method, specifically the in situ precipitation of particulate silica either after or during network formation. Others were filled using the customary method of mechanically blending already-prepared silica into the elastomer prior to its crosslinking, and some were prepared without any filler at all. The resulting materials exhibited a variety of relaxation behaviors over the temperature range 120–260 K. The glass transition temperatures Tg showed only a slight dependence on the presence of the filler particles and crosslinks, but the filler was found to reduce both the degree and rate of crystallization for the in situ filled networks. The results obtained document how the techniques employed for incorporating particulate fillers change the viscoelastic properties of an elastomeric network, and how dynamic testing can yield a great deal of insight and useful information on the mechanical properties of polymers in general.
The Effect of Abrading Surfaces on the Wear of Rubber Tread Compounds
Authors: Ramakrishnan R. , Donovan J. A. , Medalia A. I.
Published: February 2011

The wear rate, produced by a modified Lambourn abrader, of rubber tread compounds, depends on the normal load, frictional force, the grit size and the number of grits per unit area of the grindstone. A preliminary model for the wear rate incorporating the grindstone characteristics, the normal and frictional force, and the fatigue exponent of the compound has been developed. The model needs further refinement but predicted the wear rate of SBR and EXXPRO™ rubber compounds well enough to be developed further. The current major limitation is accurate characterization of the grindstone.
Diffusion of Antioxidants in Rubber
Authors: Pushpa S. A. , Goonetilleke P. , Billingham N. C.
Published: February 2011

Migration of compounding ingredients such as antioxidants is a problem that has been recognized by rubber compounders. The literature is almost void of quantitative data in this area. Therefore an investigation of the diffusion of some commonly used phenolic antioxidants in three different rubber vulcanizates was carried out. The antioxidants were chosen so that they included a wide range of molecular weights as well as structural differences to enable us to study the effect of size and molecular nature on diffusion in the medium of rubber. The effect of crosslink density on diffusion was studied by using rubber vulcanizates of three different crosslink densities. BHT (butylated hydroxytoluene), the smallest antioxidant in the series, shows the highest diffusion coefficient. As the molecular weight of the diffusant increases the diffusion coefficient decreases. The molecules of polar nature, such as Antioxidant 754 (2,6-di-t-butyl-4-hydroxymethyl phenol), show higher diffusion coefficient compared to the nonpolar molecule of the same size, such as BHT. The crosslink densities of vulcanizates effect the diffusion of antioxidants in that there is an optimum value at which the diffusion coefficient is highest.
The Chemistry of Phenol-Formaldehyde Resin Vulcanization of EPDM: Part I. Evidence for Methylene Crosslinks
Authors: van Duin Martin , Souphanthong Aniko
Published: February 2011

The application of phenol-formaldehyde resins as crosslinking agents is increasing in importance due to the good high temperature properties of the corresponding vulcanizate and the use in thermoplastic vulcanizates. With respect to the chemistry of phenol-formaldehyde cure (reaction mechanism and structure of crosslink) there are still problems that have to be resolved. The reaction products of the phenol-formaldehyde resin curing of EPDM, contain 2-ethylidene norbornene (ENB) as the third monomer, have been studied. Since such an investigation is rather difficult to perform for the polymer system, a low molecular weight model for EPDM was used: 2-ethylidene norbornane (ENBH). Reaction of ENBH and a resole results in scission of the dimethylene ether bridges, i.e. in degradation of the resole into mono-, bis- and terisooctylphenol units. These are consequently converted into products, consisting of two ENBH molecules linked by mono-, bis- and terisooctylphenol units. The solid resole seems to be a technological solution for storing phenol in combination with formaldehyde. These results support the use of 2-hydroxymethylphenol (HMP) as a low molecular weight model for the resole. At low temperatures and/or short reaction times HMP oligomers (= resoles) and HMP oligomers linked to one ENBH molecule are formed, which are converted into ENBH/HMP (1:1) condensation products. The reaction products of ENBH with both the resole and HMP are shown to contain methylene linked structures, as demonstrated by the formation of monisooctylphenol crosslinks and the presence of residual unsaturation and hydroxyl groups, besides chroman linked structures. This is the first experimental evidence that during phenol-formaldehyde resin cure of rubber, formation of methylene bridges occurs.
Uniaxial Deformation of Rubber Cylinders
Authors: Mott P. H. , Roland C. M.
Published: February 2011

