Cotton

Cotton: is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. Under natural conditions, the cotton bolls will tend to increase the dispersion of the seeds.

The plant is a shrub native to tropical and subtropical regions around the world, including the Americas, Africa, and India. The greatest diversity of wild cotton species is found in Mexico, followed by Australia and Africa. Cotton was independently domesticated in the Old and New Worlds. The English name derives from the Arabic which began to be used circa 1400 AD The Spanish word, "algodón", is likewise derived from the Arabic.

The fiber is most often spun into yarn or thread and used to make a soft, breathable textile. The use of cotton for fabric is known to date to prehistoric times; fragments of cotton fabric dated from 5000 BC have been excavated in Mexico and the Indus Valley Civilization (modern day Pakistan and some parts of India). Although cultivated since antiquity, it was the invention of the cotton gin that so lowered the cost of production that led to its widespread use, and it is the most widely used natural fiber cloth in clothing today.

Current estimates for world production are about 25 million tones or 110 million bales annually, accounting for 2.5% of the world's arable land. China is the world's largest producer of cotton, but most of this is used domestically. The United States has been the largest exporter for many years. In the United States, cotton is usually measured in bales, which measure approximately 0.48 cubic meters (17 cubic feet) and weigh 226.8 kilograms (500 pounds).

Types of Cotton:Main article: Types of cotton

There are four commercially grown species of cotton, all domesticated in antiquity:

Gossypium hirsutum – upland cotton, native to Central America, Mexico, the Caribbean and southern Florida, (90% of world production)

Gossypium barbadense – known as extra-long staple cotton, native to tropical South America (8% of world production)

Gossypium arboreum – tree cotton, native to India and Pakistan (less than 2%)

Gossypium herbaceum – Levant cotton, native to southern Africa and the Arabian Peninsula (less than 2%)

The two New World cotton species account for the vast majority of modern cotton production, but the two Old World species were widely used before the 1900s. While cotton fibers occur naturally in colors of white, brown, pink and green, fears of contaminating the genetics of white cotton have led many cotton-growing locations to ban the growing of colored cotton varieties, which remain a specialty product.

History of Cotton:Cotton plants as imagined and drawn by John Mandeville in the 14th century Cotton was used in the Old World at least 7,000 years ago (5th millennium BC). Evidence of cotton use has been found at the site of

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Mehrgarh, where early cotton threads have been preserved in copper beads. Cotton cultivation became more widespread during the Indus Valley Civilization, which covered parts of modern eastern Pakistan and northwestern India. The Indus cotton industry was well developed and some methods used in cotton spinning and fabrication continued to be used until the industrialization of India Between 2000 and 1000 BC cotton became widespread across much of India.] For example, it has been found at the site of Hallus in Karnataka dating from around 1000 BC.

Cotton fabrics discovered in a cave near Tehuacán, Mexico have been dated to around 5800 BC, although it is difficult to know for certain due to fiber decay. Other sources date the domestication of cotton in Mexico to approximately 5000 to 3000 BC.

Organic production of Cotton:

Organic cotton is generally understood as cotton, from plants not genetically modified, that is certified to be grown without the use of any synthetic agricultural chemicals, such as fertilizers or pesticides. Its production also promotes and enhances biodiversity and biological cycles. United States cotton plantations are required to enforce the National Organic Program (NOP). This institution determines the allowed practices for pest control, growing, fertilizing, and handling of organic crops. As of 2007, 265,517 bales of organic cotton were produced in 24 countries, and worldwide production was growing at a rate of more than 50% per year.

Pests and weeds of Cotton:

The cotton industry relies heavily on chemicals, such as herbicides, fertilizers and insecticides, although a very small number of farmers are moving toward an organic model of production, and organic cotton products are now available for purchase at limited locations. These are popular for baby clothes and diapers. Under most definitions, organic products do not use genetic engineering. All natural cotton products are known to be both sustainable and hypoallergenic.

Historically, in North America, one of the most economically destructive pests in cotton production has been the boll weevil. Due to the US Department of Agriculture's highly successful Boll Weevil Eradication Program (BWEP), this pest has been eliminated from cotton in most of the United States. This program, along with the introduction of genetically engineered Bt cotton (which contains a bacterial gene that codes for a plant-produced protein that is toxic to a number of pests such as cotton bollworm and pink bollworm), has allowed a reduction in the use of synthetic insecticides.

Other significant global pests of cotton include the pink bollworm, Pectinophora gossypiella; the chili thrips, Scirtothrips dorsalis; the cotton seed bug, Oxycarenus hyalinipennis; the tarnish plant bug, Lygus lineolaris; and the fall armyworm, Spodoptera frugiperda, Xanthomonas citri subsp. malvacearum.

Harvesting of Cotton:

Most cotton in the United States, Europe, and Australia is harvested mechanically, either by a cotton picker, a machine that removes the cotton from the boll without damaging the cotton plant, or by a cotton stripper, which strips the entire boll off the plant. Cotton strippers are used in regions where it is too windy to grow picker varieties of cotton, and usually after application of a chemical defoliant or the natural defoliation that occurs after a freeze. Cotton is a perennial crop in the tropics and without

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defoliation or freezing, the plant will continue to grow. Cotton continues to be picked by hand in developing countries.

