Thursday, 18 June 2009

Polyurethane Fibres ( Spandax, Lycra)



Polyurethane Fibres ( Spandax, Lycra)

Polyurethane is produced by action of butanediol and hexamethylene diisocyanate.

The polyurethane thus formed has rubber like properties. It gives an elastomeric fibre, which displays elasticity associated with natural rubber and hence can be stretched several times its original length and on releasing the stretching loads it will snap back quickly to recover its original length almost completely. Therefore polyurethane fibres are called snap back or elastomeric fibres.

Different Steps in Fiber Manufacture

Prepolymer Production:

The soft segments of the final polymer are formed in this step. The segments are the source of amorphous regions which permit unfolding of the molecular chains leading to the extension of the fibre under tensile stresses. These segments are made by normal condensation polymerisation techniques. These segments have hydroxy groups at the end.

Reaction Between prepolymers and Diisocyanate

The first prepolymer is reacted with excess of diisocyanate to form urethane groups in the molecular chains.

Segmented polyurethane production

In this step the hard segment is created by chain extension in which second prepolymer is treated with glycols or diamines.

Spinning

When the final polymer contain essentially linear macromolecules then it is dissolved in the solvent ( eg. DMF- Dimethyl Formamide) and extruded through spinnerettes into a coagulating bath ( water) as in wet spinning or into an atmosphere to remove the solvent as in dry spinning.

Properties

Strength: 0.55-1.0 gpd

Extension at Break: 520-610 %

Specific Gravity: 1.20-1.25

Set % at 600% stretch: 70%

Moisture Regain: 0.8-1.2

It is a thermoplastic fibres which sticks at 170 deg C and melts at 230 deg C

It has an excellent resistance to sunlight

It is resistant to insects and microorganisms.

It is resistant to common solvents such as dry cleaning solvents and saturated hydrocarbons.

Chemical Properties

It has good resistance to cold dilute Acids, Hot concentrated acids slightly yellow it.

It has a good resistance to weak and cold alkalies. It has good resistance to cosmetic oils and lotions. Chlorites and hypochlorites attack the fibre.

When heated the fibres fuse and do not shrink from the flame. They burn and produce soft fluffy black ash.

3 comments:

Srinivasa Rao said...

WHAT CAN BE DONE TO SUCH LYCRA/SPANDEX SCRAP OR CUT PIECES. CAN IT BE RECYCLED OR IS THERE A PROCESS TO GENERATE/MAKE PRE-POLYMER?

Team Asia said...

Great Post. I have to bookmark this article. Not only does it list the best social networking websites, it also explains what they can do. two thumbs up.

pu synthetic leather trader in india

Hide said...

your post is very useful for me. Thank you very much!

Related Posts Plugin for WordPress, Blogger...

Total Pageviews