Browsing by Author "Zheleva D."
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Item In vitro bioactivity of Polyurethane/85S Bioglass composite scaffolds(2013-09-01) Radev L.; Zheleva D.; Michailova I.In the present work Polyurethane (PU)/Bioglass (BG) composite materials were synthesized with different content of BG (10 and 20 mol.%) as filler. The 85S Bioglass was synthesized via polystep sol-gel method. The chemical composition of BG is 85SiO2-10CaO-5P2O5 (wt.%). The synthesis of PU was carried out by a two-step polyaddition reaction. The 85S BG was added in situ during the polymerization reaction. In vitro bioactivity of the prepared composites was examined in the presence of 1.5 SBF for 7 days in static conditions. The structure of synthesized PU/BG composites before and after in vitro test was determined by XRD, FTIR and SEM. XRD of the samples before in vitro test proved that the phase of γCa 2P2O7 in the PU/20BG is visible. FTIR revealed the presence of urethane bond between OH-(from BG) and NCO groups (from PU). Based on FTIR results after in vitro test in 1.5 SBF solutions, A/B-carbonate containing hydroxyapatite (CO3HA) was formed. XRD proved that HA was formed on the surface of the samples, but Ca2P2O 7 does not undergo any changes in the 1.5 SBF solution. SEM depicted the nano-HA agglomerated in spherical particles after immersion in 1.5 SBF for 7 days. © 2013 Versita Warsaw and Springer-Verlag Wien.Item Influence of the measuring conditions on the rheological properties over the ``bounded`` rubber concentration in rubber compounds(2013-05-22) Zheleva D.; Ginev I.The purpose of present work is to investigate the influence of measuring conditions on the rheological properties of filled rubber compounds in presence of different amountsof stearic acid over the ``bounded`` rubber concentration. The measurements were performed at different revolutions per minute of Brabender Plasticorder rotors in the mixing camera, respectively 0, 3, 10, 20 and 30 min-1. After the measurements the concentration of ``bounded`` rubber was determined.The obtained dependencies (concentration of ``bounded`` rubberat different rotor revolutions) are quite complex and is affected both by the amount of stearic acid and the revolutions of rotors in the mixing camera during the torque measurements. This diverse change of the concentrations of ``bounded`` rubber in the compounds after the measurement explains smaller variations in torque maximum compared with the effective viscosity. These results are due to the fact that in the camera a further intensive homogenization of the compound ingredients is carried out as well as further dispersion of carbon black in it. Such processes cannot be observed in capillary viscometer.Item Influence of type of pre-hair treatment from different types of animal sources on the degree of hydrolysis of keratin(2020-01-01) Zheleva D.; Koleva M.Keratin biomaterials have many different advantages over other biomolecules. A number of techniques have been studied to prepare keratin hydrolysates. Many of them use strong reagents and the processes take place under very drastic conditions. The present study focuses on the following aspects: Producing keratin hydrolysates from various animal sources; application of various methods for extraction; comparison of the type of treatment over the degree of hydrolysis. Sheep wool samples were used, respectively native and alkaline pre-treated and samples of goat hair, respectively native and enzyme pre-treated. The methods used for the hydrolysis of keratin materials are: 1) by sulfotolysis with sodium pyrosulfate and urea; 2) with thioglycolic acid and 3) with sodium hydroxide. The obtained hydrolysates were characterized by qualitative reactions, spectrophotometric and FTIR analysis. It was found that the samples from one and the same animal source show very different properties and different degrees of hydrolysis. The highest degree of hydrolysis was achieved for the pre-treated samples. It was proved that the method of hydrolysis with NaOH is the most appropriate for sheep wool and to a much greater extent for the alkaline treated wool than for the native. The reducing agent: Sodium pyrosulfate and urea is the most appropriate for enzyme pre-treated samples of goat skin. Therefore, pre-treatment of animal hair samples facilitates the hydrolysis process and makes it easier to break disulfide bonds. The disadvantage of proteins, and in particular keratins, is the difference in the structure of macromolecules, which are obtained from different animal sources. Therefore, this requires a specific approach to the hydrolysis of keratin from each