Yarn Count/Linear Density | Determination of Yarn Count

The thickness or diameter of a yarn is one of its most fundamental properties. However, it is not possible to measure the diameter of a yarn in any meaningful way. This is because the diameter of a yarn changes quite markedly as it is compressed. Most methods of measuring the diameter of yarn, apart from optical ones, involve compressing the yarn as part of the measurement process. Therefore the measured diameter changes with the pressure used so that there is a need for agreement on the value of pressure at which the yarn diameter is to be defined. On the other hand optical systems of measuring yarn diameter have the problem of defining where the outer edge of the yarn lies as the surface can be rather fuzzy, having many hairs sticking out from it.

Therefore the positioning of the yarn boundaries is subject to operator interpretation. Because of these problems a system of denoting the fineness of a yarn by weighing a known length of it has evolved. This quantity is known as the linear density and it can be measured with a high degree of accuracy if a sufficient length of yarn is used. There are two systems of linear density designation in use: the direct and the indirect.

Direct System
The direct system of denoting linear density is based on measuring the weight per unit length of a yarn. The main systems in use are:

• Tex - weight in grams of 1000 metres
• Decitex - weight in grams of 10,000 metres
• Denier - weight in grams of 9000 metres
1 tex = 10 decitex.

Tex is the preferred SI unit for linear density but it is not yet in common use throughout the textile industry. Other direct systems can be converted into tex by multiplying by the appropriate factor. In the direct system the finer the yarn, the lower is the linear density.

Indirect System
The indirect system is based upon the length per unit weight of a yarn and is usually known as count because it is based on the number of hanks of a certain length which are needed to make up a fixed weight. This is the traditional system of yarn linear density measurement and each branch of the industry has its own system based on the traditional length of hank associated with the locality and the type of yarn manufactured.

The main English ones which are still used every day in the relevant parts of the industry are:

• Yorkshire Skeins Woollen Ny

Count = number of hanks all 256 yards long in 1 pound

• Worsted Count New

Count = number of hanks all 560 yards long in 1 pound

• Cotton Count Nec

Count = number of hanks all 840 yards long in 1 pound

• Metric count Nm

Count = number of kilometre lengths per kilogram

In the indirect systems the finer the yarn, the higher the count. One way of measuring count is to measure the linear density using the tex system in the first instance and then to convert the result to theappropriate count system using the appropriate conversion factor K .

Count =K/Tex

Dyeing Process of Jigger Dyeing Machine | Working Process of JiggerDyeing Machine

Jigger Dyeing Machine:

Jigg or jigger dyeing machine is one of the oldest dyeing machine used for cloth dyeing operations. Jigger machine is suitable for dyeing of woven fabrics, up to boiling temperature without any creasing . Jigs exert considerable lengthwise tension on the fabric and are more suitable for the dyeing of woven than knitted fabrics. Since the fabric is handled in open-width, a jig is very suitable for fabrics which crease when dyed in rope form.

Jigger Dyeing Machine

Some wovens are conveniently dyed on jigger are ,

• Taffettas
• Plain wovens
• Satins
• Poplins
• Ducks
• Suiting and Shirting material.
• Sheetings etc.

But have limited application on fabrics which are tension sensitive such as crepes , flat crepes , knits , net fabrics and elastomeric warps etc.
 
Machine Description
The jigger machines have two main rollers which revolve on smooth bearings and are attached to with a suitable driving mechanism , which can be reversed when required. The fabric is wound on one of the main rollers and fed from the other. The fabric move from one roller to the other through the dye liquor trough located at the lower part of the machine . There are various arrangement of guide rollers at the bottom of liquor trough ,and during each passage the cloth passes around these guide rollers .
 
The concentrated dye liquor is usually introduced directly into the dyebath in two equal portions, which are added just before commencing the first and second ends. The liquor is agitated by the movement of the fabric through the dyebath. Several horizontal spray pipes are fitted across the full width of the trough in order to expedite fabric rinsing.
 
Live steam injected into the bottom of the trough through a perforated pipe across the width of the jig heats the liquor. Some modern jigs also have heat exchangers for indirect heating.
 
Covering the top of the jig minimizes the heat loss to the atmosphere, keeps the temperature uniform on all parts of the fabric and minimizes exposure of the liquor and the cloth to air. Minimizing exposure to air is important when using sulphur or vat dyes since these dyes can be oxidized by atmospheric oxygen.
 
