Electromagnetic characteristic and microwave absorbing performance of different carbon-based hydrogenated acrylonitrile–butadiene rubber composites

Hydrogenated acrylonitrile–butadiene rubber (HNBR) was mixed with carbon fiber (CF), conductive carbon black (CCB) and multi-walled carbon nanotubes (MWCNT) to prepare microwave absorbing composites, their complex permittivity was measured in microwave frequencies (2–18 GHz), and their electromagnetic characteristics and microwave absorbing performance were studied. The real part and imaginary part of permittivity of the composites increased with increasing carbon filler loading, showing dependency on filler type. The microwave reflection loss of the composites also depended on the loading and type of fillers. The matching thickness of the absorber layer decreased with increasing permittivity, while the matching frequency decreased with increasing layer thickness. The minimum reflection loss was −49.3 dB for HNBR/MWCNT (100/10) composite, while −13.1 dB for HNBR/CCB (100/15) composite and −7.1 dB for HNBR/CF (100/30) composite. The efficient microwave absorption of HNBR/MWCNT composites is accounted from high conduction loss and dielectric relaxation of MWCNT, and strong interface scattering.     

Effect of rubber aggregates on the physico-mechanical behaviour of cement–rubber composites-influence of the alveolar texture of rubber aggregates

The study presented herein has been undertaken in order to examine the physico-mechanical properties of cement–rubber composites by use of two types of rubber aggregates, in the aim of developing a highly deformable material. The results obtained highlight the importance of the alveolar feature and the elasticity of the rubber aggregates in helping improve the flexural strength and deformability of the material. An optical analysis reveals the best level of bonding between the expanded rubber aggregates and the cement matrix.     

Utilization of new micronized and nano-CoO·MgO/kaolin mixed pigments in improving the properties of styrene–butadiene rubber composites

The present work highlights the role of a new prepared core–shell pigment based on kaolin as the bulk (core) covered with cobalt oxide and magnesium oxide comprising the surface of the pigment (shell). The new pigment was prepared in the micronized and nano-sized particles and its effect on the different properties of styrene–butadiene rubber (SBR) vulcanizates was studied. Incorporation of these two particle sized pigments and their varied content of cobalt oxide to magnesium oxide in the shell of the different pigments in different styrene–butadiene rubber vulcanizates was done, and their effects on the rheological, physical, mechanical and dielectric properties was studied. The study showed that there was a significant effect of these new pigments on SBR properties, and that the optimum micronized pigment loading in SBR was 30 phr, while that of the nano-pigment was 6 phr. The different measured properties were in good agreement with each other.     

Rheology of asphalt and styrene–butadiene blends

In recent years, many authors have researched polymer-modified asphalt blends and tried to better understand the rheological behavior of these materials. In this work, the thermomechanical response of an asphalt formulation was researched trying to find better asphalt-modified blends that allow for the construction of improved asphalt roads. The experimentation included several polymer–maltene formulations developed at different polymer concentrations and temperatures where the asphaltenes of the original asphalt were removed. Such separation was carried out because the maltene fraction represents the portion of the asphalt that chemically reacts with the polymer modifier. The rheological behavior of the blends was determined from oscillatory shear flow data. Analysis of the G′, G′′, G* moduli and phase angle (δ) as a function of oscillatory frequency for various temperatures led to the conclusion that the maltenes behaved as a pseudo-homogeneous viscoelastic material that could dissipate stress without presenting structural changes. Furthermore, all maltenes–polymer blends behaved more viscoelastically than the non-blended maltenes depending on the amount of the polymer contained in the formulation. The blend viscosity increased with polymer concentration, and this increase was seen in both the viscous and elastic moduli. Furthermore, performance grade trials were also performed according to the AASHTO TP5 to determine the failing temperature. It was noticed that the limiting temperature increased with the modifier concentration with a δ between 50° and 60°, indirect value of elasticity found to have industrial applications for asphalt pavements.     

Mesoscale analysis of rubber particle effect on young’s modulus and creep behaviour of crumb rubber concrete

International Journal of Mechanics and Materials in Design - This paper presents a mesoscale model to investigate the rubber particle effect on the mechanical properties of crumb rubber concrete...     

