Whitening Agent, OBA, FWA

Prepared By : Mazadul Hasan sheshirID: 201000040000813th Batch (session 2009-2013)Department : Wet Processing Technology Email: mazadulhasan@yahoo.comBlog : www. Textilelab.blogspot.com (visit)

Southeast University Department Of Textile Engineering

I/A 251,252 Tejgaon Dhaka Bangladesh

Prepared By :

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HISTORICAL DEVELOPMENT,FUNCTION, MECHANISM, PROPERTIES & IT’S USES

The coloring matter ,whether it is natural or present as a conta- minant in the fiber is generally decolorized by different bleaching methods.

However the appearance of the textile substrate is some what creamish after the bleaching, therefore chemical treatments are become necessary to neutralize the yellow tint ofthe textile fibers.

Contents

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Optical Brighteners

1. Optical brighteners, also called Fluorescent Brighteners or Fluorescent Brightening

Agents (FBA) are colorless dyes that work by emitting visible light when exposed to

invisible ultra-violet light.

2. They are used to make white or light-colored fabrics appear brighter. Mostly bleached

white fabrics are treated with these brighteners.

3. Fabrics and garments that are truly prepared for dyeing should not contain brighteners.

Optical brighteners can interfere with some dyes by competing for the "dye sites" on

the fibers.

4. Optical brighteners have the property of absorbing ultra- violet (UV) light and re-

emitting energy in the form of weaker energy, i.e. visible light (violet-blue light) so that

the yellow color of the material will appear white.

Optical Brighteners

1. The chemical structures of these agents contain an aliphatic carbon-carbon double

bond, which is sensitive to sunlight, oxidation, weathering, etc.

2. Therefore, these compounds do not have good fastness properties, and tend to loose

their ability to absorb UV light over short periods of time in use.

3. The presence of high concentrations or improper application or cheaper quality of

fluorescent brighteners could lead to yellowing of the material instead of whitening.

What is whitening agent

A optical brightener ( sometimes called optical bleaches or fluorescent whitening agents )

agent is a compound which, when applied to a textile material, absorbs the short

wavelength electromagnetic radiation (300-400 nm) which is invisible to the human eye,

and converts it into visible light of longer wavelength between 400 and 500 nm, which is

emitted either as violet, pure blue or greenish blue. Because the main use of these dyes in

laundry detergents and Textile finishing, Optical Brightener are generally found in domestic

waste waters that have a component of laundry effluent. Its characteristic is the incident

light to generate fluorescence excitation, so that the stained material was similar fluorite

sparkling effect, to the naked eye to see the material is white, especially when added to a

yellowish-white material. Fluorescent whitening agents may be used to whiten or brighten a

textile or paper material. Further more, well all round fastness property and a good yield are

also desired. In addition to this, different shades of whites are desired, as white shades are

subject to fashion trends They are requires to be used on a verity of finishing processes and

they should be compatible with practically all chemicals and auxiliaries used at different

stages.

History of whitening agent

Textile material (cotton, wool, linen and silk) and synthetic (mainly polyamide, polyester and polyacrylonitrille ) are not completely white and effort have been made since ancient time to free from this yellowish tings. Bleaching in the sun, bluing and mater chemical bleaching of textile and other materials increased the brightness of the products and eliminated to a certain hue or the local impurity of the original or industrially treated material.

When optical brighteners first came up they regarded as bleaching auxiliaries which enable short or milder bleach when used in very small quantities (approx 0.001 – 0.05%) they were also called as optical bleaching agents it could be improved with the help of horse chestnut extra acts. This is due to fact the inner back of the horse chestnut contains aesculin or esculinic acid, a glucoside which is derivative of coumain and which has ultra violet fluorescent. Then came the introduction of organic products based on Diaminostilbine sulphonic acid derivatives.

