SBR Phase Research Articles

Effect of deep eutectic solvents on vulcanization kinetics and strain-softening behavior of natural rubber/styrene-butadiene rubber

Natural rubber/styrene-butadiene rubber (NR/SBR) blends are widely used as tyre sidewall compounds; however, discrepancies in vulcanization rates and the selective distribution of vulcanization additives in SBR and NR contribute to suboptimal dynamic properties. In this study, we propose a straightforward strategy to modulate the multi-scale structure in NR/SBR blends by incorporating an ionic liquid-like deep eutectic solvent (DES) as a novel reactive vulcanization agent. The addition of DES substantially enhances the dispersion of ZnO within NR/SBR blends, accelerates the vulcanization process of SBR and the NR/SBR blend and increases their crosslinking densities. Furthermore, DES interacts with the non-rubber components of NR, facilitating the vulcanization of NR. The impact of DES on the linear and non-linear rheological behavior of NR, SBR and NR/SBR vulcanizates is minimal, except for an enhancement in weak strain overshooting. The distribution of DES within NR/SBR blends can be manipulated by varying the mixing sequence of DES with NR and SBR, while selectively positioning DES within the SBR phase may synchronise the vulcanization rates of the NR/SBR blend, thereby improving tensile strength and reducing mechanical hysteresis. This approach may provide a viable method for producing NR/SBR blend products characterised by high strength and low hysteresis energy.

REINFORCEMENT OF RUBBER USING REACTIVE OLIGO(β-ALANINE) SUPRAMOLECULAR FILLERS

ABSTRACT Oligo(β-alanine)–based supramolecular fillers that possess an 11-mercaptoundecanoyl oleophilic moiety and an oligo(β-alanine) oleophobic moiety of varied lengths (SA1, SA2, and SA3, having a β-alanine unimer, dimer, and trimer moiety, respectively) have been systematically investigated for reinforcement of SBR. An analog of SA2 with 11-mercapto-undecanoyl being replaced by 3-mercaptopropanoyl, SA2′, was also studied for comparison. Fourier transform infrared evidence has confirmed that all supramolecular fillers exist exclusively as hydrogen-bonded β-sheets in the rubber composites. Differential scanning calorimetry studies have revealed that SA2, SA2′, and SA3 form crystalline domains in the SBR phase at all filler loadings, while SA1 only forms crystalline domains at >15 phr, indicating that microphase separation from the SBR phase is weaker for SA1 than for its higher congeners. Transmission electron microscopy investigations have shown that the filler crystalline domains are dispersed uniformly as short fibers in a continuous SBR phase. The widths of the fibers are below 10 nm, and the lengths range from a few tens to a couple of hundreds of nanometers. The oligo(β-alanine)–based supramolecular fillers exhibit diverse reinforcing characteristics among themselves and in comparison with carbon black. SA1 gives comparatively high extensibility and low tensile strength, while SA2 and SA3 give relatively low extensibility, high stiffness, and high strength. SA2′ behaves similarly to SA1 at low filler loadings but significantly compromises the extensibility at relatively high loadings. Cyclic tensile testing shows that SA1 gives high hysteresis and high set, while SA2 and SA3 give low hysteresis at low elongation and high hysteresis at high elongation in comparison with carbon black. Dynamic mechanical study at 2% strain shows that SA1, SA2, and SA3 result in markedly lower tan δ at 60 °C than carbon black. In addition, abrasion study shows that SA1 and SA2 result in lower weight loss than carbon black at 30 phr of filler loading.

Diblock-Copolymer-Based Composites for Tire-Tread Applications with Improved Filler Network Topology

We present in this Letter the results of a study focusing on vulcanized poly(butadiene–styrene butadiene rubber) (PB–SBR) diblock copolymers in the microphase-separated state filled with various amounts of silica nanoparticles. It is demonstrated that the microphase separation of PB and SBR blocks is preserved in composites with a silica mass content of ≤60 parts per hundred rubber (phr). The only effect of silica incorporation is a more restricted long-range order of the block copolymer morphology. The most interesting finding is, however, that through mechanical mixing the silica nanoparticles are highly selectively incorporated in the SBR phase up to high filler contents. This opens new opportunities toward a rational design of the filler network in composites with self-assembled elastomer matrixes and results in advantageous mechanical properties for tire-tread applications.

