bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Accelerator Type and Curing Temperature on Crosslink Distributions and Tensile Properties of Natural-Acrylic Rubber Blends
Authors: Clythong N. , Wootthikanokkhan J.
Published: February 2011

Effects of curing temperature and accelerator type on tensile properties of natural-acrylic rubber blends (NR:ACM) were investigated. Three different types of accelerators namely, MBT, ZDEC and DPG, were separately compounded with the rubber blends (50/50, % w/w) along with stearic acid, ZnO, sodium stearate, and sulfur (S) on a two-roll mill. The compounded blends were vulcanized to their optimum cure time in a hydraulic press at 150 and 170 °C. Morphology and tensile properties of the rubber blends were determined by using a scanning electron microscope and a universal testing machine, respectively. Crosslinking characteristics of both NR and ACM phases in the rubber blends were investigated by using a swollen state 1H-NMR and a differential swelling technique. From the tensile test, it was found that strength and strain of the blend vulcanized with the S/ZDEC curing system were remarkably lower than those of the blends vulcanized with the S/MBT and S/DPG systems. The superior tensile properties of the two latter blending systems were accompanied by greater chain mobility of both of the NR and ACM molecules, along with a lower volume fraction of rubber in swollen gel (Vr) of the both NR and ACM phases. These changes were discussed in the light of various possibilities including curative distribution, which were affected by the accelerator type. In term of the effects of curing temperature, it was found that Vr and tensile properties of the blends did not significantly change with the temperature.
Determination of Chemical Components that Cause Mal-Odor from Natural Rubber
Authors: Hoven Vipavee P. , Rattanakaran Kesinee , Tanaka Yasuyuki
Published: February 2011

Odorous components emitted from different forms of solid natural rubber (NR) were analyzed using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) associated with head space sampling technique. The most odorous components from most samples were identified as low molecular weight volatile fatty acids (C2-C5). Other volatile organic contents verified based on characteristic ions of mass spectra included carbonyl compounds, low molecular weight compounds containing nitrogen or sulfur and aromatic compounds. The total content and composition of volatile organic compounds were directly correlated to the rubber quality and drying process. Low-grade NR samples, i.e. STR 20 from cup lumps with intense smell, had high quantity of volatile organic contents especially low molecular weight volatile fatty acids. On the other hand, high-quality rubber, i.e. deproteinized NR and STR 5L from which no smell was detected, contained only minute quantities of volatile organic contents. Aromatic components were regarded as other major odorous contents found in ribbed smoked sheet (RSS) samples. The results suggested that the odorous components were the by-products of non-rubber components which had undergone microbial breakdown during storage or thermal degradation during processing.
Gel Formation in Natural Rubber Latex: 2. Effect of Magnesium Ion
Authors: Tarachiwin L. , Sakdapipanich J. T. , Tanaka Y.
Published: February 2011

The effect of Mg2+ ions on the gel formation in fresh and commercial high ammonia natural rubber latices (FL-latex and commercial HA-latex) was analyzed from the gel content and 2+ content after treatment with (NH4)2SO4. The gel content of rubber from commercial HA-latex decreased significantly after (NH4)2SO4 treatment comparable to that of FL-latex. Long-storage commercial HA-latex containing 50% gel fraction showed no decrease in 2+ content after (NH4)2SO4 treatment. This gel fraction was not solubilized in toluene by the treatment of a proteolytic enzyme in latex or ethanol/toluene mixed solvent extraction of rubber. The 2+ content of rubber in long-storage commercial HA-latex, 0.005% (w/w rubber), decreased after treatment with (NH4)2SO4, while the same treatment showed little change on FL-latex, 0.035%. The toluene soluble fraction of these latices showed a decrease in the Mn value with an increase in the (NH4)2SO4 concentration. The gel content of FL- and HA-lattices increased with an increasing storage period in the presence and absence of (NH4)2SO4. The initial rate of increase in the gel content was slow in the case of FL-latex. These findings indicate that the gel fraction in HA-latex is partly formed by ionic crosslinks caused by 2+ ions. Whereas, the gel phase in long-storage commercial HA-latex is presumed to be a hard gel predominantly formed by covalent bonding.
Crack Growth in Twisted Rubber Disks. Part 3. Effects of Crack Depth and Location
Authors: Gent A. N. , Yeoh O. H.
Published: February 2011

A simple analysis of the fracture energy for a shallow ring crack in a twisted rubber disk is presented and compared to a linear fracture mechanics solution for a similar crack in an infinitely long cylinder. The analysis predicts that the fracture energy increases linearly with crack depth. Since a previous analysis shows that the fracture energy subsequently decreases with crack depth when the crack is deep, it follows that the fracture energy passes through a peak as it transitions from shallow crack to deep crack behavior. The transition occurs when the crack depth becomes comparable to a fraction of the disk height. The analysis is supported by the results of finite element analysis. In addition, the effects of disk size, crack location (in the middle of the cylinder vs. at the bonded ends) and material properties are also considered.
Ground Tire Rubber (GTR) Reclamation: Virgin Rubber / Reclaimed GTR (RE)Vulcanizates
Authors: Grigoryeva O. , Fainleib A. , Starostenko O. , Danilenko I. , Kozak N. , Dudarenko G.
Published: February 2011

