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Sodium chlorite and its application in the textile industry
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  • 1. Sodium Chlorite and its Application in the Textile IndustryDr. J. J. SHROFFResearch and Development Department, The Arvind Mills Ltd., Ahmedabad-2.http://www.clo2.com/reading/textile/application.htmlCopied on August 16, 2004Recently, it has been announced that sodium chlorite, a chemical useful for bleachingtextiles and paper pulp, will be produced on large scale for the first time in India. In thisconnection, a comprehensive review of the chemistry of sodium chlorite is presented.INTRODUCTIONBLEACHING of polyester-cotton blend fabrics is mainly required for the cottoncomponent. However, if pure white goods are to be marketed, the polyester componentalso requires a bleaching treatment as the polyester fibres have a slight colouration, asthey are manufactured. The bleaching treatment also becomes essential if sighting colourswhich are difficult to remove are used or the polyester fibres have turned yellow duringheat-setting.BLEACHING AGENTSSodium or calcium hypochlorite, hydrogen peroxide or sodium chlorite are the bleachingagents which can be used with these blend fabrics.Disadvantages of the hypochlorite bleachingWhenever cotton fibres are acted upon by either calcium hypochlorite or sodiumhypochlorite, a compound known as oxycellulose tends to form. This degradation productis objectionable in yarn or cloth because it causes tendering of the fibre, the developmentof yellowish or brownish stains on storage and uneven dyeing.In bleaching cotton goods with hypochlorite, the amount of oxycellulose formed can bekept down to a minimum by a careful chemical control of every step of the process, andespecially, by stopping the bleaching action before it has gone beyond a certain point.However, it is ordinarily impossible to prevent completely the formation of oxycellulose.Advantages of the sodium chlorite bleaching 1. Research work carried out by R&D department of the Mathieson Alkali Works, Inc., (B.P. 380,488) showed that all danger of forming oxycellulose can be
  • 2. avoided by bleaching the goods by means of sodium chlorite (NaClO,) in an acid solution instead of using hypochlorite in an alkaline solution. Under acid conditions of pH 3 and greater, cellulose is not injured and the presence of sodium chlorite does not change this. 2. Sodium chlorite has sufficient oxidizing power to destroy all the colouring matter associated with cotton fibre, but it is not powerful enough to attack the fibres themselves. Hence, it can be used safely, producing better and more permanent whites without loss of tensile strength. 3. Sodium chlorite is not decomposed rapidly by acid or temperature. It, likewise, does not react with synthetic detergents to injure the detergents cleansing properties. This non-reactivity is mutual and the detergent does not injure the oxidizing properties of the sodium chlorite or its stability. 4. Hard water does not interfere with the process. 5. Sodium chlorite is very soluble in water, to the extent of about 40 per cent by weight, at 20°C. 6. Solutions prepared for commercial oxidizing or bleaching processes are extremely stable. 7. Sodium chlorite oxidizes many of the naturally occurring waxes and pectins in the cellulose which tends to solubilize them and make for a more even piece of goods. 8. The bleached material has high absorbency and permanent whiteness. 9. Another very definite advantage is concerned with hand. This is due to the processing of the fabric entirely on the acid side. 10. The process reduces the total time of bleaching with the corresponding reduction in handling of the material.In general, the use of sodium chlorite offers a finishing plant the opportunity of reducingprocessing time, and obtaining a superior result at no additional cost and very often at areduced cost.Drawbacks of sodium chlorite-bleaching and preventive measuresThere are certain drawbacks with this bleaching agent. 1. Acid solution of sodium chlorite which generates chlorine dioxide (ClO2) has a great corrosive action on the materials of construction including stainless steel. Special material such as glass, porcelain, earthenware or some selected plastics are therefore required for fabricating machinery if sodium chlorite is to be used as a bleaching agent. Titanium is the most resistant metal used for this purpose today. In the textile industry, molybdenum alloy stainless steels are used for acid chlorite bleach apparatus. Type 316 stainless steel is preferred. For best operation, the stainless steel sheet should be cold rolled and polished, and all welds should be ground smooth and polished.
