bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Chain Length of Amine and Nature and Loading of Clay on Styrene-Butadiene Rubber-Clay Nanocomposites
Authors: Sadhu Susmita , Bhowmick Anil K.
Published: February 2011

Polymer nanocomposite is one of the highly discussed research topics in recent time. In this paper, we have reported the preparation and the properties of different nanoclays based on sodium montmorillonite, bentonite and potassium montmorillonite and organic amines of varying chain lengths, and Styrene Butadiene Rubber (SBR)-clay nanocomposites. The clays and the rubber nanocomposites have been characterized with the help of Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). X-ray results suggest that the intergallery distance is increased by incorporation of various amines. There is a great improvement in mechanical properties like tensile strength, elongation at break, modulus, work to break, and hysteresis on incorporation of nanoclay in SBR. TEM photographs show exfoliation of the clays in rubber to 5–10 nm range. The X-ray diffraction peak observed in the range of 3°– 10° for the control and the modified clays also disappears in rubber nanocomposites. Increasing chain length of clay modifiers and loading and nature of clays affect the mechanical and thermal properties significantly.
Role of Strain Crystallization in the Fatigue Resistance of Double Network Elastomers
Authors: Santangelo P. G. , Roland C. M.
Published: February 2011

Double networks were prepared from guayule rubber (GR), deproteinized natural rubber (DPNR), and styrene-butadiene rubber (SBR), and their properties compared to conventional “single networks” having the same crosslink density. Substantial residual strains (> 150%) were obtained in all double networks, whereby the modulus parallel to the residual strain was enhanced. For the two strain-crystallizing elastomers, the fatigue resistance of the double networks (for extensions parallel to the residual strain) was higher than for their single network counterparts. Moreover, the guayule rubber, which is more strain-crystallizable than DPNR, exhibited the greater enhancement. For the amorphous SBR, on the other hand, the network structure had an insignificant effect on the fatigue life. These results demonstrate that longer mechanical fatigue lifetimes in double network rubbers are a consequence of their intrinsic orientation. This provides the capacity to retain crystallinity at the front of growing cracks, even in the absence of stress. The origin of the improved fatigue resistance is similar to the mechanism responsible for the better performance of strain-crystallizing rubbers subjected to non-relaxing cyclic deformations.
A Morphometric Investigation by TEM/AIA on Elastomer-Based Compounds Filled with an Untreated Precipitated Silica
Authors: Falqui L. , Costa G. , Castellano M. , Turturro A. , Valenti B.
Published: February 2011

An accurate morphological investigation has been carried out on vulcanized compounds based on different matrices, butadiene rubber, natural rubber and styrene-butadiene rubber, filled with 35phr of a precipitated silica. The analysis has been performed by using transmission electron microscopy (TEM) and automated image analysis (AIA) to achieve quantitative information on the filler dispersion. Significant differences in the aggregate size and shape distribution of silica within the different matrices which, in principle, can be related to the polymer-filler interactions, have been found. The results are in a very satisfactory agreement with thermodynamic predictions obtained by inverse gas chromatography. The use of two complementary techniques, TEM/AIA, allows attainment, in a reasonably short time, quantitative information on the filler dispersion and, consequently, on the performances of these elastomers-based composite materials.
Continuous Mixing and Compounding of Polymer/Filler and Polymer/Polymer Mixtures with the Aid of Ultrasound
Authors: Isayev A. I. , Hong C. K. , Kim K. J.
Published: February 2011

High power ultrasound is applied to break down silica agglomerates in EPDM/silica mixtures and to compatibilize plastic/rubber and rubber/rubber blends during extrusion process. Ultrasonically treated EPDM/silica mixtures without silane treatment of silica indicated significantly reduced sizes of silica agglomerates in comparison with those obtained by an internal mixer and lower than the EPDM/silica mixtures treated by the silane. The viscosity of the ultrasonically treated mixtures was found to be higher than that of the silane treated mixtures, while the extrudate swells of both mixtures were close to each other. Ultrasonically treated plastic/rubber and rubber/rubber blends indicated in-situ copolymer formation and compatibilization in the melt state leading to significant enhancement of the mechanical properties of the blends. An idea is put forward about the possibility of in-situ copolymer formation at the interfaces and their vicinities in the ultrasonically treated blends during extrusion. Data obtained by a solvent extraction indicating reduction in the amount of the extractable component, gel permeation chromatography indicating formation of the high molecular weight tail, atomic force microscopy indicating smooth interfacial region and scanning electron microscopy indicating stabilization of the phase morphology in the melt state of the ultrasonically treated blends point towards the occurrence of in-situ copolymer formation. The discovery creates a new field of the study of ultrasonic-assisted mixing of rubber with filler and compatibilization of immiscible polymer blends during extrusion.
Atomic Force Microscopy Studies on Morphology and Distribution of Surface Modified Silica and Clay Fillers in an Ethylene-Octene Copolymer Rubber
Authors: Ray Sudip , Bhowmick Anil K. , Bandyopadhyay S.
Published: February 2011

