Rheology and dispersion behavior of high‐impact polystyrene/ethylene–vinyl acetate copolymer/TiO2 nanocomposites

TiO₂ nanoparticles were introduced into high‐impact polystyrene (HIPS) in the form of a master batch in which TiO₂ was predispersed in composites of HIPS and ethylene–vinyl acetate copolymer (EVA) by melt compounding. The resulting materials were analyzed with a Rosand Precision rheometer, transmission electron microscopy, atomic force microscopy, and ultraviolet–visible light spectrophotometry. The results showed that the introduction of TiO₂ nanoparticles into HIPS influenced the apparent viscosity of the composites to a rather small extent. The addition of EVA could regulate the rheological behavior of the HIPS/TiO₂ master batch greatly. EVA helped the dispersions of the agglomerates of TiO₂ nanoparticles in the flow; this was featured by the distinct yielding in the flow after the introduction of EVA, as well as the large change in the non‐Newtonian indices. The dispersions of the HIPS/TiO₂ master batch in the HIPS matrix were improved greatly by the addition of EVA. TiO₂ nanoparticles were dispersed randomly in HIPS/EVA/TiO₂ nanocomposites. The dispersion improvement of the HIPS/EVA/TiO₂ master batch was also proved by atomic force microscopy and ultraviolet–visible spectroscopy investigations. The mechanical properties of HIPS/EVA/TiO₂ nanocomposites with low TiO₂ contents were slightly higher than those of pure HIPS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4434–4438, 2006     

Enhancement of UV-aging resistance of UV-curable polyurethane acrylate coatings via incorporation of hindered amine light stabilizers-functionalized TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> nanoparticles

In this study, polymeric hindered amine light stabilizers (HALS)-functionalized silica coated rutile titanium dioxide (TiO₂-SiO₂) nanoparticles were prepared by encapsulating commercially available TiO₂-SiO₂ nanoparticles with methyl methacrylate (MMA) and 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (PMPM) copolymers via miniemulsion polymerization. The obtained functional (TiO₂-SiO₂/P(MMA-co-PMPM)) fillers have been added to polyurethane acrylate (PUA) oligomers to get UV-curable nanocomposite coatings. The functionalization of the TiO₂-SiO₂ nanoparticles with polymeric HALS has been confirmed by infrared spectra (IR), thermogravimetric (TG), and X-ray photoelectron spectroscopy (XPS) analyses. The scanning electron microscope (SEM) micrographs indicated that homogeneous dispersion of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles resulted in improved transparency and mechanical properties of the UV-curable PUA coatings. Rhodamine B (Rh.B) photodegradation measurement confirmed the excellent UV-shielding performance of PUA nanocomposite coatings containing TiO₂-SiO₂/P(MMA-co-PMPM). The addition of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles reduced the UV-curable PUA coatings degradation rate dramatically. The UV-aging resistance of PUA coatings was improved significantly. Over all, the combination of TiO₂-SiO₂ nanoparticles and polymeric HALS offers an attractive way to fabricate the multi-functional fillers, which can be used to improve the mechanical properties and UV-aging resistance of PUA coatings simultaneously.     

Innovative direct nanoparticle dispersion injection into injection molding processing

Nanoparticles are applied in polymer matrices because of building up an inorganic network within an organic network resulting in a simultaneous increase of stiffness and toughness provided that a good degree of dispersion with a very low amount of agglomerates can be realized. To prevent these kinds of agglomerates, the incorporation of appropriate nanoparticle dispersions is promising. Using nanoparticle containing dispersions, we can produce nanocomposites via a direct injection molding process with excellent nanoparticle dispersion in the resulting nanocomposite. TiO₂‐ (15 nm and 300 nm) and Al₂O₃‐ (13 nm) particle containing dispersions were manufactured and incorporated in polyamide 6 (PA6) via the addition of a nanoparticle containing dispersion within an injection molding process (IM). Agglomeration has to be suppressed during injection molding process and the nanoparticles have to cross over from the dispersing agent to the polymer matrix melt in which they have to be well distributed. The resulting mechanical (tensile and Charpy impact) and morphological (SEM and TEM) properties of those nanocomposites are discussed. The impact toughness and Young's modulus could be enhanced with slightly decreasing tensile strength. The nanoparticles could be well distributed in the polymer matrix. The achievable distribution quality is equal to the distribution achieved in a melt kneading process. Thus, materials with enhanced elongation at break with a very good dispersion quality were produced in a single production process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40641.     