  • 3. The nitrate ion is found to reduce corrosion of the bleaching machinery and is supposed to have a passivating effect. Addition of 1/2 g/l of sodium nitrate is therefore recommended to the bleaching bath. Some bleaching auxiliaries, for example, Bleaching-auxiliary HC and HV (Hoechst) are marketed which have been found to be useful in preventing corrosion as well as reducing the objectionable smell of chlorine dioxide. These auxiliaries possibly contain sodium nitrate which prevents corrosion and a synthetic detergent which gives a foam cover on the surface of bleaching bath and thereby reduces the trouble of smell. A double salt of sodium chlorite and sodium nitrate has also received some commercial acceptance. 2. Fumes of chlorine dioxide (ClO2) are toxic and can cause sickness, lack of appetite and nausea to the operatives and therefore, effective renewal of air is essential.Method of bleachingHydrogen peroxide is the major bleaching chemical for textiles. However, in 1960,sodium chlorite made a new bid in the United States and was adopted for a continuousbleaching system in a major finishing plant. Contrary to European practices, thiscontinuous bleaching range consisted of three J-Box operations. First, a 1.5 per centcaustic soda solution (later, sodium bromite) was applied to the cloth to be steamed 30minutes for desizing After a rinse, the cloth was saturated with a 3 per cent caustic sodasolution and steamed one hour in a J-Box. The scoured cloth was rinsed and thensaturated with the sodium chlorite solution prior to steaming for one hour in the third J-Box. The alkaline desize and scour was used in an effort to achieve an outstandingprepare to reduce the amount of sodium chlorite required for the bleach. An elaboratecontrol system using caustic soda or phosphoric acid was used to maintain the pH of thesodium chlorite with a very narrow predetermined range.The following is a typical formula for bleaching polyester-cotton blend fabrics: 2 g/1NaClO2, 2 ml/1 formic acid (85%) to adjust pH to 3, 1 g/l NaNO3,.The goods are treated in an enclosed jig for 1-1.5 hours at boil. An after treatment withantichlors such as sodium bisulphite (1-2% at 70°C, for 10 minutes) is sometimesdesirable. To remove the colour from motes of cotton it is necessary to use a peroxidebleach after this treatment.Commercial sodium chlorite bleaching solutionThe commercial sodium chlorite bleaching solution containing, in addition, specialingredients such as anticorrosive agent. buffering agent, chlorine dioxide fume controller,stabilizer surfactant and wetting agent is also available as weakly alkaline highlyconcentrated solution of 200 gms. sodium chlorite per litre. Thus, a pre-preparedbleaching solution needs no other bleaching auxiliaries. except acid, for pH control.
  • 4. Anticorrosive agent prevents the corrosion of bleaching equipment constructed fromstainless steel. buffer salts control the liberation of chlorine dioxide produced during thebleaching process, avoiding the loss of chlorine dioxide. Mixture of surfactant salts hasvery good washing, cleaning and penetration effect on soiled goods which are to bebleached and therefore produces a purer white and stabiliser controls the pH of the bathduring the bleaching process. Such stabilised sodium chlorite bleaching solutions possessgood storability so that stock solution can be kept without loss of active bleachingsubstance. Even heating of this leads to hardly any reduction in bleaching power. Thus,the use of sodium chlorite is economical in operation and highly effective.Precautions to be observedSodium chlorite bleaching solution which is applied should not be allowed to dry oncombustible substances such as wood or paper, since this may lead to outbreaks of firedue to spontaneous combustion.Sodium chlorite is a highly effective