Fracture morphology and mechanical properties of ethylene/vinyl acetate rubber vulcanizates reinforced by in situ prepared sodium methacrylate

Ethylene/vinyl acetate rubber (EVM) was reinforced by sodium methacrylate (NaMAA) that was in situ prepared through the neutralization of sodium hydroxide and methacrylic acid in EVM during mixing. The mechanical properties of EVM vulcanizates with different NaMAA loadings and at different crosslink densities were studied and compared with those of high abrasion furnace carbon black (HAF) filled EVM vulcanizates. The fracture surfaces of gum and filled EVM vulcanizates were observed with scanning electron microscopy. The results showed that NaMAA‐reinforced EVM vulcanizates had better mechanical properties than HAF/EVM vulcanizates. When the NaMAA loading was 50 phr, the tensile strength of the NaMAA/EVM vulcanizate was 30 MPa, the tear strength was 102 kN/m, and the elongation at break was over 400%. Fourier transform infrared analysis confirmed that NaMAA formed in the compounding process and underwent polymerization during vulcanization. Scanning probe microscopy analysis revealed that nanoscale particles dispersed in the NaMAA/EVM vulcanizates. The mechanical properties were correlated with the fracture morphology of all the vulcanizates. The tensile rupture of NaMAA‐filled EVM vulcanizates occurred through tearing from a crack in the bulk of the samples. Tear deviation occurred with the addition of NaMAA and resulted in a rough surface, leading to an improvement in the tear strength of NaMAA‐filled EVM vulcanizates. The micrographs of the tear surfaces of the vulcanizates indicated that the different fracture modes depended on the NaMAA loading and the crosslink density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1715–1724, 2004     

Microbial desulfurization of SBR ground rubber by Sphingomonas sp. and its utilization as filler in NR compounds

Microbial desulfurization of waste tyre rubber has been investigated with great efforts since 1990s, because waste rubber has created serious ecological and environmental problems. A microbial desulfurization technique for SBR ground rubber has been developed by a novel sulfur‐oxidizing bacterium Sphingomonas sp. The adaptability of Sphingomonas sp. with SBR ground rubber was tested with the amounts of SBR ground rubber varying from 0.5 to 4% g/l. The sol fraction of desulfurized SBR ground rubber increased 70%, compared with SBR ground rubber without desulfurization. Fourier transform infrared spectroscopy‐attenuated total reflectance (FTIR‐ATR) spectrum and X‐ray photoelectron spectroscopy (XPS) analysis of the desulfurized surface of vulcanized SBR flakes revealed that not only the oxidation of crosslinked S? S and S? C bonds, but also the rupture of C?C double bonds had happened to SBR vulcanizates during microbial desulfurization. The cure characteristics, such as scorch time and optimum cure time of natural rubber (NR) vulcanizates filled, were found to decrease with increasing contents of desulfurized SBR ground rubber, due to some reactive groups on its surface. NR vulcanizates filled with desulfurized SBR ground rubber had lower crosslink density and hardness, higher tensile strength and elongation at break, compared with those filled with SBR ground rubber of the same amount. Dynamic mechanical properties indicated that there were better crosslink distribution and stronger interfacial bonding between NR matrix and desulfurized SBR ground rubber. Scanning electron microscope (SEM) photographs showed that the fracture surfaces of NR vulcanizates filled with desulfurized SBR ground rubber had more smooth morphologies. Copyright © 2010 John Wiley & Sons, Ltd.     

A comparison between the SBR vulcanizates reinforced by magnesium methacrylate added directly or prepared in situ

The styrene-butadiene rubber (SBR) cured by dicumyl peroxide was reinforced by magnesium methacrylate [Mg(MAA)₂], which was added into SBR directly or prepared in situ in SBR through the neutralization of magnesium oxide (MgO) and methacrylic acid (MAA). The experimental results show that the SBR vulcanizates reinforced by Mg(MAA)₂ prepared in situ have better mechanical properties than those reinforced by Mg(MAA)₂ added directly. The SBR vulcanizates with Mg(MAA)₂ prepared in situ are semi-transparent, but those with Mg(MAA)₂ added directly are opaque. The Fourier transform infrared analysis shows that the polymerization conversion of Mg(MAA)₂ in the SBR vulcanizates with Mg(MAA)₂ prepared in situ is much higher than that in the SBR vulcanizates with Mg(MAA)₂ added directly. The scan probe microscopy photographs show that the particles in the SBR vulcanizates with Mg(MAA)₂ prepared in situ are much finer and disperse more evenly than that in the SBR vulcanizates with Mg(MAA)₂ added directly.     

