bluuebunny/crossref_metadata_2025 huggingface dataset:
Quality or decomposer efficiency – which is most important in the temperature response of litter decomposition? A modelling study using the GLUE methodology
Authors: Wetterstedt J. Å. M. , Ågren G. I.
Published: February 2011

Abstract. We still lack full mechanistic understanding of how the temperature history affects the future decomposition rate of litter and soil organic matter. To explore that, we used the GLUE modelling framework together with the Q-model and data from a needle litter incubation experiment to compare a differential temperature response of litter qualities to a temperature-dependent decomposer efficiency. The needle litter incubation was a full factorial design with the initial and final temperatures 5, 15 and 25 °C. Samples were moved from the initial to the final temperature when approximately 12% of the initial carbon had been respired and the experiment terminated when an additional 12% had been lost. We used four variations of the Q-model; the litter was described as having one or two initial quality values and the decomposer efficiency was either fixed or allowed to vary with temperature. All variations were calibrated with good fits to the data subsets with equal initial and final temperatures. Evaluation against temperature shift subsets also showed good results, except just after the change in temperature where all variations predicted a smaller response than observed. The effects of having one or two initial litter quality values (fixed decomposer efficiency) on end-of-experiment litter quality and respiration were marginal. Letting decomposer efficiency vary with temperature resulted in a decrease in efficiency between 5 and 15 °C but no change between 15 and 25 °C and in substantial differences in litter quality at the end of the initial incubation in response to incubation temperature. The temperature response of decomposition through temperature dependent decomposer efficiency proved, therefore, to be more important than the differential response to different substrate qualities. These results suggests that it may be important to consider other factors (e.g. microbial efficiency, changing substrate composition) than the temperature sensitivity coupled to substrate quality when evaluating effects of temperature changes on soil organic matter stability.
Identification of earthquake precursors in the hydrogeochemical and geoacoustic data for the Kamchatka peninsula by flicker-noise spectroscopy
Authors: Ryabinin G. V. , Polyakov Yu. S. , Gavrilov V. A. , Timashev S. F.
Published: February 2011

Abstract. A phenomenological systems approach for identifying potential precursors in multiple signals of different types for the same local seismically active region is proposed based on the assumption that a large earthquake may be preceded by a system reconfiguration (preparation) on different time and space scales. A nonstationarity factor introduced within the framework of flicker-noise spectroscopy, a statistical physics approach to the analysis of time series, is used as the dimensionless criterion for detecting qualitative (precursory) changes within relatively short time intervals in arbitrary signals. Nonstationarity factors for chlorine-ion concentration variations in the underground water of two boreholes on the Kamchatka peninsula and geacoustic emissions in a deep borehole within the same seismic zone are studied together in the time frame around a large earthquake on 8 October 2001. It is shown that nonstationarity factor spikes (potential precursors) take place in the interval from 70 to 50 days before the earthquake for the hydrogeochemical data and at 29 and 6 days in advance for the geoacoustic data.
Comment on "Another look at climate sensitivity" by Zaliapin and Ghil (2010)
Authors: Roe G. H. , Baker M. B.
Published: February 2011

Abstract. Zaliapin and Ghil (hereafter, ZG) claim that the linearity of the climate feedback model in Roe and Baker (2007) (hereafter, RB) invalidates our derivation of the well-known skewed shapes of published probability distributions (pdfs) of climate sensitivity. We show here that linearity is fully justified. Nonlinearity could be of some importance only if the focus is on exotic and improbable events, which appear to be the focus of ZG, instead of the sensitivity pdfs, which were the focus of RB.
Reply to Roe and Baker's comment on "Another look at climate sensitivity" by Zaliapin and Ghil (2010)
Authors: Zaliapin I. , Ghil M.
Published: February 2011

Abstract. G. H. Roe and M. B. Baker (hereafter R&B) claim that analysis of a global linear approximation to the climate system allows one to conclude that the quest for reliable climate predictions is futile. We insist that this quest is important and requires a proper understanding of the roles of both linear and nonlinear methods in climate dynamics.
3-D thermo-mechanical laboratory modelling of plate-tectonics
Authors: Boutelier D. , Oncken O.
Published: February 2011

Abstract. We present an experimental apparatus for 3-D thermo-mechanical analogue modelling of plate-tectonics processes such as oceanic and continental subductions, arc-continent or continental collisions. The model lithosphere, made of temperature-sensitive elasto-plastic with softening analogue materials, is submitted to a constant temperature gradient producing a strength reduction with depth in each layer. The surface temperature is imposed using infrared emitters, which allows maintaining an unobstructed view of the model surface and the use of a high resolution optical strain monitoring technique (Particle Imaging Velocimetry). Subduction experiments illustrate how the stress conditions on the interplate zone can be estimated using a force sensor attached to the back of the upper plate and changed because of the density and strength of the subducting lithosphere or the lubrication of the plate boundary. The first experimental results reveal the potential of the experimental set-up to investigate the three-dimensional solid-mechanics interactions of lithospheric plates in multiple natural situations.
Lithiated Thiaacetals as Initiators for Living Anionic Polymerization of Diene Elastomers: Polymerization and Compounding
Authors: Hogan Terrence E. , Yan Yuan-Yong , Hergenrother William L. , Lawson David F.
Published: February 2011