bleaching agent for the following textile fibres: (1)Cotton, (2) bast fibres (flax, hemp, jute {used as a delignifying agent for lignocellulosic materials such as jute, woodpulp etc., the latter process being accompanied by a simultaneous bleaching action}, ramie), (3) man-made fibres, (a)based on cellulose: viscose filament, viscose staple, cuprammonium filament,cuprammonium staple, acetato filament, acetate staple. (b) Fully synthetic: polyamidegroup, e.g., Nylon, Perlon; polyacrylonitrile group, e.g., Dralon, Orlon, Radon, Dolan:polyester group, e.g., Dacron, Diolen. Terylene, Trevia; polyvinyl group, e.g., Pe-Ce,Rhovyl.It is also suitable for fibre blends and blended fabrics composed of the above mentionednatural and man-made fibre.In the following table an attempt is made to summarize different methods of bleachingwith sodium chlorite for various types of fibre including conditions of bleaching.Manufacture: Since sodium chlorite is manufactured from chlorine dioxide, a shortdescription of the properties and the processes for the manufacture of chlorine dioxidewill not be out of place here.Chlorine dioxidePhysical properties: Chlorine dioxides is a gas at ordinary temperatures. It has an intensegreenish-yellow colour, a density of approximately 2.4 and a pungent, irritating odour.The boiling point of liquid chlorine dioxide is 11°C and its melting point 59°C.Decomposition: Pure gaseous chlorine dioxide decomposes at a measurable rate attemperature above 30°C and from 50 to 60°C it decomposes explosively. Chlorinedioxide is usually handled in dilute mixtures with air in the range of 8-12 per cent byvolume. Spontaneous decomposition can and does occur at this dilution in the presence ofiron rust, grease, and many organic particles. Direct sunlight also causes decomposition.
  • 5. With dilute mixture, the explosions are relatively mild and are referred to in the industryas "puffs". To take care of "puffs", generators, storage tanks, and bleaching towers areequipped with explosion lids.Corrosion: Chlorine dioxide solutions are very corrosive and must be stored in suitablylined equip" meet. Suitable materials for storage vessels are: (1) glass-lined steel, (2)fibre glass polyester and (3) til lined steel. Piping pumps valves and lines may be made ofglass, glass-lined, titanium, PVC, Saran, "kel F", "Teflon", and Karbate.Preparation: Because of its unstable nature, chlorine dioxide is always generated at thepoint of use.There are five principle methods of generating chlorine dioxide which are now in usethroughout the world: (1) The Mathieson process, (3) The Day-kesting process, (4) TheHooker R-2 process (ER-2 process in Canada), and (5) The Persson process.The mechanism of the formation of chlorine dioxide from sodium chlorate is the same forall processes. The fundamental reactions producing chlorine dioxide from chlorates are: HClO3 + HCl --> HClO2 + HClO HClO3 + HClO3 --> 2ClO2 + H2OThe R-2 process which is extremely simple to operate and which gives the highest yieldof chlorine dioxide of any commercial process is given below:The R-2 process: This process, covered by U.S., Patent 2,863,722 issued to W. HowardRapson, is assigned to Hooker Chemical Corporation in the U.S.A., and the equivalentCanadian Patent 543,589 is assigned to Electric Reduction Company in Canada.The process consists of feeding a solution containing both sodium chlorate and sodiumchloride in essentially equimolar ratio, and concentrated 66° Be sulphuric acid into areaction vessel. Air is blown into the bottom of the vessel to provide rapid agitation,stripping, and dilution of the ClO2 produced. In this process, ClO2 and Cl2 are evolved inwhat is nearly a 2 to 1 ratio. The ClO2 is absorbed in a conventional tower with chilledwater. About 25 percent of Cl2 evolved (12 to 15 per cent based on ClO2) dissolves