bluuebunny/crossref_metadata_2025 huggingface dataset:
Chain Conformation in Elastomeric Multiblock Copolymers as Measured by Small-Angle Neutron Scattering
Authors: Cooper Stuart L. , Miller John A.
Published: February 2011

Small-angle neutron scattering has been shown to be an effective technique for investigating segment conformation in two-phase multiblock copolymer systems. By choosing the appropriate isotopic compositions, either segment can be investigated, as can the whole chain. The best approach to the experiment is to use a phase-contrast matched sample, one where no interphase scattering occurs. This allows the experiments to be carried out on a single sample, simplifying the experiment, and reducing the beam time requirements. Equations (2) and (3) describe the phase-contrast matched criterion. At room temperature, the polyether soft segments in the polyurethane elastomer-and in the polyether-polyester block copolymers are somewhat extended on the average relative to the bulk oligomer conformation. In the polyether-polyester with a lower hard-segment content, the soft segments are less extended than in the higher ester content material. A distribution of conformations occurs in these materials, with a majority of the soft segments being nearly in a random-coil conformation. A substantial number of segments are fairly taut, leading to an average conformation that is somewhat extended relative to the random coil conformation. The soft-segment radius of gyration in the polyurethane material initially decreases with increasing temperature. As the temperature rises, the retractive force on the taut soft segments increases, thus facilitating the extraction of hard segments from the amorphous hard phase into the soft phase. One would expect that the degree of phase separation would decrease with increasing temperature due to such a mechanism, and in fact this is borne out by small-angle x-ray scattering studies. Above 150°C, an upturn in the soft-segment radius of gyration is observed. Koberstein et al. propose a phase mixing transition around this temperature in polyurethane systems. Such a transition implies a greater compatibility between the hard and soft segment types at elevated temperatures. Thus, a swelling of the soft segments is seen due to favorable interactions with the hard segments located in the soft phase. A schematic diagram of the polyurethane microstructure and chain conformation is presented in Figure 9. The soft-segment radius of gyration in the polyether-polyester materials decreases smoothly with increasing temperature. This is primarily due to a decrease in the number of taut tie molecules present at elevated temperatures due to the rearrangement of the hard crystalline domains. In addition, relaxation of stresses introduced by molding these samples below the hard-segment crystalline melting temperature may contribute to the decrease in the soft-segment Rg.
Novel Wet Process Silica Prepared from Alkyl Silicates. Part III: Use in Silicone Elastomers for Optical Applications
Authors: Polmanteer Keith E. , Chapman Harry L. , Lutz Michael A.
Published: February 2011

The first two papers of this three-part series of papers dealing with a novel wet-process hydrophobic (WPH) silica technology covered the silica synthesis (Part I) and reinforcement performance (Part II) respectively. The WPH silica was highly reinforcing and provided optically clear compositions as well. The first optically clear, high consistency silicone elastomer was developed in the midnineteen fifties by Polmanteer et al., using different technology from that described in this paper. Optical clarity was accomplished in the earlier work by matching the refractive indices of the filler and polymer at 25°C, making them isorefractive at this specific temperature. This paper will discuss the unique features of this new silica technology as it relates to optically clear silicone elastomers. The term, optically clear, in the context of this paper refers to an elastomeric material, 2.54 mm in thickness, that exhibits less than 4% haze, and more than 85% transmission. It will be shown that, when using the older technology based on isorefractive compositions, optical clarity is reduced with temperature change from the isorefractive temperature, due primarily to an increase in haze. The new silica technology eliminates this problem and effectively broadens the application temperatures for optically clear, thermally stable silicone elastomers.
The Effect of Modifying Resins on the Viscoelastic Properties of Styrenic Block Copolymers
Authors: Class J. B.
Published: February 2011

Viscoelastic data from dynamic measurements show that modifying resins produce complex changes in the properties of styrenic block copolymers. These property changes are generally consistent with compatibility concepts. Resins which are compatible with the midblock of these polymers, Resins AL-1, Al-2, and RE, will increase the tan δ peak temperature and reduce plateau modulus, as is observed with other elastomers. They will also reduce the temperature of entry into the terminal zone. This is believed to result from a reduction in the concentration of the endblock phase as well as dilution of the entanglement network at elevated temperatures. A resin which is incompatible with the midblock, Resin AR, has no effect on the tan δ peak temperature but does cause an increase in the plateau modulus of S-B-S and S-EB-S, as seen with typical high molecular weight rubbers. However, in the S-I-S polymers, Resin AR appears to be at least partially compatible at the low volume fractions examined. It does not increase the plateau modulus, but appears to reduce it slightly. The aromatic resin, Resin AR, has no effect on the G′, G″ crossover temperature of S-EB-S or S-I-S(20) at the concentration examined. However, it increases the temperature of the high diblock S-I-S(40) and lowers the temperature of S-B-S, suggesting at least partial compatibility at elevated temperatures. G′(tan δmin ) data are useful for estimating the compatibility of resins with styrenic block copolymers. Minimum and maximum values, calculated from rubber elasticity theory and filler effects, can serve as reference points for compatibility.
Effect of Brown Vulcanized Vegetable Oil on Ozone Resistance, Aging, and Flow Properties of Rubber Compounds
Authors: Botros Samir H. , El-Mohsen Fawzia Fabd , Meinecke Eberhard A.
Published: February 2011

