80 QUANTITATIVE DETERMINATION OF CARBOXYL GROUPS IN CELLULOSE BY COMPLEXOMETRIC TITRATION Lidija Fras, 1 Karin Stana-Kleinschek, 1 Volker Ribitsch, 2 Majda Sfiligoj-Smole, 1 Tatjana Kreze 1 1 Univ. of Maribor, Inst. of Textile Chem., Lab. for Characterization and Processing of Polymers, Smetanova 17, 2000 Maribor, Slowenia fax: +386-62 220 7990; e-mail: karin.stana@uni-mb.si 2 University of Graz, Institute of Chemistry, Rheology & Colloid Science Complexometric titration was used to determine the carboxyl group content of a series of oxidatively treated (selective and non-selective oxidation) nature cellulose fibers (cotton). The results were correlated with those obtained from the conventional methylene blue method; both methods show an excellent correlation. The progress of the cellulose fibers oxidation was monitored using viscosimetric determination of the molecular weight. The content of carboxyl groups depends on the oxidation procedure and it is, in the case of selectively oxidized fibers, twice as high as the content of carboxyls in raw fibers. The carboxyl group content for non-selectively oxidized fibers increased by approximately 180%, relative to untreated fibers. The results of our investigation demonstrate clearly that complexometric titration is an excellent tool for monitoring the influence of chemical modifications on the carboxyl group content. This method is sensitive enough to determine small changes in the content of functional groups for chemically modified fibers. __________________________________________________ Introduction Cellulose fibers have a number of essential advantages expressed by costumer friendliness in comparison to synthetic textile polymers (PES, PA, PAC). Their main disadvantage is of technological nature, i.e., their finishing process is much more complex, and, therefore, environmentally aggravating. Although finishing processes have been used for several years, they are only partially understood, and better basic understanding is needed in order to gain some knowledge about their influence on fiber adsorption ability, hydrophilicity or the accessibility of active groups for the final fiber finishing as dyes or surfactants. During the production and processing of cellulose materials, chemical (oxidation and hydrolysis) and structural modifications (degree of crystallinity and form of the unit cell) are applied in order to change the reactivity due to an alteration in the number and allocation of functional groups and possible degradation. The processing of cellulose has an influence on the fibrillar structure, i.e., the cellulose structure is loosened, causing swelling of the polymer and increased accessibility of active groups on the fiber surface [1]. It is assumed that these modifications on the solid phase surfaces mainly change the interaction ability of the cellulose fibers with components at the liquid phase. The fine structure of the cellulose fiber is already quite well understood, contrary to the reaction abilities of the fiber surfaces, which is correlated with the quantity and quality of the cellulose reactive accessible groups. It is extremely important to be able to determine the number of the accessible groups in order to judge the polymers’ interaction ability, their ion exchange capacity and the progress of technological processes during the manufacturing of cellulose polymer materials.