230
F. Hermanutz et al.
[15, 41, 42]. Once IL-technology-based processes comply with the above conditions,
a significant step toward Green Chemistry in cellulose-processing technology can be
realized [43, 44].
10.2.2 Ionic Liquids as Solvents for Cellulose
Swatloski et al. used imidazolium-based ILs like [C 4 C 1 im]
+ with different anions,
such as [Cl]
− , [Br]
− , and [SCN]
− [7]. Depending on the temperature and IL, solutions
containing up to 25 wt% cellulose were realized. Since then, there has been a dramatic
rise in interest in dissolving cellulose in ILs for both scientific and industrial applications. So far, the most common ILs used for the processing of cellulose are based
on imidazolium-derived cations [27, 45–59]. A summary of different imidazoliumbased ILs and the solubility of cellulose within these ILs is given in Table 10.1 [60,
61]. A selection of non-imidazolium-based ILs is given in Table 10.2.
However, despite the vast number of ILs available, the only ILs of interest are
those in which cellulose possesses a sufficient solubility. It is therefore of interest
to understand how the solubility of cellulose depends on the structure of the IL
and the mechanism for the dissolution of cellulose in ILs. Disappointingly, both the
mechanism and the connection between IL structure and solubility of cellulose are
still not fully understood in detail [58, 67]. Indeed, the high ionic strength of the
ILs interrupts the inter- and intra-molecular hydrogen-bonding-based interactions
in cellulose chains [50, 67–69]. Some studies show that the nature of the anion
is responsible for the dissolution of cellulose. However, it has also been shown
that the structure of the cation especially influences the solvation process [69–72].
Additionally, the degree of polymerization (DP) of the cellulose is a factor in the
dissolution process [73].
10.3 Cellulosic Fiber Spinning Using IL-Technology
The most important and also oldest process used in the manufacturing of cellulosic
fibers is the viscose process outlined in Fig. 10.2. In contrast to the Lyocell process,
this process involves activation of pulp in aqueous sodium hydroxide solution followed by reaction with CS 2 to form a cellulose xanthate. After dissolution in alkaline
solution, the cellulose xanthate is spun into a sulfuric acid bath. Along with other
auxiliaries (e.g., carbon disulfide, sodium hydroxide, sulfuric acid, and zinc sulfate),
a significant volume of fresh water is required and amounts to approximately one
ton of water per kg of cellulosic fiber produced [74]. Also, the cellulose concentration in solution is limited to a range of 8–10 wt%, which is critical in terms of the
environmental effects caused by the process [9, 75–77].
F. Hermanutz et al.
[15, 41, 42]. Once IL-technology-based processes comply with the above conditions,
a significant step toward Green Chemistry in cellulose-processing technology can be
realized [43, 44].
10.2.2 Ionic Liquids as Solvents for Cellulose
Swatloski et al. used imidazolium-based ILs like [C 4 C 1 im]
+ with different anions,
such as [Cl]
− , [Br]
− , and [SCN]
− [7]. Depending on the temperature and IL, solutions
containing up to 25 wt% cellulose were realized. Since then, there has been a dramatic
rise in interest in dissolving cellulose in ILs for both scientific and industrial applications. So far, the most common ILs used for the processing of cellulose are based
on imidazolium-derived cations [27, 45–59]. A summary of different imidazoliumbased ILs and the solubility of cellulose within these ILs is given in Table 10.1 [60,
61]. A selection of non-imidazolium-based ILs is given in Table 10.2.
However, despite the vast number of ILs available, the only ILs of interest are
those in which cellulose possesses a sufficient solubility. It is therefore of interest
to understand how the solubility of cellulose depends on the structure of the IL
and the mechanism for the dissolution of cellulose in ILs. Disappointingly, both the
mechanism and the connection between IL structure and solubility of cellulose are
still not fully understood in detail [58, 67]. Indeed, the high ionic strength of the
ILs interrupts the inter- and intra-molecular hydrogen-bonding-based interactions
in cellulose chains [50, 67–69]. Some studies show that the nature of the anion
is responsible for the dissolution of cellulose. However, it has also been shown
that the structure of the cation especially influences the solvation process [69–72].
Additionally, the degree of polymerization (DP) of the cellulose is a factor in the
dissolution process [73].
10.3 Cellulosic Fiber Spinning Using IL-Technology
The most important and also oldest process used in the manufacturing of cellulosic
fibers is the viscose process outlined in Fig. 10.2. In contrast to the Lyocell process,
this process involves activation of pulp in aqueous sodium hydroxide solution followed by reaction with CS 2 to form a cellulose xanthate. After dissolution in alkaline
solution, the cellulose xanthate is spun into a sulfuric acid bath. Along with other
auxiliaries (e.g., carbon disulfide, sodium hydroxide, sulfuric acid, and zinc sulfate),
a significant volume of fresh water is required and amounts to approximately one
ton of water per kg of cellulosic fiber produced [74]. Also, the cellulose concentration in solution is limited to a range of 8–10 wt%, which is critical in terms of the
environmental effects caused by the process [9, 75–77].