The role of titania on the microstructure,biocorrosion and mechanical properties of Mg/HA-based nanocomposites for potential application in bone repair

Bone defects are very challenging in orthopedic practice. The ideal bone grafts should provide mechanical support and enhance the bone healing. Biodegradable magnesium (Mg)–based alloys demonstrate good biocompatibility and osteoconductive properties, which are promising biomaterials for bone substitutes. However, the high rate of their biodegradation in human body environment is still challenging. For this scope, synthesis Mg-based composites with bioceramic additives such as HA and titania (TiO₂) is a routine to solve this problem. The aim of this study was to evaluate the effect of addition TiO₂ nanopowders on the corrosion behavior and mechanical properties of Mg/HA-based nanocomposites fabricated using a milling-pressing-sintering technique for medical applications. The microstructure of Mg/HA/TiO₂ nanocomposites, in vitro degradation and biological properties including in vitro cytocompatibility were investigated. The corrosion resistance of Mg/HA-based nanocomposites was significantly improved by addition 15 wt% of TiO₂ and decrease HA amount to 5 wt% this was inferred from the lower corrosion current; 4.8 µA/cm² versus 285.3 µA/cm² for the Mg/27.5 wt%HA, the higher corrosion potential; −1255.7 versus −1487.3 mV_SCE, the larger polarization resistance; 11.86 versus 0.25 kΩ cm² and the significantly lower corrosion rate; 0.1 versus 4.28 mm/yr. Compressive failure strain significantly increased from 1.7% in Mg/27.5HA to 8.1% in Mg/5HA/15TiO₂ (wt%). The Mg/5HA/15TiO₂ (wt%) nanocomposite possessed high corrosion resistance, cytocompatibility and mechanical properties and can be considered as a promising material for implant applications.     

Synthesis and characterization of alkyd resins based on Camelina sativa oil and polyglycerol

A one pot synthesis of alkyd resins based on the Camelina sativa oil as a new renewable raw material and on polyglycerols as polyols was carried out. The oligomerization of glycerol was conducted in the presence of LiOH (0.1 wt%) at 245 °C. The total content of diglycerol reached its maximum (about 33.5 wt%) after 7 h. The oligomerization product with no additional treatment was subjected to the alcoholysis reaction with purified camelina oil. The alkyd resin was obtained after polycondensation of the alcoholysis products with phthalic and maleic anhydrides at 230–250 °C. A real possibility was determined for the synthesis of alkyd resins with some properties similar to those which can be found in equivalent products manufactured on the basis of semi drying oil and pentaerythritol like flexibility and drying time.     

Ionic liquid assisted fabrication of high performance SWNTs reinforced ceramic matrix nano-composites

A Novel approach to fabricate high performance SiCN ceramic nanocomposites containing well dispersed single-walled carbon nanotubes (SWNTs) assisted by room temperature ionic liquids (RTILs) is developed. This method is straightforward, environment-friendly and overcome the typical challenges in the synthesis procedures of SWNTs reinforced precursor derived ceramics (PDCs). The microstructural and elemental characteristics of these ceramic matrix nanocomposites present highly-dispersed SWNTs were introduced and a profitably BN(C) interlayer could be formed in situ between the SWNTs and the ceramic matrix, which resulting in a high performance and a crack free ceramic product. Compared to the pure monolithic SiCN ceramic, the Young's modulus enhanced by ~11% and the electrical conductivities increased up to 0.06 S cm⁻¹ for ceramic composite in the case of the 1 wt% SWNTs was containing. Furthermore, the electrochemical investigation shows the potential application of these SWNTs-IL/Ceramics composites in electrochemical hydrogen storage.     

Polyimide/nano-TiO2 hybrid films having benzoxazole pendent groups: In situ sol–gel preparation and evaluation of properties

Polyimide/titania (PI/TiO₂) nanocomposite films have been successfully fabricated through the in situ formation of TiO₂ within a PI matrix via sol–gel method. Poly(amic acid) (PAA), which is the precursor of PI, was successfully synthesized by mixing pyromellitic dianhydride (PMDA), with equimolar amount of a diamine monomer having a pendent benzoxazole unit and two flexible ether linkages in N,N-dimethylformamide (DMF) solvent. Tetraethyl orthotitanate [Ti(OEt)₄] and acetylacetone were then added to the resulted PAA. After imidization at high temperature, PI/TiO₂ hybrid films were formed. The structure and morphology of the hybrid nanocomposites with different titania contents (0 wt%, 5 wt%, 10 wt%, and 15 wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that the TiO₂ nanoparticles were homogeneously dispersed in the hybrid films. The thermogravimetric analysis of nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. Transmission electron microscopy showed that the nanoparticles with an average diameter of 25–40 nm were dispersed in the polymer matrix.     