Polybutadiene and poly(butadiene-co-styrene) elastomers were prepared in high conversions using 2-lithio-2- methyl-1,3-dithiane as the initiator. Polymers were readily prepared with a polydispersity index (PDI) of 1.05 to 1.26 and a Mn of up to 208 kg/mol. The replacement of the 2-methyl substituent with phenyl, trimethylsilyl or 4-dimethylamino phenyl also gave active initiators that incorporated at the head of the chain. However, initiation rates appeared to vary somewhat with the structure of the initiators. The polymerizations obtained are in all cases controlled and apparently living with the live chain ends capable of further reactions. The initiators could be generated prior to addition to the polymerization mixture or by an in-situ procedure. Model studies gave evidence that the dithiane chain end can be opened under cure conditions and react with unsaturation present in the polymer chain. Several of the product polymers were found to impart improved hysteresis to carbon and silica-filled rubbery vulcanizates possibly through an endlinking mechanism.
Composition of Color Substances of Hevea Brasiliensis Natural Rubber
Authors: Sakdapipanich Jitladda , Insom Kittipong , Phupewkeaw Nataphon
Published: February 2011

It is accepted that NR gives naturally occurring color, which restrict many applications such as light-color products. Therefore, characterization of color substances presenting in NR is very useful to develop the certain methodology to eliminate them completely or partly from NR in the future. In this work, an attempt was made to purify and characterize the color substances extracted from various fractions of Hevea rubber latex by certain methods, using high-resolution structural characterization techniques. It was found that the content of color substances extracted from fresh latex (FL), rubber cream, bottom fraction (BF), Frey Wyssling (FW) particles and STR 20 were different. Based on the high-resolution spectroscopic analyzes, it was found that the color substances extracted from NR were composed of carotenoids, tocotrienol esters, fatty alcohol esters, tocotrienols, unsaturated fatty acids, fatty alcohols, diglyceride and monoglyceride. The results will be useful for rubber-technologist to identify the origin to make obnoxious color in natural rubber, especially in some applications which are restricted by such the color.
Fiber Structure and Mechanical Properties of Electrospun Butyl Rubber with Different Types of Carbon Black
Authors: Threepopnatkul P. , Murphy D. , Mead J. , Zukas W.
Published: February 2011

Breathable butyl rubber non-woven mats have been successfully produced by the electrospinning technique, providing a fibrous membrane with controlled porosity and surface area. These properties are directly related to the barrier properties of the product, including water vapor transmission, air flow resistance, aerosol resistance, and the transportation of chemical vapors. Butyl rubber is also known as a highly chemical resistant elastomer material, which can be used for applications requiring high elongation. The use of carbon black filled elastomers provides the ability to tailor the properties, such as processability, mechanical properties, and barrier properties through proper selection of carbon black type and loading. In this work, the structure and mechanical properties of electrospun butyl rubber non-woven mats were investigated using a series of carbon black types with variation in particle size and structure. Fiber diameter decreased with decreasing particle size and increasing carbon black structure. Mechanical properties can be explained by variation in density and fiber morphology of membranes. Decreasing carbon black particle size and increasing structure decreased the density, and increased tensile strength, ultimate elongation and modulus.
Thermoplastic Vulcanizates by Reaction-Induced Phase Separation of a Miscible Poly(ε-Caprolactone)/Epoxy System
Authors: l'Abee R. M. A. , Goossens J. G. P. , van Duin M.
Published: February 2011

A new method for the preparation of thermoplastic vulcanizates (TPVs) was successfully applied. Starting with a miscible system of a semi-crystalline thermoplastic polymer and an elastomer precursor, phase separation was induced by the increase in molecular weight during selective crosslinking of the elastomer precursor. As a model system, the semi-crystalline thermoplastic poly(Ε-caprolactone) (PCL) was used in combination with a rubbery epoxy resin based on poly(propylene oxide) (PPOn-epoxy). This approach enables the dispersion of up to 80 wt% of crosslinked rubber in a thermoplastic matrix, providing morphologies that are typical for TPVs. A range in rubber particle size of 0.5 to 3 μm was obtained by this new method, without the need of blend compatibilization or dynamic processing. The materials exhibit mechanical and rheological properties typical for TPVs and the rubber particles feature a high crosslink density. At high curing temperatures and high PPOn-epoxy contents, connectivity of the rubber particles is observed, which is attributed to the phase separation mechanism. Connectivity of the rubber particles has a negative influence on both the mechanical properties and the rheological behavior.
Preparation of Cyclized Deproteinized Natural Rubber in Latex State via a Combination of Benzotrichloride and Sulfuric Acid System, and Its Properties
Authors: Riyajan Sa-ad , Tanaka Yasuyuki , Sakdapipanich Jitladda T.
Published: February 2011

