Browsing by Author "Yavorov N."
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Item APPLICATION POSSIBILITIES OF BIOMASS FROM FENNEL FRUITS(2023-01-01) Nikolova М.; Pencheva M.; Dimov M.; Bozadzhiev B.; Lazarov L.; Damyanova S.; Lasheva V.; Stoyanova A.; Yavorov N.During the processing of fennel fruits (Foeniculum vulgare Mill.) for obtaining essential and vegetable oils, biomass is released. It is mainly used as an additive for feeding or as an organic fertilizer. The aim of this research is to investigate the possibilities of using biomass obtained during the processing of fruits from harvest 2020 and 2021 as a biosorbent of Cr (VI) from aqueous solutions or as a biofuel. The two biomasses were milled and the final fractions obtained by sieve analysis (between 384 and 413 μm) were analyzed. The FTIR spectrum was recorded as 4000 - 400 с-1. Both biomasses act as biosorbent under the following conditions: pH 1.0, agitation speed 300 rpm, adsorbent dose 1.05 g L-1, initial Cr (VI) concentration 80 mg L-1, temperature 30°C. The energy indices used in the assessment of fennel fruit biomass potential as conditional biofuel were calculated: calorific value (15783.40 - 15968.16 kJ kg-1), density (464.19 - 582.91 kg m-3), and heat equivalent (250.05 - 317.68 kJ m-3)Item Chitosan-Coated Packaging Papers—Strength and Thermal Stability(2023-05-01) Vrabič-Brodnjak U.; Yavorov N.; Lasheva V.; Todorova D.The aging of paper depends on various factors, including environmental conditions, microbiological factors and chemical composition. Chitosan-coated paper is an eco-friendly material that has potential use in various packaging applications due to its mechanical, barrier and antibacterial properties. In this study, the aging stability of chitosan-coated wood-free wrapping paper was evaluated by examining pulp and four paper samples with different quantities of chitosan. Accelerated thermal aging and dynamic thermogravimetric analysis were used to assess the aging stability, while color changes were examined to understand the impact of chitosan coating. The study found that increasing chitosan coating led to improved aging stability due to the improved crosslinking process between chitosan and paper. The coated paper samples displayed a yellowish hue after 72 h of aging, with increased strength and resistance to weight loss. TGA results indicated that the temperature of complete burning of the sample increased with increasing chitosan coating. Additionally, coated paper samples exhibited a more even surface and improved barrier properties. Overall, chitosan-coated paper is a promising material for sustainable and eco-friendly packaging, printing and wrapping applications. This study’s findings have important implications for the development of environmentally-friendly packaging materials that possess desirable mechanical and barrier properties.Item COMPARATIVE ANALYSIS OF ANTIBACTERIAL ACTIVITY AND PHYSICOCHEMICAL PROPERTIES OF PEPPERMINT AND CORNMINT ESSENTIAL OILS AND THEIR MAIN COMPOUND MENTHOL(2023-01-01) Gandova V.; Fidan H.; Iliev I.; Lasheva V.; Stankov S.; Stoyanova A.; Yavorov N.The aim of the present paper was to study and present a comparative analysis of the antibacterial activity and physicochemical properties of commercial mint essential oils from two different species - peppermint (Mentha piperita Huds. (L.)) and cornmint (Mentha arvensis L.). Peppermint oils exhibited weak antibacterial activity, but were more pronounced against Gram-positive bacteria Staphylococcus aureus (1.3 - 2.0 mm) and Gram-negative bacteria Escherichia coli (1.2 - 1.9 mm) and Klebsiella sp. (2.6 mm). The essential oil of the species M. arvensis did not exhibit antimicrobial activity against the tested cultures. L-menthol, which is a commercial sample isolate, exhibited activity against all tested microorganisms, with the exception of Gram-positive bacteria Listeria monocytogenes and Bacillus cereus. The diameter of the inhibition zones was the largest against Gram-positive bacteria Bacillus subtilis (3.4 mm), and the smallest was against Gram-positive bacteria Staphylococcus aureus (1.6 mm) and Gram-negative bacteria Klebsiella sp. (1.4 mm). The surface tension, density and refractive index of different mint essential oils were determined experimentally. The surface energy and surface heat capacity were calculated based on the calculations of surface tension. All experiments and calculations were provided at a temperature range between 6℃ and 30℃. A dependence between surface tension and temperature was not observed.Item Impact of Silver Nanoparticle Treatment and Chitosan on Packaging Paper’s Barrier Effectiveness(2024-08-01) Todorova D.; Yavorov N.; Vrabič-Brodnjak U.In this study, a comparative analysis of silver nanoparticles treatment and chitosan coating on packaging paper barrier properties was carried out. In order to examine the water, grease, and antibacterial barrier properties of silver nanoparticle-treated and chitosan-coated laboratory-obtained paper samples, a mixture of bleached softwood and hardwood celluloses was used. In order to conduct the comparative analysis SEM, water contact angle, Cobb60, and Kit tests were carried out on a cellulose sample, and four paper samples (three of them treated with silver nanoparticles—1, 2, and 3 mL/20 cm2 or chitosan coated—0.5, 1, and 2 g/m2) together with the inhibition activity against nine Gram-positive and Gram-negative bacteria, yeast, and fungal strains. The study found out that increasing the silver nanoparticle treatment and chitosan coating led to improved water resistance, while grease resistance was improved only for chitosan coated paper samples. Additionally, paper treated with 3 mL/20 cm2 of silver