Complexing agent assisted synthesis of high aspect ratio Fe3 +/Mg2 + layered double hydroxides

A new, facile synthesis for Fe^3 +/Mg^2 + LDHs is developed and investigated. The crucial feature of the synthesis is the usage of a complexing agent (diethylenetriamine, DETA) to increase the solubility of iron phases precipitated intermediately. The influences of different synthesis parameter like DETA concentration, pH value, and temperature are investigated. The optimized synthesis route yields high aspect ratio Fe^3 +/Mg^2 + LDHs which are expected to be interesting filler materials for flame retardant nanocomposites.     

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

The nanocomposites of WO₃ nanoparticles and exfoliated graphitized C₃N₄ (g-C₃N₄) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO₃ nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C₃N₄ particles were prepared by calcination of melamine forming bulk g-C₃N₄, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m² g⁻¹.The nanocomposites were prepared by mixing of WO₃ nanoparticles and g-C₃N₄ structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO₃ was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C₃N₄ particles were covered by the WO₃ nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO₃ nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO₃, which was explained by shielding of the g-C₃N₄ surface by bigger WO₃ agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.     

Mesua ferrea L. seed oil based acrylate-modified thermostable and biodegradable highly branched polyester resin/clay nanocomposites

Mesua ferrea L. seed oil based highly branched polyester resin was modified by methyl methacrylate through grafting polymerization technique. The nanocomposites of this acrylate-modified polyester and 1–5 wt% loadings of organically modified montmorrilonite (OMMT) nanoclay were prepared by an ex situ technique using strong mechanical mixing and ultrasonication. Formation of nanocomposites was confirmed by X-ray diffractometeric (XRD), scanning electron microscopic (SEM) and transmission electron microscopic (TEM) analyses. The absence of d_0 0 1 reflections of OMMT in XRD and TEM study revealed the partial exfoliation of OMMT by the polymer chain. The homogeneous surface morphology was also ascertained from SEM. Mechanical and thermal studies of the nanocomposites showed an appreciable improvement in tensile strength and thermal stability by OMMT loading. The enhancement of tensile strength by 2.5 times and thermal stability by 32 °C for 5 wt% OMMT filled nanocomposite was observed compared to that of pristine system. The rheological behavior of the nanocomposites was also investigated and shear thinning was observed. Biodegradation of the nanocomposite films was assayed using two strains of Pseudomonas aeruginosa, SD2 and SD3 and one strain of Bacillus subtilis, MTCC736. The nanocomposites exhibited enhanced biodegradability as compared to pristine acrylate modified polyester. All the results showed the potentiality of the nanocomposites as advanced thin film materials for suitable applications.     

Polymer-assistant ceramic nanocomposite materials for advanced fuel cell technologies

In this study,nanocomposites of LaCePr-oxide (LCP) and Ni_0.8Co_0.15Al_0.05LiO_2-δ (NCAL) with different contents of polyvinylidene fluoride (PVDF) were prepared and applied to solid oxide fuel cells. The composite materials were characterized by X-ray diffraction analysis (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and electrochemical impedance spectrum (EIS). The effect of PVDF concentration on the conductivity and performance of the fuel cells was investigated. It was found that PVDF plays a template role of pore forming in the nanocomposites, and the changed microstructure by as-formed pores greatly influences the electrochemical property of the nanocomposites. The cell with 3 wt% PVDF heat-treated at 210 °C achieved the highest power density of 982 mW cm⁻² at 520 °C, which enhanced performance by more than 57% than when no heat-treatment was implemented. It is 66% higher than the cell with no PVDF and no heat-treatment. Pores formed by PVDF after heat-treatment enlarged the triple phase boundary (TPB), which results in improved fuel cell performance.     

