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.

Natural Dyes and their Application Classes

Natural Dyes and their Application Classes

S. No.	Common Name	Dye Class
1	Indigo	Vat
2	Madder	Mordant/Disperse
3	manjeet	Acid/ Mordant/Disperse
4	Sappanwood	Mordant /Disperse
5	Lac dye	Acid/ Mordant
6	Berberine	Basic
7	Tesu	Mordant/ Disperse
8	Kamala	Mordant/ Disperse
9	Dolu	Mordant/Disperse
10	Gall Nuts	Acid/ Mordant
11	Cutch	Acid/ Mordant/ Disperse

An excellent paper on the status of natural dyes in India can be downloaded from here

Here is a great blog talking about mordanting on wool.

Defects in Dyeing with Reactive Dyes

Defects in Dyeing with Reactive Dyes

Defect: Colors are not fast to washing, Abrasion;Staining in the fabric when transporting from place to the other, water marks on the fabric

Remedy : Wash the fabric with soap and soda ash at right temperature. Adding sequestering agent will yield good results. Treating with Ammonia will also give good results.

Defects in the fabric due to Printing- Need to take out full color

Remedy: Treat the dyed fabric with Sodium Hydrosuphite with 5-10 gm Sodium Hydrosulphite at 75 deg C for 30-45 minutes. Add 5-7 gms Caustic Soda for even removal of colors. The color becomes light yellow or brown after removal. Wash it thoroughly with soap.

The color can also be removed by solution of Sodium Hypochlorite. Treat the fabric with a sodium hypochlorite solution ( 3-5 gms Chlorine) for 20-30 minutes. Keep the pH between 9-10. The fabric is treated with Acetic acid after removal of color to remove chlorine and to neutralise the fabric.

The fabric can be redyed after removal of color

Defect: Bleeding in colors during washing, abrasion

Remedy: Boil the fabric with caustic, Treat the fabric with Hydrogen Peroxide ( 5-10 gpl, 60-70 deg C) to make the color fast.


Defect: The fabric has been dyed in darker shade, uneven dyeing

Remedy: To take out color from the fabric treat it with caustic for 45-60 min at 70 deg C. Thereafter treat the fabric with 10-20 gpl Acetic Acid for 40-60 min at 80-85 deg C.

Defect: Uneven dyeing, marks of water, marks of colors

Remedy: Wash the fabric in soap and redye in a darker shade

Defect : The fabric has become stiff and rough after dyeing

Remedy: Finish after adding right softner

Defect: Color staining of fabric, uneven dyeing

Remedy: Redye the fabric in darker shade.

Defect: Color staining in fabrics of darker shade, uneven undyeing

Remedy: Dye the fabric in Sulphur black

Caution: Please treat a small length fabric to check the effectiveness and any harmful effects before commencing a full treatment.

Polypropylene Fibres- Manufacturing Process

Polypropylene Fibres

Propylene is one of the constituents obtained from thermal or catalytic cracking of petroleum. Under suitable polymerising conditions, propylene produces fibres forming polypropylene.

Polymerisation: It is done by dissolving propylene in heptane using TiCl3Al(C2H5)3 catalyst system at about 100 deg C under a pressure of 30 Atm for 8 hours. The polymer has a molecular weight of about 80000.

Spinning : Polypropylene is melt spun. The filaments are extruded at 100 deg C above the melting point, cooled in air chamber and collected on bobbins. The filaments are hot drawn (polyethene- cold drawn) and twisted into yarns.


Properties:

1. PP fibres are colorless and have a smooth surface, with round cross section.

2. Tenacity- 4.5-6 gpd
Elongation at Break: 17-20 %
Elastic Properties at 2% extenstion: Instantenous
Stretch for 30 Seconds: 91%, delayed - 9%
Moisture Regain: Nil

3. Boiling water shrinks PP by about 15-20% in 20 minutes

4. Specific Gravity: 0.85-0.92

5. Softening point- 150 deg C, Melting Point: 160-170 deg C

6. PP is also attacked by atmospheric oxygen in presence of sunlight

7. It has excellent resistance to common organic solvents

8. It is resistant to insects and microorganisms

9. PP is generally resistant to common chemicals.