Ternary elastomer nanocomposites based on NR/BR/SBR: Effect of nanoclay composition

Elastomer nanocomposites based on natural rubber (NR), butadiene rubber (BR), and styrene butadiene rubber (SBR) containing Cloisite 15A were prepared using a two‐roll mill. Mechanical, morphological, and rheological characterization of the prepared nanocomposites was carried out in order to study the effect of different nanoclay compositions, i.e., 1, 3, 5, 7, and 10 wt %. Intercalation of the elastomer chains into the silicate layers was evidenced by d‐spacing values calculated according to the results of the X‐ray diffraction (XRD) patterns. This was directly confirmed by transmission and scanning electron microscopy (TEM and SEM). The results depict a decreasing trend in the optimum cure time (t₉₀) and scorch time (t₅) values of the nanocomposite samples with increasing nanoclay loading; where the elastic modulus (G′) and complex viscosity (η*) of the samples considerably increased. The mechanical properties of the nanocomposites show a considerable increase in the tensile modulus of NR/BR/SBR/Cloisite 15A nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

ESR study of silica‐filled SBR with different rubber/filler interactions

Silica‐filled styrene–butadiene rubber (SBR) unvulcanizates and their vulcanizates with different rubber/filler interactions were prepared by using several kinds of coupling agents. Tensile tests and electron spin resonance (ESR) measurements were carried out for both unvulcanized and vulcanized samples to get information on the effects of filler/rubber interactions on the breakdown of carbon–carbon (C? C) linkages in SBR and carbon–sulfur (C? S? C, C? S? S? C) linkages at the crosslinked points between rubber and sulfur by a tensile force. The combination of ESR results and stress–strain data suggested that with increasing the mechanical energy applied to the samples by the stretching, the carbon–sulfur linkages around silica particles were broken first, followed by the breakdown of carbon–sulfur and C? C linkages in the rubber matrix. The assignment of ESR spectrum was also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Curing characteristics and mechanical properties of rattan‐powder‐filled natural rubber composites as a function of filler loading and silane coupling agent

Curing characteristics, tensile properties, morphological studies of tensile fractured surfaces using scanning electron microscopy (SEM), and the extent of rubber filler interactions of rattan‐powder‐filled natural rubber (NR) composites were investigated as a function of filler loading and silane coupling agent (CA). NR composites were prepared by the incorporation of rattan powder at filler loading range of 0–30 phr into a NR matrix with a laboratory size two roll mill. The results indicate that in the presence of silane CA, scorch time (t_s2), and cure time (t₉₀) of rattan‐powder‐filled NR composites were shorten, while, maximum torque (M_H) increased compared with NR composites without silane CA. Tensile strength and tensile modulus of composites were enhanced whereas elongation at break reduced in the presence of silane CA mainly due to increase in rubber‐filler interaction. It is proven by SEM studies that the bonding between the filler and rubber matrix has improved. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synergistic reinforcement of nanoclay and carbon black in natural rubber

The synergistic reinforcement of nanoclay (NC) and carbon black (CB) in natural rubber (NR) has not been much studied. Therefore, the reinforcement mechanism was probed using synchrotron wide‐angle X‐ray diffraction and transmission electron microscopy (TEM) observation and analyzed in terms of tube model theory. A synergistic effect in reinforcement between NC and CB was proved by the marked enhancement in tensile strength from 11.4 MPa for neat NR to 28.2 MPa for NR nanocomposite with 5 wt% NC and 20 wt% CB. From a study of crystallization under deformation it was found that crystallization plays a less important role in the reinforcement of NR/NC/CB. Analysis using tube model theory provided more evidence for the synergistic effect. NR containing a combination of NC and CB exhibited an increase of topological tube‐like constraints in comparison with NR/CB. That is to say, in NR/NC/CB nanocomposites, a CB–NC local filler network, as indicated by TEM images, induced a more entangled structure in which mobility of rubber chains was hindered for lateral fluctuations by the presence of neighboring chains. The synergistic reinforcement of NC and CB in NR/NC/CB nanocomposites can be reasonably understood as due to the formation CB–NC local filler networks. Copyright © 2010 Society of Chemical Industry     

