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Fibre and Filament Production

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For now you may find the following links useful;

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Fibre Synthesis 

There are 3 basic steps of fibre synthesis, these include;

  • Production of polymer solution
  • Extrusion of fibres
  • Solidification of fibres; through cooling, coagulation or evaporation

The term spinning has been borrowed from the spinning process required to make yarns from natural fibres, such as wool, and is somewhat incorrect to the process, the fibre solution is extruded, not spun. 

Different methods of fibre extrusion include;

  • Melt Spinning
  • Wet Spinning
  • Dry Spinning
  • Gel Spinning
  • Emulsion
  • Electro spinning

Useful Links (general to spinning)

http://www.fibersource.com/f-tutor/techpag.htm

http://www.teonline.com/knowledge-centre/polymer-processing.html

http://www-unix.ecs.umass.edu/~rlaurenc/Courses/che333/Reference/Fiber%20Spinning.pdf

http://www.epa.gov/ttn/chief/ap42/ch06/final/c06s09.pdf

BISFA (International Bureau for the Standardization of Man-Made Fibres) Terminology of man made fibres booklet

http://www.bisfa.org/Portals/BISFA/Terminology/BISFA%20Terminology2009%20(final%20version).pdf

This booklet not only defines each fibre, but also provides diagrams and explanations of their production. 

Melt Spinning 

The simplified explanation of melt spinning is that polymer granules are melted and then extruded through the spin head. The metering pump controls the flow of molten liquid to the spin head, where it is filtered before extrusion to ensure any un-melted are removed so that they do not form pert of the fibre, which would cause weak points. The quench air cools the fibres as they emerge. In order to then spin the cooled Filament? fibres a Lubricant? must be applied as the synthetic fibres are not conductive and therefore static can be problematic. The winding speed is a critical element to the alignment of the polymers in the fibre which will influence the strength of the resultant fibre. 

Melt Spinning

The melt spun method has a variety of benefits;

  • It is very cost effective, the least expensive of the spinning methods- In larger providers the polymer solution is sent direct to the extruder taking out the steps of granule production and melting
  • As no solvent is used no washing is required
  • It is high speed, making around 8000m/minute

It is the preferred method of production of polymers that will not suffer thermal degradation at temperatures required to form a melt solution of the desired viscosity.

Fibres produced in this manner include nylon, PE, PP and polyester.

Monofilament yarns can also be produced in this method, however due to their larger Cross section? they require cooling in water instead of air. 

Useful links;

http://oecotextiles.wordpress.com/tag/melt-spinning/

http://www.ipfdd.de/Theory-and-Model-of-Fibre-Formation.167.0.html?&L=0

Wet Spinning

Wet spinning is required for polymers that require dissolving in a solvent to be spun. It is named wet spinning because the fibres are extruded directly into a liquid bath. Being extruded into a liquid provides a greater drag force on the Filament? than those extruded directly into air, therefore the speeds at which this occurs is reduced from that of melt and dry spinning. Once evaporated these fibres then have to be drawn or stretched in order to orient the polymers to give the fibre its strength.

The fibre solution is extruded into a liquid that will draw out the solvent, leaving behind only the polymer. The rate at which this occurs is crucial, as if it occurs too quickly the bath liquid can create micro-voids in the fibre which will be a weak points.

Wet spinning is based on precipitation, where a polymer is drawn through a spinneret into a non-solvent. The prepared spinning dope is extruded into the non-solvent and precipitation or coagulation occurs.

Fibres spun using this process include Acrylic, Rayon, Aramid, and Spandex.

Wet Spinning

Figure 2. Wet Spinning. Image from; http://www.sciencedirect.com/science/article/pii/S014486170700152X

Dry spinning

In dry spinning the polymer is dissolved in its solvent and then extruded, as the fibres emerge through the spinneret the solvent is evaporated off with hot air, in most cases this is then collected and re-used. Figure 3 illustrates the process. Dry spinning is required for polymers with a melt temperature equal to or close to their thermal degradation temperature, therefore they require dissolving in a solvent in order to be processed into fibres. 

Dry Spinning

Figure 3. Dry Spinning. Image from http://wwwchem.uwimona.edu.jm/courses/CHEM2402/Textiles/Synthetic_Fibres.html

Links;

http://www.gatewaycoalition.org/files/fundamentals_of_manufacturing/web/hidden/synth/Ch4/4_2f.htm

Dry-jet wet spinning method

In this method the polymer is dissolved in an appropriate solvent to make the fibre solution. This solution is then extruded under heat and pressure into an air gap before it enters a coagulation bath. The produced fibre is then washed and dried before it is heat treated and drawn. This is an alternative method to wet spinning and is required as spinning directing into the bath, for some fibres, creates microvoids that negatively affect the fibre properties, this is due to the solvent being drawn out of the liquid too quickly. An inert atmosphere may be required to prevent oxidisation in some polymers, if so fibres are extruded into a nitrogen atmosphere.

This method is often required for high performance fibres with a liquid crystal structure. Due to their structural properties their melt temperature is either the same as, or dangerously close to their decomposition temperature, therefore they must be dissolved in an appropriate solvent and extruded in this manner. dry-jet wet spinning

Figure 4. Dry-jet wet spinning. Image from RR Mather, Chemistry of Textile Fibres, 2011, royal society of Chemistry, Chapter 6 High Performance Fibres.