Stress, strain and optical birefringence measurements were made on elastomeric cylinders deformed in tension and compression. The birefringence data enables the actual stress to be determined even when the deformation is not homogeneous. In the absence of lubricant, uniaxially loaded rubber cylinders deviate from homogeneous deformation due to bonding of the cylinder ends. The existing analysis to correct the force-deflection curve for the effect of this sticking, strictly valid for infinitesimal strains, is premised on the idea that the deformed cylinder has a parabolic profile. Experimentally, however, it was found that slender rubber cylinders assume a much flatter profile, while maintaining constant volume, when deformed. Nevertheless, the accuracy of the stress-strain curve when the standard correction is applied turns out to be quite good, partially a result of cancellation of two, relatively small, errors. This accuracy was assessed by comparison of force-deflection data from bonded cylinders both to stress-strain data obtained on lubricated cylinders and to the stresses deduced from the measured birefringence.
A New Theoretical Approach to Cavitation in Rubber
Authors: Ganghoffer J. F. , Schultz J.
Published: February 2011

In order to analyse the stability and bifurcation phenomena occurring during expansion of a small void in a rubbery material, the behavior of spherical shells submitted to a combined far-field pressure and uniaxial tension has been investigated, considering a general nonlinear isotropic elastic compressible behavior of the material and without any restrictions on the shell thickness. A radial solution for the deformation gradient with a spherical symmetry has been exhibited, which is valid for any behavior law and consists of a homogeneous deformation. The three-dimensional problem is then linearized around this trivial solution, and we show the existence of a pressure interval containing the zero value, in which the solution is reduced to the trivial solution, which is therefore infenitesimally stable. When the applied pressure lies outside the stability interval, we determine the bifurcation points of the shell around the trivial solution, first when only a pressure is applied and secondly when there is an additional far-field tension, much smaller than the applied pressure. The form of the stress distribution on the boundary of the cavity suggests a possible bifurcation of the spherical solution towards a family of axisymmetric solutions. Within this hypothesis, we get a relation between the geometrical parameter of the shell (its radius and thickness), the mechanical properties of the material and the critical load.
Analysis of Mixing Efficiency in a Multi-Cut Transfermix
Authors: Li Tao , Cheng Hongfei , Manas-Zloczower Ica
Published: February 2011

Three-dimensional flow patterns of a power-law model fluid in a Multi-Cut Transfermix were calculated. A particle tracking algorithm was used to study the dynamics of mixing. Distributive mixing efficiency was quantified in terms of length stretch distributions and average values. The influence of rotational speed and axial pressure difference on mixing efficiency, under constant output was analyzed. The mixing performances in the MCT was also compared with that in a single screw extruder with the same dimensions as the entrance region of MCT and operating at the same flow rate.
Chemical Interaction between Chlorosulfonated Polyethylene and Silica—Effect of Surface Modifications of Silica
Authors: Roychoudhury A. , De P. P. , Roychoudhury N. , Vidal A.
Published: February 2011

