Pretreatment of Polyester/Cotton Blended fabric
|Deweighting, splitting of PES||X||X||X|
|One bath alkali and bleaching phase||X|
|Acid After treatmeny||X||X||X||X|
Scouring : The scouring of polyester
fabric mainly depends on the type of sizing agents used on the yarn. Flat polyesterfilament
fabrics are commonly scoured to remove sizes and lubricants, after spotting
(if necessary) to assist the removal of loom stains. The preferable condition for scouring of polyester in alkaline reagents (caustic soda, soda-ash, ammonium hydroxide) is about 2 g/1 with a treatment time of 30-60 min at a temperature of 75-80~ Alternatively, scouring can be carried out with anion active detergents in
an amount 1-2 g/1 at 80-95~ for 20-30 min.
Special precaution is necessary when polyester is scoured with strong alkali at higher temperatures and care has to be taken not to hydrolyse the fibre.
Acid aftertreatment : The material to be dyed should exhibit a weakly acid (pH 6 to 6.5) or at
least a neutral reaction.
Drying : Only if the piece goods are set before dyeing. PES/VVo blends are not dried before
presettting if this is to take place on the crabbing machine.
Presetting : This is usually carried out before dyeing but after pretreatment so that no impurities
are fixed in the material. VVhether presetting is necessary depends on the quality of the material.
The conditions to be selected for presetting (temperature and time) should be determined
according to the available machines and the recommen-dations of the fibre producer. PES/VVo
blends can be preset on the crabbing machine or a stenter.
Singeing, shearing : After dyeing, the goods are sheared and singed (except PES/Wo),
depending on their quality.