Study on Dispersion of TiO2 Particles During Polymerization of PET

An important factor influencing the stability of colloidal suspension is zeta potential (ζ-potential) on the surface of particles. In this work, ζ-potential of TiO₂ particles in ethylene glycol (EG) with various additives for poly(ethyleneterephthalate) (PET) polymerization, such as metallic salts, phosphoric acid and alkyl phosphates, were investigated by electrophoretic mobility method. The dispersion stability of TiO₂/EG suspension was influenced by decrease in the absolute value of the ζ-potential by the addition of metal acetates as well as phosphates. The addition of triethylamine (TEA) in the TiO₂/EG suspension restrained the change of ζ-potential from negative to positive, which resulted from phosphoric acid. The molar ratio of phosphoric acid to an acetate was found to have an influence on the dispersion ability of TEA in TiO₂/EG suspension. Effect of metallic salts, phosphoric acid and TEA on the stability of TiO₂/EG suspension was studied in the actual polymerization of PET. It was proved that the addition of TEA is highly effective for the dispersion of TiO₂ particles in PET, even in the presence of metallic salts, phosphoric acid and its alkyl phosphates.     

Synthesis and Non-isothermal Crystallization Behavior of PET/Surface-treated TiO 2 Nanocomposites

Poly(ethylene terephthalate) (PET)/TiO ₂ nanocomposites were prepared by melt-blending PET and surface-treated TiO ₂ . The crystallization behavior and the non-isothermal crystallization kinetics of these composites were investigated by differential scanning calorimetry (DSC). Jeziorny and Mo's methods were applied to describe the kinetics of the non-isothermal crystallization process. It was found that the PET matrix with incorporated surface-treated TiO ₂ particles has lower crystallization temperature and melting point than that with incorporated pure nano-TiO ₂ particles. Unlike plain TiO ₂ , surface-treated TiO ₂ particles showed less effect on the degree of crystallization of the PET matrix.     

The Formation of Nano-sized Selenium–titanium Dioxide Composite Semiconductors by Photocatalysis

Nano-sized selenium (Se) particles were deposited onto titanium dioxide (TiO₂) by the photocatalytic reduction of selenate (Se(VI)) and selenite (Se(IV)) ions. Se particles deposition on TiO₂ was only observed in the presence of formic acid, which acted as the organic hole scavenger. The Se particles formed were crystalline. Se particles of different size could be formed onto the TiO₂ particles by manipulating experimental parameters such as pH and the Se precursor used. When Se(VI) ions were used as the precursor, the Se particles formed on TiO₂ were found to be spherical in shape, up to 6 times bigger than the TiO₂ particles (up to 145nm) and discretely formed on the TiO₂ particles. The growth and sphericity of the Se particles were explained in terms of electron transfer across the p–n junctions formed by the p-type Se and n-type TiO₂ semiconductors under illumination and the adsorption of the Se(VI) ions. The size of the Se particles were found to be dependent on the amount of Se(VI) photoreduced. When Se(IV) ions were used as the precursor for Se particles formation, the particles formed were much smaller than that of TiO₂ crystals (less than 25nm) and also more evenly dispersed on the TiO₂ particles.     

Preparation and Properties of Poly(ethylene terephthalate)/Silica Nanocomposites

A kind of poly(ethylene terephthalate) (PET)/Silica nanocomposite (PETS) was synthesized via in situ polymerization using the compatibility between silica nanoparticles and ethylene glycol (EG). Transmission electron microscopy (TEM) micrographs revealed that the silica nanoparticles were well dispersed in the PET matrix, the particle size was about 10 nm with narrow distribution, and there existed strong interaction between the particles and the polymer chains. Differential scanning calorimetry (DSC) results indicated that the thermal properties of PETS with 2 wt% silica (PETS‐2) are different from those of pure PET (PETS‐0). The properties of the as‐spun fibers show that the tenacity and LASE‐5 (load at a specified elongation of 5%) of PETS‐2 were higher than those of PETS‐0, while the heat shrinkage of PETS‐2 was lower than that of PETS‐0. We suggest that the increasing of crystallinity and the strong interface interaction of the nanocomposite caused the fibers of PETS‐2 to not only have higher tenacity and LASE‐5 but also to have lower heat shrinkage.     

