bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Crosslink Density on Cut Growth in Black-Filled Natural Rubber Vulcanizates
Authors: Hamed G. R. , Rattanasom N.
Published: February 2011

Tensile strengths, σb, of gum and N115-filled natural rubber test pieces, with and without edge pre-cuts, have been determined. At low crosslink density, the regular (uncut) σb of filled and gum vulcanizates is similar. However, at high crosslink density, the gum NR becomes brittle, while the corresponding filled rubber remains strong and resistant to cut growth. It is proposed that the tightly linked gum does not strain-crystallize appreciably during stretching, but that its filled counterpart does. Carbon black appears capable of inducing crystallization in a network that alone remains amorphous during extension.

Filled vulcanizates of various crosslink densities have similar normal tensile strengths ( ≈ 30 MPa), but strengths differ, sometimes more than twofold, if a pre-cut is present. Lightly crosslinked specimens containing a small cut have strengths that depend very weakly on cut size, c. Furthermore, these develop long longitudinal cracks from which catastrophic rupture initiates. With larger cuts, strength decreases more rapidly with increasing c, there is less longitudinal crack growth, and rupture initiates near the original cut tip. In contrast, the strength of a highly crosslinked vulcanizate is sensitive to small cuts and test pieces exhibit minimal longitudinal cracking before failure.
The Influence of Silane Sulfur and Carbon Rank on Processing of a Silica Reinforced Tire Tread Compound
Authors: ten Brinke J. W. , van Swaaij P. J. , Reuvekamp L. A. E. M. , Noordermeer J. W. M.
Published: February 2011

The effect of the sulfur rank (4-0) and of the carbon rank (2-10) of equivalents of bis(triethoxysilylpropyl)tetrasulphide TESPT as coupling agents for silica-reinforced tire tread compounds, is the subject of this study. The coupling agents are added in quantities equimolar to TESPT. Sulfur correction for lower sulfur ranks than TESPT is performed either in the final mixing step or in the first mixing step in an internal mixer.

Without sulfur correction the silanes studied show a marked difference in processing as well as in the final properties of the rubber. When sulfur correction is made in the final mix together with the addition of vulcanization ingredients, all sulfur-containing silanes behave more like TESPT. The disulphide (TESPD) shows final properties similar to those of TESPT; the mixing behavior shows improved scorch safety. This is lost when sulfur correction is applied in the first mix.

Sulfur-free silanes do not react on sulfur correction during processing and show only a slight improvement in mechanical properties. A silane without sulfur, having a carbon rank of 10 (DTES) shows the best processing, although final mechanical properties are inferior to TESPT.
Superior Mechanical Properties of Ultrasonically Recycled EPDM Rubber
Authors: Yun Jushik , Isayev A. I.
Published: February 2011

This paper describes the results of an extensive study involving the continuous ultrasonic devulcanization of unfilled EPDM rubber. Die pressure and ultrasound power consumption were measured as a function of processing conditions. The mechanical properties of aged and fresh revulcanized EPDM rubber were measured. Gel fraction, crosslink density, and dynamic properties were also determined for the virgin vulcanizate, the ultrasonically devulcanized rubber, and the revulcanized rubber. Additionally, the cure behavior of virgin and devulcanized EPDM rubber was investigated. The tensile strength of revulcanized EPDM rubber was found to be much higher than that of the virgin vulcanizate with the elongation at break being practically intact. A mechanism explaining the increase in mechanical properties of revulcanized rubbers was proposed.
Adhesion Failure in Bonded Rubber Cylinders Part 2: Fatigue Life Prediction of External Ring-Shaped Cracks Using Tearing Energy Approach
Authors: Leicht Douglas C. , Rimnac C. , Mullen R.
Published: February 2011

Rubber disks bonded between flat parallel metal plates are often used as adhesion test specimens; for example, ASTM D 429 1999, Method A. However, the mechanics of adhesion failure (debonding) for this geometry have not previously been fully analyzed. Therefore, a study was conducted to determine the strain energy release rate (tearing energy) for bonded rubber disks having external ring cracks at the rubber-to-metal bond and to develop a method for predicting the fatigue life.

Finite element analysis was used to determine the tearing energy as a function of crack length for disks of various dimensions (shape factors). The crack configurations considered were an external-ring-shaped crack located at the outside circumference of either one or both rubber-to-metal bonds. The fatigue crack propagation (FCP) behavior was characterized for a generic filled natural rubber material.

The tearing energy was found to be a non-linear function of crack length. For small cracks, the tearing energy was small and approached zero as the crack length decreased. The tearing energy then increased as the crack grew, indicating accelerating growth, until it passed through a maximum value. The peak tearing energy was found to depend on the height of the disk. Finally at large cracks, the tearing energy decreased or was essentially constant as the crack grew.