A few meters of leading fabric, similar in construction to the cloth under process, is stitched to each end of the cloth batch , to allow the entire length of the fabric to pass through the dye bath during the dyeing process. When jig processing is completed, the fabric is run onto an A-frame via a nip or suction device to remove extraneous water during unloading.
 
Modern machines such as automatic and jumbo jiggers have full automation in drive , tension regulation and control , fabric speed and metering, smooth and jerk less stop and start , counters for number of turns , gradual and noiseless reversal, automatic temperature regulation and control etc.
 
Dyeing Process by Jigger Dyeing Machine:

The dyeing process on jigger is regarded as a series of intermittent padding operation followed by dwelling periods on the main roller , during which the dyeing action and diffusion takes place. The factors controlling the rate of dye absorption are:

1. The amount of interstitial dye liquor retained in the interstices of the fabric weave.
2. The exhaustion of the interstitial liquor in the dwell period between successive immersions.
3. The degree of interchange of liquor during one immersion (interchange factor).

In the dyeing on jigger machines the cloth revolves on two main rollers , The open-width fabric passes from one roller through the dyebath at the bottom of the machine and then onto a driven take-up roller on the other side. When all the fabric has passed through the bath, the direction is reversed . Each passage is called an end. Dyeing always involves an even number of ends. The dye bath has one or more guide rollers , around which the cloth travels , and during this immersion achieves the desired contact with the dye liquor. During this passage the fabric picks up adequate quantity of dye liquor , excess of which is drained out but still a good quantity is held in the fabric . During rotation of rollers this dye penetrates and diffuse into the fabric. The real dyeing takes place not in the dye liquor but when the cloth is on the rollers, since only a very small length of fabric is in the dyebath and major part is on the rollers . Therefore the speed of cloth during immersion in dye liquor has a very little effect on percentage of shade produced.
 
Some critical problems related to the conventional jigger dyeing machines ( which are minimized in the modern day machines) The major problems are side-to-centre color variations, called listing, and lengthways color variations, called ending.
 
Other problems are

• Temperature control from side-to-side and end-to-end of the roll
• Tension control from end-to-end
• Constant speed control from end-to-end
• Prevention of creases
• Prevention of air

Limitations of Jigger Dyeing

1. Jigs exert considerable lengthwise tension on the fabric and are more suitable for the dyeing of woven than knitted fabrics.
2. In textile preparation due to the swelling and dissolution of size, which makes the fabric slippery and unstable in roll form.
3. The low liquor ratio makes washing-off difficult.
4. There is little mechanical action in a jig machine and it is less suitable where vigorous scouring is required before dyeing.
5. Moiré effects or water marks may arise on some acetate and nylon fabrics because of pressure flattening the structure of the rolled fabric.

Fiber Fineness Measurement by Projection Microscope

The projection microscope is the standard method for measuring wool fibre diameter, and all other methods have to be checked for accuracy against it. The method is also applicable to any other fibres with a circular cross-section. The method involves preparing a microscope slide of short lengths of fibre which is then viewed using a microscope that projects an image of the fibres onto a horizontal screen for ease of measurement. The apparatus is shown diagrammatically in Fig. Techniques are followed that avoid bias and ensure a truly random sample. 

Method of Test
A suitable random and representative sample is conditioned for 24 h in a standard testing atmosphere. Using a modified Hardy microtome the fibres are cut to a suitable length (0.4mm for fibres below 27 (im) and a slide is prepared by carefully mixing the fibres into the mountant. The use of short fibres gives a length-biased sample so that proportionally more of the longer fibres will have their diameter measured. The mounting agent should be non-swelling and have a suitable refractive index (for example liquid paraffin). The mixture of fibres and mountant is spread thinly on the slide and covered with a cover glass, carefully avoiding air bubbles and finger prints.

The projection microscope

The slide is placed on the stage, coverglass down (microscope inverted) and fibres are selected for measurement in the following way. The slide is traversed in a zigzag fashion, measuring every fibre that complies with the following requirements: 1 has more than half its length visible in the 7.5cm circle which is drawn in the centre of the field of view; 2 is not in contact with any other fibre at the point of measurement. The traverse of the slide is continued until the required number of fibres has been measured. The magnification of the microscope is adjusted to be 50Ox so that on the scale used to measure the fibres each millimetre represents 2 um.

