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Mercerization

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Mercerization

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  1. MERCERIZATION

  2. Prepared By : Prepared By : Mazadul Hasan sheshir ID: 2010000400008 13thBatch (session 2009-2013) Department : Wet Processing Technology Email: mazadulhasan@yahoo.com Blog : www. Textilelab.blogspot.com (visit) Southeast University Department Of Textile Engineering I/A 251,252 Tejgaon Dhaka Bangladesh ©right

  3. Mercerization Mercerization is a finishing treatment of cotton with a strong caustic alkaline solution in order to improve the luster, hard and other properties, was names after its discoverer, John Mercer, and has been in use for sometime. It has been seeing an increase in application recently.

  4. John Mercer (1791-1866) John Mercer invented a process which gives cotton a lustre resembling silk - a process known as 'mercerization'.

  5. Mercerization Mercerizing Definition : It is a treatment for cotton articles and/or natural fibres composed by cellulose in a concentrated solution of caustic soda (300 g/l), under tension and ambient temperature. Objective: Fibre swelling and simultaneously there is a longitudinal shrinkage, modifying the morphological structure of the fibre and achieving a shinier surface, resistant to wear and washing.

  6. Types of Mercerization Mercerization are Two Types: 1) 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. 2) 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.

  7. THEORY: Native cellulose (Cellulose I) forms alkali cellulose I with concentrated sodium hydroxide. On washing and neutralization cellulose II is formed. As a result of the penetration of the alkali into the lattice, internal hydrogen bonds are broken and in Cellulose II the number of available hydroxyl groups (-OH) is increased by 25%. The process is commercially known as mercerisation. The treatment with alkali and subsequent washing may be performed so that the fabric or yarn may either freely contract or they may be held under tension. In both cases the mercerised cotton has an increased affinity for both reactive and direct cotton dyes, water and an increased strength. Cotton yarn or fabric mercerised without tension contracts, but if held under tension it retains its original dimensions and the lustre is increased.

  8. At which stage cellulose can be Mercerized? Mercerization is possible - on greige goods - after desizing - after desizing and scouring - after bleaching - after dyeing.

  9. General Process of mercerization: Mercerisation alters the chemical structure of the cotton fibre. The structure of the fibre inter-converts from alpha-cellulose to a thermodynamically more favourable beta-cellulose polymorph.Mercerising results in the swelling of the cell wall of the cotton fibre. This causes increase in the surface area and reflectance, and gives the fibre a softer feel. An optional last step in the process is passing the thread over an open flame; this incinerates stray fibers, improving the fabric's appearance. This is known as "gassing the thread" due to the gas burner that is typically used.

  10. Mercerization Note: Fabric Mercerization is Cheaper than double Mercerization which provides a softer hand

  11. SURFACE OF COTTON Enlarged fiber segment showing the wrinkled primary wall surface Tubular showing a smoother surface. mercerized cotton fiber,

  12. Fibre cross section: untreated (left) und mercerised (right) cotton MERCERIZED COTTON UNTREATED COTTON

  13. THE ADVANTAGES OF THIS PROCESS ARE: 1. Larger dyeing affinity 2. Larger dimensional stability of the articles 3. Increasing of the lustre 4. Increasing of the tensile strength 5. Better covering of dead and/or mossy cotton 6. Improving to the touch Effects of the chain mercerization of cotton fabric

  14. Effect of Mercerization: 1. Improve Luster. 2. Increase ability to absorb dye. 3. Improve reaction with a verity of chemicals. 4. Improve stability of form. 5. Improve strength/elongation. 6. Improve smoothness. 7. It has been shown that the increase in the luster occurs because of an effect. 8. The cotton fiber do convoluted. 9. The cross-sectional shape changes.

