Unfilled Styrene-butadiene Rubber Research Articles

An investigation on Moringa oleifera fruit (drumstick)‐derived cellulose micro and nanofiber reinforced styrene butadiene rubber composites

AbstractThe current focus in the elastomer industry is to look for biobased or natural filler for various compounds. The reinforcing effect of waste drumstick‐derived cellulose micro and nanofiber in styrene butadiene rubber (SBR) was investigated for the very first time. Cellulose microfibers and nanofibers were isolated from the drumstick fruit peel and characterized using different techniques such as x‐ray diffraction, scanning and transmission electron microscopy, and x‐ray photoelectron spectroscopy. The filler‐polymer interaction in the composites was studied using the bound rubber measurements, which showed that the bound rubber content of the composite increased from 0.5% to 8.1% at 5 phr cellulose nanofiber loading. The tensile strength and modulus of the modified cellulose microfiber‐containing composite were higher than both the unfilled SBR and the raw fiber‐SBR composites. The addition of 5 phr nanofiber to SBR showed a 46% increment of the tensile strength than the control compound. The die swell index of the cellulose fiber reinforced composites came down attesting the better processability of the extrudates. The addition of cellulose fiber also improved the wet skid resistance of the composites as seen from dynamic mechanical thermal analysis. Hence, this work confirms the application of modified drumstick microfibers and nanofibers as sustainable fillers for high‐performance elastomers composites.

Carbon Nanotubes Networking in Styrene‐Butadiene Rubber: A Dynamic Mechanical and Dielectric Spectroscopy Study

AbstractThe study of the reinforcement network in elastomer compounds is one of the most relevant issues for the application of these materials because their properties are strongly dependent on the obtained morphology. To this regard, the viscoelastic and dielectric behavior of vulcanized styrene butadiene rubber (SBR) reinforced with different amounts of carbon nanotubes (CNT) have been investigated and compared with the vulcanized unfilled SBR and the vulcanized SBR samples reinforced with a conventional amount of carbon black (40 phr). Differential scanning calorimetry (DSC) measurements have been carried out to highlight possible differences of the glass transition temperatures for all the reinforced compounds. The percolation threshold value of the nanocomposite samples has been estimated by dielectric analysis. Finally, dynamic mechanical analysis (DMA) measurements have been performed in tensile mode in the temperature range of −60 to 80 °C to obtain bothE′ andE′′. From these experimental data, the master curve for each sample has been estimated by using the time–temperature superposition principle in combination with the vertical shift approach. From the analysis of this latter, the activation energy, associated to the thermal movement of the reinforcement network, has been calculated to better elucidate the reinforcement mechanism in the nanocomposites.

Improvement of nanosilica effects on the performance of mechanically processed styrene-butadiene rubber by rational hybridization with nanodiamond

Hybrid nanoparticle comprising of nanosilica (NS) and nanodiamond (ND), denoted by [email protected], was synthesized by a two-step chemistry route and then incorporated into styrene-butadiene rubber (SBR) at low concentrations up to 5 phr by a two-roll mill. Physical hybrids of NS and ND, i.e., ND&NS, with a weight ratio similar to chemical hybrid (80:20 for NS:ND), were also incorporated into SBR. Field emission scanning electron microscopy observations revealed very fine dispersion of nanoparticles in the case of physical hybrids (ND&NS). In contrast, agglomerations and aggregation of nanoparticles were evidenced for [email protected] Tensile and dynamic mechanical analyses exhibited a higher reinforcing effect of hybrid nanoparticles with respect to single nanoparticles; however, ND&NS showed even better performance compared with [email protected] due to better filler-rubber interaction caused by improved filler dispersion. So, tensile strength, elastic modulus, and elongation at break of unfilled SBR increased about 23 %, 40 %, and 110 %, respectively, in the case of ND&NS. It was also realized that the incorporation of [email protected] and ND&NS, both at 5phr, enhanced the thermal conductivity of SBR by around 46 % and 31 %, respectively, with slightly better influence of [email protected] on thermal conductivity due to the improvement of the phonon energy transfer mechanism in this case.

