Browsing by Author "Velev P."

Now showing 1 - 10 of 10
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    A study of the influence of the composition and the design of polyvinyl chloride profiles for doors and windows on energy efficiency
    (2014-01-01) Naydenova P.; Velev P.
    Energy efficiency requirements for new buildings demand the creation of new technologies for the production of rigid PVC profiles. The operational production line ``Weiss profile, Ltd. ``was used to study the influence of different brands stabilizers, modifiers, fillers and pigments on the performance properties offinished products. The influence on the energy efficiency of the relative density of the material is presented, as well as the number of chambers in the profile design. The performance properties ofproducts with a surface layer of fresh material and a core ofrecycled orfoam material, that provide a greater thermal resistance of the finished window system, have been studied also.
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    An investigation on the possibility of fiberglass manufacture using a matrix obtained from water diluted mixtures of unsaturated lyester and polyurethane resins
    (2017-01-01) Matev A.; Velev P.; Herzog M.
    Four types of matrices obtained from a mixture of unsaturated polyester resins diluted by water and a waterdispersible polyurethane-acrylate oligomer ((Bayhydrol® UV 2317) of different percentage (20 %, 40 %, 60 %, 80 %) are used for production of glass reinforced composites. Then composites are obtained from the matrices mentioned above and glass fabric of a weight of 81g/m2 and 163 g/m2. The physical properties of the composites prepared are investigated by ATR- FTIR. Some mechanical properties, such as tensile strength, elongation at break and thermal properties of the composites are measured. Specific matrices are selected as they are suitable for composites preparation. The latter can be used for fiberglass production. Future study is required aiming to decrease the styrene emissions during lamination and curing.
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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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    Development And Verification Of Mechanical Characteristics Of A Composite Material Made Of A Thermoplastic Matrix And Short Glass Fibers
    (2021-01-01) Isametova M.; Abilezova G.; Dishovsky N.; Velev P.
    The paper presents the results of computer modeling and prediction of the mechanical properties of composite materials with a polycarbonate matrix filled with short glass inclusions. At the micro-level, the influence of the volume of inclusions on the mechanical properties of the designed composite based on polycarbonate matrix is studied in the DIGIMAT (France) program. It was found that with a ratio of the sizes of inclusions in the range of 468÷60, the particles have a needle shape, and the material with such inclusions has a higher stress limit and elastic modulus than with a shape coefficient less than 50. The components of the fiber orientation tensor were also determined, at which the values of computer modeling are in good agreement with experimental data. The influence of the size of the finite element grid on the characteristics of the composite at the macro level was studied, and recommendations were given for choosing the size of the face of the finite element. The adequacy of computer models was confirmed by the results of field tests. The paper presents the results of testing flat samples made by injection molding technology. Mechanical tests were carried out for three variants of samples made of composite material based on a polycarbonate matrix with 10 %, 20 % and 30 % inclusions. The discrepancy between the experimental and computer results for samples with 10 %, 20 % content of short chopped fibers is explained by the influence of technological factors on the properties of the material at the macro-level. The conducted research allowed us to develop a computer modeling technique used at the stage of development of polymer composites based on thermoplastic matrices with short glass inclusions
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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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    Novel magnetic composites based on water soluble unsaturated polyester resin and iron oxide nanoparticles
    (2016-06-01) Velev P.; Bryaskova R.
    Magnetic nanocomposites on the basis of water soluble unsaturated polyester resin filled with different amount of iron oxide nanoparticles have been successfully prepared. The mechanical properties of thus prepared composites as tensile, impact and flexural strength were determined. The specific volume and surface resistance of the magnetic nanocomposites were also determined.
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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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    PROPERTIES OF GLASS-FIBER REINFORCED POLYCARBONATES FOR CENTRIFUGAL PUMPS IMPELLERS
    (2022-01-01) Isametova M.; Dishovsky N.; Velev P.; Duisengali A.
    A significant number of properties of composites based on polycarbonates, unfilled and filled with 10 - 30 % short glass fibers of E-glass, treated with 3-(aminopropyl) triethoxy silane, were studied. The purpose of the study is to determine whether these composites can be used to manufacture impellers for centrifugal pumps. It was found that with increasing the amount of filler, the properties of polycarbonate composites change as follows: in general, the physico-mechanical parameters (all modules, tensile strength), stiffness and flexural strength increase, maximum deformation, as well as elastic and impact resistance decrease somewhat. The volume and surface resistivity decrease, the coefficient of thermal conductivity increases. The main reason for these changes in the properties of the composites is the good adhesion at the polymer matrix-fiber interphase which is attributed to the strong physical interaction due to silane used and as a result of the good wetting of the fibers from the polycarbonate matrix and improved compatibility. Based on the results obtained, it can be concluded that polycarbonate composites, filled with 10 - 30 % short glass fibers can be successfully used for the production of centrifugal pumps impellers, as they meet a significant number of requirements for materials with such application.