Useful Articles

                      WHY TEXTILE AUXILIARIES SHOULD BE USED ?

THE NEED FOR TEXTILE AUXILIARIES

There is hardly a dyeing or printing process of commercial importance that can be
adequately operated by the use of dyes and water alone. Practically every colorant–substrate system requires the use of additional products, known as auxiliaries, to ensure its reliable functioning and control. This was the case even centuries ago, when the use of natural vat and mordant dyes depended entirely on the proper, albeit rule of thumb, use of additives.These controlled pH, reduction, oxidation and mordanting to enable the dyes to be applied to the natural fibres of those days. Many of the auxiliaries, like the dyes and fibres, were of natural origin. Dung and urine [1] were among the agents used, and soap was clearly the first surfactant to be employed. Indeed, from the standpoint of today, one can only wonder at the degree of purely empirical expertise so successfully developed and applied by the ancient dyers and printers.

Our current level of understanding is clearly a phenomenal advance on the ancient arts,
yet our need for auxiliaries remains. For example, even before dyeing or printing the
substrate must be cleaned and wetted. Products are needed to convert non-substantive vat and sulphur dyes to substantive forms, to help stabilise the conditions that bring about the substantivity, and then to reconvert the dyes to their insoluble forms in the substrate

Mordant dyes still require the appropriate chelating agents, as well as other agents to create and maintain the optimum chelating conditions .

Printers still need thickening agents to facilitate the localized application of dyes. Inevitably, however, the present-day plethora of dyes, fibres and coloration processes has created additional reasons for the use of auxiliaries, whilst the concurrent evolution of the

chemical industry has satisfied these needs as they arose. Moreover, a vastly more comprehensive understanding of the physico–chemical processes involved has enabled auxiliaries to be precisely engineered for specific purposes.

Hand in hand with this theoretical knowledge, practical evaluation has become
increasingly sophisticated. Nevertheless, it is often difficult to differentiate between
auxiliaries promoted purely for commercial reasons and those that serve a definite technical need. Dye manufacturers are acutely aware of the positive part played by auxiliaries in helping to sell dyes, and dyers today are under constant pressure to use more of them. Some additives offer cost savings by improving reproducibility and minimising reprocessing; nevertheless it is all too tempting to incorporate too many products without critically evaluating their efficacy, thus inevitably and unnecessarily increasing processing costs.

Consequently it is more important than ever that the dyer or printer understands the
functions of auxiliary products and is equipped to evaluate their use realistically and to
monitor it continually.

As has been implied already, functional demands for auxiliaries continue to grow, with
each dye–fibre system and dyeing or printing process having particular needs.

The primary functions of auxiliaries are:

(a) to prepare or improve the substrate in readiness for coloration by
– scouring, bleaching and desizing
– wetting
– enhancing the whiteness by a fluorescent brightening effect

(b) to modify the sorption characteristics of colorants by
– acceleration
– retardation
– creating a blocking or resist effect
– providing sites for sorption
– unifying otherwise divergent rates of sorption
– improving or resisting the migration of dyes

(c) to stabilise the application medium by
– improving dye solubility
– stabilising a dispersion or solution
– thickening a print paste or pad liquor
– inhibiting or promoting foaming
– forming an emulsion
– scavenging or minimising the effects of impurities
– preventing or promoting oxidation or reduction

(d) to protect or modify the substrate by
– creating or resisting dyeability
– lubricating the substrate
– protecting against the effects of temperature and other processing conditions

(e) to improve the fastness of dyeings, as in
– the aftertreatment of direct or reactive dyes
– the aftertreatment of acid dyes on nylon
– the chroming of mordant dyes on wool or nylon
– giving protection against atmospheric influences, as in UV absorbers or inhibitors of
gas-fume fading
– back-scouring or reduction clearing

(f) to enhance the properties of laundering formulations (fluorescent brightening agents).

Some auxiliaries fulfil more than one of the above functions. For example, an auxiliary to improve dye solubility may also accelerate (or retard) a coloration process, or an emulsifying agent may also act as a thickening agent; pH-control agents may both stabilise a system and also affect the rate of dye sorption.

Thus the range of auxiliaries available is very large indeed, covering a multiplicity of uses for all stages of textile processing. However, a factor which has assumed great importance regarding the use of auxiliaries in recent years is that of their effects on the environment.

