Browsing by Author "Malinova P."

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    Biogenic amorphous silica as filler for elastomers
    (2018-06-01) Dishovsky N.; Malinova P.; Uzunov I.
    Natural products from agricultural wastes are finding importance in the polymer industry due to their many advantages such as being lightweight, low cost and environmentally friendly. In the present study the potential of the two types of rice husk ash (RHA) prepared under different conditions as fillers in natural rubber-based elastomer composites was investigated. The fillers were prepared by rice husks incineration and characterized by means of X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) specific surface area, Hg-porosimetry and N2-adsorption. The evaluation involved determining the vulcanization characteristics of the compounds and their physical and mechanical characteristics, resistance to thermal aging as well as the dynamic properties of the vulcanizates containing RHA. It has been found that the ash from rice husk has good potential as filler in elastomers, especially as a substitute for synthetic commercially available silica. RHA improves the grip on ice and snow better than standard silica and may be used in formulations for shoe soles used for winter sports, extreme hiking footwear, ski boot soles, winter tire protectors, etc. Its quality depends on the conditions under which rice husk is incinerated. It is recommended to run the process at a temperature not higher than 800 Ā°C. In particular, cases in which the vulcanizates contain biogenic silica have very interesting characteristics like improved modulus at 300% of elongation, lower residual elongation, higher mechanical loss angle tangent at 0 Ā°C and lower at 60 Ā°C, and are superior to those of the vulcanizates containing commercially available filler UltrasilĀ® 7000 GR.
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    COMPOSITES OF WASTE RUBBER VULCANIZATES AND MODIFIED ADHESIVE SOLUTIONS TO CREATE CONTINUOUS COATINGS
    (2021-01-01) Dishovsky N.; Delchev N.; Ivanova N.; Malinova P.; Lachev A.
    Composites of waste rubber vulcanizates and polyurethane-based adhesive solutions have been developed, containing a waste sunflower oil as a modifying additive, intended for use as seamless floorings. The floorings are made in two versions: in laboratory conditions and in real conditions. The floorings of both variants are characterized by a number of important performance parameters: mechanical properties - in terms of tension and pressure, glass transition temperature, shock absorption according to head injury criterion (HIC) and criterion for maximum value of dynamic impact of free fall acceleration (G), potential elastic energy and energy density. It was found that the most important factors for the formation of the characteristics of the composites are the size, the specific surface of the rubber crumbs, respectively, the chemical nature of the adhesive used, the amount of the adhesive solution and the amount of the modifying additive. Based on the HIC and the G criteria, it is concluded that the created seamless coating has a safe fall height of 1 meter and can be used to cover playgrounds and sports facilities.
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    EFFECT OF MODIFIED PYROLYSIS CARBON ON THE PROPERTIES OF ELASTOMER COMPOSITES BASED ON STYRENE-BUTADIENE RUBBER
    (2022-01-01) Malinova P.
    Recycling of waste car tires is important from an economic and environmental point of view. There are various methods for their recovery, one of which is pyrolysis. This study reports on modifying pyrolysis carbon black obtained from waste car tires with hydrochloric, nitric and a mixture of the two acids. As a result of the demineralization, the ash content in the pyrolysis carbon black has been reduced four times, and the zinc oxide content has decreased more than 20 times. Modified and virgin pyrolysis carbon black have been used to fill SBR-based elastomeric composites. For a comparison, commercial PM-15 carbon black has been used. A number of characteristics of the composites thus prepared have been studied. The stress at 100 % and 300 % elongation has increases in the vulcanizates containing modified pyrolysis carbon black compared to that of vulcanizates containing virgin pyrolysis carbon black and to the reference sample. The tensile strength of all vulcanizates containing modified pyrolysis carbon black is higher than that of the vulcanizates containing virgin pyrolysis carbon black. The observed effects are associated with the reduced ash content in pyrolysis carbon black upon the modification and with its enlarged specific surface area.
