bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymer Surface Modification
Authors: Waddell Walter H. , Evans Larry R. , Gillick James G. , Shuttleworth Derek
Published: February 2011

Surface modification as a technology has been employed in various ways for many years, however, the breadth and magnitude of its applications have grown significantly during the last decade. Much of this growth has been facilitated by the development and spread of rapid and reliable surface characterization techniques. And, as would be expected of a maturing field, the bulk of investigations are now turning to applications rather than a pure understanding. Publications in both the scientific literature and patents describe research on a diverse range of polymeric substrates and potential applications using a wide range of modification techniques. Methods include chemical, photochemical, and high-energy physical techniques to modify polymer surfaces. Searches were made of these methods as applied to the surface modification of polymeric materials of particular interest to the rubber industry. Chemical methods include reactions such as halogenation, addition, etching, and oxidation. Photochemical techniques include surface reactions such as oxidative and nonoxidative degradation, halogenation, and photografting. Physical methods include corona discharge, plasma, electron and ion beam treatments. The 1980's literature on these subjects is published in a variety of languages, including a number of informative review articles and books printed in English on various aspects of this subject. The subject of this review concentrates on the surface modification of polymeric materials of particular interest to the rubber industry by focussing largely on scientific literature published in English and patent literature published during this time period that describe interesting and useful surface chemistry on elastomer substrates and rubber articles containing polymers such as natural rubber, cis-polyisoprene, styrene-butadiene copolymer, nitrile rubber, silicone, etc, and fibers and fabric made from fiber-forming polymer materials such as aramid, nylon, polyester, and carbon fiber, and those techniques reported successful in altering their surfaces. For organizational simplicity, three basic categories are used: elastomers, fibers and others. The latter category refers to those substrates without specific, current application in the rubber industry, but which have interesting or novel scientific features. Restriction of interest to rubber-relevant materials greatly reduced the scope of this work, and the interested reader should be aware that a great deal of activity is to be found in the rigid plastic and, to a lesser extent, biopolymer industries.
Applications of Chemiluminescence in Rubber Research
Authors: Forsström Dan , Kron Anna , Mattson Bengt , Reitberger Torbjörn , Stenberg Bengt , Terselius Björn
Published: February 2011

The oxidation of most organic materials is accompanied by the emission of weak light, so called chemiluminescence (CL). This emission has previously often been designated oxyluminescence. CL has been known for several years, but it is not until recently that the development of photon counting equipment has allowed detection of levels down to a few photons per second. This development makes CL a promising nondestructive and extremely sensitive technique to provide data which may be useful to estimate the service life of polymeric materials. Various applications of the CL-method for the detection of oxidation of elastomers are reported: such as, stabilization of hydroxyl-terminated polybutadiene; degradation of latex coating of paper; long-term thermo-oxidation of natural rubber; indication of ultrathin coating of cellulose fiber with polybutadiene.
Applications of FT-NMR to Crosslink Density Determinations in Natural Rubber Blend Vulcanizates
Authors: Brown Paul S. , John M. , Loadman R. , Tinker Andrew J.
Published: February 2011

Previously 90 MHz CW-NMR spectroscopy has been used to estimate the crosslink density in individual components of elastomer blends. Transfer of the technique to a 300 MHz FT instrument is not straightforward. Chemical shifts of polymer resonances in spectra of single-polymer vulcanizates are dependent on crosslink densities of the vulcanizates. Additionally, two resonances are observed for small molecules such as TMS and residual protonated solvent. The smaller resonance of each pair changes in shape and position in synchrony with the polymer signals and is considered to originate from solvent within the swollen polymer. The secondary TMS peak is used as the reference position from which to locate polymer signals in the spectrum. The position of these secondary peaks, and thus the polymer spectrum, relative to the “free” TMS is a function of crosslink density and also of carbon-black loading and type in filled vulcanizates. 13C-NMR line widths are observed to increase with crosslink density and this effect was used to study blends of NR with EPDM or a maleic acid modified EPDM. NR crosslink densities determined from 13C line-width analyses were in good agreement with those obtained from 1H-NMR and increased crosslinking in the modified EPDM was confirmed.
The Mechanical Properties of a Thermoplastic Elastomer Produced by the Bacterium Pseudomonas oleovorans
Authors: Gagnon K. D. , Lenz R. W. , Farris R. J. , Fuller R. C.
Published: February 2011

PHO, a poly(β-hydroxyalkanoate) copolymer containing mostly β-hydroxyoctanoate repeating units, was produced in a fed batch fermentation process by Pseudomonas oleovorans when grown on sodium octanoate as the sole carbon source. The polymer from different batches—evaluated with regards to composition, molecular weight distribution, thermal transition temperatures, and decomposition temperature—was found to be highly consistent batch-to-batch. Polymer composition as a function of growth time did not change significantly once the culture reached the stationary growth phase. PHO when crystallized at room temperature from the melt, forms a physically crosslinked network with the crystalline regions acting as the physical crosslinks. The molecular weight between physical crosslinks was determined to be approximately 4000. The stress-strain properties, hardness, and tensile set of PHO were found to be within the range of values defined by a variety of commercially available thermoplastic elastomers with differing chemical structures. The tensile set of PHO was high, 35% after 100% elongation. Experimental evidence supports three possible sources of the high tensile set: permanent strain-induced orientation or displacement of the physical crosslinks, irreversible strain-induced crystallization, and deformation-induced changes of the size and purity/perfection of crystalline regions.
Simulation of the Breakup of Dense Agglomerates in Simple Shear Flows
Authors: Horwatt Steven W. , Manas-Zloczower Ica , Feke Donald L.
Published: February 2011

