Determination of Strength & Weight Loss Due to Single Bath Scouring & Bleaching Action on Cotton

Determination of Strength & Weight Loss Due to Single Bath Scouring & Bleaching Action on Cotton

Md. Ujjal Bhuiya & Md. Atikur Rahman
Department of Textile Engineering
Dhaka University of Engineering & Technology (DUET)
Gazipur -1700, Bangladesh

ABSTRACT
The textile sector of Bangladesh is now facing stiff competition in the international market. Because, every country invented of new technology. Modern development is setting new parameters and standard everyday. In Bangladesh, the textile sector mainly dyeing and finishing industries are now facing severe energy problem because they are not getting uninterrupted gas supply. The combined scouring & bleaching process increases production with reduction in labor cost and reduced treatment time, lower consumption of water, steam and electricity. The loss in weight and strength of material is less.

For perfect coloration of a substrate, it is necessary that all the impurities and natural color be removed from the surface so that the colorants can perfectly sit on the surface or penetrate inside the substrate as require the particular system. The colorants should also be clearly visible without interference by the color of the impurities. The minimum strength and weight loss of cotton are obtained by working on different sample in different concentration of Hydrogen peroxide and Sodium hydroxide in single bath scouring & bleaching process.

CHAPTER 1
INTRODUCTION TO SCOURING & BLEACHING

1.1  Introduction
Scouring & Bleaching is the most important wet process applied to textile materials before dyeing and printing. It is mostly cleaning & whitening process in which all impurities and natural colors are removed. The impurities may be natural, added or accidental as discussed earlier. When the impurities are removed, the cotton becomes absorbent. More specifically  scouring & bleaching is done in order to remove or destruction of natural and adventitious coloring maters and unwanted oils, fats, waxes, soluble impurities and any particulate or solid dirt adhering to the fibres, which otherwise hamper dyeing, printing and finishing processes. The process essentially consist of treatment with soap or detergent, hydrogen peroxide with addition of alkali.

The scouring and bleaching of cellulose fibres are quit simple. The natural Impurities such as natural color, cotton wax, pectic substance and proteins are associated mainly with the cell wall within the primary wall, the scouring process is aim to remove this wall. Bleaching agents convert colored impurities into colorless particles. Color is impart by a chromophor, i.e. a moiety usually involving alternating carbon-carbon single and double bonds. Bleaching destroys these double bonds addition (saturation) or rupture. Once type free electrons of a double bond are tied by substitution or by rupturing the double bond, electromagnetic radiation is not absorbed and is reflected in visible region of the spectrum and color ceases to exist.

1.2 Definition of Scouring & Bleaching
Natural fibres (cotton) are yellowish or off-white in color due to color bodies present in the fibre and contain oils, fats, waxes, minerals, leafy matter and motes as impurities that interfere with dyeing and finishing. The process of destruction of yellowish or off-white color bodies is called Bleaching and The process of removing of impurities and make good absorbency is called Scouring.

Even though these impurities are not soluble in water, they can be removed by Extraction, dissolving the impurities in organic solvents, Emulsification, forming stable suspensions of the impurities in water and Saponification, Converting the contaminates into water soluble components.

1.3 Aims of this study
The aim of this study of single bath scouring & bleaching is to treat the cotton goods by standard procedures so that the process should have the following performances:

• More economical process.
• Minimum Strength loss.
• Minimum weight loss.
• Good scouring & bleaching effect

The cotton goods are treated by standard procedures so that they are brought to a state in which they can be dyed, printed or finished without showing any fault or damage on the material. The prepared materials should have the following properties:

• Uniform power of absorption for dyes and chemicals in subsequent processes.
• An even water imbibitions value.
• Removal of all type of impurities including broken seeds etc.
• Minimum damage of the material.
• Absence of creases and wrinkles.
• High whiteness value.

1.4 Merits of Combined Scouring and bleaching.
The advantages of this process are increased production with reduction in labor cost and reduced treatment time, lower consumption of water, steam and electricity. The loss in weight and strength of material is less. The disadvantage is increased chemical cost as a higher dose of hydrogen peroxide is required. The declining price-rates of peroxide with increasing cost utilities may make the process more economical. In the presence of hydrogen peroxide, the scouring process is accelerated and less time is generally required to achieve good absorbency of the material.