ALL ABOUT OPTICAL BRIGHTENING AGENTS :

Fluorescent brighteners and optical whitening agents

white textile articles become yellowish on storage. This undesired effect can
be removed as follows:

(1) By using chemical bleaching agent such as hypochlorite or peroxide. In this
method, there are chances of spoiling coloured goods and damage the fiber.

(2) By using small amount of blue colouring matter, which absorbs yellow light
and due to this yellowed fabric appears white.

(3) By using fluorescent compound which absorbs ultra violet light and converts
the energy into visible light of higher wavelength. In this way, a yellow
appearance can be corrected by the emission of a corresponding amount of
blue-violet light by the fluorescent compound. The effectiveness of fluorescent
agent depends on the presence of ultraviolet light in the illuminant.
The first use of fluorescent compound to whiten textile materials was,
described by Krais in 1929, but it has been commercialised only in 1940. Many
brightening agents have been described in patent literature, and used commercially.

They are sold in different names such as Blankophor (FBY), Calcofluor (ACY),
Fluolite (ICI), Leucophor (S), Photine (HWL), Pontamine White (DUP), Tinopal (GY),and Uvitex (Cac, Ciba). As a class, they are termed fluorescent or optical whitening or brightening agents.

By far the greatest use of brighteners is in detergents, and almost every
commercial detergent contains one or more brighteners, in the proportion 0.05% to 0.3%. Brighteners are also used in textile processing and the manufacture of paper.
They are also used in plastics, waxes, polishes, cosmetics and in hair rinse. They are also used in the manufacture of synthetic fiber of all types.

For fluorescent substances to act as brightening or whitening agents, the
emitted light must be essentially blue light so that it effectively neutralises the normal pale yellow or cream colour of so called white materials. In practice the dominant wavelength of the emitted light must be around 450mμ.

Optical brightening is based on an addition of light, whereas the bluing
method achieves its white effect through the removal of light. The optical brighteners should fulfill the following two requirements.

(i) It should be optically colourless on the substrate and

(ii) It should not absorb in the visible part of the spectrum.

Since the fluorescent light of an optical brightener is itself coloured, i.e. blue
to violet or, sometimes, a bluish-green cast.

The overall effect given by a whitening agent therefore depends on a number
of factors.

(i) Its intrinsic effectiveness as a fluorescent.

(ii) Its spectral absorption and emission characteristics.

(iii) The ultra-violet content of the viewing light.

(iv) The self-colour of the substrate.

(v) The concentration on the substrate, which will of course depend on the
substantivity of the whitener for the substrate, and on the method of
application.

(vi) The physical form of the whitener on the substrate: the shade given by a
fluorescent on nylon, for example, is normally much more violet than the
shade on cotton.

Chemical Constitution

    Stilbene derivatives

Most water soluble brighteners for the textile materials are stilbene derivatives, and bistraizinyl derivatives of 4,4'-diaminostilbene-2,2' disulphonic acid are of special interest. One of the early brighteners manufactured by IG was 4, 4' bis (phenyluereido) stilbene 2, 2' disulphonic acid, obtained by reaction of 4, 4' diaminostilbene - 2, 2' disulphonic acid with phenylisocyanate in aqueous medium. It was marketed as Blankophar R. (I).

The usefulness of this product is limited by its instability in a boiling bath.
Present day commercial products are of the same general types as Blankophor B with varing substituents on the tiazine ring.

In a similar manner a number of other optical brightening agents of this type (CC/DAS) can be prepared.

The principal effect of these variations are changes in solubility, affinity, acid
fastness, etc. The class of bistriazinyl compounds, in solution, is not fast toward
hypochlorite; some compounds, however, show a certain amount of stability after
application to the fiber. The bistraizinyl brightners are employed principally on
cellulosics, such as cotton or paper. Some products also show affinity for nylon at the weakly alkaline pH of most of the commercial detergents.

By coupling diazotised 4-aminostilbene-supphonic acid with 2-aminoaphathalene-6-sulphonic acid and oxidising the product with alkaline hypochlorite a compound is obtained with structure (III; X=SO3Na, Y=SO3Na); it can be added to a detergent as a brightner and has an advantage over many other stilbene derivatives in that it remains effective in presence of bleaching agents.

Unsulphonated agents such as (III; X=CN, Y=H) can be applied as brightners
for synthetic fibres or plastic materials; other such as (III; X-SO2OPh or SO2N (alkyl)2 Y=H) are said to be suitable for similar purposes and also for application to oils, fats and waxes. Cationic groups such as SO2NHC2H4NMe2 can be used to confer affinity for polyacrylonitrile fibers.

