Ageing behavior of acrylic polyurethane varnish coating in artificial weathering environments

Polyurethane-based coatings reinforced by ZnO nanoparticles (about 27 nm) were prepared via solution blending. The ZnO/PU films and coats were fabricated by a simple method of solution casting and evaporation. The mechanical properties of the films were investigated by a universal material test, and the abrasion resistance of the prepared coats was evaluated by a pencil-abrasion-resistance tester. It was found that significant improvement of the PU films in Young’s modulus and tensile strength was achieved by incorporating ZnO nanoparticles up to 2.0 wt%, and that the abrasion resistance of the PU coats was greatly enhanced due to the addition of ZnO nanoparticles. Moreover, the antibacterial property test was carried out via the agar dilution method and the result indicated that PU films doped with ZnO nanoparticles showed excellent antibacterial activity, especially for Escherichia coli.     

Preparation and characterization of UV-cured polyurethane acrylate/ZnO nanocomposite films based on surface modified ZnO

A series of polyurethane acrylate (PUA)/ZnO nanocomposite films with different ZnO contents were prepared via a UV-curing system. To ensure good dispersion in the PUA matrix, ZnO nanoparticles were modified with a silane coupling agent and confirmed by FT-IR analysis. The morphological structures, thermal properties, mechanical properties and water transfer properties of the prepared films were investigated as a function of their ZnO concentration. WAXD and SEM analyses showed that the surface-modified ZnO nanoparticles were homogeneously dispersed in the PUA matrix and the molecular ordering increased with increasing ZnO content. Compared with neat PUA, the hardness and elastic modulus in films increased from 0.03 to 0.056 GPa and from 2.75 to 3.55 GPa, respectively. Additionally, the water uptake and WVTR in the PUA/ZnO nanocomposite films decreased as the ZnO content nanoparticles increased, which may come from enhanced molecular ordering and hydrophobicity in films. UV light below approximately 450 nm can be efficiently absorbed by incorporating ZnO nanoparticles into a PUA matrix, indicating that these composite films exhibit good weather ability and UV-shielding effects. The enhanced physical properties achieved by incorporating modified ZnO nanoparticles can be advantageous in various applications, whereas the thermal stability of the composite films should be increased.     

ZnO nanosphere fabrication using the functionalized polystyrene nanoparticles for dye-sensitized solar cells

The nano-hollow spherical ZnO (NHS ZnO) photoelectrodes were prepared using functionalized polystyrene nanoparticles with flexible dimensional control of the particle diameter for dye-sensitized solar cells applications. NHS ZnO was formed by ZnO nanoparticles that accumulated on the surface of functionalized polystyrene with a high ionic strength. This method represents a one-step preparation method for an inorganic shell via polymerization between ZnO complexes. Even though NHS ZnO has a submicron size, it composed of nanoparticles that connect with each other, thereby implying good electron transfer properties, and has a high surface area. The submicron-sized diameter NHS ZnO has an enhanced light scattering capacity, which promotes the photons with more opportunities to be absorbed by the N719 dye molecules. Therefore, the ZnO films prepared from 600 nm to 1000 nm NHS ZnO possessed higher IPCE values over a wide range (from 400 nm to 750 nm) compared to films of the 300 nm ZnO due to the enhanced light scattering capacities of the film. In photocurrent-voltage measurements, the short-circuit current density of 300 nm and 600 nm NHS ZnO increases from 3.33 mA/cm² to 6.53 mA/cm² while the cell efficiency increases from 1.04% to 3.02% due to the light scattering efficiency. Electrochemical impedance spectroscopy showed that electrons in NHS ZnO with a larger particle size have a longer electron lifetime than NHS ZnO with a smaller particle size, as the latter hinders the electron transport in the NHS ZnO nanostructured films.     

Preparation and properties of poly(propylene carbonate) and nanosized ZnO composite films for packaging applications

A series of polypropylene carbonate (PPC)/ZnO nanocomposite films with different ZnO contents were prepared via a solution blending method. The morphological structures, thermal properties, oxygen permeability, water sorption, and antibacterial properties of the films were investigated as a function of ZnO concentration. While all of the composite films with less than 5 wt % ZnO exhibited good dispersion of ZnO in the PPC matrix, FTIR and SEM results revealed that solution blending did not lead to a strong interaction between PPC and unmodified ZnO. As such, poor dispersion was induced in the composite films with a high ZnO content. By incorporating inorganic ZnO filler nanoparticles, the diffusion coefficient, water uptake in equilibrium, and oxygen permeability decreased as the content of ZnO increased. The PPC/ZnO nanocomposite films also displayed a good inhibitory effect on the growth of bacteria in the antimicrobial analysis. The enhancement in the physical properties achieved by incorporating ZnO is advantageous in packaging applications, where antimicrobial and environmental‐friendly properties, as well as good water and oxygen barrier characteristics are required. Furthermore, UV light below ～ 350 nm can be efficiently absorbed by incorporating ZnO nanoparticles into a PPC matrix. ZnO nanoparticles can also improve the weatherability of a PPC film. In future research, the compatibility and dispersion of the PPC matrix polymer and the inorganic ZnO filler nanoparticles should be increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