in theClO3 solution. The remainder passes through the tower and is picked up as either calciumor sodium hypochlorite in the second, smaller tower or suitable absorption system. Theyield of ClO2 by the R-2 process is 95 to 96 per cent of the theoretical under-millconditions. This process is currently operating in four mills in the U.S.A. and is beinginstalled in a number of other millet It produces ClO2 at the lowest cost of any process inmills where full use can be made of the chlorine, salt cake, and effluent acid. Advantagesof the R-2 process are as follows: (1) The process gives the highest yield of ClO2 of anycommercial process. (2) The process is extremely simple to operate. (3) The processresponds immediately to a change in production rate and can be started up from full shut-down to full steady production in less than 20 minutes. (4) The ClO2 production is strictlyproportional to chlorate fed at all production rates. (5) The process can be run in any
  • 6. existing ClO2 generator and will produce at upto 10 times the rated capacity of theexisting generator. (6) The process can be fully automated to run off a float valve in theClO2 storage tank.Sodium chloriteIn 1921, E. Schmidt discovered that cellulosic fibres can be purified by chlorine dioxidewith no appreciable degradation. This discovery led to extensive ret search to developeconomical methods for bleaching with chlorine dioxide. Being extremely explosive athigh concentrations, chlorine dioxide gas could not be transported as such. It wasnecessary to develop a stable chemical which could be safely transported and whichcould be easily reacted to form chlorine dioxide at the bleaching site. MathiesonChemical Corporation successfully developed sodium chlorite as the economicalcommercial chemical for this purpose.Preparation: Sodium chlorite may be prepared by passing chlorine dioxide through amoderately strong solution of sodium hydroxide.2 ClO3 + 2 NaOH --> NaClO2 + NaClO3 + H2OHowever, sodium chlorate is formed in an equimolar quantity and is difficult to separate.The formation of chlorate may be minimized by adding reducing agents to the alkali. Forexample, in the presence of sulphur or sodium sulphate, a high yield of sodium chlorite isobtained. In an early method, carbonaceous matter such as animal charcoal, sugar, coke,wood saw dust, paper pulp etc., nitrogen compounds such as ammonia, or one of a rangeof compounds containing the NH2 or CN group were used for the reduction. Followingthe chlorate reduction, the sodium chlorite solution is evaporated and drum dried.Suitable reducing conditions are obtained if an aqueous solution of chlorine dioxide istreated with sodium amalgam (Na 0.1%), hydrogen peroxide or sodium peroxide. Sodiumchlorite is formed witH negligible amounts of sodium chlorate. Since the mercurycathode of an alkali chloride electrolyte cell can serve as the amalgam, this process isclearly capable of large scale application. Sodium chlorite may also be prepared bypassing chlorine dioxide into a solution and allowing it to bubble over a cathode at whichhydrogen (nascent) is being evolved. Formation of chloric acid is much reduced and theunstable chlorous acid immediately reacts with alkali to give the more stable chlorite.On a large scale it is convenient to absorb the chlorine dioxide in an aqueous solutioncontaining hydrogen peroxide and the alkali metal bicarbonate preferably at about 25°.Purification: Because of large differences in solubility between chlorite and other relatedsalts, fractional crystallisation provides a useful means of purifying metal chlorites.Anhydrous sodium chlorite: To prepare anhydrous sodium chlorite, the trihydrate is madeinto a slurry with water at 38°, and the solution saturated at this temperature is separatedand cooled to 25° when the anhydrous salt crystallises.