British standard yarn measures: 1 thread = 55 in or 140 cm 1 skein or rap = 80 threads (120 yd or 110 m)

1 hank = 7 skeins (840 yd or 770 m)

1 spindle = 18 hanks (15,120 yd or 13.83 km)

Fiber properties of Cotton:

Property Evaluation

ShapeFairly uniform in width, 12–20 micrometers; length varies from

1 cm to 6 cm (½ to 2½ inches); typical length is 2.2 cm to 3.3 cm (⅞ to 1¼ inches).

Luster High

Tenacity(strength)DryWet

3.0–5.0 g/d3.3–6.0 g/d

Resiliency Low

Density 1.54–1.56 g/cm³

Moisture absorptionraw: conditioned

saturationmercerized: conditioned

saturation

8.5%15–25%

8.5–10.3%15–27%+

Dimensional stability Good

Resistance toacidsalkali

organic solventssunlight

microorganismsinsects

damage, weaken fibersresistant; no harmful effects

high resistance to mostProlonged exposure weakens fibers.

Mildew and rot-producing bacteria damage fibers.Silverfish damage fibers.

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Thermal reactionsto heat

to flame

Decomposes after prolonged exposure to temperatures of 150°C or over.

Burns readily.

Cotton fibers viewed under a scanning electron microscope

The chemical composition of cotton is as follows:

cellulose 91.00% water 7.85%

protoplasm, pectins 0.55%

waxes, fatty substances 0.40%

Flow chart of wet processing:

Before dyeing a fabric or yarn some pre-treatment and after treatment is needed. A flowchart is drawn here by combining these:

Grey Fabric Inspection

↓

Sewing or Stitching

↓

Singeing

↓

Desizing

↓

Scouring

↓

Bleaching

↓

Mercerizing

↓

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Dyeing

↓

Printing

↓

Finishing

↓

Final Inspection

↓

Delivery

This is the most widely used wet processing flow-chart on the contemporary textile industry.  But sometimes on some factories the scouring and bleaching is done simultaneously. Here is a brief description of every process steps i have mentioned in above Dyeing flowchart:-

Gray Fabric Inspection : In this step all of the gray and already colored fabric is separated. Mainly we will work with the gray fabric is to make this colored in our next process.

Sewing or Stitching : If the fabrics are in part or in separate segments; then we have to bring these all together by stitching or sewing.

Singeing : Singeing is the process to remove or burn the protruding fibers over the cloth. While weaving a fabric; some protruding fibers is created at the surface of the fabric and we should remove these short fibers before further dyeing processing.

Desizing : At the beaming section of making a Fabric we uses various starch and sizes to make the warp yarn more stronger. But while we planned to make this fabric colored we have to remove the applied starch and sizes as it might causes negative reaction with colors and chemicals.

Scouring : The main objective of Scouring process of wet processing technology is to polish the fabric service by rubbing it hard or cleaning the surface and brighten it.

Bleaching : Bleaching process is one of the crucial processes of Dyeing as it helps to gray fabric brighter than usual.

Mercerizing : Mercerizing is a costly process but due to buyer requirements we might have to give the fabric extra luster and brighter appearance.

Dyeing : After mercerizing the cotton or fabrics; this is the time to apply dye along with chemicals. Dyeing process is a broad topic and it is discussed in another category of this textile blog.

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Printing : While dyeing is conducted to put color in all over the body of the fabric; Printing is done in a specific zone of the fabric. A specified design is created on the fabric surface before printing application is manipulated.

Finishing : In the finishing department of this Wet processing Flowchart; the faults of fabrics, faults of dyeing is to be monitored and possible spots is to be fixed.

Final Inspection: After dyeing a fabric it is to be finally monitored and rechecked.

Dispatch or Delivery : This is the last sector of Dyeing department and in this stage the dyed fabrics is to be exported or sent to the buyers.

Scouring

Scouring : Scouring is the process by which all natural and adventitious impurities such as oil, wax, fat etc. are removed to produced hydrophilic and clean textile material. It is the vital process of wet processing.

Objects of Scouring: To make the fabric highly hydrophilic. To remove impurities such as oils, waxes, gum, husks as completely as possible. To increase absorbency of fabric or textile materials without undergoing physical and chemical

damage. To produced a clean material by adding alkali. To remove natural colour and make the fabric for next process.

To remove non-cellulosic substance in case of cotton.

Scouring methods of Cotton:Generally, there are two principle methods of cotton scouring.

Kier boiling process Horizontal Vertical. Scouring in J or L box. (Continuous)

Continuous scouring process of cotton (Scouring in J- box): The scouring vessel is looks like the English letter ‘J’ hence, this process is called j box process. In the process, desizing, scouring and bleaching can be performed at a time.

Standard recipe:Alkali (NaOH) 4-5gm/LWetting agent +Detergent 4-5gm/LM:L 1:3Pick up 90-100%Impregnation Temp 70-800CImpregnation Time 45-90sec

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Storing time in J-box 2-4hrTemperature in J-box 102-105oC

Process: The working process in J-box can be divided into four units. There are Saturation. Pre – heater. J – box. Washing unit.