1.5 Cotton fibre
The word ‘cotton’ is derived from the Arabic. Depending upon the Arabian dialect, it is pronounced kutan, qutn, qutun etc. As the cotton fibre is obtained from a plant, it is classified as a natural cellulose, seed, mono-cellular, staple fibre. The density of the fibre is 1.52 gm/cm³, which makes cotton a rather heavy fibre.

Cotton is the most important natural fibre. It accounts for about 50% of the total fibre production of the world. Cotton fibre is obtained from the seed of the plant of the botanical family Gossypium. Cotton was being produced and used in India from ancient times. At present cotton is cultivated in many countries- the largest producers are the USA, India, Russia, Brazil, Egypt, and China. Some important varieties of cotton are Sea Island(51mm, dia 0.017mm), Egyptian(38-44mm, 0.017mm), American(23-32mm, 0.21mm), Indian(15-20mm, varying dia)- the quantities in brackets are average fibre length and diameter respectively, in each case.

1.6 Chemical composition of cotton fibre
The chemical composition of cotton fibres and the quantity of different constituents vary greatly with the type of plant, soil and climate. Raw cotton fibre, after ginning, is essentially composed of 94% cellulose.

Table 1.1: Composition of Ginned Cotton

1.7 The Chemistry of cotton fibre
The cotton fibre is a single biological cell. Its cross-section is oval, compared with the normal hexagonal plant cell. It is built up in four parts- Lumen, secondary wall, primary wall and cuticle (inside to outside). Lumen is the nutrient transportation tube for the cotton cell. It still contains small amounts of bioorganic materials, which add a yellowish shade to the fibre. The secondary cell wall is built up of cellulose layers – it adds about 91.5% of fibre and has a crystallinity index of 70%.

The primary cell wall, which mainly consist of protein, pectic substances and glucans, is about 2.5% of fibre weight. It has a crystallinity index of about 30%. The protective cuticle is made of wax compounds, mineral matters, pectin’s, fatty acids, high molecular weight alcohol and their esters.

The outer layer was originally thought to be made of two layers. However, later it was found the waxes do not constitute separate layer. It is provably distributed in the primary cell wall, but highest concentration is at the surface and seen to be closely connected to the pectic substances. The composition of combined primary cell wall and cuticle is as follows:

Table-1.2: The composition of combined primary cell wall and cuticle.

The pectic substances act as adhesive binding wax to the fibre. When it is removed, wax can be subsequently emulsified. Among all non-cellulosic materials has to be removed in order to obtain a fully wettable and dyeable fibre.

The Scouring & Bleaching Process, purifying the α-glucose, imparts the hydrophilic character and produce pure white materials.

CHAPTER 2
CHEMICALS AND THEIR FUNCTIONS

2.1 Hydrogen peroxide (H₂O₂)
Hydrogen peroxide (H₂O₂) is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It has strong oxidizing properties, and is a powerful bleaching agent. Hydrogen peroxide was first used to bleach cotton in the 1920’s. By 1940, 65 % of all cotton fabrics were bleached with hydrogen peroxide, largely brought about by the invention of the J-box which lead to continuous processing. Today, it is estimated that 90 to 95 % of all cotton and cotton/synthetic blends are bleached with hydrogen peroxide. It is available commercially as 35, 50 and 70 % solutions. It is a corrosive, oxidizing agent which may cause combustion when allowed to dry out on oxidizable organic matter.

The bleaching action of hydrogen peroxide was thought to be due to the liberation of nascent oxygen, but this explanation is no longer valid. Under certain conditions, particularly with regard to PH, hydrogen peroxide decomposes into hydrogen and perhydroxyl ion (HO₂–), which is thought to be responsible for bleaching action.

H₂O₂  →  H+  + HO₂ –

Hydrogen peroxide can also decompose. This reaction is catalyzed by metal ions e.g. Cu++, Fe+++. This reaction is not desired in bleaching because it is an ineffective use of hydrogen peroxide and causes fibre damage.

2H₂O₂   →    2H₂O  + O₂

The liberated oxygen has no bleaching power and the catalysts, therefore, cause wastage of hydrogen peroxide.