The surface of precipitated silica was modified by heat treatment (800°C, 4 h) and hexadecanol treatment. Diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) measurements reveal that the modification of the silica surface reduces the silanol content. Heat treatment causes condensation of the silanol groups forming siloxane linkages, while hexadecanol treatment causes esterification, thereby, shielding the free silanol groups. As a result, the modified silicas exhibit much less interaction with polar molecules (e.g. water, chloroform), compared to the unreacted silica. Bound rubber formation in the chlorosulfonated polyethylene (CSM)/silica system is also adversely affected by the modification of the filler surface. CSM upon heat treatment (180°C, 1 h) loses -SO2Cl groups and the modified polymer lacks in its ability to form bound rubber. Accordingly, it is believed that the rubber-filler interaction occurs between the silanol groups of the silica and sulfonyl chloride groups of CSM.
Kinetics of Morphological Development in Elastomer Modified Silica Xerogels
Authors: Beaucage G. , Guo L. , Hyeon-Lee J.
Published: February 2011

Acid-catalyzed, sol-gel chemistry is used to incorporate polysiloxane elastomers in ceramic gels in order to prevent pore collapse on drying. These rubber-modified, ceramic gels can lead to low-density nano-porous materials for uses such as thermal insulation. The morphological mechanisms by which these materials are toughened by elastomers is the focus of this paper. Structural development in these multiphase systems involves a complex interplay between nano-scale hydrolysis/condensation reactions and colloidal to macroscopic phase separation and network formation. The interplay between these morphological features as a function of reaction time is studied using microscopy as well as small-angle x-ray and light scattering. The initial reaction mixture is phase-separated on a micron scale due to the immiscibility of poly-siloxanes and water. At an early stage of the sol-gel reaction, mass-fractal domains in the nano-scale develop, while micron-scale phase-separated domains are diminished. Near the gel-point, a macroscopic network forms whose morphological features are strongly influenced by the presence of polysiloxane elastomer. A model is proposed for the interplay between these structural levels during growth.
Some Attempts to Force Poly(Dimethylsiloxane) Chains through Zeolite Cavities to Improve Elastomer Reinforcement
Authors: Pu Zhengcai , Mark James E. , Beaucage Gregory
Published: February 2011

The reinforcing effects of zeolites in poly(dimethylsiloxane) (PDMS) elastomers were characterized using two preparative approaches. In the first, end-functionalized polymer chains were blended into the zeolite, and were then endlinked into the required network structure. The second approach represented an attempt to force some chains through the cavities, by blending the monomer itself into the zeolite and then polymerizing it to obtain the PDMS elastomer. The two types of zeolite-filled PDMS were characterized using stress-strain measurements in elongation, equilibrium swelling, and small-angle X-ray scattering. The second synthetic approach did seem to give improvements in mechanical properties, particularly when the average cavity size of the zeolite particles was relatively large. Ascribing the observed improvements in reinforcement at least partly to the threading of some PDMS chains through the zeolites was supported by the results obtained in the swelling and scattering experiments.
Studies of Elastomer Oxidation via Thermal Analysis
Authors: Burlett D. J.
Published: February 2011

Elastomers are used in many industrial applications because of their remarkable toughness and elasticity. However, the source of these properties is also a weakness, in that loss of properties via oxidation is an important factor in their selection. Thermoanalytical techniques, such as differential scanning calorimetry (DSC), provide useful tools for the characterization of the stability of elastomers. DSC can not only be used to determine oxidative induction times under isothermal conditions but can also be used to determine apparent overall activation energies of the oxidation process. An evaluation of these techniques is made and the technique is used to compare the oxidation susceptibility of polybutadienes of different microstructure. The results of these DSC scans are interpreted in terms of the chemistry of the oxidation process using FTIR results.
Identification of Tackifying Resins and Reinforcing Resins in Cured Rubber
Authors: Kim Seung Wook , Lee Gae Ho , Heo Gwi Suk
Published: February 2011

