pH in Dyeing:
pH is a measure of the hydrogen ion
concentration of a solution. It is used to specify the acidity or alkalinity of
an aqueous solution. There are various factors that can influence the quality
of dyeing and batch-to-batch reproducibility, but pH ranks as one of the most
important factors. Effect of pH on dye adsorption is very important. Besides,
controlling pH is very important in dye bath because its effect on the dyeing
cycle . Generally, pH greatly influences the uptake of dye. In the case of acid dyeing, a low
pH helps to form the hydrogen bonds that attach acid dyes to protein fibers,
such as silk and wool, as well as nylon. In the case of most popular fiber
reactive dyes, a high pH actually activates the cellulose (cotton) fiber,
forming a cellulosate anion, which can then attack the dye molecule, leading to
a reaction that produces a strong, permanent covalent bond.
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| Fig: Checking pH in dye bath |
pH Levels for Different Stages of
Cotton Dyeing:
- Initial Bath pH 6.5~7.0.
- Before Enzyme, bath pH 4.5~4.7.
- After Enzyme and Aquachoron ,pH 5.5~6.0.
- Before Scouring and Bleaching, pH (With Enzyme) 5.5~5.8.
- Before Scouring and Bleaching, pH (Without Enzyme) 5.5~5.8.
- Scouring and Bleaching, bath pH 10.0~10.5.
- After Scouring and Bleaching, pH 8.5~9.0.
- Before Leveling Chemicals, pH 6.5~7.0.
- After Leveling Chemicals, pH 6.7~7.0.
- After Adding Dyes, pH 6.2~6.35.
- After Addition of Salt, pH 7.5~8.0.
- After Addition of Soda, pH 10.5~11.0.
- Before Hot Wash, Bath pH 6.8~7.2.
- Hot Wash, bath pH 8.5~8.7.
- Before Softener, bath pH 7.2~7.8.
- After Softener Addition, bath pH 6.5~6.8.
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| Fig: pH test trip |
pH Levels for Different Stages of
Polyester Dyeing:
- Initial bath pH, 6.5~7.0.
- Scouring, bath pH, 10.0~11.5.
- After Scouring, bath pH, 8.5~9.0.
- Before Addition of Leveling Chemicals, pH 6.0~6.5.
- After Addition of Leveling Chemicals, pH 4.5~4.7.
- After Addition of Colors, bath pH 4.2~4.3.
- During Reduction Clearing, bath pH 10.5~11.5.
- Before Softener, bath pH 6.3~6.8.
- After Softener Addition, bath pH 5.8~6.2
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