Saturation: Saturation is prepared by above recipe without caustic soda in the saturator. Then the wet fabric is passed through the guide roller and immersed into the solution by immersion roller. The fabric is saturated either by open width or in rope form. Here temperature is kept 70˚C – 80˚C for about 40-90 sec then the fabric squeezed and passed to the preheated.

Pre heater: In pre heater, material is passed into the thermostatic controlling system at temperature 110˚C – 120˚C for 30 se and passed to the J- box by drawing roller.

J-box: The fabric brought in J- box after pre heater. In j-box, solution of caustic soda are kept and fabric is stored in this solution for about 30 min, here temperature 100˚C. In j-box, NaOH, reacted with the impurities present in the fabric and finally removed.

In J-Box generally 12000- 15000 lb fabric can be scoured after J- box the fabric is squeezed and passed to the washing unit.

Washing unit: The water soluble impurities or products that are left on the mtl are removed here. First the materials are washed in hot water then cold water and finally dried.

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Advantage: This process is a continuous process, so it consumes less time. This process is economical use. Use for scouring obtained; Scouring, de sizing and bleaching performed at a time.

Disadvantages: The result is not good as compared with kier boiler. Huge damage may occur due to power failure.

Bleaching

Bleaching: Bleaching of textile material is a chemical or commercial process which can be defined as Destruction of natural coloring matters to impart a pure permanent and basic white effects suitable for the production of white finishes, level dyeing and desired printed shade with the minimum or no tendering(degradation) or without diminishing the tensile strength.

Object: To ensure a pure and permanent basic white color fabric. Destruction of natural coloring matters from the fabric. To increase absorbing for dyeing operation. To ensure level dyeing property. To make the textile materials suitable for subsequent processing (dying printing etc.)

Bleaching agents:Two types of bleaching agent i.e oxidizing bleaching agent and Reducing bleaching agent.

I) Oxidizing bleaching agent : Ozone(O3) Hydrogen peroxide (H2O2) Calcium hypochlorite [Ca(OCl)2] Sodium hypochlorite [NaOCl] Sodium Chlorite (NaClO2) Potasium Permanganate (KMnO4) Per acetic acid Bleaching powder[Ca(OCl2).2Ca(OH)2] generally [Ca(OCl)Cl] Potasium di- Chromate(K2Cr2O7) Sodium di Chromate(Na2Cr2O7) Potasium chlorate(KClO3) Sodium per oxide (Na2O2)

II) Reducing bleaching agent: Zinc dust(Zn) Staneous chloride (SnCl2) Ferrous sulphate (FeSO4) Sulphar di-oxide(SO2) Sodium bi- Sulphate(NaHSO4) Hydrogen Sulphide(H2S)

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Sodium Sulphite formaldehyde Sdium sulphate (Na2SO4) Hydrogen (H2) Carbon (C)

Classification of bleaching agent:

Chlorine-based bleaches:

Chlorine-based bleaches are found in many household cleaners. The concentration of chlorine-based bleaches is often expressed as percent active chlorine where one gram of a 100% active chlorine bleach has the same bleaching power as one gram of chlorine. These bleaches can react with other common household chemicals like vinegar or ammonia to produce toxic gases. Labels on sodium hypochlorite bleach warn about these interactions.

Chemical interactions:

Mixing hypochlorite bleach with an acid can liberate chlorine gas. Hypochlorite and chlorine are in equilibrium in water; the position of the equilibrium is pH dependent and low pH (acidic) favors chlorine,

Cl2 + H2O H+ + Cl− + HClO

Chlorine is a respiratory irritant that attacks mucous membranes and burns the skin. As little as 3.53 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine has been limited to 0.5 ppm (8-hour time-weighted average—38 hour week) by OSHA in the U.S.

Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed. The main reaction is chlorination of ammonia, first giving chloramine (NH2Cl), then dichloramine (NHCl2) and finally nitrogen trichloride (NCl3). These materials are very irritating to the eyes and lungs and are toxic above certain concentrations; nitrogen trichloride is also a very sensitive explosive.

NH3 + NaOCl → NaOH + NH2Cl

NH2Cl + NaOCl → NaOH + NHCl2

NHCl2 + NaOCl → NaOH + NCl3

Additional reactions produce hydrazine, in a variation of the Olin Raschig process.

NH3 + NH2Cl + NaOH → N2H4 + NaCl + H2O

The hydrazine generated can react with more chloramine in an exothermic reaction to produce ammonium chloride and nitrogen gas:

2 NH2Cl + N2H4 → 2 NH4Cl + N2

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Atmospheric carbon dioxide and water react with bleaching powder (CaCl(OCl)) to release hypochlorous acid which gives a characteristic smell to the bleaching powder. Hypochlorous acid decomposes readily to atomic oxygen. This atomic oxygen acts as bleaching agent through oxidation.