The fatigue life of the rubber cylinders at different shape factors was determined experimentally. An empirical model coupled with the fatigue crack propagation behavior (FCP) for the material at different tearing energies was used to predict the fatigue life. The experimental and predicted fatigue life showed excellent agreement at low and moderate shape factors. However at high shape factors, fatigue life was not well predicted. From the experimental results, it was found that, at high shape factors, cavitation occurs causing a series of “dimples” to form, which leads to the development of an internal penny-crack, thereby violating the assumed model of an external ring-shaped crack.
Chemical Additives Migration in Rubber
Authors: Ignatz-Hoover Frederick , To Byron H. , Datta R. N. , De Hoog Arie J. , Huntink N. M. , Talma A. G.
Published: February 2011

Migration of compounding ingredients is an important factor in the overall properties and performance of rubber articles containing a number of layers for example, a tire, a hose or a conveyor belt. In certain cases, migration of compounding ingredients before, during and after vulcanization in rubber compounds can be of benefit. For example, waxes and p-phenylenediamines antiozonants rely heavily on the migration mechanism to provide optimum protection of rubber products during service against degradation by ozone. In addition, the dispersion of compounding ingredients such as oil, curatives, and antidegradants can be enhanced by diffusion within rubber. In other cases, however, diffusion across a rubber-to-rubber interface can be detrimental to performance. Diffusion will change the distribution of materials which in turn may result in changes in mechanical properties, loss in adhesion or antidegradant protection, and staining of light-colored products. Thus, a better understanding of the migration of chemical additives in rubber could provide the desired distribution of ingredients for obtaining the optimum compound performance.
Anisotropic Swelling of EPDM Rubber Discs by Absorption of Toluene
Authors: Azaar K. , Vergnaud J. M. , Rosca I. D.
Published: February 2011

Anisotropic swelling is observed when thin ethylene propylene diene monomer discs are immersed in a liquid such as toluene, whatever the percent peroxide acting as the curing agent ranging from 2 to 20. The process is studied either by experiments or calculation. The process of absorption is controlled by transient radial and longitudinal diffusion, with a concentration-dependent diffusivity and a finite and constant coefficient of convective transfer at the liquid-rubber interface. The problem is thus complex with a moving boundary since a rather high swelling takes place during the stage of absorption, leading to an increase in dimensions of the flat discs. The increase in the thickness of the discs is around 1.17– 1.18 times larger than that in the radius, at every time, while the diffusivity is the same for the radial and longitudinal transport. The extent of the change in the volume resulting from the toluene absorption varies from 1 to 1.5 depending on the value of the percent peroxide, the lower volume being obtained for the higher value of the curing agent The diffusivity is about the same whatever the percent curing agent. The state of cure is around 96 as obtained by calculation taking into account the heat transfer and the kinetics of the cure reaction. The kinetics of the cure reaction has been determined by measurements made either with a moving die rheometer run under isothermal conditions at three temperatures selected within the 170–190 °C temperature window, or a calorimeter in scanning mode. This fact can be explained by an orientation of the polymeric chains obtained during the cure, resulting from the pressure of the slabs of the heating press. Various percent peroxide as a vulcanizing agent have been used, e.g., 2, 10, and 20%.
Examination of Rubber-Brass Inter-Reacted Layer of Steel Cord by Cross Sectional TEM Observation
Authors: Yamauchi Michael T. , Shimizu Toshi , Doi Mitch , Yasunaga David , Nakayama Takenori , Okumura Kazuo
Published: February 2011

Cross sectional TEM observation was conducted with the aim of investigating the interfacial reaction of commercially manufactured steel cord and rubber during vulcanization. At the initial phase of the reaction, an inter-reacted layer was uniformly generated regardless of uneven brass thickness. As vulcanization progresses, the thickness of the interreacted layer becomes uneven, i.e. the thicker the brass plate, the thicker the inter-reacted layer becomes. Thus, the inter-reacted layer grows unevenly making a mirror image of the uneven brass plate, while a Zn-rich brass layer was formed between the brass plating and the inter-reacted layer.
Use of χ As a Function of Volume Fraction of Rubber to Determine Crosslink Density by Swelling
Authors: Hergenrother William L. , Hilton Ashley S.
Published: February 2011

A technique is described allowing a relatively simple determination of χ as a function of vr from swelling in heptane. A good measure of the true νe of the cured elastomer at all values of vr was demonstrated by substituting this relationship for χ in the Flory-Rehner (F-R) equation. The relationship was established over a wide range of vr values by using samples that had the νe of the cured elastomer determined by tensile retraction (TR). Applying this function to samples treated using the thiol probe method of Campbell gave an improved measure of the types of crosslinks present in sulfur-cured stocks. An identical equation describing χ as a function of vr in heptane was obtained with NR, EPDM and SBR containing up to a 0.31 volume fraction of carbon black (CB) and other fillers. The presence of up to 10 % of clay, talc, silica, resins or metal oxides in the CB had no noticeable effect on the relationship measured. However, when the filler contained about 50% silica a distinctly different slope in the relationship was found. The percent S1, S2 and Sx distribution measured was contrasted between measurements made by 13C NMR, swelling with χ = constant or χ as a function of vr.
Prevention of Rubber Degradation by Use of Microencapsulated Antioxidants
Authors: Kataoka Takahiro , Zetterlund Per B. , Yamada Bunichiro
Published: February 2011