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    Effect of the modified solid product from waste tyres pyrolysis on the properties of styrene-butadiene rubber based composites
    (2014-01-01) Delchev N.; Malinova P.; Mihaylov M.; Dishovsky N.
    Being resistant to moisture, oxygen, ozone, solar radiation, microbiological degradation, etc., waste car tyres and their deposition present a great environmental problem. Pyrolysis is an environment-friendly process for their recycling. This paper presents data referring to the study of the effect of the solid product from waste tyres pyrolysis on the properties of styrene-butadiene rubber (SBR) based composites. It is found that the further modification of the pyrolysis carbon black decreases two times the ash content and six times the zinc oxide concentration in the ash but the curing characteristics of the investigated SBR based compounds remain unaffected. The values of the modulus 100, the tensile strength and Shore A hardness of vulcanizates containing modified pyrolysis carbon black increase, while the elongation at break and the residual elongation decrease slightly. The effects observed are related to the decreased ash content of the pyrolysis carbon black following the modification as well as to the increased silicon oxide concentration in the remaining ash.
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    Investigation of elastomers ratio influence in the composites for truck tires treads production
    (2022-01-01) Malinova P.; Ilieva N.; Metodiev V.
    An experimental design of model tread compounds for truck tires treads was carried out to test the possibilities for optimizing the ratio between the combination of elastomers (butadiene styrene rubber, isoprene rubber and butadiene rubber) used in their compositions. The experiment was designed using a Scheffe simplex lattice. The target functions, object of the optimization problem, are the main characteristics of the obtained vulcanizates: abrasion, stress at 100 % elongation, stress at 300 % elongation, tensile strength, elongation at break, residual elongation and Shore A hardness. The optimization was performed in the barycentric factor space with limits of variation of all factors from 0 to 1. Since the seven target functions obtain their extreme values at different points, a generalized criterion for optimality is formulated using the desirability function. The composition of the rubber compound at which this function receives its maximum has been established.
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    Microwave properties of natural rubber based composites containing carbon black-magnetite hybrid fillers
    (2018-04-25) Al-Ghamdi A.; Al-Hartomy O.; Al-Solamy F.; Dishovsky N.; Malinova P.; Shtarkova R.
    The paper presents the synthesis and characterization of a carbon black-magnetite hybrid filler. The complex study on the structure of the filler has shown the magnetite phase to be distributed both over the surface (inter-aggregately) and inside (intra-aggregately) the carbon black particles, thus forming a true hybrid material. The results from the investigations on the mechanical and microwave properties of natural rubber-based composites filled with the new hybrid filler have been also reported. They have been compared to those of a composite comprising the physical mixture of carbon black and magnetite (at the same ratio as in the hybrid filler). The determined microwave characteristics of the composite comprising the hybrid filler obtained reveal the possibility for its use in manufacturing elastomer-based microwave absorbers.
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    PERFORMANCE AND TECHNOLOGICAL MODEL FOR PRODUCTION OF SOUND- AND SHOCK-ABSORBING COMPOSITES ON THE BASIS OF WASTE ELATOMERIC MATERIALS
    (2020-01-01) Dishovsky N.; Delchev N.; Ivanova N.; Mihaylov M.; Malinova P.; Lachev A.
    The aim of the present work is to investigate the possibilities of using waste sunflower oil as a modifying additive in order to eliminate some disadvantages of polyurethane adhesives used in the production and performance of insulating composites from ground waste rubber vulcanizates. A composition and a technological model for the production of sound- and shock-absorbing composite material have been developed as a result of the present study. A positive effect of the modifying additive on the technological process and the properties of the composite materials has been established. It is attributed to the composition of the waste sunflower oil comprising different types of fatty acids. The conducted tests and the obtained results give grounds to believe that the composite material developed can find applications as a sealing element in railways of rail and tram transport, in construction for sound insulation of buildings, as well as for covering childrenā€˜s and sports grounds.