The Causes of Yellowing of Yarn After Whitening

After bleaching, whitening yarn placed for a certain period of time, there are two problems you may meet: one is to produce yellow spots, and the second is to extend the whiteness with time.

The main reason

1. The yellow spot is due to bleaching with poor water quality, containing divalent iron ions higher due to divalent iron ions over time by oxidation or trivalent iron ions, so that the formation of yellow spots on the yarn. This yellow spot not only affects the appearance of quality, but also make the fibre brittle.

Solution:

When the water quality is poor, the yarn bleaching with oxalic acid 1.5-2.0g / L, at 80-85 ℃ for pickling. Because oxalic acid can generate complex ions with iron ions and dissolved in water, the iron in the water can be removed to achieve the purpose of non-yellowing.

2. The main reason why the whiteness of the bleached and whitened yarn decreases with the extension of time is due to insufficient cooking. If the yarn is not fully boiled, impurities in the cotton fibre is not completely removed, with this yarn immediately bleaching, whitening, a long time, the impurities within the fibre and natural pigments will be revealed resulting in a decline in whiteness.

Solution:

To ensure that the gross effect of the bleached yarn reaches 13-15cm/30min, and the gross effect should be uniform and consistent, in order to ensure that the bleached and whitened yarn does not yellow.

In addition, when dechlorinating after bleaching with sodium hypochlorite, the amount of baking soda is too much or not washed, which can also make the yarn yellowing.

Yarn drying, drying room temperature is too high, drying time is too long will also cause yarn yellowing.

Other possible causes

1.With acid with alkali, hydrogen peroxide wash is not clean, softener, etc. will produce yellowing.

2. The process is not the same will produce different yellowing. Yarn drying, drying room temperature is too high, drying time is too long will also cause yellowing of yarn.

Too high a dosage of whitening agent will make the fabric yellowing, especially when placed for a period of time, the greater the moisture content of the fabric yellowing is more pronounced, can not be used to increase the amount of whitening agent to achieve the whiteness requirements.