Enhanced microwave absorbing performance of hydrogenated acrylonitrile–butadiene rubber/multi-walled carbon nanotube composites by in situ prepared rare earth acrylates

Rare earth oxides (REO = Gd₂O₃, Dy₂O₃, Tm₂O₃) and acrylic acid (AA) were in situ reacted in hydrogenated acrylonitrile–butadiene rubber (HNBR) to prepare HNBR/multi-walled carbon nanotube (MWCNT)/REO/AA composites. The HNBR/MWCNT/REO/AA composites have higher permittivity and dielectric loss than HNBR/MWCNT composite, leading to significantly enhanced microwave absorbing performance of the HNBR/MWCNT/REO/AA composites. Dielectric permittivity analysis reveals that the HNBR/MWCNT/REO/AA composites have longer dielectric relaxation time and higher conductivity than the HNBR/MWCNT composite. The HNBR/MWCNT composite has the minimum reflection loss of −15.1 dB, while the HNBR/MWCNT/REO/AA composites have the minimum reflection loss of −48.8 dB. The improvement of microwave absorbing performance is attributed to the stronger interfacial polarization and higher conductivity after formation of in situ prepared rare earth acrylates.     

Synthesis of nickel–rubber nanocomposites and evaluation of their dielectric properties

Nanocomposites based on natural rubber and nano-sized nickel were synthesized by incorporating nickel nanoparticles in a natural rubber matrix for various loadings of the filler. Structural, morphological, magnetic and mechanical properties of the composites were evaluated along with a detailed study of dielectric properties. It was found that nickel particles were uniformly distributed in the matrix without agglomeration resulting in a magnetic nanocomposite. The elastic properties showed an improvement with increase in filler content but breaking stress and breaking strain were found to decrease. Dielectric permittivity was found to decrease with increase in frequency, and found to increase with increase in nickel loading. The decrease in permittivity with temperature is attributed to the high volume expansivity of rubber at elevated temperatures. Dielectric loss of blank rubber as well as the composites was found to increase with temperature.     

Application of artificial intelligence to modelling asphalt–rubber viscosity

The viscosity of binder is of great importance during the handling, mixing, application and compaction of asphalt in highway surfacing. This paper presents experimental data and the application of artificial intelligence techniques (statistics, artificial neural networks (ANNs) and fuzzy logic) to modelling of apparent viscosity in asphalt–rubber binders. The binders were prepared in the laboratory by varying the rubber content (RC), rubber particle size, duration and temperature of mixture in conformity with a statistical design plan. Multi-factorial analysis of variance showed that the RC has a major influence on the viscosity observed for the considered interval of parameters variation. When only limited experimental data of design matrix are available for modelling, the fuzzy logic model is the best model to be used. In addition, the combined use of ANN and multiple regression analysis improved the characteristics of the neural network.     

Eco-friendly nanocomposites between carboxylated acrylonitrile–butadiene rubber (XNBR) and graphene oxide or graphene at low content with enhanced mechanical properties

A crucial step in rubber nanocomposites is the homogenous dispersion of the nanofillers within the elastomer matrix. Herein, a green and modified latex co-coagulation strategy was conducted to develop high-performance nanocomposite materials based on carboxylated acrylonitrile-butadiene rubber (XNBR) latex with graphene oxide (GO) or reduced graphene oxide (RGO). Aqueous solutions with different concentrations of GO or RGO were mixed with XNBR rubber latex under vigorous magnetic stirring. The incorporation of graphene-derivative fillers in the XNBR matrix provided significant improvements in the rheological and mechanical properties compared to the unfilled rubber. Indeed, with increasing fillers loading, the maximum torque, tensile strength and crosslink density of obtained nanocomposites were found to increase. These results were correlated to the better dispersion of fillers through the matrix and, thus, to stronger interactions between the oxygen-containing functional groups of fillers and the carboxyl ones in XNBR matrix.     