The transmission of stress within an agglomerate and hence the stress required for the agglomerate breakup is strongly dependent on the agglomerate structure. In this work, the influence of agglomerate structure on the dispersion process has been investigated through the use of computer simulations. Two different particle-particle agglomeration mechanisms, similar to the conditions under which carbon black is pelletized, have been used in this study. The linear trajectory agglomeration mechanism results in highly branched structures having a dense core, while the Eden model results in very dense clusters exhibiting rough surfaces but little internal porosity. The critical stresses to initiate dispersion of these structures, as well as the fragment size distributions resulting from the application of a simple shear flow field at stresses in excess of the critical value, were simulated. The results show that for the highly ramified agglomerates, the amplification of stress at the roots of the branches in the structure is controlling the dispersion process, whereas for the dense, unbranched agglomerates, the presence of strength-limiting flaws determines the breakup behavior. The results of the simulations were compared to previously performed experimental studies of dispersion for carbon-black agglomerates.
The Dispersion of Carbon Black in Rubber Part III. The Effect of Dispersion Quality on the Dynamic Mechanical Properties of Filled Natural Rubber
Authors: Coran A. Y. , Donnet J-B.
Published: February 2011

The Part I of this series described a rapid method for determining the quality of carbon-black dispersion. The second paper (Part II) was concerned with the kinetics of the dispersion of carbon black into natural rubber (dispersion quality as a function of mixing time) in an internal mixer. In this paper we consider the effects of changes in dispersion quality on the dynamic mechanical properties of both unvulcanized and vulcanized natural rubber. The effects of changes in the degree of carbon-black dispersion were measured by using a new prototype moving-die rheometer (which is presently being developed at Monsanto Instruments & Equipment Research Laboratory). By using this prototype rheometer, G′ and G″ were measured as functions of shear-strain amplitude, temperature, and frequency. Increases in the degree of carbon-black dispersion in uncured natural rubber (starting from very poor dispersion quality) give decreases in the values of both G′ and G″. The decrease in dynamic moduli with increases in the degree of carbon-black dispersion might be explained on the basis of a network of agglomerates which exists when the quality of dispersion is extremely poor. In the case of uncured samples, values of G′, measured at low strains (e.g. ±1%), become reduced after the imposition of a larger (±50%) sinusoidal shear strain for a short period of time (e.g. 3 s). Then, with the passage of time, the reduced value of G′ partially recovers. The extent of this recovery increases with increases in the dispersion rating DR. Similar results were obtained with respect to the loss modulus G″. In both cases, the extent of recovery is much less when the carbon black is very poorly dispersed. The unrecoverable proportion of G′ or G″ is also considered to be due to a network composed of mutually interactive agglomerates of carbon black.
Mill Processing Behavior of Polychloroprene and Acrylic Rubbers
Authors: Kumar Nalini R. , Bhowmick Anil K. , Gupta B. R.
Published: February 2011

Mill processing behavior, with respect to front to back roll (F-B) transition, of polychloroprene and acrylic rubbers has been studied. The critical nip gap at which F-B transition occurs has been determined for these rubbers and their filled compounds (including HAF, MT, silica, and whiting) over a range of friction ratios and temperatures. The nip gap increases with friction ratio and temperature. The theoretical model of Tokita based on dimensional analysis, reveals three conditions corresponding to three types of behavior of various rubbers in drop mill operation. Mill band formation indices corresponding to these behavior types have been defined. These indices can be used to determine the conditions for front roll band formation. The systems investigated satisfy one of the conditions of the model. The mill processing behavior of these systems in a continuous milling operation has also been reported.
Spin-Spin Motional Analysis of Accelerated Sulfur Vulcanized Cis-Polyisoprene
Authors: Krejsa M. R. , Koenig J. L.
Published: February 2011

Spin-spin relaxation (T2) measurements were used to analyze the motional behavior of accelerated-sulfur vulcanized cis-polyisoprene. Biexponential decay behavior was found in all samples studied. This was modeled to consist of T2s (short) and T2l (long) components, with the T2s due to crosslinked regions and T2l due to regions distant from nodal points. T2 behavior was shown to depend strongly on crosslink density, but not to vary with concentration of cyclic structures. A simplified model was used for calculation of the average correlation time.
The Effect of Mold Pressure on the Electrical Resistivity of Elastomers
Authors: Thompson Corley M. , Allen J. Scott
Published: February 2011