Ordered mesoporous carbon–TiO2 materials for improved electrochemical performance of lithium ion battery

A series of ordered mesoporous carbon–TiO₂ (OMCT) materials with various weight percentages of TiO₂ (50–75 wt%) were synthesized by evaporation-induced self-assembly and in-situ crystallization at various calcination temperatures (600–1200 °C) to evaluate the Li-ion storage performance. The OMCT has ordered 2D hexagonal mesoporous structures and the TiO₂ nanocrystals with different phases are embedded into the frameworks of carbonaceous matrix. The reversible capacity of OMCT is highly dependent on the phase and content of TiO₂, and the anatase TiO₂ is a superior crystalline phase to rutile and TiN for Li-ion insertion. The OMCT₆₅ which contains 35 wt% carbon and 65 wt% TiO₂ shows a high capacity of 500 mAh g^?1 at 0.1C after 80 cycles. In addition, OMCT₆₅ exhibits a good cyclability and rate capability. The reversible capacity remains at 98 mAh g^?1 at a high rate of 5C, and then recoveries to 520 mAh g^?1 at 0.1C after 105 cycles. The excellent reversible capacity and rate capability of OMCT₆₅ are attributed to the embedment of well-dispersed anatase TiO₂ nanocrystals into the specific porous structure of OMCT, which can not only facilitate the fast Li-ion charge transport but can also strengthen the carbon–TiO₂ co-constructing channels for lithiated reactions.     

Flame retardancy and thermal stability of ethylene-vinyl acetate copolymer nanocomposites with alumina trihydrate and montmorillonite

The development of fire retardant for wire and cable sheathing materials has oriented toward low smoke and halogen-free flame retardant technology to achieve better safety for electrical equipment and devices and to satisfy standards. However, many polymer flame resistance materials require a very high proportion of metal hydrate filler within the polymer matrix (60 wt%) to achieve a suitable level of flame resistance, which may lead to inflexibility, poor mechanical properties and problems during compounding and processing. In this study, the alumina trihydrate (ATH) was added to montmorillonite (MMT) as the halogen-free flame retardant of ethylene-vinyl acetate (EVA) copolymer, with various ratios of EVA/ATH/MMT. The prepared nanocomposites were characterized through various techniques of XRD, tensile test, DSC analysis, TGA, LOI evaluation, and FE-SEM to explore the effects of organic modified clay (OMMT) and the layer distance on the mechanical, thermal, and flame resistance properties. In the XRD examinations, the layer-distance of MMT increased from 1.27 to 1.96 nm when polymer was added to the octadecylamine modified MMT. The best tensile strength was obtained at 3 wt% MMT. In addition, the halogen-free flame resistance grade of EVA containing 3 wt% OMMT and 47 wt% ATH revealed the best elongation and fire resistance (LOI = 28). The tensile and flame resistance properties of the nanocomposites were also significantly improved.     

One-step hydrothermal synthesis of Sb2S3/reduced graphene oxide nanocomposites for high-performance sodium ion batteries anode materials

Sb₂S₃/reduced graphene oxide (SSR) nanocomposites were successfully synthesized through a facile one-step hydrothermal process, as used as anode materials for sodium ion batteries (SIBs). The characterization and electrochemical performance of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption isotherms, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of reduced graphene oxide (RGO) can improve the electrochemical performances of SSR nanocomposites. SSR nanocomposites with 10 wt% RGO exhibits the highest reversible capacity of 581.2 mAh g⁻¹ at the current density of 50 mA g⁻¹ after 50 cycles, and excellent rate performance for SIBs. The improved electrochemical performance is attributed to the smaller Sb₂S₃ nanoparticles dispersed on RGO crumpled structure and synergetic effects between Sb₂S₃ and RGO matrix, which can increase specific surface area and improve electrical conductivity, reduce sodium ion diffusion distance, and effectively buffer volume changes during cycling process.     

Si3N4/graphene nanocomposites for tribological application in aqueous environments prepared by attritor milling and hot pressing

Advanced ceramic materials have proved their superior wear resistance as well as mechanical and chemical properties in a wide range of industrial applications. Today there are standard materials for components and tools that are exposed to severe tribological, thermal or corrosive conditions. The main aim of this work is to develop novel, highly efficient tribological systems on the basis of ceramic/graphene nanocomposites as well as to prove their superior quality and to demonstrate their suitability for technical applications e.g. for slide bearings and face seals in aqueous media. Current research in the field of ceramic nanocomposites shows that is possible to make ceramic materials with improved mechanical and tribological properties by incorporating graphene into the Si₃N₄ structure. Multilayered graphene (MLG) was prepared by attritor milling at 10 h intensive milling of few micrometer sized graphite powders. The large quantity, very cheap and quick preparation process are a main strengths of our MLG. Si₃N₄/MLG nanocomposites were prepared by attritor milling and sintered by hot pressing (HP). The Si₃N₄ ceramics were produced with 1 wt%, 3 wt%, 5 wt% and 10 wt% content of MLG. Their structure was examined by transmission electron microscopy (TEM). The tribological behavior of composites in aqueous environment was investigated and showed the decreasing character of wear at increased MLG content. This new approach is very promising, since ceramic microstructures can be designed with high toughness and provide improved wear resistance at low friction.     