A new approach of preventing evaporation and migration of antioxidants in rubber is presented. The antioxidant N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD) was microencapsulated in silica (MC6PPD) prior to compounding with the rubber. The microencapsulated antioxidants were characterized by differential scanning calorimetry and thermogravimetric analysis, indicating reduced rates of evaporation compared to free antioxidant. The stress-strain properties, flex cracking resistance and discoloration of the rubber were examined as samples containing equal amounts of antioxidant but in the different forms of 6PPD and MC6PPD. The results clearly indicated superior rubber performance in the case of MC6PPD, suggesting that antioxidant encapsulation is an effective technique to prevent rubber degradation due to aging.
Rheology of PVC Plastisol - VIII: Mechanism of Non-Linear Viscoelastic Behavior
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

The mechanism of the strain-amplitude dependence (non-linearity) of viscoelastic properties of a PVC plastisol was examined. The range of amplitude was 0.02 to 10.24 and the range of frequency was 0.1 to 100 rad/s. The amplitude dependence of dynamic viscosity was very similar to its frequency dependence in that with the increase of amplitude or frequency it decreased first, reaching a minimum and then increased. In the preceding series of papers, the decrease of viscosity with the increase of frequency, i.e. pseudo-plasticity, was attributed to shear-induced phase separation into immobilized layer and mobile phase. In the present work, it is shown that the same mechanism is responsible for the decrease of viscosity with the increase of amplitude. The increase of viscosity with the increase of amplitude (after the minimum) is explained by the dilatation of the immobilized layer. Subsequently, the normal stress acting on the immobilized layer is calculated from the difference of the osmotic pressure between the mobile phase and immobilized layer. The shear deformation of the immobilized layer is estimated to be extremely small, although the deformation in the normal direction, i.e. the dilatation, is significant.
Gel Formation in Natural Rubber Latex: 1. Effect of (NH4)2HPO4 and TMTD/ZnO Additives
Authors: Tarachiwin L. , Sakdapipanich J. T. , Tanaka Y.
Published: February 2011

The rubber from commercially obtained high-ammonia latex (commercial HA-latex) increased in gel content significantly after long preservation of the latex with 1.0% w/v tetramethylthiuram disulfide (TMTD) and zinc oxide (ZnO). Deproteinization of the HA-latex did not decrease the gel content. The gel fraction of deproteinized commercial HA-latex (DPHA-latex) was not solubilized by toluene containing 1.0% ethanol, showing that the gel fraction is composed of chemically crosslinked rubber. The addition of (NH4)2HPO4, which is usually added to fresh latex (FL-latex) to remove excess amounts of Mg2+ ions by centrifugation, decreased the gel formation in FL-latex preserved with 0.6 % v/v NH4OH due to the removal of Mg2+ ions. The excess amounts of (NH4)2HPO4 accelerated the gel formation in preserved FL-latex and commercial HA-latex. The addition of 0.1% w/v TMTD/ZnO to preserved FL-latex treated with 5% w/v (NH4)2HPO4 caused an increase of gel content during storage. The gel formation in the commercial HA-latex during long time storage was presumed to be caused by excess amounts of Mg2+ ions, TMTD/ZnO and (NH4)2HPO4. Here, TMTD/ZnO accelerated the gel formation at the initial stage of storage, while (NH4)2HPO4 affected in long storage.
Understanding the Chemistry of the Rubber/Silane Reaction for Silica Reinforcement, Using Model Olefins
Authors: Debnath S. C. , Datta R. N. , Noordermeer J. W. M.
Published: February 2011

Although bifunctional organosilanes, particularly bis-(triethoxy-silyl-propyl) tetrasulfide (TESPT), are very efficient silica-rubber coupling agents, a high level is required to realize an optimum balance of processing as well as other performance characteristics. As to the functionality of TESPT in silica stocks, till today there remain numerous speculations rather than a clear understanding. An investigation has been carried out to understand the mechanism of the coupling of TESPT with rubber using a model olefin 2,3-dimethyl-2-butene (TME). Reverse Phase High Performance Liquid Chromatography in combination with Mass Spectroscopy shows that when pure TESPT is heated at 140 °C, the concentration of higher S-ranks in TESPT decreases, but in the presence of S8 the concentration of higher S-ranks increases. Treating TME with TESPT at 140 °C yields a mixture of crosslink products differing in the length of the sulfur-link. A mechanistic model for the reaction of TESPT with rubber is proposed, where TESPT donates activated sulfur-radicals, which can react with the rubber or model compound without the need for additional accelerators or vulcanizing agents. As ZnO plays no role in this mechanism, the TESPT merely acts as a sulfur-donor, not in the sense of an accelerator.
On Characterization of Anisotropic Elastomeric Materials for Structural Analysis
Authors: Gurvich Mark R.
Published: February 2011

Existing efforts in constitutive modeling of elastomers are primarily focused on isotropic materials. On the other hand, anisotropic elastic models were successfully developed for traditional composites with relatively small strains, where geometrical non-linearity of deformation may be ignored. There are, however, certain materials where neither large deformation and incompressibility nor anisotropy of material stiffness may be neglected. This study proposes a general constitutive approach to model both hyperelasticity (including incompressibility) and full anisotropy of material deformation in structural analysis. According to the proposed approach, an original hyperelastic anisotropic body is modeled as a combination of two hypothetical components (hyperelastic isotropic and elastic anisotropic ones). The proposed approach shows simplicity and convenience of practical application along with high accuracy of analysis. It may be easily implemented in computational analysis of 2- and 3-D problems using commercially available FEA codes without additional programming efforts. Analytical and computational implementation of the approach is considered on representative examples of elastomeric structures and rubber-based composites. Analytical solutions are shown for examples of biaxial tension of composites and inflation of a toroidal anisotropic tube. FEA solutions are discussed on examples of an inflated anisotropic sphere and non-uniform deformation of a composite layer. Obtained results are discussed to emphasize benefits of the proposed approach. Finally, a methodology to evaluate material parameters using corresponding test results is considered according to the proposed approach.
Testing of Compositional Distribution in Brominated Isobutylene Elastomers
Authors: Svec F. , Fréchet J. M. J. , Duvdevani I.
Published: February 2011

