Oligomers

Oligomers are still the biggest problem in wet processing of polyester fabric leading to variety of problems.

When the dyeing is not solid and appears skittery, the fabric is rejected. Warp-wise and weft-wise streaks lead to streakiness which usually occurs during warping and weft insertion. Some of the main causes of warp streaks in processing include:

• Rubbing of fabrics on a rough surface on roller
• Faulty shearing blades
• Faulty stitching leading to stitch opening during processing
• Superimposed ends during mercerising
• Improper functioning of tension guide bar on jigger
• Channeling during jigger dyeing
• Shrinkage of leader cloth on jigger
• Improper jet dyeing nozzle
• Low M:L in jet dyeing
• Insufficient rinsing of dyed fabric in rope form
• Faulty calendar rolls
• Improper sequence (e.g. singeing before dyeing in P:V fabric)

Pilling

Pilling is the formation of fibre balls on the fabric surfaces, when a group of loose, or short and broken fibres get entangled or accumulated on the fabric after abrasion. The tiny balls are pill. It cannot be eliminated totally, but it can be minimised by proper handling during fabric washing.

A possible explanation for its occurrence is that polyester fibres have a high strength compared to the natural fibres. The problems of pilling is severe in the case of 67/33 PET/COT blends.

Migration

Migration is the shifting of the colour to the surrounding areas. It is the unwanted reaction between the dye and the fibre.

Migration is a serious problem encountered both in dyeing and printing. Dye migration is generally more on 100 per cent polyester fabrics. It results in the colouring of unintended areas. Hence, any fabric containing the polyester is vulnerable to dye migration and bleeding.

References

• ND Iyer, Polyester the most versatile synthetic fibre, Colourage, September 01 to February 04 (series of 26 articles)
• AK Samnta, Road map for wet processing of micro denier polyester fabric and relevant studies on its dyeability, Man Made Textiles, October 03
• Dr Bharat Desai, Oligomer control in polyester fibre processing, Colourage June 05
• Prof VA Shenai, Technology of dyeing
• Mr CN Sivaramkrishnan, Dispersing Agent, Colourage, September 05
• AD Sule, Practical Problems in dyeing of polyester off shades, Man Made Textiles, December 03
• Search engine google.com

The author is associated with Resil Chemicals, Ahmedabad