  • 7. Important properties of sodium chlorite 1. The anhydrous salt is not hygroscopic and samples have been kept for ten years with only slight loss. 2. Heating for 30 minutes at 150°C causes no explosion. 3. The decomposition temperature varies with moisture content, being 202°C with 3.7% of water, and 177°C. with 10.7% of water. 4. The mode of decomposition of aqueous solutions is profoundly influenced by the pH of the solution. In alkaline solution sodium chlorite is stable in the absence of light. However. for pH values less than 7, the rate of decomposition increases considerably with decrease in pH. Decomposition is very slow at pH values above 4.6. The decomposition of sodium chlorite in neutral solution can be accelerated by metallic catalysts, the decomposition rate increases with increase in temperature and quantity of catalyst. 5. The reactions of chlorites are considerably modified in the presence of chlorine or hypochlorites. The action of chlorine on sodium chlorite is a preparative method for chlorine dioxide. With sodium hypochlorite, the products are sodium chlorate and chlorine dioxide, in a ratio depending on the pH of the solution. Thus, at pH2 chlorine dioxide is liberated while in alkaline solutions chlorate is formed exclusively. The relative amounts of chlorate and chlorine dioxide produced also on the chlorite/hypochlorite ratio of the reactants. When this ratio is 2:1, chlorine dioxide predominates. On increasing ratio beyond 1:1 immediate chlorate formation occurs. While with a ratio of 1:4 the chlorine dioxide is completely converted to chlorate within 30 minutes at room temperature. 6. The action of certain reducing agents, such as aldehydes on sodium chlorite yields chlorine dioxide, with iodides and iodine. 3 HClO3+ I- --> 2IO3 + 3 Cl- + 3H+ This forms the basis of the analytical determination of chlorites. 7. Oxidizing agent if sufficiently strong, will oxidize chlorite to chlorate. In neutral solution oxidation by potassium permanganate proceeds according to the equation: 3 ClO2- + 2 MnO-4, + H2O --> 3 ClO-3 + 2MnO2, + 2 OH-ESTIMATIONEstimation of sodium chlorite in bleaching solutionTheory: Determination of sodium chlorite is Carried out by iodometric means andproceeds in accordance with the following reactions:2NaClO2 + 8KI + 4H2SO4 = 2NaCl + 4K2SO4 8I + 4H2OI 8I + 8Na2S203 = 8NaI +4Na2S4O6
  • 8. This means that: 2NaClO2 = 8I= 8Na2S2O3 or NaClO2= 4Na2S2O3Reagents required: (i) 10 per cent potassium iodide (A.R.) solution in distilled water. (ii)5 per cent sulphuric acid (A.R.). (iii) O.1N sodium thiosulphate solution.Determination of sodium chlorite (solid)Procedure: One gm. of sodium chlorite is dissolved in distilled water and is made upto1000 ml. with distilled water. 50 ml. of this solution is allowed to run, while shaking theflask into 10 ml. of the 10% potassium iodide solution, and the whole is subsequentlyacidified with 10 ml. 10% sulphuric acid. The reaction mixture is left to stand for 3minutes in dark and is then titrated with O.1N sodium thiosulphate solution, until paleyellow colour is obtained. After adding about 1 ml. starch solution, titration is continueduntil the solution becomes colourless. After titration the solution should have acidreaction to congo red paper.Calculation: ml. of O.1N sodium thiosulphate solution consumed x 4.52 = per cent ofsodium chlorite.Determination of sodium chlorite in solution containing upto 10 g/l. sodium chloriteProcedure: An Erlenmeyer flask of 100 ml. capacity is first charged with about 10 ml.potassium iodide solution followed by exactly 10 ml. of the sodium chlorite solution tobe tested and the whole is then acidified with about 10 ml. of 5 per cent sulphuric acid.The reaction mixture is left to stand for 3 minutes in the dark and is then titrated withO.1N sodium thiosulphate