Advanced Materials Research Vol. 804

Abstract: Poly (phenylene sulfide) (PPS) was blended with polyamide 66 (PA66) in a wide range of compositions by using a co-rotating twin-screw extruder. Dynamic mechanical analysis was used in determination of the co-continuous phase. The results allowed to precisely detecting the range of co-continuity. In addition, the mechanical properties of PPS/PA66 composites can also be used to identify the dispersed/matrix phase or co-continuous phase structure.

Abstract: Positive properties of wood materials and advantages of their application substantiate the wide application of wood materials in the green building process. Latvia has forests; therefore, wood as the building material can be considered as the resource available on the local market [1,2,3]. It is one of the oldest materials, which is used in civil engineering, as its positive properties ensure the stable demand for it. Timber is the only widely available renewable material in Latvia, and this fact has a major importance for the decrease in the consumption of the non-renewable resources, therefore, wide application of wood material in the green building is a rather topical issue [4,5]. The aim of the present research is, analyzing the forest industry management in Latvia, to submit proposals for the sustainable development of the forest industry and to ensure the profitability, simultaneously considering the ecological and social aspects.

Abstract: Phthalate esters (PAEs) have been widely added as the plasticizer to increase the flexibility and ductility of polymeric materials. In this study, organic solvents, such as methanol, hexane, ethyl ether and acetone, were used for the direct extraction of plasticizers in neoprene, nitrile, and PVC gloves, under a temperature range of 20-80°C. The results showed that DEHP (Di-2-ethylhexyl phthalate) and DBP (Di-n-butyl phthalate) were analyzed in all three glove samples. The extraction capability of PAEs from the PVC gloves was the highest, while that from the neoprene gloves was the lowest. It was found that the extraction capabilities of DEHP from the glove samples were proportional to Log K_ow of the extraction solvents. This result implied that PAEs were more soluble in a non-polar solvent and likely to be extracted from the glove samples. In addition, the amount of extracted PAEs increased with the experimental temperatures. As workers wearing the chemical protective gloves, there is a need to understand the dissolution potential of PAEs in the gloves and to assess the skin exposure of PAEs.

Abstract: The microstructure, especially porosity, of PTC (positive temperature coefficient) thermistor based on BaTiO₃ was controlled with a forming pressure. The relationship between theirPTCR properties and microstructureswas investigated with an optical and SEM (Scanning Electron Microscope) images and digital multimeter. Disk samples were fabricated by pressinguniaxially at various pressures of 100~15000kg/cm² and sintering at 1265°C in reducing atmosphere and finally re-oxidizing at 700°C in air. The porosity of the samples decreased rapidly from 45% to 8% with increasing the forming pressure from 100 to 1000kg/cm²andbecame 4% at 15000kg/cm²with slowdecreasing of porosity in the pressure range of 1000~15000kg/cm².With increasing the forming pressure, the resistivity jump of samplesdecreased rapidlyfrom 0.5 to 2.9 at about1000kg/cm²that corresponds tothe porosity of 15% and was saturated above this pressure. It is considered that there is a critical amount of porosity for having PTCR effect, which was about 15% in our samples. In addition, the porosity of the sample has a greater influence on the resistivity jump than on theresistivity at room temperature, which is due to the oxidation of grain boundary through a favorable channel of oxygen such as a pore.

Abstract: Composite microspheres of polystyrene and nanoFe3O4 particles were prepared through emulsifier-free polymerization with ultrasonic dispersion. The properties of composite microsphere were investigated by FT-IR spectrum, X-ray diffraction analysis, TEM, SEM and VSM. The determine results showed that Fe₃O₄ particles prepared by coprecipitation in lab were about 7~8 nm and with a narrow size distribution and superparamagnetic characteristics. The composite microsphere of polystyrene and Fe₃O₄ showed a diameter around 20~30 nm under TEM and SEM. The data of XRD indicated crystal forms of Fe₃O₄ in the composite microsphere did not change. The XRD spectrum of composite microsphere was a overlap of Fe₃O₄ crystal and amorphous polystyrene. The result of hysteresis curve indicated that the composite microspheres still had superparamagnetic characteristics.

Abstract: This paper is devoted to the use of Phase Change Materials as a cement concrete modifier in Middle East climate. Due to large amplitude of daily air temperature in these conditions, Phase Change Materials can be used to reduce the dynamic of thermal peak in an ageing concrete. Partial results of studies to determine the influence of various factors on the effects of modifications are presented

Abstract: Gas-sensing elements based on Ag-containing polyacrylonitrile (PAN) films using different temperature and time modes of a two stage IR-pyrolysis have been fabricated. It has been investigated that the gas sensitivity of the samples depends on the composition of the original film-forming solution and on the process parameters of forming the film material. It has been studied that the samples demonstrate gas-sensing properties to Cl₂ at room temperature. The outcome of this study is that Ag-containing PAN films can be considered as one of the most promising material to be used in electronic engineering.

Abstract: The purpose of this study was to investigate the effect of liquid polishing system (BisCover) on color stability of the bleached enamel upon exposure to a staining agent-red wine. Forty specimens were prepared. They were divided into 2 groups and different procedures, including only bleaching with Opalescence PF (PF) or Opalescence regular (R) gels, and application of BisCover after blaeching (PF-B, R-B) were used. Unbleached specimens were served as control groups (control-1 and control-2). The specimens were stored for 48 h in red wine. The color of all specimens was measured before and after exposure with a spectrophotometer, and total color change (ΔE*) were calculated. The data were analyzed with a one-way ANOVA and the means were compared by Tukeys post hoc analysis (α=0.05). PF-B and R-B groups demonstrated significantly less color change than PF and R groups. the control-1 and control-2 groups had the least color change. No significant difference were observed between PF and R group. BisCover improved the color stability of bleached enamel in red wine.

Abstract: Materials that exhibit negative Poissons ratio are called auxetic materials. Although such materials are quite rare, they nevertheless exist as naturally occurring materials and artificially made materials. Due to their unique material properties, auxetic materials have been intensively investigated for the past 20 years. This paper studies the effect of auxeticity on the maximum stresses in spherical shells. The results suggest that auxetic materials are not suitable for shells with built-in edge, but highly suitable for shells that are simply supported. For the latter boundary condition, it was found that the ratio of maximum bending stress to the maximum membrane stress diminishes as the Poissons ratio of the shell material approaches-1. This means that under the boundary condition of simple supports, a geometrically thick shell is mechanically equivalent to a thin or membrane shell, and therefore the use of membrane shell theory suffices even for a reasonably thick shell if the shell material is highly auxetic.

Abstract: Sliver wire was the novel material to replaced gold wire in wire bonding process, and rare earth element was often added to improve the properties of silver wires. The annealing effect (at 225°C~275°C for 30min) on the tensile mechanical properties of silver wires with φ=20μm was investigated. In addition, the microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Free-air ball (FAB) of 85μm diameter from 20μm diameter pure silver wire was too huge for bonding process, otherwise the silver wire was added 0.05 wt.% lanthanum to form Ag-La alloy wire to reduce the diameter of FAB. FAB of Ag-La alloy wire with a 55μm diameter, and can avoid short-circuited. In addition, microstructures, tensile properties and the micro-hardness of Ag-La alloy wires indicated that the best annealing temperature was 425 °C.