A living cell quartz crystal microbalance biosensor for continuous monitoring of cytotoxic responses of macrophages to single-walled carbon nanotubes

Background

There is growing evidence that exposure to small size particulate matter increases the risk of developing cardiovascular disease.

Methods

We investigated plaque progression and vasodilatory function in apolipoprotein E knockout (ApoE ^-/-) mice exposed to TiO₂. ApoE ^-/- mice were intratracheally instilled (0.5 mg/kg bodyweight) with rutile fine TiO₂ (fTiO₂, 288 nm), photocatalytic 92/8 anatase/rutile TiO₂ (pTiO₂, 12 nm), or rutile nano TiO₂ (nTiO₂, 21.6 nm) at 26 and 2 hours before measurement of vasodilatory function in aorta segments mounted in myographs. The progression of atherosclerotic plaques in aorta was assessed in mice exposed to nanosized TiO₂ (0.5 mg/kg bodyweight) once a week for 4 weeks. We measured mRNA levels of Mcp-1, Mip-2, Vcam-1, Icam-1 and Vegf in lung tissue to assess pulmonary inflammation and vascular function. TiO₂-induced alterations in nitric oxide (NO) production were assessed in human umbilical vein endothelial cells (HUVECs).

Results

The exposure to nTiO₂ was associated with a modest increase in plaque progression in aorta, whereas there were unaltered vasodilatory function and expression levels of Mcp-1, Mip-2, Vcam-1, Icam-1 and Vegf in lung tissue. The ApoE ^-/- mice exposed to fine and photocatalytic TiO₂ had unaltered vasodilatory function and lung tissue inflammatory gene expression. The unaltered NO-dependent vasodilatory function was supported by observations in HUVECs where the NO production was only increased by exposure to nTiO₂.

Conclusion

Repeated exposure to nanosized TiO₂ particles was associated with modest plaque progression in ApoE ^-/- mice. There were no associations between the pulmonary TiO₂ exposure and inflammation or vasodilatory dysfunction.     

Agglomeration Mechanism of Nanoparticles by Adding Coarse Fluid Catalytic Cracking Particles

The agglomeration mechanism of SiO₂, TiO₂, and ZnO nanoparticles by adding coarse fluid catalytic cracking (FCC) particles is studied. The core‐shell structure of agglomerates is revealed on the basis of experimental analyses. Nanoparticles can be fluidized by forming agglomerates of the core‐shell structure with coarse FCC particles. The porosity of core‐shell structure agglomerates and the average roundness value were found to be distinctly lower than those of pure nanoparticle agglomerates. In addition, the cohesion of the core‐shell structure agglomerates is far less than that of the agglomerates formed by pure nanoparticles. Due to the smaller porosity, irregular shape, and relatively low cohesion, the fluidization behavior of core‐shell structure agglomerates is better than that of pure nanoparticle agglomerates.     

Investigation of surface modification of rutile TiO2 nanoparticles with SiO2/Al2O3 on the properties of polyacrylic composite coating

Surface modification and characterization of TiO₂ nanoparticles as an additive in a polyacrylic clear coating were investigated. For the improvement of nanoparticles dispersion and the decreasing of photocatalytic activity, the surface of nanoparticles was modified with binary SiO₂/Al₂O₃. The surface treatment of TiO₂ nanoparticles was characterized with FTIR. Microstructural analysis was done by AFM. The size, particle size distribution and zeta potential of TiO₂ nanoparticles in water dispersion was measured by DLS method. For the evaluation of particle size and the stability of nanoparticles in water dispersions with higher solid content the electroacoustic spectroscopy was made. To determine the applicability and evaluate the transmittance of the nano-TiO₂ composite coatings UV–VIS spectroscopy in the wavelength range of 200–800 nm was employed. The results showed that surface treatment of TiO₂ nanoparticles with SiO₂/Al₂O₃ improves nanoparticles dispersion and UV protection of the clear polyacrylic composite coating.     

