The effect of fillers on relaxation phenomena of vulcanized styrene–butadiene elastomers

Standard recipe mixtures, based on styrene/butadiene rubber SBR 1500 and oil-extended SBR 1712, with varying amounts of carbon black, silica, or kaoline fillers were prepared and the stress relaxation curves of vulcanized samples were determined. The measurements were restricted to slow relaxation phenomena, observed after 50% initial elongation. Three λ-processes and a fourth ?-process, existing only in filled rubbers, were observed. The relaxation times and activation energies, determined graphically, reflect the amount and activity of the fillers. All relaxation times are lower for filled vulcanizates and decrease with increasing temperature; however, the type of filler does not affect the activation energy. The higher parameters observed for the ?-processes are discussed in terms of filler particle mobilities and rearrangements and of filler/rubber contact layer phenomena. © 1994 John Wiley & Sons, Inc.     

Principal mycotoxins in wheat flour from the Serbian market: Levels and assessment of the exposure by wheat-based products

The presence of eleven principal mycotoxins from the wheat flour bought in supermarkets in Novi Sad, the capitol of the northern Serbian province of Vojvodina, was determined. The samples were prepared by simple one-step method and analyzed by ultra-high performance liquid chromatography with heated-electrospray ionization triple quadrupole mass spectrometry (UHPLC/HESI-MS/MS). Deoxynivalenol (DON) was the predominant mycotoxin for all analyzed samples followed by zearalenone (ZON) and T-2 toxin, with frequency of occurrence: 88.7%, 33.3% and 26.7%, respectively. Aflatoxins (AFs), ochratoxin A (OTA), HT-2 toxin, fumonisins B1 (FB1) as well as B2 (FB2) were below the limit of detection. All the samples complied with current European/Serbian legislation, except one sample that exceeded the DON maximum level of 750 μg/kg. In addition, mycotoxin intakes through consumption of wheat-based products were estimated for average adult consumers based on Serbian market basket and then compared with the tolerable daily intake (TDI) proposed by Scientific Committee on Food of the European Union. The calculated intakes of ZON and T-2 were lower than the respective TDIs. However, intakes of DON were assessed to be close to the level of TDI for adults. This is the first study on the intake assessment for mycotoxins present in the wheat flour through the consumption of wheat-based products on the Serbian market.     

Modified softwood sawdust as adsorbent of heavy metal ions from water

The sawdust of deciduous softwood-poplar, and coniferous softwood-fir, have been found to possess some adsorption capacities for heavy metal ions. Their adsorption capacities can be increased by previous treatment with a sodium hydroxide solution. Adsorption capacities of alkali modified adsorbents were higher than for unmodified ones from 2.5 to 5 times for copper ions, and about 15 times for zinc ions. Also, for modification can be used solution of sodium carbonate, but that alkaline solution is less efficient than sodium hydroxide solution. The 1% sodium hydroxide solution is suggested for modification of softwood sawdust. It was established that the ion exchange is not only adsorption mechanism, than microprecipitation of metal-hydroxide in the pore liquid was happened, too. At the same time, the leaching of organic matters from modified softwood sawdust were less than from unmodified ones for about 7% for poplar and 23% for fir.     

Epidemiology of end‐stage renal disease and hemodialysis treatment in Serbia at the turn of the millennium

The study presents the epidemiological features of patients treated with renal replacement therapy (RRT) in Serbia from 1997 to 2009 and compares the results of hemodialysis treatment in 1999 and 2009. Epidemiological data were obtained from the National Registry of RRT patients and data on hemodialysis treatment from special surveys conducted in 1999 and 2009. Within the period 1997–2009 the incidence of patients on RRT increased from 108 to 179 per million population (pmp), prevalence rose from 435 to 699 pmp, while mortality rate fell from 20.7% to 16.7%. The frequency of patients with glomerulonephritis decreased, while that of patients with diabetes and hypertensive nephropathy increased. In late 2009 there were 5208 patients receiving RRT in Serbia. Within the examined period new hemodialysis and reverse osmosis equipment were purchased, high‐flux dialyzers with synthetic membranes were increasingly used and the number of patients receiving hemodiafiltration increased to 17.6%. Kt/V greater than 1.2 was recorded in 16% of the patients in 1999 but 52% in 2009. Options for correction of anemia and mineral disorders have also improved. The percentage of patients with HbsAg (13.8% vs. 4.8%) as well as anti‐hepatitis C virus antibodies positive patients (23.2% vs. 12.7%) was significantly lower in 2009 than in 1999. Both the incidence and prevalence of RRT patients in Serbia are rising continuously, while the mortality rate is falling. More favorable conditions for dialysis treatment have brought about significant improvement in the results over the last 10 years.     