Mechanical and thermal performances of styrene butadiene rubber nanocomposites with boron nitride nanosheets, carbon nanotubes, and the hybrid filler system

AbstractPreparation of rubber nanocomposites using two or more nanofillers with different geometries is a new and promising approach. In this work, the effects of boron nitride nanosheets (BNNS), carbon nanotubes (CNT) and their hybrid (BNNS‐CNT) on the performances of styrene butadiene rubber (SBR) nanocomposites are systematically studied. The mechanical properties of the nanocomposites are significantly enhanced by the nanofillers. The tensile strength of unfilled SBR is only 1.30 ± 0.18 MPa, which increases to 1.72 ± 0.24 MPa (BNNS), 4.09 ± 0.35 MPa (CNT), and 3.37 ± 0.29 MPa (BNNS‐CNT) at 4 phr, respectively. Similarly, the tear strength of unfilled SBR is 8.0 kN/m, which increases to 13.8 kN/m (BNNS), 16.1 kN/m (CNT) and 18.2 kN/m (BNNS‐CNT) at 4 phr, respectively. Moreover, the thermal behavior of the nanocomposites are analyzed. Compared with single nanofiller BNNS or CNT, BNNS‐CNT hybrid nanofiller not only effectively improves the mechanical properties of nanocomposites, but also imparts better thermal properties. It is proved that the thermal decomposition temperature of SBR/4phr BNNS‐CNT is increased by nearly 7°C compared with unfilled SBR.

Detailed understanding of the carbon black–polymer interface in filled rubber composites

To characterize the nature of the interface between styrene-butadiene rubber (SBR) and carbon black (CB) in a filled rubber compound, we introduce an extraction protocol that uses toluene solvent in a high-pressure autoclave with sequential temperature steps of 90, 110, and 150 °C. This new approach removes unbound and physically bound (physisorbed) polymer from the CB-filled SBR compound to leave only chemically bound polymer which is 0.86% (0.0172 g polymer/g CB) and not zero as implied from extrapolating prior literature results. Rheological time sweeps on the unfilled gum SBR indicate that significant crosslinking can occur during annealing at 150 °C for this unsaturated polymer. This was the motivation for using the sequential extraction procedure versus direct extraction at 150 °C which gives a nearly six-fold higher amount of unextracted polymer due to such crosslinking. Analysis of the temperature dependence of bound rubber from 23 to 150 °C indicates that the physical interactions between the polymer and CB surface have a weaker component with a desorption energy (Ed) of 6.8 kJ/mol and a stronger component with Ed = 90.7 kJ/mol, the latter requiring an extraction temperature of 110 °C to remove the majority of it from the CB.

Compressive Fatigue Behavior of Gum and Filled SBR Vulcanizates.

The influence of carbon black on physical mechanical properties, compressive fatigue life, and the temperature changes during compression fatigue process of styrene-butadiene rubber (SBR) vulcanizates were explored. A series of unfilled and filled SBR compounds were prepared, and the compressive fatigue behaviors of the vulcanizates were performed on a mechanical testing and simulation (MTS) machine. The top surfaces of the filled SBR were imaged using scanning electron microscopy (SEM) after 105 cycles of compressive fatigue. The filled SBR shows greater compressive fatigue resistance than the unfilled SBR. The incorporation of carbon black into SBR improves the creep resistance. The best compressive fatigue resistance for the filled SBR was achieved by the addition of 30 phr carbon black. With the increase of carbon black content, the energy dissipation and the heat build-up increase simultaneously. Furthermore, SEM images of the vulcanizates suggest that the crack propagation mechanism of the unfilled and the filled SBR was different. For the unfilled SBR, due to periodical compressive stress, the polymer chains can be destroyed, and the cracks can be easily initiated and propagated, showing serious damage on the top surfaces of the specimen. However, for the filled SBR, the carbon black agglomeration around the cracks can greatly delay the generation of the cracks, decrease the fatigue damage, and ultimately improve the fatigue resistance.

Rational design for enhancing mechanical and conductive properties of Ti3C2 MXene based elastomer composites

Herein, we propose a novel Ti3C2 grafted SiO2 (Ti3C2-g-SiO2, 21.2% loading weight content of SiO2) multifunctional filler with an average thickness of 10 ± 2 nm, which is skillfully prepared via an in-situ growing approach, to blend with styrene-butadiene rubber (SBR) and create high-performance elastomer composites. Thanks to the incorporation of SiO2, the Ti3C2-g-SiO2 not only disperses better (a uniform state) than Ti3C2 in the rubber matrix but also obtains innumerous nano protuberances on its surface to constrain more rubber chains than Ti3C2, significantly improving the interfacial interaction. Therefore, by comparison of the unfilled SBR sample, the mechanical strengths of the prepared Ti3C2-g-SiO2 filled SBR sample are dramatically enhanced, including tensile strength (enhanced by 244%, from 4.09 to 14.1 MPa) and elongation at break (enhanced by 93%, from 271 to 522%). More importantly, the Ti3C2-g-SiO2 filled SBR sample featuring excellent electrical (8.96 × 10−4 S m−1) and thermal conductivities (0.449 W m−1 k−1), which could exceed the reduced graphene oxide filled SBR sample.

