bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Simulations on Sliding Friction between Amorphous Si-DLC Films
Authors: Wang Yang , Lan Hui Qing , Liu Can
Published: February 2011

Diamond-like carbon films have been extensively studied over the past decades due to their unique combination of properties, in particular, Si-DLC films are of significant interest for tribological effects. They possess the potential to improve wear performance in humid atmospheres and at higher temperatures. MD simulations were carried out to generate Si-DLC films at different silicon contents from 0 to 50%, in order to theoretically investigate the influence of silicon contents on microstructures and tribological properties between Si-DLC films. The results show that the sp3/sp2 ratio in Si-DLC films increases with the increasing silicon content. The MD simulation results suggest that the friction force increases with addition of silicon to DLC films. The bond numbers of interfilms have showed that the silicon addition promotes the bonding of interfilms forming, which results in the friction force increased.
Micro/Meso Scale Metallic Sheet Forming Process Analysis Based on the Strain Gradient Plasticity Theory
Authors: Hu Peng , Peng Lin Fa , Lai Xin Min , Zhang Wei Gang
Published: February 2011

Increasing demands for miniature metallic parts have driven the application of micro/meso forming process in various industries. The present study focuses on the size effect which appears in the micro/meso scale sheet forming process. Micro/meso scale stamping experiments and finite element simulations incorporating the CMSG plasticity theory are conducted, respectively. It is found that the numerical simulation results, with strain gradient and strain gradient path taken into account, match the experimental results better than those of conventional simulation method.
Processing of Lightweight Metal Matrix Composites via In Situ Gas/Liquid Reaction
Authors: Borgonovo Cecilia , Apelian Diran
Published: February 2011

Aluminum nitride (AlN) possesses superior thermal and electrical properties and is an ideal candidate for high-temperature, as well as for packaging and optoelectronic applications. Aluminum based composites reinforced with AlN have been manufactured via an in situ gas-assisted process, where a nitrogen-bearing gas is injected in the molten aluminum at 1273-1323 K. The process is carried out in an inert atmosphere in order to avoid oxygen contamination. Addition of Mg lowered the oxygen content in the melt by forming MgO and thus favoring the nitridation reaction. Particle size formed in the matrix varied from 1- 3 μm to sub-micron scale depending on the gas injection time. Longer bubbling times give rise to improved reinforcement dispersion. Addition of Si is detrimental for the synthesis of AlN; Mg2Si phase precipitates, replacing the formation of MgO and hindering the nitridation reaction. The challenges of controlling the kinetics are discussed.
Effects of Reinforcement Parameters on Fatigue Strength of Aluminium-Based Particulate-Reinforced Composites
Authors: Vedani Maurizio
Published: February 2011

A study on low-cycle and high-cycle fatigue behaviour of 6061-Al2O3composites reinforced with nominal volume fractions of 10% and 20% of Al2O3particulates is presented. The effects of reinforcement geometrical features (volume fraction and size) and of the loading mode experienced during the different kind of fatigue tests (strain controlled and stress controlled tests) were evaluated. A relation with crack growth mechanisms was drawn by analyses on fracture surfaces and on longitudinal sections of specimens subjected to the fatigue tests. The micromechanisms of cyclic deformation and of microstructural damage acting in the materials are discussed and compared to data and observations available from the wide published literature.
Strengthening Evaluation in a Composite Mg-RE Alloy Using TEM
Authors: Cabibbo Marcello
Published: February 2011

Magnesium alloys containing rare earth elements are known to have high specific strength and corrosion resistance. The addition of SiC ceramic particles makes the metal matrix composite stronger with better wear and creep resistance and a still good machinability. The role of the reinforcement particles to the enhanced strength can be quantitatively evaluated using transmission electron microscopy (TEM). This paper presents a quantitative strengthening evaluation in a SiC Mg-RE composite alloy. The different contributions were determined by TEM inspections. The microstructure strengthening mechanism was studied after room temperature compression specimens. The way of combining the different contributions and the comparison to the measured yield stress, is also discussed and justified.
Hot Drilling of Aluminium Matrix Composite
Authors: Donnini Riccardo , Santo Loredana , Tagliaferri Vincenzo
Published: February 2011

The aim of this paper is to investigate the behaviour in terms of drilling forces and roughness of Metal Matrix Composites (MMC) in hot drilling machining. In particular, Al2009/(SiC)w, Al6061/(SiC)w, and Al6061(Al2O3)p metal matrix composites were used, and the adopted temperature were in the range 20°C-160°C. A comparison with drilling at room temperature has been discussed. The results have shown the sensible influence of the working temperature on drilling forces and on surface material properties. In the case of Al2009/(SiC)w a minimum in the drilling forces has been found, making possible the dry machining and improving the cutting conditions. Instead, for Al6061/(SiC)W and Al6061(Al2O3)p in the used temperature range no minimum appears.
Preparation of Poly(Hydroxamic Acid) for Separation of Zr/Y, Sr System
Authors: Hassan Khaled F. , Kandil Shaban A. , Abdel-Aziz Hossam M. , Siyam Tharwat
Published: February 2011