individual animal source.Item Mechanisms of interaction between the components in adhesive compositions based on chloroprene rubber(2013-11-05) Zheleva D.The aim of this study is to investigate the mechanisms of interaction between the components in adhesive compositions based on chloroprene rubber (CR) during the formation of an adhesive joint. Investigations are made on the influence of the phenol-formaldehyde resin amount, of the rubber compounds processing regime, of reaction conditions, and of interactions occurring between the rubber and the other components within the adhesive compositions, on the adhesive properties of the polychloroprene adhesives. A comparison between the data from mechanical tests and the data from FTIR and rheological studies of these adhesives is provided. The IR spectroscopic results prove that adding the resin to the rubber on the rolls during the mixing process favors the creation of physical and chemical interactions between the resin and the rubber and the rest of the components of the adhesive composition. The necessary minimum resin amount as an agent improving the compatibility between the associates of the oxides and the chloroprene rubber, and the associates of the rubber itself, is determined.Item METHODS FOR MODIFICATION OF COTTON FABRICS WITH GELATIN - GLUTARALDEHYDE AND ZNO NANOPARTICLES(2022-01-01) Zheleva D.; Koleva M.; Angelova D.; Grabcheva D.; Todorov P.Cotton fabrics have good water absorption properties, air permeability, non-toxicity, but microorganisms easily damage them. Collagen is a commonly used biomaterial that has properties such as biocompatibility, biodegradability, non-toxicity, but with poor mechanical properties. Glutaraldehyde is the main cross-linking agent for collagen and characterized by antimicrobial properties. ZnO nanoparticles exhibiting antibacterial, antifungal, anticorrosive and protective properties against UV, is widely applicable in medicine. The combination of all these components in one biocomposite with potential antimicrobial properties and healing effect can find application in medical practice. In this study, an attempt was made to improve the properties of cotton fabric by impregnating it with gelatin hydrogel cross-linked with glutaraldehyde and containing ZnO nanoparticles. Three methods of modification were applied, varying the mixing regimes of the components and the conditions. The composite materials were investigated by means of SEM, FTIR, and fluorescence analysis. The morphological analyzes of the samples modified by different methods show that the spher ical particles of ZnO have changed into a flower-like structures; the particles are covered by the collagen film; and dispersed and agglomerated in certain places. FTIR analyzes prove interactions between the organic and inorganic components. This is also confirmed by the observed fluorescent properties, which are of different intensity. All these observations suggest good antibacterial properties that will be the subject of future research.Item METHODS FOR OBTAINING OF KERATIN HYDROLYSATES FROM SHEEP WOOL(2022-01-01) Koleva M.; Zheleva D.Leather and textile production have the largest share in the generation of keratin-containing waste (hair, wool, etc.). For example, wool contains up to 95 % pure keratin, which can be extracted and used. However, a number of difficulties exist in the production of keratin hydrolysates due to the non-reactivity and stability of keratin. In addition to peptide bonds, the presence of disulfide bonds makes these processes extremely difficult. A number of technics have been studied to obtain keratin hydrolysates. Optimizing these processes and finding the best available technique is a major challenge for environmental protection. The aim of the present study is to obtain and characterize keratin hydrolysates from sheep wool, respectively in native form and alkaline treated, using various oxidative and reductive methods. Three methods for hydrolysis were used, respectively: 1) hydrolysis with thioglycolic acid; 2) sulfitolysis with sodium pyrosulfate and urea; 3) hydrolysis with sodium hydroxide. The hydrolyzing ability of the three methods was compared, and the influence of the preliminary chemical treatment of the wool was taken into account. The obtained hydrolysates were characterized by qualitative reactions, spectrophotometric and FTIR analysis. It was proved that the method of hydrolysis with sodium hydroxide has the highest hydrolyzing effect and to a much greater extent for the alkaline treated wool than for the native one.Item METHODS FOR THE SYNTHESIS OF TiO2 NANOPARTICLES. PROPERTIES OF TEXTILE MATERIALS