Synthesis, characterization, and mechanical and dynamic mechanical studies of β-alanine trimer-grafted SBR

Two β-alanine trimer-grafted SBRs with varied grafting densities, 3a and 3b, have been synthesized. The grafting density of 3b is about twice of that of 3a. FT-IR and DSC evidences suggest that the β-alanine trimer segments in both 3a and 3b exist exclusively in the β-sheet secondary structure, and the β-sheets stack to form crystals in the continuous SBR phase. The Tm of the β-sheet crystals in 3b is higher than the Tm of those in 3a. This likely suggests that the size of the crystals is somewhat larger in 3b than in 3a. TEM revealed that the β-sheet crystals are rod-like, with lengths on the order of a few tens of nanometers and widths of a few nanometers. The aspect ratio is much lower than that of the β-sheet crystals in segmented TPEs. The most prominent difference in the tensile behavior between 3a and 3b is strain hardening. The former is devoid of strain hardening, while the latter displays strong strain hardening. Overall, the high β-alanine content in 3b leads to improvement of stiffness, ultimate strength and overall toughness at the sacrifice of extensibility and elastic recovery compared to 3a. Dynamic mechanical studies showed that both 3a and 3b display very low loss factors, typical for TPEs with monodisperse hard segments that form β-sheet crystals, at temperatures up to 105 °C.

UV Fenton and sequencing batch reactor treatment of chlorpyrifos, cypermethrin and chlorothalonil pesticide wastewater

This study examined the effect of operating conditions of UV Fenton pretreatment combined with aerobic sequencing batch reactor on degradation and biodegradability (BOD5/COD ratio) improvement of chlorpyrifos, cypermethrin and chlorothalonil pesticide wastewater. The optimum operating conditions in the pretreatment phase were H2O2/COD molar ratio 2.0, H2O2/Fe2+ molar ratio 25, pH 3 and reaction time 60 min and achieved COD and TOC removal were 64.8 and 45.9% for COD and TOC removal, respectively and biodegradabilty (BOD5/COD ratio) improved from 0.02 to 0.31. In the aerobic SBR phase, five different UV Fenton operating conditions were investigated and UV F-SBR 1 appeared to be the most significant (p < 0.05). Increasing UV Fenton pretreatment time and combining the pretreated pesticide wastewater and municipal treatment plant wastewater enabled sustenance of the SBR operation. The UV Fenton-SBR (C) achieved COD and TOC removal efficiency of 96.2 and 97.4%, respectively after 40 d operation at 12 hr HRT. Effluent COD, TOC and BOD5 were 24, 19 and 18 mg L−1, respectively and BOD5/COD ratio was 0.75. Applying the Monod model, values of the biological first order kinetic constant (Kob), cell yield (Yx/s) and decay coefficients (kd) were 0.1332 hr−1, 0.5301 (mg COD mg−1 MLSS) and 0.0072 hr−1, respectively. The UV Fenton-SBR (C) process is effective in treatment of pesticide wastewater containing chlorpyrifos, cypermethrin and chlorothalonil to meet Malaysian industrial effluent discharge standard.

Dynamic mechanical properties of styrene butadiene rubber and poly (ethylene-co-vinyl acetate) blends

The dynamic mechanical behaviour of uncrosslinked and crosslinked styrene butadiene rubber/poly (ethylene-co-vinyl acetate) (SBR/EVA) blends was studied with reference to the effects of blend ratio, crosslinking systems, a compatibilizer viz. maleic-anhydride grafted poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS-g-MA), frequency and temperature. The two separate tan δ peaks, obtained during DMA, indicated the immiscibility of SBR/EVA system. The damping properties increased with SBR content for uncrosslinked and crosslinked blends. In the case of crosslinked systems, depending upon the type of crosslinking agent used, the glass transition temperature (T g) of SBR phase has been found to be shifted to higher temperatures. The damping characteristics of the blends were observed to be affected by the variations in frequency. The addition of the compatibilizer improved the storage modulus and reduced the damping properties. These results have been correlated with the morphology of the blends, attested by scanning electron micrographs. The activation energy for glass transition has been computed. The experimental data on storage modulus were compared with theoretical predictions.

