Styrene Butadiene Rubber Phase Research Articles

Dynamic mechanical properties in natural rubber/styrene‐butadiene rubber blends: The local strain behavior in the glass transition region

AbstractA study of the local strains developed in vulcanized blends of natural rubber (NR) and styrene butadiene rubber (SBR), prepared by solution mixing, is presented. A semi‐EV system based on sulfur and accelerator was used for curing unfilled compounds at 160°C and 170°C. Samples were characterized by dynamic mechanical properties between −80°C and 20°C. Special interest was placed on the glass transition region of the vulcanized immiscible blends, where the NR and SBR phases are rubbery and glassy respectively. From the study of loss modulus, this research demonstrates how the local strain in the NR phase changes as a function of the amount of SBR in the blend. Assuming a coalescence behavior of the SBR glassy phase above a certain concentration, differences in the local stiffness of each phase in the glass transition regime were found. While in the glassy SBR phase the stiffness slightly varies with the NR/SBR content, a notorious increase was obtained in the rubbery NR phase at higher SBR content. The local strain on the NR phase of the blends shows a slight decrease for the samples vulcanized at 170°C compared with those vulcanized at 160°C.

Cover Image, Volume 138, Issue 45

The cover image by Shin Horiuchi and co-authors shows how the distribution of nano-sized silica in binary rubber blends is characterized by scanning transmission electron microscopy (STEM) tomography, combined with energy dispersive X-ray spectrometry (EDX). 3D distribution of silica, is visualized by STEM-EDX tomography. The phase-separated morphologies of polyisoprene rubber (IR) and styrene-butadiene rubber (SBR) meanwhile is visualized by STEM-tomography in high-angleannular-dark field (HAADF) mode. The combination of STEM-EDX and STEM-HAADF tomography determines the distribution of silica between the two rubber phases quantitatively. The silica in IR (light blue) and in SBR (dark blue) phases can be identified as yellow and pink regions, respectively. DOI: 10.1002/app.51443

Spatial distribution of silica fillers in phase‐separated rubber blends investigated by three‐dimensional elemental mapping

AbstractThe distribution of nano‐sized silica in binary rubber blends is characterized by scanning transmission electron microscopy (STEM) tomography combined with energy dispersive X‐ray spectrometry (EDX). 3D distribution of silica is visualized by STEM‐EDX tomography with the tilt‐series of silicon elemental maps, while the phase‐separated morphologies of polyisoprene rubber (IR) and styrene‐butadiene rubber (SBR) are visualized by STEM‐tomography in high‐angle‐annular‐dark field (HAADF) mode. The combination of STEM‐EDX and STEM‐HAADF tomography enables us to determine the distribution of silica between the two rubber phases quantitatively even with high contents of silica up to 70 phr (weight parts per hundred rubber). It is found that silica is preferentially distributed in the SBR phase, but it is also distributed in the IR phase when the IR fraction in the total rubber components is higher than 40 wt%. The preferential distribution of silica in the SBR phase improves the dispersion of the IR domains. This is the first use of this technique for a multicomponent polymer system, showing the advantage to characterize the complicated multicomponent polymer composite morphologies.

NMR Studies on the Phase-Resolved Evolution of Cross-Link Densities in Thermo-Oxidatively Aged Elastomer Blends

A knowledge of the distribution of cross-link densities (CDs) in the constituent rubber phases of an elastomer blend is essential to understand its overall service properties, but phase-resolved CD estimations have so far been limited to qualitative assessments. In a first study of its kind, we demonstrate a phase-resolved quantification of the CDs in sulfur-cured blends of natural rubber (NR) and styrene–butadiene rubber (SBR) using solid-state ¹H homonuclear dipolar double-quantum (DQ) magic-angle spinning (MAS) NMR spectroscopy. The blends were also subjected to prolonged thermo-oxidative aging to monitor the chemical changes in the two phases. Analyses of the residual dipolar coupling constant (Dᵣₑₛ), arising due to spatial restrictions by cross-links to molecular motions, as observed in MAS and static ¹H DQ experiments, suggest that unaged NR and SBR cross-link to similar extents. A minimum in Dᵣₑₛ after around 500 h of aging duration is observed in NR, associated with the formation of highly mobile defect fractions, as seen from free induction decay (FID) combined with transverse relaxometry, with further cross-linking up to 1000 h. SBR appears more stable, with a gradual increase in Dᵣₑₛ over the aging duration. Phase-resolved experiments reveal a somewhat less cross-linked SBR phase in an unaged 50:50 blend. The phase-specific distribution of CDs in the blend phases becomes significant upon aging, which suggests that NR ages more strongly in the blend as compared to the aged single vulcanisates, thus dictating the blend properties.

