Browsing by Author "Nedkova M."

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    Investigation of long time stored propellants
    (2014-01-01) Nedkova M.; Shishkov P.; Serafimova E.; Dishovsky N.
    An investigation of double based propellants and pyroxiline, produced before the year 2000 was carried out. The process of ageing during long time storage of single and double-based propellants and pyroxilin in non heated military stores and in heated building at room temperature was studied by elemental analysis (EA). The velocities of burning were measured by DSC and the decomposition energy of the propellants was calculated. Obtaining of a shift of the bands, con-nected by hydrogen bonds formation between the obtained-OH groups at the place of-ONO2 groups after ageing was confirmed by FTIR spectroscopy.
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    THE INFLUENCE OF ACID DYES UPON SOME STRUCTURAL AND PHYSICO-MECHANICAL INDICES OF POLYAMIDE FIBRES
    (2005-09-01) Nedkova M.; Pavlov P.; Pishev D.
    The influence of three acid dyes upon some physico-mechanical indices of polyamide multifilament yarn has been studied as a consequence of the structure modifications which occur during the dyeing process. It has been established that, irrespective of the differences in the chemical composition of the dyes, the modifications in the properties of the samples used are quite similar. Some structural characteristics, tenacity and elongation at break, crease resistance and the critical time of dissolution, have been determined. The dependencies of the indices listed on the dye concentration are of a complex character, which reflects the gradual penetration of the dye molecules into the inter-fibrillar and intra-fibrillar amorphous areas of the structure which are different in solidity. The fluctuations in the course of the dependencies in the area of the lowest concentrations are the result of the combined influence of the processes of improvement of the crystal phase and the relaxation phenomena, occurring in the most accessible amorphous areas of the fibrous structure. With the increase in the dye concentration, the so-called ‘cross-linking effect’ starts to appear, as a result of the formation of intermolecular links of the polymer-dye-polymer type, which influence the properties under investigation in a characteristic way. The increase in the dye presence in the substrate provokes the repeated alternation of the above-mentioned phenomena in the thicker amorphous areas of the samples, with a pronounced influence of the ‘cross-linking effect’ in the highest concentrations.