*2.2. Suppression of Colour Reversion Using Rongalite Treatment*

second AOP treatment 15 min after ironing (red).

second AOP treatment 15 min after ironing (red).

Figure 9 shows the reflectance spectra of cotton samples with and without rongalite treatment. The reflectance spectrum of the cotton fabric subjected to AOP treatment for 60 min increased with respect to that of the untreated sample. The reflectance spectrum of the cotton fabric ironed after AOP treatment decreased below 550 nm. On the other hand, the cotton fabric ironed after rongalite treatment did not show a decrease in the reflectance spectrum below 550 nm, and the reflectance spectra were maintained after AOP treatment. Figure 10 shows photographs of the cotton fabrics after AOP for 60 min, after ironing at 200 ◦C, and after ironing at 200 ◦C following rongalite treatment. The cotton sample after AOP was white. The cotton sample after ironing was not as white as that treated by AOP alone. The cotton sample after rongalite treatment and ironing was as white as that after AOP alone.

**Figure 8.** Reflectance spectra of cotton samples before (black dots) and after (black line) advanced oxidation processes (AOP) for 60 min, colour reversion after ironing at 200 °C (green), and after a

**Figure 8.** Reflectance spectra of cotton samples before (black dots) and after (black line) advanced oxidation processes (AOP) for 60 min, colour reversion after ironing at 200 °C (green), and after a

**Figure 6.** Reflectance spectra of the cotton samples after advanced oxidation processes (AOP) treatment for different periods (black, green, and red indicate 0, 30, and 60 min AOP treatment,

**Figure 7.** Photographs of cotton samples before scouring and bleaching and after advanced oxidation

Figure 8 shows the reflectance spectra of AOP-treated samples (0 and 60 min) before and after ironing at 200 °C. When the cotton was dried after AOP treatment, the reflectance decreased below 500 nm. When the ironed fabric was again subjected to AOP treatment, the spectrum was restored to the pre-ironing state. Ironing and AOP treatment were repeated five times, but only the results of the

respectively) with (dots) and without (solid line) scouring.

processes (AOP) treatment for 30 min treated with a drop of water.

**Figure 8.** Reflectance spectra of cotton samples before (black dots) and after (black line) advanced oxidation processes (AOP) for 60 min, colour reversion after ironing at 200 °C (green), and after a second AOP treatment 15 min after ironing (red). **Figure 8.** Reflectance spectra of cotton samples before (black dots) and after (black line) advanced oxidation processes (AOP) for 60 min, colour reversion after ironing at 200 ◦C (green), and after a second AOP treatment 15 min after ironing (red). cotton sample after AOP was white. The cotton sample after ironing was not as white as that treated by AOP alone. The cotton sample after rongalite treatment and ironing was as white as that after AOP alone. cotton sample after AOP was white. The cotton sample after ironing was not as white as that treated by AOP alone. The cotton sample after rongalite treatment and ironing was as white as that after AOP alone.

**Figure 9.** Reflectance spectra of cotton samples before (black dots) and after (black line) advanced oxidation processes (AOP) for 60 min and those of samples ironed at 200 °C with (red) and without (green) rongalite treatment. **Figure 9.** Reflectance spectra of cotton samples before (black dots) and after (black line) advanced oxidation processes (AOP) for 60 min and those of samples ironed at 200 ◦C with (red) and without (green) rongalite treatment. **Figure 9.** Reflectance spectra of cotton samples before (black dots) and after (black line) advanced oxidation processes (AOP) for 60 min and those of samples ironed at 200 °C with (red) and without (green) rongalite treatment.

**Figure 10.** Photographs of cotton samples after advanced oxidation processes (AOP) for 60 min, after ironing at 200 °C, and after ironing at 200 °C following rongalite treatment. **Figure 10.** Photographs of cotton samples after advanced oxidation processes (AOP) for 60 min, after ironing at 200 °C, and after ironing at 200 °C following rongalite treatment. **Figure 10.** Photographs of cotton samples after advanced oxidation processes (AOP) for 60 min, after ironing at 200 ◦C, and after ironing at 200 ◦C following rongalite treatment.