Elastomers are commonly used as electrical insulators in marine acoustic devices. A previous paper discussed the very large decrease in electrical resistivity of a Neoprene GRT formulation when subjected to moderately high molding pressures. In the present paper, data will be presented showing similar dependencies on mold pressure for natural, polybutadiene, 39%-acrylonitrile NBR, and chlorobutyl elastomers and the absence of the effect for an EPDM, and a 27%-acrylonitrile NBR elastomer. These data are not easily explained. The previous paper also discussed that increasing the carbon-black loading caused the electrical resistivity to decrease at even lower molding pressures. Similar trends are presented here for the other elastomers whose electrical resistivities are dependent on molding pressure. Data will also be presented that show that the addition of poly-para-dinitrosobenzene (Poly DNB®) to a CR formulation will eliminate the mold pressure vs. electrical resistivity effect.
Universal Relationship between Abradability and Breaking Energy, Shear Loss Modulus, and Ridge Spacing
Authors: Thavamani P. , Bhowmick Anil K.
Published: February 2011

An attempt is made here to find a universal relationship between abradability and breaking energy, shear loss modulus and ridge spacing per unit frictional force for a series of filled and unfilled rubbers (NR, SBR, and HNBR) tested under a variety of experimental conditions.
Effects of Temperature on Fatigue and Fracture
Authors: Young D. G. , Danik J. A.
Published: February 2011

Although fatigue tests at varied temperatures are not common due to the added burden of testing, there are times when variable temperature testing is important to ensure that rubber compounds will be suitable for the full range of use conditions. This is particularly true when materials with high Tg(>−50°C) are being considered for use in tires. Results for two high Tg rubber compounds (ECO and HS-SBR) showed fatigue crack growth (FCG) rates that were roughly 100 times those of a BIIR liner compound over the temperature range of −25 to 100°C. Additional tests with BIIR and NR showed that most crack growth results for temperatures of −25 to 100°C, and various strains, followed similar fatigue functions (dc/dn vs. T). The exception was some data for NR at 0 and −25°C which showed inhibited rates of FCG due to strain crystallization. There appears to be a window of strain rate, temperature and strain level where this effect is noticed, but these results need to be confirmed for NR and other strain crystallizable elastomers. Two fully cured NR belt skims used in truck tires showed linear results for log dc/dn vs. log T at temperatures of 70 to 100°C. However, undercured samples of one compound exhibited more temperature sensitivity of FCG results; specifically, rates of FCG increased significantly with temperature at low strain levels. This suggests the need for further evaluation of the effect of cure state on FCG over a range of test temperatures.
Universal Properties in Filler-Loaded Rubbers
Authors: Kilian H. G. , Strauss M. , Hamm W.
Published: February 2011

Stress-strain cycles in filler loaded rubbers can be described with the aid of the van der Waals-network model. Reinforcement comes about by drawing pairs of filler particles apart. Reinforcement is observed because the intrinsic strain within the rubber bridge which is located between the filler particles exceeds the macroscopic strain very much, so much that interfacial slippage is enforced. The rubbery intra-cluster bridge distribution is represented by three dominant filler particle distances. One of them describes direct filler-to-filler (FF-) contacts, the critical strength of which is different from the filler-to-matrix (FM-) contacts of the filler-to-filler chains which are located on the whole surface of the filler particles. Formation of clusters is described by a power law. Stress-strain experiments are described with the aid of this model for different filler-matrix combinations (NR, SBR, carbon blacks, silica). Many universal features are observed: The intra-cluster rubber bridges display the same mean thickness when being related to the radius of the primary filler particles. The exponent in the power law is always identical. The deformation mechanisms, including irreversible slippage, do not to depend on the type of strain (simple extension, uniaxial compression). Yet, the Einstein-Smallwood effect turns out to be anisotrop so far as quasipermanent filler-to-matrix interactions seem to be determined by normal forces in the particles surfaces only. Different filler and matrix combinations display different strengths of the FF- and FM-contacts independent of the type of strain.
Filler-Elastomer Interactions. Part XI. Investigation of the Carbon-Black Surface by Scanning Tunneling Microscopy
Authors: Wang Meng-Jiao , Wolff Siegfried , Freund Burkhard
Published: February 2011

Scanning tunneling microscopy (STM) has recently been demonstrated to be a powerful and versatile tool to image the microstructure of the surface of carbonaceous materials. In this study, the surfaces of carbon blacks, both graphitized and nongraphitized, were investigated with this technique. The STM images show that the carbon-black surface can be classified into two domains, an organized and an unorganized one. The degree of carbon atom organization varies with the carbon-black grade and increases drastically upon graphitization. The surface energies and energy distributions of graphitized and nongraphitized carbon blacks, measured by inverse gas chromatography, correlate well with their surface microstructure. Mapping of the carbon-black topography showed that although the surface is not smooth, there is no significant porosity either.
Mechanical Seal with Elastomeric Rotating Element. Part 2: Experimental Study
Authors: Rivkin Michael , Kholodenko Arnold
Published: February 2011