Thermochemically partially devulcanized ground tire rubber (GTRD) was revulcanized in compositions with different virgin rubbers. Two different devulcanizing groups (mixture of softeners) with and without processing oil have been used for GTR treatment. As virgin rubbers methylstyrene/butadiene (SBR), isoprene (IR) and butadiene (BR) rubbers or their combinations were selected. They were cured by using sulfur, tetramethyl thiuram disulfide (TMTD) or peroxide based vulcanizing systems. The Rubber/GTRD (re)vulcanizates with the GTRD content from 20 to 80 wt. % have been prepared and studied. Vulcanization by sulfur system was found as preferable for IR/GTRD formulations. The best properties for BR/GTRD and SBR/GTRD vulcanizates were reached with the vulcanization system based on TMTD. The co-curing in the interphase between the GTRD particles and the surrounding rubber matrix improves the mechanical properties of (re)vulcanizates obtained. The reclaimed GTRD studied has been used successfully in standard formulations for tires instead of the part of virgin rubbers.
Online Characterization of the Effect of Mixing Parameters on Carbon Black Dispersion in Rubber Compounds Using Electrical Conductivity
Authors: Le H. H. , Ilisch S. , Jakob B. , Radusch H.-J.
Published: February 2011

The influences of mixing parameters on the carbon black dispersion can be characterized using the electrical conductivity online measured from internal mixer. As a measure for monitoring the development of carbon black dispersion, a normalized conductivity with regard to the conductivity measured at the BIT (black incorporation time) has been suggested. It is observed that in spite of different mixing parameters, the mixtures possessing the same normalized conductivity factor K/KBIT deliver the same carbon black dispersion and the same mechanical properties. Based on normalized conductivity, a deeper insight into the mixing kinetics can be provided to find an optimal mixing regime.
FTIR Spectroscopic Studies on Curing of Brominated Poly(Isobutylene-co-4-Methylstyrene)
Authors: Xie Donghang , Wang Hsien C.
Published: February 2011

The curing of brominated poly(isobutylene-co-4-methylstyrene) or BIMS with ZnO/HSt, ZnO/Zn(St)2 or Zn(St)2 was investigated using FTIR spectroscopy. Changes of carbonyl absorption were monitored by FTIR during the course of curing, which revealed a four-step curing process: 1) formation of zinc salts, 2) esterification to generate Zn-containing Lewis-acid catalysts, 3) Friedel-Crafts alkylation, and 4) post cure. It was found that for the ZnO/HSt system, the ZnO concentration had to be high enough to meet the ZnO/Br molar ratio of 0.9 for complete conversion of curing functionalities. HSt was an effective accelerator, which reduces the induction time and increases the curing rate. HSt of 2 to 3 phr was recommended to achieve optimum acceleration results. Over use of HSt would lead to dramatic reduction of crosslinking density, due to the fact that significant amounts of curing functionalities were consumed to form stearate esters instead of crosslinks. The curing with ZnO/Zn(St)2 was similar to the ZnO/HSt system but faster due to the fact that zinc salt was directly added. Zn(St)2 alone was effective to initiate a cure, but the reversion of curing was observed at high concentrations, probably due to the presence of large amount of acids, such as HSt and HBr both of which were generated during curing, and the stearate esters. Addition of ZnO eliminates the reversion through neutralization of the acids.
Tear Strength of Black-Filled Natural Rubber Crosslinked via Conventional and Efficient Sulfur Cures
Authors: Hamed G. R.
Published: February 2011

Two common types of sulfur cures for diene elastomers are so-called conventional and efficient systems. It is widely thought that the former results in higher tear strength, when vulcanizates are compared at the same crosslink density. However, using data taken from the literature, this behavior is shown to occur at higher crosslink density, while the opposite is true at lower crosslink density.
A Simple Model for Predicting Heat Aging of EPDM Rubber
Authors: Paeglis Arnis U.
Published: February 2011

Heat aging stability is a hallmark of EPDM rubber and a requirement for use in automotive, roofing and other applications. Retention of physical properties after accelerated heat aging is a typical specification for such long-term uses. This paper examines the utility of such tests in predicting results over a range of temperatures, 116 °C, 125 °C, 135 °C and 150 °C, in some cases for as long as 365 days.

A simple empirical model was developed to predict the retention of physical properties using fractional strain energy, that is, the ratio of the aged to unaged products of tensile strength and elongation at break. Characteristic rates, an Arrhenius rate relationship and activation energies were determined. This model provides a basis to predict physical property changes over a wide range of temperatures and times, as well as for considerations of equivalent heat aging tests and use in different applications.
Adhesion Strength Evaluation via Constrained Blister Test I. SIBS / Polystyrene and Polypropylene
Authors: Mousa A. M. , Mekewi M. A. , El-Mosallamy E. S. H. , Baer E.
Published: February 2011

