Haque et al. (2018) bleached single jersey cotton knitted fabric with 1.8–2.2 g/L hydrogen peroxide (H2O2). Reading the surface plots of their prediction model for that range, they wrote: “However the individual effect of peroxide concentration on whiteness index is pretty low and no change in whiteness is found at higher concentrations if temperature remains constant.”
What did Haque et al. find about bleach-bath temperature and time on single jersey cotton knitted fabric?
Haque et al. bleached 40 samples of 130 GSM single jersey cotton knitted fabric in a laboratory dyeing machine, at a 1:10 liquor ratio, with sodium hydroxide at 2 g/L and a peroxide stabiliser at 1 g/L. They changed the peroxide amount, the bath temperature and the time, measured whiteness index (WI) on a spectrophotometer, and built a fuzzy-logic model to predict WI. From that model they reported:
“WI increases around 17.65% for raising temperature from 78 to 88 °C, but it increases only about 6.12% for raising temperature from 88 to 108 °C. Similarly WI increases around 19.95% for increasing time from 20 to 30 min, but it increases only about 4.83% for increasing time from 30 to 50 min.” (pp. 9–10)
Their conclusion was that “temperature of the bleaching bath has a very important positive influence on whiteness index which can be improved by increasing time duration” (p. 10).
| H2O2 (g/L) | 78 °C, 20 min | 78 °C, 40 min | 98 °C, 20 min |
|---|---|---|---|
| 1.8 | 47.21 | 58.65 | 58.65 |
| 2.0 | 47.76 | 59.64 | 59.16 |
| 2.2 | 48.25 | 59.64 | 59.98 |
What did Kabir et al. measure about the tensile strength of cotton fabric as the peroxide amount rose?
S.M.F. Kabir and colleagues (2014) bleached cotton fabric in a laboratory washing machine (Gyrowash) at a 1:30 liquor ratio. They used eight different amounts of hydrogen peroxide on the same fabric and measured both whiteness index and tensile strength (Table B). They wrote: “Tensile strength decreases with the increase of H2O2 concentration and at the same time the concentration of hydrogen peroxide contributes to the increment of whiteness value” (p. 206).
They also wrote: “The statistical correlation between fabric strength with hydrogen peroxide concentration is negative, found very good and significant” (p. 206). Their Figure 5 gives a Pearson correlation of r = −0.97 (p < 0.0001) between strength and peroxide amount, and r = 0.78 (p = 0.02) between whiteness and peroxide amount.
| H2O2 (g/l) | Whiteness index | Tensile strength (N) |
|---|---|---|
| 1 | 43.59 | 935 |
| 3 | 63.75 | 922 |
| 5 | 73.48 | 894 |
| 7 | 74.16 | 839 |
| 9 | 76.05 | 787 |
| 11 | 78.19 | 665 |
| 13 | 77.84 | 657 |
| 15 | 75.84 | 627 |
What did Miljković et al. measure at each stage of scouring and peroxide bleaching of cotton knitted fabric?
Miljković et al. (2020) took raw 100% cotton knitwear with a reddish shade, scoured it, and bleached it with hydrogen peroxide by two routes: one bath, or two baths in sequence. After each stage they measured CIE whiteness index (WI) and b*, the yellow–blue colour coordinate, where a higher b* means a yellower shade (Table C). They wrote:
“The largest increase in the whitening index (WI) occurs after the chemical bleaching of the washed fabrics with H2O2. As expected, a further rise in WI value occurs after the second degree of bleaching with H2O2 exhaustion (Table 2); this sample had the lowest K/S values (Table 1) and the smallest redness.” (p. 61)
| Stage | WI | b* |
|---|---|---|
| Untreated | −10.74 | 15.44 |
| Scoured | 12.48 | 11.05 |
| Single bath | 60.32 | 5.16 |
| Two-bath, step I | 66.08 | 3.83 |
| Two-bath, step II | 80.75 | 1.73 |
What did Kabir et al. and Miljković et al. find when an optical brightener was added to bleached cotton fabric?
Kabir et al. compared peroxide bleaching alone with bleaching followed by a commercial blue or by an optical brightening agent (OBA). They wrote: “OBA gives the higher whiteness index than the commercial blue and peroxide bleaching when the fabric and process parameters remain same. Here commercial blue/OBA are applied after bleaching” (p. 205).
On cotton woven fabric they then varied the amount of OBA and wrote that “whiteness index on the same fabric increases with the increasing of the concentration of OBA and it decreases after a certain point. It is found that at 1.2% concentration of OBA optimum whiteness is obtained” (p. 208). They explain that “An excess over this critical quantity can promote reflection at selective wave-length causing a deviation from white” (p. 208).
Miljković et al. treated their peroxide-bleached knitwear with a fluorescent bleaching agent (FB), UVITEX BHT, at 0.1%, 0.5% and 1.0%. On fabric first bleached by the two-bath route, WI was 88.82, 78.65 and 86.90 at 0.1%, 0.5% and 1.0%. On fabric first bleached in a single bath, WI was 104.9, 94.72 and 102.3 at the same three amounts (their Tables 4 and 6).
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References
- Haque, A.N.M.A., Smriti, S.A., Hussain, M., Farzana, N., Siddiqa, F. and Islam, M.A. (2018). Prediction of whiteness index of cotton using bleaching process variables by fuzzy inference system. Fashion and Textiles 5:4. doi:10.1186/s40691-017-0118-9
- Kabir, S.M.F., Iqbal, M.I., Sikdar, P.P., Rahman, M.M. and Akhter, S. (2014). Optimization of parameters of cotton fabric whiteness. European Scientific Journal 10(36), 200–210.
- Miljković, M., Miljković, V., Trajković, D. and Konstantinović, S. (2020). Degree of cotton fabric whiteness obtained by the fluorescent bleaching agent UVITEX BHT and H2O2. Facta Universitatis, Series Physics, Chemistry and Technology 18(1), 57–63. doi:10.2298/FUPCT2001057M
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