A method based on high-performance liquid chromatography (HPLC) method has been developed for the characterization of the compositional distribution of brominated poly(isobutylene-co-4-methylstyrene) and poly(isobutylene-co-isoprene). The desired separations in normal-phase chromatographic mode could only be achieved by using columns packed with specifically developed 10 and 3 µm porous monodisperse poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads that have a homogeneous coverage of aliphatic hydroxyl groups. Linear gradients of tetrahydrofuran in hexane and dichloromethane in heptane were used respectively as the mobile phases for the selective elution of brominated poly(isobutylene-co-4-methylstyrenes) and brominated poly(isobutylene-co-isoprenes). In-column solvo-thermal treatment of the stationary phase further improved both selectivity and retention and enabled the easy detection and detailed quantification of differences in bromine content well below 1 mol %.
On the Filler Flocculation in Silica and Carbon Black Filled Rubbers: Part II. Filler Flocculation and Polymer-Filler Interaction
Authors: Lin Chenchy J. , Hogan Terrence E. , Hergenrother William L.
Published: February 2011

Filler flocculation and polymer-filler interaction in silica and carbon black filled rubbers containing different functional end-groups were investigated. Lithium-hexamethyleneimine initiated polymers terminated with a proton (HMI-P-H), SnCl4 (HMI-P-Sn), and a mixture of SnCl4 and tetraethyl orthosilicate (HMI-P-TEOS) were employed to determine the affinities of various functionalities toward fillers. Reduced filler flocculation was found for compounds of HMI-P-Sn and HMI-P-TEOS after thermal annealing at 171 °C for 15 minutes when compared to the annealed HMI-P-H stock. Curing at the same condition used for annealing gave further suppression of filler flocculation for HMI-P-TEOS stock by increased polymer-filler interaction during cure. Polymer-filler interaction was followed by examining G′ strain dependence and the differences in G′ obtained between HMI-P-Sn or HMI-P-TEOS and HMI-P-H (δG′). This treatment gave a peak maximum in the δG′ plot as a function of strain. The magnitude of the maximum in HMI-P-TEOS stock is double that of HMI-P-Sn stock and increased after thermal annealing. The compound tanδ temperature dependence showed higher hysteresis around the Tg transition and strong dependence at elevated temperatures was found for HMI-P-TEOS stocks. This increased polymer-filler interaction is manifested with increased 0 °C tanδ and reduced 50 °C tanδ which relates to the improved wet traction and rolling resistance for tires.
Effect of ZnO Particle Size on the Curing of Carboxylated NBR and Carboxylated SBR
Authors: Hamed G. R. , Hua K.-C.
Published: February 2011

A carboxylated nitrile rubber (XNBR) and a carboxylated SBR (XSBR) were mixed with zinc oxide particles of different specific surface areas (“S”, 35 m2/g; “M”, 3.5m2/g; “L”, 0.5 m2/g) and cure behavior at 165 ºC studied using oscillating disc rheometry. Without added zinc oxide, both raw rubbers slowly stiffen over many hours of heating. This is probably due to condensation of carboxyl groups to form anhydride crosslinks. XNBR compositions containing the finely divided “S” crosslink much more rapidly. Full cure is reached after about 10 minutes of heating. Cure rate decreases markedly as the specific surface area of the ZnO decreases. A composition containing “M” at twice stoichiometry requires about an hour to cure well, while with “L”, about 10 hours are required. In contrast, curing of the XSBR depends little on the specific surface area of the ZnO, either with “S” or “L”, curing is essentially complete after 30 minutes. After simply mixing ZnO into either rubber, it remains as a dispersed particulate. With XNBR, curing appears to be controlled by the rate of dissolution and diffusion of ZnO, while, with XSBR, reaction is not diffusion limited and may be confined to regions near particle surfaces.
The Compression of Bonded Rubber Disks
Authors: Anderson M. L. , Mott P. H. , Roland C. M.
Published: February 2011

Compressive stress-strain measurements are reported for bonded disks of natural rubber having shape factors (= d/4t, where d is the diameter and t the thickness) ranging from 0.87 to 12.95. The data are compared to various models for compressed rubber, utilizing the tensile and bulk moduli determined for this material. We find that for thin disks, the measured stiffness is less that the theoretical predictions by roughly a factor of two. A similar discrepancy was found previously, both for elastomers and semi-crystalline polymer films. However, for smaller aspect ratios, the difference between experiment and theory is less than the measurement error.
Zinc Loaded Clay as Activator in Sulfur Vulcanization: A New Route for Zinc Oxide Reduction in Rubber Compounds
Authors: Heideman Geert , Noordermeer Jacques W. M. , Datta Rabin N. , van Baarle Ben
Published: February 2011

Concern about the release of eco-toxic zinc species from rubbers into the environment leads to an increasing interest in potential substitutes. Although alternative metal oxides and zinc compounds as activators for sulfur vulcanization have been studied thoroughly, at present no viable alternative has been found to eliminate ZnO completely from rubber compounds, without significantly jeopardizing processing as well as performance characteristics.