Adhesion of Styrene-Isobutylene-Styrene (SIBS) triblock copolymers to polystyrene and polypropylene was investigated at controlled ratios and molecular weights of the SIBS's polystyrene. Comparative studies of the cohesive and adhesive strengths were carried out using a carefully designed system based on monitoring a constrained blister growth. The acquired data was simulated mathematically to express adhesion main parameters of the energy of interfacial adhesion (γ) and dissipation coefficient (b). Polystyrene content of 30–40% in the SIBS exhibited maximum interfacial adhesion energy (γ) and, consequently, the highest adhesion strength compared to other SIBS samples of other polystyrene ratios. ATR-FTIR spectroscopic analysis and scanning electron microscopy (SEM) were carried out on both the substrate and the film surfaces before adhesion and after failure to assist understanding the failure process. Interpretation of SEM microphotographs and the ATR-FTIR confirmed the process to be adhesion in nature rather than cohesion.
Synthesis of Cyclic Polysulfides and their Properties as Curing Agents
Authors: Choi Wonmun , Matsumura Tomoyuki
Published: February 2011

The reactions of dichloroalkanes and sodium tetra-sulfide (Na2S4) were carried out in a mixture of water and toluene to produce corresponding cyclic polysulfides and polysulfide polymer. The low molecular weights of cyclic sulfides were obtained by the reaction at 90 °C, while the high molecular weight of polysulfide polymer was obtained by the reaction at 50 °C. GPC chromatograms and Mass spectra revealed that the structures of cyclic polysulfide were 1:1, 2:2, and 3:3 adducts of dichloroalkane and sodium tetra-sulfide. The mechanical properties of vulcanized NR at 148 °C with cyclic sulfides were similar to that with sulfur. However, both tensile strength and elongation at break of vulcanized NR at 170 °C with cyclic sulfides are much higher than that with sulfur. The aging properties of vulcanized NR at 148 °C or 170 °C with cyclic polysulfides indicate better stability.
Factors that Affect the Fatigue Life of Rubber: A Literature Survey
Authors: Mars W. V. , Fatemi A.
Published: February 2011

Many factors are known to influence the mechanical fatigue life of rubber components. Four major categories of factors are reviewed here: the effects of mechanical loading history, environmental effects, effects of rubber formulation, and effects due to dissipative aspects of the constitutive response of rubber. For each category, primary factors are described, and existing literature is presented and reviewed. Rubber's fatigue behavior is extremely sensitive to both the maximum and minimum cyclic load limits. Other aspects of the mechanical load history are also discussed, including the effects of static loaded periods (“annealing”), load sequence, multiaxiality, frequency, and loading waveform. Environmental factors can affect both the short and long term fatigue behavior of rubber. The effects of temperature, oxygen, ozone, and static electrical charges are reviewed. A great range of behavior is available by proper manipulation of formulation and processing variables. Effects of elastomer type, filler type and volume fraction, antidegradants, curatives, and vulcanization are discussed. The role of dissipative constitutive behavior in the improvement of fatigue properties of rubber is also reviewed. Four distinct dissipative mechanisms are identified, and their effects on fatigue behavior are described.
Addressing Durability of Rubber Compounds
Authors: Huntink N. M. , Datta R. N. , Noordermeer J. W. M.
Published: February 2011

The developments on long-term protection of rubber against aerobic aging are reviewed. Although conventional antidegradants such as N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD) and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) are still the most widely used antidegradants in rubber, there is a trend and demand for longer-lasting and non-staining products. The relatively low molecular weight (MW) antioxidants have undergone an evolutionary change towards higher molecular weight products with the objective to achieve permanence in the rubber polymer, without loss of antioxidant activity. In the last two decades, several approaches have been evaluated in order to achieve this objective: attachment of hydrocarbon chains to conventional antioxidants in order to increase the MW and compatibility with the rubber matrix; oligomeric or polymeric antioxidants; and polymer bound or covulcanizable antioxidants. The disadvantage of polymer bound antioxidants was tackled by grafting antioxidants on low MW polysiloxanes, which are compatible with many polymers. New developments on antiozonants have focused on non-staining and slow migrating products, which last longer in rubber compounds. Several new types of non-staining antiozonants have been developed, but none of them appeared to be as efficient as the chemically substituted p-phenylenediamines. The most prevalent approach to achieve non-staining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The disadvantage of this approach, however, is the complicated mixing procedure needed to ensure that the required small polymer domain size is achieved.
Metallocene Catalyzed Ethylene/Alpha Olefin Copolymers Used in Thermoplastic Elastomers
Authors: Walton Kim L.
Published: February 2011

Thermoplastic elastomers (TPEs) continue to be a focus of significant research as well as commercial development in the rubber industry since their origin over forty years ago. A wide variety of TPEs exist today. Ethylene copolymer and terpolymer based elastomers continue to play an increasing role in this arena. New ethylene copolymers and terpolymers, based upon metallocene catalysis, have further diversified the TPE portfolio. Compounders are now using these new elastomers as modifiers for existing TPEs as well as the principle elastomer in new TPEs
Influence of Electron Beam Irradiation as One of the Mixed Crosslinking Systems on the Structure and Properties of Nitrile Rubber
Authors: Vijayabaskar V. , Costa Francis Rene , Bhowmick Anil K.
Published: February 2011