A high-performance, thermal and electrical conductive elastomer composite based on Ti3C2 MXene

In this study, a single-layered Ti3C2 hybrid SiO2 filler (Ti3C2-h-SiO2) was proposed to fabricate high-performance styrene-butadiene rubber (SBR) elastomer composites. It was found that incorporating SiO2 not only facilitated the uniform dispersion of Ti3C2-h-SiO2 in the SBR matrix but also endowed the surface of Ti3C2-h-SiO2 with nano protuberances for immobilizing more rubber chains, resulting in the improvement of the interfacial interaction between Ti3C2-h-SiO2 and SBR matrix. Thus, the tensile strength of the SBR/Ti3C2-h-SiO2 elastomer composite was reinforced by 174% compared with the unfilled SBR. Moreover, the wet skid resistance and rolling resistance of the SBR/Ti3C2-h-SiO2 elastomer composite were also remarkably improved. Noteworthily, the exceptional thermal conductivity (0.401 W m−1 k−1) and electrical conductivity (4.87 × 10−4 S m−1) of the SBR/Ti3C2-h-SiO2 elastomer composite were comparable to the SBR/reduced graphene oxide (rGO) elastomer composite, implying that the conductivity of Ti3C2-h-SiO2 may be competitive with the rGO.

High-performance styrene-butadiene rubber nanocomposites based on carbon nanotube/nanodiamond hybrid with synergistic thermal conduction characteristics and electrically insulating properties

Reinforcement of rubbery materials with carbon nanotube (CNT) has gained much attention over the last few decades due to the inherent ability of CNT to improve the physical and mechanical properties of polymer composites. However, CNT renders electrical conductivity to the rubber composites, which could be problematic for a number of applications. In an attempt to overcome such issues, we controlled the insulating properties of styrene-butadiene rubber (SBR) nanocomposites by hybridization of CNT with nanodiamond (ND) particles without scarifying desirable features of the nanoparticles. In this respect, the effects of carbon nanotube (CNT) and nanodiamond (ND), either individually or in hybrid form, on mechanical, physical, morphological and thermal properties of styrene-butadiene rubber (SBR) nanocomposites were well characterized in the present research using bound rubber, tensile, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), electrical, and thermal conductivity characterizations. The SBR nanocomposites holding nanoparticle concentrations ranging from 1 to 5 phr were fabricated at various CNT/ND compositions. The results indicated that the hybridization of nanoparticles improved the dispersion state of individual nanoparticles in SBR, successfully controlled the insulating behavior of the SBR nanocomposite and enhanced the thermal conductivity of SBR in synergistic manner; while the mechanical improvement retained as CNT filled SBR. The SBR nanocomposites holding 5 phr hybrid-nanoparticles with appropriate nanoparticles composition possessed thermal conductivity more than two-fold of unfilled SBR and 20% more than nanocomposite with 5 phr loading of single CNT.

Four Non-Gaussian-Type Tube Models of Rubber-Like Elasticity: Analysis of Tensile Data for Lightly and Highly Carbon-Black Filled Styrene-Butadiene Elastomers

Recently, using a new, non-Gaussian, tube-based entropy model for active-filler filled elastic networks with the polymer phase influenced by the filler loading, proposed by the author, a data analysis of literature tensile data for carbon-black filled styrene-butadiene rubber (SBR) networks of different loadings was carried out; the data-fittability and the particular influence of the filler loading were examined in detail. In this report, the data-fitting performances of three other non-filled network models, all tube-based and finite chain extensible, along with a common strain-amplification factor that is necessary to extend them to the analysis of the filled networks, as well as the model which was employed in the above study were compared. As tensile data for this analysis, those observed for the same unfilled SBR, the same lightly loaded SBR and one of the same highly loaded SBR networks, as in our previous study, were chosen.

Study on the effect of silica–graphite filler on the rheometric, mechanical, and abrasion loss properties of styrene–butadiene rubber vulcanizates

Silica–graphite filler was prepared via two-step grafting procedure by grafting silica particles onto the expanded graphite. In the first step, isocyanatopropyltriethoxysilane was chemically introduced onto the silica aggregates, which was followed by grafting onto the expanded graphite via urethane linkage in the second step. Successful grafting of silica aggregates onto the graphite was corroborated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The presence of a thin graphene layer on silica aggregates corroborated using transmission electron microscopy confirmed the grafting of silica aggregates onto the graphite surface. Styrene–butadiene rubber (SBR) composites with various silica–graphite loadings were prepared by melt processing technique to generate pristine silica and silica–graphite-filled elastomeric composites. Rheometric cure studies revealed that the torque difference (Δ S) increased with pristine silica loading, when compared to the unfilled SBR system, and this effect is more pronounced on loading silica–graphite filler. Improvements in mechanical properties such as modulus and tensile strength were observed with increasing loading of silica particles and this effect is more pronounced on loading silica–graphite fillers, indicating that this is due to the rise in the elastomer–filler interactions in the silica–graphite-loaded SBR systems. This fact was further corroborated using bound rubber content and equilibrium swelling ratios of the unvulcanized and vulcanized SBR composites.