On-line thermogravimetic analysis/Fourier transform-infrared spectroscopy (TGA/FT-IR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were employed to identify the tackifying resins and reinforcing resins in cured rubber. Py-GC/MS gave better results in the identification of the resins than the on- line TGA/FT-IR method. The mass spectra of resins in cured rubber were characterized by comparing the mass spectra of the pyrolyzates of raw resins and those of cured rubber containing the resins. t-Butylphenol acetylene condensed resin, coumarone-indene, C5-oligomeric Escorez 1102, modified wood rosin, and reinforcing modified cashew resin were studied. The results show that on-line Py-GC/MS is powerful tool in the analysis of the resins in cured rubber. The diagnostic m/z values of the resins for direct analysis in cured rubber were summarized. Reasonable structural information for resins could be acquired by the characteristic fragmentation patterns.
Adhesion of Natural Rubber to Steel Substrates: The Use of Plasma Polymerized Primers
Authors: Boerio F. J. , Tsai Y. M. , Kim D. K.
Published: February 2011

Plasma-polymerized acetylene films are excellent primers for bonding natural rubber (NR) to steel substrates. The purpose of this research was to determine the mechanisms responsible for adhesion at the NR/primer interface. Interactions between natural rubber and plasma-polymerized acetylene films were simulated using model systems containing squalene (C30H50) or squalane (C30H62), carbon black, sulfur, stearic acid, N, N-dicyclohexyl-benzothiazole-sulfenamide (DCBS), cobalt naphthenate, and diaryl-p-phenylene-diamine. Analysis of plasma-polymerized acetylene films before and after reaction with model rubber systems was accomplished using Fourier transform infrared spectroscopy (FTIR). The importance of the unsaturation in the reaction was demonstrated by comparing the behavior of the two model systems. In the squalane-based system, squalane itself was stable throughout the reaction, with only a slight reaction with the antioxidant and sulfur. No significant reactions occurred between the squalane-based model system and plasma-polymerized acetylene films with the exception of slight adsorption of antioxidant and zinc and/or cobalt stearate onto the films. Reactions between plasma polymerized primers and the squalene-based model system were complex. Squalene itself went through double-bond migration. ZnO and cobalt naphthenate reacted with stearic acid to form zinc and cobalt stearates which then reacted with DCBS and sulfur to form zinc and cobalt accelerator perthiomercaptide complexes. These complexes reacted with squalene and with the primer film to form accelerator terminated, perthiomercaptide pendant groups and, eventually, short polysulfide crosslinks. Since there was little reaction of squalane-based model rubber compounds with plasma polymerized primers but extensive reaction of squalene-based models, it was concluded that an intermediate formed in that reaction was responsible for crosslinking between squalene and the primer in the model system and for adhesion at the NR/primer interface in an actual bond.
1H NMR Relaxation Studies of Cured Natural Rubbers with Different Carbon Black Fillers
Authors: Leisen J. , Breidt J. , Kelm J.
Published: February 2011

1H NMR relaxation data provide insight into the effects of carbon black fillers on the structure of polymer networks in products based on natural rubber so that accepted ideas concerning the interaction between elastomeric networks and active filling materials are confirmed. A new 1H NMR relaxation experiment allows the direct investigation of dangling chains within the polymeric network. In samples containing carbon black a motional anisotropy is observed for these chain ends, while dangling chains in samples without carbon black fillers show isotropic rotational motions. The parameter q′, quantifying the motional anisotropy, is suggested to be a measure of the physico-chemical interactions between elastomer and filler.
Homogeneous Zinc(II) Catalysis in Accelerated Vulcanization III. Degradation Modes of Mono- and Disulfidic Cross-Links
Authors: Nieuwenhuizen P. J. , van Veen J. M. , Haasnoot J. G. , Reedijk J.
Published: February 2011