The influence of electron beam on the nitrile rubber vulcanizates at varying levels of sulfur is reported. A higher crosslinking density, reduced elongation at break, increased modulus and tensile strength have been observed for the irradiated rubbers, as compared to the control rubber vulcanizates. The vulcanizate containing higher amount of sulfur, tends to form more crosslinkages on impinging with electron beam. This behavior is explained by the formation of monosulphidic linkages and is ascertained with the help of IR analysis (ATR mode), solid-state NMR analysis and chemical probe treatments of the irradiated vulcanizates. The implausible nature of these mixed crosslinking systems with electron beam as an additional crosslinker is explained with a kinetic model using steady state principle. A mechanistic path is suggested for explaining the structural changes on irradiation of these vulcanizates, which is supported by this model.
Model Reaction of Polysulfide with Olefin
Authors: Hergenrother William L. , Hilton Ashley S. , Lin Chenchy J.
Published: February 2011

A model polysulfide, t-butyl polysulfide (TBPS) and an olefin, cyclododecene (CDD), were used to study the reactivity of polysulfanes in silica filled rubbers. The TBPS has a similar sulfur rank and distribution as bis (3-triethoxysilylpropyl) tetrasulfide (TESPT) without the complication of reactivity of the triethoxysilyl group that would cause a loss of soluble components of the reactants and products by hydrolytic coupling. Thermal reaction between the polysulfide and olefin was investigated by following the TBPS loss in the CDD solution at 171 °C as a function of time. The loss of TBPS and the formation of reaction products during heating were followed, identified and quantified using HPLC. These include attachment of t-butyl sulfide group from the TBPS to CDD, coupling between CDD, and redistribution of the sulfur rank. It was found that after six minutes, less than 2 weight % of the sulfur in the TBPS was utilized to couple CDD molecules. Since these thermal conditions are more severe than what a rubber compound is normally subjected to, this sulfur coupling would not be expected to give a vulcanization problem during mixing. The model reaction was also followed in the presence of added peroxide or typical vulcanization ingredients. The strongest catalytic effect was seen with N-cyclohexyl-2-benzothiazolesulfenamide and zinc oxide.
Investigation of Mechanical and Fracture Mechanical Properties of Elastomers Filled with Precipitated Silica and Nanofillers Based upon Layered Silicates
Authors: Reincke Katrin , Grellmann Wolfgang , Heinrich Gert
Published: February 2011

The aim of this paper is to show possibilities of experimental methods of polymer diagnostics and fracture mechanics for quantitative characterization of crack initiation and propagation properties of elastomeric materials. At first, a general overview of methods of technical fracture mechanics is given. This is followed by a short discussion of some possibilities for determination of tearing energy T for elastomers. In the main part, results of various mechanical and fracture mechanics experiments on filled natural rubber vulcanizates are shown. The vulcanizates were filled with different contents (5–70 phr) of two filler types. The fillers were precipitated silica and an organic-modified nano-disperse layered silicate. Th aim of the experiments was to prove possibilities of several fracture mechanics testing methods for quantifying the influence of the filler content, filler type and additionally the specimen direction on the deformation and fracture behavior. Tear-analyzer results were used to assess the crack propagation behavior under fatigue-like loading conditions. Furthermore, instrumented tensile-impact tests were performed for the characterization of the crack resistance of the materials under impact-like loading conditions. To obtain information about the initiation and propagation of a stable crack, a quasi-static fracture mechanics test was applied, and crack resistance curves were recorded. Here, specimens with various thicknesses were investigated. Additionally, conventional tear tests were done and the results were compared to that of the fracture mechanics test. Generally, it was found that all methods are useful for the description of the fracture properties. Furthermore, the fracture behavior is influenced positively especially by high filler contents. Strong differences of several parameters were found depending on the filler type. Another important result is that again differences were found between the crack initiation and propagation behavior.
Carbon Black Dispersion Measurement in Rubber Vulcanizates via Interferometric Microscopy
Authors: Smith Archie P. , Aybar Toni L. , Magee Ricky W. , Herd Charles R.
Published: February 2011

A new method for characterizing the carbon black dispersion in rubber compounds is introduced. This technique is based on interferometric microscopy (IFM) and utilizes the interference fringes between in-phase light beams reflected from the rubber sample and a smooth reference surface to measure the three-dimensional surface topography. The peaks and valleys present on the fresh-cut surface are representative of the carbon black agglomerates and are used to characterize the dispersion. A series of samples with different base rubbers and varying dispersion levels were created and characterized by both light microscopy and IFM. These results were used to generate a universal dispersion index based on the IFM data that correlates well with the LM dispersion index values. In addition, three-dimensional peak statistics were obtained from the IFM data and used to provide additional information about the carbon black agglomerate distribution. This data can be used for a more complete understanding of the compound behavior as a function of the carbon black dispersion and agglomerate distribution.
A Comparison of the Hart-Smith Model with Arruda-Boyce and Gent Formulations for Rubber Elasticity
Authors: Chagnon G. , Marckmann G. , Verron E.
Published: February 2011

The present paper demonstrates that the Hart-Smith constitutive model and the more recent Arruda and Boyce eight chains and Gent constitutive models are closely related. The ability of these three models to predict both small and large strain responses of rubbers is highlighted and equations that relate their material parameters are established.
A Two-Step Emulsion Polymerization Process Catalyzed by an Organic Diperoxide
Authors: Bauer R. F.
Published: February 2011

An emulsion polymerization process is described which consists of consecutively polymerizing at least two olefinic monomers using an organic diperoxide with two independently functioning peroxy groups, namely 2,5-dimethyl-2-t-butylperoxy-5-hydroxy hexane.