An innovative flexible faced mechanical shaft seal using common elastomeric materials was designed and tested to determine its friction coefficient at a wide range of temperatures and speeds, its rate of heat generation, and its feasibility for use in the process industry. The new seal was constructed using an elastomeric rotating element stretched over the sleeve to at least 20 percent of its original length and an unlapped silicon carbide stationary annular ring. It was found that the main advantage of the elastomeric seal is its ability to maintain stable lubrication with a fluid film considerably thinner than that of traditional hard face seals, and consequently achieve negligible net leakage. This is particularly significant with respect to control of volatile organic carbon emissions. An experimental device was designed for precise measurement of the friction coefficient as well as the long term friction behavior of seal pairs in a wide range of liquid pressure and temperature. The original data were obtained for friction coefficient of EPDM, HNBR, FKM, and TFE/P type elastomers in contact with silicon carbide in the temperature range 15–110°C, linear speeds 0–12 m/s, water pressure 0.15–0.40 MPa, and effective contact pressure 0.8–1.2 MPa. Experiments showed that the friction coefficient constantly grows, typically from 0.05 to 0.15 at sliding speeds of 2–12 m/s, with temperature increases from 15 to 70°C. The temperature behavior of the friction coefficient above 70°C greatly depends on the elastomer. For high temperature elastomers, such as FKM, the friction coefficient may decrease slightly at 70°C; whereas, for EPDM, it continues to increase as temperature increases.
Vulcanization Chemistry. Comparison of the New Accelerator N-t-Butyl-2-Benzothiazole Sulfenimide (TBSI) with N-t-Butyl-2-Benzothiazole Sulfenamide (TBBS)
Authors: Hann Cynthia J. , Sullivan Alfred B. , Host Brian C. , Kuhls George H.
Published: February 2011

The sulfur vulcanization chemistry of cis-polyisoprene formulations accelerated with N-t-butyl-2-benzothiazole sulfenimide (TBSI) is compared to the chemistry of equivalent formulations accelerated with N-t-2-benzothiazole sulfenamide (TBBS). High performance liquid chromatographic analysis (HPLC) is utilized to examine the kinetics of accelerator-sulfur disappearance and the formation-appearance profiles of extra-network cure intermediates across the vulcanization process for stocks with a wide range of sulfur/accelerator ratios. Some unique features of TBSI vulcanization that distinguish it from TBBS are defined. A major distinction is the apparent consecutive step-wise kinetics of accelerator decay across the vulcanization process. A sequential reaction process may be indicated. Evidence is also offered that BtSxBt(x=2→6) is the crosslink precursor in TBSI vulcanization just as with TBBS formulations.
Steady-State Shear Flow Properties of Carbon-Black Filled Rubber Compounds
Authors: Ertong S. , Eggers H. , Schümmer P.
Published: February 2011

The steady shear viscosities of four model rubber/carbon-black compounds are measured with a modified Weissenberg Rheometer in a range of moderate shear rates. Yield stresses and low-shear viscosities are determined from creep-flow experiments. Yield stresses are found to increase strongly with filler content while their dependence on temperature can be described by an Arrhenius-type function. Flow curves are reduced to master curves by means of the time-temperature superposition principle. The shift factors are well approximated by the WLF-relation. The contribution of the “secondary” carbon-black network to the viscoelastic behavior requires additional vertical shifting for the filled compounds. Viscosities are found to be in very good agreement with the Herschel-Bulkley model when using the experimentally determined yield values.
The Dispersion of Carbon Black in Rubber Part IV. The Kinetics of Carbon Black Dispersion in Various Polymers
Authors: Coran A. Y. , Ignatz-Hoover F. , Smakula P. C.
Published: February 2011

A rapid technique for evaluating the rate and state of dispersion of carbon black in natural rubber has been extended to study the dispersion of carbon black in various polymers. The technique measures the extent and rate of dispersion of the black in the rubber. The kinetics of dispersion was characterized for a variety of polymers (e.g. SBR, EPDM, IR, IIR, BR and NR). Kinetic parameters were correlated with molecular weight and molecular weight distribution.
Sulfur Vulcanization of Simple Model Olefins, Part II: Characterization and Reactivity of Intermediate Vulcanization Products of 2,3-Dimethyl-2-Butene
Authors: Versloot P. , Haasnoot J. G. , Reedijk J. , van Duin M. , Duynstee E. F. J. , Put J.
Published: February 2011

In a study of the mechanism of the sulfur vulcanization of unsaturated rubber, 2,3-dimethyl-2-butene (C6H12) was used as a simple, low-molecular model alkene. Only equivalent allylic positions are present in this alkene. Treating C6H12 with a mixture of ZnO, S8 and the accelerator tetramethylthiuramdisulflde at 140°C for 20 minutes yields a mixture of addition products (C6H11—Sn—C6H11) and also intermediate products (C6H11—Sn—S(S)CN(CH3)2). The formation of C6H11—Sn—C6H11 from these intermediate products only proceeds in the presence of the zinc dimethyldithiocarbamate complex and free alkene.
Minimizing Nitrosamines Using Sterically Hindered Thiuram Disulfides/Dithiocarbamates
Authors: Layer Robert W. , Chasar Dwight W.
Published: February 2011

