Bleaching cotton canvas due to baking caused by yellowing how to do?

The ways to improve the yellowing of bleached cotton canvas due to baking are:

1 scouring conditions: cooking pot scouring usually 1.96 × 105Pa

(2kg/cm2) under the pressure of cooking 4-5h, although 100 °C, most of the impurities have been removed, but the temperature increased to 116-140 °C, is conducive to the removal of wax. The content of caustic soda in scouring should be 7-8g/L. Water glass, sodium bisulfite, surfactant and other auxiliary agents should also be added. Synthetic detergents are used to help improve the efficiency of the hair.

2. Rolling alkali and detergent stacking: directly scouring the fabric, the gross effect only reached about 6cm, and thanks to the rolling of alkali and detergent heap, the gross effect is greatly increased. Experience has shown that when the caustic soda is 10-12g/L and the detergent is 2g/L, the temperature of the rolling liquid is 85°C and the stacking time is 20h. The whiteness of the semi-finished product is high, and after curing, the degree of yellowing is very small. Moreover, the above scouring can be dispensed with.

3. "Acid - bleach - acid" bleaching process: After the fabric is scouring, the "acid-float-acid" process is used to help remove pigments and improve whiteness. After the scouring, pickling is first performed to remove acid-soluble impurities and reduce the pressure of bleaching, thereby significantly improving whiteness. When the second acid is rolled, oxalic acid g/L is added because oxalic acid has a complexing effect and can more effectively remove impurities and improve whiteness.

4. Washing: Washing does not cause serious yellowing. The measures for improving the water washing effect and saving water are as follows: First, the number of the pad rolls should be more, and the pressure should be higher, in order to facilitate the exchange of impurities and lotion and reduce the liquid carrying rate on the fabric. Second, the water supply method should be reversed, and the flow of the wash solution should be suitable instead of overflowing in a short-flow manner.

5. Reasonable blue lightening: The fabric is refined, bleached, and the pigment is basically removed. It is quite white but still slightly brownish. By fluorescent whitening and blue at the same time, the fabric can have a clear white feeling without leaving a yellow light trace.

6. pH: for shoes with bleached cotton canvas, the pH value should be 6.5-9.5, otherwise, once the high temperature baking quickly loses the fluorescent brightener whitening effect, which is determined by the structure of VBL on the acid-base Sensitivity.

7. The amount of fluorescent whitening agent: The amount of whitening agent in the general pad dyeing and whitening solution should be 1.3-1.8g/L, and should not exceed 2g/L. Excessive use will not only have no whitening effect but will cause yellowing.