Topographic and phase imaging in tapping mode atomic force microscopy (TMAFM) has been performed to investigate the effect of surface modification of silica and clay fillers on the morphology and the microdispersion of the filler particles in the rubber matrix. The above fillers have been modified by using surface coating agents like an acrylate monomer (trimethylolpropane triacrylate, TMPTA) or a silane coupling agent (triethoxy vinylsilane, TEVS) followed by electron beam modification at room temperature. Both unmodified and surface modified fillers have been incorporated in an ethylene-octene copolymer rubber. The phase images of the above composites elucidate the reduction in aggregate size due to the filler surface modification, which is more pronounced in the case of silane modification. The results obtained from the section analysis and the histogram of the filler distribution further corroborate the above findings. The corresponding topographic images are characterized by various statistical quantities like roughness parameters and two-dimensional power spectral density (2-D PSD). As compared to the control silica and clay filled rubbers, a noticeable reduction in the surface roughness is observed in the case of modified filled composites. Thus, the whole study based on AFM suggests that the surface modification of the above fillers significantly reduces the filler-filler interaction, which in turn reduces the filler aggregate size and helps in improving the filler dispersion.
Morphology and Crystallization Behavior of Lightly Crosslinked Natural Rubber in Blend
Authors: Kawazura Tetsuji , Kawahara Seiichi , Isono Yoshinobu
Published: February 2011

Isothermal crystallization of natural rubber (NR) dispersed in styrene-butadiene rubber (SBR) was made at −25 °C to investigate effects of both gel fraction of the rubber and morphology of the blend on the crystallization. NR, thus used, was lightly crosslinked model compound (model-NR), which was cured with dicumylperoxide at 160 °C after mastication. The model-NR was mechanically mixed with a large amount of SBR to form droplets of the rubber, a size of which was dependent upon both gel content and crosslink density of the gel fraction. The crystallization of the model-NR in the droplets was quite slow, corresponding to the level reported in the previous work. A rate of crystallization and Avrami exponent were dependent upon the size of the droplets, but not on the gel content and the crosslink density of the model-NR. The suppression in the crystallization was attributed to the homogeneous nucleation occurring in the droplets. This finding was proved, using rubbers obtained from two clones of Hevea brasiliensis, i.e. RRIM600 and RRIM2025, respectively.
Axial Loading of Annular Bonded Rubber Blocks
Authors: Horton J. M. , Tupholme G. E. , Gover M. J. C.
Published: February 2011

Closed-form expressions are derived using a superposition approach for the axial deflection and stress distribution of axially loaded rubber blocks of annular cross-section, whose ends are bonded to rigid plates. These satisfy exactly the governing equations and conditions based upon the classical theory of elasticity. Readily calculable relationships are derived for the corresponding apparent Young's modulus, Ea, and the modified modulus, Ea′, and their numerical values are compared with the available experimental data. Elementary expressions for evaluating Ea and Ea′ approximately are deduced from these, in forms which are closely analogous to those given previously for blocks of circular and long, thin rectangular cross-sections. The profiles of the deformed lateral surfaces of the block are discussed and it is confirmed that the assumption of parabolic lateral profiles is not valid generally.
Some Benchmark Problems for FEA from Torsional Behavior of Rubber
Authors: Yeoh O. H.
Published: February 2011

Two commercial finite element analysis (FEA) programs, ANSYS and FLEXPAC, were compared in benchmark problems involving torsion of cylindrical rubber specimens. The effects of using different element types, material models, bulk moduli and specimen geometry were studied and compared with Rivlin's theoretical solution. This was done as an exercise to help build confidence in the analyst's ability to use these codes properly and in the reliability of the results. Some problems with certain element types were identified. With suitable choices, FEA results consistent with the theoretical solution were obtained.
Effect of Non-Rubber Components on Storage Hardening and Gel Formation of Natural Rubber During Accelerated Storage under Various Conditions
Authors: Yunyongwattanakorn Jintana , Tanaka Yasuyuki , Kawahara Seiichi , Klinklai Warunee , Sakdapipanich Jitladda
Published: February 2011

The phenomenon of storage hardening in solid natural rubber (NR) is presumed to occur by means of reactions between some non-rubber components and abnormal groups in rubber molecule. The main non-rubber constituents in NR are composed of proteins and lipids. The storage hardening behavior of NR purified by enzymatic deproteinization and transesterification was analyzed under high and low humidity conditions using phosphorus pentoxide (P2O5) and sodium hydroxide (NaOH). The NR obtained from centrifuged fresh natural rubber latex (CFNR) and deproteinized NR latex (DPNR) showed significant increase in the hardening plasticity index (PH) value during storage; while that of the transesterified NR (TENR) and transesterified DPNR (DPTE-NR) was almost constant during storage. After keeping samples under high humidity conditions, the fresh natural rubber (FNR), CFNR and DPNR showed constant PH value, while that of the TENR and DPTE-NR decreased during storage. The FNR, CFNR and DPNR showed a clear increase in the gel fraction after the occurrence of storage hardening reaction. The gel fraction showed molecular weight between crosslinks (Mc) of about 104. Glass transition temperature (Tg) of gel fraction was higher than that observed in the case of sol fraction. The formation of crosslinking and branching during accelerated storage was presumed to be due to the chemical bonding between the active functional groups in the long-chain fatty acid of phospholipids at the terminating end of rubber molecules under low humidity conditions.
A Phenomenological Model for the Effect of R Ratio on Fatigue of Strain Crystallizing Rubbers
Authors: Mars W. V. , Fatemi A.
Published: February 2011