Application of carboxylated styrene–butadiene emulsion-Portland cement mixture as road base material

This study investigated the effects of the addition of a carboxylated styrene–butadiene emulsion (CSBE) and Portland cement on the long-term performance of road base. The specimens stabilised with Portland cement (0–6%) and CSBE (5–10%) were subjected to different stress sequences in order to study the unconfined compressive strength, flexural strength (FS), soaked and unsoaked California bearing ratio, dynamic creep and wheel-tracking characteristics of seven-day-cured specimens. The FS tests showed that the addition of a 4% Portland cement–7% CSBE mixture resulted in improvements of 48.9% of modulus of rupture as compared to the sample with 4% cement. The permanent strain behaviour of the samples was assessed by the Zhou three-stage creep model. The results of dynamic creep and wheel-tracking tests showed that the permanent deformation characteristics were considerably improved by the addition of a 4% Portland cement–7% CSBE mixture, which resulted in reduction of permanent strain of the mixture. Therefore, this research presents a new polymer additive with outstanding engineering properties for use in road bases.     

The influence of hybrid phosphate–alumina pigments on properties of Ethylene-propylene-diene rubber composites

In this work Ethylene-propylene-diene (EPDM) rubber vulcanizates were pigmented with a new hybrid pigment containing nano-phosphate layer deposited on surface of micronized alumina. This new pigment contains both single and double-ion phosphates. Different rheological, chemical and physical properties of the nano-pigmented EPDM vulcanizates were studied and compared to the non-pigmented EPDM composites. These pigmented composite properties were studied in the presence and absence of maleic anhydride (MAH) which was employed as a compatibilizer. The bound rubber and cross-linking density were calculated. The results revealed that composites pigmented with 3Zn·1Ca phosphate/alumina/EPDM and 1Zn·3Ca phosphate/alumina/EPDM exhibited the best properties compared to other pigmented composites.     

Morphology and mechanical behavior of 1,2 polybutadiene — natural rubber blends

The effect of a thermoplastic rubber, 1,2 polybutadiene, on the mechanical behavior of natural rubber (NR) at different compositions has been studied. The morphology of the blends was studied by dynamic mechanical analysis and by solvent extraction of NR. The mechanical properties such as tensile strength, tear strength and hardness are found to increase with increasing 1,2 polybutadiene content in the blend. 50/50 blend has been found to exhibit the highest elongation. The abrasion resistance decreases with increasing NR content but the decrease is faster beyond 50% by weight of NR. The tear and abrasion fracture surfaces as revealed by scanning electron microscopy complement the quantitative results obtained by standard testing methods. The blends are found to exhibit higher hysteresis loss than either of the components at low strain level. The mechanical properties have also been correlated to the morphology of the blends.     

Pavement performance evaluation of recycled styrene–butadiene–styrene-modified asphalt mixture

More and more styrene–butadiene–styrene (SBS)-modified asphalt waste materials are being discarded with the increase in road service life. The recycling of these waste pavement materials can reduce environmental pollution and help save resources. However, the low-temperature performance and the fatigue resistance of recycled asphalt mixture are significantly affected by the addition of reclaimed asphalt pavement (RAP). In order to evaluate the low-temperature performance and the fatigue resistance of recycled SBS-modified asphalt mixture, three points bending test, Fénix test and Ensayo de BArrido de DEformaciones test were conducted. Additionally, the differences of recycling between SBS-modified RAP with different ageing conditions and ordinary unmodified RAP were compared. The results showed that fatigue resistance of modified recycling of asphalt mixture with different RAPs did not vary much under low temperature (?5 °C) while displaying an obvious difference under higher temperature. SBS-modified RAP under light ageing condition was suitable for modified recycling. However, the SBS-modified asphalt from RAP under serious ageing condition would lose modification effect resulting in a great reduction of the low-temperature crack resistance and the fatigue resistance. Therefore, it is necessary to evaluate the ageing degree of RAP before recycling SBS-modified asphalt mixture. The SBS-modified RAP under serious ageing condition (SM-RAP) is not recommended for directly modified recycling. But considering for further utilisation, the SM-RAP used for unmodified recycling as ordinary unmodified RAP can be regarded as a good choice and the RAP content should be restricted to less than 30%.     

