Rumen Krastev

Bulgarian Academy of Sciences, Ulpia Serdica, Sofia-Capital, Bulgaria

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Publications (6)0.62 Total impact

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    ABSTRACT: An experimental study was conducted to investigate the influence of ageing on the morphological, thermal and mechanical properties of virgin and two types of recycled (from technological and postconsumer wastes) modified polyolefin blends. Immiscible blends of virgin low-density polyethylene (LDPE) and polypropylene (PP) in weight ratio 1:1 were modified with the ethylene–propylene diene monomer (EPDM) rubber impact modifier. The efficiency of modification was investigated as a function of modifier content in the range from 7 to 15 wt%. The blends were prepared by extrusion using a corotating twin screw extruder Brabender DSE35/ 17D at melt temperature in the range from 150 to 200�C and a screw speed of 20 rpm. Compression-molded samples were subjected to natural and accelerated ageing and characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mechanical testing.
    Journal of Elastomers and Plastics 01/2014; Vol. 46(5):427–447. · 0.62 Impact Factor
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    ABSTRACT: The research deals with the preparation and the further comprehensive characterization of metallocene polypropylene-based composite materials by incorporation of carbon black nanoparticles. Composites containing up to 10 wt% of carbon black were prepared by direct melt mixing in a single screw extruder Brabender Extrusiograph type 30/25D with attached static mixer at melt temperature of 200oC and a screw speed of 30 rpm, according to a two-step process. Some composites were treated with 3 wt% maleic anhydride grafted polypropylene (MAH-PP). The rheological behaviour of the miPP nanocomposites was determined by cone/plate rheological measurements at 180oC. The composites were characterized by SEM for morphological details and uniaxial stress-strain measurements for determining the mechanical parameters. Electric conductivity of injection molded plates from these composites was investigated. The different miPPs studied are ranked in an ascending order according to their increasing molecular weight concerning the magnitude of their rheological parameters. The maleic anhydride compatibilizer leads to lower viscosity values even at high shear gradients and to better homogenization of the nanofiller in the polymer matrix. The processing conditions, carbon black concentration and viscosity of the virgin polymer have an impact on the final conductivity of the miPP/carbon black composites.
    Macromolecular Symposia 02/2012; 311:64-69.
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    [Show abstract] [Hide abstract]
    ABSTRACT: The research deals with the preparation and the further comprehensive characterization of metallocene polypropylene-based composite materials by incorporation of carbon black nanoparticles. Composites containing up to 10 wt% of carbon black were prepared by direct melt mixing in a single screw extruder Brabender Extrusiograph type 30/25D with attached static mixer at melt temperature of 200 °C and a screw speed of 30 rpm, according to a two-step process. Some composites were treated with 3 wt% maleic anhydride grafted polypropylene (MAH-PP). The rheological behaviour of the miPP nanocomposites was determined by cone/plate rheological measurements at 180 °C. The composites were characterized by SEM for morphological details and uniaxial stress-strain measurements for determining the mechanical parameters. Electric conductivity of injection molded plates from these composites was investigated. The different miPPs studied are ranked in an ascending order according to their increasing molecular weight concerning the magnitude of their rheological parameters. The maleic anhydride compatibilizer leads to lower viscosity values even at high shear gradients and to better homogenization of the nanofiller in the polymer matrix. The processing conditions, carbon black concentration and viscosity of the virgin polymer have an impact on the final conductivity of the miPP/carbon black composites.
    Macromolecular Symposia 01/2012; 311(1).
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    ABSTRACT: Fabrication of polypropylene/carbon black composites was carried out in an original extrusion system developed in our laboratory. It consists of an extruder and a mixing die in which flow channel the polymer melt is subjected to mechanical vibrations by a moveable mandrel. Two types of polypropylene (PP) with different melt flow index (MFI) and Ketjenblack EC-300J were used for preparation of the composites. The experiments were carried out at melt temperature in the range from 170 to 210 0C varying the frequency and amplitude of vibrations. Microscopic images of the extrudates were analyzed using an image software package. They demonstrated a better dispersion of the filler in the composites produced by vibration-assisted process in comparison with the conventional extrusion without vibrations. As a result of the better dispersion of the fillers the composites prepared by the vibration-assisted process reach the percolation threshold at filler concentration of about 5.0 wt %, while the composites prepared without vibration reach this point in the range of 7.0-7.5 wt %. It was confirmed that the composites of low viscosity polymers (HT648T) have higher electrical conductivity. The better dispersion of the filler in the composites corresponds to their higher tensile strength.
    Nanoscience and Nanotechnology, Sofia, Bulgaria; 01/2011
  • Nanoscience & Nanotechnology 10; 01/2010
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    Nanoscience & Nanotechnology 8; 01/2008

Publication Stats

2 Citations
0.62 Total Impact Points

Institutions

  • 2012
    • Bulgarian Academy of Sciences
      • Institute of Mechanics
      Ulpia Serdica, Sofia-Capital, Bulgaria