The fatigue crack growth rate in strain crystallizing rubbers depends not only on the maximum energy release rate experienced during a loading cycle, but also on the minimum, or equivalently, the R ratio. The R ratio is the quotient of the minimum and maximum energy release rates occurring during a loading cycle. This article proposes a simple phenomenological model for the effect of R ratio on fatigue crack growth rate in strain crystallizing rubbers. The model may also be applied for Wohler-style (S-N style) fatigue life curves. The model is compared against experimental results reported by Lindley, by Cadwell, Merrill, Sloman, and Yost, and by the authors. The ability of the model to represent the experimental data is found to be reasonable. The model provides a simple approach to estimating fatigue performance when limited data are available, and may find application in the analysis of load histories from actual service. Such variable amplitude load histories typically contain cycles covering a wide range of R ratios.
Study of Vulcanization and Degradation Chemistry in Natural Rubber by Solid-State 13C NMR and Physical Property Measurements
Authors: Mori Makio
Published: February 2011

Sulfur-vulcanization and heat aging of natural rubber was investigated by solid-state 13C NMR along with the measurements of physical properties. 13C NMR detects all of the sulfurization occurring in natural rubber network including inter- and intra-molecular crosslink and pendant linkages, while physical measurements such as modulus at small strain and equilibrium swelling postulate detect only an amount of physically effective crosslinks. By comparing those two approaches, the efficiency of sulfur bonding in contributing to physical strength can be determined. It was found that the efficiency became lower for the samples with higher curing temperature, longer cure time, and also at higher sulfur level.

It was assumed by 13C chemical shift analysis that all of the sulfurized isoprene units were cis-to-trans isomerized during the vulcanization and heat aging, even for ineffective sulfurization. Furthermore, it was found that the configuration of those units remained in the trans-1,4 form after the desulfurization at either reversion or heat aging. The nature of the trans-1,4 form in the isoprene series was assumed to be more rigid compared to that of a cis-1,4 form. This resulted in an introduction of chain scission at large deformation for the rubber with higher trans-1,4 content. Comparing several samples with different cure temperatures, cure degrees, and sulfur levels, it was postulated that such cis-to-trans isomerization is a main factor governing a degradation chemistry at elevated cure temperature, overcuring and heat aging.
The Influence of Block Copolymers on Silica-Filled Polyisoprene
Authors: Gurovich Daniel , Macosko Christopher W. , Tirrell Matthew
Published: February 2011

In the present work, precipitated silica, liquid polyisoprene, and PDMS-PI block copolymer are mixed in different formulations. The dynamic rheological properties of the resulting uncured materials are measured and are used to assess filler-filler networking. In small-amplitude tests, composites containing PDMS-PI exhibit lower values of the dynamic storage modulus (G′) than those observed in control samples prepared without copolymer additives. The control samples remain stable during several months of storage, while samples containing low molecular weight block copolymers show evidence of an aging process. The rheological manifestations of this aging include a pronounced decrease in small-amplitude G′ with time, accompanied by weakening amplitude-dependence of both G′ and G″. These suggest a progressive reduction of filler-filler interactions, presumably caused by the development of a block copolymer layer at the filler-polymer interface. The make-up of that interfacial region is investigated by means of magic-angle spinning solid-state 1H NMR experiments carried out on bound polymer fractions that survive extraction in a good solvent. Spin-spin relaxation times and the intensities of the relaxation modes associated with these characteristic times are used to identify the proportion of both PDMS and polyisoprene among the segments strongly immobilized by close contact with the silica surface and among the rest of the bound (un-extracted) interfacial layer. The changes in mechanical properties are correlated not with the overall composition of the bound polymer fraction, but with the increase in PDMS segments in close contact with the filler surface.
Microstructure-Properties Correlation in Silica-Reinforced Dynamically Vulcanized EPDM/PP Thermoplastic Elastomers
Authors: Bazgir S. , Katbab A. A. , Nazockdast H.
Published: February 2011

Silica filled dynamically crosslinked thermoplastic elastomers (TPEs) based on ethylene-propylene diene monomer (EPDM) and polypropylene (PP) with 60/40 (w/w) ratio have been prepared to investigate the effects of silica upon the interfacial interaction between the two phases as well as microstructure/properties relationship. Blends loaded with 10 to 30 phr silica (premixed with EPDM) showed more reduction in the mixing torque after the maximum torque peak with lower and constant viscosity and hence better melt processability compared with similar but unfilled sample. This is showed to be due to the formation of tight agglomerate structure as a result of lower EPDM/PP viscosity ratio for the unfilled sample. Increasing the concentration of silica to 50 phr leads to the sharp increase in the mixing torque during dynamic vulcanization with high final melt viscosity. SEM examination showed that silica remains shelled by EPDM, but at high concentration, migration of silica occurs from EPDM onto PP during melt mixing leading to the enhancement of the adhesion between the PP shelled rubber particles which gives rise to the formation of strong networks. Rheometric mechanical spectrometer (RMS) showed less fractionation of the relaxation times for the PP segments in the silica filled samples with lower damping behavior (Tan. δmax). Addition of functionalized PP promotes the interfacial interaction between the matrix and the silica filled crosslinked rubber networks. More rubbery behavior and increased extensibility observed for the blends incorporated by 10 to 30 phr silica, while the 50 phr filled sample is characterized by higher elastic modulus. Crystallization of the highly silica filled blends is promoted as the migrated silica acts as nucleating agent for PP.
Increasing the Force Torque Transducer Sensitivity of an RPA 2000 by a Factor 5 – 10 via Advanced Data Acquisition
Authors: Hilliou L. , van Dusschoten D. , Wilhelm M. , Burhin H. , Rodger E. R.
Published: February 2011