Effect of different nanoparticles on thermal,mechanical and dynamic mechanical properties of hydrogenated nitrile butadiene rubber nanocomposites

Organically modified and unmodified montmorillonite clays (Cloisite NA, Cloisite 30B and Cloisite 15A), sepiolite (Pangel B20) and nanosilica (Aerosil 300) were incorporated into hydrogenated nitrile rubber (HNBR) matrix by solution process in order to study the effect of these nanofillers on thermal, mechanical and dynamic mechanical properties of HNBR. It was found that on addition of only 4 phr of nanofiller to neat HNBR, the temperature at which maximum degradation took place (T_max) increased by 4 to 16°C, while the modulus at 100% elongation and the tensile strength were enhanced by almost 40–60% and 100–300% respectively, depending upon nature of the nanofiller. It was further observed that T_max was the highest in the case of nanosilica‐based nanocomposite with 4 phr of filler loading. The increment of storage modulus was highest for sepiolite‐HNBR and Cloisite 30B‐HNBR nanocomposites at 25°C, while the modulus at 100% elongation was found maximum for sepiolite‐HNBR nanocomposite at the same loading. A similar trend was observed in the case of another grade of HNBR having similar ACN content, but different diene level. The results were explained by x‐ray diffraction, transmission electron microscopy, and atomic force microscopy studies. The above results were further explained with the help of thermodynamics. Effect of different filler loadings (2, 4, 6, 8, and 16 phr) on the properties of HNBR nanocomposites was further investigated. Both thermal as well as mechanical properties were found to be highest at 8 phr of filler loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of carbon black loading on curing characteristics and mechanical properties of waste tyre dust/carbon black hybrid filler filled natural rubber compounds

Curing characteristics, tensile properties, fatigue life, swelling behavior, and morphology of waste tire dust (WTD)/carbon black (CB) hybrid filler filled natural rubber (NR) compounds were studied. The WTD/CB hybrid filler filled NR compounds were compounded at 30 phr hybrid filler loading with increasing partial replacement of CB at 0, 10, 15, 20, and 30 phr. The curing characteristics such as scorch time, t₂ and cure time, t₉₀ decreased and increased with increment of CB loading in hybrid filler (30 phr content), respectively. Whereas maximum torque (M_HR) and minimum torque (M_L) increased with increasing CB loading. The tensile properties such as tensile strength, elongation at break, and tensile modulus of WTD/CB hybrid filler filled NR compounds showed steady increment as CB loading increased. The fatigue test showed that fatigue life increased with increment of CB loading. Rubber–filler interaction, Q_f/Q_g indicated that the NR compounds with the highest CB loading exhibited the highest rubber–filler interactions. Scanning electron microscopy (SEM) micrographs of tensile and fatigue fractured surfaces and rubber–filler interaction study supported the observed result on tensile properties and fatigue life. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of dispersion state of Cloisite15A® on the performance of SPEEK/Cloisite15A nanocomposite membrane for DMFC application

The introduction of 2,4,6‐triaminopyrimidine (TAP) into sulfonated poly(ether ether ketone) (SPEEK)/Cloisite15A® nanocomposite membranes were investigated for the purpose of maintaining low methanol permeability and suppressing swelling in direct methanol fuel cell (DMFC). SPEEK with 63% of degree of sulfonation (DS) was prepared by sulfonation of PEEK. Cloisite15A (7.5 wt %) along with various weight loading of TAP was incorporated into SPEEK matrix via solution intercalation method. The effect of TAP loading on the SPEEK/Cloisite15A/TAP morphology was studied. The beneficial impact of the SPEEK/Cloisite15A/TAP morphology on the physicochemical properties of the membrane was further discussed. Swelling behavior, ion exchange capacity (IEC), proton conductivity, and methanol permeability of the resultant membranes were determined as a function of Cloisite15A and TAP loadings. Uniform distribution of Cloisite15A particles in the SPEEK polymer matrix in the homogenous SPEEK/Cloisite15A/TAP nanocomposite membranes was confirmed by scanning electron microscopy and X‐ray diffraction. The water uptake of the SPEEK nanocomposite membranes decreased dramatically in the presence of TAP. The significant selectivity of SP/7.5/7.5 nanocomposite membranes could indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of valence electron spin polarization on the physical properties of CuCl2‐filled poly(vinylidene fluoride) as a microwave modulator