Poly(hydroxamic acid) resin (PHA) was prepared by modification of polyacrylamide (PAAm) prepared through -irradiation technique and used for the first time in separation of Zr(IV) from Y(III) and Sr(II) as a simulation mode for the purification of89Zr from its parents (Y or Sr). The adsorption behaviors of zirconium, yttrium, and strontium on the prepared PHA resin in different media, namely, hydrochloric acid, acetate buffer, and citrate buffer were studied as a function of pH. In addition, in cation-exchange column chromatography experiments using PHA, three different eluants, namely,  mol/L HCl, acetate buffer pH 3.5, and 2 mol/L HCl, were employed for elution of Zr(IV), Y(III) and Sr(II), respectively, where Zr(IV), Y(III) and Sr(II) were eluted in amounts of 80%, 99.9%, and 100%, respectively. The purification process of Y(III) from Zr(IV) was carried out using regenerated PHA.
Physical Activity and Telomere Biology: Exploring the Link with Aging-Related Disease Prevention
Authors: Ludlow Andrew T. , Roth Stephen M.
Published: February 2011

Physical activity is associated with reduced risk of several age-related diseases as well as with increased longevity in both rodents and humans. Though these associations are well established, evidence of the molecular and cellular factors associated with reduced disease risk and increased longevity resulting from physical activity is sparse. A long-standing hypothesis of aging is the telomere hypothesis: as a cell divides, telomeres shorten resulting eventually in replicative senescence and an aged phenotype. Several reports have recently associated telomeres and telomere-related proteins to diseases associated with physical inactivity and aging including cardiovascular disease, insulin resistance, and hypertension. Interestingly several reports have also shown that longer telomeres are associated with higher physical activity levels, indicating a potential mechanistic link between physical activity, reduced age-related disease risk, and longevity. The primary purpose of this review is to discuss the potential importance of physical activity in telomere biology in the context of inactivity- and age-related diseases. A secondary purpose is to explore potential mechanisms and important avenues for future research in the field of telomeres and diseases associated with physical inactivity and aging.
Outcome of management of obstetric genito-urinary fistulae in the general hospital, Ikot Ekpene, Akwa Ibom state, Nigeria
Authors: Ekanem Etim I. , Ekott Mabel I. , Ekabua John E. , Agan Thomas U. , Inyang-Otu Atta
Published: February 2011

Background: Obstetric fistula with urinary incontinence is one of the most distressing maternal morbidities. It is associated with physical and social deprivation such as wife abandonment and violent reactions against the victims, particularly in the developing countries of the world. This study was carried out to assess the demographic and reproductive profiles as well as outcome of management of patients with obstetric genito-urinary fistulae in the General Hospital Ikot Ekpene, Akwa Ibom State, Nigeria. Design and Methods: A five-year cross sectional observational study of medical records of 37 patients managed in maternity section of General Hospital Ikot Ekpene, Akwa Ibom State, Nigeria was conducted. Results: One delivery every 122 ones during the study period was complicated by urinary fistula. Eleven (29.7%) were teenagers. Most patients were married (54.1%), primiparous (59.4%) from low socioeconomic class (72.9%) who did not utilize modern obstetric facilities effectively. Many cases were the consequence of prolonged obstructed labour (51.4%) and majority presented with total incontinence of urine (70.2%). Eighteen (48.7%) patients presented within 6 months of delivery. They were mainly vesico-vaginal (34.4%) or complex (10.8%) fistulae that were managed conservatively (21.6%) or with bladder repairs. About a third was referred for further treatment management due to unsatisfactory outcome. Conclusion: This age-long obstetric morbidity is common among young married women in Ikot Ekpene, Akwa Ibom, mainly due to poor utilization of modern obstetric care facilities. Results of treatment are largely unsatisfactory in a third of these patients; therefore resources should be channeled towards effective and comprehensive preventive programs especially among this vulnerable group of women.
Training Novices to Make Expert, Occupationally Focused, Community Mental Health Referral Decisions
Authors: Harries Priscilla , Gilhooly Kenneth
Published: February 2011

Introduction:

Currently, British health policy requires services to be prioritised according to an individual's level of need. This is particularly necessary for community mental health services, where referral demand far exceeds service availability.

Purpose:

The purpose of this study was to use expert occupational therapists' referral prioritisation policies, derived from judgement analysis, to train novices in the skill of referral prioritisation.

Method:

The therapists' policies chosen were those that supported the occupationally focused practice advocated by the profession. Thirty-seven pre-registration students were asked to prioritise a set of referrals, before and after being trained with graphical and descriptive representations of these experts' policies.

Findings:

Pre-training, the students overvalued the client's history of violence and undervalued the reason for referral and the client's diagnosis, as compared with the experts. Post-training, the students' policies were better matched to those of the experts. The effect of training was demonstrated through several measures: more accurate prioritisation scores when matched with expert ratings on the same referrals, improved consistency on repeat referrals and higher group agreement.