The addition of accelerator to vegetable oils during the preparation of brown V.V.O. results in a decrease of the free sulfur and the acetone extract values of the obtained V.V.O. In addition, the reaction time necessary to achieve the gel state is reduced. NR vulcanizates containing brown V.V.O. based on soybean oil are superior in retention of their tensile strength and 100% modulus after aging to those containing V.V.O. based on boiled linseed oil and dehydrated castor oil. The heat resistance of NR vulcanizates which contain brown V.V.O. increases as the amounts of the free sulfur and the acetone extract in the V.V.O. decrease. Addition of small amounts of brown V.V.O. to NR and SBR compounds helps to maintain the tensile strength after aging. However, the addition of high concentrations of the V.V.O. reduces the aging properties. The addition of brown V.V.O. based on soybean oil and TMTD to NR compounds used for the manufacture of printer rolls and rubber hoses enhances the ozone resistance of the rubber vulcanizates. Furthermore, the addition of this type of V.V.O. to NR and SBR compounds is advantageous because of: (1) delay of the onset of melt fracture, (2) reduction of extrudate swell, (3) smoother extrudate surfaces, (4) dimensional stability of NR and SBR extrudates.
Characterization of Polymers by GPC-LALLS. III. Branching Structure of EPDM
Authors: Shiga S. , Sato Y.
Published: February 2011

Gamma ray-irradiated EPM's, as the model polymers of branched EPDM, are investigated using the relationship g′=gb, where g′ is the ratio of intrinsic viscosities of the branched and the linear molecules of equal molecular weight, [η]br/[η]l, and g, the ratio of the mean square radii of gyration of the two, 〈s2〉br/〈s2〉l. The molecular weight distributions measured by GPC-LALLS coincide well with theoretical curves of tetrafunctionally and statistically branched polymers obtained by the ideal degradation and crosslinking of the raw EPM, which was assumed to have the most probable molecular weight distribution, and the b-value is then determined to be 1.1. EPDM samples, polymerized with a soluble vanadium compound—alkyl aluminum halide type catalyst in a continuous well-stirred pilot-reactor, are characterizedas to the number of branching points per molecule for various molecular weights by using the b-value. The higher the molecular weight, the smaller the distance between neighboring crosslinking points. The reason is discussed. The unsaturated bond of dicyclopentadiene crosslinks more readily in the manufacturing process than 5-ethylidene-2-norbornene. The largest high molecular weight portion and the broadest molecular weight distribution are observed in the EPDM with the maximum dicyclopentadiene content.
Structural Characterization of Diene Block Copolymers by GPC and Ozonolysis—GPC Measurements
Authors: Tanaka Yasuyuki , Sato Hisaya , Adachi Junichi
Published: February 2011

The sequence distribution and block structure of styrene units in commercial styrene—butadiene and styrene-isoprene copolymers were analyzed by GPC measurements on the original copolymers and on ozonolysis products. Tapered-block structures are clearly differentiated by ozonolysis—GPC measurements. The content of large block styrene sequences in S-B-S type block copolymers was found to be 77 to 99% or more. S-B and S sequences in addition to the S-B-S sequence were observed for most of the triblock copolymers. A star-shaped S-B-S copolymer was distinguished from a linear copolymer by comparison of the molecular weight and chemical composition of the main and shoulder peaks by GPC and also by reference to the molecular weight of the block styrene sequence determined by ozonolysis—GPC measurements. A mixture of block copolymers was estimated for a high-styrene thermoplastic elastomer by GPC and ozonolysis—GPC measurements together with the measurement of chemical composition distribution. In a similar way the block structure was analyzed for S-I-S triblock copolymers.
The Kinetics of Crazing and Shear Yielding in Rubber-Toughened Plastics
Authors: Bucknall C. B.
Published: February 2011

The work presented and reviewed in this paper leads to the following conclusions: (a) The kinetics of creep in HIPS containing 0.2 µm diameter core-shell rubber particles are similar to those in more conventional HIPS containing larger multiple-inclusion particles. Both deform by multiple crazing. (b) Comparisons of mechanical properties should be made on the basis of equal rubber volume fractions ϕ rather than equal elastomer contents. (c) The kinetics of creep in rubber-toughened PMMA, also containing small core-shell particles, are quite different from those of HIPS. Deformation occurs by shear yielding accompanied by a small volume increase which is probably due to cavitation in the rubber particles. (d) The dependence of deformation rates upon applied stress and temperature is well described by the Eyring model for activated flow. (e) Analysis based on the Eyring slopes can be used to compare stress concentration factors γ in toughened plastics. In polymers that deform by shear yielding, absolute values of γ can be obtained by comparison of data from toughened and untoughened plastics. Difficulties remain in applying a similar approach to polymers that deform by multiple crazing. (f) The rate-determining step occurs in regions of maximum stress concentration in HIPS and appears to be identified with initiation of crazing. (g) The rate-determining step in toughened polymers that deform by shear yield is not associated with regions of maximum stress concentration.
A High-Performance Curing System for Halobutyl Elastomers
Authors: Edwards D. C.
Published: February 2011