Numerous materials especially textiles, both classical (Cotton, wool, linen and silk) and synthetic (mainly polyamide, polyester and polyacrylonitrile ), are not completely white and efforts have been made since ancient times to free from their yellowish tinges. Bleaching in the sun, blueing and later chemical bleaching of textile and other materials increased the brightness of the products and eliminated to a certain extent the yellowish tinge to grayish yellow hue or the local impurity of the original or industrially treated material. When Optical brighteners first came up they were regarded as bleaching auxiliaries, which enabled a shorter or a milder bleach when used in very small quantities {Approximately 0.001 to 0.05% }.

They were also called as Optical Bleaching Agents. Cotton and linen bleachers knew 200 years ago the effect of bleaching could be improved with the help of horse chestnut extracts. This is due to the fact the inner bark of the horse chestnut contains aesculin or esculinic acid, a glucoside which is a derivative of coumarin and which has ultra violet fluorescence. Scientist recommended aesculin for improving the whiteness on the basis of theoretical considerations. An aqueous solution of a esculin proved more suitable, but had two major draw backs. Firstly it was not fast to washing and secondly aesculin on the fiber was very sensitive to light. Then came the introduction of organic products based on Diaminostilbine sulphonic acid derivatives.

Historical Development of Optical Brightening Agents:

About 80% of all OBAs produced are derived from stilbene derivatives, the latter

absorbing in the ultra violet regions at (α) = 342 nm. All optical brighteners are dyestuffs,

but in place of the chromophoric system which is the characteristic for dyes, it contains a

fluorescening system and like a normal dye certain substituents which promote the affinity,

depending on the type of fiber on which it is applied. In this manner, brighteners which are

suitable for cotton are more or less substantive derivatives of diaminostilbene disulphonic

acid.

The stilbene derivatives can be present in two isomeric forms, ie in the Cis

configuration and in the Trans configuration .Optical brighteners in the Trans form can be

made both in the powder and liquid form.The Cis form, which is rapidly formed under the

action of light from the trans form will not go on cotton and for this reason, the solutions of

this whitener is protected against light. Many of the optical brighteners are derived from

the heterocyclic compounds containing nitrogen atoms.

Chemistry of whitening agent:

Fluorescence is produced by the absorption of radiation having a high energy on the part of the molecule, which re – emits this radiation of lower energy i.e. of longer wave length, the difference in energy being transformed in to kinetic energy. To enable a molecule to fulfill this function, it must be built according to certain structure principles. For example Anthranilic acid has very strong blue violet fluorescence in the aqueous solution, but nevertheless unsuitable as a brightener. Most of the brightener will hardly fluoresce in powder form; their fluorescence will only appear in solution. There are some types, which will not fluoresce in solution and will only show this property after they have been applied on the fiber. Thus, it can be concluded that fluorescence is not only depended on the structure of the molecule but also on its condition. Whether a fluorescent substance is suitable as brightener can only be determined after it has been applied to the textile fiber. Apart from this the product must meet certain demands in respect of properties such as fastness to washing and light etc .On comparering different textile fabrics treated with different brighteners and processing approximately the same brightness difference in hue can be deleted, since the human eye is particularly sensitive to difference in whiteness. If an optically brightened fabric with radish white shade is compared with another fabric having a greenish white shade both of which appear to be equally brilliant if viewed in daylight which is incident from a northerly direction, it will be seen that the greenish shade will appear more brilliant then the radish one in bright sunlight.

Chemistry of whitening agent:

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.

Desired properties of Good OBA

Chemistry of whitening agent:

Stilbene Type OBA

OBA,s are not a substitute for bleaching. They are used to obtain brilliant market whites. These "white" whites can be obtained without over bleaching and damaging the fiber. On cellulose, they have poor wash fastness but most commercial laundry detergents contain OBA's so they are constantly replenished. Some OBAs have poor washfastness - some nonionics types have excellent light fastness. Fiber producers can include OBA,s in their spinning process.These can have excellent durability to both light and washing.