Conclusion:

Decision training may be useful in promoting the type of service that aims to target clients' occupational needs in the field of community mental health.
Nano-Structural Elucidation in Carbon Black Loaded NR Vulcanizate by 3D-TEM and In Situ WAXD Measurements
Authors: Ikeda Yuko , Kato Atsushi , Shimanuki Junichi , Kohjiya Shinzo , Tosaka Masatoshi , Poompradub Sirilux , Toki Shigeyuki , Hsiao Benjamin S.
Published: February 2011

Three dimensional (3D) visualization of nanometer structure of carbon black dispersion in rubbery matrix has successfully been studied and reported in this paper. Use of 3D-TEM, which is computerized tomography combined with transmission electron microscopy (TEM), enabled us to reconstruct 3D images of carbon black aggregates in natural rubber (NR) matrix. The TEM measurements were conducted by a bright-field method on thin samples without any electron staining. The sample was subject to uni-axial tilting (+65 degree to −65 degree with 2 degree increment) in the sample chamber, and 66 TEM images were taken on each sample. These TEM images were used for computerized tomography to reconstruct the 3D image. This technique is designated as 3D-TEM. The nano-structural features observed by 3D-TEM were in conformity with the electron-conductivity results, and the percolation behavior was recognized. These results were further supplemented by in situ wide-angle X-ray diffraction (WAXD), i.e., simultaneous WAXD and tensile measurements on the sample to observe the strain-induced crystallization in NR vulcanizate. Upon tensile elongation, the crystallization was clearly observed in WAXD in the presence of carbon black, and it contributed to the tensile properties. In order to understand the performances of filled NR vulcanizates, it surely is necessary to know the structural states of the mixed nano-filler and the crystallites produced upon elongation.
Mechanistic Study on the Role of Sulfurized Para-Aramid Short Fibers in Rubber to Brass Adhesion
Authors: Datta R. N.
Published: February 2011

Adhesion between steel cord and rubber is an important factor determining the durability of tires, conveyer belts, hoses and other rubber based products using steel cord as reinforcement. With the advancement in tire technology, steel reinforced radial tires have captured 90–95% of the tire market in most of the advanced countries and brass coated steel cord has been established as the premium carcass and belt material for radial truck tires. Apart from the use of cobalt salts to improve adhesion, the adhesion characteristics can also be improved through the use of resin systems such as resorcinol/hexamethoxymethyl melamine (R/HMMM), often together with silica as a partial replacement for carbon black. This combination accomplishes several things. It acts as a modulus and hardness enhancer providing a more compatible system with regard to the stiffness of the steel cord compared to that of the cured skim compound. Secondly, the combination can improve resistance to the negative effects of humidity on adhesion. Thirdly, the pro-oxidant effect of cobalt salts is counteracted to some degree. There is, however, a drawback with regard to this resin system; resorcinol generates toxic fumes at high temperatures encountered during mixing and processing. There is demand, therefore, to replace the R/HMMM adhesion system due to health and safety issues. This paper presents the results of studies to achieve adequate steel cord adhesion whilst seeking to improve aged compound characteristics and to reduce compound heat build up through the use of sulfurized para-aramid short fibers. This combination not only improves the properties of steel cord skim compounds, but also can be used effectively to replace the bonding system based on resorcinol and hexamethoxymethylmelamine. Further studies were carried out in squalene model to elucidate the changes in the chemistry of vulcanization both in the presence and absence of sulfurized p-aramid short fibers. Additional studies were carried out on sulfidized brass cords to analyze the adhesion layer's elemental composition using the Electron Dispersive X-ray Spectroscopy (EDX) characterization techniques.
Modeling of the Linear Viscoelastic Behavior of Partially Hydrogenated Polymer-Modified Asphalts
Authors: Vargas M. A. , Herrera R. , Manero O.
Published: February 2011

The modeling of the linear viscoelastic behavior of asphalt modified with 8 wt % of partially hydrogenated poly (styrene-butadiene-styrene) triblock copolymers is analyzed. Time-temperature superposition renders master curves in a wide range of frequencies and temperatures, from which a logarithmic distribution of relaxation times is obtained using the multimode Maxwell model. In addition, the linear viscoelastic data is analyzed with an emulsion model and agreement is only found at high frequencies, where the contribution from interfacial tension is negligible. Enhanced polymer-asphalt interactions at low frequencies evidenced by a decreasing limiting slope of the storage modulus in the terminal region are not predicted by the emulsion model, and relative agreement is found considering two viscoelastic phases. The Cole-Cole representation and the fractional Maxwell model predict the viscosity of asphalt in the complex plane, but strong asymmetry in the semicircular arcs is found in the polymer-modified asphalt blends. The Havriliak-Negami model accounts for asymmetric arcs and represents the data better in specific ranges of frequency.
Molecular Mobility of Unfilled and Carbon-Black-Filled Isoprene Rubber: Proton NMR Transverse Relaxation and Diffusion
Authors: Sun Ximei , Isayev Avraam I. , Joshi Tirtha R. , von Meerwall Ernst
Published: February 2011

In an effort to understand the effect of ultrasound on the devulcanization of gum and filled isoprene rubber vulcanizates, solid state NMR 1H transverse relaxation (T2) was employed to analyze rubber molecular mobility. The T2 relaxation decay of the unfilled and the black filled IR was successfully described by a two-component model. The short T2 component arose from the chemically crosslinked (gel) and physically entangled (heavy sol) network. The long T2 decay came from the unentangled sol and dangling network chain ends. Vulcanization decreased the molecular mobility; however, ultrasound devulcanization partially reversed this effect. Addition of processing oil in the filled IR significantly altered the dependence of T2 on the sol fraction. T2 and pulsed-gradient diffusion experiments were carried out on IR melt specimens after sonication with or without subsequent vulcanization. The lowered and broadened M-distribution produced results quantitatively related to earlier work in natural rubber.
Optimization of Composites Based on PP/Elastomer Blends and Short Pet Fibers
Authors: López-Manchado M. A. , Arroyo M.
Published: February 2011

