Network structure/mechanical property relationship in crosslinked dimethacrylates of different chain lengths

In this article, the syntheses of three novel dimethacrylates of different chain lengths as well as the mechanical and thermal properties of their copolymers with methyl methacrylate and styrene were studied. The monomers were prepared by the reaction of glycidyl methacrylate with dicarboxylic acid esters obtained from maleic anhydride and ethylene, 1,4‐butylene and 1,6‐hexylene glycols. The addition reaction of glycidyl methacrylate and the acidic compound was carried out in the presence of basic catalyst, tetraethylammonium bromide. The monomers were UV‐copolymerized with methyl methacrylate and styrene in the presence of a photoinitiator which was 2,2‐dimethoxy‐2‐phenyloacetophenone. The prepared polymers were subjected to different studies concerning evaluation of their flexural properties, thermal stability, dynamic mechanical behavior as well as qualitative estimation of the content of unreacted double bonds. The dependence of glass transition temperatures (T_g) as well as degree of inhomogeneity on the crosslinking density has been examined in different copolymer systems. Evidence that the dependence of the T_g on the crosslinking density is not straightforward is presented. Dynamic mechanical measurements have demonstrated that the heterogeneity of the crosslinked polymers depends strongly on the crosslinking density of the system and the nature of methacrylate monomers used. Depending on the monomer size as well as its functionality, the resultant polymer may have features such as crosslinks or residual unsaturations that influence and define the properties of the materials. It is proved that the new dimethacrylates change their functionality in copolymerization with different monovinyl monomers. Also, the degree of unsaturated bonds conversion was found to be growing with the amount of monovinyl in the copolymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of metal cations on betanin stability in aqueous-organic solutions

An effect of metal cations on betanin stability was investigated in aqueous and organic-aqueous solutions. The presence of organic solvents (methanol, ethanol, and acetonitrile) affects substantially the pigments decomposition in acidic media induced by metal cations whose degrading action in such media is significantly higher than in aqueous solutions. The influence of Cu²⁺ on the stability was studied by spectrophotometry in more detailed manner, because of its ability to form complexes with betanin. The possibility of a complex formation between betanin and Ni²⁺ was also stated at pH 7–8; its relatively high stability in aqueous samples was observed. A presence of numerous products of betanin decomposition was detected in the wavelength range 380–500 nm in spectra obtained for most of metal cations investigated, especially for higher concentrations of the organic solvents.     

Levels of 13 multi-class pesticide residues in Polish honeys determined by LC-ESI-MS/MS

Levels of 13 pesticides in 40 honey samples form Poland are reported. A rapid and sensitive method was developed for the LC-ESI-MS/MS determination of multi-class pesticide residues in honey samples. Liquid–liquid extraction (LLE) on a diatomaceous earth support (requiring the use of small amounts of organic solvent), followed by chromatographic separation on a C₁₈ column and gradient elution were employed. The method quantifies over a dynamic linear range from respective MQLs (0.06–1.3 ng/g) to 5 ng/g. Matrix effects were evaluated by comparing the slopes of matrix-matched and solvent-based calibration curves. The mean recoveries obtained for three fortification levels (0.5, 1.0 and 4.0 ng/g) were 63–117% for most compounds, with an expanded uncertainty of <10%. The results for real honey samples collected from five regions of Poland (Pomerania, Wielkopolska, Lublin Region, Lower and Upper Silesia), showed that residue concentrations were <5 ng/g and did not pose a threat to human health.     

A comparative study of a vitreous biological composition suitable for coating steel prostheses

A correlation between composition and quality of a biological glass used as a bioglaze and an industrial glaze for sheet-steel coating was carried out. Apart from the extremely different conditions, particularly relative to the temperature for application of the coating to the metallic substrate, it was noted that the compositions are not very much different; this led us to think that the doping of the vitreous system with substances favouring the bonding of glaze to support (according what has been suggested by enamellists) is trustworthy in this case too. Some hypotheses relative to the role of nickel and the fluidity of the vitreous system were made to explain the observations, and to suggest the best way to improve the adhesion of metal to glaze.     

Influence of the lubricant on temperature distribution in the forging dies

Experimental and theoretical analysis of the influence of the lubricant on the temperature distribution in the tool during forging is presented. Finite element solution of the general diffusion equation is used to calculate the heat transfer contact between the die and the hot workpiece and during the interpass times. The results of calculations are compared with the results of measurements carried out using thermocouples inserted in the die. Two ways of modelling heat transfer through the contact surface are considered. The first treats a lubricant as a separate layer with the relevant thermal properties. The second assumes a temperature discontinuity at the interface and introduces the heat transfer coefficient. Insulating properties of various lubricants are compared. White-water lubricant shows the best insulating properties. The values of the heat transfer coefficient obtained from the inverse analysis vary from 2600 (without lubrication) to 1500 W/m²K (white lubricant).     