Sulfenamide accelerators and sulfur donors based on secondary amines must liberate all of their amine in order to function. Consequently, they are capable of producing relatively large amounts of nitrosamines. Thiuram disulfides and dithiocarbamates, on the other hand, only liberate their amines because of undesired side reactions. Accordingly, compared to sulfenamides, they produce significant, but much lower levels of nitrosamines during the cure. In an effort to reduce these side reactions, and thus the amount of nitrosamine which forms, we investigated the effect of steric factors on nitrosamine formation. We find that thiurams and dithiocarbamates made from sterically bulky amines, like diisobutylamine, produce orders of magnitude lower levels of nitrosamine than TMTD. At the same time, when used as a kicker for 2-benzothiazole sulfenamides, N,N,N′,N′-tetraisobutylthiuram disulfide has better scorch safety but cures at the same rate as TMTD. Uniquely, N,N,N′,N′-tetraisobutylthiuram monosulfide acts as a retarder as well as a kicker for 2-benzothiazole sulfenamides.
A Review of Methods to Characterize Rubber Elastic Behavior for Use in Finite Element Analysis
Authors: Charlton D. J. , Yang J. , Teh K. K.
Published: February 2011

The purpose of this paper is to provide a review of methods used to characterize the elastic behavior of rubber for use in Finite Element Analysis (FEA). A sample of elastic strain energy density functions used to characterize rubber is given, along with the tests required to characterize rubber according to these functions. The use of synthetic test data as an alternative to full physical testing is discussed, and highlighted by a case study. The paper closes with a discussion on potential errors associated with FEA of rubber components.
Studies of Mixing Efficiency in Batch and Continuous Mixers
Authors: Manas-Zloczower Ica
Published: February 2011

In this paper we have reviewed some of the results of 3-D, isothermal flow simulations for batch and continuous mixers. The flow patterns were obtained by using FIDAP, a fluid dynamics analysis package based on the finite element method. The problem of time dependent flow boundaries due to the rotations of the rotors in the Banbury mixer, was solved by selecting a number of sequential geometries to represent a complete cycle. Non-slip boundary conditions for the stationary and moving surfaces were employed. For different regions of continuous mixers we used a nominal value for the normal stress difference in the axial direction as an additional boundary condition. The results obtained in terms of velocity and pressure profiles were further processed to analyze mixing efficiency. Dispersive mixing efficiency was studied in terms of the shear stresses generated and the elongational characteristics of the flow field. Distribution plots for shear stresses and a parameter λ, quantifying the elongational flow components, were obtained in various regions of the mixing equipment. Volumetric distributions for the same parameters as well as average values can be also used to analyze dispersive mixing efficiency. Distributive mixing was studied numerically by means of tracking particles in the mixing equipment. In batch mixers or batch elements of continuous mixers distributive mixing can be well characterized in terms of the pairwise correlation function. In continuous mixing equipment, distributive mixing can be analyzed in terms of concentration functions and the spatial evolution of pairwise correlation functions. The framework developed to analyze dispersive and distributive mixing efficiency opens the way for an unambiguous evaluation of the performance of any mixing equipment and, furthermore, for their design and process optimization.
Methods of Devulcanization
Authors: Warner Walter C.
Published: February 2011

The literature contains the record of numerous methods which have been used to reverse the vulcanization process. Indeed, many of these methods have long been used, especially for purposes of analysis and/or studying mechanisms of vulcanization, so that they are commonplace in most large laboratories. The purpose of this paper is to review the literature on an eclectic basis. The opportunity exists to take a fresh look at some of these techniques with a view to consider up-scaling for recovery of rubber and other ingredients for eventual commercialization. The processes would have to be studied from the standpoint of fine-tuning reactants, solvating media, conditions of minimal degradation, keeping toxic exposure to safe levels, economics, etc. The possibility also exists of combining some of these techniques with others, such as those presented at a recent symposium, which have been developed to a more advanced stage of engineering. Included in a list of the chemical probes which will be discussed and/or referenced are propanethiol, hexanethiol, sodium di-n-butyl phosphite, triphenylphosphine, lithium aluminum hydride, methyl iodide and phenyl lithium. Related methods which have been mentioned include microbial action, grafting reactions, catalysis, microwaves, sonics and solution by o-dichlorobenzene.
Measurement of the Unsaturation of Butyl Rubbers by the Iodine Index Method
Authors: Dhaliwal G. K. , Wilson G. J.
Published: February 2011

Iodine index is used in the rubber industry to measure the unsaturation of butyl polymers. The procedure involves a complex mixture of iodine, mercuric acetate, and trichloroacetic acid (TCAA), and requires an empirical calibration to convert the iodine index to the degree of unsaturation. In this paper, the chemistry of the iodine index test is discussed and, the factors affecting the measurement, are detailed. Acetyl hypoiodite formed in situ by the reaction of I2 and Hg(OAc)2 is postulated to be the reactive species which iodinates the unsaturation in butyl rubber. Mercuric acetate is not a catalyst, as usually believed, but is consumed in stoichiometric amounts. Hence, care has to be exercised not to use too little of the mercuric acetate when determining the iodine index of polymers with high levels of unsaturation. A large excess of mercuric acetate must also be avoided, as it may form complexes with iodine and, thereby, lower the effective concentrations of both the reactive reagents.
Chemical Surface Treatments of Natural Rubber and EPDM Thermoplastic Elastomers: Effects on Friction and Adhesion
Authors: Ellul M. D. , Hazelton D. R.
Published: February 2011

