Effect of microstructure of fluorinated acrylic coatings on UV degradation testing

This paper presents research results on the relationships between the microstructure and the performance/weatherability of fluoropolymer/acrylic coatings. We studied fluoropolymer/acrylic blends of identical composition, prepared as films using three different methods: 2-stage emulsion polymerization followed by latex film formation; cold-blending (physically mixing) acrylic and fluoropolymer latex dispersions followed by latex film formation; and solution casting using an organic solvent. We investigated the effects of the mixing method, and the level of acrylic in the blend on the microstructure/morphology and on the durability-related physical properties of the fluoropolymer/acrylic films. Small angle neutron scattering was performed to determine the microstructure/morphology of fluoropolymer-rich micro-domains in the coatings prepared using these three methods. The physical properties tested included the glass transition temperature, the crystallinity fraction, and the tensile strength. The mass loss rates observed during UV exposure testing correlate with the final microstructures of the films.     

Effects of UV degradation on surface hydrophobicity, crack, and thickness of MWCNT-based nanocomposite coatings

Surface degradation is a common problem in polymeric coatings when they are exposed to sunlight, moisture, and oxygen. In order to reduce their surface degradation, thus keeping the coatings’ original properties, multi-wall carbon nanotubes (MWCNTs) were added, and the coatings were exposed to UV light and salt fog for various lengths of time. At 0 days of UV exposure, contact angle values of 0%, 0.25%, 0.5%, 1%, and 2% MWCNT-based nanocomposite coatings of 75 μm (∼3 mil) thickness were between 85° and 89°. However, after 16 days of UV exposure, contact angle values of the same samples were reduced to 11°, 13°, 34°, 50°, and 54°, respectively. Longer UV exposures resulted in several microcracks on the surface of the coated samples in the absence of nanoscale inclusions, while very minimal cracks or degradation appeared on the MWCNT-loaded samples. Test results also showed that UV exposure along with salt fogging reduced the coating thickness up to 24% at 0% CNTs; in contrast, this reduction was only 7% with a 2% MWCNT coating. These results clearly indicate that MWCNTs added to polymeric coatings reduce UV degradation, lessen surface cracks, protect the film thickness, and hence increase the lifetime of the polymeric coatings.     

Influence of operating parameters on photocatalytic degradation of phenol in UV/TiO2 process

The use of hydrogen peroxide (H₂O₂) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO₂ powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H₂O₂/UV, TiO₂/UV, and H₂O₂/TiO₂/UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H₂O₂ concentrations on photodegradation process were examined. It was shown that photodegradation using H₂O₂/TiO₂/UV process was much more effective than using either H₂O₂/UV or TiO₂/UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10⁻⁴ min⁻¹ by direct photolysis to 1.4 × 10⁻² min⁻¹ using H₂O₂/TiO₂/UV process. The role of H₂O₂ on such enhanced photodegradation of phenol in aqueous solution was finally discussed.     

Cu基ZnO薄膜紫外光催化降解水中有机污染物

利用Cu基ZnO薄膜紫外光催化降解水体中的有机污染物是一项非常有前景的水处理技术,本文利用电化学沉积方法,在锌盐的水溶液中沉积制备Cu基ZnO薄膜,并以较难降解的偶氮类有色化合物甲基橙是为例,紫外光照射下,用制备好的Cu基ZnO薄膜降解水中甲基橙.结果表明有很好的催化降解效能.该技术还没有得到广泛应用,有待于进一步完善...     

Electrochemical degradation of 2,4,5-trichlorophenoxyacetic acid in aqueous medium by peroxi-coagulation. Effect of pH and UV light

Acidic aqueous solutions with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) concentrations up to 270 ppm in the pH range 2.0-6.0 at 35 °C can be rapidly degraded by peroxi-coagulation using an Fe anode and an O₂-diffusion cathode. 2,4,5-T and its products are then efficiently oxidized with OH radicals produced from Fenton's reaction between Fe²⁺ and H₂O₂ generated by the electrodes. Under pH regulation at low currents, more than 90% of organics are destroyed at pH 3.0, although its optimum pH is 4.0. Higher degradations are reached without pH regulation. Solutions with 2,4,5-T concentration ≤200 ppm are more rapidly depolluted under UV irradiation, because of the production of more OH from photo-Fenton reaction. Coagulation of products with the Fe(OH)₃ precipitate formed predominates when pH is regulated to 2.0 and 3.0 in the absence of UV light, whereas parallel mineralization is favored without pH regulation and under UV irradiation. The 2,4,5-T decay follows a pseudo first-order reaction, with the same rate constant in the presence and absence of UV light. 2,4,5-trichlorophenol, 2,5-dichlorohydroquinone, 4,6-dichlororesorcinol and 2,5-dihydroxy-p-benzoquinone have been identified and quantified as aromatic intermediates by reverse-phase chromatography. Chloride ions are released from the oxidation of these chlorinated products. The evolution of generated carboxylic acids, such as glycolic, glyoxylic, formic, malic, maleic, fumaric and oxalic, has been followed by ion-exclusion chromatography. The great stability of oxalic acid and its complexes with Fe³⁺ at pH regulated to 3.0 can explain that concentrated solutions can not be completely degraded.     

Kinetics,degradation pathway and reaction mechanism of advanced oxidation of 4‐nitrophenol in water by a UV/H2O2 process

Photooxidation of 4‐nitrophenol (4‐NP) in water by the UV/H₂O₂ advanced oxidation process was carried out in order to investigate the kinetics and pathway of 4‐NP degradation. The experimental results showed that the photodegradation of 4‐NP accorded well with pseudo‐first order kinetics. The effects of different parameters, such as H₂O₂ dosage, pH value and various anion scavengers on the degradation of 4‐NP have been investigated in detail. It was found that acidic conditions are more favorable to the degradation of 4‐NP but many anions, such as HCO₃^?, NO₃^? and Cl^?, slow down the photooxidation rate of 4‐NP. Hydroquinone, 1,2,4‐trihdroxybenzene, 4‐nitropyrogallol, and 4‐nitrocatechol were tentatively identified as the intermediates of 4‐NP degradation by GC/MS after samples were derivatized by N,O‐bis(trimethylsilyl)‐trifluoroacetamide (BSTFA). A degradation pathway was proposed to account for the observed intermediates produced during 4‐NP degradation by the UV/H₂O₂ process. Copyright © 2003 Society of Chemical Industry