A study on the anticorrosion performance of the epoxy-polyamide nanocomposites containing ZnO nanoparticles

Epoxy nanocomposites were prepared using different loadings (2, 3.5, 5 and 6.5 wt%) of ZnO nanoparticles. Nanocomposites were applied on steel substrates. Samples were immersed in 3.5 wt% NaCl solution for 1344 h. Corrosion resistance of the coatings was studied by an electrochemical impedance spectroscopy (EIS). The effects of addition of nanoparticles on the mechanical properties of the epoxy coating were studied by a dynamic mechanical thermal analysis (DMTA). Curing behavior of the coatings containing nanoparticles was studied by a differential scanning calorimeter (DSC). Atomic force microscope (AFM) was utilized to investigate the surface topography and surface morphology of the coatings. Coating resistance against hydrolytic degradation was studied by FTIR (Fourier Transform Infrared).Results showed that addition of low loadings of nanoparticles can increase T_g of the composite. Decrease in T_g and cross-linking density of the coating were observed at high loadings of nanoparticles. It was found that nanoparticles can influence the curing behavior of the epoxy coating. Nanoparticles improved the corrosion resistance of the epoxy coating. Increase in coating resistance against hydrolytic degradation was obtained using nanoparticles.     

Bimetallic Zn/Ag doped polyurethane spider net composite nanofibers: A novel multipurpose electrospun mat

The objective of this study was to develop a new class of bimetallic ZnO/Ag embedded polyurethane multi-functional nanocomposite by a straightforward approach. Bimetallic nanomaterials, composed of two unlike metal elements, are of greater interest than the monometallic materials because of their improved characteristics. In the present study the bimetallic composite was prepared using sol–gel via the facile electrospinning technique. The utilized sol–gel was composed of zinc oxide, silver and poly(urethane). The physicochemical properties of as-spun composite mats were determined by X-ray diffraction pattern, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. The antibacterial activity was tested using Escherichia coli as model organism. The antibacterial test showed that ZnO:Ag/polyurethane composite possesses superior antimicrobial activity than pristine PU and ZnO/PU hybrids. Furthermore, our results illustrate that the synergistic effect of ZnO and Ag resulted in the advanced antimicrobial action of bimetallic ZnO/Ag composite mat. The viability and proliferation properties of NIH 3T3 mouse fibroblast cells on the ZnO:Ag/polyurethane composite nanofibers were analyzed by in vitro cell compatibility test. Our results indicated the non-cytotoxic behavior of bimetallic ZnO:Ag/polyurethane nanofibers towards the fibroblast cell culture. In summary, novel ZnO:Ag/polyurethane composite nanofibers which possess large surface to volume ratio with excellent antimicrobial activity were fabricated. The unique combination of ZnO and Ag nanoparticles displayed potent bactericidal effect due to a synergism. Hence the electrospun bimetallic composite indicates the huge potential in water filtration, clinical and biomedical applications.     

聚氨酯/纳米氧化锌复合材料研究进展

综述了聚氨酯/纳米氧化锌复合材料的制备方法及研究进展。介绍了纳米氧化锌复合材料力学性能、抗静电性能、紫外屏蔽性能、耐磨与抗腐蚀性能和阻尼减振性能及应用。指出聚氨酯/纳米氧化锌复合材料存在的问题及发展方向。     

Preparation and characterizations of highly transparent UV-curable ZnO-acrylic nanocomposites

A sol–gel chemical route was adopted to prepare the zinc oxide (ZnO) nanoparticles as small as 4 nm. UV-curable ZnO-acrylic nanocomposites were then prepared by employing 3-(trimethoxysilyl)propyl methacrylate (TPMA) as the surface modification agent of ZnO particles. UV–vis analysis revealed a high optical transparency (>95%) in visible light region for nanocomposite thin films with ZnO contents up to 20 wt.%. The addition of ZnO nanoparticles also enhanced the dielectric constants of nanocomposites and the dielectric constants greater than 4 in frequencies ranging from 1 to 600 MHz was obtained in the samples containing 10 wt.% of ZnO nanoparticles. A comparison of experimental results and theoretical calculation indicated that the interfacial polarizations in between ZnO nanoparticles and polymer matrix may play an important role in the enhancement of dielectric properties of nanocomposites.     

