Mild processing and characterization of silica epoxy hybrid nanocomposite

Previous research has shown that the inclusion of the spherical silica (SiO₂) nanoparticles into epoxy resin can achieve simultaneous improvement of fracture toughness and modulus. However, the glass transition temperature of the nanocomposite was significantly decreased when loading the nanosilica was higher than 5 wt.%. This perhaps was caused by utilization of the ultrasonication probe in the processing of these materials. In this paper, milder processing procedures were applied to make spherical silica epoxy nanocomposites while investigating if the homogeneous dispersion and morphology of the individual silica nanoparticle dispersed in the epoxy matrix could still be achieved. The results show that even at high loading of the silica nanoparticle, such as 30 wt.% silica, the perfect morphology of the nanocomposite could still be achieved with these milder processing conditions which indicates that ultrasonication is not needed. With the use of milder processing conditions, the glass transition temperature of the nanocomposite of 5 wt.% silica loading did not change, and the drop in the T_g was minimal for silica loading up to 15%, but some effects of self-polymerization of the epoxy were noted on T_g up to 30 wt.% loading of silica. Thermal analysis and flammability testing of the resulting materials suggest that nanosilica has only an inert filler effect (dilution of fuel) on flammability reduction and char yield increase, not a synergistic decrease in heat release as is often observed for clays and carbon nanotubes/nanofibers. So the mild and easy processing procedure only achieved uniform nanoscale morphology with excellent dispersion in the final nanocomposite, but also the effect on the change in the T_g can be minimized as nanosilica loading was increased.     

The effect of synthesis procedure on the structure and properties of palladium/polycarbonate nanocomposites

In this paper, we compare two procedures for the synthesis of palladium (Pd)/polycarbonate (PC) nanocomposites as well as their morphological, optical, thermal and electrical properties. Pd nanoclusters were produced by the reduction of palladium chloride using a variation of Brust's method. Discrete Pd nanoclusters of ∼15 nm size were formed in the absence of PC in the reaction mixture (ex situ method) while agglomeration of Pd nanoclusters was noticed in the presence of PC in the reaction mixture (in situ method). Fourier transform infrared spectroscopy (FTIR) suggests nanoparticle-polymer interactions and polymer conformational changes in the in situ nanocomposite films. Even after having the same Pd content, the ex situ nanocomposites films were found to transmit more light than the in situ nanocomposites. The glass transition temperature (T_g), decreased by ∼16 °C for both the ex situ and in situ samples. Thermogravimetric analysis (TGA) indicated that the presence of Pd nanoclusters significantly improved the thermal stability of the nanocomposites, as evidenced by the enhanced onset of degradation by ∼20 °C and ∼40 °C for the in situ and ex situ nanocomposites, respectively. The electrical conductivity measurement shows a dramatic difference between these nanocomposites with a significantly higher value for the in situ nanocomposite (resistivity = 2.1 × 10⁵ Ωm) compared to the ex situ nanocomposite (resistivity = 7.2 × 10¹³ Ωm).     

Comparatively electrochemical studies at different operational temperatures for the effect of nanoclay platelets on the anticorrosion efficiency of DBSA-doped polyaniline/Na-MMT clay nanocomposite coatings

In this paper, DBSA-doped polyaniline (PANI)/Na⁺-montmorillonite (MMT) clay nanocomposite (PCN) materials have been successfully prepared with dodecylbenzenesulfonic acid (DBSA) as emulsifier and dopant for the emulsion polymerization of aniline. The as-prepared DBSA-doped samples were subsequently characterized by FTIR spectroscopy, WAXRD patterns and TEM. It should be noted that the nanocomposite coating containing 1 wt.% of clay loading was found to exhibit an observable enhanced corrosion protection on cold-rolled steel (CRS) electrode at higher operational temperature of 50 °C, which was even better than that of uncoated and electrode-coated with PANI alone at room temperature of 30 °C based on the electrochemical parameter evaluations (e.g., E_corr, R_p, I_corr, R_corr and impedance). In this work, all electrochemical measurements were performed at a double-wall jacketed cell, covered with a glass plate, through which water was circulated from a thermostat to maintain a constant operational temperature of 30, 40 and 50 ± 0.5 °C. Moreover, a series of electrochemical parameters shown in Tafel, Nyquist and Bode plots were all used to evaluate PCN coatings at three different operational temperatures in 5 wt.% aqueous NaCl electrolyte. Effect of material composition on the molecular weight and optical properties of neat PANI and PCN materials, in the form of solution, were studied by gel permeation chromatography (GPC) and UV-vis spectra, respectively. Finally, electrical conductivity at three different operational temperatures of PANI and PCN powder-pressed pellets doped with different inorganic acids such as HCl, HNO₃ and H₂SO₄ was also investigated through the measurements of standard four-point-probe technique.     

