Browsing by Author "Koleva M."
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Item Characterization of polyester resins solidification process by the method of mechanical impedance(2000-01-01) Koleva M.; Bechev C.; Petkov S.Mechanical impedance measurements were carried out in order to characterize the curing process of unsaturated polyester resins. A dynamic model of experimental set-up composed of two elements: an inertial (mass of the probe) and viscous element (damper) was constructed. The influence of additive, such as high impact polystyrene, was also investigated. The experimental results obtained show that the method of mechanical impedance spectroscopy has very good resolution when viscosity (or inertial damping) is changed over a relatively wide range.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 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 Polymer composites containing waste dust from power production: II Strength characteristics of composites based on UPR/HIPS polymer system(2008-01-01) Koleva M.; Vassilev V.; Vassilev G.Polymer composite material based on ``unsaturated polyester resin/ high impact polystyrene`` polymer system as matrix and waste dust from power production as filler was studied. The waste was mechanically activated at dry conditions at room temperature for 30 minutes. Strength characteristics - impact, bending and compressive strength - dependance on the waste concentration was determined. The optimal results were achieved at waste concentration of 10 w.%. Morphology observations of filled systems were performed to clarify the influence of the structure on composite's properties.