Chemistry of whitening agent:

Textile materials like cotton or cotton/polyester blends are almost always pre-brightened when manufactured. This is because the printing and colors will be brighter and more attractive if applied to bright fabric. Moreover, the washing agents and commercial detergents available nowadays commonly have optical brighteners combined in them and while washing the fabric gets whiter. It is known that, in most cases, the presence of an optical brightener causes a decrease in the light fastness of a dyed fiber. These compounds can also have a direct photochemical effect on the fiber in the absence of dyes, as in the case of wool. Optically whitened wool will yellow on exposure to light much faster than untreated wool by a photocatalytic process. However, in colored textiles, sometimes a difference on hue is detected already in the first domestic wash, even in the case of solid colors. This undesirable effect has been a considerable obstacle for several textile industries, with clients and consumers becoming more and more demanding. Therefore, it’s important to study the effect in order to avoid, as much as possible, similar situations.

Chemistry of whitening agent:

Commercial name of whitening agent in textile

Product Name Strength Application Shade Area of application

Kolorcron BA Powder 450 E Value

Cellulose-Exhaust in H2O2 bleach. Polyami- de/Wool/ Silk –Exhaust Single bath scouring bleaching at high Temp. with Hydro.

Neutral to Bluish White

Cellulose, Polyam- ide, Wool/ Silk

Kolorcron WHN 180 E Value

Cellulose-Exhaust in H2O2 bleach. Polyami- de/Wool/ Silk –Exhaust Single bath scouring bleaching at high Temp. with Hydro.

Neutral to Bluish White

Cellulose, Polyam- ide, Wool/ Silk

Kolorcron 4BB 125 E ValueNo Padding application Exhaust at 80* C & above

Bluish Violet White Cellulose Fibers

Kolorcron BA Liquid 125 E Value

Cellulose-Exhaust in H2O2 bleach. Polyami- de/Wool/ Silk –Exhaust Single bath scouring bleaching at high Temp. with Hydro.

Neutral to Bluish White

Cellulose, Polyam- ide, Wool/ Silk

Kolorcron CXT Liquid 100 E Value

Padding & Low Temp Exhaust application. Single bath scouring and Bleaching at high Temp.

Bluish Violate WhiteCellulose Fiber & Cellulose Blend

Kolorcron S 70 E ValueNo padding application Exhaust 40* - 60* C & regenerate

Bluish WhiteCellulose Fiber & Cellulose Blend

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.

Properties of whitening agent

WHITENESS & BRIGHTNESS

To the trained observer, even bleached are whit textile material has a slight

yellow tinge. This small amount of yellow can give the impression of slight soiling

and may detract from their aesthetic appeal the presence of slight amount of blue

gives the impression that the textile material is whiter. Before advent of OBAs.

Improved whiteness was obtained using a laundry blue, which is a blue pigment.

The development of OBAs had meant that this slight addition of blue can be

obtained through the light reflected by the OBAs in the presence of ultraviolet

radiation. This makes white textile whiter and brighter. Colored textile materials tend

to appear brighter. OBAs are present in most domestic but these are usually only

suitable for cellulosic textile material.

LIGHT FASTNESS

There is large variation in the light fastness rating of these compounds when applied to cellulosic and protein fibers their light fastness range 1 to 2, and in some instance may reach 3. It should be pointed out that this poor light fastness is not too important in the cause of cellulosic’s, since any loss of OBAs effect due to sunlight will be replaced in subsequent laundering with domestic detergent. Fluorescent brighteners on xylon can reach a light fastness rating 4 with selected OBAs, a rating as high as 7 for polyesters, and in this class of acrylic fibers a light fastness of about 4 – 5.

Figure : Light-sheet interactions

Figure: A: Specular reflectance, B: Semi glossy-paper and C: Diffused reflectance (Re-drawn from Pauler 2002)

The poor overall light fastness of fluorescent brighteners is due to their continuous absorption & emission of light which result in their chemical degradation.