1. In halobutyl elastomers, zinc oxide interacts synergistically with aromatic amine antioxidants such as APDA 86, DPPD, or DNPD, to produce fast, tight cures. 2. In the case of DNPD, compound storage stability appears to be satisfactory, and the resistance to scorch at processing temperatures is ample. 3. The cure behavior of these systems, particularly in bromobutyl, is exceptionally favorable: a rapid rise to a remarkably flat plateau. 4. The vulcanizates exhibit excellent thermal stability (compression set) and excellent ozone resistance. Measurable elastic properties are retained following 72 h air aging at 200°C.
Effect of Chain Length Distribution on the Tearing Energy of Silicone Elastomers
Authors: Yanyo L. C. , Kelley F. N.
Published: February 2011

The tearing energies of two endlinked PDMS networks, one a monomodal distribution of chain lengths and the other a bimodal mixture of very short and rather long chains, at the same average molecular weight between crosslinks, were compared. The bimodal network exhibited higher tearing strengths than the monomodal network under the same experimental conditions. At threshold conditions, the bimodal network tearing energy was 70% higher than the threshold strength of the monomodal network. A rederivation of the Lake and Thomas theory for the threshold tearing strength which includes a bimodal probability distribution of chain lengths is shown to predict the observed behavior. The strength increase of these bimodal networks is attributed to the presence of the long chains which increases the energy required for fracture while maintaining the same number of chains crossing the fracture plane as in the monomodal network of the same crosslink density, by including a large number of short chains.
A Postcrosslinking Accelerator System for Natural Rubber Based on Thiocarbamyl Sulfenamides
Authors: Layer Robert W.
Published: February 2011

Thick natural rubber articles require long cure times in order for the central portion of the article to reach optimum cure. Even at relatively low cure temperatures, using conventional cure systems, the outer portions of the article become overcured and lose physical properties due to reversion of the crosslinking process. The primary result is a decrease in the number of crosslinks and a loss of modulus. To lessen reversion, low sulfur and/or sulfur donor cure systems are used. These systems produce fewer of the thermally labile polysulfide crosslinks and more of the more thermally stable di and monosulfide crosslinks. But even these EV systems undergo reversion, albeit much more slowly than conventional cure systems, due to the slower cleavage of the disulfide crosslinks. Even better reversion resistance can be obtained with a sulfurless cure system, such as TMTD, which produces only very thermally stable monosulfide crosslinks. Unfortunately, fatigue properties become progressively poorer as one goes from polysulfide to disulfide to monosulfide crosslinks. Thus, in practice, a compromise between thermal stability and fatigue resistance is reached for each particular application. For many applications, such as treads of large off-the-road tires and aircraft tires, the heat generated during the demanding service conditions to which they are exposed is itself sufficient to cause reversion. This reversion is self-perpetuating since it lowers the modulus, which in turn speeds the heat buildup. The final result can be premature failure. Consequently, efforts continue to find ways to improve reversion resistance. Recently, the use of “postcrosslinking” additives, which form new crosslinks to replace those lost by reversion, have been reported. It is also known that certain accelerators show a postcrosslinking effect in NR, but only when high levels of sulfur are used. No accelerators have been reported to give postcrosslinking in a low-sulfur EV-cure system. We now find that an OTOS/OBTS (2:1) synergistic EV-cure system continues to generate new crosslinks on overcure. This can be utilized to improve physical properties or to slightly raise cure temperatures.
Molecular Weight of Rubber Contained in Guayule Bark, Wood, and Whole Stem
Authors: Estilai A.
Published: February 2011

Guayule bark not only produces most of the plant's rubber, its rubber Mw and Mn are also significantly higher than those of the wood. Further studies are expected to throw light on the mechanisms that control the production of different-sized polymers in different guayule tissues. This investigation shows that every guayule genotype may yield rubbers with three different molecular weights. Based on needs of the industry, whole guayule shrub, its bark, or its wood may be processed for rubber extraction. Since, depending on genotypes, 70 to 85% of the rubber is in the bark, and since bark rubber has the highest molecular weight, the possibility of processing only bark needs serious considerations as new cultivars with increased rubber yield become available. Based on the observed variation of molecular weight relative to the tissues used, the genotype, and the age of the plant, it is critical to develop standardized procedures for molecular-weight determination so that molecular-weight values, obtained by different laboratories, may be compared.
Solid State Carbon-13 NMR Studies of Vulcanized Elastomers. III, Accelerated Sulfur Vulcanization of Natural Rubber
Authors: Zaper A. M. , Koenig J. L.
Published: February 2011

