Browsing by Author "Kandeva M."

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    Friction behavior produced in the course of a contact enabled between composite materials and eco-friendly soles prototypes made of elastomeric material with regard to ice-covered surface
    (2019-03-01) Kandeva M.; Dishovsky N.
    The subject matter of the present research constitutes a study of the technique of friction between samples and prototypes of soles made of composite materials comprising natural rubber characterized with ingredients originating from renewable sources produced in the course of their contact with an ice surface. Methods and devices were developed in order to investigate the static and dynamic friction force and the change with regard to frictional force in the event of contact with regard to three varieties of forms of ice: melting ice (ice with a layer of water on it, temperature: 0 to 1 °C), wet ice (temperature: - 4° -5° C) and dry ice (temperature: - 10° - 12° C). Coefficients of static and dynamic friction, along with change of the friction coefficient were obtained for 14 types of elastomers and ingredients from renewable sources - natural rubber, silicon dioxide extracted from the process of burning rice husks and microcrystalline cellulose, and using rapeseed oil as a technological additive. It has been ascertained and concluded that all tested materials have demonstrated highest friction coefficient in the event of contact produced with dry ice being the maximum coefficient of friction equal to 0.61. The most unfavorable and dangerous hypothesis for exposure of pedestrians to the effect of on an ice- covered surface are the cases of contact with wet ice and melting ice. There is no correlation of the coefficient of friction for the different materials under conditions of dry ice, wet and melting ice. The composites with the highest coefficient of friction under circumstances of wet and melting ice have been used to produce prototypes of soles, having identical pattern, and experimental results were obtained for the coefficients of friction and the friction coefficient change /rise/ in the event of contact produced with regard to dry, wet and melting ice. By means of implementation of the 3D printing technology, patterns of footwear soles with identical dimensions were made of the same material but with different patterns and results were obtained for the impact of the pattern on the static and dynamic coefficient of friction produced in the course of a contact with an ice surface in its three relevant states - dry, wet and melting ice. The implementation of this study has been funded by the Operational Program 2014BG16RFOP002 - Innovation and Competitiveness, Procedure: BG16R-FOP002-1.002 - Support for the development of innovations by start-ups, Grant Agreement BG16R-FOP002-1.002-0028-C01 Eco-footwear soles on elastomeric basis with improved ice and snow grip.
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    Studies on natural rubber based composites filled with products from renewable resources with improved adhesion to icy surfaces
    (2018-01-01) Dishovsky N.; Mitkova F.; Angelov Y.; Kandeva M.; Vladimirova L.
    Slips and falls on icy surfaces can cause serious injuries of people. The primary risk factor for slipping incidents is undoubtedly the decreased friction coefficient between the shoe sole and the ice or snow surface. Nowadays environmental protection has been gaining significance and becoming highly important for the various innovation strategies. In rubber industry the concept of environmental protection is more often associated with the maximum use of elastomers and ingredients from renewable sources in the manufacture of rubber products. The aim of this work is to investigate the possibilities of using elastomers and ingredients from renewable sources - natural rubber, silica obtained by rice husks incineration and microcrystalline cellulose - as fillers and rapeseed oil as a process additive in compositions, intended for the manufacture of soles for winter footwear having an increased coefficient of friction to various types of icy surfaces. Dynamic mechanical thermal analysis has been used to predict the adhesion of the materials to ``dry ice``, ``wet ice`` and melting ice. It has been found that, in all the cases examined, the composites containing natural rubber and a combination of microcrystalline cellulose (20 phr) and silica (40 phr) as fillers are the most suitable for the purpose. The silica used can be both synthetic and from renewable sources. The tribological tests carried out have confirmed these composites under the conditions of ``dry ice`` and ``wet ice`` fall into the class of the highest resistance against slip but on melting ice they do not have the necessary degree of resistance. It is believed that the use of a polar elastomer and hydrophobilizing the surface of microcrystalline cellulose particles will solve the problem.