Polymer Spinning• Polymer Spinning means manufacturing process for

creating polymer fibers.• It is a specialized form of extrusion that uses

a spinneret to form multiple continuous filaments.• There are many types of spinning:

– wet– dry– melt– gel– electro spinning

• Polymer Spinning means manufacturing process for creating polymer fibers.

• It is a specialized form of extrusion that uses a spinneret to form multiple continuous filaments.

• There are many types of spinning:– wet– dry– melt– gel– electro spinning

Wet Spinning• Wet spinning is the oldest of the five processes.• Wet spinning is based on precipitation, where a polymer

is drawn through a spinneret into a non-solvent.• This process is used for polymers that need to be

dissolved in a solvent to be spun.• The spinneret is submerged in a chemical bath that

causes the fiber to precipitate, and then solidify, as itemerges.

• The process gets its name from this "wet" bath.• Acrylic, rayon, aramid, modacrylic, and spandex are

produced via this process.

• Wet spinning is the oldest of the five processes.• Wet spinning is based on precipitation, where a polymer

is drawn through a spinneret into a non-solvent.• This process is used for polymers that need to be

dissolved in a solvent to be spun.• The spinneret is submerged in a chemical bath that

causes the fiber to precipitate, and then solidify, as itemerges.

• The process gets its name from this "wet" bath.• Acrylic, rayon, aramid, modacrylic, and spandex are

produced via this process.

Schematic figure of Wet Spinning

Wet Spinning…• The prepared spinning dope is extruded into the non-solvent and

precipitation or coagulation occurs.• Being extruded into a liquid provides a greater drag force on

the Filament than those extruded directly into air. Therefore thespeeds at which this occurs is reduced from that of melt and dryspinning.

• Once evaporated these fibres then have to be drawn or stretched inorder to orient the polymers to give the fibre its strength.

• The fibre solution is extruded into a liquid that will draw out thesolvent, leaving behind only the polymer.

• The rate at which this occurs is crucial, as if it occurs too quickly thebath liquid can create micro-voids in the fibre which will be a weakpoints.

• The prepared spinning dope is extruded into the non-solvent andprecipitation or coagulation occurs.

• Being extruded into a liquid provides a greater drag force onthe Filament than those extruded directly into air. Therefore thespeeds at which this occurs is reduced from that of melt and dryspinning.

• Once evaporated these fibres then have to be drawn or stretched inorder to orient the polymers to give the fibre its strength.

• The fibre solution is extruded into a liquid that will draw out thesolvent, leaving behind only the polymer.

• The rate at which this occurs is crucial, as if it occurs too quickly thebath liquid can create micro-voids in the fibre which will be a weakpoints.

Wet Spinning…

Basic Process of Wet Spinning

(i) Preconditioning of polymer dope

In a typical wet spinning line, the dope solution is filtered to remove gel particles or any solid impurity and de-aerated to remove trapped air/gasses.

If necessary, the polymer dope may also be heated to a pre-determined temperature.

This ensures smooth extrusion of the polymer solution into the spinning line.

A metering pump is used similar to that in melt spinning to regulate the flow of the polymer solution to the spinneret

(i) Preconditioning of polymer dope

In a typical wet spinning line, the dope solution is filtered to remove gel particles or any solid impurity and de-aerated to remove trapped air/gasses.

If necessary, the polymer dope may also be heated to a pre-determined temperature.

This ensures smooth extrusion of the polymer solution into the spinning line.

A metering pump is used similar to that in melt spinning to regulate the flow of the polymer solution to the spinneret

(ii) Spinneret in solution spinning

The spinneret plate, in solution spinning, is made of a softcorrosion resistant material, such as special grade SS or platinum.

It is usually thin with diameter of individual spinneret holes in therange of 0.025 – 0.1 mm and L/D ratio of 1.

Both the diameter of the spinneret and the length of thespinneret are much smaller than those kept in melt spinning. Thisis because the viscosity of the polymer solution is significantlylower (300-500 poise) and a high pressure is not required to pushthe dope through the spin pack or spinneret holes.

The holes are also placed very close to each other because the elasticity of thepolymer solution is much less compared to that in melt spinning and thepolymer solution shows only a limited extent of extrudate swell.

(ii) Spinneret in solution spinning

The spinneret plate, in solution spinning, is made of a softcorrosion resistant material, such as special grade SS or platinum.

It is usually thin with diameter of individual spinneret holes in therange of 0.025 – 0.1 mm and L/D ratio of 1.

Both the diameter of the spinneret and the length of thespinneret are much smaller than those kept in melt spinning. Thisis because the viscosity of the polymer solution is significantlylower (300-500 poise) and a high pressure is not required to pushthe dope through the spin pack or spinneret holes.

The holes are also placed very close to each other because the elasticity of thepolymer solution is much less compared to that in melt spinning and thepolymer solution shows only a limited extent of extrudate swell.

(iii) Coagulation bath in wet spinning The polymer solution is extruded inside a coagulation bath which

normally has a mixture of a solvent and a non-solvent. The composition of the coagulation bath, said as “bath concentration”,

is expressed as the concentration of solvent in the solvent/non-solventmixture.

(iv) Washing/ Drying (Post coagulation processes) The fibre from the coagulation bath is washed several times, stretched,

crimped, and/or heat-set (as may be required for a particular fibre)before winding it as a filament or cutting it into staple fibres.

Attempts are made to maintain concentration of coagulation bath byconstantly removing a certain amount of spent coagulation fluid andreplacing it with fresh coagulation fluid.

