Browsing by Author "Brodnjak U.V."

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    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.
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    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.