solution until a pale yellow colour is obtained. After adding Iml. starch the solution, titration is continued until the solution become colourless.Calculation: Ml. of O.IN sodium thiosulphate solution consumed x 0.226. = g/l. sodiumchlorite.Determination of sodium chlorite in solution containing more than 10 g/l. sodiumchloriteProcedure: Determination is carried out as described above with the exception that only 1ml. of sodium chlorite solution is used.Calculation: ml. of O.IN sodium thiosulphate solution consumed x 2.26 = g/1. sodiumchlorite.Determination of sodium chlorite in solution containing more t~ 100 g/L sodiumchlorite
  • 9. Procedure: From sodium chlorite solution, 1 ml. is removed with a pipette and diluted ina 100 ml. volumetric flask upto the mark. Take 10 ml. from this for estimation.Determination is carried out as described above.Calculation: ml. of O.1N sodium thiosulphate solution consumed x 22.6 = g/1. sodiumchlorite.Determination of chlorine dioxide produced in bleaching of textiles with sodiumchloriteChlorine dioxide reacts with H-acid at pH 4.1 to 4.3, to form a pinkish blue, lightsensitive compound having an absorption maximum at 525 mµ. Addition of ferricchloride increases the colour intensity and of malonic acid eliminates the interference offree Cl.For determination, 90 mL of the bleach liquor, after treatment with 5 ml. of acetate bufferof pH 4.1 to 4.3 and I ml. of FeCI3 solution (10 mg/l) is made upto 100 ml. Free Cl isremoved by adding 2 ml. of 1% malonic acid solution and keeping aside for 20 minutesin the dark. If any turbidity is formed it should be removed by addition of ZnSO4 andNaCH. To this, 0.4 ml. of H-acid reagent (0.85 g. H- acid dissolved in 5O ml. of boilingenthanediol and diluted with to 100 ml.) is added and the extinction is measured at 525mµ after keeping the solution in the dark. Phosphates, if present, interfere and hencecorrected calibration graph should be used.BIBLlOGRAPY 1. Kulkarni, G.G., and Trivedi, S.S., Processing of Polyester Cotton Blends, ATIRA (1967). 2. Taylor, M.C., White, J.F., Vincent, G.P., and Cunningham, G.L., "Sodium Chlorite; Properties and Reactions," Industrial and Engineering Chemistry 32, No. 7, 899-903 (July 1940). 3. White, J.F., Taylor, M.C., and Vincent, G.P., "Chemistry of Chlorites," Industrial and Engincering Chemistry, 34, No. 7., 782-792 (July 1942). 4. Dubeau, A.L., MacMahon, J.D., and Vincent, G.P., "A New Oxidizing Agent," Am. Dyestuff Reptr., 28, 590-592 (1939). 5. Vincent, G.P., "Textone," Am. Dyestuff Reptr., 29, 269-271 (1940). 6. Vincent, G.P., Dubeau, A.L, and Ivey, J.W., "The Treatment of Spun Rayons with Textone," Am. Dyestuff Reptr., 29, 296-299 (1940). 7. Vincent, G.P., Dubeau, A.L., Synan, J.F., "BIeaching Cotton Goods with Textone Activated with Hypochlorite," Am. Dyestuff Rcptr., 30, 358-360 (1941) 8. Sneed, M C., Maynard, J.L., Brasted, R.C., "Comprehensive Inorganic Chemistry," Vol. 3, D. Van Nostrand Co., Inc, (1954). 9. Remy, H., "Treatise on Inorganic Chemistry," Vol. 1, Elsevier (1956). 10. Wood, C.W., and Holliday, A.K., "Inorganic Chemistry," Butterworths (1963). 11. Partington, J.R., "General and Inorganic Chemistry," MacMillan and Co., Ltd., (1954).
  • 10. 12. Salus S, O.E., "Chlorates by Electrolysis of Alkaline Chlorides the Effect of Some Factors," Bol. Soc. Chilena Quim. 4, 43 (1952); Chem. Abstr., 17, 9823 (1953) 13. Sconce, J.S., "Chlorine, its Manufacture, Properties and Uses," American Chemical Society, Monograph Series, Reinhold, (1967} 14. Rapson, W.H., Tappi, 41, 181 (1958); U.S.P. 2, 863, 722. 15. Patridge, H.D., and Rapson, W.H., "Mill Trials of R-2 Proccss," Hooker Bulletin 262; Tappi, 44, No. 10 (1961). 16. Mellor, J.W., "Comprehensive Treatise on Inorganic and Theoretical Chemistry," (supplement II) Part.I, Longmans (1956). 