Effects of modified silica on the co‐vulcanization kinetics and mechanical performances of natural rubber/styrene–butadiene rubber blends

ABSTRACTRubber blends are widely used for combining the advantages of each rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co‐vulcanization process is still a challenge. Herein, high‐resolution pyrolysis gas chromatography–mass spectrometry (HR PyGC‐MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene–butadiene rubber (SBR) in NR/SBR blends filled with modified silica (SiO2). The reaction rates of crosslinking of each rubber phase in NR/SBR were calculated, which showed that the crosslinking rates of NR were much lower than those of SBR phase in the unfilled blends and blends filled with unmodified and silane modified silica. Interestingly, the vulcanization rates of NR and SBR phase were approximately same in the vulcanization accelerator modified silica filled blends, showing better co‐vulcanization. In addition, the vulcanization accelerator modified silica was uniformly dispersed and endowed rubber blends with higher mechanical strength compared to the untreated silica. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48838.

Styrene butadiene rubber/epoxidized natural rubber/carbon filler nanocomposites: microstructural development and cure characterization

Microstructural development of elastomeric nanocomposites based on (50/50 wt%) styrene butadiene rubber (SBR) and epoxidized natural rubber (50 mol% epoxidation, ENR50) as the rubber matrix including two types of carbon fillers, carbon black (CB) and functionalized multiwall carbon nanotube (NH2-MWCNT), which were prepared through melt mixing, was studied. The results from FTIR analysis show that there is interaction between functional groups on MWCNT surface and the rubber chains. The AFM analysis also indicates good dispersion of filler particles in the rubber phases. FESEM images from cryo-fractured surface of samples have revealed that nanotubes were rarely pulled out of matrix and their diameter increased, resulting from good interaction between MWCNTs and rubber chains. The DMA results confirm good interfacial interaction between them. Furthermore, the reduced difference between the two Tgs of phases (ΔTg) shows that the incorporation of 3 phr MWCNT into the blend leads to increment in rubber phase compatibility but at higher MWCNT content (5 phr) due to lower Mooney viscosity of SBR phase, MWCNTs tend to remain in this phase. The bound rubber was adopted to characterize the polymer–filler interaction, showing that bound rubber content has an increasing trend with increasing in fillers content. The cure rheometric studies reveal that MWCNTs accelerate the cure process due to the presence of amine groups on the nanotube surface. In addition, the mechanical properties of samples show an increasing trend by increasing nano-filler content.

Compatibilization of Vulcanized SBR/NBR Blends using Cis-Polybutadiene Rubber: Influence of Blend Ratio on Elastomer Properties

Blends composed of styrene butadiene rubber (SBR) and acrylonitrile-butadiene rubber (NBR) were fabricated by melt blending technique using two-roll mill blend machine. Cis- polybutadiene rubber (CBR) was used as a compatibilizer for enhancing the homogeneity between SBR and NBR phases in blends. Although, no previous reports were found to discuss improving electrical properties of vulcanized SBR/NBR blends using unfilled rubber system (i.e. no fillers incorporated). Raman spectra and SEM images indicate that a significant compatibility within the rubber matrix is observed, due to using CBR compatibilizer. The effect of SBR/NBR blend ratio on curing characteristics, physico-mechanical properties, and physicochemical properties (e.g. network characteristics and thermodynamic parameters) were studied. SBR/NBR blend showed comparatively better mechanical properties, compared to each other individually rubber system. Curing parameters e.g. Mooney viscosity and hardness were increased, while a reduction in cure time and specific gravity was observed with increasing SBR ratio in blends. Results revealed that increasing SBR resulted in an enhancement of the tensile strength, modulus at 300 % and elongation at break up to 40 phr, and then gradually decreased. The TGA results indicated that SBR/NBR blends were thermally decomposed at a temperature range of 340-520°C. The notable decrease of DC conductivity (?dc) of vulcanized blends is owing to the decrease of NBR, which is a polar portion and is responsible for increasing the conductivity of vulcanized blends. This proved that the targeted industrial applications for vulcanized blends are entirely depending upon SBR/NBR blend in elastomers matrix.