Natural rubber thermoplastic elastomers (NRTPEs) made by dynamic vulcanization of natural rubber during its mixing with polypropylene were subjected to various halogenation surface treatments. Marked reduction in the coefficient of friction is possible depending on the chemical treatment employed, TPE composition and the presence of a lubricant. As a result of halogenation there is an increase in the microroughness and hardness of the NRTPE surface. These effects in part explain the large decrease in the friction coefficients since the contact area is decreased. Thus NRTPE can be employed in applications requiring low friction, such as certain types of seals. Another consequence of halogenation of NRTPE is the increase in its surface energy which in turn promotes adhesion to various polar substrates. Indeed it was determined that halogenation of NETPE is an effective way of priming the surface of these materials for adhesion to acrylic and other substrates. Ethylene Propylene Diene Monomer rubber-Polypropylene thermoplastic elastomers (EPTPEs) were used as a control in this study to assess how a low unsaturation EPDM-based TPE compares with the high unsaturation NRTPEs in different halogenation surface treatments.
Effects of Aging on the Fracture Behavior of Chlorinated Polyethylene and Chlorosulfonated Polyethylene
Authors: Nichols Mark E. , Pett Robert A.
Published: February 2011

The thermoxidative aging behavior of chlorosulfonated polyethylene (CSM) and chlorinated polyethylene (CPE) vulcanizates has been investigated. Aging rates were determined by measuring isothermal oxidative induction times in a differential scanning calorimeter. Aging rates were also determined by measuring the decrease in the critical tearing energy of compounds as a function of aging time and temperature. Rate constants determined from induction time and tearing energy experiments displayed typical Arrhenius behavior. Below 240°C, rate constants from both experiments fell on the same line, suggesting that both experiments probe the same reaction. Activation energies for degradation of CSM and CPE were 88 and 108 kJ/mol respectively. Above 240°C, the mechanism of degradation changes with a corresponding change in activation energy to 190 and 232 kJ/mol for CSM and CPE, respectively. In the unaged state, the critical tearing energy of the carbon black-filled CPE compound is 50% higher than that of the carbon black-filled CSM compound. The rate of aging of CSM compound is approximately twice that of the CPE compound at equal temperatures. Decreases in tearing energy were attributed to additional crosslinking of the elastomer network. Combining oxidative induction times and critical tearing energy measurements may offer significant advantages in streamlining accelerated testing of elastomeric materials.
NMR Study of Miscibility in Polyepichlorohydrin/Poly(Vinylmethylether) Blends
Authors: McGrath K. J. , Roland C. M.
Published: February 2011

129Xe NMR spectroscopy is employed to demonstrate that polyepichlorohydrin and poly(vinylmethylether), which have virtually equal glass transition temperatures, form thermodynamically miscible blends. This conclusion is drawn from the appearance of a single resonance in the blend spectrum, at a chemical shift differing from that calculated for the fast exchange regime. 13C NMR results are consistent with thermodynamic miscibility, and reflect the similarity of the component dynamics.
Cure and Mechanical Behavior of Rubber Compounds Containing Ground Vulcanizates. Part I—Cure Behavior
Authors: Gibala David , Hamed Gary R.
Published: February 2011

SBR compounds containing ground vulcanizates of known composition and cure state were prepared and the cure behavior studied. Decreases in scorch times and maximum rheometer torques were observed when ground vulcanizates were added to the SBR compounds. Two primary phenomena are proposed to explain these findings: (1) migration of sulfur from the matrix rubber to the ground vulcanizate (causing torque reduction) and (2) migration of accelerator fragments from the ground vulcanizate to the matrix (causing decreased scorch time). The first proposal is based on direct measurement of sulfur concentrations in both ground particles and the matrix. The second is based on the detection, by high performance liquid chromatography, of mercaptobenzothiazole in the extract from ground vulcanizates. The second also is inferred from the fact that ground vulcanizate particles cured with peroxide do not alter scorch time. Moreover, a compound containing sulfur and ground (accelerated-sulfur vulcanized) rubber, but no added accelerator, nonetheless exhibits acceleration of cure.
Reduction in Viscosity of an SBR Compound Caused by Mastication and Disagglomeration during Mixing
Authors: Clarke J. , Freakley P. K.
Published: February 2011

It would be advantageous to determine the causes of changes in rheological behavior of a compound during mixing, so that mixing times and conditions could be optimized to give the desired processing behavior and properties of the final product. The causes of changes in viscosity during mixing of a compound containing only elastomer and carbon black were investigated by examining concurrent changes in viscosity of the gum, density of the compound and degree of carbon-black disagglomeration. The reduction in viscosity occurring during mixing could be attributed to mastication of the elastomer and disagglomeration of the carbon black. The effect of mastication could be removed by calculating values of relative viscosity, using the viscosity of the gum treated in a similar way to the compound and with an allowance being made for strain-rate amplification. The decrease in relative viscosity of the compound with increased mixing was attributed to a reduction in effective volume fraction of filler caused by immobilized rubber being released as carbon black agglomerates were broken down. The dibutyl phthalate absorption (DBPA) value of the carbon black gave a good indication of the amount of immobilized rubber present in an agglomerate.
Characterization of the Behavior of Rubber for Engineering Design Purposes. 1. Stress-Strain Relations
Authors: Davies C. K. L. , De Dilip K. , Thomas A. G.
Published: February 2011