Figure 11 shows the reflectance spectra of linen samples with and without rongalite treatment. The percentage reflectance of the linen fabrics subjected to AOP treatment for 120 min increased compared with that of the untreated sample. The reflectance spectrum of the linen fabric ironed after AOP treatment decreased at all wavelengths. In contrast, the cotton fabric ironed after rongalite treatment did not show a decrease, and the reflectance spectra were maintained after AOP treatment. Figure 11 shows the reflectance spectra of linen samples with and without rongalite treatment. The percentage reflectance of the linen fabrics subjected to AOP treatment for 120 min increased compared with that of the untreated sample. The reflectance spectrum of the linen fabric ironed after AOP treatment decreased at all wavelengths. In contrast, the cotton fabric ironed after rongalite treatment did not show a decrease, and the reflectance spectra were maintained after AOP treatment. Figure 11 shows the reflectance spectra of linen samples with and without rongalite treatment. The percentage reflectance of the linen fabrics subjected to AOP treatment for 120 min increased compared with that of the untreated sample. The reflectance spectrum of the linen fabric ironed after AOP treatment decreased at all wavelengths. In contrast, the cotton fabric ironed after rongalite treatment did not show a decrease, and the reflectance spectra were maintained after AOP treatment.

sample after AOP alone.

sample after AOP alone.

Figure 12 shows photographs of the linen fabrics after AOP for 120 min and after ironing at 200 °C,

Figure 12 shows photographs of the linen fabrics after AOP for 120 min and after ironing at 200 °C,

Figure 12 shows photographs of the linen fabrics after AOP for 120 min and after ironing at 200 ◦C, with and without rongalite treatment. The linen sample after AOP was white, but, after ironing, some whiteness was lost. After rongalite treatment and ironing, the sample remained as white as the sample after AOP alone. *Catalysts* **2020**, *10*, x FOR PEER REVIEW 7 of 12 *Catalysts* **2020**, *10*, x FOR PEER REVIEW 7 of 12

**Figure 11.** Reflectance spectra of linen samples without advanced oxidation processes (AOP; black dots) and after AOP for 120 min (black line) and of AOP-treated samples after ironing at 200 °C without (green) and with (red) rongalite treatment. **Figure 11.** Reflectance spectra of linen samples without advanced oxidation processes (AOP; black dots) and after AOP for 120 min (black line) and of AOP-treated samples after ironing at 200 ◦C without (green) and with (red) rongalite treatment. **Figure 11.** Reflectance spectra of linen samples without advanced oxidation processes (AOP; black dots) and after AOP for 120 min (black line) and of AOP-treated samples after ironing at 200 °C without (green) and with (red) rongalite treatment.

**Figure 12.** Photographs of the linen samples after advanced oxidation processes (AOP) for 120 min, after AOP and ironing at 200 °C, and after AOP and ironing at 200 °C following rongalite treatment. **Figure 12.** Photographs of the linen samples after advanced oxidation processes (AOP) for 120 min, after AOP and ironing at 200 °C, and after AOP and ironing at 200 °C following rongalite treatment. **Figure 12.** Photographs of the linen samples after advanced oxidation processes (AOP) for 120 min,after AOP and ironing at 200 ◦C, and after AOP and ironing at 200 ◦C following rongalite treatment.