Combustion characteristics of wheat straw in a fixed bed

Combustion of wheat straw was investigated in a fixed-bed reactor for two air flow rates, 1,151 and 2,125 kg/m²h. Measured temperatures, mass loss, and gas composition were used to evaluate the combustion characteristics in terms of ignition front speed, burning rate, and quality of combustion in general. At lower value of air flow rate difference between the ignition rate and burning rate was significant, which can be easily noticed by the measurement results. At higher value of air flow rate, there was still a small difference between the ignition and burning rate, while the content of oxygen in the flue gas was 10%, which leads to the conclusion that a change in the method of delivering the combustion air is necessary.     

Intergranular Nanostructure Effects on Strength and Toughness of Si3N4

Strength, toughness, microstructure, and atomic adsorption arrangement in silicon nitrides with MgO and RE₂O₃ additions (RE = La, Gd, Y, Lu) were examined. Mechanical properties were high for La, Gd, and equal La–Lu additions, but surprisingly were progressively lower for Y‐ and Lu‐doped samples. The lower strength and toughness were associated with fewer visible crack deflections and grain bridges. Detailed microstructural analysis of the Lu‐doped material revealed a complex intergranular nanostructure with variable Lu content and Si₃N₄ nanocrystals. Furthermore, the Lu‐rich areas showed an extra Lu‐adsorption site on the Si₃N₄ prismatic planes not previously observed in other studies. This inhomogeneous structure was attributed to grain growth impingement and higher viscosity of the Lu‐doped oxynitride glass that slows homogenization. The Y‐doped material with nearly identical glass viscosity demonstrates intermediate behavior. Finally, substituting half of the Lu₂O₃ with La₂O₃ resulted in a homogenous intergranular structure, attributed to a lower viscosity of the oxynitride glass phase, and high mechanical properties. Overall, care must be taken when adapting Si₃N₄ processing parameters for the smaller ionic radius rare earth dopants such as Lu and Y.     

Potential Barrier of (Zn,Nb)SnO2‐Films Induced by Microwave Thermal Diffusion of Cr3+ for Low‐Voltage Varistor

The effect of Cr³⁺ on the electrical properties of SnO₂‐based films deposited by electrophoresis on Si/Pt substrate was considered. The films were sintered in a microwave oven at 1000°C/40 min and then the surface was modified with deposition of Cr³⁺ ions by electrophoresis. The diffusion of Cr³⁺ contributes to the modification of the potential barrier formed on the grain boundary improving the electrical properties due to electron acceptor species adsorption on the grain boundary. The influence on the properties of grain boundary was verified by I versus V characterization in as a function of temperature. The films showed nonlinear coefficient over 9, potential barrier height over 0.5 eV and resistivity greater than 10⁷ Ω·cm. 4 samples were prepared at same conditions and presented similar electrical behavior, showing the efficiency of technique on reproducibility to varistor properties control. Thereby the nonlinear coefficient increases while decreasing the conductivity of the system is noticed.     

Structural Changes in the Fabrication and Ageing of PA66 Textured Yarn

Summary: The characterization of textured yarn is of great significance for both producers and final users. The influence of the texturing parameters (draw ratio and heater temperature) on the characteristics of the textured polyamide yarn has been investigated in this study. Textured yarn was characterized by the degree of orientation, degree of crystallinity, breaking characteristics, shrinkage, elasticity characteristics, the contents of the end groups and degree of whiteness. It was observed that the mentioned characteristics changed as a function of time. The influence of yarn ageing on its characteristics was assessed. The parameters of polyamide textured yarn structure were determined by DSC.

Reflectance curve changes after ageing of PA 66 yarn.