Polyster Fiber Specification and Properties

Physical and Chemical Properties of Polyester Fiber

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 CSoftening temp : 230 - 240 degree C

Melting point : 260 - 270 degree C

Effect of Sunlight : turns yellow, retains 70 - 80 % tenacity at long exposure

Resistance to Weathering: good
 

Cut Length

Cut lengths available are 32, 38, 44, 51 and 64mm for cotton type spinning and a blend of 76, 88 and 102 mm - average cut length of 88m for worsted spinning. The most common cut length is 38 mm.
For blending with other manmade fibres, spinners preferred 51mm to get higher productivity, because T.M. will be as low as 2.7 to 2.8 as against 3.4 to 3.5 for 38mm fibre. If the fibre legnth is more, the nepping tendency is also more , so a crompromise cutlength is 44 mm. With this cut length the T.M. will be around 2.9 to 3.0 and yarns with 35 to 40% lower imprfections can be achieved compared a to similar yarn with 51 mm fibre. In the future spinners will standardise for 38 mm fibre when the ringspinning speed reaches 25000 rpm for synthetic yarns.

For OE spinning , 32 mm fibre is preferred as it enables smaller dia rotor(of 38mm) to be used which can be run at 80000 to 100000 rpm.

Air jet system uses 38 mm fibre.

Tensile Properties

Polyester fibres are available in 4 tenacity levels.
  • Low pill fibres- usuall in 2.0 / 3.0 D for suiting enduse with tenacities of 3.0 to 3.5 gpd(grams per denier). These fibres are generally used on worsted system and 1.4D for knitting
  • Medium Tenacity - 4.8 to 5.0 gpd High tenacity 6.0 to 6.4 gpd range and
  • Super high tenacity - 7.0 gpd and above
Both medium and high tenacity fibres are used for apparel enduse. Currently most fibre producers offer only high tenacity fibres. Spinners prefer them since their use enables ring frames to run at high speeds, but then the dyeablity of these fibres is 20 to 25% poorer, also have lower yield on wet processing, have tendency to form pills and generally give harsher feel.

The super high tenacity fibres are used essentially for spinning 100% polyester sewing threads and other industrial yarns. The higher tenacities are obtained by using higher draw ratios and higher annealer temperatures upto 225 to 230 degree C and a slight additional pull of 2% or so at the last zone in annealing.

Dye Take Up

  • Each fibre producer has limits of 100 +- 3 to 100+-8. Even with 100+-3 dye limits streaks do occur in knitted fabrics. The only remedy is to blend bales from different days in a despatch and insist on spinning mills taking bales from more than one truck load.
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