Morphology and mechanical properties of semi-interpenetrating polymer networks from polyurethane and benzyl konjac glucomannan

A series of semi-interpenetrating polymer network (semi-IPN) films coded as UB from castor oil-based polyurethane (PU) and benzyl konjac glucomannan (B-KGM) were prepared, and they have good or certain miscibility over entire composition range. Morphology, miscibility and properties of the UB films were investigated by using scanning electron microscopy (SEM), differential scanning calorimetry, dynamic mechanical analysis, ultraviolet spectrometer, wide-angle X-ray diffraction and tensile test. The results indicated that the UB films exhibited good miscibility when B-KGM content was lower than 15 wt%, resulting in relatively high light transmittance, breaking elongation and density. With an increase of the B-KGM content from 20 to 80 wt%, a certain degree of phase separation between PU and B-KGM occurred in the UB films. The tensile strength of the films UB increased from 7 to 45 MPa with an increase of B-KGM content from 0 to 80 wt%. By extracting the B-KGM with N, N-dimethylformamide from the semi-IPN, the morphology and phase domain size of the UB films were clearly observed by SEM. A continuous phase and dual-continuous phase model describing the semi-IPN were proposed to illustrate the morphology and its transition.     

Abrasion resistance of waterborne polyurethane films incorporated with PU/silica hybrids

We describe polyurethane (PU)/silica hybrids (PSHs) prepared through hydrolysis and condensation reactions of tetraethoxysilane (TEOS) with or without methyltriethoxysilane (MTES) in the presence of polyurethane dispersion, which were subsequently incorporated into waterborne polyurethane (WPU) to prepare composites. The effects of the solid mass ratio of PSHs/WPU on the particle size of composite emulsions, the dispersion of silica nanoparticles in composite films, and the hardness and abrasion resistance of the corresponding films were examined. Composite emulsions possess a nanoscale particle size when incorporated with PSHs prepared using TEOS and MTES as precursors, and are superior to those with PSHs prepared using TEOS alone. Transmission electron microscopy revealed that silica nanoparticles had a uniform distribution in the polymer matrix and agglomerates could be almost completely avoided through in situ modification of silica with Si-CH₃ groups in the polyurethane dispersion. Composite films prepared with this method exhibited a superior hardness and abrasion resistance even at a lower silica content compared with that containing unmodified silica. In particular, optical microscopy and scanning probe microscopy observations demonstrated wear behavior differences among these composite films from the macro- and nanoscale viewpoints, respectively. It is proved that abrasive wear occurs, and surface morphology studies are in accordance with the results of abrasion resistance tests.     

Mechanical and antibacterial properties of modified nano‐ZnO/high‐density polyethylene composite films with a low doped content of nano‐ZnO

Nano‐ZnO/high‐density polyethylene (HDPE) composite films were prepared via melt blending and a hot compression‐molding process. The properties, including ultraviolet absorption, mechanical and antibacterial properties of the films, and plasticizing behavior of the composites, were investigated. The results show that the absorbance in the ultraviolet region of the HDPE films was enhanced after the addition of modified nano‐ZnO to the HDPE matrix. Also, we found that improvement in the HDPE films of the tensile strength and elongation at break was achieved by the incorporation of modified ZnO nanoparticles up to 0.5 wt % in contrast with the original nano‐ZnO/HDPE composite films. Antibacterial testing was carried out via plate counting, and the results indicate that the HDPE films doped with modified ZnO nanoparticles showed favorable antibacterial activity, especially for Staphylococcus aureus. However, the low doped content of modified nano‐ZnO in the HDPE matrix made the balance torque of the composites increase slightly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Green synthesis,characterization and antimicrobial activity of carbon quantum dots-decorated ZnO nanoparticles

In this research, ZnO nanoparticles (ZnO NPs) and Carbon Quantum Dots-decorated ZnO nanoparticles (ZnO/CQDs NCs) were prepared via different procedures and precursors. Soya chunk was applied as a source of carbon for the preparation of CQDs. Crystalline structure, purity, size, and morphological properties of products were investigated via X-ray diffraction (XRD) analysis, energy dispersive spectroscopy (EDS), Transmission Electron Microscopy (TEM), FT-IR, and Scanning Electron Microscopy (SEM) respectively. Findings showed that homogeneity, size, and morphological properties of products can be intensively affected via different precursors and procedures. From the homogeneity, size, and morphological point of view, the hydrothermal route, ammonia, 5 h, and 180 °C were the optimum procedure, pH adjuster, temperature, and time respectively. Optimum product was applied for carrying out minimum inhibitory concentration (MIC) and Agar disk-diffusion tests against various microorganisms. Results demonstrated that prepared ZnO NPs have maximum antibacterial activity against Staphylococcus aureus (19.53 μg/ml) and ZnO/CQDs NCs have no inhibitory effect against tested microorganisms. For ZnO NPs, the disk diffusion test proved that the highest growth inhibition zone was related to Staphylococcus aureus (15 mm). The presence of CQDs in ZnO/CQDs NCs reduces the inhibitory effect of ZnO NPs intensively.     