Compatibilization of Vulcanized SBR/NBR Blends using Cis-Polybutadiene Rubber: Influence of Blend Ratio on Elastomer Properties

Blends composed of styrene butadiene rubber (SBR) and acrylonitrile-butadiene rubber (NBR) were fabricated by melt blending technique using two-roll mill blend machine. Cis- polybutadiene rubber (CBR) was used as a compatibilizer for enhancing the homogeneity between SBR and NBR phases in blends. Although, no previous reports were found to discuss improving electrical properties of vulcanized SBR/NBR blends using unfilled rubber system (i.e. no fillers incorporated). Raman spectra and SEM images indicate that a significant compatibility within the rubber matrix is observed, due to using CBR compatibilizer. The effect of SBR/NBR blend ratio on curing characteristics, physico-mechanical properties, and physicochemical properties (e.g. network characteristics and thermodynamic parameters) were studied. SBR/NBR blend showed comparatively better mechanical properties, compared to each other individually rubber system. Curing parameters e.g. Mooney viscosity and hardness were increased, while a reduction in cure time and specific gravity was observed with increasing SBR ratio in blends. Results revealed that increasing SBR resulted in an enhancement of the tensile strength, modulus at 300 % and elongation at break up to 40 phr, and then gradually decreased. The TGA results indicated that SBR/NBR blends were thermally decomposed at a temperature range of 340-520°C. The notable decrease of DC conductivity (σdc) of vulcanized blends is owing to the decrease of NBR, which is a polar portion and is responsible for increasing the conductivity of vulcanized blends. This proved that the targeted industrial applications for vulcanized blends are entirely depending upon SBR/NBR blend in elastomers matrix.

Impact of mixing procedure on phase morphology and fracture mechanical properties of carbon black-filled NR/SBR blends

Based on a viscoelastic model, the filler distribution and the amount of interphase of carbon black-filled blends of natural rubber (NR) with styrene-butadiene rubber (SBR) are evaluated. Hereby, the total dissipated energy \(G''\) during dynamical straining is decomposed into the contributions of the different polymer phases and the interphase. For the NR/SBR blends, we find a higher filling of the SBR phase and the interphase and a lower filling of the NR phase. The filler distribution itself depends not only on the affinity of the polymer to the filler but also on the mixing procedure. This is investigated by studying NR/SBR blends prepared by two different mixing procedures. In the standard mixing procedure, the polymers are mixed first, and then, the filler is added. In the batch mixing procedure, the filler is previously mixed in the NR only and then blended with SBR. Batch mixing is resulting in an increase in the filling of the interphase due to filler transfer from NR to SBR. The results for the filler distribution are compared to fatigue crack propagation rates under pulsed excitation. The crack propagation is accelerated when substituting NR with SBR. The batched samples show higher crack propagation rates at higher tearing energies due to a worse dispersion of the carbon black and/or higher filler loading of the interphase.

