Spinning Process of Synthetic Fibers

Spinning process of Synthetic Fibers

Anagha Arjun Chaudhari

Department of Textile Technology

Veermata Jijabai Technological Institute, Mumbai, Maharashtra State, India

                                              
To convert fibres from polymer involves three steps :

1. Dissolution of polymer in suitable solubilizing agent .
2. Extrusion of liquid solution through spinneret under pressure.
3. Continuous solidification of extruded liquid.

Methods used for fiber formation :

1. Melt spinning
2. Dry spinning
3. 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 :

1. Feeding and melting of polymer which are initially in the form of chips.
2. Homogenization of melt in melt block.
3. Melt pump is to maintain constant rate and pressure of 70-150 kg/cm2.
4. Filtration of molten polymer in filter pack spinneret.
5. Extrusion of polymer through spinneret.
6. Solidification of extruded molten filament by cooling (quench) air.
7. Application of lubricant or spin finish
8.  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 : 

1. Formation of dope, dissolution of polymer in the suitable solvent. Solvent should be inert with the polymer.
2. Filtration of polymer solution
3. Extrusion of polymer solution through spinnerette in drying chamber at pressure of 100-150 kg/cm2.
4. 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.
5. 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 :

1. Homogeneous mixing of polymer and suitable solution in dope tank.
2. Dope is transferred to gear pump through pipes, feed is controlled by gear pumps.
3. Solution is filtered before extrusion.
4. 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).
5. Solvent is dissolved in spinning  bath and filament solidifies.
6. After that filament wash to remove any remnant solvent and then draw up to desire length. 
7. 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.