Infrared and optical spectra, differential thermal analysis, dc electrical resistivity, magnetic susceptibility, electron spin resonance, and microwave response of CuCl₂‐filled poly(vinylidene fluoride) (PVDF) films, over the filler mass fraction range 0.05 ≤ W ≤ 0.4, were measured. The infrared spectra evidenced the presence of β‐phase, for all of the filler levels with main deformations of 20% (for W = 0.25) and 30% (for other filler levels) head‐to‐head and tail‐to‐tail units, which were considered as polaron and bipolaron defects. Optical activity was mainly influenced by PVDF structure. Differential thermal analysis revealed dipole relaxation and premelting endothermic peaks. A quasi–one‐dimensional interpolaron hopping was thought to proceed in the direct current electric conduction, with a hopping distance less than the distance between two successive head‐to‐head sites. A temperature‐independent Pauli paramagnetic behavior was observed, confirming the presence of induced energy bands due to CuCl₂ filling. Most of the observed electron spin resonance signals were antisymmetric, with superimposed repels due to the hyperfine interactions characterizing PVDF. The obtained linear dependence of the isotropic hyperfine coupling constant (ΔA` ), for Cu(II), on average g‐factor, implied that ΔA` is a measure of the valence electron spin polarization. An octahedral or distorted octahedral configuration was suggested for Cu(II). The present system is a good microwave modulator. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 771–781, 1999     

Nanoclay distribution and its influence on the mechanical properties of rubber blends

The distribution of modified and unmodified nanoclays inside the rubber phases of immiscible rubber–rubber blends composed of nonpolar–polar natural rubber (NR)/epoxidized natural rubber (ENR) and nonpolar–nonpolar NR/polybutadiene rubber (BR) was investigated for the first time. The distribution of clays at various loadings in the blends was calculated from the viscoelastic properties of the blends. For example, in the 50 : 50 NR/ENR blend, 42% Cloisite 30B migrated to the NR phase, and 58% went to the ENR phase. However, in the same blend, only 7% Cloisite Na⁺ was found in the NR phase, and 93% was found in the ENR phase. Again, in the 50 : 50 NR/BR blends, the NR phase contained 85% Cloisite 30B, whereas 55% Cloisite Na⁺ migrated to the NR phase. All these observations were explained with the help of viscosity, X‐ray diffraction, and morphology analyses. The effect of the distribution of the clay on the mechanical properties was also discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

New approach for preparation of dry natural rubber nanocomposites through acid‐free co‐coagulation: Effect of organoclay content

Natural rubber (NR) vulcanizates exhibit good mechanical properties compared to vulcanizates of synthetic rubbers. Incorporation of a conventional filler at higher loadings to NR enhances its modulus, while reduction in tensile strength and elongation. This paper presents a new strategy for development of a NR‐clay nanocomposite with enhanced mechanical properties by incorporation of lower loadings (2–8 phr) of cetyl trimethyl ammonium bromide modified montmorillonite clay (OMMT‐C) under acid‐free environment. The effect of OMMT‐C loading on cure characteristics, rubber‐filler interactions, crosslink density, dynamic mechanical thermal properties, and mechanical properties were evaluated. Incorporation of OMMT‐C accelerated the vulcanization process and enhanced mechanical properties. X‐ray diffraction analysis and scanning electron microscopy images revealed that the formation of intercalated clay structures at lower OMMT‐C loadings, and clay aggregates at higher loadings. A nanocomposite at OMMT‐C loading of 2 phr exhibited the best balanced mechanical properties, and was associated with highest crosslink density and rubber–filler interactions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46502.     

Curing studies of bisphenol a based bismaleimide and cloisite 15a nanoclay blends using differential scanning calorimetry and model‐free kinetics

Blends of 2,2‐bis[4‐(4‐maleimidophenoxy phenyl)]propane [bismaleimide (BMIX)] with different proportions (1, 2, 3, 4, 5, 7, and 9%) of the nanoclay Cloisite 15a were prepared with ultrasonication. Fourier transform infrared studies reveal the existence of interactions between the clay particles and the imide rings in BMIX. The difference in the melting characteristics and the decrease in the curing window caused by the incorporation of the clay particles in BMIX, as evidenced by detailed differential scanning calorimetry investigations, confirmed the existence of interactions between the nanoclay particles and BMIX molecules. The Flynn–Wall–Ozawa, Vyazovkin, and Friedman kinetics methods were used to calculate the activation energies (E_a's) for the curing of the BMIX materials. E_a for the polymerization varied, depending not only on the amount of clay loaded in the BMIX but also on the extent of the curing reaction. Because of the loss of interaction between the clay platelets and the imide rings of BMIX, a decrease in E_a at higher reaction extents was noted when there was lower clay loadings (1–4% Cloisite 15a) in BMIX. A reversal in the previous behavior was noted at higher clay loadings (7 and 9% Cloisite 15a) in BMIX and was attributed to the restriction of the molecular mobility due to the presence of increased concentrations of clay platelets and the decreased availability of reaction sites for polymerization. These two opposing factors played were equal at the optimum level of Cloisite 15a loading (5%) in BMIX, which was reflected in the constancy of E_a variation noted with increasing reaction extent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Organoclay localization in polyamide 6/ethylene-butene copolymer grafted maleic anhydride blends: the effect of different types of organoclay

Localization of organoclays between two phases of polyamide 6 (PA6)/maleic anhydride grafted ethylene-butene copolymer (EB-g-MAH) blends, prepared via melt mixing, was investigated as a function of organoclay type. Cloisite 30B, Cloisite 20A and Cloisite 15A were used as different types of organoclay. The influence of different blend compositions and clay contents were also studied. Contact angle measurements have been applied to determine surface tension of components and then to calculate the wetting coefficient which is a useful parameter for prediction of the organoclay location. In general, all organoclays were found to locate in the more hydrophilic polyamide 6 phase. However, for Cloisite 20A and Cloisite 15A transmission electron microscopy (TEM) observations revealed some organoclay layers in the EB-g-MAH phase. Phase structure and nanocomposite morphology were evaluated using scanning and transmission electron microscopy and small angle X-ray scattering (SAXS). Results indicated the formation of an exfoliated or an intercalated morphology in different samples. Dynamic-mechanical thermal analysis and thermal gravimetric analysis were used as an experimental probe to confirm the location of nanoclays predicted via wetting coefficient. The shifting of glass transition temperature for PA6 phase confirmed that nanoclays are more distributed in this phase.     

Comparative study on the natural rubber nanocomposites reinforced with carbon black nanoparticles and graphite oxide nanosheets

To achieve dramatic improvements in the performance of natural rubber (NR), the graphite oxide nanosheets (GON)‐reinforced NR nanocomposites have been prepared through solution mixing on the basis of pretreatment of graphite. The mechanical and thermal properties of GON/NR nanocomposites were characterized in contrast to the carbon black (CB)/NR nanocomposite. The mechanical properties of the GON‐reinforced NR showed a considerable increase compared to the neat NR and traditional CB/NR nanocomposite. The initial modulus of pure NR was increased for up to 53.6% when 7 wt% GON is incorporated. The modulus and strength of NR with GON appear to be superior to those of CB with the same filler content. The dispersion state of the nanofillers into NR was investigated by scanning electron microscopy and X‐ray diffraction, and the results indicated that nanofillers have been dispersed homogeneously in the NR matrix. Fourier transform infrared spectra showed possible interfacial interactions between fillers and NR matrix. Differential scanning calorimetry and thermogravimetric analysis showed that the T _g and thermal decomposition temperature of NR slightly increased with the addition of the fillers, especially for that of GON/NR nanocomposites. According to this study, application of the physical and mechanical properties of GON to NR can result in rubber products which have improved mechanical, physical, and thermal properties, compared with existing NR products reinforced with CB. POLYM. COMPOS., 38:1427–1437, 2017. © 2015 Society of Plastics Engineers     