Transport behaviour of aromatic solvents through styrene butadiene rubber/poly [methyl methacrylate] (SBR/PMMMA) interpenetrating polymer network (IPN) membranes

Sequential polymerization technique has been adopted for the synthesis of a series of full and semi interpenetrating polymer network (IPN) membranes based on styrene butadiene rubber (SBR) and poly [methyl methacrylate] (PMMA). IPN morphology has been tuned by varying the blend composition and extent of cross-linking of both the phases. The dispersed and co-continuous morphologies of IPNs were characterised by AFM, SEM and TEM analysis. The transport behaviour of aromatic hydrocarbons through the membranes has been studied in detail by tracing the solvent uptake up to equilibrium. As the PMMA content in the IPN increases to 60 wt %, the solvent uptake value decreases by about 50% which is in tune with the morphological changes of the system where PMMA phase forms a well interconnected network structure with the SBR phase. The network structure has been compared with the Phantom and the Affine models and also with the theoretical predictions.

INFLUENCE OF PHASE MORPHOLOGY AND FILLER DISTRIBUTION IN NR/BR AND NR/SBR BLENDS ON FRACTURE MECHANICAL PROPERTIES

ABSTRACTThe filler distribution and the amount of interphase are determined for carbon black (CB) filled blends of natural rubber (NR) with butadiene rubber (BR) and styrene–butadiene rubber (SBR) and compared with fatigue crack propagation rates under pulsed excitation. A viscoelastic model is used to separate the contributions of the different polymer phases and the interphase to the total dissipated energy G″ during dynamic straining. The filler amount in any phase can be calculated from the increase of the energy dissipation. For NR/SBR blends a higher filler load of the SBR phase and the interphase and a lower filling of the NR phase are identified. In contrast NR/BR blends show a very low filled BR phase and higher filling of the NR phase and the interphase. The carbon black distribution also depends on mixing procedures. Through a batch mixing procedure, in which the filler is previously mixed in the NR only and then blended with BR, the filler transfer from NR to BR increases the filling of the BR phase. The phase morphological results deliver information for a better understanding of crack propagation in CB filled NR/BR and NR/SBR blends. The fracture behavior differs significantly if NR is successively replaced by BR or SBR, respectively. A less pronounced effect is found for the variation of mixing procedure, although it seems that the more heterogeneous filler distribution with a high amount of CB in NR of the batched samples delivers slightly reduced crack propagation rates.

Preparation and Characterization of Properties of Acrylonitrile Butadiene Styrene Waste Plastic Blended with Virgin Styrene Butadiene Rubber

In this research, the effect of adding a virgin Styrene Butadiene rubber (SBR) on the morphology and properties of Acrylonitrile Butadiene Styrene (ABS) waste plastic has been investigated. The blends were prepared by melting method and characterized by means of mechanical testing, Scanning Electron Microscopy (SEM), Thermogravimatric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The obtained results indicated that virgin SBR phase dispersed efficiently, effectively in the ABS matrix and impact strength along with thermal resistance of the blends significantly improved. Thus, investigated results in this work will open promising approach for recycling ABS waste plastic.

Effect of different ionic liquids on the dispersion and phase selective wetting of carbon nanotubes in rubber blends

Abstract The aim of this work was to study the effect of the ionic liquids (ILs) with respect to their anion type and the length of alkyl chain as dispersing and coupling agent in carbon nanotube (CNT) filled styrene butadiene rubber (SBR)/natural rubber (NR) blends. We characterized the ILs by their surface tensions whereupon their different values explain the different compatibilities of ILs with the rubber components and the filler. The wetting concept was further developed in order to experimentally characterize the effect of the rubber-IL and CNT-IL compatibility on the selective wetting of CNTs in rubber blends. It was found that all the used ILs improved the dispersion of CNTs in rubber blends significantly. During the mixing process the IL layer pre-bound to the CNT surface was replaced mainly by the NR phase and, partly, by the SBR phase. Thus, ILs cannot be used as coupling agent in this rubber blend. For the ILs with surface tension similar to that of CNTs the filler was partly wetted by IL that imparts the mixture a high electrical conductivity directly after the mixing process. This high conductivity can be used for triggering the vulcanization of the blend by means of the Joule heating. The preferential localization of ILs in the rubber matrix - but not in rubber-filler interphase - considerably influences the cross-link behavior of the vulcanizates and thus their final mechanical properties significantly.