Partially cyclized deproteinized natural rubber (DPNR) in latex form was successfully prepared by using a combination of sulfuric acid (H2SO4) and benzotrichloride (PhCCl3) in the presence of Terric 320 as a non-ionic surfactant. The main parameters of the cyclization process such as various reaction times, dry rubber contents, concentrations of catalyst and temperatures were investigated. The resulting rubber was subjected to characterization by proton Nuclear Magnetic Resonance (1H-NMR), Fourier-Transform Infrared spectrometer (FTIR), Thermal Gravimetric Analysis (TGA), and Differential Scan Calorimeter (DSC). In addition, the topology of partially cyclized rubber was also analyzed by Transmittance Electron Microscopy (TEM). The mechanism will be also discussed. It was interesting to note that the obtained partially cyclized rubber using this catalyst system contained no gel, which was easily soluble in rubber solvents. This is different from the partially cyclized rubber obtained from the other methods. Through, using structural characterization, it was found that the PhCCl3 linked onto the rubber chain. It was also found that the thermal stability of this cyclized rubber was better than that of normal rubber. The efficiency of cyclization in this system could be increased by an increase of PhCCl3 concentration.
Study of the Influence of Microwaves in the Mechanism of Sulfenamide Accelerated Vulcanization of Natural Rubber Using Squalene as a Model Compound
Authors: Vega B. , Agulló N. , Borrós S.
Published: February 2011

The natural rubber vulcanization mechanism has been studied using microwaves as a heating source. The influence of such heating system on the mechanism reaction has been elucidated. In order to simplify the study of this process, squalene has been used as a Model Compound Vulcanization (MCV) for natural rubber and N-cyclohexyl-2-benzothiazolesulfenamide (CBS) as an accelerator. The accelerator fading, the crosslinking degree, the reversion process and the effect of the double bond have been studied and the results have been compared with previous results of our group using MCV with conventional heating. As well as the expected reaction rate increase, a noticeable change in the crosslink degree has been observed. Furthermore, some differences have been detected in the amount of the intermediate compounds formed during the reaction and in the sulfur transfer to the squalene chain. Strong differences have been also observed regarding the role of the activator in the vulcanization when microwaves are used.
Generalized Concept of the Reinforcement of Elastomers. Part 3: Self-Reinforcement by the Formation of Continuous Hard Phase in Segmented Polyurethane Elastomer
Authors: Fukahori Yoshihide
Published: February 2011

The author proposed the third concept in the reinforcement of elastomers for segmented polyurethane with the direct observation by microscopic techniques. The structure in segmented polyurethane elastomers fundamentally consists of three domains of different sizes, two kinds of micro-domain, cluster of 100 nm in diameter and spherulite of µm order. Of the micro-domains, one is the hard-segment (HS)-rich micro-domain consisting of hard segment (4 nm thickness) and soft segment (7 nm) and the other is the hard-segment (HS)-poor micro-domain of hard segment (4 nm) and soft segment (15∼20 nm). The HS cluster is constructed by the assembly of the HS-rich micro-domains. The spherulite seems to be composed of the dense packing of the HS cluster, growing up radially or circularly from the center to the outside surface. From physical and mechanical points of view, we can regard the above structures in the segmented polyurethane as bi-continuous structure of the HS clusters whose volume fraction is 0.2, and the matrix phase consisting of the HS-poor domains (0.8 in the volume fraction). The characteristic stress-strain relation of the segmented polyurethane is generated by the combination of both the continuous structures. That is, the initial very high stress (modulus) at small extension and the following gradual increase in stress at medium extension mainly result from the extension and the sliding of the HS cluster, respectively. The very large stress-upturn at large extension and the final great tensile strength are generated by the contribution of both the continuous structures. Thus, the third reinforcement is achieved by the formation of bicontinuous structure of the hard and strong cluster and also the strong matrix phase, in which the absolute structural defects seem not to be included.
Polyhedral Oligomeric Silsesquioxane (POSS) Nanoparticles as New Crosslinking Agent for Functionalized Rubber
Authors: Sahoo Suchismita , Bhowmick Anil K.
Published: February 2011

Polyhedral oligomeric silsesquioxane (POSS) was synthesized with hydroxyl functional groups and the nanoparticles were characterized by infrared spectroscopy and transmission electron microscopy. They were found to have an average diameter of 50 nm.The effect of these synthesized POSS nanoparticles as curing agent on fluorocarbon rubber (FKM) and carboxylated nitrile rubber (XNBR) was studied with special reference to mechanical, dynamic mechanical properties and swelling behavior. The hydroxyl groups of the POSS nanoparticles were observed to effectively crosslink FKM and XNBR, which was indicated by a tremendous improvement in mechanical properties. A remarkable positive shift in glass transition temperature (Tg) was observed, which further supported the crosslinking effect of POSS nanoparticles. Formation of crosslink was confirmed from the increase in the volume fraction of rubber in swollen gel. In the case of FKM, when MgO as activator and CaO as promoter were used along with POSS nanoparticles, maximum improvement in mechanical properties was observed.
The Effect of a Dwell Period on Fatigue Crack Growth Rates in Filled SBR and NR
Authors: Harbour Ryan J. , Fatemi Ali , Mars Will V.
Published: February 2011

