Yaa Whitening Agent: Properties, Function, Machinery As Well As Usages (Part-4)

Whitening Agent: Properties, Function, Mechanism together with Usages (Part-4)

Authors: Md. Mosharaf Hossain
Kiriti Kingkar Mondal
Tawhidul Islam
Dept. of Textile Engineering
Primeasia University, Dhaka

Previous Part

Desired Properties of Fluorescent Whitening Agents for Textiles Use:

Before selecting an optical brightener for textile application nosotros must hold off for next properties-

It should bring proficient solubility , should non bring its ain color together with proficient substantivity for the textile substrate nether OBA application.
OBA’s should bring proficient calorie-free every bit good every bit moisture fastness properties.
Its charge per unit of measurement of strike on the substarte.
Build upwards together with exhaustion properties.
Requirement of electrolytes together with its sensitivity towards dissimilar exhausting agents.
Effect of temperature on the exhaustion together with construct upwards properties.
Application pH arrive at together with sensitivity towards modify inward pH.
Effect of H2O hardness.
It should bring proficient leveling together with penetrating properties.
Should non decompose to colored products on exposure to atmospheric weather condition every bit good every bit storage, together with it should non absorb calorie-free inward the visible region.
It should move compatible together with stable amongst finishing chemicals, auxiliary together with procedure such every bit oestrus together with temperature.
It should move stable together with fast to the mutual oxidative together with reductive bleaching chemicals together with bleaching systems.

Composition
Members of this shape of diaminostilbene sulfonate derivatives are highly conjugated molecules having planar construction together with anionic charge. All of these adjectives likewise apply to straight dyes. What makes this item shape of straight dyes dissimilar is that they absorb ultraviolet calorie-free together with re-emit calorie-free inward the bluish percentage of the visible spectrum. Another traditional term for fluorescent whitening agents (FWAs) is "optical brightening agents" (OBAs). Three full general types of FWAs are widely available. The type almost frequently used past times papermakers has 4 sulfonate groups (tetrasulfonated). It has intermediate solubility inward H2O together with it is readily retained on fibers, peculiarly if alum or about other cationic cloth is present. Hexasulfonated FWAs don't retain every bit good when added at the moisture end, but they may arrive at higher optical efficiency when used at the size press due to less association betwixt the molecules inward the dried starch film. Disubstituted FWAs are sometimes used for specialty purposes, for illustration when H2O bleed-fastness is critical.

Function
Increasing the white appearance of papers past times absorbing invisible ultraviolet calorie-free together with re-emitting it inward the bluish percentage of the visible spectrum. This strategy tin compensate for a yellowish tint of many types of pulps that bring been bleached to moderate levels.

Classification of OBA
The classification of OBA tin move either on the chemic construction of the brightener or on its method of application.

They tin move classified inward to ii large groups-

Direct (substantive) brightener.
Disperse brightener.

1) Direct optical brightening agents are predominantly H2O soluble nub used for the brightening of natural fibers together with occasionally for synthetic cloth such every bit polyamide.

2) Disperse optical brightening agents are mainly H2O insoluble together with every bit amongst disperse dyes they are applied either to colored from an aqueous dispersion on they tin move used for volume coloration. They are used for synthetic materials such every bit polyamide polyester acetate.

From the chemic shout out for of persuasion they are classified according to either chemic structure. Chemical optical brightening agents are classified inward to derivatives of stlibene, coumarin, 1, iii diphenyl pyrazoline, derivative of naphthalene dicarboxylic acid, derivatives of heterocyclic dicarboxylic acid, derivatives of cinnamic acid together with nub belonging to other chemic system.

Basic Types of Whiteners
Basic shape types of brighteners include:

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

Factors Influencing Whitening Process
The factors influencing whitening procedure are every bit follows :

pH of the privy
Temperature of the bath, together with
Time required for the process.

Mechanism of activity
Absorption (A) of calorie-free quanta past times the brightener molecules induces transitions from the singlet the world terra firma S0 to vibrational levels of the electronically excited singlet states (S1).

Brighteners inward the S1 terra firma are deactivated past times several routes. Fluorescence results from radiative transitions to vibrational levels of the the world terra firma (F). Deactivation processes competing amongst fluorescence are mainly non-radiative deactivation to the S0 terra firma (IC) together with non-radiative transition to the triplet terra firma (intersystemcrossing, ISC).

The efficiency of fluorescence is measured past times the quantum yield :

Number of quanta emitted
The quantum yield (Φ) = ………………………………………
Number of quanta absorbed

It is determined past times the relative rates of fluorescence emission together with the competing processes. When fixed inward venture substrates, brighteners fluoresce amongst high quantum yields .