(iii) Coagulation bath in wet spinning The polymer solution is extruded inside a coagulation bath which

normally has a mixture of a solvent and a non-solvent. The composition of the coagulation bath, said as “bath concentration”,

is expressed as the concentration of solvent in the solvent/non-solventmixture.

(iv) Washing/ Drying (Post coagulation processes) The fibre from the coagulation bath is washed several times, stretched,

crimped, and/or heat-set (as may be required for a particular fibre)before winding it as a filament or cutting it into staple fibres.

Attempts are made to maintain concentration of coagulation bath byconstantly removing a certain amount of spent coagulation fluid andreplacing it with fresh coagulation fluid.

Dry-jet wet spinning

• A variant of wet spinning is dry-jet wet spinning, where the solution isextruded into air and drawn, and then submerged into a liquid bath.

• This method is used in Lyocell spinning of dissolved cellulose.• In this method the polymer is dissolved in an appropriate solvent to make

the fibre solution. This solution is then extruded under heat and pressureinto an air gap before it enters a coagulation bath.

• The produced fibre is then washed and dried before it is heat treated anddrawn.

• This is an alternative method to wet spinning and is required as spinningdirecting into the bath, for some fibres, creates microvoids that negativelyaffect the fibre properties, this is due to the solvent being drawn out of theliquid too quickly.

• An inert atmosphere may be required to prevent oxidisation in somepolymers, if so fibres are extruded into a nitrogen atmosphere.

• A variant of wet spinning is dry-jet wet spinning, where the solution isextruded into air and drawn, and then submerged into a liquid bath.

• This method is used in Lyocell spinning of dissolved cellulose.• In this method the polymer is dissolved in an appropriate solvent to make

the fibre solution. This solution is then extruded under heat and pressureinto an air gap before it enters a coagulation bath.

• The produced fibre is then washed and dried before it is heat treated anddrawn.

• This is an alternative method to wet spinning and is required as spinningdirecting into the bath, for some fibres, creates microvoids that negativelyaffect the fibre properties, this is due to the solvent being drawn out of theliquid too quickly.

• An inert atmosphere may be required to prevent oxidisation in somepolymers, if so fibres are extruded into a nitrogen atmosphere.

Schematic figure of Dry-jet wet Spinning

Wet Spinning

Dry-jet wet Spinning

Molecular orientation during dry-jet wet spinning

Dry Spinning• In dry spinning the polymer is dissolved in solvent and then

extruded, as the fibres emerge through the spinneret thesolvent is evaporated off with hot air, in most cases this is thencollected and re-used.

• Because there is no precipitating liquid involved, the fiber doesnot need to be dried, and the solvent is more easily recovered.

• It differs in that the solidification is achieved throughevaporation of the solvent. This is usually achieved by a streamof air or inert gas.

• In dry spinning the polymer is dissolved in solvent and thenextruded, as the fibres emerge through the spinneret thesolvent is evaporated off with hot air, in most cases this is thencollected and re-used.

• Because there is no precipitating liquid involved, the fiber doesnot need to be dried, and the solvent is more easily recovered.

• It differs in that the solidification is achieved throughevaporation of the solvent. This is usually achieved by a streamof air or inert gas.

Dry spinning…

• Dry spinning is required for polymers with a melt temperatureequal to or close to their thermal degradation temperature.

• In order to be processed into fibres, polymers must bedissolved in solvent.

• Acetate, triacetate, acrylic, modacrylic, polybenzimidazolefiber, spandex, and vinyon are produced via this process.

• Dry spinning is required for polymers with a melt temperatureequal to or close to their thermal degradation temperature.

• In order to be processed into fibres, polymers must bedissolved in solvent.

• Acetate, triacetate, acrylic, modacrylic, polybenzimidazolefiber, spandex, and vinyon are produced via this process.

Dry spinning…

Dry Spinning Process…

• In dry spinning, the polymer dope solution, after filtration and deaeration, is metered using a metering pump and pushed through a multihole spinneret into a closed spinning chamber/tower circulated with heated air/gas.

• The solvent from the extruded filaments evaporates due to the high surrounding temperature of the gas and is carried out of the spinning chamber by the circulating hot gas.

• The solvent and the gas are separated and recycled back into the spinning system.

• In dry spinning, the polymer dope solution, after filtration and deaeration, is metered using a metering pump and pushed through a multihole spinneret into a closed spinning chamber/tower circulated with heated air/gas.

• The solvent from the extruded filaments evaporates due to the high surrounding temperature of the gas and is carried out of the spinning chamber by the circulating hot gas.

• The solvent and the gas are separated and recycled back into the spinning system.

Dry Spinning Process…

• The extruded filament solidifies through partial crystallization, as the solvent is removed with spinning distance from the spinneret.

• The solidified filament is collected on a bobbin or guided to washing baths containing non-solvent to remove traces of the solvent present inside the spun filaments.

• The filaments are subsequently drawn, dried, crimped, heat-set and cut to staple fibres as required.

• The extruded filament solidifies through partial crystallization, as the solvent is removed with spinning distance from the spinneret.

• The solidified filament is collected on a bobbin or guided to washing baths containing non-solvent to remove traces of the solvent present inside the spun filaments.

• The filaments are subsequently drawn, dried, crimped, heat-set and cut to staple fibres as required.

Schematic ofthe three principaltypes of fibrespinning:

(a) melt spinning

(b) dry spinning

(c) wet spinning

Schematic ofthe three principaltypes of fibrespinning:

(a) melt spinning

(b) dry spinning

(c) wet spinning