2.2 Advantages of H2O2 Bleaching over other bleaching agents
Although hydrogen peroxide is costlier than hypochlorite, the former has several advantages, which have contributed to its greatly increased use during recent years. The advantages are:

1. It is a universal bleaching agent and can bleach most of the textile fibres without damaging the materials.
2. It is eco-friendly. As the decomposition products of hydrogen peroxide are oxygen and water, bleaching can be safety carried out in an open vessel.
3. Hydrogen peroxide does not react with proteins. Hence, a permanent whiteness can be achieved without preliminary alkali treatment.
4. As peroxide bleaching is done under alkaline conditions at boil, both scouring and bleaching can be combined. In fact, it is the only bleaching agent, which can be used for the combined process.
5. Weight of fabric after H2O2 bleaching is higher than that of hypochlorite bleaching.
6. Tensile strength is greater after H2O2 bleached fabric than that of hypochlorite bleached.
7. Another important advantage of hydrogen peroxide bleaching is that there is little risk of tendering due to over bleaching.
8. The number of operation and stages in the bleaching can be reduced and continuous one stage process can be worked.
9. It is compatible with the most fibres and can be applied to the wide variety of fabric under a wide range of bleaching condition and machines.
10. Colored goods dyed with vat dyes can be safely bleached with hydrogen peroxide.

2.3 Sodium hydroxide (NaOH)
Sodium hydroxide (NaOH), also known as lye and caustic soda, is a caustic metallic base. It is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Sodium hydroxide is a common base in chemical laboratories. Pure sodium hydroxide is a white solid; available in pellets, flakes, granules and as a 50% saturated solution. It is hygroscopic and readily absorbs water from the air, so it should be stored in an airtight container. It is very soluble in water with liberation of heat. It also dissolves in ethanol and methanol, though it exhibits lower solubility in these solvents than does potassium hydroxide. Molten sodium hydroxide is also a strong base, but the high temperature required limits applications. It is insoluble in ether and other non-polar solvents. A sodium hydroxide solution will leave a yellow stain on fabric and paper.

Uses
Sodium hydroxide is the principal strong base used in the chemical industry. In bulk it is most often handled as an aqueous solution, since solutions are cheaper and easier to handle. It is used to drive chemical reactions and also for the neutralization of acidic materials. It is also used for heavy duty and industrial cleaning. Sodium hydroxide is frequently used as an industrial cleaning agent where it is often called “caustic”. It is added to water, heated, and then used to clean the process equipment, storage tanks, etc. It can dissolve grease, oils, fats and protein based deposits. The sodium hydroxide solution can also be added surfactants to stabilize dissolved substances to prevent redeposition.

2.4 Stabilizer
Stabilizers must be added to the bleach solution to control the decomposition of hydrogen peroxide. Stabilizers function by providing buffering action to control the pH at the optimum level and to complex with trace metals which catalyze the degradation of the fibres. Stabilizers include sodium silicate, organic compounds and phosphates.

1. Sodium Silicates
Sodium silicates are the most commonly used and most effective hydrogen peroxide bleach stabilizers. They may be used as colloidal silicate (water glass), ortho silicate or metasilicate. The mechanism by which silicate stabilize is not completely 64 understood, however it is known that silicates have a natural affinity for ferrous ions and ferrous ions are naturally present in cotton. It is possible that the silicates are adsorbed onto the ferrous ions in the fibre, producing a species that catalytically enhances bleaching while reducing bleach decomposition and fibre damage. Stabilization by silicates is enhanced by the presence of magnesium ions. Magnesium serves as a pH buffer. As the concentration of OH- rises during bleaching, magnesium hydroxide (Mg(OH)2) precipitates, reducing the OH- concentration.

Bleach solutions containing only magnesium ions have good stability but the bleaching effectiveness is not as good as when silicates are included. Silicates as stabilizers have one drawback, they tend to polymerize and form insoluble silicates. They becomes hard deposits which build-up in the machines causing the fabric to be abraded. Also some of the deposits will form in the cloth, giving it a harsh, raspy hand, a real negative for terry toweling.

2. Organic Stabilizers
Organic stabilizers avoid the problems associated with sodium silicates. These products are often referred to as silicate free or non-silicate stabilizers. They may be based on sequestering agents, protein degradation products or certain surfactants. The commercial products are of two types, those designed only to be stabilizers and those which combine stabilization with other properties such as detergency and softening. For some bleaching methods, organic stabilizers may be used alone, while in others, they are best used in combination with silicates.