LIGHT FASTNESS

WASHING FASTNESS

The washing fastness rating of fluorescent brighteners if about 3. The fair washing

fastness of fluorescent brighteners is due to partly to their lack of substantively of

textile material and their gradual degradation by exposure to sunlight. The fair

washing fastness may not be noticeable in cellulose because of the presence OBAs in

domestic detergents when fluorescent are used on other fibers they are applied in the

manufacturing situation and brighteners are chosen which will last the expected life of

the textile article.

METAMERIC EFFECT OF OBA

Metamerism is a normal phenomenon relating to how the human eye perceives color. It occurs when “two different color object have the same color appearance to normal human viewer under one light source ( metameric match ) but look different under another light source( metameric mismatch )” To a print marker, this means that the painstakingly precise color information applied to each print will be compromised whenever that print in viewed under a different light source. Thus, one primary goal of any print marker should be to avoid metamerism in order to validate the time spent on color management and to uphold the integrity of the reproduction. After all, what good is reproduction if it does? Now that we understand metamerism and why it should be avoided, how do OBAs fit into the picture? When OBAs are exposed to UV light, the treated paper appears brighter and whiter. When OBAs are not exposed to UV light (in the evening), the OBAs “lose activity” causing your eye to actually see the paper color without OBAs. This will look creamy or somewhat yellowed. This amount of “OBAs activity loss” will vary constantly depending upon how much exposure the paper has to UV light. Picture the lightening condition inside of an art gallery and how they will change depending upon the time of day. This will have subsequent effect on the art itself; your print could be illuminating the print. It a case like this, where there is a high UV component, inkjet papers that contain OBAs will strongly fluoresce and will appear bright white. However, in the evening when the same print is displayed with low or non – existent UV component (or incandescent tungsten illumination), the OBAs will not fluoresce, making the paper appear yellow, therefore causing your eyes to see the image color differently.

Fluorescence

The ability of a substance to absorb light at a specific wavelength and emit it at a higher wavelength is called fluorescence. Optical brighteners or fluorescent whitening agents are added to improve the appearance properties (brightness, whiteness etc.) of printing and writing papers (Heikkilä et al. 1998). When light strikes a fluorescent material, some of the electrons acquire energy and a portion of energy is converted into heat. Thus, the emitted light has lower energy as compared to the incident light, which results in longer wavelengths (Hubbe et al. 2008). In contrast, non-fluorescent material either completely absorbs and converts such energy to heat, or instantly releases the energy by emitting light at a wavelength equal to the incident light (Hubbe et al. 2008).

Desired Properties of Fluorescent Whitening Agents for Textiles Use

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.

Before selecting an optical brightener for textile application we must look for following properties-

Composition

Members of this class of diaminostilbene sulfonate derivatives are highly conjugated molecules having planar structure and anionic charge. All of these adjectives also apply to direct dyes. What makes this particular class of direct dyes different is that they absorb ultraviolet light and re-emit light in the blue region of the visible spectrum.

Another traditional term for fluorescent whitening agents (FWAs) is "optical brightening agents" (OBAs).

Three general types of FWAs are widely available. The type most often used by papermakers has four sulfonate groups (tetrasulfonated). It has intermediate solubility in water and it is readily retained on fibers, especially if alum or another cationic material is present. Hexasulfonated FWAs don't retain as well when added at the wet end, but they may give higher optical efficiency when used at the size press due to less association between the molecules in the dried starch film. Disubstituted FWAs are sometimes used for specialty purposes, for instance when water bleed-fastness is critical.

Function

Increasing the white appearance of papers by absorbing invisible ultraviolet light and re-emitting it in the blue region of the visible spectrum. This strategy can compensate for a yellow tint of many types of pulps that have been bleached to moderate levels.

CLASSIFICATION OF OBA

The classification of OBA can be either on the chemical structure of the brightener or on its method of application.

