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F. Hermanutz et al.
precursor [98, 102]. Finally, substitution of expensive PAN fibers by the cheaper cellulose as CF precursors could reduce process costs for CFs [98]. Among the numerous
possibilities, the processing of cellulose/chitin and cellulose/chitosan blends from
ILs especially stands out since chitin is the second-most abundant polymer in nature.
Reviews about chitin and chitosan polymers, addressing their solubility, fiber formation, properties, and applications, have been provided by Silva et al., Pillai et al., and
Rinaudo [104–106]. Different applications in the medical field, like chitin sutures,
have been reported. Chitin itself is chemically stable, is biodegradable, and has the
most appealing properties, such as the acceleration of wound healing and the suppression of tumor cell growth. It is remarkable that the IL-technology enables a direct
fiber spinning process of chitin. This new research field is based on the wet spinning
process because chitin decomposes before melting. A list of different ILs having high
potential for dissolution and wet spinning of chitin was provided by Walther et al.
Among the ILs tested, [C 2 C 1 im][O 2 C 3 ] and [C 2 C 1 im][O 2 C 4 ] were found the most
promising for chitin. Chitin concentrations up to 14 wt% could be realised, which is
high enough for technical conversion [107]. Special chemically purified chitin with
purification steps to remove minerals and proteins was used in their study. Alternatively, Qin et al. used [C 2 C 1 im][Ace] for the extraction and dissolution process using
microwave irradiation heating for a much faster dissolution process. Purified, high
molecular-weight chitin powder was obtained and directly spun into fibers [108, 109].
In addition to standard wet spinning, chitin was also electrospun into fibers [110].
In contrast, NaOH/urea was used as a solvent by Huang et al. for the preparation of
chitin fibers and nonwovens [111]. This product showed better wound healing than
traditional materials based on the inherent antibacterial properties and the ability to
regulate inflammatory mediators of chitin. Chitosan produced by deacetylation is
more soluble in ILs than chitin. However, it can also be processed from acetic acid.
The use of IL for the processing of chitosan is not necessarily required as is the case
for chitin and cellulose. Toskas et al. produced pure microfibers on an industrial scale
using 8.5 wt% chitosan dissolved in acidic acid. These fibers were recently tested
as medical products [112, 113]. Studies by Pillai et al. have shown that the dry–wet
spinning of chitin in acetic acid results in highly deacetylated products [104]. This
polymer-analogous reaction can be avoided by using ILs. For the preparation of
spinning dopes, it is important that the solubility of chitin increases with increasing
hydrogen-bond acceptance properties of the IL and also depends on the dissolution
temperature [114]. Notably, it was found that pure chitin fibers are brittle due to the
high crystallinity of chitin [108]. This issue can be improved by blending chitin with
cellulose. Up to now, there are some cellulose/chitin blend materials, like membranes,
films, and even multifilament fibers, described in the literature [100, 115, 116].
F. Hermanutz et al.
precursor [98, 102]. Finally, substitution of expensive PAN fibers by the cheaper cellulose as CF precursors could reduce process costs for CFs [98]. Among the numerous
possibilities, the processing of cellulose/chitin and cellulose/chitosan blends from
ILs especially stands out since chitin is the second-most abundant polymer in nature.
Reviews about chitin and chitosan polymers, addressing their solubility, fiber formation, properties, and applications, have been provided by Silva et al., Pillai et al., and
Rinaudo [104–106]. Different applications in the medical field, like chitin sutures,
have been reported. Chitin itself is chemically stable, is biodegradable, and has the
most appealing properties, such as the acceleration of wound healing and the suppression of tumor cell growth. It is remarkable that the IL-technology enables a direct
fiber spinning process of chitin. This new research field is based on the wet spinning
process because chitin decomposes before melting. A list of different ILs having high
potential for dissolution and wet spinning of chitin was provided by Walther et al.
Among the ILs tested, [C 2 C 1 im][O 2 C 3 ] and [C 2 C 1 im][O 2 C 4 ] were found the most
promising for chitin. Chitin concentrations up to 14 wt% could be realised, which is
high enough for technical conversion [107]. Special chemically purified chitin with
purification steps to remove minerals and proteins was used in their study. Alternatively, Qin et al. used [C 2 C 1 im][Ace] for the extraction and dissolution process using
microwave irradiation heating for a much faster dissolution process. Purified, high
molecular-weight chitin powder was obtained and directly spun into fibers [108, 109].
In addition to standard wet spinning, chitin was also electrospun into fibers [110].
In contrast, NaOH/urea was used as a solvent by Huang et al. for the preparation of
chitin fibers and nonwovens [111]. This product showed better wound healing than
traditional materials based on the inherent antibacterial properties and the ability to
regulate inflammatory mediators of chitin. Chitosan produced by deacetylation is
more soluble in ILs than chitin. However, it can also be processed from acetic acid.
The use of IL for the processing of chitosan is not necessarily required as is the case
for chitin and cellulose. Toskas et al. produced pure microfibers on an industrial scale
using 8.5 wt% chitosan dissolved in acidic acid. These fibers were recently tested
as medical products [112, 113]. Studies by Pillai et al. have shown that the dry–wet
spinning of chitin in acetic acid results in highly deacetylated products [104]. This
polymer-analogous reaction can be avoided by using ILs. For the preparation of
spinning dopes, it is important that the solubility of chitin increases with increasing
hydrogen-bond acceptance properties of the IL and also depends on the dissolution
temperature [114]. Notably, it was found that pure chitin fibers are brittle due to the
high crystallinity of chitin [108]. This issue can be improved by blending chitin with
cellulose. Up to now, there are some cellulose/chitin blend materials, like membranes,
films, and even multifilament fibers, described in the literature [100, 115, 116].