In summary, the solid state C-13 NMR technique has proven to be a significant method for the detection of crosslinks and other structural modifications in accelerated sulfur-vulcanized NR systems. When the amount of accelerator is high in proportion to the amount of sulfur used, the network structure appears to be simpler with less crosslinking, less main chain structural modification, and fewer cyclic sulfide structures as observed in the C-13 NMR spectra. Polysulfidic crosslinks have been detected in addition to polysulfides terminated by accelerator residues. Cis-to-trans chain isomerization is also evident in these vulcanizates.
Flow Visualization Investigations of the Addition of Carbon Black and Oil to Elastomers in an Internal Mixer
Authors: Min Kyonsuku , White James L.
Published: February 2011

Internal mixing is one of the most important of processing operations, being used to incorporate fillers, oils, and other compounding ingredients into elastomers and plastics. The development of internal mixers has a long history largely described in the patent literature. Published experimental studies of flow in an internal mixer have been few, and primarily involved measurements of energy consumption, temperature histories, and characteristics of dumped mixes. It is only recently that efforts have been made to directly observe the motions of elastomers in an internal mixer. Freakley and Wan Idris and Asai et al. have made flow visualization studies of the motions of silicone rubber and aqueous carboxymethyl cellulose solutions at room temperature. Freakley and his coworkers and Toki et al. have followed motions of rubber in an internal mixer using mounted pressure transducers. More recently, the present authors have developed experimental techniques to visualize the flow of commercial elastomers and plastics at processing temperatures. The first study visualized flow in the plane perpendicular to the rotor axes and contrasted the behavior of various synthetic rubbers (polybutadiene, butadiene-styrene copolymer), natural rubber, and thermoplastics. In a later study, Min has made observations of flow in the plane parallel to the rotor axes for various rotor designs. The techniques developed in the first two papers were subsequently applied by Min to investigate the blending of an elastomer and a thermoplastic. It is the purpose of the present paper to present a detailed investigation of the addition of the primary compounding ingredients of carbon black and oil to an internal mixer. Much has been theorized and written about the incorporation of carbon black and oil. However, this has largely been conjecture based upon observations of torques, power consumption, temperature profiles, and the condition of dumped compounds. We present in this paper a unique flow visualization investigation of the flow phenomena and material distribution resulting from the addition of these ingredients to elastomers in an internal mixer. This paper continues our investigations of flow visualization during rubber processing.
The State of the Art of Rubber-Seal Technology
Authors: Nau B. S.
Published: February 2011

The understanding of the engineering fundamentals of rubber seals of all the various types has been developing gradually over the past two or three decades, but there is still much to understand, Tables V–VII summarize the state of the art. In the case of rubber-based gaskets, the field of high-temperature applications has scarcely been touched, although there are plans to initiate work in this area both in the U.S.A. at PVRC, and in the U.K., at BHRA. In the case of reciprocating rubber seals, a broad basis of theory and experiment has been developed, yet it still is not possible to design such a seal from first principles. Indeed, in a comparative series of experiments run recently on seals from a single batch, tested in different laboratories round the world to the same test procedure, under the aegis of an ISO working party, a very wide range of values was reported for leakage and friction. The explanation for this has still to be ascertained. In the case of rotary lip seals, theories and supporting evidence have been brought forward to support alternative hypotheses for lubrication and sealing mechanisms. None can be said to have become generally accepted, and it remains to crystallize a unified theory.
Structure and Mechanical Properties of Rubberlike Proteins in Animals
Authors: Gosline John M.
Published: February 2011

Polymer networks formed from protein molecules that adopt kinetically-free, random-coil conformations are found in many animals, where they play a number of important roles. The 5 rubberlike proteins isolated and studied to date indicate that animal rubbers, like their synthetic counterparts, contain random networks which are usually stabilized by covalent crosslinks. Long-range elasticity in rubberlike proteins is based on changes in the conformational entropy of random-coil molecules. Further, these protein networks show viscoelastic glass transitions similar to all other amorphous polymer networks. Future research on protein sequences should increase our understanding of how polypeptide chains can function as random-coil molecules, and studies into the mechanical state of elastin in arterial tissues may provide important clues about the mechanisms of some forms of human disease.
Chromatographic Analysis of Elastomeric Polyurethanes
Authors: Vimalasiri P. A. D. T. , Burford R. P. , Haken J. K.
Published: February 2011

Both alkali and acid fusion reactions can be used to cleave polyurethane polymers successfully. Fusion reaction rates are much faster than conventional aqueous alkali or acid fusion methods. Separation of fragments could be carried out using the liquid-liquid extraction procedures described. After quantitative and qualitative analysis of fragments using GC, SEC, and HPLC, chemical structure of the polymer can be established. Although the work described uses only elastomeric polyurethanes for the development of the analytical schemes, these schemes can be used to analyze other types of polyurethanes such as “Spandex” fibers, adhesive coating films, and plastics. The procedures described have also been used for the analysis of polyamide resins which are condensation products.
The Development of a Real-Time Control System for Internal Mixers
Authors: Freakley P. K. , Matthews B. R.
Published: February 2011

