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Scouring and bleaching in textiles
This document summarizes scouring and bleaching processes in textiles. Scouring removes impurities like oils, wax and dirt to make materials hydrophilic. Bleaching destroys natural colors to produce a white material. Key points include: scouring uses saponification and emulsification, while bleaching uses hypochlorite or peroxide reactions; continuous processes use a J-box machine and batch processes use a kier boiler; the mechanisms and importance of each process are described.
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Scouring and bleaching in textiles
- 1. Scouring And BleachingIn Textiles Prepared by Takbir Ahmed Department of Textile Engineering Daffodil International University
- 2. What is scouringand bleaching? Scouring: Scouring is a process of removing impurities such as oil, wax, fats, dust and dirt from textile material to make it hydrophilic. Bleaching: Bleaching is the destruction of natural coloring(Gray) matters to produce a white material.
- 3. Importance of scouringin textiles. To remove impurities such as oil, wax, dirt etc. To clean the textile material. To make the material more hydrophilic To increase the absorbency
- 4. Importance of bleachingin textiles 1.To impart a permanent white effect to the fiber. 2. To destroy natural the coloring matter.
- 5. Types of Scouringand Bleaching Types of Scouring process. 1. Dis-continuous process. 2. Continuous process. Types of Bleaching Process. 1.Hydrochlorite Bleaching. 2.Peroxide Bleaching. 3. Sodium Chlorite Bleaching.
- 6. Mechanism Of Scouring Saponification: The vegetable oil, which is immiscible with water, is glyceride of fatty acids. When such oils are heated with a solution of sodium hydroxide in water, the oil splits up into its constituents-fatty acid and glycerin. Glycerin is miscible with water easily and the fatty acids reacts with sodium hydroxide present in the solution forming its sodium salt i.e. soap which is also soluble in water. Thus oil is removed Emulsification: Wax and non saponifiable oils are removed by emulsification as they are immiscible in water. Normal washing soap is used as a emulsifying agent which makes emulsion of them.
- 7. Mechanism Of Bleaching(Hypochlorite Bleaching ) Used Sodium or Calcium Hypochlorite. Produces Metallic Hydroxide and Hypochlorous acid. Ca(OCl)2 + H2O Ca(OH)2 + 2HOCl NaOCl + H2O NaOH + 2HOCl Hypochlorous acid produces Hydrogen ion(H+ )and Hypochlorous ion(OCl- ) HOCl H+ + OCl- Hypochlorous ion is responsible for bleaching process. OCl- + Colored Material White Material.
- 8. Mechanism Of Bleaching Mechanism of peroxide bleaching Hydrogen Peroxide Used as Bleaching agent. H2O2 produces Hydrogen and perhydroxyl ion. H2O2 H+ + OH2 - This process carried out in alkaline condition PH =11.5. perhydroxyl ion is responsible for bleaching action. OH2 - + Colored Material White material.
- 9. Machine Used inScouring And Bleaching Process. Same used both machine is in scouring and bleaching. For continuous process J- Box Machine. For discontinuous/batch process kier boiler machine.
- 10. J –box Process Machine Description: Impregnation bath: Padded with caustic soda/Peroxide and wetting agent at 70-80⁰ C for 30-40 sec. Pre Heater : Thermostatically control system for 30 sec at temp 90-100⁰ C . J-box : Fabric is stored for 1-2 hours at 98-102⁰ C.NaOH/H2O2 solution reacts with impurities and dissolves them. Washing Unit: Fabric firstly hot wash and then cold wash.
- 11. J –box Processfor scouring and bleaching
- 12. Kier Boiler Process Filled with solution about ½ or 1/3 of the kier. Filled fabric about 80-85%. Steam is passed through the whole kier. Remove the pocket air otherwise it will damage the cellulose structure. After 1-2 hours kier is closed for 6 hours then scouring or bleaching will be completed.
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