In this paper, the application of a new activator for sulfur vulcanization will be discussed. This activator is developed based on the assumption that an increase in the availability of Zn2+-ions could lead to a considerable reduction of ZnO in rubber compounds. Montmorillonite clay was used as carrier material and loaded with Zn2+-ions via an ion-exchange process.

Application in a wide range of natural and synthetic rubbers has been explored. Results clearly demonstrate that this Zn-Clay can substitute conventional ZnO, retaining the curing and physical properties of the rubber products but reducing the zinc concentration with a factor 10 to 20. Model Compound Vulcanization studies have been used to gain an insight into the mechanism of this activator.

It can be concluded that systems with Zn2+-ions on a support represent a new and novel route to reduce the zinc level, and therefore to minimize its environmental impact significantly.
Filler Dispersion in Hyperbranched Polyisobutylene
Authors: Roland C. M. , Robertson C. G. , Nikiel L. , Puskas J. E.
Published: February 2011

The microdispersion of carbon black filler in linear and hyperbranched polyisobutylene (PIB) was assessed from dynamic mechanical and volume resistivity measurements. While no significant differences were observed in the carbon black concentration necessary for formation of a filler network, in comparison to the linear polymer, the highly branched PIB was found to have substantially more carbon black agglomeration. This occurs despite its higher viscosity, due to the relative inaccessibility of large portions of the molecule, as a result of the profuse treelike branching. The consequence is more extensive interaggregate interaction, and thus a larger Payne effect and greater mechanical hysteresis.
Elastomers for Shoe Applications
Authors: Ames Kimberly A.
Published: February 2011

This review covers the various polymeric materials now used to produce outsoles and midsoles for footwear. Thermoset rubbers are considered to be the best material in terms of performance, but many new materials are challenging in the marketplace, due to their ease of production and lighter weight. While the focus of this review is on improvements made in the last 15 years, the history of footwear and footwear materials is discussed to provide a background for the development of the various alternatives to thermoset rubber.
Biaxial Tensile Behavior of Rubber Vulcanizates: I. Silica and Gum Stocks
Authors: Kajiwara Kanji , Kameda Yoshihiro , Ikeda Yuko , Urakawa Hiroshi , Kawamura Takanobu , Urayama Kenji , Kohjiya Shinzo
Published: February 2011

We have studied the strip biaxial tensile behavior of natural rubber vulcanizates filled with silica by the conventional milling method and by the in-situ silica filling method. The rapid increase of both stresses along the stretching and the fixed axes after the initial stretching was observed on samples filled with a conventional silica by the milling method. Low strain dependence of stresses in the successive strain regions was followed by the rapid increase of the stresses at the higher deformation region. On the other hand, we did not observe such behavior for the samples filled with silica generated in-situ in the rubber matrix before curing. The transmission electron microscopic measurements showed that a highly developed aggregated structure of silica particles was suggested in the conventional silica filled samples and just a simple aggregation was suggested in the case of the in-situ silica filled samples. The differences between samples reinforced with two different filling methods in low tensile region are mainly attributed to the aggregate structure of the silica particles dispersed in the rubbery matrix. We estimated the functional form of the strain energy density function for the samples filled with silica in intermediate and large deformation regions:

        =C10(I1−3)+C01(I2−3)+C20(I1−3)2

The estimated W was found to reproduce the experimental stress-strain curves in intermediate and large deformation region. The relative contributions of three terms in the estimated W for the samples prepared by the in-situ method show the different dependence on the silica content from those of the samples containing silica mixed by the conventional method.
Low Cis Polymerization of Butadiene Using TiCl4 and Bisupported with SiO2/MgCl2(Ethoxide Type)/TiCl4 Catalysts
Authors: Zohuri G. H. , Mohebat R. , Jah R. Jam , Ahmadjo S.
Published: February 2011

To obtain low cis polymer of butadiene (PBR), heterogenous and homogeneous Ziegler-Natta catalyst of TiCl4 were used. SiO2 and Mg(OEt)2 were used as supports for the heterogenous catalyst, while TiCl2 was used as a soluble catalyst. Triisobutylaluminium (TIBA) was used as a cocatalyst. Optimum molar ratio of Al/Ti = 1.5 : 1 and Al:Ti = 13 : 1 were obtained for TiCl4/TIBA and SiO2/MgCl2 (ethoxide type)/TiCl4/TIBA catalyst systems, respectively, regarding productivity of the catalysts. Effect of the temperature of 25–65 °C on polymerization was studied for the bisupport one; while for the TiCl4 temperature control was difficult. This could be due to the obtained high gel content of polymer. The highest yield of PBR was obtained at 55 °C using the bisupported catalyst. Addition of H2 as a chain transfer agent decreased cis%, gel content and the yield of polymer obtained. Increasing polymerization temperature when H2 was used was negligible, which had an affect on the gel content of the polymer. Productivity of the bisupported catalyst was higher than the TiCl4 catalyst itself and the polymerization temperature was under control as well. Polymer with cis content of 4 to 65% was obtained using different catalyst and different polymerization conditions.
Molecular Mobility in Ultrasonically Devulcanized Unfilled Butadiene Rubber
Authors: Oh Jeong Seok , Isayev A. I. , von Meerwall E.
Published: February 2011

