Introduction


The estimated polyester fibre production, in 2007, was 34million tons (approx)-39.7% of the whole textile fibre production-while, cottonproduction was 28 million tons (approx) and other cellulosic fibres, 2.8 million tons (approx). On a positive note,polyester fibres are estimated to grow by 5% annually, even as other textilefibres stagnate or decrease.


What is PET?


The development of fibres from polyester have come a fullcircle since scientists at ICI, UK, first produced dimethyl terephthalate fromethylene glycol and terephthalic acid. Subsequent years saw the arrival of thisnew fibre in the market, chemically known as polyethylene terephthalate (PET).


Independent of this research, DuPont (US) and Hoechst (Germany) also developed this synthetic fibre. By today's standards, it is the mostversatile synthetic fibre ever invented. It lends itself beautifully alone, asa textile fibre, or as blends with cotton, viscose, polynosic, linen, silk,wool or hemp. The chief characteristics of this fibre include:


  • Good crease recovery
  • Good shape retention
  • High bulking capacity
  • Good abrasion
  • Tear resistance
  • Good dye ability
  • Acceptable moisture absorption
  • No strength loss during wetting and other chemical treatments
  • Resistance to microorganism, insects, mildew, etc.


Structure and modifications


Mainly manufacture by the direct reaction of terephthalicacid and ethylene glycol, polyester is devoid of functional groups.


Polyester modifications are made to alter the innerstructure of the fibre. These modifications are physical, using specialmethods, or they contain copolymers or different chemical components, givingthe desired end results like low pilling, dyeing behavior to anionic andcationic dyes, etc. An interesting modification is the process known astexturising, where the molten fibre is first stretched and then cooled. Itgives the fabric a luxurious bulkiness, softness and extra shine.


Various types of additions and modification also affect theperformance of the fibre/ fabric. For example, delustering agents (usuallytitanium dioxide) results in dull polyester, while adding optical whitener tothe fibre before spinning produces white fibre.


Physical Properties


  • Density: 1.38 - 1.5
  • Melting point: 252 - 256oC
  • Softening point: 230 - 250oC
  • Glass transition temperature: 68oC


Drawbacks

The major drawback of the low moisture regain polyesterfibres is its wearing comfort. Hence, 67/ 33% blends with cotton result inexcellent fabrics having the best properties of both the fibres. Anotherdisadvantage is that oils, fats, grease, etc. can easily soil polyester fabricsbecause of the electrostatic charge build up and the fibres tend to pill.Hence, adding a singeing process takes care of this problem by burning off thesurface fibre.

 

Dream come true


In the 90s the polyester micro fibre was a commercial breakthrough in the world of synthetic textiles. A polyester fibre of exceptional soft feel, comfort, and rich appearance, was a synthetic fibre technologists dream. Micro fibres made it a reality.


What is so special about micro fibre?


  • Excellent softness
  • High drape
  • Silky handle
  • Good breath ability
  • Super comfort
  • Rich appearance


Thus its use is rapidly growing in the fashion apparel sector as well as the technical textile sector which itself is growing at rate of 35% in India. Considering these trends and the versatile uses of polyester microfilament fabrics, studying aspects of wet processing and problems in coloration of microfilament textiles is worthwhile.


Right first time


In textile wet processing problems and their remedies are very important. As a wrong first time is followed by harsh consequences like:


  • Extended processing time
  • Substandard fabric
  • Extra cost
  • Additional energy
  • Late delivery
  • Late delivery of following batches

 

      On X-Axis: Different Probabilities (If Not Right First Time) On Y-Axis: Relative Batch Cost

References

  1. N.D.Iyer, polyester the most versatile synthetic fibre, COLOURAGE, SEP-01 TO FEB-04 (SERIES OF 26 ARTICLES)
  2. A.K.Samnta, Road map for wet processing of micro denier polyester fabric and relevant studies on its dye ability, MAN MADE TEXTILES, OCT 03
  3. Dr. Bharat Desai, Oligomer control in polyester fibre processing, COLOURAGE JUNE 05
  4. Prof. V.A.Shenai, Technology of dyeing
  5. Mr. C.N.Sivaramkrishnan, Dispersing Agent, Colourage, September 05
  6. A.D.Sule, Practical Problems in dyeing of polyester off shades, MAN MADE TEXTILES, DEC 03
  7. Search engine goggle.com

 

The author is associated with Resil Chemicals, Ahmedabad

 

Also read "Problems and Their Remedies in Polyester Processing-Part II"