Strain‐induced crystallization and mechanical properties of functionalized graphene sheet‐filled natural rubber

The effects of functionalized graphene sheets (FGSs) on the mechanical properties and strain‐induced crystallization of natural rubber (NR) are investigated. FGSs are predominantly single sheets of graphene with a lateral size of several hundreds of nanometers and a thickness of 1.5 nm. The effect of FGS and that of carbon black (CB) on the strain‐induced crystallization of NR is compared by coupled tensile tests and X‐ray diffraction experiments. Synchrotron X‐ray scattering enables simultaneous measurements of stress and crystallization of NR in real time during sample stretching. The onset of crystallization occurs at significantly lower strains for FGS‐filled NR samples compared with CB‐filled NR, even at low loadings. Neat‐NR exhibits strain‐induced crystallization around a strain of 2.25, while incorporation of 1 and 4 wt % FGS shifts the crystallization to strains of 1.25 and 0.75, respectively. In contrast, loadings of 16 wt % CB do not significantly shift the critical strain for crystallization. Two‐dimensional (2D) wide angle X‐ray scattering patterns show minor polymer chain alignment during stretching, in accord with previous results for NR. Small angle X‐ray scattering shows that FGS is aligned in the stretching direction, whereas CB does not show alignment or anisotropy. The mechanical properties of filled NR samples are investigated using cyclic tensile and dynamic mechanical measurements above and below the glass transition of NR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Colouring Agents for SBR Vulcanizates and Their Effects on Ageing and UV Radiation Resistance

Summary: Metal free and some metal-perylene polymers as well as some metal phthalocyanine polymers were incorporated into styrene butadiene rubber (SBR) compounds as colouring agents. The ageing and UV resistance of the vulcanizates obtained were studied in terms of their mechanical properties. The results obtained revealed that cobalt perylene and cobalt phthalocyanine polymers showed superior performance in SBR vulcanizates against thermal ageing and UV radiation. The optimum concentration of cobalt phthalocyanine polymer was found to be 1 phr (parts per hundred parts of rubber).     

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3‐dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass‐transition temperatures, indicating that the system is immiscible. It was also found that the glass‐transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time–temperature superposition and Cole–Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2189–2211, 2000     

A SAXS and swelling study of cured natural rubber/styrene–butadiene rubber blends

A small‐angle X‐ray scattering (SAXS) and swelling study of natural rubber and styrene–butadiene rubber blends (NR/SBR) is presented. To this aim, specimens of NR and SBR and blends with 75/25, 50/50, and 25/75 NR/SBR ratios (in phr) were prepared at a cure temperature of 433 K and the optimum cure time (t₁₀₀). This time was obtained from rheometer torque curves. The system of cure used in the samples was sulfur/n‐t‐butyl‐2‐benzothiazole sulfenamide. From swelling tests of the cured samples, information about the molecular weight of the network chain between chemical crosslinks was obtained. For all cured compounds, in the Lorentz plots built from SAXS scattering curves, a maximum of the scattering vector q around 0.14 Å^?1 was observed. However, the q position shows a linear‐like shift toward lower values when the SBR content in the SBR/NR blend increases. In pure NR or SBR the q values show a different tendency. The results obtained are discussed in terms of the existence of different levels of vulcanization for each single phase forming the blend and the existence of a third level of vulcanization located in the interfacial NR/SBR layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2320–2327, 2009     

Open spaces and molecular motions in carbon‐black‐ and silica‐loaded SBR investigated using positron annihilation