For accurate tests three slides should be measured from randomly selected areas of the material and not less than 150 fibres per slide should be measured. The coefficient of variation of diameter for unblended wool lies between 20% and 28%. From this value the number of tests to give certain confidence limits has been calculated.

Fashion Models | Different Types of Fashion Models

Fashion Model

• Models may be used to display and promote clothing. Fashion modeling may involve catwalk or runway modeling or editorial modeling, covering photography for magazine spreads, ad campaigns, catalogues, print etc. The emphasis of fashion photography is on the clothes or accessories, not the model. Fashion models may be used to display or promote various types of clothing, such as lingerie, swimsuit,bikinis, etc. Other models may be used in showroom,fit modeling, fitness or sporty modeling. Some are used for petite modeling or plus-size modeling. 
• The first person described as a fashion model is believed to be parisian shopgirl, Marie Vernet Worth. She was a house model in 1853, to her fashion designer husband, Charles Frederick Worth.

Female Body Type

*Main articles: Size zero and Female body shape

* The British Association of model Agents (AMA) says that female models should be around 34-24-34 in (86-61-86 cm) and at least 5 ft 8 in (1.73 m) tall. The ideal measurements used to be 35.5-23.5-35.5 in (90-60-90 cm) which were the alleged measurements of Marilyn Monroe. However, today’s fashion models tend to have measurements closer to the AMA recommended shape, although by no means all models have these exact statistics, and fashion houses may require other sizes for their models.

*The unusually thin shape of fashion models has been criticized for allegedly warping girls’ body image and encouraging eating disorders.Organizers of a fashion show in Madrid in September 2006 turned away models who were judged to be underweight by medical personnel who were on hand. In February 2007, six months after her sister, Luisel Ramos - also a model - died, Uruguayan model Elina Ramos became the third international model to die of malnutrition in six months. The second victim was Ana carolina Reston . Luise Ramos died of heart failure caused by anorexia nervosa just after stepping off the catwalk.

Male Body Type
*The preferred average dimensions for a male model are a height of 5 ft 11 in (1.80 m) to 6 ft 2 in (1.88 m), a waist of 26–33 in (66.04–83.82 cm) and a chest measurement of 32–40 in (81.28–101.60 cm)

Supermodels
* Supermodels are highly paid, high profile fashion models. These (usually female) celebrities, also known as cover girls, appear on top fashion magazine covers, in catalogues and in fashion shows.

* The first model to pave the way for what would become the supermodel was Lisa Fonssagrives. The relationship between her image on over 200 Vogue covers and her name recognition led to the importance of Vougue in shaping future supermodels. Her image appeared on the cover of every fashion magazine during the 1930s, 1940s and 1950s from Town & Country,Life and Vogue to the original Vanity Fair.

* Model Janice Dickinson has asserted that she was the person for whom the term was coined, as she popped the term herself while talking to her agent at the climax of her career by saying, “I’m not superman, I’m a supermodel” In the 1980s, regulars like Gia Carangi, Carlol Alt,Janice Dickinson, Clindy Crawford, Christie Brinkley, Kim Alexis and Poulina Porizkova began to endorse products with their names as well as their faces, getting in front of everything from Diet Pepsi to Ford Trucks.
Glamour Model:
* Glamour models posing on the red carpet - Hollywood, CA 03/09/2008
* Main articles: Glammour photography and Pin-up girl
* Glamour photography emphasizes the model and the model’s sexuality rather than products, fashion or the environment. Glamour modelling often focuses on the body of the subject and insinuations of sexuality serve to enhance a product’s attractiveness. Glamour models may be used for mass-produced calanders, pinup and for men’s magazines, such as Playboy magazine. Famous glamour models include Pamela Anderson, Jordan, Jodie Marsh,Lucy Pinder, Megan Fox etc.

Optical Brightening Agents (OBA) | Properties of Fluoroscent WhiteningAgents for Textiles

The coloring matter ,whether it is natural or present as a contaminant in the fiber is generally decolorized by different bleaching methods. However the appearance of the textile substrate is somewhat creamish after the bleaching, therefore chemical treatments are become necessary to neutralize the yellow tint of the textile fibers.

There are two methods ,which are generally used for this purpose. By using a blue tinting agent , which absorbs the yellow part of the light and reflected light appears to be of bluish tint. The total light reflected by this mean is less than the total incident light.

