Magnetically-sensitive shape memory polyurethane composites crosslinked with multi-walled carbon nanotubes

Magnetically-sensitive polyurethane composites, which were crosslinked with multi-walled carbon nanotubes (MWCNTs) and were filled with Fe₃O₄ nanoparticles, were synthesized via in situ polymerization method. MWCNTs pretreated with nitric acid were used as crosslinking agents. Because of the crosslinking of MWCNTs with polyurethane prepolymer, the properties of the composites with a high content of Fe₃O₄ nanoparticles, especially the mechanical properties, were significantly improved. The composites showed excellent shape memory properties in both 45 °C hot water and an alternating magnetic field (f = 45 kHz, H = 29.7 kA m⁻¹). The shape recovery time was less than one minute and the shape recovery rate was over 95% in the alternating magnetic field.     

Polysaccharidic binders for the conception of an insulating agro-composite

The objective of this study is the formulation of a natural polysaccharidic binder for the conception of an insulating bio-based composite made with sunflower stalk particles. The formulation was performed using chitosan cross-linked with Genipin and mixed with alginate, guar gum and starch. A fractional factorial experimental design within 32 essays was established to find the formulation leading to composites with the best combination between good mechanical properties and limited amount of chitosan in the binder. Composites with a thermal conductivity (κ) of 0.07 W m⁻¹ K⁻¹ and a maximum tensile stress (σ_max) of 0.2 MPa were obtained with a total binder ratio of 5.5% (w/w). The results of this study show that the insulating bio-based composites evaluated have competitive mechanical and thermal performances compared with other eco-friendly insulating materials available on the market.     

Investigation of microstructure and mechanical properties of nano MgO reinforced Al composites manufactured by stir casting and powder metallurgy methods: A comparative study

In the present work, Al–nano MgO composites using A356 aluminum alloy and MgO nanoparticles (1.5, 2.5, and 5 vol.%) have been fabricated via stir casting and powder metallurgy (PM) methods. Different processing temperatures of 800, 850, and 950 °C for stir casting and 575, 600, and 625 °C for powder metallurgy were considered. Powder metallurgy samples showed more porosity portions compare to the casting samples which results in higher density values of casting composites (close to the theoretical density) compare to the sintering samples. Introduction of MgO nanoparticles to the Al matrix caused increasing of the hardness values which was more considerable in casting samples. The highest hardness value for casting and sintering samples have been obtained at 850 and 625 °C respectively, in 5 vol.% of MgO. Compressive strength values of casting composites were higher than sintered samples which were majorly due to the more homogeneity of Al matrix, less porosity portions, and better wettability of MgO nanoparticles in casting method. The highest compressive strength values for casting and sintered composites have been obtained at 850 and 625 °C, respectively. Scanning electron microscopy images showed higher porosity portions in sintered composites and more agglomeration and aggregation of MgO nanoparticles in casting samples which was due to the fundamental difference of two methods. Generally, the optimum processing temperatures to achieve better mechanical properties were 625 and 850 °C for powder metallurgy and stir-casting, respectively. Moreover, casting method represented more homogeneous data and higher values of mechanical properties compare to the powder metallurgy method.     

Reliable synthesis of bismuth nanoparticles for heavy metal detection

A reliable and facile pathway is described here for preparing high-quality bismuth nanoparticles. Combined with hydrothermal method and confined growing effect of polymer, bismuth nanoparticles with uniform size and shape were obtained with remarkable productivity. The nanoparticles is proved to be pure Rhombohedral structure Bi crystals with R-3m space group and the diameter of the nanoparticles is about 80 nm with a quite narrow particle size distribution. Those bismuth nanoparticles were predicted to grow from a rolling process by sheet-like Bi nanocrystal intermediates. The obtained bismuth nanoparticles were used to prepare modified electrode for the detection of Cd²⁺ and Pb²⁺ in water solution by stripping analysis. Compared with naked glassy carbon electrodes, the modified electrode showed two obvious responses at −0.85 V and −0.62 V, corresponding to the reduction process of Pb²⁺ and Cd²⁺ and this well-resolved stripping response can be observed when the concentration is as low as 10 μg/L, indicating potential application in electroanalysis for environmental inspection.     

Low-temperature synthesis,structural and magnetic properties of self-dopant LaMnO3+δ nanoparticles from a metal-organic polymeric precursor

Self-dopant LaMnO_3+δ nanoparticles have been successfully synthesized by metal citrate complex method based on Pechini-type reaction route, at low temperature (773 K). Powder X-ray diffraction and transmission electron microscope revealed pure and nanostructured phase of LaMnO_3+δ (δ = 0.125) with an average grain size of ∼72 nm (773 K) and ∼80 nm (1173 K). DC-magnetization measurements under an applied magnetic field of H = ±60 kOe showed an increase in the magnetization with the increase of calcination temperature. Ferromagnetic nature shown by non-stoichiometric LaMnO_3+δ was verified by well-defined hysteresis loop with large remanent magnetization (M_r) and coercive field (H_c). Surface areas of LaMnO_3+δ nanoparticles were found to be 157.4 and 153 m² g⁻¹ for the samples annealed at 773 K and 1173 K, respectively.     

Bio-directed synthesis of gold nanoparticles using Ananas comosus aqueous leaf extract and their photocatalytic activity for LDPE degradation

A bio-directed synthesis of gold nanoparticles (Au NPs) was developed via the reduction of hydrogen tetrachloroaurate (III) (HAuCl₄·3H₂O) solution by the aqueous leaf extract of Ananas comosus. The polyphenol stabilized Au NPs were characterized by UV–visible, Fourier transform infrared (FTIR), powder X-ray diffraction (PXRD)/selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDX) analyses. The HRTEM images revealed that Au NPs were well dispersed with spherical structures. The size ranges from 7.39 to 32.09 nm with average particle size of 18.85 ± 6.74 nm. The peaks of XRD analysis at (2θ) 37.96°, 44.06°, 64.54°, 77.50° and 81.73° were respectively assigned to (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) planes of the face-centered cubic (fcc) lattice of gold. The photocatalytic potential of Au NPs was studied through the solid-phase degradation of low-density polyethylene (LDPE) film. The photoinduced degradation of LDPE@Au nanocomposite film was higher than that of the pure LDPE film. The weight loss of LDPE@Au (1.0 wt%) nanocomposite film steadily increased and reached 51.4 ± 4.8% in 240 h under solar light irradiation, compared to the photo-induced LDPE with only 8.6 ± 0.7%. However, LDPE film with 1.0% Au NPs gave a weight loss value of 4.72 ± 0.71 under the dark condition at the end of 240 h. Thus, LDPE film with 1.0% Au NPs showed a degradation efficiency of 90.8% under solar irradiation after 240 h. The sustainability of the nanoparticles was confirmed through reusability in the photocatalytic degradation reaction up to five consecutive cycles without substantial loss in its catalytic performance.     

Tailoring of thermal and dielectric properties of LDPE-matrix composites by the volume fraction,density, and surface modification of hollow glass microsphere filler

Hollow glass microsphere (HGM) filled low-density polyethylene (LDPE) composites were prepared, and the effects of density, content, and surface modification of HGM on the thermal and dielectric properties of the composites were investigated. It is found that the thermal conductivity of the composites decreases with increasing HGM content or decreasing HGM density. At the same HGM content and density, the composites filled with suitable amount of silane coupling agent (KH570) modified HGM exhibit higher thermal conductivity than unmodified-HGM filled composites. The dielectric constant at 1 MHz of the composites also decreases with increasing HGM content or decreasing HGM density, but their dielectric loss increases with increasing HGM content or increasing HGM density. By modifying the surface of HGM with suitable amount of KH570, the dielectric constant and loss at 1 MHz of the composites can be decreased at the same time. The results of microwave dielectric properties of the composites indicate that the dielectric constant decreases with increasing HGM content or decreasing HGM density, the quality factor (Q × f) decreases with increasing HGM content or increasing HGM density, but both dielectric constant and quality factor are slightly affected by the surface modification of HGM. Due to lower intrinsic thermal conductivity and dielectric constant but higher dielectric loss of HGM than LDPE, the thermal conductivity and dielectric properties of the composites can be controlled with adding HGM and varying its volume fraction. The surface modification of HGM improves the interface contact between HGM and LDPE in the composites, which is confirmed by the SEM observation, and thus the heat conduction and dielectric properties at low frequency are improved. Based on calculated thermal conductivity and dielectric constant of HGM, the experimental trends of thermal conductivity and dielectric constant at 1 MHz of the composites are analyzed by using different models, including typical models for particles-filled composites and special models developed for hollow microsphere filled composites. The results from suitable models show close correlation with the experimental values.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Pt nanoparticles modified by rare earth oxides: Electronic effect and influence to catalytic hydrogenation of 3-phenoxybenzaldehyde

The rare earth elements (La, Ce, Nd, Sm, Pr, and Gd) modified Pt/Al₂O₃ catalysts were prepared by the colloidal deposition and chemical reduction methods, respectively. Pt nanoparticles with average size 3 ± 0.5 nm were uniformly dispersed on the surface of Al₂O₃ for the samples prepared by the colloidal deposition method, which exhibited higher activities in the hydrogenation of 3-phenoxybenzadehyde than the corresponding samples prepared by chemical reduction method. Moreover, except Gd, the catalysts modified by rare earth elements showed better catalytic performance than unmodified Pt/Al₂O₃. For Pt–Ce/Al₂O₃ catalyst, when the weight percent of Pt and Ce was 0.5 and 0.25, respectively, the hydrogenation conversion of 3-phenoxybenzaldehyde was 97.3% after 6 h reaction. This activity improvement is due to the electronic interaction between Pt and rare earth elements, which was investigated by X-ray photoelectron spectroscopy.     

Improving core bond strength and dimensional stability of particleboard using polymer powder in core layer

Low density polyethylene powder (LDPE) was used as polymer binder in the core layer of three layer particleboard. In the first phase, six levels of the LDPE powder (5–30 wt.%) based on the composition by weight, were mixed with the core particles with 8 wt.% urea–formaldehyde (UF) resin. In the second phase, the LDPE powder content was kept constant at 10 wt.% in all treatments and the UF resin content applied to the core layer was decreased gradually from 8 to 4 wt.%. Thickness swelling and water absorption of the particleboards significantly decreased with increasing the LDPE content in the core layer. Similarly, incorporation of the LDPE powder into the core layer of the particleboard greatly improved internal bond strength. The flexural properties of the particleboards, the modulus of rupture (MOR) and modulus of elasticity (MOE), were positively affected by increasing LDPE content up to 10 wt.% but the further increment of the LDPE decreased the MOR and MOE. The UF resin content can be reduced in the core layer of the particleboard as a function of increasing the LDPE powder.     

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.     

Effect of cellulose nano fiber (CNF) on fatigue performance of carbon fiber fabric composites

The effect of cellulose nano fibers (CNF): micro-fibrillated cellulose and bacteria cellulose fibers were investigated on the fatigue life of carbon fiber (CF) fabric/epoxy (EP) composites. Epoxy used as the matrix was physically modified with CNF in advance before fabricating the laminates. The high cycle fatigue strength was significantly improved at 0.3 wt% CNF. There exists an appropriate CNF content which makes the fatigue life longest. An increase of adhesive strength between CF and matrix results due to physical modification with CNF. The adhesive strength much increases with increasing the CNF content. Almost no interfacial debonding occurs at 0.8 wt% CNF content when CF breakage takes place. On the other hand, some debonding occurs along CFs from the breaking point at 0.3 wt% CNF. Debonding is more significant in the case of no CNF addition to the matrix. An appropriate interfacial strength brought at 0.3 wt% CNF is the key of fatigue life extension.     

Microwave-polyol controlled synthesis and magnetic properties of monodisperse CoxNi1−xFe2O4/MWCNT nanocomposites

Monodisperse Co_xNi_1−xFe₂O₄ nanoparticles (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) with controllable composition attached on the multi-walled carbon nanotubes (MWCNTs) were prepared by microwave-polyol method. The composition of Co_xNi_1−xFe₂O₄ nanoparticles can be controlled through adjusting the atomic ratios of cobalt and nickel nitrate in the mixed solution. The influence of the microwave power and microwave irradiation time on the monodispersion of nanoparticles was also investigated. The results show quasi-spherical Co_xNi_1−xFe₂O₄ nanoparticles with the face-centered cubic structure and average crystallite size (6 nm) are uniformly dispersed on MWCNTs. The saturation magnetization of Co_xNi_1−xFe₂O₄/MWCNT nanocomposites increases gradually from 12.90 to 20.03 emu/g with increasing Co²⁺ concentration. The coercivity is almost zero at room temperature, which indicates the superparamagnetic behavior.     