The influence of the crystal structure of TiO2 support material on Pd catalysts for formic acid electrooxidation

The influence of the crystal structure of TiO₂ support material on Pd catalyst-mediated formic acid electrooxidation was investigated. Pd/TiO₂ catalysts were synthesized by loading Pd on TiO₂ with different crystal structures obtained by calcinations at different temperatures. Electrochemical tests showed that TiO₂ with the rutile structure improved the catalytic activity of Pd nanoparticles toward formic acid electrooxidation. Physicochemical and electrochemical characterizations revealed that the enhancement of Pd/TiO₂ (rutile) catalytic activity arose from uniform dispersion of Pd nanoparticles, an increase in surface-active sites, and good tolerance to the adsorption of poisonous intermediates (such as CO_ad, COOH_ad and so on).     

The effect of drying on dispersions of nano-particulate titanium dioxide in ethylene glycol

This paper first demonstrates that the UV attenuation of a well-milled aqueous dispersion of nano-particulate rutile TiO₂ is 200 times greater than the attenuation of visible 550 nm light. The corresponding UV attenuation of rutile dispersions in ethylene glycol is however only ∼ 50% of that of the aqueous dispersion. It is shown that the different behaviour of suspensions in water and in ethylene glycol depends on the way in which the TiO₂ was dried. If the rutile is pre-treated, by washing in ethanol before conventional oven drying, the differences between the optical properties of the aqueous and non-aqueous suspensions can be eliminated. Possible reasons for the beneficial effects of the ethanol pre-treatment are proposed.     

Genotoxic responses to titanium dioxide nanoparticles and fullerene in gpt delta transgenic MEF cells

Background  

Titanium dioxide (TiO₂) nanoparticles and fullerene (C₆₀) are two attractive manufactured nanoparticles with great promise in industrial and medical applications. However, little is known about the genotoxic response of TiO₂ nanoparticles and C₆₀ in mammalian cells. In the present study, we determined the mutation fractions induced by either TiO₂ nanoparticles or C₆₀ in gpt delta transgenic mouse primary embryo fibroblasts (MEF) and identified peroxynitrite anions (ONOO^-) as an essential mediator involved in such process.     

Yield stress and zeta potential of washed and highly spherical oxide dispersions — Critical zeta potential and Hamaker constant

The linear relationship between yield stress and the square of the zeta potential based on the yield stress-DLVO force model, was used to determine the zeta potential at the point of transition from flocculated to dispersed state of a range of oxide dispersions. The critical zeta potential at this point for washed α-Al₂O₃, TiO₂ and ZrO₂ dispersions was of magnitude 40, 49 and 52 mV respectively. For highly spherical silica and alumina dispersions, this value was 23 and 38 mV respectively. The square of the critical zeta potential is proportional to the Hamaker constant of the oxide in water when the van der Waals force is the only attractive force in play. Thus the critical zeta potential data obtained allowed the Hamaker constant ratio between the three oxide dispersions to be determined. This ratio between rutile TiO₂/water and α-Al₂O₃/water was 1.50. In comparison, a similar value of 1.46 was obtained for the ratio calculated from Hamaker constant value determined via Lifshitz theory. The ratio between rutile TiO₂/water and ZrO₂/water is ∼ 0.90. Using the Hamaker constant of rutile TiO₂/water of 61.2 zJ as the standard, the Hamaker constant determined by our method is 41 zJ for α-Al₂O₃, 68 zJ for ZrO₂ and 13.6 zJ for silica.     

Asbestos, carbon nanotubes and the pleural mesothelium: a review of the hypothesis regarding the role of long fibre retention in the parietal pleura, inflammation and mesothelioma

Background

Increasing environmental and occupational exposures to nanoparticles (NPs) warrant deeper insight into the toxicological mechanisms induced by these materials. The present study was designed to characterize the cell death induced by carbon black (CB) and titanium dioxide (TiO₂) NPs in bronchial epithelial cells (16HBE14o- cell line and primary cells) and to investigate the implicated molecular pathways.