Loading conditions for rubber components are often more complex than the constant amplitude signals used in material characterization. During a series of uniaxial fatigue crack growth experiments on filled SBR under variable amplitude loading conditions, test signals that included a dwell period produced higher crack growth rates than corresponding constant amplitude test signals without a dwell period. These test signals alternated periods of cyclic loading with dwell periods ranging from 1 to 100 seconds at a near zero stress level. Dwell period tests produced average experimental crack growth rates up to 30 times greater than constant amplitude crack growth rates in filled SBR. The length of dwell time and the number of applied cycles between dwell periods were the most significant influences on the crack growth results. An empirical model was developed that captured the dwell effect based on these parameters. Dwell periods also produced increased crack growth rates in natural rubber, but the effect was less significant. It is proposed that the effect is caused by the time-dependent recovery in the rubber microstructure at the crack tip producing a localized and temporary elevated stress-state during loading events immediately following a dwell period. Current fatigue prediction methods do not account for the dwell effect.
Trapped Entanglements in Polymer Networks
Authors: Lang Michael , Kreitmeier Stefan , Göritz Dietmar
Published: February 2011

This work focuses on density, complexity, and experimentally observable effects of trapped entanglements in polymer networks. Using the bond-fluctuation method we crosslinked and end-linked systems with a random initial distribution of polymer and crosslinker. The structure of the generated networks has been analyzed by knot theory and graph theory concerning defects, ring structures, and trapped entanglements, resulting in a detailed description of network topology and connectivity. The knowledge on network structure is used to analyze computer simulations of swelling and solfraction experiments. The simulated swelling experiments show that the size of the fully swollen network depends strongly on the presence of trapped entanglements although the zero second Money-Rivlin term upon deformation indicates the absence of a tube like environment for individual network chains. Permanently trapped rings and the formation of network defects affect the weight of the measured gel component as function of the degree of crosslinking. The experimentally observed shift in size of the gel can be estimated based on the data of this study and is typically smaller than the shift due to ineffective reactions that lead to the formation of dangling rings and network defects.
New Developments in Dynamically Cured PP—EPDM Blends
Authors: López-Manchado Miguel A. , Arroyo Miguel , Kenny José M.
Published: February 2011

Different procedures for preparing thermoplastic vulcanizates (TPVs), based on isotactic polypropylene (iPP) and ethylene—propylene—diene terpolymer rubber (EPDM), are used and analyzed in this work. In order to determine the effect of the vulcanization method on material properties, a rheological study, dynamic-mechanical analysis, mechanical properties and morphological study have been carried out. In all cases, the sulfur is used as crosslinking agent of the elastomeric phase. It has been shown that the dynamically cured blends (referred in the work as V2 and V3) present better properties in relation to those statically cured (V1) and uncrosslinked (V). Thus, the elastic ability, mechanical properties and rheological characteristics of these systems sensibly increase when the samples are dynamically vulcanized. Morphological analysis performed by scanning electron microscopy (SEM) is clearly in agreement with the analyzed properties, showing a better dispersion between both polymeric chains, when the blends are dynamically cured. These results seem to indicate that the dynamic vulcanization process gives rise to the formation of a thermally stable three-dimensional network, and as a consequence of it, a sensible increase of the properties is obtained.
Rubber Nanocomposites: Morphology and Mechanical Properties of BR and SBR Vulcanizates Reinforced by Organophilic Layered Silicates
Authors: Ganter Markus , Gronski Wolfram , Reichert Peter , Mülhaupt Rolf
Published: February 2011

Rubber compounds based on butadiene rubber (BR) or styrene—butadiene rubber (SBR) containing organophilic layered silicates were prepared. Organophilic silicates were swollen in a rubber/toluene solution. Matrix—filler reactive bonding was performed by adding bis(triethoxysilylpropyl)-tetrasulfan (TESPT) during swelling. Excellent dispersion of organoclay nanofillers in rubber matrices was demonstrated by transmission electron microscopy (TEM) and atomic force microscopy (AFM) exhibiting intercalated and partially exfoliated silicate layers. Matrix—filler interfacial coupling by TESPT led to reduced strain at break and reduced hysteresis for both organoclay and silica-based vulcanizates as expected for successful matrix filler coupling. Organoclay vulcanizates exhibited enhanced hysteresis when compared to silica compounds. This is related to orientation and sliding of anisotropic silicate layers, as determined by online wide-angle X-ray scattering (WAXS) measurements during cyclic tensile testing.
High-Resolution Solid State NMR Investigation of the Filler-Rubber Interaction: Part III. Investigation on the Structure and Formation Mechanism of Carbon Gel in the Carbon Black-Filled Styrene—Butadiene Rubber
Authors: Dutta N. K. , Roy Choudhury N. , Haidar B. , Vidal A. , Donnet J. B. , Delmotte L. , Chezeau J. M.
Published: February 2011