Fluorescence properties and relaxation processes of Tb3+ ions in ZnCl2-based glasses

60ZnCl₂–20KCl–20BaCl₂–xTbCl₃ glasses (x = 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25) were prepared by melt-quenching method, and Tb³⁺ fluorescence properties were investigated under 355 nm excitation. Regardless of x values, the electrons that were relaxed from the ⁵D₃ to ⁵D₄ level of Tb³⁺ ions by the multiphonon relaxation, were repressed to 28% of all the excited electrons because the ZnCl₂-based glass had much lower phonon energy than oxide glasses. For 0 < x ≤ 0.34, the cross relaxation, (⁵D₃ → ⁵D₄) → (⁷F₀ ← ⁷F₆), was repressed, and consequently 72% and 28% of all the excited electrons were radiatively relaxed by the ⁵D₃ → ⁷F_J (J = 6, 5, 4, 3, and 2) and ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions, respectively. The lifetimes of the ⁵D₃ and ⁵D₄ initial levels were obtained to be 1.1 and 2.1 ms, respectively.     

Structure and microwave dielectric characteristics of lithium-excess Ca0.6Nd0.8/3TiO3/(Li0.5Nd0.5)TiO3 ceramics

Compositions based on (1−x)Ca_0.6Nd_8/3TiO₃−x(Li_1/2Nd_1/2)TiO₃ + yLi (CNLNTx + yLi, x = 0.30–0.60, y = 0–0.05), suitable for microwave applications have been developed by systematically adding excess lithium in order to tune the microwave dielectric properties and lower sintering temperature. Addition of 0.03 excess-Li simultaneously reduced the sintering temperature and improved the relative density of sintered CNLNTx ceramics. The excess Li addition can compensate the evaporation of Li during sintering process and decrease the secondary phase content. The CNLNTx (x = 0.45) ceramics with 0.03 Li excess sintered at 1190 °C have single phase orthorhombic perovskite structure, together with the optimum combination of microwave dielectric properties of ɛ_r = 129, Q × f = 3600 GHz, τ_f = 38 ppm/°C. Obviously, excess-Li addition can efficiently decrease the sintering temperature and improve the microwave dielectric properties. The high permittivity and relatively low sintering temperatures of lithium-excess Ca_0.6Nd_0.8/3TiO₃/(Li_0.5Nd_0.5)TiO₃ ceramics are ideal for the development of low cost ultra-small dielectric loaded antenna.     

Effect of CuO nanostructure morphology on the mechanical properties of CuO/woven carbon fiber/vinyl ester composites

The effect of CuO nanostructure morphology on the mechanical properties of CuO/woven carbon fiber (WCF)/vinyl ester composites was investigated. The growth of CuO nanostructures embedded in the surface of woven carbon fibers (WCFs) was carried out by a two-step seed-mediated hydrothermal method; i.e., seeding and growth treatments with controlled chemical precursors. CuO nanostructural morphologies ranging from petal-like to cuboid-like nanorods (NRs) were obtained by controlling the thermal growth temperature in the hydrothermal process over a growth time of 12 h. The Cu²⁺/O⁻ ratio and the rate of reaction greatly influenced the formation of CuO nanostructures as self-assembled shapes on the crystal planes in the order L[0 1 0] > L[1 0 0] > L[0 0 1]. Morphological variations were analyzed by scanning electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller surface area analysis. The impact behavior, in-plane shear strength, and tensile properties of the CuO/WCF/vinyl ester composites were analyzed for different CuO NR morphologies at various growth temperatures and molar concentrations. The CuO/WCF/vinyl ester composites had improved impact energy absorption and mechanical properties because the higher specific surface area of CuO NRs grown as secondary reinforced nanomaterials on WCFs enhanced load transfer and load-bearing capacity.     

