Page 40 - New Cloth Market November 2022 Digital Edition

Chitosan-Based Sustainable Textile Technology: Process, Mechanism, Innovation & Safety

fibers where the extrusion chamber is
comprised of a reservoir, a metering
pump, and a spinneret. The chitosan
dope is extruded less than 1.5 bar
pressure into a coagulation bath. The Figure 4: A typical block diagram of wet spinning.
coagulation bath contains an aqueous
solution of the coagulant such as NaOH Table 2: Solvent system for the dissolution of chitin and chitosan
[7], KOH [8], cupric ammonia [9],
Chitin dissolution Chitosan dissolution
alcohol/calcium chloride/acetate [10],
(solvent system) (solvent system)
NaOH–Na2SO4, NaOH–AcONa [11],
NaOH-40% methanol, CuSO4–NH4OH, Trichloroaceticacid (40%)-chloral Dilute aqueous organic acid
CuSO4-concentrated ammonia [12], hydrate (40%)-methylene chloride (20%) (acetic acid, formic acid)
etc. The presence of tailors mentioned
LiCNS/Ca(CNS)2/CaI2/CaBr2 Dimethylsulfoxide/N,N-
above chemicals acts as coagulation
dimethylformamide (DMF)
retardants. In this process, the take-
up rollers, drawing system, drying Lithium thiocyanate p-Toluene sulfonic acid
rollers, and winding up are optimized
Formic acid-dichloroacetic acid- Guanidine hydrochloric acid-urea
according to the production rate and
isopropylether
required properties of fibers. The
excess amount of coagulant on fiber Sodium N-acylchitosan xanthate Ionic liquid, 1-butyl-3-
is washed off using distilled water or [O-(sodium thio) thiocarbonyl methylimidazolium bromide
aqueous methanol and ethanol. This N-acylchitosan]-xanthate ([BMIM][Br])
washing bath is also called predrying [O(sodium thio) thiocarbonyl cellulose]
bath. Some additional physical and
chemical processes are practiced to coagulation bath containing NaOH is is done by maintaining 14% of the
enhance the desired mechanical easier to prepare and strengthens the maximum first roller speed that
property in drying treatments. chitosan fibers within a short time. produces a straight fiber line during
coagulation. It is important to maintain
Dry spinning process
Solvent system the speed exactly to avoid un-
The chitosan used for dry spinning [13] stretching. A second roller having
A proper selection of solvent system should have the initial concentration higher speed is used to maintain a
and coagulation bath leads to produce over the critical concentration of chain stretching ratio of 1:12 to the produced
desired fiber structures and properties. entanglement which is equal or more monofilament. In the drying process
Many researchers have studied (Table than 0.5% (w/w). Acetic acid is (Figure 5), the hot air around 110°C is
2) different types of solvent systems frequently used for the dispersion of passed through a 65 cm oven, while
such as dichloroacetic acid-isopropyl chitosan. Similarly, the above- the air flow of 1.5 m3/h is used and
ether-formic acid, trichloroacetic acid, mentioned process is followed up by the retention time of monofllament in
dimethylacetamidelithium chloride; a the extrusion process. During the the oven is around 10s. Then, the
mixture of trichloroacetic acid-chloral coagulation process, 125 ml of chitosan fiber is treated in the wet air
hydrate-dichloromethane (DCM) is concentrated ammonia (20% w/w) in circulating at 25°C and water content
used for dissolving chitin. Besides, the the gaseous state comes in contact is 55% w/w for one week before final
pH-sensitive behavior of chitosan is with chitosan monofilament. The flow storage [13].
very useful in the processing of fiber. of gaseous ammonia is around 0.24
Electrospun
Acetic acid is effcient enough to m3/h for 7.5 s based on the relation
dissolve chitosan, a simple solvent between extruder and speed of the first In 1934, Antonin Formhals applied for
system, especially <pH 6. Moreover, roller around 3.4 m/min. The stretching a patent to manufacture textile yarn.

Figure 5:
A typical block
diagram of dry
spinning.

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