17. Yntema, L.F., and Fleming, T., "Volumetric Oxidation of lodide to Iodate by Sodium Chlorite,"Ind. Eng. Chem. Anal., 11, 375-7 (1939). TABLEMaterial Machinery Liquor: Sodium pH value Bleaching Remarks and material material chlorite of liquor of ratio and acid to construction be used1. Loose cotton Molybdenum- 5:1 20 kg. 5: 3.5 hours at Residual(1000 kg) stainless steel Sulphuric 80-85°C concentration or stoneware acid 1:10 (176-185°F), of sodium with verticle heating in chlorite 0.2 g/l. circulation first 2 hours For full white a from 40-80°C subsequent (104-176°F) bleach may be necessary with 4 kg. hydrogen peroxide 35% by weight 2.0 g/l. 2 hours at 85 °C (185°F).2. Cotton yarn Stainless steel 4:1 16 kg. 3.8-4.0; 3 hours at Residual(1000 kg) with verticle Formic 85°C concentrationMercerised circulation acid or (185°F), of sodiumtreated with acetic acid. heating in chlorite 0.2 g/l.hydrochloric first 2 hours Rinse: warmacid and from 40-85°C and cold,rinsed. (104-185°F) optical whitening the Blankophor BA in batches on a Gerber hank dyeing machine.3. Cotton Molybdenum 12:1 4 kg. 3.5-3.8 1 hour at Rinse: hot andcheese 34/2 steel V-14A Formic 90-95°C cold. Optical
  • 11. (250 kg) type closed acid or (194-203°F) whitening with cheese acetic acid. heating in Blankophor bleaching first 30 BA. machine with minutes from radial 40-90°C circulation (104-194°F)4. Viscose Closed winch, 20:1 1.6gm. 3.5; Formic 20-30 If suctionstaple fibre stainless steel acid 85% minutes at ventilation is(100 kg) 316 80-85°C lacking, raise (176-185°F) temperature in 30 minutes from 40-80°C (104-176°F) and bleach for 10-15 minutes at this temperature.5. Viscose Closed winch, 25:1 12 kg. 3.5; Formic Speed of Subsequentmuslin (3000 steel 316. Liquor acid 85% goods: 70 m/ additionskg) Continuous (3000 litres 2500 minute. which consistbleach. capacity) litres Treatment of 12.0 kg. Goods time: 15 Sodium in the minutes. chlorite and beck Total 1.5 litre, 85% 100 kg. bleaching Formic acid time 15 should flow minutes. continuously Temperature: into the 85°C (185°F) bleaching bath through a metering device. If the chlorite bleaching proper is given on several winches, subsequent additions are often made only to the first one, and the second winch is merely kept to a pH of 3.5
  • 12. by the addition of acid. This continuous bleach can be combined with pre-treatment of the viscose staple to form a continuous process.6. Viscose Stainless steel 4:1 8 kg. 3.5-3.8; Heat to Rinse: warmstaple fabric 316 with Formic 75-80°C and cold.(2000kg) pump and acid 85% (167-176°F)enzymatically, circulation and bleachdesized, pipes of for 1 hour atscoured on a stainless steel. thisrope soaper. temperature.7. Visco Closed jig. 4:1 640 gm. 3.5-3.8;For 4-5 passagesfilament and Stainless steel mic acid at 75-80° Cacetate 316. 85% (167-176°F)filament unionfabrics (100kg)8. Nylon fabric Closed jig. 8:1 12.5 4; Acetic 4-6 passages(50 kg) Stainless steel gm. acid 60% at 80-85°C 316 type. (176-185°F)9. Perlon (50 Winch 30:1 1.2 kg. 3.8; Acetic Heat in 30kg) soiled stainless acid 60% minutes from steel-316. 40-85° (104-203°F); 30 minutes 85°C (185°F)10. Acrylic Stainless 30-40:1 1.2-2.0 2.5-3.0; Heat in 30 If a full whitefibres steel-316. g/l. Oxalic acid minutes from is desired on solution 1-2 g/l, 40-95°C acrylic fibres, added in solution, (104-203°F); optical portion. added in 30 minutes at whitening with portion. 95-98°C 2.5 % (203-208°F). Blanlcophor ACF on weight of goods is advisable. Blankophor DCB ultrafine
  • 13. (now replaced by Blankophor DBS) is highly suitable for the optical whitening of acrylic fibres in an after treatment operation.11. Polyester 1.2-2.0 1.0-3.0 g/l. Heat in 30fibres g/l. Oxalic acid minutes from added in solution 40-95°C portion added in (104-203°F) portion 30 minutes at 95-98°C (203-208°F).