  15. Factors of Mercerizing: In mercerizing followings are important: 1. Twaddle 2. Temperature 3. Tension 4. Time

  16. (1) Twaddle (Concentration of NaOH): If the concentration of NaOH is increased above 56oTw improvement in luster will be attained but if it is decrease below 48o Tw. The quality of luster will begin to be adversely affected. (2) Temperature: High degree of luster is attained at temperature 18-20oC. As the temperature is increased the quality of luster is adversely affected but on lowering the temperature no improvement in the luster is obtained.

  17. (3) Tension: For acquiring better luster the material must be stretch to its original dimension (both in warp and weft direction during mercerization). If the material is allowed to shrink during mercerizing then quality of luster will be impaired on the other hand if the material is stretched more no improvement in luster is achieved. (4) Time: The optimum time for mercerizing is 30-60 seconds by increasing the duration of time no applicable improvement in the quality of mercerization can be achieved but if the time limit is less than 30 seconds in the quality of mercerization will be improved.

  18. A treatment of cotton yarn or fabric to increase its luster and affinity for dyes. The material is immersed under tension in a cold sodium hydroxide (caustic soda) solution in warp or skein form or in the piece, and is later neutralized in acid. The process causes a permanent swelling of the fiber and thus increases its luster.It is the process of treatment of cellulosic material with cold or hot caustic conditions under specific conditions to improve its appearance and physical as well as chemical properties.

  19. Purpose of mercerizing • To improve the lusture • To improve the strength • To improve the dye uptake and moisture regain.

  20. What is the mercerizing process The mercerizing involves these three subsequent steps, 1. Impregnation of the material in in relaxed state,cold caustic solution of required strength and wettability.. 2. Stretching while the material is still impregnated in the caustic solution. 3. Washing off the caustic soda from the material while keeping the material still in the stretch state.

  21. THEORY OF MERCERIZING Neales theory in Broad The hydroxyl groups on long cellulose chains attract the water molecules when cellulose takes up water, the structure expands transversily as some of the mutual secondary valency linkages are replaced by water hydroxyl linkages.Now in alkali solution ,some of the hydroxyl hydrogen atoms are replaced by sodium atoms and a system of high ionic concentration is established.Owing to osmosis ,water tends to enter this system and more secondary linkages are broken and are replaced by linkages with alkali in water.When the alkali cellulaose is washed the sodium ions and the hydroxyl ions are diffused away, and the osmotic pressure falls, the cellulose gel contracts by virtue of its elasticity. During this contraction , hydroxyl –hydroxyl linkages are reform but not in such a great number as before and the orientation of the micells is more random.The greater proportions of free hydroxyl groups accounts for the increase in the reactivity and absorptive capacity.The decrease in this high absorptive capacity on drying,particularly at high temperature ,is due to the formation of new secondary linkages on account of greater amplitude of thermal vibrations of hydroxyl groups as suggested by Urqhart.

  22. FIG.THE MATERIAL FLOW CHART IN YARN MERCERIZING

  23. Changes during mercerizing process 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.

  24. Q. Why there is a swelling in cellulose ??? 1.Due to Swelling Swelling is due to molecular attraction with associated hydration in this instance. Since the alkali cellulose is more hydrated than native cellulose ,maximum swelling concentration is result of attraction of alkali cellulose in solution on one hand and free alkali on the other. Hydration of the cellulose increases with increased fixation of alkali in solution of rinsing concentration upto a certain limit, after which the free alkali exerts a dehydrating effect on alkali cellulose to a greater extent. Dissociation of alkali ions from the alkali cellulose compound corresponds to an absorption of OH- ions ,and in this manner a negative charge results.The cellulose molecules repel each other and absorb water ,this absorption being greater, the greater is the charge. If however the dissociation of alkali cellulose salt is forced back ,then there is reduction in the charge. Further if the concentration of the electrolyte is high in swelling liquor ,then charge of cellulose particles is shielded by free ions and force of repulsion is diminished. 2.Due to osmotic phenomenon. The fiber is surrounded by a hardened euticle which acts as a dialyzing membrane to induce osmotic action ,which is better explained with the help of Neales theory

