In the dyeing process different test is carried out to determine the better dyeing. We know that peroxide is applied during bleaching and it is harmful to the human body. So it needs to remove from the yarn or fabric. Some points are needed to consider during dyeing. Absorbency and pH test is essential for dyeing and it checks during dyeing. A short description of some tests is given below.
Test carried out during dyeing process
This test is carried out after the bleaching process. This test determines the amount of peroxide present in yarn or fabric. It requires making sure that the material is peroxide-free because peroxide is harmful to the yarn or fabric. A peroxide test paper is used. A wet yarn package or fabric is used for this. The test stick is hidden in the middle for 15-20 sec. then takes it out from the package or fabric and matches it with the test scale. If the color changes then it contains peroxide. If the color doesn’t change then there have no peroxide.
An absorbency test is carried out after bleaching. At first, the sample is dried and immersed in water. The standard time for absorbency is up to 5 sec. Better absorbency of sample facilities better-dyeing operation.
It needs to control the PH of the dyeing bath because it affects the exhaustion and fixation rate. Some dyeing process is carried out in an alkaline medium and some are carried out in an acidic medium. Generally, natural fibers dyeing is carried out in an alkaline medium and synthetic fibers dyeing is carried out in an acidic medium. It also depends on dyes characteristics and what’s a type of dyes are used for which fiber. In a practical way following parameters are maintained for dyeing cotton and polyester and in different stages of dyeing PH levels vary.
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 & Aquachoron, pH: 5.5~6.0
- Before Scouring & Bleaching, pH (With Enzyme): 5.5~5.8
- Before Scouring & Bleaching, pH (Without Enzyme): 5.5~5.8
- Scouring & Bleaching, bath pH: 10.0~10.5
- After Scouring & 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 the Addition of Salt, pH:7.5~8.0
- After the 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
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 the Addition of Leveling Chemicals, pH: 6.0~6.5
- After the Addition of Leveling Chemicals, pH: 4.5~4.7
- After the 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
So, that’s all about the test carried out during dyeing. It also increases the dyeing efficiency and these tests should be carried out during dyeing.
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