Miscibility and Crystallization Behavior of Poly (Ethylene Terephthalate)/Phosphate Glass Hybrids

Fundamental studies on miscibility and crystallization behavior of poly (ethylene terephthalate) (PET) and inorganic phosphate glass (Pglass) hybrids were conducted. The Flory–Huggins interaction parameter (χ) value of ?0.075 for the PET/Pglass hybrids was obtained using the Nishi–Wang equation, demonstrating that the Pglass and PET components were miscible in the melt state. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the phase separation occurred during quenching from the melt. The phase boundaries between PET and Pglass were blurred, which indicated partial compatibility of the components in the solid state. Contact angle measurements indicated the interfacial tension of PET/Pglass hybrids was 1.5 mN/m, and the work of adhesion was 78.0 mN/m at 28 °C. Based on the Hoffman–Lauritzen theory, the nucleation constant (K_g) and fold surface free energy (σ_e) of PET/Pglass hybrids were less than those of neat PET.     

The preparation of clay nanosheets-poly(ethylene terephthalate) hybrid materials

The preparation of hybrid materials of poly(ethylene terephthalate) (PET) with montmorillonite (Mont) clay was investigated using anchor monomers, i.e. hydroxyethyl isonicotinamide (HENA) or hydroxypentyltrimethylammonium iodide (HPTA), which both have cationic substituents to adsorb onto clay surfaces and a hydroxyethyl moiety (–CH₂CH₂OH) to react with the polymer chain terminal of PET. The condensation of the mixtures of the intercalation compounds, bis (2-hydroxyethyl) terephthalate (BHET) and HENA/Mont or HPTA/Mont, led to a homogenous and transparent PET hybrid in which the Mont clay particles were scattered homogenously. The HPTA/Mont hybrid films copolymerized with BHET exhibited a dramatic improvement in such characteristics as tensile strength and optical transparency.     

Structure Formation of Blend and Sheath/Core Conjugated Fibers in High-Speed Spinning of PET,Including a Small Amount of PMMA

The blend of poly(ethylene terephthalate) (PET) and a small amount of polymer that has higher T _g than PET, such as polymethylmethacrylate (PMMA)—and is dispersed finely as immiscible particles in PET—exhibits lower molecular orientation than pure PET under high-speed fiber spinning. To obtain insight into the mechanism of the lower molecular orientation of the blend fiber, the sheath/core structure of PET (sheath)/PMMA (core) conjugated fiber (the same PET/PMMA weight ratio as in the blend fiber), was produced as a model. The thinning profile of the fiber diameter along the spinning line and the birefringence distribution of the cross-section were examined and compared among pure PET fiber, the conjugated fiber, and the blend fiber. The conjugated fiber had the lowest molecular orientation of PET in the sheath part, and its thinning process was accelerated similar to the blend fiber. As a result of the distribution of molecular orientation across the diameter of the conjugated fiber, it is considered that PMMA, having the high T _g , tends to solidify at a higher temperature (upstream) than PET in the thinning process, making the flow of PET accelerate as if it was pushed by PMMA. This causes the maximum dv/dx just before the solidification point to be smaller; therefore, the lower spinning stress, resulting in smaller birefringence of PET, can be considerable. This acceleration was generated at the interface of PET and PMMA, and spread toward the fiber surface as both polymers were thinning in elongational flow (in melt). On the other hand, close to the interface, molecules of PET were stretched by PMMA, resulting in an increase of birefringence. Such discussion is also considered to apply to the blend fiber. However, because the blend fiber had a significantly larger interface area compared with the conjugated fiber, it is considered that the increase of birefringence of PET by the interface drag force cannot be neglected. The larger particles of PMMA dispersed in PET results in the lower birefringence of PET that is supported by the elongation effect (i.e., the interface drag force).     