2CaCl(OCl) + H2O + CO2 → CaCO3 + CaCl2 + 2HClO

HClO → HCl + [O]

2HCl + [O] → H2O + Cl2

However, the place of atomic oxygen in accounting for the formation of chlorine is not as plausible as another theory based on the so-called 'chloride system' employed in modern hydrometallurgy to dissolve ores with weak acids in highly ionic and concentrated salt solutions. Salts particularly effective, in this regard, include MgCl2, CaCl2, FeCl3 and, to a less extent the mono-valent NaCl. This is, in effect, an application of the non-common ion theory, or as discussed in Wikipedia under Solubility Equilibrium as the 'salt effect'. With respect to Bleaching powder, which has been described as a compound salt of the form Ca(ClO)2.CaCl2.Ca(OH)2.xH2O, the presence of CaCl2 in very concentrated solutions can greatly increase the 'activity level' of weak acids. So, in this particular proposed application, H2CO3 from CO2

and moisture on the Bleaching powder, acts on the CaCl2 to release some HCl which acts on the HClO releasing Chlorine:

HClO + HCl → H2O + Cl2

or, the increasing acidity creates more HClO which moves the following known (and old, see Watt's Dictionary of Chemistry) equilibrium reaction to the right:

CaCl2 + 2 HClO = Ca(OH)2 + 2 Cl2

Now, the strength of the particular application of this theory is that a similar release of Chlorine is not as easily observed with concentrated NaClO solutions (which it should be if one subscribes to the action of atomic oxygen on HCl). As the latter Chlorine bleach also contains NaCl, and as the NaCl is not quite as effective as previously noted as, for example, with CaCl2, the ionic strength is not as great for noticeable Chlorine formation.

Sodium hypochlorite:Main article: Sodium hypochlorite

Sodium hypochlorite is the most commonly encountered bleaching agent, usually as a dilute (3-6%) solution in water. This solution of sodium hypochlorite, commonly referred to as simply "bleach", was also one of the first mass-produced bleaches. It is produced by passing chlorine gas through a dilute sodium hydroxide solution

Cl2 (g) + 2 NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)

or by electrolysis of brine (sodium chloride in water).

2 Cl− → Cl2 + 2 -e

Cl2 + H2O ↔ HClO + Cl− + H+

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The dilute solution of sodium hypochlorite is used in many households to whiten laundry, disinfect hard surfaces in kitchens and bathrooms, treat water for drinking and keep swimming pools free of infectious agents.

Moreover, due to transport and handling safety concerns, the use of sodium hypochlorite is preferred over chlorine gas in water treatment, which represents a significant market expansion potential.

Calcium hypochlorite:Main article: Calcium hypochlorite

Calcium hypochlorite, also known as chloride of lime, is made by reacting chlorine with calcium hydroxide:

2Cl2 + 2Ca(OH)2 → Ca(ClO)2 + CaCl2 + 2H2O

It is used in many of the same applications as sodium hypochlorite, but has the advantages of being more stable and containing more available chlorine. Calcium hypochlorite is the active ingredient in bleaching powder or "chlorinated lime", which is usually a white powder containing calcium hypochlorite, calcium hydroxide and calcium chloride. A purer, more stable form of calcium hypochlorite is called HTH or high test hypochlorite. Bleaching tablets contain calcium hypochlorite plus other ingredients to prevent the tablets from crumbling. A supposedly more stable mixture of calcium hypochlorite and quicklime (calcium oxide) is known as "tropical bleach Percent active chlorine in these materials ranges from 20% for bleaching powder to 70% for HTH.

Chlorine:Main article: Chlorine

Chlorine is produced by the electrolysis of sodium chloride.

2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH

Chlorine is used to prepare sodium and calcium hypochlorites. It is used as a disinfectant in water treatment, especially to make drinking water and in large public swimming pools . Chlorine was used extensively to bleach wood pulp, but this use has decreased significantly due to environmental concerns.

Chlorine dioxide:Main article: Chlorine dioxide

Chlorine dioxide, ClO2, is an explosive gas and must be used where it is made or shipped and stored as dilute aqueous solutions. Despite these limitations it finds applications for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, skin, and in a number of other industries. It can be prepared by oxidizing sodium chlorite with chlorine

2 NaClO2 + Cl2 → 2 ClO2 + 2 NaCl

But more commonly it is prepared by reducing sodium chlorate with a suitable reducing agent like methanol, hydrogen peroxide, hydrochloric acid, or sulfur dioxide

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2 NaClO3 + 2 HX + "R" → 2 NaX + 2 ClO2 + "RO" + H2O

Where "R" is the reducing agent and "RO" is the oxidized form.

Sodium per carbonate:

Sodium percarbonate is produced industrially by reaction of sodium carbonate and hydrogen peroxide, followed by crystallization. Also, dry sodium carbonate may be treated directly with concentrated hydrogen peroxide solution.

2Na2CO3 + 3H2O2→2Na2CO3.3H2O2

Dissolved in water, it yields a mixture of hydrogen peroxide (see above) and sodium carbonate. It is generally considered to be an eco-friendly cleaning agent.

Sodium perborate:

Sodium perborate, Na2H4B2O8, is made by reacting borax with sodium hydroxide to give sodium metaborate (NaBO2) which is then reacted with hydrogen peroxide to give hydrated sodium perborate.

