Splitting tendency of cellulosic fibers – Part 1. The effect of shear force on mechanical stability of swollen lyocell fibers Hale Bahar O ¨ ztu¨rk 1 , Satoko Okubayashi 2 and Thomas Bechtold 1, * 1 Christian-Doppler Laboratory of Textile and Fiber Chemistry of Cellulosics, Institute of Textile Chemistry and Textile Physics of Leopold –Franzens-University Innsbruck, Hoechsterstrasse 73, A-6850, Dornbirn, Austria; 2 Venture Business Laboratory, University of Fukui, Bunkyo 3-9-1, Fukui, 910-8507, Japan; *Author for correspondence (e-mail: textilchemie@uibk.ac.at; phone: +43-5572-28533; fax: +43-5572-28629) Received 10 October 2005; accepted in revised form 11 January 2006 Key words: Alkali, Fiber, Fibrillation, Lyocell, Solvent retention value, Split number, Swelling Abstract A procedure for splitting of a lyocell fiber into a multitude of finer fibrils was developed. Crockmeter, usually used for rub-fastness of colored textiles, was modified and used for obtaining required shear force on swollen lyocell fiber. The shear force applied on fibers, and the concentration of NaOH, which affects swelling degree of fiber, were shown to be the leading parameters determining split number of lyocell fiber. While number of shear cycles was found to be of minor relevance for fiber splitting, the applied pressure directly influences the number of splitted fibrils. For example, at a pressure of 34.8 kPa, the average split number of lyocell fiber in 2.5 M NaOH solution was observed as 15, whereas it was observed as 30 for 47 kPa and 41 for 59.3 kPa. Splitting was not observed above 5 M of NaOH solution. Analyses of fiber splitting permit new aspects to study inner structure of lyocell. Introduction Lyocell is regenerated from cellulose by using wet spinning process where N-methylmorpholine-N- oxide monohydrate solution is used as dissolving agent (Albrecht et al. 1997). The spinning solution of cellulose in NMMO –water mixture having greater concentration than 20% has been reported to form lyotropic liquid crystal solutions. The spinning solutions used here have a cellulose con- centration of 12%, which lies below this value but the spinning solution already presents a certain preordering and that statistically no coiled mole- cules are present (Schurz 1994; Schurz and Lenz 1994). Lyocell fiber differs from other cellulosic regenerated fibers by its high crystallinity, high longitudinal orientation of crystallites, high amorphous orientation, low lateral cohesion be- tween fibrils, low extent of clustering and relatively large void (pore) volume (Schurz 1994; Schurz and Lenz 1994; Crawshaw and Cameron 2000; Craw- shaw et al. 2000). Hence, these peculiar features prevent the distortion of high longitudinal stability of lyocell fiber by the penetration of swelling agents (Lenz et al. 1993; Ibbett et al. 2001). The water penetrates inside the fiber by breaking down the secondary interactions between cellulose macromolecules and is absorbed into the fiber by hydrogen bonds, which causes swelling of the fi- bers (Preston et al. 1949; Lewin et al. 1983; Peter et al. 1989). By swelling, fiber becomes soft and flexible (Mantanis et al. 1994). After immersion in Cellulose (2006) 13:393 –402 Ó Springer 2006 DOI 10.1007/s10570-006-9053-4