This paper reports a Reaction-Stage-Modeling study dealing with degradation of mono- and disulfidic cross-links, providing new information about the molecular processes underlying the macrophysical phenomenon of reversion. The monosulfidic model cross-link (2,3-dimethyl-2-buten-1-yl)(2,3-dimethyl-1-buten-3-yl)sulfide was found to degrade at a relatively low temperature of 140 °C to yield olefins and α, β-unsaturated thioaldehydes. The latter species are not stable enough to be observed directly, but instead dimerize via an auto-Diels-Alder reaction to give a—fully-characterized—1,3-dithiin. The disulfidic model cross-link bis(2,3-dimethyl-2-buten-1-yl)disulfide was observed to degrade according to a previously unknown mechanism, involving a 1,4-hydride shift, to furnish a 1,3-dipolar intermediate. The reaction is catalyzed by bis(diethyldithiocarbamato)zinc(II), ZDEC, and the activation enthalpy ΔH‡ of the reaction has been determined to be ∼ 71(7) kJ mol− . Several dienophiles and dipolarophiles were applied to trap the α, β-unsaturated thioaldehyde and 1,3-dipolar intermediate, but neither was successful. Overall, this study has furnished direct evidence for degradation of mono- and disulfidic cross-links via hydrogen shifts and indicates, for the first time, in what way zinc complexes may cause cross-link degradation and induce reversion in rubber vulcanizates.
Homogeneous Zinc(II) Catalysis in Accelerated Vulcanization IV. The Mechanism of Cross-Link (De)Sulfuration
Authors: Nieuwenhuizen P. J. , van Veen J. M. , Haasnoot J. G. , Reedijk J.
Published: February 2011

This paper reports a detailed re-examination of the mechanism of zinc-mediated cross-link desulfuration by means of Reaction-Stage Modeling. Heating the model cross-link bis(2,3-dimethyl-2-buten- 1-yl)disulfide in the presence of catalytic amounts of bis(diethyl-dithiocarbamato)zinc(II), ZDEC, results in slow but definite formation of monosulfides displaying retention and isomerization of the double-bond position. The formation of monosulfides with retained double bonds implies that cross-link desulfuration occurs according to SNi reactions; whereas, the formation of isomerized monosulfides points to the operation of SNi′- and/or thione-like desulfuration reactions. Importantly, these observations constitute the first evidence for zinc accelerators acting as homogeneous catalysts in desulfuration. The activation energy for cross-link desulfuration of SNi reaction was established to be 86(16) kJ mol−1. In addition, ZDEC is reported to sulfurate model cross-links. The required sulfur atoms may originate either from desulfuration of other sulfides, or from elemental sulfur added to the mixture. Just as for cross-link desulfuration, zinc-mediated sulfuration was found to occur both with and without double-bond isomerization.
Elastomer Swelling in Mixed Solvents
Authors: Westbrook P. A. , French R. N.
Published: February 2011

A critical performance factor for elastomers in chemical service is absorption of solvents. Since swelling data are often limited to single component exposure, methods to estimate elastomer compatibility with mixed solvents have received considerable theoretical attention. The evolution of these methods is reviewed. Then, an alternative empirical procedure is proposed which is based upon a generalization of Flory's network-solvent phase equilibrium concept. The resulting linear and nonlinear partition coefficient models are used to predict swelling behavior of various elastomers in nearly ideal hydrocarbon solutions as well as other non-ideal solutions. Advantages of the current methods are that they utilize readily available swelling data of the elastomers in pure solvents and also thermodynamic data of the solution of interest. Adjustable parameters are required only when strong associative swelling agents are present. Finally, information regarding the chemical structure of the elastomer is not required.
Carbon Black Distribution in Rubber Blends: A Dynamic-Mechanical Analysis
Authors: Klüppel M. , Schuster R. H. , Schaper J.
Published: February 2011