The Batch Condition Control System has been shown to give good batch-to-batch repeatability of both viscous flow behavior and crosslinking characteristics for both fixed speed and variable speed mixing. It has also been shown to be capable of adjusting the mixing treatment to compensate for substantial changes in the properties of NR. Stress-relaxation results showed unexpectedly broad distributions. Lack of a comprehensive history of stress-relaxation results from the Negretti TMS biconical rotor rheometer makes it difficult to reach firm conclusions. The results for highly filled and thixotropic compounds are not comparable with those from other stress relaxometers such as the Monsanto SRPT and the BFGoodrich DSR, due to the small initial strain imposed on the sample by these instruments. Two possible causes of the broad distributions can be identified: 1) The sensitivity of the stress relaxation measurement. 2) The mode of flow in the chamber of a Farrel Banbury Mixer.
J-Integral and Crack Opening Displacement as Crack Initiation Criteria in Natural Rubber in Pure Shear and Tensile Specimens
Authors: Lee R. F. , Donovan J. A.
Published: February 2011

For PS and SEN specimens: 1) Jδ (one half Jθ) can be determined from one specimen and is independent of crack size and specimen geometry. 2) J and T at initiation differed. 3) J at initiation increased with carbon black content, but the critical crack-tip radius did not.
Transient Electromechanical Behavior of Carbon-Black-Filled Rubber
Authors: Parris Donald R. , Burton Larry C. , Siswanto Muliawati G.
Published: February 2011

This work has shown the sensitivity and uniqueness of conductivity and dielectric constant transient response to compressional stress for natural rubber filled with specific types of carbon black. The strong correlation between conductivity and capacitance (both steady-state magnitudes and transients) is attributed to the polymer itself. A qualitative model for these effects is based on changes of conductive and resistive microelements due to fracture of the carbon black matrix. Transient electrical measurements of this type should be applicable to carbon-black- (or metal-) filled dielectrics over a large range of resistivity.
HPLC Procedure for the Determination of Free Sulfur in Natural Rubber Formulations
Authors: King R. J. , Mondimore D. M.
Published: February 2011

The conventional ASTM method for the determination of the percent of free sulfur is a time-consuming method. Additionally, because of the many steps involved and the necessity of subjective endpoint determination, the data would vary from operator to operator. This lack of precision is detrimental in a quality-control type environment, and a retest can literally hold up production. The HPLC method described is almost totally automated. Sample preparation involves no exposure to such toxic chemicals as formaldehyde, cadmium salts, or glacial acetic acid. Quantitation is a computer operation negating operator to operator variations which can cause up to 20% relative standard deviation.
Structure and Properties of a New Synthetic Tire Rubber: High-Trans SBR
Authors: Fabris H. J. , Hargis I. G. , Livigni R. A. , Aggarwal S. L.
Published: February 2011

Solution SBR's are presently widely used as tire rubbers, and can be tailor-made for specific property advantages. Although still at an early stage of evaluation, high-trans-1,4 SBR's (HTSBR's) must certainly be considered serious contenders for at least partial replacement of NR to increase tire durability. Their excellent green and tack strengths, excellent oxidative stability and, in blends with NR, good fatigue life constitute valuable assets for radial tire sidewall constructions, while their outstanding abrasion resistance combined with acceptably low hysteresis properties will make them highly useful as components in tire tread compounds.
Viscoelastic Characterization of Long Branching and Gel in Elastomers by Comparison of Large and Small Deformational Behavior
Authors: Nakajima N. , Scobbo J. J. , Harrell E. R.
Published: February 2011

Ten different raw elastomers of varied chemical structure and Mooney viscosity were characterized with both tensile stress-strain behavior and dynamic shear behavior. The room temperature tensile stress-strain behavior was determined at strain rates of 0.239, 0.0892, and 0.00653 sec−1. These stress-strain data were reduced with a use of strain-time correspondence principle. The dynamic-shear behavior was observed over the frequency range from 10−2 to 102 rad/s. Double logarithmic Cole-Cole plots were used to characterize a relative degree of long branching and gel content. The reduced data of tensile stress-strain measurements were compared to the data of dynamic measurements. From this comparison, the sample containing a long-range crosslinked network was differentiated from that containing microgel.
Cure Modification Effected by 2-Iminothiophthalimides in the Vulcanization of NR Accelerated by Thiocarbamyl Sulfenamides and Dibenzothiazyl Disulfide
Authors: Das Prasanta Kumar , Datta Rabindra Nath , Basu Dipak Kumar
Published: February 2011