This investigation describes the elastomer—filler interaction and its formation mechanism using solid state high-resolution, high-speed 1H magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. Pulsed NMR measurements were carried out on pure styrene-butadiene rubber (SBR), and solvent extracted carbon gels from freshly prepared and storage matured master batches. The effects of filler loading, storage maturation, severity of extraction and experimental temperature on the elastomer-filler interaction were examined and discussed. High resolution in NMR was achieved by higher temperature/low spinning rate, room temperature/high spinning and combined rotation and multiple-pulse spectroscopy (CRAMPS) techniques. High-speed magic-angle spinning (MAS) was found to be the most suitable method to achieve high resolution. Proton spin—spin relaxation time, T2, was measured successfully for each of the principal resonance species present in the samples. These measurements reveal an insight into the site-specific nature of the polymer—filler interaction. The relative immobilization of the dynamics of different protons, due to the presence of carbon black filler, and their temperature dependence evidence that the main chain vinyl proton is the most significantly immobilized one compared to the aromatic and methylene species. The effects of storage maturation and severity of extraction on the dynamics of the conformational jump have also been discussed. This work clearly demonstrates the importance of unsaturation on the bound rubber formation. It also provides first direct physical evidence confirming the hypothesis that bound rubber variation during the storage maturation is due to slow progressive replacement of short rubber chains by larger ones.
High-Resolution Latex State 13C-NMR Spectroscopy: Part II. Effect of Particle Size and Temperature
Authors: Kawahara Seiichi , Isono Yoshinobu , Washino Keiko , Morita Toshiko , Tanaka Yasuyuki
Published: February 2011

Latex state C-NMR measurements were made for colloidal dispersions of polymer, using the observation conditions similar to those used in solution state measurement. The colloidal dispersion which showed broad and bimodal distributions in particle size was fractionated by centrifugation into four fractions with different volume mean particle diameter ranging from 0.121 to 1.31 µm with narrow and unimodal distributions. The signal to noise ratio, half width and intensity of each resolved carbon resonance for the fractionated dispersions were dependent upon the particle diameter. The intensity of the carbon resonances increased to 100% as the particle diameter decreased and temperature was raised. This is explained with respect to the increase in diffusion coefficient of Brownian motion of the particle. The intensity and the half width of the signals were superimposed against the diffusion coefficient of Brownian motion.
Ultrasonic Devulcanization of Precipitated Silica-Filled Silicone Rubber
Authors: Shim Sang E. , Isayev A. I.
Published: February 2011

This investigation involves the recycling of precipitated silica-filled silicone rubber using a continuous ultrasonic reactor. The processing conditions utilized in devulcanization of the filled systems were similar to those in our previous work on unfilled systems. Significant differences were observed in devulcanization of unfilled and filled systems. A decrease in gel fraction and crosslink density was sufficient for devulcanized silica-filled silicone rubber to be reprocessed and revulcanized. The cure behavior of silicone rubber and the mechanical properties of virgin, and revulcanized rubber were measured. Results showed that unfilled silicone rubbers gave no change in vulcanizate mechanical properties after revulcanization. However, in the filled rubbers there was a decrease in the mechanical properties of revulcanizates. In order to achieve an improvement in the properties, devulcanized filled rubbers were blended with virgin filled rubber in various proportions. The obtained results indicated a considerable enhancement of the performance characteristics of these blend vulcanizates.
Ultrasonic Devulcanization Reactors for Recycling of GRT: Comparative Study
Authors: Yun Jushik , Oh Jeonq Seok , Isayev A. I.
Published: February 2011

The present paper describes the comparative study of a continuous ultrasonic devulcanization of ground tire rubber (GRT) using two reactors. The devulcanization zone in the first reactor (coaxial reactor) is located at the exit from an extruder without imposition of additional shearing. In the second reactor (barrel reactor), the devulcanization zone is located in barrel where additional shearing takes place due to screw rotation. Gel fraction, crosslink density, cure behavior and physical properties of GRT obtained in these two reactors were measured. Also, the distribution of gel fraction and crosslink density at various locations in the devulcanization zone of the barrel reactor were determined. Gel fraction and crosslink density show that GRT in both reactors is partially devulcanized. A unique correlation between gel fraction and crosslink density obtained in both reactors indicated that additional shearing had a positive influence on improving the efficiency of devulcanization. Under the optimal devulcanization condition, the physical properties of revulcanized GRT and the output are higher in the barrel reactor. Power consumption density in the barrel reactor is found to be significantly higher.
Characterization and Constitutive Modeling of a Plasticized Poly(vinyl Chloride) for a Broad Range of Strain Rates
Authors: Wang Yan , Arruda Ellen M. , Przybylo Phillip A.
Published: February 2011

The mechanical behavior, morphological characterization and constitutive modeling of plasticized poly(vinyl chloride) (or PVC) are studied in this paper. The plasticized PVC is tested to large strains over a broad range of strain rates. Uniaxial and plane strain compression data at various constant strain rates ranging from −0.001 to −10 s−1 are collected on a conventional servohydraulic test system. Additional uniaxial impact compression data at approximately constant strain rates ranging from −1160 to −5560 s−1 are obtained using an aluminum split Hopkinson pressure bar apparatus. The large strain load/unload response of the plasticized PVC is nonlinear, it contains hysteresis and plastic deformation, and the initial response is highly rate dependent when the strain rate spans the transition zone between quasi-static and impact strain rates at room temperature. The morphology of plasticized PVC is analyzed via differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and described as a physically entangled network. A three-dimensional rate dependent constitutive model for plasticized PVC is developed and shown to successfully predict its stress—strain behavior over a broad range of strain rates.
Blends of Butyl and Bromobutyl Rubbers and Polystyrene—Polyisobutylene—Polystyrene (PS—PIB—PS) Block Copolymers with Improved Processability and Physical Properties
Authors: Puskas Judit E. , Kaszas Gabor
Published: February 2011

