Lecture 2 preparatory processes
Download as PPT, PDF6 likes3,207 views
The document discusses various preparatory processes for cotton textiles including desizing, scouring, and bleaching. Desizing involves removing added starches used in sizing through processes like hydrolysis or oxidation. Scouring uses alkaline solutions to remove natural impurities like fats, waxes, pectins and proteins from cotton. Bleaching removes color pigments through oxidation, with common bleaching agents being sodium hypochlorite, hydrogen peroxide, and peracetic acid. These preparatory processes are important to remove impurities, improve dyeability and finishability of cotton textiles.
Lecture 2 preparatory processes
- 1. PREPARATORY PROCESSES FOR COTTON R.B.CHAVAN Department of Textile Technology Indian Institute of Technology Hauz-Khas, New Delhi 110016 E-mail rbchavan@hotmail.com
- 2. Composition of cotton Natural impurities 8.0 Moisture 1.0 Mineral Matter 0.5 Colouring matter 1.1 Proteins 0.7 Pectins 0.5 Oils, Fats and Waxes 88 Cellulose % Constituent
- 3. Fats and Waxes Fatty acids Stearic acid Palmitic acid Oleic acid Fatty alcohols Gossipyl alcohol (C30H61OH) Ceryl alcohol (C26H53OH) Montanyl alcohol (C28H57OH)
- 4. Pectins Derivatives of pectic acid Polymer of high molecular weight Composed of Galactouronic acid Some COOH groups are present as Ca and Mg salts Free acid and Ca and Mg salts are insoluble in water
- 5. Proteins Nitrogenous compounds Present in primary wall and Lumen Some of the amino acids identified are Leucine Valine Proline, Alanine etc. Yellowish (Creamish) colour of cotton is related to Proteins and Colouring matter
- 6. Colouring matter Colour pigments present are 3,5,7,2’, 4’ Penta hydroxy flavone (Morrin) 3,5,7,8,3’,4’ Hexa hydroxy flavone (Gossypetine)
- 7. Mineral Matter Depends on soil composition Can be determined by ash analysis 5.0 Aluminium oxide 3.0 Ferric oxide 8.4 Magnesium sulphate 10.3 Calcium carbonte 9.0 Calcium sulphate 9.3 Potassium sulphate 9.9 Potassium chloride 44.8 Potassium carbonate
- 8. Added Impurities Sizing agents: Agents used to give protective coating to warp threads Minimize the breaking of warp threads during weaving Improve weaving productvity. The operation is known as sizing. Starch is one of the most important sizing agent for cotton
- 9. PREPARATORY PROCESSES Purpose To remove added and natural impurities from textile material Removal impurities to the maximum extent possible with minimum effect on fibre strength. To impart desirable properties to textile material
- 10. Principle of preparatory processes The impurity is insoluble in water Conversion of water insoluble impurity to its water soluble form. Chemical reactions involved are Hydrolysis Oxidation The choice of chemicals depends on chemical nature of impurity.
- 11. Desizing Process of removal of size is known as desizing Facilitates penetration of chemicals and dyes applied during subsequent processing operations Starch is the main ingredient for sizing of cotton warp Chemically starch is Chemically it is Amylose: Linear polymer of low mol. Wt. Amylopectin: High molecular wt. Branched polymer Water insoluble
- 12. Desizing methods Starch solubilization Hydrolysis
- 13. Oxidation
- 15. SCOURING TREATMENT OF COTTON WITH ALKALINE SOLUTION PURPOSE REMOVE NATURAL IMPURITIES : FATS AND WAXES, PECTIC SUBSTANCES, PROTINES REMOVE ADDED IMPURITY : OIL STAINS SEED COAT FRAGMENTS IMPROVE WATER ABSORBENCY FOR UNIFORM DYEING, PRINTING AND FINISHING . PRINCIPLE Hydrolysis of impurities
- 16. BLEACHING Removal of colouring matters by Oxidation BLEACHING AGENTS sodium and calcium hypochlorite Hydrogen peroxide Sodium Hypochlorite Peracetic acid HYDROGEN PEROXIDE MOST POPULAR ON INDUSTRIAL SCALE It is environment friendly
- 17. INDUSTRIAL PRACTICES EQUIPMENT USED BATCH WISE OPERATION KIER ( ROPE FORM ) JIGGER (OPEN WIDTH ) WINCH (ROPE FORM, PARTICULARLY FOR KNITS ) JET DYING (ROPE FORM, PARTICULARLY FOR KNITS ) CONTINUOUS J – BOX ( ROPE FORM ) VARIOUS PAD STEAM PROCESSES (OPEN WIDTH ) SEMI-CONTINUOUS 1. PAD – ROLL (OPEN WIDTH)
- 18. Kier(Rope Form) Winch (Rope Form) Jet machine (Rope form) Jigger (Open width form)
- 19. Continuous Processing J-Box (Rope Form) Continuous (Open width) Saturator, Steamer, Washer.
- 20. Semi-Continuous Pad-Batch (Open Width form)
- 21. PRESENT PRACTICE COMBINED (OPEN WIDTH) DESIZING - SCOURING SCOURING – BLEACHING DESIZING – SCOURING – BLEACHING EQUIPMENT SATURATOR – PADDER – STEAMER - WASHER
- 22. ENVIRONMENTAL ISSUES DESIZING the wash water from desizing may contain up to 70 % of the total COD load in the final effluent , Neither enzymatic nor oxidative desizing allows size recovery . H2O2 BLEACHING H2O2 decomposition forms water and oxygen some stabilzers may from complexes with metal in the effluent, releasing them in the receiving waters effluents containing inorganic chlorides (e.g. NaCI from dyeing can be oxidised to their chlorites/hypochlorites when they are mixed with hydrogen peroxide bleach waste water. In this way AOX may be found in waste water even if bleaching is carried out without chlorine-based bleaching agents.