Distribution of Elastomers and Silica in Polymer Blends Characterized by Raman Microimaging Technique

Abstract Raman microimaging technique was used to study the distribution of silica filler and elastomer domains in binary and ternary polymer blends containing cis1–4-polybutadiene BR; brominated poly(isobutylenecoparamethylstyrene) BIMS; Natural Rubber, NR; and/or Styrene-Butadiene Rubber, SBR. Contour maps depicting distribution of the elastomer phases and silica within each phase were obtained for 1 μm thick sections of blends having different compositions. All polymers were uniformly distributed throughout the blends. However, on a micrometer scale local fluctuations were clearly observed using Raman microimaging. The BR component is not as compatible with BIMS as are the other polymers based upon the presence of some single-phase BR domains exceeding 5 μm. Addition of the third polymer, either SBR or NR, to the blend improves the BR compatibility with BIMS since the BR domains are not as large. At low concentrations in a ternary blend, the NR phase appears concentrated near the BR domains, but in samples with higher NR concentrations, the natural rubber forms it own network and may also be found near the BIMS domains. The SBR phase was found to be near or within the BR domains. Silica was dispersed throughout the polymers in each blend, but tended to aggregate near the boundaries of the BIMS domains. Sometimes the silica was present within the BIMS domains, but did not locate within a BR domain.

The compatibilization of SBR/EVA by mercapto-modified EVA

Styrene–butadiene copolymer/ethylene–vinyl acetate copolymer (SBR/EVA) blends with different ratios were prepared by using a Haake internal mixer. These blends were compatibilized with mercapto-modified EVA (EVALSH), which promotes bonding between the SBR phase and the EVALSH through a chemical reaction between the mercapto groups of the reactive compatibilizing agent and the double bond of the unsaturated rubber. The presence of EVALSH resulted in an improvement of the tensile strength of the unvulcanized SBR/EVA blends and also a more uniform dispersion of the EVA phase inside the SBR matrix for blends containing higher amount of the rubber phase. The formation of insoluble material in the blends containing EVALSH indicates reactive compatibilization, which was confirmed by Fourier transform infrared analysis and also by dynamic mechanical analysis. In this case, a decrease in damping properties of the SBR phase was observed as a consequence of decreasing chain mobility. EVALSH also caused a decrease in degree of crystallinity of the EVA phase as observed by differential scanning calorimetry analysis.

Carbon Black Distribution in Rubber Blends: A Dynamic-Mechanical Analysis

Abstract The influence of phase morphology and carbon black distribution on energy storage and dissipation during dynamic excitations of rubber blends is discussed. It is shown that differences in the local stiffness of the phases in the glass transition regime of unfilled blends lead to characteristic deviations of the local strain from the external strain amplitude. These deviations are governed by a critical phenomenon due to the formation of a phase network above a critical blend ratio. As a result, a strongly nonlinear dependence of the glass transition maxima of the loss modulus on the volume fraction of the phases is observed. By counting the elastically effective bonds of the phase network, the local strain amplitude is estimated by purely geometrical arguments. Based on a consideration of the phase network, the distribution of carbon black in the different phases of filled blends is estimated from the height of the local maxima of the loss modulus in the glass transition regime. Thereby, a linear increase of the maximum value of the loss modulus with rising carbon black concentration is exploited that relates the enhanced energy dissipation of filled rubbers to the internal friction of the filler particles. Results on EPDM/BR/N550 blends indicate that carbon black is preferably located in the BR phase. A somewhat higher concentration of carbon black in the SBR phase is found in the case of NR/SBR(40% Styrene)/N330 blends.

Nitrification monitoring in activated sludge by oxygen uptake rate (OUR) measurements

A simple measuring system was developed that yields information about the presence of NH + 4 and NO − 2 nitrogen in mixed liquor samples. In addition, it allows monitoring of the rate of both NH + 4 and NO − 2 oxidation simultaneously with the carbon substrate oxidation using OUR measurements. The method is based on the subsequent addition of NaClO 3 and allylthiourea, selective inhibitors of Nitrobacter and Nitrosomonas respectively, to the mixed liquor sample in a closed batch respirometer. The presented method is valuable for detailed monitoring of the nitrification process in a reactor: it is simple, inexpensive, robust and generally applicable for nitrifying reactor systems. The measurement of NH + 4 and NO − 2 oxidation rates enables the operator to detect the presence of NH + 4 and NO − 2 species. This allows action to be taken to improve the performance of the system. The method is validated on a SBR. It is indicated that optimal SBR phase scheduling can be based on such OUR measurements.