An investigation of the effects of polystyrene—polyisobutylene linear triblock and three-arm star block thermoplastic elastomers on the processability and properties of butyl and bromobutyl rubbers was undertaken. All properties improved, with the exception of bromobutyl adhesion, which remained acceptable. The green strength of raw polymer blends improved by 30–80% and 5–20% improvement was seen on the carbon black compounds. Die swell was reduced by as much as 60% for compounds containing a triarm-star block. Tear strength doubled and air permeability decreased (by about) 20–40%. Fatigue life improved dramatically (20-fold on 300% crack growth and 80-fold on 600% crack growth). The cured blends can be viewed as interpenetrating networks of the chemically crosslinked rubber and the physically crosslinked thermoplastic elastomers.
Adhesive and Cohesive Strength in Polyisoprene/Polychloroprene Blends
Authors: Kardan Mahmoud
Published: February 2011

This study concerns the use of polymer blends to produce advanced high performance adhesive systems based on material economics as well as to gain knowledge about the thermodynamics of multi-component adhesive systems. In the adhesive industry, blends of natural rubber (polyisoprene) and polychloroprene are used not only to lower cost, but also to provide certain properties, which are not obtainable with either elastomer alone. This paper investigates the contribution of each elastomer in the blend to the cohesive and adhesive strength and durability of the system. Composites of synthetic cis-1,4-polyisoprene with different types of polychloroprene with modified structures have been prepared by mill compounding. Infrared spectra obtained for these composites when coated on metallic surface have been extremely useful in the elucidation of the molecular orientation and conformational changes associated with these polymers. Each sample has been laminated between metallic substrates and for each lamination; the lap shear has been measured. The measured lap shears have been correlated with the structural changes associated with polymer—polymer interactions, detected by reflection infrared spectroscopy. These results could have a significant bearing on the mechanism of the strength development in rubber blends for use in adhesive and sealant systems.
Synthesis and Use of Colloidal Silica for Reinforcement in Silicone Elastomers
Authors: Kwan Kermit S. , Harrington Daniel A. , Moore Patricia A. , Hahn James R. , Degroot Jon V. , Burns Gary T.
Published: February 2011

Aqueous suspensions of colloidal silicas are readily silylated with either chlorosilanes or disiloxanes in the presence of acid and isopropyl alcohol without aggregation of the silica particle. By using a mixture of chlorosilanes or disiloxanes, spherical nanoparticles with controlled functionality can be made and transferred to an organic phase to provide stable, water free suspensions. The hydrophobic silica particles readily disperse into silicone polymers. At sufficient loading levels, they provide mechanical reinforcement comparable to traditional fillers but with improved clarity and lower viscosities. Modulus and durometer control in the cured elastomer is possible by varying the ratio of the vinyl concentration on the filler particle to the vinyl concentration in the polymer phase.
Surface Chlorination of Ground Rubber Tire and its Characterization
Authors: Naskar Amit Kumar , De S. K. , Bhowmick Anil K.
Published: February 2011

Ground rubber tire (GRT) powders were chlorinated by trichloroisocyanuric acid (TCLCA). GRT powders of different chlorination levels were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDAX), attenuated total reflection infrared (ATR-IR) spectroscopy, thermal, dielectric, and stress—strain properties on molded GRT specimens. Surface energy of the powders was estimated. Dynamic mechanical thermal analysis of molded GRT specimen reveals a biphasic structure. Plasticized poly(vinyl chloride) (PVC) compound, when blended with chlorinated GRT, shows improved physical properties in comparison to non-chlorinated GRT.
A New Class of Ethylene—Propylene—Diene Terpolymers Produced from Constrained Geometry Metallocene Catalysts
Authors: Walton Kim L. , Hughes Morgan M. , Parikh Deepak R.
Published: February 2011

Until recently, ethylene/propylene/diene (EPDM) terpolymers have been manufactured exclusively using vanadium based Ziegler—Natta catalyst systems. The vanadium based catalysts are known to have both product and process limitations. These limitations are due to a complex combination of factors including monomer reactivity, catalyst activity, reactor temperatures and pressures. Single-site metallocene constrained geometry catalyst (CGC) technology enables the manufacture of EPDM terpolymers at higher reactor temperature and catalyst efficiency than standard Ziegler—Natta catalyst systems. The unique combination of monomer, catalyst and process technology enables the manufacture of highly crystalline EPDMs having ethylene contents over 90 wt %. This study investigated these new highly crystalline EPDM terpolymers and their differentiation from commercially available EPDMs. The results indicated that these new EPDMs had very high green strength and barrier properties, yet could be cured by conventional vulcanization techniques. The cure response of these EPDMs to either peroxide or sulfur increased with increasing ethylene content. Sulfur cured vulcanizates had much higher tensile strength than peroxide cured vulcanizates. These new EPDMs demonstrated utility as additives to enhance the abrasion, hot tear, and tensile properties of natural rubber compounds. Sponge compounds, having the unique combination of polyethylene physical properties and the utility of sulfur vulcanization were developed from these new polymers.
Mooney Viscosity Stability and Polymer Filler Interactions in Silica Filled Rubbers
Authors: Lin Chenchy , Hergenrother William L. , Hilton Ashley S.
Published: February 2011