Effects of the Synergy of Hardness and Resilience on the Akron Abrasion Properties of SBR Vulcanizates

The hardness (H) and resilience (R) of rubber vulcanizates were combined together in this paper, named as hardness–resilience product (H4R), and its relationship with the Akron abrasion loss was investigated using various styrene-butadiene rubber (SBR) vulcanizates possessing specific hardness and resilience characteristics as samples. For the unfilled SBR vulcanizates with different chain microstructure, possessing high elastic resilience and low hardness, the results showed that their Akron abrasion loss had a good linear relationship with the log(H4100R). This linear relationship also occurred when these SBRs were filled with 50 phr carbon black. For two particular types of SBR, after being filled with different fractions of carbon black and aged for different times, all their Akron abrasion losses (including unaged, aged for 24 h, and aged for 48 h) also had a good linear relationship with the log(H4100R). However, this linear relationship weakened for one of the SBRs after being aged for 48 h. In the high H4R region (the carbon black fractions being 60 and 70 phr), the data obviously deviated from the fitting curve due to the high hardness of the aged vulcanizates. However, after being filled with 50 phr of various kinds of carbon blacks, the relationships between abrasion loss and log(H4100R) were also approximately linear, with the correlation coefficient of the fitting curves being 0.99966 and 0.99878, respectively, for the two types of SBR.

Rubber friction: Comparison of theory with experiment

We have measured the friction force acting on a rubber block slid on a concrete surface. We used both unfilled and filled (with carbon black) styrene butadiene (SB) rubber and have varied the temperature from -10 °C to 100 °C and the sliding velocity from 1 μm/s to 1000 μm/s. We find that the experimental data at different temperatures can be shifted into a smooth master-curve, using the temperature-frequency shifting factors obtained from measurements of the bulk viscoelastic modulus. The experimental data has been analyzed using a theory which takes into account the contributions to the friction from both the substrate asperity-induced viscoelastic deformations of the rubber, and from shearing the area of real contact. For filled SB rubber the frictional shear stress σ(f) in the area of real contact results mainly from the energy dissipation at the opening crack on the exit side of the rubber-asperity contact regions. For unfilled rubber we instead attribute σ(f) to shearing of a thin rubber smear film, which is deposited on the concrete surface during run in. We observe very different rubber wear processes for filled and unfilled SB rubber, which is consistent with the different frictional processes. Thus, the wear of filled SB rubber results in micrometer-sized rubber particles which accumulate as dry dust, which is easily removed by blowing air on the concrete surface. This wear process seams to occur at a steady rate. For unfilled rubber a smear film forms on the concrete surface, which cannot be removed even using a high-pressure air stream. In this case the wear rate appears to slow down after some run in time period.

Influence of the filler type on the rupture behavior of filled elastomers

AbstractThis work is devoted to the rupture behavior of elastomers filled with carbon black (CB) or silica. Two elastomers have been studied: one which crystallizes under strain, natural rubber (NR), and another one which does not crystallize, styrene butadiene rubber (SBR). The study of the crack propagation of Single Edge Notched specimen (SENT) during stretching at different speeds focuses on the crack initiation and crack deviation phenomenon. This deviation is of main importance in the materials crack resistance as it leads to a large increase in the energy needed for rupture. The deviation in filled or unfilled NR is controlled by crystallization, which is a slow process. In unfilled SBR, deviation is controlled by polymer chain orientation, which is hindered by relaxation mechanisms. The introduction of fillers promotes strain amplification, and strain anisotropy in the crack tip region of the notched samples, and therefore crack deviation. In term of energy density at break of the SBR composites, the SBR filled with silica treated with a covering agent is the most efficient. Thus, a weak interface between the silica and SBR promotes better rupture properties. When comparing Silica and CB filled NR, the highest strain energy to rupture is also obtained with silica. This might be due to the weaker filler‐matrix interface for silica. Thus, these results evidence the kinetic aspect of the rupture, and of the mechanisms it involves: the polymer relaxation, the crystallization (for NR), and the filler‐matrix interaction and decohesion, all of them being strongly interrelated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The steady state abrasion of rubber: Why are the weakest rubber compounds so good in abrasion?