Results

Detailed time course studies revealed that both CB (13 nm) and TiO₂(15 nm) NP exposed cells exhibit typical morphological (decreased cell size, membrane blebbing, peripheral chromatin condensation, apoptotic body formation) and biochemical (caspase activation and DNA fragmentation) features of apoptotic cell death. A decrease in mitochondrial membrane potential, activation of Bax and release of cytochrome c from mitochondria were only observed in case of CB NPs whereas lipid peroxidation, lysosomal membrane destabilization and cathepsin B release were observed during the apoptotic process induced by TiO₂ NPs. Furthermore, ROS production was observed after exposure to CB and TiO₂ but hydrogen peroxide (H₂O₂) production was only involved in apoptosis induction by CB NPs.

Conclusions

Both CB and TiO₂ NPs induce apoptotic cell death in bronchial epithelial cells. CB NPs induce apoptosis by a ROS dependent mitochondrial pathway whereas TiO₂ NPs induce cell death through lysosomal membrane destabilization and lipid peroxidation. Although the final outcome is similar (apoptosis), the molecular pathways activated by NPs differ depending upon the chemical nature of the NPs.     

Preparation of ceramic nanospheres by CO2 laser vaporization (LAVA)

In order to prepare ceramic nanoparticles by CO₂ laser vaporization (LAVA) coarse ceramic powders (e.g. ZrO₂, Al₂O₃, and TiO₂) were used as raw materials. The raw powder was vaporized into a flowing process gas under normal pressure. Expanding into the gas, the vapor instantly cools down. Gas-phase condensation leads to the formation of nanoscale particles with a composition that corresponds to that of the raw powder. LAVA nanoparticles are chemically pure, spherical, crystalline, exhibit a narrow size distribution, and form merely soft agglomerates. The co-laser vaporization of mixtures of ceramic raw powders allows for the preparation of nanoparticles of multi-phase (e.g. Fe₂O₃-SiO₂) or single-phase (e.g. CaTiO₃) mixed-oxides and dispersion ceramics (e.g. ZrO₂-Al₂O₃). In order to modify the surface of the nanoparticles they can be coated in-process with an organic additive. Thus, the LAVA method allows for the targeted development of a wide range of ceramic nanopowders with tailored properties.     

Effects of carbon‐coated titanium dioxide nanoparticles as a photostabilizer on the photodegradation of rigid poly(vinyl chloride)

In this study, nanocomposites of rigid poly(vinyl chloride) (UPVC) using the synthesized carbon‐coated titanium dioxide (TiO₂) nanoparticles and commercial powder of titanium dioxide (with rutile structure) were prepared by melt blending. The presence of carbon‐coated TiO₂ nanoparticles with rutile structure in UPVC matrix led to an improvement in photo stability of UPVC nanocomposites in comparison with commercial UPVC. The photocatalytic degradation behavior of nanocomposites was investigated by measuring their structural changes, surface tension, and mechanical and morphological properties before and after UV exposure for 700 h. It was found that mechanical and physical properties of UPVC nanocomposites are not considerably reduced after UV exposure in the presence of carbon‐coated TiO₂ nanoparticles even in small percentage of nanoparticles in comparison with the presence of commercial TiO₂ particles. Therefore, it can be concluded that UPVC/TiO₂ nanocomposite with low content of carbon‐coated TiO₂ nanoparticles(0.25 wt %) illustrated high stability under light exposure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40228.     

TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles containing hindered amine light stabilizers encapsulated by MMA–PMPM copolymers

TiO₂–SiO₂ composite nanoparticles containing hindered amine light stabilizers (HALSs) were prepared by encapsulation of commercially available TiO₂–SiO₂ nanoparticles using methyl methacrylate (MMA) and 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (PMPM) copolymers through mini-emulsion polymerization. The Fourier transform infrared spectral analysis (FTIR) showed that the hindered amine light stabilizer PMPM was incorporated into the TiO₂–SiO₂/P(MMA-co-PMPM) composite nanoparticles. The X-ray photoelectron spectroscopy analysis (XPS) showed that the surface of TiO₂–SiO₂ nanoparticles was enriched with HALS moieties. The formation of P(MMA-co-PMPM) random copolymers on the surface of TiO₂–SiO₂ nanoparticles was determined by differential scanning calorimetry (DSC), and the percentage of the chemically grafted P(MMA-co-PMPM) coverage on the TiO₂–SiO₂ nanoparticles surface was 40.9 wt% determined by thermogravimetric analysis (TGA), which revealed that the TiO₂–SiO₂ nanoparticles were successfully encapsulated by MMA–PMPM copolymers. Scanning electron microscopy analysis indicated that the TiO₂–SiO₂/P(MMA-co-PMPM) composite nanoparticles were mainly homogeneous spherical shape particles, with an average size of about 90 nm. Rhodamine B (Rh.B) photocatalytic degradation study revealed UV-shielding characteristics for TiO₂–SiO₂/P(MMA-co-PMPM) composite nanoparticles and showed a remarkable decrease in photocatalytic activity of TiO₂–SiO₂ nanoparticles. These results indicated that TiO₂–SiO₂/P(MMA-co-PMPM) composite nanoparticles may be promising light stabilizers with covalent functionalization of polymeric HALS, which has little photocatalytic activity, and can be introduced into the weathering-resistant polymer materials to improve their application properties.     

Rheological investigation of polyamide 6 TiO2‐ and BaSO4‐nanocomposites

Commercially available TiO₂ and BaSO₄ nanoparticles were incorporated in polyamide 6 (PA 6) via twin screw extrusion. The primary particle size of nanoparticles was 15 nm and 20 nm. The compounds were manufactured via multiple extrusion and dilution processing steps. The dispersion of the nanoparticles in the matrix was investigated by scanning electron microscopy and image analysis, micro‐tomography, and transmission electron microscopy. The rheological properties were determined via plate–plate‐rheometer. It was found that for TiO₂ fillers a threefold extrusion process is sufficient to realize a dispersion index of 94.4%. BaSO₄ fillers were hardly dispersible, ending up with a maximum dispersion index of 71%. Deagglomeration does not lead to a change in rheological properties but the number of extrusion steps decreases the rheological properties. A good particle‐matrix interaction leads to higher moduli and viscosity. The remaining agglomerates seem to act as defects decreasing the energy absorption of the respective compounds. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structure and functional properties of glycerol-plasticized starch/TiO<Subscript>2</Subscript> nanocomposite materials obtained through resonant wave mixing

Resonant wave mixing is a promising technology based on employing non-linear waves to intensify heat and mass transfer and enhancing dispersion processes in mixed materials. In the present work, for the first time, resonant wave mixing was used to prepare film-forming dispersions based on gelatinized maize starch and spherical TiO₂ nanoparticles (0.5–1.5 wt%) synthesized by sol–gel technique. Then, nanocomposite films were obtained by solution casting method. The dynamic viscoelastic properties, including relaxation spectra of the film-forming dispersions were investigated by oscillatory squeeze film rheometry, while the structure of the nanocomposite films was studied by X-ray diffraction, FTIR spectroscopy and scanning electron microscopy. The mechanical, water-related and UV-protective properties of the film materials were evaluated. It was shown that nanofiller incorporation enhanced the density of the 3D network structure of a gelatinized starch dispersion. The resonant wave treatment favored homogenous dispersion of the TiO₂ nanoparticles in the nanocomposites. All nanocomposite film samples displayed higher tensile strength and lower water vapor permeability in comparison with starch films without the nanofiller. The obtained nanocomposites possessed UV-protective properties, which could be potentially applied to produce biodegradable packaging materials with improved functional characteristics.     

