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Abstract

Graphene is a very promising material for potential applications in many fields. Since manufacturing technologies of graphene are still at the developing stage, low-frequency noise measurements as a tool for evaluating their quality is proposed. In this work, noise properties of polymer thick-film resistors with graphene nano-platelets as a functional phase are reported. The measurements were carried out in room temperature. 1/f noise caused by resistance fluctuations has been found to be the main component in the specimens. The parameter values describing noise intensity of the polymer thick-film specimens have been calculated and compared with the values obtained for other thick-film resistors and layers used in microelectronics. The studied polymer thick-film specimens exhibit rather poor noise properties, especially for the layers with a low content of the functional phase.
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Abstract

Filtering nonwovens produced with melt-blown technology are one of the most basic materials used in the construction of respiratory protective equipment (RPE) against harmful aerosols, including bio- and nanoaerosols. The improvement of their filtering properties can be achieved by the development of quasi-permanent electric charge on the fibres. Usually corona discharge method is utilized for this purpose. In the presented study, it was assumed that the low-temperature plasma treatment could be applied as an alternative method for the manufacturing of conventional electret nonwovens for the RPE construction. Low temperature plasma treatment of polypropylene nonwovens was carried out with various process gases (argon, nitrogen, oxygen or air) in a wide range of process parameters (gas flow velocity, time of treatment and power supplied to the reactor electrodes). After the modification, nonwovens were evaluated in terms of filtration efficiency of paraffin oil mist. The stability of the modification results was tested after 12 months of storage and after conditioning at elevated temperature and relative humidity conditions. Moreover, scanning electron microscopy and ATR-IR spectroscopy were used to assess changes in surface topography and chemical composition of the fibres. The modification of melt-blown nonwovens with nitrogen, oxygen and air plasma did not result in a satisfactory improvement of the filtration efficiency. In case of argon plasma treatment, up to 82% increase of filtration efficiency of paraffin oil mist was observed in relation to untreated samples. This effect was stable after 12 months of storage in normal conditions and after thermal conditioning in (70 ± 3)°C for 24 h. The use of low-temperature plasma treatment was proven to be a promising improvement direction of filtering properties of nonwovens used for the protection of respiratory tract against harmful aerosols.
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Abstract

In this paper starch gelatinisation in Couette-Taylor flow (CTF) apparatus (equipped with a water heat jacket) has been investigated. CTF (characterised by the presence of Taylor vortices) provides good environment for gelatinisation, e.g. effective mixing, fast heat transfer, positive influence on starch rheological properties. During experiments starch gelatinisation degree and starch swelling has been studied. It was accompanied by temperature measurements performed along the apparatus. Additionally, starch gelatinisation was investigated by computer simulation. A complete starch gelatinisation was obtained for the shortest investigated residence time in the apparatus when the temperature in the heat jacket was above 85 °C. Nevertheless, it seems that it is still possible to reduce a residence time value, as well as, the value of Thj, but it may require some acceleration of rotor rotation. The swelling degree of gelatinised starch increased with growing values of residence time, rotor rotation and process temperature. Heat transferred could be affected by the structure of the Taylor vortex flow. No significant destruction of starch granules was observed during the treatment in Couette-Taylor flow apparatus. A quite satisfactory agreement between computer simulation and experiments results was achieved.
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