They can be classified in to two large groups-

•Direct (substantive) brightener.•Disperse brightener.

a)Direct optical brightening agents are predominantly water soluble substance used for the brightening of natural fibers and occasionally for synthetic material such as polyamide.

b)Disperse optical brightening agents are mainly water insoluble and as with disperse dyes they are applied either to colored from an aqueous dispersion on they can be used for mass coloration. They are used for synthetic materials such as polyamide polyester acetate.

From the chemical point of view they are classified according to either chemical structure. Chemical optical brightening agents are classified in to derivatives of stlibene, coumarin, 1, 3 diphenyl pyrazoline, derivative of naphthalene dicarboxylic acid, derivatives of heterocyclic dicarboxylic acid, derivatives of cinnamic acid and substance belonging to other chemical system.

Basic types of whiteners

Basic class types of brighteners include:

1. Triazine-stilbenes (di-, tetra- or hexa-sulfonated)

2. Coumarins

3. Imidazolines

4. Diazoles

5. Triazoles

6. Benzoxazolines

7. Biphenyl-stilbenes

Factors_Influencing_Whitening_Process

The factors influencing whitening process are as follows :

a) pH of the bath

b) Temperature of the bath, and

c) Time required for the process.

Mechanism of action

Absorption (A) of light quanta by the brightener molecules induces transitions from the singlet ground state S0 to vibrational levels of the electronically excited singlet states (S1).

Brighteners in the S1 state are deactivated by several routes. Fluorescence results from radiative transitions to vibrational levels of the ground state (F).Deactivation processes competing with fluorescence are mainly non-radiative deactivation to the S0 state (IC) and non-radiative transition to the triplet state (intersystemcrossing, ISC).The efficiency of fluorescence is measured by the quantum yield :

It is determined by the relative rates of fluorescence emission and the competing processes. When fixed in solid substrates, brighteners fluoresce with high quantum yields .

A = absorption

F = Fluorescence

IC = internal conversion

ISC = intersystem crossing

S = singlet state

T = triplet state

Figure : Energy Diagram of Optical Brighteners and Transitions

Method of whitening agent

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 theFluorescent 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.

Measurement of Whiteness and Evaluation of OBA

OBA are evaluated in the same way as dyes. Their concentration in powder and liquid form is determined by subjective (visual ) comparison of the samples in daylight or under an ultra violet lamp, by titration with cetylpyridiniumchloride or spectrophotometrically against a standard of known concentration. Objects can only be seen as colored objects when they are illuminated by light. Since light is an electro magnetic radiation, which is either absorbed or reflected by the object which appears, colored due to the action of electro magnetic radiation on the human eye. Fluorescers or optical brighteners, as they are also called, are to improve the whiteness of textiles. Objective measurement of the whiteness and of the change in whiteness can be accomplished by color measurement, since different hues of whiteness can be measured like any other color.

To assist in a correct interpretation of such measurements, knowledge of the fundamentals of colorimetry is required, that is color measurement comprising the systematic compilation and evaluation of physical data supplied by suitable measurements. The wavelengths of the colors perceived in the range from violet { 400- 430 nm}{ shorter wavelengths are called ultra violet }, to 430- 485 nm blue, 485 to 570nm green, 570- 585 nm yellow, 585 to 610 nm orange, and above 610 nm red. There are many cases in practice where it is interesting to know the degree to which an optically brightened fabric has been bleached, as it is often important to know the original whiteness and the increase in whiteness achieved by the optical brightener. Besides, it is often interesting to know whether a shading dyestuff was used in addition to the brightener to enhance the whiteness. It is necessary to use a special spectrophotometer for the measurement of optically brightened specimens. Although the reflectance curve will not be in accordance with actual conditions up to a wave length of approximately 420nm (i.e. in the excitation range of the brightener), the reflectance curve of the substrate will be reproduced accurately at higher wavelengths where fluorescence is no longer observed.

Exhaustion of OBAs

The exhaustion of fluorescent brighteners is dependent on several factors:

• Nature of textile goods

• Temperature

• Addition of salt

• Liquor ratio

• Concentration of fluorescent brightener

• pH of bath

Application of Florescent Brightening Agent FBA

The FBA can be divided into three application categories.

