1. J.I.N. Rocha Gomes, C.J.E. Lima and J.R.Almeida
OXIDATIVE CLEARING OF POLYESTER AS AN ALTERNATIVE TO REDUCTION CLEAR: A COMPARATIVE STUDY
J.I.N. Rocha Gomes, C.J.E. Lima and J.R.Almeida
Textile Department, University of Minho
4810 Guimarães, Portugal

2. Introduction
Four main factors must be considered for any new process in the dyehouse:
water , due the scarce resources available
energy, due to its cost.
pollution due to the limits imposed and the ecological awareness of today’s society.
time, or duration of the process, which must be in line with the requirements for high productivity
The process of dyeing Cotton/Polyester blends with reactive/disperse dyes is an example of a typical process that is highly polluting, wastes water, energy and time

3. Reduction Clearing Process
Necessary for destroying and removing the disperse dye deposited on polyester fibre
Cause of large wastage of water, energy and time due to the rinses necessary to remove reducing agent
Highly polluting due to the high conductivity and COD values produced

4. Oxidative Clearing
An oxidative clearing process with peroxide can be applied as an alternative for destroying and removing the deposited disperse dye
It can be applied after the process of dyeing Cotton/Polyester blends with reactive/disperse dyes unlike the reduction clearing
It is less polluting since the process uses an oxidising agent
It saves on water and time since there’s no need to rinse the peroxide

5. Oxidative clearing vs. Reduction clear

6. Post-Bleaching
Bleaching after dyeing (post-bleaching) saves even more time since it avoids rinsing after bleaching
Post-bleaching conditions for cotton dyed with reactive dyes (alkaline hydrogen peroxide) when applied to cotton/polyester, clear disperse dye
For polyester/cotton blends dyed with reactive dyes, need to protect the reactive dye. Free radical quenchers have been used with success. However, even with protection some dyes are not resistant to the peroxide in alkaline conditions.

7. Effect of different conditions of oxidative clearing process on reactive dye C.I. Black 5
I- Untreated -
II- Oxidative treatment with 1.5 g/l H2O2 + soda ash
3.09
III-Oxidative treatment with 1,5 g/l sodium perborate
2.87
IV- Oxidative treatment with 1.5 g/l of sodium perborate and 2% Quencher
0.96

8. Post-Bleaching vs Reduction Clear

9. Oxidative clearing: Process conditions
Different process conditions were tested with and without alkali
Sodium perborate was tested as an alternative to alkaline hydrogen peroxide
Process was carried out in a laboratory machine with fabric movement so as to resemble the industrial reduction clearing process (Linitest of Heraeus)

10. Washfastness
Samples of fabric were taken after after dyeing and washing off and submitted to ISO 105 C06-C2 standard test (60ºC., 30 minutes, 4g/l sodium carbonate)
Samples of fabric were also stentered so as to evaluate the influence of the thermomigration on the washfastness

11. S.D.C. Multifiber Test Fabric
Values of staining for dyebath formula A on PE/CO after ISO 105 C06 C2 (60ºC, 30 min, ECE detergent, 4g/l sodium carbonate)
Process
S.D.C. Multifiber Test Fabric
Sec acetate
Cotton
NYLON 66 PE
Acrylic
Wool
I -Reduction clearing
1-2 4 2 3
4-5
II - H2O2 + sodium carbonate
2-3
3-4
III - H2O2
IV – sodium perborate

12. S.D.C. Multifiber Test Fabric
Values of staining after ISO 105 C06 C2 for dyebath formula A on PE/CO - after stentering
Process
S.D.C. Multifiber Test Fabric
Sec acetate
Cotton
NYLON 66 PE
Acrylic
Wool
I -Reduction clearing 2 5 3
4-5
II - H2O2+ sodium carbonate
2-3
III - H2O2
IV – sodium perborate

13. Values of staining after ISO 105 C06 C2 for dyebath formula B on PE/CO
Process
S.D.C. Multifiber Test Fabric
Sec acetate
Cotton
NYLON 66 PE
Acrylic
Wool
I -Reduction clearing
4-5 5
II - H2O2 + sodium carbonate 4
III - H2O2
3-4
IV – sodium perborate

14. S.D.C. Multifiber Test Fabric
Values of staining after ISO 105 C06 C2 for dyebath formula B on PE/CO - after stentering
Process
S.D.C. Multifiber Test Fabric
Sec acetate
Cotton
NYLON 66 PE
Acrylic
Wool
I -Reduction clearing 4 5
II - H2O2 + sodium carbonate
3-4
III - H2O2
4-5
IV – sodium perborate

15. S.D.C. Multifiber Test Fabric
Values of staining after ISO 105 C06 C2 for dyebath formula C on 100% PE
Process
S.D.C. Multifiber Test Fabric
Sec acetate
Cotton
NYLON 66 PE
Acrylic
Wool
I -Reduction clearing 4 5
4-5
II - H2O2+ sodium carbonate
III - H2O2 3
IV – sodium perborate

16. S.D.C. Multifiber Test Fabric
Values of staining after ISO 105 C06 C2 for dyebath formula C on 100% PE - after stentering
Process
S.D.C. Multifiber Test Fabric
Sec acetate
Cotton
NYLON 66 PE
Acrylic
Wool
I -Reduction clearing
3-4
4-5 5
II - H2O2 + sodium carbonate 4
III - H2O2
IV – sodium perborate

17. Discussion of results
For PE/CO, for dyes of low fastness (A) reduction clearing gave worse results than any of the oxidative clearing processes, both before and after stentering(tables 1 and 2)
For PE/CO, for dyes of higher fastness (B) processes II and IV, with alkaline peroxide and with sodium perborate respectively, gave the best results before stentering, and equivalent to reduction clearing after stentering (table 3 and 4)
For 100% PE, for dyebath formula C, the results are again better for processes II and IV, both before and after stentering

18. Pollution parameters

19. DIFFERENCE IN TIME (PE/CO)

20. Comparison of costs

21. Recipe costs

22. Conclusions 1. Ecological advantages
Besides the considerable savings on the water consumed, there is the ecological advantage of not using reduction clearing for polyester.
This factor alone lowers the COD values.

23. Conclusions 2. Productivity 17% less time for PE/CO
At 75% application: 12,5% average more productivity
Example:
Kg PE/CO production /year:
62 000Kg more of PE/CO

24. Conclusions Washfastness
Oxidative Clearing is as efficient in providing good washfastness or even more efficient with some dyes than Reduction Clearing