The physical and mechanical properties of ternary composites based on isotactic polypropylene (iPP) and ethylene—octene copolymer blends reinforced with poly(ethylene terephthalate) (PET) fibers have been studied. In order to evaluate the effect of the matrix composition and fiber content on the final properties of the composite, an experimental design based on a Doehlert Uniform Net has been employed. The results show that PET fibers behave as a reinforcing agent for PP/ethylene—octene copolymer blends, this effect being more evident at high copolymer percentages in the blend. It is important to notice that the analyzed mechanical properties are more dependent on matrix composition than on fiber percentage. So, as PP content is increased, the blend becomes more rigid and stable, and a noticeable increase in tensile and flexural modulus and strength are observed. Moreover, dynamic mechanical measurements provide a further confirmation of the reinforcing effect of these fibers. A displacement of the glass-transition temperature ((Tg)) of the elastomeric phase to higher temperatures is observed as fiber content in the composite increased. The morphology of the composites has been also analyzed by scanning electron microscopy (SEM). Good interfacial adhesion between fibers and matrix is observed, especially when the copolymer is the continuous phase. Hence, it is possible to correlate good interaction at the fiber—matrix interface with an improvement of composite properties.
Monitoring Thermal Oxidation of Sulfur Crosslinks in SBR-Elastomers by Quantitative Analysis of Sulfur K-Edge XANES-Spectra
Authors: Modrow H. , Hormes J. , Visel F. , Zimmer R.
Published: February 2011

This paper presents a quantitative description of the processes occurring at the sulfur crosslinks of vulcanized rubber during thermo-oxidative aging. To extract this information in a nondestructive way, sulfur K-edge X-ray absorption near-edge structure (XANES) spectra have been analyzed quantitatively. We find that reversion takes place before the onset of oxidative processes at the sulfur bridges. Parallel to the oxidative processes, the production of cyclic sulfanes takes place. Both the relative and absolute contributions of the different reactions involving the sulfur crosslinks vary strongly with sample composition. Whereas antidegradants delay the thermo-oxidative aging without actually changing the aging resistance of the sulfur bonds, both the amount of S8/TBBS (N-tert-butylbenzothiazole-2-sulfenamide) and the presence of carbon black in the sample enhance this parameter considerably.
A Novel Biocidal Elastomer
Authors: Elrod D. B. , Figlar J. Gibb , Worley S. D. , Broughton Royall M. , Bickert J. R. , Santiago J. I. , Williams J. F.
Published: February 2011

Biocidal elastomeric materials have been produced by a three-step chemical process on commercial elastomers which are composed of a styrene/ethylene-butylene/styrene triblock copolymer. The commercial elastomeric material employed was Kraton®G, produced by the Shell Chemical Company in Houston, Texas. The three-step process involved a Friedel-Crafts acylation of the styrene blocks of the elastomer, followed by a hydantoin ring formation reaction, and subsequent halogenation with chlorine or bromine. Both raw and processed elastomeric materials were studied. The biocidal efficacies of the materials were demonstrated using several species of bacteria. A few applications for the technology may include prevention of disease by biocidal surgical gloves, condoms, protective clothing, food packaging, and the prevention of biofouling in elastomeric tubing.
A New Constitutive Model for the Compressibility of Elastomers at Finite Deformations
Authors: Bischoff Jeffrey E. , Arruda Ellen M. , Grosh Karl
Published: February 2011

Although traditional constitutive models for rubbery elastic materials are incompressible, many materials that demonstrate nonlinear elastic behavior are somewhat compressible. Clearly important in hydrostatic deformations, compressibility can also significantly affect the response of elastomers in applications for which several boundaries are rigidly fixed, such as bushings, or triaxial states of stress are realized. Compressibility is also important for convergence of finite element simulations in which a rubbery elastic constitutive law is in use. Volume changes that reflect compressibility have been observed historically in both uniaxial tension and hydrostatic compression tests; however, there appear to be no data obtained from both types of tests on the same material by which to validate a compressible hyperelastic law. In this paper, we propose a new compressible hyperelastic constitutive law for elastomers and other rubbery materials in which entropy and internal energy changes contribute to the volume change. Using data from the literature, we show that this law is capable of reproducing both the pressure—volume response of elastomers in hydrostatic compression, as well as the stress—stretch and volume change—stretch data of elastomers in uniaxial tension.
Quantum Mechanical Calculations to Assess the Antireversion Effects of Several Dienophiles
Authors: Talma A. G. , Datta R. N. , Aerts J.
Published: February 2011

The utilization of Quantum mechanical calculations for substituted dienophiles in the Diels—Alder reaction is very useful in assessing the antireversion effect of various dienophiles. It has been demonstrated that citraconimides provide better antireversion properties than maleimides. A useful explanation is that although maleimides are better dienophiles, they do not survive the vulcanization medium and consequently are not available during the onset of reversion. The antireversion effect of dienophiles varies with the electronic and steric nature of the substituents on the double bond of the dienophile. Calculations are made to demonstrate the effectiveness of various dienophiles in a Diels—Alder reaction. A good correlation has been obtained between the calculations and experimental results.
Initial Development of Structure—Property Relationships for Dynamically Vulcanized EPDM/IPP Elastomers
Authors: Wright Kathryn J. , Lesser Alan J.
Published: February 2011