Derivatives of dibenzothiophene-5, 5-dioxide

A further group of brightners, which has been studied primarily by American Cyanamid, was found in the derivatives of 3, 7- diaminodibenzothiophene-2, 8-disulfonic acid 5, 5 dioxide IV. These compounds are relatively weak in comparison with stilbene derivatives and give a greenish fluorescence. However, they do show good fastness to hypochlorite.

Azoles (derivatives of 5-membered-ring heterocycles)

Monoazoles

The group based on compound V arose from efforts to find hypochlorite stables
compounds with neutral fluorescence, and was patented by Geigy. With warer solubilising group these types of compounds are suited to brightening cellulosic
materials or nylon from soap and detergent baths. Water insoluble derivatives of this family, e.g. compounds having sulfamyl, arysulfnate, or nitrile groups, are suitable for brightening synthetic fibers and resins.

Blankophor WT, has been proposed as a brightner in the dyeing of wool from an acid bath. This compound is not effective in the presence of soap or synthetic detergents.

Bisazoles

Bisnaphotriazzolyl compounds of structure VI are obtained by coupling
tetrazotised amino compounds with 2 moles of a naphthyamine derivative
coupling in ortho-position, followed by oxidation. These products have good
hypochlorite stability. Compounds of structure VII are combinations of azoles
with napthotriazoles.

These compounds posses good fastness to hypochlorite and show mostly a redviolet fluorescence.

Coumarin Derivatives

The optical brightening of textile fibers by fluorescent compounds was mentioned by Krais. By treatment of flax with esculin, a glucoside of esculeting (VIII) a brightening effect was achieved, but this effect was not fast to washing and light. Later the use of β-menthylumbelliferone (IX) and similar compounds as brightners for textiles and soap was patented. As an improvement over β-menthylumbelliferone, 7-aminocoumarin were proposed. These latter are used for brightening wool and nylon either in soap powders or detergents or as salts under acid dyeing conditions.

A further development of the coumarin group consists in the use of derivatives of 3-phenyl-7-aminocoumarin (x). These compounds displace the hue towards more neutral shades and, at the same time, significantly improve the lightfastness. Brightners of this type are suitable by synthetic fibres and plastics.

Coumarin derivatives substituted at position 3 by an aryl radical and 7 by a group such as ureido or a substituted triazinylamino group Fig. XI, XII are of special
interest in that they can be applied to fibers of cellulose, wool, polyanide, polyurethane, cellulose acetate of polyacrylonitrile by dyeing processes or
to inert fibers such as polyesters by incorporation in the melt. They have good
fastness to light and impart a neutral white appearance to treated fibers.

Derivatives of 6-membered-ring heterocycles

A further class of brightners is derived from pyrazine. These compounds may be employed for brightening wool and various synthetic fibers from a weakly acid to neutral bath or from soaps and synthetic detergents.

Derivatives of pyrazoline

Knorr discovered this Class of optical brightening agents. It displays intensive blue fluorescence and high affinity and substantivity for the fibers. Optical brightening agents based on this group are used mainly for the surface brightening of polyamide, acetate and polyacrylonitrile. They are unstable against oxidants.

Finishing of Commercial Optical Brightners

Optical brightners may be obtained as powders, pastes, liquid water-soluble
forms or stable dispersions.

Pastes

Pastes are prepared from wet cake with various additives such as sodium
chloride, sodium sulphate, urea, etc. in a mixer.

Powder

The powder form is produced from above paste and dried in spray drier. The
powder are produced either diluted i.e. with additives or as concentrates where the content of additive is low or completely absent.

Instant finish (easily water soluble)

Lately "instant" finishing has been used in the preparation of powders. It
involves converting poorly wettable powders of optical whitening agents into easily
wettable or soluble material, which is also non-powdering during addition. For
achieving the "instant" finish, optical brightening agent wetted powder is submitted to a mechanical treatment during which individual powder particles are brought into contact, stick together agglomerate to fine beads, which dried in spray drier.

Liquid forms

The most common liquid forms involve the preparation directly from the final
product.

