Determination of dissociable groups in natural and regenerated cellulose fibers by different titration methods

Different titration methods were applied with the purpose to determine the dissociation properties of a natural (cotton) and regenerated (viscose, modal and lyocell) cellulose fibers. Potentiometric and conductometric titration were used to determine the content of acidic groups. pK values were determined by potentiometric titration. Polyelectrolyte adsorption was used for surface and total charge determination, and to obtain information about charge location and accessibility of charged groups. It was found that the average content of acidic groups is higher in cotton fibers than in regenerated fibers. The fiber charge of cotton is due to the dissociation of two type of acidic groups, one with pK ≈3.5 and the other with pK ≈5.5. In regenerated fibers there is only one type of acidic groups (pK ≈3.5). The pK value of the stronger acid is typical for carboxyl group in uronic acids. The polyelectrolyte adsorption indicates that most of the carboxyl groups are located in an inner region of all cellulose samples (cotton and regenerated fibers). It is concluded that titration methods are powerful tools for monitoring the content, strength, and distribution of acidic groups, as well as the total charge of natural and regenerated cellulose fibers. The three methods give similar results on all analyzed samples and show good repeatability. The results of investigation make it quite clear that combination of all titrations yields relevant information about content and strength of acidic groups in both natural and regenerated cellulose fibers used in the manufacture of textiles.