Research Article
Roles of electrostatic interactions in the peroxide systems for bleaching of cotton fiber
https://doi.org/10.21203/rs.3.rs-2356560/v1
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cotton fiber
hydrogen peroxide
bleach activator
bleaching
electrostatic interaction
Cotton fiber occupies a large share of the global textile materials due to its comfort, good warmth retention, and easy dyeing properties (Wakelyn et al. 2007). In the manufacturing process of cotton-based textiles, it is necessary for raw cotton to be pretreated to remove natural impurities such as cotton seed shell, protein, pectin, and pigments (Abidi et al. 2010), providing a white uniform matrix for subsequent processes such as dyeing and printing. Bleaching with hydrogen peroxide (H2O2) is the most widely used process in the textile industry for removing natural pigments in cotton fiber (Zeronian and Inglesby 1995). H2O2 dissociates in an aqueous solution to the perhydroxyl anion (HOO−) that is thought to be the active species for bleaching of cotton fiber. In practice, cotton fiber is bleached in an H2O2 solution with the addition of sodium hydroxide (NaOH) at a boiling temperature (Brooks and Moore 2000), which causes a high energy consumption. Therefore, activated peroxide systems are proposed to be established for energy saving by adding so-called bleach activators to aqueous H2O2 solutions, in which the bleach activators react with H2O2 to generate more kinetically active bleaching species that enable cotton fiber to be bleached at low temperatures (Hofmann et al. 1992; Wang et al. 2020).
Tetraacetylethylenediamine (TAED), sodium nonanyloxybenzenesulfonate (NOBS) and N-[4-(triethylammoniomethyl)benzoyl]caprolactam chloride (TBCC) are three typical bleach activators for low-temperature bleaching of cotton fiber (Cai et al. ; Yu et al. 2017). It is reported that TBCC is a more effective bleach activator than others because it is designed with a cationic charge that has a strong affinity to the negatively charged cotton fiber and enables the bleaching species to closely approximate the fiber surface (Xu et al. 2010). It is assumed that the electrostatic interactions between the bleach activator and cotton fiber should play an important role in improving the bleaching performance. However, there are very few literatures reported on the effects of electrostatic interactions on the performance of the peroxide systems for bleaching of cotton fiber. In this work, the surface charge of cotton fiber was changed by modification with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC), and the cotton fiber was bleached with the H2O2/NaOH system, the TAED-activated peroxide system, and the TBCC-activated peroxide system, to which sodium chloride (NaCl) and ionic surfactants were added to explore the effects of electrostatic interactions on their bleaching performances. The findings will provide new insight into the bleaching mechanism of cotton fiber, and help develop more effective bleaching technologies for cotton fiber.
Scoured cotton knitted fabric (180 g/m2) was supplied by Weiqiao Textile Co., Ltd., Shandong, China. H2O2 (30% w/w), NaOH, NaCl, Stearyl trimethyl ammonium chloride (STAC), sodium dodecyl benzene sulfonate (SDBS), and sodium bicarbonate (NaHCO3) were purchased from Sinopharm Chemical Reagent, Shanghai, China. A commercial peroxide stabilizer (DM1403) was supplied by Dymatic Chemicals, Inc., Guangzhou, China. CHPTAC as a 65% solution was purchased from Macklin Biochemical Co., Ltd., Shanghai, China. TBCC was supplied by Qingdao Frontierchem Co., Ltd., Shandong, China. TAED was purchased from Aladdin Bio-Chem Technology Co., Shanghai, China. All other chemicals were used as received. Distilled water was used throughout the experiments unless otherwise stated.
The cotton fiber was cationized with CHPTAC according to the method reported previously (Nallathambi and Venkateshwarapuram Rengaswami 2017). The cationized process of cotton fiber was carried out in an infrared laboratory dyeing machine (Datacolor International, USA) at a liquor-to-goods ratio of 10:1. A sample of cotton fabric was immersed in a solution to which CHPTAC and NaOH were added with a mass ratio of 4:1. The cotton fabric was processed at 80°C for 60 minutes. When cationization was completed, cotton fabric was taken out for neutralization with 1 g/L acetic acid, and rinsed thoroughly with water. The cationized cotton fabric was dried under ambient conditions.