Na2B4O7 + 2 NaOH → 4 NaBO2 + H2O

2 NaBO2 + 2 H2O2 + 6 H2O → [NaBO2 (OH) 2 x 3 H2O] 2

Sodium perborate is useful because it is a stable, source of peroxide anions. When dissolved in water it forms some hydrogen peroxide, but also perborate anion (B(OOH)(OH)3

-), which is activated for nucleophilic oxidation.

Hydrogen peroxide:

Hydrogen peroxide is produced in very large amounts by several different processes. Its action as an oxidizer is why it is made and used in such large quantities. It is used by itself as a bleaching agent, for example to bleach wood pulp, hair and so on, or to prepare other bleaching agents like the perborates, percarbonates, peracids, etc.

Hydrogen peroxide bleached uses chemicals: Required chemical:

Hydrogen peroxide (H2O2) Stabilizer Caustic soda. Soda ash Wetting agent

Bleaching action of Hydrogen per oxide: Under certain condition, particularly regard to PH , hydrogen peroxide will liberate hydrogen ion and per hydroxyl ions in the following manner

Per hydroxyl ions responsible for bleaching.

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Alkalinity favours the liberation of Per hydroxyl ions because the positively charged hydrogen ion is neutralized but excessive alkalinity cause the peroxide to become unstable. The hydro – peroxide ion is resposible for bleaching action.In presence of catalyst such as CaCO3, Fe, Cu, Cr, Mg etc. liberated oxygen by decomposing H2O2 and lower the strength of H2O2.

2H2O2 2H2O + O2

Hence (20 – 70) or (60 - 80) hardness are suitable for bleaching.

Methods of bleaching with Hydrogen Peroxide:There are two chief methods for bleaching of cotton goods with H2O2.

Bleaching in kier (Discontinuous) Bleaching in J – Box (Continuous)

Bleaching in j-box: (continuous bleaching process): The bleaching vessel is looks like ‘J’ the english letter ‘J’ hence this process is J – Box process. J-Box is made of stainless steel or ceramic. Scouring in J-Box mode, the scouring in short duration and easily controlled. As scouring and bleaching are performed continuously, hence two J-Boxes are required. In textile mill, this process are used commercially. Capacity of J-Boxes are 6-40 tones per day.Following recipe is required for bleaching:

Caustic soda – 2 lbsH2O2 (35%) – 1.5 gallonMagnesium sulphate – 0.2 lbsSodium silicate – 15 lbsWater – 97 gallonsPH – 10.9

This process is done by following three processes:(1)Processing in impregnation box: At first, above chemicals are dissolved and make liquor is impregnation box. After processing from 1st J-box for scouring the mtls. then wash. The mtls. are immersed into impregnation box by immersion roller then squeezed and brought to the J – box.

(2) Storing in J-Box: After impregnation of fabric from bleaching liquor then, the mtl. store in J-Box where, steaming is done at 93-990c for 60-90 mins. and bleaching is completed.

(3) Washing: Then the mtls are washed in hot water then in cold water and finally dried or first the mtls are washed with 2% solution of sodium carbonate at 80-890c and finally washed with cold water.

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Advantages of H2O2 bleaching over other bleaching agent: H2O2 does not react with residual protein of fibre and hence no need antichloro treatment. Permanent white cotton is obtainable and the bleached fabics are highly hydrophilic since the

waxes are solublised and removal by the hot alkaline solution. Its reaction products are relatively non toxic and it decomposes to oxygen and water thus

reducing greatly the effluent pollution of the bleaching plant. H2O2 bleaching is carried out in alkaline medium and elevated temp. is about 1000c, hence

scouring and bleaching completed together. Small amount of impurities present in cotton fibre, give stability of H2O2 in solution and so needs

scouring. For this reason, impurities in cotton acts as stabilizer in H2O2 bleaching. Weight of fabric after H2O2 bleaching is higher than that of hypochlorite bleaching. Tensile strength is greater after H2O2 bleached fabric than that of hypochlorite bleached. Another advantage is degradation possibility of fabric is less due to over bleached. Hard water preferable.(20-70C). Bleaching and dyeing can be sometimes combined in a single operation. The no. of operation and stages in the bleaching can be reduced and continuous one stage

process can be worked. It si compatible with the most fibres and can be applied to a wide variety of fabric under a wide

range of bleaching condition and machines.

Disadvantages of H2O2 bleaching over other bleaching agent: Bleaching is slow unless high temperature is applied energy Catalytic decomposition of H202 occurs along with catalytic degradation of cellulose due to iron,

Ne, Cu and Pb hydroxide present in the bleaching solution or I the fabric. The above metals and their alloys cannot be used as material of construction of H 202 bleaching

containers.Causes of H2O2 universal bleaching agent:Hydrogen peroxide is successfully used to bleach both cellulosic (vegetable) and protein (animal) fibre.

In case of cellulosic fibre, H2O2 permanently destroy the natural color and obtained good result. In case of protein fibre H2O2 oxidized the protein mtl. but if no chloride ion. For this di-

appearance, it has no effect on protein fibre and also destroys the natural color permanently. H2O2 bleaching is done at elevated temperature is about 1000c in alkali medium and hence

scouring and bleaching can be performed together. So, H2O2 is called univesal bleaching agent.