### **3. Discussion 3. Discussion 3. Discussion**

Figure 1a shows that the combination of aqueous ozone and UV light was most suitable for bleaching, although a bleaching effect was also obtained when using aqueous ozone alone and water + UV. Moreover, the reaction rate constant of the aqueous ozone + UV system was not a simple sum of those of the aqueous ozone and water + UV systems. Therefore, it appears that the cotton was bleached by the synergistic effect of ozone and UV irradiation. Figure 1b shows that OH radicals were generated by UV irradiation of the aqueous ozone. It is known that OH radicals decompose coloured components in fabrics during AOP [19,20], and the generation of OH radicals is likely responsible for the high reaction constant shown in Figure 1a. Specifically, excited singlet oxygen is produced by the UV irradiation of ozone at 310 nm, whereas excited triplet oxygen is produced by the visible light irradiation of ozone (> 460 nm). The bleaching OH radicals are generated from excited singlet oxygen [21]. Disodium terephthalate (NaTA) can be used as an indicator of the generated OH radicals, forming 2-terephthalic acid in the process [17]; approximately 0.35 ppb OH radicals were produced by UV irradiation. OH radicals are extremely reactive [22]; thus, their lifetime is very short. For these reasons, the OH radical concentration in Figure 1b is low, compared with the ozone concentration. Figure 1a shows that the combination of aqueous ozone and UV light was most suitable for bleaching, although a bleaching effect was also obtained when using aqueous ozone alone and water + UV. Moreover, the reaction rate constant of the aqueous ozone + UV system was not a simple sum of those of the aqueous ozone and water + UV systems. Therefore, it appears that the cotton was bleached by the synergistic effect of ozone and UV irradiation. Figure 1b shows that OH radicals were generated by UV irradiation of the aqueous ozone. It is known that OH radicals decompose coloured components in fabrics during AOP [19,20], and the generation of OH radicals is likely responsible for the high reaction constant shown in Figure 1a. Specifically, excited singlet oxygen is produced by the UV irradiation of ozone at 310 nm, whereas excited triplet oxygen is produced by the visible light irradiation of ozone (> 460 nm). The bleaching OH radicals are generated from excited singlet oxygen [21]. Disodium terephthalate (NaTA) can be used as an indicator of the generated OH radicals, forming 2-terephthalic acid in the process [17]; approximately 0.35 ppb OH radicals were produced by UV irradiation. OH radicals are extremely reactive [22]; thus, their lifetime is very short. For these reasons, the OH radical concentration in Figure 1b is low, compared with the ozone concentration. Figure 1a shows that the combination of aqueous ozone and UV light was most suitable for bleaching, although a bleaching effect was also obtained when using aqueous ozone alone and water + UV. Moreover, the reaction rate constant of the aqueous ozone + UV system was not a simple sum of those of the aqueous ozone and water + UV systems. Therefore, it appears that the cotton was bleached by the synergistic effect of ozone and UV irradiation. Figure 1b shows that OH radicals were generated by UV irradiation of the aqueous ozone. It is known that OH radicals decompose coloured components in fabrics during AOP [19,20], and the generation of OH radicals is likely responsible for the high reaction constant shown in Figure 1a. Specifically, excited singlet oxygen is produced by the UV irradiation of ozone at 310 nm, whereas excited triplet oxygen is produced by the visible light irradiation of ozone (> 460 nm). The bleaching OH radicals are generated from excited singlet oxygen [21]. Disodium terephthalate (NaTA) can be used as an indicator of the generated OH radicals, forming 2-terephthalic acid in the process [17]; approximately 0.35 ppb OH radicals were produced by UV irradiation. OH radicals are extremely reactive [22]; thus, their lifetime is very short. For these reasons, the OH radical concentration in Figure 1b is low, compared with the ozone concentration.

Figures 2 and 3 show that the AOP treatment that combined aqueous ozone and UV (60 min) had the same bleaching effect as the conventional method. As unbleached cotton contains coloured Figures 2 and 3 show that the AOP treatment that combined aqueous ozone and UV (60 min) had the same bleaching effect as the conventional method. As unbleached cotton contains coloured Figures 2 and 3 show that the AOP treatment that combined aqueous ozone and UV (60 min) had the same bleaching effect as the conventional method. As unbleached cotton contains coloured

components, it had a low reflectance spectrum below 550 nm. Cotton contains approximately 90%

components, it had a low reflectance spectrum below 550 nm. Cotton contains approximately 90%

coloured components, like cotton, and the low reflectance spectrum of the unbleached linen shown in Figure 4 is due to these components. As shown in Figures 4 and 5, in the case of linen, it took 120