Liquid forms are solutions of optical brightening agents which are completely
miscible with water. Both soluble and insoluble brightening agents are used in such
preparations, and they are brought into solution either by dissolution in a solvent, or by chemical processes, in which the brightening agent is converted into the salt of a soluble quaternary base. The second type of liquid form is prepared most frequently from water-soluble derivatives of 4, 4'-diaminostilbene-2, 2' -disulphonic acid. A paste or the dry product is acidified and the acid paste is dried and suspended in an excess of amine and required concentration adjusted by water and quaternisation is carried out with the hydrotropic substance.

A hydrotropic substance monoglycols diglycols or triglycols, glycerol, various
sugars, sulphite mother liquors, easily water-soluble amides, mono-alkanolamines,
dialkanolamines, trialkanolamines, urea and urethanes are used.

The liquid forms contain 10 to 40% active substance and 25 to 60%
hydrotropic substances; based on the weight of solid brightening agent.

Hydrotropic substances used in Optical Brightening Agent

Commercial Name                               Hydrotropic Substances

Albaphan CBS flussig                           deithylene glycol
Blankophor flussig                               urea, ammonia
Blankophor BBU flussig                       urea, ammonia
Blankophor BBH flussig                       urea, ammonia
Blankophor BE flussig                          urea, diethylene glycol
Blankophor BA flussig                          urea, ammonia
Blankophor RA flussig                          urea, ammonia, diethylene glycol
Blankophor CI flussig                           oxyethylated phenol
Celumyl CSP flussig                              ethanolamine, diethylene glycol
Fluolite MP liquid                                   diethylene glycol, ethanolamine
Leukophor AC flussig                           diethylene glycol, tamol
Leukophor BS flussig                            urea, ammonia
Tmopal CH 3632                                    diethanolamine
Tinopal UP liquid                                   ethanolamine, ethylene glycol
Tmopal 2BF flussig                               diethanolamine
Tmopal 4BM flussig                              triethanolamine, urea
Tmopal LAT flussig                              oxyethylated phenol
Uvitex PRS fluss, konz                        triethanolamine, urea

Stable Dispersions

Stable dispersion of optical whitening agent is prepared by utilising suitable
non-ionic dispersing agent. Disperse optical brightening agents are produced mainly or the brightening of polyester fibers, cellulose acetate and polyacrylonitrile. The aqueous dispersion of the optical brightner can be tinted with a blue dye. The additional blue colouration of the dispersion brings about an increase in the
brightening effect up to maximum 30%.

Evaluation and testing

The evaluation of fluorescent brightening agents and assessment of their practical performance are of prime importance to the user of these agents. The main analytical tests applied to fluorescent brightening agents are designed to determine the strength of fluorescent activity either in its own right or comparatively against a known product and to establish the type of product and, if possible its identity.

Active strength of fluorescent brightners

As all fluorescent brightening agents operate by absorption of ultraviolet light,
which can be used to measure the active fluorescent strength of a product. The
extinction coefficient of a solution of the fluorescent brightening agent at wavelengths from 200 to 400 nm is determined by spectrophotometer. It can, however, be a measure of active strength of a product, as the peak absorption at between 345 to 365 run is a direct measure of its active fluorescent strength. For cellulose fluorescent brightening agents this is usually around 350 nm and the absorption at this peak is used to calculate the extinction coefficient through a 1 cm cell at a concentration of 1% weight/volume solution, usually expressed at E (1%1cm). This value is used extensively in evaluation and standardisation, as a direct measure of the fluorescent activity.

To establish the type of product, thin-layer chromatography is perhaps right
instrument.

Uses

The major consuming industry for optical whitener are as follows:

Detergent mixtures 40%

Paper 30%

Synthetic fibers and plastics 05%

Textiles 25%

Detergent Brighteners

Today scarcely a detergent exists which does not contain some cellulose brightner. One of the principal requirements of such a product is that it has satisfactory affinity in the presence of detergent. The brightening agent should have satisfactory build up in multiple washing, but should not discolour the textile. In addition, the product must be chemically stable to the other components of detergents.

Detergent brighteners should have adequate lightfastness. The washed textiles must not become discoloured in light. Certain brighteners can brighten the detergent itself, so that the agent appears pure white.

Brighteners for the textile industry

Textile finishing requires brighteners of very good solubility and substantivity.
Mostly bistriazinyl derivatives of 4, 4'-diminostillbene 2, 2'-disulfonic acid are
preferred. Brightening agents must possess definite stability in combined processes. The lightfastness of textile brighteners should be as high as possible. It is important again that the brightener does not decompose to light in form coloured by-products.