Synthesis of large-scale uniform mulberry-like ZnO particles with microwave hydrothermal method and its antibacterial property

Large-scale uniform mulberry-like ZnO particles were successfully synthesized via a fast and simple microwave hydrothermal method. The formation mechanism of mulberry-like ZnO particles was investigated by adding different types of alkalis and different amounts of triethanolamine (TEA). Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the morphology and crystal structure of the obtained ZnO. The results revealed that the as-prepared ZnO products had an average diameter of about 150 nm and polycrystalline wurtzite structure. The existence of TEA was vital for the formation of nanoparticle-assembled mulberry-like ZnO particles. These mulberry-like ZnO particles exhibited stronger antibacterial effects on Candida albicans than did sheet-like and flower-like ZnO.     

Surface mechanical properties of transparent poly(methyl methacrylate)/zirconia nanocomposites prepared by in situ bulk polymerization

Poly(methyl methacrylate)/zirconia (PMMA/ZrO₂) nanocomposites with ZrO₂ content as high as 15 wt% were prepared by modifying non-aqueous synthesized ZrO₂ nanoparticles with methacryloxypropyltrimethoxysilane (MPS) in tetrahydrofuran, dispersing MPS-functionalized ZrO₂ nanoparticles in MMA and following in situ bulk polymerization with controlled pre-polymerization time. The MPS-functionalized ZrO₂ nanoparticles showed an efficient crosslinking role in the polymerization, leading to a complete gel of PMMA at 5 wt% of ZrO₂ content. Homogeneous dispersion of the ZrO₂ nanoparticles at primary particle size level was observed in all nanocomposites, which results in good clarity of the obtained nanocomposites. Hardness tests (pendulum hardness tests and indentation tests) and anti-scratch tests (abrasion tests and nano scratch tests) were employed to probe the surface mechanical properties of the nanocomposites. The properties of nanocomposites as a function of ZrO₂ content, revealing from various characterization techniques, are not consistent and discussed in detail. At low ZrO₂ content, the mechanical properties are enhanced by the formed crosslinking structure. However, remarkable improvements of hardness and scratch resistance of PMMA were achieved when 15 wt% of ZrO₂ content was embedded.     

Solvothermal synthesis of microsphere ZnO nanostructures in DEA media

Microsphere ZnO nanostructures (ZnO-MNs) were synthesized via solvothermal method in diethanolamine (DEA) media. DEA was utilized to terminate the growth of ZnO nanoparticles which forms the ZnO-MNs. The ZnO-MNs were characterized by a number of techniques, including X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (SEM). The ZnO-MNs prepared by solvothermal process at the temperature of 150 °C for 6, 12, 18, and 24 h exhibited a hexagonal (wurtzite) structure with sizes ranging from 2 to 4 μm. The growth mechanism and morphology of the ZnO-MNs were also investigated, and it was found that the ZnO-MNs were formed by ZnO nanoparticles with average particle size of 25 ± 5 nm. To show role of DEA in the formation of Zn-MNs, effect of MEA (monoethanolamine) and TEA (triethanolamine) on morphology of the final product are also investigated. The results showed that DEA is a good polymerization agent that can be used as a stabilizer in the solvothermal technique for preparing fine ZnO powder.     

Synthesis and characterization of novel UV-curable polyurethane–clay nanohybrid: Influence of organically modified layered silicates on the properties of polyurethane

Nanohybrids based on UV-curable polyurethane acrylate (PU) and cloisite 20B (C-20B) have been synthesized by solution blending method using different loading levels of C-20B. The structures of PU/C-20B nanohybrids were confirmed by Fourier transform infrared spectroscopy (FTIR) while X-ray diffraction and transmission electron microscopy (TEM) showed the intercalation of PU into layer silicates. The thermal properties of PU and PU/C-20B nanohybrids were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetric (DSC). TGA tests revealed that the thermal decomposition temperature (T_d10%) of the nanohybrid containing 5 wt% of C-20B increased significantly, being 61 °C higher than that of pure PU while DSC measurements indicated that the introduction of 5 wt% of clay increased the glass transition temperature from 89.7 to 101 °C. Accordingly, the mechanical and anti-water absorption properties proved also to be enhanced greatly as evidenced by nanoindentation anylsis and water absorptions data in which the nanohybrid containing 5 wt% of clay have highest elastic modulus (4.508 GPa), hardness (0.230 GPa) and lowest water absorption capacity. Thus the formations of nanohybrids manifests through the enhancement of thermal, mechanical and anti-water absorption properties as compared with neat PU due to the nanometer-sized dispersion of layered silicate in polymer matrix.     