The influence of phase morphology and carbon black distribution on energy storage and dissipation during dynamic excitations of rubber blends is discussed. It is shown that differences in the local stiffness of the phases in the glass transition regime of unfilled blends lead to characteristic deviations of the local strain from the external strain amplitude. These deviations are governed by a critical phenomenon due to the formation of a phase network above a critical blend ratio. As a result, a strongly nonlinear dependence of the glass transition maxima of the loss modulus on the volume fraction of the phases is observed. By counting the elastically effective bonds of the phase network, the local strain amplitude is estimated by purely geometrical arguments. Based on a consideration of the phase network, the distribution of carbon black in the different phases of filled blends is estimated from the height of the local maxima of the loss modulus in the glass transition regime. Thereby, a linear increase of the maximum value of the loss modulus with rising carbon black concentration is exploited that relates the enhanced energy dissipation of filled rubbers to the internal friction of the filler particles. Results on EPDM/BR/N550 blends indicate that carbon black is preferably located in the BR phase. A somewhat higher concentration of carbon black in the SBR phase is found in the case of NR/SBR(40% Styrene)/N330 blends.
Surface Instabilities in Compressed or Bent Rubber Blocks
Authors: Gent A. N. , Cho I. S.
Published: February 2011

Biot carried out theoretical analyses of the critical strains at which surface instabilities would be encountered in large blocks of a neo-Hookean material subjected to different degrees of compression in two directions. Three special cases are reviewed here: simple compression in one direction, compression in one direction with the perpendicular direction constrained (pure shear), and equibiaxial compression. In all cases a surface instability is predicted to occur at a moderate compressive strain, ranging from about 33% to about 55%. Because unidirectional compression occurs on the inner surface of a rubber block subjected to simple bending, a similar surface instability would be expected at a critical degree of bending, when the surface compression is about 46%. Observations on bent rubber blocks are compared with this theoretical prediction. Sharp creases occurred on the inner surface at a critical degree of bending but the critical compressive strain there was only about 35% and the bending curvature was less than predicted, only about one-half as severe. The cause of this discrepancy is not known.
Elastic Instabilities of Inflated Rubber Shells
Authors: Gent A. N.
Published: February 2011

Using a simple constitutive law for elastic behavior that includes the feature of a maximum allowable strain, equations are derived for inflation pressure as a function of the amount of inflation for three rubber shells: a thin-walled spherical balloon, a small spherical cavity in a large rubber block, and a thin-walled cylindrical tube. The results are compared with those obtained using the neo-Hookean constitutive law. Uniform expansion is generally predicted to become unstable at a modest degree of inflation but the new relations give a second stable inflation state, in accord with experience.
New Polyolefin Elastomers Containing “Reactive” p-Methylstyrene Units: Preparation by Metallocene Catalysts
Authors: Chung T. C. , Lu H. L. , Hong S.
Published: February 2011

This paper summarizes the experimental results of three new polyolefin elastomers, i.e., poly(1-octene-co- p-methylstyrene (O-p-MS), poly(ethylene-ter-propylene-ter-p-methylstyrene) (EP-p-MS) and poly(ethylene-ter-1-octene-ter-p-methylstyrene) (EO-p-MS), containing “reactive” p-MS units. Both Ziegler-Natta and metallocene catalysts were used in studying co- and ter-polymerization reactions. In the copolymerization of 1-octene and p-MS, Ziegler-Natta catalyst TiCl3/AlEt3 exhibits higher catalyst reactivity to produce high molecular weight O-p-MS copolymers, containing up to 20 mol % p-MS. However, the copolymers show very broad composition and molecular weight distributions. On the other hand, two EP-p-MS and EO-p-MS terpolymers with narrow molecular weight and composition distributions were prepared by [C5Me4(SiMe2NtBu)]TiCl2 metallocene catalyst with constrained ligand geometry. The sharp glass transition temperature (Tg) with flat baseline in each differential scanning calorimetry (DSC) curve indicates homogeneous terpolymer microstructures. The Tg of EP-p-MS is very sensitive to the terpolymer composition (ethylene/propylene ratio and p-MS content). In the compositions with ideal ethylene/propylene ratio ∼ 55/45, the Tα is almost proportional to the content of p-MS. Only with the concentration of p-MS < 2 mol %, does the EP-p-MS show alow Tg<−45°C. On the other hand, the EO-p-MS system exhibits a low Tg<−50°C in a wide range of copolymer compositions, even ones with relatively high p-MS contents (< 7 mol %).
Cure and Mechanical Behavior of Rubber Compounds Containing Ground Vulcanizates: Part III. Tensile and Tear Strength
Authors: Gibala D. , Thomas D. , Hamed G. R.
Published: February 2011