coloured components, like cotton, and the low reflectance spectrum of the unbleached linen shown in Figure 4 is due to these components. As shown in Figures 4 and 5, in the case of linen, it took 120 components, it had a low reflectance spectrum below 550 nm. Cotton contains approximately 90% cellulose and approximately 10% non-cellulosic matter, comprising proteins, waxes, pectin, and ash [1]. Therefore, on the basis of the results, these components were decomposed by AOP treatment to the same extent as in the conventional bleaching method. The linen before bleaching also contained coloured components, like cotton, and the low reflectance spectrum of the unbleached linen shown in Figure 4 is due to these components. As shown in Figures 4 and 5, in the case of linen, it took 120 min of AOP to bleach to the same extent as the conventional method. Thus, bleaching time is dependent on the amount of coloured components contained in the linen. Unlike cotton, linen contains only ~70% cellulose and a high proportion of non-cellulosic matter, which complicates the bleaching process. In addition, non-cellulosic matter contains a small amount of dark-coloured lignin [23], which suggests that linen will require a longer treatment time. As shown in Figure 6, AOP-treated cotton fabrics without scouring were bleached to the same degree as those with scouring and AOP treatment. In addition, Figure 7 shows that AOP treatment eliminated the water repellence of the cotton fabrics observed before scouring, resulting in hydrophilicity. As previously mentioned, before scouring, cotton contains wax [1], which yields water repellence. Therefore, the results in Figures 6 and 7 suggest that AOP treatment removes both coloured compounds and residual components (wax and oil) simultaneously. Thus, unlike conventional processes, our AOP process achieves scouring and bleaching at the same time.

In Figure 8, the colour return after the AOP process is shown by the reflectance spectra. In particular, the reflectance of the ironed sample was reduced, compared with that of the sample after AOP treatment. However, the reflectance recovered again after AOP treatment following ironing. However, repeated ironing resulted in the appearance of colour. The ironing and AOP treatment were repeated five times, but only the second cycle is shown in Figure 8. These results suggest that the colour reversion after ironing and AOP treatment is a reversible reaction. Cellulose, the main component of cotton, can be oxidised, and the oxidised form shows absorption in the near-UV to visible light region [24]. Even after AOP treatment, the cellulose in cotton may be oxidised, resulting in colour reversion. Therefore, in this study, rongalite, a reducing agent, was used to suppress colour reversion after AOP treatment and ironing. As shown in Figures 9 and 10, without rongalite treatment, reflectance decreased after ironing, whereas rongalite-treated fabrics did not show a decrease in reflectance in the wavelength region below 500 nm, even after ironing. In addition, even in the case of linen, rongalite-treated fabrics did not show a decrease in reflectance after ironing; the reflectance spectra after AOP treatment were similar to those before treatment (Figures 11 and 12).

Figure 13 shows the proposed mechanisms of colour reversion and suppression of colour reversion after rongalite treatment of fabrics. AOP treatment could damage the fabric [12,25], and previous studies on the cause of colour reversion after oxidative bleaching have reported that some of the OH groups of cellulose (particularly those at the 2nd and 3rd positions) are oxidised, resulting in the formation of C=O groups and some conjugated double bonds [24]. Thus, colour reversion could be suppressed by the reduction of the C=O groups generated in the cellulose fibres of OH groups after bleaching. Therefore, before ironing, the AOP-treated fabric was treated with a strongly reducing rongalite solution to reduce the C=O groups. Consequently, subsequent heat treatment (ironing) did not result in the formation of conjugated double bonds.

achieves scouring and bleaching at the same time.

(ironing) did not result in the formation of conjugated double bonds.

min of AOP to bleach to the same extent as the conventional method. Thus, bleaching time is dependent on the amount of coloured components contained in the linen. Unlike cotton, linen contains only ~70% cellulose and a high proportion of non-cellulosic matter, which complicates the bleaching process. In addition, non-cellulosic matter contains a small amount of dark-coloured lignin [23], which suggests that linen will require a longer treatment time. As shown in Figure 6, AOPtreated cotton fabrics without scouring were bleached to the same degree as those with scouring and AOP treatment. In addition, Figure 7 shows that AOP treatment eliminated the water repellence of the cotton fabrics observed before scouring, resulting in hydrophilicity. As previously mentioned, before scouring, cotton contains wax [1], which yields water repellence. Therefore, the results in Figures 6 and 7 suggest that AOP treatment removes both coloured compounds and residual components (wax and oil) simultaneously. Thus, unlike conventional processes, our AOP process