In the first polymerization step, the hydroperoxide group is activated by a redox reaction at low temperatures without decomposing the t-butyl peroxide portion of the initiator molecule. After charging fresh monomer, the t-butyl peroxide can then be thermally activated to initiate a second-stage polymerization reaction.

This polymerization process employs conventional emulsion polymerization technology. It yields polymeric product with unique physical properties. Polymers with butadiene monomer in the first polymerization step, followed by styrene polymerization in the second step, resemble SBS tri-block polymers. They are thermoplastic, highly resilient and of good strength at high ultimate elongations. The consecutive polymerization of butadiene and acrylonitrile yields elastomers with a superior balance of low-temperature flexibility and resistance to swelling in organic solvents, when compared with random NBR copolymers of equivalent chemical composition. Combinations of butadiene and styrene in the first polymerization stage followed by styrene/acrylonitrile polymerization in the second, yield transparent ABS polymers with superior low-temperature impact resistance.

Reference is also made to the polymerization of additional vinyl monomers.
Correlation Between Road Wear of Tires and Computer Road Wear Simulation Using Laboratory Abrasion Data
Authors: Grosch K. A.
Published: February 2011

Any laboratory abrasion method has to take account of the well known fact that the ranking and wear rating of tire tread compounds depend strongly on the testing conditions. The severity of road tests, particularly when carried out with customer vehicles is not well defined. Any result obtained in this way is a spot reading which contains no information about its general validity.

A road wear computer program was designed which is able to simulate a very wide range of road wear testing severities and the effect which they have on achievable mileage and wear rating of tread compounds. The program uses the laboratory abrasion test system designed to be used with the Laboratory Abrasion Tester designated as LAT 100. It is shown that good agreement is obtained with actual road test results, not only for the rating of compounds but also for the achieved mileages.
Study on Parameters Affecting the Morphology Development of Dynamically Vulcanized Thermoplastic Elastomers Based on EPDM/PP in a Co-Rotating Twin Screw Extruder
Authors: Sararoudi S. Shafiei , Nazockdast H. , Katbab A. A.
Published: February 2011

The morphology development of dynamically vulcanized thermoplastic elastomers (TPVs) based on EPDM/PP in a modular intermeshing co-rotating twin screw extruder was studied. Effects of the blend composition and screw speed were considered. The morphological studies were carried out on the cryogenically fractured surface of the samples using Scanning Electron Microscopy (SEM) technique. The flow behavior and melt viscoelastic properties of the samples were also investigated by using Rheometric Mechanical Spectrometer (RMS). The SEM results from TPV samples produced in the twin screw extruder showed a matrix-disperse type morphology similar to those reported for the TPV samples prepared in an internal mixer. The dynamic vulcanization process imposed on the molten blends resulted in a remarkable increase in the steady state torque of the extruder whose extent was found to be dependent upon the EPDM content and screw speed. These results were explained in terms of an agglomerate structure formed between the cured rubber particles. The TPV samples, in particular the samples containing 60% of EPDM, showed a pronounced viscosity upturn and strong elastic modulus (G′) at low frequency range. It was demonstrated that these results in conjunction with the results of relaxation time distribution H(λ) of the samples can provide a great insight into understanding the role of the blend composition and the processing variables on morphology development in the TPV samples in the co-rotating twin screw extruder.
Experimental Study and Simulation of Interface Development and Penetration in Two-Component Transfer Molding of Rubber Compounds
Authors: Li C. T. , Isayev A. I. , Warley R. L.
Published: February 2011

Simulation and experimental studies of pressure-controlled sequential transfer molding of two SBR rubber compounds under isothermal condition have been carried out to obtain a two-layered sandwich structure. One SBR compound, intended for the skin, is first laid up in the cavity; and another SBR compound, intended for the core, is used for transfer. The SBR is subjected to pressure in order to penetrate into the skin and push the layup to fully fill the cavity. The obtained moldings have an encapsulated skin/core sandwich structure. Two material combinations with different viscosity ratios have been studied. The rheological interaction of skin/core components and its effect on the penetration behavior and interface shape have been investigated. The influence of processing conditions, such as the volume fraction transferred and pressure, is elucidated. From the experiment and simulation it is found that the penetration and the interface development are significantly affected by the rheological properties of the compounds and the volume fraction transferred. At the same time, the pressure imposed during transfer molding is found to have little effect on the interface development at a constant volume fraction transferred.
Natural Rubber-g-Glycidyl Methacrylate/Styrene as a Compatibilizer in Natural Rubber/PMMA Blends
Authors: Suriyachi P. , Kiatkamjornwong S. , Prasassarakich P.
Published: February 2011

