Page 313 - Advances in Textile Biotechnology

294 Advances in textile biotechnology

the natural renewable resources as materials with potential for fi bres pro-
duction, were major breakthroughs in preparation of chitin and chitosan

fibres achieved, i.e. since the 1970s. In most studies, chitin and chitosan fi bres
are obtained by wet-spinning, comprising dissolving the polymer in an
appropriate solvent followed by extrusion of the polymer solution through
the spinneret into a non-solvent to solidify the fi bres. The polymer precipi-

tates in the form of filament, which can be washed, drawn and dried to form

the fibres (Agboh and Qin, 1997).
Traditional chitin solvents are organic and can contain di- or trichloro-
acetic acid alone or in conjunction with other organic solvents such as
formic acid, acetic acid, chloral hydrate, and methylene chloride. Moreover,
amide compounds such as dimethylacetamide (DMAc) and N-methyl-2-
pyrrolidone (NMP) or mixtures of these amides in conjunction with LiCl
form a stable spinning solution. The most commonly used chitosan solvent
is aqueous acetic acid (normally 2%). Additionally, 2% acetic acid–metha-
nol (1 : 1, v/v) aqueous solution is considered to be a particularly suitable

spinning solvent for preparation of chitosan fi laments (Hirano et al., 1999).

The mechanical properties of chitin/chitosan fibres produced by wet-spin-
ning depend on both the chemical nature (e.g. degree of deacetylation) of
the fibre and production (spinning) conditions. Fibres obtained from poly-

mers with a lower degree of deacetylation showed dry and wet strength
higher than those fibres obtained using more deacetylated polymers. Higher

fibre strengths can be achieved also by using special spinning conditions

such as the dry-jet wet-spinning technique where the biopolymer solutions
are extruded, loaded to an air gap of different lengths still as a solution and
precipitated in coagulation bath (Kim and Pak, 2005) and the use of special
solvent system to obtain a liquid crystal phase chitin and chitosan solutions.

Different drying conditions can affect fibre arrangement in e.g. 3D meshes
where the fibres are stuck to each other resulting in better mechanical

properties (Tuzlakoglu et al., 2004). However, chitin and chitosan fi bres
formed by the wet-spinning method have relatively low tensile strength and
are partially soluble at pH below 5.5, thus need further improvement for
specifi c applications.

A recent breakthrough in nanofibre technology is the use of electrospin-
ning as a convenient method for preparation of polymer fi brous materials
with very fine diameters, enormous surface-to-weight area and superior

mechanical properties. In this process, nanofibres are produced from the

polymer solution by electrostatic forces. In a simplified form, the electro-
spinning process consists of a syringe that holds polymer solution and two
electrodes where the positive one is connected to the syringe and the
negative one is the collector under a direct current (dc) voltage supply in
the kV range. The electrified jet of polymer solution drops from the tip of

the syringe and onto the collector, where it sets into a fibre owing to

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