Mercerization

shortly described mercerization process.

1. M ercerization Presented by Fatema Sharmin Department of wet processing engineering Bangladesh University of Textiles

2. Mercerization Mercerization,  in textiles, a chemical treatment applied to cotton  fibres or fabrics to permanently impart a greater affinity for dyes and various chemical finishes . Mercerizing is a pre-treatment or finishing treatment for cotton articles and/or natural fibres composed by cellulose in a higher concentrated solution of caustic soda (300 g/l), under tension and ambient temperature

3. Cont …   T ypically cotton (or cotton-covered thread with a polyester core)  but hemp and linen can be mercerized also – to increase luster.  It is done after weaving (in the case of fabrics) or spinning (for yarns or threads).  But early on it was found that the process also had secondary benefits as the mercerized fibers were able to absorb more water, and therefore absorb more dye, making the color of the dyed cloth brighter and deeper.  The difference is dramatic.   As mercerization increases the absorption of dyestuffs by as much as 25 %

4. History . The process goes back to the 1880’s. The effect of caustic soda on cotton was discovered in 1844 by John Mercer, an English calico printer, who received a patent for it in 1850. John Mercer was granted a British Patent for his discovery that cotton and other fibers changed character when subjected to caustic soda ( NaOH , also known as sodium hydroxide or lye), sulfuric acid, and/or other chemicals. One of the changes was that caustic soda caused the fiber to swell, become round and straighten out. But so what – these changes didn’t impart any luster to the fibers, so his patent was largely ignored.

5. H. A. Lowe Then in 1890 Horace Lowe found that by applying Mercer’s caustic soda process to cotton yarn or fabric under tension, By holding the cotton during treatment to prevent it from shrinking The fabric gained a high luster as a result of the light reflection off the smooth, round surface created by the NaOH . It became an overnight success and revolutionized the cotton industry. By applying this Lowe found that the fibre gained a lustrous appearance

6. To improve the luster To improve the strength To improve the dye uptake and To improve water absorbency Purpose

7. Internal hydrogen bonds are broken Native cellulose (Cellulose I) forms alkali cellulose I with concentrated sodium hydroxide. On washing and neutralization cellulose II is formed In Cellulose II, the number of available hydroxyl groups (-OH) is increased by 25 %. Mercerised cotton has an increased affinity for reactive, direct cotton dyes, water and an increased strength As a result of the penetration of the alkali into the lattice thus lustre is increased.

8. Change due to mercerization Round surface can reflect the light better than a rough surface. Due to mercerization cotton shape become round. Luster is a result of light reflection off a surface. The more glass like the surface, the better the luster Yarn has a very fine covering of tiny fiber ends (fuzz). This fuzz is removed by passing the yarn (or fabric) through a controlled heated atmosphere termed singeing (gas fired in the past, electric more currently) resulting in a cleaner surface. (

9. What happens to cotton during Mercerization Swelling of the fibre takes place. the cross section ,like kidney shaped becomes circular or oval-shaped, thus enhancing the luster Shrinkage of length wise. Strength improved Cellulosic chains gets rearranged .

10. MICROSCOPIC VIEW

11. WHAT HAPPENS INSIDE COTTON After swelling NaOH thoroughly penetrates amorphous phase of the fibre, reaction between the alkali and the micelle occurs completing the generation of alkali cellulose I. At higher concentrations, the hydrate volume is smaller. Hydrates cause lower swelling but able to penetrate the crystalline phase and change the crystal structure. Such changes are capable of inducing important structural modifications in fibre structure .

12. Cellulose-I to cellulose-II The native form of cellulose which occurs in cotton and other natural cellulosic fibres , is known as cellulose I . It has it unique crystal diffraction pattern (monoclinic). It is a thermodynamically less stable form of cellulose . When cellulose in converted to regenerated cellulosic fibres like viscose, dissolution of cellulose is an intermediate step. During regeneration, it gets converted to a different crystalline form, known as Cellulose II.

13. CHEMICAL REACTION

14. EFFECT OF MERCERIZATION Fibre level Molecular level Chemical change Mechanical change

15. Change due to mercerization A. Fiber level 1 . Swelling 2 . Cross sectional morphology changes from beam shape to round shape . 3. Shrinkage along with longitudinal direction. B . Molecular level 1 . Hydrogen bond readjustment 2. Orientation (parallelization) of molecular chains in amorphous region along the direction of fiber length . 3. Orientation of the crystallinity in the direction of the fiber length . 4. Increased crystallinity C . Chemical Changes 1 . Increased rate of reaction on hydrolysis and oxidation 2. Liberation of heat during the caustic treatment.(heat of sorption and heat of reaction) 3 . Increase in the alkali absorption . 4. Increase in the absorption of iodine. Changes during mercerizing process

16. Effect on crystallinity

17. Swelling on mercerization

18. Effects of the mercerization of cotton fabric

19. How it is done To get the desired luster and tensile strength, cotton is held under specified tension for about 10 minutes with an application of between 21-23% caustic soda ( NaOH ) and wetting agents (used to facilitate the transfer of the NaOH into the fibers), at room temperature. Then the fabric is neutralized in an acid bath . The material is then treated with water or acid to neutralize the sodium hydroxide . If the material is held under tension during this stage, it is kept from shrinking appreciably; if no tension is applied, the material may shrink by as much as 25%. Higher-quality cotton goods are usually mercerized; cloths so treated take brighter, longer-lasting colors from less dye .

