Browsing by Author "Todorova D."
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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 EFFECT OF CHITOSAN ADDITION DURING PAPER-MAKING ON AGEING STABILITY OF DOCUMENT PAPER(2021-09-01) Todorova D.; Lasheva V.The aim of the present work has been to study the influence of chitosan addition into the composition of paper intended for documents on its ageing stability, with a view of enhancing the resistance of paper strength and optical properties over time. The chitosan solution was added during the formation of the paper sheets in various amounts: 0.2%, 1% and 2% o.d.f. Paper samples of different fibrous compositions were prepared from bleached sulphate softwood pulp (BSWP) and bleached sulphate hardwood pulp (BHWP) in the following ratios: 50% BSWP:50% BHWP, 80% BSWP:20% BHWP, 100% BSWP and 100% BHWP. Then, paper samples were subjected to accelerated thermal ageing for 24 hours at 105 °C. It was found that the use of chitosan as additive in the composition of bleached cellulose paper samples led to improved strength and hygroscopic properties. The study showed that chitosan could be used in the production of kraft document papers comprising aluminium sulphate, as the presence of aluminium sulphate had no negative effect on the action of the biopolymer. Regarding the complex evaluation of the properties of the obtained papers, it could be summarized that, for the studied fibrous compositions, the optimum amount of the additive was 1% chitosan for a fibrous composition of 50% bleached softwood pulp and 50% bleached hardwood cellulose. Therefore, preparing document paper with the addition of chitosan is a convenient procedure to enhance a number of paper properties, even after the ageing process.Item Effect of magnetic field on cellulose refining process and strength properties(2019-01-01) Todorova D.; Dimitrov K.This study presents the results from the investigation of the effect of constant magnetic field over the refining process of soft and hardwood pulp suspensions and an evaluation of its white waters and paper samples strength properties. In our experiment were used two types of kraft pulp - 100 % of softwood (pine and spruce) and 100 % of hardwood (acacia). The refining degree and dewatering time for 700 ml filtrate were determined by the Schopper Riegler Value °SR, according to ISO 5267-1/AC: 2004. The magnetic treatment of pulp suspensions was performed by using magnetic stator device with field intensity of 0,1 T. Aqueous stream (the paper furnish) was passed vertically downwards through the pole gap space with linear speed 0,6 - 0,8 m s-1 at quintuple and octuple crossing of the fluid. Of each pulp type were produced sheet samples 70 g/m2 without and with quintuple and octuple magnetic treatment. Tensile index, N m/g of papers was determined on a tensile testing machine Zwick/Roell, (ISO 1924-2:1985), Burst index, kPa m2/g (ISO 2759:2014) and Tear index, mNm2/g (ISO 1974:2012). The results show positive effect of the magnetic treatment over the cellulose refining time, cellulose suspensions dewatering effect and paper samples strength properties. For both investigated types of cellulose with a view of complete evaluation of the parameters studied out the quintuple magnetic treatment is optimal.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 Investigation of the optical properties of chitosan and rice starch blends, as a filler in paper or as a film for packaging applications(2020-01-01) Brodnjak U.V.; Todorova D.Bio based materials fall under the broad category of bio-products or bio-based products, which includes materials, chemicals and energy derived from renewable biological resources. This research shows the preparation of both, paper sheets with blend fillers of chitosan and rice starch and chitosan and rice starch films, which could be used as packaging material for a variety of applications. In this research, we used a blend mixture, different concentrations of chitosan and rice starch both in paper production and in films to investigate the optical properties of the obtained materials with a combination of ultrasonic treatment during the film formation. The research showed that the optical properties of the obtained packaging materials improved. It also showed that blend fillers of chitosan and rice starch are effective paper fillers in the preparation of cellulose mixture for bio based packaging materials and the optical properties are with slight changes. The investigation on the optical properties of the obtained paper samples during accelerated thermal showed that the ageing of paper with addition of chitosan and chitosan and rice starch blends had the same behaviour through the 72 hours of ageing. The ultrasonic treatment of the films improved transparency. The surface at untreated blend film was more uneven compared to chitosan and rice starch films, which improved after the treatment.Item Investigation on the kinetics of coated paper thermal aging(2019-01-01) Todorova D.; Lasheva V.; Radeva G.; Cenkova R.The paper aging is primarily attributed to the presence of carbonyl groups formed as a result of the oxidation of the hydroxyl groups at the second and third carbon atom in the elementary unit of the cellulose macromolecule and the presence of both aldehyde and carboxyl groups in the cellulose materials. Reduction of paper whiteness degree is mainly connected with the presence of lignin, hemicelluloses, the presence of metals and the sizing agent type. The paper as an elasto-plastic, capillary porous material quickly breaks down at an elevated temperature. The latter accelerates the chemical reactions that occur in paper in the course of aging. The depth of the paper changes depends not only on the temperature but also on the duration of the impact. For different paper types differing in composition the reaction