The optical brightener should possess following properties to give best results.

(i) Substantivity for the fiber

(ii) Rate of strike

(iii) Build-up shade

(iv) Sensitivity to electrolyte

(v) Effect of temperature

(vi) Effect of pH of bath.

Textile can be divided as follows:

(a) Natural fibers, cellulose and protein fibers

(b) Synthetic fibers

(c) Mixed fiber blends

Natural Fibers

These are dealt with under two groupings

(a) Cellulose fibers

(b) Wool fibers

Brightener for cellulose

The brightening of cellulose fibers constitutes the most important use of
optical brighteners.

Cellulose yams in the form of crops, cheeses and beams can all be treated
with fluorescent brightening agents on package dyeing machines. The selection of
brightener and method of operation are of major importance in obtaining level
brightening. It is important with prepared packages, such as cops, cheeses and
beams, that the preparation should produce the most stable and permeable
construction.

Brighteners with good penetrating properties and of medium substantivity are
required to obtain even brightening for cellulose. These are two methods that can be applied:

(a) Two-bath method, in which the brightener is applied to the fabric initially, then
dried and subsequently resin-finished.

(b) One-bath method, in which the brightener is applied in conjunction with the resin finish by inclusion in the actual resin finishing bath.

It is important to take into consideration the resin and catalyst combination.
The solution of fluorescent brightener should never be mixed with a strong catalyst
solution.

Brighteners for wool

The introduction of fluorescent brightening agents that can be applied to wool
enhances the whiteness but cannot achieve the brilliance of fluorescent.

The most common brighteners for application to wool are a select range of
dastriazinc derivatives with certain pyrazolene derivatives. The application is
invariably in conjunction with hydrosulphite, either alone or in the stabilised form.
Certain brighteners yield excellent results under these mildly acid conditions, while
others require an acid addition to exhaust them effectively onto the fiber.

Brighteners for synthetic fibers

Synthetic fiber can be divided as:

(i) Cellulose acetate

(ii) Polyamide fibers

(iii) Polyester fibers

(iv) Polyacrylonitrile fibers

(v) Acrylic fibers

Brighteners for Cellulose Acetate

Cellulose acetate show no affinity for the water-soluble cellulose brighteners
normally applied to cellulose, though they have some affinity for the soluble coumarin type. Their main affinity if for the disperse dye type of brightener.

Acetate fiber can be brightened by a large number of compounds, such as
(aminocoumarin); (derivatives of 7-amino-3-phylecoumarin); (pyrazines);
(pyrazolines), provided the derivatives are water-insoluble; (bis (benzazoyl)
ethylenes). Brighteners for cellulose acetate can also be used in combination with
light-duty detergents.

Brighteners for polyamide fibers

Polyamide fibers and fabrics are produced from polyamide-6 and -66 type.
Fluorescent brighteners of the acid-dyeing coumarin type and of the stilbene-triazine types are widely used, as well as the disperse type of synthetic-fiber brighteners.

In general, the easily water soluble products are preferred in textile applications, but aqueous dispersions of difficulty soluble compound are also employed. Water-soluble anionic brighteners are applied very much like acid wool dyes. Polyamide brightening in the spinning mass ("Dope Dyeing") requires particularly heat and reduction stable products.

Mainly das-triazine are the most widely used fluorescent brighteners for
polyamide-6 and -66 fibers. Most brighteners give better results when applied from a bath containing a reducing agent which in itself is of advantage by acting as a mild bleach.

Brighteners for polyester fibers

As a rule, polyester fibers require disperse dye-type fluorescent brighteners
due to their hydrophobic nature. These brightener particles penetrate into the fiber in a state of molecular dispersion and they are held in the fiber not by polar affinity but by Van der Waals forces. Polyester fibers show only very little swelling in water, ionic processes are not assumed to be of importance for the movement of brightener in the polyester fiber. The fitness of dispersion of the brightener particles is stabilised by the addition of dispersing agents during manufacturing.

They are all water-insoluble products which usually must be applied in conjunction with a carrier. The maximum in brightness and fastness is achieved only by means of a final heat treatment. It is of fundamental importance for the brightener
to remain stable at the relatively high condensation temperature. Effective polyester brighteners are compounds such as (biscbenzoxazoly) ethylenes; (naphthotriazolyl stilbenes), and (derivative of 7-amino-3-phenylcoumarin).