Lifetime spectra of positrons were measured for styrene–butadiene rubber (SBR) vulcanizates filled with carbon black (CB) or silica. At temperatures between 10 and 420 K, no large difference between the size of the open spaces in the CB/SBR vulcanizate and that in the specimen without the filler was observed. Above the glass‐transition temperature (T_g = 230 K), the same was true for the silica/SBR vulcanizate. Below T_g, however, the size of the open spaces was reduced by the incorporation of silica as a result of the suppression of local molecular motions in the SBR. The density of the open spaces was reduced by the incorporation of the fillers. However, above 400 K it started to increase in the silica/SBR vulcanizate. For the CB/SBR vulcanizate, the introduction of open spaces was well suppressed, even at 420 K. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 835–842, 2001     

XNBR/LDH nanocomposites: Effect of vulcanization and organic modifier on nanofiller dispersion and strain‐induced crystallization

In elastomer/organo clay nanocomposites, the morphological characteristics, and hence the mechanical properties, of the vulcanizates are strongly influenced by the organic modifier and the vulcanization process. When the elastomer itself undergoes strain‐induced crystallization, both the organic modifier and the dispersed filler particles could significantly influence the crystallization process. These phenomena are very common in case of natural rubber‐based vulcanizates. In this study, the similar effects have been demonstrated with carboxylated nitrile rubber (XNBR) and organically modified layered double hydroxide (O‐LDH)‐based nanocomposites. The effect of size of the organic modifier was obviously visible on the interlayer distance of O‐LDH and also on the morphological reorganization of the dispersed O‐LDH particles during vulcanization process. The strain‐induced crystallization of the XNBR was found to be strongly dependent on the morphological change that occurs during vulcanization process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Stimuli‐responsive polymer nanocomposites based on styrene‐butadiene rubber and bacterial cellulose whiskers

Water‐induced mechanically adaptive rubber nanocomposites were prepared by mixing bacterial cellulose whiskers (BCWs) suspension with styrene‐butadiene rubber (SBR) latex, followed by evaporation method. The structure, morphology, dynamic mechanical properties, water stimuli‐responsive behavior, and biodegradability of SBR/BCWs nanocomposite films were investigated. The results showed that the hydrophilic whiskers had a significant reinforcement effect on the storage modulus of SBR matrix, which originated from the formation of a rigid three‐dimensional filler network within matrix by strong hydrogen bonding between whiskers. The SBR/BCWs nanocomposites showed pronounced water stimuli‐responsive behavior compared with neat SBR. The storage modulus of SBR/BCWs nanocomposite could be decreased by 99.2% after equilibrium water swelling. This remarkable water‐triggered modulus change is attributed to the disentanglement of BCWs network via competitive hydrogen bonding with water.     

Effect of nature and extent of crosslinking on swelling and mechanical behavior of styrene–butadiene rubber membranes

The influence of crosslink type and crosslink density on the swelling and mechanical behavior of styrene–butadiene rubber (SBR) membranes were studied in four aliphatic hydrocarbons. To vary the crosslink type and crosslink density, SBR was vulcanized by four different vulcanizing systems viz conventional, efficient, peroxide and a mixture of sulfur and peroxide. SBR vulcanizates having mono or disulfidic crosslinks (efficient system) exhibited the highest solvent uptake whereas those with C–C bonds (peroxide system) showed the lowest. SBR crosslinked by the mixed system showed superior mechanical properties in the unswollen, swollen and deswollen conditions. Arrhenius and thermodynamic parameters were evaluated from the diffusion data. Finally, a comparison between theoretical and experimental diffusion results was carried out.     

Molecular Structures and Mechanical Properties of Microbe Rapid Coagulation Natural Rubber

In this work,molecular structures,dynamic mechanical properties and glass transition temperatures of microbe coagulated natural rubber(NR) samples were analyzed by using pyrolysis gas chromatography-mass spectrometry(py-GC/MS),rubber process analyzer(RPA) and dynamic mechanical thermal analysis(DMA).And the cross-linked network structures and mechanical properties of the corresponding NR vulcanizates were further determined by using nuclear magnetic resonance(NMR) crosslink density spectrometer(XLDS-15) and universal testing machines.The results show that NR raw rubber produced by rapidly coagulated with microorganism exhibits a simple molecular structure composition and good dynamic mechanical properties,and the corresponding NR vulcanizates possess the aggregation structure of high cross-linked density,a high glass transition temperature of-61.5 ℃ and high mechanical properties(tensile strength reaches 25.2 MPa),as compared with that coagulated with acetic acid.     

