Fibre Manufacturing Process
Today over 70 to 75% of polyester is produced by CP( continuous
polymerisation) process using PTA(purified Terephthalic Acid) and MEG.
The old process is called Batch process using DMT( Dimethy
Terephthalate) and MEG( Mono Ethylene Glycol). Catalysts like 5b3O3
(ANTIMONY TRIOXIDE) are used to start and control the reaction. TiO2
(Titanium di oxide) is added to make the polyester fibre / filament
dull. Spin finishes are added at melt spinning and draw machine to
provide static protection and have cohesion and certain frictional
properties to enable fibre get processed through textile spinning
machinery without any problem.
Polymerisation
- PTA which is a white powder is fed by a screw conveyor into hot
MEG to dissolve it. Then catalysts and TiO 2 are added. After that
Esterification takes place at high temperature. Then monomer is formed .
Polymerisation is carried out at high temperature (290 to 300 degree
centigrade) and in almost total vacuum. Monomer gets polymerised into
the final product, PET (Poly ethylene Terephthalate).
-
Melt Spinning
- This is in the form of thick viscous liquid. This liquid is them
pumped to melt spinning machines. These machines may be single sided or
double sided and can have 36/48/64 spinning positions. At each position
, the polymer is pumped by a metering pump-which discharges an accurate
quantity of polymer per revolution ( to control the denier of the
fibre) through a pack which has sand or stainless steel particles as
filter media and a spinnerette which could be circular or rectangular
and will have a specific number of holes depending on the technology
used and the final denier being produced. Polymer comes out of each hole
of the spinnerette and is instantly solidified by the flow of cool dry
air. This process is called quenching. The filaments from each
spinnerette are collected together to form a small ribbon, passed over a
wheel which rotates in a bath of spin finish: and this ribbon is then
mixed with ribbon coming from other spinning positions, this combined
ribbon is a tow and is coiled in cans. The material is called undrawn
TOW and has no textile properties.
Drawing and Cutting
At the next machine ( the draw machine), undrawn tows from
severl cans are collected in the form of a sheet and passed through a
trough of hot water to raise the temperature of polymer to 70 degrees C
which is the glass transition temperature of this polymer so that the
polymer can be drawn. In the next two zones, the polymer is drawn
approximately 4 times and the actual draw or the pull takes place either
in a steam chamber or in a hot water trough. After the drawing is
complete, each filament has the required denier, and has all its sub
microscopic chains aligned parallel to the fibre axis, thereby improving
the crystallinity of the fibre structure and imparting certain
strength.