3. Phosphates
Tetra sodium pyrophosphate (TSPP) and hexametaphosphates are of interest as stabilizers in alkaline bleach baths under the following conditions: 1. The alkalinity of the bleach must not be higher than pH 10 since above this, the stabilizing effect decreases rapidly. 2. Temperature of the bleach bath is limited to 60 0C. Higher temperatures reduce stabilizing properties. They should be used with ammonia, not caustic soda or soda ash. TSPP at high pH and temperature is converted to trisodium phosphate which has little stabilizing effect. The use of TSPP is limited to bleaching wool and silk which are sensitive to high pH and high temperatures. As opposed to silicates, pyrophosphates are precipitated from solution in the presence of calcium and magnesium and therefore do not develop full stabilizing power.

2.5 Detergent
The term detergent is reserved for those agents capable of removing, dispersing and suspending solid soils from the surface being cleaned. Detergents are surfactants that help remove soils from solid surfaces. Detergents are considered to be surface active agents, which lower the surface tension of their solutions and promote wetting out of solid particles. Over and above reducing water’s surface tension, detergents must adsorb onto the soil’s surface to aid in spontaneous release. Detergents must also keep the soil suspended to prevent redeposition.

Detergents may be anionic or nonionic in nature. Anionic detergents are most powerful and popular. Chemically they belong to sulphate of fatty alcohols, olefins, oils, monoglycerides, amide condensates, alkyl aryl polyether and sulphonates of alkyl amides, ethers, olefins ( α-olefin sulphonate), etc.

2.6 Theory of Detergency
In textile scouring and in most detergency jobs, a film of oil (and wax in case of scouring) accompanied by dirt is to be removed from the fibre or fabric surface. The job can be divided in to four steps:

1. At first, the materials surface is to be wetted by the aqueous phase.
2. The oil, the wax and the dirt must be detached from the material.
3. The oil/soil is to be dispersed in the deterging medium.
4. A stable emulsion/dispersion of the oil should be formed to prevent redeposition on the cleaned surface.

2.7 Sequestering Agent: Disodium-Ethylenediaminetetraacetic acid (EDTA)
The principles behind sequestration is the formation of a water soluble complex between a sequestering agent and a polyvalent metal ion. The technique can be used for softening water; however, it is more often used as a component in many textile wet processing steps to remove metallic ions that interfere with the process.

Advantages and Disadvantages:
They will sequester metal ions and aid detergency by dispersing and suspending soil. They are more stable than inorganic polyphosphates in hot water and exhibit threshold effect. They are more expensive than inorganic polyphosphates.

CHAPTER 3
METHODOLOGY OF SCOURING & BLEACHING

3.1 Wet process sequence for the cotton
Scouring & Bleaching of textile finishing forms the most important stage in the textile processing sequence as shown in Figure 3.1. Wet textile processes are called ‘wet’ because they use water as the medium for transport of mass and heat across textile materials. Wet pre-treatment consists of desizing, scouring and bleaching. A short description of pre-treatment process is given below.

The desizing process involves the removal of starch from the fabric. Starch is added to yarns before weaving to strengthen them. Once a cooked starch solution dries, the resulting film will not readily redissolve in water; therefore, to completely remove starch from a fabric, the polymer must be chemically degraded to make it water soluble. Three chemical methods can be used to degrade starch into water soluble compounds namely, Enzymes, Acid Hydrolysis and Oxidation. Natural fibres (cotton) contain oils, fats, waxes, minerals, leafy matter and motes as impurities that interfere with dyeing and finishing. The process of removing of impurities and make good absorbency is called Scouring. The objective of a scouring process is to make the material hydrophilic, before it undergoes other processes like bleaching, dyeing and printing (Figure 3.3). Bleaching is the last chemical process before dyeing that eliminates unwanted colored matter from fibres, yarns or fabrics. Cootton fibres are yellowish or off-white in color due to color bodies present in the fibre and The process of destruction of yellowish or off-white color bodies is called Bleaching.

3.2 Chemistry of Oils, Fats and Waxes
Many of the contaminates removed in scouring, both natural and manmade are fats, oils or waxes. Many useful products, some used in scouring, are derived from them. This section will review some of the pertinent chemistry.

Fats
Chemically, fats and waxes are esters of fatty acids; fats are tri esters of glycerine and waxes are monoesters of fatty alcohols. Fats, also known as triglycerides, are abundantly produced by nature as vegetable oils (corn, olive, coconut, linseed, castor and soy bean oil) and, as fatty deposits in animals (beef, mutton, pork and fish). Marine animals produce both fats and waxes while land based animals produce only fats. Another source of waxes is vegetable matter, predominately the hard shiny outer coating on tropical leaves.

