Analysis of the Causes of Disperse Small Color Dots in the Dyeing of Polyester/Cotton Fabrics

Problem: When the polyester-cotton blend fabric is impregnated (jet overflow dyeing, air flow dyeing, and jigger dyeing) with light color, sometimes the cloth surface will have a dense "small color point", and it is difficult to modify the "small color point" once it is formed. Can only be dyed with dark shades.

Cause: It is caused by singeing before dipping.

Polyester-cotton blended fabrics are intertwined with blended yarns of cotton-based polyester staple fibers and cotton fibers. The surface of the fabric is covered with a layer of hairiness, which affects the brightness and uniformity of the color. Therefore, singeing must be performed.

However, the hairiness of polyester staple fiber leaves a burning point (also known as melting point) after singeing. Due to the high temperature melting, the original structure (such as crystal, orientation, etc.) is destroyed, the fiber structure is significantly relaxed, the glass transition temperature is significantly reduced, and the dye absorption rate and the color-sucking capacity are greatly increased. Therefore, the melting point left by singeing absorbs more dye than conventional polyester fibers during dyeing and dyeing. After testing, the color depth can be more than doubled (especially light color in dyeing is prominent). Therefore, there will be a clear "small color point" on the surface of the fabric.

Therefore, when the polyester-cotton blend fabric is dyed and dyed, it can only be singed after dyeing, and must not be singed before dyeing.

While continuous hot-melt pad dyeing, due to the small ability of the fiber itself to absorb color, the effect on the color depth is small, and the “small color point” performance is not obvious.

The polyester/cotton fabrics made of polyester filaments and cotton yarns, although their fabrics have less hairiness (only the hairiness of cotton and no polyester hairiness), still have a certain influence on the surface finish of fabrics. However, the fabric of polyester filament and cotton yarn should not be singed. Because the singeing process of this type of fabric in the >900 °C, once the singeing flame is uneven (such as partial crater blockage), the polyester filaments will be heated unevenly, resulting in different shrinkage, resulting in "scarring frizz" . In addition, due to the difference in microstructure (crystallinity, alignment, etc.), the ability to absorb color differs. After dyeing and dyeing, warp color bars (also known as slivered bars) are produced.

The safest method is to add an “enzyme wash” before dyeing and use cellulase to remove the hairiness of the fabric cotton fibers.