Studies have been made on the effect of N-oxydiethylene thiophthalimide (ODTP) and N-cyclopentamethylene thiophthalimide (CPTP) as retarders in the vulcanization of NR. N-oxydiethylenethiocarbmyl-N′-cyclopentamethylene sulfenamide (OTCS) and N-oxydiethylene thiocarbamyl-N′-oxydiethylene sulfenamide (OTOS) have been used separately with MBTS to form the binary systems of accelerators. Retardation exhibited by the combinations OTCS-MBTS-ODTP and OTOS-MBTS-CPTP is noteworthy. In these systems, both CBDS and OBDS are formed. The enhanced activity with regard to torque, scorch, modulus, tensile strength, etc. is believed to be due to the presence of CBDS and OBDS. Probable reactions for the formation of various compounds responsible for acceleration and retardation of vulcanization of NR have been explored. It has been observed that ODTP and CPTP provide better cure-retardation than CTP and in almost all the cases, the cure rate and torque values of the resulting vulcanizates are increased. In the case of filled vulcanizates containing HAF, it seems that the nature of the reaction is of the same kind as observed in the case of gum stocks but differs only in degree. The physical data of the vulcanizates containing HAF also indicate that both ODTP and CPTP excel CTP in many respects.
A Large-Deformation Finite-Element Analysis for Multilayer Elastomeric Bearings
Authors: Seki Wataru , Fukahori Yoshihide , Iseda Yutaka , Matsunaga Tsutomu
Published: February 2011

Finite element methods are applied for multilayer elastomeric bearings under large deformation. The method is capable of handling nonlinear elasticity and incompressibility of rubber-like materials. The strain energy density function which determines elastic properties of the materials is obtained empirically through strip biaxial testing. The computation using the strain energy density function is conducted to analyze the stress and strain distribution and the performance characteristics of multilayer elastomeric bearings, which is in good agreement with the results of actual experiments.
GPC Analysis of Rubber in Guayule and Five Species of Parthenium (Asteraceae)
Authors: West Jan , Rodriguez Eloy
Published: February 2011

The genus Parthenium includes one species, guayule (P. argentatum Gray), that produces large amounts of good quality rubber. At present, guayule is the subject of research to determine if it can be developed as an alternative crop for the arid areas of the United States and other countries. Interspecific hybridization between guayule and other species of Parthenium can be accomplished without major difficulties, and there are several desirable agronomic traits that can be transferred from these species to guayule. These other species have not been reported to have large amounts of rubber. Rollins reported that some biotypes of Parthenium incanum H.B.K. contain small amounts of rubber. Taylor and Benedict reported that P. tomentosum D.C. var. stramonium (Greene) Rollins contained 0.02% rubber. Angulo-Sanchez examined 21 guayule plants from native stands near Saltillo and found Mw values varied between 6.10×104, 6.10×105, and 1.13×106; Mn values varies between 6.10×104 and 6.10×105 (Reference 7). These values are comparable to Hevea clones examined by Subramanian. In this study, the molecular weights of guayule and five species of Parthenium are reported, the F1 hybrids between guayule and one of these species, P. alpinum was also examined to determine the size of polymers that characterize this particular hybrid.
Effect of Carbon Black on the J-Integral and Strain Energy in the Crack Tip Region in a Vulcanized Natural Rubber
Authors: Liu H. , Lee R. F. , Donovan J. A.
Published: February 2011

1) The J-integral is path independent in both PS and SEN specimens and equals the tearing energy. 2) The critical J-integral at initiation is less in PS specimens than in SEN specimens, because the greater biaxial stress in PS restricts the process zone. 3) At initiation, the crack-tip radius, proportional to the local strain, is independent of CB. 4) The energy density within and the size of the process zone near the crack tip increase with CB; these are major contributions to CB reinforcement.
Elastic Stability of Rubber Products
Authors: Tabaddor Farhad
Published: February 2011

Due to severe nonlinearities, inherent in the finite-element elasticity, uniquely defined boundary-value problems of rubber elasticity may have multiple stable and unstable solutions. An early example was given by Rivlin, who considered the problem of a Neo-Hookean cube, in a state of pure homogeneous deformations, and subjected to three pairs of equal and opposite forces acting normally on the faces of the cube and distributed uniformly over them. He found that, for forces below a certain value, the only possible solution is the symmetric solution, as might be expected. Beyond that certain value, however, there are seven possible equilibrium solutions. One of these seven solutions is the symmetric solution. It is interesting to notice that the symmetric solution, which is initially stable, becomes unstable when loads have reached a certain threshold. The stability problems of homogeneous deformations of Mooney-Rivlin type of materials, under symmetric loading, for triaxial loading and for the plane stress and plane strain cases, are dealt with in Reference 3. It was shown that a finite-element method can be applied for such analyses. The stability of a sheet of Mooney-Rivlin type of material has been studied for a symmetrical loading condition. Such instability phenomenon was first observed by Treloar. In this work, the problem of a sheet of Mooney-Rivlin type of material, subject to general biaxial loading, is studied both analytically and by finite element. An energy approach to the problem is first presented. This problem represents the biaxial loading of rubber sheets or combined extension and inflation of rubber tubes, which are often used in experimental work for characterization of rubber materials. It is shown that the problem has multiple solutions for a certain domain of loading. The equilibrium state, actually attained, is dependent on the manner of quasistatic loading. Various stable solutions are obtained by finite element.
The Influence of Frictional Heating on the Sliding Friction of Elastomers and Polymers
Authors: McC. Ettles C. M. , Shen Jui Hsieh
Published: February 2011