Graft copolymer of glycidyl methacrylate and styrene onto natural rubber latex was synthesized by emulsion polymerization using cumene hydroperoxide and tetraethylene pentamine as a redox initiator. The effects of initiator and monomer concentration, reaction temperature and time on grafting efficiency and monomer conversion were investigated. The dynamic mechanical properties and morphology of grafted natural rubber were studied. The grafted natural rubber product could be used as a compatibilizer for natural rubber/PMMA blends. The mechanical properties such as tensile strength, elongation at break, tear strength, hardness, and impact energy were evaluated as a function of grafted natural rubber content. A good compatibility of natural rubber/PMMA blends was obtained at 5–10 phr of grafted natural rubber content. The fracture surface examined by scanning electron microscopy showed that the grafted natural rubber acted as an interfacial agent and gave a good adhesion between the two phases of the blend.
Improved Differential Scanning Calorimetric Measurement Method for the Small Reaction Heat Capacities
Authors: Danes Florin , Garnier Bertrand
Published: February 2011

Heat capacities of the different rubber states are important features for the engineering calculation of rubber manufacturing. The heat capacity change Δcp due to the vulcanization process has been measured with a differential scanning calorimeter (DSC) only after reducing the standard error of a Δcp measurement under 5 J kg−1 K−1. For this purpose, we used sealed (up to 150 bar) DSC sample pans which avoid mass losses. Heat capacities before and after vulcanization were measured on the same samples using special DSC procedure and reversible thermal effects due to rubber components were corrected. For natural rubber vulcanized with sulfur at t=40…110 °C we found, in J/(kg S)−1 K−1: Δcp=76+11 t, whatever the temperature vulcanization between 100 and 160 °C.
AFM Study of Rubber Compounds
Authors: Wang C. C. , Donnet J. B. , Wang T. K. , Pontier-Johnson M. , Welsh F.
Published: February 2011

A series of rubber compounds filled with carbon blacks and silica has been studied by atomic force microscopy (AFM). The microdispersion of carbon black aggregates in rubber compounds can be clearly observed. The surface morphology of worn treads after road testing studied by AFM is also reported.
The Payne Effect in Double Network Elastomers
Authors: Wang J. , Hamed G. R. , Umetsu K. , Roland C. M.
Published: February 2011

Double network elastomers were prepared by curing under strain previously-crosslinked natural rubber or styrene-butadiene copolymer. The rubbers were reinforced with carbon black, so that the conventional (singly-cured) materials exhibited a substantial Payne effect, reflecting agglomeration of the filler particles. This effect was much reduced in the double networks - the storage modulus varied more weakly with strain amplitude, and the mechanical hysteresis was substantially smaller. Comparable results were obtained for dynamic mechanical measurements employing different test geometries; that is, the effect is independent of the direction of the strain relative to the orientation of the double network. These results indicate that deformation during the imposition of a second network disrupts the carbon black agglomerates, and this deflocculated structure is stabilized by the second crosslinking. Thus, double network processing is a general means to lower the hysteresis of filled rubbers.
Response of Elastomeric Blocks During Large Compression Strains
Authors: Patenaude K. J. , Tao Z. , Mead J. L. , Stacer R. G. , Rodriguez G.
Published: February 2011

An experimental investigation has been conducted to evaluate the response of rubber blocks under large compressive loadings. Quantitative measurements of the nonlinear behavior of two rubber compounds were tested over compressive strains ranging from 17 to 74 percent. Three distinct phenomena were observed in the deformation behavior of both materials. The first was a dramatic increase in contact area (over 130 percent) between the rubber and the platens, beginning at strains above approximately 33 percent. This increased surface area is used to provide stress corrections in several quantitative models, and appears to physically represent a rolling flow phenomenon, similar to fountain flow in observed in polymer melts. The second and third phenomena are associated with a nonlinear normal stress distribution across the sample's surface. These two phenomena are stress maxima and minima associated with stress singularities predicted by nonlinear elastic models. Deviations in stresses across the specimen surface of up to a factor of four are reported. It is concluded that appropriate constitutive equations describing these phenomena are required before meaningful predictive models can be developed.
New Technique for Measurement of Rubber-to-Metal Bond Failure
Authors: Lawrence C. C. , Lake G. J. , Thomas A. G.
Published: February 2011

A new test, involving combined pure and simple shear, that can produce failure very close to the interface between the rubber and the bonding agent in a rubber-to-metal joint, is described. The test allows changes in the position of the tip of the de-bonded region to be followed with time, enabling the failure rate to be determined. The latter can be related to the strain energy release rate so that a fracture mechanics based analysis can be applied. Failure characteristics can be correlated with features of the de-bond surface. The results suggest that even when failure is very close to the interface, the measured strength is similar to that of the rubber.
Dynamic Mechanical Properties of High Density Polyethylene and Nitrile Rubber Blends: Effect of Blend Ratio, Compatibilization and Filler Incorporation
Authors: George Josephine , Neelakantan N. R. , Varughese K. T. , Thomas Sabu
Published: February 2011