The change in Mooney viscosity (ML1+4) with aging was followed for silica filled compounds containing various silanes and polar additives. Several mechanisms for the aging stability are postulated and evaluated through experimentation. The type of silane or polar additive used can cause the ML1+4 to increase or even decrease during aging. When bis(triethoxy silanes) are used in silica filled rubbers, the ML1+4 growth during aging is caused by hydrolysis. Silica-silica bridging was found to be responsible for the ML1+4 growth in rubber compounds containing a more thermally stable polysulfide or a sulfur-free bis(triethoxy silane). When the bis(triethoxy silane) is bis(3-triethoxysilylpropyl) tetrasulfide (TESPT), a fraction of TESPT is attached to the unsaturated rubber to give polymer-silica attachments. These attachments further enhance the hydrolytic ML1+4 increase during aging. Chemical coating of the silica with a monofunctional silane or a physical coating with a trialkyl amine compound effectively stops the ML1+4 increase upon aging. The prevention of ML1+4 growth is so efficient that a reduction in the ML1+4 can be realized by absorption of ambient moisture. The extent of ML1+4 reduction caused by moisture depends on the degree of hydrophobation of the coated silicas. Hydrolytic stability was also studied with an amine or a sugar fatty acid ester that formed either strong or weak polar associations to the silica.
Rheological Model of Uncured Silica-Filled Tire Compounds: Application to a Simple Shear Start-Up Flow
Authors: Schaal Stéphane , Coran Aubert Y.
Published: February 2011

A constitutive equation that describes the rheological behavior of highly filled uncured tire compounds was developed and applied to the special case of a low shear rate start-up flow. Start-up flow rheology is related to processability. This model is consistent with the interpretation, that the peak stress in a start-up flow experiment (Mooney peak) performed at low strain rates may be described as a yield stress. As the system is stretched, more and more structural members rupture according to their respective ultimate strains described by a Weibull distribution function. Moreover, the model describes the effects of storage time on start-up flow rheology through a kinetic analysis and relates the changes in rheology to the formation of bound rubber during storage.
Simulation and Verification for Sulfur Accelerated Vulcanization of Gum Natural Rubber Compound
Authors: Fan Ru-liang , Zhang Yong , Huang Chen , Gong Peng , Zhang Yin-xi
Published: February 2011

A simplified and realistic kinetic scheme was proposed for the cure reversion mechanism of accelerated sulfur vulcanization for gum natural rubber (NR) compounds. The vulcametric curves at different temperatures were simulated from curing to overcuring periods by using a kinetic approach. The different rate constants and activation energies were calculated from the simulation process. The simulated results showed a good agreement with isothermal vulcametric data over a wide range of temperatures and showed that the relationships between the rate constants and the cure temperatures were in accordance with the Arrhenius Equation. The activation energies (Ea1, Ea2, and Ea3) of the formation, desulfurization and decomposition of polysulfidic crosslink obtained from Arrhenius plots were 79.5,102.6 and 138.8 kJ/mol, respectively. The experimentally measured crosslink densities determined by using swelling equilibrium and chemical probe techniques agreed with the simulated vulcametric curves to some extent.
Effect of Bis (Diisopropyl) Thiophosphoryl Disulfide on the Co-Vulcanization of Carboxylic-Acrylonitrile-Butadiene Rubber and Ethylene-Propylene-Diene Rubber Blends
Authors: Naskar Nityananda , Debnath Subhas Chandra , Basu Dipak Kumar
Published: February 2011

The objective of the work is to prepare compatible, coherent and technologically feasible blends comprising non-polar EPDM rubber and polar carboxylic-acrylonitrile-butadiene rubber (XNBR). Using an efficient sulfur vulcanization system containing bis(diisopropyl) thiophosphoryl disulfide (DIPDIS), a coupling agent cum accelerator, EPDM-XNBR blend has been co-vulcanized. The blend vulcanizates thus produced exhibit substantially enhanced physical properties which are superior to those of either component. The compatibility of the rubber blends as judged by SEM micrographs can further be improved through a two-stage vulcanization process which promotes interphase crosslinking between the polymer phases. The interphase crosslinking was recognized from swelling experiments. The study of the blends containing carbon black reveals a profound increase in physical properties of the vulcanizates as compared to those of gum vulcanizates. The SEM micrographs of the blend vulcanizates both in one-stage and two-stage distinctly indicate the blend morphology, which accounts for the significant improvement in physical properties of EPDM-XNBR blends through in situ reactive compatibilization. A reaction scheme for the interphase crosslinking has been proposed for the co-curing of EPDM-XNBR blend.
Effect of Crosslink Density on Cut Growth in Gum Natural Rubber Vulcanizates
Authors: Hamed G. R. , Rattanasom N.
Published: February 2011