Mechanical and physical properties of epoxy composites reinforced by vapor grown carbon nanofibers

Epoxy/vapor grown carbon nanofiber composites (VGCF) with different proportions of VGCF were fabricated by the in situ process.The VGCFs were well dispersed in both of the low and high viscosity epoxy matrices, although occasional small aggregates were observed in a high viscosity epoxy of 20 wt.%. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus and the glass transition temperature (T_g) of the polymer were increased by the incorporation of VGCFs.The electrical and mechanical properties of the epoxy-VGCFs nanocomposite sheets with different weight percentages of VGCFs were discussed. The results were that both had maximum tensile strength and Young’s modulus at 5 wt.% for both materials and reduced the fracture strain with increasing filler content. The electrical resistivity was decreased with the addition of filler content. Mechanical, electrical and thermal properties of low viscosity epoxy composites were resulted better than that of the high viscosity composites.     

Tubular composite PVA ceramic supported membrane for bio-ethanol production

Thin polyvinyl alcohol (PVA) layers loaded with fumed silica were coated on porous ceramic supports. Scanning electron microscope (SEM) was used to characterize the ceramic-supported thin PVA active layers and the effects of coating gel PVA concentration on thickness and density of the active layers were investigated. Pervaporation (PV) dehydration of 90 wt.% ethanol was performed at temperatures of 30, 45 and 60 °C. The values of water flux (0.05–2.92 kg/m² h) and selectivity (3–180) exceed typical values obtained for pure PVA membranes. Besides the pervaporation separation index (PSI) varies from 5.84 to 82.81. Compared to pure PVA membrane with maximum PSI of 47.2, the pervaporation performance was significantly improved. The best separation performance was obtained using the membrane prepared from 5 wt.% PVA solution containing 6 wt.% fumed silica and at pervaporation temperature of 45 °C with permeation flux of 1.69 kg/m² h, and selectivity of 50. The highest permeation flux, selectivity and PSI was 2.92 kg/m² h, 180 and 82.81, obtained at 60, 30 and 45 °C, respectively, while using membranes loaded with 8, zero and 6 wt.% of fumed silica in PVA membrane prepared from 5, 10 and 5 wt.% PVA solutions, respectively. The novel ceramic support increased mechanical strength of the membrane and protected the ultrathin polymeric top active layer under aggressive operating conditions, especially high pressure gradient across the membrane. Incorporation of fumed silica also resulted in higher water permeation flux. Due to these results, the synthesized membranes are suitable for ethanol purification in industrial scales.     

Synthesis and film performances of SiO2/P(MMA-BA) core–shell structural latex

In this study, we have successfully synthesized silica/poly(methyl methacrylate-butyl acrylate) (SiO₂/P(MMA-BA)) core–shell nanocomposite colloids via in situ emulsion copolymerization using cationic 2,2′-azobis(2-amidinopropane)dihydrochloride (AIBA) as the initiator and the 3-Glycidoxypropyl-trimethoxysilane (GPTMS)-modified SiO₂ nanoparticles as the seeds. The SiO₂ nanoparticles embedded can reach as high as 60 wt%. The nanocomposite film presents almost the same high transparency as the pure polymer film (>90% transmittance in visible range), and displays significantly improved mechanical and UV weathering resistant properties over its pure polymer film.     

Ultrafine SnO2 dispersed carbon matrix composites derived by a sol-gel method as anode materials for lithium ion batteries

Ultrafine crystalline SnO₂ particles (2-3 nm) dispersed carbon matrix composites are prepared by a sol-gel method. Citric acid and hydrous SnCl₄ are used as the starting constituents. The effect of the calcination temperatures on the structure and electrochemical properties of the composites has been studied. Structure analyses show that ultrafine SnO₂ particles form and disperse in the disordered carbon matrix in the calcination temperature range of 500-800 °C, forming SnO₂/C composites, and the carbon content shows only a slight increase from 35.8 wt.% to 39.1 wt.% with the temperature. Nano-Sn particles form when the calcination temperature is increased to 900 °C, forming a SnO₂/Sn/C composite, and the carbon content is increased to 49.3 wt.%. Electrochemical testing shows that the composite anodes provide high reversible cycle stability after several initial cycles, maintaining capacities of 380-400 mAh g⁻¹ beyond 70 cycles for the calcination temperature of 600-800 °C. The effect of the structure feature of the ultrafine size of SnO₂ and the disordered carbon matrix on the lithium insertion and extraction process, especially on the reversible behavior of the lithium ion reaction during cycling, is discussed.     

