Yaa Whitening Agent: Properties, Function, Machinery In Addition To Usages (Part-8)

Whitening Agent: Properties, Function, Mechanism together with Usages (Part-8)

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

Previous Part


End uses of optical brighteners include:

1. Detergent whitener (instead of bluing agents)
2. Paper brightening (internal or inwards a coating)
3. Fiber whitening (internal, added to polymer melts)
4. Textile whitening (external, added to cloth finishes)
5. Color-correcting or brightening additive inwards advanced cosmetic formulas (shampoos, conditioners, oculus makeup)

Role of Optical Brightening agents inwards Textile Wet-Processing:

The functioning of whitening, i.e., bleaching or brightening, is concerned alongside the training of fabrics whose commercial value is subject on the highest possible whiteness. In bleaching, textile physical care for houses are concerned alongside the removal of colored impurities or their conversion into colorless substances. In chemic 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 oculus inwards an optical manner, eg, inwards bluing the yellowish cast of substrates such every bit textiles, paper, sugar, etc. is eliminated yesteryear way of blueish or blue-violet dyes. Through color compensation the treated production appears whiter to the eye; however, it is genuinely grayer than the untreated material.

OBA on textile material

With the assist of Optical brightening agents (OBAs), likewise referred to every bit fluorescent whitening agents, optical compensation of the yellowish cast may endure obtained. The yellowish cast is produced yesteryear the absorption of short-wavelength lite (violet-to-blue). With OBAs, this lost lite is inwards component replaced; thus a consummate white is attained without loss of light. This additional lite is produced yesteryear the whitener yesteryear way of fluorescence. Fluorescent whitening agents absorb the invisible UV part of the daylight spectrum together with convert this liberate energy into the longer-wavelength visible part of the spectrum, i.e., into blueish to blue-violet light. Fluorescent whitening, therefore, is based on the add-on of light, whereas the bluing method achieves its white consequence through the removal of light.

A fluorescent whitener should endure optically colorless on the substrate, together with should non absorb inwards the visible component of the spectrum. In the application of OBAs, it is possible to supersede the lite lost through absorption, thereby attaining a neutral, consummate white. Further, through the usage of excess whitener, soundless to a greater extent than UV radiations tin endure converted into visible light, together with so that the whitest white is made to a greater extent than sparkling. Since the fluorescent lite of a fluorescent whitener is itself colored, ie, blue-to-violet, the usage of excess whitener ever gives either a blue-to-violet or a bluish greenish cast.

Many chemic compounds conduct maintain been described inwards the literature every bit fluorescent compounds that render a suitable whitening effect. Collectively these materials are aromatic or heterocyclic compounds; many of them incorporate condensed band systems. An of import characteristic of these compounds is the presence of an uninterrupted chain of conjugated double bonds, the disclose of which is subject on substituents every bit good every bit the planarity of the fluorescent component of the molecule. Almost all of these compounds are derivatives of stilbene or 4,4-diaminostilbene; biphenyl; 5-membered heterocycles such every bit triazoles, oxazoles, imidazoles, etc. or 6-membered heterocycles, e.g. coumarins, naphthalimide, s-triazine, etc.

Textile substrates of natural or synthetic fibers are contaminated inwards the raw nation yesteryear substances of varying degrees of yellowness. Bleaching is required to take the yellowish cast. Chemical bleaching agents destroy the yellowish coloring affair inwards fibers. However, fifty-fifty if bleaching processes are carried to the technically acceptable limits of harm to the fibers, they never succeed inwards completely removing this intrinsic color. To create the color white, it is necessary to dye alongside a fluorescent whitener.

OBAs used inwards textiles tin endure divided into 3 categories

1. Products containing sulfonic acid groups, corresponding to acid dyes, for cotton, wool, together with polyamides;
2. Cationic whiteners that comport inwards the same way every bit basic dyes, for polyacrylonitrile fibers; together with
3. Whiteners containing no solubilizing groups, corresponding to disperse dyes, for polyester together with secondary acetate fibers.

This is non a strict segmentation since nonionic OBAs tin whiten polyacrylonitrile together with polyamide, together with certainly cationic OBAs create effects on polyester. For dyeing fiber blends such every bit viscose–polyamide, polyamide–Spandex, or polyester–cotton, solely compatible OBAs may endure used that practice non interfere alongside 1 around other or conduct maintain whatever detrimental consequence on fastness properties.

Before handling alongside optical brighteners, due attention should endure taken during pretreatment, scouring together with removal of sizing chemicals. Otherwise these volition hinder the consequence of OBA onto the substrate together with may final result inwards uneven brightening consequence on the fabric.

In an exhaust physical care for the fluorescent whitener is exhausted from a long liquor onto the substrate until an guess equilibrium is reached betwixt whitener inwards the lav together with whitener on the substrate. In this physical care for the equilibrium is biased primarily toward OBA on the substrate, ie, the highest possible flat of exhaustion is desired. Exhaust procedures are used for loose stock, yarns, woven fabrics, together with knit goods which give piteous or unsatisfactory results inwards padding processes, together with for garments together with garment parts.

Padding methods, i.e. application from brusque liquors, are increasingly of import for whitening piece-goods. Woven fabrics or knit goods are passed inwards an unfolded, open-width nation through a modest trough charged alongside handling liquor containing OBA together with later on betwixt squash rollers to limited the liquor to a just defined liquor pick-up.

In conjunction alongside the increased usage of synthetic fibers together with blends of synthetic together with natural fibers, together with the modernization of application processes which has taken house simultaneously, the technique of textile whitening has been improved considerably.

In illustration of polyester fibers brighteners are applied inwards the shape of fine aqueous dispersions. The brightener particles penetrate into the fiber inwards a nation of molecular dispersion together with they are held inwards the fiber yesteryear Vander waals forces. Influenza A virus subtype H5N1 component of finely dispersed particle forms a molecular solution inwards the dye-bath. Some of the finely dispersed particles may diffuse direct into the fiber. In add-on to the dispersion together with diffusion of the brightener, stability is likewise of vital importance.

During the drying and, if required, the estrus handling that follows, the fluorescent whitener is fixed on the substrate. OBAs used inwards padding procedures must conduct maintain depression substantivity during the padding operation. This is an of import prerequisite for flat whitening alongside no tailing.

Furthermore, fluorescent whiteners are applied inwards combination alongside bleaching together with finishing steps. Fluorescent whiteners used inwards such processes must endure stable together with should non interfere alongside the operation. Whitening inwards combination alongside the finishing physical care for is used primarily for woven fabrics of cellulosic fibers together with their blends alongside synthetic fibers.

We at Matex offering Optical brightening agents nether the build mention Megawhite. Highest brightness together with best fastness tin endure achieved yesteryear using Megawhite serial of brighteners. It meets all the requirements alongside regard to whiteness, hues together with fastness properties.

Despite the difficulties faced yesteryear OBA producers together with customers alike inwards the midst of the electrical flow global economical downturn at that spot is soundless room for innovative producers to prepare together with to innovate onto the marketplace novel products offering to a greater extent than cost-effective, rubber together with environmentally audio solutions for the customer. There is every argue to believe that OBAs conduct maintain a vivid future. 

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