Tuning hardness of swollen viscose fibers

Viscose fibers are man-made, regenerated cellulose fibers. They offer versatile uses ranging from hygiene articles to textiles and medical applications. The great advantage over natural pulp and cotton fibers are the possibilities to design the fibers' cross-sections and modify the material by directly mixing additives to the viscose dope. In this study, the effects of two additives - carboxymethyl cellulose (anionic) and cationic starch (cationic) - on the fibers' mechanical properties are studied. Atomic force microscopy-based nanoindentation is the method of choice to investigate swollen viscose fibers with circular as well as flat, rectangular cross-sections. It was found that carboxymethyl cellulose addition always leads to a significant decrease of hardness from 14 0 MPa for the unmodified fiber down to 4 4 MPa, a value comparable to swollen pulp fibers. Cationic starch, on the other hand, causes an increase of hardness to 16 0 MPa for round viscose fibers at a low concentration, whereas higher concentrations of cationic starch resulted in a slight decrease of hardness to 12 8 MPa. This possibility to tune the hardness of swollen viscose fibers expands the application spectrum of viscose fibers substantially.