Reactive Dyes

Reactive dyes: in a reactive dye a chromophore contains a substituent that reacts with the substrate. Reactive dyes have good fastness properties owing to the bonding that occurs during dyeing. Reactive dyes are most commonly used in dyeing of cellulose like cotton or flax, but also wool is dyeable with reactive dyes. Reactive dyeing is the most important method for the coloration of cellulosic fibres. Reactive dyes can also be applied on wool and nylon; in the latter case they are applied under weakly acidic conditions. Reactive dyes have a low utilization degree compared to other types of dyestuff, since the functional group also bonds to water, creating hydrolysis Usage

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Reactive dyes react with the fibres.

Mainly react with cellulosic fibres

e.g. cotton, jute, bast fibres, viscose, flax

It can be applied to protein fibres e.g. wool & silk.

Reactive dye contains reactive group and this reactive group makes covalent bonds with the fibres and

becomes part of the fibre.

The general formula of Reactive dye can be written as follows:

D-X-Y

Here D --> Chromophore of Dye post

X --> Bridge

Y --> Functional group

D-X-Y + Fibre --> D-X-Y-Fibre Covalent bond.

Reactive dyes water soluble

D-F + Cell-OH --> Dye-F-O-cell F = Functional group

D-F + H-OH --> Dye-F-OH

Hydrolysis

Properties of Reactive dyes:

Water Soluble dyes.

Makes covalent bonds with the fibres.

A certain amount of dye is hydrolyzed during dyeing (10-60%)

Dyeing is carried out in alkaline condition (PH

= 11.5).

Huge electrolyte is necessary for dyeing with reactive dyes.

Fastness (wash, light, Rubbing, perspiration) properties are generally good.

Easy applicable to cellulosic as well as protein fibres. (Wool & Silk)

Very popular and wide used in the wet processing industry in Bangladesh.

Comparatively cheap.

All kinds of shade is found.

Dyeing method is easy.

History of Reactive dye: On the occasion of 100 years celebration of Synthetic dye manufacturing,

two chemists of ICI Company (UK) named Stephen and Rattee tried to manufacture a new dye stuff.

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Thus they succeed to invent a new dye in 1956 which was named REACTIVE DYE. This was

manufactured for dyeing cellulosic fibres. The 1st three Reactive dyes were Procion Yellow R, Procion

brilliant Red 2B and Procion Blue 3G. For this effort they were awarded Gold Medal of the Society of

Dyes and colourists for the year 1960.

These dyes came to our country in Mid 60’s and became very popular during 80’s.

Advantage of Reactive dyes:

Good washing fastness (Rating 4-5)

very good light fastness (Rating 6)

Lower cost.

Simple dyeing method

Good reproducibility.

Low dyeing temp (below 100oC)

Ability to produce bright shade

Dye molecular composition

Easily applicable to cellulosic fibre as well as protein

All kinds of shade is found.

Importance of Reactive group present in Reactive dye:

Reactive groups do not contribute colour which is determined by chromogen group.

the reactivity of vinyl sulphone group is less than halogen group.

If no of reactive group increases, binding also increases depending on dye structure.

reactive dye absorb up to 90%.

If the molecular wt of reactive group increases, reactivity also increases

Reactivity of vinyl sulphone group increases with increases of PH and temp.

Sulphone group has mere solubility but it is not stable

Chlorine imparts medium reactivity, but it is cheap.

Reactivity of Fluorine is the least and its rate of hydrolysis is also less.

Criteria of cellulose for attaching Reactive dye:Chemical structure of cellulose molecule

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Glucose unit:

Each glucose unit contains one primary hydroxyl group (-CH

2OW) and two secondary hydroxyl

groups (>OH)

Primary hydroxyl group (-CH

2OH) at C

6 position is more reactive than the secondary hydroxyl

groups at C2 and C

3 position

C

2 Hydroxyl group is supposed to be acidic than C

3 hydroxyl group under suitable alkaline

condition and more reactive.

The hemiacetal group at C

1 position is the most active.

The reaction betn reactive group and cellulose takes place predominantly with primary hydroxyl

group.

In case of monochloro triazinyl dyes, the reaction ratio of

-CH2OH & -CHOH is 15:1

i.e. C6:C

2 or C

3 = 15:1

In case of dichloro triazinyl dyes, the reaction Ratio of

-CH2OH & -CHOH 3:1 to 7:1

Secondary hydroxyl group is the least reactive while primary one is the most reactive

Classification of Reactive dyes:1. On the Basis of Reactive group: Two types

Halogenated heteroycles

Triazine group :

Example: Procoin, Cibacron

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Pyrimidine

Quinoxaline

Activated Vinyl compounds:

Vinyl Sulphone (D-SO

2-CH

2-CH

2-) Ex: Ramazol.

Vinyl Sulphonamide (D-SO

2-NH-CH

2-CH

2-) Ex. Levafix

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Vinyl acrylamide (D-NH CO-CH

2-CH

2-) Ex: Primazine

2. On the Basis of Reactivity:

High reactivity : Ex: Procion M

Moderate reactivity: Ex: Liva fix-E

Low reactivity : Ex: Premazine

Dyes can be devided into 2 groups

Cold Brand

Hot Brand.

Chemical Classification of Reactive Dyes:Reactive dyes can be classified chemically into three (3) different groups:

Chloro triazinyl Reactive dyes.