Blends of high density polyethylene (HDPE) and acrylonitrile butadiene rubber (NBR) were prepared by a melt blending technique. Dynamic mechanical analysis revealed that elastic modulus has a strong dependence on blend ratio. Loss factor peaks increase with increase in rubber content. Pure components exhibit single Tg whereas two Tgs can be observed in the blends indicating incompatibility between the constituents. Loss modulus data also give similar information. The addition of compatibilizer has only a marginal effect on tan δ peak corresponding to the transitions in NBR. The elastic modulus values of the compatibilized blends are slightly higher than that of incompatible blends. In dynamically vulcanized blends the Tg due to α-relaxation of NBR is increased in blends containing a high concentration of rubber phase. In filled blends the elastic modulus showed significant increase over unfilled system. Also, the damping factor is enhanced by filler incorporation indicating that such materials could find application in vibration dampers. The suitability of various theoretical models in predicting the blend moduli is examined. The Takayanagi model fits well with the experimental data in unfilled blends.
Accelerated Aging of Tires, Part II
Authors: Baldwin John M. , Bauer David R. , Ellwood Kevin R.
Published: February 2011

The purpose of this research is to determine the conditions whereby a new tire can be artificially aged in an accelerated manner, in order to duplicate the actual mechanism of chemical aging observed in field-aged tires. The ultimate goal of the study is to age tires to a desired level, say equivalent to 4 years old, and then test the tires in various durability, high speed and performance tests. The first step was to determine the aging characteristics of field-aged tires, which has been the subject of another paper. For this work, tires were statically aged in ovens. Tires were mounted, inflated, then oven aged continuously at temperatures ranging from 40 °C to 100 °C for various periods of times (from 2 weeks to 12 weeks). Both air and a 50/50 blend of N2/O2 were used as the inflation media. The tires were then dissected and analyzed for tensile and elongation properties of the rubber at the end of the steel belts. The results show that as the temperature was increased from 40 °C to 70 °C, the property degradation of the steel belt rubber accelerated. Shift factors were determined based on time-temperature superposition and the results analyzed by using the Arrhenius methodology. The oven results were similar to the field data, meaning the chemical aging mechanism was the same for both. As the oven temperature increased above 70 °C, degradation reactions began to dominate and the apparent aging mechanism changed.
A Review of Rubber Oxidation
Authors: Li Gui-Yang , Koenig J. L.
Published: February 2011

The aging of rubber caused by oxidative degradation leads to the deterioration in the physical and mechanical properties of vulcanized rubbers. In an effort to improve the oxidative stability of rubbers and elastomers, considerable amount of work has been carried out over the past 50 years (especially in the most recent 5 years) in order to understand degradation modes and effects in rubber due to the action of oxygen and ozone in the air. Different mechanisms have been proposed to interpret the experimental data relative to the oxidation of rubber. The diffusion limited theory has been widely used in the literature and verified by many experiments. Various instrumental techniques have been utilized to characterize the oxidation and degradation and their mechanisms in rubber compounds. Recently, FTIR imaging has demonstrated a unique combination of spectral and spatial resolution which allows not only the identification of the oxidation products but also their spatial distribution from the oxygen penetrating surfaces. This critical review will cover the major developments in our understanding of the oxidation of rubbers.
Steel Tire Cord-Rubber Adhesion, Including the Contribution of Cobalt
Authors: Fulton W. Stephen
Published: February 2011

This review will discuss the mechanisms that are responsible for the adhesion between brass-coated steel tire cord and rubber. In particular, the role of cobalt as an adhesion promoter and how it influences the stability of the bond between the steel tire cord and rubber are examined. Some of the techniques by which the morphology of the interfacial layers has been investigated will be discussed, along with a brief review of the latest bonding mechanisms.
Role of Compatibilization in Recycling Rubber Waste by Blending with Plastics
Authors: Mangaraj D.
Published: February 2011

Blending ground rubber with thermoplastic and thermoset polymers is a very cost effective and efficient method for recycling rubber waste. However it is important for vulcanized rubber particles and the thermoplastic matrix to adhere to each other to form co-continuous type morphology to provide necessary strength properties. The paper discusses the principles underlying compatibilization and discusses the three types, namely mechanical, non-reactive and reactive compatibilization. Past work in compatibilizing ground rubber from tire waste (GRT) with thermoplastics has been reviewed and the use of compatibilized GRT/ plastic products in the preparation of a variety of value-added products, including thermoplastic elastomers has been discussed.
Continuous Ultrasonic Treatment of Uncured and Sulfur Cured SBR: Effect of Styrene Content
Authors: Isayev A. I. , Kim S. H. , Feng Wenlai
Published: February 2011

Unvulcanized and vulcanized SBR samples with styrene content of 18 and 23.5% were used to investigate the effect of ultrasound treatment on their structural characteristics. Gel fraction and crosslink density of gel are measured. Molecular weight and molecular weight distribution of sol are studied to determine the level of degradation of the macromolecular chain in ultrasonically treated unvulcanized and vulcanized rubbers. It is shown that the weight and number average molecular weight of sol in devulcanized SBR is, respectively, lower and higher in the samples having higher styrene content. Ultrasonic treatment of virgin unvulcanized SBR causes generation of gel along with its main chain modification due to the competition between chain scission and crosslinking. The competitive reactions taking place during this treatment are discussed. It was found that the intermolecular bonds in SBR vulcanizates containing higher styrene content are easier to break. The structural characteristics of devulcanized SBR rubber were simulated using the Dobson-Gordon theory of rubber network statistics. A fairly good agreement between experimental data and theoretical prediction on normalized gel fraction vs. normalized crosslink density was achieved. The simulation of devulcanized SBR rubber indicated that the rate of crosslink rupture is much higher than that of main chain. The styrene content in SBR rubber does not affect kp/kα substantially.
Asphalt Modified by Partially Hydrogenated SBS Tri-Block Copolymers
Authors: Vargas M. A. , Chávez A. E. , Herrera R. , Manero O.
Published: February 2011