The friction of polymers and elastomers has been widely researched, both in practical applications and in fundamental experiments. Although some of the basic mechanisms of elastomer friction have been well explored, the effect of frictional heating has not received much attention. This is surprising since the low thermal conductivity of elastomers can result in quite high temperatures being generated at the interface. This paper is concerned specifically with the influence of heat generation on the level of friction at the interface. Some present theories of elastomer friction are well established. The important factors that govern friction are considered to be the strength of interface bonds and the loss tangent, tan δ, where δ is the phase lag between harmonically applied strain and the stress response. On a rough surface, friction is considered to occur from hysteretic losses. On a smooth surface, friction is considered to occur from the formation of bonds across the interface, the extension of the bonds and their eventual fracture. In several quantitative models of elastomer friction summarized by Moore and Geyer, the result for friction is directly proportional to tan δ, thus for a perfectly elastic material, the friction (according to these models) tends to approach zero. Factors affecting the interface bond strength are somewhat better understood, Schallamach proposed that the bonds were molecular. This allowed an Eyring-type rate process theory to be applied, as illustrated with great clarity by Grosch. Grosch showed that the Williams-Landel-Ferry transformation could be applied to condense the friction-speed characteristics measured at various temperatures to a single “master curve.” These experiments gave convincing evidence that rubber friction is a thermally activated, molecular kinetic, stick-slip process. Grosch's experiments were later confirmed by Ludema and Tabor.
Friction on Ice
Authors: Ahagon Asahiro , Kobayashi Toshio , Mlsawa Makoto
Published: February 2011

The friction on ice is strongly dependent on temperature. At sufficiently low temperatures, the frictional resistance on ice is high comparable to those on wet or even dry solid surfaces. As temperature rises and approaches the melting point of ice, however, friction rapidly decreases. Differing from the friction of a rubber on ordinary dry or wet solid surfaces the energy loss processes in the rubber do not seem to be the direct source of the frictional resistance on ice. Although frictional melting of ice could occur at high sliding speeds, an ice surface is inherently lubricated with a persistent mobile fluid layer at relatively high temperatures, near the melting point of ice. When a rubber slides on an ice surface, the fluid layer is sheared and undergoes drag flow. The energy loss process necessary for the frictional resistance takes place primarily in the fluid layer, and not in the rubber. The frictional resistance on ice is primarily determined by the viscosity and the thickness of the lubricating fluid layer. What is required of a rubber for better traction under such a condition is that the rubber surface follows the topography of the ice surface as closely as possible, so that more patches of ice surface can be sheared. Therefore, the rubber has to be sufficiently soft to show high friction on ice. Further improvement of the friction could be obtained by making it more resilient. Thus, a rubber with high friction on ice must be compounded so that the polymer chains maintain a high level of mobility at moderately low temperatures. This can be achieved by using polymers with low glass-transition-temperatures. An increased softener loading level helps to improve friction, but to a limited extent. In order to take maximum advantage of softeners, the choice of softener system is important. A relation common to all the mixed softener systems, except the ones containing high-viscosity softeners, was found to exist between the friction on ice and the solubility parameter of the softener mixture in the rubber. The friction on ice was maximized by selecting a softener system with a solubility parameter near that of the polymers in the rubber. The solubility parameter dependence of the friction was consistent with those of softness and resilience.
Polyurea Synthesis and Properties as a Function of Hard-Segment Content
Authors: Chen Z. S. , Yang W. P. , Macosko C. W.
Published: February 2011

High-molecular-weight linear polyureas of different hard-segment content are obtained with a two-step solution polymerization. Elimination of water, careful choice of solvent, reactant concentration, and good control of reaction temperature are essential to obtain satisfactory results. We have studied the influence of the hard-segment content on the mechanical, dynamic-mechanical, and thermal properties of these solution polymerized amine-terminated polypropylene-oxide-based thermoplastic polyureas. Two-phase morphology is predominant within the range of the hard-segment concentration studied. Inversion of the continuous and dispersed phase might occur in the polyurea series at about 60 wt.% of hard segment. This changes the nature of the polyureas from a tough elastomeric material to a more brittle, high-modulus plastic. The modulus of the rubbery plateau measured from dynamic-mechanical spectra increases with hard-segment concentration due to the reinforcing effect of hard-segment domains. However, continuous improvement in dynamic-mechanical modulus is not significant when the hard segment is above 50 wt.% due to higher degree of phase mixing in high hard-segment concentration systems. The amount of solubilized hard segment in the soft-segment phase in these polyureas is limited as judged from the relatively constant soft-segment Tg. However, the extent of phase separation, as determined by the heat capacity change ΔCp across the soft-segment Tg, decreases with increasing hard-segment content. The same characterizations and analyses have also been carried out on a series of RIM produced polyurea samples of the same composition. Great difference in properties is observed in comparison of these two sets of samples due to their different synthesis routes. In general, samples produced by RIM exhibit lower molecular weight, lower dynamic-mechanical modulus, higher soft-segment Tg, more phase-mixed, and more tensile elongation than those synthesized by solution polymerization. The detailed comparison will be treated in a separate paper.
Application of Magnesium Hydroxide as a Flame Retardant and Smoke Suppressant in Elastomers
Authors: Holloway L. R.
Published: February 2011