The sensitivity of an RPA 2000 under oscillatory shear conditions can be extended by a factor of 5 – 10 into the low torque region. This increases the overall dynamic range of this robust industrial instrument to 5 decades. This dynamic range is close to that of rheometers used in academic environments. This increased sensitivity is not a result of mechanical improvement, but the result of an advanced, but straight forward, data treatment of the raw torque transducer output in the time domain using “on the fly” averaging. This method is possible through the availability of modern ADC-cards. The underlying ideas of this averaging procedure, together with experimental verification on polyethylene are described in detail.
The Influence of Filler-Filler and Filler-Polymer Interactions on the Physical Properties of Silica-Filled Liquid Polyisoprene
Authors: Gurovich Daniel , Macosko Christopher W. , Tirrell Matthew
Published: February 2011

The dynamic rheological properties of uncured dispersions of silica in liquid polyisoprene are measured and are used to assess filler-filler networking. An increase in the dynamic storage modulus (G′) is observed with decreasing polyisoprene molecular weight and with increasing silica concentration. For sufficiently high silica concentrations, a low-frequency plateau is observed in the frequency-dependence of G′, indicating the presence of a volume-spanning filler-filler network. The height of this plateau scales with silica volume fraction to the power of 5.2, consistent with several models describing the elasticity of polymer materials filled with fractal clusters of colloidal particles. Treatment of the silica filler surface with a silane coupling agent leads to a decrease in the modulus of the resulting dispersion. The properties of the filler-polymer interface were further investigated by bound polymer measurements and by solid-state 1H NMR experiments on the bound polymer fractions. The mobility of the polymer segments immediately adjacent to the filler surface is significantly reduced, as evidenced by faster spin-spin relaxation. The bound polymer per m2 of silica surface increases with increasing silica concentration, primarily due to entrapment of loosely bound polymer chains in the filler-filler network.
Effect of Zinc Oxide on the Reaction of TESPT Silane Coupling Agent with Silica and Rubber
Authors: Reuvekamp L. A. E. M. , Debnath S. C. , Ten Brinke J. W. , Van Swaaij P. J. , Noordermeer J. W. M.
Published: February 2011

The addition of a coupling agent to silica-rubber compounds enhances filler-matrix compatibility. The coupling agent under study, TESPT, can also act as a sulfur donor, which leads to premature scorch in the mixer. The effect of the presence of zinc oxide in the internal mixer at higher dump temperatures was demonstrated by dynamic mechanical testing. A lower tendency to scorch was seen when zinc oxide was omitted during the internal mixing stage and added only later together with the curing additives on a two roll mill. Zinc oxide primarily interferes with the reaction between the coupling agent and the silica surface, as shown by the reaction rate constants obtained with rheological experiments. Further confirmation was obtained by HPLC-experiments: the reaction rate constants of TESPT with silica for the samples with zinc oxide present, were lower at higher temperatures in comparison with samples without zinc oxide. XPS data confirmed that zinc oxide can indeed react with the silica surface. When zinc oxide is included in the internal mixer stage, shorter scorch times are obtained for curing when compared to compounds where no zinc oxide is included during mixing and only added later on. These shorter scorch times are the result of filler flocculation of the silica during the curing stage.
Spectroscopic Studies on Reaction between Squalene and Vulcanizing Agents in the Presence and Absence of Zinc-2-Mercaptopyridine-N-Oxide
Authors: Pierre C. C. , Datta R. N.
Published: February 2011

Model compound vulcanization in combination with reversed-phase high-performance liquid chromatography and NMR spectroscopy was used to elucidate the reactions of accelerator, sulfur, zinc stearate and zinc-2-mercaptopyridine-N-oxide (ZPNO) in natural rubber vulcanization. Studies of different curing ingredient formulations in squalene have been done to determine the influence of each component during the vulcanization. It was found that 2-mercaptopyridine-N-oxide bridged adducts (R-Sx-Pyr(O)) were formed when squalene was heated in the presence of sulfur, curing ingredients and 2,2′-dithiobis(pyridine-N-oxide) (PyrO-S2-PyrO). Possible interactions of R-Sx-Pyr(O) with carbon black have been proposed.
Study on the Compressible Hyperelastic Constitutive Model of Tire Rubber Compounds under Moderate Finite Deformation
Authors: Xia Yong , Li W. , Xia Yuanming
Published: February 2011

In this paper, the Automated Grid Method is applied to the uniaxial tension test of tire rubber compounds under moderate finite deformation. The test precision is improved, and the strains along axial and transversal directions are obtained simultaneously, so that compressibility of the rubber compounds can be studied directly. Based on the Eight-Chain model, and inspired with the physical idea of Van der Waals model, we put forward a modified Eight-Chain model, and generalize it into compressibility. All of the model parameters can be determined with the data obtained merely in uniaxial tension test with the Automated Grid Method, without the dependence on the data of any other test form. Fitted results show that modified Eight-Chain model can better characterize the hyperelastic mechanical behavior of incompressible and compressible rubber compounds under moderate finite deformation.
Neural Network Based Constitutive Model for Rubber Material
Authors: Shen Y. , Chandrashekhara K. , Breig W. F. , Oliver L. R.
Published: February 2011

