3. Stage of Dyeing:
First stage (Dissolving of the dye):
In this first stage, the dye, in solid form, is equilibrated according to
the dye dissolved in molecular form , or in form of dispersed micro
powder.
Second stage (Adsorption):
During this stage, by the effect of the dye-fibre affinity, the dye is
adsorbed at the surface of the fibre, thus forming chemical bonds
with it. A quick adsorption of the dye on the surface of the fabric
reduces the dye concentration near the fibre, thus reducing the
adsorption speed. A correct speed of the liquor change in contact
with the fibre allows the maximum concentration of the dyeing
solution near the fibre, and consequently the correct speed.
At the same time, the liquor flow in contact with the material is
spread homogeneously and allows a good distribution of the dye in all
the areas of the textile surface; this enhances the dye consistency
with the same operating times
4. Third stage (Diffusion):
During this stage the dye, adsorbed in molecular form by the surface,
by breaking and restoring the bonds many times tends to penetrate
into the bulk of the fibre through amorphous areas, to spread
homogeneously and fix steadily.
Fourth stage (Migration):
Stages 2 and 3 are reversed in this fourth migration stage; the dye
must diffuse toward the external layers of the fibre, and then come
back always in solution and migrate in areas of the fibre where there is
a lower concentration of dye, thus enhancing the colour consistency.
8. PROCESS OF MANUFACTURING POLYESTER
FILAMENT YARN
Polymerization
To form polyester, dimethyl terephthalate is first reacted with ethylene
glycol in the presence of a catalyst at a temperature of 302-410°F (150-
210°C).
The resulting chemical, a monomer (single, non-repeating molecule)
alcohol, is combined with terephthalic acid and raised to a temperature
of 472°F (280°C). Newly-formed polyester, which is clear and molten, is
extruded through a slot to form long ribbons.
Drying
After the polyester emerges from polymerization, the long molten
ribbons are allowed to cool until they become brittle. The material is
cut into tiny chips and completely dried to prevent irregularities in
consistency.
9. Melt spinning
Polymer chips are melted at 500-518°F (260-270°C) to form a syrup-like
solution. The solution is put in a metal container called a spinneret and forced
through its tiny holes, which are usually round, but may be pentagonal or any
other shape to produce special fibers. The number of holes in the spinneret
determines the size of the yarn, as the emerging fibers are brought together to
form a single strand.
At the spinning stage, other chemicals may be added to the solution to make
the resulting material flame retardant, antistatic, or easier to dye.
Drawing the fiber
When polyester emerges from the spinneret, it is soft and easily elongated up
to five times its original length. The stretching forces the random polyester
molecules to align in a parallel formation. This increases the strength, tenacity,
and resilience of the fiber. This time, when the filaments dry, the fibers become
solid and strong instead of brittle.
Drawn fibers may vary greatly in diameter and length, depending on the
characteristics desired of the finished material. Also, as the fibers are drawn,
they may be textured or twisted to create softer or duller fabrics.
Winding
After the polyester yarn is drawn, it is wound on large bobbins or flat-wound
10. Manufacturing Staple Fibre
In making polyester staple fibre, polymerization, drying, and melt spinning (steps 1-4 above) are
much the same as in the manufacture of filament yarn. However, in the melt spinning process,
the spinneret has many more holes when the product is staple fibre. The rope-like bundles of
polyester that emerge are called tow.
• Drawing tow
• 1 Newly-formed tow is quickly cooled in cans that gather the thick fibers. Several lengths of
tow are gathered and then drawn on heated rollers to three or four times their original
length.
• Crimping
• 2 Drawn tow is then fed into compression boxes, which force the fibers to fold like an
accordion, at a rate of 9-15 crimps per inch (3-6 per cm). This process helps the fiber hold
together during the later manufacturing stages.
• Setting
• 3 After the tow is crimped, it is heated at 212-302°F (100-150°C) to completely dry the fibers
and set the crimp. Some of the crimp will unavoidably be pulled out of the fibers during the
following processes.
• Cutting
• 4 Following heat setting, tow is cut into shorter lengths. Polyester that will be blended with
cotton is cut in 1.25-1.50 inch (3.2-3.8 cm) pieces; for rayon blends, 2 inch (5 cm) lengths are
cut. For heavier fabrics, such as carpet, polyester filaments are cut into 6 inch (15 cm) lengths
11. DYEING PROCESS OF POLYESTER
Polyester is the most commonly used synthetic fiber in the world.
Polyester fiber is dyed with disperse dyes. It can also be dyed during
extruding the fiber but we can dye after yarn preparation.
The process involves dye transfer from liquid (water) to
a solid organic fibre and it takes as following:
Dispersion of the dye in the solid phase into water by
breaking up into molecules( dissolution of the Dye)
Adsorption of the dissolved dye from the solution onto
the fibre surface
Diffusion of the dye molecules from the fibre surface into
the interior of the fibre
14. Poly Cotton
Poly Cotton fabric is made of a combination of cotton and
polyester. It combines the benefits of cotton, such as its
absorbency and breathing qualities, with the toughness
and lack of wrinkling that polyester possesses.
In order to weave a poly cotton blend, yarn of both cotton
and polyester are put on a loom. The loom is then used to
weave a single fabric out of both the cotton and the
polyester yarn, creating a new fabric that is sometimes
called poly cotton. Most common types of poly cotton
fabric boast slightly more cotton content than polyester
content in the end.
15. Dying of Polyester/Cotton Blends Goods
(One bath one stage dyeing with disperse/ direct dyes at atmospheric pressure)
In this method the PC or CVC goods can be dyed at one single bath with disperse and selected
direct dyes (stable in high temperature and compatible with polyester dyeing)- disperse for
polyester and direct for cotton. Some direct dyes , for example , C.I. Direct Black 22 – the pH
may be adjusted to 8-9 with soda ash.
Dyeing Procedure:
1. Set the dyebath with substrate at 50 temperature and add dispersing agent, leveller, acetic
acid , carrier and other auxiliaries , then urn the dyebath for 5-10 minutes.
2. Add both dyes and raise the temperatur4e to 90- 100 @ 1-2 C/min
3. Add glauber salt and run the bath for one to two hours at the same temperature .
4. Lower down the bath temperature to 70 – 80 over 10-15 minutes.
5. Drip the dyebath and carry on the after treatment process.
After Treatment Process:
1. Rinse twice with hot and cold water.
2. Treat the fabric with suitable fixing agent for improving the wet fastness properties of dyed
goods .
3. Soap wash according to vender recommendation.
4. Rinse twice with hot and cold water and then
5. Neutralize with acetic acid.