Interfacial mechano-chemical grafting in styrene-butadiene rubber/halloysite nanotubes composites

SBR/unmodified HNT composites were prepared by open-mill mixing and vulcanization. The results showed that HNT could decrease the scorch and optimum cure time, and play a significant role in reinforcing SBR vulcanizates. Mechano-chemical grafting at the interface between HNT and SBR was investigated by using infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), solid-state ¹³C NMR spectra and bonded rubber content, etc. The results showed the shearing force during the mixing process can impel the grafting reaction of SBR onto the surfaces of HNT, which leads to interfacial chemical bonding between phenyl’s α-H of SBR and the surface groups of HNT with Si-OH or Al-OH. Thus, the mechanical properties of the composites were significantly enhanced.     

Aggregation structure and mechanical properties of functionally graded polyurethane elastomers

Functionally graded polyurethane elastomers (FGPUEs) were prepared with two molds fixed at different temperatures (30 and 150 °C). The effects of the molar ratio of the curing agent (60/40, 75/25, or 97/3 1,4‐butane diol/1,1,1‐trimethylol propane) and the molecular weight of the polymer glycol (number‐average molecular weight = 2000 or 3000) on the molecular aggregation state and mechanical properties of the FGPUEs were investigated with differential scanning calorimetry, polarized optical microscopy, dynamic viscoelastic measurements, and tensile tests. The aggregation state of the FGPUEs was changed continuously from the one side (lower temperature side) to the other side (higher temperature side); for example, the glass‐transition temperature gradually increased in this direction. Also, the number of spherulites formed in the FGPUEs increased in the same manner. In the mechanical tests, the tensile strength and elongation at break of the lower temperature side were higher than those of the higher temperature side. This was correlated with the strong phase separation of the lower temperature side. The poly(oxytetramethylene glycol)‐based FGPUE with a chain extender of 75 wt % showed the largest degree of the temperature gradient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2355–2363, 2003     

Physical properties and structure of a poly(styrene-co-butadiene) rubber/poly(acrylonitrile-co-butadiene) rubber latex mixture film

The physical properties and the structure of a poly(styrene-co-butadiene) rubber (SBR) and poly(acrylonitrile-co-butadiene) rubber (NBR) latex mixture film are studied in relation to the composition of SBR/NBR for optimization as the precursor of a polymer electrolyte. The composition of SBR50/NBR50 is most suitable in terms of mechanical strength and ionic conductivity. The relationship between the mechanical strength and the structure is analyzed using a simple equivalent mechanical model modified from the Takayanagi model. Our model gives better agreement with experimental results and extends the range of validity of the model to the cocontinuous phase type morphologies. It is possible to estimate the mechanical strength from the continuity of the mechanical supporting phase, calculated from the mechanical model. The tensile properties are found to be strongly affected by the fragile component. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2493–2501, 1998     

Cure temperature influence on natural rubber—A small angle X‐ray scattering study

To analyze the natural rubber behavior during vulcanization under different cure treatments, an experimental investigation using small angle X‐ray scattering was performed. To achieve this, a set of samples were prepared using sulfur and N‐t‐butyl‐2‐benzothiazole sulfenamide as accelerator and then cured at temperatures between 403 and 463 K reaching their optimum mechanical properties considering rheometer tests. The crosslink density of the samples was evaluated by means of the swelling technique in solvent. In the usual Lorentz corrected representation of the X‐ray scattered intensity, a maximum was observed in the plots corresponding to the cured samples, revealing a highly correlated structure. This maximum shifted toward higher values of the scattering vector when the cure temperature of the samples increased. This behavior is discussed in terms of the crosslinks type present in the vulcanized rubber network at different cure temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2966–2971, 2007     