Rubber hyperelasticity is characterized by a strain energy function. The strain energy functions fall primarily into two categories: one based on statistical thermodynamics, the other based on the phenomenological approach of treating the material as a continuum. This work is focused on the phenomenological approach. To determine the constants in the strain energy function by this method, curve fitting of rubber test data is required. A review of the available strain energy functions based on the phenomenological approach shows that it requires much effort to obtain a curve fitting with good accuracy. To overcome this problem, a novel method of defining rubber strain energy function by Feedforward Backpropagation Neural Network is presented. The calculation of strain energy and its derivatives by neural network is explained in detail. The preparation of the neural network training data from rubber test data is described. Curve fitting results are given to show the effectiveness and accuracy of the neural network approach. A material model based on the neural network approach is implemented and applied to the simulation of V-ribbed belt tracking using the commercial finite element code ABAQUS.
Stress-Induced Crystallization Properties of Natural and Synthetic CIS-Polyisoprene
Authors: Trabelsi S. , Albouy P.-A. , Rault J.
Published: February 2011

Stress-induced crystallization and melting of natural and synthetic cis-isoprene are compared by simultaneous Wide Angles X-ray Scattering (WAXS) and mechanical measurements.

Natural (NR) and synthetic polyisoprene (SR) rubbers have the same composition and sulfur crosslink density. At fixed elongation and during cyclic deformation, the properties X of the semi crystalline phase are determined as function of draw ratio λ; X being crystallites dimensions and orientation, half-time of crystallization, melting temperature, crystallinity and crystalline zone dimensions around a crack tip. It is shown that all the curves X(λ) of both types of rubber at room temperature can be superposed by a simple translation δλ along the draw ratio axis. This translation factor of the order of 0.5 to 1 does not depend on the property X. These effects are explained by the decrease of the melting and crystallization temperatures due to the presence of chain defects in synthetic rubber.
Strain-Induced Molecular Orientation and Crystallization in Natural and Synthetic Rubbers under Uniaxial Deformation by In-situ Synchrotron X-ray Study
Authors: Toki Shigeyuki , Sics Igors , Ran Shaofeng , Liu Lizhi , Hsiao Benjamin S. , Murakami Syozo , Tosaka Masatoshi , Kohjiya Shinzo , Poompradub Sirilux , Ikeda Yuko , Tsou Andy H.
Published: February 2011

In-situ synchrotron wide-angle X-ray diffraction (WAXD) studies and simultaneous measurements of stress and strain during uniaxial stretching of various vulcanized rubbers were carried out (at room temperature and 0°C) to reveal the strain-induced molecular orientation and crystallization relationships. Rubbers evaluated included natural rubber (NR), synthetic poly-isoprene rubber (IR), poly-cis-1,4-butadiene rubber (BR) and butyl rubber (IIR). Some universal features were observed in these systems: (i) At high strains (> 5.0), the majority of the chains (up to 50 ≈ 75%) in natural and synthetic rubbers remained in the un-oriented amorphous state with only a small amount of crystalline fraction formed (10–20%). The rest of the chains were in the oriented amorphous state. (ii) During deformation, the oriented amorphous chains acted as precursors to strain-induced crystallization. A network of micro-fibrillar crystallites is formed within the closely populated vulcanization points, leading to the enhancement of mechanical properties at high strains. Different rubbers exhibited different behaviors during strain-induced crystallization. For example, poly-isoprenes (NR and IR vulcanized with sulfur and peroxide) showed strain-induced crystallization at a low strain of 2.5, resulting in larger crystalline but smaller oriented amorphous fractions. In contrast, BR and IIR crystallized at a higher strain of 4.0 lead to higher molecular orientation, higher oriented amorphous, but smaller crystalline fractions. The relationship between the molecular orientation and crystallization in strained rubber depends on the intrinsic crystallizability of the chains and the topology of the crosslinked network.
Specialty Elastomer Modifiers with Isotactic Propylene Crystallinity for Polypropylene Modification
Authors: Dharmarajan N. , Williams M. G. , Datta S.
Published: February 2011

Specialty elastomers possessing isotactic propylene crystallinity are a novel class of polyolefins made possible by advances in metallocene polymerization. These polymers contain a propylene rich component endowed with isotactic crystallinity, and the balance of the composition is ethylene with other alpha olefins. Typical molecular weight of these elastomers is greater than 100,000. These polymers, when used as modifiers for toughening polypropylene (PP) homopolymers demonstrate improved impact strength to stiffness balance, enhanced low temperature toughness and improved impact to flow balance over conventional ethylene alpha-olefin modifiers.