The stress-strain behavior of a range of black-filled rubbers has been studied in extension, compression, pure shear and simple shear. The data have been analyzed to examine the validity of Gregory's hypothesis that the stored energy function U of filled rubbers can be expressed solely in terms of the strain invariant I1, ignoring I2, to an accuracy adequate for most engineering design requirements. Our results confirm his suggestion. An analytical form for U is proposed which gives a very good fit to the experimental data for strains from less than 0.1% to somewhat greater than 100%, which cover the range of interest for most engineering applications. The dependencies of the parameters in the expression for U on filler level and degree of crosslinking have been examined. It has thus been demonstrated that, for a given material, the form of U can be determined from the measured stress-strain relation in any simple deformation mode, shear or tension for example, without the necessity of relatively difficult biaxial measurements, and that this function should then be applicable to any deformation mode, complex or simple.
On the Puncture Mechanics of Rubber
Authors: Stevenson A. , Malek Kamarudin Ab
Published: February 2011

The mechanics of puncture have been studied experimentally and theoretically, by means of fracture mechanics. When a sharp cylindrical indentor penetrates rubber, a starter crack initiates as a ring on the rubber surface before puncture occurs. By treating this as militating puncture, an equation has been derived for the energy of puncture. The elastic energy stored in the rubber is considered in terms of the energy beneath and surrounding the indentor. An equation for the energy beneath the indentor is determined with the aid of a model experiment based on the biaxial stretching of rubber by inflation. The energy stored in the rubber surrounding the indentor is calculated using elasticity theory. The magnitude of these contributions is assessed for different indentor sizes and different rubber vulcanizates, The theoretical approach is shown to be verified by a series of experiment for sharp indentors. The values of puncture energy so obtained were found to agree well with the catastrophic tearing energy obtained from trouser tear tests. For blunt indentors which do not cause ring crack formation, other considerations are needed. These are discussed together with experimental results for hemispherical indentors.
Quantitative Metathetic Degradation of Rubbers and Sulfur Crosslinked Rubbers—Including Tires
Authors: Thorn-Csányi Emma
Published: February 2011

Unsaturated polymers can be converted metathetically to fragments of low molecular weight by adding monoolefins. Since the scission of the polymer backbone always occurs at the double bonds, analysis of the degradation products enables a conclusion about the polymer microstructure. Our earlier works have shown that in case of polybutadienes and styrene-butadiene copolymers, the catalyst system “tungsten hexachloride/tetraalkyltin/diethylether” allows a selective degradation and detailed determination of the microstructure. On the other hand complete degradation of polyisoprenes and sulfur crosslinked rubbers failed using conventional metathesis catalysts. Our latest investigations show that using stable transition metal carbenes as catalysts, degradation of polyisoprenes and sulfur-crosslinked rubbers (including tires) proceeds quantitatively. This opens up a method of microstructure determination of crosslinked rubbers, including tires. Results obtained using well denned transition metal carbenes will be compared with those gained employing conventional catalyst systems.
Influence on Friction Force of Adhesion Force between Vulcanizates and Sliders
Authors: Mori Kunio , Kaneda Satoshi , Kanae Kentaro , Hirahara Hidetoshi , Oishi Yoshiyuki , Iwabuchi Akira
Published: February 2011

The effects of vulcanizate and slider surface free energy—as well as the adhesion force (P) between them—on friction the force (F) and the coefficient of friction (μ) has been investigated. SBR and NBR vulcanizates were prepared using three molds differing in surface free energy. The mold with a high surface free energy gave a vulcanizate surface possessing polar groups. The mold with low surface energy gave a vulcanizate surface with many nonpolar groups. The coefficient of friction increased with the surface free energy of SBR and NBR vulcanizates. With SBR vulcanizate (surface free energy, 31.3 mJ·m−2) and teflon slider (surface free energy, 28.1 mJ·m−2) combination having the least surface free energy, the coefficient of friction was constant at greater than a 0.2N load. With vulcanizates and an aluminum slider with high surface free energy, friction force could be detected even at zero load because of the adhesion force at the interface. Friction force increased linearly with adhesion force between vulcanizates and sliders when the physical properties of the vulcanizates and net work chain density were constant. The present results clearly demonstrate the contribution of adhesion force to the friction of vulcanizates.
Rheological and Mechanical Properties of Filled Rubber: Silica-Silicone
Authors: Aranguren Mirta I. , Mora Elsi , Macosko Christopher W. , Saam John
Published: February 2011

This work focuses on the relationship between the morphology of filled rubbers and their behavior at small and large deformations. Composites were made from vinyl terminated polydimethylsiloxane (PDMS) and different fumed silicas. Filler concentration range was kept between 0 to 40 phr (parts of silica per hundred parts of PDMS). Small deformation tests done in oscillatory shear showed that there is coupling of the filler agglomeration and crosslinking effects at high crosslink density while the coupling is negligible at low crosslinking levels. Since crosslinking (hydrosilation) proceeds through the end vinyl groups of the PDMS, lower molecular weight polymers produce rubbers with higher elastic modulus than do high molecular weight silicones. However, the rubbers formed from low molecular weight PDMS break at lower extensions. As in the case of uncured composites, the moduli of the samples increase with silica concentration and amount of silanols on the silica. A silica treated with divinyltetramethyldisilazane gave rubbers of high modulus similar to those obtained from untreated silicas, highlighting the importance of good adhesion between filler and polymer.
Thermally Induced Crosslinking between Polyacrylic Acid and Epoxidised Natural Rubber: Effect of Carbon Black Filler on Strain Dependent Dynamic Mechanical Properties
Authors: Mallick A. , Tripathy D. K. , De S. K.
Published: February 2011