Anionic: containing sulfonate group used for Cotton, Wool and Nylon.

Cationic: used for mostly Polyacrylonittrile fibers.

Nonionic: used for PET, Acetate, Polyacrylonittrile and Polyamide.

FBA are applied by exhaust or padding process and then fixed by heat treatment.

FBA for Cellulogic Fiber

Tiponal BV, 2B, GS, RBN, 4BM. Applied by exhaustion or padding method. Exhausts at pH 8-11 or higher. Salt should be used for exhausting Tiponal BV on the fiber. Tiponal 4BM is suitable for application by the padding technique.

Blancophor CL is intending for whitening cellulogic fiber. It is stable to Hydrochloride and Chloride Bleach bath, so that it may be applied while bleaching with these bleaching agents. Fluorite BW stables alkaline hydrogen peroxide and per salt bleach and hence can be applied during bleaching. It can be applied by exhaust dyeing method. Since it have affinity for cellulogic fiber. Uvitex CK stable to hard water.

Materials / Chemicals Used

Following materials/chemicals are used in the whitening process:

1. Water

2. Steam

3. Compressed Air

4. Wetting agent

5. Detergent

6. Sequestering agent

7. Acid

8. Anti-creasing agent

9. Optical Brightener for Cotton & Polyester

10.Caustic Soda,

11.Hydrogen per Oxide, and

12.Stabilizer, etc.

Whitening Process for 100% Cotton

The sequence for whitening process for 100% cotton fabric is as follows:

1. Take water in bath at required level .

2. Add Detergent, Sequestering Agent, Anti-creasing Agent, Stabilizer .

3. Circulate the fabric for 5 minutes at 500C .

4. Add Caustic Soda and circulate for 5 minutes at 500C .

5. Add Hydrogen per Oxide and circulate for 5 minutes at 500C.

6. Add Optical Brightener agent and raise the temperature at 1000C .

7. Continue circulating the fabric for 50 minutes at constant temperature (1000C) .

8. Circulate the fabric and decrease the temperature at 600C .

9. Check the shade with approved shade.

10. Rinse and Drain.

11. Add Acetic acid and circulate for 10 minutes at 500C.

12. Drain .

13. Unload .

Graphical Representation of Whitening Process of 100% Cotton

The whitening process for 100% Cotton can be graphically presented as below :

Graphical Representation of Whitening Process of 100% Cotton

Whitening Process for Polyester-Cotton Blended Fabric

Steps of Whitening Process for Polyester-Cotton Blended Fabric:

The sequence of Whitening Process for Polyester-Cotton Blended fabric is as follows : 1. Take water in bath at required level 2. Add Detergent, Sequestering Agent, Anti-creasing Agent, Stabilizer 3. Circulate the fabric for 5 minutes at 500C4. Add Caustic Soda and circulate for 5 minutes at 500C5. Add Hydrogen per Oxide and circulate for 5 minutes at 500C 6. Add Optical Brightener agent and raise the temperature at 1100C 7. Continue circulating the fabric for 30 minutes at constant temperature (1100C) 8. Circulate the fabric and decrease the temperature at 600C 9. Check the shade with approved shade 10. Rinse and Drain 11. Circulate the fabric for 10 minutes at 800C 12. Drain 13. Add Acetic acid and circulate for 10 minutes at 500C 14. Drain 15. Unload

Graphical Representation of Whitening Process for Polyester Cotton Blended Fabric

The whitening process for Polyester-Cotton blended fabric can be graphically presented as below :

Graphical Representation of Whitening Process for Polyester Cotton Blended Fabric

OBA Removal process

A simple OBA stripping technique given below can be adopted in jiggers very efficiently and you can strip off almost 98% of OBA.