Morphology Development in Multi‐Component Polymer Blends: I Composition Effect on Phase Morphology in PP/PET Polymer Blends

The relationship of the phase morphology of polypropylene/polyethylene‐terephthalate (PP/PET) blends and their corresponding compatibilized blends with composition was investigated using digital image analysis. A diameter, d _g , was defined and calculated to discuss the phase morphology of this polymer blend system. A figure‐estimation method was introduced to determine the width of the distribution of d _g . Based on the method, it is proven that the distribution of d _g obeys a log‐normal distribution and consequently, the distribution width, σ was calculated. Further, a fractal dimension, D _f , was introduced to describe the distribution of main sizes of the particles of the dispersed phase. The results showed that, while d _g increased with the concentration of the dispersed phase, σ and D _f show different dependence relations on composition;σ increases monotonously but D _f shows a maximum at a PET content of 30%, indicating that, even though the whole size distribution is much broader, the distribution of the main body of size becomes more uniform when the content of PET is less than 30%.     

Organic-ligand-assisted supercritical hydrothermal synthesis of titanium oxide nanocrystals leading to perfectly dispersed titanium oxide nanoparticle in organic phase

Titanium oxide (TiO₂) nanocyrstals which are perfectly dispersed in organic solvents are synthesized by organic-ligand-assisted supercritical hydrothermal synthesis. The addition of hexaldehyde to the supercritical hydrothermal synthesis of TiO₂ leads to the in-situ surface modification, which enables the synthsized TiO₂ nanocrystals to be perfectly dispersed in iso-octane because of its hydrophobic nature. Further, the one-pot synthesis of hybrid materials results in the significant reduction of the particles size, probably due to the capping effect of hexaldehyde to suppress the particles growth.     

Combined ultrasonic and gamma-irradiation to prepare TiO2@PET-g-PAAc fabric composite for self-cleaning application

The grafting of polyacrylic acid (PAAc) onto the fabric of Poly(ethyleneterephthalate) (PET) was loaded with TiO₂ by a mixture sonication of TiO₂ dispersed in AAc dissolved in acetone solvent. Ultrasonic irradiation was utilized as a tool for a good dispersion of TiO₂ onto the PET fabric. The grafted PET fabrics with acrylic acid AAc monomer were successfully obtained using gamma-ray induced graft polymerization, the degree of grafting PET-g-PAAc fiber was 105%. The chemical compositions and crystal structure of grafted TiO₂@PET-g-PAAc fabrics were characterized by ATR-FTIR and XRD. It was found that loading of PET fiber with in TiO₂ particles showing the formation of anatase and rutile as performed by XRD. The thermal property of TiO₂@PET-g-PAAc was investigated by differential thermal analysis (DTA). The obtained result indicated the thermal property of the grafted TiO₂@PET-g-PAAc was increased. Image of scanning electron microscope (SEM) indicated the good adherent and good distribution of PAAc and TiO₂ with PET fabric. The self-cleaning property of TiO₂@PET-g-PAAc has been evaluated by using three kinds of dyes as models.     

TiO2包覆石墨颗粒/硅油电流变液的研究

理论计算表明,介质包覆导体颗粒用作电流变液的分散相,可以获得高剪切应力的电流变液.采用溶胶-凝胶技术在尺度为5—10μm的石墨颗粒表面成功地包覆了TiO₂,获得了金红石相TiO₂包覆石墨的复合颗粒.配制成复合颗粒/硅油电流变液,其剪切应力与纯TiO₂/硅油电流变液相比,可提高一个数量级.当电场强度为1.7kV/mm时,复合颗粒/硅油电流变液的剪切应力可达1.25kPa,电流密度小于10μA/cm². 关键词： 电流变液 包覆 2')" href="#">TiO₂ 石墨     

Surface Effect of Two Different Calcium Fluoride Fillers on the Non-Isothermal Crystallization Behavior of Poly(ethylene Terephthalate)