We have used NMR relaxation and pulsed-gradient diffusion measurements at 70 °C in unfilled butadiene rubber (BR) before and after crosslinking, and after subsequent devulcanization by intense ultrasound. In an effort to support this method of rubber recycling, characterization has been performed at the molecular level. The transverse relaxation (T2) decay was successfully described using a three-component model. The components are attributed to entangled and crosslinked networks; light sol and dangling network fragments; and partially unreactive oligomers. All component molecular mobilities and the relative contributions of the components to the echo were investigated. Devulcanization decreases the diffusivity of the oligomer remnants and increases mean diffusivity of the light sol. The additional amount of extractable sol produced by devulcanization of BR is more than that of silicone rubber, indicating that the ultrasonic devulcanization of BR is more efficient than that of silicone rubber. The present results are compared with our previous NMR studies of devulcanized rubbers.
Epoxidized Natural Rubber / Silica Nanoscale Organic-Inorganic Hybrid Composites Prepared by Sol-Gel Technique
Authors: Bandyopadhyay Abhijit , De Sarkar Mousumi , Bhowmick Anil K.
Published: February 2011

Epoxidized natural rubber (ENR) / silica organic-inorganic hybrid nanocomposites were prepared by using a sol-gel technique. Tetraethoxysilane was used as the precursor for the in-situ generation of silica. The choice of ENR as a matrix was made because of its polar nature which can interact with the in-situ generated silica. The sol-gel reaction was carried out at room temperature by dissolving the rubber in tetrahydrofuran solvent using hydrochloric acid as the catalyst. The resultant composite films appeared transparent up to 50 wt% of tetraethoxysilane loading. Dispersion of the discrete silica particles having dimensions of 15 – 100 nm was observed through transmission electron microscope. Scanning electron microscopic studies did not produce any evidence for formation of silica network within the bulk of the composite. Infrared spectroscopic studies indicated the occurrence of chemical interaction within the rubber /silica organic-inorganic interfaces which was further supported by the insolubility of the respective samples in tetrahydrofuran under the ambient conditions. Mechanical reinforcement within the hybrid nanocomposites, both at high and low temperature regions, was demonstrated through dynamic mechanical analysis. The composites exhibited superior tensile strength and tensile moduli compared to the gum rubber samples. Further reinforcement was noticed when the rubber phase in the nanocomposites was cured with either benzoyl peroxide or dicumyl peroxide. The dicumyl peroxide cured hybrid composites displayed 112% improvement in tensile strength over the control crosslinked rubber sample, probably due to synergisms of nanosilica reinforcement and crosslinking of the rubber phase in the hybrids.
Extension of the Bergström-Boyce Model to High Strain Rates
Authors: Quintavalla S. J. , Johnson S. H.
Published: February 2011

A filled polybutadiene elastomer, typical of that used in the construction of golf balls, is tested at high (> 5000s−1) and low (< 0.5s−1) strain rates. By using nonlinear least-squares estimation, limited to a physically realizable search domain, suitable parameters are found for the Bergström-Boyce model of time dependent finite strain elasticity. These parameters are shown to successfully represent the material behavior over this broad range of strain rates.
Examination of Rubber Adhesion Property of Brass Film on Steel Formed by Magnetron Sputtering
Authors: Yamauchi Michael T. , Shimizu Toshi , Doi Mitch , Yasunaga David T. , Nakayama Takenori , Okumura Kazuo
Published: February 2011

Brass films were formed on steel rods by magnetron sputtering by using 63 wt% Cu - 37 wt% Zn target in Ar plasma. The brass plated steel rods were inserted in crude rubber and then cured to form various samples. Rubber-brass inter-reacted layers were investigated by cross sectional TEM observation. Evaluation of adhesion force was also conducted in order to compare with the TEM investigation. The magnetron sputtering brass film has strongly oriented columner crystal structure and thickness of the film is uniform in whole area. The magnetron sputtering film has excellent adhesion regardless of the film thickness that cannot be attained by that of commercially manufactured steel cord.
Determination of Residual Vulcanization Accelerators in Natural Rubber Latex Films Using FTIR Spectroscopy
Authors: Temel A. , Schaller R. , Höchtl M. , Kern W.
Published: February 2011

Many vulcanization accelerators are well known contact sensitizers (Type IV allergy) and therefore pose a serious problem in latex applications like gloves and condoms. In this study, a vulcanization system for NR latex based on diisopropylxanthogen polysulfide (DiPXP) and Zn-diisononyl dithiocarbamate (ZDiNC) was investigated. The thermal decomposition of DiPXP during and after the vulcanization process was assessed. FTIR methods for the determination of residual vulcanization accelerators ZDiNC and DiPXP in latex films and extracts therefrom were developed. When appropriate conditions are selected for the production of NR latex films, the accelerator DiPXP was no more detectable in extracts from the finished NR latex product. The use of thermally decomposable vulcanization accelerators is a way towards NR latex products with significantly reduced allergenic potential.
Moisture Effects on TESPD-Silica/CB/SBR Compounds
Authors: Kim Kwang-Jea , VanderKooi John
Published: February 2011