Formation of nano SiC whiskers in bauxite-carbon composite materials and their consequences on strength and density

SiC whisker is excellent in characteristics such as specific strength and chemical stability, and is useful as a composite reinforcing material. In this paper, the effect of the formation of in situ nano SiC whiskers on strength and density of bauxite-carbon composites was studied. Samples were prepared composed of 65 wt.% bauxite, 15 wt.% SiC-containing material, 10 wt.% coke, 10 wt.% resole and different values of silicon additives. The pressed samples were cured at 200 °C (2 h) and fired at 1100 °C and 1400 °C (2 h). XRD, SEM, TEM, EDX, FTIR and STA were used to characterize the samples. These characterizations indicated that SiC nano whiskers, 50-90 nm, are single crystalline β-SiC with mechanism of the formation VLS. So, firing temperature is an important factor. As, SiC nano whisker was formed at 1400 °C and improved CCS values up to four times in sample containing 6 wt.% ferrosilicon.     

Effect of heat treatment on the mechanical properties of PIP–SiC/SiC composites fabricated with a consolidation process

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been considered as candidates for heat resistant and nuclear materials. Three-dimensional (3D) SiC/SiC composites were fabricated by the polymer impregnation and pyrolysis (PIP) method with a consolidation process, mechanical properties of the composites were found to be significantly improved by the consolidation process. The SiC/SiC composites were then heat treated at 1400 °C, 1600 °C and 1800 °C in an inert atmosphere for 1 h, respectively. The effect of heat treatment temperature on the mechanical properties of the composites was investigated, the mechanical properties of the SiC/SiC composites were improved after heat treatment at 1400 °C, and conversely decreased with increased heat treatment temperature. Furthermore, the effect of heat treatment duration on the properties of the SiC/SiC composites was studied, the composites exhibited excellent thermal stability after heat treatment at 1400 °C within 3 h.     

Synthesis of silver-polystyrene nanocomposite particles using water in supercritical carbon dioxide medium and its antimicrobial activity

A novel method based on ex situ dispersion of silver nanoparticles within the monomers and subsequent emulsion polymerization using water-in-sc-CO₂ medium is introduced in this paper. Silver nanoparticles were synthesized by chemical reduction of silver nitrate using sodium borohydrate as a reducing agent and polydimethylsiloxane (PDMS) as a stabilizer in the water-in-sc-CO₂ medium. The stable dispersion of silver nanoparticles was added slowly during the polymerization of styrene in the water-in-sc-CO₂ maintaining the temperature at 70 °C and pressure at 20.68 MPa, respectively. The silver nanoparticles encapsulated within polymer particles were characterized by UV-visible spectroscopy, XRD, TGA, SEM and TEM. The silver/polystyrene nanocomposite particles exhibited antimicrobial activity against a number of bacteria. The current work represents a simple, reproducible and universal way to prepare a variety of metal-polymer nanocomposite particles.     

Enhanced mechanical and dielectric behavior of BaTiO3/Cu composites

BaTiO₃/xCu composite ceramics with x = 0-30 wt.% were fabricated by the traditional mixing method in nitrogen gas. The mechanical properties and electric properties of the obtained composites were investigated as a function of the Cu mass fraction using a three bending test and impedance spectroscopy. The results indicated that the relative density of the sintered composites reached above 91%, the Cu-dispersed BaTiO₃ composites enhanced the mechanical properties, particularly the high fracture toughness (∼3.9 MPa m^1/2) and bending strength (∼134 MPa), compared to the monolithic BaTiO₃. Furthermore, the percolation threshold of BaTiO₃/Cu composites was x = 25 wt.%. The permittivity (?_r) markedly increased from ∼2000 for monolithic BaTiO₃ to ∼9000 with increasing Cu up to 30 wt.%. Additionally, the temperature coefficient of this system was less than 5% in the temperature range of 25-115.     

Modeling of the mechanical properties of nanoparticle/polymer composites

A continuum-based elastic micromechanics model is developed for silica nanoparticle/polyimide composites with various nanoparticle/polyimide interfacial treatments. The model incorporates the molecular structures of the nanoparticle, polyimide, and interfacial regions, which are determined using a molecular modeling method that involves coarse-grained and reverse-mapping techniques. The micromechanics model includes an effective interface between the polyimide and nanoparticle with properties and dimensions that are determined using the results of molecular dynamics simulations. It is shown that the model can be used to predict the elastic properties of silica nanoparticle/polyimide composites for a large range of nanoparticle radii, 10-10,000 Å. For silica nanoparticle radii above 1000 Å, the predicted properties are equal to those predicted using the standard Mori-Tanaka micromechanical approach, which does not incorporate the molecular structure. It is also shown that the specific silica nanoparticle/polyimide interface conditions have a significant effect on the composite mechanical properties for nanoparticle radii below 1000 Å.     