Composition-dependent depression of the glass transition temperature of the rubber phase in a PE-SBR blend

AbstractA thermoplastic elastomeric blend was introduced based on high-density polyethylene and styrene-butadiene rubber (SBR). The morphology of the blend system was found to change from two-phase to co-continuous, depending on the polyethylene (PE) concentration. The thermo-mechanical measurements showed that, at the PE concentrations, which seemed to have a co-continuous morphology, the SBR inclusions were very fine. The fineness of the SBR domains resulted in a 20° depression of the glass transition temperature (Tg) of the SBR phase. This was attributed to the smooth interfaces at which the SBR chain sensed a higher free volume as compared with that in bulk SBR. A model correlating thin polymer thickness to the Tg of the confined polymer in the films was employed to correlate SBR domain size to the experimental Tg measured. The adjusting parameters A=129 and δ=1.45 were successfully used to fit the experimental data.

Binary and ternary composites of polystyrene, styrene–butadiene rubber and boehmite produced by water-mediated melt compounding: Morphology and mechanical properties

Binary and ternary composites composed of polystyrene (PS), styrene–butadiene rubber (SBR), and synthetic boehmite alumina (BA) were produced by water-mediated melt compounding technique. SBR latex and/or aqueous BA suspension was injected into the molten PS in a twin-screw extruder to prepare toughened and/or reinforced polymer composites. The dispersion of the BA (two fractions with different mean particle sizes) and SBR was studied by scanning- and transmission electron microcopy techniques (SEM and TEM, respectively), and discussed. The mechanical properties of the composites were determined in static tensile, Charpy impact and short-time stress relaxation tests (performed at various temperatures). It was found that BA was mostly embedded in the SBR phase in the ternary PS/SBR/BA composite. BA incorporation increased the stiffness and tensile strength and reduced the elongation at break and impact toughness. Effect of the BA particle size was most pronounced in the tensile mechanical and stress relaxation tests. Additional incorporation of BA in the PS/SBR blend enhanced the tensile modulus and stress relaxation modulus compared to the PS/SBR blend. Relaxation master curves were constructed by applying the time–temperature superposition (TTS) principle. It was established that the inverse of the Findley power law model was fairly applicable to the stress relaxation results.

Segmental mobility in the vicinity of Tg in PS/SBR blends: Nanodomain size prediction of the dispersed phase

AbstractThe blends of polystyrene (PS) and styrene‐butadiene rubber (SBR) are melt‐blended at different ratios to form physical thermoplastic elastomers. This polymeric blend is expected to behave more or less similar to chemically synthesized block copolymers such as styrene‐butadiene block copolymers (SBS). In this study, mechanical and the thermomechanical properties of this blend are investigated and compared to those of SBS copolymer. As far as morphology is considered, the blend shows a two‐phase morphology with an interface, which shows very weak interactions. According to the observed morphology and the domain size of dispersed phase the blends are of good integrity. The mechanical properties of the blends confirm the integrity of the blend and effective interface stress transfer. The tensile and Izod impact properties of the blends shows improvements upon increase in SBR content of the blend. As SBR content augments the elongation at break increases, whereas tensile dissipated energy and impact resistance go through a maximum. Therefore, blend with SBR‐content in 60–75% range can be considered as preferred one. In a wide range of concentration a phase inversion was observed and Tg‐depression was detected also for the SBR phase. This Tg‐depression was correlated to the changes in dynamics of segments (segmental mobility) near the surfaces. Using the proposed relationships between Tg‐depression and the thickness of the thin films, it was tried to calculate domain size of SBR inclusions in PS matrix. A rough correlation between SBR domain sizes in SEM images and calculated thicknesses using Tg‐depression in thin films was found. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A study about the structure of vulcanized natural rubber/styrene butadiene rubber blends and the glass transition behavior

