In the dying 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 the peroxide needs to remove from the yarn or fabrics. 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 test is given below.
Test carried out during the dying process
- Peroxide Test: This test is carried out after the bleaching process. This test identifies the amount of peroxide present in yarn or fabrics. It requires to make sure that material is peroxide-free because peroxide is harmful to the yarn or fabric. A peroxide test paper is used. Wet yarn packages or fabrics are used for this. This test stick is hiding in the middle for 15-20 seconds. Then takes out from the packages or fabrics and match with the test scale. If color change then it contains peroxide. If the color doesn’t change then there have no peroxide.
- Absorbency Test: Absorbency test is carried out after bleaching. At first, the sample is dried and immerse into water. The standard time for absorbency is up to 5 sec. Better absorbency of sample facilities better-dyeing operation.
- PH Test: It needs to control the PH of the dyeing bath because it affects the exhaustion and fixation rate. Some dyeing processes are carried out in alkaline medium and some are carried out in acidic medium. Generally, natural fibers dyeing are carried out in alkaline medium and synthetic fibers dyeing is carried out in acidic medium. It also depends on dyes characteristics and what’s the type of dyes are used for which fiber. In a practical way following parameters are maintained for dyeing cotton and polyester and in a different stage of dyeing PH level 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 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
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
So, that’s all about the test carried out during dyeing. It also increases the dyeing efficiency and these test should be carried out during dyeing.