Bleaching of cotton was carried out on an infrared laboratory dyeing machine (Datacolor International, USA) at a liquor-to-goods ratio of 20:1. A sample of cotton fabric (5 g) was immersed in a bleaching solution containing 1 g/L peroxide stabilizer, and amounts of H2O2 and alkali (NaOH or NaHCO3). A bleach activator (TAED or TBCC) was added to the bleaching solution as required. The sample was bleached at a specific temperature for a certain time. When bleaching was completed, the cotton sample was taken out for rinsing with water, and then dried under ambient temperature.
The bleached cotton fabric was measured by the CIE Whiteness Index (WI) according to the AATCC Test Method 110-2015e2. The cotton fabric was folded twice and measured on a Datacolor 800 spectrometer (Datacolor, USA), using the D65 illuminant and the CIE 1964 standard observer.
Zeta potential was tested by a zeta potential tester for solid surface (SurPASS 3, Anton Paar, Austria). The measuring fluid (1 mmol/L NaCl solution) was streamed through the samples until equilibrium was reached. The pH value was adjusted to 7. All the data in this experiment are repeated three times to take the average value.
The absorbance of the bleaching activator in water was collected from 200 nm to 400 nm on a UV-2600i UV-Vis spectrophotometer (Shimadzu, Japan).
The decomposition rate of H2O2 was determined by the method of potassium permanganate titration, and calculated as follows,
Decomposition rate of H2O2 \({\text{=}}\frac{{{{\text{V}}_0} - {{\text{V}}_1}}}{{{{\text{V}}_0}}}\)× 100% (1)
where V0 and V1 are the volumes of potassium permanganate consumed by 5 mL of bleaching solution before and after bleaching, respectively.
The adsorption of bleach activator on cotton fiber was determined by HPLC analysis performed on a Shimadzu LC-20A high-performance liquid chromatography system (Shimadzu, Tokyo, Japan) equipped with a C18 reversed-phase column (Shimadzu C18, 5 µm). A sample of 2 g cotton fabric was added to a 100 mL water solution containing 1 g/L bleach activator and 0.05 g/L surfactants. The HPLC mobile phase was 80% acetonitrile and 20% water. Analysis was performed using a flow rate of 1 mL/min and a detection wavelength at 235 nm. The temperature of the C18 column was maintained at 25°C. The adsorption of bleach activator on cotton (Ccotton, mg/g) was obtained using Eq. (2),
Ccotton = 0.05(C0 – Ct) (2)
where Ct is the residual concentration of bleach activator in solution adsorbed by cotton for various times, and C0 is the concentration of bleach activator in solution before adsorption.
In the alkaline solution, H2O2 dissociates to perhydroxyl anion (HOO−) which is the active species for bleaching of cotton, and at the same time, the hydroxymethyl groups (CH2OH) in cellulose can also be ionized to anions (CH2O−) resulting in a negatively charged surface of cotton fiber. During the bleaching process, HOO− needs first to come into contact with the surface of cotton fiber before it chemically breaks down the natural pigments. However, the negative charges on cotton fiber would repel HOO−, leading to a decrease in the bleaching performance. In order to clearly present the effect of electrostatic repulsion on the bleaching performance, cotton fiber was bleached by the H2O2/NaOH system (6 g/L 30% w/w H2O2, and 3 g/L NaOH) with the addition of various concentrations of NaCl. As shown in Fig. 1, an increase in the NaCl concentration resulted in an increase in the whiteness of cotton fabric. The main reason is that NaCl dissociates to sodium ions (Na+) that are adsorbed onto the negatively charged surface of cotton fiber to neutralize the negative surface charges. As the concentration of NaCl increased, the electrostatic repulsion to HOO− was suppressed by Na+ to a greater extent. Hence, HOO− can easily come into contact with cotton fiber and plays the role of bleaching. In practical industrial production, NaOH is often used as an alkali to promote the dissociation of H2O2, but it also intensifies the ionization of the hydroxymethyl group (CH2OH) in cotton cellulose. Though a relatively high H2O2 concentration is required for the bleaching of cotton fiber, only a small portion is effective for bleaching, and most remain in solution and decompose invalidly. As seen in Fig. 1, the whiteness of cotton fabric is not as good as required (normally higher than 70) when cotton fabric was bleached with alkaline H2O2 at 40°C and 60°C. An effective approach to improving whiteness is to increase the bleaching temperature above 95°C. Therefore, the bleaching of cotton fabric with H2O2 is a high energy consumption process. More importantly, a high H2O2 concentration used in bleaching can cause the breakage of the cellulose molecule chain and as such serious damage to cotton fiber (Xu et al. 2015).