In Figure 8, the colour return after the AOP process is shown by the reflectance spectra. In particular, the reflectance of the ironed sample was reduced, compared with that of the sample after AOP treatment. However, the reflectance recovered again after AOP treatment following ironing. However, repeated ironing resulted in the appearance of colour. The ironing and AOP treatment were repeated five times, but only the second cycle is shown in Figure 8. These results suggest that the colour reversion after ironing and AOP treatment is a reversible reaction. Cellulose, the main component of cotton, can be oxidised, and the oxidised form shows absorption in the near-UV to visible light region [24]. Even after AOP treatment, the cellulose in cotton may be oxidised, resulting in colour reversion. Therefore, in this study, rongalite, a reducing agent, was used to suppress colour reversion after AOP treatment and ironing. As shown in Figures 9 and 10, without rongalite treatment, reflectance decreased after ironing, whereas rongalite-treated fabrics did not show a decrease in reflectance in the wavelength region below 500 nm, even after ironing. In addition, even in the case of linen, rongalite-treated fabrics did not show a decrease in reflectance after ironing; the reflectance spectra after AOP treatment were similar to those before treatment (Figures 11 and 12). Figure 13 shows the proposed mechanisms of colour reversion and suppression of colour reversion after rongalite treatment of fabrics. AOP treatment could damage the fabric [12,25], and previous studies on the cause of colour reversion after oxidative bleaching have reported that some of the OH groups of cellulose (particularly those at the 2nd and 3rd positions) are oxidised, resulting in the formation of C=O groups and some conjugated double bonds [24]. Thus, colour reversion could be suppressed by the reduction of the C=O groups generated in the cellulose fibres of OH groups after bleaching. Therefore, before ironing, the AOP-treated fabric was treated with a strongly

**Figure 13.** Proposed mechanisms of the suppression of colour reversion in fabrics and the effect of rongalite treatment. **Figure 13.** Proposed mechanisms of the suppression of colour reversion in fabrics and the effect of rongalite treatment. *Catalysts* **2020**, *10*, x FOR PEER REVIEW 9 of 12

### **4. Materials and Methods 4. Materials and Methods**

radicals.

Cotton and linen cloths were provided by Nisshinbo Textrail Co., Ltd. (Tokyo Japan). The colour differences of the fabrics were measured using a colour reader (CR-10, Konica Minolta Japan, Inc., Tokyo, Japan) and expressed as *L*\**a*\**b*\* and ∆*E*\**ab* values [26,27]. Here, *L*\* represents brightness, equalling zero for a black diffuser and 100 for a perfectly reflecting one; *a*\* represents colour on the red–green axis, being positive for red and negative for green; and *b*\* represents colour on the blue–yellow axis, being positive for yellow and negative for blue. The colour difference was calculated as ∆*E*\**ab* = ((∆*L*\*)<sup>2</sup> + (∆*a*\*)<sup>2</sup> + (∆*b*\*)<sup>2</sup> ) 1/2 , where ∆*L*\* is the difference in brightness between two vivid surfaces and ∆*a*\* and ∆*b*\* are the differences in the colour coordinates *a*\* and *b*\*, respectively. Figure 14 shows the bleaching experiment in which aqueous ozone and UV irradiation were combined. UV light is emitted above a cloth sample placed on a glass plate. As a UV light source, an LA-310UV manufactured by Hayashi Clock Industry Co., Ltd. (Tokyo, Japan) was used. In addition, the electrolytically generated aqueous ozone was produced by an aqueous ozone generator (Quick O<sup>3</sup> Pico, AOD-TH2 manufactured by Aidenshi Co., Ltd., Nasushiobara, Japan) and dropped onto the fabric at the same position as the UV spot. Cotton and linen cloths were provided by Nisshinbo Textrail Co., Ltd. (Tokyo Japan). The colour differences of the fabrics were measured using a colour reader (CR-10, Konica Minolta Japan, Inc., Tokyo, Japan) and expressed as *L*\**a*\**b*\* and ∆*E*\**ab* values [26,27]. Here, *L*\* represents brightness, equalling zero for a black diffuser and 100 for a perfectly reflecting one; *a*\* represents colour on the red–green axis, being positive for red and negative for green; and *b*\* represents colour on the blue– yellow axis, being positive for yellow and negative for blue. The colour difference was calculated as ∆*E*\**ab* = ((∆*L*\*)2 + (∆*a*\*)2 + (∆*b*\*)2) 1/2, where ∆*L*\* is the difference in brightness between two vivid surfaces and ∆*a*\* and ∆*b*\* are the differences in the colour coordinates *a*\* and *b*\*, respectively. Figure 14 shows the bleaching experiment in which aqueous ozone and UV irradiation were combined. UV light is emitted above a cloth sample placed on a glass plate. As a UV light source, an LA-310UV manufactured by Hayashi Clock Industry Co., Ltd. (Tokyo, Japan) was used. In addition, the electrolytically generated aqueous ozone was produced by an aqueous ozone generator (Quick O3 Pico, AOD-TH2 manufactured by Aidenshi Co., Ltd., Nasushiobara, Japan) and dropped onto the fabric at the same position as the UV spot.