Recipe and method of process flow given below may be used as new hint.

a) Wetting the fabric:Soap - 1 gm/liter, Soda ash 1 gm/liter - treat the fabric at 70°C for 30 minutes.

b) Oxidative Bleaching:Potassium Permanganate (KMnO4) - 0.5% wof at cold for 30 minutes - to the same

bath add Hydrochloric acid (35% conc.), 3 times the quantity of KMnO4 continue run for another 30 minutes. Then raise the temperature to 50°C and run for 30 minutes.

Drain the bath - cold wash - 30 minutes.

3) Reductive Bleaching:Run 10 minutes with Caustic soda 5 gms/liter and then add 5 gms/liter of Hydros

(Sodium Hydro Sulphite) at room temperature and run for 10 minutes. Then slowly raise the temperature to 60°C. During this process the brown coloration you have got would be converted to light beige like shade. Now do one thorough cold wash.

4) Oxalic Acid Treatment:Treat with 2 gms/liter of Oxalic acid at room temperature for 30 minutes or 2 ends

followed by a cold wash. 5) Soda ash Neutralization:Treat with 2 gms/liter of soda ash at room temperature for 30 minutes and again

do a cold wash. 6) Acetic acid Neutralization:Treat the fabric with 1 gm/liter of acetic acid for 10 minutes at cold. Check the pH

and let it be 6.Now you will wonder to see thorough removal of OBA.

OBA Removal process

Strategies for Use

Some of the critical factors in FWA use include (a)retention, (b) quenching, (c) competition with other UV-absorbers, and (d) metamerism.

The strategies for adding and retaining FWAs to the wet end of a paper machine are very similar to those used with direct dyes. For instance, FWA retention can be increased by sequential addition of alum to the pulp stream, either before or after the whitener. But there is a key difference; highly charged cationic polyelectrolytes easily can destroy the fluorescent character of the molecule. The effect is called "quenching." (The effect is related, but much more problematic, than the tendency of the highly cationic polymers to modify the hue of certain direct dyes.) Both lignin and titanium dioxide are potent absorbers of ultraviolet light. For this reason, internal addition of FWAs to high-yield furnish or to furnish that contains TiO2 is likely to be ineffective. This is one of the reasons why it is common for papermakers to add all or most of the FWA at the size press. The idea is that light first encounters material nearer to the surface of the paper, and this is where much of the size-press formulation ends up. Metamerism refers to the phenomenon that two objects may appear to have identical color when viewed under a certain type of illumination, but the same objects might not match under a different lighting. This is a very common occurrence in the case of samples that contain different levels of activity of fluorescent whitening agents.

Common uses

Brighteners are commonly added to laundry detergents to replace whitening agents removed during washing and to make the clothes appear cleaner. Optical brighteners have replaced bluing which was formerly used to produce the same effect. Some brighteners can cause allergic reactions when in contact with skin, depending on the individual.

Brighteners are used in many papers, especially high brightness papers, resulting in their strongly fluorescent appearance under UV illumination. Paper brightness is typically measured at 457 nm, well within the fluorescent activity range of brighteners. Paper used for banknotes does not contain optical brighteners, so a common method for detecting counterfeit notes is to check for fluorescence.

Optical brighteners have also found use in cosmetics. One application is to formulas for washing and conditioning grey or blonde hair, where the brightener can not only increase the luminance and sparkle of the hair, but can also correct dull, yellowish discoloration without darkening the hair. Some advanced face and eye powders contain optical brightener microspheres that brighten shadowed or dark areas of the skin, such as "tired eyes".

A side effect of textile optical whitening is to make the treated fabrics more visible with Night Vision Devices than non-treated ones. This may or may not be desirable for military or other applications. Optically brightened paper is often not useful in exacting photographic or art applications, since the whiteness decreases with time.