By using fluorescent optical brightening agents :-
The OBA s (optical brightening agents ) are most widely used in textiles , paper, detergents and plastics . The optical brightening effect is obtained by the addition of light , which means that the amount of light reflected by the Fluorescent Whitening Agents (also called optical brightener) absorb high energy radiation in the ultraviolet to violet region (330nm-380nm) on the part of characteristic molecules and emit lower energy radiation in blue region in visible spectrum (400nm-450nm), which yields the counteracting the yellowing appearance. FWA should be transparent on the substrate and should not absorb the visible region of the spectrum. The OBAs are effective only when the incident light has a significance proportion (such as daylight) of UV rays. When material treated with OBAs are exposed to UV black light source , it glows in the dark.Anionic OBA’s exhaust on cotton, wool and silk., cationic OBA’s exhaust on acrylic and certain polyesters and nonionic OBA’s are exhaust on all synthetics.

Desired Properties of Fluoroscent Whitening Agents for Textiles Use:
Before selecting an optical brightener for textile application we must look for following properties,
1.it should have good solubility , should not have its own color and good substantivity for the textile substrate under OBA application.
2.OBA’s should have good light as well as wet fastness properties.
3.Its rate of strike on the substarte.
4.Build up and exhaustion properties.
5.Requirement of electrolytes and its sensitivity towards different exhausting agents.
6.Effect of temperature on the exhaustion and build up properties.
7.Application pH range and sensitivity towards change in pH.
8.Effect of water hardness.
9.It should have good leveling and penetrating properties.
10.Should not decompose to colored products on exposure to atmospheric conditions as well as storage , and it should not absorb light in the visible region.
11.it should be compatible and stable with finishing chemicals, auxiliary and process such as heat and temperature.
12.It should be stable and fast to the common oxidative and reductive bleaching chemicals and bleaching systems.

Bleaching Process for Full Whites and OBA application | Desiredproperties of Good OBA | Mechanism of Fluorescent Whitening

Introduction

The coloring matter ,whether it is natural or present as a contaminant in the fiber is generally decolorized by different bleaching methods. However the appearance of the textile substrate is somewhat creamish after the bleaching, therefore chemical treatments are become necessary to neutralize the yellow tint of the textile fibers.

There are two methods ,which are generally used for this purpose,
By using a blue tinting agent , which absorbs the yellow part of the light and reflected light appears to be of bluish tint. The total light reflected by this mean is less than the total incident light.

By using fluorescent optical brightening agents :- 

The OBA s (optical brightening agents ) are most widely used in textiles , paper, detergents and plastics . The optical brightening effect is obtained by the addition of light , which means that the amount of light reflected by the substrate is more than the incident light , due to which the object appears brighter.

Desired properties of Good OBA
Before selecting an optical brightener for textile application we must look for following properties, it should have good solubility , should not have its own color and good substantivity for the textile substrate under OBA application.  

1. OBA’s should have good light as well as wet fastness properties.
2. Its rate of strike on the substarte.
3. Build up and exhaustion properties.
4. Requirement of electrolytes and its sensitivity towards different exhausting agents.
5. Effect of temperature on the exhaustion and build up properties.
6. Application pH range and sensitivity towards change in pH.
7. It should have good leveling and penetrating properties.
8. Should not decompose to colored products on exposure to atmospheric conditions as well as storage , and it should not absorb light in the visible region.
9. it should be compatible and stable with finishing chemicals, auxiliary and process such as heat and temperature.
10. It should be stable and fast to the common oxidative and reductive bleaching chemicals and bleaching systems.

Chemical Constitution of Optical Brighteners
Optical brighteners are usually derivatives of

• Triazine-stilbenes (di-, tetra- or hexa-sulfonated)
• Coumarins
• Imidazolines
• Diazoles
• Triazoles
• Benzoxazolines
• Biphenyl-stilbenes

Brighteners can be “boosted” by the addition of certain polyols like high molecular weight polyethylene glycol or polyvinyl alcohol. These additives increase the visible blue light emissions significantly. Brighteners can also be “quenched”. Too much use of brightener will often cause a greening effect as emissions start to show above the blue region in the visible spectrum. Besides the formation of cis isomer in stilbene-containing brighteners (only the trans isomer is optically active), continued exposure to UV-containing light will actually cleave the molecule and start the process of degradation.