Double-layer electromagnetic wave absorber based on barium titanate/carbon nanotube nanocomposites

The electromagnetic wave absorption properties of double-layer barium titanate/carbon nanotube (BTO/CNT) nanocomposites were evaluated. The BTO/CNT nanomaterials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy. The reflection loss (R.L.) of the samples was calculated based on the measured complex permittivity and permeability. The minimum R.L. of single-layer BTO/CNT 30 wt% nanocomposites sample with a thickness of 1.1 mm reached ~−30.3 dB (over 99.9% absorption) at 13.8 GHz, and the bandwidth of the reflection loss less than −10 dB (over 90% absorption) was 1.5 GHz. The double-layer composites consist of BTO/CNT 30 wt% (absorption layer) with thickness of 1.0 mm and BTO 30 wt% (matching layer) with thickness of 0.3 mm showed a minimum R.L. of ~−63.7 dB (over 99.9999% absorption) at 13.7 GHz, and the bandwidth of the reflection loss less than −10 dB was 1.7 GHz. Wider response bandwidth, >1.7 GHz also can be achieved with different designs of double-layer absorbers. The R.L. significantly improved and wider response bandwidth can be obtained with double-layer composites. The capability to modulate the absorption and bandwidth of these samples to suit various applications in different frequency bands indicates that these nanocomposites could be an excellent electromagnetic wave absorber.     

Biocompatibility and antimicrobial evaluation of montmorillonite/chitosan nanocomposites

Delaminated montmorillonite particles (DMtP) are novel two-dimensional nanomaterials. Chitosan (CS) is a biodegradable polysaccharide with good biocompatibility. New nanocomposites of CS and 10−10⁴ ppm of DMtP were prepared. The good dispersion of DMtP in the CS matrix was probably a result of the charge interaction between the two components. The nanocomposites demonstrated better dynamic mechanical moduli. DMtP were found to be enriched on the surface of the nanocomposites when the amount of DMtP was > 10³ ppm. This was accompanied by a decrease of the contact angle. The proliferation of fibroblasts on DMtP/CS 10³ ppm was significantly greater than on other materials. The antimicrobial activity was enhanced markedly with the increased amount of DMtP in DMtP/CS. The inflammatory responses of DMtP in vitro and in subcutaneous rats were not obvious until the concentration of DMtP was > 10³ ppm. The biocompatibility of DMtP/CS at 10³ ppm was even better than that of CS. The biodegradation rate of CS of the DMtP/CS nanocomposite was much faster than that of the pure CS polymer. These results suggested potential antimicrobial applications for DMtP/CS nanocomposites, especially for those containing 10³ ppm (0.1%) of DMtP.     

Bio-inspired cross-linking with borate for enhancing gas-barrier properties of poly(vinyl alcohol)/graphene oxide composite films

The demand for flexible and transparent barrier films in industries has been increasing. Learning from nature, borate ions were used to cross-link poly(vinyl alcohol) (PVA) and graphene oxide (GO) to produce flexible, transparent high-barrier composite films with a bio-inspired structure. PVA/GO films with only 0.1 wt% GO and 1 wt% cross-linker exhibited an O₂ transmission rate <0.005 cc m⁻² day⁻¹, an O₂ permeability <5.0 × 10⁻²⁰ cm³ cm cm⁻² Pa⁻¹ s⁻¹, and a transmittance at 550 nm >85%; thus, they can be used for flexible electronics. Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy indicated that the outstanding barrier properties are attributed to the formation of chemical cross-linking involving borate ions, GO sheets, and PVA, similar to the borate cross-links in high-order plants. Comparing our experimental data with the Cussler model, we found that the effective aspect ratio was significantly increased after cross-linking, suggesting that cross-linking networks connected GO with each other to form ultra-large impermeable regions. A feasible green technique, with potential for commercial production of barrier films for flexible electronics was presented.     

Highly thermal conductive composites with polyamide-6 covalently-grafted graphene by an in situ polymerization and thermal reduction process

The thermal conductive polyamide-6/graphene (PG) composite is synthesized by in situ ring-opening polymerization reaction using ε-caprolactam as the monomer, 6-aminocaproic acid as the initiator and reduced graphene oxide (RGO) as the thermal conductive filler. The generated polyamide-6 (PA6) chains are covalently grafted onto graphene oxide (GO) sheets through the “grafting to” strategy with the simultaneous thermal reduction reaction from GO to RGO. The homogeneous dispersion of RGO sheets in PG composite favors the formation of the consecutive thermal conductive paths or networks at a relatively low GO sheets loading, which improves the thermal conductivity (λ) from 0.196 W m⁻¹ K⁻¹ of neat PA6 to 0.416 W m⁻¹ K⁻¹ of PG composite with only 10 wt% GO sheets loading.     