Polyamide-6,6/in situ silica hybrid nanocomposites by sol-gel technique: synthesis, characterization and properties

The organic-inorganic hybrid nanocomposites comprising of poly(iminohexamethyleneiminoadipoyl), better known as Polyamide-6,6 (abbreviated henceforth as PA66), and silica (SiO₂) were synthesized through sol-gel technique at ambient temperature. The inorganic phase was generated in situ by hydrolysis-condensation of tetraethoxysilane (TEOS) in different concentrations, under acid catalysis, in presence of the organic phase, PA66, dissolved in formic acid. Infrared (IR) spectroscopy was used to monitor the microstructural evolution of the silica phase in the PA66 matrix. Wide angle X-ray scattering (WAXS) studies showed that the crystallinity in PA66 phase decreased with increasing silica content. Atomic force microscopy (AFM) of the nanocomposite films revealed the dispersion of SiO₂ particle with dimensions of <100 nm in the form of network as well as linear structure. X-ray silicon mapping further confirmed the homogeneous dispersion of the silica phase in the bulk of the organic phase. The melting peak temperatures slightly decreased compared to neat PA66, while an improvement in thermal stability by about 20 °C was achieved with hybrid nanocomposite films, as indicated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) exhibited significant improvement in storage modulus (E′) for the hybrid nanocomposites over the control specimen. An increase in Young's modulus and tensile strength of the hybrid films was also observed with an increase in silica content, indicating significant reinforcement of the matrix in the presence of nanoparticles. Some properties of the in situ prepared PA66-silica nanocomposites were compared with those of conventional composites prepared using precipitated silica as the filler by solution casting from formic acid.     

Mixed matrix membranes of Matrimid 5218 loaded with zeolite 4A for pervaporation separation of water–isopropanol mixtures

Mixed matrix membranes were prepared by incorporating zeolite 4A into polyimide of Matrimid 5218 using solution-casting technique. The fabricated membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA). It was found that the higher annealing temperature of 250 °C is more favorable to improve adhesion between zeolite and polymer phases. Effects of different parameters such as temperature (30–60 °C), water content in feed (10–40 wt.%), zeolite loading (0–15 wt.%) and polymer content (10 and 15 wt.%) on pervaporation dehydration of isopropanol were studied. Sorption studies were carried out to evaluate degree of swelling of the membranes in feed mixtures of water and isopropanol. The experimental results showed that both pervaporation flux and selectivity increase simultaneously with increasing the zeolite content in the membranes. The membrane containing Matrimid 5218 (10 wt.%)–zeolite 4A (15 wt.%) exhibits the highest separation factor (α) of 29,991 with a substantial permeation flux (J) of 0.021 kg/m² h at 30 °C for 10 wt.% of water in the feed. The PV performance was also studied in term of pervaporation separation index (PSI). Permeation flux was found to follow the Arrhenius trend over the investigated temperature range.     

Preparation,structure and properties of comb-branched waterborne polyurethane/OMMT nanocomposites

Comb-branched waterborne polyurethane/organo-montmorillonite (CWPU/OMMT) nanocomposites were prepared by in situ intercalating polymerization process based on the main materials including IPDI, DMPA, polycaprolactone diols, comb-branched polymeric diols and OMMT. The average particle size of emulsion increases and the particle size distribution of emulsion becomes broader with the increase of OMMT content. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) show that OMMT is homogeneously dispersed into the CWPU matrix with intercalated or exfoliated structure. The properties of CWPU/OMMT nanocomposites are dependent on OMMT content. When the OMMT content is 3 wt%, CWPU/OMMT nanocomposite exhibits excellent overall properties: the particle size of emulsion 63.6 nm, tensile strength 42.0 MPa, E′ 20.3 MPa at 80 °C, water absorption 13% at 24 h and surface contact angle for water over 100°.     