In the TBCC-activated peroxide system, 4-(triethylammoniomethyl)perbenzoic acid (TPA) was generated as a more active bleaching species (as shown in Fig. 2) that enabled cotton fiber to be bleached at a lower temperature (Luo et al. 2015). It is assumed that TPA has a positive charge that has an affinity for the negatively charged surface of cotton fiber. Figure 3 shows the whiteness of cotton fabrics that were bleached, respectively, by the H2O2/NaOH system (6.00 g/L 30% w/w H2O2 and 3.00 g/L NaOH) and the TBCC/H2O2/NaHCO3 system (11.00 g/L TBCC, 4.08 g/L 30% w/w H2O2, and 3.53 g/L NaHCO3). It can be seen that, at low temperatures, the TBCC/H2O2/NaHCO3 system was much more effective than the H2O2/NaOH system in improving the whiteness of cotton fabric. It is believed that, besides the chemical potential of TPA, the electrostatic interactions of TBCC and TPA with cotton fiber also contribute to the bleaching performance of the TBCC/H2O2/NaHCO3 system on cotton fiber. When the cotton fabric was added to the solution of the TBCC/H2O2/NaHCO3 system, the positive charges of TBCC were attracted to the negative charges on cotton fiber. TPA was generated in close proximity to the fiber surface, and could easily come into contact with the natural pigments and break them down. The effect of electrostatic attraction of cotton fiber to TBCC and TPA on the bleaching performance can be observed by adding various concentrations of NaCl to the bleaching solution, as shown in Fig. 4. It can be seen that the whiteness of cotton fabric decreased as the concentration of NaCl increased. This is due to the fact that the negative charges of cotton fiber were suppressed by Na+, especially in a high concentration of NaCl, and thus the attractive forces of cotton fiber to TBCC and TPA were weakened. Therefore, the contribution of electrostatic interaction to the bleaching performance was reduced to some extent due to the addition of NaCl to the TBCC/H2O2/NaHCO3 system.
In the TAED/H2O2/NaHCO3 system (3.42 g/L TAED, 4.08 g/L 30% w/w H2O2, and 3.53 g/L NaHCO3), a molecule of TAED reacted with two molecules of H2O2 to generate two molecules of peracetic acid (PAA) as shown in Fig. 5, which is the active species for bleaching of cotton fabric (Long et al. 2013; Xu et al. 2013). Since TAED contains no charge, it cannot be attracted or repelled by the negative charges on cotton fiber. Therefore, it is reasonable that the performance of the TAED/H2O2/NaHCO3 system on bleaching of cotton fabric should depend on the activity of PAA but have nothing to do with the negative surface charges on cotton fiber. Figure 6 shows the effect of the concentration of NaCl on the whiteness of cotton fabric bleached with the TAED/H2O2/NaHCO3 system. It can be seen that the whiteness of cotton fabric was not affected by the concentration of NaCl. This indicates that the negative charges of cotton fiber would not affect the effectiveness of PAA on bleaching of cotton.