Triglycerides
Regardless of whether it is of vegetable or animal origin, a fat can be either liquid or semi-solid. A major factor in determining the physical nature of the fat is the makeup of the fatty acid components. There shows a generalized structure of a triglyceride. R1, R2 and R3 are used to indicate various combinations of fatty acids.

3.3 Hydrolysis of Triglycerides
When a triglyceride is hydrolyzed, the reaction products consist of three moles of fatty acid and one mole of glycerine. The reaction is either acid or base catalyzed. Acid hydrolysis is used to manufacture free fatty acids whereas base hydrolysis is called Saponification, the process for making soap.

Acid Hydrolysis
The hydrolysis is catalyzed by strong acids to yield free fatty acids which are separated by fractional distillation under reduced pressure. Fatty acids are important starting materials for many useful products and this point will be discussed in greater detail in later sections.

Saponification
The hydrolysis can also be carried out under alkaline conditions where one mole of alkali is consumed per mole of fatty acid. The alkali salts of fatty acids are called soaps. Laundry and toilet soaps are made this way.

TRIGLYCERIDE + 3NaOH  →  3 RCOONa   +  GLICERINE

3.4 The changes occurring during Scouring & Bleaching
The natural impurities such as cotton wax, pectic substances and  protein are associated mainly with the cell wall within primary wall, the scouring process aims to remove this wall and hydrogen peroxide destroy the double bond of color within the fibre. The changes caused by the treatment with boiling alkali have been summarized as follow:

1. The carbon-carbon double bond of natural color is destroyed by epoxidation and hydroxylation.
2. Hemicelluloses as well as cellulose fractions with a low DP are dissolved.
3. Saponifiable oils and fats are converted into soap.
4. Unsaponifiable oils and waxes are melted at the scouring temperature and are emulsified by the soap formed during saponification.
5. Pectins and pectoses are converted into soluble salts of pectic acid and metapectic acid.
6. Proteins are hydrolyzed with the formation of soluble sodium salts of amino acids or ammonia.
7. Water soluble mineral substances are dissolved.
8. Insoluble dirt is removed and retained in suspension.
9. Sizing and other added impurities, if present, are broken into soluble products.

3.5 Bleaching action
In peroxide bleaching, the carbon-carbon double bond  is destroyed by epoxidation and hydroxylation:

Earlier bleaching action of hydrogen peroxide was thought to be due to the liberation of nascent oxygen, but this explanation is no longer valid. Under certain conditions, particularly with regard to PH, hydrogen peroxide decomposes into hydrogen and perhydroxyl ion (HO2–), which is thought to be responsible for bleaching action. The very recent work has strongly implicated the superoxide radical anion(. O2–). Hydrogen peroxide solution normally require the addition of an activator to bring about bleaching. The most common activator is alkali, which presumably encourages the formation of perhydroxyl anion, this then reacts further with hydrogen peroxide to give the superoxide ion.

H₂O₂  →  H+  + HO₂ –

HO₂ –  +   H₂O₂  →    . OH +  . O₂—  + H₂O

Alkalinity fabours the liberation of perhydroxyl ions i.e. the rate of forward reaction is increased due to neutralization oh H + ion released forming water. However, excessive alkalinity makes hydrogen peroxide unstable. Hydrogen peroxide can also decompose. This reaction is catalyzed by metal ions e.g. Cu++, Fe+++.

This reaction is not desired in bleaching because it is an ineffective use of hydrogen peroxide and causes fibre damage.

2H₂O₂   →    2H₂O  + O₂

The liberated oxygen has no bleaching power and the catalysts, therefore, cause wastage of hydrogen peroxide.

3.6 Effect of PH
Hydrogen peroxide is an extremely weak acid, Ka = 1.5 X 1012. Since the perhydroxyl ion is the desired bleaching specie, adding caustic neutralizes the proton and shifts the reaction to the right. Therefore:

1. At pH < 10, hydrogen peroxide is the major specie so it is inactive as a bleach.
2. At pH 10 to 11, there is a moderate concentration of perhydroxyl ions. pH 10.2 to 10.7 is optimum for controlled bleaching. Sodium hydroxide is used to obtain the proper pH.
3. At pH > 11, there is a rapid generation of perhydroxyl ions.
4. When the pH reaches 11.8, all of the hydrogen peroxide is converted to perhydroxyl ions and bleaching is out of control.