This study has provided information about the performance of magnesium hydroxide in two EVA copolymers while also comparing the performance of the copolymers. The low-ethylene EVA tolerates the higher filler loadings of magnesium hydroxide more readily than the high-ethylene EVA. On the other hand, the latter has certain advantages, exhibiting higher tensile and tear strength values. Increasing the loading of magnesium hydroxide has a beneficial influence on tear strength and water adsorption. It was also interesting to note the differences in limiting oxygen index between the two sets of filled compounds. Compared with EPDM, much lower filler loadings are needed to achieve similar values of oxygen index. Taking all properties into account, the range 100 to 150 phr of magnesium hydroxide would be recommended for further development work.
Thermoplastic Elastomer Compounds from Sulfonated EPDM Ionomers
Authors: Paeglis A. U. , O'Shea F. X.
Published: February 2011

The zinc sulfonate of EPDM, an ionic elastomer polymer, can be readily formulated into useful thermoplastic elastomer compounds having beneficial properties and processing characteristics. The thermoplastic processing characteristics of these ionic elastomers are uniquely controlled by “ionolyzers,” preferential ionic plasticizers. These additives induce thermal reversibility in the ionic crosslink and control the response of the ionic associations to temperature. Ionic elastomer compounds maintain many of the performance features characteristic of vulcanized EPDM, such as low-temperature flexibility, thermal stability, and weatherability, while providing the added advantages of heat weldability and elimination of vulcanization. We have developed a cost-effective ionic elastomer formulation that meets or exceeds the RMA recommendations for black EPDM in a demanding, high performance application, single-ply roofing membrane. High-strength lap seams can be rapidly fabricated using portable hot air welders, a technique unavailable to conventional vulcanized EPDM sheet. Other applications have been investigated for these polymers, such as hose, footwear, mechanical goods, adhesives, impact modifiers, and asphalt modifiers both as thermoplastic elastomers and as modifiers for other materials. These applications have taken advantage of the unique rheological and solubility properties of these polymers. In addition, a new polymer grade offers an advance in the ability to formulate higher strength and more highly filled and extended ionic elastomer compositions.
Peroxide Curing of Ethylene-Propylene Elastomers
Authors: Keller Robert C.
Published: February 2011

1. Ethylene-propylene elastomers, suitably compounded for extrusion applications, can be readily vulcanized with organic peroxides to meet emerging requirements of improved performance and longer service life. 2. Aralkyl or dialkyl classes of peroxides produce the preferred cure performance, highest physical properties, and lowest compression set. Choice of peroxide governs rate of cure but not necessarily the optimum in crosslinking efficiency. 3. Coagents are essential to the development of optimum cure and stress-strain properties. The bis-maleimide is very effective in compounds that contain significant quantities of process oil, antioxidants for increased heat resistance, or other materials that consume free-radicals. 4. Ethylene-propylene compositional parameters influencing vulcanization activity are the diene, both type and concentration, and the ethylene content. Reactivity of the terpolymers is dependent on the type and amount of diene utilized in the polymer synthesis. High ethylene content improves crosslinking efficiency because there are fewer propylene sequences where chain scission can occur. 5. Increasing levels of hydrocarbon process oil needed in fast extruding compounds require higher peroxide concentrations to maintain cure and stress-strain properties.
A New Pull-Out Test for Tire Cord Adhesion—Part II. Cold Bonding
Authors: Ellul M. D. , Emerson R. J.
Published: February 2011

Coaxial Shear Pull-out Test samples which are essentially free from residual stresses can be fabricated using a cold-bonding procedure for the outer metal sleeve. Encapsulation of the rubber-cylinder—cord entity by the metal sleeve changes the type of deformation in the rubber from tensile as in the TCAT to simple shear. Consequently, a linear strain-energy analysis can be readily performed with good accuracy for the CSPT. This is the principal advantage of the CSPT over the TCAT. The work of adhesive or cohesive rupture, G, can then be easily determined with reasonable accuracy. G is a more meaningful estimate of the composite strength than the pull-through force used in standard ASTM tests, especially if adhesion with materials of different moduli and cords of various sizes are to be compared. Since shear stresses are predominant in tire belts, this model is assumed to simulate relative failures of such cord—rubber composites and is useful as a laboratory test for adhesion of tire cords to rubber.