Increases in dynamic strain amplitude (DSA) causes changes in the dynamic mechanical properties of high abrasion furnace (HAF) carbon black filled polyacrylic acid (PAA) and epoxidised natural rubber (ENR) blends. But the changes are more prominent in comparison to conventional rubber vulcanizates. It is believed that crosslinking between PAA and ENR in the presence of carbon black results in the formation of a network-induced-agglomerate superstructure which, however, breaks down on the application of dynamic strain.
Measurement of Elastomer's Bulk Modulus by Means of a Confined Compression Test
Authors: Peng Shu H. , Shimbori Takao , Naderi Akbar
Published: February 2011

The bulk modulus represents a material's resistance to volume change when subjected to pressure loading. Determination of bulk modulus is important for evaluation of applications where compression is involved. Most methods proposed for this purpose are complicated and costly. A simple method is to compress an elastomer button, fully confined in a metal fixture, on a tensile/compression machine. The reliability of this method is studied and a data-treatment technique is proposed to improve the accuracy. It shows that the testing method, with the new analysis technique recommended, is efficient and can be used as a routine test.
Flow Visualization of Intermeshing and Separated Counter-Rotating Rotor Internal Mixer
Authors: Kim Pan Soo , White James L.
Published: February 2011

A flow visualization investigation of material motions and compounding in an internal mixer with intermeshing rotors is described. Rotors based on the design of R. T. Cooke of Francis Shaw and Company are used. Compared with separated rotor designs developed by F. H. Banbury, the distinctive feature is the passage of the rubber and compounding ingredients through the calendering gap between the rotors during mixing. The intermeshing rotors were found to rapidly circulate the materials from rotor to rotor around the mixing chamber and to more rapidly incorporate carbon black and oil relative to double-flighted separated rotors.
Structural and Rheo-Optical Characterization of Random Bicomponent Networks Prepared of Hydroxyl-Telechelic Polyisobutylene and Polytetrahydrofuran
Authors: Kyu Thein , Lee Hak-Soo , Gadkari Avi , Kennedy Joseph P. , Lin Jar-Shyong
Published: February 2011

The structure of a bicomponent network prepared of hydroxyl-telechelic polyisobutylene (HO—PIB—OH) and polytetrahydrofuran (HO—PTHF—OH) has been characterized by small-angle and wide-angle x-ray scattering, birefringence, and differential scanning Calorimetry. A single phase random network was obtained by endlinking HO—PIB—OH/HO—PTHF—OH mixtures using triphenyl methane triisocyanate (TTI) as a crosslinking agent. A small-angle x-ray scattering peak was observed in the PIB networks as well as in the PIB/PTHF bicomponent networks. The glass transition temperature of the random bicomponent network increased with decreasing PTHF molecular weight as the network became tighter. Network tensile properties were analyzed in terms of Gaussian and non-Gaussian network models. The stress-optical law was tested for random networks by measuring the variation of birefringence and stress as a function of elongation. Author to whom correspondence should be addressed. Present Address: Exxon Chemical Co. , Baytown Polymer Research Center, Baytown, TX 77520.
Adhesion and Autohesion of Rubber Compounds: Effect of Surface Roughness
Authors: Gent A. N. , Lai S-M.
Published: February 2011

Sheets of various rubber compounds were pre-molded using different mold surfaces: Mylar film, smooth steel, and roughened steel. Two sheets of the same compound were then bonded together by crosslinking them in contact. Measurements of peel strength were carried out over a range of temperatures from −40°C to + 130°C. When an uncured sheet was crosslinked in contact with a smooth fully-cured sheet, the peel strength was generally lower than the tear strength of either sheet and the degree of interlinking was inferred to be only about one-half of the degree of crosslinking. On the other hand, when a sheet was cured in contact with a rough surface the strength of adhesion was 2× to 3× higher than with a smooth surface, probably because of increased area for bonding. Thus, when a rubber compound was cured in contact with a fully-cured sheet having a roughened surface, the two effects largely cancelled out and the resultant bond was about as strong as the material itself. Examples are given for carbon-black-filled and unfilled compounds based on polybutadiene, a styrene-butadiene copolymer, and natural rubber.
Mechanical Behavior of a Solid Composite Propellant during Motor Ignition
Authors: Traissac Y. , Ninous J. , Neviere R. , Pouyet J.
Published: February 2011

In order to understand the behavior of composite propellants during motor ignition, a particular study about mechanical and ultimate properties of a Hydroxy-Terminated Polybutadiene (HTPB) filled propellant under superimposed hydrostatic pressure was carried out. The mechanical response of the propellant was obtained for uniaxial tensile and simple shear tests at various temperatures, strain rates and superimposed pressures from atmospheric pressure to 15 MPa. The experimentally observed ultimate properties were found to be strongly pressure sensitive and the data were formalized in a specific stress failure criterion.