The mechanical behavior and morphology of dynamically vulcanized blends of ethylene—propylene—diene monomer and isotactic polypropylene are investigated. The composition of the thermoplastic elastomers dictates their morphology, which in turn controls their mechanical behavior. Six compositions are examined under quasi-static and dynamic mechanical loading conditions. Although these elastomers are processable thermoplastics, they all exhibit a Payne effect much like traditional crosslinked materials. However, the mechanisms responsible for this behavior are different than those of crosslinked systems. The “Payne effect” response is studied and characterized over a range of compositions, and the results are discussed in light of the elastomer morphologies.
Barrier Properties of Thermoplastic Elastomer Films
Authors: Xu R. , Mead J. L. , Orroth S. A. , Stacer R. G. , Truong Q. T.
Published: February 2011

One application of barrier materials is chemical protective clothing. A variety of chemical protective clothing options are currently available, but many of the barrier materials combine good fluid resistance with high resistance to moisture vapor transport. This generates heat stress to the wearer. For certain applications it is desirable to find materials which are elastic, easy to process, and comfortable to use, while still having good fluid resistance. Thermoplastic elastomers (TPE) represent a developing family of materials that may provide an answer to those requirements, but have not been thoroughly investigated for this application. In this work, commercially available thermoplastic elastomers and their blends were evaluated. Film samples were prepared by either extrusion or compression molding, and their barrier properties evaluated in terms of water vapor transmission, fluid vapor transmission, and fluid absorption. Films prepared from a polyester TPE showed the highest water vapor transport. Blends of the polyester TPE with more fluid resistant TPEs offered protection with enhanced water vapor transport. These results indicate that blends of TPEs can be tailored to offer fluid/vapor protection with significant improvements in water vapor transmission. For some fluids these materials offer even better protection, with enhanced water vapor transmission, than currently available materials.
Characterization of the Large and Small Rubber Particles in Fresh Hevea Latex
Authors: Sakdapipanich Jitladda T. , Nawamawat Kanjanee , Kawahara Seiichi
Published: February 2011

The rubbers from small and large rubber particles were separated from the serum and cream phases of centrifuged fresh Hevea latex, respectively. The small rubber particles (SRP) consist of rubber molecules showing a unimodal molecular weight distribution (MWD), with a peak-top value falling between the two peak values of the bimodal MWD observed in rubbers from the large rubber particles (LRP). The rubbers in LRP from mature trees and SRP from seedlings are polyisoprene molecules terminated by phospholipids comprising branching points, while those in SRP from mature trees are presumed to be linear molecules containing no phospholipid terminal. The serum rubber was found to be soft and viscous rubber differing from the cream rubber containing in LRP. Thus, it can be presumed that the particle size of rubber latex is an important parameter influencing the MW, MWD and physical properties of Hevea rubber.
Modeling Step—Strain Relaxation and Cyclic Deformations of Elastomers
Authors: Johnson A. R. , Chen T. , Mead J. L.
Published: February 2011

Data for step—strain relaxation and cyclic compressive deformations of highly viscous short elastomer cylinders are modeled using a large strain rubber viscoelastic constitutive theory with a rate—independent friction stress term added. In the tests, both small and large amplitude cyclic compressive strains, in the range of 1% to 10%, were superimposed on steady state compressed strains, in the range of 5% to 20%, for frequencies of 1 and 10 Hz. The elastomer cylinders were conditioned prior to each test to soften them. The constants in the viscoelastic—friction constitutive theory are determined by employing a nonlinear least-squares method to fit the analytical stresses for a Maxwell model, which includes friction, to measured relaxation stresses obtained from a 20% step—strain compression test. The simulation of the relaxation data with the nonlinear model is successful at compressive strains of 5%, 10%, 15%, and 20%. Simulations of hysteresis stresses for enforced cyclic compressive strains of 20%±5% are made with the model calibrated by the relaxation data. The predicted hysteresis stresses are lower than the measured stresses.
Parameter Dependence and Prediction of Fatigue Properties of Elastomer Products
Authors: Alshuth T. , Abraham F. , Jerrams S.
Published: February 2011

Fatigue tests on ethylene propylene (EPDM) and styrene-butadiene (SBR) rubber reveal physical behavior that is not seen in conventional linear elastic solids. Uniaxial cyclical tests, using cylindrical dumbbell specimens, with the same minimum stress of zero (Smin=0) and varying stress amplitude (sa), predictably gave decreased fatigue life with increased stress amplitude and hence maximum stress (Smax). However, tensile uniaxial cyclic tests where Smin was increased in successive tests while alternating stress (sa) remained constant, produced longer fatigue lives for higher values of Smax.

