Obtaining of special properties cellulose fibers by chemical modification

Abstract

In the theoretical part of this thesis, the most relevant literature data on chemical composition, structure and reactivity of cellulose are reviewed. Basic characteristic of natural (cotton and hemp) and man-made (lyocell) cellulose fibers are shown. An overview of the achieved results and published papers related to field of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)mediated oxidation, with special attention to the TEMPO-mediated oxidation of cellulose material is given. This review is the basis for the experimental part. In the experimental part of the thesis, the influence of the TEMPO-mediated oxidation on chemical composition, structure and properties of natural and man-made cellulose fibers was studied. As natural fibers cotton and hemp fibers, and from man-made liocel fibers have been modified. Unmodified and modified fibers were characterized in terms of weight loss values, carbonyl (Ca-acetate, Cu-number and GPC/CCOA method) and carboxyl contents (Ca-acetate, potentiometric titration and GPC/FDAM method), molecular weight distribution (GPC technique), crystallinity index (iodine sorption value), and changes on the surface of fibers (SEM technique). Also, oxidised fibers were characterized in terms of the geometric (fineness), physico-mechanical (tensile strength and elongation) and sorption properties (moisture sorption, water retention power, iodine sorption), as well as the capacity of sorption of different ions. The TEMPO-mediated oxidation has influence on weight loss and changes in fineness of the modified fibers. Oxidized cotton and lyocell fibers show minimal increase of fineness, while oxidized hemp fibers get a significant increase in fineness. In the case of hemp fibers, which contain noncellulosic materials beside the cellulose, TEMPO-oxidation leads to a significant removal of hemicelluloses and lignin. For all oxidized fibers, depending on the conditions of modification, a higher crystallinity index is obtained, while the tensile strength of fiber decreases. By the TEMPO-mediated oxidation of cellulose fibers, significant amount of carboxyl groups can be introduced into cellulose fibers, and the amount of these functional groups is controllable by selecting the oxidation conditions. Due to introduced hidrophylic carboxyl groups, the hemisorption properties od oxidized fibers increase. Good sorption properties and changes in the structure of modified fibers, allow the use of these fibers for sorption of different ions and molecules from their aqueous solution. Increasing of the sorption properties was confirmed by sorption of silver ions, which are selected to achieve the antimicrobial properties of oxidized fibers, which makes them very suitable for bioactive and medical fibers obtaining. The antimicrobial activity of silver-loaded cellulose fibers against different pathogens: Staphylococcus aureus, Escherichia coli, and Candida albicans was evaluated in vitro. This study demonstrates the potential of the selective TEMPO-mediated oxidization towards natural and man-made cellulose fibe...