Degradation products formed during UV-irradiation of humic waters

Natural humic lake water and aqueous solutions of humic substances were treated with ultraviolet (UV) radiation (λ = 254 nm). The effects on the dissolved organic carbon content (DOC) and the absorbance at 254 nm (Abs254) and 460 nm (Abs460) were monitored and the identity and concentrations of gas chromatographable organic degradation products were determined. The DOC content and the (Abs254) of the humic solutions decreased continuously with increasing UV-dose. Several aromatic and aliphatic degradation products were identified and roughly quantified The concentrations of aromatic hydroxy carboxylic acids and hydroxy aldehydes increased when relatively low UV-doses were used, but declined following further irradiation. The concentrations of aliphatic dibasic acids increased over the full range of UV-doses

Degradation of aquatic humic material by ultraviolet light

Natural humic water was treated with ultraviolet (UV) light and UV + hydrogen peroxide . The effects on the dissolved organic carbon content (DOC), the UV-absorbance at 254 nm (UV-abs.), the molecular size distribution, pH, and mutagenic activity were monitored, and the identity and concentrations of the most abundant gas chromatographable organic degradation products were determined. The DOC content and the UV-abs. of the water decreased substantially during treatment with. The decreases were dependent on the time of irradiation (UV dose) as well as on the H2O2 dose applied. The humus macromolecules were degraded to smaller fragments during irradiation. At higher UV doses, however, part of the dissolved organic matter (DOM) was found to precipitate, probably as a result of polymerization. Oxalic acid, acetic acid, malonic acid, and n-butanoic acid were the most abundant degradation products detected. These acids were found to account for up to 20% and 80% of the DOM in UV- and waters, respectively. No mutagenic activity was generated by the UV irradiation or the treatment. It is further concluded that the substantial mutagenic activity formed during chlorination of humic waters cannot be decreased by using UV irradiation as a pretreatment step.

Grassland degradation in the

Supported by MSS images in the mid and late 1970s, TM images in the early 1990s and TM/ETM images in 2004, grassland degradation in the "Three-River Headwaters" region (TRH region) was interpreted through analysis on IRS images in two time series, then the spatial and temporal characteristics of grassland degradation in the TRH region were analyzed since the 1970s. The results showed that grassland degradation in the TRH region was a continuous change process which had large affected area and long time scale, and rapidly strengthen phenomenon did not exist in the 1990s as a whole. Grassland degradation pattern in the TRH region took shape initially in the mid and late 1970s. Since the 1970s, this degradation process has taken place continuously, obviously characterizing different rules in different regions. In humid and semi-humid meadow region, grassland firstly fragmentized, then vegetation coverage decreased continuously, and finally "black-soil-patch" degraded grassland was formed. But in semi-arid and and steppe region, the vegetation coverage decreased continuously, and finally desertification was formed. Because grassland degradation had obviously regional differences in the TRH region, it could be regionalized into 7 zones, and each zone had different characteristics in type, grade, scale and time process of grassland degradation.

Influences of Gd on the microstructure and strength of Mg-4.5Zn alloy

Microstructure and mechanical properties of peak-aged Mg-4.5Zn-xGd (x=0, 0.5, 1.0 and 1.5 wt.%) alloys have been investigated. The results showed that the grain size of the alloys was refined gradually with increasing Gd. Mg5Gd and Mg3Gd2Zn3 phases were found in the Gd-containing alloys. The strengths were greatly improved with Gd additions, and the highest strength level was obtained in the Mg-4.5Zn-1.5Gd alloy, in which the ultimate tensile strength and yield strength were 231 MPa and 113 MPa, respectively.

Characterization of High Melt Strength Polypropylene Synthesized via Silane Grafting Initiated by In Situ Heat Induction Reaction

High melt strength polypropylene (HMSPP) was synthesized by in situ heat induction reaction, in which pure polypropylene (PP) powders without any additives were used as a basic resin and vinyl trimethoxysilane (VTMS) as a grafting and crosslinking agent. The grafting reaction of VTMS with PP was confirmed by FTIR. The structure and properties of HMSPP were characterized by means of various measurements. The content of grafted silane played a key role on the melt strength and melt flow rate (MFR) of HMSPP. With increasing the content of grafted silane, the melt strength of HMSPP increased, and the MFR reduced. In addition, due to the existence of cross-linking structure, the thermal stability and tensile strength of HMSPP were improved compared with PP.