EPDM and SBR compounds were chosen for the tests because they do not strain crystallize during deformation. Consequently, this phenomenon has no influence. The results show that Smax can not be used as criterion to predict fatigue life of elastomers. Preliminary evaluation of recorded data of stress vs. strain gave evidence that energies control the fatigue life rather than stress and strain. Experimental results on filled and unfilled rubber materials are evaluated and discussed as well as the consequences on predictions of component properties.
Methods for Measuring the Crack Length in Rubbery Pure Shear and Sent Specimens
Authors: Yang K. J. , Kang K. J.
Published: February 2011

A new approach for measuring crack length, which can be used for automization of fatigue test of rubber materials, is described. The crack length in the pure shear and SENT(Single Edge Notched Tension) specimens is evaluated from the variation of the peak loads under a constant cyclic displacement. For the pure shear specimen, a simple equation to give the crack length was derived from elementary consideration of the deformation pattern. The equation was applied to two constitutive models to simulate the hyperelastic behavior. It was experimentally proven that the crack length can be measured well. For the SENT specimen, an equation to give the crack length was derived from dimensional analysis. The function was assumed to be separated as the product of the deformation and geometry functions. Experiments were performed to prove the validity of the separation and to evaluate the details of the function.
Influence of Powder Surface Treatment on the Dispersion Behavior of Silica into Polymeric Materials
Authors: Scurati Alberto , Manas-Zloczower Ica , Feke Donald L.
Published: February 2011

The effect of surface treatment on silica agglomerate dispersibility was investigated. Precipitated silica powders were treated with a commercially available coupling agent Bis-(triethoxysilylpropyl)-tetrasulphane (TESPT) in a blender. Spherical agglomerates of known density were prepared and dispersed in styrene butadiene rubber (SBR) under controlled flow conditions. The erosion kinetics was monitored by measuring the reduction in size of parent agglomerate with time. Silica dispersibility was greatly enhanced upon surface treatment. The coupling agent used in surface treatment is known to reduce filler—filler interactions and therefore affects the intrinsic cohesivity of the powder. However powder surface treatment can also induce changes in agglomerate morphology and filler-liquid interactions. The work presented in this paper evidences such changes.
The Variation with Temperature of the Dynamic Properties of Rubber and Synthetic Rubberlike Materials
Authors: Fletcher W. P. , Schofield J. R.
Published: February 2011

(1) Over the range from 5° to 40° C, the temperature coefficients of the dynamic compression moduli of all the rubber and rubberlike materials studied are negative and fall numerically with increasing temperature. (2) The highest numerical value of this coefficient for natural rubber is −2.7×10−3 per ° C. Neoprene-Gn has a coefficient 3 to 4 times this value and Buna-S about 5 times. Hycar OR-15 shows the highest coefficient of −1.3×10−1 per ° C from 10 to 20° C, the value changing sharply at 20.2° C to −0.14×10−1, which is maintained up to 40° C. (3) Results for Neoprene-E were not reproducible, owing to a type of slow freezing effect. (4) In all cases but Thiokol-RD resilience tended to increase with increasing temperature throughout the range. (5) Resilience-temperature curves for natural rubber, Neoprene-GN, Neoprene-YD, and Buna-S take the form of straight lines intersecting at 20° to 22.5° C. Neoprene-Z shows a similar effect with intersection at 30.5° C. and Hycar OR-15 similarly at 31.5° C. (6) Copolymers of butadiene and acrylonitrile show increasing modulustemperature coefficient, and in the region 10° to 20° C decreasing resilience with increasing acrylonitrile content. The resilience-temperature diagrams for these polymers, except Hycar OR-15, are smooth curves which appear to reach steady values towards the upper end of the temperature range. (7) Thiokol-RD appears to have a freezing-point, under the dynamic conditions employed, somewhere in the region of 15–20° C; there is evidence that Hycar OR-15 shows a similar effect between 0° and 10° C. (8) The relationships enumerated above refer to basic compounds of the various materials. How far the temperature effects may be reduced or modified by suitable compounding is the subject of continuing investigation.
Swelling of Synthetic Rubbers in Mineral Oils. Effect of Temperature and Aniline Point
Authors: Powers P. O. , Billmeyer B. R.
Published: February 2011

The aniline point of hydrocarbon oils and solvents is a satisfactory index of the swelling of oil resistant synthetic rubber compositions. The logarithm of the percentage volume increase varies inversely with the aniline point up to 100 per cent swelling. The slope of the swelling curve is apparently characteristic of each synthetic rubber, and is not affected by loading, temperature or degree of cure. Slight swelling does not greatly decrease the tensile strength, but above 100 per cent swelling the strength is greatly reduced.
The Fatigue Life of Hevea and Guayule Rubbers
Authors: Santangelo P. G. , Roland C. M.
Published: February 2011

The enhanced crystallizability of guayule rubber (GR) in comparison to Hevea-based natural rubbers (NR) gives rise to better failure properties in unfilled, or “gum,” GR. The origin of this behavior is the ability of the non-polymeric contaminants in GR to nucleate strain crystallization; a similar effect is operative in less pure grades of NR. However, when compounded with carbon black, this superiority of GR over NR is lost. The mechanical hysteresis arising from the carbon black, along with the latter's enhancement of strain crystallization, supercede the contribution from the contaminants. Consequently, in contrast to the behavior of the gum rubbers, the fatigue lifetimes of GR- and NR-based compounds are equivalent.
A Review of Some of the Factors Affecting Fracture and Fatigue in SBR and BR Vulcanizates
Authors: Zhao J. , Ghebremeskel G. N.
Published: February 2011