Growth of Ag and Au Nanoparticles on Reduced and Oxidized Rutile TiO2(110) Surfaces

The nucleation and growth of Au and Ag nanoparticles on rutile TiO₂(110)–(1 × 1) surfaces in different oxidation states is studied by means of photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM). Au and Ag nanoparticles were found to bind much more strongly to oxidized TiO₂(110) model supports than to reduced TiO₂(110) surfaces, as directly revealed by STM. Detailed PES studies addressing small Au and Ag particles complete this picture and show that the PES core level spectra acquired on Au/TiO₂(110) and Ag/TiO₂(110) can be best described by fitting with two binding energy (BE) components. Particularly for coverages in the sub-monolayer regime and for depositions at low temperatures (100 K) the PES core level spectra must be fitted with at least two BE components. The higher BE component is attributed to atoms at the interface between the metal clusters and the TiO₂(110) support. For Au/TiO₂(110), the two BE components were evident in the core level spectra for higher coverage than for Ag/TiO₂(110), consistent with different growth modes for Au (initially 2D) and Ag (3D) on TiO₂(110). Finally, strong evidence for charge transfer from Ag nanoparticles to the TiO₂(110) support is presented, whereas the charge transfer between Au nanoparticles and the TiO₂(110) support is very small.     

TiO2, TiO2/Ag and TiO2/Au photocatalysts prepared by spray pyrolysis

TiO₂, TiO₂/Ag and TiO₂/Au photocatalysts exhibiting a hollow spherical morphology were prepared by spray pyrolysis of aqueous solutions of titanium citrate complex and titanium oxalate precursors in one-step. Effects of precursor concentration and spray pyrolysis temperature were investigated. By subsequent heat treatment, photocatalysts with phase compositions from 10 to 100% rutile and crystallite sizes from 12 to 120 nm were obtained. A correlation between precursor concentration and size of the hollow spherical agglomerates obtained during spray pyrolysis was established. The anatase to rutile transformation was enhanced with metal incorporations and increased precursor concentration. The photocatalytic activity was evaluated by oxidation of methylene blue under UV-irradiation. As-prepared TiO₂ particles with large amounts of amorphous phase and organic residuals showed similar photocatalytic activity as the commercial Degussa P25. The metal incorporated samples showed comparable photocatalytic activity to the pure TiO₂ photocatalysts.     

Cellulose acetate butyrate membrane containing TiO2 nanoparticle: Preparation, characterization and permeation study

Cellulose acetate butyrate/TiO₂ hybrid membranes were prepared via phase inversion by dispersing the TiO₂ nanoparticles in casting solutions. The influence of TiO₂ nanoparticles on the morphology and performance of membranes was investigated. The scanning electron microscope images and experiments of membrane performance showed that the membrane thickness and pure water flux were first increased by adding the TiO₂ nanoparticles to the casting solution up to 4 wt% and then decreased with the addition of further nanoparticles to it. The obtained results indicated that the addition of TiO₂ in the casting solution enhanced the rejection and permeate flux in filtration of bovine serum albumin solution. Furthermore, increasing the TiO₂ nanoparticle concentration in the casting solution increased the flux recovery and consequently decreased the fouling of membrane.     

Photocatalytic degradation of ammonia by light expanded clay aggregate (LECA)-coating of TiO2 nanoparticles

Photocatalytic degradation of ammonia on supported TiO₂ nanoparticles was investigated. The TiO₂ nanoparticles used as photocatalyst were coated on light expanded clay aggregate granules (LECA), which is a porous and light weight support. Photocatalytic reaction activity of prepared catalyst was determined by ammonia degradation from water synthetically polluted with ammonia. Experiment results showed significantly high photocatalytic activity for the immobilized catalysts. The ammonia was removed more than 85% within 300 min of the process with optimum calcinations temperature 550 °C and pH 11. Kinetics of the photocatalytic reaction followed a pseudo-first order model. XRF, XRD and SEM analyses revealed a rather uniform coating of TiO₂ on the support. By using floated TiO₂/LECA as a photocatalyst in aqueous solution of NH ₃ ^? , the ammonia was photodegraded into N₂ and H₂ gases, while NO ₂ ^? and NO ₃ ^? were formed at very low concentrations.