This work examines the modification of asphalt with hydrogenated poly (styrene-butadiene-styrene) copolymer containing different amounts of butadiene and ethylene-co-butylene. The polymer composition can be described generically as poly (styrene−[(butadiene)1−x−(ethylene−co−butylene)x]−styrene), where x is the hydrogenated fraction of the molecule. These hydrogenated (SBEBS) copolymers were produced by in-situ hydrogenation following a Ziegler-Natta catalytic reaction of poly (styrene-butadiene-styrene) tri-block copolymers (SBS), which were previously synthesized by anionic polymerization. Control over the hydrogenation time produces SBEBS polymers with various degrees of saturation of the polybutadiene block, as characterized by FTIR, HNMR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Polymer-modified asphalts (PMA) were obtained by a high-temperature mixing process with AC-20 asphalt (Salamanca, Mexico) and SBS or SBEBS copolymers. PMA samples were characterized before and after high-temperature storage tests by fluorescence microscopy, rheometry, and mechanical tests. Results indicate that PMA obtained from SBEBS contain a polymer matrix with well-dispersed asphalt rich phase, with improved mechanical and thermal stability over those PMA produced with SBS. Compatibility between SBEBS and the aromatic fraction of maltenes can explain the dispersion of the polymer in asphalt and the enhanced properties.
Reactions of Radicals in Filled Rubber Compounds: II. Generation and Subsequent Reactions of Radicals Upon Deformation
Authors: Kawakubo Makoto , Tsunoda Katsunori , Yajima Hirofumi , Ishii Tadahiro , Kaidou Hiroyuki , Ahagon Asahiro
Published: February 2011

Effect of stretching on oxidative crosslinking of a carbon black filled IR vulcanizate at a normal temperature was studied by means of ESR and crosslink density measurements. Upon deformation, ESR intensity increased and crosslink density decreased, indicating scission of load supporting bonds generating free radicals. Bond scission increased with increasing strain. Resting after deformation, the ESR intensity decayed steadily following simple combination of first order and second order kinetics. The decay was overwhelmingly caused by first order reactions, which were considered to be irrelevant to crosslinking. On the other hand, crosslink density increased during resting. The results strongly suggested that ESR observed the radicals at the surface of the carbon black filled rubber, while crosslink density evaluated the bulk property. The crosslink density increase during resting outweighed the reduction due to deformation. Deformation accompanied by radical generation apparently accelerated oxidative crosslinking.
Wear Behavior of Silica Filled Tire Tread Compounds by Various Rock Surfaces
Authors: Nayek Suprakash , Bhowmick Anil K. , Pal Samir K. , Chandra Arup K.
Published: February 2011

Wear of silica filled tire tread compounds made from natural rubber (NR) and styrene butadiene rubber (SBR) against various rock surfaces at different normal loads and frictional work was investigated. The rocks chosen, i.e. granite, quartzite, limestone and shale, had variation in hardness and chemical composition. Wear, V, increased with normal load, N and frictional work, Fw, and these were related by V=βNα and V=k Fw n, where β,α,k and n were constants and dependent on the nature of the abraded surface and the rubber. The rate of wear of SBR was found to be much lower than that of NR against all rock surfaces. All the results could be explained with the help of dynamic co-efficient of friction, frictional work and structural changes during abrasion. The rate of wear as well as the dynamic coefficient of friction decreased with silica filler loading up to certain loading and then increased. These were 60 phr silica for NR and 70 phr silica for SBR. The surfaces of NR and SBR when abraded against different rock surfaces became tarry on prolonged abrasion. The debris were oily and aggregated for NR compound and were particulate for SBR compound. The debris and the ridges were analyzed by an image processing technique.
The Difference between Iodine Number and Nitrogen Surface Area Determinations for Carbon Blacks
Authors: Donnet J. B. , Santini A. , Maafa D. , Balard H. , Padella F. , La Barbera A.
Published: February 2011

The iodine number furnishes surface area values in disagreement with the NSA technique in the case of disordered carbon i.e., lower than NSA in case of high oxygen content (more than 2%), but higher for low oxygen content (less than 1%). Because carbon blacks are solids which exhibit graphitic structure, some milled graphite samples, were taken as model materials and analyzed. Surface area was determined by using both NSA and N≩I2 techniques, and the difference between the results given by the two techniques were observed and related to the microstructure, which was analyzed by using X-ray diffraction, Raman spectroscopy, and the oxygen content was measured by using elementary analysis. Two different models of iodine adsorption have been proposed, respectively, for the graphitic parts of the graphite grains and for the disordered part of the grains. An analytical relationship between the differences of iodine and nitrogen surface area values, microstructure and oxygen content was proposed and successfully tested. The same relationship was applied to some commercial and experimental carbon black with good results.