Morphological features of the blends were determined using Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). The detailed morphological characterization indicates that the isotactic propylene crystallinity species of the elastomers function by localizing themselves at the interface of the polypropylene matrix and the ethylene-alpha olefin component of the modifier. We believe that such a tailored localization is effective because of the simultaneous co-crystallization of the isotactic propylene crystallinity elastomers with the isotactic PP matrix, and the thermodynamic compatibility of the propylene crystallinity species with the other elastomeric components of the modifier.
Activators in Accelerated Sulfur Vulcanization
Authors: Heideman Geert , Datta Rabin N. , Noordermeer Jacques W. M. , van Baarle Ben
Published: February 2011

This review provides relevant background information about the vulcanization process, as well as the chemistry of thiuram- and sulfenamide-accelerated sulfur vulcanization with emphasis on the role of activators, to lay a base for further research. It commences with an introduction of sulfur vulcanization and a summary of the reaction mechanisms as described in literature, followed by the role of activators, particularly ZnO. The various possibilities to reduce ZnO levels in rubber compounding, that have been proposed in literature, are reviewed. A totally different approach to reduce ZnO is described in the paragraphs about the various possible roles of multifunctional additives (MFA) in rubber vulcanization. Another paragraph is dedicated to the role of amines in rubber vulcanization, in order to provide some insight in the underlying chemical mechanisms of MFA systems. Furthermore, an overview of Model Compound Vulcanization (MCV) with respect to different models and activator/accelerator systems is given. In the last part of this review, the various functions of ZnO in rubber are summarized. It clearly reveals that the role of ZnO and zinc compounds is very complex and still deserves further clarification.
Naval Applications of Elastomers
Authors: Roland C. M.
Published: February 2011

The fact that rubber can be studied in a state of mechanical equilibrium makes it the most fundamentally interesting polymeric material. Elastomers also find wide application both in industry and the military, due to the unique combination of obtainable properties. This short review describes selected uses of rubber by the U.S. Navy on surface vessels, submarines and aircraft. The emphasis is applications which exploit rubber's capacity for energy transmission, storage and dissipation.
Thermoplastic Elastomers Based on Waste Rubber and Plastics
Authors: Rajeev R. S. , De S. K.
Published: February 2011

This paper reviews the utilization of waste rubber and waste plastics for the preparation of thermoplastic elastomers (TPEs). TPEs based on ground rubber tire (GRT), waste EPDM rubber, waste nitrile rubber, recycled rubber, latex waste, and waste plastics are described with respect to composition and physical properties. It is found that part of the rubber phase or plastics phase or both in the rubber-plastics blend can be replaced with corresponding waste polymer for the preparation of thermoplastic elastomers. In many cases, the materials prepared from waste polymers show properties comparable to those prepared from fresh polymers. However, in some cases, the materials prepared from waste rubber or waste plastics cannot be classified as TPEs, as the blend compositions show very low elongation at break. Modification of the waste polymer or the use of compatibilizers result in stronger composites.
Models for the Component Dynamics in Blends and Mixtures
Authors: Ngai K. L. , Roland C. M.
Published: February 2011

Four models for the component dynamics in polymer blends are briefly reviewed, with an emphasis on their ability to describe anomalous segmental relaxation behavior, secondary relaxations in blends, mixtures which include small molecules, and properties in the concentration limits of probe molecules and neat polymers. While general features of the segmental dynamics of polymer blends can be accounted for by all of these models, only that of the authors addresses all these particular aspects of blend dynamics. Our conclusion is that assessment of blend dynamics models should extend beyond intuitive appeal or general properties, with due attention given to the more subtle and exceptional behaviors.
Cure State Distributions in Rubbers by Dynamic Nano-Indentation
Authors: Tsou Andy H. , Westwood Alistair D. , Schulze Jonathan S. , Herbert Erik G.
Published: February 2011

A depth-sensing and frequency-specific dynamic indentation technique was used to determine the spatial distributions of dynamic moduli, including storage (E′) and loss moduli (E″), in poly-cis-1,4-butadiene (BR) and brominated poly(isobutylene-co-p-methylstyrene) (BIMS) rubbers with varying degrees of cure and with or without carbon black fillers as a function of penetration depth. The BR rubbers were cured with sulfur and a sulfur accelerator and the BIMS rubbers were cured using zinc oxide and stearic acid. The dynamic modulus reached a constant bulk value after the Berkovich indentor penetrated into rubbers far beyond the surface. Spatially averaged bulk dynamic moduli thus determined using the nano-indentation technique were compared with the tensile extensional moduli and the frequency-dependent dynamic tensile moduli both measured from the bulk rubbers. Spatial distributions of cure and its dependence on penetration depth were evaluated as functions of cure level, filler loading, and sample surface preparation. The ultimate goal is to provide quantitative cure distribution maps in rubber blends and compounds through a combination of Atomic Force Microscopy (AFM) and dynamic nano-indentation characterization.
Effect of Network-Chain Length on Strain-Induced Crystallization of NR and IR Vulcanizates
Authors: Tosaka Masatoshi , Kohjiya Shinzo , Murakami Syozo , Poompradub Sirilux , Ikeda Yuko , Toki Shigeyuki , Sics Igors , Hsiao Benjamin S.
Published: February 2011