Role of vermiculite and zirconium–vermiculite on the formation of zircon–cordierite nanocomposites

The Zr^4 +–vermiculites were studied in their new role of the zircon precursor in the clay minerals mixtures which were prepared for firing of the zircon–cordierite nanocomposites. Currently there is a lack of data available about the structure of Zr^4 +–vermiculites, on which this study was performed. The modeling of the arrangement of interlayer material in the Zr^4 +–vermiculite led to new findings that water molecules are attracted more strongly by Mg^2 + cations than by Zr-tetrameric cations, and that both the tetrameric cations [Zr₄(OH)₁₄(H₂O)₁₀]^2 + and [Zr₄(OH)₈(H₂O)₁₆]^8 + may be present in the interlayer space of the Zr^4 +–vermiculites. Vermiculites from two different localities Czech Republic (Verm1) and from Brazil (Verm2) were intercalated using the zirconyl chloride (ZrOCl₂–30% solution in HCl) and the prepared Zr^4 +–vermiculites were designated as Zr^4 +–Verm1 and Zr^4 +–Verm2, respectively. Influence of the Zr^4 +–Verm1 and Zr^4 +–Verm2 in the mixtures of clay minerals on the properties of zircon–cordierite nanocomposites were investigated by their comparison with the properties of the zircon–cordierite nanocomposites, which were prepared using saturation of the clay minerals mixtures containing Verm1 and Verm2 with the zirconyl chloride (ZrOCl₂–30% solution in HCl). The zircon–cordierite nanocomposites fired from the clay mineral mixtures containing Zr^4 +–Verm1 and Zr^4 +–Verm2 showed a maximum porosity of P = 58 and 60%, skeletal density SD = 3.2 and 3.6, and the smallest pores with a median pores diameter MDP = 18 and 15 μm, respectively, in comparison with the zircon–cordierite nanocomposites fired from the clay mineral mixtures containing Verm1 and Verm2 and saturated with zirconyl chloride solution. The type of vermiculite Verm1 or Verm2 in the clay mineral mixtures did not affect the contents of the crystalline mineral phases in cordierite and zircon–cordierite nanocomposites.     

Structural study of mullite based ceramics derived from a mica-rich kaolin waste

Mullite-based ceramics have been synthesized by reactive sintering of a mixture containing kaolin and a mica-rich kaolin waste. Samples fired in the temperature range from 1300 to 1500 °C were characterized by X-ray diffraction (XRD). The quantitative phase analysis and unit cell parameters of the mullite were determined by Rietveld refinement analysis of the XRD data. Mullite-based ceramics with 1.2 wt% quartz, 56.3 wt% glass (amorphous phase), 2.64 g/cm³ of apparent density, and 35±1.2 MPa of flexural strength were obtained after firing at 1500 °C. A liquid phase sintering mechanism activated by a total mica content of 13.3 wt% allowed to increase the mullite content to 47.6 wt% (2.3 wt% quartz and 50.1 wt% glass phase) and improve the flexural strength (70±3.9 MPa) after firing at 1400 °C.     

SDS-stabilized graphene nanosheets for highly electrically conductive adhesives

We report sodium dodecyl sulfate (SDS) stabilization of graphene nanosheets, with two different sizes as auxiliary fillers inside the conventional electrically conductive adhesive (ECA) composite. Using this non-covalent modification approach we were able to preserve the single-layer structure of graphene layers and prevent their re-stacking inside the composite, which resulted in a significant electrical conductivity improvement of ECAs at noticeably low filler content. Addition of 1.5 wt% small and large SDS-modified graphene into the conventional ECAs with 10 wt% silver flakes led to low electrical resistivity values of 5.5 × 10³ Ω cm and 35 Ω cm, respectively, while at least 40 wt% of silver flakes was required for the conventional ECA to be electrically conductive. A highly conductive ECA with very low bulk resistivity of 1.6 × 10⁻⁵ Ω cm was prepared by adding 1.5 wt% of SDS-modified large graphene into the conventional ECA with 80 wt% silver flakes which is less than that of eutectic lead-based solders.