The electrostatic interactions of bleach activators with cotton fiber can be represented by the adsorption of the bleach activators on cotton fiber. As shown in Fig. 7a, when cotton fabric was immersed in the TBCC solution, the absorbance was found to significantly decrease because TBCC was adsorbed onto cotton fiber under the electrostatic interactions. As NaCl was added to the TBCC solution, Na+ suppressed the negative charges of cotton fiber, which caused a reduction in the electrostatic attraction of cotton fiber to TBCC so that the absorbance of the TBCC solution increased. In Fig. 7b, however, the absorbance of the TAED solution was found to change little no matter whether NaCl was added or not, for which the main reason is that the electrostatic interaction between TAED and cotton fiber was not significant.
In order to confirm the effects of the surface charges of cotton fiber on the bleaching performance, the cotton fiber was modified with CHPTAC which contained a quaternary ammonium cation. Figure 8 shows the zeta potential of the modified cotton fiber that was measured at pH 7. It can be seen that the zeta potential of the cotton fiber increased from − 20.34 to 1.46 mV as the concentration of CHPTAC increased from 0 to 120g/L. This indicates that positive charges were introduced onto the cotton fiber and counteracted the negative charges on cotton fiber. Cotton fiber presented various zeta potentials when modified with different dosages of CHPTAC.
Figure 9 shows the whiteness of the cationized cotton fabrics which were bleached with the TBCC/H2O2/NaHCO3 system (11.00 g/L TBCC, 4/08 g/L 30% w/w H2O2, and 3.53 g/L NaHCO3) and the TAED/H2O2/NaHCO3 system (3.42 g/L TAED, 4.08 g/L 30% w/w H2O2, and 3.53 g/L NaHCO3), respectively. It can be seen that, when the cationized cotton fabric was bleached with the TBCC/H2O2/NaHCO3 system, the whiteness decreased as the concentration of CHPTAC increased. An important reason is that CHPTAC brought more positive charges onto cotton fiber to partially neutralize the negative charges of cotton fiber (Fu et al. 2013; Pruś et al. 2022). The affinities of TBCC and TPA to cotton fiber were significantly deceased as cotton fiber was cationized with an increased concentration of CHPTAC. Therefore, the modification of cotton fiber with CHPTAC caused a reduction in the electrostatic attraction of interactions between cotton fiber to TBCC and TPA and even formed electrostatic repulsions to TBCC and TPA when the cotton fiber was modified for positive surface charges, thereby resulting in a decrease in the bleaching effectiveness. However, when the cationized cotton fabric was bleached with the TAED/H2O2/NaHCO3 system, the whiteness had little change as the concentration of CHPTAC increased. This is mainly because that TAED is a non-ionic bleach activator, and the surface charges of the modified cotton fiber had no direct electrostatic interactions with TAED and PAA.
Surfactants play an important role in textile wet processing as they can help wet the fiber surface, and allow chemicals to penetrate into fiber quickly (Simončič and Rozman 2007). It is known that surfactants can affect the adsorption of ions on cotton fibers (Fras-Zemljič et al. 2006). In the present work, SDBS and STAC were used to examine the effects of their charges on the performance of the peroxide systems on the bleaching of cotton fiber. Figure 10 shows the whiteness of cotton fabric bleached with the TBCC/H2O2/NaHCO3 system with the addition of various concentrations of surfactants. It can be seen that the addition of SDBS and STAC resulted in an entirely different effect on the whiteness of cotton fabric. To the TBCC/H2O2/NaHCO3 system, the addition of SDBS increased the whiteness of cotton fabric but the addition of STAC decreased the whiteness of cotton fabric. Table 1 shows the decomposition of H2O2 in the TBCC/H2O2/NaHCO3 system with the addition of SDBS and STAC, indicating that the addition of the ionic surfactants would not impact the generation of peracids. Hence, it is possible that the charges of the ionic surfactants affected the performance of the TBCC/H2O2/NaHCO3 system on bleaching of cotton fabric. This was further confirmed by measuring the adsorption of TBCC onto cotton fiber with the addition of SDBS and STAC as shown in Fig. 11. It can be seen that compared with the adsorption of TBCC on cotton fiber without the addition of ionic surfactants (Normal), the addition of SDBS increased the adsorption of TBCC on cotton fiber but the addition of STAC decreased the adsorption of TBCC on cotton fiber. When SDBS was added to the TBCC/H2O2/NaHCO3 system, SDBS brought more negative charges to the surface of cotton fiber to attract more TBCC molecules close to cotton fiber. When STAC was added to the TBCC/H2O2/NaHCO3 system, however, STAC brought positive charges to the surface of cotton fiber to counteract part of negative charges of the cotton fiber so as to reduce the attraction of cotton fiber to TBCC molecules.