Strain-induced crystallization of natural rubber (NR) and synthetic isoprene rubber (IR) with various crosslinking densities was investigated by wide angle X-ray diffraction using a synchrotron radiation and simultaneous tensile measurements. The elongation ratio at the onset of crystallization (αc) was almost independent of crosslinking density. IR samples showed larger αc values than NR because of the lower stereoregularity of IR. These results suggest that the onset of crystallization is determined by increased melting temperature by strain due to an entropic reason. The amount of oriented amorphous component changed approximately linearly with strain, and was a little larger in IR than in NR when compared at the same elongation ratio. At small strain (and stress), crystallinity in IR was lower than in NR. These results indicate that, at small strain region, the more stress is assigned to oriented amorphous in IR than in NR.
Modeling of Stress-Softening for Elastomeric Materials
Authors: Gentot Laetitia , Brieu Mathias , Mesmacque Gérard
Published: February 2011

An experimental study of deformed reinforced elastomeric materials in uni-axial tension test has been carried out and brings to the fore a significant stress-softening during the first cycles. A new predicted stress-softening model is proposed and well adapted to many rubber-like materials.
Online Electrical Conductivity as a Measure to Characterize the Carbon Black Dispersion in Oil Containing Rubber Compounds with a Different Polarity of Rubber
Authors: Le H. H. , Prodanova I. , Ilisch S. , Radusch H.-J.
Published: February 2011

The influence of viscosity, polarity of the rubber matrix and the types and contents of extender oil on the carbon black dispersion has been characterized using the online electrical conductivity measurement. A corresponding change of the online conductivity with the rubber infiltration and extent of carbon black dispersion has been observed. The infiltration rate increases with increasing polarity and decreasing viscosity of the rubber matrix, whereby the matrix polarity shows a stronger effect than the viscosity. The oil addition accelerates the infiltration process. This is caused by the reduction of the matrix viscosity and the intensification of the filler-matrix interaction. Oil addition affects the carbon black dispersion in non-polar rubber much more than in polar rubber. Furthermore, in non-polar rubber, polar oil shows a stronger effect than non-polar oil.
Mechanistic Study of the Role of One-Component Resins in Rubber-to-Brass Bonding in Tires
Authors: Patil Pankaj Y. , van Ooij William J.
Published: February 2011

Adhesion between rubber and brass-coated steel cords is enhanced by using resins as adhesion promoters. Experiments were carried out using a squalene liquid rubber modeling approach to study the effect of resins on the chemistry of the vulcanization reaction. The formation of new intermediates during vulcanization and changes in chemical concentrations with reaction time was studied using Gel Permeation Chromatography (GPC) analysis of the reacted squalene mixtures. Also, the effect of presence of resins on the surface of sulfidized brass cords was studied by analyzing the adhesion layer's elemental composition using the Electron Dispersive X-ray Spectroscopy (EDX) and Secondary Ion Mass Spectrometry (SIMS) characterization techniques. The changes in surface morphology of the adhesion layer with reaction time was noted by taking micrographs using the Scanning Electron Microscopy (SEM) technique. In this paper, a new mechanism is proposed for the role of resins in the improvement of initial and aged adhesion performance between rubber and brass-coated steel tire cords.
Pre-Vulcanization Inhibition of a N-t-Butyl-2-Benzothiazole Sulfenamide Cure by N-(Cyclohexylthio)Phthalimide
Authors: Gradwell M. H. S. , Stephenson N. R.
Published: February 2011

The reactions of N-(cyclohexylthio)phthalimide (CTP), in the absence of zinc oxide, leading to the inhibition of vulcanization in a N-t-butyl-2-benzothiazole sulfenamide (TBBS) accelerated sulfur cure were studied in the presence and absence of rubber. Mixtures of CTP, TBBS and sulfur were heated in a DSC and the reaction products and residual curatives analyzed by HPLC. Cyclohexanethiol, a decomposition product of CTP, reacted with TBBS producing 2-mercaptobenzothiazole (MBT) and t-butylamine, both of which reacted with CTP. In a polyisoprene compound, the addition of CTP did not delay the formation of the initial crosslinks, however the crosslink density did not increase substantially until the CTP had been consumed. MBT, a product of the crosslinking reaction, reacted preferentially with the CTP and not the TBBS. In the absence of CTP, the MBT was shown to accelerate the rate of TBBS polysulfide formation leading to a rapid rise in crosslink density.
Dynamical Mechanical Analysis of Conductive BR/EPDM/CB Blends
Authors: Ibarra-Gómez Rigoberto , Márquez Alfredo , Mendoza-Duarte Mónica
Published: February 2011

In the present work, Dynamical Mechanical Analysis (DMA) was employed in order to evaluate viscoelastic properties of polybutadiene (BR)/EPDM/Carbon black (CB) blends as a function of the strain amplitude. As expected, storage modulus, G', of conductive samples presented a strong dependence on strain amplitude as described by the Payne effect. This effect appears in compounds at the electrical percolation threshold and is stronger as CB content is rinsed. However, linear viscoelastic region (LVR), a characteristic section of the curve which has had little attention in this type of studies, presented also a great dependence on CB concentration, i.e. LVR is shorter as carbon black content and, hence, the conductivity of samples, increases. Respect to the influence of the elastomeric ratio BR/EPDM, EPDM alone (ratio 0/100), which had the highest viscosity, was the only formulation without a significant G' dependence on strain at 15 % w/w of CB. Also, conductivity was measured before and after the deformation cycle, in such a way that these data were useful as an indication of the structure recovery. As electrical end mechanical hysteresis is related to the state of (CB) distribution these results are envisaged to balance mechanical and electrical stability.
Dynamically Vulcanized PP/EPDM Blends: Multifunctional Peroxides as Crosslinking Agents — Part I
Authors: Naskar Kinsuk , Noordermeer Jacques W. M.
Published: February 2011

