Page 359 - Handbook of Properties of Textile and Technical Fibres

332 Handbook of Properties of Textile and Technical Fibres

Cellulose

NMMO +H 2 O Dissolving

Filtering

Spinning NMMO recovery

Washing
bleaching
fiber finishing
drying

Fiber
Figure 10.2 Schematic illustration of the lyocell process. NMMO, N-methylmorpholine N-
oxide.
Redrawn from Kampl R, Schaumann W: The finishing behaviour of cellulosic man-made fibers
of the second and third generation, Lenzing Berichte 75:91e96, 1996.

acetate ([DBNH][OAc]) (Hermanutz et al., 2008; Sixta et al., 2015). Cellulose can be
regenerated from the solutions with polar nonsolvents such as water, acetone, ethanol,
dichloromethane, or acetonitrile (Zhu et al., 2006; Pinkert et al., 2009). For example,
“Ioncell-F” fibers are spun from the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-ene

acetate ([DBNH]OAc) at 70 C into a water bath via an air gap (dry-jet wet spinning)
(Michud et al., 2016). However, at this point in time, ionic liquids are not used in
industrial scale production of regenerated cellulosics, as there remain challenges in
efficient recovery and reuse of the solvents.
Other reported solvent systems for fiber production that are not as yet employed in
industrial-scale processes include phosphoric acid (Boerstoel et al., 2001) and mix-
tures of NaOH with urea and thiourea (Ruan et al., 2004; Mao et al., 2008; Zhang
et al., 2009). Electron micrographs of typical examples of fibers produced with the
different technologies are shown in Fig. 10.3.

10.3 Supramolecular structure

The polymer chains in cellulosic fibers consist of b(1/4)-linked anhydrous D-glucose
units and are thought to lie alongside each other forming strand- or thread-like clusters,
which are termed as “fringed fibrillar structure” (Hearle, 2001). The residues obtained
after hydrolysis and ultrasonication of cellulosic fibers, when examined under a trans-
mission electron microscope, resemble aggregates of beaded stringelike structures, or