Mechanism of Fluorescent Whitening

Fluorescent Whitening Agents (also called optical brightener) absorb high energy radiation in the ultraviolet to violet region (330nm-380nm) on the part of characteristic molecules and emit lower energy radiation in blue region in visible spectrum (400nm-450nm), which yields the counteracting the yellowing appearance. FWA should be transparent on the substrate and should not absorb the visible region of the spectrum. The OBAs are effective only when the incident light has a significance proportion (such as daylight) of UV rays. When material treated with OBAs are exposed to UV black light source , it glows in the dark.Anionic OBA’s exhaust on cotton, wool and silk., cationic OBA’s exhaust on acrylic and certain polyesters and nonionic OBA’s are exhaust on all synthetics.

Bleaching with Peroxides | Bleaching Process with Hydrogen Peroxide

Bleaching with Peroxides
The bleaching bath is composed of hydrogen peroxide (35% or 50% by wt.) as the bleaching agent, an activator (usually alkali) and stabilizers.

Bleaching Process with Hydrogen Peroxide
Hydrogen peroxide bleaching can be done by

1.Batch wise,
2.Continuous
3.Semi continuous method.

Factors of Peroxide Bleaching:
a.Quantity of peroxide required in Bleaching
 
b.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.

c.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. In general these bleaching process correspond to a preliminary bleach.

d.pH:- 
The pH value depend on the fibres to be bleached and pre-treatment.

NaOH is used in case of H2O2 bleaching. This is used to bring the PH upto 9-10 because H2O2 become active at this PH or oxidation is start at this PH.

For the bast fibres, such as linen, weaker alkaline or soda alkaline baths are used in order to avoid a cottonizing. Regenerated cellulose fibres 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.

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

f.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 stabiliser.

Advantages of Peroxide Bleaching:
1.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.

2.Peroxide bleaching keeps the fibre quality intact.

3.Cotton can be bleached with peroxide in a single stage. Other processes require two or three bleaching stages,(desize with scour, scour with bleach and desize with scour and bleach).

4.No separate pre treatment 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.

5.Animal fibres 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.

6.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).

Bleaching of Wool with Hydrogen Peroxide
After scouring, wool may be bleached by immersion or pad and dry techniques, using alkaline or acid solutions.

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.

Bleaching of synthetic fibres 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.

Advantages and disadvantages of peroxide over hypochlorite bleaching.

Bleaching with Sodium Perborate
Sodium perborate (PBS, NaBO3.nH2O where n=1 or 4) can readily be incorporated. It has been described as a stable, solid form of hydrogen peroxide allowing its introduction into the wash at the same time as the detergent. Sodium perborate is a gentler bleach than sodium hypochlorite, causing less damage to fabrics and dyes, but by itself is only effective at high (>60ºC) temperatures. Although solid chlorine bleaches exist, they are rarely used in laundry detergents.

Bleaching with Sodium Chlorite.(NaClO2 )
The sodium chlorite is available as a powder , and it is applied under strongly acidic conditions to textiles. Its application produce a toxic and corrosive gas.

a. bleaching mechanism
b. effect of pH.
c. effect of temperature.
d. effect of metals

Bleaching with Peracetic Acid
Peracetic acid is produced by the chemical reaction of acetic acid and hydrogen peroxide. It works in a very narrow pH range of 7 to 8. Below pH 7.0 the bleaching is not proper and above pH 9.0 fiber degradation takes place. Peracetic acid is used a bleaching agent for nylon and acetate where hydrogen peroxide can not be used.

Reductive Bleaching Systems
Reductive bleaches work by reducing colored impurities into colorless forms.

1.sodium hydrosulphite.
Sodium hydrosulphite is available as free flowing powder and a strong reducing agent. This is explosive in nature when come into contact with water. It is available in different purity ranges.

2.sodium sulphide.
Sodium sulphide is also a strong reducing agent

3.sulphur dioxide
Sulphur dioxide was used as a bleaching agent in early 20th century for bleaching of wool.
 

Reductive Bleaching of silk
Commonly Sodium hydrosulphite, Sulfurdioxide and sodium sulphoxylates are the reductive bleaching agents which are used for silk.

Reductive bleaching of nylon
Oxidative bleaching isn’t suitable for polyamides as H2O2 attacks the polymer, instead reductive dyeing using sodium hydrosulphite is used.

Hypochlorites Bleaching Process | Bleaching with Hypochlorites

Bleaching with Hypochlorites

Bleaching Powder
Calcium hypochlorite is usually a white or grayish-white powder, but it is also available as tablets. It is a strong oxidizer and is considered more stable than sodium hypochlorite. It is also believed to provide more chlorine.