Mechanical and dynamic mechanical properties of rice husk ash–filled natural rubber compounds

A laboratory‐sized two‐roll mill was used to incorporate rice husk ash into natural rubber (NR). A conventional vulcanization system was used for curing and cure studies were carried out on a Monsanto rheometer. Physical testing of the NR vulcanizates involved determining tensile and tear resistances and hardness. Swelling behavior of NR compounds and scanning electron microscopy were used to investigate the interaction between rice husk ash and natural rubber. Also, dynamical mechanical thermal analysis was used to assess filler–rubber interactions in terms of storage modulus (E′) and loss tangent (tan δ). For comparison purposes, two commercial fillers, precipitated silica (Zeosil‐175) and carbon black (N774), were also used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2331–2346, 2002     

Development of acrylic‐based powder coatings with incorporation of montmorillonite clays

Powder coatings have been receiving attention because they are environmentally friendly. They do not contain solvents in their composition, and their components have decorative and corrosion‐protection functions, among many others. However, the presence of polymers in their composition increases the risk of combustion in adverse situations. In this context, this study aims to develop and characterize acrylic‐based powder paints with the addition of 2 wt % and 4 wt % montmorillonite clays (MMT) as Cloisite 30B (MMT‐30B) and Cloisite 15A (MTT‐15A), employed as flame retardants. The characterization of the coatings was carried out by thermogravimetric analysis (TGA), X‐ray diffraction, and scanning electron microscopy. After application of the coatings on carbon steel substrates, flammability tests were performed. The coatings with 2 wt % MMT‐30B showed overall better results, especially in the flammability tests. Flames spread less on these coatings than on the other systems. However, when the surface and bottom temperatures were analyzed by the cone calorimeter test, the samples prepared with 4 wt % MMT‐15A were considered safer to be applied in fire scenarios. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45031.     

Transmission electron microscopy study of room temperature cured PMMA grafted natural rubber toughened epoxy/layered silicate nanocomposite

Abstract

A morphological study was conducted on ternary systems containing epoxy, poly(methyl methacrylate) grafted natural rubber and organic chemically modified montmorillonite (Cloisite 30B), using TEM. The following four materials were prepared at room temperature: cured unmodified epoxy, cured toughened epoxy, cured unmodified epoxy/Cloisite 30B nanocomposites and cured toughened epoxy/Cloisite 30B nanocomposites. Mixing process was performed by mechanical stirring. Poly(etheramine) was used as the curing agent. The detailed TEM images revealed cocontinuous and dispersed spherical rubber in the epoxy–rubber blend, suggesting a new proposed mechanism of phase separation. High magnification TEM analysis showed good interactions between rubber and Cloisite 30B in the ternary system. In addition, it was found that rubber particles could enhance the separation of silicate layers.     

Ion-dipole interactions in the dispersion of organoclay nanocomposites based on polystyrene-block-poly(2-vinylpyridine) copolymer