Polymer Electrolytes with Multiple Conductive Channels Prepared from NBR/SBR Latex Films Impregnated with Lithium Salt and Plasticizer

Polymer electrolytes with high ionic conductivity (>10−3 S/cm) and good tensile strength were prepared by swelling poly(acrylonitrile‐co‐butadiene) (NBR)/poly(styrene‐co‐butadiene) latex films with γ‐butyrolactone (γ‐BL) or plasticizer. Before swelling, the phase is formed at the particle interface. After plasticization, two ion‐conductive channels are present: the phase is present at the interface of the latex particles, and the NBR phase is formed from NBR latex particles. These regions are polar and impregnated selectively with polar γ‐BL solvent or solution, building primary and secondary ion‐conductive channels, respectively. The SBR phase (formed from SBR latex particles) is nonpolar and not impregnated, providing a mechanically supportive matrix. High ionic conductivity on the order of 10−3 S/cm is achieved when latex film was saturated with 0.2 to 0.4M solutions. Various microscopic and macroscopic analyses suggest that two types of ion‐conductive channels exist in the polymer electrolyte film.

Dual‐Phase structure of polymer electrolytes comprised of NBR/SBR latex films swollen with lithium salt solution

AbstractDual‐phase polymer electrolytes (DPE) that have high ionic conductivity (&gt; 10−3 S/cm) and good mechanical strength were prepared by mixing NBR and SBR latices and casting films. The latex films absorbed large quantities of lithium salt solution (e.g., 1M lithium perchlorate in γ‐butyrolactone) to obtain DPE films but did not dissolve with swelling. The NBR phase is polar and was impregnated selectively with the polar lithium salt solution, whereas the SBR phase is nonpolar and formed a mechanically‐supportive matrix. Transmission electron microscopic (TEM), electron energy loss spectral (EELS), and energy‐dispersive x‐ray (EDX) analyses showed microscopically the dual‐phase structure. Evidence for swelling by lithium salt solution was found only in the NBR phase and not in the SBR phase by EDX microanalysis. Ionic conductivity as a function of NBR content or swelling degree showed clearly that a percolation threshold for ionic conductivity exists. © 1994 John Wiley &amp; Sons, Inc.

Mixing of Carbon Black with Rubber. VI. Analysis of NR/SBR Blends

Abstract The distribution of carbon black in NR/SBR blends was determined through the analysis of bound rubber. The NR/SBR blends were found to be very different from the previously studied SBR/BR compounds: these differences were assigned to mutual insolubility of the two polymers and a very high molecular weight of NR. In NR/SBR blends, it was found that changes in molecular weight of the polymer has no effect on the carbon black distribution in the blend. While the “activity” of carbon black did not affect the distribution, the loading of the black in NR decreased linearly with increasing surface area of the black. Approximately 35% of normal tread blacks (surface area 80–100 m2/g) was found in the NR phase. However, the bond between NR and carbon black is quite weak, and black continues to migrate into the SBR phase on prolonged mixing or during blending of NR and SBR masterbatches.

Multiphase polymer processing: Controlled‐ingredient‐distribution mixing and its effect on some properties of styrene‐butadiene (SBR)/butadiene‐acrylonitrile copolymer rubber blend compounds

AbstractThe flex‐crack‐growth resistance and oil‐swelling resistance of a styrene‐butadiene (SBR)/butadiene‐acrylonitrile co‐polymer (NBR) rubber blend are studied as a function of the distribution of ingredients in the individual rubber phases. The blends consist of 70:30 weight ratio of SBR:NBR with incorporation of 82.5 phr carbon black and other ingredients via the controlled‐ingredient‐distribution mixing procedure. The results show that flex crack growth is affected by the distribution of carbon black. Better flex crack growth resistance could be achieved by adding 10 percent of carbon black to the NBR rubber phase and 90 percent to the SBR phase. The swelling of these rubber blends in ASTM #2 oil is also affected by the location of carbon black and by the mixing history. The blends with more black initially preloaded in the SBR phase have lower swelling, as have blends with shorter cross‐mixing time or the mill. A simple equation based on the permeation/moduli of composite materials is proposed to describe the swelling of this rubber blend in terms of the swelling of the constituent rubber phases, the distribution of ingredient in the individual rubber phases, and the blend morphology. One of the key assumptions is to consider the individual black preloaded rubber as a continuum. The quantitative correlation with the observed swelling data is reasonably good.