Thermoplastic vulcanizates (TPVs) or dynamic vulcanizates are a special class of thermoplastic elastomers, produced by mixing and crosslinking of a rubber and a thermoplastic polymer simultaneously. In a previous study, it was demonstrated that the use of dicumyl peroxide in combination with triallyl cyanurate as crosslinking agents provides a good overall balance of physical properties of PP/EPDM TPVs. Commonly used peroxides like dicumyl peroxide generally produce volatile decomposition products, which sometimes provide a typical smell or show a blooming effect. In this paper multifunctional peroxides are described, which reduce the above-mentioned problems. They consist of a peroxide and co-agent-functionality combined in a single molecule. The multifunctional peroxides provide properties of TPVs, which are comparable with commonly employed co-agent assisted peroxides. The solubility and kinetic aspects of the various peroxides are highlighted, as well as the decomposition products of the multifunctional peroxides with respect to the avoidance of smelly by-products. Particularly, 2,4-diallyoxy-6-tert-butylperoxy-1,3,5-triazine turns out to be a very good alternative to the dicumyl peroxide/triallyl cyanurate combination.
Simultaneous Control of 1,4-cis Selectivity and Molecular Weight of Polymer in Polymerization of Butadiene with Co(acac)3/MAO Catalyst
Authors: Endo Kiyoshi , Hatakeyama Naoyoshi
Published: February 2011

Simultaneous control of 1,4-cis selective polymerization and molecular weight of polymer in the polymerization of butadiene (BD) with Co(acac)3/MAO catalyst was investigated. The polymerization of BD with the Co(acac)3/MAO catalyst strongly depended on catalyst preparation, and the polymerization rate of BD with Co(acac)3 activated by MAO in the presence of BD was faster than that with previous reported results that the Co(acac)3 activated by MAO in the absence of BD. From a kinetic study, linear relation between ln[BD]0/[BD]t and polymerization time and no induction period for the polymerization were observed in the polymerization of BD with Co(acac)3 activated by MAO in the presence of BD. This indicates that the active site for the polymerization kept constant throughout polymerization. The molecular weights of the polymers increased linearly with polymer yields, and the line passed through the original point. The Mw/Mn of the polymers kept constant during reaction time. The polymerization of BD performed at 0 °C in the Co(acac)3/MAO catalyst gave high molecular weight 1,4-cis poly(BD) (1,4-cis content > 95) and narrow polydispersity (Mw/Mn=1.36). On the basis of these results, it is clear that simultaneous 1,4-cis selective and molecular weight control is possible in the polymerization of BD with the Co(acac)3/MAO catalyst.
Utilization of Maleic Anhydride Modified Ground EVA Waste in NBR Vulcanizates
Authors: Soares Bluma G. , Gomes Ana C. O. , Moreira Viviane X. , Oliveira Marcia G.
Published: February 2011

The influence of poly(ethylene-co-vinyl acetate) (EVA) waste (EVAW) on the rheological and mechanical properties of NBR vulcanizates compounds was studied. The optimum concentration of EVAW, which has presented higher ultimate tensile strength, was found to be 70 phr. In addition, the influence of EVAW modified with maleic anhydride as adhesion promoter was studied. Two distinct routes of modification with maleic anhydride were selected, originating a carboxylated EVA waste (EVAWCOOH) and an anhydride EVA waste (EVAWMA). An improvement of tensile strength and aging resistance was observed with the substitution of EVAW by EVAWCOOH or EVAWMA. A very good resistance to compression set has been achieved with the addition of EVAWCOOH. The improvement of mechanical performance was attributed to a better dispersion of EVAW along NBR matrix, promoted by the enhanced modified-waste polarity, which allowed a good interaction with polar NBR. The presence of anhydride group in functionalized EVAW resulted in the highest values of tensile strength but lower elongation at break and also lower values of tan delta obtained from dynamic testing. These behaviors have been attributed to an increase of crosslink density due to the reaction between zinc oxide and succinic pendant groups of EVAWMA.
Structure-Property Relationship of a Thermoplastic Vulcanizate (Tpv)/Layered Silicate Nanocomposites Prepared Using Maleic Anhydride Modified Polypropylene as a Compatibilizer
Authors: Mishra Joy K. , Kim Il , Ha Chang-Sik , Ryou Jin-Ho , Kim Gue-Hyun
Published: February 2011

Thermoplastic vulcanizate(TPV)/organoclay nanocomposites have been successfully prepared by melt intercalation method. Maleic anhydride modified polypropylene has been used as a compatibilizer. The TPV/organoclay nanocomposites have been characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The nanocomposite as evidenced by X-ray diffraction is an intercalated one. The nanocomposites exhibited remarkable improvement in tensile and storage modulus over their pristine counterpart. The dynamic mechanical analysis reveals that the glass transition temperature of the polypropylene phase of the nanocomposite is increased (compared to its pristine counterpart), whereas the EPDM phase remains same. The nanocomposites showed improved solvent resistance over its pristine counterpart. The structure-property correlation of the nanocomposites is attempted.