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.     

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.     

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.     

The effects of electron beam irradiation on the thermal properties,fatigue life and natural weathering of styrene butadiene rubber/recycled acrylonitrile–butadiene rubber blends

The effects of electron beam (EB) irradiation on the thermal properties, fatigue life and natural weathering of styrene butadiene rubber/recycled acrylonitrile–butadiene rubber (SBR/NBRr) blends were investigated. The SBR/NBRr blends were prepared at 95/5, 85/15, 75/25, 65/35, or 50/50 blend ratios with and without the presence of a 3 part per hundred rubber (phr) of polyfunctional monomer, trimethylolpropane triacrylate (TMPTA). Results indicate that the crystallisation temperature (T_c) observed in polymeric blends is due to the alignment of polymer chains forming a semi-crystalline phase. Addition of TMPTA helps to align polymer chains through crosslinking. More crosslinking occurred between polymer blends with the help of TMPTA, upon irradiation. The improvement in fatigue life can also be associated with the stabilisation of SBR/NBRr blends upon irradiation and irradiation-induced crosslinking, which was accomplished with relatively low radiation-induced oxidative degradation in the presence of TMPTA. The tensile properties of both blends decreased over the periods of environmental exposure due to the effect of polymer degradation. After 6 months, the irradiated SBR/NBRr blends could not retain better retention [mainly with 25, 35 or 50 phr of recycled acrylonitrile–butadiene rubber (NBRr) particles] due to the samples becoming brittle over the long period of outdoor exposure.     

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.     

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.     

Evaluation of the surface physical properties of β-tricalcium phosphate/silicone rubber, a prospective soft-tissue implant material

Silicone rubber (SR) is one of the most commonly used and effective implant materials for soft-tissue augmentation, but it has been implicated in many adverse reactions. To overcome this drawback, a novel composite β-tricalcium phosphate/silicone rubber (β-TCP/SR) was prepared by compounding a SR matrix with β-TCP. The surface physical properties of β-TCP/SR were evaluated. AFM images showed that β-TCP/SR exhibited greater surface roughness than SR. The XRD and XPS analyses revealed that the addition of β-TCP changed the surface microstructure and charge distribution. FTIR analysis showed that the interaction between β-TCP and SR was weak, which may be due to the tetrahedral structure of PO₄³⁻. These results suggest that the addition of β-TCP in a SR matrix can change the surface microstructure and may improve cytocompatibility, consistent with results from a previous study.     

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.     

Modified zinc silicate — an active rubber filler

Physico-chemical properties have been characterized for zinc silicates obtained in various conditions in reaction of sodium metasilicate solution with water soluble zinc salt (zinc sulphate or chloride). Attempts have been made to apply the precipitated zinc silicates in rubber mixtures based on butadiene-styrene rubber. Appropriate tests have been conducted. Also, a possibility has been tested of eliminating zinc oxide (an activator in the vulcanization process) from the rubber mixture. Studies have been presented on the modification of zinc silicate surface with silane and titanate coupling agents. The extent of surface modification has been estimated measuring heats of surface immersion and determining chemisorbed carbon on the surface which has originated from coupling agents. The effect of modifying zinc silicate surface has been evaluated by strength tests performed on vulcanizates filled with the modified silicates.     

Toughening performance of glass fibre composites with core–shell rubber and silica nanoparticle modified matrices

The fracture energies of glass fibre composites with an anhydride-cured epoxy matrix modified using core–shell rubber (CSR) particles and silica nanoparticles were investigated. The quasi-isotropic laminates with a central 0°/0° ply interface were produced using resin infusion. Mode I fracture tests were performed, and scanning electron microscopy of the fracture surfaces was used to identify the toughening mechanisms.The composite toughness at initiation increased approximately linearly with increasing particle concentration, from 328 J/m² for the control to 842 J/m² with 15 wt% of CSR particles. All of the CSR particles cavitated, giving increased toughness by plastic void growth and shear yielding. However, the toughness of the silica-modified epoxies is lower as the literature shows that only 14% of the silica nanoparticles undergo debonding and void growth. The size of CSR particles had no influence on the composite toughness. The propagation toughness was dominated by the fibre toughening mechanisms, but the composites achieved full toughness transfer from the bulk.     

Dynamic mechanical analysis of electron beam irradiated sulphur vulcanized nitrile rubber network—some unique features

Mixed crosslinking system with electron beam irradiation as one of the crosslinkers in rubber has been developed for the first time. This paper describes some unique features of dynamic mechanical properties of the electron beam irradiated nitrile rubber vulcanizates at varying levels of sulphur in the network. Dynamic mechanical thermal analysis (DMTA) was performed on these vulcanizates over a range of temperatures (−80°C to +80°C), frequencies (0.032 to 32 Hz) and strains (0.001 to 10%). The results showed that there were significant changes in tan delta peak temperature and storage modulus on irradiation of these vulcanizates. The vulcanizates containing higher amount of sulphur formed intense crosslinked networks and crosslink rearrangements, which were supported by the increase in the storage modulus and shift in tan delta towards higher temperature as compared to their control counterpart. There is also an increase in the peak height due to chain scission and subsequent plasticization. A concept of network distribution using the plots of the storage modulus ratio divided by frequency against inverse of frequency was introduced. This contravening nature was also affirmed with the help of these curves showing broader network distribution for irradiated samples having lower amount of sulphur. This was also supported from the crossover frequency values estimated from the plot of storage and loss modulii against frequencies observed.     

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.     

Microwave dielectric properties of flexible silicone rubber – Ba(Zn1/3Ta2/3)O3 composite substrates

Silicone rubber composites filled with Ba(Zn_1/3Ta_2/3)O₃ (BZT) were prepared by hot pressing and the effect of filler content on the microwave dielectric, mechanical and thermal properties as well as on moisture absorption were investigated. The observed relative permittivity (ɛ_r) was compared with different theoretical models. Among the different theoretical models Jayasundere Smith and Modified Lichtenecker were in good agreement with experimental values of ɛ_r. The study of the mechanical property showed that the silicone rubber – BZT composites were flexible and stretchable. The coefficient of thermal expansion and specific heat capacity decreased whereas thermal conductivity, thermal diffusivity and the moisture absorption increased with increase in filler loading.