Monochloro dyes.

Dichloro/Bifunctional

Trichloro.

Monochloro dyes:

Dichloro:

Trichloro pyrimidyl:

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2. Vinyl sulphone Dyes:

Dye. SO2 CH = CH

2

3. Heterocyclic helogen containing Reactive dyes-

Drimarine K

Levafix E:

Primazine P Dyes:

Hydrolysis of Reactive Dye/Technical defficiency of R.D:Under alkaline condition, Reactive dyes react with the terminal hydroxyl group of cellulose. But if the

soln of the dye is kept for long time, its concentration drops. Then the dye react with the hydroxyl group

of water. the reaction of dye with water is called Hydrolysis of reactive dye.

I) Incase of Triazinyl dyes:

a)

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II ) In case of Vinyl Sulphone Dyes:

Dye-SO

2CH = CH

2 + HO – cellulose Dye – SO

2 CH

2 -CH

2 O cellulose

Dye-SO

2CH = CH

2 + H-OH Dye-SO

2 CH

2 CH

2 OH

Mono hydroxy group

Dyeing mechanism of reactive dye:

The dyeing mechanism of material with reactive dye takes place in 3 stages:- Exhaustion of dye in presence of electrolyte or dye absorption. Fixation under the influence of alkali. wash-off the unfixed dye from material surface.

Now they are mentioned below: Dye absorption:

When fibre is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize the negative charge formed in the fibre surface and puts extra energy to increase dye absorption. So when the textile material is introduces to dye liquor the dye is exhausted on to the fibre.

Fixation: Fixation of dye means the reaction of reactive group of dye with terminal –OH or-NH2 group of fibre and thus forming strong covalent bond with the fibre and thus forming strong covalent

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bond with the fibre. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this purpose depends on brand of dye and dyeing temperature. Here generally caustic soda, soda ash or NaHCO3 is used as alkali depending upon reactivity of dye. They create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place in this stage is shown below: -

1. D-SO2-CH2-CH2-OSO3Na + OH-Cell D-SO2-CH2-CH2-O-Cell + NaHSO3

2. D-SO2-CH2-CH2-OSO3Na + OH-Wool D-SO2-CH2-CH2-O-Wool + NaHSO3

3.

Wash-off: As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good wash-fastness. It is done by a series of hot wash, cold wash and soap solution wash.

Controlling Parameters/Factors:

PH

Temperature

Dyeing time.

Liquor Ratio.

Concentration of electrolyte (salt)

PH of dye bath: PH range for Reactive dyes 10-11.5

Dyeing time:

Dyeing time ; Hydrolysis

The exhausion takes place in 20-30 min

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Temperature: Temperature of dyeing Hydrolysis

40o-100oC temp is applied.

Liquor Ratio: M:L may be 1:5 – 1:20

Concentration of electrolyte: Common salt and glauber’s salt.

Concentration of salt may be 20-100 g/L depends on the shade (0.1-5.0%)

2. Semi continuous method

3. Continuous method

Stripping: Stripping becomes necessary when uneven dyeing occurs. By stripping azo groups (-N=N-) brom the

dye is removed.

I) Partial stripping methods: Partial stripping is obtained by treating the dyed fabric with dilute acetic acid or formic acid. The

commanded conc. is betn 5 to 10 parts glacial aid or 2.5 –10 parts of formic acid per 1000 parts of water

Recipe: Glacial acetic acid = 5 – 10 parts

Water --> 1000 parts

OR

Formic acid --> 2.5 to 10 parts

Water --> 1000 parts

Temp --> 70-100oC

Time --> Until the desired shade is obtained.

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Process- The goods are entered and temp is raise to 70-100oC and the treatment is continued until the

shade has been reduced to the desired amount thoroughly washing is then necessary to remove the

products of hydrolysis.

II) Full stripping: For complete stripping, the goods are treated with Na2S2O4 Sodium hydrosulphite & Soda at boil.

Materials and Methods of Reactive Dyeing:

Raw materials:Same fabric of Table 1 has been used in all trials done both in lab and bulk.

Methods:The fabric was dyed in exhaust method in the laboratory and in bulk scale at Aman tex Ltd.

Processes followed in laboratory trial:

Pretreatment:

Table-2: Recipe for Pretreatment in laboratory trials.

With Bleaching Without Bleaching

Name of Chemical

Qty (g/l) Name of Chemical Qty (g/l)

Wetting agent 1.00 Wetting agent 1.00Sequestering agent

0.50 Sequestering agent 0.50

Anti Creasing agent

1.00 Anti Creasing agent 1.00

Caustic soda (NaOH)

2.00 Caustic soda (NaOH) 3.00

Hydrogen per oxide(H2O2) 50%

3.00 Hydrogen per oxide(H2O2)

-

Stabilizer 0.50 Stabilizer -24

Peroxide Killer 0.30 Peroxide Killer -M:L 1:10 M:L 1:10Temperature 100*c Temperature 100*cTime 50min Time 50min

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The samples were categorized as dyed samples with bleaching and dyed samples without bleaching at same dye bath and same recipe

Process followed in testingFor colour fastness to wash ISO 105 C03 was method followed; for colour fastness to rubbing /crocking  EN ISO 105×12 was method followed and for color fastness to perspiration ISO 105 E02 method was followed In respect to colour fastness properties, the unbleached samples revealed the same better results as it was in case of bleached samples.

