Pretreatment of Elastic Fabric

Pretreatment of Elastic Fabric
Rana Sohel
Executive Engineer
Sunman Textile Mills Ltd. Chittagong
Cell: +8801912-420118
Email: rsohel07tex@gmail.com



Elastic Fabric:
For elastic fibers, treatments depend on the chemical composition, which can be extremely variable. As far as the fabrics containing segmented polyurethane fibers are concerned, the suggested treatments to be carried out are the following:
Relaxation:
Before carrying out any further treatment, it is recommended to relax woven or knitted goods to obtain a uniform shrinkage and avoid stitch distortion or fabric deformation, creases or wrinkles. The fabric relaxation is a crucial step to allow good shrinkage and give excellent elasticity since the fabric width on looms is always bigger than the finished one (tensioned yarns on the loom). Many techniques are used but here are some of the most frequently used ones: table stealing, steaming carried out at the entry of the stenter, scouring carried out with hot solvents, relaxation in hot water with tensionless scouring; these techniques give poorer stabilization results and do not provide permanent crease resistance to textiles and fabrics.

Heat setting:
This process is crucial to give the fabric an optimum dimensional stability. It is recommended to carry out a heat setting treatment before any further wet treatment in order to avoid the formation of possible creases and folds. An optimum heat setting requires a temperature ranging between1800C-2000C, which must be maintained constant for at Ieast 45 minutes. An optimum heat setting also requires the use of an indirect-air heating stenter, allowing more uniform temperatures and no-gas conditions, which could lead to fibre yellowing. The fabric is weighed at the entry of the stenter and then subjected to steaming. Since the fabric shrinks during the heat setting treatment, the fabric width on the stenter must exceed the desired width by5-10%. An excessive heat setting could decolorize the fabric while an insufficient heat setting will result in poor fabric stability.
Heat setting of elastic fabric
Heat setting of elastic fabric
Scouring: 
It is necessary to carefully consider the characteristics of the fibre combined with the polyurethane elastomer.

Bleaching: 
This treatment is carried out using sodium hydrosulphite; a suitable optical bleaching agent can also be added.

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