AbstractA study of the thermal behavior of cured elastomeric blends of natural rubber (NR) and styrene butadiene rubber (SBR) prepared by solution blending in toluene is presented. Binary blends with different compositions of NR/SBR were produced using a conventional cure system based on sulfur and TBBS (n‐t‐butyl‐2‐benzothiazole sulfonamide as accelerator. The compounds were vulcanized at 433 K up to an optimum time of cure determined by rheometric tests. From swelling tests, the crosslink densities of the compounds were obtained and compared with those obtained in similar blends prepared by mechanical mixing. The results were analyzed in terms of the disentangling of the chain structures of the SBR and NR phases and the achieved cure state of the blend. Using differential scanning calorimetry, the glass transition temperature Tg of each blend was measured. In most compounds, the value of Tg corresponding to each phase of the blend was determined, but in some blends a single value of Tg was obtained. The variation of Tg with the composition and cure level in each phase was analyzed. On the other hand, a physical mixture of two equal parts of NR and SBR vulcanized was measured and the results were compared to those of the NR50/SBR50 cured blend. Besides, to analyze the influence of the network structure, pure NR and SBR unvulcanized samples were measured. On the basis of all the obtained results, the influence of the interphase formed in the blend between SBR and NR phases is discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

PHASE SELECTIVE LOCALIZATION OF FILLER IN TERNARY RUBBER BLENDS

Abstract The present work introduces a new concept based on the analysis of the rubber–filler gel for the determination of the phase selective filler localization in ternary rubber blends. Natural rubber (NR)/styrene–butadiene rubber (SBR)/ethylene–propylene rubber (EPDM) blends filled with silica were the focus of the experimental investigations. Because of the higher wetting rate of the NR component to silica, in the first stage of the preparation of SBR/NR/EPDM blends, more silica is found in the NR phase than in the SBR and EPDM phase. In the subsequent stage, silica is transferred from the NR phase to the SBR phase until the loosely bound NR-layer at the silica surface is fully replaced by SBR molecules. An extremely low amount of silica was found in the EPDM phase because of the poor EPDM–silica interaction. After a long mixing time, a large amount of silica whose surface was not yet wetted by any rubber phase could be found in the composites that can lead to fatal effects on the mechanical performance of the composites.

Kinetics of the phase selective localization of silica in rubber blends

AbstractThe Fourier transformed infrared (FTIR) spectroscopy on the rubber‐filler gel has been used as a tool for the quantitative characterization of the phase selective silica localization in styrene butadiene rubber (SBR)/natural rubber (NR) blends. The so‐called rubber‐layer L was introduced to describe the selective wetting behavior of the rubber phases to the filler. SBR/NR blends filled with silica were the focus of the experimental investigation. NR shows a higher wetting rate than SBR. Silane addition does not affect the wetting of NR but slowdowns the wetting of SBR. With increasing chamber temperature the value of the rubber‐layer L of all mixtures increases owing to the different thermal activated rubber‐filler bonding processes. Using the wetting concept the kinetics of silica localization in the phases of heterogeneous rubber blends was characterized. Because of the higher wetting rate of the NR component, in the first stage of mixing of NR/SBR blends more silica is found in the NR phase than in the SBR phase. In the next stage, silica is transferred from the NR phase to the SBR phase until the loosely bonded components of NR rubber‐layer are fully replaced by SBR molecules. POLYM. COMPOS., 31:1701–1711, 2010. © 2010 Society of Plastics Engineers.

Physico-mechanical properties and thermal stability of thermoset nanocomposites based on styrene-butadiene rubber/phenolic resin blend

Effect of organoclay (OC) on the performance of styrene-butadiene rubber (SBR)/phenolic resin (PH) blend prepared by two-roll mill was investigated. The influence of OC content ranging between 2.5 and 30phr on the performance of SBR/PH was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), interfacial energy analysis, tensile, dynamic mechanical, swelling, cure rheometry and thermogravimetric analysis (TGA). It was found that the OC is mainly localized in the SBR phase of SBR/PH blend through the kinetically favored mechanism relevant to rubber chains. The results also demonstrated the positive role of PH on the dispersion of OC. Both PH and OC showed accelerating role on the cure rate of SBR and increased the crosslinking density of the rubber phase. Additionally, the mechanical and dynamic mechanical properties of SBR were influenced by incorporation of both PH and OC. TGA showed that the OC improves thermal stability of SBR vulcanizate, while it exhibits a catalytic role in presence of PH.