In-chain multi-functionalized random butadiene–styrene copolymer via anionic copolymerization with 1,1-bis(4-dimethylaminophenyl)ethylene: synthesis and its application as a rubber matrix of carbon black-based composite

In-chain multi-functionalized random butadiene–styrene copolymer possessing definite dimethylamino groups along the polymer backbone, poly(butadiene-co-styrene-co-1,1-bis(4-dimethylaminophenyl)ethylene) (poly(Bd-co-St-co-BDADPE)), has been designed and synthesized via living anionic copolymerization of excess BDADPE with butadiene and styrene in benzene at 50 °C, using sec-butyllithium as initiator. The incorporation of BDADPE unit results in increases both in glass transition temperature and thermal decomposition temperature of the terpolymers. Such multiple dimethylamino groups along the rubber backbone effectively improve the dispersity of carbon black (CB) in the corresponding composites, as verified by scanning electronic microscopy observation. Also the tensile strength, elongation at break and the value of dynamic loss coefficient at 0 °C of the CB/poly(Bd-co-St-co-BDADPE) vulcanized composites, are significantly enhanced. This in-chain multi-functionalization of matrix rubber via anionic copolymerization employing BDADPE as copolymerizable monomer, provides a facile and effective method to prepare CB-based rubber composites with improved tensile strength and elongation at break, as well as good wet skid resistance.     

Natural rubber — Its engineering characteristics

Natural rubber is an elastomer with excellent properties, which have been exploited in a wide range of applications. Despite the fact that it is a well-defined engineering material, with comprehensive documentation on both mechanical data and design principles, many engineers remain ignorant of natural rubber's potential. This article outlines the nature of the raw material and how it is compounded & shaped into useful products; the physical properties and engineering characteristics of natural rubber vulcanizates are also described. Environmental effects and their minimization by suitable compounding are discussed. Examples of several applications are given, including some showing the long service life of natural rubber engineering components. The aim is to introduce engineers to natural rubber and to show that information exists for the design of components with known mechanical properties and predictable in-service behaviour.     

The microstructure and fracture performance of styrene–butadiene–methylmethacrylate block copolymer-modified epoxy polymers

The microstructure and fracture performance of an anhydride-cured epoxy polymer modified with two poly(styrene)-b-1,4-poly(butadiene)-b-poly(methyl methacrylate) (SBM) block copolymers were investigated in bulk form, and when used as the matrix material in carbon fibre reinforced composites. The ‘E21’ SBM block copolymer has a higher butadiene content and molecular weight than the ‘E41’. A network of aggregated spherical micelles was observed for the E21 SBM modified epoxy, which became increasingly interconnected as the SBM content was increased. A steady increase in the fracture energy was measured with increasing E21 content, from 96 to 511 J/m² for 15 wt% of E21. Well-dispersed ‘raspberry’-like SBM particles, with a sphere-on-sphere morphology of a poly(styrene) core covered with poly(butadiene) particles, in an epoxy matrix were obtained for loadings up to 7.5 wt% of E41 SBM. This changed to a partially phase-inverted structure at higher E41 contents, accompanied by a significant jump in the measured fracture energy to 1032 J/m² at 15 wt% of E41. The glass transition temperatures remained unchanged with the addition of SBM, indicating a complete phase separation. Electron microscopy and cross polarised transmission optical microscopy revealed localised shear band yielding, debonding and void growth as the main toughening mechanisms. Significant improvements in fracture energy were not observed in the fibre composites, indicating poor toughness transfer from the bulk to the composite. The fibre bridging observed for the unmodified epoxy matrix was reduced due to better fibre–matrix adhesion. The size of the crack tip deformation zone in the composites was restricted by the fibres, hence reducing the measured fracture energy compared to the bulk for the toughest matrix materials.     

Mechanical and damage behaviour of mortar–rubber aggregates mixtures: experiments and simulations

The reuse of rubber wastes of worn tires in aggregate form, to serve as a building material, is appreciated to preserve environment. This study aims to examine the mechanical behaviour of a mortar–rubber aggregates material. A multi-phase model called 2M2C (2 Mechanisms and 2 Criteria) which take the volume fraction substitution of rubber into account is investigated with the help of stress–strain curves. The proposed model is based on the localization of the stress on the phases level (rubber and mortar, respectively) and the homogenization of the local plastic strains. The model has also incorporated an isotropic damage variable to describe the loss of compressive strength. The experimental tests are well simulated by the model. Also, the simulations provide local informations such as damage evolution and local plastic strains.