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.     

Electromagnetic and microwave absorbing properties of amorphous carbon nanotube–cadmium selenide quantum dot hybrids

Amorphous carbon nanotubes (α-CNTs) have been synthesized by heating a mixture of ferrocene and ammonium chloride at a low temperature of 200 °C. Surface morphological studies reveal that the as-prepared nanotubes are straight tubular structures with open ends. The Raman spectra reveal the presence of defects in the nanotubes. Both chemical oxidation and hybridization treatments result in hybridization between α-CNTs and cadmium selenide quantum dots (CdSe QDs), giving an increase in the average outer diameter, surface roughness and the number of defects for the α-CNTs. The decreasing outer diameter size of nanotubes reduces the permittivity contribution in overall due to size quantization effect. Chemical functionalization initiated by the oxidation and attachment of CdSe QDs due to hybridization improve the dispersion stability and permittivity of α-CNTs. The α-CNTs–CdSe QD hybrids have the potential for electromagnetic and microwave absorption applications as they exhibit a high imaginary component of permittivity (dielectric loss).     

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.     

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.     

Significant improvement in static and dynamic mechanical properties of graphene oxide–carbon nanotube acrylonitrile butadiene styrene hybrid composites

Herein, hybridization of graphene nanosheets and carbon nanotubes (CNTs) has been made to solve the problem of restacking of graphene nanosheets and agglomeration of CNTs. The multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (RGO) and graphene oxide–carbon nanotubes (GCNTs) reinforced acrylonitrile butadiene styrene (ABS) composites have been prepared using micro-twin-screw extruder. The effect of these reinforcements on static and dynamic mechanical properties of composites is studied. The ultimate tensile strength and elastic modulus for 7 wt.% GCNT–ABS composites show enhancement of 26.1 and 71.3% over pure ABS matrix, respectively. Various parameters such as coefficient “C” factor (the ratio of storage modulus of the composite to polymer in glassy and rubbery regions), degree of entanglement, crosslink density and adhesion factor have been calculated to analyze the interaction between fillers and polymer matrix. The 3-D hybrid structure of GCNTs overcomes the associated problem of CNTs agglomeration and graphene restacking. GCNT hybrid composites show higher dispersion as well as effectiveness for increased filler amount as compared to RGO and MWCNTs based composites. GCNTs prove its superiority over MWCNTs and RGO by showing a synergistic effect in the glass transition temperature and storage modulus. Raman spectroscopy and scanning electron microscopy are used to confirm the interaction and distribution of the filler and matrix, respectively.     

Development of polycarbonate/acrylonitrile–butadiene–styrene copolymer based composites with functional fillers for car audio chassis

Environmental regulations require the improvement of automobile fuel efficiency. This can be achieved mainly by reducing the weight of automobile components. In this study, polycarbonate/acrylonitrile–butadiene–styrene copolymer (PC/ABS) based composite mixed with glass fibers and metal fibers was developed and its suitability of application into car audio chassis was investigated. The test materials were prepared with various contents of metal fibers because of the fibers’ excellent mechanical and electrical properties. In this study, the morphologies of the materials were investigated to confirm the dispersion of the fillers and the interfacial characteristics between the fillers and the base material. In addition, the mechanical and electrical characteristics of the PC/ABS based composites, which depended on the metal fiber content, were evaluated using key mechanical (impact, tensile and flexural) and electrical tests such as electromagnetic interference (EMI) and surface resistance. The proper proportion of the metal fibers in PC/ABS based composites was determined from the test results. Finally, the applicability of PC/ABS based composites in car audio chassis was evaluated through weight reduction analysis and cost-benefit analysis.     

Synthesis and microwave absorbing properties of Mn–Zn nanoferrite produced by microwave assisted ball milling

In this paper, well dispersed spinel Mn_xZn_1?xFe₂O₄ (x = 0.3,0.5 and 0.7) were obtained by microwave assisted ball milling at 2.45 GHz through only one step. The synthesized products were characterized by X-ray diffraction, high resolution transmission electron microscope, vibration sample magnetometer, and vector network analysis. Synthesized Mn–Zn nanoferrite showed the saturation magnetization reached 84.91emu/g when the x was 0.7 and the largest magnetic loss tangent at the frequency of 2.45 GHz. Microwave absorbing properties of these composites were studied at the frequency range of 2–18 GHz. Two microwave reflection loss peaks appeared for all the spinel ferrite. When x was 0.5, the minimum reflection loss appeared at the highest frequency. When x was 0.7, these two minimum reflection loss peaks, ?17.36 and ?48.13 dB, were calculated with the ?10 dB bandwidth at the frequency ranges of 2.24–5.04 and 13.28–14.88 GHz, respectively. Resonance reflection loss peaks shifted to lower frequencies when the matching thickness increased.     

Encapsulation and microwave hybrid processing of Al 6061–Graphene–SiC composites

The demand for new aluminum alloy–based metal matrix composites with combinations of novel reinforcements, processed through innovative methods are very much needed for critical engineering applications. With this perspective, the current research work is aimed at the development of Al 6061 composites reinforced with two-dimensional Graphene nanoflake-encapsulated SiC. Ultrasonic liquid processing method is used to disperse the Graphene flake and the mixture is ball milled by adding SiC to achieve the encapsulation. Subsequently, the Al 6061 powder is added to the milled mixture and consolidated through uniaxial vacuum hot press followed by microwave hybrid sintering. Scanning electron microscope (SEM) analysis, X-ray diffraction analysis, hardness, density, and microstructure analysis were carried out on developed composites. Raman analysis was carried out to analyze the distortion on Graphene physical structure during various processing stages. Further, effects on novel combination of material with combined processing approach on flexural and tribological behavior have been analyzed.     

