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Chitin, chitosan and bacterial cellulose for textiles 295

evaporation of the solvent (Fig. 12.3). The solvent plays two crucial roles in
the electrospinning process: fi rst, to solvate the polymer molecules to form

the electrified jet and carry the solvated polymer molecules towards the

collector, then to leave the polymer fibres by rapid vaporization of the
solvent molecules (Park et al., 2007).
Variations in the morphology of the prepared nanofibres are infl uenced

by both system and process parameters. System parameters include polymer
solubility and concentration, molecular weight, molecular weight distribu-
tion, pH, architecture (branched or linear) of the polymer and solution
properties (viscosity, conductivity and surface tension). For example, higher
polymer concentration leads to increased uniformity and fibres with cylin-

drical shape (Deitzel et al., 2001). Thinner fibres are obtained from solutions
with lower polymer concentrations (Shin et al., 2001a). Although solvent
viscosity typically ranges from several dozens to few hundreds of millipas-
cals per second and conductivity from nano- to microsiemens per centime-
tre, general recommendations for system parameters are usually avoided
because the ideal values vary considerably with the polymer-solvent system
(Greiner and Wendorff, 2007). The formation and structure of the electro-
spuns are also greatly affected by process parameters such as: electric
potential, polymer flow rate, capillary–collector distance, ambient parame-

ters (temperature, humidity and air velocity in the chamber) and motion of

Syringe

Polymer or blend solution

Metallic needle

Electrified jet

High-voltage power supply

Fibre mat

Collector

12.3 Schematic representation of electrospinning fi bre production.

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