3.7 Causes of weight loss
The cotton fibre is a single plant cell. Its cross-section is oval, compared with the normal hexagonal plant cell. It is built up in four parts- Lumen, secondary wall, primary wall and cuticle (inside to outside). The cuticle is the very outside or skin of the cotton fibre. The protective cuticle is made of wax compounds, mineral matters, pectins, fatty acids, high molecular weight alcohol and their esters. The primary cell wall, which mainly consist of protein, pectic substances and glucans, is about 2.5% of fibre weight and 200 nm thick. It has a crystallinity index of about 30%.The secondary cell wall is built up of cellulose layers – it adds about 91.5% of fibre and has a crystallinity index of 70%. The Scouring & Bleaching Process, purifying the α-glucose by removing much of the cuticle layer, protein and pectic substance which causes weight loss occur. The standard range of weight loss is 4 – 8% of materials.

3.8 Causes of Strength loss
Cotton macromolecule contains three functional groups that’s are susceptible to oxidizing agents. For bleaching processes, raw cotton fibres are treated with oxidizing agents like H2O2. These reagents lead to chemically attack (oxidized) initially on the functional groups and then progressively cause the chain scission, lowering the DP and almost invariably, reducing the tensile strength of the fibres. Products of oxidation of cellulose are usually called ‘oxycellulose’, which differs from each other to a great extent in their physical as well as chemical properties.

3.9 Process description

Selection of Raw Materials

• Fabric Type = Single Jersey
• Yarn count = 24S (carded),
• GSM = 180

Selection of process parameter for scouring & bleaching:
Raw material treat with different concentration of H₂O₂ & NaOH

1. Hydrogen peroxide (H₂O₂)= 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6  g/l
2. Sodium Hydroxide (NaOH)= 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6  g/l
3. Stabilizer= 1  g/l  (2-3.5 g/l H2O2) and 1.5 g/l  (4-6 g/l H₂O₂)
4. Detergent= 1  g/l
5. Sequestering Agent (EDTA)= 1 g/l
6. Anticreasing agent= 1 g/l
7. Temperature= 105⁰C
8. Time= 30 minutes
9. Materials Liquor Ratio= 1: 20
10. Sample weight= 5 gm

3.10 Process Sequence of Scouring & Bleaching:

3.11 Used of Machine for this process

Table 3.1: Specification of machine-used.

CHAPTER 4
EFFICIENCY OF SCOURING & BLEACHING

4.1 Estimation of scouring effect
The main changes which occur in cotton goods during scouring process are loss in weight (about 4-10%), loss in length due to shrinkage during boiling treatment, alternation in goods count affected by both losses and changes in tensile strength. However, the most important characteristic of scoured fabric is increased wettability, which is necessary for subsequent processing. The scouring effect can be estimated by the following tests-

1. Determination of weight loss.
2. Absorbency test

• Immersion test
• Drop test
• Column test

1. Determination of weight loss:
The loss in weight of goods during scouring shows that a considerable amount of impurities are removed. The weight of unscoured and scoured samples was taken separately at the same moisture content and then the weight loss is measured in percentage.

………………………………Weight (before scouring – after scouring)
Weight loss  = ………………………………………………………………………………………..  × 100 %
……………………………………………….Before scouring

Standard range of weight loss = 4 – 8 %

2. Absorbency test:

a. Immersion test: Sample of 1cm × 1cm is cut and it is left on water surface. With the help of stop watch, the time of the sample for immersing is recorded. The standard time is 5 second.

b. Drop test: In a pipette a solution of 0.1% direct red or Congo red is taken and droplet of solution put on the different places of the fabric. Then the absorption and area of colored drop is observed.

c. Column test: Here fabric sample of 18 cm long and 5 cm width is taken. In a beaker 0.1% direct solution is taken. After that a mark is drawn at 1cm above from the sample bottom. Now the sample is hung from a wood stick supported by immersing that 1cm portion of fabric in the dye liquor. Then measure the point up to which the colored solution is absorbed straight above way by the sample in 5 minutes time. Standard range 30 – 50 mm.

4.2 Estimation of Bleaching Effect
Bleaching effect can be estimated in two ways-

1. Measurement of reflectance.
2. Measurement of whiteness.

1. Measurement of reflectance
When a cotton fabric is bleached, its light reflecting capacity increases. The reflectance of a bleached fabric is measured by leucometer. It is a light measuring meter which is able to measure total reflectance but does not give reflectance curve. Standard range of reflectance 85% and up to 90%. But in practical above 78% is allow.