High‐power ultrasonic treatment of butyl rubber gum: Structure and properties

The ultrasonic treatment of butyl rubber gum during extrusion with a grooved‐barrel ultrasonic reactor was carried out at a mean residence time of 3.6 s and at different ultrasonic amplitudes. Gel permeation chromatography, NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic and mechanical property measurements were performed. The changes in the structure, curing behavior, and physical properties of the gum were found to be highly dependent on the applied ultrasonic amplitude. In particular, the molecular weight of the treated gum decreased and the molecular weight distribution increased with the ultrasonic amplitude. The number of double bonds in the ultrasonically treated gum was less than that in the virgin gum. The dynamic properties of the ultrasonically treated gums also indicated the occurrence of degradation during the ultrasonic treatment. The tensile strength and modulus of the vulcanizates prepared from the treated gums were reduced in comparison with those of the virgin vulcanizate because of degradation. In contrast, the elongation at break was higher. However, no significant changes in the thermal stability between the virgin and treated gums and among the vulcanizates were observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 334–344, 2005     

Structure and properties of star‐shaped solution‐polymerized styrene‐butadiene rubber and its co‐coagulated rubber filled with silica/carbon black‐I: morphological structure and mechanical properties

The morphological structure and mechanical properties of the star‐shaped solution‐polymerized styrene‐butadiene rubber (SSBR) and organically modified nanosilica powder/star‐shaped SSBR co‐coagulated rubber (N‐SSBR) both filled with silica/carbon black (CB) were studied. The results showed that, compared with SSBR, silica powder could be mixed into N‐SSBR much more rapidly, and N‐SSBR/SiO₂ nanocomposite had better filler‐dispersion and processability. N‐SSBR/SiO₂/CB vulcanizates displayed higher glass‐transition temperature and lower peak value of internal friction loss than SSBR/SiO₂/CB vulcanizates. In the N‐SSBR/SiO₂/CB vulcanizates, filler was dispersed in nano‐scale resulting in good mechanical properties. Composites filled with silica/CB doped filler exhibited more excellent mechanical properties than those filled with a single filler because of the better filler‐dispersion and stronger interfacial interaction with macromolecular chains. N‐SSBR/SiO₂/CB vulcanizates exhibited preferable performance in abrasion resistance and higher bound rubber content as the blending ratio of silica to CB was 20:30. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure and property relationships in model diglycidyl ether of bisphenol‐a and diglycidyl ether of tetramethyl bisphenol‐a epoxy systems. I. Mechanical property characterizations

Model epoxy networks, with variations in crosslink density and in epoxy monomer rigidity, were prepared to study how the network structure affects modulus, T_g, and toughness/toughenability of epoxy resins. Diglycidyl ether of bisphenol‐A and diglycidyl ether of tetramethyl‐bisphenol‐A, along with the corresponding chain extenders, were chosen to study how monomer backbone rigidity and crosslink density affect physical and mechanical properties of epoxies. The present study indicates that, as expected, the backbone rigidity of the epoxy network, not the crosslink density alone, will strongly influence modulus and T_g of epoxy resins. Upon rubber toughening, it is found that the rigidity of the epoxy backbone and/or the nature of the crosslinking agent utilized are most critical to the toughenability of the epoxy. That is, the well‐known correlation between toughenability and the average molecular weight between crosslinks (M_c) does not necessarily hold true when the nature of epoxy backbone molecular mobility is altered. The potential significance of the present findings for a better design of toughened thermosets for structural applications is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2137–2149, 1999     

Microstructure and properties of styrene‐butadiene rubber based nanocomposites prepared from an aminosilane modified synthetic lamellar nanofiller

In this work, a novel nanocomposite series based on styrene‐butadiene rubber (SBR latex) and alpha‐zirconium phosphate(α‐ZrP) lamellar nanofillers is successfully prepared. The α‐ZrP lamellar filler is modified at the cation exchange capacity by γ‐aminopropyltrimethoxysilane and the filler surface modification is first discussed. A significant improvement of the mechanical properties is obtained by using the surface modified nanofillers. However, no modification of the gas barrier properties is observed. The impact of addition of bis(triethoxysilylpropyl)tetrasulfide (TESPT) as coupling agent in the system is discussed on the nanofiller dispersion state and on the filler–matrix interfacial bonding. Simultaneous use of modified nanofillers and TESPT coupling agent is found out with extraordinary reinforcing effects on both mechanical and gas barrier properties and the key factors at the origin of the improvement of these properties are identified. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1051–1059