Polyester is a category of polymer whose monomer contains the ester functional group.The most common polyester for fiber purposes is poly (ethylene terephthalate), or simply PET. This is also the polymer used for many soft drink bottles and it is becoming increasingly common to recycle them after use by remelting the PET and extruding it as fiber. This saves valuable petroleum raw materials, reduces energy consumption, and eliminates solid waste sent to landfills .
PET is made by reacting ethylene glycol with either terephthalic acid or its methyl ester in the presence of an antimony catalyst. The reaction is carried out at high temperature and vacuum to achieve the high molecular weights need to form useful fibers. PET is melt spun.
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.
- Denier: 0.5 – 15
- Tenacity : dry 3.5 – 7.0 : wet 3.5 – 7.0
- %Elongation at break : dry 15 – 45 : wet 15 45
- %Moisture Regain: 0.4
- Shrinkage in Boiling Water: 0 – 3
- Crimps per Inch: 12 -14%
- Dry Heat Shrinkage: 5 – 8 (at 180 C for 20 min)
- Specific Gravity: 1.36 – 1.41%
- Elastic Recovery @2% =98 : @5% = 65
- Glass Transition Temp: 80 degree C
- Softening temp : 230 – 240 degree C
- Melting point : 260 – 270 degree C
- Effect of Sunlight : turns yellow, retains 70 – 80% tenacity at long exposure
- Resistence to Weathering: good
- Rot Resistence: high
- Alkali Resistence: damaged by CON alkali
- Acid Resistence: excellent
- Organic Chemical Resistence: good