Spinning
process of Synthetic Fibers
Anagha Arjun Chaudhari
Department of Textile
Technology
Veermata Jijabai
Technological Institute, Mumbai, Maharashtra State, India
- Dissolution of
polymer in suitable solubilizing agent .
- Extrusion of
liquid solution through spinneret under pressure.
- Continuous solidification of
extruded liquid.
Methods used for fiber formation :
- Melt spinning
- Dry spinning
- Wet spinning
Melt
spinning :
This process can be applied to the polymer which gives viscous
liquid on melting without decomposition at high temperature i.e. they should
not degrade on the application of heat and have specific melting point.
fibre production through melt spinning consist of
following steps :
- Feeding and
melting of polymer which are initially in the form of chips.
- Homogenization
of melt in melt block.
- Melt pump is to
maintain constant rate and pressure of 70-150 kg/cm2.
- Filtration of
molten polymer in filter pack spinneret.
- Extrusion of
polymer through spinneret.
- Solidification
of extruded molten filament by cooling (quench) air.
- Application of
lubricant or spin finish
- Collection
of filament on bobbin.
Advantages :
- Simple and
economical process.
- Lowest to
highest production rate can be achieved.
- No requirement of chemical
recovery.
Disadvantages :
- Applicable to
limited polymers (polymers which are not decompose at its melting point)
- Structural
development in filament is poor as solidification rate is high and
ultimately maximum strength cannot be achieved.
- Temperature control is critical.
Dry
spinning :
This process involves formation of dope by mixing polymer
and solvent. The polymer concentration in dope is from 20% - 30%, higher
concentration results higher viscosity and ultimately difficulty in handling.
Polymer solution heated to higher temperature to reduce viscosity. Therefore
solvent should contain good heat stability and free for explosive
characteristics.
Following
s teps involved in fib
Following steps involve in fibre formation through dry spinning
:
- Formation
of dope, dissolution of polymer in the suitable solvent. Solvent should be
inert with the polymer.
- Filtration of polymer solution
- Extrusion of polymer solution through spinnerette in
drying chamber at pressure of 100-150 kg/cm2.
- Solidification of polymer solution in presence of heat
and inert gas, solvent is removed in this stage therefore solvent should
have low boiling point for ease in recovery.
- Application
of spin finish for lubrication.
Advantages :
- Mostly useful for heat sensitive polymer.
- Spinning conditions can be changed according to
requirement or end use.
- High spinning speed.
- Post spinning operations are simple.
- Moderated
concentration of polymer required.
Disadvantages :
- Solvent recovery process
- Addition post spinning operation, for complete removal
of solvent.
- Difficult to achieve proper dimension of filament
because solvent evaporates from the extruded
filament leave behind irregular surface.
- If
solvent is flammable then there will be chances of explosion, therefore
proper selection of solvent is required.
Wet spinning :
This
process is applicable for the polymers which dissolved only in non-volatile
solvent and does not melt. Feeding solution is dissolved polymer in suitable
solvent. Polymer solution is more diluted for complicated solidification
processes. Concentration of polymer solution is ranges between 5%-25% with
viscosity 20-5000 poise.
Following
steps involve in the fibre formation through wet spinning process :
- Homogeneous mixing of polymer and suitable solution in
dope tank.
- Dope is transferred to gear pump through pipes, feed is
controlled by gear pumps.
- Solution is filtered before extrusion.
- Then solution is extruded in coagulating (spinning)
bath, which contains the low molecular weight chemicals which are non
solvent to polymer but freely miscible with solvent (which is used to
prepare dope).
- Solvent is dissolved in spinning bath and filament
solidifies.
- After that filament wash to remove any remnant solvent
and then draw up to desire length.
- Solvent
also can be extracted from spinning bath by certain chemical processes.
Advantages :
- Fibre can attain maximum strength.
- Applicable
for temperature sensitive polymers.
Disadvantages :
- Low production rate.
- Process is lengthy and so cost is high
- Solvent
recovery is difficult.
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