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Bleaching of Cellulosic and Synthetic Fabrics
Published in Menachem Lewin, Stephen B. Sello, Handbook of Fiber Science and Technology: Volume I Chemical Processing of Fibers and Fabrics, 2018
As with linen, the greater the bleaching effect the greater also the loss in fiber weight. A combination (two-stage) bleach is usual: sodium hypochlorite as the first stage followed by treatment with hydrogen peroxide, potassium permanganate, or sodium chlorite [327, 329, 330]. Bleaching with sodium hypochlorite (using 1–3 g/liter active chlorine) should be in a neutral or slightly alkaline medium; in an acid bath there is a strong tendency for chlorine retention by the lignin [327]. Optimum conditions for bleaching with sodium chlorite (7 g/liter) are for 80 min at 65–70°C and at pH 4. This causes the minimum reduction in degree of polymerization. At higher temperatures bleaching is more rapid [306, 330]. Jute has been bleached by hydrogen peroxide at 75–85°C for 2 hr in the presence of sodium silicate and soda ash. Under these conditions no degradation of the α-cellulose is observed at concentrations of 1 vol. and below [326]. With peroxide concentrations of up to 2 vol., dry strength of yarn is slightly increased, but wet strength falls by about 25% [326].
Advanced Technologies for the Removal of Refractory Contaminants from Pulp and Paper Mill Wastewater
Published in Maulin P. Shah, Removal of Refractory Pollutants from Wastewater Treatment Plants, 2021
Lignin is a polyphenolic polymer which is one of the most difficult to degrade of the biomass components. Lignin and its derivatives are hazardous and refractory in nature which imparts a dark brown color (called black liquor) and high BOD and COD to the wastewater generated during the pulp making process. The lignin and its derivatives will further react with chlorine during pulp bleaching and lead to the formation of various toxic and refractory compounds, including benzaldehydes, catechols, chlorinated lignosulfonic and resin acids, chlorinated phenols, syringo-vanillins, and guaiacols. Some of the most highly toxic and persistent chlorinated compounds present include chlorophenols like tri- and penta-chlorophenols, guaicols, catechols, anisoles, and verathroles. Dioxins and furans are examples of highly dangerous chlorinated compounds available in P&P mill wastewater. These chlorinated compounds are generated in large quantities during the chlorine bleaching stage of kraft pulp in the P&P industry. In order to decrease the generation of these toxic refractory compounds, various measures are adopted during the bleaching stage, including the utilization of oxygen bleaching and the use of chlorine dioxide bleach (elemental chlorine free). The other strategies available include the extended delignification process which can remove more lignin, modified cooking, enhanced delignification efficiency, spill collection systems, and highly efficient washing and reusing condensate facilities. Some researchers also reported the setting up of external treatment plants with modified designs for further reducing the levels of toxic and refractory chlorinated organic contaminants that are released into the water bodies.
Care labelling
Published in Rajkishore Nayak, Saminathan Ratnapandian, Care and Maintenance of Textile Products Including Apparel and Protective Clothing, 2018
Rajkishore Nayak, Saminathan Ratnapandian
Bleaching helps to remove stains on white clothes and retain their brightness. It can remove the colour when used on coloured clothes. The bleaching agents can be classified as (1) chlorine bleach and (2) non-chlorine bleach.
Creative exploration: zero-waste fashion design practices with traditional Korean clothing
Published in International Journal of Fashion Design, Technology and Education, 2023
Go (袴) used natural fabrics with natural dyeing. Various fabrics were used, including linen, cotton, hemp and pongee, which are well-ventilated, and various cottons including calico, quilted cotton or silk were used for breathability and warmth depending on the season. Vegetable dyeing was the most common method in this era (Soh, 2013, p. 36); white, symbolising ‘purity’, was often worn, as well as so (素)-colour, the range of colours from pale off-white to beige of raw materials used for clothing. Silk and cotton could be bleached pure white naturally through repeated washing and sun drying (p. 43). Naturally derived materials and dyeing methods have zero-waste aspects, reducing waste sent to a landfill via biodegradation without leaving any municipal solid waste (MSW) during or after manufacturing.
Chemical footprint of textile and apparel products: an assessment of human and ecological toxicities based on USEtox model
Published in The Journal of The Textile Institute, 2020
The ChF for ecological toxicity of bleach is 7.59 × 10−1 [PAF]m3·day, which ranks second, and its contribution rate is 10.88% of the total ChF. Bleach is mainly used to remove natural pigments and impurities from fibers for improved dyeing. Hydrogen peroxide is a common oxidizing bleaching agent and the main source of ecological toxicity. In addition, the ChFs of blue VAT dyestuff and oxidizing agent are also high at 5.61 × 10−1 [PAF]m3·day (8.03%) and 4.34 × 10−1 [PAF]m3·day (6.21%), respectively. The main ingredient of blue VAT dyestuff is indigo. Before dyeing, indigo must be reduced to a soluble colorant to dye the fibers, and then the insoluble indigo particles are oxidized to complete the coloring. The pollutant that mainly generates the ecological toxicity of oxidizing agent is hydrogen peroxide.
Characterization of kraft pulp delignification using sodium dithionite as bleaching agent
Published in Chemical Engineering Communications, 2020
Jishnu Krishnan, Susmith Sunil Kumar, R. Krishna Prasad
The bleaching using molecular oxygen requires relatively high temperature and the drawback of this process is decreased quality of pulp when extent of degree of delignification is 40%–45% (Gasper et al., 2002). The oxygen delignification efficiency of 30.33% was achieved based on kappa reduction for Melia Dubia kraft pulp (Sharma et al., 2015; Kumar Anupam et al., 2018). The chlorine based bleaching techniques are increasingly being replaced by chlorine-free bleaching agents and oxygen-based reagents (Kim et al., 2006). Hydrogen peroxide is a common chlorine-free alternative. The chemical under consideration for delignification of kraft pulp in this study is sodium dithionite which is used for dyeing and bleaching of pulp. It has an odor similar to sulfur dioxide and about 50% of mechanical pulps are produced using sodium dithionite (Malkavaara et al., 2000). The bleaching agents used to bleach pulp include chlorine dioxide, peracetic acid (Jiménez et al., 2008), hydrogen peroxide (Chai et al., 2004) and using alkali and Caro acid (Abou Yousef et al., 2005).