Overexpression of the Bcl-2 protein increases the half-life of p21Bax

Bcl-2 and Bax are homologous proteins which can heterodimerize with each other. These proteins have opposing effects on cell survival when overexpressed in cells, with Bcl-2 blocking and Bax promoting apoptosis. Here we demonstrate that gene transfer-mediated elevations in Bcl-2 protein levels result in a marked increase in the steady-state levels of endogenous p21Bax protein as determined by immunoblotting in the Jurkat T-cell and 697 pre-B-cell leukemia cell lines, but not in several other cell lines including CEM T-cell leukemia, 32D.3 myeloid progenitor, PC12 pheochromocytoma, and NIH-3T3 fibroblasts. Steady-state levels of p21Bax protein were also elevated in the lymph nodes of Bcl-2 transgenic mice in which a BCL-2 transgene is expressed at high levels in B-cells. Northern blot analysis of BCL-2-transfected and control-transfected Jurkat and 697 leukemia cells revealed no Bcl-2-induced alterations in the steady-state levels of BAX mRNAs. In contrast, L-[35S]methionine pulse-chase analysis indicated a marked increase in the half-life (t1/2) of the p21Bax protein in BCL-2-transfected 697 cells compared to control-transfected cells (t1/2 > 24 h versus approximately 4 h), whereas the rate of Bax degradation was unaltered in Bcl-2-transfected CEM cells. The results demonstrate that levels of the proapoptotic p21Bax protein can be post-translationally regulated by Bcl-2, probably in a tissue-specific fashion, and suggest the existence of a feedback mechanism that may help to maintain the ratio of Bcl-2 to Bax protein in physiologically appropriate ranges.     

Removal of arsenic(III) and arsenic(V) from sulfuric acid solution by liquid–liquid extraction

Extraction of arsenic(III) and arsenic(V) from sulfuric acid solution was studied. Cyanex^® 923, Cyanex^® 925, dialkyldithiophosphinic acids (Cyanex^® 301), hydrophobic glycol (2‐ethylhexane‐1,3‐diol), and hydroxamic acids were used as extractants. The efficiency of extraction depended on extractant, diluent, valency of arsenic, and sulfuric acid concentration. Acidic reagents extracted As(III) better than As(V), while the opposite order of extraction efficiency was observed for the solvating extractants. The use of an aromatic diluent (toluene) was preferred. Toluene was found to be a better diluent for the Cyanex^® 923 and Cyanex^® 925 than Exxsol D 220/230 and octane. In the case of neo‐decanohydroxamic acids, the type of diluent had no significant effect on extraction of arsenic. The extraction of both As(III) and As(V) increased when the concentration of the sulfuric acid in the feed increased. The co‐extraction of sulfuric acid was observed. The extraction with hydroxamic acids was significantly slower in comparison to the extraction with other reagents. Extractant: arsenic species: sulfuric acid molar ratios were determined and they confirmed the composition of extracted species. Copyright © 2003 Society of Chemical Industry     

The effect of particle reinforcement on the creep behavior of single-phase aluminum

The effect of TiC particle reinforcement on the creep behavior of Al (99.8) and Al-1.5Mg is investigated in the temperature range of 150 °C to 250 °C. The dislocation structure developed during creep is characterized in these materials. The addition of TiC increases creep resistance in both alloys. In pure aluminum, the presence of 15 vol pct TiC leads to a factor of 400 to 40,000 increase in creep resistance. The creep strengthening observed in Al/TiC/15_p is substantially greater than the direct strengthening predicted by continuum models. Traditional methods for explaining creep strengthening in particle-reinforced materials(e.g., threshold stress, constant structure, and dislocation density) are unable to account for the increase in creep resistance. The creep hardening rate(h) is found to be 100 times higher in Al/TiC/15_p, than in unreinforced Al. When incorporated into a recovery creep model, this increase inh can explain the reduction in creep rate in Al/TiC/15_p. Particle reinforcement affects creep hardening, and thus creep rate, by altering the equilibrium dislocation substructure that forms during steady-state creep. The nonequilibrium structure generates internal stresses which lower the rate of dislocation glide. The strengthening observed by adding TiC to Al-1.5Mg is much smaller than that found in the pure aluminum materials and is consistent with the amount of strengthening predicted by continuum models. These results show that while both direct (continuum) and indirect strengthening occur in particle-reinforced aluminum alloys, the ratio of indirect to direct strengthening is strongly influenced by the operative matrix strengthening mechanisms. This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ASM-MSD Composite Materials Committee.