Development of expanded graphite filled natural rubber vulcanizates in presence and absence of carbon black: Mechanical,thermal and morphological properties

As nanosized expanded graphite (EG) reveals a similar layered structure like organoclay and also it has a high expansion ratio so rubber chains can easily be intercalated into the gallery space. To improve the dispersion of EG in the rubber matrices, primarily the surface modification of the expanded graphite have been done and then the modified expanded graphite (MEG)/polar compatibilizer [epoxidized natural rubber (ENR)] master batch have been prepared by solution mixing method in the laboratory. After that the MEG/ENR master batch have been mixed with bulk natural rubber (NR) in presence and absence of carbon black (CB) in a laboratory scale open two roll mixing mill. Wide angle X-ray diffraction (WAXD) and high resolution transmission electron microscopic (HR-TEM) analysis of the nanocomposites revealed that MEG was intercalated and as well as delaminated in the NR matrix. Scanning electron microscope (SEM) images of the nanocomposites showed very rough surface than the pure NR matrix. In presence of expanded graphite the crack paths are channelized and coincide in one point suggesting the effect of plate like expanded graphite to acts as a barrier. We have got improved mechanical, thermal and dynamic mechanical properties for the MEG and MEG/CB loaded NR compounds compared to EG and EG/CB loaded NR compounds.     

Morphology development in nanoclay filled rubber compounds and rubber blends detected by online measured electrical conductance

The online measured electrical conductance (OMEC) during the rubber mixing process has been used as a novel method to characterize the dispersion of organoclay in rubber compounds and blends. This method was also used for the investigation of morphology development and kinetics of organoclay distribution in carboxylated hydrogenated nitrile butadiene rubber (XHNBR) and hydrogenated nitrile butadiene rubber (HNBR) as well as blends of HNBR with natural rubber (NR). The synchronized increase of the OMEC measured directly in the mixing chamber of the internal mixer along with dispersion of organoclay in the rubber matrix has been observed. The conductivity signal is sensitive to the intercalation/exfoliation process of organoclay in rubber compounds. The correlation between the OMEC and intercalation/exfoliation of organoclay has been determined by various offline experimental techniques like atomic force microscopy (AFM), transmission electron microscopy (TEM), and small angle X-ray scattering (SAXS). In heterogeneous blends the organoclay not only has the tendency to localize in one specific phase, but also strongly influence the development of the blend morphology, which has been nicely correlated with the OMEC chart of HNBR/(NR–clay) blends. A deeper insight into the mixing kinetics, clay transfer as well as development of the blend morphology was achieved on the basis of OMEC chart.     

Effect of epoxidized natural rubber–organoclay nanocomposites on NR/high styrene rubber blends with fillers

Epoxidized natural rubber (ENR) and organoclay nanocomposites (Cloisite 20A) were prepared by solution mixing in this study. The obtained nanocomposites were incorporated in natural rubber (NR) and high styrene rubber (HSR) blends in presence of ISAF and SRF types of carbon black as reinforcing fillers. Morphology, curing characteristics, mechanical and thermal properties and wear characteristics of the nanocomposites against standard abrader and different mining rock surfaces were analyzed. The morphology of the ENR/nanoclay showed a highly intercalated structure. The nanocomposites containing SRF N774 type of carbon black has showed increase in cross-link density, maximum torque and cure rate index compared to ISAF N231 type of carbon black. The overall mechanical properties and thermal stability was higher for the nanocomposites containing SRF type of carbon blacks. The compounds containing EC in NR–HSR have higher barrier properties compared to without EC. EC with SRF N774 carbon black has showed minimum compression set value due to the increased formation of effective network chains due to higher reinforcing efficiency of the nanoclay in the rubber matrix. EC with SRF N774 type of carbon black showed high abrasion resistance property against Du-Pont abrader, DIN abrader and rock–rubber experimental study and also it has been found to be the toughest rubber compound against all types of rock under the present study. Concrete has been identified as the major abrader against the blends than other rock types.     