Synthesis, preparation and properties of novel high-performance allyl-maleimide resins

Three novel allyl-maleimide monomers (i.e., A₂B, AB and AB₂) were designed, synthesized and thermally cured to yield a series of high-performance allyl-maleimide resins. All the monomers obtained are readily soluble in common organic solvents enabling an easy solution processing. The thermal properties of the three monomers were studied by the differential scanning calorimetry (DSC). A₂B and AB showed fairly low melting temperature (T_m < 90 °C) and wide processing window ranging from 90 °C to 260 °C. The thermal stability of the cured allyl-maleimide resins (i.e., PA₂B, PAB and PAB₂) was studied by the thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) was used to investigate the dynamic mechanical properties of the composites based on the cured allyl-maleimide resins. PA₂B and PAB₂ showed good glass transition temperatures (T_g > 270 °C) and their corresponding composites showed high bending modulus (E′ > 1900 MPa). Allyl-compound-modified BMI resins based on AB monomer were prepared. Rheometer revealed that the processability of the prepolymer (BR-AB-pre) was improved by the addition of AB monomer. The cured BMI resins (BR and BR-AB) showed good thermal stability (T_d > 400 °C, both in nitrogen and in the air), high glass transition temperature (T_g > 320 °C), and good mechanical properties and low water uptake (<2.6%, 120 h).     

Carbon nanotube dispersion and exfoliation in polypropylene and structure and properties of the resulting composites

Nitric acid treated single and multi wall carbon nanotubes (SWNT and MWNT) have been dispersed in polypropylene using maleic anhydride grafted polypropylene (MA-g-PP) and butanol/xylene solvent mixture. SWNT exfoliation was characterized by Raman and UV-vis-NIR spectroscopies. Evidence for hydrogen bonding between maleic anhydride grafted polypropylene and nitric acid treated nanotubes was obtained using infrared spectroscopy. Polypropylene/carbon nanotube composites were melt-spun into fibers. Dynamic mechanical studies show that for fibers containing 0.1 wt% SWNT, storage modulus increased by 5 GPa at −140 °C and by about 1 GPa at 100 °C, suggesting temperature dependent interfacial strength. The crystallization behavior has been monitored using differential scanning calorimetry and optical microscopy. Control fibers exhibited 27% shrinkage at 160 °C, while the shrinkage in the composite fibers was less than 5%. Fibers heat-treated to 170 °C show very narrow polypropylene melting peak (peak width about 1 °C).     

Microstructures and mechanical properties of carbon/carbon composites reinforced with carbon nanofibers/nanotubes produced in situ

Using ferrocene as catalyst and toluene as the liquid precursor, carbon/carbon (C/C) composites were prepared by chemical liquid-vapor infiltration at 850-1100 °C. The microstructures and properties of C/C composites obtained with different ferrocene contents were studied. The results show smooth laminar and isotropic pyrocarbon are obtained after adding ferrocene to the precursor. Carbon nanofibers can be formed as the catalyst content is 0.3-1 wt.%. When the ferrocene content is 2 wt.%, multi-walled carbon nanotubes with the diameter about 20-90 nm are obtained together with carbon-encapsulated iron nanoparticles. After adding ferrocene to the precursor, the fracture modes of the composites change from brittle facture to tough fracture. The flexural strength of the composites is a maximum for 0.3 wt.% ferrocene in the precursor, higher than for ferrocene contents of 0, 0.5, 1 and 2 wt.%. The flexural modulus of the composites decreases after adding ferrocene to the precursor.     

Pressureless sintering of B4C-TiB2 composites with Al additions

The effects of Al addition on pressureless-sintering of B₄C-TiB₂ composites were studied. Different amounts of Al from 0% to 5 wt.% were added to B₄C-TiB₂ mixtures (containing up to 30 wt.% TiB₂) and the samples were pressureless sintered at 2050 °C and 2150 °C under Ar atmosphere. Physical, microstructural and mechanical properties were analysed and correlated with TiB₂ and Al additions and sintering temperature. Addition of Al to B₄C-TiB₂ results in increased shrinkage upon sintering and final relative density and lower porosity, the effect is being more evident when both Al and TiB₂ are present. Fracture strength, elastic modulus and fracture toughness of 450 MPa, 500 GPa and 6.2 MPa.m^1/2, respectively were measured.     

Carbon nanotube/epoxy composites fabricated by resin transfer molding

Carbon nanotube (CNT)/epoxy composites with controllable alignment of CNTs were fabricated by a resin transfer molding process. CNTs with loading up to 16.5 wt.% were homogenously dispersed and highly aligned in the epoxy matrix. Both mechanical and electrical properties of the CNT/epoxy composites were dramatically improved with the addition of the CNTs. The Young’s modulus and tensile strength of the composites reach 20.4 GPa and 231.5 MPa, corresponding to 716% and 160% improvement compared to pure epoxy. The electrical conductivity of the composites along the direction of the CNT alignment reaches over 1 × 10⁴ S/m.