Bleaching time | Decomposition of H2O2 (%) | ||
---|---|---|---|
None | SDBS | STAC | |
10 | 56.37 | 56.99 | 57.49 |
30 | 72.82 | 72.82 | 72.82 |
50 | 79.18 | 79.31 | 79.37 |
70 | 79.86 | 80.85 | 79.81 |
The effect of the surfactants on the TAED/H2O2 bleaching system is shown in Fig. 12. It can be seen that the addition of ionic surfactants had no apparent effects on the whiteness of the bleached fabric. This can be ascribed to the fact that TAED and PAA contain no apparent ionic charges, and their interactions with cotton fiber would be affected by the addition of ionic surfactants.
In bleaching of cotton fiber with peroxide systems, electrostatic interactions between bleaching species and cotton fiber have important effects on the bleaching performance. Perhydroxyl anions (HOO−) dissociated from the H2O2/NaOH system and worked on bleaching of cotton fiber, but the negative charges on the surface of cotton fiber repelled HOO−, causing a reduction in the bleaching performance. In the TBCC/H2O2/NaHCO3 system, TPA is generated as the bleaching species with a cationic charge that had a high affinity towards the negatively charged surface of cotton fiber and promoted bleaching performance. In the TAED/H2O2/NaHCO3 system, however, PAA was generated as the bleaching species without an apparent ionic charge, and its bleaching performance had not been affected by the negative charges on the surface of cotton fiber. When NaCl was added to these bleaching systems, the dissociated sodium cations (Na+) counteracted the negative charges on the surface of cotton fiber, so that the effects of electrostatic interactions on the bleaching performances of the H2O2/NaOH system and the TBCC/H2O2/NaHCO3 system were greatly diminished. When cotton fiber was modified with CHPTAC, its surface exhibited positive charges which repelled TPA in the TBCC/H2O2/NaHCO3 system, causing a reduction in the bleaching performance, but had no significant effect on PAA in the TAED/H2O2/NaHCO3 system. When ionic surfactants were used in the peroxide bleaching systems, the ionic surfactants were adsorbed onto the surface of cotton fiber and their charges would interfere with the electrostatic interactions between bleaching species and cotton fiber, thereby affecting the bleaching performance. It is important to understand the electrostatic interactions between the bleaching species and cotton fiber for optimizing the bleaching performance and developing environmentally benign bleaching process for cotton fiber.
Ethics approval and consent to participate
There is no potential conflict of interest and no human participants or animals are involved.
Consent for publication
All authors were informed and agreed to publish in cellulose.
Availability of data and materials
The datasets used and/or analysis during the current study are available from the corresponding author on reasonable request.
Competing interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.
Funding
The National Natural Science Foundation of China (No. 21978117).
Authors' contributions
Jiangpeng Fu: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - Original Draft, Writing - Review & Editing. Jinmei Du: Validation, Writing - Original Draft. Dagang Miao: Validation, Writing - Original Draft. Guowei Xiao: Formal analysis, Investigation. Yang Jiang: Methodology, Resources, Supervision, Project administration. Changhai Xu: Conceptualization, Supervision, Writing - Review & Editing, Funding acquisition.
Acknowledgments
This study was funded by the National Natural Science Foundation of China (No. 21978117).
No competing interests reported.
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