  25. Q.Why there is a rise in temperature of caustic solution during mercerization? Ans ;- Because when cellulose is treated with a moderately concentrated caustic solution ,the heat is evolved due to heat of sorption and heat of reaction. Q.What should be caustic concentration for yarn mercerization? Ans:- Although mercerization can be done with the caustic concentration ranging between 150Be to 380Be, As for as the economy of the process and optimum mercerizing effect in yarn , the concentration of the caustic used is 250Be(225 gpl) to 32 0Be(325 gpl) at room temperature. Q.Whether the recovered caustic from mercerizing process is reusable? Ans:- The caustic soda from the washing process is recoverable and can be reusable ,but it has to be free from the contaminants and must be purified to remove the undesirable impurities.

  26. Q. Why there is increase in luster of yarn after mercerization? Ans:-The cotton hair swells in strong caustic soda solution ,which change its cross section from squashed circular pipe shape to an oval shaped . if the fibers are placed under a tension or stretched position in the swollen state and then washed to reduce the caustic concentration below a particular limit, then there is an increase in the luster of the fiber.

  27. Q. What shall be the ideal temperature for mercerization? Ans:- The relation between the shrinkage of cotton fiber, the concentration of alkali and the processing temperature was studied by H. Flecken, and the result is shown in this Figure. He treated cotton yarn at 0°C to 40°C, using 30°/38° Bé caustic soda and measured the shrinkage by mercerization, and found that the least shrinkage variation is obtained at 10°C and 30° Bé. Therefore, robust conditions insensitive to the concentration of alkali and temperature must be selected for stable mercerization.

  28. Q. What is the mercerizing cycle for yarn mercerizing?

  29. A typical mercerizing cycle in yarn mercerizing is having following steps 1. Loading of material on the rollers in rest position. 2. Lowering of rollers 3. Caustic tray movement 4. Pre tensioning 5. Free shrinkage 6. Lye tensioning 7. Squeezing 8. Washing tray movement 9. First wash and tensioning 10. Second wash 11. Third wash 12. Final wash 13. Squeezing 14. Lifting Of Rollers 15. Unloading the hanks

  30. What is the significance of different steps in mercerizing cycle? 1.Pre tensioning This is the first step in yarn mercerizing cycle ,which runs to uniformly distribute the greig yarn hanks on the rollers in combination with reversal of direction of motion of rollers, without any entanglement. The material should become completely wet in this step. 2.Shrinking This is the actual caustic treatment step or the mercerizing step in which the yarn is allowed to shrink freely , the yarn runs for sufficient time in relaxed state to react completely with the caustic , higher the shrinkage achieved better will be the mercerizing. 3. Lye tensioning The lye tensioning is done to stretch the yarn back to original length. 4.Squeezing To remove the unbound caustic solution from the material, so that the material can be washed effectively, and quickly to reduce the caustic content . This step also ensure the to minimize the wastage of excess caustic liquor during washing

  31. What is the significance of different steps in mercerizing cycle? 5. Washing and tensioning The stretch applied to get the maximum luster , material is washed along with stretching beyond its original length produce better luster. The amount of stretch applied depends upon the luster required and quality of yarn. The washing temperature is kept near boil to make washing efficient and short. Time or sequence of washing is so adjusted to reach a residual caustic content below 10% within a shortest possible time. 6.Final caustic content The final caustic content should be below 10% ,because if it is more it will be sufficient to carry out further mercerizing effect and the material will shrink back. During the storage of mercerized material , the water from the exposed areas will evaporate and got concentrated locally causing mercerizing effect ,which is called local mercerizing and will lead to patchy dyeing. The level of residual caustic in the yarn is achieved less than 3% , if it is on the higher side ,then the washing is not effective.