This paper examines the blade abrasion of four different rubber materials, unfilled natural rubber (NR), unfilled styrene butadiene rubber (SBR), unfilled butadiene rubber (BR) and carbon black filled styrene butadiene rubber. Each is abraded until the steady state abrasion pattern is developed on the surface of moulded rubber wheels. The steady state conditions are measured using the weight loss per revolution of the wheel. The abraded surface is cut to examine the typical asperity profile. Each profile is modelled using finite element analysis to calculate the stored energy release rate for each combination of material and test condition. The stored energy release rate when combined with an independent measure of the rate of crack growth measured using a fatigue crack growth test gives a reasonable prediction of the abrasion rate for both SBR materials as well as the BR. However, the NR materials appear to be about 30 times worse in abrasion than would be expected from the cyclic fatigue crack growth measurements. This is most likely to result from the strain induced crystallisation being suppressed by the very rapid loading rates that are encountered during blade abrasion. It is apparent that the low strength of the BR material results in much smaller asperities being formed under steady state abrasion. When these asperities are modelled they create very low values of strain energy release rate which results in a much slower abrasion rate. Conversely the strongest material NR has the longest tongue on the asperity and this in turn generates much larger values for the tearing energy at the tip of the asperity and this contributes to its poor abrasion resistance.

Synthesis and Characterization of Chemically Crosslinked Styrene-Butadiene Rubber Nanogels and their Effect on Various Properties of the Rubber

Abstract Nano-sized styrene-butadiene rubber (SBR) latex gels were prepared by pre-vulcanizing SBR latex with different sulfur to accelerator ratios. These gels were characterized by swelling studies, dynamic light scattering, atomic force microscopy, mechanical and dynamic mechanical properties. With the increase in sulfur to accelerator ratio, the gels had higher amount of crosslink density and gel content. Particle size distribution did not alter much in the crosslinked gels. Incorporation of these nanogels into raw SBR led to the considerable drop in viscosity of the gel filled systems under capillary melt flow conditions. However, the reduction in viscosity was found to be dependent on the loading and crosslink density of the nanogels. Energy dispersive X-ray mapping of sulfur was used to check the dispersion of these gels into raw SBR matrix. The die swell values of gel filled SBR were much lower than that of the raw SBR. The reduction in principal normal stress difference values combined with the reinforcement effect of the gels was found to be responsible for the lowering of die swell values. Scanning electron photomicrographs of extrudates of gel filled systems showed much-improved surface smoothness compared to the unfilled SBR. The mechanical and dynamic mechanical properties also showed excellent improvement in modulus with the addition of gels in the raw rubber. A new empirical relationship was proposed to explain the reinforcement properties of nanogels as viscoelastic fillers.

Thermomechanical Degradation of SBR During Ultrasonic Treatment under the Static Conditions

Abstract The paper presents the results of experimental and theoretical studies of the ultrasonic treatment of ground vulcanized unfilled styrene-butadiene rubber (SBR) in a static device (no flow). Degradation of the rubber network took place during the treatment. Crosslink density and gel fraction were measured in the samples ultrasonically treated at various pressures, ultrasonic amplitudes and exposure times. Consumption of the ultrasonic energy was also monitored. The structural characteristics of SBR ultrasonically treated under static conditions have been found to be significantly different from those reported previously for the continuous process. Theoretical calculations have demonstrated that the observed differences could be attributed to a partial depolymerization of broken rubber chains caused by a significant temperature rise in the course of ultrasonic treatment under static conditions. It has also been shown that the non-linearity of compressibility of a thin ground rubber layer has to be taken into account in the calculations of ultrasonic power consumption.

Comparative analysis of ultrasonically devulcanized unfilled SBR, NR, and EPDM rubbers

AbstractThe comparative study of the continuous ultrasonic devulcanization of various unfilled rubbers [natural rubber, styrene–butadiene rubber (SBR), ethylene–propylene–diene rubber (EPDM)] is carried out by means of a ultrasonic reactor. The power consumption, gel fraction, crosslink density, cure behavior, and physical properties of devulcanized rubbers were measured. The glass transition temperatures of virgin, vulcanized, and devulcanized rubbers were determined in order to characterize the difference in the mobility of rubber molecules for each rubber before and after devulcanization. Thermogravimetric analysis was also used to determine thermal stability of the various rubbers. A unique correlation between gel fraction and crosslink density indicated significant differences in the efficiency of devulcanization of various rubbers. Under certain devulcanization conditions, the mechanical properties of revulcanized SBR and EPDM rubbers were found to improve compared to those of the original rubbers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 434–441, 2003