TREATED WITH TiO2 NANOPARTICLES(2024-01-01) Koleva M.; Angelova D.; Zheleva D.In recent decades, interest in oxide nanomaterials with multifunctional properties has grown significantly. Titanium dioxide undoubtedly belongs to them, characterized by exceptional photocatalytic activity, non-toxicity, high availability, biocompatibility, antibacterial properties, and low cost. The treatment of textile materials with TiO2 nanoparticles is relatively simple, but the insufficient bonding efficiency between certain fibers and TiO2nanoparticles creates a problem regarding the stability and durability of the nanocomposites. In this study, an attempt was made to improve the properties of cotton modified with gelatin hydrogel, which was cross-linked by glutaraldehyde, and incorporated titanium nanoparticles. Three modification methods were applied, varying the mixing regimes of the components and the conditions. The composite materials were investigated via SEM, FTIR, UV-Vis and elemental analysis. For the first time, titanium nanoparticles obtained by the reduction of TiO2 with oxalic acid were used to modify cotton. Cotton samples were modified with gelatin hydrogel cross-linked with glutaraldehyde to increase the active groups of cellulose fibers that bind to Ti ions. Using the hydrogel, the nanoparticles are deposited on the surface of the textile substrate. The elemental analysis shows the presence of TiO2 nanoparticles. Lines for Ti atoms appear, which is evidence that the particles retain their composition after immobilization. Microscopic analyzes showed that TiO2 nanoparticles were distributed unevenly in the cotton matrix. In the UV analysis, the appearance of a new absorption at 890 cm-1 was observed due to the attachment of Ti-NPs. The appearance of the IR peak at 878 cm-1 confirms the formation of chelate complexes of the nanoparticles in the composite material.Item STUDY OF ADHESION-COHESION INTERACTIONS BETWEEN POLYMERS IN ADHESIVE COMPOSITIONS ÉTUDE DES INTERACTIONS D’ADHÉSION ET D’COHÉSION ENTRE LES POLYMÈRES DANS LES COMPOSITIONS ADHÉSIVES STUDIUL INTERACȚIUNILOR DE ADERENȚĂ-COEZIUNE DINTRE POLIMERI ÎN COMPOZIȚIILE ADEZIVE(2023-01-01) Zheleva D.; Dimitrov R.The results of the research prove that adhesives based on chloroprene rubber can be obtained not only in combination with phenol-formaldehyde resins, but also with other polymers. Selected chlorobutyl rubber (CIIR) and high styrene rubber (KER) proved to be substitutes for phenolic resins, which were used to obtain adhesive compositions with good properties. Despite the existing opinion on the same polarity of the components of the adhesive composition, guaranteeing the most favorable properties, it was shown that compositions with different polarity have all the parameters of quality adhesives. Components with different polarity also show the effect of mutual reinforcement, which determines the alignment, orientation ability of macromolecular chains and occurrence of cohesion and adhesion interactions. The observed textures obtained after mechanical impact proved this claim. Adhesives with more developed textures have better adhesive properties. The selected research methods successfully predict the properties of the components and facilitate their selection and amount.Item STUDY OF ADHESION-COHESION INTERACTIONS BETWEEN POLYMERS IN ADHESIVE COMPOSITIONS ÉTUDE DES INTERACTIONS D’ADHÉSION ET D’COHÉSION ENTRE LES POLYMÈRES DANS LES COMPOSITIONS ADHÉSIVES STUDIUL INTERACȚIUNILOR DE ADERENȚĂ-COEZIUNE DINTRE POLIMERI ÎN COMPOZIȚIILE ADEZIVE(2023-01-01) Zheleva D.; Dimitrov R.The results of the research prove that adhesives based on chloroprene rubber can be obtained not only in combination with phenol-formaldehyde resins, but also with other polymers. Selected chlorobutyl rubber (CIIR) and high styrene rubber (KER) proved to be substitutes for phenolic resins, which were used to obtain adhesive compositions with good properties. Despite the existing opinion on the same polarity of the components of the adhesive composition, guaranteeing the most favorable properties, it was shown that compositions with different polarity have all the parameters of quality adhesives. Components with different polarity also show the effect of mutual reinforcement, which determines the alignment, orientation ability of macromolecular chains and occurrence of cohesion and adhesion interactions. The observed textures obtained after mechanical impact proved this claim. Adhesives with more developed textures have better adhesive properties. The selected research methods successfully predict the properties of the components and facilitate their selection and amount.