Browsing by Author "Samichkov V."

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    Characterization of gamma irradiated polypropylene with prodegradable additive
    (2017-01-01) Velev P.; Samichkov V.; Takev M.
    Compound of polypropylene that contains 1,5 % prodegradable additive D2W has been prepared using a single screw extruder. The obtained blend was grinded and injected in the form of standard specimens for tensile testing. The samples thus manufactured were irradiated with different dosage of gamma radiation up to 476 kGy. The physical, mechanical, and rheological characteristics such as tensile strength, relative elongation and melt flow index were determined in accordance with the radiation dosage applied. The effect of the gamma radiation on the structure of the oxo degradable polypropylene was examined by IR spectroscopy and X-ray diffraction analysis.
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    Investigation of the biodegradability of polymer blends consisting of polypropylene and Poly(lactic acid)
    (2015-01-01) Velev P.; Samichkov V.; Takev M.
    Foils from oxo-degradable polypropylene and poly(lactic acid) in various ratios were prepared, using a single screw extruder and a three-roll calender. The samples of the blend were subjected to aging in natural conditions and to biodegradation in composting conditions. The intensity of biodegradation of the various components was investigated through the change in tensile strength and elongation at break, as well as through Fourier transform infrared spectroscopy. It was established that the blends obtained from both polymers degraded in composting conditions, and it was possible to control the polylactide degradation and to obtain the required properties of the final products by varying the polypropylene content in the blend.
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    Physicomechanical properties of biodegradable composites, based on polypropylene and paper from old newspapers
    (2014-01-01) Takev M.; Velev P.; Samichkov V.
    This paper examines the main physical and mechanical properties ofaged and non-aged polymer composites made of a matrix filled with 10% fiberized or chopped old newspaper oxo-degradable into polypropylene. The impact of the modification of the filler with a polyvinyl acetate water dispersion and with carboxymethyl cellulose on the properties of the extrudedflatfoil made of composites was studied. Adding a lignocellulosefiller worsens the properties of the products obtained, but significantly accelerates the degradation of the composite material. The used filler modifiers improve the examined physical and mechanical properties, but increase the weather resistance of the foil products.
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    PREPARATION AND CHARACTERIZATION OF BIODEGRADABLE POLYMERIC NANOCOMPOSITES BASED ON POLYLACTIDE AND GRAPHENE OXIDE
    (2020-01-01) Velev P.; Samichkov V.; Atanasov V.; Tsvetanov K.
    A homogeneous dispersion had been prepared with a concentration of 1 % nanosized graphene oxide in ammonium hydroxide. In a simple mixer, the polylactide granulate was homogenized with varying amounts of nanosized dispersion and then dried to a constant mass. From the so-treated granulate test specimens were prepared using injection molding. The resulting nanoparticles containing graphene oxide in concentrations of 0.01, 0.05 and 0.1 % were characterized by tensile strength and elongation at break, infrared spectroscopy, dynamic mechanical thermal analyzer, X-ray diffraction, scanning electron microscopy (SEM). The results show that nanocomposites are homogeneous enough, having in mind their preparation method. Their physicomechanical characteristics are some lower than those for pure polylactide. These types of composites could find an application as a nutrient medium for definite bacterial strain.
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    Preparation and Characterization of Polylactide and Natural Rubber Based Composites with Improved Impact Resistance
    (2021-01-01) Tsvetanov K.; Velev P.; Samichkov V.
    The properties of poly(lactic acid) (PLA) based composite materials with natural rubber (NR) or epoxidized natural rubber (ENR) have been investigated in order to improve the impact strength of the polylactide. The influence of glycidopropyl- 3-methoxysilane as a compatibilizer between the polylactide and the epoxidized rubber to improve adhesion on the phase/medium boundary was investigated. The physico-mechanical properties of the resulting molecular composites have been determined, dynamic mechanical analysis and IR spectroscopy have been performed. It is established that filling PLA with low concentrations of NR or ENR significantly improves the impact strength of the resulting composite material.
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    SILVER NANOPARTICLES INCORPORATED INTO POROUS COLLAGEN SCAFFOLDS
    (2022-01-01) Samichkov V.; Mladenova B.; Diankov S.; Foteva T.; Hinkov I.
    In this work, we present a simple, rapid and cost-effective microwave-assisted method for silver nanoparticles synthesis by chemical reduction using an aqueous solution of silver nitrate, ethanol and ammonia. The effect of reagent concentrations and the heating time was investigated. Samples were analyzed through UV-Vis spectroscopy and transmission electron microscopy. Furthermore, the obtained silver nanoparticles were mixed with collagen dispersions to prepare porous scaffolds by vacuum-sublimation drying. Silver nanoparticles can adhere to the bacterial cell wall subsequently causing its death. The microbiological study showed that the collagen scaffolds with incorporated silver nanoparticles exhibited antibacterial activity against Bacillus subtilis NBIMCC 3562 and Escherichia coli NBIMCC 407 bacteria and could find potential applications in medicine.
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    STUDY OF SELF-HEALING ABILITY OF THERMOSETTING POLYMER COMPOSITES, CONTAINING HOLLOW GLASS FIBERS AND MICROCAPSULES USING ULTRASONIC NON-DESTRUCTIVE TESTING
    (2023-01-01) Samichkov V.
    This study presents a comparison of the self-healing ability of two types of thermosetting polymer composites based on unsaturated polyester resin as a matrix. The first type contains hollow glass-fiber fabric as a healing agent carrier. In the second type, microcapsules made of urea-formaldehyde condensation, containing a healing agent were introduced. In both cases butanediol diglycidyl ether was used as a healing agent. The kinetics of the healing process of studied polymer composites was estimated via alteration of Young and shear moduli (G’) during a time, using ultrasonic defectoscopy. It was found that the healing process of the micro-cracks made in the volume of composites was complete in 5 hours.