**Figure 14.** Photograph of a bleaching experiment. The fabric sample was set on a glass plate. Water containing electrochemically generated ozone was dropped onto the fabric, and the sample was irradiated with ultraviolet (UV) light. **Figure 14.** Photograph of a bleaching experiment. The fabric sample was set on a glass plate. Water containing electrochemically generated ozone was dropped onto the fabric, and the sample was irradiated with ultraviolet (UV) light.

The rongalite treatment was carried out by the dipping method. The sample after AOP treatment was immersed in a 0.5 wt% rongalite aqueous solution for 1 h, then drained and dried on a hot plate The rongalite treatment was carried out by the dipping method. The sample after AOP treatment was immersed in a 0.5 wt% rongalite aqueous solution for 1 h, then drained and dried on a hot plate at

at 200 °C for 1 min. Figure 15 shows photographs and a schematic of the measurement of the amount

disodium terephthalate chemical probe [17,18]. As shown in Figure 15, aqueous ozone irradiated with UV was collected and then mixed with disodium terephthalate (NaTA, TCI Co., Ltd., Tokyo, Japan) until completely dissolved. Then, while irradiating the solution with UV light, the generated fluorescence was detected. An SEC-2000-UV/VIS Spectrometer manufactured by ALS Co., Ltd. (Tokyo, Japan) was used for UV light generation and fluorescence detection. Disodium terephthalate, used as an indicator, reacts with OH radicals in aqueous solution to produce 2-hydroxyterephthalic acid, which fluoresces at 425 nm under UV irradiation, allowing quantification of the generated OH 200 ◦C for 1 min. Figure 15 shows photographs and a schematic of the measurement of the amount of OH radicals in the aqueous ozone under UV irradiation. It is well known that OH radicals are generated by AOP treatment with aqueous ozone and UV irradiation [15,16,19,20]. In this study, the OH radical concentration in the ozone solution during AOP treatment was measured using a disodium terephthalate chemical probe [17,18]. As shown in Figure 15, aqueous ozone irradiated with UV was collected and then mixed with disodium terephthalate (NaTA, TCI Co., Ltd., Tokyo, Japan) until completely dissolved. Then, while irradiating the solution with UV light, the generated fluorescence was detected. An SEC-2000-UV/VIS Spectrometer manufactured by ALS Co., Ltd. (Tokyo, Japan) was used for UV light generation and fluorescence detection. Disodium terephthalate, used as an indicator, reacts with OH radicals in aqueous solution to produce 2-hydroxyterephthalic acid, which fluoresces at 425 nm under UV irradiation, allowing quantification of the generated OH radicals. *Catalysts* **2020**, *10*, x FOR PEER REVIEW 10 of 12

**Figure 15.** Photographs and schematic of OH radical quantification by fluorescence spectroscopy. **Figure 15.** Photographs and schematic of OH radical quantification by fluorescence spectroscopy.