20. Cont … The process, done in a continuous way, involves 4 subsequent steps : a. Impregnation of the material in relaxed state, cold caustic solution of required strength and wettability . b. Stretching while the material is still impregnated in the caustic solution . c. Washing off the caustic soda from the material while keeping the material still in the stretch state . d. Neutralizing with acids and rinsing.

21. According to the form of the tension A . tension mercerization slack mercerization Mercerization are Two Types:

22.   Tension Mercerization   The purpose of mercerization is to increase luster of Cotton fibers   The fiber untwists and swells, lumen becomes rounder in cross-section and it gains luster.   Dye affinity and chemical reactivity increase. Fabric becomes stronger and smoother . Slack Mercerization   Not as lustrous as tension method   Elongation and recovery properties improve and thus have been used to produce comfort stretch garments and fabric bandages, which need to conform to body shapes.  

23. Form of mercerization B . On basis of product: a)   Yarn mercerization 1.Batch    Hank mercerization Cheese mercerization 2.Continuous    Single end mercerization Tow mercerization Warp mercerization

24. MERCERISATION MACHINE 1.Yarn mercerizing machine a.Hank mercerizing machine b. Cheese mercerizating machine c. Warp mecerizatng mache

25. H ank mercerization

26. Fabric mercerizing Woven fabric roller type chainless ( clip type) pin type

27. Clip system mercerizing machine

28. 2.Fabric mercerization machine a. Knit mercerizing machine a. open width b. tubular

29. Open width & tubular form

30. Mercerization machine of Fabric :

31. Guide roller, Immersion roller, Alkali tank, Alkali recovery tank, Spray, Horizontal clip; Main parts:

32. Fabric Passing Speed: Fabric Type Speed (m/min) Grey Fabric Single Mercerizing 12 Grey Fabric Double Mercerizing 15 Yarn Dyed Double Mercerizing 15 Nip pressure: Position For yarn dyed fabric in Bar For gray fabric in Bar After NaOH bath 1.5 1.5 Before acid bath 1.0 1.0 After acid bath 1.0 1.0 After washing 1.0 1.0

33.   Factors of mercerization: There are 4 factor which are called 4T. They are------- Time   Temperature   Twaddle Tension

34.   Time: The time of the mercerization is 30 to 60 seconds. If the mercerization takes longer time it will not improve the quality but if the time is limited to 30 s the good quality in appearance can be achieved . Temperature: The optimum temperature of mercerization ranges between 18 -20°c   Twaddle (conc. of NaOH ) :the concentration of NaOH is 48° Tw to 54° Tw   Tension: Tension will be applied both in warp and weft of the fabric  

35. CONTROLING POINT

36. RECIPE NaOH ------25-35% MERCERIZING OIL-------8 g/L TIME ----- 2-6 min Pick up%------ 70-80%

37. Mercerization is possible - on greige goods - after desizing - after desizing and scouring - after bleaching - after dyeing. At which stage mercerization can be done?

38. Application Sewing thread Denim Corduroy Chambray Pillow material cotton PET blend Cotton /nylon

39. Test For Mercerization : AATCC test method 89 is the most common test for quantifying the degree of mercerization. It is based on the fabric’s ability to absorb barium hydroxide. It is also called Barium No test . Ba No= × 100 Generally mercerized cotton has Ba No 115 t0 130  

40. Test For Mercerization : Mercerized and un-mercerized cotton samples (2 gm each) are treated with 30 ml of N/4 Barium hydroxide for two hours in conical flasks at room temperature. Preferential absorption of barium hydroxide by cotton samples reduces the strength of Barium Hydroxide solutions . The amount of Ba(OH) 2  absorbed can be determined by taking 10 ml of Ba(OH) 2  solution from each of the flasks and titrating it with N/10 HCl , phenolphthalein being used as an indicator. Fresh Ba(OH) 2  is also titrated (blank titration) to accurately assess the actual Ba(OH) 2  in solution.

41. Larger dyeing affinity Larger dimensional stability of the articles Increasing of the lustre Increasing of the tensile strength Better covering of dead and/or mossy cotton Improving to the touch THE ADVANTAGES OF THIS PROCESS ARE:

42. Environmental effect We know about the toxicity profile of sodium hydroxide, which is considered one of the building blocks of chemistry.  It’s a very powerful alkali.   It’s used in industry in a broad range of categories: chemical manufacturing; pulp and paper manufacturing; cleaning products such as drains, pipe lines and oven cleaners ; petroleum and natural gas; cellulose film;  and water treatment as well as textiles . The US Food and Drug Administration (FDA) considers sodium hydroxide to be generally safe, and recognizes it as not being found to pose unacceptable dietary risks, though it is generally only used on food contact surfaces rather than in foodstuffs.

43. Cont … The Barium Activity Number is given as: BAN = (B-M) / (B-C)*100 Where B = Volume of HCl (ml) required for blank titration M = Volume of HCl (ml) required with mercerized cotton C= Volume of HCl (ml) required with un-mercerized cotton For completely mercerized cotton the value of BAN is around 155 and for semi mercerized cotton it varies in between 115 and 130.

44. The chemical is toxic to wildlife, and the EPA requires that effluent containing NaOH not be discharged into groundwater.  Because sodium hydroxide falls in the group of chemicals (salts) which are by far the most often used in textile processing, the sheer volume of NaOH used by the textile industry is important to recognize.  Usual salt concentrations in cotton mill wastewater can be 2,000 – 3,000 ppm, far in excess of Federal guidelines for in-stream salt concentrations of 230 ppm .   So treatment of effluent is very important, as prevention is the only reasonable alternative to solve the environmental problems associated with this hard-to-treat, high volume waste .  

45. Thank you