rate constant is different. Its temperature dependence is described by the Arenius equation. The aim of this work is to carry out a kinetic analysis of the influence of the temperature increase on the ageing of coated paper used for book covers. The accelerated thermal aging is conducted at three different temperatures-90°C, 105°C and 120°C with duration of 6 h, 12 h, 18 h, 36 h and 48 h. In order to examine the kinetics of the process the level of whiteness is determined. The data obtained from the thermal aging of the paper are treated using the laws of polychrome kinetics.Item Investigation on the printability of specialty papers for luxury labels(2020-01-01) Todorova D.; Pavlova N.Specialty luxury label papers mainly are results from the search for all that stimulates our creativity and senses. They are from papers that awaken the desire to create, as a magnificent mix of texture and colours that elevates luxury packaging to the category of art and a brilliant collection that ultimately shows that luxury packaging really is. In order to achieve the desired complex effect on the customer with its combined impact through the texture, colour of the paper and graphic design for each manufacturer of luxury labels, it is undoubtedly essential to be familiar with the printability of the paper used. The aim of the present work was to study the main properties of the commonly used papers for printing of self-adhesive labels, in view of their printability. It is especially important for the production, as well as for the awareness of the designers working in this field, to know the specifics of these papers, to know the main indicators influencing their printability, to know all the facts allowing the right choice of printing technology and finishing processes. To achieve this goal, various properties of five types of paper have been determined: structural-dimensional, physical-mechanical, capillary-hygroscopic and optical. In addition, with all paper analysis, a printing sample have been made with different types of printing (offset UV, flexo UV, screen, cold foil, hot foil, silk foil) and converting (emboss, laser cutting, laser engraving) techniques. Based on the obtained results, new designer labels for wine have been printed. The results show that there is a clear dependence between the paper composition, its main and specific properties and the quality of the different printing and finishing processes, as well as the overall appearance of the produced labels. The printing and finishing processes have been carried out in Rotoprint Printing House, Bulgaria and the obtained results could give a valuable information not only for the particular printing house, but for other specialists in the field of labels production.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 Magnetic-spinning effects in sack paper technology(2016-01-01) Todorova D.The latest tendency data show that the reduction of consumption of office paper, newspapers and magazines will continue. Only packaging and tissue papers maintain or increase their values. The ever-increasing demands on quality and ecology in paper production are currently being solved mostly through a variety of different chemical additives. These facts require alternative and non-traditional methods and technologies of improved environmental friendliness to increase further the efficiency of the processes. Magnetic treatment of water systems is a relatively new method for the optimization of industrial processes. It is technically comfortable and environmentally friendly but it cannot replace the use of the suitable Wet-End chemical additives. Furthermore, it is technologically easy to apply and requires minimum investment and costs, which provides its wide application. The purpose of the present study is to investigate the effect of magnetic treatment on the sack paper furnish behavior in dependence of the quantity of the anionic high-molecular mass modified polyacrylamide at a constant consumption of other system components. The investigations are carried out with 100 % unbleached sulphate softwood pulp, cationic starch, anti-dusting additive, modified rosin sizing agent, Alum and retention additive. The experimental results obtained show the positive impact of the magnetic treatment on the behavior and properties of the paper furnish.Item Polycarbonate diols to produce elastic polyurethane foams - A method of immobilization of carbon dioxide into a polymer structure(2017-01-01) Dimitrov K.; Todorova D.; Nenkova S.; Herzog M.Using carbon dioxide as feedstock for polymers is a big challenge and a chance for our sustainable future. It has an immense potential for the coming decade, which comes much faster than expected. Scientists are very active lately in carbon dioxide chemistry research, especially in the field of carbon dioxide based chemicals and polymers. We report here on the stability of higher molecular weight polycarbonate diols and the formation of specialty polyurethanes such as UV stable elastomers, semi-rigid foams, and elastic sealants. These polyurethanes are produced from polycarbonate diols (ETERNACOLL®) and aromatic 4,4'-diphenyl-methane diisocyanate, from aliphatic hexane-1,6-diisocyanate, or the trimer, diisocyanates. We use butane-1,4-diol or pentane-1,5-diol as a chain extender. The thermal and mechanical properties of the polyurethanes obtained are determined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The data obtained show no phase segregation or any type of crystallinity. Any possible changes in the molecular mass distribution of the samples are investigated with the application of gel permeation chromatography (GPC). It is evidenced that only heat treatment brings about molecular mass distribution shifts to lower values.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 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.