Conventional sulfur-cured, gum natural rubber vulcanizates of various crosslink densities were prepared. Dumbbell test pieces with and without edge precuts were tested in uniaxial tension. Relative strengths of the different vulcanizates depended on cut size. Lightly crosslinked specimens exhibited an abrupt drop in strength at a critical cut size, ccr, which became smaller as crosslink density increased because of reduced strain crystallizability. At all cut depths, crack growth was simply perpendicular to the loading direction and crack surfaces were smooth. A moderately crosslinked composition exhibited crack deviation prior to rupture. This was associated with an unusual increase in strength with increasing cut size. Densely crosslinked networks exhibited lateral fracture, like the lightly crosslinked gums, but produced a jagged crack contour path reflective of a rough fracture surface. Moreover, for the highly crosslinked samples, a critical cut size was not found. Rather, log-log plots of strength versus cut depth were linear and had slopes slightly greater than minus one-half.
Influence of Material Non Homogeneity on the Shearing Response of a Neo Hookean Slab
Authors: Bilgili Ecevit , Bernstein Barry , Arastoopour Hamid
Published: February 2011

Vulcanized rubber components possess material non-homogeneities due to either non-uniform vulcanization during their fabrication or attack of thermal and oxidative environments during their service life. The primary objective of this paper is to theoretically investigate the effect of a material non-homogeneity on the shearing response of an isotropic, incompressible neo-Hookean slab. The non-homogeneity considered in the slab is the spatially varying shear modulus that is approximately described by a spatial-distribution function. A parabolic and a boundary layer-like spatial-distribution function are assumed; then exact solutions for the stress—strain fields in the slab are obtained by solving the linear momentum balance equations based on a postulated inhomogeneous shearing deformation. Our theoretical results show that the shear strain is more inhomogeneous and localized for the slabs with a greater degree of spatial non-homogeneity. In the non-homogeneous slabs, we have also determined the existence of a uniform shear stress and an inhomogeneous first normal-stress difference whose variation is similar to that of the shear strain. The implications of these results are considered in terms of the fabrication, performance and mechanical characterization of the rubber-elastic materials.
Influence of Different Silanes on the Reinforcement of Silica-Filled Rubber Compounds
Authors: Luginsland Hans-Detlef , Fröhlich Joachim , Wehmeier André
Published: February 2011

The silane modification of precipitated silica for rubber applications is state-of-the-art. Usually, bifunctional silanes are used to provide a silica-to-rubber coupling. In this paper, the general effect of the silane modification on the Payne-effect of silica-filled compounds (S-SBR/BR) is investigated by applying the Rubber Process Analyzer (RPA). For this purpose, the amount as well as the type of silane have been varied. The alkyl chain length of monofunctional silanes determines their hydrophobation efficiency and therefore influences the degree of the silica network, whereas bifunctional silanes also contribute to the crosslinking and build up an in-rubber structure. The degree of the filler network is not only determined by the kind of silica modification, but also by the reinforcement behavior of the silica, mainly characterized by the CTAB surface area. The findings of this study give a better insight into the reinforcement of silica-filled rubber compounds and their dynamic properties.
Modification of Dual Phase Filler by Electron Beam Irradiation: Physical Characterization
Authors: Shanmugharaj A. M. , Bhowmick Anil K.
Published: February 2011

Electron beam modification of carbon black (N220) and carbon-silica dual phase filler affects the microstructure of carbon black. This is confirmed from X-ray diffraction studies. The scanning electron microscopy /energy dispersive X-ray analysis reveals surface oxidation, which is further corroborated from nitrogen and iodine adsorptions. Transmission electron microscopy studies show the aggregation of fillers upon electron beam irradiation. Linear fractal dimension calculated by image analysis increases upon irradiation, due to the formation of filler aggregates.
Interaction Between Rubber and Carbon Black Studied by ToF-SIMS
Authors: Bertrand P. , Weng L.-T. , Lauer W. , Zimmer R.
Published: February 2011

In order to study the rubber—carbon black filler interaction, different styrene-butadiene rubbers were adsorbed from solution on carbon black. Afterwards, the samples were washed to keep only the thin layer of bound rubber. The surface of these samples was characterized by ToF-SIMS. It was found that the carbon black surface was completely covered by the polymer, except for pure 1,4-polybutadiene where a non-uniform adsorption was seen. Moreover, the ToF-SIMS data showed that the parameters related to the polymer aromaticity and unsaturation decreased after adsorption. These results indicated a change in polymer chain conformation at the surface upon adsorption on carbon black. This was explained by a preferential interaction between phenyl (and in a weaker manner, 1,2-vinyl) groups with the carbon black surface. Indeed, when these groups tend to orientate toward the filler surface, their surface concentration seen by ToF-SIMS is expected to decrease.
Effect of Gel on the Green Strength of Natural Rubber
Authors: Kawahara Seiichi , Isono Yoshinobu , Sakdapipanich Jitladda T. , Tanaka Yasuyuki , Aik-Hwee Eng
Published: February 2011

The outstanding properties of natural rubber, e.g., green strength and rapid crystallization, were attributed to the chemical branching that formed at both chain ends of the rubber molecule during the preservation of the latex in the presence of ammonia. The gel content of natural rubbers from various clonal origins increased during the preservation, but decreased after deproteinization of the aged latex. The crystallization of acetone-extracted rubber was slightly suppressed as the gel content increased. The increase in green strength during the preservation was studied in connection with the gel content and degree of branching of the rubber.