Moisture was treated on a silica surface and it was added into bis(triethoxysilylpropyl)disulfide (TESPD)/carbon black (CB)/S-SBR compound and mixed in an internal mixer. The effects of moisture were investigated with respect to the temperature rise during mixing, processability, cure characteristics, and mechanical properties and two-pass (2P) mixings were compared with conventional three-pass (3P) mixings. Addition of the moisture treated silica into the compound lowered the heat generation during mixing, lowered the drop temperature, decreased the scorch time, lowered the heat build up, lowered the tanδ (E″/E′), increased the Mooney viscosity, increased the torque rise (MH-ML), increased the elongation modulus, increased the blow out time, and increased the deformation%. The properties of each compound were gradually increased with the level of moisture and the 2P mixing procedure generated less heat during mixing and exhibited better mechanical properties than the 3P mixing one. The addition of water molecules improved the silane reaction with silica surface via improved hydrolysis and resulted in an increased level of cross-linking. It also seemed hydrolyzes the benzothiazolesulfenamide accelerator and resulted in a faster scorch and an increased cure rate.
Investigation of the Payne Effect and its Temperature Dependence on Silica-Filled Polydimethylsiloxane Networks. Part I: Experimental Results
Authors: Clément F. , Bokobza L. , Monnerie L.
Published: February 2011

The Payne effect is studied in silica-filled polydimethylsiloxane networks, containing various silica loadings and at variable temperature. The effect of a permanent surface treatment of the silica particles, as well as the influence of the incorporation in the system of a processing aid agent, have been investigated. The amplitude of the Payne effect is reduced by introducing a permanent treatment of the silica or a processing aid. Contrary to the unfilled network which shows the typical entropic dependence of the elastic modulus, the low shear strain elastic modulus of filled networks decreases when temperature increases. When the shear strain increases, this temperature dependence becomes less and less pronounced, and reaches a plateau value at deformations above 100%.
Effect of Zinc Complexes as Activator for Sulfur Vulcanization in Various Rubbers
Authors: Heideman Geert , Noordermeer Jacques W. M. , Datta Rabin N. , van Baarle Ben
Published: February 2011

Because of environmental concerns, the zinc content in rubber compounds has come under scrutiny; therefore it is necessary to explore possibilities to reduce this zinc content. In this article the application of several zinc complexes as activator for sulfur vulcanization are discussed, in order to find alternatives for the conventionally used ZnO and fatty acid activator system. The effects of different zinc complexes on the cure and physical properties of two widely different rubbers, viz. EPDM and s-SBR, are studied. It can be concluded that zinc-m-glycerolate is a good substitute for ZnO as activator for sulfur vulcanization, in EPDM as well as in s-SBR rubber, without detrimental effects on the cure and physical properties. Furthermore, the results indicate that, dependent on the intended applications, zinc-2-ethylhexanoate represents a substitute for the commonly used ZnO. Zinc stearate is considerably less active as activator in sulfur vulcanization.
Effect of Nanoclay on the Dynamic Mechanical Properties of Styrene Butadiene and Acrylonitrile Butadiene Rubber Vulcanizates
Authors: Sadhu Susmita , Bhowmick Anil K.
Published: February 2011

Nanocomposites based on Styrene Butadiene Rubber (SBR) and Acrylonitrile Butadiene Rubber (NBR) with varying acrylonitrile contents (19%, 34% and 50%, respectively) and octadecyl amine modified and unmodified Na-Montmorillonite clays were prepared. Dynamic mechanical thermal analysis (DMTA) was performed on these composites over a range of temperatures (−80 °C to +80 °C), frequencies (0.032 Hz to 32 Hz) and strains (0.001% to 10%). The results showed that there were significant changes in tan delta peak temperature and height and storage modulus with the addition of small amount (4 phr) of the modified and the unmodified fillers. These were magnified with the increase of filler loading. The tan delta peak heights decreased and the storage modulus increased in general. With increasing strain, the nanocomposites showed lowering of storage modulus, because of the breakdown of the agglomerated structures. The torage modulus increased with increasing frequency, and the modified filler loaded samples registered higher E' values compared to those of the gum rubber.
Tearing of Vulcanized Rubber
Authors: Hamed G. R.
Published: February 2011

This short review summarizes some results of studies of rubber fracture carried out in the author's laboratory over the past several years. Particular attention has been focused on the details of cracking in technically important natural rubber vulcanizates with very high resistance to tearing. Such rubbers develop auxiliary cracks that grow essentially parallel to the loading direction and inhibit the main tear front from advancing. This crack splitting is attributed to oriented structure at the tear front and is predicted to occur when strength anisotropy at a tear tip reaches a critical value.
Preparation of Functionalized Low Molecular Weight Natural Rubber Latex Using Solid Nanometric TiO3 Film as a Photocatalyst
Authors: Sakdapipanich Jitladdat , Suksawad Patjaree , Insom Kittipong , Kawahara Seiichi
Published: February 2011