Fluorescent brighteners are applied to polyester fibers by exhaust processes
or by pad. Thermosol processes, the choice being dependent on the characteristics
of the material and the machinery available in the works.

The stability of the brightener dispersion within the fiber is of vital importance.

To ensure that the stability of the dispersion is maintained it is necessary:

(a) To dilute the dispersion with water at approximately 40"C just before it is
required.

(b) To control the build-up of temperature of the liquor.

(c) That any additional dispersing agent should be compatible and have protective
colloid effect.

(d) To avoid any auxiliaries that a cloud point, especially for high temperature
applications.

(e) To use no electrolyte and adjust pH with acetic acid; and

(f) Preferably to maintain acidity of the bath between pH 4 and pH 6.

Brighteners for Acrylic fibers

Acrylic fibers are extremely temperature-sensitive and, for each type of fiber,
there is a temperature (known as the glass transition temperature). For most acrylic fibers, the glass transition temperature is in the region of 80-90"C. The majority of fluorescent brighteners for acrylic fibers are cationic in reaction. Any acrylic fiber cannot bind a larger number of cationic brightener molecules, than the total number of the fiber's anionic groups.

Brighteners for Polyacrylonitrile fibers

Basic brighteners are suitable for brightening polyacrylonitrile fibers. The
basicity of the brightener can be attained through either external amino groups or
heterocyclic rings of basic character.

Multi-fiber brightening

Ideally, a laundry detergent should brighten all washable fibers; no such
formulation has been achieved practically. The diaminostilbene dissulfonate
brighteners show about 80% exhaustion on cotton; they have no affinity for cellulose acetate. Viscose rayon and wash 'n' wear cotton usually show lowered affinity for these brighteners. While nylon presents no problems, polyester even in cotton blends-is still
a challenge; so are acrylic and spandex fibers, with polypropylene still to make its appearance. The development of a brightener for anyone of these fibers is a formidable task. The development of a single brightener suitable for all fibers is highly improbable because optimum conditions for brightening one fiber will not necessarily be satisfactory for another fiber.

Paper Brightener

Most papers are brightened by addition of brightener both to the pulp and to
the surface coatings. The exact proportion varied with the type and quality of the
paper. Besides satisfactory exhaust at low temperatures, good paper brighteners
also requires good acid and alum stability as well as compatibility with the paper
fillers. Good affinity to the pulp is also needed, because and unabsorbed whitener is lost in the effluent or white water from the screen.

Fine papers require relatively less brightener in the pulp, as the pulp is of a
better quality. Fine papers, which require a surface treatment with white pigments
and synthetic resin, are brightened by an after-treatment.

Brighteners for plastics

Plastics are brightened in the melt. The brightener must withstand special conditions; for example, it must have stability to polymerisation catalysts (peroxides); sublimation fastness; and the highest possible light fastness. The brightening agent must not
migrate to the surface and, by so doing, cause, "blooming". Good plastics brighteners, which are especially suited to polyvinyl chloride, are such as (bisbenzoxazolyl) (ethylenes) and (derivatives of 7-amin-3-phenylcoumarin). In addition to polyvinyl chloride, plastics based on polystryene, polyethylene, polypropylene, polyacrylates and polymemthacrylates and cellulose acetate are also brightened.

Brighteners for Cosmetic Preparations

The use of brighteners for cosmetic preparations, such as creams, salves,
lipsticks, etc. has been proposed, but so significant commercial usage has as yet
developed. Naphthotriazolyl stilbene derivatives may be used for this purpose.

Brighteners for Miscellaneous Application

In addition to the textile, detergent and paper industries, optical brighteners
are also used in various other branches of industry. Such as for the brightening of
feathers, fast, gelatine, wood shavings and sawdust, for the brightening of paints,
leather, furs and straw. The photographic industry makes extensive use of optical
brightening agents. They are also added into developers for coloured photographs
where they improve the coloured on the one hand and slow down the fading of
colour photographs on the other. They are added to lubricants to increase their
fluorescence.

Biological aspects

Brighteners have no detrimental effect on bacteria. The recent reports of Snyder, Neutomm Glashoof and co-workers indicate that brighteners in general use are not hazardous. Brighteners do not affect the appearance of water, not the taste,at 1ppm.

Dr. Himadri Panda
&
Dr. (Mrs.) Rakhshinda Panda