Sodium Hypochlorite
Sodium Hypochlorite is a greenish-yellow liquid commonly referred to as “Bleach.” The chemical compound formula for Sodium Hypochlorite is NaOCl.Sodium Hypochlorite is prepared by reacting dilute caustic soda solution with liquid or gaseous chlorine, accompanied by cooling. It is used extensively as a bleaching agent in the textile, detergents, and paper and pulp industries.

The active ingredients in hypochlorite bleaches vary with pH. At pH 2 is the main component in solution; at pH 4 to 6, HOCl is the dominant species; at pH > 9, OCl − is the only component present. It is the hypochlorite ion in basic solution that is the active ingredient in household bleach, which is typically about 5 to 6 percent NaOCl. The OCl − ion oxidizes chromophores in colored materials, and is itself reduced to chloride and hydroxide ions.

Hypochlorite Bleaching Process
The conditions of the bleaching agent varies according to the result required, the concentration depends upon the fabric quality, degree of whiteness required, types of machine and next operation.

Quantity Required:-
Normally 2.5-3.0 gpl of available chlorine is sufficient for good bleaching , but it is necessary to optimize it on a possible lower value for safe bleaching process.

Analysis Method
Determination of available Chlorine.
Method : Iodometric(Standard)

Apparatus :

• Erlemeyer flask(100 ml) -I
• Burette stand -I
• Pipette(50 ml) -I
• Spatula -I
• Measuring Cylinder -I
• Micro burette(10ml.) -I
• Measuring Cylinder. -I

Reagent

• Sodium Thio Sulphate Solution(.1N)
• Glacial acetic acid
• Pottassium Iodide(KI crystal)
• Starch indicator solution.

Typical Bleaching Recipe for Hypochlorites

Wetting agent                                        0.3-0.5g/l

Caustic Soda                                        0.5-1.0g/l

Soda ash                                              2.0-4.0g/l

Sodium hypochloride solution                5.0-15.0ml/l

Temperature                                         25-60C

Time                                                     30-60 mins

pH                                                       10.5 
M:L                                                      1:10

Procedure :-
1) Collect sample solution ( Sodium hypo chlorite ) in an air-tight bottle.

[NOTES / CAUTION
a) Keep sample solution away from excessive light and do not agitate the sample solution.
b) Start chlorine determination IMMEDIATELY after sampling. ( i.e. do not store sample to be analysed for chlorine ).]

2) Introduce 10ml of glacial acetic acid and about 0.5 g of Pottassium Iodide (Spatula full ) crystal into a 100ml erlemeyer flask.
3) Withdraw y ml of sample solution with bulb pipette and introduce into above Solution.
4) Swirl the flask to well mix the solution.
5) Titrate with 0.1N Sodium Thio Sulphate Solution from upto a light Yellow Colour.
6) Add 1 ml of starch indicator solution and continue to titrate until the last drop of titrant causes the solution to turn colourless.

% active chlorine = 3.545 x N x V/y (i;e 3.545 x N x V divided by y)
Where :
V = Volume of (N ) Na2S2O3
N = Normality of Na2S2O3
y = Sample amount


Important Factors for Bleaching:
pH :-

General PH range is 10-11 or 10.5-11.5 during bleaching if PH reaches 9 then it is a danger level and at 7 PH the bleaching is worse and causes extreme damage to the cloth.The PH value is maintained by adding sod ash or by buffering agent.

Temperature:-

The suggested temperature for hypochlorite bleaching is 37-40oC. Generally reaction is accelerated with increases of temperature.

Water Quality:-

Water for bleaching should be soft and even hard water can be used but should be free from Cu++ and Fe++.

Effect of Metals:-
The bleaching equipment should be made of stainless steel , to avoid the catalytic degradation of the cellulose in the presence of copper and iron.

Substrate Preparation
The substrate must be pre scoured in the presence of chelating agents , it should be free from rust spots and traces of metallic impurities when bleaching with hypochlorites.

Bleaching Time :-

The time factor depends upon the following consideration.

(a) Concentration.
(b) PH value.
(c) Degree of Whiteness.
(d) The type of machine used in bleaching.

Roughly for normal machine the time is 2-3 hrs is required for completion of bleaching process antichlor and proper neutralization treatments should be followed by proper wash for removal of reagents after hypochlorite bleaching process.