Investigation of Degradation Behavior of Polymer on Surface of Film Due to the Existence of Monochromatic X-ray

Degradation and its temperature dependence of poly(methyl methacrylate) (PMMA) in the blend film of PMMA/SAN were investigated via ire-situ X-ray photoelectron spectroscopy(XPS). The results show that thermal degradation of PMMA takes place at 185, 130, 80 degrees C and even room temperature due to the existence of monochromatic X-ray. Furthermore, the degradation rate depends crucially on the experiment temperature.

Stabilization of poly(lactic acid) by polycarbodiimide

Polycarbodiimide (CDI) was used to improve the thermal stability of poly(L-lactic acid) (PLA) during processing. The properties of PLA containing various amounts of CDI were characterized by GPC, DSC, rheology, and tensile tests. The results showed that an addition of CDI in an amount of 0.1-0.7 wt% with respect to PLA led to stabilization of PLA at even 210 degrees C for up to 30 min, as evidenced by much smaller changes in molecular weight. melt viscosity, and tensile strength and elongation compared to the blank PLA samples. In order to examine the possible stabilization mechanism, CDI was reacted with water, acetic acid, L-lactic acid, ethanol and low molecular weight PLA. The molecular structures of the reaction products were measured with FTIR.

Hollow DNA/PLL microcapsules with tunable degradation property as efficient dual drug delivery vehicles by alpha-chymotrypsin degradation

Hollow deoxyribonucleic acid (DNA)/poly-L-lysine (PLL) capsules were successfully fabricated through a layer-by-layer (LbL) self-assembly of DNA and PLL on porous CaCO3 microparticles, followed by removal of templates with ethylenediamine tetraacetic acid disodium salt (EDTA). The enzymatic degradation of the capsules in the presence of alpha-chymotrypsin was explored. The higher the enzyme concentration, the higher is the degradation rate of hollow capsules. in addition, glutaric dialdehyde (GA) cross-linking was found to be another way to manipulate degradation rate of hollow capsules.

Novel Method for Preparation of Polypropylene Blends with High Melt Strength by Reactive Compounding

Ultrafine full-vulcanized polybutadiene rubber(UFBR) with particle sizes of ca. 50-100 nm were used for modifying mechanical and processing performances of polypropylene(PP) with PP-g-maleic anhydride(PP-g-MA) as a compatibilizer for enhancing the interfacial adhesion between the two components. The morphology, dynamical rheology response and mechanical properties of the blends were characterized by means of SEM, rheometer and tensile test, respectively.

Monitoring catalytic degradation of dye molecules on silver-coated ZnO nanowire arrays by surface-enhanced Raman spectroscopy

Catalytic degradation of organic dye molecules has attracted extensive attention due to their high toxicity to water resources. In this paper, we propose a novel method for the fabrication of uniform silver-coated ZnO nanowire arrays. The degradation of typical dye molecule rhodamine 6G (R6G), as an example, is investigated in the presence of the as-prepared silver-coated ZnO nanowire arrays. The experimental results show that such composite nanostructures exhibit high catalytic activity, and the reaction follows pseudo-first-order kinetics. Furthermore, these nanowire arrays are desirable SERS substrates for monitoring the catalytic degradation of dye molecules. Compared with traditional UV-visible spectroscopy, SERS technology can reflect more truly the catalytic degradation process occurring on the surface of the catalysts.

Adhesive strength of new thermal barrier coatings of rare earth zirconates

La2Zr2O7 (LZ) and La-2(Zr0.7Ce0.3)(2)O-7 (LZ7C3) as novel candidate materials for thermal barrier coatings (TBCs) were prepared by electron beam-physical vapor deposition (EB-PVD). The adhesive strength of the as-deposited LZ and LZ7C3 coatings were evaluated by transverse scratch test. Meanwhile, the factors affecting the critical load value were also investigated. The critical load value of LZ7C3 coating is larger than that of LZ coating, whereas both values of these two coatings are lower than that of the traditional coating material, i.e. 8 wt% yttria stabilized zirconia (8YSZ). The micro-cracks formed in the scratch channel can partially release the stress in the coating and then enhance the adhesive strength of the coating. The width of the scratch channel and the surface spallation after transverse scratch test are effective factors to evaluate the adhesive strength of LZ and LZ7C3 coatings.

NOVEL COMPOSITES OF POLY(L-LACTIDE) AND SURFACE MODIFIED BIOACTIVE SiO2-CaO-P2O5 GEL NANOPARTICLES: MECHANICAL AND BIOLOGICAL PROPERTIES

Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite.