Effects of bleaching on cotton fabric

Department of Textile Engineering

PROJECT (THESIS) REPORT

Course Code: TE-407

Project Report On:

EFFECT OF BLEACHING PARAMETERS ON BURSTING STRENGTH AND WHITENESS OF COTTON KNITTED FABRIC

Submitted by:

Kazi Sazed Salman ID: 111-23-130

Md. Hasan Mojumdar ID: 111-23-129

Md. Asraful Haque ID: 111-23-132

Supervised by

Abu Naser Md. Ahsanul Haque

Senior Lecturer, Depertment of Textile Engineering, DIU

Daffodil International University 102, Shukrabad, Mirpur road,

Dhaka, Bangladesh December 2014

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DECLARATION

We hereby declare that, this project has been done by us under the supervision of Abu Naser Md. Ahsanul Haque, Senior Lecturer of Department of Textile Engineering, Daffodil International University. We also declare that neither this project nor any part of this project has been submitted elsewhere for award of any degree.

Supervised by: Submitted by: ____________________________ Abu Naser Md. Ahsanul Haque Senior Lecturer, Department of Textile Engineering Daffodil International University

___________________________Kazi Sazed Salman

Student ID: 111-23-130Department of Textile Engineering

Daffodil International University

___________________________Md. Hasan MojumdarStudent ID: 111-23-129

Department of Textile EngineeringDaffodil International University

___________________________Md. Asraful Haque

Student ID: 111-23-132Department of Textile Engineering

Daffodil International University

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ACKNOWLEDGEMENT

At first all gratefulness goes to the Almighty ALLAH to give us the strength and ability to complete the Thesis (project) and this report.

We are grateful to Dr. Md. Mahbubul Haque, Head of the department of Textile Engineering for giving us the opportunity to accomplish the project work.

We would like to express sincerest gratitude to our respected teacher Abu Naser Md. Ahsanul Haque, Senior Lecturer of Department of Textile Engineering, Daffodil International University for his valuable suggestion, encouragement constructive criticism and for providing gall necessary supports to complete our thesis.

We are also expressing special thanks to Mr. Sumon Chandra Dey, Textile Engineer of Impress Newtex Composite Textiles Ltd. for his guidance & advice while doing the practical works for this project. We would like to be thankful to Impress Newtex Composite Textiles Ltd. for their helpful support to this work. We got the most excellent opportunity and consider it a rare fortune to work under them.

Last but not least, thanks go to our precious family for their never ending love and inspire at every stage of our life. Without their continuous support we realize that we would not be a person what we are right now.

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ABSTRACT

This study comprises the effect of different bleaching parameters of Hydrogen peroxide (H2O2) bleach on scoured single jersey fabrics. There were 7 samples in total with the weight of 12.5 grams each which were bleached using different parameters of bleaching.

One of the samples was bleached by the general factory sample bleaching parameter. Other six samples were bleached by changing the concentration of bleaching agent, time & temperature differently.

After bleaching we tested the whiteness and bursting strength of the samples. The sample bleached with more peroxide (5.5cc) gives the best whitening result and the sample bleached for less time (20min) gives lowest result of all. During bursting strength testing the sample the sample bleached in less temperature (88oC) gives the best strength result and the sample bleached in high temperature (108oC) shows the lowest strength result.

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INDEX

Chapter Topic Page no

Declaration i

Acknowledgement ii

Abstract iii

Index iv-vi

Chapter-1 INTRODUCTION 1-7

1.1 Introduction 2

1.2 History of knitting 2

1.3 Fiber type 3

1.4 Fiber Properties 3

1.5 Yarn twist 3

1.6 Fabric structure 3

1.7.1 pretreatment 4

1.7.2 Objective of pretreatment 4

1.7.3 Steps in pretreatment 4

1.8.1 Scouring 4

1.8.2 Objects of scouring 5

1.9.1 Bleaching 5

1.9.2 The aim of bleaching 5

1.9.3 Bleaching agent 6

1.10 Whiteness 6

1.11 Bursting strength 6

1.12 Objects of this project 7

Chapter-2 LITERATURE REVIEW 8-29

2.1 Fiber properties 9

2.2 Fibers identification 9

2.3 Classification of yarn 9

2.4 Common yarns 11

2.5 Properties of yarn 11

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2.6 Knitting 12

2.7.1 Weft knit structure 13

2.7.2 Warp knit structure 13

2.8 Raw materials 13

2.9 Cam 13

2.10 Knitting Process flow chart 14

2.11 Yarn quality requirement 14

2.12 Effects of knitting parameters 14

2.13 Fabric scouring 15

2.14 Scouring process depends on 15

2.15 Alkaline Enzyme scouring 16

2.16 How to use scouring 16

2.17 Advantages of scouring 17

2.18 Disadvantages of scouring 17

2.19 Scouring effect 17

2.20 Assessment of scouring 17

2.21 Bleaching agent 17

2.22 Types of bleaching agent 17

2.23 Bleaching of cotton with peroxide 17

2.24 Factors of peroxide bleaching 19

2.25 Advantages 20

2.26 Wool bleaching with peroxide 20

2.27 Silk bleaching with peroxide 20

2.28 Synthetic bleaching with peroxide 21

2.29 Bursting strength 21

2.30 Diaphragm bursting test 22

2.31 Reported measurements 23

2.32 Color vision 24

2.33 Physiology of color perspiration 24

2.34 Cone cell of human eye 24

2.35 Theory of color vision 25

2.36 Trichromatic theory 25

2,37 Opponent-process theory 26

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2.38 Spectrophotometer 27

2.39 Datacolor-650 27

2.40 Whiteness & yellowness 28

Chapter-3 MATERIALS & METHODS 30-41

3.1 Materials and machines used 31

3.2 Fabric structure and type 33

3.3 Chemicals used 34

3.4 Methods of working 34

3.5 Scouring procedure 35

3.6 Standard recipe of scouring 35

3.7 Process of scouring 36

3.8 Bleaching procedure 36

3.9 Process curve of bleaching 38

3.10 Spectrophotometer working procedure 38

3.11 Working steps 38

3.12 Results from spectrophotometer 39

3.13 BST working procedure 40

3.14 BST test results 41

Chapter-4 RESULTS AND DISCUSSIONS 42-45

4.1 Effect of H2O2 on strength 43

4.2 Effect of H2O2 on whiteness 43

4.3 Effect of Temperature on strength 44

4.4 Effect of Temperature on whiteness 44

4.5 Effect of Time on strength 45

4.6 Effect of Time on whiteness 45

Chapter-5 CONCLUSION 46-47

5.1 Conclusion 47

REFERENCES 48-50

© Daffodil Int. University

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CHAPTER ONE

INTRODUCTION


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1.1 Introduction

Knitting is a method by which thread or yarn may be turned into cloth or other fine crafts. Knitted fabric consists of consecutive loops, called stitches. As each row progresses, a new loops pulled through an existing loop. The active stitches are held on a needle until another loop can be passed through them. This process eventually results in a final product, often a garment.

Knitting is an old method of weaving cloth in which thread or yarn are used to make items of clothing like sweaters and shawls etc. To knit, one generally uses a knitting needle and forms a series of loops with some thread or yarn through which more yarn is pulled using another knitting needle. This process is repeated either in round formations or in rows. In modern times, there are also knitting machines available which can be used to create the same effects with less effort and in less time. There are two main kinds of knitting stitches called knit and purl which are very similar in many ways. However, while a knit stitch involves inserting the needle in front of the loop, a purl stitch involves inserting it behind the loop.

Other knitting stitches are usually variations of combinations of knits and purls. For instance, when knits and purls are used back and forth to form rows, this formation is called a garter stitch.

The jersey stitch – which is another formation of rows of pearls and knits – is the knitting stitch which is most often used in commercial garments? There are many patterns which can be thus created using different kinds of stitches.

1.2 History of Knitting

Knitting is older than written history. No one knows exactly when people began to knit, but we do know that as far back as A.D. 200, knitting was an advanced and accomplished art. The people of Scotland are believed to have been the first to knit with wool. A knitted fabric stretches more than a woven fabric, and it snaps back to its original size after it is stretched. For example, a woolen knitted fabric can stretch as much as 30 percent and spring back to its original size. Long ago people found out how much better a knitted fabric was than a woven fabric for clothing that needs to stretch and then spring back to fit snugly. Sweaters, mittens, and stockings are examples of this kind of clothing. Knitting is probably more popular today than it has been at any other time in history. With the hundreds of different kinds and textures of yarns available, plus the constant development of new synthetic fibers and various combinations of them, there is no end to the beautiful and useful things you can learn to make.


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1.3 Fiber type

It is thought that the ability of a fiber to withstand repeated distortion is the key to its abrasion resistance. Therefore high elongation, elastic recovery and work of rupture are considered to be more important factors for a good degree of abrasion resistance in a fiber than is a high strength. Nylon is generally considered to have the best abrasion resistance. Polyester and polypropylene are also considered to have good abrasion resistance. Blending either nylon or polyester with wool and cotton is found to increase their abrasion resistance at the expense of other properties.

Acrylic and mod acrylic have a lower resistance than these fibers while wool, cotton and high wet modulus viscose have a moderate abrasion resistance. Viscose and acetates are found to have the lowest degree of resistance to abrasion. However, synthetic fibers are produced in many different versions so that the abrasion resistance of a particular variant may not conform to the general ranking of fibers.

1.4 Fiber properties

One of the results of abrasion is the gradual removal of fibers from the yarns. Therefore factors that affect the cohesion of yarns will influence their abrasion resistance. Longer fibers incorporated into a fabric confer better abrasion resistance than short fibers because they are harder to remove from the yarn. For the same reason filament yarns are more abrasion resistant than staple yarns made from the same fiber. Increasing fiber diameter up to a limit improves abrasion resistance. Above the limit the increasing strains encountered in bending counteract any further advantage and also a decrease in the number of fibers in the cross-section lowers the fiber cohesion.

1.5 Yarn twist

There has been found to be an optimum amount of twist in a yarn to give the best abrasion resistance. At low-twist factors fibers can easily be removed from the yarn so that it is gradually reduced in diameter. At high twist levels the fibers are held more tightly but the yarn is stiffer so it is unable to flatten or distort under pressure when being abraded. It is this ability to distort that enables the yarn to resist abrasion. Abrasion resistance is also reported to increase with increasing linear density at constant fabric mass per unit area.

1.6 Fabric structure

The crimp of the yarns in the fabric affects whether the warp or the weft is abraded the most. Fabrics with the crimp evenly distributed between warp and weft give the best wear because the damage is spread evenly between them. If one set of yarns is predominantly on the surface then this set will wear most; this effect can be used to protect the load-bearing yarns


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preferentially. One set of yarns can also be protected by using floats in the other set such as in a sateen or twill weave. The relative mobility of the floats helps to absorb the stress. There is an optimum value for fabric set for best abrasion resistance. The more threads per centimeter there are in a fabric, the less force each individual thread has to take. However, as the threads become jammed together they are then unable to deflect under load and thus absorb the distortion. Again different types of fibers can have different type of structure depending of their origins and other properties and purpose of uses in textile or other places.

1.7.1 Pretreatments:

Natural fibers and synthetic fibers contain primary impurities that are contained naturally, and secondary impurities that are added during spinning, knitting and weaving processes. Textile pretreatment is the series of cleaning operations. All impurities which cause adverse effect during dyeing and printing is removed in pretreatment process.

Pretreatment processes include de-sizing, scouring, and bleaching which make subsequent dyeing and softening processes easy. Uneven de-sizing, scouring, and bleaching in the pretreatment processes might cause drastic deterioration in the qualities of processed products, such as uneven dyeing and decrease in fastness.

1.7.2 Objective of Pretreatment:

To convert fabric from hydrophobic to hydrophilic state. To remove dust, dirt etc. from the fabric. To remove oil & wax from the fiber. To achieve the degree of desire whiteness.

1.7.3 Steps in Pretreatment Process of Cotton and Natural Fibers:

1. Singeing 2. De-sizing, 3. Scouring, 4. Mercerization 5. Bleaching.

1.8.1 Scouring

The term ‘scouring’ applies to the removal of impurities such as oils, was, gums, soluble impurities and sold dirt commonly found in textile material and produce a hydrophilic and clean cloth.


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1.8.2 Objectives of Scouring:

To remove natural as well as added impurities of essentially hydrophobic character as completely as possible

To increase absorbency of textile material To leave the fabric in a highly hydrophilic condition without undergoing chemical or

physical damage significantly.

1.9.1 Bleaching

Bleaching is chemical treatment employed for the removal of natural coloring matter from the substrate. The source of natural color is organic compounds with conjugated double bonds , by doing chemical bleaching the discoloration takes place by the breaking the chromophore , most likely destroying the one or more double bonds with in this conjugated system. The material appears whiter after the bleaching. Natural fibers, i.e. cotton, wool, linen etc. are off-white in color due to color bodies present in the fiber. The degree of off-whiteness varies from batch-to-batch. Bleaching therefore can be defined as the destruction of these color bodies. White is also an important market color so the whitest white has commercial value. Yellow is a component of derived shades. For example, when yellow is mixed with blue, the shade turns green. A consistent white base fabric has real value when dyeing light to medium shades because it is much easier to reproduce shade matches on a consistent white background than on one that varies in amount of yellow. The purpose of bleaching is to remove colored impurities from the fiber and increase the whiteness level of fabric.

1.9.2 The aim of bleaching can be described as following:

Removal of colored impurities. Removal of the seed coats. Minimum tendering of fiber. Technically reliable & simple mode of operation. Low chemical & energy consumption. Increasing the degree of whiteness. Making good appearance of white cloth.


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1.9.3 Bleaching Agent

A bleaching agent is a substance that can whiten or decolorize other substances. Bleaching agents essentially destroy chromophores (thereby removing the color), via the oxidation or reduction of these absorbing groups. Thus, bleaches can be classified as either oxidizing agents or reducing agents.

Type of Bleaching Agents

1. Oxidative Bleaching Agents 2. Reductive Bleaching Agents 3. Enzymatic Bleaching Agents

1.10 Whiteness

Whiteness and blackness are experiences of perceptions by humans. Similar to all perceptual experiences they are subjective and depend strongly on illumination, surround and a number of other perceptual phenomena.

In the textile, paper and plastic industries, white materials are commonly employed for many aesthetic and technical applications. Due to their high lightness and achromatic nature white materials are also very important to provide the necessary base for dyeing, printing and finishing. Most textile materials, however, are polymers containing natural colorants which affect their appearance. Two common approaches are used to improve the whiteness of textile materials: chemical bleaching and fluorescent whitening.

1.11 Bursting Strength

Tensile strength tests are generally used for woven fabrics where there are definite warp and weft directions in which the strength can be measured. However, certain fabrics such as knitted materials, lace or non-woven do not have such distinct directions where the strength is at a maximum. Bursting strength is an alternative method of measuring strength in which the material is stressed in all directions at the same time and is therefore more suitable for such materials. There are also fabrics which are simultaneously stressed in all directions during service, such as parachute fabrics, filters, sacks and nets, where it may be important to stress them in a realistic manner. A fabric is more likely to fail by bursting in service than it is to break by a straight tensile fracture as this is the type of stress that is present at the elbows and knees of clothing.

When a fabric fails during a bursting strength test it does so across the direction which has the lowest breaking extension. This is because when stressed in this way all the directions in the fabric undergo the same extension so that the fabric direction with the lowest extension at


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break is the one that will fail first. This is not necessarily the direction with the lowest strength.

1.12 Objects of this project

Learn to preparation of samples in dyeing lab Learn to prepare liquor according to recipe Learn to use sample dyeing machine To bleach different samples with different parameters Determine the effects of bleaching on S/J fabric Learn to use spectrophotometer for whiteness testing Learn to use Bursting Strength Tester for bursting strength testing of the fabric To get some specific ideas on changing of parameters during bleaching.


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CHAPTER TWO

LITERATURE REVIEW


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2.1 Fibers Properties

Mechanical Process: This is the response to applied forces and recovery like-

Abrasion resistance

Flexibility

Stress

Absorption properties: This is a measure of the quantity of water vapor or liquid water orabsorbed by fabric.

Water vapor absorption

Water absorption

Thermal properties: The behavior of textile in the presence of heat or when exposed to a flame.

Heat resistance capacity or

Specific heat

2.2 Fibers Identification

Test Wool Acrylic Cotton Burning test/ Flammable test

Non-flammable, Hair burn smell

Flammable Petroleum flame

Flammable Paper burn smell

Chemical test (acid & alkalis) wet finish

Acid (+) Alkalis (-)

Acid (+) Alkalis (+)

Acid (-) Alkalis (+)

Microscopic test (Cell structure of yarn)

2.3 Classification of Textile yarn:

Spun yarn Filament yarn


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Classification of yarn

a) Mono filament:

b) Multi filament:

c) Staple:

d) Two ply yarn:

e) Multi ply:

f) Cords:

g) Cable:

h) Loop yarn:


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i) Spun yarn: Spun yarn are made by twisting together of fibers. j) Filament yarn: Filament yarns are made by the assembly of continuous filament. k) Mono-filament: Consists of only a single continuous. l) Multi filament: Made from multiple filaments. m) Complex/Novelty/Fancy: This has special effects on its own appearance. n) Cords: cords are made by twisted plied yarn. o) Cables: Cables are produced by plying cords. p) Slub yarns: Contains partially bulky/fluffy region q) Loop yarns: This yarn requires a base yarn (core yarn) around which the fancy or

effect yarn is wrapped.

2.4 Common yarn used in the fully fashioned knitwear

Basic type:

1. 100% Acrylic 2. Acrylic mélange 3. Blended Acrylic 4. 100% wool 5. Mixed wool 6. 100% cotton 7. Blended cotton

Fancy type:

1. Chenille 2. Angora tweed 3. Nep/slub yarn 4. Loop yarn (Popcorn, Boucle) 5. Mohair 6. Tape yarn 7. Kashmiri like etc.

2.5 Properties of Yarn

Wool:

Bulky/fluffy appearance Poor strength Good resistance to acid Poor resistance to sun-light and insects End use for sweater and suiting Mainly fibers collects from sheep fleece


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Garment become heavier and also more weighted Garment appearance is not shine More expensive product Warmth feelings

Acrylic:

Sources are Acrylonitrille – Ethylene or Acetylene Bulky/fluffy appearance like wool More shiny than wool Good strength Light in weight Good resistance to sun-light and insects Wet finish & dry finish applied End uses heavy knitwear product Less expensive than wool Warmth feeling

Cotton yarn:

Smooth surface Cool feeling (suitable for hot) More expensive Moisture absorbency high

2.6 knitting

Knitting: It is a process of fabric manufacture by converting yarn into loop form and then these loops interlock/intermesh/interloped together which form a structure is called knitting or knitted structure.

Wales: vertical column of knitted fabric. Course: horizontal column of knitted fabric. Loop: bending of yarn is called loop. WPI = Wales per Inch CPI = Course per Inch


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2.7.1 Weft Knit Stitches It is the most common types used by the manufacturer in produce textile knitted products such as Shirts and Socks. In terms of color patterning, weft knit may be knitted with multiple yarns to produce interesting pattern design. There are few types or technique to produce weft knit structure, Single jersey, Purl, and Rib are some of the technique that been used to produce weft knitted structure 2.7.2 Warp Knit Stitches Warp knitted is produced from a set of warp yarn. It is parallel knitted to each other down the length of the fabric. Since knitted fabric may have hundreds of wales, warp knitted is typically done by machine. 2.8. Raw material: Raw material is a unique substance in any production oriented textile industry. It plays a vital role in continuous production and for high quality fabric. Types of raw material:

1. Yarn 2. Fabric 3. Dye stuff 4. Chemical and auxiliaries

2.9 Cam: Cams are the devices which convert the rotary machine drive into a suitable reciprocating action for the needles and other elements. The cams are carefully profiled to produce precisely-timed movement and dwell periods and are of two types, engineering cams and knitting cams. There are 3 types of cams: Knit cam, Tuck Cam, Miss Cam


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2.10 Process Flow Chart of Knitting:

Yarn in Package Form

↓ Place the yarn cone in the creel

↓ Feeding the yarn in the feeder via trip tape positive feeding arrangement and tension device

↓ Knitting

↓ Withdraw the rolled fabric and weighting

↓ Inspection

↓ Numbering

2.11 Yarn Quality Requirements:

Yarn quality parameters such as

Breaking strength,

Elongation,

Twist,

Moisture contents,

Yarn winding,

Yarn lubrication

Yarn hairiness

Quality raw material feed to knitting

2.12 Effects of knitting Parameter in fabric production:

o Stitch Length 1. GSM decrease with the increase of stitch length 2. If stitch length increase then fabric width increase and WPI decrease. 3. For deep shade stitch length should be higher and vice-versa.

o GSM 1. Gray GSM should be less than finish GSM 2. GSM increase with increase of stitch length and it is adjusted by VDQ pulley 3. Enzyme Level 4. Color 5. If shrinkage increase then GSM increase.


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6. GSM control according to buyer requirement.

o Count 1. If count increase then fabric width increase 2. GSM depends on yarn count

o Gauge 1. For finer gauge finer count should be use 2. If machine gauge increase then fabric width decrease 3. If gauge decrease then stitch length increase.

o Feeder 1. Production increase with increase of feeder no. 2. Feeder is settled in case of stripe fabric.

o Design 1. Cam setting 2. Set of needle 3. Size of loop shape.

2.13 Scouring of fabric

Yarns and fabrics may be dirty, contain natural waxes or oils, or have been treated with size or lubricants used in spinning, weaving or knitting. These can all interfere with dyeing, often leading to non-level results. Scouring is a large topic, and the process used depends on the fiber type and its condition. True scouring of grease cellulosic fabrics is typically done, after desizing, at the boil or at higher temperature in pressure vessels, with as much as 10 grams sodium hydroxide per litter of water, plus surfactants, and the process may last for several hours. Commercial scouring of wool may use solvents, similar to dry cleaning, as part of the process. White fabrics sold at retail have normally be scoured at the mill; “natural” fabrics usually have not (some “natural” fabrics have been scoured but not bleached).

Art dyeing literature often refers to what amounts to laundering as scouring. This is inadequate for grease fabrics, but often quite acceptable for white goods. A long machine wash with the hottest water possible, about a gram of soda ash per litter of water (about a teaspoon per gallon) and some (preferably optical brightener free) detergent, followed by two rinses is usually acceptable. Sodium hexametaphosphate may be helpful if the water is hard. Woven white cottons often contain starch that will not be removed by such a limited process.

2.14 Scouring process depends on:

The type of cotton


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The color of cotton The cleanliness of cotton The twist and count of the yarn The construction of the fabric.

2.15 Alkaline Enzyme Scouring of Cotton Textiles

The invention relates to a process for treatment of cellulosic material, as for example, knitted or woven cotton fabric, comprising the steps of preparing an aqueous enzyme solution comprising pectinase, treating the cellulosic material with an effective amount of the aqueous enzyme solution under alkaline scouring conditions; e.g., pH of 9 or above and a temperature of 50° C. or above, in a low calcium or calcium-free environment, yielding a modification of the cellulosic material such that exhibits an enhanced respond to a subsequent chemical treatment. Traditionally, cotton scouring has required the use of harsh alkaline chemicals (caustic), extreme temperatures and large volumes of water. Expenses include not only the cost of the caustic and energy, but also the cost of treating waste water to remove residual caustic and by-products. Today, textile producers have a new, effective alternative to chemical scouring with the advent of the Cottonase enzyme. This novel enzyme not only cleans better than chemical scouring, but also greatly reduces the need for extensive waste water treatment and energy consumption. The Cottonase enzyme is a versatile, economically viable and environmentally friendly alternative to chemical scouring in cotton preparation.

2.16 How to Scouring Textile Fabric:

Simply wash the fabric; this includes PFD fabric, in the washing machine in hot water with Soda Ash. Do not add any fabric softeners to the wash.

Using an large enamel or stainless steel pot, fill the pot at least half full and place one ounce of soda ash into the pot per pound of cotton or linen fabric/fiber.

Place fabric into water; swish it around using a stainless steel spoon. Bring water to a boil. Adjust heat to a low boil/hard simmer and allow to boil for two hours. stir the fabric

every 15 minutes or so to make sure that the fabric is being adequately scoured After two hours remove from heat source, allow fabric to cool down until the fabric is

at room temperature. Remove the fabric from the water and rinse.


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2.17 Advantages of scouring:

The process is a continuous process. So consumes less time. The process is economical. This is the most popular process.

2.18 Disadvantages of scouring:

The result of scouring is not good as compared with kier boiler. The process is not hydrophilic as kier boiler. Damages some fiber strength & other properties.

2.19 Estimation or Scouring Effect:

The scouring effect can be estimated by carrying out one of the following tests-

Measurement of weight loss.

Test of (absorbency) Immersion test.

Drop test.

Wicking or column test.

2.20 Assessment of Scouring:

In a pipette a solution of0.1% direct red or Congo red is taken and droplet of solution put on the different places of the fabric. Then the absorption time of the fabric is observed. The standard time for the absorption of one drop of solution is 0.5-0.8 sec up to 1 sec.

2.21 Bleaching Agent

A bleaching agent is a substance that can whiten or decolorize other substances. Bleaching agents essentially destroy chromophores (thereby removing the color), via the oxidation or reduction of these absorbing groups. Thus, bleaches can be classified as either oxidizing agents or reducing agents.

2.22 Type of Bleaching Agents

Oxidative Bleaching Agents Reductive Bleaching Agents Enzymatic Bleaching Agents

2.23 Bleaching of Cotton with Hydrogen Peroxide

Hydrogen peroxide is virtually the only bleaching agent available for protein fibers and it is also used very extensively for the cellulosic fibers. Hydrogen peroxide is a colorless liquid


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soluble in water in all proportions. It is reasonably stable when the pH is below 7, but tends to become unstable as the alkalinity increases. Commercial hydrogen peroxide, therefore, is made slightly acid so that it will not lose strength during storage. Solutions of hydrogen peroxide of more than 20 volumes cause intense irritation when they come into contact with skin and should be washed away immediately.

Cotton is usually bleached in 1-volume liquor at the boil. The most important factor in bleaching is to achieve the right degree of stability in the bleach liquor. If the pH were too low no per hydroxyl ions are set free and bleaching does not take place; when the liquor is too unstable the whole of the oxygen is liberated and escapes into the atmosphere before it has had time to act upon the cotton.

The bleaching liquor must be made alkaline, otherwise it would be too stable, but it is virtually impossible to adjust to the optimum pH with alkali alone and there is a marked tendency for the liquor to is too unstable, however carefully it has made alkaline. It is, therefore, necessary to add a stabilizer, and of all the substances, which have been, tried sodium silicate is the most effective.

Hydrogen peroxide is a stable chemical under acidic conditions and needs the addition of an alkali for activating it. Above pH 10, it is extremely unstable when it gets decomposed under water and oxygen.

2H2O2 = 2H2O + O2

This liberated oxygen, however, has no bleaching action and the catalysts are therefore a cause of loss of bleaching power. In fact, hydrogen peroxide is used bleaching under alkaline conditions (pH 10) after stabilizing at this pH by adding sodium silicate, borax, phosphate etc. Generally bleaching is done at 80ºC to 85ºC temperature.

Hydrogen peroxide solution at any concentration can be stable or unstable depending upon the several factors listed below.

pH: Stable in acidic solution and unstable in alkaline baths. Temperature: As temperature increases the solution becomes increasingly unstable. Buffers: Silicates, Phosphates, Borax, Proteins and others tend to stabilize peroxide. Metals:Ca and Mg in the presence of silicates tend to stabilize baths; (b) other metals

as Cu, Fu, etc. tends to stabilize bleach solutions. Hard water: Depending upon the hardness of water and the metals making it hard,

peroxide is unsterilized.

It was at one time believed that the bleaching action of hydrogen peroxide was due to the liberation of nascent oxygen but this explanation is no longer tenable. It is known that under certain conditions, particularly with regard to pH, hydrogen peroxide will liberate hydrogen and per hydroxyl ions in the following manner:

H2O2 = H+ + HO2-


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Hydrogen peroxide (H2O2) is a universal bleaching agent and is used extensively for the bleaching of cotton materials. The advantages in its use are:

It can be employed for bleaching fibers like wool, silk and jute also. It requires less manipulation of fabric and hence less labor. The loss in weight in bleaching is less than that with hypochlorite bleaching Less water is required with peroxide bleaching and there is no need for souring after

bleaching. Peroxide bleached goods are more absorbent than hypochlorite bleached goods. After – yellowing of white goods bleached with peroxide or less than with

hypochlorite bleached goods. Peroxide bleaching is safer in regard to chemical degradation and Continuous scouring and bleaching in one operation is possible by employing

peroxide.

2.24 Factors of Peroxide Bleaching:

Temperature

Cotton and Bast fibers are bleached at 80 - 95°C in bath processes, while blends of cotton and regenerated cellulose fibers are bleached at 75 - 80°C. The bleaching time is generally between 2 and 5 hours. In a pressurized high temperature (HT) apparatus cotton can also be bleached at temperatures of 110 - 130°C in only 1 to 2 hours.

Time

During the impregnation processes the temperature and as well the retention time varies widely. During a cold bleach process a dwell time of 18 to 24 hours is necessary. In the pad steam process under atmospheric pressure the bleaching time is generally between 1 to 3 hours. The above mentioned processes describe batch processes. Today a lot of continuously, intelligent finishing equipment exists in which the bleaching step is only one of some other treatments and the reaction time of the impregnated material in such steamer is only between 7 to 20 minutes.

pH

The pH value depends on the fibers to be bleached and pre-treatment.NaOH is used in case of H2O2 bleaching. This is used to bring the PH up to 9-10 because H2O2 become active at this PH or oxidation is start at this pH. For the bast fibers, such as linen, weaker alkaline or soda alkaline baths are used in order to avoid a cottonizing. Regenerated cellulose fibers are more sensitive. Therefore, they are only bleached in weak alkaline baths. Alkali sensitive animal fibers must be bleached in very weak alkaline solutions. Phosphates and ammonia are most widely used as alkalization source. With tetrasodium pyrophosphate simultaneously a stabilization of the bleaching liquor can be attained.


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Water Quality

Soft Water free of iron and copper impurities is recommended for peroxide bleach treatment.

Peroxide Stabilizers

High pH and temperature lead to the faster decomposition of peroxide bleaching liquor and degradation of cellulose. The role of the stabilizer is simply to control or regulate these effects the act as buffers, sequestrates and in special cases, enhancing performance of the surfactant used in the bleach bath.

For caustic alkaline bleach sodium silicate, organic stabilizers or the combination of both are suitable. In weak alkaline baths the addition of tetrasodium pyrophosphates can be used alone or together with an organic stabilizer.

2.25 Advantages of Peroxide Bleaching:

Among the oxidizing bleaching agents, only hydrogen peroxide provides a high bleaching effect at reasonable costs, especially if modern short-term bleaching processes are used with only a few minutes bleaching time.

Peroxide bleaching keeps the fiber quality intact. Cotton can be bleached with peroxide in a single stage. Other processes require two or

three bleaching stages, (desize with scour, scour with bleach etc.). No separate pretreatment is necessary because hot, alkaline bleaching has not only a

bleaching but also a cleaning effect; it therefore combines the advantages of an alkaline extraction with the bleaching treatment.

Animal fibers can only be bleached with peroxide to a high and stable degree of whiteness. Corrosion of stainless steel equipment does not occur during peroxide bleaching.

The spent peroxide baths still contain residuals of hydrogen peroxide which fever the degradation of the organic impurities in the effluent, and this helps to decrease the chemical oxygen demand (COD).

2.26 Bleaching of Wool with Hydrogen Peroxide

After scouring, wool may be bleached by immersion or pad and dry techniques, using alkaline or acid solutions. This peroxide bleaching on wool would give satisfactory result in whiteness level.

2.27 Bleaching of Silk with Hydrogen Peroxide

Prior to bleaching, silk is usually degummed. Hydrogen Peroxide addition assists this process and it is universally used as the bleaching agent for natural silk, usually in an alkaline solution.


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Industrial Scouring/Bleaching/Dyeing machine for knitted fabric

2.28 Bleaching of synthetic fibers Hydrogen Peroxide

When used alone, synthetic fibers do not normally require bleaching. However, blends of synthetic fibers with natural or regenerated fibers, e.g. cotton-polyester are frequently bleached. The most popular bleaching agent is Hydrogen Peroxide and it is used in both batch and continuous processes.

2.29 Bursting Strength

Tensile strength tests are generally used for woven fabrics where there are definite warp and weft directions in which the strength can be measured. However, certain fabrics such as knitted materials, lace or non-woven do not have such distinct directions where the strength is at a maximum. Bursting strength is an alternative method of measuring strength in which the material is stressed in all directions at the same time and is therefore more suitable for such materials. There are also fabrics which are simultaneously stressed in all directions during service, such as parachute fabrics, filters, sacks and nets, where it may be important to stress them in a realistic manner. A fabric is more likely to fail by bursting in service than it is to


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break by a straight tensile fracture as this is the type of stress that is present at the elbows and knees of clothing.

When a fabric fails during a bursting strength test it does so across the direction which has the lowest breaking extension. This is because when stressed in this way all the directions in the fabric undergo the same extension so that the fabric direction with the lowest extension at break is the one that will fail first. This is not necessarily the direction with the lowest strength.

2.30 Diaphragm Bursting Test

The British Standard describes a test in which the fabric to be tested is clamped over a rubber diaphragm by means of an annular clamping ring and an increasing fluid pressure is applied to the underside of the diaphragm until the specimen bursts. The operating fluid may be a liquid or a gas. Two sizes of specimen are in use, the area of the specimen under stress being either 30mm diameter or 113mm in diameter. The specimens with the larger diameter fail at lower pressures (approximately one-fifth of the 30mm diameter value). However, there is no direct comparison of the results obtained from the different sizes. The standard requires ten specimens to be tested.

Bursting Strength Testing method


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In the test the fabric sample is clamped over the rubber diaphragm and the pressure in the fluid increased at such a rate that the specimen bursts within 20 ± 3 s. The extension of the diaphragm is recorded and another test is carried out without a specimen present. The pressure to do this is noted and then deducted from the earlier reading.

Bursting Strength tester

2.31 The following measurements are reported:

Mean bursting strength kN/m2

Mean bursting distension mm

Liquid

Piston

Rubber

diaphragm

Specimen

Clamp

The US Standard is similar using an aperture of 1.22 ± 0.3 in (31 ± 0.75mm) the design of equipment being such that the pressure to inflate the diaphragm alone is obtained by removing the specimen after bursting. The test requires ten samples if the variability of the bursting strength is not known. The disadvantage of the diaphragm type bursting test is the limit to the extension that can be given to the sample owing to the fact that the rubber diaphragm has to stretch to the same amount. Knitted fabrics, for which the method is intended, often have a very high extension.


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2.32 Color vision

Color vision is the ability of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect, emit, or transmit. Colors can be measured and quantified in various ways; indeed, a human's perception of colors is a subjective process whereby the brain responds to the stimuli that are produced when incoming light reacts with the several types of Cone cells in the eye. In essence, different people see the same illuminated object or light source in different ways.

2.33 Physiology of color perception

Perception of color begins with specialized retinal cells containing pigments with different spectral sensitivities, known as cone cells. In humans, there are three types of cones sensitive to three different spectra, resulting in trichromatic color vision.

Each individual cone contains pigments composed of Opsinapoprotein, which is covalently linked to either 11-cis-hydroretinal or more rarely 11-cis-dehydroretinal. The cones are conventionally labeled according to the ordering of the wavelengths of the peaks of their spectral sensitivities: short (S), medium (M), and long (L) cone types. These three types do not correspond well to particular colors as we know them. Rather, the perception of color is achieved by a complex process that starts with the differential output of these cells in the retina and it will be finalized in the visual cortex and associative areas of the brain.

For example, while the L cones have been referred to simply as red receptors, micro spectrophotometry has shown that their peak sensitivity is in the greenish-yellow region of the spectrum. Similarly, the S- and M-cones do not directly correspond to blue and green, although they are often described as such. The RGB color model, therefore, is a convenient means for representing color, but is not directly based on the types of cones in the human eye.

The peak response of human cone cells varies, even among individuals with so-called normal color vision; in some non-human species this polymorphic variation is even greater, and it may well be adaptive.

2.34 Cone cells in the human eye

Cone type Name Range Peak wavelength

S β 400–500 nm 420–440 nm

M γ 450–630 nm 534–555 nm

L ρ 500–700 nm 564–580 nm


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2.35 Theories of Color Vision

There are two major theories that explain and guide research on color vision: the trichromatic theory also known as the Young-Helmholtz theory, and the opponent-process theory. These two theories are complementary and explain processes that operate at different levels of the visual system.

2.36 Trichromatic Theory

Evidence for the trichromatic theory comes from color matching and color mixing studies. Young and Helmholtz carried out experiments in which individuals adjusted the relative intensity of 1,2, or 3 light sources of different wavelengths so that the resulting mixture field matched an adjacent test field composed of a single wavelength. Individuals with normal color vision needed three different wavelengths (i.e., primaries) to match any other wavelength in the visible spectrum. This finding led to the hypothesis that normal color vision is based on the activity of three types of receptors, each with different peak sensitivity. Consistent with the trichromatic theory, we now know that the overall balance of activity in S (short wavelength), M (medium wavelength), and L (long wavelength) cones determines our perception of color as shown in the figure below.

Trichromatic Theory

Several color perception phenomenon cannot be explained by the trichromatic theory alone, however. For example, it cannot account for the complementary afterimages in which the extended inspection of one color will lead to the subsequent perception of its complementarycolor (see demonstration below). Complementary afterimages are better explained by the opponent-process theory.


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2.37 Opponent-Process Theory

Developed by WealdHerring (1920/1964), the opponent-process theory states that the cone photoreceptors are linked together to form three opposing color pairs: blue/yellow, red/green, and black/white. Activation of one member of the pair inhibits activity in the other. Consistent with this theory, no two members of a pair can be seen at the same location, which explains why we don't experience such colors as "bluish yellow" or "reddish green". This theory also helps to explain some types of color vision deficiency. For example, people with dichromatic deficiencies are able to match a test field using only two primaries. Depending on the deficiency they will confuse either red and green or blue and yellow.

The opponent-process theory explains how we see yellow though there is no yellow cone. It results from the excitatory and inhibitory connections between the three cone types. Specifically, the simultaneous stimulation of red (L cones) and green (M cones) is summed and in turn inhibits B+Y-, which results in the perception of yellow. However, when blue light is present, the S cone is activated, the B+Y- cell receives excitatory input and blue is perceived.

Opponent-Process Theory You can see the opponent relationships between red and green, and blue and yellow. View the four-color patch afterimage stimuli below for 30 seconds. Then remove the color stimuli by moving your cursor mouse over the image causing it to become a blank white field. When you fixate at the dot in the center of the field you should notice that the original colors are all reversed - where you saw red it is now green and vice versa. Likewise is for blue and yellow.

In fact, as you have seen, both theories are needed to explain what is known about color vision. The trichromatic theory explains color vision phenomena at the photoreceptor level; the opponent-process theory explains color vision phenomena that result from the way in which photoreceptors are interconnected neutrally.


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2.38 Spectrophotometer

Spectrophotometry uses photometers that can measure a light beam's intensity as a function of its color-wavelength known as spectrophotometers. Important features of spectrophotometers are spectral bandwidth, the range of colors it can transmit through the test sample, and the percentage of sample-transmission, and the logarithmic range of sample-absorption and sometimes a percentage of reflectance measurement.

A spectrophotometer is commonly used for the measurement of transmittance or reflectance of solutions, transparent or opaque solids, such as polished glass, or gases. However they can also be designed to measure the diffusivity on any of the listed light ranges that usually cover around 200 nm - 2500 nm using different controls and calibrations. Within these ranges of light, calibrations are needed on the machine using standards that vary in type depending on the wavelength of the photometric determination.

An example of an experiment in which spectrophotometry is used is the determination of the equilibrium constant of a solution. A certain chemical reaction within a solution may occur in a forward and reverse direction where reactants form products and products break down into reactants. At some point, this chemical reaction will reach a point of balance called an equilibrium point. In order to determine the respective concentrations of reactants and products at this point, the light transmittance of the solution can be tested using spectrophotometry. The amount of light that passes through the solution is indicative of the concentration of certain chemicals that do not allow light to pass through.

The use of spectrophotometers spans various scientific fields, such as physics, materials science, chemistry, biochemistry, and molecular biology. They are widely used in many industries including semiconductors, laser and optical manufacturing, printing and forensic examination, and as well in laboratories for the study of chemical substances. Ultimately, a spectrophotometer is able to determine, depending on the control or calibration, what substances are present in a target and exactly how much through calculations of observed wavelengths.

2.39 Some features of Datacolor-650 spectrophotometer

This high-precision, close-tolerance, reference grade spectrophotometer has special capabilities to handle fluorescent materials.

Exceptional inter-instrument agreement, easy maintenance, exceptional stability Automated UV control-UV Exc, UV Inc, 420nm, 460nm and UV calibration modes Optional Vertical Configuration High-precision, close-tolerance, reference grade spectrophotometer with capability to

handle fluorescent measurements Automated zoom lens and specular port Multiple viewing apertures with automatic aperture recognition Automatic gloss compensation


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Datacolor spectrophotometers provide high resolution color measurement and excellent short and long-term repeatability

The optional 3.0 mm aperture can measure unusually small sample areas The exceptionally large (30mm) aperture means you can maximize the surface area to

be measured – ideal when measuring color without regard to a textured surface.

Spectrophotometer (Datacolor-650)

2.40 Whiteness and Yellowness Indices in a Spectro-Eye

Yellowness

Yellowness is defined as a measure of the degree to which the color of a surface is shifted from preferred white (or colorless) towards yellow. Yellowness, as defined by ASTM E 313, has been applied successfully to a variety of white or near-white materials, including paints, plastics, and textiles. In terms of colorimeter readings, it was YI=100(1-B/G) where B and G are respectively amber blue (B) and green (G) colorimeter readings. Its derivation assumed that, because of the limitation of the concept to yellow (or blue) colors, it was necessary to take account of variations in the amber or red colorimeter readings.


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Yellowness according to ASTM E 313 (D 1925) was developed specifically for determining the yellowness of homogeneous, non-fluorescent, nearly colorless, transparent, nearly white translucent or opaque plastics, as viewed under daylight lighting conditions. It can also be applied to materials other than plastic fitting this description. The indices can be calculated, rounded, and adjusted in the last retained significant digit to minimize the residual error in the white point values. The equation is: YI=100(CxX-CzZ)/Y, where Cx and Cy standard coefficients described in the standard and correspond with observer angle and color temperature.

Whiteness

Whiteness is defined as a measure of how closely a surface matches the properties of a perfect reflecting diffuser, i.e. an ideal reflecting surface that neither absorbs nor transmits light, but reflects it at equal intensities in all directions. For the purposes of this standard, the color of such a surface is known as preferred white.

ASTM E313 – measuring procedure and settings are described in the same standard (ASTM E313: whiteness and yellowness of paper) like the Yellowness indices. This method is based on the use of colorimeter readings B and G. The idea was that chromaticity factor G-B required three times the weighting of the lightness factor G of the lightness. The equation is: WI=G-4(G-B)=4B-3G

Different whiteness & yellowness values of different fabrics


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CHAPTER THREE

MATERIALS & METHODS


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3.1 Materials& Machines:

S/J fabric &cutting Scissors Scissors was used for sampling the S/J fabric by cutting them in equal size and exact weight.

Electronic Balance Electronic balance was used for determining the weight of the samples.

Lab Sample Dyeing m/c This is the machine where some of the samples bleaching were done. Only temperature can be controlled by this m/c, not the time.


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Digital Lab Sample Dyeing m/c Rests of the sample bleaching were done in this machine. Both time & temperature can be controlled by this machine.

Digital Sample Dryer This machine was used for drying of the wet samples after washing.

Spectrophotometer Spectrophotometer was used for the whiteness test of the bleached sample.


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Bursting Strength Tester Bursting strength tester m/c was used for testing the bursting strength of scoured-bleached samples.

Electronic pipette This pipette was used for measuring the amount of peroxide to be taken for bleaching recipe.

3.2 Fabric Structure & Type:

Fabric Type : Knitted Fabric Specification Type : Single Jersey fabric Fabric GSM : 120-30 Color : Off white Each Sample Weight : 12.5 gm. Fabric Treatment : Scoured in regular factory parameter.


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3.3 Chemicals used:

Chemical Name Functions

Caustic Soda (NaOH) Used for scouring of the gray S/J fabric

Hydrogen Peroxide (H2O2) Used for bleaching of scoured S/J fabric

Detergent Used for hot wash of scoured-bleached S/J fabric

Wetting agent To increase the wet pick up of the fabric

3.4 Method of working:

Bursting strength testing

Whiteness testing

Drying

Hot washing

Bleaching in 7 different parameters

Scouring in factory parameter

Gray S/J fabric


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3.5 Scouring Procedure:

Fabric is preparing for industrial Scouring-Bleaching

3.6 Standard recipe of scouring:

This recipe of scouring is for knitted fabric. Different recipe is used for woven fabric scouring process.

Alkali (NaOH) : 2 to 5 gm per litre. Soda ash : 1 gm per litre (to adjust PH) pH : 10.5 Wetting agent : 1 gm per litter. Sequestering agent : 1 gm per litter. Detergent : 1 to 2 gm per litter. Temperature : 100 to 125o C. Time : 6 hours (close vessel) or 8 hours (open vessel) M : L : 1 : 10


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3.7 Process of scouring:

The fabric is loaded in the m/c and kept in rope form. The hot liquor is pumped and sprayed by circular tube on to the fabric The liquor passes slowly over the packed cloth and collects at the false bottom of

the kier. The liquor again pumped into the heater by a centrifugal pump and this cycle is

repeated After scouring ,the fabric is washed in 800C water to remove impurities.

3.8 Bleaching procedure:

Bleaching processes were done in 7 different recipes and processes. Sample wise bleaching process& recipeare described below.

Sample no-1 (Standard Sample) Recipe: Hydrogen Peroxide (H2O2) : 2.00 g/L (Stock Solution 5%) Temperature : 98oC Time : 30 min M:L : 1:10 Sample weight : 12.5 g Sample no-2 Recipe: Hydrogen Peroxide (H2O2) : 2.20 g/L (Stock Solution 5%) Temperature : 98o C Time : 30 min M:L : 1:10 Sample weight : 12.5 g

Sample no-3 Recipe: Hydrogen Peroxide (H2O2) : 1.8 g/L (Stock Solution 5%) Temperature : 98o C Time : 30 min M:L : 1:10 Sample weight : 12.5 g


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For sample no- 1, 4, 5, 6, 7: required peroxide is 5ml

For sample no- 2: required peroxide is 5.5 ml

For sample mo-3: required peroxide is 4.5 ml


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3.9 Process curve for bleaching:

Process curve for sample bleaching

3.10 Spectrophotometer (Datacolor-650) working procedure:

Sample Presentation and Measurement Overview:

When positioned correctly, the sample rests between the sample holderand the front panel door. The sample must completely cover the aperture opening.

Reflectance Measurements:

1. Grasp the sample holder and pull forward. 2. Position the sample, then carefully bring arm back up to normal operating position.

3.11 Working steps

i. First the standard recipe bleached sample was taken as the standard whitening index for the whiteness test

ii. Then the other samples were tested against the value of the standard sample. iii. Different values were found for different samples. iv. We took all the sample results and compared them. v. Tests were done under D-65 light index.

Temperature (o C)

Time (min)

Chemical

+ Fabric

25

88/98/108

0 |‐‐‐‐‐‐ 20/30/40 ‐‐‐‐‐‐|

Stop heating

Start heating Wash

sample


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Testing the whiteness of the bleached samples in Datacolor-650

3.12 Results obtained from Spectrophotometer

Sample Whiteness Index DELTA WI (BATCH WI - STD WI)

Sample no-1 (STD WI)

58.65 0

Sample no-2

61.46 2.81

Sample no-3

51.86 -6.79

Sample no-4

59.32 0.67

Sample no-5

55.55 -3.1

Sample no-6

61.00 2.35

Sample no-7

48.53 -10.12


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Screenshot of whiteness test in Datacolor-650 spectrophotometer

3.13 Bursting Strength Testing Working Procedure

Working Steps:

1. First we took a sample for the testing of its bursting strength 2. Then we opened the strength testing lid and spaded the fabric perfectly 3. Then we put the lid off and started the machine for the work 4. One operator operated the machine through the computer system 5. Through the machine the working process was visible clearly 6. the diaphragm forced the fabric and after a while the fabric got busted 7. we took the read of time, pressure & other values from the computer 8. other samples were tested in the same way 9. we took all the data & information and compared them


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Bursting strength testing of sample

3.14 Bursting strength test result

Sample Bursting strength (kPa)

Sample no-1 (STD)

627.3

Sample no-2

614.3

Sample no-3

630.5

Sample no-4

598.4

Sample no-5

638.1

Sample no-6

609.7

Sample no-7

630.6


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CHAPTER FOUR

RESULTS &

DISCUSSIONS


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4.1 Effect of peroxide concentration on bursting strength

Sample-1 was bleached in regular factory parameter (2.0 g/L). And so that’s why we considered it as our standard and tested other sample parameters against this.

In Sample-2 According to the result, we can see that, by increasing the bleaching agent amount (2.2 g/L); the strength of the fabric decreases. In sample-3, we have decreased the amount of peroxide agent (1.8 g/L). From the result, we can see that strength increases here slightly.

4.2 Effect of peroxide concentration on whiteness

In sample-2 (2.2 g/L) whitening index or the whiteness of the sample increases for increasing peroxide amount and we have got the best whiteness value of the samples for sample-2. Whereas for sample-3 (1.8 g/L) whiteness decreases for the lack of bleaching agent.

630.5

627.3

614.3

605

610

615

620

625

630

635

1.8 g/L 2 g/L 2.2 g/L

Strength (kPa)

strength (kPa)

51.86

58.65

61.46

46

48

50

52

54

56

58

60

62

64

1.8 g/L 2 g/L 2.2 g/L

Whiteness

Whiteness


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4.3 Effect of bleaching temperature on bursting strength

In standard sample, the temperature was 98o C. In sample-4 temperature was increased (108o C). For the increase in temperature, some damage occurred in the fiber. So the strength of the sample decreased. In sample-5 we decreased the temperature (88 o C). The fibers of the fabric didn’t get much damage and so that strength increased here. We have got the best strength result for reducing the temperature.

4.4 Effect of bleaching temperature on whiteness

The whiteness gets increased in sample-4 because of the increase in temperature (108o C). But the whiteness falls for the lack of temperature in sample-5 (88 o C).

638.1

627.3

598.4

570

580

590

600

610

620

630

640

650

88(°C) 98(°C) 108(°C)

Strength (kPa)

55.55

58.65

59.32

53

54

55

56

57

58

59

60

88(°C) 98(°C) 108(°C)

Whiteness


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4.5 Effect of bleaching time on bursting strength

In Sample-6 we have increased the bleaching time (40 min) in the standard of 30 minuites. We have got that for giving heat for more time, the strength of the sample decreases. And in sample-7, it got the shortest bleaching time than other samples. And we got better strength of fabric here.

4.6 Effect of bleaching time on whiteness

Here, for the increase in reaction time (40 min), whitening index is increased for ample-6.

And in sample-7, for the shortest time bleaching (20 min), we got the worst whitening index.

630.6627.3

598.4

580

590

600

610

620

630

640

20 minutes 30 minutes 40 minutes

Strength (kPa)

48.53

58.6561

0

10

20

30

40

50

60

70

20 minutes 30 minutes 40 minutes

Whiteness


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CHAPTER FIVE

CONCLUSION


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5.1 Conclusions:

Bleaching is an essential process for the white fabric production. By doing this project we have got very good idea about the bleaching parameter effects. During bleaching we have to look after these points:

Increasing the amount of bleaching agent can increase the whiteness of the fabric. But it can affect the strength.

Bleaching temperature should not raise more than 100o C because for increasing the temperature, the strength gets much damaged. So the bleach should be done in the range of 95-99o C for the better strength and good whiteness

Bleaching time should not extend more than range. Though the whiteness increases, but the fibers get so much damaged for the temperature.

Amount of peroxide bleach, time and temperature should not decrease than the range without reason. Because of that the whiteness is not properly obtained though the strength gets improved. After all we know that bleaching process is done for obtaining the whiteness from the fabric.

So considering all the facts, we can say that the standard recipe for bleaching is the best in overall. Here we can get good whiteness and better strength of the fabric. So for the factory production that standard recipe is used as default bleaching recipe.


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REFERENCES

http://textilelearner.blogspot.com/2011/03/textile-bleaching-process_5937.html (26.11.2014)

http://www.textileworld.com/Issues/2009/March-April/Dyeing_Printing_and_Finishing/Gentle_Bleaching (26.11.2014)

http://www.slideshare.net/mainulrony/scouring-13515271 (27.12.2014) http://www.slideshare.net/tadele_asmare/bleaching-18854378 (27.11.2014) http://www.datacolor.com/products/ (29.12.2014) http://industrial.datacolor.com/portfolio-view/datacolor-650/ (29.11.2014) http://en.wikipedia.org/wiki/Textile_bleaching (29.11.2014) http://thesmarttime.com/pretreatment/scouring-bleaching-of-cotton.html (29.11.2014) http://textilelearner.blogspot.com/2013/08/preparatory-process-of-cellulosic-

fiber.html (29.11.2014) http://textilelearner.blogspot.com/2014/03/bleaching-pro_8997.html (30.11.2014)) www.burstingstrengthtester.com/bursting_strength_tester.html (30.11.2014) http://l-w.com/produkt/lw-bursting-strength-tester/ (30.11.2014) http://textilelearner.blogspot.com/2012/12/bleaching-of-cotton-fiberfabric-with.html

(01.12.2014) http://greenopedia.com/hydrogen-peroxide-bleach-alternative (01.12.2014) www.thwingalbert.com/bt21-burst-strength-tester.html (01. 12.2014) http://textilelearner.blogspot.com/2012/02/bursting-strength-test-diaphragm-of.html

(01.12.2014) http://textilelearner.blogspot.com/2011/08/pretreatment-object-of-pretreatment.html

(01.12.2014) www.smitherspira.com/services/primary-pack-testing/burst-strength (02.12.2014)