Results and discussions

Color Measurement Committee (CMC) DE pass/fail values:

Table 4: CMC pass/fail values for different shade %

Shade %  CMC DE DL Da  Db   Comments

Nova. Red SB

 0.10  1.15  -2.10 1.60 0.25  Fail 0.25  0.60 -0.73 0.87  0.55  Pass 0.50  0.99 -1.52 1.32  0.88  Pass

Nova. Yellow S3R

 0.10  0.32 -0.29 -0.26 0.34  Pass 0.25  3.42 -2.90 3.91 6.26  Fail 0.50 1.47  -1.23 1.52 3.48 Fail

Nova. Blue FNR

 0.10 1.20 -0.99 -0.49 1.43 Fail 0.25  0.88 -1.98 -0.22 0.50 Pass 0.50  0.78 -1.75 0.16 -0.33 Pass

 Combination (R-0.2, Y-0.2, B-0.1)  0.5  0.40  -0.76 -0.15  -0.14 Pass

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The above result shows that dyeing without bleaching is possible up to 0.5% red, 0.5% blue and 0.1% yellow shades and also for specific combination shades (0.5%)

Cost analysisIn the bulk trial bleaching process needed 9 chemicals and without bleaching process only 6 chemicals were used. So process without bleaching saves extra 3 chemicals.

Cost of chemicals (Source: Purchasing department of Amantex Ltd.)

From the table it is clear that process without Bleaching saves 757Tk/1000kg (approx.) fabrics.

Time saved: As per table 3, the process with bleaching needs 243 min and process without bleaching needs 185 min. So process without bleaching saves 58 min. As a result process without bleaching provides following benefits because of less time consumption:1. Production will increase  2. Labor cost will decrease 3. Saves machine running cost. i.e. electricity, gas, and power cost.

Energy cost calculation for MCS dyeing machine:1kw hour = 1 unit of electricity1 unit cost  = 5.5Tk (approx)Dyeing machine is of 60 KW capacityo it consume 60×1 = 60 unit per hourCost =60×5.5 = 330Tk/hrSince process without bleaching save 58 minutes, So it saves 58×5.5 = 319Tk (approx.) energy cost.Source: Maintenance department of Amantex Ltd.

Water saved due to elimination of per-oxide:the trial was done in Material: Liquor = 1:6. For conventional pretreatment process 30000lt water was required, whereas without bleaching pretreatment process required 24000lt. So proposed process saves extra 6000lt of water.

Cost of treated water after Water Treatment Plant (WTP):

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So for 6000 lit of water process without bleaching saves 6x5.11 = 30.66 Tk (approx.)

Cost in ETP:

So, for 6000Lt of water process without bleaching saves 6x11.97 = 71.82 Tk (approx.) Total cost for 6000lt water = 30.66+71.82 = 102.48Tk = 103 Tk. (approx.)

Savings from cost of heating:

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HereHeat Needed= Specific Heat of Water (4.186 kj/kg/°C)*mass of water*change in temperature.Heating Cost Savings= (Heat Needed/Specific Enthalpy of steam)*cost of steamCost of steam: Considering the steam cost of PPC

Total saving in cost:

So proposed process saves 1466Tk/1000kg (approx.) and 58 minute duration.

Conclusion:Detailed experimental data were manipulated through the research work. As the elimination of bleaching results the grayness retaining in cotton fabric, CMC DE pass/fail comparison with conventionally treated fabric were investigated.  Consequently color fastness to wash, rubbing and perspiration have been tested. During this experiment dyeing is performed for shade percentages of 0.50, 0.25, and 0.10 with bleaching and without bleaching for Red, Yellow, Blue and combination shades. For Red, Blue and combination color up to 0.5% shade has been passed in data color result but below 0.5% the result in data color did not pass. It was passed up to 0.1% shade in case of yellow color. Besides, samples passed in data color results have been shown good color fastness (washing, rubbing and perspiration) values. Some bulk dyeing has been performed in factory after successful completion of laboratory trials. Experiments were done on different combination shades the results have been derived successfully. It can be concluded that dyeing with red (0.2%), blue (0.1%) and yellow (0.2%) excluding bleaching process passed at data color 650 (CMC pass/fail) with conventional (including bleaching) dyeing process. In case of specific combination shade it was found that 0.5% shade is possible without bleaching operation. Cost analysis displays that 1220Tk (approx.) was saved per 1000 kg fabric dyeing through the proposed way.

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References:1.http://www.fibre2fashion.com/industry-article/4/316/cost-effectiveness-in-textile-processing1.asp2. Hasan, Md. Rakibul, "Scopes of Improvisation in Knit-Dyeing process of Cotton in Bangladesh to optimize the process-time", Bangladesh Textile Today, March-April-2010.4. Interview from Mr. Neaj Mohammad Soyeb, Dyeing Manager of Amantex Ltd.

5.Interview from Md Arshad, Manager of the department of ETP and WTP. Amantex Ltd.

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