Natural rubber (NR) is a high molecular weight (MW) hydrophobic polymer, which can not be easily dissolved in several kinds of solvents, leading to the limitation of usage. NR latex containing low MW and reactive-terminal groups is another interesting form to extend the applications of NR. In this study, a photochemical degradation of NR using H2O2, nanometric TiO2 film and UV irradiation was applied to prepare the hydroxylated low MW NR (LNR). A solid nanometric TiO2 film prepared from titanium solution was applied in the present work. The photosensitivity of the self-assembled TiO2 film was determined by the decomposition rate of methylene blue stock solution using UV/VIS spectrophotometer. The effect of type of NR latex used, H2O2, UV light and TiO2 film on the molecular weight reduction was studied, based on change in intrinsic viscosity determined by Ubbelohde solution viscosity. The structural characterization of the resulting LNR was analyzed by FT-IR and NMR techniques. It was found that hydroxylated LNR with number average molecular weight of 1 × 104 g/mol was obtained by UV irradiation (40 W) of deproteinized natural rubber (DPNR) latex (10% DRC) containing 30% w/w H2O2, on a petri dish coated with TiO2 film for 5 hr. The advantage of this method is that the obtained hydroxylated LNR in either latex or dry rubber form is very clean without further purification.
Field Aging of Tires, Part II
Authors: Baldwin John M. , Bauer David R. , Hurley Paul D.
Published: February 2011

In an attempt to better understand the mechanism of rubber aging in tires, used tires were retrieved from customer cars. Consumers were contacted in six cities located throughout the United States (Detroit, MI; Hartford, CT; Phoenix, AZ; Miami, FL; Denver, CO; and Los Angeles, CA) and interviewed with regards to driving and maintenance habits. A total of approximately 2,500 tires were obtained from the field and of those, around 1,500 were dissected and analyzed. Some of the tests performed were tensile and elongation properties of the rubber at the belt edges, swelling ratio measurements across the belt skim rubber, and the peel adhesion force required to separate the two steel belts. This paper is concerned with the determination of aging mechanisms based on the change in rubber properties within the tire. Analysis of rubber property evolution with respect to time and mileage are the subject of another paper. Three analytical approaches were taken to investigate the mechanism of aging in field retrieved tires. The first approach, the ‘Ahagon’ analysis, showed that for the three tires collected from the vehicle class SUV/Minivan all tires aged oxidatively in the field, regardless of geographic location. The second approach explored the relationship within the skim rubber between the swelling ratio and the peel strength. The results showed that a significant correlation exists, and that as the swelling ratio decreases, the peel strength also decreases. The third methodology employed investigated the link between swelling ratio of the skim rubber and the strain ratio at break of the wedge rubber, which also showed a significant correlation between the two properties. Spare tires obtained from the same vehicles (2 out of the 3 vehicles came equipped with a full size spare) were then compared to the road tires using the same analytical techniques. In every case, the spare tire data was statistically identical to the road tire data, meaning that mechanical fatiguing does not impact the aging process with regards to property change of the rubber. This also means that statically aging a tire (either as a spare or in an oven) completely duplicates the oxidative aging seen in road tires. Oven aged tires of different constructions were compared to the spare tire data and shown to be similar. Future work will be to oven age tire constructions that field data is available for, so direct comparisons can be made.
Investigation of the Adhesion Layer Formed on Brass Using Field Emission-Scanning Electron Microscope
Authors: Kim Jong Myoung
Published: February 2011

Change in the morphological features of the adhesion layer formed on brass was observed with Field Emission-Scanning Electron Microscopy (FE-SEM). The effect of the key compounding ingredients on the morphology of the adhesion layer was studied. Morphology of the various metal sulfides of cobalt, zinc, copper, bronze and brass was also observed with FE-SEM. Fracture mode appeared during the pull-out test was categorized and was correlated with the adhesion strength. The damage on the adhesion layer after humidity aging test was examined by FE-SEM.
Comparative Investigation on the Reclamation of NR Based Latex Products with Amines and Disulfides
Authors: Rajan V. V. , Dierkes W. K. , Noordermeer J. W. M. , Joseph R.
Published: February 2011

The latex industry has expanded over the years to meet the world demands for gloves, condoms, latex thread, etc. Due to the strict specifications for the products and the unstable nature of the latex, as high as 15% of the final latex products are rejected. Since waste latex rubber (WLR) represents a source of high quality rubber hydrocarbon, it is a potential candidate for generating reclaimed rubber of superior quality. In the present investigation, two reclaiming agents for WLR vulcanizates were studied in a thermo-mechanical reclaiming process. Parameters investigated were the concentration of the reclaiming agents, as well as reclaiming temperature and time required for proper reclamation. The efficiency of the reclamation process was studied by measurement of the Mooney viscosity, sol-gel analysis and swelling measurements. The ratio of main-chain scission to crosslink scission was studied and the distribution of mono-, di-, and polysulfidic crosslinks was analyzed by thiol-amine reactions. Of the two chemicals investigated, diphenyldisulfide proves itself very effective as reclaiming agent. On the other hand, amines are not suitable as reclaiming agents, because they result in the formation of crosslinks compared to the case where no reclaiming agent is used for reclaiming.