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.     

Forming performance and biodegradability of woodfibre–Biopol™ composites

A Taguchi approach to experimental design has been used to analyse the hotpressing and vee-bending of woodfibre–Biopol™ composites. Analysis of the hotpressing process clearly shows that platen temperature is the parameter with the most influence on tensile performance of the composite sheet produced. In bending (a common manufacturing situation), geometric conformance is maximised when forming time is 60 s, forming rate is 250 mm/min and forming radius/thickness ratio is 2 for the composite sheets studied in this paper. A study of the influence of fibre volume fraction on the biodegradability of these sheets show that these composites are highly biodegradable, often degrading at a rate greater than that of pure Biopol™. The results also suggest that a woodfibre mass fraction of ∼15% maximises the degradation of the woodfibre–Biopol™ composites.     

Preparation and microwave absorbing properties of hollow glass microspheres/Fe3O4/Ag composites with core–shell structure

The low-density, conductive and magnetic hollow glass microspheres (HGM)/Fe₃O₄/Ag composites have been successfully synthesized via co-precipitation and chemical plating method. The morphology, composition, microstructure, magnetic and microwave absorbing properties of the composites were investigated based on the analyses of the results using scanning electron microscope, energy dispersive spectroscopy, X-ray diffraction, vibrating sample magnetometer and vector network analyzer. The results showed that the HGM/Fe₃O₄ composites were successfully prepared, and the coating layers on the surface of HGM are compact and continuous. Moreover, the final composites were completely covered with Ag nanoparticles. With the addition of Ag nanoparticles, the saturation magnetization of the HGM/Fe₃O₄ composites reduces from 32.08 to 14.77 emu/g, whereas its conductivity increases to 0.48 S/cm. The reflection loss (R) of HGM/Fe₃O₄/Ag composites is lower than ?10 dB at 8.2–8.7, 9.6–10.8 and 11.4–11.9 GHz, and the minimum loss value is ?19.1 dB at 9.9 GHz.     

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.     

Effects of multi-walled carbon nanotube (MWCNT) dispersion and compatibilizer on the electrical and rheological properties of polycarbonate/poly(acrylonitrile–butadiene–styrene)/MWCNT composites

In this study, the effects of multi-walled carbon nanotube (MWCNT) dispersion and poly(styrene-co-acrylonitrile)-g-maleic anhydride (SAN-g-MAH) as a compatibilizer on the electrical conductivity, electromagnetic interference shielding effectiveness (EMI SE), and rheological properties of polycarbonate (PC)/poly(acrylonitrile–butadiene–styrene) (ABS)/MWCNT composites were investigated. The morphological results from the scanning and transmission electron microscope images showed that the droplet size of the ABS decreased when the SAN-g-MAH (5 phr) was added to the PC/ABS (80/20) blend. This result suggests that the SAN-g-MAH acts as an effective compatibilizer in the PC/ABS blend. Also, the MWCNT appeared to be located more in the ABS phase (dispersed phase) than in the PC phase (continuous phase). The interfacial tension of the ABS/MWCNT composite was lower than that of the PC–MWCNT composite, and the lower value of interfacial tension of the ABS/MWCNT composite affected the preferred location of the MWCNT in the ABS phase more than in the PC phase. The electrical conductivities and EMI SE of the PC/ABS/MWCNT composite with the compatibilizer were higher than those of the composite without compatibilizer. The complex viscosity of the PC/ABS/MWCNT composite containing the SAN-g-MAH increased with the frequency compared to that of the composite without SAN-g-MAH. This result is possibly due to the increased degree of MWCNT dispersion. The result of rheological properties is consistent with the results of the morphology, electrical conductivity, and EMI SE of the PC/ABS/MWCNT composite.     

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%.     

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.     

Microwave absorbing properties of double-layer cementitious composites containing Mn–Zn ferrite

Double-layer cementitious composites filled with Mn–Zn ferrite as microwave absorbers were designed based on the impedance matching theory and electromagnetic wave propagation laws. The results showed that the addition of silica fume can improve the impedance matching between the cementitious composites and free space. Comparing with the single-layer structure, the reflectivity of the double-layer cementitious plates can decrease by 6–8 dB and decrease by 15 dB maximum with 30 wt.% ferrite; in addition, the reflectivity of electromagnetic wave is lower than 10 dB in the frequency range of 11.4–18 GHz. These composites can be potentially used as electromagnetic interference (EMI) materials for buildings.     

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.     

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.     

One-step synthesis,electromagnetic and microwave absorbing properties of α-FeOOH/polypyrrole nanocomposites

One-step synthesis of α-FeOOH/polypyrrole (PPy) nanocomposites is reported for the first time via a facile one-step chemical method in the presence of OH⁻, Fe²⁺, Fe³⁺ and pyrrole monomer. α-FeOOH nanorods are in situ formed in PPy matrix and the content of α-FeOOH nanorods increases with decreasing the molar ratio of pyrrole to Fe²⁺ ([Py]/[Fe²⁺] ratio). The electromagnetic and microwave absorbing properties of the nanocomposites are investigated as a function of the [Py]/[Fe²⁺] ratio. The results show that the PPy nanocomposites exhibit good conductivity (up to 16.10 S/cm) and antiferromagnetic behavior. The reflection loss evaluation based on the absorbing wall theory at the thickness of 2 mm shows that the nanocomposite at [Py]/[Fe²⁺] = 1.0 exhibits the best microwave absorbing property in the 2–18 GHz. And the corresponding reflection frequency range under −10 dB and −5 dB is 4.2 GHz and 5.8 GHz, respectively.