A range of 90-94% reflectance is also possible in a high temperature treatment in a kier (120oC). In high temperature bleaching, we can get high range of reflectance. But high temperature bleaching is risky and reduce strength. Reflectance is also measured by portable reflectometer and whiteness meter. 100 is perfect white and 0 is perfect black.

2. Measurement of whiteness
 Whiteness of fabric can be of three types:

• Pure white
• Optimum white
• Permanent white.

For a bleached fabric, permanent white effect is desired.

In hypochlorite bleaching, chloramines produce which destroys the whiteness of cotton and forms yellowish of cotton. To contain the permanency of whiteness, anti chloro treatment is used. The reflectance of a bleached fabric is observed for 7 days. If every day we get more or less fixed values of reflectance, we can comment that permanent white effect has been obtained.

4.5 Estimation of strength loss
Estimation of bleaching damage can be expressed two ways: –

1. Physical test.
2. Chemical test.

• Fluidity test.
• Copper number test.
• Methylene blue test.

4.6 Physical test
The main principal of physical test for bleaching damage is based on strength loss of fabric sample because of bleaching. For this, the strength of fabric sample is measured before and after bleaching by any fabric strength tester. Naturally due to removal of oil, wax, impurities(in scouring) and coloring matters(bleaching), the bleached fabric losses some part of its strength.

In case half bleached fabric, acceptable strength loss up to 4% and in case full bleached fabric, the acceptable strength loss up to 8%.

4.7 Graphical presentation of weight loss Vs Concentration of NaOH.

Comments: From the above graphical curve we see that weight loss of cotton is increasing with the increasing of concentration of Sodium Hydroxide. In this case absorbency is also increasing. But we select the point which is economically acceptable because in this point weight loss is minimum and absorbency is in acceptable range.

4.8 Graphical presentation of strength loss Vs Concentration of H2O2

Comments: From the above graphical curve we see that strength loss of cotton is increasing with the increasing of concentration of Hydrohen peroxide. In this case whiteness value (reflectance %) is also increasing. But we select the point which is economically acceptable because in this point strength loss is minimum and whiteness value (reflectance %)  is in acceptable range.

4.9 Graphical presentation of whiteness value Vs Concentration of H2O2

Comments: From the above graphical curve we see that whiteness value (reflectance %) of cotton is increasing with the increasing of concentration of Hydrohen peroxide. Here we select the point which is economically acceptable because in this point strength loss is minimum and whiteness value (reflectance %)  is in acceptable range.

CHAPTER 5
CONCLUSION

5.1 Result & discussion
Our ‘Project and Thesis’ work determines the strength and weight loss of cotton goods due to single bath scouring & bleaching process on different samples in different concentration of Hydrogen peroxide and Sodium hydroxide which increased the production with reduction in labor cost and reduced treatment time, lower consumption of water, steam and electricity. From our Thesis and Project of the scouring & bleaching process, the standard recipe was found which indicates the following results:

1. More economical process.
2. Minimum Strength loss.
3. Minimum weight loss.
4. Good scouring & bleaching effect is obtained by measuring the-

• Immersion test
• Drop test
• Measurement of reflectance by datacolor.

Table 5.1: Standard recipe of scouring & bleaching

Recipe	Strength loss (%)	Weight loss (%)	Whiteness value (%)	Immersion test	Drop test
H2O2 = 2.5 g/l NaOH = 2.5 g/l Stabilizer = 1g/l Detergent = 1g/l Seq. agent = 1g/l Anticreasing = 1g/l	5.24	4.4	79.14	Within 1 second

5.2 Conclusion
In conclusion it is said that the “Project and Thesis” programme helps to determine the strength and weight loss of cotton goods due to single bath scouring and bleaching process in various concentration of H₂O₂ and NaOH. From the experimental data, it can easily be taken the decision that if this standard recipe is applied in scouring and bleaching the following findings are achieved.

1. Increased production with reduction in labor cost
2. Reduced of treatment time
3. Lower consumption of water
4. Lower consumption steam and electricity
5. More economical process.
6. Minimum Strength loss.
7. Minimum weight loss.
8. Good scouring & bleaching effect.

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APPENDIX A

Experimental data

APPENDIX B

Laboratory result of whiteness value of different sample

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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