Experimental studies of the relationship of processing to the crack growth of carbon‐black‐loaded SBR—cis‐polybutadiene compounds

AbstractThe crack growth of a highly carbon‐black‐loaded SBR—cis‐polybutadiene (BR) blend is investigated as a function of the distribution of carbon black in the individual rubber phases. The blend compound consists of SBR/BR/carbon black/oil = 60/40/85/60 by weight ratio and curatives. A new “old process” is devised to control the carbon black distribution in the individual rubber phases, that is, cross mixing the SBR and BR black master batches with different amounts of carbon black in the SBR and BR patches. The results show that crack growth is very sensitive to the carbon black distribution. A better crack growth resistance compound is seen containing proportionately more carbon black in the major rubber SBR phase. A simple analogy of rubber blends to the rubber‐modified thermoplastics is proposed to interpret these findings. The heat buildup of the blends is also affected by the carbon black distribution. A low heat buildup compound is observed in the system in which more carbon black is in the SBR batch, which is also a better crack growth resistance compound. It is not unexpected that the strength of rubbers decreases with increase of temperature, and so the rate of crack growth becomes faster as heat builds up.

Tackification Studies of Natural Rubber/Styrene-Butadiene Rubber Blends

Abstract A 50:50 blend of NR and SBR 1011 is heterogeneous. When tackified with a resin which is compatible with the NR phase, but not the SBR phase, the resin appears to partition unequally between the NR and the SBR. The resulting heterogeneous pressure-sensitive adhesives exhibit very broad storage modulus transition zones. The increased breadth occurs predominantly at the lower frequency portion of the transition. This is quite different from the NR/SBR blends tackified with a resin which is compatible with both NR and SBR. The NR/SBR blend with compatible resins exhibits a single sharp transition which is similar in character to either pure NR or pure SBR adhesives prepared with completely compatible resins. The differences due to heterogeneity are clearly manifested in the mechanical properties of the blend and are reflected by the rolling ball tack and shear strength to steel properties. Rolling ball tack data are consistent with the hypothesis that the NR phase is more highly tackified than is the SBR phase. Shear adhesion to steel data further support this conclusion.

Elastomer Blend Properties—Influence of Carbon Black Type and Location

Abstract Criteria for minimizing hysteresis in carbon-black-filled elastomer blends are: (1) large black unit size, wide distribution, and low structure; (2) higher black loading in the discrete polymer phase (large zones); and (3) polymer of lower hysteresis as the continuous phase (low black loading). Of the different strength properties that were evaluated, tear and fatigue resistance showed the greatest dependence on black location in NR-BR and NR-SBR blends. Both properties were markedly higher for NR-BR, with most of the black in the NR phase. In NR-SBR, tear strength was higher with high loadings of black in the SBR. Fatigue life showed a reverse pattern, but the variations were not as great in this system. Criteria for maximizing tear resistance are: (1) small black unit size, low structure; (2) higher loading of carbon black in the continuous polymer phase ; and (3) the polymer of higher strength as the continuous phase. There may also be optimum levels of polymer zone size and black size distribution which affect tear strength. Optimized performance in a 50:50 NR-BR radial truck tire tread stock was obtained with a wide-distribution N-375 (50:50 N-351-N-110 blend) black with 75% location in the NR phase. This black gave 5–6°C lower heat buildup, equivalent modulus, 35% higher tear strength, and almost double the fatigue life of a conventionally mixed N-220 at essentially equivalent tread wear resistance (−4%). Optimized performance in 50:50 NR-SBR was indicated for a wide-distribution N-231 type (50:50 blend of N-351-N-119) with 75% of the black in the SBR phase. In comparison to conventionally mixed N-234 and N-220, this black gave about 8–10°C lower heat buildup, about 15% lower modulus, and essentially equal tensile, tear, and fatigue properties. Alternatively, a standard N-231 type with 75% location in the NR phase showed about 5–6°C lower heat buildup, about 20% lower modulus, equivalent tensile strength, 60% higher tear resistance, and 75–120% higher fatigue life.

New Methods for Electron Microscopy of Polymer Blends

Abstract Two new methods of sample preparation have been developed for electron microscopical examination of polymer blends. The first is an ebonite method where the blend is hardened in a sulfur-sulfenamide-zinc stearate mixture and then microtomed. The second is a cryogenic method where the blend is microtomed in the frozen state and then stained with osmium tetroxide. These methods have been used to examine styrene—butadiene rubber/cispoly (butadiene), natural rubber/ethylene propylene diene monomer rubber, NR/trans Polypentenamer blends, and a NR/starch mixture. Sharp, clear phase differentiation is obtained with all blends studied. SBR/PB blends were obtained when the viscosities of the blended polymers were similar. Similarity of molecular structure, increased milling time, and increased milling temperature also decreased the zone size of the dispersed phase. A three-phase system was observed when a high-styrene SBR was blended with PB ; the third phase consists of block poly (styrene) embedded in the SBR phase. Under all conditions SBR/PB blends were found to be heterogeneous, with no evidence of a single homogeneous phase.