Two different types of calcium fluoride (CaF₂) particles were incorporated into a poly(ethylene terephthalate) (PET) matrix, fine particles (～350 nm), and nanoparticles (～70 nm). Both of them were synthesized by a chemical precipitation method using triethanolamine (TEA) as stabilizer. To obtain the nanoparticles, a greater amount of TEA was added during the synthesis in order to limit their growth. Therefore, unlike the fine particles, nanoparticles contained a greater amount of the stabilizer. Once CaF₂ particles were obtained, the composite materials were prepared by melt-blending PET and particles at different filler loadings. The influence of both kinds of particles on the non-isothermal crystallization behavior of PET was investigated by using differential scanning calorimetry and field emission scanning electron microscopy. The Jeziorny-modified Avrami equation was applied to describe the kinetics of the non-isothermal crystallization, and several parameters were analyzed (half-crystallization time, Avrami exponent, and rate constant). According to the results, it is clear that CaF₂ particles act as nucleating agents, accelerating the crystallization rate of PET. However, the effect on the crystallization rate was more noticeable with the addition of the fine particles where the surface plays an important role for epitaxial crystallization, while the addition of the nanoparticles with an organic surface coating resulted in a crystallization behavior similar to the observed for PET.     

Room‐Temperature Synthesis of High Surface Area Anatase TiO2 Exhibiting a Complete Lithium Insertion Solid Solution

The synthesis of highly divided anatase TiO₂ nanoparticles displaying 300 m² g^?1 surface area is achieved by following a two‐step synthetic process at room temperature. The particles exhibit a needle‐like morphology composed of self‐assembled 4 nm nanoparticles. The crystallization process from amorphous TiO₂.1.6H₂O to oriented aggregation of anatase TiO₂ proceeds according to a slow solid dehydration process taking place in a large range of pH in deionized water (1 < pH < 12) or alternatively when including a low amount of NH₄F_(aq) in solution. Driven by their high surface area enhancing the chemical/electrochemical reactivity, it is reported in the case of the anatase TiO₂ that a modification in the lithium insertion mechanism is no longer attributable to a two‐phase reaction between the two‐end members Li_εTiO₂ and Li_0.5±αTiO₂ when downsizing the particle size, but instead through a complete solid solution all along the composition range.     

Electrodeposition and properties of Zn-nanosized TiO2 composite coatings

Nanosized TiO₂ particles were prepared by sol-gel method. The TiO₂ particles were co-deposited with zinc from a sulphate bath at pH 4.5 using electrodeposition technique. The corrosion behavior of the coatings was assessed by electrochemical polarization, impedance, weight-loss and salt spray tests. Wear resistance and microhardness of the composite coating was measured. The smaller grain size of the composite coatings was observed in the presence of TiO₂ and it was confirmed by the images of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.     

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T _m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.     

Mechanism of enhanced photocatalysis of TiO2 by Fe in suspensions

In this work, the mechanism of enhanced photocatalysis of TiO₂ with Fe³⁺ was studied using Sulfadiazine (SD) as the model compound. Results indicated that degradation rate of SD was enhanced by the addition of Fe³⁺ in TiO₂ suspension. The crystalline structure of TiO₂ particles was stable in suspensions. The hydroxyl radical generated by TiO₂/Fe³⁺ (both TiO₂ and Fe³⁺) photocatalysis was in a higher yield. Moreover, Fe²⁺ was found not to give an obvious impact on the SD degradation in TiO₂ suspension, whereas Fe³⁺ had a notable effect. The adsorption amount of TiO₂ was greatly enhanced by the addition of Fe³⁺ in suspensions. Finally, an interaction model of SD degradation in TiO₂ suspension containing Fe³⁺ was also proposed by investigating of surface behaviors of TiO₂ particles. It will be beneficial to use Fe³⁺ as the electron acceptors on the surface of TiO₂ particles, which helps to improve the yield of hydroxyl radical.     