A black-filled styrene-butadiene rubber (SBR) vulcanizate was ambiently ground, then used as an additive to the original, uncured compound. Sheets of the resulting composite (matrix/ground rubber particulate) were cured, and tensile and trouser tear strength determined. The composite had reduced tensile strength, but enhanced tear strength relative to the original vulcanizate. The contrasting behavior is attributed to the effects of sulfur migration into the particulate rubber and differences in the responses of a tensile and a tear testpiece to discontinuities. In brief, ground rubber acts as a stress-raising flaw in tensile testing, while promoting crack tip blunting and stick-slip behavior in trouser tearing.
Carbon Black Surface Characterization by TOF-SIMS and XPS
Authors: Bertrand P. , Weng L. T.
Published: February 2011

The functional groups present at the carbon black (CB) surface contribute, along with the surface microstructure, to the CB surface activity which is known to be an important parameter for the rubber reinforcing properties. A direct detection of the foreign elements (H, N, O, S, Cl, …) present at the CB surface can be achieved with surface analytical techniques such as Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and X-ray Photoelectron Spectoscopy (XPS). The combination of these two techniques is found to be very fruitful. Indeed, although the TOF-SIMS sensitivity is much higher than for XPS, allowing trace detection, this technique suffers from a lack of quantification which can be fulfilled by XPS. The chemical information on the functional groups obtained by both methods is complementary. In XPS, this information is deduced from the electron core level chemical shifts which are mainly influenced by the first neighboring atoms; whereas, in TOF-SIMS, the full molecular environment can be detected. Not only information on the surface groups, but also some structural information can be obtained. Indeed, the TOF-SIMS spectra of carbon black exhibit molecular ions which are characteristic of the surface aromaticity (graphene structure) and also specific clusters at high masses which seem to be related to the basic building block of carbon black particles.
The Role of Filler Networking in Dynamic Properties of Filled Rubber
Authors: Wang Meng-Jiao
Published: February 2011

Fillers, when added to polymer systems, are known to cause a considerable change in dynamic properties. For a given polymer and cure system, this paper discusses the impact of the filler network, both its strength and architecture, on the dynamic modulus and hysteresis during dynamic strain. It was found that the filler network can substantially increase the effective volume of the filler due to rubber trapped in the agglomerates, leading to high elastic modulus. The amount of trapped rubber was estimated according to Van der Poel theory. During cyclic strain, while the stable filler network can reduce the hysteresis of the filled rubber, the breakdown and reformation of the filler network would cause an additional energy dissipation resulting in higher hysteresis.
Compatibilization of Ionomeric Polyblends by Intermolecular Ionic Interactions
Authors: Antony Prince , De S. K.
Published: February 2011

Ionomeric polyblends based on the zinc salt of carboxylated nitrile rubber, abbreviated as Zn-XNBR, and the zinc salt of poly(ethylene-co-methacrylic acid), abbreviated as Zn-EMA, were prepared by melt blending technique. Zn-XNBR/Zn-EMA ionomeric polyblends, in the compositions ranging from 90/10 to 50/50, parts by weight, behave as ionic thermoplastic elastomers, and show synergism in physical properties. The synergism in physical properties is attributed to the formation of a technologically compatible polyblend, wherein intermolecular ionic interactions between the neat ionomers take part in the compatibilization mechanism. Dynamic mechanical thermal analyses show a high temperature transition, owing to the presence of ionic clusters in the neat ionomers and the ionomeric polyblends. The ionomeric polyblend exhibits higher physical properties and melt viscosity than the corresponding non-ionomeric polyblend.