nanoparticles had the highest antibacterial protection (81.6%) against the Gram-positive bacterium Staphylococcus aureus, followed by Gram-negative Escherichia coli (75.8%). For the rest of the studied microorganisms, the average efficiency of the treated paper was 40.79%. The treatment of the paper with 1 and 2 mL/20 cm2 of silver nanoparticles was less effective—27.13 and 39.83%, respectively. The antibacterial protection of 2 g/m2 chitosan-coated paper samples was the most effective (average 79%) against the tested bacterial, yeast, and fungal strains. At 1 and 0.5 g/m2 chitosan coatings, the efficiency was 72.38% and 54.67%, respectively. Gram-positive bacteria, yeasts, and fungal strains were more sensitive to chitosan supplementation.Item Lavender Essential Oil as Antibacterial Treatment for Packaging Paper(2023-01-01) Todorova D.; Yavorov N.; Lasheva V.; Damyanova S.; Kostova I.Based on many years of experience, packaging is considered as an inactive barrier that protects materials and goods from environmental factors. The applicability of native chemical additive such as essential oils in wrapping papers can be used in the forms of films, treatments, coatings or others. Essential oils or extracts from different aromatic plants are used as bioactive substances for antimicrobial activity. In this research, lavender essential oil treatment of packaging papers is examined for its inhibition activity under nine microorganisms—two Gram-positive bacteria, three Gram-negative bacteria, two yeast and two fungal strains. The effectiveness of the treatment on the structural and strength indicators of the obtained paper samples is monitored. In detail, a five-day examination is conducted on the antibacterial effectiveness of lavender essential oil treatment. Results indicate that the lavender treatment of the obtained packaging paper is successful and the antifungal effect is more pronounced. The antimicrobial efficiency of paper treated with lavender essential oil is between 60 and 90% in the first two hours after treatment and gradually decreases to 40%–50% at the end of the 120 h period. The lavender essential oil treatment of wrapping paper has a promising perspective for preserving products from microbial spoilage and extending their shelf life.Item Possibilities for Efficient Furniture Construction Made of Thin and Ultra-Thin Materials by Using Mitre Joints(2023-11-01) Petrova B.; Jivkov V.; Yavorov N.One of the biggest challenges for designers and manufacturers of furniture is to reduce the thickness of conventional furniture materials such as particleboard (PB), medium-density fibreboard (MDF) and plywood. Designing furniture based on thin (less than 16 mm) and ultra-thin materials (less than 10 mm) is desirable for aesthetic reasons and because of the substantial material savings. However, the use of thin and ultra-thin materials reduces the strength of the furniture, especially the strength and deformation resistance of the joints. This study aimed to establish the possibilities for efficient furniture construction made of thin and ultra-thin materials using mitre joints. For this purpose, 14 types of L-type joints were tested: 12 glued and 2 detachable. The joints were made of eight wood-based panels and one non-wood panel. The bending moments and the stiffness coefficient under compression were determined. The obtained results show that the mitre joints made of laminated material with high-pressure laminate (HPL), 8 mm thick, MDF achieved the highest bending moment, and the highest stiffness coefficient was achieved by joints made of 10 mm thick compact HPL. Compact HPL joints were significantly affected by the type of adhesive used. Detachable joints had a relatively high bending strength but very low stiffness.Item POSSIBILITIES FOR IMPARTING ANTIBACTERIAL PROPERTIES TO PAPERS(2023-01-01) Lasheva V.; Todorova D.; Yavorov N.; Damyanova S.; Kostova I.Paper is widely used as a packaging material because it is biodegradable and completely safe for the environment. The use of antimicrobials as a coating on paper can improve its mechanical, optical, physical and antimicrobial properties. Antimicrobial packaging suppresses the development of pathogenic microorganisms in order to ensure the safety of the product, extend the shelf life and protect the quality of the product. Giving antibacterial properties to papers and cardboards expands their use in different areas and for different purposes. Antibacterial paper prevents the entry and development of harmful microorganisms such as bacteria, fungi, mould. Antimicrobials that occur naturally in nature have a number of advantages, as they are considered to pose less risk to the consumer. One of the modern directions in research is the inclusion of different types of active substances in the packaging material, which can give it additional functions, such as elimination of oxygen, moisture, ethylene, ethanol emission, antimicrobial activity and others. The present work aims to obtain plant extracts, their characterization and their surface application on paper. Extracts of Bulgarian herbs St. John’s wort, cumin, rosemary, thyme and basil were obtained and characterized and studied. Plant extracts are applied by spraying on the surface of various papers. The antimicrobial effect of treated papers on gram-positive and gram-negative bacteria was studied. The results of the analysis of the obtained papers show the possibility of using plant extracts containing biologically active ingredients for the production of papers with barrier properties. The use of plant extracts is a promising and innovative solution.Item Producing bleached microcrystalline cellulose by two-stage dilute acid hydrolysis(2020-01-01) Valchev