Photodegradation of CH3I on mesoporous TiO2-B nanofibers with Au nanoparticles

Au nanoparticles deposited on mesoporous TiO₂-B nanofibers have been prepared, characterized, and used to catalyze photoreactions of iodomethane. High-density gold-particle deposition on TiO₂-B is obtained by electrostatic and/or chemical force between the particles of TiO₂-B and Au capped with -SC(H)(CO₂H)(CH₂CO₂H) through pH control. The capping groups on the gold particles can be removed after 400 °C calcination. It is found that the nature of the inorganic acids used for pH adjustment has effects on particle morphology and deposition. Two other methods, i.e., preparation of TiO₂-B nanofibers in the presence of gold particles and preparation of gold nanoparticles in the presence of TiO₂-B particles (deposition-precipitation method), are also investigated. However, the former method produces a low-density deposition and the latter one induces a morphology change of the TiO₂-B and an increase of the Au in size. Fourier transform infrared spectroscopy has been employed to study and to compare the photoreactions of CH₃I on TiO₂-B and Au/TiO₂-B and the effect of O₂. The presence of gold particles on TiO₂-B increases the efficiency of CH₃I photodegradation, forming adsorbed methoxy and formate. The role of gold is also discussed.     

Nonisothermal Crystallization of Recycled Poly(Ethylene Terephthalate)/Poly(Ethylene Octene) Blends

Recycled poly(ethylene terephthalate) (r-PET) was blended with poly(ethylene octene) (POE) and glycidyl methacrylate grafted poly(ethylene octene) (mPOE). The nonisothermal crystallization behavior of r-PET, r-PET/POE, and r-PET/mPOE blends was investigated using differential scanning calorimetry (DSC). The crystallization peak temperatures (T _p ) of the r-PET/POE and r-PET/mPOE blends were higher than that of r-PET at various cooling rates. Furthermore, the half-time for crystallization (t _1/2 ) decreased in the r-PET/POE and r-PET/mPOE blends, implying the nucleating role of POE and mPOE. The mPOE had lower nucleation activity than POE because the in situ formed copolymer PET-g-POE in the PET/mPOE blend restricted the movement of PET chains. Non-isothermal crystallization kinetics analysis was carried out based on the modified Avrami equation, the Ozawa equation, and the Mo method. It was found that the Mo method provided a better fit for the experimental data for all samples. The effective energy barriers for nonisothermal crystallization of r-PET and its blends were determined by the Kissinger method.     

Characterization of TiO<Subscript>2</Subscript> nanoparticle suspensions for electrophoretic deposition

The rheology of suspensions is critically important for the successful achievement of defect-free TiO₂ deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO₂ nanoparticle suspensions in acetylacetone with and without iodine was investigated over a broad solid-concentration range (0.3–2.5 wt.%) and at different shear rates ( = 10–250 s⁻¹). The influence of these parameters on the quality of TiO₂ films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO₂ nanoparticles suspension without iodine exhibited shear-thickening flow behaviour. For other concentrations, the suspensions showed shear-thinning behaviour followed by an apparent shear-thickening effect at a critical shear rate (100 s⁻¹). For the suspension with 1 wt.% TiO₂ containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (ϕ_m) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was ϕ_m = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO₂ deposits on stainless steel planar substrates were obtained by EPD at constant voltage condition. The influence of pH on suspension stability was determined in the range pH = 1–9, being pH ≈ 5 the optimal value for this system in terms of EPD results.     

Preparation and characterization of polyethylene/TiO2 nanocomposites

The rheological behaviour, dispersion, crystallization behavior, mechanical properties, fracture surface morphology of polyethylene (PE)/TiO₂ nanocomposites prepared by melt compounding were investigated using rheometer, energy dispersive X-ray spectrometer (EDX), polarized microscopy, impact tester, universal testing machine and field-emission scanning electron microscopy (FE-SEM). The rheological analysis indicated a fine dispersion of TiO₂ during the melt compounding. The large scaled surface dispersion of TiO₂ nanoparticles was revealed by the EDX composition distribution maps. The introduction of 2.0 wt% TiO₂ in composites improved the mechanical properties significantly compared to neat PE, and resulted in 45% increase in notched impact strength. Moreover, the further analysis and discussion showed the mechanical properties of the composites were controlled by the dispersion conditions of TiO₂ and its nucleating effect on PE crystallization.