End uses of optical brighteners include

1. Detergent whitener (instead of bluing agents)

2. Paper brightening (internal or in a coating)

3. Fiber whitening (internal, added to polymer melts)

4. Textile whitening (external, added to fabric finishes)

5. Color-correcting or brightening additive in advanced cosmetic formulas

(shampoos, conditioners, eye makeup)

Role of Optical Brightening agents in Textile Wet-Processing:

The operation of whitening, i.e., bleaching or brightening, is concerned with the preparation of fabrics whose commercial value is dependent on the highest possible whiteness. In bleaching, textile process houses are concerned with the removal of colored impurities or their conversion into colorless substances. In chemical bleaching, impurities are oxidized or reduced to colorless products. Physical bleaching involves the introduction of a complementary color whereby the undesired color is made invisible to the eye in an optical manner, eg, in bluing the yellow cast of substrates such as textiles, paper, sugar, etc. is eliminated by means of blue or blue-violet dyes. Through color compensation the treated product appears whiter to the eye; however, it is actually grayer than the untreated material.

With the aid of Optical brightening agents (OBAs), also referred to as fluorescent whitening agents, optical compensation of the yellow cast may be obtained. The yellow cast is produced by the absorption of short-wavelength light (violet-to-blue). With OBAs, this lost light is in part replaced; thus a complete white is attained without loss of light. This additional light is produced by the whitener by means of fluorescence. Fluorescent whitening agents absorb the invisible UV portion of the daylight spectrum and convert this energy into the longer-wavelength visible portion of the spectrum, i.e., into blue to blue-violet light. Fluorescent whitening, therefore, is based on the addition of light, whereas the bluing method achieves its white effect through the removal of light.

A fluorescent whitener should be optically colorless on the substrate, and should not absorb in the visible part of the spectrum. In the application of OBAs, it is possible to replace the light lost through absorption, thereby attaining a neutral, complete white. Further, through the use of excess whitener, still more UV radiation can be converted into visible light, so that the whitest white is made more sparkling. Since the fluorescent light of a fluorescent whitener is itself colored, ie, blue-to-violet, the use of excess whitener always gives either a blue-to-violet or a bluish green cast.

Many chemical compounds have been described in the literature as fluorescent compounds that provide a suitable whitening effect. Collectively these materials are aromatic or heterocyclic compounds; many of them contain condensed ring systems. An important feature of these compounds is the presence of an uninterrupted chain of conjugated double bonds, the number of which is dependent on substituents as well as the planarity of the fluorescent part of the molecule. Almost all of these compounds are derivatives of stilbene or 4,4-diaminostilbene; biphenyl; 5-membered heterocycles such as triazoles, oxazoles, imidazoles, etc. or 6-membered heterocycles, e.g. coumarins, naphthalimide, s-triazine, etc.

Role of Optical Brightening agents in Textile Wet-Processing:

1.Textile substrates of natural or synthetic fibers are contaminated in the

raw state by substances of varying degrees of yellowness.

2.Bleaching is required to remove the yellowish cast.

3.Chemical bleaching agents destroy the yellow coloring matter in fibers.

4. However, even if bleaching processes are carried to the technically

acceptable limits of damage to the fibers, they never succeed in completely

removing this intrinsic color.

5.To produce the color white, it is necessary to dye with a fluorescent

whitener.

Role of Optical Brightening agents in Textile Wet-Processing:

OBAs used in textiles can be divided into three categories

1. products containing sulfonic acid groups, corresponding to acid dyes, for cotton, wool, and polyamides;

2. cationic whiteners that behave in the same way as basic dyes, for polyacrylonitrile fibers; and

3. whiteners containing no solubilizing groups, corresponding to disperse dyes, for polyester and secondary acetate fibers.

At first conclusion we can say that most of the typical commercial detergents of

domestic use appear to contain a considerable amount of optical brighteners. The

effect of optical brighteners on colored textiles appears to be different depending on

color, that is to say, on the corresponding region of the spectrum. It seems to be more

visible on the violet-blue colors and almost insignificant on orange and red. However,

even in these colors a slight effect can be observed in case of lower fastness. The

lighter the color is more intense the optical brightener’s effect can be, even in colors

with a good fastness.

Dark colors presenting lower fastness to washing showed only a small difference

on hue.

CONCLUSION

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