天然橡胶与其环氧化物并用胶基复合材料的黏弹阻尼性能

为改善天然橡胶（NR）的阻尼性能,在密炼机中以质量比20：80混合不同环氧度环氧化天然橡胶（ENR）与天然橡胶制备ENR-NR并用橡胶基体,在橡胶基体的混炼与开炼过程加入其他填充组分（硫磺、促进剂2,2'-二硫代二苯并噻唑（DM）、促进剂N-环己基-2-苯并噻唑次磺酰胺（CZ）、ZnO、硬脂酸、炭黑）得到了宽温域阻尼ENR-NR基复合材料。采用橡胶加工分析仪和动态力学热分析仪,研究了ENR-NR混炼胶和硫化胶的动态力学和阻尼性能。结果表明：NR环氧化增强了分子链局部刚性,改善了胶体与填料的黏结性,但ENR吸附较多炭黑后不易均匀分散于连续相NR中。因此,ENR-NR并用混炼胶的黏度和储能模量随ENR环氧度增大而增加;在NR中加入ENR可改善硫化胶的弹性和阻尼性能。ENR-NR并用胶的有效阻尼温度范围拓宽到较高温度,环氧度为25的ENR与NR并用后,有效阻尼温度范围为-57~1℃,明显宽于NR的-57~-20℃,但高环氧度并用胶则出现阻尼失效区。加入少量ENR对NR的硬度、模量和断裂伸长率影响不大。     

环氧化天然橡胶改性石墨烯-炭黑/天然橡胶复合材料的制备及性能

以环氧化天然橡胶(ENR)为界面改性剂,制备了石墨烯-炭黑/天然橡胶-ENR(GR-CB/NR-ENR)复合材料,研究了ENR用量对GR-CB/NR-ENR复合材料的加工性能、力学性能和动态力学性能的影响。结果表明,ENR的加入可以改善GR-CB/NR-ENR复合材料的加工性能及CB粒子在天然橡胶基体中的分散性,增加GR与NR的相容性,增强填料与NR基体间的界面相容性,同时改善GR-CB/NR-ENR硫化胶的动态力学性能、物理性能和耐老化性能。当ENR添加量为6 wt%时,GR-CB/NR-ENR复合材料撕裂强度和拉伸强度最高,硫化胶耐老化性最好。随着ENR含量的增加,GR-CB/NR-ENR复合材料的压缩疲劳温度先升高后降低;随着应变的不断增大,GR-CB/NR-ENR复合材料的储能模量G'不断减小,损耗因子tanδ先增大后减小;动态模量随着应变的增加急剧下降。      

Natural rubber/epoxidised natural rubber-25 blends: morphology, transport phenomena and mechanical properties

Blends of natural rubber (NR)/epoxidised natural rubber (ENR) were prepared and their morphology, transport behaviour and mechanical properties have been studied. Ebonite method was used to study the blend morphology. Transport behaviour of pentane, hexane, heptane and octane was studied in the temperature range 27–60 °C. Different transport parameters such as rate constant, diffusion and permeation coefficients, and sorption coefficient have been calculated. Temperature dependence of diffusion has been used to estimate the activation parameters. The improved performance of NR/ENR blends has been established from the mechanical studies of unswollen, swollen and deswollen samples.     

Investigation of fracture resistance of natural rubber/clay nanocomposites by J-testing

The present work is aimed at studying the fracture behavior of a series of vulcanized natural rubber/organoclay samples obtained by melt blending. A fracture mechanics approach based on J-testing was adopted to evaluate the material resistance to crack initiation and propagation from a J-resistance curve as experimentally obtained by a single specimen procedure. The basis of the method and the experimental procedure adopted are described. Further, the effect of the organoclay content within the elastomeric matrix on the fracture properties is analyzed. It is found that the capability of the organoclay to improve fracture resistance is rate dependent indicating the viscoelastic character of the fracture process in such filled systems.     

Development of nanocomposite with epoxidized natural rubber and functionalized multiwalled carbon nanotubes for enhanced thermal conductivity and gas barrier property

Multiwalled pristine carbon nanotubes (mwCNTs) were treated with conventional mixed acid to functionalize outer surface of nanotubes with two unique chemical approaches using aminosilane solution and TiO₂ dispersion. Pristine and functionalized mwCNTs were dispersed subsequently in matrices of natural rubber (NR)–chlorobutyl rubber (CIIR) and epoxidized natural rubber (ENR)–CIIR to prepare nanocomposites by simple and eco-friendly melt blending method. The effect of surface treatment of mwCNTs, and epoxidation of NR on the composite properties was evaluated for thermal conductivity and gas barrier property. Nanocomposites prepared with surface functionalized mwCNTs and epoxidized NR were found to exhibit greater thermal conductivity and excellent gas barrier properties compared to pristine mwCNT reinforced CIIR–NR nanocomposites. A maximum thermal conductivity was observed for nanocomposite obtained from 20% ENR and 3% (by weight) mwCNTs functionalized with aminosilane. While a maximum gas barrier property was exhibited by nanocomposite with 20% ENR and 3% (by weight) mwCNTs treated with TiO₂. Results indicate that the presence of epoxy moieties of ENR provided a stronger network formation between aminosilane treated mwCNT surface and rubber matrices to exhibit higher thermal conductivity and metal oxide particles adhered to TiO₂ treated mwCNTs found to impart maximum resistance in transfer of oxygen gaseous molecules nanocomposite.     

Ceramic/natural rubber composites: influence types of rubber and ceramic materials on curing,mechanical, morphological,and dielectric properties

Influence of different types of rubber and ceramic material on cure characteristics, mechanical, morphological, and dielectric properties of natural rubber (NR) vulcanizate was studied. Two types of ferroelectric ceramic materials: barium titanate (BaTiO₃) and lead titanate (PbTiO₃) were prepared by solid-state reaction with calcinations at 1100 °C for 2 h. The ceramic powders were then characterized by X-ray diffraction (XRD), particle size analyzer, and SEM techniques. Ceramic/rubber composites were then prepared by melt mixing of rubber and ceramic powders. Two different types of NR (i.e., epoxidized NR [ENR] and unmodified NR) and two types of ceramic powders (i.e., BaTiO₃ and PbTiO₃) were exploited. It was found that incorporation of ceramic powders in rubber matrix and the presence of epoxirane rings in ENR molecules caused faster curing reaction, and higher delta torque but lower elongation at break. This is attributed to lower mobility of molecular chains and higher interaction between ENR molecules. Furthermore, SEM results revealed that the BaTiO₃ composites showed finer and better distribution of the particles in the rubber matrix than that of the PbTiO₃ composite. This caused superior mechanical properties of the BaTiO₃ composites. Furthermore, higher dielectric constant and loss tangent was observed in the ENR/BaTiO₃ composites.     

Effect of montmorillonite modification on mechanical properties of vulcanized natural rubber composites

Natural rubber-clay composites were prepared by direct polymer melt intercalation. Ca-montmorillonite Jelšovy Potok (JP; Slovakia) and Na-montmorillonite Kunipia-F (KU; Japan) were ion exchanged with octadecyltrimethylammonium (ODTMA) bromide and were used as aluminosilicate fillers. Silica Ultrasil VN3 was used in amount of 15 phr as conventional filler. The effect of clay or organoclay loading from 1 up to 10 phr on the mechanical properties was evaluated from the tensile tests (stress at break, strain at break and modulus M100). Organic modification resulted in an increase of toluene uptake degree for both fillers. While an addition of unmodified KU had no effect on tensile strength and deformation at break, a reinforcing effect was observed for the mixture containing 10 phr of unmodified JP. Both ODTMA modified fillers (KU and JP) exhibited substantial increase in tensile strength and deformation at break; JP proved to be more effective compared to KU also if modified with ODTMA. The highest stress at break and strain at break values for natural rubber composites were obtained with 15 phr of SiO₂ and 10 phr of montmorillonite; however, the effect of exchangeable cation was minor.     

Mechanical reinforcement in natural rubber/organoclay nanocomposites

Aim of this work is to get an insight into the mechanisms by which nanofillers produce mechanical reinforcement in polymers above their glass transition temperature. To this purpose, the mechanical behaviour of natural rubber/organo-modified montmorillonite vulcanisates produced by melt mixing with various filler contents was investigated. Data of the initial modulus, evaluated from stress–elongation curves obtained in tensile tests carried out at room temperature and a fixed cross-head rate, were analysed as a function of the organoclay content by applying mechanical models proposed in the literature. Such analysis provided an evaluation of the filler percolation threshold. Further, tests performed with varying temperature and rate pointed out appreciable rate and temperature dependence only for samples containing amounts of organoclay higher than the percolation limit, that is in presence of filler networking. Such a typical viscoelastic behaviour associated to the presence of the filler network contributes to support the hypothesis that in filled rubbers the mechanisms of filler networking is based on the formation of confined regions of immobilised polymer that join the filler particles of the network, as recently proposed.     

Tensile and tear failure of plasticized poly (vinyl chloride)/epoxidized natural rubber miscible blends

A study on the tensile and tear failure of miscible blends of plasticized poly (vinyl chloride), PVC, and epoxidized natural rubber (ENR) was carried out. Fractographs were taken in a scanning electron microscope in order to obtain an insight into the failure mechanism of the samples. It was found that low ENR blends failed by shearing in tensile testing, and they exhibited irregular stick-slip deformation and characteristics like vulcanizates in tear testing. Blends of plasticized PVC and ENR were more flexible than the individual components. As a result of the geometrical effect the tear fracture surface has rougher features than the tensile fracture surface. Sinusoidal wavy tear patterns in the form of a typical sine wave and rectified half sine wave of the fracture surface are characteristic features of tear resistant non-vulcanizates of rubber-like materials. Moreover, the study revealed that there were no features of phase separation of PVC and ENR due to incompatibility at any of the fracture surfaces examined.     

Styrene-butadiene rubber/halloysite nanotubes composites modified by epoxidized natural rubber

The reinforcement effects of halloysite nanotubes on styrene-butadiene rubber and the modification effect of epoxidized natural rubber on styrene-butadiene rubber/halloysite nanotubes composites were studied. The structure, morphology and properties of styrene-butadiene rubber/halloysite nanotubes composites before and after the incorporation of epoxidized natural rubber were investigated. The results indicated that epoxidized natural rubber can promote the dispersion and orientation of halloysite nanotubes in styrene-butadiene rubber matrix at nanoscale and strengthen interfacial combination between halloysite nanotubes and styrene-butadiene rubber by the formation of covalent bonds and hydrogen bonds between epoxidized natural rubber and halloysite nanotubes. Consequently epoxidized natural rubber can improve the mechanical properties of the vulcanizates of styrene-butadiene rubber/halloysite nanotubes composites. Besides epoxidized natural rubber can decrease the rolling resistance of the vulcanizates and increase the wet grip property of the vulcanizates.     

Fracture behaviour of polypropylene sheets filled with epoxidized natural rubber (ENR)-treated coal gangue powder

The morphology, deformation and fracture properties of polypropylene sheets filled with untreated and epoxidized natural rubber (ENR)-treated coal gangue powder (CGP) were investigated by scanning electron microscope (SEM) and the essential work of fracture (EWF) method. The results show that ENR obviously improves the dispersion of CGP particles in the PP matrix and the interfacial adhesion between CGP particles and PP matrix with the well-established interfacial layer. It is found that all composites fracture in a ductile manner as ligament yields completely and crack propagates steadily. The fracture toughness (w _e ) of the composites is significantly improved with the complete interfacial layer formed by ENR on the surface of CGP particles. With increasing ENR content, the specific plastic work (w _p ) per volume unit of plastic zone of the composites increases considerably in spite of the restricted plastic deformation of plastic zones. In Addition, the fracture parameters of different stages of tensile process demonstrate that the positive effect of ENR on the fracture performance of the composites is mainly achieved by notably reinforcing crack resistance at the stage of necking-tearing after yielding.     

Effect of molecular weight and testing rate on adhesion property of pressure-sensitive adhesives prepared from epoxidized natural rubber

The dependence of peel strength and shear strength of epoxidized natural rubber (ENR 25)-based pressure-sensitive adhesive on molecular weight and rate of testing was investigated using coumarone-indene as the tackifying resin. Toluene and polyethylene terephthalate (PET) were used as the solvent and substrate respectively throughout the study. A SHEEN hand coater was used to coat the adhesive on the substrate at a coating thickness of 120 μm. All the adhesion properties were determined by a Llyod Adhesion Tester operating at different rates of testing. Result shows that peel strength and shear strength increases up to an optimum molecular weight of 6.5 × 10⁴ of ENR 25. For peel strength, the observation is attributed to the combined effects of wettability and mechanical strength of rubber at the optimum molecular weight, whereas for the shear strength, it is ascribed to the increasing amount of adhesive present in the coating layer which enhances the shear resistance of the adhesive. Peel strength and shear strength also increases with increase in rate of testing, an observation which is associated to the viscoeslastic response of the adhesive. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) study confirms the miscibility of tackifier and the ENR 25.     