  32. Q. What are tests to be carried out during mercerization? In general following process control tests are carried out in yarn mercerizing , 1. The circumference of the hank 2. The machines settings for shrinkage and stretching and actually achieved values 3. Concentration of the lye and level of contaminants such as carbonate content, bicarbonate content etc. 4. Temperature of caustic 5. Timings of different steps 6. Washing sequence, timings and temperature, 7. Shrinkage % or wetting power of caustic 8. Residual caustic content of the mercerized material.

  33. Properties of wetting agents in mercerizing 1. Generally non crysilic type of wetting agents are used in mercerizing, 2. which Gives uniform wetting and better penetration of caustic liquor of mercerizing and causticising strength. , 3. Improves luster and strength of mercerized cotton. 4. Does not interfere during caustic recovery. 5. Effective over a wide range of temperature. 6. Non-foaming. 7. And odor free

  34. How can we quantify the mercerizing effect? There are several tests which are done to quantify the mercerizing effect, 1. 2. X ray analysis showing changes in the fine structure Increased reactivity (a) Reactivity ratio (b) Hydrolysis number Absorption Methods (a) Moisture absorption or regain (b) Dyestuff absorption (C) Absorption from alkaline solutions (i)Sodium hydroxide absorption (ii) Barium Hydroxide absorption or Barium Number (iii) Cuprammonium hydrate 4.Counting methods (a) deconvolution caount (b) Cross section count 5.Lusture 6.Shrinkage or Swelling 7.Mechanical properties (a) Breaking load (b) Extension or elongation at break (c) Dimensional stability of yarn 3.

  35. Estimation of Mercerization: 1. De Convulation Test 2. Brightness Test 3. Dye Absorbency Test 4. Benzo Purpurine Test 5. NaOH Spotting Test

  36. DYE ABSORBENCY TEST: In this method we determine barium activity number & estimate mercerization. Procedure: • In a flask 2 gm sample & 30 ml of 0.25 N Ba(OH)2 solutions for 4 hours is shaken by a shaker. Then the sample is taken out. • 10 ml of Ba(OH)2 from leftout solution is taken & treated with 0.1 N HCl. Methyl orange indicator is used. First the color will be yellow & finally color of saturated solution will be pink. • At the same time 10 ml of fresh Ba(OH)2 will be titrated with 0.1 N HCl in presence of methyl orange.

  37. DYE ABSORBENCY TEST: Calculation: 10 ml of Ba(OH)2 solution (blank) required 24.3 ml of 0.1 N HCl. 10 ml of Ba(OH)2 from an unknown sample of cotton required 19.58 ml of 0.1 N HCl. 10 ml of Ba(OH)2 from an unmercerized sample of cotton required 21.2 ml of 0.1 N HCl Acceptable standard = 115 – 135 Note: • Mercerization contains concentrated NaOH solution of 28 – 32 Be or 270 – 330 gm/l • 15 – 20% tension is maintained.

  38. Benzopurpine Test: 1. Mercerized &unmercerized cotton samples are treated in 0.5% solution of benzopurpine for 30 min boiling temperature 2. Treated sample is washed, dried & compared visually or spectrophotometrically 3. Mercerized sample are more deeply dyed than unmercerized sample. NaOH Spotting Test: 1. Undyed fabric is spotted with 30% solution of NaOH 2. Then both mercerized &undyed spotted fabrics are dyed using Benzopurpurine. Observation:  If fully mercerized: No spot  If not mercerized: Dark Spot

  39. Shrinkage test The above shown instrument is used for the test of shrinkage % of mercerizing liquor as well as to test the mercerizing wetting agents. There is a vertical tube in which the caustic lye is filled , a 12 folded 20s carded yarn is attached to a 10 gm load and hanged as shown in the figure. The shrinkage after different time intervals is recorded and plotted against time in seconds. Shrinkage % is calculated with following formula : Where L0 is original length of the yarn L is the length of yarn after a particular time of wetting. The test is carried out at different caustic concentrations ,temperatures by varying the GPL of wetting agents.