The dispersion characteristics of organoclay nanocomposites based on polystyrene-block-poly(2-vinylpyridine) (S2VP diblock) copolymer were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), and solid-state nuclear magnetic resonance (NMR) spectroscopy. For the investigation, S2VP diblock copolymers having three different compositions were synthesized via sequential anionic polymerization. Each S2VP diblock copolymer was used to prepare nanocomposites by solution blending with natural clay (montmorillonite, MMT) or commercial organoclays (Cloisite 30B, Cloisite 10A, Cloisite 15A, and Cloisite 25A from Southern Clay Products). All four organoclays employed were treated with a surfactant having quaternary ammonium salt with N⁺ ion. It was found, via TEM and XRD, that the nanocomposites with MMT show very poor dispersion characteristics regardless of block copolymer composition. However, the block copolymer composition was found to have a profound influence on the dispersion characteristics of the nanocomposites with an organoclay. Specifically, the nanocomposites based on S2VP-5 having 5 wt% poly(2-vinylpyridine) (P2VP) block gave rise to a very high degree of dispersion, irrespective of the chemical structure of the surfactant residing at the surface of the organoclay employed, whereas the dispersion characteristics of the nanocomposites became progressively poorer as the amount of P2VP block in an S2VP diblock copolymer increased from 5 to 25 wt% and to 56 wt%. The observed dispersion characteristics were explained by hypothesizing the presence of ion-dipole interactions between the positively charged N⁺ ions in the surfactant residing at the surface of the organoclay nanoparticles and the dipoles in the P2VP block of S2VP diblock copolymers. The validity of this hypothesis was confirmed using solid-state NMR spectroscopy, by determining the dependence of the composition of S2VP diblock copolymer on the extent of ion-dipole interactions and thus on the dispersion characteristics of the nanocomposites prepared.     

Synergistic reinforcement of NBR by hybrid filler system including organoclay and nano‐CaCO3

Rubber nanocomposites containing one type of nanofiller are common and are widely established in the research field. In this study, nitrile rubber (NBR) based ternary nanocomposites containing modified silicate (Cloisite 30B) and also nano‐calcium carbonate (nano‐CaCO₃) were prepared using a laboratory internal mixer (simple melt mixing). Effects of the hybrid filler system (filler phase have two kind of fillers) on the cure rheometry, morphology, swelling, and mechanical and dynamic–mechanical properties of the NBR were investigated. Concentration of nano‐CaCO₃ [0, 5, 10, and 15 parts per one hundred parts of rubber by weight (phr)] and organoclay (0, 3, and 6 phr) in NBR was varied. The microstructure and homogeneity of the compounds were confirmed by studying the dispersion of nanoparticles in NBR via X‐ray diffraction and field emission scanning electron microscopy. Based on the results of morphology and mechanical properties, the dual‐filler phase nanocomposites (hybrid nanocomposite) have higher performance in comparison with single‐filler phase nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42744.     

Stabilization of free radicals in filled oligoesteracrylates

A study of the formation and decay of free radicals in the process of photocuring oligocarbonatmethacrylate (OCM-2), filled by two types of silica differing in particle size and hydroxylapatite, was carried out by electron spin resonance (ESR) spectroscopy. The results were correlated with the data for molecular mobility obtained by the means of a spin probe. It was shown that the interface layers are able to stabilize free radicals that appear in the process of photocuring. The lifetime of stabilized radicals is about 20–30 min at 50°C. The existence of a wide distribution of molecular mobility in filled oligomers was established. Sorption of oligomer molecules with filler surface was accompanied by their vitrification. When the content of filler achieved 25–35 mass%, vitrification of the half-volume of polymer matrix occurred. The strongest stabilizing effect was provided by hydroxylapatite.     

Properties of natural rubber composites reinforced with silica or carbon black: influence of cure accelerator content and filler dispersion

Filler dispersion is a critical factor in determining the properties of filled rubber composites. Silica has a high density of silanol groups on the surface, which lead to strong filler–filler interactions and a poor filler dispersions. A cure accelerator, N‐tert‐butyl‐2‐benzothiazole sulfenamide (TBBS), was found to improve filler dispersion in silica‐filled natural rubber (NR) compounds. For the silica‐filled NR compounds without the silane coupling agent, the reversion ratio generally increased with increase in TBBS content, whereas those of the silica‐filled NR compounds containing the silane coupling agent and carbon black‐filled NR compounds decreased linearly. The tensile strength of the silica‐filled NR vulcanizate without the silane coupling agent increased as the TBBS content increased, whereas carbon black‐filled samples did not show a specific trend. The experimental results were explained by TBBS adsorption on the silica surface and the improvement of silica dispersion with the aid of TBBS. Copyright © 2003 Society of Chemical Industry