### **5. Conclusions 5. Conclusions**

**References** 

In this paper, we reported a two-step fabric treatment method based on AOP treatment using aqueous ozone and UV irradiation with rongalite treatment. The AOP process removed coloured components in fabric via decomposition with active oxygen species (ozone and the OH radicals generated in aqueous solution). The OH radical concentration in the aqueous solution was measured by a chemical probe, which can easily and quickly measure OH radicals on the spot, and it is applicable to industrial-scale process control. The reflectance spectra of the fabric samples revealed an increase in bleaching with increasing treatment time, and, after 60 min for cotton and 120 min for linen, bleaching comparable to that of the conventional method was achieved. In addition, we confirmed that AOP treatment is suitable for decomposing waxes and oils contained in the fabric before scouring. Therefore, this AOP process can replace conventional scouring and bleaching processes. Furthermore, we succeeded in preventing colour reversion by reducing cellulose oxidised by the AOP treatment with inexpensive rongalite. The AOP + rongalite treatment for fabrics is attractive because it produces little waste and consumes little energy compared with the conventional method. Thus, this method is a promising alternative to conventional bleaching in natural fibre In this paper, we reported a two-step fabric treatment method based on AOP treatment usingaqueous ozone and UV irradiation with rongalite treatment. The AOP process removed coloured components in fabric via decomposition with active oxygen species (ozone and the OH radicalsgenerated in aqueous solution). The OH radical concentration in the aqueous solution was measured by a chemical probe, which can easily and quickly measure OH radicals on the spot, and it is applicableto industrial-scale process control. The reflectance spectra of the fabric samples revealed an increase in bleaching with increasing treatment time, and, after 60 min for cotton and 120 min for linen, bleaching comparable to that of the conventional method was achieved. In addition, we confirmed that AOP treatment is suitable for decomposing waxes and oils contained in the fabric before scouring. Therefore, this AOP process can replace conventional scouring and bleaching processes. Furthermore, we succeeded in preventing colour reversion by reducing cellulose oxidised by the AOP treatmentwith inexpensive rongalite. The AOP <sup>+</sup> rongalite treatment for fabrics is attractive because it produces little waste and consumes little energy compared with the conventional method. Thus, this method isa promising alternative to conventional bleaching in natural fibre processing.

processing. **Author Contributions:** K.H., T.O., K.M., Y.I., T.N., and N.K. participated in the study design and conducted the study; K.H., T.O., and Y.T. collected and analysed the data. K.H wrote the manuscript. All authors have read **Author Contributions:** K.H., T.O., K.M., Y.I., T.N. and N.K. participated in the study design and conducted the study; K.H., T.O. and Y.T. collected and analysed the data. K.H. wrote the manuscript. All authors have read and agreed to the published version of the manuscript.

and agreed to the published version of the manuscript. **Funding:** This research received no external funding.

321, doi:10.1016/j.carbpol.2012.05.044.

doi:10.1016/j.carbpol.2009.07.019.

**Conflicts of Interest:** The authors declare no conflicts of interest.

1. Abdel-Halim, E.S. An effective redox system for bleaching cotton cellulose. *Carbohydr. Polym.* **2012**, *90*, 316–

2. Hebeish, A.; Hashem, M.; Shaker, N.; Ramadan, M.; El-Sadek, B.; Hady, M.A. New development for combined bioscouring and bleaching of cotton-based fabrics. *Carbohydr. Polym.* **2009**, *78*, 961–972,

insightful discussion. We would like to thank Editage (www.editage.com) for English language editing.

**Funding:** This research received no external funding.

**Acknowledgments:** We are grateful to Nisshinbo Textile Inc. for preparing the fabrics. We are also grateful to Ayato Koibuchi and Kosuke Miura (Nagaoka University of Technology) for help with the experiments and for insightful discussion. We would like to thank Editage (www.editage.com) for English language editing.

**Conflicts of Interest:** The authors declare no conflict of interest.