I.; Yavorov N.; Todorova D.This study investigates the process of producing microcrystalline cellulose (MCC) through two-stage acid hydrolysis with intermediate washing and removal of dissolved sugars. The temperature–time dependence shows fast xylose extraction in the initial phase of the process, while the glucose increases slowly and permanently over the period. After the second stage of hydrolysis, a cleaning effect and an increase in pulp brightness is observed. This method allows obtaining MCC, with high brightness and properties appropriate for usage in the pharmaceutical, cosmetics and food industries, as well as in the chemical industry, from paper grade pulp, which contains large amounts of hemicelluloses.Item Producing bleached microcrystalline cellulose by two-stage dilute acid hydrolysis(2020-01-01) Valchev I.; Yavorov N.; Todorova D.This study investigates the process of producing microcrystalline cellulose (MCC) through two-stage acid hydrolysis with intermediate washing and removal of dissolved sugars. The temperature–time dependence shows fast xylose extraction in the initial phase of the process, while the glucose increases slowly and permanently over the period. After the second stage of hydrolysis, a cleaning effect and an increase in pulp brightness is observed. This method allows obtaining MCC, with high brightness and properties appropriate for usage in the pharmaceutical, cosmetics and food industries, as well as in the chemical industry, from paper grade pulp, which contains large amounts of hemicelluloses.Item Structural application of eco-friendly composites from recycled wood fibres bonded with magnesium lignosulfonate(2020-11-01) Antov P.; Jivkov V.; Savov V.; Simeonova R.; Yavorov N.The pulp and paper industry generates substantial amounts of solid waste and wastewater, which contain waste fibres. The potential of using these recycled wood fibres for producing eco-friendly composites that were bonded with a formaldehyde-free adhesive (magnesium lignosulfonate) and their use in structural applications was evaluated in this study. Fibreboards were produced in the laboratory with a density of 720 kg·m−3 and 15% magnesium lignosulfonate gluing content, based on the dry fibres. The mechanical properties (bending strength, modulus of elasticity and internal bond strength), physical properties (thickness swelling and water absorption) and formaldehyde content were determined and compared with the European Standards requirements for wood-based panels. In general, the laboratory-produced panels demonstrated acceptable mechanical properties, such as bending strength (18.5 N·mm−2) and modulus of elasticity (2225 N·mm−2), which were higher than the minimum requirements for type P2 particleboards and equal to the requirements for MDF panels. The moisture properties, i.e., thickness swelling (24 h) and water absorption (24 h) significantly deteriorated. The free formaldehyde content of the laboratory-produced composites (1.1 mg/100 g) reached the super E0 grade (≤1.5 mg/100 g), which allowed for their classification as eco-friendly, low-emission wood-based composites. The L-type corner joints, made from the developed composites, demonstrated significantly lower bending capacity (from 2.5 to 6.5 times) compared to the same joints made from MDF panels. Nevertheless, the new eco-friendly composites can be efficiently utilised as a structural material in non-load-bearing applications.Item THERMAL STABILITY OF PACKAGING PAPERS TREATED OF SILVER WATER(2022-01-01) Yavorov N.; Todorova D.; Brodnjak U.V.; Lasheva V.Paper aging depends on the type and chemical composition of the fiber raw materials, the chemical additives used, such as dyes, fillers, sizing additives, pH and others as storage conditions of the paper (relative humidity and temperature) and the degree of exposure of temperature, light and some microbiological factors. The durability of paper is its ability to retain certain physic-mechanical, optical and chemical properties unchanged over time. In this context and in line with the increased consumption of coated or treated printing and packaging papers, the aging resistance of treated or coated paper is of a great scientific, research and applied interest. This research work inherently involves preparation and properties evaluation of thermal stability of packaging papers treated of silver water. In order to examine this process for woodfree packaging paper, accelerated thermal aging for 72h at temperature of 105°C and dynamic thermogravimetric analysis (TGA) was carried out of a pulp sample and four paper samples (three of them treated with silver water – 1, 2 and 3 ml) together with the structural-dimensional and strength properties of the laboratory obtained paper samples. The degree of colour changes in the CIELab colour space have been studied, bearing in mind that the changes in colour characteristics define the stability over time and even more – the influence of the silver water treatment. As a result of the studies carried out it was found out that paper do not change significantly during 72h of accelerated thermal ageing, but it is not recommended to be used more than 2 ml of silver water, as silver ions probably catalyze the aging process and the paper darkens and turns yellow in a greater degree. The change of the weight of the paper samples as a function of temperature was monitored by TGA. When comparing the weight losses, it was found out that for the paper sample treated with 2 ml of silver water the temperature of complete burning of the sample increased by 2.28°C. In addition, the surface of the treated paper samples is more even compared to the untreated due to the callandering effect of the manufacturing process.