Thermal,mechanical and rheological properties of polylactide toughened by expoxidized natural rubber

This paper concerns on the use of epoxidized natural rubber (ENR) as toughening agent for polylactide (PLA). ENR with epoxidation content of 20 mol% (ENR20) and 50 mol% (ENR50) were separately melt blended with PLA using an internal mixer. DSC results suggested that PLA/ENR blends were amorphous after melt blending while they were crystalline and revealed two melting peaks in the thermograms after being annealed at 100 °C. Mechanical tests showed that the introduction of ENR reduced the tensile modulus and strength but enhanced the elongation and the impact strength of PLA. The impact strength of the 20 wt% ENR20/PLA and ENR50/PLA blends increased to 6-fold and 3-fold, respectively, compared to that of pure PLA. This enhancement was due to a good interfacial adhesion between ENR and PLA. Both ENR20/PLA and ENR50/PLA blends performed very strong shear thinning behavior, and the complex viscosity, storage and loss modulus of the blends also increased after blending with ENR.     

液体聚异戊二烯对天然橡胶/环氧化天然橡胶共混物结构与性能的影响

研究了液体聚异戊二烯(LIR)对天然橡胶(NR)/环氧化天然橡胶(ENR)共混体系的加工性能、硫化特性、物理力学性能、耐热氧硫化性能、动态力学性能及微观结构的影响。结果表明,加入LIR提高了体系的加工性能,硫化性能和物理力学性能基本不变,体系的耐热氧老化性能提高。少量的LIR的加入可提高体系的抗湿滑性,同时滚动阻力略有下降。LIR还可有效提高炭黑在NR/ENR体系中的分散。     

天然橡胶/固相改性蒙脱土纳米复合材料的制备与表征

在固相对蒙脱土进行有机改性,并与天然橡胶机械混炼插层制备了纳米复合材料。利用X射线衍射仪(XRD)、橡胶加工分析仪(RPA)和透射电镜(TEM)等研究了天然橡胶/固相改性蒙脱土纳米复合材料的结构,同时考察了材料的力学性能和耐老化性能。结果表明:固相改性蒙脱土在天然橡胶中可以实现纳米级分散,得到天然橡胶/蒙脱土纳米复合材料。固相改性蒙脱土对天然橡胶不但具有明显的补强效果,大幅度提高材料的力学性能和耐热氧老化性能,而且还具有很好的促进硫化作用。     

Epoxy resin/liquid natural rubber system: secondary phase separation and its impact on mechanical properties

An investigation was carried out to explore the morphology and mechanical properties of diglycidyl ether of bisphenol A epoxy resin (DGEBA) with liquid natural rubber possessing hydroxyl functionality (HLNR). Though modification of epoxies by synthetic rubber has been extensively studied not much attention has been paid to liquid natural rubber. Photo depolymerisation of natural rubber enables us to synthesise low molecular weight oligomers by varying the experimental parameters. Epoxy resin was cured using nadic methyl anhydride as hardener in presence of N,N-dimethyl benzyl amine accelerator. Hydroxylated natural rubber of different concentrations is used as modifier for epoxy resin. The addition of such chemically modified liquid rubber to an anhydride hardener–epoxy resin mixture has given rise to the formation of a two-phase microstructure in the cured systems, consisting of spherical particles of liquid natural rubber strongly bonded to the surrounding matrix, there by providing the required mechanism for toughness enhancement. Subinclusions of epoxy resin were present in the elastomer domains as secondary particles (particle in particle morphology) as evidenced from the SEM (scanning electron micrograph) photomicrographs. The origin of the so-called secondary phase separation is due to the combined effect of hydrodynamics, viscoelastic effects of rubber phase, diffusion, surface tension, polymerisation reaction and phase separation. In a dynamic asymmetric system, the diffusion of the fast dynamic phase is prevented by the slow dynamic phase, and hence the growth of fast dynamic phase gets retarded due to the slow dynamic phase. In the case of low viscosity blends the growth of fast dynamic phase turns fast and hence diffusion of fast dynamic phase cannot follow geometrical growth and cannot establish local concentration equilibrium and hence double phase separation takes place. The double phase separation is responsible for the enhanced impact and toughness behaviour of the blends. The mechanical behaviour of the liquid rubber-modified epoxy resin was evaluated in terms of tensile and flexural properties.     

Influence of carbon blacks on butadiene rubber/high styrene rubber/natural rubber with nanosilica: Morphology and wear

The effect of fillers on morphology and wear characteristics are studied in butadiene rubber (PBR)/high styrene rubber (HSR)/natural rubber (NR) blends with different types of carbon black. SAF N110 with SRF N774 type of carbon black shows a significant effect on curing studies and mechanical properties by reacting at the interface between PBR, HSR and NR matrix. Blends containing the same carbon blacks show high abrasion resistant properties against Du-Pont abrader, DIN abrader and different mining rock surfaces and also is found to be the toughest rubber against all types of rock.