Study on H2O2/TAED and H2O2/TBCC bleaching mechanism related to hydroxyl radical with a fluorescent probe

Energy-Saving One-Step Pre-Treatment Using an Activated Sodium Percarbonate System and Its Bleaching Mechanism for Cotton Fabric

The traditional pre-treatment of cotton fabric hardly meets the requirement of low carbon emissions due to its large energy consumption and wastewater discharge. In this study, a low-temperature and near-neutral strategy was designed by establishing a tetraacetylethylenediamine (TAED)-activated sodium percarbonate (SPC) system. First, the effects of SPC concentration, temperature and duration on the whiteness index (WI) and capillary effect of cotton fabrics were investigated. Particularly, excess SPC's ability to create an additional bleaching effect was studied. The optimized activated pre-treatment was compared with the traditional pre-treatment in terms of the bleaching effect and energy consumption. Further, the degradation of morin, which is one of the natural pigments in cotton, was carried out in a homogeneous TAED/SPC system to reveal the bleaching mechanism. Lastly, the application performance of the treated cotton was evaluated by characterizing the dyeability, mechanical properties, morphology, etc. The research results showed that temperature had a significant influence on both the WI and capillary effect, followed by the SPC concentration and duration. The WI was positively correlated with the SPC concentration, but excess SPC could not produce an obvious additional effect. The WI of the fabric increased by 67.6% after the optimized activated bleaching using 10 mmol/L SPC and 15 mmol/L TAED at 70 °C for 30 min. Compared with the traditional process performed at 95 °C for 45 min, the activated process produced approximately 39.3% energy savings. Research on the bleaching mechanism indicated that the reactive species that participated in degrading the morin were the hydroxyl radical and superoxide radical, and the contribution degree of the former was larger than that of the latter. Two degradation components with molecular weights of 180 and 154 were detected using mass spectroscopy. Based on this, the bleaching mechanism of the TAED/SPC system was proposed. Moreover, the fabric after the activated pre-treatment had a suitable dyeability and strength, a lower wax residual and a smoother and cleaner fiber surface. The encouraging results showed that TAED/SPC is a promising bleaching system that is conducive to the sustainable advance of the textile industry.

Separation and Characterization of Cellulose Fibers from Cannabis Bast Using Foamed Nickel by Cathodic Electro-Fenton Oxidation Strategy

Degumming is the most important link in the textile industry. The main purpose of degumming is to effectively remove non-cellulose substances in plant bast fibers. In this research, we propose an electro-Fenton (EF) system with a nickel-foam (Ni-F) cathode in weak acid pH (EF/Ni-F) to degum cannabis fiber in EF while reducing the content of pollutants in degumming wastewater. FT-IR, XPS, XRD, SEM, and TG were employed to thoroughly understand the reaction characteristics to characterize chemical components, element qualities, the crystallinity, and the morphologies of degummed fibers. Additionally, physical and mechanical properties such as breaking strength, elongation at breaking, residual glue rate, whiteness, and diameter of degummed fibers were measured. Through testing, it was found that the fiber degummed by the EF method had higher breaking strength, lower residual tackiness, and higher whiteness than other methods. The antibacterial test was used to detect the effect of fiber on Staphylococcus aureus before and after degumming. EF could remove more colloidal components from cannabis than other methods, and the mechanical properties were also enhanced. The characteristics of the degummed fiber further confirmed the effectiveness of the new degumming method. Moreover, the antibacterial experiment found that the antibacterial property of the degummed fiber was enhanced. The colloidal components in the degumming wastewater were flocculated and precipitated. The upper liquid of the solution had low chromaticity, low COD value, and weak acid pH value, which can meet the discharge requirements. The above test proves that EF is an effective degumming method that is environmentally friendly, takes less time, and enhances antibacterial performance.

Establishing an ultrasound-assisted activated peroxide system for efficient and sustainable scouring-bleaching of cotton/spandex fabric

This study presents a high-efficient and cost-effective ultrasound-assisted strategy for one-bath one-step scouring and bleaching of cotton/spandex fabric using sodium percarbonate (SPC) and tetraacetylenediamine (TAED) couple. SPC plays both roles of pH regulator and H₂O₂ donor to initiate the peracetic acid (PAA) release from TAED. The significance and interaction effects of operating parameters (TAED concentration, temperature and time) on the WI (Whiteness Index) of fabrics were investigated through a central composite design. The bleaching mechanism was studied by exploring the relationship between WI and PAA and hydroxyl radical (HO·) concentrations. The mechanical and dyeing performances of treated fabrics were also evaluated. Results show that temperature exerted a significant impact on WI followed by TAED concentration and time. The PAA concentration decreased and HO· concentration increased upon the temperature rise. Both PAA and HO· were significant to upgrade WI and ultrasound was effective in enhancing their bleaching efficiency. The fabric treated only with 15 mmol/L TAED and 10 mmol/L SPC at 40 °C for 40 min under ultrasound could achieve a WI of 68.6 (43% higher than greige fabric), which was almost equivalent to that of the fabric treated at 60 °C without ultrasound. This verifies the contribution of ultrasound technology in reducing bleaching temperature for energy-saving purpose. Moreover, the treated fabric displayed less than 5% tensile strength loss, having a marginal impact on the apparel performance. The wettability of fabric was greatly improved leading to a good dyeing performance. Encouraging results demonstrate the high efficiency of the ultrasound-assisted pre-treatment process of cotton/spandex fabric, which contributes to the sustainable production of textiles.

Bleaching of cotton fabric with tetraacetylhydrazine as bleach activator for H2O2

Tetraacetylhydrazine (TH) as bleach activator for H₂O₂ cotton bleaching was synthesized and characterized by ¹H NMR, ¹³C NMR and MS spectra. TH has better solubility than that of TAED. The CIE whiteness index (WI), H₂O₂ decomposition rate and bursting strength were employed to investigate the performance of H₂O₂/TH bleaching system. By addition of TH, WI and H₂O₂ decomposition rate increased significantly at 70 °C. Bleaching temperature, NaHCO₃ concentration and bleaching time were also discussed in detail and the loss of bursting strength is not clear. By using benzenepentacarboxylic acid (BA) as a fluorescent probe for hydroxyl radical detection, the bleaching process of H₂O₂/TH system was investigated. Acetylhydrazine and diacetylhydrazine were also utilized to further confirm the process. In addition, bimolecular decomposition was investigated by using 9,10-dimethylanthracene (DMA) as fluorescent probe of ¹O₂. Based on these experimental results, the bleaching mechanism of H₂O₂/TH system was proposed.

Generation of hydroxyl radicals and effective whitening of cotton fabrics by H2O2 under UVB irradiation

Chemically crosslinked cotton fabrics may show yellowish appearance, especially citric acid (CA) crosslinked ones. Hydrogen peroxide (H₂O₂) bleaching under alkaline condition could improve the whiteness of the CA-crosslinked cotton fabrics but sacrificing certain crosslinking performance of the products due to alkaline hydrolysis of ester connections. Regular H₂O₂ and UV irradiation (H₂O₂/UV) system can destroy color but also damage fibers due to the use of very short wavelength of UVC such as 254nm or shorter. Now, it was found that longer wavelength UV such as 312nm performed better in H₂O₂/UV systems on CA-crosslinked cotton fabrics. The reaction mechanism and potential product of the oxidation reaction on CA-crosslinked cotton were proposed and demonstrated. UV-vis spectrophotometer and Fourier transform infrared spectroscopy provided key evidence. Whiteness, wrinkle recovery angle and tensile strength of the fabrics were evaluated, and the results support the mechanism. The process is environmentally friendly and highly efficient.