Effect of nano ZnO on the phase mixing of polyurethane hybrid dispersions

In the present study series of aqueous polyurethane (PU)/ZnO hybrid dispersions were prepared using dimethylolpropionic acid (bis-MPA) as an ionic center. For this, NCO terminated PU prepolymers with pendent acid groups were prepared first, then different concentrations of nano ZnO powder was incorporated into the PU matrix. The hybrid dispersions were prepared by adding required amount of triethylamine (TEA), water and chain extender. The prepared PU/ZnO hybrid dispersions were casted in a Teflon petri dish and the dried films were used for TGA, DMTA, SEM, gel content and contact angle measurements. The phase mixing behavior was studied from FT-IR peak deconvolution technique and DMTA analysis and the result suggests that phase mixing increases with ZnO content. The DMTA data suggest that the phase mixing and soft segment glass transition increases but storage modulus decreases with increasing with ZnO content. The FT-IR deconvolution result supports to the DMTA analysis. The coating properties like adhesive strength, water absorption, contact angle, gel content and corrosion resistance of the hybrid coatings were also evaluated.     

Transparent and thermally stable improved poly (vinyl alcohol)/Cloisite Na/ZnO hybrid nanocomposite films: Fabrication,morphology and surface properties

A series of poly(vinyl alcohol)/Cloisite Na⁺-Tyrosine/Zinc oxide (PVA/Cloisite Na⁺-Tyr/ZnO) bionanocomposites were prepared by dispersing ZnO nanoparticles in solution containing mixture of the PVA and modified Cloisite Na⁺. Structure of nanocomposite coatings was investigated by X-ray diffraction and Fourier-transform infrared spectroscopy. The thermal stability and optical properties of bionanocomposite were characterized by thermogravimetric analysis and UV–vis spectroscopy, respectively. The introduction of ZnO nanoparticles into PVA/Cloisite Na⁺-Tyr mixed solutions significantly increased the thermal stability of the obtained films. The results revealed that the high UV-shielding efficiency of the composites: for a film containing 6.0 wt% of ZnO nanocrystals, over 92% of UV light at wavelengths of 368 nm was absorbed while the optical transparency in the visible region was slightly below that of a PVA/Cloisite Na⁺-Tyr film.     

Synthesis, characterization and optical properties of Zn1−xTixO nanoparticles prepared via a high-energy ball milling technique

Zn_1−xTi_xO (x = 0, 0.01, 0.03 and 0.05) nanoparticles were prepared by high-energy ball milling at 400 rpm. The milled powders were characterized by X-ray diffractometer (XRD) and the results exhibited that Ti-doped ZnO nanoparticles consisted of single phase with hexagonal structure when the mixtures of ZnO and TiO₂ powders were milled for 20 h. The crystallite size reduced as a function of the doping content and milling time from 1 to 10 h then increased after milling for 20 h and when the annealing temperature increased. The strain changed inversely to the crystallite size. A wider band-gap was obtained by increasing the doping content and annealing temperature because of a reduction in defect concentration. Both ZnO- and Ti-doped ZnO nanoparticles caused damage to S. aureus, E. coli, P. mirabilis, S. typhi and P. aeruginosa.     

Preparation,dielectric property and infrared emissivity of Fe-doped ZnO powder by coprecipitation method at various reaction time

Fe-doped ZnO powders have been synthesized by the coprecipitation method at 600 °C with various reaction time, using zinc nitrate as the staring material, urea as the precipitator, and ferric nitrate as the doping source, respectively. The phase and morphology of the prepared powders have been characterized by X-ray diffraction and scanning electron microscopy, respectively. It was found that the prepared product synthesized for 1 h had a pure ZnO wurtzite structure and was a ZnO(Fe) solid solution powder. The real part, imaginary part, and dielectric loss of complex permittivity of prepared powders in the frequency range of 8.2–12.4 GHz decreased with increasing reaction time. The average infrared emissivities of prepared powders at the waveband range of 8–14 μm increased with extending reaction time.