  40. Test for Mercerizing: Necessary Equipment: • • • • • • • • Volumetric flask Beaker Burette Pipette Measuring flask Electric balance Shaker Scissors Necessary Chemicals: • • • • Barium hydroxide, Ba(OH)2 0.25(N) Hydrochloric acid, HCl, 0.1(N) Water Methyl Orange

  41. Test for Mercerizing: Sample: Yarn sample → 58/2 s singed and mercerized Single mercerized fabric → Grey mercerized, Yarn count – 58/2s , Speed – 10m/min. Double mercerized fabric → Grey mercerized, Yarn count – 58/2s, Speed – 10m/min. Stock solution preparation: To prepare 0.25(N) Ba(OH)2 Solution from a hydride barium hydroxide powder following formula should be applied Where, N = Normality W = Weight of Ba(OH)2 M = Molecular mass equivalent of hydride Ba(OH)2 i.e. Ba(OH)2 . 8H2O, V = Volume of Ba(OH)2 solution, For 250 ml solution of 0.25(N) Ba(OH)2 following parameters should maintained,

  42. Test for Mercerizing:  Now dissolve this Ba(OH)2 in to 250 ml distilled water.  Keep the solution overnight in a safe position in a volumetric flask

  43. Test for Mercerizing: Procedure:  2 gm of mercerized sample (fabric or Yarn) has to taken  The sample has to immerse in 30 ml 0.25(N) Ba(OH)2 solution.  The sample in immersion under Ba(OH)2 solution should keep 4 hrs  After 4 hrs the sample mercerized cotton should remove from the solution and shaken carefully and well by a shaker.  From the left out solution 10 ml has to take for titration.  The solution is titrated with 0.1 (N) HCl in presence of methyl orange indicator.  The volume of HCl required to titrate the Ba(OH)2 solution has been recorded.  Now the mother/stock solution of Ba(OH)2 also titrated with same HCl and the amount has been recorded. Then can be calculated by the following formula,

  44. Test for Mercerizing: Chart: Ba(OH)2% Impregnation Sample Required ml of HCl Sample type absorbed by the to titrate Ba(OH)2 no Start time End time mercerized sample 1 Mercerized Yarn 20 20.319% 2 Single mercerized 19.1 23.904% 3 Double mercerized 18.7 25.5% Result: Ba(OH)2 % absorbed by the mercerized Yarn sample = 20.319% Ba(OH)2 % absorbed by the single mercerized fabric sample = 23.904% Ba(OH)2 % absorbed by the double mercerized fabric sample = 25.5% Evaluation: Below 15% → Unmercerized Above 15% → Mercerized 70% → Fully mercerized So the samples are mercerized.

  45. Test for Mercerizing: Remarks: The easy test done is not a standardize test. It is generally practiced in mills and factories for quicker evolution of mercerization. In this test accuracy is maintained as much as possible. Titration is done manually. More over the concentration of HCl and Barium Hydroxide also measured by the same titration procedure. As the test result comes in a percentage basis the initial concentration variation does not hamper the test result. For this reason the test result is claimed accurate and satisfactory.

  46. MERCERISING UNIT FOR TUBULER KNIT FABRIC

  47. Dornier ASM mercerizing system for circular-knitted fabric

  48. FLOW DIAGRAM

  49. FEATURES 1. Continuous tubular mercerizing machines 2. Mercerizing of all types of knitted fabrics such as single jersey, interlock, fine rib and piqué in cotton or its blends. 3. Power-adjustable circular expanders in the stabilizing, washing and neutralizing sections 4. Optimum length and width control is ensured for every diameter. 5. Uniformity of stitches and Wales throughout the entire length and width of the fabric. 6. Uniform fabric appearance, weights and shrinkage values as well as improved dimensional stability and a permanent, high luster. 7. Automatic control via PC of all variable machine parameters. 8. Heat recovery system for the waste water. 9. Lye cooling system and heat exchangers, precise temperatures in the impregnating and individual washing troughs

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