The effect of polymer spatial configuration on the microwave absorbing properties of non-covalent modified MWNTs

The polar polymer of linear and star polymethyl methacrylate (PMMA) was used to modify the surface of multi-walled carbon nanotubes (MWNTs). Raman and TGA were used to characterize structure of the functionalized MWNTs. The effect of polymer spatial configuration on the MWNTs dispersion, morphology and interfacial interaction was investigated by scanning electron microscopy and transmission electron microscopy. The aim of the work is to investigate the effect of polymer spatial configuration on the microwave absorbing properties. The results showed that the maximum reflection loss of linear PMMA/MWNTs hybrids was −37 dB in the frequency of 8.8 GHz, and the bandwidth below −10 dB was more than 2.1 GHz. While the maximum reflection loss of the S-PMMA/MWNTs hybrids reached −50 dB in the frequency of 8.4 GHz, and the bandwidth below −10 dB was 2.3 GHz. The results indicated that the microwave absorbing properties of star PMMA polymers modified MWNTs were superior to that of linear PMMA polymers.     

Influence of Ga3+ ions on spectroscopic and dielectric features of multi component lithium lead boro bismuth silicate glasses doped with manganese ions

Multi-component glasses of the chemical composition 19.5Li₂O–20PbO–20B₂O₃–30SiO–(10 − x)Bi₂O₃–0.5MnO:xGa₂O₃ with 0 ≤ x ≤ 5.0 have been synthesized. Spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties were investigated. Optical absorption and ESR spectral studies have indicated that managanese ions do exist in Mn³⁺ state in addition to Mn²⁺ state in the samples containing low concentration of Ga₂O₃. The IR and Raman studies indicated increasing degree of disorder in the glass network with the concentration of Ga₂O₃ up to 3.0 mol%. The dielectric constant, loss and ac conductivity are observed to increase with the concentration of Ga₂O₃ up to 3.0 mol%. The quantitative analysis of the results of dielectric properties has indicated an increase in the insulating strength of the glasses as the concentration of Ga₂O₃ is raised beyond 3.0 mol%. This has been attributed to adaption of gallium ions from octahedral to tetrahedral coordination.     

Effects of Au/Fe and Fe nanoparticles on Serratia bacterial growth and production of biosurfactant

The overall objective of this study was to compare the effects of Au/Fe and Fe nanoparticles on the growth and performance of Serratia Jl0300. The nanoparticle effect was quantified not only by the bacterial growth on agar plate after 1 hour interaction with the nanoparticles, but also by its production of a biosurfactant from used vegetable oil. The nanoparticles were prepared using the foam method. The concentrations of the nanoparticles used for the bacterial interaction study were varied from 1 mg/L to 1 g/L. The test results showed that the effect of nanoparticles on the bacterial growth and biosurfactant production varied with nanoparticle type, concentrations, and interaction time with the bacteria. Au/Fe nanoparticles didn't show toxicity to Serratia after short time (1 h) exposure, while during 8 days fermentation Au/Fe nanoparticles inhibited the growth of Serratia as well as the biosurfactant production when the concentration of the nanoparticles was higher than 10 mg/L. Fe nanoparticles showed inhibition effects to bacterial growth both after short time and long time interaction with Serratia, as well as to biosurfactant production when its concentration was higher than 100 mg/L. Based on the trends observed in this study, analytical models have been developed to predict the bacterial growth and biosurfactant production with varying concentrations of nanoparticles.     

La-doped ZnO nanoparticles: Simple solution-combusting preparation and applications in the wastewater treatment

La-doped ZnO nanoparticles have been successfully synthesized by a simple solution combustion method via employing a mixture of ethanol and ethyleneglycol (v/v = 60/40) as the solvent. Zinc acetate and oxygen gas in the atmosphere were used as zinc and oxygen sources, and La(NO₃)₃ as the doping reagent. The as-obtained product was characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. Experiments showed that La-doped ZnO nanoparticles exhibited the higher capacities for the removal of Pb²⁺ and Cu²⁺ ions in water resource than undoped ZnO nanoparticles.