This paper reviews the effects of polymer macrostructure (molecular weight and the styrene content of SBR) and diene microstructure on the fracture and fatigue life of styrene-butadiene rubber (SBR) and butadiene rubber (BR) vulcanizates. Effects of experimental parameters, such as carbon black and vulcanizing systems, on fracture and fatigue are also discussed. Investigations were performed under static (tensile and tear) and dynamic (fatigue) testing conditions. Finally, the underlying failure mechanisms are discussed.
Influence of Processing History and Composition on the Basic Structure and Biaxial Deformation Behavior in Dynamically Vulcanized PP/EPDM Blends
Authors: Wang M. D. , Cakmak M.
Published: February 2011

Thermal, crystallographic and mechanical properties of unvulcanized and dynamically vulcanized polypropylene/ethylene—propylene—diene monomer rubber (PP/EPDM) thermoplastic elastomer blends were investigated. In these high PP content blends, PP forms the continuous phase. The crystalline regions of the PP is mostly in alpha crystalline form with a small fraction of beta. The additives were found to suppress the beta fraction formation. The results indicate that the PP phase maintains its integrity up to the blend concentrations containing 20% EPDM. Beyond this concentration, the unit cell structure was found to become enlarged in its basal plane. This is also manifested in other properties as the melting point began a significant decrease at this concentration level. Interestingly, the film processability greatly improved beyond this 80/20 concentration and the temperature range, over which uniform films were obtained, was significantly enlarged as a result of reduction of neck formation. This was attributed to the formation and homogeneous distribution of large numbers of micronecks in the PP phase, nucleated by the presence of rubber regions.
New Thermoplastic Elastomers from Poly(Ethylene-Octene) (Engage), Poly(Ethylene-Vinyl Acetate) and Low-Density Polyethylene by Electron Beam Technology: Structural Characterization and Mechanical Properties
Authors: Chattopadhyay S. , Chaki T. K. , Bhowmick Anil K.
Published: February 2011

New thermoplastic elastomers have been prepared from the blends of metallocene-based polyolefins (Engage) with low-density polyethylene (LDPE), and ethylene-vinyl acetate copolymers (EVA) of different grades with LDPE by electron beam modification. Structural changes of these blends with or without sensitizer in presence of irradiation have been evaluated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) in conjunction with atomic force microscopy (AFM) indicate the soft rubber domain in the continuous plastic matrix. Significant improvements of mechanical, dynamic mechanical and set properties have been obtained by electron beam modification, retaining its reprocessibility characteristics. Effects of ditrimethylol propane tetraacrylate (DTMPTA) as radiation sensitizer have also been evaluated from the mechanical, dynamic mechanical properties and reprocessibility.
Hysteretic Energy Loss in Cord/Rubber Composites under 2-D Cyclic Loading
Authors: Gurvich Mark R. , Andonian Archie T. , Kim Soojaa L.
Published: February 2011

Cord/rubber composites are often considered as homogeneous anisotropic media in macro-mechanical structural analysis. Challenges, however, are associated with significant non-linearity of their deformation and the visco-elastic nature of rubber matrix. These visco-elastic composites are often subjected to cyclic loading conditions (periodic excitations) and exhibit energy losses due to their hysteretic behavior. An approach is proposed to quantify these hysteretic energy losses under general case of two or three-dimensional cyclic loading. The approach provides a simple mathematical description of this non-linear visco-elastic phenomenon. Representative experimental data are considered to show the reliability of the approach. Uni-directionally reinforced single layer composites are considered under different off-axial cyclic loads to model 2-D stress/strain states. Possible methods are discussed to define composite properties using the proposed approach.
Rubber Chemicals Derived from Conjugate Addition. II. Synthesis of a Novel Class of Benzoquinone Diimines
Authors: Katritzky Alan R. , Odens Herman H. , Voronkov Michael V. , Rostek Charles J. , Maender Otto W.
Published: February 2011

Various 2-alkylthio-5-amino- and 2,5-diamino-1,4-phenylenediamines were prepared by treatment of N-(1,3-dimethylbutyl)- N′-phenyl-1,4-quinonediimine with thiols and amines using air as an oxidizing agent. Key 2-alkylthio-1, 4-benzoquinone diimines were prepared via Ag2O oxidation of the corresponding 1,4-phenylenediamines.
Evaluation of Crosslinking in Elastomers Using Thermoporometry, Densimetry and Diffential Scanning Calorimetry Analysis
Authors: Baba Mohamed , George Soney C. , Gardette Jean Luc , Lacoste Jacques
Published: February 2011

The classical methods available for evaluating the degree of crosslinking in elastomers are stress-strain and swelling measurements. In this study, we have adopted a new analytical approach based on thermoporometry, densimetry and DSC for comparing the crosslinking density in elastomers. Crosslinking by chemical reaction or by photo-oxidation has been studied on polymer samples Ethylene-Propylene-Diene rubber (EPDM) and PolyButadiene (PB). Analysis has been done separately for soluble and insoluble fractions. The soluble fraction has been studied by densimetry and the insoluble fraction by thermoporometry and measurement of decomposition of dicumyl peroxide (DCP). The results of both these studies are complementary to each other. The DSC thermal curves of both EPDM and PB are identical in nature, but the density of the photo-oxidized EPDM samples shows a marked increase contrary to that found in PB.
Evaluation of Natural Rubber from Clones of Hevea Brasiliensis
Authors: Ferreira Mariselma , Moreno Rogério M. B. , Gonçalves Paulo S. , Mattoso Luiz H. C.
Published: February 2011

The latex and natural rubber from rubber trees [Hevea brasiliensis (Willd. exAdr. de Juss.) Muell. Arg.] from clones (RRIM 600, IAN 873, GT 1 and PB 252) recommended to the state of São Paulo, Brazil, were studied in three different tapping systems. The parameters studied were dry rubber content (DRC), percentages of ash and of nitrogen, Wallace Plasticity (P0) and Mooney Viscosity (VR). The rubber properties vary considerably as a function of clone type, tapping method and season of the year. DRC tends to decrease in the beginning of the dry, cold season (May and June), whereas both nitrogen % and ash % increase in the same period. A good linear correlation was obtained for P0 and VR. The highest P0 and VR were obtained for RRIM 600.
Solid State 13C NMR Applied to Styrene-Butadiene Rubbers Study of the Rubber Vulcanized Network Structures
Authors: Pellicioli L. , Mowdood S. K. , Negroni F. , Parker D. D. , Koenig J. L.
Published: February 2011

This paper discusses the structural changes that occur during the accelerated sulfur vulcanization of styrene-butadiene rubbers (SBR) through characterization of the network sulfide structures influenced by the curing agent concentration, the polymer microstructure, and the nature of the filler. Magic angle spinning (MAS) 13C FT - NMR spectroscopy was used to investigate the chemical crosslink properties of unfilled vulcanized SBR in addition to carbon black and silica filled polybutadiene rubber (BR), SBR, and 1:1 BR / SBR blends. New resonances in the 13C NMR spectrum are assigned to the various sulfide crosslink structures in SBR. Structural changes during vulcanization are also discussed.
Fillers for Balancing Passenger Tire Tread Properties
Authors: Byers John T.
Published: February 2011

Strong demands for lower rolling resistance tires in Europe led to the introduction of a new filler system for auto tire treads in the early 1990s. Silica, in combination with a silane coupling agent, was used as the primary filler system despite the increased costs compared to carbon black. The adoption of silica/silane treads has been slower outside of Europe, but some conversion to silica/silane or alternative filler blends has taken place in North America and Japan. This paper is a review of the many reports related to the silica/silane filler system, as well as alternative approaches — including new carbon blacks — to lower rolling resistance, that have been generated since the introduction of the “green tire” concept in the early 1990s.
Surface Energy of Silica Xerogels and Fumed Silica by Inverse Gas Chromatography and Inverse Liquid Chromatography
Authors: Donnet J. B. , Li Y. J. , Wang T. K. , Balard H. , Burns G. T.
Published: February 2011

Inverse gas chromatography (IGC) and inverse liquid chromatography (ILC) have been used to detect the interaction energy between silicas (fumed silicas and silica xerogels) surfaces and probes molecules. The silica surfaces were modified chemically by trimethylsiloxane functions. Either IGC or ILC have detected the adsorption energy change following the surface modification. In IGC technique, the results with several probes show clearly the physico-chemical properties of the silica surfaces. ILC was developed to use bigger probe molecules which are more similar in structure to polymers. In this work, squalene, a non volatile molecule with 30 carbon atoms and several double bonds, was used in ILC to simulate elastomer molecules.
Mechanisms of Adhesion in Surface Chlorinated Thermoplastic Rubber/Thermoplastic Polyurethane Adhesive Joints
Authors: Pastor-Blas M. Mercedes , Martín-Martínez José Miguel , Boerio F. J.
Published: February 2011

Chlorination of a thermoplastic styrene-butadiene-styrene rubber (S0) with a solution of 2 wt% trichloroisocyanuric acid (TCI) in ethyl acetate improved its adhesion to polyurethane adhesives. The analysis of the failed surfaces (obtained after T-peel test of S0/PU joints) showed that the locus of failure in the rubber/polyurethane joints progresses from adhesion (in non chlorinated-S0/PU joint) to cohesion in the chlorinated layer (for chlorinated-S0/PU joint). The composition of this chlorinated layer differed from the composition of the non bonded-chlorinated rubber, i.e. the failure of the joint was located in a chlorinated layer with a distinctive chemistry. On the other hand, the analysis of the chlorinated rubber/PU adhesive interface showed that chlorination with TCI produces a crosslinking of the rubber surface as well as strong interactions between the uppermost-chlorinated layer and the PU adhesive.
Quality and Performance of Carbon Blacks from Plasma Process
Authors: Probst N. , Grivei E. , Fabry F. , Fulchéri L. , Flamant G. , Bourrat X. , Schröder A.
Published: February 2011

Plasma carbon black, a new material? For several years already, the Plasma process for carbon black production has been promoted and considered as a threat to the furnace black production.

After a brief introduction to the fundamental differences between a partial combustion process and plasma process, plasma blacks have been compared with partial combustion blacks. The plasma blacks have not been optimised but are more a selection of materials based on feedstock and operating conditions. Physico-chemical properties as well as SEM and high resolution TEM micrographs illustrate differences and similarities. Surface heterogeneity of those carbon blacks has been characterised by static gas adsorption. This way the more graphitic nature of the selection of plasma blacks could be demonstrated, explaining the specific behaviour of those blacks in rubber compounds.

The specificity of the carbon blacks investigated is not only in the production technique, namely plasma torch, but also in the variety of the row materials used, demonstrating the flexibility of the process. Methane, ethylene, pyrolysis fuel oil and even a renewable vegetable oil have been used.